An experiment-based method for focused ion beam milling profile calculation and process design

Abstract

A new experiment-based method is presented to efficiently and accurately obtain the resulting outline of micro-structures from focused ion beam (FIB) milling and to guide the design of the process parameters for some specific structures. The approach uses separate distribution equations to solve the evolution distributions of the structural profile from sputtering and redeposition during the process. Through a series of basic experiments, the experimental equations of the key process parameters are set up to describe their influence on the contour of the machining results. By combining these equations with the distributions, the spread functions of etching and deposition are established. An expectation difference function (EDF) is considered between the spread functions to describe the increasing distance between the redeposition distribution center and the scanning beam center during processing, which is a main reason of the redeposition attenuation effect. The sum of the spread functions under the influence from EDF is the effect of superposition of sputtering and redeposition, and its response developing through the scanning strategy to the profile is calculated as the final result of the process. To reduce the deviations between the simulated and experimental results caused by variations from process conditions and device conditions, particle swarm optimization (PSO) is introduced to modify these model parameters. To stress the flexibility of the method, several different process conditions are tested, including the calculation of redeposition profile on quartz for the first time. As a further application, we also evaluate the ability of the method to help with the parameter design and modification for processing complex microstructures through FIB in practice. The good agreement between profile calculation and the experiment, and the good role in the process parameter design, fully demonstrate the application prospect of the method.