Dislocation-free Silicon Crystals Research Articles

Distribution of electrically active nickel atoms in silicon crystals measured by means of deep level transient spectroscopy

Diffusion profiles of electrically active nickel atoms (substitutional nickel atoms; Nis) in dislocated n- and p-type, and dislocation-free n-type silicon crystals are investigated by deep level transient spectroscopy (DLTS). The concentrations of Nis are evaluated from DLTS signals due to amphoteric nickel center which introduces an acceptor level of E c - 0.46 eV in n-type silicon and a donor level of E v + 0.18 eV in p-type silicon. The profiles are analyzed on the basis of the theory of the dissociative mechanism. It is found that dislocations in dislocated silicon and presumably precipitates of nickel in dislocation-free silicon play the important roles as sinks and sources of vacancies existing in the crystal bulk, giving rise to the flat distribution of Nis.

Physical nature of grown-in microdefects in Czochralski-grown silicon and their transformation during various technological effects

Czochralski-grown dislocation-free silicon crystals of 50 and 80 mm in diameter have been extensively studied by techniques of transmission electron microscopy and preferential etching. Crystals were grown at various growth rates, followed by subsequent processing (thermal treatment, ion implantation). The physical nature (positive/negative sign of silicon lattice imperfection) of grown-in microdefects inside and within the OSF ring was determined. It was found that background oxygen and carbon impurities mostly affect the formation mechanism of grown-in microdefects. It was shown that crystals might grow in interstitial and interstitial–vacancy regimes. The transformation scheme of the grown-in microdefects in the course of subsequent processing is clarified. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical anisotropy in dislocation-free silicon single crystals

The optical anisotropy in silicon single crystal was evaluated by measuring the birefringence accurately. In measurement, the use of dislocation-free silicon crystals effectively avoided the influence due to dislocation-induced birefringence. The extreme small birefringence, which was supposed to be due to the point defects, was also measured and taken into consideration, by using scanning infrared polariscope (SIRP) with high sensitivity. The random error, which may occur in 1-point measurement, was eliminated by carrying scanning measurement over the checking plane of the cuboid sample. As the result, the birefringence due to the optical anisotropy in dislocation-free silicon crystals was measured to be (3.34±0.09)×10 −6, when probing light ( λ=1.52 μm) was propagating along the [ 1 10] direction (at the [ 1 10] direction). The birefringences due to the optical anisotropy were also measured at other crystallographic directions with a cylindrical silicon sample.

Heating rate dependence of melting of silicon: An in situ x-ray topography study

In situ observations of the melting processes of dislocation-free silicon crystals were carried out using x-ray topography technique. Heating procedures with various heating rates were used in the experiments. Dot contrasts were observed during the melting process at a high heating rate, while they could not be found at a low heating rate. It was found that the melting process at a high heating rate is spatially inhomogeneous, while that at a low heating rate is homogeneous. It was also found that the oxygen concentration in the sample plays an important role in the formation of dot contrasts during the melting process. The dot contrasts were assumed to originate from the dislocation loops around the oxygen precipitates.

Dislocation-Free Czochralski Silicon Crystal Growth without Dash Necking

Dislocation-free silicon crystals which underwent boron and phosphorus doping were grown by the Czochralski (CZ) method without Dash necking. The boron concentration limit in a silicon seed 7×7 mm2 in cross section without dislocations due to thermal shock was 1×1018 atoms/cm3 in ordinary CZ silicon-crystal growth. The maximum admissible discrepancy of boron concentration in the seed and grown crystal was 7×1018 atoms/cm3 without dislocations due to lattice misfit in the grown crystal. Silicon seeds with a boron concentration of 3×1018 atoms/cm3 were used to grow CZ silicon crystals from lightly boron-doped (p-type) or phosphorus-doped (n-type) silicon melt, yielding dislocation-free silicon crystals without the need for Dash necking. Heavily boron-doped silicon seed should thus be applicable in growing other practical lightly doped dislocation-free CZ-silicon crystals without the need for Dash necking.

Grown-in microdefects, residual vacancies and oxygen precipitation bands in Czochralski silicon

A model of multi-step vacancy aggregation in dislocation-free silicon crystals is analyzed. In this model, voids are first nucleated (normally just below 1100°C). The vacancy loss to voids is retarded below some characteristic temperature (about 1020°C) as the vacancies become bound by oxygen into O 2V complexes. These remaining vacancies control nucleation of oxide particles on further cooling. Some vacancies survive even this stage and control nucleation of oxygen clusters at still lower temperature (around 700°C). The oxygen clusters are major precipitation nuclei during subsequent heat treatments. It is through residual vacancies that the oxygen precipitation behavior is closely related to the grown-in microdefects (voids and particles). The microdefect properties and the residual vacancy concentration ( C res ) are computed in dependence of the starting vacancy concentration ( C 0 ). The C res (C 0) function is of a twin-peak type which results in a banded precipitation pattern if C 0 decreases gradually either in radial or axial direction. The model accounts for complicated (strongly banded) precipitation patterns, particularly those observed in halted and quenched crystals.

Application of the statistical dynamical theory to gamma-ray diffraction experiments on low-dislocation quartz single crystals.

Highly monochromatic (Deltalambda/lambda = 10(-6)) short-wavelength (lambda = 0.03 Å) gamma radiation has been used in the study of the diffraction processes in real single crystals. Dislocation-free silicon crystals and quartz crystals with small concentrations of chaotically distributed dislocations were investigated. The experimental results were processed with use of statistical dynamical theories of diffraction, both fundamental and advanced. It is shown that the advanced version is more reliable in both cases. However, the values of the average lattice phase E, describing the long-range distortions of the lattice, can differ markedly from the value of 1 for quartz crystals, and parameter L = -ln(E) has a square dependence on the extinction length.

X-Ray Structure Perfection Diagnostics of Slightly Distorted Silicon Crystals in the Bragg Case of Diffraction

A new approach to structure perfection diagnostics of dislocation-free silicon crystals has been developed using the Bragg case of diffraction. The approach is being based on successive measurements of integral reflectivity and the spatial intensity distribution of reflected beam on the same diffraction planes of a real crystal by means of a single crystal diffractometer. PACS numbers: 81.40.—z, 61.66.Bi

The influences of carbon, hydrogen and nitrogen on the floating zone growth of four inch silicon crystals

Dislocation-free silicon crystals, grown without a crucible by the floating zone (FZ) technique, were developed and are produced for manufacturing high voltage and high power devices. These crystals grow under extremely complicated thermal conditions, so that the advantage of high purity may be offset by the origin of new structural defects, which do not exist with the Czochralski method. With increasing crystal diameters microdefects may act as sources for dislocation formation. Attempts were made to suppress the microdefect formation by decreasing the carbon concentration in the starting material. To suppress arcing between the inductor electrodes and/or the inductor and the growing crystal, extinguishing gases such as hydrogen and nitrogen were added to the argon ambient. While hydrogen gives rise to the origin of anomalous defects, nitrogen even has beneficial effects on the crystal quality.

Progress in X-ray and electron-optical investigations of structural changes by fast heavy ions in semiconductors

The interaction of fast ions with matter is of great interest to many scientists. The investigation of fast ion induced effects is very important for the determination of the influence of structural changes on some physical properties of materials. The main aim of this paper is to show which kinds of structural changes can be created by fast heavy ions in matter and particularly in dislocation-free silicon crystals as a model material. X-ray and TEM methods have been applied to the respective investigations.

Formation of dislocations and other types of extended defects by ion implantation

It is shown which kinds of extended defects can be created by fast heavy ions in matter and particularly in dislocation-free silicon crystals as a model material. X-ray and TEM methods are applied.

Influence of defects on the thickness dependence of integral reflectivity of dislocation-free silicon crystals

The influence of large dislocation loops and clusters (with radius rd of the order of extinction length Λ) in dislocation-free silicon crystals grown by the Czochralsky-method on the thickness dependence of the total integral reflectivity Ri as well as on its Bragg's RB and diffuse RD components is investigated by variation of the X-ray wavelength (MoK, CuK-radiation) and of the order of Laue diffraction. For such defects diffuse scattering is concentrated near the reciprocal lattice point (RLP). Integral intensities are measured by means of the Bragg-Laue double crystal spectrometer in the positions (n, −n) and (n, −2n). The components RB and RD are determined using the formula of the dynamical theory of X-ray scattering in crystals with homogeneously distributed defects and the values of diffraction parameters i.e. the static Debye-Waller's factor L, and coefficient absorption due to diffuse scattering μds measured under conditions of weak absorption where the interfere influence of dynamical effects is negligible. The sensitivity of Ri to large defects is shown to increase at the expence of growing of the relative contribution of the RD component by transition to reflection of higher orders as well as by using of harder short-wavelength radiation. The ratio RD/Ri does not depend on the crystal thickness under conditions of strong absorption what conforms the arising of the dynamical regime for the diffuse component. This effect is absent for small (rd ≫ Λ) defects. The parameter L is shown to be more sensitive to the presence of large defects than μds. [Russian Text Ignored].

A high-resolution diffuse X-ray scattering study of defects in dislocation-free silicon crystals grown by the float-zone method and comparison with Czochralski-grown crystals

Point-defect aggregates in (111) dislocation-free silicon single crystals grown by the float-zone (FZ) method have been studied by diffuse X-ray scattering (DXS) and compared with those in the Czochralski-grown (CZ) crystals. A two-axis X-ray diffractometer was used. It employs three monochromators in (+, −, −) setting to obtain a highly collimated and monochromatic Mo Kα1 beam. DXS measurements were made around the 111 reciprocal-lattice point (r.l.p.) with K* along ±[111] and ±[01{\bar 1}]; K is the vector which joins the elemental volume of the reciprocal space under investigation to the nearest r.l.p. For FZ crystals for a given K* the DXS intensity was higher for θ < θB in comparison with that for θ > θB showing that the anisotropy (DXS Iθ > θB − DXS Iθ < θB) is negative, as expected for vacancy clusters. For CZ crystals the anisotropy was positive, owing to the presence of interstitial clusters. The magnitude of anisotropy in the FZ crystals was smaller than that observed in the CZ crystals. The DXS intensity varies approximately as K−2 near Bragg peaks (Huang scattering) and as K*−4 (Stokes–Wilson scattering) away from it. From the K* values where the changeover from Huang to Stokes–Wilson scattering takes place the size of the clusters assumed to be the origin of the observed DXS is estimated as ~ 2 × 10−4 and 2.6 × 10−3 mm for FZ and ~ 5.5 × 10−4 and 3 × 10−3 mm for CZ crystals. The experimental data were compared with theoretically calculated DXS distributions assuming the defects to be dislocation loops. The number of point defects in a loop has been estimated.

Asymmetric topography of silicon in Laue and Bragg geometries at the SRS

X-ray topography is briefly reviewed as a method of revealing microdefects in dislocation-free silicon crystals. Asymmetric topographs of silicon single crystals in Laue and Bragg geometries are described in order to examine the capabilities of the single crystal white radiation technique for the study of microdefects.

The influence of growth rate on the impurity cloud parameters in pure silicon

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Growth and properties of [100] and [111] dislocation-free silicon crystals from a cold crucible

Dislocation-free silicon crystals, approximately 15 mm in diameter, were grown from a RF-heated cold crucible at pulling speeds of 1 to 2.8 mm/min. Both [111] and [100] orientations were grown without using auxiliary heating. X-ray topography, spreading resistance, Hall mobility, minority carrier diffusion length, and other techniques were used to characterize the crystals. Solar cells fabricated on wafers from cold crucible grown ingots had 4% to 8% higher conversion efficiencies than cells on conventional Czochralski-grown wafers.

The effect of temperature oscillations at the growth interface on crystal perfection

Dislocation-free silicon crystals are grown with the Czochralski technique under various growth conditions, including changed heater positions, pulling rates, and crystal and crucible rotation rates. The correlation between the microdefect density in crystals and temperature oscillations near the growth interface is investigated. It is found that the microdefect density decreases with higher heater position, increased pullong rate and decreased crystal rotation rate. Theseresults are in accord with the behavior of the temperature oscillation amplitude. Thus, the density of microdefects decreases as the oscillation amplitude is reduced. The relation between microdefect density and temperature oscillation amplitude is well explaines by the crystal remelt model. The microdefect density in a crystal varies for annealing at more than 1000δC immediately after growth. Thus, the reduction of microdefect density by annealing depends on the defect distribution in the as-grown crystals.

The mechanism of formation of microdefects in silicon

Three types of microdefects, formed by the agglomeration of either self-interstitials or vacancies, have been observed in dislocation-free silicon crystals grown by the pedestal pulling technique. From the microdefect distribution in quenched crystals it is concluded that the dominant type of point defect at the melting point of silicon is the vacancy, whereas an excess of self-interstitials is usually present at lower temperatures. It is suggested that a fraction of the carbon atoms in the crystal is incorporated at interstitial lattice sites and that the interaction of interstitial carbon with vacancies is responsible for the change in the dominant type of point defect. A model is described, which is based on this assumption, and it is shown that the influence of different growth conditions on the formation, the elimination and the spatial distribution of all three types of microdefects can be explained with this model.

The Contributions of Metallurgy and Materials Science to the Evolution of Solid-State Electronics

The following three examples have been chosen to highlight some of the contributions of metallurgy and materials science in the development of solid-state electronics: (1) growth of high-purity, macroscopically dislocation-free silicon crystals; (2) elimination of electromigration in thin metallic conductors; and (3) minimization of growth- and processing-induced defects in silicon.

Dynamical effects of X-ray scattering in laue geometry for Si crystals with structure defects

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