Any etchant that etches Au and Cr?

Spotworthy at Spotworthy at
Tue Oct 22 18:03:07 PDT 2002

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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