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