The oxidation behavior of Al-W alloy films (500 Angstrom) deposited on Cu as a passivation layer to protect Cu from oxidation has been examined by Auger electron spectroscopy and X-ray photoelectron spectroscopy. The preferential oxidation of Al in the Al-W alloy protects underlying W and Cu from oxidation, and simultaneously, Cu is rejected by the formation of Al2O3 within the system, resulting in a successful separation of Cu from the surface oxidized layer due to the oxidation even after heating at 500 degrees C for 1 h in air.