request to use PDMS in P5000/gryphon

Alissa M. Fitzgerald amf at
Fri Jan 13 17:33:39 PST 2006

Hello SpecMat,

Regarding my requests, I need to understand what further information is
required to help move this decision process forward.

I am going to acquire data sheets from Dow on chemical composition as
requested by Mary.

It seems that the main concern is not PDMS cleanliness, but the possibility
of metal peeling off the PDMS in the chamber and creating particles that are
hard to clean out.  Is this a concern for both the P5000 and the Gryphon?

Our priority is for approval to go into the P5000.  As far as the Gryphon,
one option would be for us to do metallization at an outside vendor and then
provide TXRF data to demonstrate it is clean enough to come back in to the
lab.  That way we can dodge the need to get approval for PDMS in Gryphon.

What other information is needed to help you make the decision?  How shall
we best gather that information?  Do preliminary tests need to be done??  If
so, what are they?  Would it help for me to hunt around for literature
examples, or get testimonials from other fabs working with this material?
Would you prefer to constrain the thickness of the PDMS allowed in the
chamber to address metal peeling concerns?  

I need to emphasize that we need a decision on whether PDMS can go in the
P5000 *before* we start processing.  I can not start to burn the client's
budget on a certain process path and then be unable to finish that path
because Spec Mat eventually decided to deny the request.  

Please let me know your thoughts.  

Best regards,

> -----Original Message-----
> From: Ed Myers [mailto:edmyers at] 
> Sent: Thursday, January 05, 2006 10:17 AM
> To: specmat at
> Cc: Alissa M. Fitzgerald
> Subject: Fwd: Re: request to use PDMS in P5000/gryphon
> 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] Sent: 
> Wednesday, January 
> >>>04,
> >>>2006 7:47 AM
> >>>To: Jim McVittie
> >>>Cc: Alissa M. Fitzgerald; SpecMat at
> >>>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
> >>>
> >>>
> >>>
> >>>
> >>>
> >>
> >>
> >>
> >
> >
> >--
> >Mary X. Tang, Ph.D.
> >Stanford Nanofabrication Facility
> >CIS Room 136, Mail Code 4070
> >Stanford, CA  94305
> >(650)723-9980
> >mtang at
> >
> >

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