There could be a few different reasons for lift off of your patterns during
develop:
1: The initial adhesion to your substrate is poor. In this case, ensure that you
are performing a dehydration bake (150(C, 1-2 minutes on a hot plate) prior to
coating. If you are doing this already, then you may want to contact Silicon
Resources (at siliconresources.com) for a supply of their AP300, which has been
shown to enhance adhesion with SU-8.
2: You are underexposing your film. Bare in mind, you are patterning a negative
material on a transparent substrate. You are not getting the radiation
reflection that you could expect from a silicon substrate, so the standard
recommended dose may not be sufficient. With a negative material, if your dose
is insufficient, you may not get crosslinking at the bottom layers of the
material (especially with SU-8, where the photoactive compounds will not diffuse
and migrate within the film after activation). If the material is not
crosslinked, it will actually develop out (dissolve) in the developer solution,
causing liftoff.
3: Your post-exposure bake is not correct. The recommended post exposure bake
is with a hotplate. Due to the thickness of many SU-8 films, heat transfer in
an oven environment may hamper the curing of the portion of resist closest to
the wafer. The material may remain under-crosslinked, and again dissolve in the
developer.
Best Regards,
Chad Brubaker
EV Group invent * innovate * implement
Technology - Tel: (602) 437-9492, Fax: (602)437-9435 e-mail:
[email protected], www.EVGroup.com
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-----Original Message-----
From: [email protected] [mailto:mems-talk-
[email protected]] On Behalf Of annuar
Sent: Monday, June 14, 2004 5:55 PM
To: [email protected]
Subject: [mems-talk] SU-8 adhesion to glass substrate
Hi everyone.
I'm having problem coating my glass slide with SU-8 resist. It seems that
the SU-8 does not adhere very well to glass. After developing, some part of
my patterns are lifted off. Does anyone know how to solve this problem? Does
the softbake or PEB have anything to do with this? Thanks.
Abang Annuar
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