Kinetics of ultrathin SiO2 growth

Abstract

A new model for explaining the initial rapid oxidation of silicon in dry oxygen has been proposed. Creation of an oxygen-diffused zone near the Si-SiO2 interface is postulated. Our model takes into account the heretofore ignored phenomenon of diffusion of oxidizing species into the silicon substrate during initial exposure to such species. This occurs because of the low diffusion resistance offered by the ultrathin oxide films to the oxidizing species. The oxidizing species diffuses in such large amounts that not all of it is consumed at the Si-SiO2 interface; instead, a part of it diffuses into the substrate creating an oxygen-diffused zone in silicon. The reaction occurs over this zone instead of occurring just at the interface. As the oxide thickness builds up, the concentration of the oxidizing species at the Si-SiO2 interface decreases due to the increase in the diffusion resistance offered by the growing oxide film. Once the oxide becomes sufficiently thick all of the oxidizing species reaching the Si-SiO2 interface is consumed by the reaction at the interface, and the zone disappears. The occurrence of the reaction over a zone instead of occurring at the interface alone leads to an enhancement in the oxidation rate in the ultrathin-film regime. This enhancement has been formulated, and new oxide thickness-time relationships have been derived. This model explains all phenomena observed in silicon oxidation, and the Deal-Grove model is found to be a special case at larger thicknesses.