durusmail: mems-talk: Double layer SU-8 fabrication problem
Double layer SU-8 fabrication problem
2013-01-12
Bill Chow
2013-01-13
Gareth Jenkins
2013-01-14
Bill Chow
2013-01-15
Gareth Jenkins
2013-01-15
Daniel Figura
2013-01-16
Jocelyn Ng
2013-01-16
Bill Moffat
2013-01-15
Black, Robert
2013-01-17
Gareth Jenkins
2013-01-23
Tinka Li
2013-01-23
Bill Chow
Double layer SU-8 fabrication problem
Bill Chow
2013-01-12
Hi,

I am working on a double layer structure with bottom layer 5um and top layer at
15um. I have used SU-8 2002 and SU-8 2010, however they have passed the expiry
date for about a month (Would it be a problem?). In the last month, I was
successed to make a beautiful sample out without any problem. However, Last week
I tried to fabricate one more sample (due to misalignment of the structure in
the first sample). I found there is a terrible problem arise. After I fabricated
the first layer and spinned the 2nd layer, I put the sample on the 65C hot plate
for soft bake. However, the sample shows a “dry skin” like structure between the
interface of the first and second layer of SU-8 just after a few seconds on the
hotplate. I don’t know why a previously worked process could failed after a few
weeks.... I have try to use the same bottle of SU-8 2010 and let the sample to
cool down to room temperature before the second layer softbake, however the
problem remains. A very interest point is that, only the exposed area have the
“dry skin” appearance, for the unexposed area it don’t have any problem. I hope
someone could help me in this tough situation. Thanks.

First layer 5um:
Spin 3” Si wafer with SU-8 2002 at 500rpm for 5s, then 1000rpm for 30s.
Softbake the sample  mailto:1min@65C then 3 min@95C (hotplate)
Expose it without waiting for 25s with a total of 125mJ/cm^-2
Postbake it  without waiting for 1min@65C and 1min@95C (hotplate)

Second layer 15um:
Spin the second layer without waiting with SU-8 2010 at 500rpm for 5s, then
2000rpm for 30s.
Softbake the sample 2min@65C then 5min@95C (hotplate)
Expose it without waiting for 45s with a total of 225mJ/cm^-2
Postbake it without waiting for 1min@65C and 2mailto:2min@95C (hotplate)

Regards,
Bill
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