Hi,

The etch rate of Si3N4 in both KOH and TMAH is lower than SiO2. Please
check the literature as there are numerous papers and books with
information on this...

If your Si3N4 mask layer is not allowing you to etch for more than 2
hrs, you need a thicker layer! The etch rate of Si3N4 in TMAH is about
20 A/hr compared to about 100 A/hr for SiO2.

Cr is an option if you cannot deposit thicker Si3N4.

Regards,

michael

>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Ziaur Rahman
> Sent: Friday, May 12, 2006 2:08 PM
> To: [email protected]
> Subject: [mems-talk] TMAH Etching mask
>
>
> I need to do anitropic etching of Si and planning to etch around 200 um.
>  As we do not have DRIE we have to do wet etching. I tried KOH solution
>  with different kind of masks like PECVD Nitride, Cr, Cr and Gold. But
> nothing
>  survived more than 2 hours. So I am planning to use TMAH for etching.
>
>  What kind of material can  survive without peeling for more than 3 hours
> in TAMH?
>  I want to use sputter Cr. Is it a good idea? I know a lot of people are
> using
>  oxide and nitrides. But I prefer to use Cr as I have to etch for long
> time.
>
>  Any suggestions, comments will be highly appreciated.
>
>  Best,
>
>