Ripple topography development on ion bombarded Si

The development of a wave or ripple like topography on Si by non-normal incidence ion bombardment is a well known but poorly understood phenomenon. In an attempt to improve understanding of the processes responsible a series of studies have been made with 45° ion incidence of Ne⁺, Si⁺, Ar⁺ and Xe⁺ species with energies between 5 and 40 keV and for substrate temperatures from 100 to 700 K. Topography evolution was observed by scanning electron microscopy and atomic force microscopy. Quite generally it was found that ripples could be produced by all ion species on low temperature substrates but only by the heavier ions at room temperature. For Ar⁺, at room temperature, there appears to be an energy threshold below which ripples are not produced. It will be shown how these results cannot be explained by current models of curvature mediated stochastic sputtering coupled with atomic transport related relaxation processes and other approaches are considered.