Effect of initial target surface roughness on the evolution of ripple topography induced by oxygen sputtering of Al films

Abstract

The effect of pre-existing random roughness on the evolution of ripple structures in O2+ sputtered thin Al films has been investigated. The results show that there is a considerable reduction in initial roughness of the film surface at the early stages of sputtering. For large scale surface structures, angle-dependent first order sputtering is responsible for ion beam smoothening, while for smaller microscopic features, different relaxation mechanisms dominate for smoothing of the surface. At the later stages of sputtering, the curvature dependent erosion instability sets in leading to the development of either coherent ripples or faceted structures depending on the degree of virgin film roughness and bombarding angle. It is found that coating a flat Si surface with ultrathin Al film and subsequent removal of the Al layer by oblique O2+ sputtering leads to the formation of ripple pattern with moderate amplitude in the Si matrix at much lower effective fluence than that would be in bare Si without Al masking.