Results of testing Wet Benches for Sodium

Jim McVittie mcvittie at snf.stanford.edu
Fri Jul 19 17:55:49 PDT 2002


Wet bench Users,

As part of the clean up after the Pyrex glass wafer went through WBdiff
and Wbnonmetal,
we did a series of sodium contamination tests. For these tests, we
exposed clean 1000A oxide Si wafers to the HF baths in WBdiff and
Wbnonmetal, fabricated alumimum gate capaciators and tested for Na using
the  Bias Temperature Stress (BTS) CV method. In addition, to testing
the HF baths, we also tested the effect of dipping clean oxide wafers
into a container of 50:1 HF, which had been exposed to a Pyrex wafer for
2 minutes. The expectation was that the Pyrex wafer would contaminate
the bath with Na and pass on the Na to following clean wafers going
through the bath.

The results were surprized good, in that not only did the HF tanks in
the wet benches show no contamination, the wafer from the intensionally
contaminated HF container also showed no Na contamination to the oxide
wafers. In all cases, the mobile ion level was found to be below
5E10/cm2 which is quite good.

The conclusions are that the HF tanks in the wet benches were
successfully decontaminated, and that low levels of  Na in a HF bath
does not came out of solution onto clean oxide surfaces. These results
also say that the other parts of our lab needed for these MOS capacitors
are all in good shape in term of mobile ion contamination.  These other
parts include: the furnaces (Tylan #1 and #7, the DI water system, the
WBdiff bench with the HF tanks from the WBsilicide, the Gryphon sputter
deposition system, the litho area, the Wbmetal bench, the spin dryers
and the Tylan FGA tube.

Thanks for all your cooperation in help to keep the lab contamination
free.

       Jim McVittie




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