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

Mary Tang mtang at stanford.edu
Thu Jan 5 15:00:45 PST 2006

I agree with Ed, in that we could work on approving semiclean use of 
PDMS, but it may take a little while to collect info and understand the 
issues.  This should not gate Alissa's ability to get started on the 
project, which seems to pose several process concerns other than the 
P5000 etch.  If I were doing this project, I would, as Ed suggests, put 
Al on PDMS and do wet etch to characterize adhesion and peel, as a quick 
test.  I do think, however, that Alissa will bring up an objection to 
using the innotec, based on the perceived difficulty in acquiring 


Paul Rissman wrote:

> 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 contaminants.
> Can we get Alissa to obtain the specification for contamination?
> At 10:16 AM 1/5/2006, Ed Myers wrote:
>> All,
>> 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 Gryphon.
>> Let's get another iteration of comments and try to resolve the 
>> request this week.
>> Ed
>>> 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...
>>> Mary
>>> 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
>>>> aluminum.
>>>> Regards,
>>>> Alissa
>>>>> -----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 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:
>>>>>>>  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
>>>>> (650)723-9980
>>>>> mtang at stanford.edu
>>>>> http://snf.stanford.edu
>>> -- 
>>> 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

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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