Composition and structure of native oxide on silicon by high resolution analytical electron microscopy

Abstract

Compositional analysis of thin nanoscale native oxide films formed on {001} silicon wafer surfaces at room temperature was done with an electron energy loss spectrometer coupled to an analytical electron microscope having a field emission source, with better than 4 nm spatial resolution. The electron energy loss spectra show a shift in the threshold onset energy of the Si–L edge of the native oxide from ∼99 eV loss corresponding to pure elemental silicon to ∼105 eV loss, and elemental analysis using the ionization regions of the core loss edges showed the composition to be SiO, within a few percent. Microdiffraction and high resolution electron microscopy (HREM) results showed that the native oxide was completely amorphous, and did not contain detectable nanocrystals. The native oxide can be removed from the Si surface by heating in UHV for a short time at 1000 °C. However, this procedure resulted in the formation of small amounts of a crystalline phase on the Si wafer surface, which was shown to be β-SiC by the same methods.