I have a requirement for a thick (~6+ um) positive resist layer. I've been
trying to use AZ4620 at 4000 rpm for this purpose, but it always gives me
an uneven, streaky coating, with the streaks running in the  radial
direction on the wafer. I have tried ramping the spin rate to avoid this,
but the streaks remain. If anybody has had a similar experience, and could
help me out, it would be great. Alternately, I'd appreciate any
suggestions for another resist that could give me a thick coat, and could
be exposed on an i-line stepper.
Thanks
Alok Paranjpye

Graduate Student
University of California,
Santa Barbara