This could definitely work, especially depending on the time between exposure
and develop. As soon as the SU-8 is exposed, it begins crosslinking, but at room
temperature, this crosslinking occurs slowly. Its possible that enough crosslink
occurred to allow development with reasonable fidelity, without crosslinking
beyond the point of ashability.
I've done processes similar to this myself. Based on my observations, SU-8
crosslinking is a catalyzed process - once the photo-acid is present (in any
quantity), it will begin the cross-link process. Concentration of acid
(controlled by exposure dose) influences rate of reaction, as does temperature
(as in most chemical reactions, heat accelerates the process).
By reducing the concentration of the acid (reduced exposure), and reducing
reaction kinetics (lower temp bake), I've been able to crosslink SU-8
sufficiently to pattern it (at >100 µm thick, and maintaining near 90º
sidewalls), while still being able to bond the material via standard
thermocompression bonding (which requires some degree of reflow in the SU-8).
Best Regards,
Chad Brubaker
EV Group
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Senior Process Technology Engineer - Direct: +1 (480) 305 2414, Main: +1 (480)
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-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Bob Henderson
Sent: Tuesday, September 15, 2009 1:23 PM
To: 'General MEMS discussion'
Subject: Re: [mems-talk] SU8
James:
This has been a long time ago but if I remember right we treated it just
like negative working resist. That is we had a special SU8 that would
produce a 5 micron film at 3,000 rpm spin speed. After coat we did a soft
bake at 70 degrees C for 30 minutes in a Blue M oven. Then we exposed on a
contact aligner to cross-link the exposed areas with proper wavelength of
light. Then we developed using Xylene followed by N-Butyl Acetate for a
rinse. The sidewall profile was 90 degrees and it had much better
selectivity to a silicon etch than any positive resist we tried. That is all
I remember but you can contact MicroChem as I am sure they have advanced
the formulations since then.
Bob Henderson
