Practical Aspects of FIB Milling: Understanding Ion Beam/Material Interactions

Abstract Nanometer scale, high resolution Ga+ ion probes, attainable in commercially available focused ion beam (FIB) instruments, allow imaging, sputtering and deposition operations to be performed with a high degree of spatial precision. Of particular interest is how this precision milling/deposition capability has enabled a wide range of site specific micromachining and microfabrication operations (e.g., TEM, SEM, SIMS, and AUGER specimen preparation and circuit modification). The applications of FIB instruments frequently involve the creation of high aspect ratio features (i.e., deep narrow trenches). Ideally, the sidewalls of an FIB milled feature should be vertical; however, it has been generally observed that the trenches tend to exhibit a gradual sloping. The observed deviation from vertical milling has been attributed to the redeposition of sputtered material, and is especially pervasive at high beam currents and confining trench geometries. A hole milled with an FIB tends to be widest at the top surface and taper down to a point at the bottom.