polymer issues?

Jim McVittie mcvittie at snf.stanford.edu
Thu Aug 30 12:45:36 PDT 2007


On the P5000, we see a lot more black Si problems in large open Si areas 
when the chamber needs cleaning.   In fact, we use the formation of 
rough Si surfaces as the indicator for when the Si etch chamber needs a 
wet clean. So the scheduled chamber cleaning should help.


jim kruger wrote:
> This is not polymer and is not a problem.
>  It is "black Si",  a roughening of the Si caused by
> Cl2 + O2.  The O2 causes SiO2 "nanospots" to nucleate.
>  The etchrate is low on SiO2 so Si "Peaks" start to
> develop.  The higher etch rate on sloped corners
> continues to form the peaks.  The blackness is the
> result of high optical absorption due to multiple
> reflections in the "valleys" ("stack of razorblades"
> effect).  
> Mike Wiemer had similar suspicions a year or 2 ago and
> did SEM to show the roughness and EDAX to show no
> contamination, just Si, O2 and Cl2.  I think I still
> have his images but won't spam everyone with them. 
> Ask more if you are still concerned.
> jimkruger
> --- Patrick Lu <patlu at Stanford.EDU> wrote:
>> I think what I'm seeing now is some polymer buildup
>> on my samples that I
>> didn't see previously (this started before the
>> change of the Cl2 supply).
>> After using my usual chrome etch recipe the last few
>> times, I've noticed
>> that not only was I not getting through the chrome
>> layer that I once did
>> before, but also that there was a black soot-like
>> film building up on my
>> handle wafer. After running my etch for 20 minutes,
>> that stuff was
>> everywhere! I can only assume that it's gotten on
>> the inside of the chamber
>> as well. I'm not able to describe this very well, it
>> might be better if I
>> show someone. The gases I'm using are Cl2 and O2 in
>> a 10:1 ratio.
>> I am really at a loss! I've run the same recipe
>> dozens of times before
>> without any problems. Any input would be greatly
>> appreciated.
>> Patrick
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