A semiconductor device comprising: a semiconductor substrate; a via layer insulating film formed on the semiconductor substrate and made of an insulator containing oxygen; a via hole formed through the via layer insulating film; a conductive plug embedded in the via hole, the conductive plug comprising a plug main body made of copper or copper alloy, and a first alloy film formed between the via layer insulating film and the plug main body and containing at least two elements selected from a group consisting of Al, Mg, Mn, Cr, Ti, Ta, Zr, Sn, In, Zn, Ni and Co in addition to Cu; a via metal oxide film formed at an interface between the via layer insulating film and the first alloy film and containing at least two elements selected from a group consisting of Al, Mg, Mn, Cr, Ti, Ta, Zr, Sn, In, Zn, Ni and Co in addition to Cu and O; a wiring layer insulating film formed on the via layer insulating film; a wiring trench formed through the wiring layer insulating film and exposing an upper surface of the conductive plug; a wiring embedded in the wiring trench and connected with the conductive plug, the wiring comprising a wiring main body made of copper or copper alloy, and a second alloy film formed between the wiring layer insulating film and the wiring main body and containing at least two elements selected from a group consisting of Al, Mg, Mn, Cr, Ti, Ta, Zr, Sn, In, Zn, Ni and Co in addition to Cu; and a wiring metal oxide film formed at an interface between the wiring layer insulating film and the second alloy film and containing at least two elements selected from a group consisting of Al, Mg, Mn, Cr, Ti, Ta, Zr, Sn, In, Zn, Ni and Co in addition to Cu and O, wherein a total atomic concentration of carbon, oxygen, nitrogen, sulfur and chlorine in the wiring is higher than that in the conductive plug. a semiconductor substrate; a via layer insulating film formed on the semiconductor substrate and made of an insulator containing oxygen; a via hole formed through the via layer insulating film; a conductive plug embedded in the via hole, the conductive plug comprising a plug main body made of copper or copper alloy, and a first alloy film formed between the via layer insulating film and the plug main body and containing at least two elements selected from a group consisting of Al, Mg, Mn, Cr, Ti, Ta, Zr, Sn, In, Zn, Ni and Co in addition to Cu; a via metal oxide film formed at an interface between the via layer insulating film and the first alloy film and containing at least two elements selected from a group consisting of Al, Mg, Mn, Cr, Ti, Ta, Zr, Sn, In, Zn, Ni and Co in addition to Cu and O; a wiring layer insulating film formed on the via layer insulating film; a wiring trench formed through the wiring layer insulating film and exposing an upper surface of the conductive plug; a wiring embedded in the wiring trench and connected with the conductive plug, the wiring comprising a wiring main body made of copper or copper alloy, and a second alloy film formed between the wiring layer insulating film and the wiring main body and containing at least two elements selected from a group consisting of Al, Mg, Mn, Cr, Ti, Ta, Zr, Sn, In, Zn, Ni and Co in addition to Cu; and a wiring metal oxide film formed at an interface between the wiring layer insulating film and the second alloy film and containing at least two elements selected from a group consisting of Al, Mg, Mn, Cr, Ti, Ta, Zr, Sn, In, Zn, Ni and Co in addition to Cu and O, wherein a total atomic concentration of carbon, oxygen, nitrogen, sulfur and chlorine in the wiring is higher than that in the conductive plug.