Hi,
this behaviour is against all models for orientation dependent
etching and I am very interested to get some information about this
problem, as soon you have found the answer.

One possible explanation could be, that your oxide is completely
removed after the time you need for 100 µm etch depth. If it is, you
get of course a stable etch depth because the etch ground and the
wafer surface are etched with the same etch rate.

To get more information about the orientation dependent etching and
its simulation please see also http://gemac.c.ntg.de/mst_eng.htm


> Date:          Thu, 22 Oct 1998 14:17:11 -0500 (CDT)
> From:          cmk 
> Subject:       KOH etch question
> To:            MEMS@ISI.EDU
> Reply-to:      cmk , mems-cc@ISI.EDU

> Hello,
>
>    I am trying to anisotropically etch a 200 um well in a silicon wafer
> coated with 1 um of oxide. I'm using KOH mixed at 30% concentration and
> have tried temperatures at 60 C and 70 C. Both trials the etch worked fine
> all the way up to about 90-100 um, and then it just stopped. Even if I
> leave the wafer in for extra hours, the etch still remains at 90-100 um.
> Nothing else has been done to the wafer before this except a BOE etch to
> pattern the oxide. Any ideas would be greatly appreciated.
>
> ---Chris
>
>
>
Dirk Zielke
GEMAC mbH
Matthesstrasse 53
09113 Chemnitz
Germany
Tel.: +49 371 3377 131
Fax.: +49 371 3377 272
email: gemac.chemnitz@t-online.de
http://gemac.c.ntg.de (Deutsch)
http://gemac.c.ntg.de/mst_eng.htm (English)