A method of forming an interconnect structure is provided. The method includes depositing a cobalt metal layer in an interconnect opening formed within a dielectric material containing a dielectric reactant element. The method further includes, in any order, thermally reacting at least a portion of the cobalt metal layer with at least a portion of the dielectric material to form a diffusion barrier containing a compound of the reactive metal from the cobalt metal layer and the dielectric reactant element from the dielectric material, and forming a cobalt nitride adhesion layer in the interconnect opening. The method further includes filling the interconnect opening with Cu metal, where the diffusion barrier and the cobalt nitride adhesion layer surround the Cu metal in the interconnect opening.