I have made fixtures for one-sided TMAH etching, and it is not an easy
thing to do!
Expect to run through a few generations before you get it right. The big
problem is that stressing the wafer by clamping down on it causes breaks
as you etch.

To answer your questions:
(1) PDMS is the fancy name for silicone rubber. Dow Corning makes a lot
of varieties, so do others.  It all depends on the curing chemistry.
Anyway, you need O-rings, so the place to go is Oring makers.
(2) I found that TMAH does attack silicone rubber eventually, and that
Viton O-rings worked better.
(3) Get the lowest durometer O-rings you can get.
(4) And look into the O-rings with a clower-leaf cross-section - they
seal with lower applied force.

Another suggestion: look into the design Eric Peeters (now at Xerox
Parc, peeters@parc.xerox.com) published in his Ph.D. thesis, p. 65. It
uses vacuum rather than mechanical clamping, and should be gentler.
The thesis is worth getting, it has lots of interesting information.

Luc Bousse
Caliper Technologies

> ----------
> From:         Alan Wilson
> Reply To:     Alan Wilson
> Sent:         Tuesday, January 27, 1998 10:17 AM
> To:   MEMS@ISI.EDU
> Subject:      PDMS
>
> I am trying to find a source for poly(dimethylsiloxane) (PDMS) as used
> to
> make sealing rings for TMAH etching (Transducers '97, 2D3.13P). I have
> heard that this might be commercially available as Silgaurd (Silgard?)
> made
> be? (DuPont? - but I can not find it in their web pages). Any ideas?
>
> Thanks
>
>
> Dr Alan Wilson
> Defence Science and Technology Organization, Australia
>                on attachment to the
>        Center for Integrated Systems, Room 206X,
>    Stanford University, Stanford CA 94305-4075, USA.
>
> E'mail: alan@sensors.stanford.edu  (alan.wilson@dsto.defence.gov.au)
>
> Tel (+1 650) 725 1682  Fax (+1 650) 725 9020
>
>
>
>