Dynamic binary collision simulation of focused ion beam milling of deep trenches

A new model is presented for the simulation of focused ion beam milling in two-dimensional targets. It combines dynamic Monte Carlo binary collision simulation with cell-based topography simulation, and includes relaxation of cell densities. In the Monte Carlo model advanced algorithms are used for surface treatment, trajectory termination, and collision partner selection. Cell relaxation is performed by minimization of an energy function written in terms of the grid point coordinates, taking the deviation of the cell area from its relaxed value into account, but neglecting viscous forces. Relaxation is limited to areas where nuclear collisions have occurred during cascade simulation. The code is applied to deep trench formation in Si targets by 50 keV Ga focused ion beams. The simulation results indicate the importance of material flow and compare well with experiments.