Octahedral void defects and related circular stains on thermal oxides

We have found that thermal oxidation of Czochralski-grown-silicon substrate s produces local circular stains around octahedral void defects. A plan vie w revealed that an octahedral void defect is situated near the center of a circular stain. Oxidation at 1150 degrees C for 400 min in a pure oxygen am bient (oxide thickness 430 nm) produced stains with a diameter of about 3 m u m, which was clearly larger than the diameter (1 mu m or less) of the oxi de 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. Fr om the etching rate caused by the scanning observation, we estimated that t he thickness of the stain was about 0.5-1.0 nm. Micro Auger analysis reveal ed that the concentration of carbon was higher in the circular stain than i n the surrounding region. A model is presented which shows how octahedral v oid defects on the silicon surface lead to the formation of circular stains during oxidation. (C) 1999 American Institute of Physics. [S0021-8979(99)0 5415-8].