Czochralski-grown Silicon Single Crystals Research Articles

Simulation ofV/GDuring Φ450 mm Czochralski Grown Silicon Single Crystal Growth Under the Different Crystal and Crucible Rotation Rates

For discovering the principle of processing parameter combination for the stable growth and better wafer quality of Φ450 mm Czochralski grown silicon single crystal (shortly called Cz silicon crystal), the effects of crystal rotation rate and crucible one on the V/G ratio were simulated by using CGSim software. The results show that their effect laws on the V/G ratio for Φ450 mm Cz silicon crystal growth are some different from that for Φ200 mm Cz silicon one, and the effects of crucible rotation rate are relatively smaller than that of crystal one and its increasing only makes the demarcation point between two regions with different V/G ratio variations outward move along radial direction, and it promotes the wafer quality to weaken crystal rotation rate and strengthen crucible one.

Comparative Spatially Resolved Characterization of a Czochralski-Grown Silicon Crystal by Different Laser-Based Imaging Techniques

The axial distribution of electrical and optical properties of a 4 inch Czochralski-grown silicon single crystal were analyzed by different methods that can be applied in the scanning mode. These methods were tested with respect to the suitability to reveal growth striations. The residual stress was visualized by SIRIS (Scanning Infrared Stress Inspection System) and SIREX (Scanning Infrared Stress Explorer), the electrical resistivity by LPS (Lateral Photovoltage Scanning) and SRP (Spreading Resistance Profiling), and the lifetime of the minority charge carriers by MDP (Microwave Detected Photoconductivity) mapping. The concentration of interstitial oxygen (Oi) across the growth striations was determined by FTIR (Fourier Transform Infrared) spectroscopy. We demonstrate for the first time on the micrometer scale that the Oi scan is very well-correlated with the profile of Δσ (difference of the in-plane principal stress components). The stress field is tensile oriented in growth direction, i. e. perpendicularly to the growth striations. The stress-concentration coefficient has been estimated to be in the order of 10-13 Pa cm-3 what does agree well with previous XRD results.

Three-dimensional evaluation of gettering ability of Σ3{111} grain boundaries in silicon by atom probe tomography combined with transmission electron microscopy

Three-dimensional distribution of impurities (boron, phosphorus, oxygen, and copper) at Σ3{111} grain boundaries was determined in a Czochralski-grown silicon single crystal by laser-assisted atom probe tomography (APT) combined with transmission electron microscopy, with a detection limit as low as the order of 0.001 at. %. The location of a boundary was determined by APT even when the boundary was not contaminated. Unlike the boundaries in multicrystalline silicon grown by the casting method, the impurities did not segregate at the boundaries even when the impurity concentrations were high. The gettering ability of the boundaries was discussed.

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.

Interaction of copper impurity with radiation defects in silicon doped with boron

The spectrum of deep levels formed in boron-doped Czochralski-grown silicon single crystals as a result of interaction of radiation defects with copper impurity is studied. It is shown that, irrespective of the order of introduction of defects (both in the case of low-temperature copper diffusion into crystals preliminarily irradiated with electrons and in the case of irradiation of the samples contaminated with copper), the same set of deep levels appears. In addition to conventional radiation defects, three types of levels have been detected in the band gap of copper-containing crystals. These levels include the level E v + 0.49 eV (already mentioned in available publications), the level E v + 0.51 eV (previously not related to copper), and a level close to the donor level of a vacancy. Based on the analysis of concentration profiles, the interstitial carbonoxygen pair is excluded from possible precursors of the copper-containing center with level E v + 0.49 eV.

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.

New shallow donor centres in high-purity Czochralski-grown silicon single crystals

Two new shallow donor centres NSD(i) and NSD(ii) with binding energies of 38.32 meV and 40.09 meV, respectively, were observed in n-type high-purity Czochralski-grown silicon single crystals by means of high-resolution photothermal ionization spectroscopy. Their spectral features and the temperature dependence of the intensity of their spectral lines imply that they are two new independent hydrogenic shallow donors. Low magnetic field investigations were performed to support our statement. The existence of the new donor centres seems to be related to the micro-defects in the sample.

Diagnostics of highly doped czochralski-grown silicon crystals

It is shown that effective diagnostics of strongly doped Czochralski-grown silicon single crystals in the initial (as-grown) state is provided by methods based on the interference phenomena of dynamic x-ray diffraction: the Lang section topography and the Borrmann effect diffractometry. The conditions of a test for the structural perfection of as-grown crystals, based on the observation of interference bands on the section topographs, are refined.

Effect of hydrogen implantation on semiconductor–metal transition and high-pressure thermopower in Si

In the present work Czochralski-grown silicon single crystals were investigated implanted with different doses of H + ions. The Si wafers were characterized by the Raman scattering technique. Thermoelectric power was studied in a pressure range of 0–20 GPa of p-type Si single crystal wafers containing a thin hydrogenated layer consisting of amorphous Si, nanocrystalline Si and H-rich Si layers. In the region of the pressure-induced phase transition from the initial semiconductor diamond-like into the metal β-Sn lattice, a lowering of thermopower values was noticed in comparison with ones of p-Si.

Quality evaluation of resistivity-controlled silicon crystals

The segregation phenomenon of dopants causes a low production yield of silicon crystal that meets the resistivity tolerance required by device manufacturers. In order to control the macroscopic axial resistivity distribution in bulk crystal growth, numerous studies including continuous Czochralski method and double crucible technique have been studied. The simple B–P codoping method for improving the productivity of p-type silicon single-crystal growth by controlling axial specific resistivity distribution was proposed by Wang [Jpn. J. Appl. Phys. 43 (2004) 4079]. In this work, the quality of Czochralski-grown silicon single crystals with a diameter 200 mm using B–P codoping method was studied from the chemical and structural points of view. It was found that the characteristics of B–P codoped wafers including the oxygen precipitation behavior and the grown-in defects are same as that of conventional B-doped Czochralski crystals.

Numerical analysis for transient point defect behavior in Czochralski silicon crystal growth

r− To study the transient point defect distribution in Czochralski-grown silicon single crystals, a contin- uum model of point defect dynamics to predict the concentrati on of interstitial and vacancy is established by estimating expressions for the thermo-physical properties of point defect s and the point defect distribution in silicon crystals. It is well known that the concentration of intrinsic point def ects in growing silicon crystals is a function of the crystal pull rate (V) and the temperature gradient (G) at the solid ification interface inside the crystal, and steady state predictions from point defect dynamics are well agreed with experiment. In this study, finite element simulations have been performed for the growth halt experiment with 150 mm silicon single crystals to study the transient behavior of intrinsic point defects. It has been demonstrated that predicted point defect distributions are in good agreement with experimental results.

Thermoelectric properties of high-pressure silicon phases

The thermo emf in Czochralski-grown silicon single crystals (Cz-Si) was experimentally studied in a range of pressures up to 20 GPa. The pressure dependences revealed phase transitions in the metallic phase of silicon, which passed from tetragonal to orthorhombic and then to hexagonal lattice. The high-pressure silicon phases, as well as the metallic high-pressure phases in ANB8−N semiconductors, possess conductivity of the hole type. As the pressure decreases, the emf behavior reveals transitions to the metastable phases Si-XII and Si-III. Preliminary thermobaric treatment of the samples at a pressure of up to 1.5 GPa and a temperature of T=50–650°C influences the thermoelectric properties of Cz-Si at high pressures.

On the influence of a Si single-crystal real surface on the low-frequency internal friction and the behavior of an effective shear modulus

The spectra of low-frequency internal friction and the behavior of the effective shear modulus Geff(T) in a Czochralski grown silicon single crystal were investigated after mechanical and chemical-mechanical treatment of the surface and after natural aging at room temperature over a long period of time. The mechanical treatment of the Si surface was shown to initiate unusual structural phase transitions accompanied by an inverse hysteresis in the Geff(T) dependence. Such a behavior of Geff(T) is assumed to be associated with the formation of incommensurate phases. It was also found that aging at room temperature for more than 10000 h leads to the onset of decomposition of the supersaturated solid solution of oxygen in silicon and to the generation of substantial stresses that initiate structural phase transitions in the samples.

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.

A study of the oxygen precipitation kinetics in zirconium-doped silicon

The kinetics of oxygen precipitation at 900 and 1050°C was studied in Czochralski-grown silicon single crystals doped to various levels with zirconium. It is established that zirconium, while not participating in the nucleation of oxygen precipitates, decreases the concentration of interstitial oxygen in the crystals.

Analysis of local lattice strain around oxygen precipitates in silicon crystals using CBED technique

Oxygen precipitates (SiO x ) in Czochralski-grown silicon single crystals (CZ-Si) have been used for the `getter' sink for impurities introduced during the LSI wafer manufacturing process. In order to understand the `gettering' phenomena, lattice strain fields around the precipitates have been measured quantitatively using convergent beam electron diffraction (CBED). The local lattice strain can be measured from higher order Laue zone (HOLZ) patterns since the HOLZ pattern in the bright field disk is sensitive to the lattice displacement. As a result, a tetragonal distortion of silicon lattices was found in the vicinity of a platelet of an oxygen precipitate. That is, the strain due to the displacement of (001) Si planes is compressive along the direction normal to [001] Si and is tensile along the direction parallel to [001] Si. The normal strain is estimated to be about 0.3% near the flat plane of the platelet and 0.1% near the edge of the platelet whose edge length is about 500 nm. The results are discussed and compared to those from the finite element method (FEM) simulation.

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

Melt quenching technique for direct observation of oxygen transport in the Czochralski-grown Si process

Oxygen distribution in the Czochralski-grown (Cz) silicon single crystal is closely associated with melt convection occurring near the growth interface because oxygen atoms in the melt are transported by fluid motion. Using melt quenching developed utilizing the double-layered (DL) Cz process, we studied oxygen transport phenomena around the growth interface. Micro-Fourier transform infrared spectroscopy (micro-FTIR) measurements showed that the oxygen concentration distribution in the growing crystal was related to melt convections, such as the Cochran flow and fluid motion from the melt surface. This also agrees with characteristic oxygen striation in both the crystal and melt observed using micro-FTIR and Wright etching. We concluded that melt quenching using the DLCz process is effective in directly observing the oxygen concentration distribution in the melt during crystal growth.

Control of oxygen concentration in heavily antimony-doped Czochralski Si crystals by ambient argon pressure

In 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 in grown crystals, heavily Sb-doped CZ silicon crystals were grown under Ar pressures of 30, 60, and 100 Torr. Increasing the 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 than that under 30 and 60 Torr when the solidified fractions are 0.5 or larger. The oxygen evaporation rate is controllable by gas phase transport of Sb 2O at high Ar pressures.

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.