Residual order within thermally grown amorphous SiO₂ on crystalline silicon

The origin of x-ray diffraction peaks observed on the crystal truncation rods (CTR’s) in reciprocal space for thermally grown SiO₂ films has been investigated by large-scale atomistic simulation of silicon oxidation. Three models of SiO₂ on Si(001), Si(111), and Si(113) were formed by introducing oxygen atoms in crystalline Si from the surfaces in an atom-by-atom manner. The SiO₂ structures are classified as being amorphous in conventional characterizations, but retain the residual order originating from the (111) atomic planes in their parent crystals. The calculated diffraction patterns exhibit intensity peaks with Laue-function-like fringe profiles along the CTR’s, at positions depending on the substrate orientations, agreeing quite well with experimental results.