Solid State Phenomena Vols. 156-158

Abstract: Fourier transform infrared absorption spectroscopy was used to study the evolution of multivacancy-oxygen-related defects in the temperature range 200-300 °C in Czochralski-grown Si samples irradiated with MeV electrons or neutrons. A clear correlation between disappearance of the divacancy (V2) related absorption band at 2767 cm-1 and appearance of two absorption bands positioned at 833.4 and 842.4 cm-1 at 20 K (at 825.7 and 839.1 cm-1 at room temperature) has been found. Both these two emerging bands have previously been assigned to a divacancy-oxygen defect formed via interaction of mobile V2 with interstitial oxygen (Oi) atoms. The present study shows, however, that the two bands arise from different defects since the ratio of their intensities depends on the type of irradiation. The 842.4 cm-1 band is much more pronounced in neutron irradiated samples and we argue that it is related to a trivacancy-oxygen defect (V3O) formed via interaction of mobile V3 with Oi atoms or/and interaction of mobile V2 with VO defects.

Abstract: We confirm the following findings obtained in our previous experiment for the low-temperature elastic softening by the vacancies in boron-doped silicon crystals: (1) the steep softening that suddenly starts at 2-4 K in the cooling process, and (2) the complete disappearance of the softening by a weak magnetic field of 4 T applied along [111] direction. We further investigate in detail how the low-temperature softening at a fixed temperature responds to the applied magnetic field, to find the following characteristic anisotropy: The manner of disappearance of the softening strongly depends on the direction of the magnetic field. For the magnetic field imposed along [1-10] direction, nearly 60 % of the full softening still remains even at a strong magnetic field of 8 T, in contrast to the case of magnetic field applied along [111] direction.

Abstract: Successful theoretical models of vacancies, self-interstitials and oxygen dynamics during an ingot growth lead us to apply these models results also to silicon wafers. The modern silicon technology uses successfully the RTA (rapid thermal annealing) in order to form MDZ (magic denude zone) in individual CZ Si wafers. The effect of RTA is based on the utilization of vacancies for control of oxygen precipitation. The question about the theory of kinetics of vacancies and interstitials, which describes its behavior within RTA, is still opened up to now. This work deals mainly with the nucleation of vacancies during RTA concerning various cooling rates and initial states.

Abstract: The results of investigation of the point defect generation and interaction with impurities in the Si-SiO2 system during the process of its formation by means of electron paramagnetic resonance (EPR) and nucleous magnetic resonance (NMR) technique are presented. It has been shown that the diference in point defects interaction with hydrogen at the Si-SO2 interface with n- and p-type conductivity are connected with the sign of hydrogen ions incorporation dependence on the Fermi level position in accordance with the proposed model. The interface properties may be improved by laser irradiation.

Abstract: Out-diffusion nitrogen profiles measured by SIMS after annealing at 850 and 800oC, have a peculiar minimum at a depth of about 5 m. The profiles are well reproduced by simulations assuming that there is a considerable fraction of nitrogen stored in substitutional clusters VN4. Upon annealing, these clusters lose nitrogen and convert into a stable high-temperature form VN1. This reaction involves a preliminary attachment of a fast-diffusing interstitial trimer, N3. Accordingly, the conversion occurs only in the bulk but not at the surface (due to out-diffusion loss of N3), and the substitutional component decreases from the surface towards the bulk. By fitting the profiles, the two basic parameters of the N2/N1 transport are deduced: P = D1K1/2 (a combination of the monomeric diffusivity D1 and the dissociation constant of dimers, K), and the dissociation time of dimers. With these data, D1(T) and K(T) are specified.

Abstract: DLTS studies of transformation kinetics of different carbon–related complexes in electron irradiated n- and p-type silicon have been performed. It has been found that silicon self-interstitials have very low mobility even at room temperature in p-Si, but become extremely mobile under elec-tron injection. It is shown that upon annealing of interstitial carbon in p-Si a metastable state for interstitial carbon-interstitial oxygen complex is formed. This state has an energy level of about Еv+0.36 eV. The formation of the stable and metastable states takes place concurrently. The observed features of the carbon-related complexes formation are likely related to the existence of different crystallographic orientation of the equiprobable pathways through which the interstitial carbon and oxygen atoms can approach each other.

Abstract: In this work we have studied the in-depth distribution of copper deposited on the surface of the hydrogen pre-implanted Cz Si wafers depending on the conditions of their subsequent annealing. In the standard n-type 4.5 ∙cm Cz Si wafers different numbers of radiation defects were formed by hydrogen ion implantation with an energy of 100 keV (0.9 m projected range, Rp) for different fluences (11015, 11016, or 41016 at/cm2) at room temperature. Then a copper layer 50-nm thick was deposited on the sample surface by magnetron sputtering at temperatures 250 or 300 oC with subsequent annealing for 4 h at the same temperatures. Whereupon the surface was chemically etched and the samples were annealed in vacuum during 2 h at 700 oC. The depth profiles of copper in the near-surface layer were controlled by RBS investigations both in the random and channeling modes. These experiments have shown that the copper in-depth distribution strongly depends on the implantation fluence and temperature of the low-temperature annealing: in case of copper deposition at 250 oC a relatively strong peak determined by copper on the surface is observed in RBS spectra after all the above-described steps. On the contrary, for higher temperatures of copper deposition (300 oC) a significant decrease in the intensity of this peak is observed in RBS spectra. A maximal concentration of copper at a depth of the projected range, Rp, was observed for the samples implanted with a maximal fluence (41016 at/cm2).

Abstract: The influence of platinum contamination on the stability of radiation defects produced by high-energy proton irradiation was investigated in the low-doped n-type float-zone oxygen rich silicon forming the base of power p+nn+ diodes. Platinum was first implanted and then in-diffused at different temperatures to obtain different levels of contamination. Diodes were then implanted with 1.8 MeV protons to a fluence of 2x1010 cm-2 and radiation defect reaction during isochronal annealing were investigated by deep-level transient spectroscopy. Results show that contamination of silicon by platinum atoms influences significantly both the introduction rates and the temperature stability of dominant radiation defects (vacancy-oxygen pairs, divacancies and VOH complexes).

Abstract: We present a review of both theoretical and experimental studies of stress effects on the solubility of dopants in silicon and silicon-germanium materials. Critical errors and limitations in early theory are discussed, and a recent treatment incorporating charge carrier induced lattice strain and correct statistics is presented. Considering all contributing effects, the strain compensation energy is the primary contribution to solubility enhancement in both silicon and silicon-germanium for dopants of technological interest. An exception is the case of low-solubility dopants, where a Fermi level contribution is also found. Explicit calculations for a range of dopant impurities in Si are presented that agree closely with experimental findings for As, Sb and B in strained Si. The theoretical treatment is also applied to account for stress effects in strained SiGe structures, which also show close correlation with recently derived experimental results for B-doped strained SiGe which are presented here for the first time.

Abstract: The measurements of stress induced dichroism on oxygen absorption band near 1107 cm-1 in Si1-xGex compounds and subsequent kinetics of the dichroism recovery upon isothermal annealing have been carried out. It has been found that the magnitude of introduced by uniaxial stress dichroism decreases with increasing Ge content. Two components in the dichroism annealing kinetics have been found. On the basis of studying absorption spectra of samples under investigations it was assumed that two components in relaxation correspond to the diffusion of oxygen being in a different nearest environment: the one component corresponds to oxygen surrounded by silicon atoms and the second one to the oxygen the neighbour of which is Ge atom. Diffusivity for each of the components has been determined. It has been shown that the diffusivity of oxygen that is in both of these configurations decreases with increasing Ge content.