Hi

we haven't made 1000um coatings, but here are a couple things we do that
might help:

-we do a piranha strip and an Buffer Oxide Etch on the wafers before hand.
There will be a lot of thermal stress for that thick a coating, so you'll
need it to bond really well.

-make sure to bake the wafer at 200C before coating to dehydrate it.

-we spincoat, remove the residue from the bottom of the wafer, then let
them sit on a flat surface overnight in a petri dish.  This lets the
resist relax and smooth out before the soft bake and has worked well for
us.

-going to too low an rpm for the spin is difficult, but around 800 rpm
works for us.

-if there is a way, it might be worth making a sacrificial wafer as a test
wafer to get the right exposure time.  I'm not sure how much data there is
on SU8 that thick.  If there is a way to expose parts of the wafer for
different amounts of time, you only have to waste one wafer.

-for you bakes, let them ramp down after the 95C bake to reduce thermal
stress.

Eric

Eric Johnston
Department of Bioengineering
University of Pennsylvania


On Sun, 13 Apr 2008, Abhishek Jain wrote:

> Dear forum members
>
> I want to make 1mm thick structures on SU8 for doing soft lithography with
> PDMS later on. It is only one mask and just straight channels.
>
> I have SU8 2075 with me and I am trying to find a recipe for doing this. If
> anyone has experience in dealing with this, I will truly appreciate if you
> may give some insight on the method...