What size are the holes and what is their aspect ratio?

One thing you might try is lowering the surface tension of your KI
solution, by adding surfactant, or diluting the solution with an
alcohol. Another thing to consider is that with the molecular weight of
the gold iodine complex, it might take awhile for the heavy Iodine to
diffuse down the hole, and the reactants to diffuse out.

Finally, you may have a surface layer of organics making you material
hydrophobic. You might try an O2 plasma treatment to remove stray
organics.

Also, what is the wetability of the copper by your etchant. If the
copper repels the etchant then you are not going to get etch solution
into a small hole. Plasma treatment would induce surface oxidation of
the copper and that might help. Surfactants might help also.

Another trick is to first put the substrate into D.I. Water loaded with
surfactants, and the D.I. water penetrates and then put the sustrate
into the etchant. The etchant diffuses into the water in the small
feature and etches the substrate.

Another issue is that the copper is acting as a sacrificial anode
protecting the gold. It is like a strip of maganesium attached to steel.
If that is the case you might try KI in a ethylene glycol solution to
prevent an electrolytic couple to defeat the anodic protection, but I am
not optimistic that it would work. However, since your large features
are etching, I doubt it is a phenomenon of a sacrificial anode.

In semiconductor processing 1 micron size vias or contacts are easily
etched with Buffered Flouride solutions, the trick is that the solutions
have surfactants which make them super wet. So very small features can
be etched.

The issue here is how big are the holes.

Ed



-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Dave Lewis
Sent: Wednesday, October 14, 2009 8:51 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Etching gold through copper micro-holes


Hello all,

I'm trying to etch gold through micro-hole features in a copper layer
(holes produced by a photoresist/lithography process).  I've tried aqua
regia vapor (maybe if I heat it up... but I don't want to hurt the
copper anymore than I have to) and I've tried potassium iodide, iodine,
water solution in a liquid state.

I've had success as long as the holes in the copper are large enough but
I need to access the gold in much smaller holes.  It seems like the
holes in the copper are too small for anything to gain access to the
gold.

Please assist me with this problem.

Best Regards,

Dave Lewis
Lake Shore Cryotronics
Ohio
Dave.Lewis@Lakeshore.com