Try using silicon nitride it protects well from koh and it withstands high
temperatures. I use it @ 85c. with no problems.

Tony galindo

-----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.