Effect of multiple scattering on high-resolution Rutherford backscattering spectroscopy

The effect of multiple scattering on high-resolution Rutherford backscattering spectroscopy was studied for 450 keV He+ ions incident on ultrathin HfO2 films on Si. There was a tail at the low energy Hf edge in the observed spectrum. The tail increases with increasing HfO2 thickness and decreasing exit angle (exit angle with respect to the surface). A notable tail was observed even for HfO2 films of 2 nm thickness at a small exit angle of 7°. The observed tail was reproduced by Monte Carlo simulations showing that the origin of the tail is multiple scattering. An analytical model was developed to estimate the tail for practical use. The derived analytical formula roughly reproduced the observed tail.