Impact of oxidation-induced strain on microscopic processes related to oxidation reaction at the SiO2/Si(100) interface

The reaction of oxygen molecules at the SiO2/Si(100) interface in the presence of oxidation-induced strain is investigated using total-energy electronic-structure calculations within the density-functional theory. It is found that the calculated effective barrier height for the O-2 reaction at the interface with strained oxide layers less than 2 monolayer (ML) thick is almost identical to that at the strain-released interface. On the other hand, it increases significantly when the strained oxide layer reaches 2 ML. This is because the energy of the O-2 near the strained oxide layer in the 2 ML oxidized interface is higher than that in the strain-released region. Given our result that the oxidation-induced strain should become large enough to prevent the oxidation reaction and the knowledge that oxide formation with smooth interface is continuous, we conclude that there must be some strain-release mechanism that is present during silicon thermal oxidation.