Dear Daxiang,

in our lab at ETH, we have tried different ways of backside protection
based on coatings, but did not find the reliable. Especially, as we have
CMOS structures on the protected side, 100% protection is required in
our case. Since many years we use wafer holders with backside protection
from AMMT GmbH (www.ammt.com) in Germany, which work perfectly for us.
They work with a wide range of etchants aside KOH, including hot
phosphoric acid and HF.

Regards,

Jan

> 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.