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In relation to intrinsic gettering, the dependence of denuded zone width and thermally induced microdefect density on thermal conditions are investigated in a three-step annealing procedure consisting of high temperature annealing, low temperature, and dry O2 oxidation at 1000 °C. Additionally, depth profiles of interstitial oxygen concentrations are studied using thermal conversion. The obtained results show that at least an initial interstitial oxygen concentration above 8×1017 cm−3 is required to achieve efficient intrinsic gettering. The depth profile obtained after the third annealing is not the simple out-diffusion profile approximated by an error function, but one with a peak in the denuded zone. The dependence of depth profiles on a third annealing condition indicates that the formation of the peak in the depth profile can be ascribed to a reduction of interstitial oxygen resulting from precipitation in the bulk region. In order to explain the obtained profiles, we propose a simple diffusion model which takes into consideration the oxygen precipitation in the bulk region. By comparing the calculated profiles with the experimental ones, it is proved that this model can be used to estimate depth profiles under various annealing conditions.

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The interface trap density (D it) of field oxide films is determined from the subthreshold characteristics of parasitic field effect transistors. A D it of 8×1014 m-2eV-1 persists in the bird's beak regions of local oxidation of silicon (LOCOS) structure after annealing at 723 K in a H2 ambient. This value is almost ten times larger than that observed for a SiO2/Si interface grown on a (100) Si plane.