Bill, What advantage does using ammonia vapor to achieve image reversal have over using an image reversal resist, such as AZ5214-E, which doesn't require any additional equipment? Roger Shile -----Original Message----- On Behalf Of Bill Moffat Subject: RE: [mems-talk] Refractive Index of Photoresists 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.