X-ray reflectometry of the specific features of structural distortions of He+-implanted Si(001) surface layers

The structural changes in the surface layers of silicon substrates, implanted by helium ions with energies from 2 to 5 keV and doses to 6 × 10¹⁵–5 × 10¹⁷ cm^?2, has been studied by high-resolution X-ray reflectometry. The damaged layer is found to have a total thickness comparable with the total ion path length (estimated from the SRIM model) and a multilayer structure: a strongly amorphized layer with reduced density, a porous (incapsulated) layer, and a deformed layer. The thickness of sublayers, their density ρ(z), and the mean strain (～5 × 10^?3) have been determined. The characteristic pore size is estimated to be 5–20 nm. It is shown that the presence of a nanoporous layer facilitates the formation of diffuse scattering, which can be used to diagnose layers by high-resolution X-ray reflectometry.