A semiconductor device is provided which comprises a metal interconnect structure having a metal alloy capping layer formed within a surface region of the metal interconnect structure, as well as methods for fabricating the semiconductor device. For example, a method comprises forming a metal interconnect structure in a dielectric layer, and applying a surface treatment to a surface of the metal interconnect structure to form a point defect layer in the surface of the metal interconnect structure. A metallic capping layer is then formed on the point defect layer of the metal interconnect structure, and a thermal anneal process is performed to convert the point defect layer into a metal alloy capping layer by infusion of metal atoms of the metallic capping layer into the point defect layer. The resulting metal alloy capping layer comprises an alloy of metallic materials of the metal capping layer and the metal interconnect structure.