Dear Chakry,

I am not surprized about the Al etch: TMAH does attack Al and the
only way to prevent this is by "doping" the solution with lots of
Si (search the list archives for earlier posts with literature on
how to do this). Alternatively, leave the Al covered by SiN and
open the contact pads after TMAH etching.
I am, however, surprized that you can "underetch" a beam. Since
TMAH does almost not etch sideways (on 100 Si at least) and leaves
a 55 deg angle slope from masking patterns (leaving a trench shape
like #\_/#, I wonder how you do that. Can you explain?

Greetings,
        Frank Berauer
        Senior R&D Engineer
        Hewlett-Packard Singapore


-----Original Message-----
From: Full Name [mailto:username@Eng.Auburn.EDU]
Sent: Saturday, May 25, 2002 3:19 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] TMAH Etching


Hi,

We were trying to Etch silicon under the cantilever beam through
TMAH(10% W/W in water)+SA(40% in aqeous solution)+APODS(Ammonium peroxy
disulphate).The entire mixure was heated to 80 degree centigrade.

After the devices were subjected to etching for 1 hour,we could get some
of the silicon under the beam got etched but the saddest part is the
aluminum bond pads which were open through the passivation layer(silicon
dioxide about 9000 Angstroms) were completely etched away.

Can anyone suggest me the proper TMAH etching of silicon that should not
touch the aluminum.

Thanks
Chakry
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