Abstract: In the invention an electrically isolated copper interconnect structural interface is provided involving a single, about 50-300 A thick, alloy capping layer, that controls diffusion and electromigration of the interconnection components and reduces the overall effective dielectric constant of the interconnect; the capping layer being surrounded by a material referred to in the art as hard mask material that can provide a resist for subsequent reactive ion etching operations, and there is also provided the interdependent process steps involving electroless deposition in the fabrication of the structural interface. The single layer alloy metal barrier in the invention is an alloy of the general type A—X—Y, where A is a metal taken from the group of cobalt (Co) and nickel (Ni), X is a member taken from the group of tungsten (W), tin (Sn), and silicon (Si), and Y is a member taken from the group of phosphorous (P) and boron (B); having a thickness in the range of 50 to 300 Angstroms.