Hi Aboto,

SU-8 is very difficult to remove with solvents once it has been hard baked; this
is why it is commonly used for permanent structures in polymer MEMS.  The surest
way to remove it is with an oxygen plasma, such as O2 RIE, but beware of
substrate damage.  You can do it with a barrel asher as well, but it may take
quite a long time to remove 10 µm of SU-8.

If the SU-8 has not been fully crosslinked, you may have some luck with an NMP
(n-methylpyrrolidone) based stripper (1165, Baker PRS, etc.), especially if you
heat the solvent to about 60 C and let it soak for several hours while warm.
(Just make sure to put a concave watch glass cover on the dish so you don't
evaporate out all the solvent, and be careful to keep the temperature below the
flash point of any flammable solvent.)  I've often been able to get the SU-8 to
delaminate and peel off my substrate with warm NMP, and then move to a barrel
asher to clean up any remaining residue.

Piranha will attack SU-8, but stripping 10 µm of organic material may cause an
overly violent reaction.  Piranha is best used to clean up smaller amounts of
organic residues in an environment when you're doing wet cleaning already.

Finally, for future use, you can spin-coat a sacrificial lift-off layer
underneath the SU-8 when you do your next sample.  MicroChem sells a product
called OmniCoat for this purpose; you might be able to get away with one of the
LOR resists for this purpose.  This adds processing steps (spin, bake, develop)
to your photo process, but makes reworking samples with thick SU-8 much more
certain.

Good luck,
Mike

On Jun 8, 2011, at 4:24, 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