In our lab, we sometimes use a piece of black tape to protect the
front-side of the wafer during KOH etching @ 80C. Although the edges of
the wafer will be etched away and you have to make sure that KOH can not
get under the tape from the edges, it works.

Behraad

 > 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.