Discrete-path transport theory of physical sputtering

Abstract

The fundamentals of low-energy physical sputtering currently attract increasing interest in relation to ion-based and plasma-based micro- and nanofabrication technologies. However, explaining sputtering in the sub-keV bombardment regime has long been a challenge for the kinetic theory, partly because of a simplistic treatment of the surface. Here, transport theory of sputtering is formulated, which includes a more realistic analytical model of the surface in a semi-infinite target. In contrast to the traditional theory, which is based on the linearized Boltzmann equation, the new approach uses the discrete-path master equation for particle transport in matter. Starting from the discrete-path formalism, the deflection of incoming projectiles and focusing of emitted particles when they pass the surface are described by a unified few-collision approach and combined with the bulk master equation through sophisticated boundary conditions. The numerical results are compared with available experiments. Major anisotropies that affect differential sputtering yields in the sub-keV bombardment regime are considered as obtained from the kinetic modeling.