No abstract

The relaxation of stress-induced dichroism of the 9-μm oxygen infrared absorption band has been investigated for Czochralski silicon annealed isothermally at various temperatures in the range 225–350 °C while the material was immersed in a hydrogen plasma. The in-diffusion of hydrogen atoms enhanced the rate of oxygen diffusion so that the dichroism was lost progressively from the external surfaces of samples. Comprehensive ancillary measurements demonstrated that the oxygen diffusion jumps were catalyzed by collisions with diffusing hydrogen atoms, rather than some other fast-diffusing species. The measurements allowed the hydrogen diffusion coefficient to be estimated as 1.7 × 102 exp( − 1.2 eV/kT) cm2 s−1 for the range of temperatures investigated. Increased rates of thermal donor formation were also found due to enhanced long-range oxygen diffusion. The new data are related to previous reports of enhanced oxygen diffusion jumps found in Czochralski silicon given post-growth heat treatments in hydrogen gas. It is implied that concentrations of hydrogen atoms as low as 108 cm−3 may significantly enhance oxygen diffusivity.

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

Six shallow donors are shown to form in Gzochralski silicon deliberately doped with hydrogen during the early stages of heat treatment at 350°C. The ground state energies of five of these donors are altered slightly in material doped with deuterium rather than hydrogen, demonstrating the presence of hydrogen in their cores. One of the donors may account for some of the weak IR absorption features detected in as-grown material. The formation of these donors appears to be linked to the generation of the well known oxygen-related double thermal donors and may reflect the partial passivation of these latter defects.