Silicon oxide decomposition and desorption during the thermal oxidation ofsilicon

The thermal oxidation of silicon is normally considered to occur via two di fferent routes. At higher O-2 pressures and lower temperature SiO2(s) film growth occurs ("passive" oxidation), while at lower O-2 pressures and highe r temperature SiO(g) is desorbed in an etching process ("active" oxidation) . We have measured the yield of SiO into the gas phase in a wide range of d ry O-2 pressures (10(-7)-10(-5) Torr) and Si substrate temperatures (620-87 0 degrees C) in the passive as well as the active oxidation regimes. A phas e diagram for silicon oxidation in this pressure-temperature region is obta ined. We have found evidence for small but measurable yields of SiO(g) deso rbing from the nascent oxide film during the initial stages of passive oxid ation, even when the oxide film continuously covers the surface. A sensitiv e method for detecting volatile products based on condensation of desorbed species is described.