Atomic Dynamics During Silicon Oxidation and the Nature of Defects at the Si-SiO2 Interface

ABSTRACTOxidation of thin-film Si, oxygen precipitation in bulk crystalline Si, and the formation of buried oxide layers (as in the SIMOX process for SOI) have been studied extensively for decades but the underlying atomic scale processes have remained elusive. Furthermore, common features of these phenomena have not been generally appreciated, in part because the kinetics are substantially different in the different cases. In this paper we review recent theoretical research based on atomic-scale first-principles calculations that provides a unified description of the three phenomena. In particular, we account for both the normal and enhanced mode of oxygen diffusion that leads to the formation of oxygen clusters known as thermal donors and their subsequent annealing and evolution into SiO2-like precipitates. It is proposed that a novel family of interface defects that are akin to thermal donors, composed of “frustrated” Si-O bonds, are a natural by-product of thin-film oxidation. An explicit mechanism for the emission of Si interstitials, which occurs during both oxidation and oxygen precipitation, is obtained. It is shown that emission of Si interstitials eliminates the frustrated-bond defects, thus explaining the high quality of the resulting interfaces. It is proposed that frustrated-bond defects are responsible for much of the behavior observed at the Si-SiO2 interface that cannot be accounted by dangling bonds and for the amphoteric traps that occur in high concentrations in SOI material.