Synchrotron x-ray studies of vitreous SiO ₂ over Si(001). I. Anisotropic glass contribution

While numerous investigations of the structure and interface of amorphous SiO ₂ thermally grown on Si, theoretical as well as experimental, have been carried out over the years, a definitive picture of this thin gate oxide and its interface remains lacking. We have explored this issue using synchrotron x rays in grazing incidence geometry. In this geometry a fourfold modulation in the first sharp diffraction peak (FSDP) from thin vitreous SiO ₂ of 100 and 500 Å thickness can be observed. While the FSDP exhibits a modulation throughout the entire film, this modulation decays away from the interface. Reflectivity measurements were also performed, which reveal an interfacial layer of 3% density increase in the SiO ₂ film over the bulk (film) density.