A metal interconnection structure for semiconductor chips has a metal
interface layer (105), preferably nickel, deposited over the metal of the
chip contact pad (104, usually aluminum or copper). A subsequent metal
layer (106) is an alloy of a metal such as copper or gold with nickel,
wherein the quantity of nickel is selected so that it diminishes the
interdiffusion rate of the nickel from the interface layer (105) during
the reflow and annealing processes. Reflowable metal (107) for
interconnection completes the structure. In another embodiment, the
reflowable metal (107) contains an admixture of the interface metal in a
quantity to diminish the interdiffusion rate of metal from the interface
layer during the annealing process. In either embodiment, the formation of
voids in the interface layer (105) is diminished.
