effect of pumping method on wafer cleaning
TRANSCRIPT
6th LEVITRONIX CMP and Ultrapure ConferenceThe Westin Park Central, Dallas, Texas
May 11-12, 2011
Effect of Pumping Method on Effect of Pumping Method on Wafer Cleaning
R Prasanna Venkatesh Jung Soo Lim and Jin Goo ParkR. Prasanna Venkatesh, Jung-Soo Lim and Jin Goo Park
May 12, 2011
Department of Materials Engineering, Hanyang University,Ansan, 426-791, Korea
Semiconductor Cleaning
Particle
Organic contaminant
M l
Interaction Force
MetalNative oxide Attached Particle
W t Cl i
Si Wafer
• Wet Cleaning
• Dry Cleaning
ex) SC1, SC2, Piranha, HF etc…
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• Dry Cleaningex) Laser shock cleaning, Plasma, Anhydrous HF, Jet Fluid, Cryogenic etc…
ITRS Roadmap for DRAM
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41 36 32 29 25 Mask defect size, nm
ITRS Roadmap for DRAM
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Semiconductor cleaning
22nm22nm
167nm
High Aspect ratio (>8 : 1)
※ Generic Logic Flow 200711Metal Layers• 11Metal Layers
• 556 Total Steps• Cu Dual Damascene Tech. Multi layer (65nm, 2006)Leaning
• No pattern damages• No pattern damages• Film loss freeN t i l
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• New materials
Issues for the next Generation
6 Nano-Bio Electronic Materials and Processing Lab.S. Nadahara, “Wet Cleaning Technology Innovation”, SPCC (2011)
Cleaning target
7 Nano-Bio Electronic Materials and Processing Lab.S. Nadahara, “Wet Cleaning Technology Innovation”, SPCC (2011)
EUVL mask contamination sources & cleaning issues& c ea g ssues
13 5 nm
Contamination sourcesA pellicle cannot be used in EUVL due to itst d ti it h ld b l d
HO i
13.5 nm EUV Light
strong adsorption, it should be cleaned morefrequently
Haze
Ru C-L(2.5nm)
TaN A-L(80nm)
Oxidation
OrganicParticle
Surface roughness
Substrate(Quartz)
Mo-Si M-L(280nm)
Defect
(Quartz)Cond. Film
(CrN, 70nm)
Zero printable defect on a finished mask• Zero printable defect on a finished mask• No pellicle adders might be formed during handling and use• To clean new material surface, development of new cleaning solution and process
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- ruthenium, TaOx (Quartz and Si included)• To prevent reflectivity loss, control of particle, roughness, carbon-contamination, pattern damage
Semiconductor cleaning methods
High effective & Low COO
Chemical Cleaning • Megasonic
But, physical damages & High initial cost
Chemical Cleaning
• RCA
• Droplet / Jet spray
• Gas aerosol
• Gas dissolved water
• Solvent / Chelating
• Gas / Vapor phase
• Dry ice cleaning
• Laser shock cleaning
• Cluster cleaning
Physical Cleaning
Gas / Vapor phase
• Plasma
• UV light
• Cluster cleaning
• ScCO2
Cheap & High Throughput
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But, chemical etching & residues
Gas dissolved DI water cleaning
Definition of gas dissolved DI
water cleaning1. DI water based solutions
2. it contains a small amount specific ESH
Low CoO
2. it contains a small amount specific
gas and chemicals in ppm level
3. W/ or W/O Application of physical
h M i Specific
ESHenvironmentenvironmentSafetySafetyHealthHealth
energy such as Megasonic
H2, O3….with
Specific gases
High Cleaning Efficiency
Megasonic
Room temp.Room temp.PPProcessProcess
LowchemicalLow
material
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residuesmaterialloss
Gas dissolved DI water generationand cleaning systemg y
Out-Gas Out-Gas
Pump Gas
LiquidH2-DIW Contactor(Phaser II, Engetris)
H2-DIW Sensor(TOA-DKK, Japan)
Hydrogen
Extra gas
H2-DIW
Buffer Tank H2-DIWPump(Levitronix)
Single Tool+ Megasonic
• Dissolved Hydrogen sensor : DHDI-1 (TOA-DKK, Japan)
• Gas contactor : pHasorⅡ (Entegris, USA)
• Circulation Pump : BPS-3 (Levitronix, USA)
• Single tool (Aaron, Korea)
• Megasonic /1 MHz (Durasonic, Korea)
Cone & twin type Cone & twin type Evaluation of H2-DIW
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Cone & twin type Cone & twin type /1MHz (/1MHz (DurasonicDurasonic, Korea), Korea) Characteristics, PRE, Analysis of Si wafer surface….
PRE of H2-DIW w/ or w/o megasonic
DIW + NH4OH100
DI water+NH4OH
PRE of w/ MS @ 1MHz PRE of w/o MS
90
1004
H2-DIW (2.0 ppm) + NH4OHMS power : 1 W80
DI water+NH4OH H2-DI water(2.0 ppm)+NH4OH
Cavitation effect
0
80
40
60
PRE
(%)
10
7020
Change of electrostatic force by zeta potential value
0
W/ 32.0 ppm NH4OHW/ 1.4 ppm NH4OHW/O NH4OHpH 10pH 9pH 6.5
0pH 10pH 9pH 6.5
W/ 32.0 ppm NH4OHW/ 1.4 ppm NH4OHW/O NH4OH
• PRE was improved as gas concentration and pH increased
• H2-DIW(2.0ppm) w/ NH4OH has Higher PRE than DIW-NH4OH
High pH and H2 concentration result in Higher PRE (cavitation effect and Zeta potential)
• Cavitation effect is highly improved by adding H2 gas in DI water
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• Cavitation effect is highly improved by adding H2 gas in DI water
• Cavitation effect by megasonic is more dominant factor than change of zeta potential value
PRE comparison with conventional method
100
MS power : 1 W
As deposited : 5000 ea
Surface scanner
90H 9 0H 9 0pH 10 5 H 10 5
scannerimages
80 +NH4OHH2-DIW pH 9.0
DIW pH 9.0
SC-1/25oCpH 10.5 pH 10.5
RE
(%) SC-1/50oC
+NH4OHH2-DIW(2.0ppm) + MS (1W)106 ea
SC-1/50℃ + MS (1W) : 322 ea
Scan range : 0.18 ~ 1.6 μm
10
70PR
106 ea
0
10
PRE : 98%PRE : 96%
• Conventional SC-1 has over 96% of PRE in single type cleaning with MS.
2ppm of H2-DIW (pH9) has the highest PRE over 98%
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• H2-DIW can be proposed as an alternative cleaning solution
Hanyang University
Wafer cleaning in DI Water using pumps with and without pulsationWafer cleaning in DI Water using pumps with and without pulsationpumps with and without pulsation
1 I t d ti
pumps with and without pulsation
1 I t d ti1. Introduction- MLC (without Pulsation) vs. Positive displacement pumps
( ith l ti )
1. Introduction- MLC (without Pulsation) vs. Positive displacement pumps
( ith l ti )(with pulsation)- Magnetic levitation centrifugal vs. Positive displacement pumps (with pulsation)
- Magnetic levitation centrifugal vs. Positive displacement pumps
2. Results & Discussion- Wafer cleaning using DI water in wet bath
2. Results & Discussion- Wafer cleaning using DI water in wet bath - Wafer cleaning using DI water in single processor tool
3. Summary- Wafer cleaning using DI water in single processor tool
3. Summary
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INTRODUCTION-Applications of Pumps in Wafer Cleaningpp p g
• For delivering and circulating chemicals for various processes in semiconductor industries such as wafer cleaning, CMP etc.
P F P F
Tank
Regulator
Tank
Regulator
HeaterHeater
Bubble CutterBubble Cutter
Dampner
FilterFilter
Dampner
Conventional (Diaphragm) Pump
Pump Check V/V Pump Check V/V
Centrifugal Pump (SC-1)
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(SC-1)
INTRODUCTION- Centrifugal vs. Positive Displacement Pumps
Merits of Centrifugal Pumps• Flow is continuous in centrifugal whereas pulsatile in positive • Flow is continuous in centrifugal whereas pulsatile in positive
displacement (PD) pumps.
Demerits of Centrifugal PumpsDemerits of Centrifugal PumpsThe process require continuous and stable flow. However PD pumps are generally used because of the following issues associated with centrifugal pumps pumps
• It accepted as high shear devices due to high speed of operation• Delivery of ultra clean and delicate fluid is a major issue due to the y j
mechanical failure of shaft seal.• Bearings in centrifugal pump get destroyed if the pumping fluid
contain abrasive particles which is common in CMP application
What is the solution?– Bearingless, sealingless centrifugal Pump :
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g , g g pMagnetic Levitation centrifugal (MLC)Pump
INTRODUCTION- MLC vs. Positive Displacement Pumps
Particle agglomeration : Higher in positive displacement pumps due to high Particle agglomeration : Higher in positive displacement pumps due to high shear force exerts on the liquid being pumped1
CMP: MLC pumps leaves less scratches on wafer surface due to lower particle p p pagglomeration2
Particle shedding: MLC pumps shed lower number of particles during Particle shedding: MLC pumps shed lower number of particles during processing when compared to positive displacement pumps3
Foaming effect: positive displacement pump generates lot of bubbles when Foaming effect: positive displacement pump generates lot of bubbles when surfactant triton X is used4
These reports confirm that MLC pump overcome the major issues associated i h i l if l d i i di lwith conventional centrifugal and positive displacement pumps
What is the influence of pumps on surface preparation?
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OBJECTIVES AND METHODOLOGIES
Objectives:
To study the effect of pumping methods (with and without pulsation) on cleaning process performance in
1. Conventional wet bath2. Single wafer processor
Methodologies:
Estimation of number of particles added onto the silicon waferduring cleaning in DI water at different flow rates when pumpswith and without pulsation were applied
Estimation of random yield loss from particle count data usingvarious correlations.
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WAFER CLEANING EXPERIMENTS
Single Processor Wet Station
SC-1
Drain
Diaphragm PumpSingle tool Supply
Bath Circulation
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Schematic diagram of Experimental set up
WAFER CLEANING EXPERIMENTS IN WET BATH
Schematic diagram and Photograph of wet bath
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Schematic diagram and Photograph of wet bath
EXPERIMENTAL FLOW CHART- WET BATH
Connecting Pump to the circulation line
DI water circulation for 24 hours
Flushing and Refilling Tank with DI water
To remove particles generated during initial pumping
Flushing and Refilling Tank with DI water
Pre -circulation for 30 min
For stable flow
Wafer pre-Cleaning : SC-1
D i Si l Aki t lTo ensure the surface is hydrophillic
-For stable flow
Drying : Single Akiron tool
Wafer immersion in circulation bath for 10 min10 min
Wafer inspection before and after immersion
End of every 4 hr
(0,4,8,12,16,20 and 24th hr)
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EXPERIMENTAL CONDITIONS
Experimental Test Conditions in Wet Bath
Pump Flow rate (LPM) Pressure (PSI)Pump Flow rate (LPM) Pressure (PSI)
BPS-600 (MLC) 10 and 15 30
Diaphragm (D1) 10 and 15 30±3
Wafer Inspection using surface scanner (ST6600, KLA Tencor, USA)
Diaphragm (D2) 10 and 15 30±6
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EFFECT OF PUMPING METHODS ON WAFER CLEANING IN WET BATH
25000
30000
35000
Particles (ea)
Out of inspection range
25000
30000
35000
articles (ea)
Out of inspection range
25000
30000
35000
Particles (ea)
Out of inspection range
5000
10000
15000
20000
Num
ber of Add
ed P
5000
10000
15000
20000
Num
ber of Add
ed Pa
5000
10000
15000
20000
Num
ber of Add
ed P
0
0 4 8 12 16 20 24
N
Pump Circulation Time (hours)
0
0 4 8 12 16 20 24
N
Pump Circulation Time (hours)
(MLC) (D1) (D2)
0
0 4 8 12 16 20 24Pump Circulation Time (hours)
No. of particles added on to the wafer during circulation is very muchlower in BPS -600 pump (< 5000) at all the flow rates
In diaphragm pumps, number of particles added onto the wafer goesbeyond the inspection range of the Instrument (>30,000).
In diaphragm pumps, increase in flow rate increases the number ofparticles. However in MLC pump, the trend is different.
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RANDOM YIELD LOSS OF DEVICES
Particle size distribution analysis shows that most number of particles in the range of 0.178 -0.326 μm which is in the critical regime for making defects5
Yield loss is simulated from this particle count data using various correlations.
Correlation for no. of particles in UPW to defect density6 Correlation for no. of particles in UPW to defect density
DO = NBSKRPD [1]where Nb : No. of particles in DI waterS : Amount of DI water that contacts wafer during fabrication stepKR : Fraction of killing particlesPD : Probability of particles deposited onto critical areas
Linear correlation exists b/w no. of particles in the bath and on the wafer7
NB = ANW [2]NB ANW [2]whereNW : No. of particles on the waferA : Constant . The value of A is same for all the pumps if the particles composition generated by
all the three pumps are same
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all the three pumps are same
RANDOM YIELD LOSS OF DEVICESContd...
Ratio of defect density of two pumps (Using Equations [1] and [2] )
O,M LC B,M LC
O,D B,D
D N =
D N
Negative binomial yield model is used to estimate the yield as a function of critical area8function of critical area
CC 0
1Y = A D
1
where
C 0A D1+
C
Y : YieldAc : Critical area of the chipC : Clustering factor
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RANDOM YIELD LOSS OF DEVICES IN WET BATH
1
MLC
Assumption: Clustering factor (C)=2; DO,MLC
= 10.6
0.8
Yield
MLCD1D2
Note: Flow rate: 15 LPM and recirculation time : 24 hrs 0.2
0.4Chip Y
0
0 2 4 6 8 10
Critical Area cm‐2
• The chip yield is higher for MLC pump
Critical Area, cm‐
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WAFER CLEANING EXPERIMENTS IN SINGLEWAFER PROCESSOR
Schematic diagram of single wafer processor
Experimental Test conditionExperimental Test condition
Flow rate: Maximum value of each pump i.e. 20 LPM for MLC pumps and 15 LPM for both the diaphragm
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pumps and 15 LPM for both the diaphragm
EXPERIMENTAL FLOW CHART- SINGLE WAFER PROCESSOR
Connecting pump to the circulation line
Line flushing with DI water *Process Recipe
1. DIW rinse (Pump circulation and supply)
pre- circulation : 30 min
Drain and refilling Tank with DI waterTime : 60 sFlow rate : 0.5 LPM
W f Cl i SC 1
pre circulation : 30 min
- For flow stableSpin speed : 500 RPM
2. Spin Dry Wafer pre-Cleaning : SC-1
Wafer cleaning* at the end of every 4th
h (0 4 8 12 16 20 d 24th h )
Time : 60 sSpin speed : 1,500 RPM
hour (0,4,8,12,16,20,and 24th hour)
Wafer inspection
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EFFECT OF PUMPING METHODS ON WAFER CLEANING IN SINGLE WAFER PROCESSOR
3500
4000
4500
cles (e
a)
1500
2000
2500
3000
er of A
dded
Partic
MLC
D1
D2
0
500
1000
0 4 8 12 16 20 24Num
bePump Circulation Time (hours)
In BPS-600, number of particles on the wafer is around 300 and inD2, only the lower number of particles on the wafer (500) isobserved
Pump Circulation Time (hours)
observed.
The number of particles in D1is relatively higher and increases withcirculation timecirculation time.
The reason for observed lower number of particles on wafer inSingle wafer tool might be due to low process time
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Single wafer tool might be due to low process time
RANDOM YIELD LOSS OF DEVICESIN SINGLE WAFER PROCESSOR
0.8
1
MLCD1
Assumption:
Clustering factor (C)=2; D 1
0.4
0.6
0.8
Chip Yield
D1D2
DO,MLC = 1
0
0.2
C
0 2 4 6 8 10
Critical Area, cm‐2
• The chip yield is higher for MLC pump
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EFFECT OF PUMPING METHODS ON TEMPERATURE RISE OF THE SOLUTION
20
25
10
15
Δ T (℃
)0
5
0 4 8 12 16 20 24
In general, there is a power loss within the pump due to the difference in thebrake horsepower and water horsepower developed. These power losses are
Pump Circulation Time (hours)
p p p pconverted in to heat and results in a temperature rise of the liquid beingpumped.
The tempe at e ise of the DI ate d ing ci c lation is highe in BPS 600 The temperature rise of the DI water during circulation is higher in BPS -600pump than Magnum 620r and Futur 50 pumps.
The influence of flow rate on ΔT is more significant in BPS -600 than the other
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gtwo pumps
SUMMARY
1. Number of particles added onto the wafer is lower in the case of MLC pump than the other diaphragm pumps in both wet bath and single wafer processor.
2. Simulated yield as a function of critical area shows that there is a significant difference between MLC pump and Diaphragm pumpsdifference between MLC pump and Diaphragm pumps
3. The temperature rise of DI water during circulation is higher in MLC pumps than both the diaphragm pumps.
Thus, choosing the right pump is critical in wafer i tprocessing steps
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