Microscopic mechanism of thermal silicon oxide growth

The atomistic mechanism of silicon oxidation is investigated by a combination of first-principles calculations and macroscopic approaches. The results of first-principles calculations show that oxidation-induced strain accumulates at the interface as oxidation proceeds, which indicates the emission of a large number of Si atoms to release the accumulated strain. Further calculations to investigate the favorable location of the emitted Si atoms indicate that most of them diffuse into the oxide layer and are oxidized there. Based on these results, we propose a model that the emitted Si atoms in the oxide govern the oxidation rate due to their high concentration. Next, based on the model, we construct the macroscopic diffusion equations, which include Si diffusion species in addition to oxidant species, and we successfully simulate the whole range of oxide thickness, including the thin film regime, in a wide range of oxidation conditions. In addition, combined with the elastic continuum theory, we show that the strain release by the Si emission can explain the recent observations of Si layer-by-layer oxidation together with the formation of many small oxide islands.