Thin films made by annealing Cu(500 nm)/Al(7 nm)/SiO2/Si are investigated using Rutherford backscattering and resistivity measurements. Annealing these films in a low pressure of oxygen results in the formation of a thin surface layer of hole‐free aluminum oxide which protects the underlying copper from oxidation. Even when heated in air at 350 °C for 4 h, no growth of copper oxide is detected. These films have a resistivity as low as 2.4 &mgr;&OHgr; cm, comparable to the resistivity of pure copper films (2.1 &mgr;&OHgr; cm) made in the same deposition system. The use of such films for microelectronic metallization is briefly discussed. ©1996 American Institute of Physics.