Our Su-8 procedure after spinning is to put the wafer on the cold hot
plate then slowly increase the temperature.  The idea is to uniformly
heat up the photoresist.  We started doing this because our spins looked
fine but when we put the wafer on the hot plate, bubbles formed below the
resist.

Adrian

>Dear all,
>
> I am in the process of running in an existing SU-8 process in a new
cleanroom, and I have come across a problem I have never seen before.
After spin coating the SU-8 looks fine, but during softbake the resist
dewets on the surface. It pulls away from the wafer edges and form
isolated drops on the wafer.
>
> I think my process parameters are fairly normal:
> 1. 30 minutes in an oven at 200 deg. C to dehydrate the silicon wafer.
> 2. Let cool to room temperature.
> 3. Spin coat as per datasheet.
> 4. place on the 65 deg. C hotplate as per datasheet. (this is when it
dewets)
> ......
>
> Normally this gives great results, but not in the new cleanroom.
> Have anyone seen SU-8 dewet on wafers? And have you found out the cause?
>
> My current thinking is along the lines of surface contamination from
the oven, or a low air humidity in the cleanroom.
>
> Any input is appreciated.
>
> Jacques Jonsmann
>
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University of California, Davis
Dept Applied Science
1 Shields Avenue
Davis, CA 95616