Relationship between beam and junction parameters in ion beam processed Josephson devices

Abstract

Planar and edge-defined niobium-lead alloy Josephson junctions were fabricated using an ion beam tunnel barrier process consisting of Ar cleaning and Ar/O2 oxidation, with ion energies as low as 50 eV in the oxidation step, during which the ion energy and flux, oxygen fraction, and process time control junction critical current density. The effect of these process parameters on junction properties was studied using a 30-mm ion source and 57-mm wafers. Both run-run and on-wafer spatial variations were measured. Comparison of ion flux profiles with distributions of junction critical current densities revealed that the Ar preclean step, as well as the oxidation step, is important in controlling process uniformity. The results indicate that uniformity adequate for large scale integrated circuit applications should be attainable.