EFFECTS OF NITROGEN ON OXYGEN PRECIPITATION IN SILICON

Defect interactions among oxygen, carbon, and nitrogen during a three-step high-low-high intrinsic gettering process (1100-degrees-C + 750-degrees-C + 1000-degrees-C) were studied using differential analysis of Fourier transform infrared (FTIR) absorption spectra of Czochralski-Si crystals intentionally doped with carbon and nitrogen. Two phenomena related to nitrogen were observed: (1) Nitrogen-enhanced oxide nucleation in the temperature range from 750 to 1100-degrees-C, thus having a negative effect on the denuding step; and (2) defect interaction associated with carbon during oxygen precipitation was significantly affected by the co-existence of nitrogen. For the latter effect the first-step annealing at 1100-degrees-C was crucial. The results presented are consistently interpreted assuming that nitrogen participates in creation of nucleation sites for heterogeneous oxygen precipitation, and also assuming that nitrogen aggregates at the strain regions surrounding precipitates and thus retards Si self-interstitial migration. This explanation was supported by observed differences in oxygen-precipitate-related FTIR absorption and by the behavior of stress-related photoluminescence D lines.