Traditionally, IC interconnects formed from Al; however due to scaling and performances needs, Copper is gradually replacing Aluminum.
Compared with Al, Copper has the following advantages:
1) Cu has higher conductivity
2) High conductivity leads to less Joule heating
3) Allows high current density and smaller size accordingly
4) Cu is more resistive to electromigration failures than Al
5) Cu has higher thermal conductivity; provides efficient heat conduction path
Meanwhile Copper also has the following disadvantages:
1) Difficult to pattern Cu by etching since by product is not volatile, e.g. CuCl2
2) Easy to diffuse into oxides and Silicone, Copper Poison/Junction spike
3) Poor oxidation/corrosion resistance; Cu oxides can not prevent underlying copper from further oxidation, as Al2O3 does.