Preferential sputtering in binary targets

Abstract

Numerous experimental data on changes of surface composition of ion-bombarded binary targets and advances in computer simulations of ion-solid interactions give grounds for discussion of characteristic features inherent to the effect of preferential sputtering. The current status of research on preferential sputtering in two-component targets under bombardment by 0.5–10 keV inert gas ions is reviewed. Both the experimental data and the results of computer simulations are discussed. The experimental data were carefully chosen so as to eliminate the effect of surface segregation. The emphasis is on the compositional changes of metal silicides and other semiconductor compounds bombarded at the room temperature and studied by AES using low-energy Auger lines (the information depth within 3–4 atomic layers). The main concern is with such subjects as: the effect of the ion energy on surface compositional changes under the steady-state conditions of sputtering; the dependence of the compositional changes on the angle of ion incidence; the influence of the bulk concentrations on the effect of preferential sputtering; correlation between the surface compositional changes and component masses and surface-binding energies. The experimental data are compared with the analytical theory of preferential sputtering. The latter is also compared with results of computer simulations by well-known Monte-Carlo codes TRIM.SP, TRIDYN, TAMIX and other numerical calculations in the framework of the binary-collision approximation. By such a way, the field of application of the theory is elucidated. The possible influence of the bulk binding energy on the effect of preferential sputtering is also briefly discussed. Experimental data on surface compositional changes of semiconductor compounds reported in the literature over the last decade are tabulated.