The roles of charged and neutral oxidizing species in silicon oxidation from ab initio calculations

摘要

We examine the roles of charged oxidizing species based on extensive ab initio density functional theory calculations. Six species are considered: interstitial atomic O, O~-, O~2- and molecular species: O_2, O~-_2, O~2-_2. We calculate their incorporation energies into bulk silicon dioxide, vertical electron affinities and diffusion barriers. In or calculations, we assume that the electrons responsible for the change of charge state come from the silicon conduction band; however, the generalization to any other source of electrons is possible, and hence, our results are also relevant to electron-beam assisted oxidation and plasma oxidation. The calculations yield information about the relative stability of oxidizing species, and the possible transformations between them and their charging patterns. We discuss the ability to exchange O atoms between the mobile species and the host lattice during diffusion, since this determines whiter or not isotope exchange is expected. Our results show very clear trends: (1) the molecular species are energetically preferable over atomic ones, (2) the charged species are energetically more favorable than neutral ones, (3) diffusion of atomic species (O, O~-, O~2-) will result in oxygen exchange, whereas the diffusion of molecular species (O_2, O~-_2, O~2-_2) is not likely to lead to a significant exchange with the lattice. On the basis of our calculation, we predict that charging of oxidizing species may play a key role in silicon oxidation process.