Growth Furnace Research Articles

High-purity rayon-based carbon fiber felt prepared by halogen gas purification for superior thermal insulation and oxidation resistance

High-purity rayon-based carbon fiber (CFRay) felt holds significant promise for applications in thermal protection systems and semiconductor crystal growth furnaces. This study employs halogen gas purification and high-temperature purification techniques in the fabrication of high-purity CFRay felt. Additionally, the influence of the purification process on the thermal insulation and oxidation resistance of CFRay felt is investigated. The glow discharge mass spectrometer analysis reveals that purification at a lower temperature of 2300 °C achieves a purity level of 6.9 ppm, surpassing both purified CFRay felt without halogen at 2300 °C (56.1 ppm) and high-temperature treated CFRay felt at 3000 °C (10.4 ppm). Thermal insulation and dynamic-static oxidation resistance tests show that the properties of CFRay felt are concurrently affected by the heat treatment temperature. Compared to high-temperature purification, halogen gas purification operates at lower temperatures, preventing the graphitization of CFRay, thereby ensuring high purity while enhancing thermal insulation and demonstrating relatively superior oxidation resistance. This study offers novel insights into the preparation and performance adjustment of high-purity CFRay felt.

Growth difficulties and growth of crack free Eu2+ activated KSr2I5 scintillator single crystal by vertical bridgman-stockbarger technique for radiation detection applications

Europium activated potassium strontium iodide (KSr2I5:0.5Eu2+) compound was synthesized and refined by indigenous zone-refinement experimental set-up. The impurities that are insoluble in the KSr2I5:Eu2+ compound was filtered by using a specifically programmed dual chamber quartz ampoule with frit filter method. Temperature profile of this in-house built vertical transparent Bridgman-Stockbarger technique growth furnace is optimized to grow quality single crystals of KSr2I5:Eu2+. From the photoluminescence emission spectrum a typical 4f6 5d1 – 4f7 transition is observed for a broad emission peak at 432 nm whereas a broad emission peak at 448 nm was obtained from the X-ray excited radioluminescence spectrum. The gamma ray spectrometer was administered to detect the scintillation properties of the grown crystal. The scintillation decay time was calculated for the KSr2I5:Eu2+ crystal wherein the energy resolution under 137Cs sealed gamma source is found to be 3.5 % at 662 KeV.

Scintillation properties of [formula omitted]:[formula omitted] crystals grown by Cz, EFG and Bridgman methods with a multifunctional melt growth furnace

Cs3Cu2I5:Tl is a novel scintillator boasting high density, a substantial light yield, and excellent energy resolution, making it promising for applications in gamma-ray spectroscopy. In this paper, we developed a multi-functional melt growth furnace capable of convenient configuration for the Czochralski (Cz), Edge-defined Film-fed (EFG), and Bridgman methods. We successfully grew Cs3Cu2I5:Tl crystals using the Cz, EFG, and Bridgman methods, yielding crystal sizes of Φ15 mm, Φ12 mm, and Φ30 mm, respectively. The obtained crystals exhibit satisfactory crystalline quality, although they are susceptible to cracks during the cooling, cutting, and polishing processes. Samples are taken from the crystals to undergo analysis to investigate their optical and scintillation properties. Findings indicate that our Cs3Cu2I5:Tl possess a large Stokes shift of 175 nm with nearly no spectral overlap between the PLE and PL spectra. The radioluminescence emission peaked at 505 nm, accompanied by a scintillation decay time of 828 ns. The samples exhibited a commendable energy resolution of 4.8% at 662 KeV and a high light yield of 83000 ph/MeV when coupled with a PMT. This study validates the viability of employing CZ and EFG methods for the growth of Cs3Cu2I5:Tl crystal, in addition to showcasing the Bridgman method for the growth of centimeter-scale Cs3Cu2I5:Tl crystals.

Study of Flow Pattern Defects and Oxidation Induced Stacking Faults in Czochralski Single-Crystal Silicon Growth

This paper emphasizes that the furnace pressure, crucible rotation, and pulling rate have important effects on interstitial oxygen (Oi) concentrations and micro-defects during growth in a Czochralski single-crystal silicon (CZ-Si) growth furnace. Since oxygen in a silicon ingot influences minority carrier lifetime, different set-points of furnace pressure and crucible rotation were controlled to achieve different degrees of Oi. The Oi content has a positive correlation with furnace pressure and crucible rotation. Various numbers of micro-defects were generated under the influence of different pulling rates, owing to the transformation from liquid to solid. The sample also underwent Secco etching and a high-temperature wet oxidation to observe defects caused by the Oi concentration and pulling rate, namely, flow pattern defects (FPDs) and oxidation-induced stacking faults (OISFs). Optical microscopy was employed to confirm the surface topography, and for defect number counting, to observe the correlation between the defects and the minority carrier lifetime. The overall results show that the minority carrier lifetime is mainly dominated by OISFs under high Oi content and FPDs under low Oi content. Therefore, growth using a CZ-Si growth furnace should be carried out with low furnace pressure, low crucible rotation, and low pulling rate to reduce micro-defects.

Micro-Vibration Signal Denoising Algorithm of Spectral Morphology Fitting Based on Variational Mode Decomposition

Environmental micro-vibration has a significant impact on the proper functioning of semiconductor production and testing equipment such as the Czochralski growth furnace, polishing machine, photoetching machine, scanning electron microscope, etc. Low-frequency micro vibration has a significant influence on the normal operation of high-precision machining and testing equipment, and even causes irreversible damage to the equipment. Therefore, the micro-vibration test has important theoretical significance and engineering value for guiding the vibration isolation design of an electronic industrial workshop and ensuring the stable operation of various precision equipment in the workshop. As the observed acceleration signal is affected by noise introduced by the acceleration sensor itself, the signal processing circuit, the external power supply and interference from environmental factors, direct integration operations can lead to problems such as baseline drift and signal distortion in the calculation results. Aiming at the problem of noise interference in the micro-vibration measurement process, this paper proposed a micro-vibration signal denoising algorithm of spectral morphology fitting based on variational mode decomposition. The observed acceleration signal is decomposed into several orders of finite bandwidth intrinsic mode function components. The asymmetric Gaussian mixture model is used to complete the fitting of the spectral curves of each order of intrinsic mode function components. We can obtain the relevant parameters of the asymmetric Gaussian mixture model curves to complete the division of the effective information frequency band and finally achieve the denoising of the observed acceleration signal. Finally, the algorithm of this paper is compared with traditional denoising algorithms through numerical simulation examples and comparative experiments on denoising effects. The results show that the proposed algorithm has higher accuracy and anti-noise ability.

CoSn3 Intermetallic Nanoparticles for Electronic Packaging.

At present, composite solder pastes are getting a lot of attention, especially composite Sn based solders reinforced by nanoparticles. Indeed, CoSn3 is a strong nucleating agent of Sn crystal, which has potential application value in the field of electronic packaging. However, there is no reliable synthetic path for CoSn3 nanoparticles at present. In this article, a chemical synthesis method for CoSn3 nanoparticles is developed. Here, CoCl2 and SnCl2 are reduced by NaHB4 in triethylene glycol (TEG), dispersed by ultrasonics, and heated to 350 °C in a tube furnace for growth. The CoSn3 nanoparticles with a diameter of about 150 nm are obtained by heating at 350 °C for 10 min. The CoSn3 nanoparticles undergo a step reaction in the process of synthesis and go through different stages of merging and annexation during their growth. The crystal growth behavior and the process of orientation change during the nucleation and growth of CoSn3 nanoparticles are studied, especially the two growth mechanisms, namely OU (orientation unified) and OA (orientation attached). By mixing CoSn3 nanoparticles with SAC305, we obtain a kind of strengthened composite soldering paste. There are obvious six-fold cyclic twins in the joints made by this soldering paste.

Application of optical velocity measurements including a novel calibration technique for micron-resolution to investigate the gas flow in a model experiment for crystal growth

An important step in the fabrication of many modern semiconductor materials and devices is the crystal growth process. These processes take place in high-temperature furnaces using inert gas and other atmospheres. The flow in the gas phase influences the transport of crystal components, dopants and impurities and hence has a significant impact on the grown crystals. In this work, we study the flow in a simplified model of a crystal growth furnace. This model is made of PMMA filled with a Diesel mixture as a model fluid to match the refractive index of PMMA and to allow for measurements in the complex geometry. The comparability to the flow in a real furnace is ensured by matching the Reynolds number. Two optical measurement methods, Particle Image Velocimetry (PIV) and the Laser Doppler Velocity Profile Sensor (LDV-PS) are used to investigate the global flow field as well as the small-scale flow structures. A calibration model is developed for the LDV-PS to reduce systematic measurement errors caused by the refractive index of the model fluid from up to 1% to less than 0,1%. The results obtained in this study improve the understanding of the gas flow behavior inside a crystal growth furnace and provide reference data for simulation. The first analysis shows a highly unsteady flow with unexpected flow direction along the crystal and melt surfaces. The near-surface flow patterns are of particular relevance in crystal growth because of their large influence on the local heat and mass transport during the crystallization process.

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.

Improving the Quality of CaWO4 Target Crystals for CRESST

The Cryogenic Rare Event Search with Superconducting Thermometers (CRESST) experiment aims at the direct detection of dark matter particles via their elastic scattering off nuclei in a scintillating CaWO_4 target crystal. The CaWO_4 crystal is operated together with a light detector at mK temperature and read out by a Transition Edge Sensor. For many years, CaWO_4 crystals have successfully been produced in-house at Technical University of Munich (TUM) with a focus on high radiopurity which is crucial to reduce background originating from radioactive contamination. In order to further improve the CaWO_4 crystals, an extensive chemical purification of the raw materials and the synthesised CaWO_4 powder has been performed. In addition, a temperature gradient simulation of the growth process and subsequently an optimisation of the growth furnace with the goal to reduce the intrinsic stress was carried out. We present results on the intrinsic stress in the CaWO_4 crystals and on the CaWO_4 powder radiopurity. A crystal grown from the purified material was installed in the current CRESST set-up. The detector is equipped with an instrumented holder which is used to measure the alpha decay rate of the crystal. We present a preliminary analysis showing a significantly reduced intrinsic background from natural decay chains.

Robust control strategies for a two‐stage soft‐switching heating power supply of silicon growth furnace

As a key element of the silicon growth furnace, the heating power supply plays an important role to form the required thermal field for mono-silicon growth. The performance of the heating power supply system is critical to implement the function, which is determined by both hardware topology and control strategies. In this paper, a novel two-stages soft-switching power supply topology is employed to improve the efficiency of the power supply system. Meanwhile, the robust control methods are proposed for both stages converter to achieve high power factor (PF), low total harmonic distortion (THD) and stable output DC voltage under parameters uncertainty or load perturbation. The simulation and experiment results show the correctness of analysis and the effectiveness of the proposed methods. The robust control strategies combined with the advanced soft switching topology improve the system performance for the practical applications.

Oxygen and Nitrogen Transfer in Furnaces in Crystal Growth of Silicon by Czochralski and Directional Solidification Processes.

Impurity concentrations of oxygen, carbon, nitrogen, iron, and other heavy metals should be well controlled in silicon crystals to maintain the crystal quality for application in electronic and solar cell devices. Contamination by impurities occurs during the melting of raw materials and during the crystal growth process. Quantitative analysis of impurity transfer using numerical and experimental analysis is important to control impurity concentrations. This paper reviews the analysis of the impurity transport phenomena in crystal growth furnaces of Czochralski and directional solidification methods by a model of global analysis and an experiment during the crystal growth of silicon.

Preparation of NbAs Single Crystal by the Seed Growth Process

A Weyl semimetal is a novel crystal with low-energy electronic excitations that behave as Weyl fermions. It has received worldwide interest and was believed to have introduced the next era of condensed matter physics after graphene and three-dimensional topological insulators. However, it is not easy to obtain a single large-sized crystal because there are many nucleations in the preparation process. A bottom-seed CVT growth method is proposed in this paper, and we acquired the large-sized, high-quality NbAs single crystals up to 4 × 3 × 3 mm3 finally. X-ray diffraction and STEM confirmed that they are tetragonal NbAs, which the key is to using the seed crystal in a vertical growth furnace. Notably, the photoelectric properties of the crystal are obtained under the existing conditions, which paves the way for follow-up work.

Optimal Magnetic Graphite Heater Design for Impurity Control in Single-Crystal Si Grower Using Crystal Growth Simulation

In this paper, we report a successfully modified single-crystal Si growth furnace for impurity control. Four types of arbitrary magnetic heater (AMGH) systems with 3, 4, 5, and poly parts were designed in a coil shape and analyzed using crystal growth simulation. The concentration of oxygen impurities in single-crystal Si ingots was compared among the designed AMGHs and a normal graphite heater (NGH). The designed AMGHs were confirmed to be able to control turbulence and convection in a molten state, which created a vortex that influenced the oxygen direction near the melt–crystal interface. It was confirmed that replacing NGH with AMGHs resulted in a reduction in the average oxygen concentration at the Si melt–crystal interface by approximately 4.8%.

Online LSSVM model to predict temperatures of furnace system in Chinese Space Station

Crystal growth furnace is the platform of material melting experiment in space station. The precision of the temperature controller of the furnace determines whether the experiment is successful or not. Generally, system identification contributes to the design of a better controller. However, many identification methods are only effective with large datasets and cannot track the changing features of the system characteristics when the environment changes. In this article, we present an online method to identify the time-varying and large time delay furnace system. Inspired by clustering theory, to track the latest characteristics of the system, the training set is dynamically updated based on sample similarities. Grid search and grey wolf optimizer are used respectively for hyperparameter optimization in a two-phase tuning process. The presented identification method is validated using Tiangong-2 furnace data set. The results show the established recursive least-squares SVMs can successfully predict the temperatures of the furnace with different experiment environment.

Carbon monoxide concentrations in a Czochralski growth furnace

High-performance power devices require silicon crystals with long minority carrier lifetimes and, subsequently, low carbon concentrations. This paper reports in-situ measurements of carbon monoxide (CO) in a Czochralski growth furnace used for the growth of single-crystal silicon. During the heating and melting processes, the major causes of CO gas generation are (i) outgassing from carbon parts inside the furnace, (ii) reactions between the quartz and carbon crucible, and (iii) reactions between the silicon melt and quartz crucible. By conducting heating experiments with and without polysilicon and quartz crucibles, we successfully measured the independent CO generation contributions of causes (i), (ii), and (iii) listed above. The outgassing process generated CO gas during the heating process of the raw material. CO generated during the melting process of the raw material was attributed to reactions between (ii), the quartz and carbon, and (iii), the silicon melt and carbon parts, which occurred after CO outgassing from carbon parts in the furnace.

Operational Semantics of Annotated Reflex Programs

Reflex is a process-oriented language that provides a design of easy-to-maintain control software for programmable logic controllers. The language has been successfully used in a several reliability critical control systems, e. g. control software for a silicon single crystal growth furnace and electronic equipment control system. Currently, the main goal of the Reflex language project is to develop formal verification methods for Reflex programs in order to guarantee increased reliability of the software created on its basis. The paper presents the formal operational semantics of Reflex programs extended by annotations describing the formal specification of software requirements as a necessary basis for the application of such methods. A brief overview of the Reflex language is given and a simple example of its use – a control program for a hand dryer – is provided. The concepts of environment and variables shared with the environment are defined that allows to disengage from specific input/output ports. Types of annotations that specify restrictions on the values of the variables at program launch, restrictions on the environment (in particular, on the control object), invariants of the control cycle, pre- and postconditions of external functions used in Reflex programs are defined. Annotated Reflex also uses standard annotations assume, assert and havoc. The operational semantics of the annotated Reflex programs uses the global clock as well as the local clocks of separate processes, the time of which is measured in the number of iterations of the control cycle, to simulate time constraints on the execution of processes at certain states. It stores a complete history of changes of the values of shared variables for a more precise description of the time properties of the program and its environment. Semantics takes into account the infinity of the program execution cycle, the logic of process transition management from state to state and the interaction of processes with each other and with the environment. Extending the formal operational semantics of the Reflex language to annotations simplifies the proof of the correctness of the transformation approach to deductive verification of Reflex programs developed by the authors, transforming an annotated Reflex program to an annotated program in a very limited subset of the C language, by reducing a complex proof of preserving the truth of program requirements during the transformation to a simpler proof of equivalence of the original and the resulting annotated programs with respect to their operational semantics.

Application of artificial neural network to optimize sensor positions for accurate monitoring: an example with thermocouples in a crystal growth furnace

We propose to utilize artificial neural network (ANN) to optimize positions of a limited number of sensors for accurate monitoring, and demonstrate its effectiveness by a case study of four thermocouples in a directional solidification furnace. Our concept consists of choosing the positions with ANN that has the lowest loss from a multiplicity of ANNs, which were trained by the simulated temperature distributions along the outer crucible wall. Interestingly, the top ten ranks of accurate predictions contain positions around the crucible’s bottom to suggest the importance of measuring temperatures carefully around high-temperature gradients that is the boundary between different materials.

Experimental and numerical investigation of laboratory crystal growth furnace for the development of model-based control of CZ process

The presented study is focused on laboratory Czochralski crystal growth experiments and their mathematical modelling. The developed small-scale CZ crystal growth furnace is described as well as the involved automation systems: crystal radius detection by image recognition, temperature sensors, adjustable heater power and crystal pull rate. The CZ-Trans program is used to model the experimental results – transient, 2D axisymmetric simulation software primarily used for modelling of the industrial-scale silicon crystal growth process. Poor agreement with the experimental results is reached; however, the proven ability to perform affordable, small-scale experiments and successfully model their transient behavior, creates a possibility to develop new process automation solutions in the future.

In-situ measurement of CO gas concentration in a Czochralski furnace of silicon crystals

Power devices with high-performance require long carrier lifetimes within their silicon crystals. This paper reports the in-situ measurement of carbon monoxide in a Czochralski growth furnace of silicon single crystals. Moreover, this paper reports analytical investigation on contamination to silicon melt as functions of pressure in the furnace, argon gas flow velocity and gap width between the melt and a thermal shield. The experimental results show the carbon contamination to the melt increases when the pressure increases and the flow rate decreases. Increase of the gap width increases the contamination of carbon. We could explain the results qualitatively using a simple transport model.

The Role of Molybdenum Oxysulfide Rings in the Formation of Two-Dimensional Molybdenum Disulfide by Powder Vaporization.

Sulfurization of molybdenum trioxide by elemental sulfur through powder vaporization is a common method used for growth of molybdenum disulfide. Optimization of complexes between sulfur allotropes and molybdenum species using Density Functional Theory has revealed the molecular mechanism of sulfurization. Complete sulfurization of molybdenum trioxide to molybdenum disulfide requires at least three sets of nucleophilic addition-elimination reactions that generate the experimentally observed molybdenum oxysulfide intermediates along the reaction pathway. Each nucleophilic addition reaction of a sulfur allotrope to a molybdenum species gives rise to a molybdenum oxysulfide ring, which can dissociate into a more sulfurized molybdenum intermediate. At the typical growth temperatures used in powder vaporization, the equilibrium constants for these reactions are essentially unity. Thus, sulfurization is driven by excess sulfur and gas flow through the growth furnace.