Microstructure modification in copper interconnect structure

A metal interconnect structure comprising:

• a dielectric material layer containing a recessed line pattern;
• a metallic barrier layer abutting said dielectric material layer at sidewalls of said recessed line pattern and overlying an entirety of said dielectric material layer;
• a copper-containing seed layer abutting said metallic barrier layer and overlying an entirety of said dielectric material layer;
• a copper-containing layer comprising electroplated copper and abutting said copper-containing seed layer;
• and
• a copper-cobalt alloy cap layer containing a cobalt concentration from about 1 ppm to about 50 atomic percent and abutting said copper-containing layer.

A metal interconnect structure comprising:

• a dielectric material layer containing a recessed line pattern;
• a metallic barrier layer abutting said dielectric material layer and embedded in said recessed line pattern;
• and
• a copper-cobalt alloy line abutting a copper alloy seed layer and embedded in said metal barrer layer and having an atomic concentration of cobalt from about 1 ppm to about 10 atomic percent, wherein an average grain size measured at a bottom of said copper-cobalt alloy line exceeds a width of said copper-cobalt alloy line.