Dear all,

          I am trying to fabricate 50um deep channels using SU-8 photoresist on
glass slides. The procedures are:

1. Piranha etch glass slides for 15mins
2. Bake glass slides at 200C for 10mins
3. Spin on 50um SU-8 resist, 0-5 sec ramp to 500rpm, keep it for 5 sec, then
ramp to 2000rpm in 5sec, keep it for 30sec)
4. Soft bake, 65C for 6mins, 90C for 23mins,
5. Cool for 5mins
6. Interval exposure, 8.35mW/cm^2 intensity, exposure for
11.5s+2s(interval)+11.5s.I also tried 15s+2s+15s and 20s+2s+20s.
7.PEB, 65C for 1min, 95C for 5min.
8. Cool for 5mins
9.Develop for 6mins, rinse with methanol, N2 blow dry.

Now the problems are: The 11.5+2+11.5 observed by naked eye white area along the
channels, which may be undercuts. Under microscope, there are two channel edges
for different microscope focus, I dont know how to determine if they are
undercuts or overcuts. I increased the exposure dose trying to eliminate those
"undercuts", for the 15+2+15 one, no white area along the channles, but still
"undercuts" under microscope, for the 20+2+20 one, things are worst. The resist
along the channels looks like going to peel off (that is the kind of "white
area" I mentioned).

All in all, I dont what went wrong. Are the exposure dose too much in all cases?
By the way, my SU-8 50 photoresist from microchem is going to expire on
Feb,2004. That is pretty close, could that be possibly the reason?

Any inputs here will be appreciated, thanks in advance!

best,
leidong


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