Measurements and calculations of FIB milling yield of bulk metals

Focused ion beam systems are applied for the creation of nano-scale structures by patterned milling into a substrate. For a given material, the local dose (nC) determines the amount of material (@mm^3) removed by the beam: this volume per dose is referred to as the milling yield. In practice the milling yield is dependent on the material type and can be predicted from modelling calculations such as applied in SRIM. Ion channelling effects however, will induce a local variation of the yield. For common construction materials such as aluminium, brass, phosphor bronze, titanium, lead, stainless steel and silicon the milling yield has been measured with averaging of channelling and compared to predicted values. Overall, the predicted values are higher than the measured values. This effect is attributed to inaccuracies in the modelling calculations as well as to re-deposition of released material during the milling process.