Grazing-incidence small-angle X-ray scattering study of correlated lateral density fluctuations in W/Si multilayers

Abstract

A structural characterization of W/Si multilayers using X-ray reflectivity (XRR), scanning transmission electron microscopy (STEM) and grazing-incidence small-angle X-ray scattering (GISAXS) is presented. STEM images revealed lateral, periodic density fluctuations in the Si layers, which were further analysed using GISAXS. Characteristic parameters of the fluctuations such as average distance between neighbouring fluctuations, average size and lateral distribution of their position were obtained by fitting numerical simulations to the measured scattering images, and these parameters are in good agreement with the STEM observations. For the numerical simulations the density fluctuations were approximated as a set of spheroids distributed inside the Si layers as a 3D paracrystal (a lattice of spheroids with short-range ordering but lacking any long-range order). From GISAXS, the density of the material inside the density fluctuations is calculated to be 2.07 g cm−3 which is 89% of the bulk value of the deposited layer (2.33 g cm−3).

Investigation of physical properties of Si crystallites in W/Si multilayers

“…The quasi-Bragg peaks, starting from the third, are completely described by roughness with partial correlation. Nikolaev et al (2019) and Medvedev et al (2019) observed the nonmonotonicity of the signal in the azimuthal sections between the quasi-Bragg peaks. We also identified features in Fig.…”

“…This is a novel observation measured by GISAXS. The W/Si structures with other parameters studied by Nikolaev et al (2019) and Medvedev et al (2019), Waist between the first and second Bragg sheets in the form of diverging filament beams. Beam divergence: = 4 0 , ' = 20 0 .…”

“…On the other hand, the diffuse scattering of interfaces is significantly greater than that of inhomogeneities, which can lead to an erroneous interpretation of grazing-incidence smallangle X-ray scattering (GISAXS) spectra. It is also possible that the observed effects may depend on the specific growth conditions, especially since the authors noted a change in the parameters of these inhomogeneities when ion polishing of the layers had been performed (Nikolaev et al, 2019;Medvedev et al, 2019). Similarly, the formation and growth of quantum dots in Ge/Al 2 O 3 strongly depends on temperature (Shaji et al, 2020).…”

“…This suggests that the volume density of the Si layer is not homogeneous because it consists of amorphous matrix and crystalline nanoparticles. Nikolaev et al (2019) and Medvedev et al (2019) studied the density inhomogeneities of the Si layers in W/Si multilayer mirrors using cross-sectional electron microscopy and X-ray scattering. The evaluation showed that the geometric and correlation characteristics of the inhomogeneities studied by these methods agreed well with each other.…”

Microstructural Transformation of Nanoscale Be Layers in the Mo/Be and Be/Mo Periodic Multilayer Mirrors Investigated by Raman Spectroscopy

“…However, the structural properties of Mo are only investigated for a few model Mo/Si multilayer systems, − while condensing it into the body-centered cubic (bcc) polycrystalline phase. The microstructure and bonding properties of the spacer layers such as Si and Be for the Mo/Si, − and Mo/Be, respectively, are rarely reported. Interphase formation in the multilayer structures is well investigated, which is manifested by the thermodynamic driving force and effective heat of formation .…”