Examining the influence of W thickness on the Si-on-W Interface: A comparative metrology analysis

W/Si thin-film multilayer structures are used in various applications such as X-ray, neutron, and extreme ultraviolet optics. The interfaces between the films play such a fundamental role in the performance of these structures that a sub-nanometer and non-destructive characterization of such interfaces is necessary, albeit challenging. In this study, we investigate the interface Si-on-W and the effect of W thickness on such an interface using low energy ion scattering (LEIS), X-ray reflectivity (XRR), and transmission electron microscopy (TEM). We extract the Si-to-W error-function-like compositional change to quantitatively compare the effective interface width measured by the different techniques. We demonstrate that, in the case of Si-on-W, the effective interface width measured by LEIS and XRR agrees with the values extracted from TEM analysis within a 0.1 nm error margin. Noting that TEM is a destructive method, these results exemplify the value of LEIS and XRR as analysis techniques for resolving thin film interfaces. Surprisingly, all techniques employed in the study show that a structure with 20 nm of W has a sharper Si-on-W interface compared to a structure with 4 nm of W, which we interpret as the effect of both the correlated roughness from the substrate - present in the case of 4 nm W - and the larger crystals - present in the W film in the case of 20 nm W- resulting in less intermixing. This directly shows the value of extracting exact interface widths for the analysis and understanding of thin film growth in multilayer systems.