Final update Au/Cr etchant

Dong-Woon Shin dwshin at
Tue Oct 22 20:08:40 PDT 2002

I would like to thank Mr. Chris Kenney and Ms. Linda W. for their
willingness to share their precious information with the member at SNF.

Their descriptions were very precise and even more accurate than those
information provided in the open sources.

While I was investigating another possibility of using Cr and Cu
simultaneously, I also noticed that:

[For MEMS people with Cu-metallization]

1) CR14 etches Cr selectively but not Au.
2) However CR14 can etch Cu (Cu and Cr have similar chemistry.)
3) If Cu should be remaining intact during the Cr etch, CR100 can be used.

Finally, I realized that MEMS-exchange website has a rough sketch of
every chemicals relevant to the micro-processings.

Thank you.


On Tue, 22 Oct 2002 Spotworthy at wrote:

> FYI, there is a fine reference book called "Thin Film Processes" edited by
> John L. Vossen and Werner Kern of the Sarnoff Research Lab, put out by
> Academic Press, Inc. 1978 that has a ton of isotropic/anisotropic wet etch
> recipes.  But to answer your question, basically, no.  It has been my
> experience that there is no isotropic wet metal etchant that will attack both
> Au and Cr.  And as Martha Stewart would say, "this is a good thing."
> The industry standard for many many years has been to use the KI etchant for
> Au, and the Cerric ammonium nitrate/acetic acid based etchants for Cr.
> Neither of these wet etchants will attack the SiO2.
> In answer to your specific questions,
> (1) Cyantek CR14 will not attack Au (if it did, it would be so slow that your
> underlying Cr would be completely undercut and your Au would lift off).
> (2) Transene TFA will not attack Cr (Au etch stops dead on the Cr and will
> undercut the photoresist mask quite rapidly, so watch your etch carefully.
> And if you have buried electronics in your wafer with some contacts open to
> the wet etch, watch out for weird electrochemical reactions that speed up the
> Au undercut even more).
> (3) Neither of these enchants will attack the SiO2.  Co is pretty much only
> etched electrochemically.  Fe will pretty much etch in
> nitric/hydrochloric/water based enchants and also certain electrochemical
> enchants.  Ni will be attacked by nitric/hydrochloric/water and nitric/acetic
> acid/sulfuric/water combinations as well as FeCl at 43-54 C, or
> nitric/phosphoric/water combos.
> Hope this helps.
> Linda W.

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