You can also use a material called ProTEK B. This is a spin on Polymeric
coating which is impermeable to KOH and TMAH base etchants. It will also
allow you to omit the use of fixtures during your TMAH etching.

You can find this material through google on the web or any search engine.



>  The way I protect the back side of a Si wafer I coat the backside with resist
> and apply wax paper.
>
>
> -----Original Message-----
> From: [email protected]
> To: [email protected]
> Sent: Sun, 27 Aug 2006 12:46 AM
> Subject: Re: [mems-talk] Unstable TMAH etching through wafer
>
>
> Mike,
>
> Thanks a lot for your prompt reply. Just one little question, how do you
> protect back side of the Si wafer when you etch for long time? If I am not
> wrong, from the etching set-up image, you etch the whole wafer, right?