Czochralski Silicon Crystal Growth Research Articles

Using of EM fields during industrial CZ and FZ large silicon crystal growth

The paper describes numerical simulation tools for electromagnetic (EM), hydrodynamic, temperature and concentration fields in industrial Czochralski (CZ) and floating zone (FZ) single silicon crystal growth facilities under the influence of several alternating current (AC) and static DC magnetic fields. Such fields are expected to provide additional means to influence the melt behaviour, especially in the industrial growth of large diameter (200–300 mm) silicon crystals. The simulation tools are based on axisymmetric 2D models for (1) AC and DC magnetic fields in the whole crystal growth facility and (2) hydrodynamics, temperature and mass transport in the melt under the influence of the EM fields. The simulation tools are verified by comparison to temperature and velocity measurements in a laboratory CZ set‐up with eutectics InGaSn model melt and to resistivity measurements in grown silicon crystals.

A continuous Czochralski silicon crystal growth system

Demand for large silicon wafers has driven the growth of silicon crystals from 200 to 300 mm in diameter. With the increasing silicon ingot sizes, melt volume has grown dramatically. Melt flow becomes more turbulent as melt height and volume increase. To suppress turbulent flow in a large silicon melt, a new Czochralski (CZ) growth furnace has been designed that has a shallow melt. In this new design, a crucible consists of a shallow growth compartment in the center and a deep feeding compartment around the periphery. Two compartments are connected with a narrow annular channel. A long crystal may be continuously grown by feeding silicon pellets into the dedicated feeding compartment. We use our numerical model to simulate temperature distribution and velocity field in a conventional 200-mm CZ crystal growth system and also in the new shallow crucible CZ system. By comparison, advantages and disadvantages of the proposed system are observed, operating conditions are determined, and the new system is improved.

Crystal growth melt flow control by means of magnetic fields

Contactless melt flow control is important in many crystal growth technologies. Typically, steady magnetic fields are used to damp convective flow. On the other hand active flow driving forces like in a rotating magnetic field can be of stabilizing character, too. We present numerical results for the combined action of steady and alternating magnetic fields for the silicon Czochralski crystal growth process. The melt flow is determined by various flow driving sources: besides the thermal convection and rotation of crystal and crucible, there are also the influence of driving and/or damping electromagnetic forces and the thermocapillarity-driven flow at the free deformable melt surface.

Simulation of almost defect-free silicon crystal growth

Detailed simulations of defect dynamics during Czochralski growth of silicon crystals demonstrate that the precipitation of either vacancies to form voids or self-interstitials to form stacking faults can be avoided by careful choice of crystal pull rate V and axial temperature gradient near the melt/crystal interface G( r). Almost perfect crystalline silicon is created, except for very small oxide precipitates, which are dissolved in subsequent annealing of the wafers. The presence of oxygen increases the range of V/ G( r) for growth of this material.

Measurement of temperature gradient in Czochralski silicon crystal growth

The temperature gradient in Czochralski (CZ) silicon crystal growth has been measured using a thermocouple of differential type. A temperature difference between two spatial points with a certain distance (5 mm) could be obtained simultaneously using only one set of thermocouples of the differential type. Silicon crystals of 70 mm diameter were grown with different growth rates, and temperature gradients near the growth interface were measured during the crystal growth. It is found that the temperature gradient in the CZ silicon crystal growth increases with increasing growth rate. A balance equation of heat transportation near the growth interface has been applied to examine the present experimental results, and it is satisfied very well.

Effects of various magnetic field configurations on temperature distributions in Czochralski silicon melts

Magnetic fields are of growing interest for improvement of the silicon Czochralski crystal growth process. The use of steady magnetic fields provides suppression of turbulent fluctuations due to their damping action on the melt flow. Recent literature data on magnetic fields show that a relatively low field strength allows to control heat and mass transfer in laboratory scale melts. This contribution presents experimental results of temperature measurements in industrial scale silicon Czochralski melts under different magnetic field conditions. Temperature distributions are obtained by using thermocouples to detect temperatures in the melt and at the crucible wall during a crystal growth process. In addition we report on results of numerical simulations carried out for growth parameters and magnetic fields as used in the experiments. All experimental data are compared with the results from numerical simulation and discussed with respect to their implication on improving the quality of the grown crystals.

Parameterization of Transient Models of Defect Dynamics in Czochralski Silicion Crystal Growth

AbstractA transient model for point defect dynamics during Czochralski silicon crystal growth is parameterized using detailed experimental data generated under varying crystal growth conditions. Simulated Annealing is used to perform the model parameterization because of the complex nature of the defined objective functions. It is shown that the method is robust and despite the computational expense associated with a large number of function evaluations, can be readily used in multiple dataset, multiple objective function environments.

Enhanced nucleation of oxide precipitates during Czochralski silicon crystal growth with nitrogen doping

Thermal stability of oxide precipitate nuclei has been investigated for Czochralski silicon crystals with nitrogen doping. The experimental result indicates that generation of the grown-in oxide precipitate nuclei stable over 800 °C is enhanced by nitrogen doping. On the other hand, even though we confirmed this existence, doped nitrogen shows no influence on further oxide precipitate nucleation during the isothermal annealing at 600 °C after an epitaxial silicon growth process. Thus, it is found that the nitrogen doping only enhances the oxide precipitate nucleation at higher temperature during crystal cooling. The enhanced precipitate nucleation during the cooling is considered to be through excess vacancies which are suppressed to agglomerate by nitrogen.

In Situ Observation of the Interfacial Phase Formation at Si Melt/Silica Glass Interface

In situ observation has been carried out to investigate the interfacial phase of “brownish rings” forming at the Si melt/silica glass interface during Czochralski (CZ) silicon crystal growth. It is found that some small brownish dots appeared at the interface immediately after Si melting, and gradually grew laterally. The growth rate of the interfacial phase increases with increasing temperature, and it only nominally depends on the silica dissolution rate when the dissolution rate is lower than a critical value. The formation mechanism of the brownish rings has been investigated and two formation mechanisms are proposed. (1) Cristobalite forms in the central region of the interfacial phase. (2) The periphery of the interfacial phase is thicker than the central region, and only part of the periphery remains after passing through the triple junction where the dissolution rate is very high.

Influence of Czochralski silicon crystal growth on wafer quality: an extensive investigation using traditional and new characterization techniques

In this paper results on the relationship between Czochralski silicon crystal growth and wafer quality characteristics are presented. Several crystals grown with different oxygen content and growth parameters are examined. The growth parameters are varied in order to obtain different types and distributions of intrinsic point defects, namely vacancies and interstitials. Traditional and more recent characterization techniques are applied in this analysis, such as gate oxide integrity and light point defects evaluation, or high resolution lifetime mapping. In this way, a comprehensive picture is generated of the properties of a silicon wafer and how it is impacted by the crystal growth process.

New developments in silicon Czochralski crystal growth and wafer technology

An overview of recent progress in large-diameter crystal pulling and associated new wafer preparation technologies is given. A clear trend can be observed that, with increasing crystal diameter, the average oxygen concentration and the density of intrinsic grown in defects is reduced. Oxygen reduction and control is achieved by using magnetic fields, while bulk defect reduction requires sophisticated hot zone engineering. New growing methods currently under development result in new crystal types with a high density of interstitials in the outer area and a lower density of vacancies in the center. In addition, crystals are grown under near-equilibrium conditions so the super-saturation of the intrinsic point defects remains below the critical value required for clustering of the point defects into larger agglomerates . Geometry and light point defects/localized light scatter requirements for future wafer generations are becoming more stringent with each decrease in design rule. This leads to the necessity of novel wafer surface preparation methodologies such as advanced single side polishing, double side polishing and plasma assisted chemical etching with local wafer surface treatment. Finally, the trend toward low thermal budget integrated circuit processes leads to the necessity of having oxygen precipitation tuning and gate oxide integrity tuning, as well as the creation of a denuded zone by the silicon wafer manufacturer. New approaches to meet these requirements are annealing at high temperature and/or rapid thermal processing. The development of the new epitaxial wafer types is highlighted.

Analysis of turbulent flow in silicon melts by optical temperature measurement

Turbulent convection in silicon melts plays a decisive role for the transport of heat and oxygen during the silicon Czochralski crystal growth. Information on the state of turbulence is usually derived from the frequency behaviour of temperature fluctuations. Until now, temperature fluctuations were mostly detected by thermocouples, which are protected from the chemically aggressive melt by silica quartz tubes. The major disadvantage of this technique is the damping effect on amplitudes of temperature fluctuations at frequencies higher than 0.5 Hz. This drew back significantly the information available on the state of turbulence. A method to overcome this disadvantage is an optical technique of measuring temperatures that provides sampling rates up to 100 Hz. In this contribution, we present optical temperature measurements using silica rods as waveguides in large-diameter Czochralski silicon melts. The detected temperature fluctuations give slopes of power spectra that are approximately proportional to f −4 for higher frequencies, in the case of the smaller crucible of 14 inch diameter. This indicates a soft turbulence state where melt flow is stabilised by rotational forces. On the other hand, a hard turbulence state of melt flow, indicated by an f −5/3 behaviour of the power spectra, was found for the large crucible with 32 inch diameter. In contrast to the smaller crucible, we found no changes of the state of turbulence by increasing the crucible rotation rate. The results are discussed with respect to its consequences on the properties of silicon crystals grown by the Czochralski method from large-scale melts.

Oxygen transportation during Czochralski silicon crystal growth

Oxygen transportation processes concerning CZSi crystal growth have been investigated, including dissolution from silica crucible to silicon melt, evaporation from silicon melt to ambient Ar atmosphere and incorporation (segregation) from silicon melt to silicon crystal. It is found that almost all of the dissolved oxygen evaporates as the form of SiO from the surface of the silicon melt to the atmosphere of Ar gas in a conventional CZSi crystal growth. The quantity of the oxygen incorporated into the silicon crystal is only a very small amount compared to the dissolved oxygen or evaporated oxygen. The equilibrium segregation coefficient of oxygen was obtained by comparing the oxygen concentration in the silicon crystal to the oxygen saturation concentration in the silicon melt and the result is suggested to be 0.8±0.1. It is confirmed experimentally that the oxygen distribution in the CZSi crystal becomes much uniform and the oxygen concentration decreases gradually with increasing the cusp magnetic field, which indicates that the application of a cusp magnetic field is an effective method to control the convection in the silicon melt.

In situ observation of the Si melt–silica glass interface concerning CZ-Si crystal growth

An in situ observation was carried out for investigating the interfacial phase of so-called ‘brownish rings’ formed at the Si melt–silica glass interface concerning Czochralski (CZ) silicon crystal growth. It is found that some small dots appeared at the interface immediately after the Si melting, and grew gradually. The growth rate of the interfacial phase increases with increasing temperature, and it is almost the same when the silica dissolution rate is lower than a critical value. It can be concluded, therefore, that the growth rate of the interfacial phase does not depend on the silica dissolution rate in a practical CZ-Si crystal growth by considering that the silica dissolution rate in CZ-Si crystal growth is also lower than the critical value. Crystalline phase forms from the central region of the interfacial phase, and the amount of the crystalline phase increases with increasing temperature and reaction time.

Investigation on grown-in defects in CZ-Si crystal under slow pulling rate

The formation process of a dislocation cluster outside the oxidation-induced stacking fault (OSF) -ring region during Czochralski (CZ) silicon crystal growth was investigated using a quenching and in situ annealing technique. Dislocation clusters were determined to be interstitial type from inside–outside contrast analysis of the transmission electron microscope (TEM) image. From the quenching experiment, the clustering temperature of dislocations which were formed by supersaturated self-interstitials and/or small dislocation loops was found to be about 1000°C during growth. Furthermore, the characteristic axitial distribution of dislocation size was observed in the halted crystal. This could be explained by the change in concentration of supersaturated self-interstitials and the clustering of dislocations due to the enhancement of diffusion of point defects.

Heavily boron-doped Czochralski (CZ) silicon crystal growth: segregation and constitutional supercooling

Heavily boron-doped silicon single crystals have been grown successfully by the Czochralski (CZ) method. The limit of boron concentration for silicon single crystal growth, the reason for polycrystallization, and boron segregation with heavy boron doping have been investigated. It is found that a silicon single crystal can be obtained even when the boron concentration in the silicon crystal is up to about 2.8×10 20 atoms cm −3. In the heavily boron-doped silicon crystal growth, the reason for polycrystallization is the constitutional supercooling. It is confirmed that the equilibrium segregation coefficient of boron decreases from 0.8 with increasing boron concentration in the silicon melt, and it affects the occurrence of the constitutional supercooling.

Inertial effects in the rotationally driven melt motion during the Czochralski growth of silicon crystals with a strong axial magnetic field

This article treats the melt motion driven by the rotations of the crystal and crucible about their common vertical axis during the Czochralski growth of silicon crystals with a strong, uniform, vertical magnetic field produced by a solenoid around the crystal growth furnace. Since molten silicon is an excellent electrical conductor, the interaction parameter N and the Hartmann number Ha are both large for typical magnetic field strengths, so that composite singular perturbation techniques for \(N\gg1\) and \(Ha\gg1\) are appropriate. An inertialess solution, which also assumed that \(N\gg Ha^{3/2}\), was presented in a previous paper. In the inertialess solution, the largest gradient of the azimuthal velocity \(v_\theta\) and the largest secondary flow with radial and axial velocities vr and vz both occur inside an interior layer with an \(O(Ha^{-1/2})\) radial thickness at the vertical cylinder directly beneath the periphery of the crystal, where the growth interface meets the free surface. For all current experimental studies, the assumption that \(N\gg Ha^{3/2}\) is not satisfied. The appropriate assumption is that \(N=O(Ha^{3/2})\), and inertial effects are not negligible inside the interior layer. An intersection region, which is formed by the intersection of the interior layer and a Hartmann layer with an \(O(Ha^{-1})\) axial thickness adjacent to the crystal-melt interface and free surface, is intrinsically coupled to the interior layer. This article treats inertial effects in the interior layer and intersection region for \(N=O(Ha^{3/2})\) and \(Ha\gg1\). Non-linear governing equations were derived and solved numerically. A fourth-order Adams-Bashforth-Moulton predictor-corrector method was used to solve the transport equations for the primary azimuthal velocity and for the secondary-flow vorticity. Poisson equations, which govern the stream functions for both the secondary flow and the electric current density, were solved using a matrix diagonalization technique. The effects of inertia on the melt motion are discussed. This type of study provides for a fuller understanding of the melt motion, without which defect-free crystals will be difficult to grow on a consistent basis.

Boron retarded self-interstitial diffusion in Czochralski growth of silicon crystals and its role in oxidation-induced stacking-fault ring dynamics

The effect of boron doping on the position of the oxidation-induced stacking-fault ring (OSF ring) during Czochralski (CZ) crystal growth is described using a comprehensive model for point defect dynamics including the role of boron. The important interactions between boron atoms and intrinsic point defects are selected on the basis of tight-binding estimates for the energies of formation for boron-point defect structures. Intrinsic point defect properties used are taken from a parameterized model of point defect dynamics for predicting OSF-ring dynamics. Entropies of formation for boron-point defect species are obtained by fitting the predictions of the model to experimental data for OSF-ring dynamics. The model successfully predicts OSF-ring dynamics for a variety of doping and growth conditions. The effect of boron on the OSF ring is caused by the retardation of point defect recombination at temperatures near the melting point caused by dynamic storage of self-interstitials in complexes with boron.

Global heat transfer analysis in Czochralski silicon furnace with radiation on curved specular surfaces

Numerical analysis of global heat transfer with coupled thermal radiation and heat conduction is investigated in Czochralski silicon crystal growth furnace with curved diffuse and specular surfaces. The finite element method and the radiation element method are adopted to solve the global heat transfer and the radiative heat exchange, respectively. The emphasis focuses on the discussion of the influence of silicon surface radiative characteristics, i.e., either diffuse or specular, on the global heat transfer and the crystal growth process. When the specular character of the silicon crystal and melt surfaces is considered, it is found that the temperature of the melt is obviously decreased and the crystal pulling rate is enhanced.

Forced Convection During Liquid Encapsulated Crystal Growth With an Axial Magnetic Field

This paper treats the forced convection, which is produced by the rotation of the crystal about its vertical centerline during the liquid-encapsulated Czochralski or Kyropoulos growth of compound semiconductor crystals, with a uniform vertical magnetic field. The model assumes that the magnetic field strength is sufficiently large that convective heat transfer and all inertial effects except the centripetal acceleration are negligible. With the liquid encapsulant in the radial gap between the outside surface of the crystal and the vertical wall of the crucible, the forced convection is fundamentally different from that with a free surface between the crystal and crucible for the Czochralski growth of silicon crystals. Again unlike the case for silicon growth, the forced convection for the actual nonzero electrical conductivity of an indium-phosphide crystal is virtually identical to that for an electrically insulating crystal. The electromagnetic damping of the forced convection is stronger than that of the buoyant convection. In order to maintain a given balance between the forced and buoyant convections, the angular velocity of the crystal must be increased as the magnetic field strength is increased.