Czochralski Crystal Growth Research Articles

Impact of Thermal Stress on Intrinsic Point Defect in Czochralski Crystal Growth: Developing a Quantitative Model for Defect Formation and Distribution

Impact of Thermal Stress on Intrinsic Point Defect in Czochralski Crystal Growth: Developing a Quantitative Model for Defect Formation and Distribution

Evaluating cooling tube effects on defect formation and distribution in Czochralski crystal growth

Evaluating cooling tube effects on defect formation and distribution in Czochralski crystal growth

Crystal growth, polarized spectral properties, and 2.3 µm laser performance of Tm:LuVO4 crystal

We report on the Czochralski crystal growth, polarized optical spectroscopy, and the first continuous-wave laser operation of 1.5 at.% Tm:LuVO4 crystal on the 3H4 → 3H5 transition. The polarized absorption and stimulated-emission properties of Tm3+ ions in LuVO4 were revised and the crystal-field splitting of the Tm3+ multiplets was determined by low-temperature (12 K) spectroscopy. The maximum stimulated-emission cross-section for the 3H4 → 3H5 transition is 2.48 × 10−20 cm2 at 2363 nm for π-polarization corresponding to an emission bandwidth of 28 nm. Evidence of phonon-assisted emissions of Tm3+ ions above 2 µm is presented. The broadband emission properties of the Tm:LuVO4 crystal make it promising for ultrashort pulse generation. Additionally, pumped by a 796 nm fiber-coupled laser diode, the Tm:LuVO4 laser generated a Watt-level output power at 2279-2295 nm with a slope efficiency of 9.2% and linearly polarized emission (π-polarization).

Adjustment of oxygen transport phenomena for Czochralski silicon crystal growth

During silicon crystal growth, oxygen, a well-known major impurity, affects the final silicon wafer's mechanical and electrical properties. This study focused on regulation of discharge of different concentrations of oxygen from the quartz crucible into the silicon melt while considering the crucible angular speed and the friction at the melt–crucible interface. The three-dimensional transient governing equations for heat transfer, fluid flow, and impurity transportation in the Czochralski (CZ) puller were solved numerically. The oxygen solvation equation representing the crucible to silicon melt was modified to evaluate the accuracy of oxygen concentration calculations during the CZ process. Experimental measurements using the Fourier-transform infrared (FTIR) technique were used to confirm the simulation results. The results demonstrate that the crucible angular speed affects the oxygen concentration near the crucible wall and therefore in the silicon ingot. The proposed modifications for evaluating oxygen concentration offer a more comprehensive understanding of the oxygen dynamics during the CZ crystal growth.

Segregation and constitutional supercooling in Nd:YAG Czochralski crystal growth

This article examines the issues of segregation and constitutional supercooling (CSC) in the context of industrial highly-doped Nd:YAG crystal growth. The study involved the growth of several Nd:YAG crystals using Czochralski method, revealing that the heavily Nd3+ doped YAG crystals often cracked during the late stage of shoulder growth. At this stage, the solid–liquid interface instability was observed, and it was found that CSC led to temperature fluctuations, ultimately causing interface instability and crystal cracking. The study also investigated the influence of growth parameters, such as growth rate and crystal rotation rate, on CSC. It was determined that convection plays an important role, and a critical growth condition was identified: when the normalized growth velocity surpasses a certain threshold, the solidification behavior changes, resulting in CSC. In the end, the article compared analytical results with experimental data, demonstrating good agreement between the two.

Extended investigation of an abrupt crystal diameter change during Czochralski silicon growth with transverse magnetic field

An investigation about the phenomenon of an abrupt diameter deviation during Czochralski crystal growth, a characteristic when using a transverse magnet, has been carried out both experimentally and computationally. 300-mm silicon crystals have been pulled under certain conditions and the diameter deviations have been recorded in these processes. Three-dimensional calculations of the melt flow have been performed using CGSim Flow Module 3D, accounting for distribution of the actual non-uniform magnetic field, to accurately simulate the heat transfer and melt flow for selected growth stages along the entire process. The sudden change of melt temperature near the triple point that leads to the diameter deviation, is attributed to the evolution of melt flow pattern, which can be altered by positioning the magnet at a different height. The discovery of such melt flow behavior proposes an effective solution to eventually eliminate the abrupt diameter deviation during body growth. The visualization of the melt flow transformation by 3-D simulation offers another adjustability to the process of modern industrial crystal growth with transverse magnet. The mechanism of how the magnet position impacts the melt flow is also discussed.

Study on the Hierarchical Predictive Control of Semiconductor Silicon Single Crystal Quality Based on the Soft Sensor Model

Silicon single crystal (SSC) quality monitoring and control has been a hot research topic in the field of the Czochralski crystal growth process. Considering that the traditional SSC control method ignores the crystal quality factor, this paper proposes a hierarchical predictive control strategy based on a soft sensor model for online control of SSC diameter and crystal quality. First, the proposed control strategy considers the V/G variable (V is the crystal pulling rate, and G is the axial temperature gradient at the solid-liquid interface), a factor related to crystal quality. Aiming at the problem that the V/G variable is difficult to measure directly, a soft sensor model based on SAE-RF is established to realize the online monitoring of the V/G variable and then complete hierarchical prediction control of SSC quality. Second, in the hierarchical control process, PID control of the inner layer is used to quickly stabilize the system. Model predictive control (MPC) of the outer layer is used to handle system constraints and enhance the control performance of the inner layer. In addition, the SAE-RF-based soft sensor model is used to monitor the crystal quality V/G variable online, thereby ensuring that the output of the controlled system meets the desired crystal diameter and V/G requirements. Finally, based on the industrial data of the actual Czochralski SSC growth process, the effectiveness of the proposed crystal quality hierarchical predictive control method is verified.

Pure and Yb-Doped LaxYySc4-x-y(BO3)4 Crystals: A Review of Recent Advances

This paper reviews the progress in developing the LaxYySc4-x-y(BO3)4-LYSB and Yb-doped LaxYySc4-x-y(BO3)4-LYSB:Yb huntite-type crystals grown by the Czochralski method as new candidates for the next generation of nonlinear optical (NLO) and/or laser crystals. Considering the incongruent melting of these crystals, the initial compositions of the melt and the pulling and rotation rates were optimized. Additionally, a special thermal setup was engineered to grow LYSB-type crystals by the Czochralski crystal growth method. The chemical compositions of the LYSB and LYSB:Yb grown crystals were found to be La0.78Y0.32Sc2.90(BO3)4 and La0.78Y0.32Yb0.04Sc2.86(BO3)4, respectively. Therefore, for the LYSB:Yb crystal, the doping concentration of Yb3+ ions was considered to be 4 at.% with respect to the nonstoichiometric (La1-xYx)1.25Sc2.75(BO3)4 undoped compounds, i.e., LYSB:Yb (4 at.%). In terms of NLO properties, the obtained results demonstrate that LYSB and LYSB:Yb (4 at.%) crystals possess remarkable properties specific to huntite-type crystals. The main advantage of these crystals consists in the fact that they may be obtained with large dimensions and excellent optical quality by the Czochralski method, which recommends them as a new class of highly efficient crystals for different NLO applications, including second harmonic generation (SHG) of high-power or high-energy laser beams. The laser performances of the LYSB:Yb (4 at.%) crystal prove its favorable intrinsic properties to generate laser emissions in the 1 µm range with high efficiency. The efficient laser emission at ~1028 nm together with good NLO characteristics to convert its own emission into emission at ~514 nm via SHG make the LYSB:Yb (4 at.%) crystal a very promising active medium to be used in self-frequency doubling configuration.

Three-dimensional modelling of 300 mm Czochralski silicon crystal growth with a transverse magnetic field

A method including a polynomial fitting step was proposed for crystallization interface correction of Czochralski crystal growth simulation, which can obtain an axisymmetric interface under a non-axisymmetric flow when the crystal rotates.

RE3+-Doped Ca3(Nb,Ga)5O12 and Ca3(Li,Nb,Ga)5O12 Crystals (RE = Sm, Dy, and Pr): A Review of Current Achievements.

Spectroscopic characteristics of RE3+ ions (RE = Sm, Dy, and Pr) doped in partially disordered Ca3Nb1.6875Ga3.1875O12-CNGG and Ca3Li0.275Nb1.775Ga2.95O12-CLNGG crystals are reviewed in detail to assess their prospects as laser crystals with emission in the visible spectral domain. All investigated crystals were grown using the Czochralski crystal growth technique. High-resolution absorption and emission measurements at different temperatures, as well as emission dynamics measurements, were performed on the grown crystals. The spectroscopic and laser emission characteristics of the obtained crystals were determined based on the Judd-Ofelt parameters. The obtained results indicate that CNGG:RE3+ and CLNGG:RE3+ (RE = Sm, Dy, and Pr) crystals can be promising materials for lasers in the visible range.

Electrical, optical, and mechanical properties of modified Czochralski grown organic 4-nitrobenzaldehyde single crystal

Growing large crystals of organic compounds with low melting points is a challenge but it was resolved by suitable modifications of the Czochralski (CZ) technique in the present study. A nonlinear optical single crystal of 4-nitrobenzaldehyde (4-NB) with a cylindrical shape, length of 2.5 cm, and diameter of 3 mm was successfully grown using an inexpensive modified CZ crystal growth technique at a temperature of 106 °C. The crystal structure and lattice parameters of the as-grown crystal were determined by single crystal and powder X-ray diffraction analyses. Intermolecular interactions were studied in the 4-NB crystal based on the Hirshfeld surface and two-dimensional fingerprint plot. The presence of various functional groups in the as-grown crystal was confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance (1H and 13C) spectroscopy. The thermal behavior of the 4-NB crystal was analyzed by thermogravimetric analysis and differential thermal analysis. High transparency (75%) with an optical band gap of 3.34 eV and lower cut-off of 370 nm were confirmed by ultraviolet–visible–near infrared spectroscopy. The temperature-dependent dielectric behavior was determined for the 4-NB crystal at a constant frequency of 5 kHz. The mechanical properties of the 4-NB single crystal were analyzed based on the Vickers microhardness and void analysis, which confirmed the soft nature of the crystal. The modified CZ technique allowed us to obtain disk-shaped organic 4-NB crystals for use in optical applications.

Development and validation of a thermal simulation for the Czochralski crystal growth process using model experiments

The Czochralski (CZ) process is one of the most important techniques for the production of bulk single crystals. Various numerical models for CZ growth furnaces exist, however, a review of the recent literature demonstrates that their validation is often questionable due to missing in-situ measurement data. In this work, a new 2D open-source thermal CZ growth model is introduced, verified with analytical solutions, and validated using dedicated model experiments with tin and hence easy access for the required measurements. A three-step procedure is applied to identify critical modeling parameters, make adjustments of these parameters, and evaluate the resulting modeling accuracy. Gas and melt convection, modeled with heat transfer coefficients and an effective heat conductivity, are found to be crucial and are adjusted using experimental data. Comparison of measured temperatures in the crucible shows good agreement, with deviations of max. 0.3 / 1.3 K under natural / forced convection. The model is able to predict the influence of crystal pull velocity and melt temperature on crystal diameter qualitatively.

Melt convection and temperature distribution in 300 mm Czochralski crystal growth with transverse magnetic field

Two-dimensional (2D) and Three-dimensional (3D) simulation solutions of the melt flow and heat transfer in the industrial scale 300 mm diameter single silicon Czochralski (Cz) growth with a transverse magnetic field were presented. The flow structure of the melt is no longer rotationally symmetric when the crystal and crucible rotate. The complex flow pattern is investigated, and simulation results show that the current caused by crystal rotation has a strong impact on melt convection beneath the interface. In addition, the mechanism through which the current influences melt flow is clarified. A special flow near the interface caused by Lorenz force is reported. All these results indicate the crystal conductivity cannot be neglected in simulation.

Multiple instabilities of thermocapillary flow in a cylindrical pool with a rotating disk on the free surface

The thermocapillary flow instabilities of silicon melt in a cylindrical pool with a rotating disk on the free surface (a simplified model of the Czochralski crystal growth) are numerically investigated by using the linear stability analysis. The complete neutral or critical stability curves are determined. Results show that the neutral stability curves form a closed region in the parameter plane, in which the steady axisymmetric flow is linearly stable. Two types of rotating wave (RW1 and RW2) instabilities and two types of hydrothermal wave (HTW1 and HTW2) instabilities are found. The energy analysis shows that all the instabilities are hydrodynamic (inertial) in nature. Specifically, RW1 and RW2 are caused by the azimuthal shear induced by the crystal rotation, while HTW1 and HTW2 are caused by the radial shear induced by the thermocapillary force.

The crystal structure of single crystalline PrCa4O[BO3]3

Abstract PrCa4O[BO3]3 was grown as a single crystal by the Czochralski method. The precursor material was synthesized by solid state reaction under O2 atmosphere and sintered after grinding under N2 atmosphere with a content of 20% H2. The Czochralski crystal growth proceeded under N2 atmosphere with an <010> oriented GdCa4O[BO3]3 crystal seed. A PrCa4O[BO3]3 crystal with a cylinder length of 20 mm, a diameter of 15 mm, and weight of 23.1 g was obtained. The crystal structure was solved from single crystal X-ray diffraction data in the monoclinic crystal system with space group C1m1 (No. 8), the lattice parameters a = 8.1293(6) Å, b = 16.062(1) Å, c = 3.6023(2) Å, β = 101.371(2)°, formula units of 2 and final R- and wR2-values below 3.8%. A mixed occupancy between Pr and Ca of 6.0% was found.

Model experiments for Czochralski crystal growth processes using inductive and resistive heating

The Czochralski (CZ) growth technique is widely applied in crystal growth, using both induction and resistance heaters. In this work, a novel model experiment platform with comprehensive in-situ measurement capability is introduced. Growth experiments with the model material tin applying both heating concepts are performed and analyzed, e.g., in terms of the maximum achievable crystal diameter. Strong asymmetries in the magnetic field of the induction heater are measured and temperature distribution on the resistance heater is found to be non-uniform. Furthermore, significant losses are observed in the power supplies of the resistance heater. The heating efficiency of both concepts is compared considering different insulation geometries. The obtained results show the capability of model experiments for design optimization and will provide valuable input for further validation of numerical simulations.

Effect of crystal rotation on the instability of thermocapillary–buoyancy convection in a Czochralski model

In Czochralski crystal growth, buoyancy convection, thermocapillary flow, and forced convection driven by crystal/crucible rotation complicate the mixed convection of the melt. The instability of this mixed convection has a crucial impact on the quality of the grown crystal, but the complex convection phenomenon poses a tough challenge to the computation of critical values through linear stability analysis. In this paper, the instability of the mixed convection phenomenon of a LiCaAlF6 melt in a Czochralski model with unit aspect ratio (Γ = melt depth/crucible radius = 1.0) was investigated using linear stability analysis in the context of the spectral element method. The underlying instability mechanism is unfolded by means of energy analysis. We observe two instability modes with increasing crystal rotation. Both instability modes correspond to the coupling between the mechanisms of buoyancy and inertial instabilities. Besides, both instability modes appear when invoking the surface tension at the free surface while only one mode is observed when switching the surface tension off, implying that thermocapillary effects influence the instability modes for the melt convection in Czochralski crystal growth.

A Deep Learning Based Dislocation Detection Method for Cylindrical Crystal Growth Process

For the single crystal furnace used in the photovoltaic industry, growth problems occur frequently due to dislocations during the shouldering and cylindrical growth steps of the Czochralski (CZ) crystal growth. Detecting the dislocation phenomenon in the cylindrical growth step is very important for entire automation of the CZ crystal furnace, since this process usually lasts for more than 48h. The irregular nature of different patterns of dislocation would impose a big challenge for a traditional machine vision-based detection method. As almost no publications have been dedicated to detecting this phenomenon, to address this issue, after analyzing the characteristics of the silicon ingot image of this process, this paper proposes a kind of deep learning-based dislocation detection method along with tracking strategy to simulate manual inspection. The model has a good detection effect whether there is occlusion or not, the experimental results show that the detection accuracy is 97.33%, and the inference speed is about 14.7 frames per second (FPS). It can achieve the purpose of reducing energy consumption and improving process automation by monitoring this process.

200 mm Ge Wafer Production for Oxide-Free Si-Ge Direct Wafer Bonding

Dislocation-free 200 mm diameter germanium wafers were manufactured via Czochralski crystal growth technique. Standard silicon wafers were used to demonstrate the feasibility of oxide-free Ge direct wafer bonding at room temperature. First the native oxides from both wafer surfaces were removed using ion beam sputtering, followed by the transfer of both wafers in ultra-high vacuum to the bonding process station in order to avoid re-oxidation. Subsequently annealing to correct for the sputter-induced amorphization was studied. For the qualification of the process the main focus was on the morphological and elemental analysis of the surfaces and of the bonded interfaces.

Mixed Oscillation Flow of Binary Fluid with Minus One Capillary Ratio in the Czochralski Crystal Growth Model

This work presented a series of three-dimensional unsteady numerical simulations on the characteristics of the mixed oscillation flows of binary mixture in a Czochralski crystal growth model. The silicon-germanium melt is investigated and the capillary ratio is minus one. The simulation results showed that, for the special capillary ratio, the thermal and solutocapillary forces are imposed in opposite directions and counteract each other. With the effect of buoyancy, the balance between the capillary forces is disturbed. Mixed with the forced convection driven by rotation, the capillary-buoyancy convection is complex. The basic mixed flow streamlines are presented as various rolling cells. The directions of the rolls are dependent on the combinations of surface and body forces. With the increase of temperature gradient, the basic flow stability is broken, and the oscillations occur. The crucible rotation has an effective influence on the stability enhancement. However, affected by the crystal rotation, the critical condition experiences an increase to a turning point, and then undergoes a sharp reduction to zero. Once the instability is incubated, the surface oscillations are analyzed. For the three-dimensional steady flow, only spatial oscillations are observed circumferentially, and the surface patterns of spokes, rosebud, and pulsating ring are obtained. For the unsteady oscillation flow, the spiral hydrosoultal waves, rotating waves, and superimposition of spirals and spokes are observed, and the oscillation behaviors are also discussed.