Qualifying Outside Sources for Processing
mcvittie at cis.Stanford.EDU
Fri Dec 1 17:50:55 PST 2000
To be consistent with the contamination control done in our lab, outside
processing sources really need to be qualified before allowing wafers back
into the lab. Most important are wafers going into the furaces with higher
temperature processes being of most concern. So far the only qualification
we have done for outside processing has been to look at a sputtered oxide
deposited on campus and at a new thick PECVD oxide process done by a
company. In both cases we did TXRF (about $100 per wfer at Charles Evans).
In the case of the sputtered oxide, we found a large amount of metals
including Fe, Mg and Cr. This was due to a previous dep done in the
sputter tool. For the PECVD oxide, we found high Na contanination. This
was probably due to poor handling and cleaning procedures. Although there
are more sensitive methods than TXRF, from a cross contamination view TXRF
( about 2E10 per cm 2) is probably good enough.
Deposition is not the only concern for concern for sources of
contamination. For instant, an improperly setup ion implanter can lead to
sputtered metal contamination. In addition, poorly cleaned wafers after
polishing can be a problem.
Overall contamination from established processing services is most likely
not a big problem. I expect that many offer a contamination specification
that we may be able to live with. I am most concern is with wafers coming
from university labs and new industrial processes.
The bottom line is that wafers with outside processing need approval to
come back into lab. In he past, we have let ion implanted wafers into the
lab without any speacial approval. Other than implanted wafers, I would
like to see, TXRF results for wafers processed on the outside. An
exception may be given for vendors who supply contamination specifications
or do complete (CMOS) device fabrication.
If there is a lot of concern about this issue, I am willing to have a
meeting to discuss what we should be doing.
James P. McVittie Senior Research Scientist
Allen Center for Integrated Systems jmcvittie at stanford.edu
Stanford University Tel: (650) 725-3640
Rm. 336, 330 Serra Mall Fax: (650) 723-4659
Stanford, CA 94305-4075
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