Liu,

  I suspect you need to wash your glass.  There are a lot of proceedures that
you could use.  Perhaps RCA (SC1), or a hot soapy alkaline wash (many are
commecially available, for example Contrad 70).  Glass cleaning can be quite
challenging but if you are not doing anything right now it may not take much to
make a big difference.

  good luck,

  Dwayne


[email protected] wrote:
  Hi All,
I am currently working on fabricating microfluidic channels on
coverglass using SU8-2025 and using the following protocol:
1. Spin SU8 2025 on No. 1 coverglass.
500 rpm -> 2000 rpm. Coverglass was blown with nitrogen before
spin coating.
2. Pre-bake.
65 degree C for 1 min and 95 degree C for 3 min.
3. Exposure.
1 min @ 4.5 mW/cm^2
4. Post Bake
65 degree C for 1 min and 95 degree C for 3 min.
5. Development
SU8 developer. No IPA rinsing.
At first, the feature came out nicely, but recently, the success
rate dropped aggressively. I could see bright edges along the channels
and sometimes it is really difficult to develop out the un-crosslinked
polymer in the un-exposed area. It seems that the resist film in
unexposed area is shattered into small pieces.
If you could kindly have a look at the following image
(http://base.google.com/base/items?oid=10375407859124322045), you may
find the Y shape channel (width 200 micron) surrounded by some
colorful bright edges. I suspect this bright edge is due to the
peel-off of SU8 from coverglass, but cannot figure out why it happens.
What puzzles me most is that by the same procedure, I can obtain
perfect channel if lucky enough. Unfortunately, I don't know what
"luck" means here. So the result changes from trial to trial without
an obvious consistent pattern. For example, I tried 10 samples today.
The first two were perfect. But the following were worse and worse.
For the last one, it takes barely 10 second to develop such edges
after I started development, but the unexposed resist wasn't desolved
even after 1 min.
I tried different combination of process configuration before and
it seems that the above protocol is the best for me. But, as the
result is not reproducible, I doubt ...
I would appreciate it very much if any of you could offer me some
hint on this issue and thanks for reading this message.

Best,
Liu Yu