Influence of surface roughness on measuring depth profiles and the total amount of implanted ions by RBS and ERDA

Abstract

For rough surfaces depth profiling of surface layers becomes questionalble if the layers to be analysed have a thickness comparable to or larger than the dimension of the surface roughness. In this work nitrogen ions have been implanted at normal incidence into carbon samples with smooth and rough surfaces, respectively. These implanted layers have been measured by Rutherford Backscattering Spectrometry (RBS) using 1.7 MeV 4He ions and by Elastic Recoil Detection Analysis (ERDA) using 35 MeV 35Cl ions at different angles of incidence. For smooth surfaces the N depth profiles obtained from both RBS and ERDA are in accordance with TRIM simulations. This is also the case for RBS measurements at normal incidence and 10° emergence relative to the surface normal of a sample displaying few 100 nm surface roughness. For this rough sample, ERDA measurements under oblique angles of incidence and emergence yield long distribution tails towards larger depths, at reduced peak N concentrations, compared to smooth surfaces, while the total N contents are roughly identical. Computer simulations using an idealised surface topography to model surface-roughness effects give qualitative agreement with the ERDA depth profiles obtained from the rough sample.