Selective etching between Cu and Ni / Ag

[Sardar Bilal]

Hello folks !

I have a question related to metal etching. I want to etch my Cu seed layer
(100 nm by sputtering). Its a bit tricky since I also have about 100 nm of
Ni and 100 nm of Ag on my wafer which I want to keep. I have tried 10%
nitric acid at room temperature, but it etches Cu and Ni at almost the same
rate, though silver is not etched significantly. I have also tested 10% HCl
and i observed the loss of adhesion of some Ni structures (strange!) and Cu
was not etched significantly. When the sample was taken out of HCl, it
oxidized and Cu color changed to purple shades. I would appreciate if
someone can recommend some wet etchants that can selectively etch Cu and
have low etch rate for Ni and Ag.

Cheers,

Bilal

Helsinki University of Technology,
FINLAND.
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[Kevin Paul Nichols]

Bilal,

I think Transene's CRE-473 or something similar (usually just called "Chrome
Etch") will work for you. Most cleanrooms keep this in stock for Cr etching..
It's an orange solution, usually slightly viscous.

If I recall correctly, it will take off the Cu pretty quickly. I know it
won't touch the Ag, and I'm pretty confident it won't touch the Ni at any
appreciable rate either.

I'm not fully confident of this, so try it with an patterned wafer first.
And, of course, if it does work, please post the results back on the list.

- Kevin

Date: Wed, 28 May 2008 21:47:16 +0300
Subject: [mems-talk] Selective etching between Cu and Ni / Ag
Hello folks !
I have a question related to metal etching. I want to etch my Cu seed layer
(100 nm by sputtering). Its a bit tricky since I also have about 100 nm of
Ni and 100 nm of Ag on my wafer which I want to keep. I have tried 10%
nitric acid at room temperature, but it etches Cu and Ni at almost the same
rate, though silver is not etched significantly. I have also tested 10% HCl
and i observed the loss of adhesion of some Ni structures (strange!) and Cu
was not etched significantly. When the sample was taken out of HCl, it
oxidized and Cu color changed to purple shades. I would appreciate if
someone can recommend some wet etchants that can selectively etch Cu and
have low etch rate for Ni and Ag.

_______________________________________________
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provider of MEMS and Nanotechnology design and fabrication services.
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[Ravi Shankar]

Hi Sardar Bilal,

Cu is the seed layer on wafer and whether Ni and Ag are in
contact with each other (and with Cu)...If the metal layers are in
contact with each other then it may lead to galvanic corrosion in
which one metal corrodes preferentially than the other type of metal
and both metals are in an electrolyte. if this is the case, then you
can try selective metal deposition instead of depositing on whole
wafer and etching later...

-Ravi Shankar
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[汪飞]

Hello, Sardar Bilal,

The best way of the patterning for Cu/Ni/Ag is lift-off, of course. But if
you have to do the etching, I recommend a extremely diluent H2SO4 and H2O2.
I have tried 0.05% H2SO4 with drops of H2O2. It etches the Cu layer quickly
(about 2min for 100nm) without obvious damage for the nickel layer.

Good luck!

Post by Sardar Bilal
Hello folks !
I have a question related to metal etching. I want to etch my Cu seed layer
(100 nm by sputtering). Its a bit tricky since I also have about 100 nm of
Ni and 100 nm of Ag on my wafer which I want to keep. I have tried 10%
nitric acid at room temperature, but it etches Cu and Ni at almost the same
rate, though silver is not etched significantly. I have also tested 10% HCl
and i observed the loss of adhesion of some Ni structures (strange!) and Cu
was not etched significantly. When the sample was taken out of HCl, it
oxidized and Cu color changed to purple shades. I would appreciate if
someone can recommend some wet etchants that can selectively etch Cu and
have low etch rate for Ni and Ag.

--
Best regards,
Yours sincerely
Fei Wang
______________
State Key Lab of Transducer Technology,
Shanghai Institute of Microsystem and Information Technology,
Chinese Academy of Sciences
865 Changning Road, Shanghai 200050, China
Email：***@gmail.com
Tel:[phone] ext.5468
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http://mai

[Gabriel Matus]

Potassium iodide based gold etchant from Transene will etch Cu and not
affect Ni. I'm not sure what it will do to Ag.

Post by Sardar Bilal
Hello folks !
I have a question related to metal etching. I want to etch my Cu seed layer
(100 nm by sputtering). Its a bit tricky since I also have about 100 nm of
Ni and 100 nm of Ag on my wafer which I want to keep. I have tried 10%
nitric acid at room temperature, but it etches Cu and Ni at almost the same
rate, though silver is not etched significantly. I have also tested 10% HCl
and i observed the loss of adhesion of some Ni structures (strange!) and Cu
was not etched significantly. When the sample was taken out of HCl, it
oxidized and Cu color changed to purple shades. I would appreciate if
someone can recommend some wet etchants that can selectively etch Cu and
have low etch rate for Ni and Ag.

_______________________________________________
Hosted by the MEMS and Nanotechnology Exchange, the country's leading
provider of MEMS and Nanotechnology design and fabrication services.
Visit us at http://www.mems-exchange.org

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