Dear Frank,

We have some spacings in the cantilever beam that
would allow the TMAH to pass through the beam  and
etch the silicon underneath the beam.Regarding the
lateral etch we would be etching for more amount of
cavity underneath the beam so that the lateral etching
would completely release the cantilever beam.

cheers
chakry
--- "BERAUER,FRANK (HP-Singapore,ex7)"
 wrote:
> 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:[email protected]]
> Sent: Saturday, May 25, 2002 3:19 AM
> To: [email protected]
> 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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