I am working with thick film SU-8 (above 300um). I found that leveling the
wafer and allowing the SU-8 to reflow worked well for reducing the edge
beads. I don't know this could be still effective for the thin film. Just
some thoughts for your reference.


> Hi Bob,
> I think the reason you are seeing an additional bead is the acetone.
> Usually the preferred solvent is the thinner for your photoresist or a
> specific edge-bead solvent sold by most PR suppliers.   Photoresist is
> highly soluble in acetone and it is possible that the fumes  from the bowl
> are enough to modify the edge profile.   If your PR is thin enough (below
> 0.75 um or so) then you can watch the color of the applied PR film during
> the EBR step.  If it goes through many color changes, then the acetone is
> affecting the entire film, which is not a good thing in any case.  Acetone
> is also highly flammable and therefore dangerous to use in a spray mode
> without other precautions.  Also, although I am not familiar specifically
> with the Suss system, the nozzle for delivery should be at a low angle and
> the flow of the solvent should not leave an excess of liquid on the edge
> of
> the wafer.

--
Peng Li
Research Assistant
Department of Mechanical Engineering & Applied Mechanics
University of Rhode Island
133D Kirk, 92 Upper College Road,
Kingston, RI  02881
Phone: (401) 874-2247