XeF₂ gas assisted focused electron beam induced etching of niobium thin films: towards direct write editing of niobium superconducting devices

In this work, we explore focused electron beam induced etching (FEBIE) of niobium thin films with the XeF₂ precursor as a route to edit, on-the-fly, 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. Given that the Nb superconducting coherence length is 38 nm and scales with thickness, this work opens the possibility to direct write Nb superconducting devices via low-damage FEBIE.