Sputtering efficiency of amorphous substances

Abstract

Sputtering efficiency is denned as the fraction of bombarding ion energy leaving a crystal via sputtering and backscattering. This quantity is calculated for the case of perpendicular incidence on a random medium with plane surface. Use is made of the spatial distribution of deposited energy as calculated by Sanders and the author. In the elastic collision region but above about 1 keV, the sputtering efficiency is predicted to be essentially independent of ion energy and to depend only on the mass ratio. For self-sputtering it should be 2.4% and increase with decreasing ion mass. The predictions appear to be consistent with existing experimental results, but a few direct checks are desirable. Qualitative arguments suggest that, in the case of single crystals, lattice effects with respect to the incoming beam are more pronounced in the sputtering efficiency than in the yield. Reversely, ejection patterns of sputtered energy should reveal less influence of lattice structure than those of sputtered intensity. The latter result is consistent with experiment.