The streaks may well be due to differential solvent evaporation rates (see
D.P. Birnie, J. Mater. Res. 16 (4), 1145, (2001)).  For thick PR coatings
try using SU-8 from Microchem Corp.  They produce resists that can generate
thick coats up to 200 microns.

Charles Lakeman,
TPL Inc.
Albuquerque, NM


----- Original Message -----
From: "Alok Paranjpye" 
To: 
Sent: Tuesday, January 15, 2002 2:47 PM
Subject: [mems-talk] AZ4620 problems


> 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
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