Steven,

To improve SU-8 adhesion on SiO2, you have two options that I'm aware of:

1) Use Omnicoat (Microchem, US) as an adhesion promoter. HDMS won't help (as far
as I know) and if anything may make your adhesion worse.

2) Use SU-8 3050 (also Microchem), instead of 2050 (or 50). It's the same epoxy,
formulated in a different solvent that will improve adhesion.

Details of both are available on the Microchem website.

Also, I wouldn't recommend doing your bakes at the temperatures you say you're
planning on using, unless it's just a short bake afterwards to remove cracks.
Just follow the data sheets, and it should work out ok for you.

- Kevin Nichols

*********************************
Kevin Paul Nichols
MESA+ Institute for Nanotechnology
Mesoscale Chemical Systems
Meander 151
University of Twente
Postbus 217
7500 AE Enschede
The Netherlands

Office: +31 (0)53 489 26 31
Mobile: +31 (0)6 49 312 471
Fax   : +31 (0)53 489 35 95
Email : k.p.nichols@utwente.nl


-----Original Message-----
From: mems-talk-bounces@memsnet.org on behalf of Steven Yang
Sent: Fri 1/11/2008 10:10 AM
To: mems-talk
Subject: [mems-talk] How to improve SU-8 adhesion?

Hi, all

Asked some questions on SU-8 2050 several days ago, still stuck on it now.

The problem is the peeling off at some SU-8 2050 microchannel
edge.(SU-8 2050 on PECVD SiO2). Without SiO2 layer, the situation will
get better with seldom cracking and peeling off. However, on PECVD
SiO2 it always turns out this problem more or less.

I have increased the temperature and time for dehrydration at 180C for
30mins. and exposured for 40s at 7mW/cm2, PEB at 65C, 95C for 5 and 15
mins respectively (Same as softbake). No much different.

If there is no any further solution based on recipe modification, will
the HMDS get the thing better? If so, could anyone give some
suggestion on the HMDS spin procedure? below is what I plan to do.
1) dehydrate at 150C for 15mins
2) spin HMDS at 7500rpm for 35s
3) dehydrate at 150C for another 15mins
4) spin SU-8 2050 at 4000rpm for 45s

Any suggestion? Thanks a lot!

Steven