Dear community,

How do I structure a Cr/Cu plating base on Silicon wafers with thermal oxide for
later acid copper
electroplating?

I have tried:

a) sputtering 20nm Cr (for adhesion) + 200nm Cu, litho AZ9260, etch copper using
ammonium persulfate
+ ammonia, etch chrome using "Chrome etch no1" (perchloric acid + ceric ammonium
nitrate): The
chrome is not etched. I suppose this is because the small 200nm sidewall of
copper at the edge of
the photoresist is in contact with the solution. Due to the difference between
the copper's
electrochemical potential and the chrome's electrochemical potential, the chrome
cannot be etched.

b) sputtering 20nm Cr (for adhesion) + 200nm Cu, litho AZ9260, etch copper using
ammonium persulfate
+ ammonia, etch chrome using hydrochloric acid (37% or 32%): As HCl etches Cr
selectively to Cu,
this method works but the HCl etches the open Cr slower than the Cr under the Cu
and the
photoresist. Thus, the copper and the photoresist peel off. Different
concentrations of HCl showed
the same results at different speed.

-> What could I do else?

In literature I have found for electropolishing I should use sodium hydroxide as
electrolyte, but
this removes the photoresist. Does anybody know an alternative?

As I can only sputter Cr, Cu, Al and SiO2, I cannot use Au plating base.
Besides, Rick Morrison from
Draper suggested on Jan 29th 2010 "Your seed payer should always be the same
material you are trying
to electroplate."

I would like to grow pillars of 50µm diameter and 400µm height (as Pradeep Dixit
has done but in a
matrix on order to get freestanding pillars) that should stick very well to the
substrate, I fear
activating the SiO2 by oxygen plasma and then directly sputter Cu (as suggested
for better adhesion
between SU-8 and Cu) does not suffice.

Kind regards

Felix

Technische Universitaet Darmstadt
Felix Greiner
Merckstr. 25
64283 Darmstadt
www.emk.tu-darmstadt.de/index.php?id=380