Metallic capped interconnect structure with high electromigration resistance and low resistivity

A method of forming an interconnect structure comprising:

• providing a structure including an interconnect dielectric material having an opening located therein;
• forming a diffusion barrier on an uppermost surface of the interconnect dielectric material and on wall portions of the interconnect dielectric material within said opening;
• forming a contiguous conductive metal liner on said diffusion barrier that is located on the uppermost surface of the interconnect dielectric material and on the wall portions of the interconnect dielectric material within said opening;
• performing a reflow anneal, wherein said reflow anneal partially fills said opening with a conductive metal that comprises a reflown portion of said contiguous metal liner, wherein a cavity that does not extend an entire width and height of said opening is provided within said opening by said reflow anneal;
• forming a metallic layer containing at least one metal selected from the group consisting of Ru, Ir, Rh, Pt, Co, Mn, and Al and that is more resistant to corrosion and oxidation than that of the conductive metal within said cavity and atop remaining portions of the contiguous conductive metal liner that are located atop the diffusion barrier that is located outside the opening and on the uppermost surface of the interconnect dielectric material;
• and
• removing a portion of the metallic layer, said remaining portions of the contiguous conductive metal liner, and a portion of said diffusion barrier that are located outside of said opening to provide a metallic cap containing a remaining portion of said metallic layer located within said cavity and on a portion of a conductive metal feature containing a remaining portion of said conductive metal within said opening, wherein said conductive metal feature has laterally extending portions located on, and in direct physical contact with, each vertical edge of the metallic cap, and each of the laterally extending portions of the conductive metal feature has an uppermost surface that is coplanar with an uppermost surface of the metallic cap, and wherein said metallic cap is separated from sidewalls of said interconnect dielectric material by an upper portion of a remaining portion of the diffusion barrier and said laterally extending portions of said conductive metal feature.