Another thing from my experience. The adhesion between SU-8 and glass
substrate seems fairly much depending on the surface conditions
(maybe roughness) of the substrate. There are a couple of times I ran
borofloat wafers using exactly the same process (pirahna cleaning,
dehydtration, spinning, soft bake, exposure and PEB) but SU-8 patterns
show up nicely on some wafers without any peel off after development
for a few mins, while nothing is left on other wafers with the same
develop time. Because the wafers used are mixed from different vendors, I
could not trace down the difference between their surface quality.
However, besides surface conditions, I could not think of any other
factors contributing to this huge difference in adhesion. So, try some
other glass substrates if nothing else helps.

Xianling Chen


On Tue, 15 Jun 2004, Brubaker Chad wrote:

> 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
:[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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