A new technique for fabricating Josephson tunneling barriers has been developed. Oxide tunnel barriers with estimated thicknesses from 20 to 50 Å have been formed on lead films with indium underlayers and on niobium films. The technique includes an rf sputter etching step in argon for cleaning followed by an rf sputter etching step in oxygen. During the latter, an oxide film is grown having a steady-state thickness which is attributed to a balance between sputtering and oxidation rates. Different oxide thickness may be obtained by varying process parameters such as oxygen pressure and rf power. © 1971 The American Institute of Physics.