I would guess your resist is not adhering to the substrate during develop.
Have you tried some sort of wafer conditioning before you put on the resist
such as a clean and HMDS.

Robert

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Edward Sebesta
Sent: Tuesday, April 01, 2008 8:15 AM
To: General MEMS discussion
Subject: [mems-talk] ZnSe on Ra photomasking problem


I have a curious problem in attempting to do photo patterning on our
substrate.

The substrate is 3,000 angstroms ZnSe on 20 angtroms RaAl alloy.

We spin on 30,000 angstroms positive resist, do a 60 seconds hot plate
softbake at 100 degrees C. Then a 30 minute oven bake.

We expose at a 150 mj/cm.2 and do a 2 minute develop in a TMAH
developer. Our feature sizes are greater than 50 microns and we have
pads that are 150 microns on a side.

After we expose and develop the wafer, we find that there absolutely no
patterned resist on the wafer.

We have tried lower exposures, shorter develop times, and have checked
the exposure intensity and imaging of our contact printer. We have
checked the oven temperatures both hotplate and oven as well as the
resist thickness.

We tried a negative resist also, but then nothing develops out and we
get a solid sheet of resist.

We are mystified as to the cause of our problem. Also, how would a
person do photomasking on such a substrate.

Ed Sebesta