Shipley does make a thick resist. Its the SJR 5700 series. I use SJR
5740, which is is the 15 to 20 um thick version. I like this resist
alot. It works well.

   The processing is very similar to normal resist, except that after
spinning the resist must 'rest' on the chuck for 6 minutes before
softbake (the resist needs to relax). BTW the resist immediately after
spinning will look horrible, don't worry, let it rest. The softbake is
on a hot plate (not a vacuum hot plate) for 6 minutes and the
development takes 6 to 7 minutes (in shipley 354). The resulting pattern
has nice vertical sidewalls and sticks well to metal films (I haven't
used it on oxide or SiN)

   I hope this helps,

      Ken