Crayon,

With regard the to the bubbles, I didn't notice if you are doing your
bakes on hot plates rather than in ovens. The hot plates, because they
are heating from the bottom up, will often be superior in driving off
the solvents, rather than trapping them in the resist. From your email
it isn't clear what the thickness of your first PR layer is. The thicker
this layer is, the more difficult to drive off those solvents.

The other point to keep in mind is alluded to by Brad. In order to
attack the release layer, you want to make sure that it is not con
formally coated by your seed layer. This is a classic problem with lift
off processes. Generally it is solved by the generation of "undercut".
There are many references on how to do this. It is most easily done with
negative resists, but can also be done with positive resists. Without
knowing about the geometry of your release layer it is hard to know what
to recommend. But the key is to examine your structure after the
deposition of your seed layer (in a SEM if possible )and verify that the
edges of the release layer will be exposed to the AZ solvent.

Finally, I don't want to recommend a complete process change, but I am a
big fan of dry release for mems. It should be possible with your device
geometry using isotropic plasma. I have used polymide release layer and
CF4/O2 plasma with great success.

Good luck,

Rob MacDonald
Shearwater Scientific
robm@shearwaterscientific.com