Since TMAH is an anisotropic etchant of silicon, for (110) plan wafer
the etched walls will be perfectly vertical (the etch is much slower
against (111) plane and this will result in vertical walls). However,
this also means that your etch mask has to be alligned with the flat,
otherwise the etch will "correct" itself and find the (111) plane even
if it's not aligned with your mask. You will have some underetching, but
these will also be vertical.
500um is one long etch.

Elina Kasman
Process Development Engineer, R&D
Engis Corporation



-----Original Message-----
From: Andrea Mazzolari [mailto:info@alientech.it]
Sent: Saturday, July 08, 2006 8:51 AM
To: General MEMS discussion
Subject: [mems-talk] Etch through Si wafer with TMAH

Hi all. I need to etch through a (110) silicon wafer 500um thick. I'm
planning to use TMAH. Will walls be perfectly vertical ? If not, which
etchant could i use ? In case of tmah etch will under etch responsible
for not vertical walls ?
Based on what i know, walls will not be perfectly vertical, this sould
be due to under etch... i'm i wrong ?
Could someone suggest me some article on this argument ?

Thanks!
Andrea