Troubleshooting
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Problems with Silicon Wafers
Problem
Probable Cause
Suggested Solution
Comments
Silicon
Damage
Excessive glass transfer
Use correct source for deposition temp.
Residual photoresist
Use "RCA Clean" immediately after stripping resist
Moisture in tube
  • Avoid backstreaming
  • Clean boats in dil. HF
  • Use improved storage techniques

Ambient Gases
Storage
(2)

Moisture absorbed by deposited
glass after dep.
  • Keep silicon dry by cooling in elephant
  • Immediately etch off deposited glass
    with dilute HF
  • Immediately rinse silicon in DI water and dry
Insufficient Oxygen in gas
  • Use 1/4-3% when dep. temp.
    is above 1000°C
  • Use trace amounts of oxygen
    (ie 1000ppm) when dep. temp is low
  • Use argon gas instead of nitrogen
Thermal gradients in
silicon wafers
  • Decrease push/pull temp. and rates
  • Decrease ramp rates
  • Cool in elephant
Failure to remove boron- silicon phase (stain)
Use LTO and etch before drive
 
Field Oxide
Damage After
Drive
Moisture absorbed by deposited glass after dep.
  • Keep silicon dry by cooling in elephant
  • Immediately etch off deposited glass with dilute HF
  • Immediately rinse silicon in DI water and dry
 
Silicon Warping
High thermal gradients across silicon wafer
  • Decrease push/pull temps. and rates
  • Decrease ramp rates
  • Cool in Elephant
 
Staining
Excessive boron-silicon phase on silicon surface
  • Increase oxygen in carrier gas
  • Use high temp source
  • Use LTO
       
Low Minority
Carrier Lifetime
Impurities from boat, tube, sources, etc
  • Use gettering (TCA, phosphorus dep., back surface damage, etc.)
  • Induce minor surface damage by decreasing oxygen in carrier gas
  • Age sources
Process-induced defects in silicon wafers
Slowly anneal doped silicon wafers
 
Increasing Beta
or Variable Beta
Moisture absorption of PhosPlus® sources
  • Insert sources in diffusion tube to dry
  • Store in dry environment
 
Rough
Polysilicon
Surfaces
Overdoping poly with phosphorus
Decrease amount of phosphorus
depositing on silicon

References

1. “Hydrogen Peroxide Solutions for Silicon Wafer Cleaning”, RCA Engineer, vol. 28-4, July/Aug 1983, pp. 99-105.

2. Hur-Ling Hsiu, “Effect of Solid Source Impurities on Silicon Devices”, Thesis at Arizona State University, Dec. 1988.

3. “Processed-Induced Defects in Borosilicate Glass-Diffused Silicon”, O. Aina and R. Kennedy, J. Electrochem. Soc., vol. 131, no. 8, pp 1884-1887.

4. J.E. Rapp, “The Planar Diffusion Technique”, Semicon Technology Asia 1998/9, Nordica International. 3.F Block B, Quarry Bay, Hong Kong, p.33.

5. T.A. Carbone, “Solid Source Doping of a Double Polysilicon Capacitor”, Semiconductor International, Nov. (1997) p. 89-95.

6. J.E. Rapp and T. A. Carbone, “Surface Roughness of Polysilicon Layers Doped with Solid Sources”, Presented at SEMICON® China 99 Technical Symposium, March 17, 1999, Beijing.

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