Grown Silicon Single Crystals Research Articles

Opportunity to use inert gas flow for control of qualitative characteristics of the grown silicon single crystals

The process of growing silicon single crystals by the Czochralski method has been improved, which involves the use of two argon streams. 1st, the main flow, 15—20 nl/min, is directed from top to bottom along the growing single crystal. It captures the reaction products of the melt with a quartz crucible (mainly SiO), removes them from the chamber through a nozzle in the lower part of the chamber and provide dislocation-free single crystals from large loads. Similar processes are known and widely used in world practice since the 1970s. 2nd, additional flow, 1.5—2 nl/min, is directed at an angle of 45° to the surface of the melt in the form of jets from nozzles arranged in a ring. This flow initiates the formation of a region of turbulent melt flow, which isolates the crystallization front from convective flows enriched with oxygen, and also enhances the evaporation of carbon from the melt. It is confirmed that the oxygen evaporated from the melt (in the form of SiO) is a «transport» for non-volatile carbon. Carrying out industrial processes showed that the carbon content in the grown single crystals can be significantly reduced, up to values smaller than in the feedstock. In single crystals grown using two argon streams, an increased macro- and micro-uniformity of the oxygen distribution, a significantly larger crystal length with a given, constant oxygen concentration, were also recorded. Achieving a carbon concentration of 5 to 10 times less than in the feedstock is possible with small amounts of argon for melting (15—20 nl/min compared to 50—80 nl/min used in conventional processes. The use of an additional argon flow, which has an outflow intensity 10 times lower than that of the main flow, does not distort the nature of the flow around the single crystal surface (“axial”), does not disrupt the growth of a dislocation-free single crystal, does not increase the density of microdefects, which indicates the absence of changes in temperature gradients and thermal shock leading to thermal stresses in a single crystal.

Effect of crystal and crucible rotations on the interface shape of Czochralski grown silicon single crystals

A set of global heat transfer simulations in Czochralski (Cz) furnace for producing silicon single crystals have been performed to investigate the effect of crystal and crucible rotations on melt convection and crystal/melt interface shape. The 2D axisymmetric simulations are carried out taking into account radiative and conductive heat transfers between furnace components, melt convection including thermocapillary forces (Marangoni) and gas flow. Melt flow pattern and temperature distribution have been studied for several combinations of crystal and crucible rotations and for different crystal heights. The result shows that crystal/melt interface shape and melt flow regime are strongly sensitive to the rate of rotations of both crystal and crucible. Interfaces with low deflection can be achieved for certain combinations of crystal and crucible rotation rates.

The Effect of Oxygen on the Brittle-to-Ductile Transition in Silicon Single Crystals

The brittle-to-ductile transition (BDT) in Czochralski (CZ) grown silicon single crystals and floating-zone (FZ) grown silicon single crystals was investigated by three-point bending. The temperature dependence of the apparent fracture toughness was measured in three different cross-head speeds. It was found that the BDT temperature in the CZ silicon crystal was higher than that in FZ silicon crystal, suggesting that the solute oxygen decreases dislocation mobility. However, the activation energies obtained from the strain rate dependence of the BDT temperatures were nearly the same in both the CZ and FZ silicon crystals, indicating that the dislocation mobility is not influenced by the solute oxygen. In this paper, the origin of the difference in the BDT temperature is discussed, focusing the role of the solute oxygen on the dislocation glide.

Hall mobility reduction in single-crystalline silicon gradually compensated by thermal donors activation

This letter focuses on the variation of the Hall majority carrier mobility with the dopant compensation level in purely Boron-doped Czochralski grown silicon single crystals. Compensation was varied continuously at the sample scale via a step by step activation of the oxygen-based thermal donors. At room temperature, we show a strong drop in mobility for high compensation levels in both p- and n -type Si. Mobility models taking into account carrier scattering on ionized impurities and phonons could not reproduce this drop. We conclude that a specific effect of compensation must be taken into account to explain the observed behaviour. We qualitatively discuss physical mechanisms susceptible to reduce mobility in highly compensated Si.

Oxygen-isotope-doped silicon crystals grown by a floating zone method

We have grown silicon single crystals doped with isotope oxygen of 18O by using a floating zone method with two ellipsoid mirrors. Two lamps through a quartz tube heated the crystal for melting during crystal growth. The isotope oxygen of 18O was doped from the gas phase with argon gas during crystal growth. The isotope of 18O was detected by using Fourier transformation of infrared (FTIR) spectroscopy at room temperature. We succeed in the doping of the isotope of 18O from the gas phase through a liquid–gas interface.

Thermoelectric properties of silicon at high pressures in the region of the semiconductor-metal transition

The thermo emf in Czochralski grown silicon single crystals annealed at 450°C was experimentally studied in a range of pressures up to 16 GPa in a chamber with synthetic diamond anvils. There is a correlation between the curves of thermo emf versus pressure, the semiconductor-metal transition pressure, and the mechanical properties (microhardness, compressibility) of samples with various oxygen content. The values of thermo emf in the high-pressure metallic phases have been determined.

Oxygen concentration inhomogeneity in the silicon melt of the czochralski single crystal growth system

The momentum, heat and mass transfer in the silicon melt of the Czochralski crystal growth system were calculated with a three dimensional numerical simulation technique. Several types of non-axisymmetric profiles of velocities, temperature and oxygen concentration appeared in the melt with axisymmetrical boundary conditions. Since the asymmetric profiles and the rotations of fluid, temperatures and oxygen concentration fluctuated in the melt. The correlations between both fluctuations at the same point became larger, as the convection grew stronger. The calculation also showed that the temperature and oxygen concentration near the interface also fluctuated. The results suggested that the oxygen concentration could be considered one of the causes of the striation pattern in grown silicon single crystals.

Defect Structure of Pressure Treated Czochralski Grown Silicon Investigated by X-Ray Topography and Diffractometry

The defect structure of Czochralski grown silicon single crystals annealed at 870-1400 K under hydrostatic pressure up to 1 GPa was investigated by conventional and synchrotron radiation X-ray topography and by reciprocal space mapping. Hydrostatic pressure promotes oxygen precipitation from oversaturated Si-O solid solution and the creation of structural defects. PACS numbers: 61.10.—i, 61.72.Yx, 81.40.Vw

Distribution of SiO2 precipitates in large, oxygen rich Czochralski-grown silicon single crystals after annealing at 750 °C

The defects due to oxygen precipitation in Czochralski grown silicon single crystals annealed for 216 h at 750 °C and with oxygen concentration varying between 18 and 12×1017 atoms per cm3 (according to DIN 50438) were studied by means of small angle neutron scattering and γ-ray diffractometry probing the same volume elements in the sample. The size and the shape of the SiO2 precipitates were determined by means of small angle neutron scattering. In the center of the disk-shaped sample of 10 cm diameter one finds spherical precipitates with a radius of ≊20 Å, at the border the precipitates are of plate-like shape, ≊146×146×41 Å in dimension. The k-space distribution of the diffuse scattering caused by the strain field of the SiO2 precipitates has been determined by means of a double-crystal diffractometer and 316 keV γ radiation. Modeling with Huang and Stokes–Wilson theory suggests that the relatively small SiO2 precipitates are loosely bound in larger clusters with a radius of ≊2000 Å in which the crystal matrix is strongly distorted. With the γ-ray diffractometer operated in the single-crystal mode the thickness dependence of the integrated reflecting power was measured from which the static Debye–Waller factor for the 2 2 0 reflection is determined using statistical dynamical theory. The results confirm qualitatively the cluster model. In the center of the sample the size of the precipitates could be calculated by additional measurement of the static Debye–Waller factor of the 4 4 0 reflection. The result is in excellent agreement with the small angle neutron scattering data. Combining all the experimental data taken in the oxygen rich center of the annealed silicon crystal the average distance between the centers of the SiO2 precipitates in the clusters is ≊80 Å and the distance between the large clusters is ≊40 000 Å.

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 DISLOCATION SOURCE IN THE FLOAT-ZONE GROWN SILICON SINGLE CRYSTALS

The impurity-striations and the dislocation loop series produced from the volume indentation by these impurity-striations in the float-zone grown silicon single crystals have been studied by means of chemical etching method. The experimental results have shown that the impurity-striations are oriented in the direction (110) of planes {111} in silicon, the length of the impurity-strialions is about 5-230μm, the dimensions on cross-section are about 2-3 pun. The geometrical structure of the dislocation loop series produced by volume indentation of the impurity-striation has been studied. The form and size of a single dislocation loop depend on the form and size of the impurity-striation. The dislocation networks resulting from the cross-superposition of the dislocation loop series and reactions between these dislocation loops have been observed and analyzed.

MOVING MASK GROWTH OF SINGLE-CRYSTAL SILICON FILMS ON AMORPHOUS QUARTZ SUBSTRATES

We have combined vapor-liquid-solid mechanisms with a moving-mask-growth technique in a study of the nucleation and condensation of single-crystal silicon films deposited on amorphous dielectric substrates by vacuum evaporation of silicon. Using this VLS-MMG approach we have grown silicon single crystals up to 50 × 300 μ in lateral dimension on fused quartz substrates at substrate temperatures of 800 to 900°C.