Growth of epitaxial silica on vicinal Si(001) surfaces during thermal oxidation in O₂

Abstract

Reflection high-energy electron diffraction (RHEED) and high-resolution transmission electron microscopy (HRTEM) show that, when vicinal Si(001) surfaces, cut with a 5° tilt about [110], are thermally oxidized in very dry O₂, an epitaxial crystalline phase of oxide grows along [110] ledges. X-ray photoemission confirms that the oxide is stoichiometric SiO₂, This crystalline SiO₂ is not a standard phase of silica. We show that it can have a cubic Bravais cell (a_o=8·8 Å). We propose simple models derived from β-cristobalite, coherent with the projected Si positions given by HRTEM. Structure factors are calculated and compared with the RHEED diagrams of oxide grown on both Si(001) vicinal surfaces and ‘rough’ Si surfaces of various orientations. Finally we discuss the process involved in the growth of very thin oxide films.