Dear Rajib Ahmed
I believe that the SU-8 xx mixtures are formulated in
gamma-butyrolactone [CAS No. 96-48-0] and the SU-8 20xx mixtures are
made with cyclopentanone [CAS No. 120-92-3].
You can add one of these readily available chemicals to your
photoresist, but I would make sure that
1) the solvents are dry (I use baked out 4A molecular sieves),
2) the solvents are filtered before use (I use a 0.1 micron PTFE syringe
filter), and
3) the resulting mixture is homogeneous.
The last point should be easy to achieve because the mixture will be
very thin and not very viscous. I usually degas the resist in a sonic
bath at about 40 C before use.
For very thin layers, I usually use a mixture that contains about 20 wt%
SU-8. SU-8 5 is 52wt% solids; I would estimate SU-8 2 to have 46-47wt%
solids. If you want to dilute that to 20wt%, you'd add about 1.3g of GBL
per gram of SU-8 5.
The spin coating parameters are: rotational speed = 4000 rpm,
acceleration & deceleration = 300 rpm/s, time at speed = 30 s. This
works well and gives an even coat on clean baked fused silica and glass.
(These are essentially featureless, though, and I don't know what your
case is.)
Regards,
Chris Blanford
On Friday, August 9, 2002, at 02:11 pm, Rajib Ahmed wrote:
> I was wondering if any of you ever used SU-8 as a dielectric coating.
> Currently we have been using it in microfluidics applications, but the
> problem is our coatings turn out quite thick. I believe we are using
> SU-8
> 2 for this process. This is supposed to give you the thinnest coating
> which I believe is in the order of ~2 micron. I was wondering if the
> coating process can somehow be altered/modified to make it even thinner.
> Any suggestions? Also we are spin coating SU-8 onto our substrates. I
> am
> suspecting that this process reveals its limitations in terms of
> coverage
> of the whole area. From visual inspection, I could see that there are
> places where the coating didn't cover at all. Could anyone kindly
> suggest
> a more effective method of coating?
--
Christopher F. Blanford
Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK
Phone: (44)/(0)-1865-282603; Fax: (44)/(0)-1865-272690
PGP keyID: 8D830BC9 http://pgp.mit.edu/
