jimkruger at yahoo.com
Tue Aug 28 06:47:08 PDT 2007
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"
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.
--- 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
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