Local Crystallization of Thermal Oxide Film of Silicon

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Abstract
The occurrence of crystallites in thermal oxide films of silicon is studied in connection with contamination by sodium and with surface irregularities on silicon, using reflecting electron diffraction technique. Crystallites formed under the presence of sodium are identified as α- and β-cristobalite. When sodium of about 1015 atoms/cm2 is deposited on the silicon surface before oxidation, the crystallites of a size discernible even by the naked eye are formed in the oxide films at 1100°C. The area of the crystallized region in the oxide film is proportional to the amount of sodium on the silicon surface before oxidation. When a lapped or sand-blasted silicon wafer is oxidized, the grown oxide film is noncrystalline, as well as the chemically etched and mechanically polished wafers.