Diving into thin-film interfaces using low energy ion scattering

Interfaces are critical to the performance of multilayer systems for EUV and X-ray optics and, in general, in semiconductor devices. As device dimensions shrink, the quality of interfaces becomes increasingly vital. In the push for ever-smaller feature sizes in the semiconductor industry, the ability to characterize buried interfaces with sub-nanometer resolution is essential. This thesis investigates whether the sub-surface signal of Low Energy Ion Scattering (LEIS) spectra can be used to measure the width of buried interfaces, with the ultimate goal of adding complementary (non-destructive, depth-resolved, and quickly accessible) information to the commonly used techniques for the analysis and understanding of thin film growth in multilayer systems.

We improved the simulation of LEIS spectra, enabling quantitative depth-resolved measurements with LEIS. Then, we applied the developed method to investigate interfaces between W, Si, and B4C, which are relevant materials for X-ray optics. Our findings demonstrate that a small difference (<0.2 nm) in effective interface width can be measured from the shape of LEIS tails in suitable conditions, such as sufficient mass contrast between elements and shallow interface depths.

Compared to a layer growth approach, buried interface profiling has the advantage of needing a single sample and a single LEIS measurement, albeit supported by simulations. Furthermore, by decoding the depth information encoded in LEIS tails, this work broadens the applicability of LEIS, enabling detailed interface characterization across a wider range of material systems. Overall, the results presented in this thesis affirm LEIS as a valuable technique for non-destructive, depth-resolved, and quickly accessible analysis of the composition of the first few nanometers of a sample.