Characterization of subnanometric layers by grazing incidence X-ray reflectometry

We present a method to characterize subnanometric layers based on grazing incidence X-ray reflectometry. For this purpose, we propose to use a “Fabry-Pérot” type multilayer structure in order to improve the sensitivity of the measurement to the layer thickness. For our study, this structure consists of a thin layer of scandium inserted between two periodic chromium (Cr)/scandium (Sc) multilayers. We describe the principle and estimate the sensitivity of the method by simulation. Experiments were performed on two optimized Fabry-Pérot structures with 0.6 and 1.2 nm Sc layer thicknesses using a laboratory grazing incidence reflectometer at 8.048 keV (Cu Kα radiation). Fitting of experimental data allows determining the Sc layer thickness. Finally, the structural parameters used in the fit were confirmed by measurements at 3 keV on the hard X-ray branch of the synchrotron SOLEIL Metrology and Tests beamline.