To provide a method for manufacturing a semiconductor substrate having copper wires.

In the method for manufacturing a composite composed of metallic copper and resin by forming a copper wire layer composing an inner layer circuit, forming an insulating layer composed of resin on the copper layer, forming a via hole for exposing a copper surface in the insulating layer, and depositing a metal on the copper surface exposed to the bottom of the via hole; copper oxide formed on the copper surface exposed to the bottom of the via hole is removed by an aqueous phosphoric acid solution of pH 1 to 3. By the method, a semiconductor substrate capable of suppressing the occurrence of haloing and forming a via hole indicating excellent solder junction can be manufactured.