Hot plate ovens seem to yield good results.  I think that slow bottom-up heating
helps to drive the solvent out without creating a crust on the resist surface.
Also, the sealed environment with a slow exhaust rate keeps a saturated solvent
atmosphere which also addresses surface crusting.

You have the right idea with the ramped bake approach.

Best Regards,
Garrett Oakes

EV Group
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-----Original Message-----
From: Shao Guocheng [mailto:[email protected]]
Sent: Monday, December 01, 2008 7:20 PM
To: General MEMS discussion
Subject: Re: [mems-talk] very thick layer of SU-8

Hi, All:

   So what kinda softbaking process u guys using for ultra-thick SU-8 layer. I'm
working with 1mm thick SU-8. My process is:

Spincoating first layer(around 500um), softbake at 65C for about 2 hours and
slowly ramp to 110c, hold for 6 hours and slowly ramp to room temp. for the
first layer I can bake out aroun 28% of the solvent which SU-8 50 should have
31%. But the remaining 3% seems not a big problem and I can finish my first
layer exposure pretty well.

for the second layer, I use almost the same process, but hold at 110c for 8hr,
but I can only bake out around 24% of solvent. Because of that, during my PEB
process, severe wrinkle happen around 50-60C, although it will smooth out after
a while, some of my fine structures r destorted by these wrinkles. I tried to
lower the baking temperature to 90C and bake for 15hrs, but still, only 24%-25%
of solvent can be bake out.

Any one has a cure for this prolem? thx a lot

Guocheng Shao