Tarun,

I am going to guess that the you need to etch from the back side of the wafer
and the Al pads are on the front. There are several options that I will list in
terms of my preference.

1) If you are etching full wafers then buy an etch fixture which will protect
the top of the wafer.  You should be able to find prior messages on the site
with the names of the manufacturers.

2) Use a material from Brewer scientific (protek?) that you spin on to protect
the front side.

3) Deposit PECVD thin films and use TMAH. For example, 2 um of oxynitride.

4) Build a system to expose only the back of the wafer to the etch solution

I have used these techniques in production and development. The fixture is my
choice if you are doing one wafer at a time.

5) Use additives in the TMAH to lower the Al etch rate. You can find papers and
probably prior messages on the site.

If the Aluminum is on the same side as the etch then I would talk to Brewer
about patterning their film.

Dan Chilcott





-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On
Behalf Of tarun mudgal
Sent: Thursday, August 20, 2009 3:31 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] anisotropic etching of silicon having aluminium pattern

Dear all,

I want to fabricate a diaphragm, in that regard i need to etch silicon
anisotropically having aluminum metal pads already patternized on the silicon
wafer.

Now, since aluminium also gets etch in TMAH or KOH therefore I am facing a
stalemate.

If anybody has any ideas or suggestions it would be very helpful.

Thanks

Tarun Mudgal