The method of forming thin oxide layers by sputter etching in a low-power rf oxygen discharge (rf oxidation) was investigated. Use of the method for oxide formation on Pb films was studied using in situ ellipsometry. A steady-state oxide thickness was observed that depended on the oxidation and sputtering parameters. For oxygen pressures of (5-40) × 10-3 Torr and cathode voltages of 175-450 V, the steady-state oxide thickness was in the 60-90-Å range. The oxide layers grown in the rf oxygen discharge had the orthorhombic form of PbO similar to that formed by thermal oxidation. However, the PbO layers were found to be nonstoichiometric due to excess oxygen; ellipsometric measurements indicated values of 2.6-2.8 and about 0.1, respectively, for their index of refraction and extinction coefficient. © 1974 American Institute of Physics.