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