Hi Brad,

Thanks for your answer.  You didn't actually say but I'm assuming from your
reply that you achieve a nice step at the edge of the resist once the bead
is removed.

The reason I was using acetone is because I read a MEMS talk thread from
2004 where someone says that acetone is better than PGMEA for EBR but was
only stopped for health and safety reasons (the flammability you mention
probably!).

I'm using JSR IX565 positive photoresist but I don't know which edge bead
solvent JSR recommend.  I find their website extremely unhelpful too... no
obvious European contacts for finding the information either.  Does anyone
know what solvent is recommended for edge bead with positive JSR resists?

The nozzle and needle that I've attached does deliver solvent at a low angle
~30 degrees so I don't think that is the cause.  Nor do I see an excess of
liquid at the edge.  I do notice the colour change during the low-speed spin
immediately after the acetone EBR so I had already assumed I was losing some
resist but since the film thickness across the wafer is very uniform I
wasn't worried.  Only the profile at the edge concerns me.  I'm still
wondering would a peak of 100nm wide right the way around the resist edge be
enough to keep me from getting a good vacuum contact?

Thanks,
Bob


> 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 edgeof
> the wafer.

> Hope this helps.
> Brad Cantos