Hi Mikael,

Have you considered using a substrate like quartz instead of glass? I do not
know how many wafers you plan to use, but if the cost of the wafers is not an
issue then this could be a way forward (see the adhesion shear analysis by
Microchem http://www.microchem.com/products/pdf/SU-8-table-of-properties.pdf).

Dietrich

-----Original Message-----
From: Mikael Evander [mailto:evander@stanford.edu]
Sent: 28 January 2011 01:08
To: General MEMS discussion
Subject: Re: [mems-talk] SU-8 3000 vs 2000 adhesion[Scanned]

Hi all.

I just wanted to let you know that I did buy the SU-8 3005 and while the
adhesion definitely is better on glass than the 2000 formulation, it is
unfortunately not good enough. All patterns survive the development and look
nice but they are not very well anchored to the surface. As I need them to stay
there as permanent structures I would need to improve the adhesion a bit
further.

All wafers are still piranha cleaned and either singed or put through HMDS in a
YES oven (since Microchem claims an improved adhesion with HMDS for the 3000
formulation). I've tried an HF-dip to clean and roughen up the surface but it
didn't seem to improve anything. I've overexposed a wafer on purpose to make
sure that it's not a matter of not cross-linking the layer closest to the glass
surface, unfortunately no effect there either.

What I have left to try, as far as I can think as least, is:
- trying longer PEB times and doing very slow ramping (although I can't see any
tendencies to cracking and my layer is really thin)
- testing a couple of hours treatment in NaOH as I've read that it might help
- try a plasma treatment of the wafer before putting it in the singe oven
- try a silanization (APTMS/AEAPS) of the wafer before putting it in the singe
oven

If anyone has any other ideas/suggestions they are still very welcome :)

best regards

Mikael