Resolving buried interfaces with low energy ion scattering

We investigate the use of low energy ion scattering (LEIS) to characterize buried interfaces of ultrathin films. LEIS spectra contain depth-resolved information in the so-called subsurface signal. However, the exact correlation between the subsurface signal and the sample’s depth composition is still unknown. For this reason, LEIS spectra so far only provided qualitative information about buried interfaces. In this study, we investigate nm-thin films of Si-on-W and Si-on-Mo, where we compare simulated data to LEIS spectra. We present a method to extract depth-sensitive compositional changes—resolving buried interfaces—from LEIS spectra for the first few nanometers of a thin-film sample. In the case of Si-on-Mo, the simulation of the LEIS subsurface signal allows obtaining a quantitative measurement of the interface profile that matches the value determined using the LEIS layer growth profile method with an accuracy of 0.1 nm. These results pave the way to further extend the use of LEIS for the characterization of features buried inside the first few nanometers of a sample.