Once it's exposed and baked, you now have a cross-linked epoxy. It
won't come off cleanly or easily.

If it's almost, but not fully cross-linked, sometimes you can
essentially crack it off the wafer by dipping it in fuming nitric
acid. Leave it in for > 1 hour, and it will partially oxidize, turn
brown, and crack in few places. Adhesion of subsequent SU-8 layers
will never be as good (or at least, I don't know how to get it to be
as good), so this is really only worth it if you have a valuable
substrate. You can also use Microchem's Remover PG, if it's only very
weakly cross-linked.

There's probably an RIE solution to this as well, but it will likely
be pretty non-specific and give you some substrate damage.

- Kevin

On Wed, Jun 8, 2011 at 3:24 AM, Le Hong Hanh  wrote:
> Hi all,
>
> It's first time I use Su-8 2010 for a micro-fabrication. Generally speaking,
Su-8 PR has been made me some trouble such as air bubbles appeared when soft
baking, non-uniformity with a non-circular sample. Now, the most difficulty is
Su-8 removal. I have spent over 1 hour to remove Su-8 layer after a Si etching.
The PR layer is about 10 um. I put it in acetone solution with a ultrasound
cleaner for over 1 hr. But I see that there is little Su-8 removed (it made the
solution cloudy). It seems nothing has been changed on the wafer surface.
>
> Please show me your experience on removing this PR!
>
> Thanks,
> Aboto