Growth Furnace Research Articles

The influence of the growth rate on the eutectic spacings, undercoolings and microhardness of directional solidified bismuth–lead eutectic alloy

Bi–Pb alloy at the eutectic composition was unidirectionally solidified upwards with five different growth rates (V = 7.05–113.09 μm/s) at constant temperature gradient (G = 2.18 K/mm) in a Bridgman type directional growth furnace in order to investigate dependency of eutectic spacing (λ), minimum undercooling (ΔT) and microhardness (HV) on the growth rates (V). The values of λ and HV were measured from the quenched samples and the minimum undercooling (ΔT) were determined from the Jackson–Hunt eutectic theory. The dependency of eutectic spacings, microhardness and undercooling on growth rate was investigated. According to these results it has been found that the value of λ decreases with increasing the value of V and that the values of HV and ΔT increase for a constant G. The values of λ2V, λΔT and ΔTV−0.5 were determined by using the values of λ, ΔT and V. The results obtained in the present work have been compared with those predicted by the Jackson–Hunt eutectic theory and with similar experimental results.

One-Dimensional Nanostructures by Pulsed Laser Ablation

One-dimensional (1D) nanostructures represent a unique system for investigating phenomena at the nanoscale and are also expected to play a critical role as both interconnects and functional components in the fabrication of nanoscale electronic devices. Pulsed laser can provide extremely intense energy in a small spot and it can ablate virtually any materials. Various nanostructures have been investigated and fabricated with pulsed laser ablation, and this technique is not limited by the type of materials or crystal structures. This article focuses on 1D nanostructures and presents an overview of the common growth mechanism of nanowires by pulsed laser ablation. We first introduce a general scheme of the pulsed laser ablation in a tube furnace for the nanowire growth. Subsequently, we discuss various growth mechanisms involved to generate 1D nanostructures from pulsed laser ablation, including vapor–liquid–solid growth, oxide-assisted growth, and vapor–solid growth. Defects can also play an important role and they have been observed in the nanowires from different growth process.

Optimization of silicon crystallization in a Bridgman growth furnace by numerical modeling

A heat transfer model of a semi-industrial furnace has been build, using a 3D FEM model in order to analyze the crystallization phase of a multi-crystalline square ingot. In the modeling of the solidification process heat transfer phenomena, such as radiation and conduction in the furnace have been taken into account. Results from crystallization experiments are used for the calibration and validation of the model. Subsequently, the model was used to test different insulating materials and analyze their effect on temperature gradients in the ingot, shape of the solid–liquid interface and the overall crystallization time.

사파이어 단결정의 초크랄스키 성장공정에 대한 유한요소분석

최근 사파이어 결정은 LED 응용부품에 사용되고 있고, CZ 성장공정은 고 품질의 사파이어 단결정을 성장시키기 위한 중요한 기술중의 하나이다. 고 품질의 단결정을 성장하기 위해서는 CZ 성장로 내부의 열 및 질량 전달현상의 제어가 필요하다. 본 연구에서는 유도 가열된 CZ 성장로에 대한 사파이어 결정의 성장공정을 FEM을 사용하여 수치적으로 분석하였다. 본 연구의 결과, 성장로의 rpm이 증가함에 따라 고온부는 도가니 표면에서 융액의 내부로 이동하고, 고-액 계면은 평편한 형태로 변화되는 것으로 분석되었다. 또한 성장된 결정의 고-액 계면은 초기에 형성된 결정의 shoulder 형상에 의해서도 영향을 받는 것으로 나타났다. Recently sapphire crystals are used in LED applications. The Czochralski (CZ) growth process is one of the most important techniques for growing high quality sapphire single crystal. A successful growth of perfect single crystals requires the control of heat and mass transport phenomena in the CZ growth furnace. In this study, the growth processes of the sapphire crystal in an inductively heated CZ furnace have been analyzed numerically using finite element method. The results shown that the high temperature positions moved from the crucible surface to inside the melt and the crystal-melt interface changed to the flat shape when the rpm was increased. Also the crystal-melt interface shape has been influenced by the shoulder shape of the grown crystal during the initial stage.

Ultra-high vacuum compatible image furnace

We report the design of an optical floating-zone furnace for single-crystal growth under ultra-high vacuum (UHV) compatible conditions. The system is based on a commercial image furnace, which has been refurbished to be all-metal sealed. Major changes concern the use of UHV rotary feedthroughs and bespoke quartz-metal seals with metal-O-rings at the lamp stage. As a consequence, the procedure of assembling the furnace for crystal growth is changed completely. Bespoke heating jackets permit to bake the system. For compounds with elevated vapor pressures, the ultra-high vacuum serves as a precondition for the use of a high-purity argon atmosphere up to 10 bar. In the ferromagnetic Heusler compound Cu(2)MnAl, the improvements of purity result in an improved stability of the molten zone, grain selection, and, hence, single-crystal growth. Similar improvements are observed in traveling-solvent floating-zone growth of the antiferromagnetic Heusler compound Mn(3)Si. These improvements underscore the great potential of optical float-zoning for the growth of high-purity single crystals of intermetallic compounds.

CVD Growth of Graphene on Three Types of Epitaxial Metal Films on Sapphire Substrate

ABSTRACTGraphene growth by chemical vapor deposition (CVD) was studied on three types of epitaxial metal films with different crystal structures on sapphire. Nickel (face-centered-cubic: fcc), Ru (hexagonal-closed-pack: hcp), and Co (fcc at temperature for graphene growth and hcp at R.T.) were deposited on c-face sapphire substrates and annealed in a furnace for solid phase epitaxial growth. Graphene layers were grown by CVD with methane gas on the epitaxial metal film. The graphene layer uniformity was consistent with the structural simplicity of the metal film. The Ru sample had a single domain in the metal film and the highest graphene uniformity. The Co sample had a very complex crystal structure in the metal film and the poorest uniformity in graphene. The Ni sample had two types of stacking domains in the metal film and the graphene layer was uniform on each domain, but inhomogeneity was observed at domain boundaries.

Integrated Control for Crystal Growth Furnace in Space

空间晶体生长炉控制对象复杂, 具有纯滞后、强耦合、非线性等不利于控制的特性. 为实现炉温的精确控制, 提出了一个空间晶体生长炉综合控制方法并通过软件来实现. 将相关系数法和增广递推最小二乘法相结合, 辨识系统模型, 使用Hooke-Jeeves模式搜索法进行PID参数的自整定, 采用PID加前馈控制的算法对系统进行仿真, 使用同样的算法和控制参数对空间晶体生长炉进行实时控制, 并在控制的过程中实时调整控制参数, 以达到最佳的控制结果. 实验结果表明, 当三个温区的温度均达到700ºC时, 温度稳定度小于±0.3ºC, 满足系统设计要求. 同时介绍了实现综合控制软件的基本原理、功能、特点及在实际中的应用. 实际工程的应用结果表明, 该软件可满足空间晶体生长炉对控制系统的要求.

Growth of ZnGeP<sub>2</sub> Single Crystal by Three-Temperature-Zone Furnace

In order to meet the requirements of growing high-quality ZnGeP2, a crystal growth furnace with three-temperature-zone was designed and fabricated based on a conventional vertical two-zone tubular resistance furnace. Appropriate temperature gradients of 12~15°C/cm at the growth interface and stable thermal profile were obtained. A crack-free ZnGeP2 single crystal with size of Φ15mm×30mm was grown successfully in the furnace mentioned above. The as-grown crystal was characterized by X-ray diffraction (XRD) and Infrared (IR) spectrophotometers. It is found that there is a cleavage face of (101) and X-ray multiple diffraction peaks of the {101} faces are observed, The infrared transmission of a ZnGeP2 wafer of 3 mm thickness is about 50% in the region of 3~10μm. These results show the designed crystal growth furnace is suitable for growth of ZnGeP2 crystal, and the as-grown ZnGeP2 crystal has good structural integrity and high quality.

Heat Treating and Detectors Characterization of α-HgI2

Abstract α-HgI 2 crystal was grown using a static sublimation method in a self-designed vertical two-zone growth furnace. After 23 days growth, a single crystal of about 15 mm×12 mm×5 mm was obtained. The as-grown crystal was characterized by means of XRD and 4155 CVIV instrument, and the performance of the detector made with the as-grown HgI 2 crystal was tested. The results indicate that excess iodine exists in the as-grown crystal, which can be removed effectively by heating at a feasible temperature. The resistivity of the as-grown crystal is about 10 12 Ω·cm. The spectroscopy response to gamma ray (an uncollimated 241 Am radiative source with the principal energy of 59.5 keV) of the detectors shows that the energy resolution is 14.6% corresponding to FWHM ≈8.69 keV at room temperature.

Global simulation of coupled carbon and oxygen transport in a Czochralski furnace for silicon crystal growth

For accurate prediction of carbon and oxygen impurities in a single crystal produced by the Czochralski method, global simulation of coupled oxygen and carbon transport in the whole furnace was implemented. Both gas-phase transportation and liquid-phase transportation of oxygen and carbon were considered. With five chemical reactions considered, SiO and CO concentrations in gas and C and O atom concentrations in silicon melt were solved simultaneously. The simulation results show good agreement with experimental data.

Optimization of the Heat and Mass Transfer Processes in a Mechanism of Polycrystalline Silicon Production by the Bridgeman’s Technique

The distribution of incoherent impurities in the melt for the polycrystalline silicone production by the Bridgeman’s technique was studied with the aid of 3D numerical simulation. Under study was the influence of the phase transition configuration on the distribution of the displaced substance near the crystallization front under the conditions of azimuthnonuniform heating of crucible side walls. The flow in the liquid is described by Navier-Stokes equations in the Boussinesq approximation, the distribution of the dissolved substance concentration is found from the solution of the convective diffusion equation. The obtained results show that the nonuniform heating of the melt changes the structure of convective flows; in the case of flat or convex crystallization front, these flows promote the displacement of the dissolved admixture toward the crucible walls. The processes were considered within the range of parameters following the real temperatures in a growth furnace and the melt, crucible size and shape

Development of an Alterable and Rotary Permanent Magnetic Field

In this paper, a system that can produce alterable and rotary permanent magnetic field is developed. It can be used for crystal growth, chemical crystal and biologic cell, etc. A homogeneous magnetic field can be produced in the central region by two annular permanent magnets, and the density of magnetic flux is controlled by changing the angle of the magnetic field produced by the inner annular magnet and that produced by the outer annular magnet. The angle can vary continuously from 0 to 180 degree, consequently, causing the density of magnetic flux varied from 0.006 to 0.18 Tesla. To obtain a rotary magnetic field, the two annular magnets are driven to rotate synchronously. After the wanted magnetic field is achieved, the relative position of the inner and the outer annular magnet is fixed, thus, the inner and outer annular magnets can rotate synchronously at a given speed. The rotation speed up to 20 rad/min can be achieved. A monitoring system, based on industrial computer, is used to set parameters to control the magnetic field and the rotation speed, and to show the real-time operation parameters and working status of the system. Through experimental verification, the measured data has good agreement with the given value. The system is also applied on a furnace for single crystal growth, the result shown that the quality of the single crystal being grown under magnetic field is significantly improved when compared to those grown under no magnetic field.

Numerical simulation of thermal and mass transport during Czochralski crystal growth of sapphire

AbstractThe thermal and flow transport in an inductively heated Czochralski crystal growth furnace during a crystal growth process is investigated numerically. The temperature and flow fields inside the furnace, coupled with the heat generation in the iridium crucible induced by the electromagnetic field generated by the RF coil, are computed. The results indicate that for an RF coil fixed in position during the growth process, although the maximum value of the magnetic, temperature and velocity fields decrease, the convexity of the crystal‐melt interface increases for longer crystal growth lengths. The convexity of the crystal‐melt interface and the power consumption can be reduced by adjusting the relative position between the crucible and the induction coil during growth. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of RF coil position on the transport processes during the stages of sapphire Czochralski crystal growth

The effect of the RF coil position during the stages of sapphire crystal growth process in an inductively heated Czochralski crystal growth furnace on the thermal and flow transport, the shape of the crystal–melt interface shape, and the power requirements is investigated numerically. The results show that although the maximum values of temperature and velocity decrease, the convexity of the crystal–melt interface increases as the crystal length grows. It is found that the least input power is required if the central position of the RF coil is maintained below the central position of the melt during the crystal growth process. Under such crystal growth conditions, the temperature gradients along the crystalline front are small.

Control over the symmetry of the heat field in the station for growing LBO crystals by the Kyropoulos method

A plant for growing single crystals from a melt-solution by the Kyropoulos method is described. The plant has a two-zone growth furnace, crystal holder movement and rotation mechanisms, and a control system based on an I-7188EG controller with an ISaGRAF built-in target system. The upper and lower zones of the furnace consist of eight heaters intended for controlling the symmetry of the heat field both in the static and dynamic (rotation of the heat field) operation modes. A high efficiency of the plant operation is demonstrated using the example of growing LiB3O5 crystals.

The creation of a method of growing large crystals of optical synthetic sapphire at the S I Vavilov State Optical Institute

This article describes the history of the creation at the S. I. Vavilov State Optical Institute (GOI) of a progressive and internationally recognized method of growing large crystals of optical synthetic sapphire (the GOI method), which is being used to grow almost half of the world's production of large crystals (as much as 300mm in diameter). The main features of the GOI method are discussed--a crystal with an extremely sharp crystallization front is grown from a seed in the direction of the walls of the growth crucible without rotating it. The perfection of a technology for growing synthetic sapphire that makes it possible to grow crystals up to 520mm in diameter and weighing up to 450kg is discussed. The current technology makes it possible to reduce the size of the growth furnaces and the electrical-energy consumption by a factor of 8.

Numerical modeling of SiC single crystal growth-sublimation and hot-wall epitaxy

On the engineering point of view, it is important to develop a design technology of the furnace for SiC single crystal growth. In this point of view, the recent progress of modeling on both sublimation bulk growth and hot-wall epitaxy were presented. For the sublimation, the active control of grown crystal shape by modifying crucible geometry was demonstrated. The effect of nitrogen doping on the heat transfer in a growing crystal were also investigated. For the hot-wall epitaxy, growth rate, surface morphology, and doping concentration could be predicted qualitatively with taking account of the depositing surface conditions. Chlorine-containing system was supposed to provide more stable and uniform process than the common SiH 4-based system.

Silicon ingot diameter modeling in Czochralski process and its dynamic simulation

Silicon wafers are manufactured by cutting an ingot into the same thickness. The Czochralski process is a representative method for making an ingot. During manufacture, the ingot diameter is affected by the pull speed and heat transfer amount. Therefore, controlling the ingot manufacturing process involves controlling the ingot diameter related to pull speed and controlling the heater power supply to maintain the pull speed within the allowable range. The modeling of ingot diameter can be established by the ingot pull speed change based on an understanding of the mechanism of heat transfer, and the calculation of the heat transfer amount between all the parties of the crystal growth furnace according to the energy balance equations. Comparing the simulation results with real process results, the step change of the heater showed 1st or 2nd process dynamics at all points with a time delay of 18 minutes, which was similar to that of the real process. Furthermore, the pull speed step change exhibited a 5 min time delay from the test spot, which confirmed the relation between the integral and process properties. This result is similar to the real process, too. With a specific ingot length, the temperature in each point of the furnace in the real process was similar to these simulation results.

Single tungsten nanowires as pH sensitive electrodes

The electrochemical potentials of tungsten nanowire samples, covered with their own oxide, were measured in dependence of the pH value. The samples were prepared by selective etching of a directionally solidified eutectic NiAl–W alloy. Directional solidification in a Bridgman-type crystal growth furnace yields nanostructured two-phase materials. Electrochemical processing allows selective etching of the phases exposing the nanoscale structures. In this work, pointed samples with a single wire 200 nm in diameter protruding from the tip were produced. Subsequently the tungsten oxide layer on these single nanowires was electrochemically modified to optimize their pH sensing capabilities. The method has a potential for further downsizing since the wire diameter and exposed length can be controlled by the process parameters during solidification and during electrochemical processing. The advantages of these nanowire pH probes along with possible applications such as the pH measurement in ultra small cavities and other small systems of interest such as corrosion pits and biological cells are discussed.

Numerical Simulation of the Growth of ZnO Nanostructures in a Tube Furnace by Physical Vapour Deposition

ABSTRACTZinc oxide is a versatile II-VI naturally n-type semiconductor that exhibits piezoelectric properties. By controlling the growth kinetics during a simple carbothermal reduction process a wide range of 1D nanostructures such as nanowires, nanobelts, and nanotetrapods have been synthesized. The driving force for the nanostructure growth is the Zn vapour supersaturation and supply rate which, if known, can be used to predict and explain the type of crystal structure that results. A model which attempts to determine the Zn vapour concentration as a function of position in the growth furnace is described. A numerical simulation package, COMSOL, was used to simultaneously model the effects of fluid flow, diffusion and heat transfer in a tube furnace made specifically for ZnO nanostructure growth. Parameters such as the temperature, pressure, and flow rate are used as inputs to the model to show the effect that each one has on the Zn concentration profile. An experimental parametric study of ZnO nanostructure growth was also conducted and compared to the model predictions for the Zn concentration in the tube.