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DIFFUSIVITY AND DIFFUSION MECHANISM OF OXYGEN IN SILICON

S.-TONG LEE AND D. NICHOLS Research Laboratories, Eastman Kodak Co.,

Rochester,

NY 14650

ABSTRACT The diffusivities of oxygen in Czochralski Si (CZ-Si) and float-zone Si (FZ-Si) have been measured by using secondary ion mass spectrometry. 0 The diffusivity at 700-1160 C deduced from the outdiffused profiles of oxygen incorporated in CZ-Si shows little or no dependence on processing 2 Diffuconditions and can be expressed as D = 0.14 exp(-2.53 eV/kT) cm /s. 0 sivity at 700-1100 C of oxygen implanted in FZ-Si is insensitive to doses 2 and follows D = 0.13 exp(-2.50 eV/kT) cm /s, which agrees remarkably well with CZ-Si data. Since large variations in point-defect concentrations existed under the conditions studied, the excellent agreement among the diffusivities leads to the conclusion that point defects in Si have little effect on oxygen diffusion. This demonstrates that oxygen diffuses primarily via an interstitial mechanism in the temperature range studied.

INTRODUCTION Oxygen diffusion plays an important role in determining donor formation and intrinsic gettering during thermal treatment. However, the mechanism of oxygen diffusion in Si is yet unsettled. Oxygen is incorporated in Si at the slightly off-center interstitial position between two neighboring Si atoms. It has thus been suggested that the interstitial oxygen should diffuse in Si by hopping between interstitial sites.1-3 Such an interstitial diffusion mechanism is not affected by point-defect concentration. However, 4 0 recently Heck et al. reported that the diffusivity of oxygen at 1100 C in Si varied by a factor of 2.4 with processing conditions. They attributed this variation to the change of point-defect concentration caused by processing conditions and suggested a vacancy-dominant diffusion mechanism for 0 oxygen in Si. At low temperature (10 and >100 have been observed during surface oxidation and phosphorus indiffusion,7 respectively, at 100, and that oxygen diffusivity D is primarily dictated by Di° in Eq. 5. Therefore, our observations have provided conclusive evidence that oxygen diffuses predominantly via an interstitial mechanism at temperatures above 7000C. Ion implantation invariably introduces damages and point defects. Radiation-enhanced diffusion of implanted dopants in Si has been ob16 17 served. " The enhancement is believed to be caused by the increase of point defects. Using Monte Carlo simulation of implantation, we estimated that for every 180 implanted in Si at 200 keV, about 1000 Si atoms are displaced from lattices and 1000 Si interstitial-vacancy pairs are generated.

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Therefore, even at the lowest dose used (10 /cm ), large amounts of point defects are generated. Undoubtedly, these supersaturated point defects will undergo recombination as anneal proceeds, and consequently, their effects on impurity diffusion will diminish with time. Even so, the implantation damages still can substantially enhance the diffusion of the rela16 17 The insensitivity of oxy'