An accurate and efficient control over the present numerical model of depth of sputtering in focused ion beam milling

Abstract

In many applications, such as fabrication of microtools, microsurgical instruments, microgears, and so on, material must be removed precisely with a focused ion beam (FIB) milling process to generate a specified geometry on substrate material. A mathematical model is available to calculate depth of sputtering at each point on substrate material in order to generate a specified geometry, but the results of the existing model deviates from experimental data. In the current paper, normalized pixel spacing and ratio of redeposition to beam velocity are the two parameters that have been considered in calculation of depth of sputtering during the FIB milling process. A proposed mathematical model incorporating the effect of redeposition has been simulated for parabolic and rectangular trench profiles, and it has been proven to be better than the existing model through comparison with experimental data of parabolic and rectangular geometry on silicon material. In addition, efforts have been made to reduce the amount of numerical calculation in the simulation process by utilizing a Gaussian mask in the existing model instead of the usual Gaussian intensity function. The Gaussian mask prevents the need for repeated calculation of Gaussian intensity function in the mathematical model of depth of sputtering, and in turn reduces the time of computation.