I have to apologize in advance, I'm not doing MEMS, but it seems
there's a lot of information on TMAH here, so I'd thought I'd ask.

I'm trying to find an wet etch process that will etch polysilicon, but
not GaAs, and TMAH was suggested.

I tried this out, and it's not working the way I expected.  It doesn't
seem to etch the GaAs, but it doesn't seem to etch the polysilicon
either.  I tried 2% TMAH at 80C as well as 12%.  The layer was pretty
thin (500A), undoped e-beam evaporated silicon.


Also, as more of a trivia question, will TMAH attack AlGaAs?  I've
read about adding Si to prevent etching Aluminum, but it's not clear
to me that it will prevent the etching of AlGaAs.

Thanks in advance for any advice.
--
Pack my box with five dozen liquor jugs.
Brian Perkins                                bperkins@netspace.org