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).