X-ray Diffraction Study of the Formation Process of SiO_2/Si Interfaces

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A lot of studies for the silicon dioxide have been carried out so far, but the oxidation process is not clear. For example, a layer-by-layer growth of the thermal oxidation is one of unprecedented phenomena. A SIMOX (seperatiorr-hy-implanted oxygen) wafer is one of the SOI (silicon-on-insulator) substrate, which is expected for low-power and high-speed devices. However, the formation process of the buried oxide layer is obscure. In this study we studied the formation process of the interface between the SiO_2 and Si crystals by X-ray diffraction technique.The growth of epitaxially ordered Si0_2 in oxygen-implanted silicon during thermal annealing was investigated. The extra diffraction streak was observed at the initial stage of annealing. This means that the small precipitate itself has the ordered structure of 2x2 symmetry with respect to the Si layers. As the size of the precipitates became larger upon further annealing, the intensity of the extra streak gradually increased. This indicates that epitaxial growth of the ordered precipitates occurred, particulary, in the lateral direction because the ordered structure has better periodicity in the lateral direction than in the perpendicular direction. The formation of the buried oxide layer in the perpendicular direction was due mainly to coalescence rather than to epitaxial growth.It was also found that the thermal oxide layer on Si(113) did not simple amorphous structure, but has the ordered sturucture with an epitaxial relation with the Si substrate, which was similar to those on the Si(001) and (111) substrates.