Effects of surface steps on oxygen migration and clustering on Si(100) surfaces studied by EHA

The effects of surface steps on mobility and clustering of oxygen atoms has been investigated quantum mechanically using the Hartree-Fock theory at semi-empirical level according to the Extended Debye Huckel Approximation. Clusters of large size (approximately 200 atoms) represent steps of a silicon surface vicinal to (10 0). A map of the energy experienced by the deposited atom is constructed by moving the atom on the terraces and down the step. Clustering is studied by constructing a similar map for two oxygen impurities located at a variable distance. The results indicate that, due to the interaction with the underlying silicon dimers, a barrier in the range 0.4 eV exists at the step edge. The effect, however, depends both on the path by which the diffusing atom approaches the step edge and on the step structure. Clustering is favored provided that the participants are at a distance below a critical value. These results are in qualitative agreement with experimental observations on nucleation of oxide films.