Characterization of SiO₂/Si heterostructures by soft x-ray reflection

Grazing incidence x-ray reflectivity has been used to characterize four as-grown SiO₂/Si(100) heterostructures with SiO₂ overlayer thicknesses ranging from about 126 to 1100 Å. Root-mean-square roughness at both the top surface and buried interface is determined, as is the (complex-valued) x-ray refractive index of the SiO₂ heterostructure material for photons in the energy range 400-800 eV. Knowledge of the SiO ₂ and Si refractive indices allows the oxygen atomic scattering factor to be deduced at these energies. Evidence that one of the four thermally grown structures may consist of more than just a single homogeneous overlayer is also examined.