Czochralski-grown Silicon Single Crystals Research Articles

Control of Oxygen Content in Heavily Sb-Doped CZ Si Crystal by Adjusting Ambient Pressure

AbstractIn Czochralski-grown (CZ) silicon single crystals, antimony (Sb) doping decreases the oxygen concentration by enhancing oxygen evaporation from the melt surface. In this study, Ar ambient pressures of around 100 Torr over the silicon melt were found to suppress evaporation of oxide species. To clarify the effect of the growth chamber ambient pressure on oxygen concentration, heavily Sb-doped CZ silicon crystals were grown under Ar pressures of 30, 60, and 100 Torr. Increasing Ar pressure increases the oxygen and Sb concentrations at the melt surface. The oxygen concentration under an Ar pressure of 100 Torr was 1.2 times higher that under 30 Torr when the solidified fractions are 0.5 or larger. The oxygen evaporation rate is controllable by gas phase transport of Sb2O at high Ar pressures.

The resolution function of a triple-crystal diffractometer for high-energy synchrotron radiation in nondispersive Laue geometry

The k-space resolution function of a triple-crystal diffractometer is calculated for an arrangement of three perfect silicon single crystals Bragg diffracting in nondispersive Laue geometry. A comparison is made with the results of measurements using synchrotron radiation in the energy range from 80 to 150 keV. In this case, absorption is very weak and according to dynamical theory the width of the diffraction pattern of thick perfect single crystals is proportional to the wavelength λ, whereas its Lorentzian tails are proportional to λ2. Together with the fact that the Bragg angles are only of the order of 2°, this leads to a concentration of the starlike k-space resolution function into a narrow band parallel to the reciprocal-lattice vector G. For diffraction of 80 keV synchrotron radiation at the silicon 111 reflection, the full width at half-maximum (FWHM) of the intensity distribution in the scattering plane is 1.1 × 10−5 Å−1 perpendicular to G and 2.2 × 10−4 Å−1 parallel to G. The observed differences in the contributions from monochromator and analyzer crystal to the resolution function are explained by the finite width of the electronic window of the detector counting chain and the non-Bragg scattering contribution from the crystals. If annealed Czochralski-grown silicon single crystals with a mosaicity of ~3′′ are used as monochromator and analyzer, the resolution is reduced by one order of magnitude, but for studies of imperfect samples or of diffuse scattering large gains in intensity can be accomplished this way.

Characterization of Interstitial Oxygen Striations in Silicon Single Crystals by the Micro-FT-IR Method

We will demonstrate that our micro-FT-IR mapping system is highly effective for investigating the behavior of interstitial oxygen (Oi) in Czochralski-grown silicon single crystals. The micro-FT-IR system experiences high space resolution, and Oi striations of as-grown silicon single crystals or of oxygen micro-precipitation after a thermal treatment are quantitatively measured. Oi micro-distribution profiles of as-grown crystals exhibit regular or irregular intervals and height, depending upon their crystal growth conditions. Oxygen micro-precipitations along growth striations are dependent upon their initial Oi micro-distribution profiles, and anomalous oxygen micro-precipitation is not observed.

X-ray diffraction studies of annealed Czochralski-grown silicon. I. Double-crystal diffractometry

X-ray reflection properties are reported of annealed Czochralski-grown silicon (ACS) single crystals at photon energies between 8 and 50 keV, studied by double- and triple-crystal diffractometry (DCD and TCD, respectively) and with X-radiation from sealed-tube sources. The report is divided into two parts. In this paper (paper I), the results of double-crystal topography and rocking-curve measurements are discussed in detail with regard to the application of ACS for the monochromatization of synchrotron X-radiation in the above-mentioned energy range. The analysis of the defects which enhance the reflectivity of ACS compared with that of perfect float-zone-grown silicon, carried out by TCD measurements and transmission electron microscopy, is presented in the following paper (paper II). [Zaumseil, Joksch & Zulehner (1993). J. Appl. Cryst. 26, 192–197].

X-ray diffracton studies of annealed Czochralski-grown silicon. II. Triple-crystal diffractometry

This paper reports a series of X-ray triple-crystal diffractometry (TCD) measurements performed on annealed Czochralski-grown silicon (ACS) single crystals to investigate in more detail the reasons for the observed broadening of double-crystal diffractometer rocking curves described in the previous paper [Joksch, Zaumseil & Zulehner (1993). J. Appl. Cryst. 26, 185–191]. It is shown that diffuse scattering by structural defects created during the high temperature heat treatment is responsible for the changes in the reflection properties. With TCD, the dominant defects are identified as stacking faults on (111) planes.

Characterization of interstitial oxygen striations in silicon single crystals

Oxygen precipitation occurs along growth striations in Czochralski-grown (CZ) silicon single crystal. Interstitial oxygen (O i) striations in various CZ and horizontal magnetic field Czochralski-grown (HMCZ) silicon single crystals were studied with a micro-Fourier transform infrared spectroscopy (micro-FTIR) mapping system. These striations were found in most crystals. The O i profiles were irregular but their periods and heights were about 0.8 mm and 0.2 × 10 17 atoms/cm 3 except for several cases. Subsequently, oxygen microprecipitation was investigated for various conditions of thermal treatment. It was found that homogeneous nucleation was inferred to be operative in CZ and HMCZ crystals.

A novel model of ‘‘new donors’’ in Czochralski-grown silicon

A new model of ‘‘new donors’’ is presented, based on electrical, infrared measurements, transmission electron microscopy, and high-resolution electron microscopy observations on Czochralski-grown silicon single crystals containing ‘‘new donors.’’ In this model, the electrical activity of ‘‘new donors’’ originates from the uncoordinated Si dangling bonds on small dislocation loops resulting from oxygen precipitation. In comparison with other models, the present model can better explain the experimental results of the heat treatment Czochralski-grown Si wafers.

Correlation of thermal history and thermal donor formation

Effects of high temperature annealing at 1050°C on the formation of oxygen-related thermal donors in Czochralski-grown silicon single crystals have been investigated. Resistivity measurements have shown that the highest maximum concentration of donor states after a subsequent isochronal annealing step at 450°C is introduced in the as-grown material while the yields obtained in pretreated samples decrease rapidly with increasing preanneal time. While the initial formation rate depends on the initial content of dissolved oxygen corresponding to the well-known fourth-power law, the total yield is additionally a function of the starting conditions. It appears that several types of precipitation kinetics exist owing to parallel diffusion mechanisms and that only a small fraction of the formed oxygen clusters are realized as donor complexes. However, IR studies have shown that the ratio of the concentrations of the different donor specimens and therefore their kinetical behaviour are independent of the thermal history.

Dynamic strain aging in Czochralski-grown silicon single crystals

Abstract Constant extension rate tensile tests were performed on dislocation-free Czochralski-grown ([O] = 24–38 ppma) silicon single crystals oriented for single slip in the temperature range 1173–1573 K. Evidence for dynamic strain aging, resulting from oxygen in solid solution, includes the observation of a plateau in the plot of the lower yield stress vs. strain rate at 1373, 1473, and 1573 K; an increase in the flow stress with temperature above 1373 K; a higher magnitude of the lower yield stress than that observed in float-zone (low-oxygen)-grown silicon for temperatures above 1373 K; and other observations resulting from the analysis of the later stages of deformation. Dynamic precipitation of oxygen caused by the supersaturated condition of oxygen in Czochralski-grown silicon complicates the application of solute hardening models for analyzing the experimental observations.

Anisotropic small-angle neutron scattering from oxide precipitates in silicon single crystals

Anisotropic small-angle neutron scattering has been observed from Czochralski-grown silicon single crystals annealed for different times at 750 degrees C. This scattering has been attributed to oxide platelet precipitates lying on the (100) planes. The precipitate size, number density and oxygen concentration in the matrix are obtained from the analysis of this scattering. The oxygen diffusion coefficient has been calculated from the increase in the size of the precipitates with anneal time and it is found to be in agreement with the value obtained from mass transport experiments. The loss of solute oxygen from the matrix follows the equation derived by Ham (1958).

Test of annealed Czochralski grown silicon crystals as X-ray diffraction elements with 145 keV synchrotron radiation

The X-ray diffraction properties of annealed Czochralski grown silicon single crystals have been studied on a triple axis diffractometer using 145 keV synchrotron radiation from the 30 keV critical energy wiggler at CHESS. The silicon crystals, containing approximately 20 ppm oxygen atoms, were annealed at 1200°C for 8 h in order to create a homogeneous distribution of defects. A 10 mm thick crystal produced a Laue diffraction rocking curve with a 4 arcsec wide plateau at 50% reflectivity, and a full width at half maximum of approximately 8 arcsec. The shape of the rocking curve could be reproduced by calculations based on Darwin's extinction theory, using a mosaic distribution determined from high resolution γ-ray rocking curves measured from the same crystal. The momentum transfer resolution function of the triple axis spectrometer using these deformed crystals as monochromator and analyzer was also measured. It was found to be enlarged by factors of 11 and 18 in the perpendicular and parallel directions, respectively, compared with the resolution using perfect crystals. This enlarged resolution element can be advantageous in diffuse scattering experiments.

A γ-ray and small-angle neutron scattering study of oxygen precipitation in silicon single crystals

Abstract Oxygen precipitation in heat-treated Czochralski-grown silicon single crystals has been investigated using γ-ray diffraction combined with small-angle neutron scattering and infrared absorption measurements. Diffuse scattering around the diffraction peaks was observed using γ-rays and this is associated with oxygen precipitation in the silicon lattice. The analysis of the diffuse scattering produces an average precipitate size in agreement with small-angle neutron scattering measurements.