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 × 10 15 –5 × 10 17 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.