INTERACTION OF LOW-ENERGY OXYGEN IONS WITH THE SI(100) SURFACE

The local atomic-bond structures in amorphous SiO2 films prepared by a nonthermal method have been investigated by electron-energy-loss spectroscopy (EELS). The method utilizes oxygen ions of energy below 600 eV impinging on Si(100) surfaces at room temperature. The results, based on an augmented-central-force model, reveal that the Si-O bond nature in the films strongly resembles a typical thermal SiO2 glass. The contribution of noncentral forces to the local Si-O bonding, in terms of the ratio of noncentral-to-central force constants beta/alpha, is estimated by reducing the low-frequency EELS vibrational band (HBAR less-than-or-equal-to 80 meV). The ratio is found to be rather temperature insensitive but increases with film thickness, in the range 0.13 < beta/alpha < 0.19. We also observe thermally activated migration of oxygen atoms in the films with an activation energy barrier of about 0.22 eV.