High-resolution transmission electron microscopy of an atomic structure ata Si(001) oxidation front

Direct observations of the atomic structure at a SiO2/Si interface have rev ealed that an epitaxial cristotbalite-like SiO2 layer is formed at a Si(001 ) oxidation front. We found that Si back-bond oxidation occurred in at leas t two atomic layers at the interface, forming cristobalite-like protrusions beneath the amorphous SiO2 layer. Each protrusion was about 1 nm in latera l width, and covered about half of the interface. We thus conclude that for mation of the crystalline SiO2 at the interface is an essential process for layer-by-layer oxidation to occur. This is because further vertical oxidat ion would be suppressed at the front of the SiO2 protrusions, thus preservi ng the initial atomic-scale flatness of the interface during the oxidation.