Did you use HF or BOE?  BOE (Buffered Oxide Etch) is HF
buffered with ammonia.  It will not attack photoresist.  If
you still have problems using BOE, you should look into the
PR adhesion.

Good luck,
Bill

---- Original message ----
>Date: Tue, 16 Nov 2004 08:54:09 -0700
>From: Zhiyan Liu 
>Subject: [mems-talk] Etch SiN
>To: [email protected]
>
>Dear friends,
>
>I want to etch 250nm of SiN without attack the GaAs
substrate. I tried the
>wet etch using HF and photoresist as the etch mask. But the
PR all peeled
>off during the etching even after hard baked. I am wondering
if anyone has
>a suggestion on the etch of SiN.
>
>Thank you very much,
>
>Zhiyan
>
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