Gareth,

SU-8 2000 materials have a bit of temperature sensitivity when it comes to the
material viscosity - this is more pronounced with the higher solids content
materials such as SU-8 2100 (which is, I think, somewhere around 77% solids).

If your clean room is a bit on the cold side (20ºC vs. 24ºC, for instance) this
could have an impact. I wouldn't expect just a temperature variation to cause
the film thickness difference you are seeing, but it may contribute.

Other contributors may be things such as exhaust, use/lack of use of a covered
coat module, completeness of soft-bake...

Best Regards,
Chad Brubaker

EV Group       invent * innovate * implement
Technology - Tel:  480.727.9635, Fax:  480.727.9700  e-mail:
c.brubaker@EVGroup.com, www.EVGroup.com

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On
Behalf Of Gareth Jenkins
Sent: Wednesday, November 29, 2006 10:33 AM
To: General MEMS discussion
Subject: [mems-talk] SU-8 2100 layer thicker than expected

Hi

When spinning SU-8 2100 (at 1000rpm) I consistently get thicker than
expected layers. According to the datasheets, I should get 260um but I
get around 400um or more instead.
I am using silicon as a substrate and everything else is fine - I have
good adhesion and uniformity.
It's not a huge issue as I can always increase the speed but it seems
odd to have such a big variation. My SU-8 is quite old so perhaps I have
lost some solvent from it?