Martyn,
       An interesting question.  As image reversal depends upon the
refractive index on resist you would think we would have the answer.  I
am ashamed to say we do not.  If you are looking for differences in
resist profile caused by refraction index changes I may be able to help
you. Using ammonia to reverse the action of your original exposure and a
controlled flood exposure and develop.  The resist side wall can be
controlled between -22 degrees through vertical to + 22 degrees.  If
this is of any help contact me directly for technical papers and
information on free testing.

Bill Moffat, CEO
Yield Engineering Systems, Inc.
2185 Oakland Rd., San Jose, CA  95131
(408) 954-8353

cell 408 590 4577

bmoffat@yieldengineering.com

www.yieldengineering.com

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Martyn Gadsdon
Sent: Friday, February 09, 2007 6:20 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Refractive Index of Photoresists

Dear All,

I am interested in finding out what the difference in refractive index
is between un-exposed (with uv radiation) and exposed photoresist.
Particularly I am interested in knowing what photoresist (or other
substance that can be applied by spinning) will give me the most
difference in refractive index between exposed and unexposed areas.