Hi Chris,

        Nice analysis. The residue I saw is flaky films. Some of them can
actually be blown away by nitrogen gun, but not all. Anyway, I have
stripping problem not only for SU-8, but also for DQN novolak positive
resist (AZ3312 and AZ4330 - same formulation but different viscosity).
Sputter-etching of the residue is the current solution to this issue.

Isaac

On Thu, 13 Mar 2003, Christopher F. Blanford wrote:

> We've also seen the ashy residue when etching with O2 plasma (barrel
> etcher, 60W forward, 5W reflected, 2x10-1 mbar O2, crossed plates). I
> put it down to non-volatile antimony oxide residue from the
> photoinitiator in the SU-8. I didn't analyse the residue for heavy
> metals, but it seems plausible.
>
> If I do a "back of the envelope" calculation, I get something like this:
> 1. Assume a mixture of 5wt% (C6H5)3SSbF6 + 95wt% SU-8. The photoacid
> generator (PAG) is more complex than this, but it's close enough for
> this estimate.
> 2. Assume the reaction gives stoichiometric antimony(III) oxide:
>     2(C6H5)3SSbF6 + xs O2 --> Sb2O3
>     2 x 499 g/mol         --> 291.5g/mol
>     That is, for every gram of PAG one starts with, there'd be 0.292g
> solid oxide left.
> 3. So for 1g SU-8 + PAG, there'd be 0.015g Sb2O3
> 4. Antimony(III) oxide is around 4.3 times more dense than SU-8
> (5.2/1.2), so for a given volume (or thickness) of SU-8, I'd expect to
> be left with a residue with 0.34% of the original volume or thickness.
> The Sb2O3 would be powdery, however.
>
> Chris
>
>
> On Thursday, March 13, 2003, at 06:15  am, Greg Reimann wrote:
>
> > Hi,
> >
> > May I add a question? I've tried to ash SU-8 with O2 plasma in
> > ICP/RIE system. But there is a film of residue on wafer. Have you seen
> > such problem?
> >
> > Isaac
> --
> Christopher F. Blanford
> Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK
> Phone: +44 (0)1865 282603; Fax: +44 (0)1865 272690
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>
>
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Yours sincerely,

Isaac Chan

Ph.D. Candidate
Dept. Electrical & Computer Engineering
University of Waterloo
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Waterloo, Ontario, Canada
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Tel: (519) 729-6409, ext. 6014
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