Considerations about multiple and plural scattering in heavy-ion low-energy ERDA

Abstract

Low-energy heavy-ion Elastic Recoil Detection Analysis (ERDA) is becoming a mature technique for high-resolution characterization of thin films, i.e. below 50nm thickness. In combination with a small tandem accelerator (∼2MV terminal voltage) and beam energies below 20MeV, it is suitable for routine analysis of key materials in semiconductor technology.At low-energies, however, small angle multiple scattering and large angle plural scattering of ions play a significant role, starting from the first nanometers. Multiple and plural scattering dominate the depth resolution deterioration with increasing depth and, when glancing angles are used, introduce long tails in the elemental energy profiles. Moreover, multiple and plural scattering may affect the elemental relative and absolute quantification. A complete characterization of ultra-thin films thus requires a detailed analysis with accurate simulation of the energy spectra.In this paper we investigate the mechanism of multiple and plural scattering for different combinations of beam/recoil atoms, energies and geometries. Simulations run with the Monte Carlo code MCERD support and generalize the experimental data. The calculations show the relative contributions of beam and recoil ions and highlight the role of ion angular distribution to the formation of tails in the energy profiles.