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The SMFL sees many types of substrates and materials. Some pose cross-contamination threats.

We detail here the specifics on processing certain materials in the SMFL.

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  • This includes Tungsten, Molybdenum, Tantalum, (and Titanium)
  • These metals have very high melting points and are generally very stable.
  • They are allowed in most equipment with a few exceptions (MOS RCA Bench, Gate Oxide Tube)

References
Wikipedia entry on refractory metals

Aluminum
  • Aluminum is a commonly deposited metal in the SMFL. This includes Al/Si alloys as well.
    • Substrates with Al should not be taken above 600C
    • Substrates with Al or that have had Al should not be processed in the MOS RCA Bench or processed in Tubes 1, 4, or 6
    • Aluminum contamination from RCA cleaning baths has been shown to have detrimental effects on thin gate oxides.

References

Restricted Materials

Copper

(warning) Copper is very mobile in silicon at lower temperatures and can cause serious degradation of device properties.

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  • Substrates with copper are allowed in very few tools and your process must be discussed before you start any work.

References

  • Ramappa, D. A., W. B. Henley. "Effects of Copper Contamination in Silicon on Thin Oxide Breakdown." J. Electrochem. Soc., Volume 146, Issue 6, pp. 2258-2260 (1999).
  • Jeon, J. S., S. Raghavan and H. G. Parksb. "Electrochemical Investigation of Copper Contamination on Silicon Wafers from HF Solutions." J. Electrochem. Soc., Volume 143, Issue 9, pp. 2870-2875 (1996).
Gold

(warning) Gold is similar to copper in that it can be deposited on wafers through baths such as HF. It can then make its way into high temperature furnaces and contaminate the quartzware and even the heating coils where it then contaminates other wafers on an ongoing basis.

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  • Substrates with gold are allowed in very few tools and your process must be discussed before you start any work.

References

High Vapor Pressure Materials
  • These are metals that are not allowed in our standard PVD systems. We do have one system that is used to deposit zinc.
  • They have vapor pressures high enough at lower temperatures that once they are in a PVD system - they will continually re-deposit on subsequent substrates.
  • These materials are restricted in what tools they may be processed in. Please contact the staff and present a detailed process flow.

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