Ues the YES technique.  Vacuum purges to promote dehydration followed by warm
Nitrogen to rewarm the areas cooled by the latent heat of evaporation.  At 1
Torr water honestly boils at -20 degrees C if you can avoid vacuum freezing.
Bill Moffat

________________________________________
From: mems-talk-bounces+bmoffat=yieldengineering.com@memsnet.org [mems-talk-
bounces+bmoffat=yieldengineering.com@memsnet.org] on behalf of Shane GUO
[shane.guo82@gmail.com]
Sent: Tuesday, July 12, 2011 2:42 PM
To: mems-talk@memsnet.org
Subject: Re: [mems-talk] make the su-8 surface flat

Hi all,

Gareth is correct. Dehydration is very important for my case. Because my last
wafer has another polymer layer beneath the SU-8 layer, I cannot bake the
substrate above 90C for dehydration. By using a clean wafer, baked at 200C for
15mins and treated by O2 plasma for 10mins, I spin coated SU-8(50) at 1500rpm
for a 80um thick film. The coated wafer was relaxed overnight and no pulling
back was observed. Surface was very flat (visually) as expected except for the
edge bead (around ~5mm wide for a 4inch wafer). I did not remove the edge bead
and it had no influence on me, since my feature size is relatively large.

Thank you all