What is the etch rate of SU-8 in O2 plasma?

[S.O. Ryu]

Dear all,

Does anybody know what the etch rate of SU-8 in O2 plasma is?
I have patterned 4 micro-m SU-8 film and plan to etch it in O2 plasma.
I wonder how much the etch rate will be.
Is it possible to etch SU-8 in pure O2 plasma or do I need O2/CF4 mixture gas?
I do not need fast etch rate ( may be 2~3 micro-m/hour)
Thanks in advance.

Jack

[B***@aol.com]

What type of reactor do you have? Is it a barrel asher or a single wafer system. OUr experience with oxygen and su8 shows it will ash but it is better if you have not done the second bake. This has been done in an icp/rie system and the etch rate is a little less than other negative working photoresists. Bob Henderson

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[Isaac Wing Tak Chan]

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

Post by B***@aol.com
What type of reactor do you have? Is it a barrel asher or a single wafer system. OUr experience with oxygen and su8 shows it will ash but it is better if you have not done the second bake. This has been done in an icp/rie system and the etch rate is a little less than other negative working photoresists. Bob Henderson
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Yours sincerely,

Isaac Chan

Ph.D. Candidate
Dept. Electrical & Computer Engineering
University of Waterloo
200 University Ave. W
Waterloo, Ontario, Canada
N2L 3V1
Tel: [phone], ext. 6014
Fax: [phone]
***@venus.uwaterloo.ca
http://www.ece.uwaterloo.ca/~a-sidic


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[Greg Reimann]

I did a similar thing. I assume that you are using a high power O2 plasma.
I think that the SU-8 doesn't etch, but sputters down until it just can't
any more. You end up with a residue anywhere there was SU-8. I got
beautiful SU-8 etching with 20% CF4 80% O2 at low power (30W) for a long
time. No residue and relatively little etching of the Oxide substrate. If
the rest of your device can handle the CF4, I think this is the way to go.

Good Luck
Greg Reimann

Post by Isaac Wing Tak Chan
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

Post by B***@aol.com
What type of reactor do you have? Is it a barrel asher or a single wafer

system. OUr experience with oxygen and su8 shows it will ash but it is
better if you have not done the second bake. This has been done in an
icp/rie system and the etch rate is a little less than other negative
working photoresists. Bob Henderson

Post by Isaac Wing Tak Chan

Post by B***@aol.com
_______________________________________________
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Yours sincerely,
Isaac Chan
Ph.D. Candidate
Dept. Electrical & Computer Engineering
University of Waterloo
200 University Ave. W
Waterloo, Ontario, Canada
N2L 3V1
Tel: [phone], ext. 6014
Fax: [phone]
http://www.ece.uwaterloo.ca/~a-sidic
_______________________________________________
options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk
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Visit us at http://www.memsnet.org/

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[Christopher F. Blanford]

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

Post by Isaac Wing Tak Chan
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: [phone]; Fax: [phone]
PGP keyID: 8D830BC9 http://pgp.mit.edu/


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[Isaac Wing Tak Chan]

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

Post by Christopher F. Blanford
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.
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(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

Post by Isaac Wing Tak Chan
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: [phone]; Fax: [phone]
PGP keyID: 8D830BC9 http://pgp.mit.edu/
_______________________________________________
options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk
Hosted by the MEMS Exchange, providers of MEMS processing services.
Visit us at http://www.memsnet.org/

Yours sincerely,

Isaac Chan

Ph.D. Candidate
Dept. Electrical & Computer Engineering
University of Waterloo
200 University Ave. W
Waterloo, Ontario, Canada
N2L 3V1
Tel: [phone], ext. 6014
Fax: [phone]
***@venus.uwaterloo.ca
http://www.ece.uwaterloo.ca/~a-sidic


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[Isaac Wing Tak Chan]

Thanks Greg, with adding a bit of CF4 into O2, it does help in cleaning
residue. I am also trying O2/Ar, which also give me some promising
results. I'll see which is the best conditions for my process. Thanks a
lot.


Isaac

Post by Greg Reimann
I did a similar thing. I assume that you are using a high power O2 plasma.
I think that the SU-8 doesn't etch, but sputters down until it just can't
any more. You end up with a residue anywhere there was SU-8. I got
beautiful SU-8 etching with 20% CF4 80% O2 at low power (30W) for a long
time. No residue and relatively little etching of the Oxide substrate. If
the rest of your device can handle the CF4, I think this is the way to go.
Good Luck
Greg Reimann

Post by Isaac Wing Tak Chan
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

Post by B***@aol.com
What type of reactor do you have? Is it a barrel asher or a single wafer

system. OUr experience with oxygen and su8 shows it will ash but it is
better if you have not done the second bake. This has been done in an
icp/rie system and the etch rate is a little less than other negative
working photoresists. Bob Henderson

Post by Isaac Wing Tak Chan

Post by B***@aol.com
_______________________________________________
options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk
Hosted by the MEMS Exchange, providers of MEMS processing services.
Visit us at http://www.memsnet.org/

Yours sincerely,
Isaac Chan
Ph.D. Candidate
Dept. Electrical & Computer Engineering
University of Waterloo
200 University Ave. W
Waterloo, Ontario, Canada
N2L 3V1
Tel: [phone], ext. 6014
Fax: [phone]
http://www.ece.uwaterloo.ca/~a-sidic
_______________________________________________
options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk
Hosted by the MEMS Exchange, providers of MEMS processing services.
Visit us at http://www.memsnet.org/

_______________________________________________
options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk
Hosted by the MEMS Exchange, providers of MEMS processing services.
Visit us at http://www.memsnet.org/

Yours sincerely,

Isaac Chan

Ph.D. Candidate
Dept. Electrical & Computer Engineering
University of Waterloo
200 University Ave. W
Waterloo, Ontario, Canada
N2L 3V1
Tel: [phone], ext. 6014
Fax: [phone]
***@venus.uwaterloo.ca
http://www.ece.uwaterloo.ca/~a-sidic


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[Park, Sang Won (Daniel)]

Hi, all.
I am trying to make devices using two positive layers, the bottom one with
about 5 um thick positive resist (Shipley SPR series),and the top one with
about 20 um thick SJR 5740 (minimum feature of 3 um) using electroplating
technique.

But when I finished the plating with first PR layer mold, I noticed very
small cracks in the resist. Those cracks made problems after I applied SJR
5740 with seed layer on it. Such cracks got bigger and bigger so that they
made another problems (e.g. shorting metal lines) to the second
electroplated structures.

The reason I am using the 5 um positive PR is to get microstructures with
5um suspended gap and it is easy to prepare and remove. But since I have had
such cracks in the first PR layer during plating process at 55 oC, I am
wondering whether there are other good positive PRs or I need to use some
thick oxide layer (PSG or BPSG).
Please let me know any possible solutions.

Thanks in advance.

Best regards.

Daniel Sang-Won Park
Graduate Research Assistant


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[Jonathan Engel]

My experience with electroplating is that increased current density will
increase PR cracking. Try reducing the current density. Good luck.

-Jonathan Engel
MASS Group UIUC
http://mass.micro.uiuc.edu

----- Forwarded Message -----
Subject: [mems-talk] What is the best first layer for the multi-layer

process?

Hi, all.
But when I finished the plating with first PR layer mold, I noticed very
small cracks in the resist. Those cracks made problems after I applied SJR
5740 with seed layer on it. Such cracks got bigger and bigger so that they
made another problems (e.g. shorting metal lines) to the second
electroplated structures.

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[B***@aol.com]

Isaac:

I have not noticed a film left behind when stripping SU-8 but normally we are just interested in the selectivity when we do deep silicon etch. Have you tried to do a chemical clean after using H2SO4+H2O2? What might be left is non organic material incorporated into the SU_8 which gives it is epoxy properties. Try a wet clean and see if it goes away. Give me a call if you want to discuss further. Bob Henderson 480-968-8818 x11

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[Isaac Wing Tak Chan]

Hi Bob,

Thank you very much for your suggestions. I am currently trying
gas mixture of O2/CF4 and O2/Ar and seems to get improvement. But I can't
conclude anything until I do some more experiments to verify. I'll keep
your contact in case I need some further discussions. Thanks a lot.


Isaac

Post by B***@aol.com
I have not noticed a film left behind when stripping SU-8 but normally we are just interested in the selectivity when we do deep silicon etch. Have you tried to do a chemical clean after using H2SO4+H2O2? What might be left is non organic material incorporated into the SU_8 which gives it is epoxy properties. Try a wet clean and see if it goes away. Give me a call if you want to discuss further. Bob Henderson 480-968-8818 x11
_______________________________________________
options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk
Hosted by the MEMS Exchange, providers of MEMS processing services.
Visit us at http://www.memsnet.org/

Yours sincerely,

Isaac Chan

Ph.D. Candidate
Dept. Electrical & Computer Engineering
University of Waterloo
200 University Ave. W
Waterloo, Ontario, Canada
N2L 3V1
Tel: [phone], ext. 6014
Fax: [phone]
***@venus.uwaterloo.ca
http://www.ece.uwaterloo.ca/~a-sidic


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