Wafer-level interconnect for high mechanical reliability applications

1. An interconnect structure comprising:

a semiconductor substrate comprising an integrated circuit;

an under bump metallurgy (UBM) on the substrate, the UBM comprising nickel and the integrated circuit electrically coupled to the UBM;

an intermetallic compound (IMC) layer on the UBM, the IMC layer comprising a compound of copper and nickel; and

a bulk solder body on the IMC layer, the bulk solder body comprising nickel (Ni), tin (Sn), silver (Ag), and copper (Cu), wherein the nickel (Ni) is in a range of 0.01 to 0.20 percent by weight (wt%).

2. The interconnect structure of claim 1 , wherein the bulk solder body comprises:

greater than about 94.5 percent by weight (wt%) tin (Sn),

less than about 4.0 percent by weight (wt%) silver (Ag),

less than about 2.0 percent by weight (wt%) copper (Cu), and

less than about 0.1 percent by weight (wt%) nickel (Ni).

3. The interconnect structure of claim 1 , wherein the bulk solder body comprises:

about 0.25 to about 4.0 percent by weight (wt %) of silver (Ag); and

less than about 2.0 percent by weight (wt %) of copper (Cu).

4. The interconnect structure of claim 1 , wherein the under bump metallurgy (UBM) is a film having a top layer of copper and an underlying layer of nickel.

5. The interconnect structure of claim 1 , wherein the IMC layer has a thickness of less than about 2.0 microns.

6. The interconnect structure of claim 1 , wherein the under bump metallurgy (UBM) is a film composed of one or more alloys selected from the group consisting of:

aluminum (Al)-nickel vanadium (NiV)-copper (Cu),

titanium (Ti)-nickel vanadium (NiV)-copper (Cu),

titanium (Ti)-nickel (Ni)-copper (Cu),

titanium tungsten (TiW)-copper (Cu),

titanium tungsten (TiW)-nickel (Ni)-copper (Cu),

titanium tungsten (TiW)-nickel vanadium (NiV)-copper (Cu),

chromium (Cr)-nickel (Ni)-copper (Cu), and

chromium (Cr)-nickel vanadium (NiV)-copper (Cu).

7. The interconnect structure of claim 1 , wherein the UBM has a structure selected from one of the following: (i) aluminum (Al)-nickel vanadium (NiV) -copper (Cu); and (ii) titanium (Ti)-nickel vanadium (NiV)-copper (Cu).

8. An interconnect structure positioned between two spaced electrical contacts, the interconnect structure comprising:

a lead (Pb)-free solder alloy reflowed and attached through an interfacial intermetallic compound (IMC) layer in an under bump metallurgy (UBM) to an under bump metal containing copper on a top surface, the under bump metal being disposed between the two contacts, and the lead (Pb)-free solder alloy comprising nickel (Ni), tin (Sn), silver (Ag), and copper (Cu);

wherein the nickel (Ni) content is in a range of 0.01 to 0.20 percent by weight (wt%); and

wherein the IMC layer comprises a compound of copper and nickel.