> I heard about Cu could be patterned by something like CMP Process (
damascene(?) process)
> Are there any wet etchants fot Cu etch? If not, what is the main reason
about that?
> Furthermore, Adhesion layer (Ti or Cr) is not required when I deposit Cu
on Si Wafer ?
> Thank you for in Advance.
> TW Lee.

The two most common chemistries for wet etching copper are
ferric chloride with some HCl and ammonium persulfate (APS).
Transene sells both commercially.

It is common knowledge that it should not be possible to plasma-etch copper
because it does not form a volatile fluoride, chloride, etc.
Nevertheless, in a single experiment, I have seen it etch,
with 3:1 selectivity over photoresist, in a high-density chlorine plasma.
It probably left a residue in the chamber!

An adhesion layer such as Ti, Cr, or TiW should be used with Cu.

    --Kirt Williams, Ph.D.   consultant