Actually, the limit is closer to 1.5 microns.  If you wish to use SiO as an
etch mask, you can try using TMAH (Tetra Methyl Ammonium Hydoroxide) as an
etchant.  It's selectivity to the <111> plane is not as good as KOH, but it
does not attack SiO.

David Nemeth
Senior Engineer
Sophia Wireless, Inc.

-----Original Message-----
From: guda reddy
Subject: [mems-talk] SiO2 As a Mask

  I have question for SiO2 as a mask while etching Si in KOH. I have been
suggested that the maximum thickness of the thermally grown SiO2 that i
could use is only 1 micrometer and if i go beyond that there would some
thermal stress and thermally grown SiO2 is not stable. I would really like
to known whether there are any papers or any book that mentions about this.
If there are, could any of you suggest me.