Sputtering of amorphous Si in the regime of ripple surface topography

The effects of ion-induced surface nanorelief on steady-state sputtering of amorphous silicon by 0.5–30 keV Ar ions have been studied using the binary-collision computer simulation. The relief was modelled as a wave-like surface along one (2D relief) or two mutually perpendicular surface axes (3D relief). Emphasis is laid on the depth-of-origin distributions of sputtered atoms. It has been shown that the ratio between the number of atoms sputtered from the top of relief and the number of atoms sputtered from its bottom is a non-monotonic function of the relief height. The shape of this function depends strongly on the angle of incidence of ion beam and the parameters of relief. At normal incidence an essential part of bombarding ions undergoes inclined incidence on the walls of surface hillocks, which increases the density of ion-atom collisions near the surface. This effect leads to an increase of the sputtering yield for a relief surface compared to that for a flat surface. At oblique incidence, shadowing (blocking) of one part of the surface by another is important and may decrease the sputtering yield by a factor of about 3. The results of simulations are in reasonable agreement with experimental data.