Fwd: Re: request to use PDMS in P5000/gryphon

Paul Rissman rissman at stanford.edu
Thu Jan 5 10:24:43 PST 2006

I would say that if Alissa takes responsibility for cleanup of any flaking 
and rework of any processes that are a problem, e.g. etch, then we should 
approve the request based on a consistent determination on the material 

Can we get Alissa to obtain the specification for contamination?

At 10:16 AM 1/5/2006, Ed Myers wrote:
>A number of good points have been made during the discussions.  Alissa is 
>correct in her recognition of increased requests for PDMS.  It would 
>benefit our community if SpecMat could categorized PDMS in to one of our 
>contamination classifications.  The question being if it needs to be gold 
>contaminated or we can place it in either Semiclean or SemicleanB, since I 
>don't think Clean is appropriate.  We will need to understand the 
>differences between the many different variations of PDMS.  I'll work with 
>Mary and see what we can find with regards to trace elements and the 
>chemical and thermal stability of the PDMS.
>The more pressing mater is to respond to Alissa's request.  From trace 
>element contamination, Mary's memory seems to indicate Alissa's requests 
>are reasonable.  I am very concerned about whether the process is 
>manufacturable.  Various concerns have been expressed over a number of the 
>process steps.  These concerns include the ability to expose 0.7um 
>features due to surface undulations in the PDMS, adhesion of the Al to the 
>PDMS and the potential for the Al to peel at numerous locations including 
>the Gryphon deposition chamber, P5000 and resist strip and the influence 
>of the PDMS on the etch process in the P5000.
>As a proposal why don't we let Alissa get started on her PDMS casting and 
>lithographic process development.  I would recommend starting with Al 
>deposition from the Innotec.  The Innotec should be the most compatible 
>deposition tool, since the wafer heating will be the lowest.  If she is 
>able to get satisfactory patterns, we will be at a decision node where we 
>either let the Innotec film in to the P5000 or we allow the PDMS in to the 
>Let's get another iteration of comments and try to resolve the request 
>this week.
>>Hello SpecMat'ers --
>>I don't know how hot the gryphon can get, but do think that  outgassing 
>>is likely lot less of a problem for PDMS than for photoresist or 
>>polyimide tape, if temperatures remain fairly low -- and if the PDMS has 
>>been sufficiently cured.  Again, I'm not sure of the purity, but I think 
>>the data exists somewhere...
>>Alissa M. Fitzgerald wrote:
>>>Hi Mary, Jim,
>>>Thanks for the info.  Based on your information, and Jim's most recent
>>>email, does this mean it is approved for use in the P5000?  (Also, as a side
>>>note, based on the number of inquiries I get regarding PDMS, SpecMat may
>>>want to consider and publicize a general policy with regards to this
>>>material.  I think it's an important material that is gaining popularity in
>>>MEMS, esp. with regards to medical and biotech applications.)
>>>The process is aggressive and experimental.  Honestly, I am not sure this it
>>>is going to work, but the customer is interested in trying it out. We may
>>>need to start with different PDMS thickness, bigger CD's, etc.
>>>We will need permission to put PDMS in the gryphon, too.  We need to use
>>>>-----Original Message-----
>>>>From: Mary Tang [mailto:mtang at stanford.edu] Sent: Wednesday, January 
>>>>04, 2006 7:47 AM
>>>>To: Jim McVittie
>>>>Cc: Alissa M. Fitzgerald; SpecMat at snf.stanford.edu
>>>>Subject: Re: request to use PDMS in P5000
>>>>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 
>>>>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.
>>>>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:
>>>>>>  Part 1.1    Type: Plain Text (text/plain)
>>>>>>          Encoding: 7bit
>>>>Mary X. Tang, Ph.D.
>>>>Stanford Nanofabrication Facility
>>>>CIS Room 136, Mail Code 4070
>>>>Stanford, CA  94305
>>>>mtang at stanford.edu
>>Mary X. Tang, Ph.D.
>>Stanford Nanofabrication Facility
>>CIS Room 136, Mail Code 4070
>>Stanford, CA  94305
>>mtang at stanford.edu

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