Have a look at http://www.ee.byu.edu/cleanroom/KOH.phtml for possible
etch rates. Also the use of IPA reduces the etch rates quite a lot, but
produces smoother surfaces.

Ariel

-----Original Message-----
From:  D. Zhou
Subject: [mems-talk] KOH etching

I am now working on silicon microbolometers based on SOI wafer for THz
detection and trying to use KOH to etch the substrate from the back
side.
Some questions:

1. How to effectively protect the front-side of the chip when doing KOH
etch??
   Black wax?? Silicon nitride?? 2. I calibrated the etch rate of KOH
mixture( 15g KOH: 50ml water: 15ml IPA)
   and obtained ~320nm/min @ 60c and 1.1um/min @ 80c. What composition
and
   concentration can achieve ~1um/min @ 60c? Because I used black wax as
the
   mask to protect the front-side, however it melt at 80c.