Why are physical sputtering yields similar for incident ions with different masses?—physical sputtering yields of the Lennard–Jones system

Abstract

Plasma etching of nano-meter-scale complex structures for semiconductor device manufacturing requires a deeper understanding of etching mechanisms. For example, it is known experimentally that the sputtering yield of a material tends to have weak dependence on the mass of incident ions except for extremely light ions such as helium. To understand this property, the sputtering yield of a system of atoms interacting with Lennard–Jones (LJ) potentials was evaluated with molecular dynamics simulation. As the simplest possible case involving two atomic species, a single-element face-centered-cubit (fcc) LJ solid surface interacting with purely repulsive atoms was examined, which emulates a solid surface sputtered by noble-gas ions. The sputtering of such a system at specific incident ion energy depends only on two parameters, i.e. the mass ratio and a parameter representing the relative interaction range between the surface atom and the incident ion. For real materials of our concern used in plasma etching, the range of these two parameters was found to be relatively limited. It was also found that the physical sputtering yield of the LJ system weakly depends on the mass ratio in this relatively narrow parameter range. Because the simple model predicts the weak yield dependence on the incident ion mass, it is considered as a generic property of physical sputtering, independent of the detailed atomic interactions of the surface material and incident ion species.