A Second Look at 2D Simulation of FIB Milling: Accounting for Mean-Free Path Effects in Redeposition and Sputtering

This work presents a predictive 2D mathematical model for focused ion beam (FIB) milling that incorporates primary sputtering, redeposition, and secondary sputtering effects. Model validity is evaluated through comparison with experimental data and simulation results. Findings show that micro-trench geometry is strongly influenced by redeposition and ion reflection, particularly in high-aspect-ratio structures. Secondary sputtering from backscattered or reflected ions becomes significant for aspect ratios above 1, while sputtering from sputtered atoms is negligible due to their low energy. The model applies the cosine law to approximate the angular distribution of sputtered atoms and reflected ions, validated using Monte Carlo simulations (TRIM). Mean free path effects, especially under long dwell times, are shown to influence local pressure and particle distribution in deep trenches. Using a string-segment method, the 2D model efficiently handles sputtering and redeposition with reduced computational cost. Simulations across varying trench aspect ratios and dwell times demonstrate good agreement with literature, confirming the model’s predictive capability for surface topography evolution.