The adhesion of a diffusion barrier or capping layer to a Cu or Cu alloy interconnect member is significantly enhanced by treating the exposed surface of the Cu or Cu alloy interconnect member: (a) under plasma conditions with ammonia and silane or dichlorosilane to form a copper silicide layer thereon; or (b) with an ammonia plasma followed by reaction with silane or dichlorosilane to form a copper silicide layer thereon. The diffusion barrier layer is then deposited on the copper silicide layer. Embodiments include electroplating or electroless plating Cu or a Cu alloy to fill a damascene opening in a dielectric interlayer, chemical mechanical polishing, then treating the exposed surface of the Cu/Cu alloy interconnect to form the copper silicide layer thereon, and depositing a silicon nitride diffusion barrier layer on the copper silicide layer.