A silane passivation process, carried out in-situ together with the formation of a subsequent dielectric film, converts the exposed Cu surfaces of a Cu interconnect structure, to copper silicide. The copper silicide suppresses Cu diffusion and electromigration and serves as a barrier material in regions where contact to further conductive material is made. An entire copper surface of a copper interconnect structure may be silicided or a local portion of the surface silicided after an opening is formed in an overlying dielectric to expose a portion of the copper surface.