Two kinds of impurity-related mark on thermal oxides originating in octahedral void defects

We have found that thermal oxidation of Czochralski-silicon substrates prod uces two kinds of impurity-related mark, both of which are located on the o xides around an octahedral void defect. We believe that both marks originat e from the octahedral void defect. One mark is circular and an octahedral v oid defect is situated in the center of the mark. The other mark has an ani sotropic shape and the octahedral void defect is not situated in the center of the anisotropic mark. The signal intensity of the circular mark became weak abruptly with repeated observations, and, in many cases, the circular mark vanished after two or three observations. The signal intensity of the anisotropic mark, on the other hand, gradually became stronger and then wea ker with repeated observations. The thickness of the circular mark and the anisotropic mark was estimated to be 0.5-1.0 nm and 15 mn, respectively. An alysis revealed that the concentration of carbon was higher in the marks th an in the surrounding region.