Hi,

You should be careful with etch rates of structures. Two materials that are
in contact behave very different in etching environment because of the
different electro chemical potential.

I suggest that you run a test on a real small area. Also, try using copper
etchant. The FeCl stuff. It might work better.

Shay

-----Original Message-----
From: mems-talk-bounces+shay=mizur.com@memsnet.org
[mailto:mems-talk-bounces+shay=mizur.com@memsnet.org] On Behalf Of Ned
Flanders
Sent: Wednesday, June 15, 2011 10:32 AM
To: General MEMS discussion
Subject: [mems-talk] aluminum etchant vs. copper vs. aluminum

Hi all,

According to "Etch Rates for Micromachining Processing - Part II" by Kirt R.
Williams, the etch rate of copper in the commercial aluminum etchant (80%
H3PO4, 5% HNO3, 5% acetic acid, 10% H2O) is almost 6 times that of aluminum
itself. So if I understand correctly, this etchant etches copper
preferentially compared to aluminum.

I am asking because I need to remove 50 nm of Cu on top of Al, without
etching Al (too much). I was thinking of maybe diluting the commercial
aluminum etchant to achieve lower etch rate and better control.

Before I do anything stupid, I wanted to ask here, whether there is a better
way to achieve what I want, i.e. an etchant that has even better etch rate
of copper vs. aluminum.

thanks in advance

m