Direct Write Editing of Electronic Materials by Gas Assisted Focused Electron Beam Induced Etching for Device Prototyping

Focused electron beam etching (FEBIE) is a direct-write material removal technique that was used with gaseous XeF₂ [xenon difluoride] for a chemical assist. FEBIE experiments took place in a scanning electron microscope (SEM) with a gas injection system (GIS) that flowed in XeF₂ coincident to the electron beam rastering across the sample surface, leading to etching. In this work, FEBIE was conducted on niobium and WS₂ [tungsten disulfide] thin films which are technologically relevant materials for magnetic superconductors and semiconductors, respectively. Atomic force microscopy (AFM) was used to measure the volume etched of box patterns, and SEM images were correlated with Raman spectroscopy to determine the electron dose to clear to the substrate and remove all material within the etch area. Etch rates (etched volume/total time) and etch efficiency (etched volume/charge) were calculated and reported for each material for changes in etching parameters such as electron beam energy, dwell time, current, pixel pitch, and XeF₂ pressure. In general, lower beam energy, lower beam current, lower dwell time, and higher XeF₂ working chamber pressure increases the etch rates efficiencies. Statistical comparisons of electron and XeF₂ flux helped rationalize etch behavior, as well as ab initio molecular dynamics (AIMD) simulations to better understand etching mechanisms. Raman and photoluminescence spectroscopy (PL) were used to probe the damage induced by the FEBIE process. The etching process quenched PL response but was found to be relatively “soft” with respect to the Raman spectra experiencing a slow decrease in intensity for increasing doses without an increasing intensity of the disorder mode. Spontaneous etching was operative for larger pattern areas but had a synergistic effect, increasing etch rate and efficiency. Line etches resulted in etched features with very high resolution at optimized parameters (17 and 21 nm etch widths for niobium and WS₂, respectively). Box etches were used to define WS₂ flakes into channels of 100 nm widths. Superconducting niobium devices were fabricated and characterized via magnetometry. Josephson junctions were made by etching lines across a 4-point probe channel, and resistive elements were made by etching triangular shapes into the channel.