you could try the following depending on your process

1) boron doping,

2) pdms

3) spin on coating from brewers science

4) Adsil

5) use a ssytem to only allow etching of one side of the wafer


The concentration i have used was 1 micron/min at 80 C

Dr. Michael Cooke
Microsystems Technology Group
School Of Engineering
University of Durham

>
> 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.
>