Hi Lin,

Are you carrying out your softbaking on a hotplate or in a convection
oven? The latter can lead to wrinkles because the resist's surface
layer dries out at a higher rate than inner regions.

If you are using a hotplate, the effect should be reduced because
heating is from below, and solvent evap from inner regions maintains
solvent concentrations in the surface layer. Nevertheless, dry-out
differential could still be pronounced on a hotplate, particularly as
your layer is ralatively thick.

I suggest a prolonged and/or ramped softbake so the solvent can
gradually escape the resist, without the surface layer drying out too
quickly and forming wrinkles. Alternatively, I recall that one of my
colleagues, facing a similar problem with thick SU-8, placed a glass
petri dish (upside down and) over thick SU-8 during softbake on the
hotplate. The dish was placed on glass slides to raise it from the
hotplate plate, creating a vent for solvent evaporation.

Hope this helps. Good luck!

Michael


>>
>> -----Original Message-----
>> From: [email protected] [mailto:[email protected]]
>> On Behalf Of Li, Lin (MU-Student)
>> Sent: Thursday, 3 July 2008 3:00 AM
>> To: [email protected]
>> Subject: [mems-talk] SU8-2075
>>
>> I have been using SU8-2075 to make 100um thick structure. But I have
>> difficulty in reducing the wrinkles and the roughness.
>> I tried 65C and 95C softbaking 5min and 10min each or even tried to cool
>> down and bake repetively as the manual suggested.
>> Could you let me know any recipe or methods to solve this problem?