Nam,
   Vacuum baking could have an effect on the resist if the wafers are
heated too much.

Hard vacuum baking can have powerful effects on the resist. Besides very
effective removal of solvents, even "high boilers", it can drive
condensation reactions.

Novolak resist can undergo two condensation reactions, the lower
temperature one gives off water. With a vacuum the reaction is driven
towards condensation since the reactant water is removed.

So you can end up with a thermoset plastic that has low solubilty.
Thought I would try NMP instead.

Ed

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Le Cao Hoai Nam
Sent: Thursday, January 03, 2008 1:12 AM
To: General MEMS discussion
Subject: Re: [mems-talk] Lift off process with S-1818

Happy New Year to all!

Thanks Ed and Jianhua for your replies. I have to notice your point next
time we do experiment. Furthermore, I also thought there might be some
problem with the evaporation. It was likely that we have heated the
photoresist too much (current around 80A). I assume when the PR getting
damaged, it is difficult to remove PR completely. Do you think this is a
problem?

Best regards,
Nam