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Single-crystal silicon and silicon dioxide remain the primary materials for high-precision mirrors and other components of X-ray and extreme ultraviolet (EUV) optics. A key feature of these elements is the stringent requirement to maintain their complex geometrical shape and high surface smoothness. One of the approaches to reducing surface roughness and shaping substrates for various X-ray optical elements is ion beam etching. However, ion treatment also significantly alters the composition and density of the near-surface layer, which may adversely affect subsequent stages of element fabrication.
In this work, structural damage in the near-surface layer of SiO₂ after ion irradiation and its influence on the angular dependence of the reflectivity R(θ) are investigated using X-ray reflectometry (XRR) and grazing-incidence small-angle scattering (1D GISAXS). The methodology is based on comparing experimental R(θ) curves with theoretical calculations. A model-independent approach [2] was employed to reconstruct the sample structure.
The samples were irradiated with accelerated argon ions at an energy of 1 keV and a current density of 0.39 mA/cm² using an ion beam etching setup described in detail in [3]. The irradiation doses were 1.24×10¹⁷, 1.24×10¹⁸, and 1.24×10¹⁹ ions/cm². The experimental study was carried out using a diffractometer setup with a mobile source–detector system, equipped with an X-ray tube with a copper anode, a Si(220) monochromator (λ = 1.5405 ± 0.1 Å), a three-slit collimation system, angular encoders (inductive resolvers), a scintillation detector SCSD4 (Radicon), and a linear detector Mythen2 (Dectris).
A change in the electron density profile of the near-surface layer of fused quartz as a function of depth due to argon ion bombardment was observed. To interpret the results, numerical simulations of ion depth distribution in the substrate were performed using two methods: Monte Carlo and classical molecular dynamics. The simulated data explain the presence of two peaks in the depth distribution of argon ions concentration.
This work was carried out within the framework of the state assignment of NRC “Kurchatov Institute” for the X-ray studies and under Agreement No. 075-15-2025-458 with the Ministry of Science and Higher Education of the Russian Federation for the experimental data analysis