concepts and principles of optical xip lithography - · pdf fileconcepts and principles of...
TRANSCRIPT
1/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Concepts and principles of optical
lithography
Francesc Pérez-Murano
Institut de Microelectrònica de Barcelona (CNM-IMB, CSIC)
2/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
1 cm
10 cm
100 um
1 mm
1 um
10 um
10 nm
100 nm
1 nm
0,1 nm
mà
Gra de sorra
Diàmetre cabell humà
Bacteries
Molècula de DNA
Distància interatòmica
Oblia
Xip
Micromotors
Circuit integrat
Transistor MOS
Dispositius quàntics
Estructures atomiques
Microelectrònica
Nanotecnologia
3/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Nan
otec
hnol
ogy,
D. M
. Ten
nant
. A
IP/S
prin
ger,
New
Yor
k, 1
999
NanolithographiesNanolithographies
4/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Summary
Concept of optical lithography
Resists
Part ii
Associated processes
Part ii
Miniaturization
Limits optical lithography
Part i
5/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011Bibliography
Nanoelectronics and Information. Chapter 9. Technology. Rainer Waser. Wiley-VCH 2003
Fundamentals of Microfabrication. Chapter 1. Marc Madou. CRC Press. 1997
Silicon Processing for the VLSI Era. Volume 1-Process Technology. Chapter 12 and 13. S. Wolf and R.N. Tauber. Lattice Press. 1986v
Principles of Lithography. Harry J. levinson. SPIE Press. 2004
Basic Books
Web sites http://www.intel.com/technology/silicon/index.htm http://www.microchemicals.de/products.html
6/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Summary
Concept of optical lithography
Resists
Part ii
Associated processes
Part ii
Miniaturization
Limits optical lithography
Part i
7/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Summary
Concept of optical lithography
Resists
Part ii
Associated processes
Part ii
Miniaturization
Limits optical lithography
Part i
8/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Fabrication using optical lithography
Mask
Resist
Exposition
Development
Etching
Initial substrate
9/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
silicon substrate
oxide
photoresist
Positive Lithography
Island
Window
Areas exposed to light become photosoluble.
Resulting pattern after the resist is developed.
Shadow on photoresist
Exposed area of photoresist
Chrome island on glass mask
photoresist
silicon substrate
oxide
Ultraviolet Light
Positive Resist Tone
10/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Negative Lithography
Island
silicon substrate
oxide
photoresist
Window
Areas exposed to light become polymerized and sustain the develop chemical
Resulting pattern after the resist is developed.
photoresistoxide
silicon substrate
Ultraviolet Light
Exposed area of photoresist
Shadow on photoresist
Chrome island on glass mask
Negative Resist Tone
11/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Optical lithographyLithography: Image a mask on a wafer
Wavelength of the light sources:Near UV and deep UV
12/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Spectral distribution: Mercury Arc Lamp
i-line (365 nm)
g-line (435 nm)
h-line (405 nm)
Optical source for UV
13/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Light source
Optical system
MaskPhotoresistSample
Gap
Contact Proximity Projection
Exposition 1:1 1:1 5:1
Optical lithography modes
14/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
UV optical lithography systems
Optical aligners Stepper
15/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Contact printing
R=MFS=(d·
d: Resist thicknessLight wavelenght
d= 1 m; = 435 nm; R=0.66 m
MFS: Minimum feature size
(difraction limited)
16/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Proximity printing
a h
R= MFS (Minimum feature size)
K: Experimental parameter (>1)
17/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Projection printing
MFS=R = k1λNA
NA: Numerical aperture
k1: technology constant(0.5 – 0.9)
k1= 0,66; = 435 nm; NA= 0.7; R = 0.4 m
18/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Resolution in projection printing
19/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Step-and scan system (stepper)
20/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
1. Surface Preparation2. Photoresist Application3. Soft Bake4. Align & Expose*
5. Develop6. Hard Bake7. Inspection8. Etch9. Resist Strip10. Final Inspection
* Some processes may include a Post-exposure Bake
Ten Basic Steps of Photolithography
21/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
1. Surface Preparation (HMDS vapor prime)
Dehydration bake in enclosed chamber with exhaust
Clean and dry wafer surface (hydrophobic)
Hexamethyldisilazane (HMDS)
Temp ~ 200 - 250C Time ~ 60 sec.
HMDS
22/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
HEXAMETHYLSILIZANE (HDMS)Dehydration
Adhesion promotion by HDMS
23/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
2. Photoresist Application
Wafer held onto vacuum chuck
Dispense ~5ml of photoresist
Slow spin ~ 500 rpm Ramp up to ~ 3000 -
5000 rpm Quality measures:
time speed thickness uniformity particles & defects vacuum chuck
spindleto vacuum
pump
photoresist dispenser
24/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Resist spinning thickness T depends on: Spin speed Solution concentration Molecular weight (measured by
intrinsic viscosity) In the equation for T, K is a
calibration constant, C the polymer concentration in grams per 100 ml solution, the intrinsic viscosity, and the number of rotations per minute (rpm)
Once the various exponential factors (, and ) have been determined the equation can be used to predict the thickness of the film that can be spun for various molecular weights and solution concentrations of a given polymer and solvent system
2. Photoresist Application
Sample
ResistT
Extra resist at the edges
25/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
3. Soft Bake
Partial evaporation of photo-resist solvents
Improves adhesion Improves uniformity Improves etch resistance Improves linewidth control Optimizes light absorbance
characteristics of photoresist
26/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
4. Alignment and Exposure
Transfers the mask image to the resist-coated wafer
Activates photo-sensitive components of photoresist
Quality measures: linewidth resolution overlay accuracy particles & defects
UV Light Source
Mask
ResistResistResistResist
27/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Alignment errors (many different types)
Mask aligner equipment Double sided alignment
especially important in micromachines
4. Alignment and Exposure
28/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
4. Alignment and Exposure
29/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
5. Develop
Soluble areas of photoresist are dissolved by developer chemical
Visible patterns appear on wafer windows islands
Quality measures: line resolution uniformity particles & defects
to vacuum pump
vacuum chuck
spindle
developerdispenser
30/17
Institut de Microelectrònica de Barcelona
CLEAN ROOM TRAINING 2009-2010. Semester II
6. Hard Bake
Evaporate remaining photoresist
Improve adhesion
Higher temperature than soft bake
31/17
Institut de Microelectrònica de Barcelona
CLEAN ROOM TRAINING 2009-2010. Semester II
7. Development Inspection
Optical or SEM metrology Quality issues:
particles defects critical dimensions linewidth resolution overlay accuracy
32/17
Institut de Microelectrònica de Barcelona
CLEAN ROOM TRAINING 2009-2010. Semester II
8. Plasma Etch-Or Add Layer
Selective removal of upper layer of wafer through windows in photoresist: subtractive
Two basic methods: wet acid etch dry plasma etch
Quality measures: defects and particles step height selectivity critical dimensions
Adding materials (additive) Two main techniques:
Sputtering evaporation
PlasmaPlasma
CF4CF4
33/17
Institut de Microelectrònica de Barcelona
CLEAN ROOM TRAINING 2009-2010. Semester II
9. Photoresist Removal (strip)
No need for photoresist following etch process
Two common methods: wet acid strip dry plasma strip
Followed by wet clean to remove remaining resist and strip byproducts
O2O2
PlasmaPlasma
34/17
Institut de Microelectrònica de Barcelona
CLEAN ROOM TRAINING 2009-2010. Semester II
10. Final Inspection
Photoresist has been completely removed
Pattern on wafer matches mask pattern (positive resist)
Quality issues: defects particles step height critical dimensions
35/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Summary
Concept of optical lithography
Resists
Part ii
Associated processes
Part ii
Miniaturization
Limits optical lithography
Part i
36/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
silicon substrate
oxide
photoresist
Positive Lithography
Island
Window
Areas exposed to light become photosoluble.
Resulting pattern after the resist is developed.
Shadow on photoresist
Exposed area of photoresist
Chrome island on glass mask
photoresist
silicon substrate
oxide
Ultraviolet Light
Positive Resist Tone
37/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Photoresists
38/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Photoresist profiles Overcut (LIFT-OFF) Vertical Undercut Dose : High
Developer: Low
Dose : Medium
Developer: Moderate
Dose : Low
Developer: Dominant
Photoresist profiles
39/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Optical Resolution
PhotosensitivityRefractive Index
Mechanical/Chemical ViscosityAdhesionEtch resistanceThermal stability
Process related Cleanliness (particle count)
Metal ContentShelf lifeToxicityStability to process variations
Photoresist Material Parameters (requirements)
40/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Positive tone photoresist: DQN
Resin (N) / sensitizer(DQ)
N: phenolic Novolak resin: low molecular weight polymer. Forms the resists films properties. It dissolves in presence of water.
DQ (Photoactive siazoquinone ester) Photosensitive, insoluble in aqueous solution. Prevents the resin to be dissolved
Upon exposure to light, the dizaoquinones photochemically decompose
41/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Example: AZ 1500 Photoresists
42/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Positive tone photoresist: PMMA
PMMA: poly(methylmethacrylate)
Chain scission under DUV exposition
Also suitable for electron-beam lithography
43/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Example: nano-PMMA
44/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Negative tone photoresist
Resin: Cyclic Synthetic rubber (non radiaton sensitive, strongly soluble in the solvent)
PAC is a bis-arylazide. Upon exposure, it dissociates into nitrene and N2. The nitrene reacts with the rubber molecules so that a cross linking between resin molecules occurs, becoming unsoluble.
45/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Example: AZ-N4035
46/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
O
CH2
CH
CH2O
Epoxy based negative photoresistNegative photoresists becomeinsoluble in developing solutionswhen exposed to optical radiation
SU-8 is a commercial name for a fixed formulation. Any variation of thisformulation becomes a very similar resist, but as it is not exactly SU-8, thevariations are called epoxy based resists.
C CH3H3C
CH2
C CH3H3C
CH2
C CH3H3C
CH2
C CH3H3C
O O O
OOOO
CH2 CH2 CH2 CH2
CH2CH2
O
CH2 CH2
CH CH CH CH
CHCH CH CH
CH2 CH2 CH2 CH2
CH2CH2CH2CH2
O O O O
O O O O
• On exposure the PAG generates a strong acid
• Protons attack oxygen on some epoxides
• Crosslinking occurs during PEB resulting in an insoluble very dense polymer network
47/56
Institut de Microelectrònica de Barcelona
Escuela de verano de Jaca July 2011
Example: SU-8