S. A. McQuaid

Hydrogen diffusion and the catalysis of enhanced oxygen diffusion in silicon at temperatures below 500°C

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...

Oxygen loss during thermal donor formation in Czochralski silicon: New insights into oxygen diffusion mechanisms

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 (T≤400 °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 [Oi] 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 H2 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 (T≥450 °C) the measured rates of [Oi] loss were less than the expected rate of Oi‐Oi int...

Effect of oxygen concentration on the kinetics of thermal donor formation in silicon at temperatures between 350 and 500 "C

Early measurements of the initial rate of thermal donor formation in Czochralski silicon at 450 °C revealed a dependency on the fourth power of the oxygen concentration. This result has led to the view that the core of the defects contained four oxygen atoms. We now show that this dependency is observed only for anneals close to 450 °C. Our results indicate that oxygen dimerization controls the thermal donor formation kinetics but that the dimers become increasingly unstable above 400 °C.

Hydrogen solubility in silicon and hydrogen defects present after quenching

Boron-doped silicon ((B) approximately 1017 cm-3) was heated in H2 gas at a temperature in the range 900<or=T<or=1300 degrees 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<or=200 degrees C leading to an increase in (H-B). The total hydrogen content, consistent with secondary-ion mass spectrometry, yielded a solubility given by SH=9.1*1021 exp(-1.80 eV/kT) cm-3. 2 MeV electron irradiation at room temperature converted Hh into defects incorporating two hydrogen atoms, suggesting that Hh may be present as H2 molecules.

Hydrogen-related shallow thermal donors in Czochralski silicon

Six shallow donors are shown to form in Czochralski silicon deliberately doped with hydrogen during the early stages of heat treatment at 350 degrees 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.

Native defects in low‐temperature GaAs and the effect of hydrogenation

A range of experimental techniques has been used to measure point defect concentrations in GaAs layers grown at low temperatures (250 °C) by molecular‐beam epitaxy (LT‐GaAs). The effects of doping on these concentrations has been investigated by studying samples containing shallow acceptors (Be) or shallow donors (Si) in concentrations of ∼1019 cm−3. Material grown under As‐rich conditions and doped with Be was completely compensated and the simultaneous detection of As0Ga by near‐band‐edge infrared absorption and As+Ga by electron paramagnetic resonance confirmed that the Fermi level was near the midgap position and that compensation was partly related to AsGa defects. There was no evidence for the incorporation of VGa in this layer from positron annihilation measurements. For LT‐GaAs grown under As‐rich conditions and doped with Si, more than 80% of the donors were compensated and the detection of SiGa–VGa pairs by infrared localized vibrational mode (LVM) spectroscopy indicated that compensating VGa de...

Solubility of hydrogen in silicon at 1300 °C

The incorporation of hydrogen in boron doped Czochralski silicon heated to 1300 °C in H2 gas has been studied. The anneal was terminated by a rapid quench to room temperature giving rise to an unknown hydrogen‐related defect as well as H‐B close pairs. All the hydrogen in the crystal can be driven into such pairs by a low temperature (200 °C) anneal, after which the values of [H‐B] [D‐B] are in agreement with the total deuterium concentration, measured by secondary ion mass spectrometry. The estimated solubility of 1.5×1016 cm−3 is not affected by the isotopic mass of the hydrogen nor by the presence of boron or oxygen impurities.

Novel aspects of oxygen diffusion in silicon

Normal diffusion of interstitial oxygen atoms (Oi ) accounts for the rate of oxygen aggregation in silicon for T > 500‡C. There is evidence for the dissociation of SiO2 precipitates (Ostwald ripening) and the formation of self-interstitials (I-atoms) to accommodate the local increase in volume. For T < 500 ‡C, measurements of the loss of oxygen atoms from solution indicate that O2 dimer formation is the rate-limiting process, but dissociation of dimers must be taken into account when modelling this process. Large clusters of up to 10–20 Oi atoms, usually assigned to thermal donor (TD) defects cannot form unless dimer diffusion is much greater (by a factor of 104 to 107 ) than diffusion of Oi atoms and unless there is dissociation of clusters with the emission of dimers. Hydrogen impurities enhance Oi diffusion by a catalytic process and speed up donor formation. Infrared absorption measurements reveal H-Oi complexes and there is also partial passivation of TD defects to produce shallow thermal donors (STDs).