request to use PDMS in P5000

[Mary Tang]

Hi Alissa, Jim --

I think I have this information somewhere, from a previous request.  As 
I vageuly recall, PDMS (Dow Corning Sylgard 182 or 184) is based on a 
Pt-catalyzed reaction, although very little Pt is actually present.  
Other metals and impurities, such as sulfur, will prevent 
polymerization.  So, other than the Pt, PDMS is actually pretty clean -- 
although perhaps not by electronics-grade standards, it's cleaner than 
your ordinary plastics.  I'll see if I can find the info.  I think that 
Claudia Richter provided it, so I'll also check with her.

Just on a side note, I'm personally less concerned about the potential 
contamination than the process flow itself (Alissa, perhaps you've got 
experience or references on this already.)  500 microns of PDMS is 
pretty thick...  It's got a high thermal expansion coefficient, so I'm 
not entirely sure that you could put 0.5 microns of Al on it without 
having it peel off due to stress differences, even with an adhesion 
layer (although having thin lines might help).   I think Claudia or 
Neville Mehenti may have experience in depositing metals on PDMS in our 
lab (although I'm pretty sure they would have used metalica or 
innotec.)  By the way, does your request entail using gryphon for Al 
deposition?

Also, PDMS is a darn good insulator -- I think the Al etch rates and 
profiles may be very different than they would be on silicon due to 
differences in plasma behavior (at least, I understand that P5000 
etching of films on quartz is very different from etching on silicon.)  
I would suggest that if you have problems, a thinner PDMS layer (tens of 
microns -- you may have to dilute and spin coat) might help.  
Constrained PDMS (by adhesion at the Si/PDMS interface) won't expand as 
much and electronic effects on plasma *might* be reduced.

Again, I'll if I still have the purity info, and if not, I'll drop a 
note to Claudia.  I think that Dow provided this info to Claudia (or 
whomever it was who gave it to me) so you might try asking them.

Mary

Jim McVittie wrote:

>Hi Alissa,
>
>During the overetch, the Al etch chamber will be contaminated by the
>decomposition products of the PDMS. So the important question what is in
>PDMS and is it a problem to other users of the chamber. My concern is
>what metals at in PDMS and at what level. Can you find a purity analysis
>for PDMS?
>
>    Thanks, Jim
>
>"Alissa M. Fitzgerald" wrote:
>
>  
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-- 
Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
(650)723-9980
mtang at stanford.edu
http://snf.stanford.edu