Self-aligned composite M-MOx/dielectric cap for Cu interconnect structures

An interconnect structure comprising:

• an interconnect dielectric material having a dielectric constant of about 4.0 or less, said interconnect dielectric material having at least one opening therein that is filled with a Cu-containing material, said Cu-containing material within the at least one opening having an upper surface that is co-planar with an upper surface of the interconnect dielectric material;
• a composite M-MOx cap located at least atop said Cu-containing material within the at least one opening, wherein said composite M-MOx cap includes an upper region M that is composed of a metal having a higher affinity for oxygen than copper and copper oxide and a lower region MOx that is composed of a non-stoichiometric oxide of said metal, wherein a bottommost surface of said lower region of said composite M-MOx cap is located directly on said upper surface of said Cu-containing material and wherein said lower region of said composite M-MOx cap has edges that are vertically coincident with edges of said Cu-containing material and wherein said upper region of said composite M-MOx cap has edges that are vertically coincident with said edges of said lower region of said composite M-MOx cap;
• and
• at least one dielectric cap layer located on at least an upper surface of the composite M-MOx cap, wherein a portion of said at least one dielectric cap layer directly contacts said upper surface of said interconnect dielectric material.