Microscopic observation of lateral diffusion at Si-SiO2 interface by photoelectron emission microscopy using synchrotron radiation

The lateral surface diffusion at Si-SiO2 interface has been observed at nanometer scale using photoelectron emission microscopy (PEEM) combined with synchrotron soft X-ray excitation. The samples investigated were Si-SiOx micro-patterns prepared by O2+ ion implantation in Si (0 0 1) wafer using a mask. The lateral spacial resolution of the PEEM system was about 41 nm. The brightness of each spot in the PEEM images changed depending on the photon energy around the Si K-edge, in proportion to the X-ray absorption intensity of the corresponding valence states. It was found that the lateral diffusion occurs by 400-450 °C lower temperature than that reported for the longitudinal diffusion at the Si-SiO2 interface. It was also found that no intermediate valence states such as SiO (Si2+) exist at the Si-SiO2 interface during the diffusion. The observed differences between lateral and longitudinal diffusion are interpreted by the sublimated property of silicon monoxide (SiO).

► PEEM combined with synchrotron soft X-ray was applied to investigate the chemical states in Si-SiO2 interface at nanometer scale. ► The mechanism of diffusion by the annealing differs between in the lateral and longitudinal directions at the Si-SiO2 interface. ► The lateral diffusion begins at lower temperature than the longitudinal diffusion. ► For the lateral diffusion, SiO is absent in the Si-SiO2 interfaces. ► The observed differences between lateral and longitudinal diffusions are interpreted by the sublimated property of SiO.