I would like to use silicone rubber in the lab

Mary Tang mtang at snf.stanford.edu
Fri Feb 4 15:58:56 PST 2005

Hi Yves and John Paul --

Thanks for giving the Sylgard a try.  The RTV is approved for use in KOH 
etching in gold-contaminated labware at wbgeneral.  Could you apply and 
cure the RTV either outside the cleanroom?  (I'm presuming that it takes 
a day or so to cure and is emitting acetic acid while it does, and that 
you probably don't want to leave this at a bench over night?)


Yves Acremann wrote:

> Dear Mary
> We did some tests with Sylgard 184 from another user and it looks like 
> the RTV we are using in our lab has better adhesion. So please give us 
> official
> approval for this material.
> Thanks
> Yves
> Mary Tang wrote:
>> Hi Yves --
>> Sylgard 184 is available from K.R. Anderson for something like 
>> $40/pound (maybe even cheaper than RTV?)  I have some, if you'd like 
>> to try it.  It probably requires more handling (you have to mix two 
>> components, and you might have to de-gas it), but it does not contain 
>> acetic acid (which RTV does -- and I believe that the silicone glue 
>> you were requesting to use was RTV.)  So, if you'd like to give it a 
>> try, you're welcome to this.  If you'd like to stick with your RTV, 
>> that's OK too -- just let us know so we can officially document this 
>> for future reference.
>> Thanks,
>> Mary
>> Yves Acremann wrote:
>>> Dear Mary
>>> Thanks for your mail. The holder does not work for us as we don't 
>>> have full wafers. I never used Sylgard 184/PDMS, but this may be a 
>>> very interesting material for us.
>>> Is that material in stock / do you know somebody who uses it?
>>> The labware we will use is a general-use beaker and a 
>>> gold-contaminated refluxer (gold contaminated) and our own glassware 
>>> (also only used for gold contaminated
>>> work).
>>> Regards
>>> Yves
>>> Mary Tang wrote:
>>>> Hi Yves --
>>>> We discussed your request in yesterday's SpecMat meeting.  I think 
>>>> this is generally OK.  But we were also wondering if you had a 
>>>> chance to explore some other tried-and-true solutions.  First, 
>>>> there is a nifty little holder designed for protection of wafers 
>>>> during KOH etching.  Uli has one of these or she can tell you where 
>>>> to purchase one.  Second, some people have used silicone elastomer 
>>>> (Sylgard 184/PDMS as opposed to the RTV your are using) for KOH 
>>>> etching.  It's a little nicer, because you don't have acetic acid 
>>>> in it.  I believe it has been used up to 80C, but don't know the 
>>>> results and would suggest you try this on test wafers before doing 
>>>> your devices, if you are interested.  The third question was which 
>>>> labware you intended to use...  If you are using a general-use 
>>>> beaker and a gold-contaminated refluxer, then it's OK, because 
>>>> these are not "clean" anyway.
>>>> In summary, please let us know if you have explored or will 
>>>> consider these other solutions -- if these don't work for you for 
>>>> some reason, please do let us know why, and then we can approve 
>>>> your RTV use (sorry, we would rather not approve "just in case" 
>>>> because we would end up with too many approved, but not-used, 
>>>> chemicals in the lab.)
>>>> Thanks,
>>>> Mary
>>>> Yves Acremann wrote:
>>>>> One of the tricky processing steps is KOH backside etching of 
>>>>> wafers with metal structures on the frontside. The main problem is
>>>>> the protection of the front side during the etch process. We 
>>>>> currently use black wax for that purpose. We had some problems with
>>>>> this in the past where the black wax layer failed during very long 
>>>>> etches (up to 40 hours for 1.2mm thick Si wafers).
>>>>> We would like to try to put two wafers front to front and use 
>>>>> silicone rubber to seal the edge. In addition, we plan to have 
>>>>> black wax on the
>>>>> front side.
>>>>> We did some tests with silicone rubber and its ability to 
>>>>> withstand KOH in our lab at SLAC and this method looks promising.
>>>>> We used the following product for our tests (copied from the home 
>>>>> depot catalog :-)) ):
>>>>> "GE 2.8 oz. Clear Silicone Household Glue
>>>>> Model GE280 3TG
>>>>> 100% silicone. Permanently flexible. Adheres to tile, porcelain, 
>>>>> glass, fiberglass, marble, wood, steel, aluminum, brick, mortar, 
>>>>> concrete, and most plastics. Lifetime satisfaction guarantee. 
>>>>> Won't dry out, crack, chip or peel. Easy to use squeeze tube. Can 
>>>>> be used as glue, sealant, caulk or gasketing, and for many patch 
>>>>> and repair applications around the house and shop."
>>>>> For our real wafers, we would like to test this method in the 
>>>>> cleanroom. As similar materials are likely used during 
>>>>> construction of the wet benches, I hope it will be possible to get 
>>>>> approval for
>>>>> this material. Of corse we only deal with gold contaminated wafers 
>>>>> and this is our last processing step (followed by solvent cleaning 
>>>>> and sawing the wafer). We also will NOT heat the
>>>>> wafer to a temperature higher than 75C (in KOH) and if necessary, 
>>>>> we can do the KOH etch in our lab at SLAC.
>>>>> I did not find the MSDS that corresponds directly to this product, 
>>>>> but there is a link containing more information about it:
>>>>> http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=brands&id=7011007 
>>>>> Sincerely
>>>>> Yves Acremann

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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