Octahedral void defects and related circular stains on thermal oxides

We have found that thermal oxidation of Czochralski-grown-silicon substrates produces local circular stains around octahedral void defects. A plan view revealed that an octahedral void defect is situated near the center of a circular stain. Oxidation at 1150 °C for 400 min in a pure oxygen ambient (oxide thickness 430 nm) produced stains with a diameter of about 3 μm, which was clearly larger than the diameter (1 μm or less) of the oxide surface pit grown on the octahedral void detect. The signal intensity of the circular stain decreased with repeated scanning observations, and, in many cases, the circular stain vanished after two or three observations. From the etching rate caused by the scanning observation, we estimated that the thickness of the stain was about 0.5–1.0 nm. Micro Auger analysis revealed that the concentration of carbon was higher in the circular stain than in the surrounding region. A model is presented which shows how octahedral void defects on the silicon surface lead to the formation...