method for cleaning si wafers
TRANSCRIPT
Method For Cleaning Si Wafers
HJ Report
23/12/2013
23/12/2013
Chemicals
Wet
HF : H2O
C3H6O
KOH
HCl:HF
CH3CH(OH)CH3:HF (or HI) (IPA)
SC1 & SC2 (RCA1 & RCA2 Cleaning)
Piranha Cleaning
HNO3 : HF
NaOH : H2O
CH3OH:HF
HF:H2O2:H2O
Dry
CF4/O2 (8% Mix)
NF3
H2
N2
O2
Ar
Marangoni drying
Etching and Cleaning
• HF Solutions
– Dilute HF (DHF) solutions - prepared by diluting
49% HF with dionized water
– Buffered HF solutions - prepared by mixing
49% HF and 40% NH4F in various proportions
• example: Buffered Oxide Etch (BOE) - patented
form of buffered HF solution
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Etching and Cleaning
• Piranha
– H2SO4 (98%) and H2O2 (30%) in different
ratios
– Used for removing organic contaminants and
stripping photoresists
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Etching and Cleaning
• SC-2 (RCA-2) : Standard Clean 2,
– HCl (73%), H2O2 (30%), dionized water
– Originally developed at a ratio of 1:1:5
– Used for removing metallic contaminants
– Typically used at 75 - 80 ºC
– To be stripped of by dilluted HF
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Alkaline Cleaning Solutions
• SC-1 (Standard Clean 1)
– NH4OH (28%), H2O2 (30%) and dionized water
– Classic formulation is 1:1:5
– Typically used at 75 - 80 ºC
– To be stripped of by dilluted HF
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Cleaning Si Wafer
1. Pre-texture cleaning
2. Texturization
3. Post-texture cleaning
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1. Pre-texture cleaning
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Piranha (optinal) : H2SO4 (40%):H2O2 (30%) ( 4:1) at 90 C 15 min.
DI water rinse
DHF : HF (2%) for 30 sec at 25 c
DI water rinse
SC-1/RCA 1 : NH4OH (29%):H2O2 (30%) H2O (1:1:5) at 75 C for 10 min
DI water rinse
DHF : HF (2%) for 30 sec at 25 c
DI water rinse
SC-2/RCA 2 HCl (30%):H2O2 (30%):H2O 81:1:5) at 75 C for 10 min
DI water rinse
HF/HCL cleaning
DI water rinse
Drying
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• Increase uniformity of pyramid (surface morphology)
• High etch rate
• Increase on Voc & efficiency of p type solar cell
• Efficiency increased 1% with compared to standard cleaning
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2. Texturization
KOH / IPA (isopropyl alchol) (reflection 12,5%)
Na2CO3/NaHCO3 (reflection 16%)
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Reflactance of wafers textured for differemt time as a function of wavelenght.
5wt% KOH & 3 vol% IPA at 80 C
3. Post-texture cleaning
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After full Rca procedure and KOH etch, diluted HNA ( hydrofloic, nitric & acetic
acid with 1:75:25
Alkaline etch cleaning
to 725- 735 mV & 81-
83 % FF
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HF/HNO3 inserted between RCA process this solves all issues relating to
surface contaminations and sharp areas