Structure of the interface between ultrathin SiO2 films and 4H-SiC(0001)

The interface between ultrathin SiO2 films and 4H-SiC(0001) has been studied by x-ray photoelectron spectroscopy (XPS) and photoelectron diffraction. The investigation was performed for two different films. An ordered silicate layer showed a clear (root 3 x root 3)R30 degrees reconstruction, whereas a second film showed no long-range order. The comparison of the photoelectron diffraction data from these two films reveals that the local atomic environments of the Si atoms at the interface are very similar in both films. Further, a comparison of the experimental data with simulation calculations within a comprehensive R-factor analysis shows that also the local environments around near-interface Si atoms inside the SiO2 film are similar, but some modifications to the model are necessary. The use of the cluster radius as a fitting parameter in the simulation allowed to estimate the size of locally ordered regions in the film without long-range order to be about 4.5 to 5.0 A. It turns out that the transition from SiC to SiO2 is abrupt and therefore the occurrence of defects in the SiO2 film near the interface is probable. These defects may be oxygen vacancies, oxygen dangling bonds or silicon interstitials.