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