Sputtering of silicon membranes with nanoscale thickness

A theoretical study of forward and backward sputtering produced by the impact of single 20 keV Ar ions on freestanding amorphous Si membranes is carried out. We use three techniques: Monte Carlo (MC) and molecular dynamics (MD) simulations, as well as analytical theory based on the Sigmund model of sputtering. We find that the analytical model provides a fair description of the simulation results if the film thickness d exceeds about 10%–30% of the mean depth of energy deposition a. In this regime, backward sputtering is nearly independent of the membrane thickness and forward sputtering shows a maximum for thicknesses d≈a. The dependence of forward sputtering on the ion's incidence angle shows a qualitative change as a function of d: while for d≲a, the forward sputter yield has a maximum at oblique incidence angles, the maximum occurs at normal incidence for d≳a. As the membrane thickness is reduced below 0.1– 0.3a, the theory's predictions increasingly deviate from the MC results. For example, the predi...