Variables affecting the passivation capability of Cu(Mg) alloy films, which were sputter deposited from a Cu (4.5 atom %) target, have been investigated. As-deposited Cu(Mg)/SiO2/Si multilayer samples were annealed for 30 min in various oxygen ambients at pressures ranging from 10 mTorr to 30 Torr and at various temperatures in the 200-800 degrees C range. The results show that the passivation capability of a Cu(Mg) alloy film is a function,of annealing temperature, O-2 pressure, and Mg content in the film. Increasing the annealing temperature favors formation of a dense MgO layer on the surface. Decreasing the O-2 pressure enhances the preferential oxidation of Mg over Cu. Furthermore, increasing the Mg content in the Cu(Mg) film promotes formation of a dense MgO layer. Vacuum preannealing before taking the as-deposited samples to O-2 annealings was found to be very effective in segregating Mg to the surface, facilitating the passivation capability of the Cu(Mg) alloy film even when the Mg content is low. In the current study, self-aligned MgO layers with low resistivity and an effective passivation capability over the Cu surface have been obtained by manipulating these factors when Cu(Mg) thin films are annealed.