The actual SU8 is holding firm to the wafer. I apologize for
the ambiguity. I meant to say that I am having trouble
adhering to Silicon and SU8 after it has been spun and
developed. I want to have the following layers:

   1) SU8, Spun and photolithed, developed (working well)
   2) AZ4620 or SU8 on top of the first layer of SU8 and on
the exposed silicon

   The adhesion problems come into play with the SU8 and
AZ4620 on top of the silicon and original SU8.

   Thanks. And I believe the YES oven is what they call an
HMDS oven, I am hoping to improve my dehydration, even though
I currently do bake the wafer prior to processing. I have
never used a YES oven though. Thanks for the tip on the
AP300. I look it up and see if it is cost effective.

  - Gabe

Replied to email-----------------------------------------

Gabe,

As Greg said, your best option to begin with is to try to
make sure that your substrate is sufficiently dehydration
baked.  Baking the wafer at 150C for a minute or two, and
then allowing to cool to room temperature (either on a cool
plate or ambient cooling)  prior to coating should accomplish
this.

HMDS (even in a YES vapor prime oven) will have little
positive effect at all (except perhaps from the dehydration
standpoint), since there is no attraction between SU-8 and
HMDS.

Should dehydration bake not work for you, there is also an
adhesion promoter recommended by MicroChem and produced by
Silicon Resources in Chandler AZ called AP300.

One final note, and that  is, verify that you are supplying a
sufficient exposure dose to the SU-8.  Since SU-8 is a
negative acting material, insufficient exposure can result in
a non-exposure condition of the material closest to the
silicon.  Upon develop, this layer dissolves, causing the
cross-linked region to lift off.  For tests sake, you can try
a severe overexposure (granted, you may sacrifice a substrate
to do so, unless your feature sizes are very large) and see
if this makes the material stick.

Best Regards,

Chad Brubaker

EV Group       invent * innovate * implement
Technology - Tel: (602) 437-9492, Fax: (602)437-9435 e-mail:
C.Brubaker@EVGroup.com, www.EVGroup.com

This message and any attachments contain confidential or
privileged information, which is intended for the named
addressee(s) only. If you have received it in error, please
notify the sender immediately and then delete this e-mail.
Please note that unauthorized review, copying, disclosing,
distributing or otherwise making use of the information is
strictly prohibited.

-----Original Message-----
From: mems-talk-bounces+c.brubaker=evgroup.com@memsnet.org
[mailto:mems-talk-
bounces+c.brubaker=evgroup.com@memsnet.org]  On Behalf Of
Greg Reimann
Sent: Monday, May 17, 2004 8:44 AM
To: 'General MEMS discussion'
Subject: RE: [mems-talk] Re: SU8 Adhesion to Si

Gabe,

How thick are your SU-8 layers?

Is it the first soft bake that causes the problem?

Does the adhesion fail during or after the bake?

I did not have a lot of success with HMDS and Microchem's
promoter
Omnicoat is for metals, not Si/SiO2.  The SU-8 normally has
really good
adhesion to Si/SiO2.

I don't know what a YES oven is, but generally, you want to
stay away
from ovens with SU-8.  You want hotplates so that the solvent
bakes out
from the bottom up.

Here are some things to watch for:

Make sure you are baking the water out of the wafer before
you apply the
SU-8.

Don't thermally shock it.  Make sure you are doing a two step
or ramped
bake.  Let it cool on a thermal insulator, like a plastic
container.

If your trouble comes after exposure, make sure you are
filtering out
stray wavelengths shorter than i-line.

Hope this helps.

Good luck,
Greg Reimann
Boston University