Hi Basar,

There are few factors which cause this. Remember bubbles are almost always
caused when you have a liquid dispersed in photoresist or sample surface. I
recommend thorough cleaning before starting any processing. Other than that,
please check the following points also.

a) Prebaking of PMMA is not adequate. This might have some solvent left in
it and create bubbles in it once it gets heated in evaporator.

b) I think the thickness of metal 3500 A might heat up the sample and melt
the PMMA itself. But for smaller thickness , it should not happen unless
your deposition rate is too low or chilling water circulation in evaporator
is not adequate.
c) You have remnants of organic solvents not cleaned completely before
spinning the resist. In such a case, before spinning resist, dry your sample
completely and use an oxygen plasma (~25 sccm) and 300 W for a few seconds
(20 s) at high pressure (200 mT) to remove molecular layer of left over
solvents.

Also, what is your substrate and sample composition, this will help others
diagnose the problem accurately.

Ananth Krishnan


---------- Forwarded message ----------
From: basar bolukbas 
To: 
Date: Tue, 20 Jan 2009 23:22:58 +0200
Subject: [mems-talk] PMMA-950K-A6 resist peeling problem after Ni-Au
deposition
Hello,

I am trying to deposite Ni-Au metal layers (500A-3500A) to PMMA-950K-A6
resist but
after every deposition, i observed some resist/metal peeling problem.
This bubble like structures trigger the removing of the metal layers.
Do you have any suggestion or solution about this problem?

Thank you for your answers.