Composition dependence ofSi1−xGexsputter yield

Abstract

Sputtering yields have been measured for unstrained ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ $(x=0--1)$ alloys when bombarded with ${\mathrm{Ar}}^{+}$ ions within the linear cascade regime. Nonlinear S-shape dependence of the sputter yield as a function of the alloy composition has been revealed. The dependence is analyzed within the frameworks of the cascade theory conventionally accepted to be the most systematic to date theoretical approach in sputtering. In view of a linear composition dependence predicted for the sputter yield by the cascade theory adapted for polyatomic substrates, the nonlinearity observed in our experiments is shown to be related to the alloying effect on the surface binding energies of the alloy components. Based on this analysis, an interpretation is proposed for the experimentally observed nonlinear composition dependence of ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ sputter yield. The yield is expressed by an equation derived from the cascade theory with additional terms of the composition parameter $x$. The form of the equation implies that for a polyatomic substrate the surface binding energy of an individual atom is determined not only by its own chemical identity but to a considerable degree by the identities of its neighbors.