Hi Suzanne,

What is your suspended membrane made from? We used to use an oxygen ash of
polyimide to release a silicon nitride membrane, but found that the oxygen
plasma would change the curvature of the membrane. Now we use a wet release,
with a polyimide that can be wet etched even after exposure fairly high
temperatures, and we use an oxygen ash to controllably flatten our
membranes. So, the warping of your membrane may be unavoidable with an O2
ash, but you can use it to your advantage. The polyimide we use is ProLIFT,
which can supposedly stand up to 400C and still be wet-etched in photoresist
developer. Of course, if you use a wet release, then you'll need to use a
critical point dryer or your membranes will collapse.

Regards

Jason Milne
PhD Candidate
Microelectronics Research Group
School of Electrical, Electronic and Computer Engineering
The University of Western Australia


-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Paradis, Suzanne
Sent: Tuesday, 7 July 2009 3:27 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Removal of polyimide sacrificial layer


Good afternoon,

I want to use  polyimide as a sacrificial layer (4 microns gap) to do a
suspended bridge.  My concern is that I do not have a asher, I have a
Tegal 903E plasma etcher which is meant to run at high pressure (1.5 to
4 torr).  I ran a sample at 1 torr and 40 SCCM O2 for 2 hours. ( I
understand that this is still too high as I read in the literature that
much lower pressure is recommended for suspended material).  Anyway, the
polyimide started to be etch in a wavy manner but the portion of the
suspended layer that started to be free was..warping.  I stopped the
process .  I tried with 275mt (even though I am out of range of the
instrument) and it took forever to remove most polyimide but the freed
layer was very warped.

Is there any hope that I can remove the polyimide with this instrument
or should I forget about it?

Thank you very much

Suzanne Paradis, ing. M.Sc.