The following link might be helpful.  I thought I'd heard this question
before.
http://mail.mems-exchange.org/pipermail/mems-talk/2002-January/005971.html

David Nemeth
Senior Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA 20151
-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org]On Behalf Of ning
Sent: Tuesday, August 02, 2005 1:38 PM
To: General MEMS discussion
Subject: SPAM-LOW: Re: [mems-talk] How to etch Silicon into oblique
walls using ICP?

Hi Hongjun,

 The tolerance of the angle is very strict. It's about 1 degree. I know the
angle of KOH etch is about 54 degree. So that's not appliable in this case.
Thanks.