ELECTROMIGRATION-RESISTANT LEAD-FREE SOLDER INTERCONNECT STRUCTURES
Embodiments of the invention include a lead-free solder interconnect structure and methods for making a lead-free interconnect structure. The structure includes a semiconductor substrate having a last metal layer, a copper pedestal attached to the last metal layer, a barrier layer attached to the copper pedestal, a barrier protection layer attached to the barrier layer, and a lead-free solder layer contacting at least one side of the copper pedestal.
1 . An interconnect structure comprising:
a semiconductor substrate having a last metal layer;
a copper pedestal having a first end coupled to the last metal layer, at least one side, and a second end;
a barrier layer formed on the second end of the copper pedestal;
a barrier protection layer formed on the barrier layer; and
a lead-free solder layer, wherein one or more of the at least one side of the copper pedestal directly contacts the solder layer.
2 . The structure of claim 1 , wherein the barrier protection layer comprises copper.
3 . The structure of claim 1 , wherein the barrier protection layer comprises copper-containing intermetallic.
4 . The structure of claim 1 , wherein the barrier protection layer is 0.5 μm to 3μm thick.
5 . The structure of claim 1 , wherein the copper pedestal is 8 μm to 12 μm thick.
6 . The structure of claim 1 , wherein the barrier layer comprises a material selected from the group consisting of nickel, iron, nickel-iron, and cobalt.
7 . The structure of claim 1 , wherein the barrier layer 1 μm to 3 μm thick.
8 . The structure of claim 1 , wherein the solder layer comprises tin-silver.
9 - 23 . (canceled)