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The precipitation of oxygen in silicon has been studied in the temperature range 650 to 1050 degrees C using the techniques of chemical etching, IR absorption applied to the 9 mu m band (4.2K), and small-angle neutron scattering (SANS). The IR data and etch pit counts, relating to the number densities of precipitate particles, have been fitted to Ham's theoretical model for the diffusion limited growth of randomly distributed particles. Full allowance is made for the increase in size of the precipitates with increasing time and good agreement is found over the complete period starting from zero time. Values of the diffusion coefficient of oxygen so determined are in excellent agreement with other data obtained by different methods, including SANS measurements at 750 degrees C described in the present work. The combined data give D=0.11 exp(-2.51 eV/kT) cm2s-1. The SANS data also indicate that the precipitates are not spherical in shape after a short initial period, and they show that the initial concentration of particles nucleated decreases with annealing time. The solid solubility cs(T) is determined at each temperature and compared with previous measurements. The authors conclude that the best combination of results leads to cs(T)=2.6*1022 exp(-1.4 eV/kT) down to 850 degrees C. At lower temperatures cs decreases more slowly with decreasing temperature, indicating a possible change in the structure or the form of the precipitated SiO2 phase.

As-grown Czochralski silicon samples with different oxygen concentrations have been heated at temperatures in the range 350-500 "C. Oxygen loss during anneals at low temperatures (Ts400 "C) is shown to follow second-order kinetics and measurements led to values of oxygen diffusivity that were larger than normal by a factor of -3, assuming the capture radius for dimer formation was 5 A. Variations in the rate of [O,] loss during more extended anneals could be explained if oxygen diffusion was initially enhanced but tended to its normal value as the anneals progressed. Much greater initial enhancements were derived from similar measurements for samples which had been hydrogenated by a heat treatment in HZ gas at 1300 "C for 30 min followed by a rapid quench to room temperature, and the enhancements were consistent with values derived from measurements of the relaxation of stress-induced dichroism. At higher temperatures (Ta450 "C) the measured rates of COi] loss were less than the expected rate of Oi-Oi interaction and tended to vary with increasingly high powers of [Oil. Modeling of the clustering process demonstrated that the reductions could be explained if the oxygen dimers were present in a quasiequilibrium concentration throughout the anneals. The establishment of this equilibrium appears to require that oxygen dimers diffuse much more rapidly than isolated Oi atoms. The kinetics of oxygen loss over the whole range of temperatures can then be explained if dimer clustering leads mainly to increases in concentrations of agglomorates containing large numbers (>8) of oxygen atoms. It is therefore possible to account for thermal donor (TD) formation based on the formation of different sizes of oxygen clusters, although the possibility that self-interstitials are involved in TD formation is not excluded. 0 1995 American Institute of Physics.

Boron-doped silicon ([B] -10" temperature in the range 900 5 T 5 1300'C and quenched to room temperature. Some of the dissolved hydrogen formed H-B pairs and the remainder (Hh), which was infrared inactive, was released during anneals at T 5200°C leading to an increase in [H-B]. The total hydrogen content, consistent with secondary-ion mass spectrometry, yielded a solubility given by S , = 9.1 x 10" exp( -1.80 eVlkT) cm-3. 2 MeV electron irradiation at room temperature converted H, into defects incorporating two hydrogen atoms, suggesting that H, may be present as H, molecules.was heated in H, gas at a Eydrogen atoms form electricacy ne-atra! complexes with defects in silicon and can be incorporated during crystal growth [l] or during low-temperature (Tc 500 "C) processing involving hydrogen plasmas [2] or ion beams [SI. At high temperatures (1092 I T I 1200 "C); the permeation ofhvdrogen through silicon has been measured [4] and the in-diffusion of hydrogen during anneals at T t 9 0 0 " C was recently shown to lead to passivation of shallow acceptors in p-type silicon, detected by infrared (IR) localized vibrational mode (LVM) spectroscopy following a quench to room temperature [S, 61. It was then demonstrated that subsequent anneals at a low temperature (TI 200°C) led to an increase in the concentration of H-B pairs, [H-B], by a factor of -3 in samples hydrogenated at 1300°C and the values of [H-B] corresponded to those of [D-B] in samples which had been heated in deuterium gas, D,(g). The total hydrogen (deuterium) concentration, m,,,, was consistent with measurements by secondary-ion mass speo trometry (SIMS) [7]. Thus, around 70% of hydrogen atoms in as-quenched material are present in a 'hidden' form, H,, which does not give rise to detectabie LVM absorption but which either dissociates or becomes mobile during low-temperature (100 5 T I 200°C) anneals. We now report IR and SlMS measurements of m],, for a range of in-diffusion temperatures to obtain values of the nydrogen solubiiity, S,(Tj, and the heat of soiution. We show that the ratio of [HI, to [H-B] increases as the TPemanent address: Hiils (UK) Ltd, MEMC Division, Featherstone

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