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.