Gas Assisted Focused Electron Beam Induced Etching for Direct Write Editing of Niobium Thin Films and Superconducting Devices

Focused electron beam induced etching (FEBIE) of niobium thin films with a gaseous XeF₂ precursor was explored as a route to direct write editing of superconducting devices. We report the effect of XeF₂ pressure, electron beam current, beam energy, and dwell time on the Nb etch rate. To understand the mass transport and reaction rate limiting mechanisms, we compare the relative electron and XeF₂ gas flux and reveal the process is reaction rate limited at low current/short dwell times, but shifts to mass transport limited regimes as both are increased. The electron stimulated etching yield is surprisingly high, up to 3 Nb atoms/electron, and for the range studied has a maximum at 1 keV. It was revealed that spontaneous etching accompanies the electron stimulated process, which was confirmed by varying the etched box size. An optimized etch resolution of 17 nm was achieved. We then demonstrated direct write editing of niobium superconducting thin film devices to produce S-C-S Josephson junctions. Niobium films of 200 nm thickness with a T_c of 8 K and H_C1 of 500 mT (at 1.9 K) and an H_C2 of 1.6 T were deposited onto SiO₂ wafers by magnetron sputtering and fabricated into four point probe patterns by photolithography and reactive ion etching (RIE) in SF₆/O₂. Josephson junctions were fabricated by FEBIE line etches to form a trench across the 3.5 μm superconducting channel width. Josephson junction gaps are generated by the FEBIE process and the superconducting transport properties of the devices are characterized. Summarily, FEBIE allows for on-the-fly processing of superconducting Nb devices, which are highly resolved, quick, with limited peripheral damage.