Also,
Trying to expose on a highly reflective surface , if you have a narrow band
exposure system, you end with a thin layer on un-exposed resist at the
bottom,
Try post exposure bake and if it doesn't help, descum

Shay


-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Scott McWilliams
Sent: Tuesday, September 19, 2006 4:37 PM
To: General MEMS discussion
Subject: Re: [mems-talk] Minimum feature size using wet etching - 3micro-m?

Hi Martyn, is it possible that you would require a descum step before the
wet etch?  I fabricate gratings of a similiar period and my process requires
and O2 plasma or O3 descum before wet etching to insure the resist is really
clear in the troughs.  I  am assuming you have a 50% duty cycle  of the
gratings and it is sometimes difficult to clear out the troughs when you
have a sinusiodal profile.  Lastly, are you using an anti-reflection
coating?  Patterning on metal can be challenging.