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:
[email protected], www.EVGroup.com
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-----Original Message-----
From: [email protected] [mailto:mems-talk-
[email protected]] 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
--------------------------------------------------------
The SiO2 is currently present on the wafer.
Would the adhesion benefit from HMDS or perhaps a YES oven
process?
- thanks - Gabe
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