1. Effective substrate cleaning before deposition
Paula Päivike

2. Cleaning is necessary!
Contaminants cause: defects, delamination, inhibition of film growth…
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3. Cleaning is necessary! HF-solution RCA Standard clean Solvents
Contaminants cause: defects, delamination, inhibition of film growth…
Wet methods
HF-solution
RCA Standard clean
Solvents
Ultra/megasonic baths
Mechanical scrubbing
Spray cleaning
Dry methods
Plasma
UV-O3
High-velocity air jets
Cryogenic aerosol
Thermal

4. Cleaning Si wafers, original RCA
SC-1 (75-85 °C)
NH4OH : H2O2 : H2O
DI water cool/rinse
SC-2 (75-85 °C)
HCl : H2O2 : H2O
Spin dry

5. Cleaning Si wafers, modified RCA
Diluting SC-1 and SC-2
Replacing SC-2 with very dilute room temperature HCl
IPA vapour drying
HF-last

6. Information slides

7. Sources of contaminants
Common sources
Machining oils
Hydraulic & cleaning fluids
Adhesives
Waxes
Human contamination
Particles
Sources during cleaning process
DI water
Cleaning jigs
Air
Cleaning chemicals
Plasma
etc...
(ref. Hattori et al. on slide 9)

8. Cleaning Si wafers, original RCA
Wafers immersed in hot (75-85 °C) cleaning solutions for min
Rinsing/cooling with overflow running DI water after both treatments
SC-1 (organic contaminants, metal particles)
NH4OH : H2O2 : H2O
1:1:5 to 1:2:7
SC-2 (alkali residues, residual trace metals, metal hydroxides)
HCl : H2O2 : H2O
1:1:6 to 1:2:8
Exact compositions not important
Spin dry to avoid water residues and inert gas storage (if not used immediately)

9. Cleaning Si wafers, original RCA
Uses large amounts of chemicals & DI water!
Ammonium hydroxide 29% by weight of NH3
30 wt% H2O2
37 wt% HCl
SC-1 dissolves native oxide, which is generated back at roughly same rate - > particles removed
SC-2 removes Au and Ag residues through oxidative desorption
Kern: Handbook of Silicon Wafer Cleaning Technology, 2nd ed. 1993
Hattori et al.: Ultraclean surface processing of silicon wafers: secrets of VLSI manufacturing, 2013

10. Example: Alternative process by prof. T. Ohmi
Ohmi, T. Total Room Temperature Wet Cleaning for Si Substrate Surface J. Electrochem. Soc., Vol. 143, No.9, Sept. 1996

11. Cleaning Si wafers, modified RCA
Hot SC-2 needed to remove residual Au & Ag (ref. Kern)
These are no more present in high purity process chemicals
-> SC-2 can be substituted with very dilute room temperature HCl
IPA vapour drying (ref. Kern)
Water is displaced and no residues left when isopropyl alcohol evaporates
HF-last
Produces an H-terminated Si-surface => no native oxide
Must be used immediately because it is easily oxidised/contaminated
Concentrated HF results in more residual fluorine on the surface
-> Low concentration -> cleaner surface
Takahagi et al. The formation of hydrogen passivated silicon single-crystal surfaces using ultraviolet cleaning and HF etching, Journal of Applied Physics 64, 3516 (1988)