We are having problems with surface uniformity after the spin cycle. The
photoresist appears to be making an "island" (mottled) pattern (areas with low
height surrounded by taller PR). The pattern is amplified when placed on a hot
plate for the soft bake.
Our process consist of the following:
1) Su-8 2050 with a goal height of 50 microns
2) Using both Silicon and glass wafers
3) The substrates were cleaned as followed
        a) Rinsed with TCE, acetone, MeOH, DI water
        b) Dried under stream of nitrogen
        c) Snow cleaned
        d) Treated in ozone cleaner
        e) baked in convection oven at 200 celsius for 20 min.
4) Spin coatomincoat on substrate (exp June 2005)
5) Spin SU-8 2050 (exp Oct. 2005)
        a) spin cycle
        b) spread cycle
5) Soft bake
        a) 65 celsius
        b) 95 celsius
Our process is carried out in a clean room with controlled humidity. The SU-8
2050 was in a glass dropper bottle
that was getting close to the bottom of the bottle (about a 100mL bottle with
maybe 10mL of PR left in it).

These patterns are something new that we have not seen before.


-Joel Ramey