To restrain a separation of a metal onto a via surface so as to prevent a short between wirings in a wafer.

In this method, a surface of a wafer 200 is cleaned by scrubbing of a brush 102 after mechanical chemical polishing of a via metal, and an amount of varnishing to the surface of the wafer 200 of the brush 102 is set at about 1.5 mm or less for scrubbing. The surface of the wafer 200 is prevented from charging to a negative side to restrain a separation of polishing scraps of a metal and of metal ions onto the via surface.