2.008 design & manufacturing ii spring 2004 mems i 2.008-spring-2004 s.g. kim
TRANSCRIPT
2008 Design amp ManufacturingII
Spring 2004
MEMS I
2008-spring-2004 SG Kim
March 10th
Ask ldquoDaverdquo and ldquoPatrdquo1048708 Petty money up to $200 Goggles1048708 Plant tour April 21 22 sign up By 421048708 Quiz 1 on March 17th1048708 HW4 due by Mondayrsquos lecture1048708 75 minutes (45 min)1048708 MEMS 1 today
2008-spring-2004 SG Kim
Elephant vs Ant
1048708 Shock and impact1048708 Scale and form factor1048708 Load carrying capability1048708 Spider silk vs steel
2008-spring-2004 SG Kim
Frog Water Strider Gecko
2008-spring-2004 SG Kim
Never try to mimic the nature eg Biomimetic researches
httproboticseecsberkeleyedu~ronfGECKOF 5 iguresHierarchy3jpg2008-spring-2004 SG Kim
Gecko adhesive system
Macro Meso Macro Nanostructures
The Scale of Things -- Nanometers and More
Transition Micro to Nano
1048708 20th Century - Microelectronics and Information Technology1048708 Semiconductors computers and telecommunication
1048708 21st Century - Limits of Microsystems Technology --- Nanotechnology1048708
Moorersquos law1048708 Hard disc drive
John Bardeen Walter Brattain and William Shockleyat Bell Laboratories ldquoFirst Transistorrdquo
2008-spring-2004 SG Kim
Moorersquos LawThe number of transistors per chip doubles every 18 monthsndash Moorersquos Law_ Rockrsquos Law
2008-spring-2004 SG Kim
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
March 10th
Ask ldquoDaverdquo and ldquoPatrdquo1048708 Petty money up to $200 Goggles1048708 Plant tour April 21 22 sign up By 421048708 Quiz 1 on March 17th1048708 HW4 due by Mondayrsquos lecture1048708 75 minutes (45 min)1048708 MEMS 1 today
2008-spring-2004 SG Kim
Elephant vs Ant
1048708 Shock and impact1048708 Scale and form factor1048708 Load carrying capability1048708 Spider silk vs steel
2008-spring-2004 SG Kim
Frog Water Strider Gecko
2008-spring-2004 SG Kim
Never try to mimic the nature eg Biomimetic researches
httproboticseecsberkeleyedu~ronfGECKOF 5 iguresHierarchy3jpg2008-spring-2004 SG Kim
Gecko adhesive system
Macro Meso Macro Nanostructures
The Scale of Things -- Nanometers and More
Transition Micro to Nano
1048708 20th Century - Microelectronics and Information Technology1048708 Semiconductors computers and telecommunication
1048708 21st Century - Limits of Microsystems Technology --- Nanotechnology1048708
Moorersquos law1048708 Hard disc drive
John Bardeen Walter Brattain and William Shockleyat Bell Laboratories ldquoFirst Transistorrdquo
2008-spring-2004 SG Kim
Moorersquos LawThe number of transistors per chip doubles every 18 monthsndash Moorersquos Law_ Rockrsquos Law
2008-spring-2004 SG Kim
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Elephant vs Ant
1048708 Shock and impact1048708 Scale and form factor1048708 Load carrying capability1048708 Spider silk vs steel
2008-spring-2004 SG Kim
Frog Water Strider Gecko
2008-spring-2004 SG Kim
Never try to mimic the nature eg Biomimetic researches
httproboticseecsberkeleyedu~ronfGECKOF 5 iguresHierarchy3jpg2008-spring-2004 SG Kim
Gecko adhesive system
Macro Meso Macro Nanostructures
The Scale of Things -- Nanometers and More
Transition Micro to Nano
1048708 20th Century - Microelectronics and Information Technology1048708 Semiconductors computers and telecommunication
1048708 21st Century - Limits of Microsystems Technology --- Nanotechnology1048708
Moorersquos law1048708 Hard disc drive
John Bardeen Walter Brattain and William Shockleyat Bell Laboratories ldquoFirst Transistorrdquo
2008-spring-2004 SG Kim
Moorersquos LawThe number of transistors per chip doubles every 18 monthsndash Moorersquos Law_ Rockrsquos Law
2008-spring-2004 SG Kim
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Frog Water Strider Gecko
2008-spring-2004 SG Kim
Never try to mimic the nature eg Biomimetic researches
httproboticseecsberkeleyedu~ronfGECKOF 5 iguresHierarchy3jpg2008-spring-2004 SG Kim
Gecko adhesive system
Macro Meso Macro Nanostructures
The Scale of Things -- Nanometers and More
Transition Micro to Nano
1048708 20th Century - Microelectronics and Information Technology1048708 Semiconductors computers and telecommunication
1048708 21st Century - Limits of Microsystems Technology --- Nanotechnology1048708
Moorersquos law1048708 Hard disc drive
John Bardeen Walter Brattain and William Shockleyat Bell Laboratories ldquoFirst Transistorrdquo
2008-spring-2004 SG Kim
Moorersquos LawThe number of transistors per chip doubles every 18 monthsndash Moorersquos Law_ Rockrsquos Law
2008-spring-2004 SG Kim
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Never try to mimic the nature eg Biomimetic researches
httproboticseecsberkeleyedu~ronfGECKOF 5 iguresHierarchy3jpg2008-spring-2004 SG Kim
Gecko adhesive system
Macro Meso Macro Nanostructures
The Scale of Things -- Nanometers and More
Transition Micro to Nano
1048708 20th Century - Microelectronics and Information Technology1048708 Semiconductors computers and telecommunication
1048708 21st Century - Limits of Microsystems Technology --- Nanotechnology1048708
Moorersquos law1048708 Hard disc drive
John Bardeen Walter Brattain and William Shockleyat Bell Laboratories ldquoFirst Transistorrdquo
2008-spring-2004 SG Kim
Moorersquos LawThe number of transistors per chip doubles every 18 monthsndash Moorersquos Law_ Rockrsquos Law
2008-spring-2004 SG Kim
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
The Scale of Things -- Nanometers and More
Transition Micro to Nano
1048708 20th Century - Microelectronics and Information Technology1048708 Semiconductors computers and telecommunication
1048708 21st Century - Limits of Microsystems Technology --- Nanotechnology1048708
Moorersquos law1048708 Hard disc drive
John Bardeen Walter Brattain and William Shockleyat Bell Laboratories ldquoFirst Transistorrdquo
2008-spring-2004 SG Kim
Moorersquos LawThe number of transistors per chip doubles every 18 monthsndash Moorersquos Law_ Rockrsquos Law
2008-spring-2004 SG Kim
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Transition Micro to Nano
1048708 20th Century - Microelectronics and Information Technology1048708 Semiconductors computers and telecommunication
1048708 21st Century - Limits of Microsystems Technology --- Nanotechnology1048708
Moorersquos law1048708 Hard disc drive
John Bardeen Walter Brattain and William Shockleyat Bell Laboratories ldquoFirst Transistorrdquo
2008-spring-2004 SG Kim
Moorersquos LawThe number of transistors per chip doubles every 18 monthsndash Moorersquos Law_ Rockrsquos Law
2008-spring-2004 SG Kim
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Moorersquos LawThe number of transistors per chip doubles every 18 monthsndash Moorersquos Law_ Rockrsquos Law
2008-spring-2004 SG Kim
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Microelectronics Technology
To meet the Moorersquos Lawline width(12 pitch) requirement
No solution yet nanolithography
2008-spring-2004 SG Kim
The International Technology Roadmap for Semiconductors 1999
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Aerial density hard disk
Superparamagnetic Effect ldquoa point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation effectively erasing the recorded data ldquo
2008-spring-2004 SG Kim
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
What is Nanotechnology
A DNA molecule is 25 nm wide
Nanomanufacturing
2008-spring-2004 SG Kim
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Nano in ME
1048708 Fluidics heat transfer and energy conversion at the micro- and nanoscale1048708 Bio-micro-electromechanical systems (bio-MEMS)1048708 Optical-micro-electromechanical systems (optical- MEMS)1048708 Engineered nanomaterials1048708 Nano manufacturing
1048708 Course 2A (Nanotrack)
2008-spring-2004 SG Kim
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
httpwwwmemsnetorgmemswhat-ishtml
MEMS
Optical MEMS RF MEMS Data Storage Bio MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space
MEMS for Nano
1048708 Materials1048708 Processes1048708 Systems
2008-spring-2004 SG Kim
Courtesy Sandia national laboratory
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
MEMS (Microelectromechanical Systems)
1048708 Intergrated systems of sensing actuation communication controlpower and computing1048708 Tiny1048708 Cheaper1048708 Less power1048708 New functions (chemical bio μ- fluidic optical hellip)
2008-spring-2004 SG Kim
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Tiny Products
1048708 DLP (Digital Micromirror Array)
106 micromirrors each 16μm2 plusmn10deg tilt(Hornbeck Texas Instruments DMD 1990)
2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS
Analog Devices2008-spring-2004 SG Kim
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Tiny Products
1048708 Airbag sensors Mechanical vs MEMS1048708 DLP (Digital Micromirror Array)1048708 DNA chip1048708 Optical MEMS
Tiny Tech venture funding 2002
2008-spring-2004 SG Kim
Smalltimes Vol2 no 6 2002
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
(Courtesy of Segway (r) Human Transporter (HT)Used with permission)
Segway
-Tilt-Rotation
D Kamen2008-spring-2004 SG Kim
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Vibrating Gyroscope
CoriolisAcceleration
By Charles Stark Draper Laboratory
2008-spring-2004 SG Kim
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Electrostatic Comb Drivesensing
1048708 Paralle Plate Capacitor1048708 Capacitance=QV=ε Ad ε Dielectric permittivity of air1048708 Electrostatic Force = frac12 ε (Ad2)V2
1048708 Pull-in point 23 d
2008-spring-2004 SG Kim
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Comb Drive
1048708 C= ε Ad = 2n ε l hd1048708 ΔC = 2n ε Δl hd1048708 Electrostatic force Fel = frac12 dCdx V2 = n ε hd V2
2008-spring-2004 SG Kim
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Suspension mode failures
2008-spring-2004 SG Kim
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Comb Drive Designs
linear rotational
2008-spring-2004 SG Kim
Grating beamsFlexuresElectrostatic comb-drives
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Capacitive Accelerometer
capacitivesensor
platemass
meanderspring
2008-spring-2004 SG Kim
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Microfabrication process flow
1048708 Single-mask process
1048708 IC compatible
1048708 Negligible residual stress
1048708 Thermal budget
1048708 Not yet packagedDevice silicon layer
Buried oxide layer
Metal layer
Bulk silicon layer
2008-spring-2004 SG Kim
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
SOI (Silicon on insulator)
1) Begin with a bonded SOI wafer Growand etch a thin thermal oxide layer to actas a mask for the silicon etch
2) Etch the silicon device layer to exposethe buried oxide layer
3) Etch the buried oxide layer in bufferedHF to release free-standing structures
2008-spring-2004 SG Kim
oxide mask layer
Si device layer 20 μm thick
buried oxide layer
Si handle wafer
silicon
Thermal oxide
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Problems of fabrication
2008-spring-2004 SG Kim
Surface micromachinedStructure 2 μm
Vertical stiction
DRIE micromachinedStructure 10 μm
Lateral stiction
DRIE micromachinedStructure 10 μm
No stiction
G Barbastathis amp S Kim
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
ADXL 50 accelerometer
Capacitive sensing
Comb drive
2008-spring-2004 SG Kim
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Process Flow
Wafers
Deposition Lithography
Devices
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
Etch
2008-spring-2004 SG Kim
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Micromachining processes
bull Bulk micromachiningbull Surface micromachiningbull Bondingbull LIGA bull x-ray lithography electrodeposition and molding
2008-spring-2004 SG Kim
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
LIGA process
2008-spring-2004 SG Kim
X-rays from a synchrotron are incident on a mask patterned with high Z absorbers X-rays are used to expose a pattern in PMMA normally supported on a metallized substrate
The PMMA is chemically developed to create a high aspect ratio parallel wall mold
The PMMA is dissolved leaving a three dimensional metal micropart Individual microparts can be separted from the base plate if desired
Ametal or alloy is electroplated in the PMMA mold to create a metal micropart
Photograph of chrome mask
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Bulk Surface DRIE
1048708 Bulk micromachining involves removal of the silicon wafer itself1048708 Typically wet etched1048708 Inexpensive equipments1048708 IC compatibility is not good1048708 Surface micromachining leaves the wafer untouched but addsremoves additional thin film layers above the wafer surface1048708 Typically dry etched1048708 Expensive equipments1048708 IC compatibility conditionally
2008-spring-2004 SG Kim
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Materials
1048708 Metals1048708 Al Au ITO W Ni Ti TiNihellip1048708 Insulators1048708 SiO2 - thermally grown above 800oC or vapor deposited (CVD) sputtered Large intrinsic stress1048708 SixNy ndash insulator barrier for ion diffusion high E stress controllable1048708 Polymers PR SU-8 PDMS1048708 Glass quartz1048708 Silicon1048708 stronger than steel lighter than aluminum1048708 single crystal polycrystalline or amorphous
2008-spring-2004 SG Kim
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Silicon
1048708 Atomic mass average 2808551048708 Boiling point 2628K1048708 Coefficient of linear thermal expansion 42 10-6degC1048708 Density 233gcc1048708 Youngrsquos modulus 47 GPa1048708 Hardness scale Mohsrsquo 651048708 Melting point 1683K1048708 Specific heat 071 JgK
Electronic grade silicon 9999999999 purity
2008-spring-2004 SG Kim
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Materials
1048708 Single crystal silicon1048708 Anisotropic crystal 1048708 Semiconductor great heat conductor1048708 Polycrystalline silicon ndash polysilicon1048708 Mostly isotropic material1048708 Semiconductor1048708 Semiconductor1048708 Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1)1048708 N-type and P-type dopants both give linear conduction1048708 Two different types of doping1048708 Electrons (negative N-type) --phosphorus1048708 Holes (positive P-type) --boron
2008-spring-2004 SG Kim
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method
1rdquo to 12rdquo diameter
httpwwwmsilabpsiwebcomenglishmsilhist4-ehtml
2008-spring-2004 SG Kim
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Silicon Crystal Structure
2008-spring-2004 SG Kim
Miller indices identify crystal planes from the unit cell
Tetrahedral bonding of silicon atoms
Cubic unit cell of silicon
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Miller indices plane
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Crystallographic planes
2008-spring-2004 SG Kim
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Miller indices
bull [abc] in a cubic crystal is just a directional vectorbull (abc) is any plane perpendicular to the [abc] vectorbull (hellip)[hellip] indicate a specific planedirectionbull helliplthellipgt indicate equivalent set of planesdirections
2008-spring-2004 SG Kim
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
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- Slide 13
- Slide 14
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- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Wafers of different cuts
2008-spring-2004 SG Kim
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Crystallographic planes
2008-spring-2004 SG Kim
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Etching
Wet
Dry
1048708 Isotropic silicon etchants1048708 HNA (ldquopoly-etchrdquo) -wet1048708 Mix of HF nitric acid (HNO3) and acetic acids (CH3COOH)1048708 Difficult to control etch depth and surface uiformity1048708 XeF2 -dry1048708 gas phase etches silicon polysilicon1048708 Does not attack SiO2 SiNxmetals PR
2008-spring-2004 SG Kim
Slow etching crystal plane
Etch mask
Anisotropic Isotropic
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Anisotropic wet etching
Many liquid etchants demonstrate dramatic etch ratedifferences in different crystal directions1048708 lt111gt etch rate is slowest lt100gt fastest1048708 Fastest slowest can be more than 10011048708 KOH EDP TMAH most common anisotropic silicon etchants1048708 Potasium Hydroxide (KOH) Tetramethyl Ammonium Hydroxide (TMAH) and Ethylene Diamine Pyrochatecol (EDP)
2008-spring-2004 SG Kim
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
KOH Etching
1048708 Etches PR and Aluminum instantly1048708 (100) to (111)rarr100 to 1 etch rate1048708 V-grooves trenches1048708 Concave stop convex undercut1048708 CMOS incompatible1048708 Masks1048708 SiO2 for short period1048708 SixNy Excellent1048708 heavily doped P++ silicon etch stop
2008-spring-2004 SG Kim
Silicon Substrate
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Anisotropic wet etching
2008-spring-2004 SG Kim
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Anisotropic wet etching
When a (100) wafer with mask featuresOriented to lt110gt direction is placed inan anisotropic etchant
A square lt110gt oriented mask featureresults in a pyramidal pit
2008-spring-2004 SG Kim
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Dry etching
1048708 RIE (reactive ion etching)1048708 Chemical amp physical etching by RF excited reactive ions1048708 Bombardment of accelerated ions anisotropic1048708 SF6 rarr Si CHF3 rarr oxide and polymers1048708 Anisotropy selectivity etch rate surface roughness by gas concentration pressure RF power temperature control1048708 Plasma etching1048708 Purely chemical etching by reactive ions isotropic1048708 Vapor phase etching1048708 Use of reactive gases XeF21048708 No drying needed
2008-spring-2004 SG Kim
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
DRIE (Deep RIE)
1048708 Alternating RIE and polymer deposition process for side wall protection and removal1048708 Etching phase SF6 Ar1048708 Polymerization process CHF3Ar forms Teflon-like layer1048708 Invented by Bosch process patent 1994
-15 to 4 μmmin-selectivity to PR 100 to 1
2008-spring-2004 SG Kim
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
-
Scalloping and Footing issues of DRIE
2008-spring-2004 SG Kim
Footing at the bottom ofdevice layerMilanovic et al IEEE TED Jan 2001
Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
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Deep Reactive Ion Etch
STS Alcatel Trion Oxford Instruments hellip
Most wanted by many MEMS students
High aspect ratio 130
Easily masked (PR SiO2)
2008-spring-2004 SG Kim
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