A Cu interconnect member is passivated by diffusing Sn, Ta or Cr atoms into its upper surface to form an intermetallic layer. Embodiments include depositing Cu by electroplating or electroless plating to fill a damascene opening in a dielectric layer, CMP, depositing a sacrificial layer of Sn, Ta or Cr on the planarized surface, heating to diffuse Sn, Ta or Cr into the upper surface of the deposited Cu to form a passivating intermetallic alloy layer, and removing any remaining sacrificial layer by CMP or etching.