Solid State Phenomena Vols. 108-109

Abstract: The paper presents the results of experimental in-situ observations of cobalt disilicide nucleation in Co+ implanted silicon and ab initio simulations of energies of small cobalt and cobaltvacancy clusters. Based on these results, microscopic nucleation mechanisms of different types of CoSi2 precipitates are discussed.

Abstract: Dislocation locking by nitrogen impurities has been investigated in float-zone silicon with nitrogen concentrations of 2.2 x 1015cm-3 and 3 x 1014cm-3. The stress required to unlock dislocations pinned by nitrogen impurities was measured as a function of annealing time (0 to 2500 hours) and temperature (550 to 830°C). For all conditions investigated the locking effect was found to increase linearly with annealing time before saturating. It is assumed that the rate of increase of unlocking stress with annealing time is a measure of transport of nitrogen to the dislocation core. This rate of increase was found to depend linearly on nitrogen concentration, which is consistent with transport by a dimeric species, whose activation energy for diffusion is approximately 1.4eV. The saturation unlocking stress has been found to be dependent on the nitrogen concentration. Additionally, the temperature dependence of the stress required to move dislocations immobilised by nitrogen impurities has been studied. By assuming a value for the binding energy of the nitrogen to the dislocation, the density of the locking species at the dislocation core has been calculated.

Abstract: In this paper we present a detailed study in which the formation, by heavy ion impact, and thermal recrystallisation of individual amorphous zones have been studied using in-situ transmission electron microscopy. In agreement with previous work, we observe a reduction in the total volume of amorphous material contained within the amorphous zones following thermal annealing over a wide range of temperatures. When the evolution of the individual amorphous zones is followed, those with similar starting sizes are observed to recrystallise over a range of temperatures from 70 °C to 500 °C. The temperature at which an amorphous zone fully recrystallises does not appear to be correlated with initial size. In addition, zones are occasionally observed to increase in size temporarily on some isochronal annealing steps. Furthermore, observations during a ramp anneal show that many zones recrystallise in a stepwise manner separated by periods of stability. These phenomenon are discussed in terms of the I-V pair.

Abstract: Silicon samples doped with gallium and intentionally contaminated with iron have been studied by means of electron beam current (EBIC), capacitance voltage (CV) and deep level transient spectroscopy (DLTS) methods. Reverse bias anneal (RBA) treatments at temperatures of 390-420K were used to move hydrogen and dissolved iron atoms away from the surface. A new procedure was developed to find dislocations lying on desirable depth from the surface and to analyze the depth distribution of their recombination contrast. Iron contaminated dislocations do not noticeably change their recombination activity when kept in an electrical field as high as 104 V/cm at 420K for several hours. This implies a tight binding of iron atoms at dislocations. The binding energy of iron with dislocations seems to be much larger than for Fe-Ga and H-Ga pairs. Low temperature hydrogenation of iron contaminated dislocations does not produce any passivation effect. In opposite, the recombination activity of the dislocations significantly increases after RBA treatment.

Abstract: The evolution of nitrogen related infrared vibrational spectra of CZ-Si implanted with nitrogen, with doses 1017 ion/cm2 and 1018 ion/cm2, at 140 keV, was studied after annealing at 1130°C/5h under different hydrostatic pressures, from 1 bar to 10.7 kbar. It was found for each pressure applied, that the increased nitrogen dose leads to transformation of broadband spectra to the fine structure ones, corresponding to crystalline silicon nitride. The spectral position of observed sharp peaks in the investigated pressure region is red shifted in comparison to the peaks of crystalline silicon oxynitride found recently by other investigators in nitrogen-containing poly-Si as well as in a residual melt of nitrogen-doped CZ-Si. The application of pressure during annealing results in further red shift of the nitrogen-related bands. The observed decrease of frequency of vibrational bands is explained in terms of the pressure induced lowered incorporation of oxygen into growing oxynitride phase.

Abstract: We investigated the effect of magnetic field on the unlocking stress for dislocations in Cz-Si, measured at 600oC, depending on the thermal prehistory of samples. The effect increases with increasing of the duration of sample annealing at 600oC before the magnetic field treatment. The experimental data are consistent with the assumption that the magnetic field stimulate some changes in configuration of oxygen accumulated at dislocations before the magnetic field treatment, but not the state of oxygen in a bulk.

Abstract: Oxygen precipitation and creation of defects in Czochralski grown silicon with interstitial oxygen concentration 9.4·1017 cm-3, subjected to irradiation with neutrons (5 MeV, dose 1x1017 cm-2) and subsequently treated for 5 h under atmospheric and high hydrostatic pressures (HP, up to 1.1 GPa) at 1270 / 1400 K, were investigated by spectroscopic and X - Ray methods. Point defects created by neutron irradiation stimulate oxygen precipitation and creation of dislocations under HP, especially at 1270 K. The effect of pressure treatment is related to changed concentration and mobility of silicon interstitials and vacancies as well as of the VnOm – type defects.

Abstract: We report on the energetics, electrical and optical activity of small self-interstitial (I3 and I4) clusters in Si, found from ab-initio density-functional modeling studies. I4 possesses nine local vibrational modes above the Raman edge, which account for up to three dipole-allowed vibronic transitions observed in recent experiments associated with the X-photoluminescent line. Another prominent photoluminescent line (known as the W-line) that shows a trigonal stress-induced splitting pattern, has been previously assigned to I3. Our analysis of the LVMs of a metastable form of I3 support this assignment.

Abstract: Effects of compressive stress on oxygen agglomeration processes in Czochralski grown silicon heat treated at T= 450OC, used as a reference temperature, and T= 600OC to 800OC are investigated in some detail. Compressive stresses of about P= 1 GPa lead to enhanced formation of Thermal Double Donors in materials annealed over a temperature range of T= 450OC – 600OC. It has been shown that the formation of thermal donors at T= 450OC under normal conditions and compressive stress is accompanied with loss of substitutional boron. In contrast, the concentration of the shallow acceptor states of substitutional boron in silicon annealed under stress at T≥ 600OC remains constant. An enhancement effect of thermal donor formation is gradually weakened at T≥ 700OC. The oxygen diffusivity sensitive to mechanical stress is believed to be responsible for the observed effects in heat-treated silicon.