Effects of multiple scattering and surface roughness on medium energy backscattering spectra

The influence of multiple scattering and surface roughness on medium energy backscattering spectra was studied using Monte Carlo simulations. These factors can influence the shape of backscattering spectra, making it difficult to accurately determine composition profiles. Using near-normal and near-glancing ion exit angles, simulations were performed for 270 keV 4He+ ions incident on targets of 33 nm Ta on Si and 5 nm ZrO2 on Si. The influence of both multiple scattering and surface roughness were found to increase with exit angle, which is measured towards the surface normal. Simulations showed that multiple scattering affected the shape of the Ta/Si spectrum even for a small exit angle of 15°, but did not significantly affect the shape of the ZrO2/Si spectrum. Monte Carlo simulated spectra from a 5 nm ZrO2/Si target with a near glancing angle of 75° and a RMS roughness of 1 nm resulted in a tail at the low energy edge of the Zr signal and the front edge of the Si signal.