Hi, I'm currently fabricating double flow focusing microfluidic chip using SU8-2100 on silicon wafer.
Previously, I fabricated single flow focusing junction with 200um square channel using the same photoresist and achieved good definition and line profile. However, when i used the same procedure for double flow focusing junction, the problem arise is i cannot get a clean development on the corner of the junction. also, undercut profile is observed for the microchannel.
my current parameter is:
spincoat: 1000rpm (for 200um thickness)
soft bake:
- 65C for 8minutes (from room temperature, 8 minutes started when hotplate reach 65C)
- then gradually increase to 95C and stayed for another 60 mins.
expose: 12s at 20mJ/s
Post exposure bake: 65C for 8 min and 95C for 14 min
develop: 15 min
I wonder what else i should change since i tried increasing/decreasing exposure time, increasing soft bake time, and increasing development time.
I recommend to give more time for Exposure time. Sometimes, overexposure better than under-exposure.
When inside corners look like that is it usually due to either the exposure being too high or the post exposure bake (PEB) being too high.
Try decreasing your exposure by a few seconds or your PEB by a few minutes and those corners should look better. You'll know you've gone too far when the channels start to look rough or they fall off.
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