GaAs milling with neon focused ion beam: Comparison with gallium focused ion beam milling and subsurface damage analysis

This study explores the usage of a neon focused ion beam (Ne FIB) as an alternative to the traditional gallium focused ion beam (Ga FIB) for the task of milling into the III-V compound semiconductor material, GaAs. While the Ga FIB is more commonly available, it is known to produce undesired artifacts such as the formation of gallium rich droplets distributed randomly on the milled surfaces. We reproduce this effect and compare directly with the Ne FIB at a comparable energy and current. Although Ne FIB mills slower, it does not produce the residual gallium rich droplets. At high energies (25 to 30 keV), the Ne FIB is observed to produce a porous texture on the milled surfaces, while at a low beam energy (10 keV), a smooth surface is created with no evidence of pores. We also find that at lower energies neon produces much less subsurface damage from transmission electron microscopy images. With this new learning, we were able to use neon at low energies to mill trenches, as small as 20 nm wide with high fidelity, less damage, and no evidence of the droplet artifacts commonly encountered when using the conventional Ga FIB.