Tao,

This paper would help for the TMAH bulk etching of
silicon without attacking aluminum.. (there may be
other papers after this one)

Diode-based thermal r.m.s, converter with on-chip
circuitry fabricated using CMOS technology
Erno H. Klaassen, Richard J. Reay, Gregory T.A. Kovacs
*
Sensors and Actuators A 52 (1996) 33-40

it works but it may be tricky if you are etching
waferthrough..
TMAH may not give good results as KOH if you are
etching through the wafer (however if you want to keep
your metals this is the only way I know)..

you may need to prepare a new solution after 6-7 hours
as etching slows down.. (but for 200-300 I don't think
you will need to prepare a second bath)

if you are just etching <100microns than it is
straightforward..

I would recommend making a test run with your worst
wafer (or piece) before doing the actual run..

kursad
sonicMEMS


> > From: Simon Garcia 
> To: General MEMS discussion 
> Date: Mon, 21 Nov 2005 21:20:06 -0500
> Subject: Re: [mems-talk] Etching Si (110) wafer
> without attacking Metal pads
>
> Tao,
>
> I am not sure about this, but I believe that you can
> passivate the
> aluminum by adding sodium silicate or silicic acid
> to your etchant
> (with proper pH adjustment, of course). I think many
> people use TMAH
> rather than KOH whenever they have metals. You
> should search Sensors
> and Actuators for more information. Search for
> "dual-doped etchant."
>
> Cheers,
> Simon
>
>
> On Nov 21, 2005, at 10:17 AM, Tao wrote:
>
> > Dear All,
> >   I want to etch (110) Si wafer (200~300um thick)
> to release my
> > cantilever. However the Al pads for electric
> contact will be etched
> > too.
> > So I am wondering if there are other metals that
> have a high resistance
> > to KOH? The important thing is that the wafer will
> be etched for about
> > 2~3 hours in KOH (20% ~ 60%, not decided yet) at
> 80 degree C.
>