Perhaps a less aggressive solvent. It could be AZ 70/30 or some EGMEA
solution. These are the solvents the novolak resin in dissolved in when
they manufacture resists. There are a variety compounds similar to
EthylGlycoMethylEtherAcetate. (I am assuming that AZ5214 is a novolak
positive resist.)

However in terms of solvents dissolving something, the rule of like
dissolves like applies. That is, the solid will be dissolved by a
solvent with a similar polar/non-polar nature. So if SU-8 is is similar
in nature to the solvent it will dissolve.

You might want to use a resist that is completely aliphatic in nature,
like a negative resist, if SU-8 has a somewhat polar nature. If SU-8 is
aliphatic in nature, then use a resist system like a novolak resist and
a gentle solvent as mentioned above.

I would also make the resist strip quick as possible. Since you are
removing an organic off an organic, the differentials of solubility will
be relative, not absolute, and some minor amount of dissolution of the
SU-8 might occur.

An additional complication is the nature of the OTS and therefore what
dissolves the OTS layer.

I would consider lowering the temperature of the softbake of the resist
to see if you could make it more soluable and thus making the resist
strip shorter. You can't go too far in reduction of the temperature
since you will lose photo contrast. You could make sure you avoid
hardbakes of the resist after patterning.  This again allows a milder
solvent.

Finally, you could perhaps process the SU-8 to make it much less
soluable. I am not familiar with it.

I would call AZ, they are fairly good in their advice.

Ed

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Steven Yang
Sent: Wednesday, January 30, 2008 12:28 AM
To: mems-talk
Subject: [mems-talk] How to remove AZ photoresist in SU-8 microchannel?

Hi, all

Always got question on microfabrication.

This one is, I use AZ5214 to pattern a OTS (a silane to modify Si
surface) at the the bottom of my SU-8 microchannel. After that, I need
to clean all AZ PR off from SU-8 channel without any damage to SU-8 and
OTS layer at bottom, as well as a Cr/Au layer.

I heard the acetone will swell the SU-8, so this is not the right
chemical I can use because it will destroy my critical pattern made by
SU-8.

RIE descum also not a good idea, as it will remove the OTS layer too.

So, which chemical or process I can use to clean the photoresist
clearly?

Thanks and regards,
Steven