I recall in an SPIE class discussion (quite a few years ago) that if you
reduce your spin time to <10 seconds and  increase the spin speed (to get
the required thickness - you have to make a new spin curve)  you can
reduce/eliminate these lines.
I use a double coat of OCG 825-100cs @ 3k rpm to get 8-10 micron coat of
resist    with deep topography (50 microns) with no lines
Liz

> From: Alok Paranjpye 
> Reply-To: [email protected]
> Date: Tue, 15 Jan 2002 13:47:52 -0800 (PST)
> To: [email protected]
> 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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