It isn't a good idea to try to spin a resist outside its designed
thickness.

The function for resist thickness is:  T = K(1/w2). That is a constant
times the inverse of the square of the angular velocity, in this case
RPM.

So if you are running a resist very much thicker than intended you will
be on a very steep part of the slope for Thickness versus RPM and will
have terrible thickness control. Also, the spin quality I think will be
poor and you might have some wafer edge problems also.

Most any photo resist vendor can offer you a positive resist that is
designed for very thick layers. I recommend AZ myself due to their
superior technical support. I am not affliated with them in anyway.

The vendor will usually be quite willing to send you a sample.

Double resist spinning doesn't really work well and is an extra process
step.

Edward H. Sebesta
Independent Semiconductor & MEMS Process Engineer "From Lab to Fab."




-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Andrea Mazzolari
Sent: Saturday, December 20, 2008 12:54 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] thick S1813


Hello all,
i need to spin and pattern a 10um thick S1813 photoresist. I've searched
for optimal parameters in the S1813 datasheet but could not find
anything which could help in this direction. Is there someone who
already have done this ?

If it is not possible to achieve such thick S1813 layer, are there other
photoresists which can provide this thickness and that are compatible
with a bosch process ?

Best regards,
Andrea