A process for selectively forming a metal barrier layer on a surface of an interconnect of a wiring substrate comprising the steps of abrading the substrate and simultaneously feeding onto the substrate a plating solution having said metal dissolved therein. The abrading step comprises contacting the substrate against an abrasive surface and causing relative linear and/or rotary motion between the abrasive surface and the substrate while the substrate is in contact with the abrasive surface. Growth of the metal barrier layer on a portion of the wiring substrate other than the interconnect layer is suppressed and the metal barrier layer thus formed is thinner, exhibits improved uniformity and superior prevention against Cu diffusion.