There's a reason why copper isn't used in chip manufacture; something to do with reacting with or diffusing into silicon dioxide.
Huh?
A number of years ago when I was still doing chips, copper was quite popular. Wikipedia claims it still is[1]: copper-based processes continue to be the state of the art for the semiconductor industry today.
As Wiki explains, the key is "dual-Damascene". They inlay copper into trenches.