Electron beam-assisted formation of silicon oxynitride layers (3.5 nm) on silicon at moderate temperatures using NO gas: growth kinetics and mechanisms

摘要

Exposure to low pressures, P_(NO), of pure nitric oxide gas (1*10~(-6) mbar <=P_(NO)<=1*10~(-4) mbar) on a clean Si(1 0 0) surface at moderate temperatures T (room temperature (RT) to 600degC) leads to the formation of a 0.5 nm thick oxynitride passivating layer. Under low-energy electron beam irradiation (primary energy=250 eV, electron current density=1.25 mA cm~(-2)) film growth occurs, independent of the temperature in the investigated range. A maximum thickness of about 3.5 nm can be obtained at 600degC and at RT. We show that the oxynitride films formed are, in fact, oxide films with an SiO_xN_y interfacial layer with the silicon substrate. The higher the temperature the larger the nitrogen content in the interfacial region without, practically, any increase in film thickness. A model for growth kinetics of these films in a nitric oxide environment is proposed. The reacting species are assumed to be O~- and NO~- ions which move in an electric field, acting as a driving force. The model assumes that the oxide growth is limited by time-dependent interface reaction of nitrogen at oxidation growth sites and by a thermally activated electron-stimulated desorption process of oxygen.