A copper metallization structure and its method of formation in which a layer of a copper alloy, such as Cu—Mg or Cu—Al is deposited over a silicon oxide based dielectric layer and a substantially pure copper layer is deposited over the copper alloy layer. The copper alloy layer serves as a seed or wetting layer for subsequent filling of via holes and trenches with substantially pure copper. Preferably, the copper alloy is deposited cold in a sputter process, but, during the deposition of the pure copper layer or afterwards in a separate annealing step, the temperature is raised sufficiently high to cause the alloying element of the copper alloy to migrate to the dielectric layer and form a barrier there against diffusion of copper into and through the dielectric layer. This barrier also promotes adhesion of the alloy layer to the dielectric layer, thereby forming a superior wetting and seed layer for subsequent copper full-fill techniques. Filling of the alloy-lined feature can be accomplished using PVD, CVD, or electro/electroless plating.