X-ray diffraction evidence for the existence of epitaxial microcrystallites in thermally oxidized SiO2 thin films on Si(111) surfaces

In X-ray diffraction from thermally oxidized thin films on Si(111) surfaces, very weak peaks were observed at the lower-angle side of the crystal-truncation-rod scattering from the 111 Bragg point of the substrate. The intensity of the peak depends on the thickness of the oxide layer, and the peak is not observed when the oxide film is removed by etching, High-resolution X-ray measurements showed that the profile of the peak intensity had Laue-function-like fine structure, for which the period varied with the thickness of the oxide layer. These features resemble previous observations from SiO2/Si(001) samples, indicating that SiO2 crystallites also exist in the oxide layer on the Si(111) surfaces. A possible structural model for the oxide layer is proposed, which can reproduce the peak quite well.