US Patent 7977791 Selective formation of boron-containing metal cap pre-layer

An interconnect structure with improved reliability is provided. The interconnect structure includes a semiconductor substrate; a dielectric layer over the semiconductor substrate; a metallic wiring in the dielectric layer; a pre-layer over the metallic wiring, wherein the pre-layer contains boron; and a metal cap over the pre-layer, wherein the metal cap contains tungsten, and wherein the pre-layer and the metal cap are formed of different materials.