Kaspars Dadzis

Kaspars Dadzis
Leibniz Institute for Crystal Growth | IKZ · Classical Semiconductors

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51
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Introduction

Publications

Publications (51)
Presentation
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The Czochralski (CZ) process is one of the most common techniques used to grow single crystals, that are the basis of many technologies such as computer chips, solar cells or power electronics. It involves a variety of physical phenomena from heat transfer to thermal stresses. Various simulation models investigating CZ growth have been published [1...
Article
Full-text available
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 therma...
Article
The melt flow plays a key role in the Czochralski (Cz) growth of silicon crystals, and in-situ measurement data are crucial for efficient process development. We present new low-temperature model experiments and numerical simulations for Cz type melt flow studies. A novel cylindrical setup is equipped with a traveling magnetic field (TMF), and with...
Presentation
Full-text available
Crystal growth simulations involve a variety of physical phenomena, e.g., heat transfer, gas and melt flows, electromagnetism and thermal stresses. The Finite element (FEM) and Finite volume methods (FVM) have been selected as the main simulation tools for a new crystal growth model. Currently, 2D axisymmetric heat transfer including radiation, pha...
Article
Full-text available
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 te...
Presentation
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Presentation at DKT 2021 Conference. File will be made available upon request.
Presentation
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Presentations slides available on request.
Presentation
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MODEL EXPERIMENTS FOR HEATER CONCEPTS IN CZOCHRALSKI CRYSTAL GROWTH PROCESSES Keywords: multiphysics, crystal growth, Czochralski method, model experiment, induction heater
Presentation
Full-text available
For the application of Elmer FEM in crystal growth simulation, a new Python interface pyelmer has been developed at the Leibniz Institute for Crystal Growth. It uses an object-oriented approach to manage the dependencies between materials, geometric bodies, boundaries, solvers, etc. In combination with the already available Python interface of the...
Presentation
Full-text available
The NEMOCRYS project in the group “Model experiments” at the IKZ funded by an ERC Starting Grant aims at profoundly validated numerical models for crystal growth. These processes involve a variety of coupled physical phenomena such as heat transfer including radiation and phase change, electromagnetism, melt- and gas flows and thermal stresses. Num...
Presentation
Full-text available
The NEMOCRYS project in the group “Model experiments” at the IKZ develops an open-source-based framework for coupled multiphysics simulation in crystal growth. Currently, Gmsh for FEM mesh generation and Elmer to solve the heat transfer problem including inductive heating are applied. These tools are wrapped in an easy-to-use python interface that...
Code
The pyelmer package provides a simple object-oriented way to set up Elmer FEM simulations in Python.
Presentation
Full-text available
Short presentation of the new Junior Research Group at the IKZ
Presentation
The NEMOCRYS project funded by an ERC Starting Grant aims at the development of profoundly validated numerical models for crystal growth processes using the Czochralski (CZ) and Floating Zone (FZ) methods. These growth processes usually involve very high temperatures and have high requirements on the degree of purity, which prevents in-depth measur...
Presentation
Full-text available
See the attached abstract, presentation slides and recording for further information.
Article
Based on own previous studies on dislocation generation in FZ- silicon crystals and in order to verify the location and conditions of dislocation generation and spreading, in the current work we present results from a model experiment using a measurement set-up close to the FZ process. Here, an as-grown dislocation-free FZ crystal with a diameter o...
Article
Full-text available
The growth of silicon crystals from a melt contained in a granulate crucible significantly differs from the classical growth techniques because of the granulate feedstock and the continuous growth process. We performed a systematic study of impurities and structural defects in several such crystals with diameters up to 60 mm. The possible origin of...
Article
Full-text available
In the present paper, a lumped parameter model for the novel Silicon Granulate Crucible (SiGC) method is proposed, which is the basis for a future model‐based control system for the process. The model is analytically deduced based on the hydromechanical, geometrical, and thermal conditions of the process. Experiments are conducted to identify unkno...
Experiment Findings
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This is a model experiment for Czochralski growth and a challenging test case for multi-physics simulations. The attached PDF file contains a description of the experimental setup and main results. The attached MP4 file contains a video of the growth process (1h 40m real time).
Presentation
The main goal of this presentation is to show how could YOU learn doing numerical simulation of crystal growth by yourself. The focus is on: 1) macroscopic aspects of crystal growth (from the melt); 2) Focus on physical understanding (instead of numerical methods). I consider Czochralski growth of tin as a case study and discuss experimental result...
Presentation
Full-text available
Many technologically relevant crystalline materials are produced in complex high-temperature processes involving a large variety of physical phenomena such as heat transfer including radiation and phase change, electromagnetism, melt and gas flows, thermal stresses. Numerous specialized or general-purpose simulation tools (e.g., Comsol, OpenFOAM) h...
Article
Full-text available
The concept of a physical model experiment is introduced and discussed in the context of melt and gas flows in bulk crystal growth processes. Such experiments allow one to "extract" selected physical phenomena from the full complexity of a real crystal growth process and “transfer” them to material systems with an easier access for experimental mea...
Article
The results of solidification experiments with gallium in a square-based 220 × 220 mm² container under the influence of alternating and travelling magnetic fields are presented. Such experiments are relevant for the growth of multi-crystalline silicon ingots for solar cells using directional solidification. The time-dependent magnetic fields are ge...
Article
A mathematical model of global 3D heat transfer in floating zone silicon single crystal growth process is used to predict the shape of the open melting front of the feed rod. The model is validated using measurement data from research-scale growth experiments. Shape profiles of the open melting front are obtained from the feed rod leftover using a...
Conference Paper
Full-text available
The granulate crucible method (Si-GC) has been proposed recently to produce monocrystalline silicon crystals for solar cell applications in particular [1–4]. This method attempts to avoid several drawbacks of the classical Czochralski and float zone growth techniques pushing the limits for impurity contents and process costs.
Conference Paper
Full-text available
Silicon growth from melt in a granulate crucible (Si-GC) is a novel concept to obtain crystals with a quality similar to Float Zone (FZ) Si at low feedstock costs [1-2]. For growth of crystals with well-defined shape, suitable process parameters can be identified by numerical simulation. In this work, a transient 2D numerical model implemented in C...
Article
A high energy conversion and cost efficiency are keys for the transition to renewable energy sources, e.g. solar cells. The efficiency of multi-crystalline solar cells can be improved by enhancing the understanding of its crystallization process, especially the directional solidification. In this paper, a novel measurement system for the characteri...
Conference Paper
Full-text available
A new method for silicon crystal growth using granulate as feedstock material has been proposed recently. This method bears resemblance to the well-known float zone growth but also places new challenges for both hardware design and numerical modeling. In this study we focus on the high-frequency induction heating. We compare and validate numerical...
Article
This paper describes novel equipment for model experiments designed for detailed studies on electromagnetically driven flows as well as solidification and melting processes with low-melting metals in a square-based container. Such model experiments are relevant for a validation of numerical flow simulation, in particular in the field of directional...
Article
The variety of physical phenomena in crystal growth processes requires diverse software tools for the numerical simulations. Both, dedicated 2D or 3D ready-to-use software for coupled simulations of a crystallization furnace and general-purpose 3D simulation packages have been used in the literature. This work proposes a general strategy for model...
Conference Paper
Full-text available
A method for residual stress measurements on large silicon samples is described. It combines strain gauge measurements in combination with the dissection of the gauge area. We report about tests and our experience with the technique and apply it on flat boards cut out of large ingots. Measurements on several boards from the same ingot are used to e...
Article
The Alexander-Haasen model is applied for the analysis of dislocation dynamics in quasi-mono crystalline silicon. Model constants are re-calibrated using stress–strain measurements on small silicon samples under uniaxial compression. It is observed that the activation energy may decrease at low temperatures and the hardening parameter generally inc...
Article
Small-scale model experiments for directional solidification processes are performed using a gallium volume with a square horizontal cross-section and dimensions of 10×10×7.5 cm3. A heater at the top and a cooler at the bottom generate a vertical temperature gradient while an external coil system produces a traveling magnetic field (TMF) leading to...
Article
Investigating the complex interaction of electrically conductive fluids and magnetic fields is relevant for a variety of applications from basic research in magnetohydrodynamics (MHD) to modeling of industrial processes involving metal melts, such as steel casting and crystal growth. However, experimental studies in this field are often limited by...
Conference Paper
Full-text available
Directional solidification (DS) is a well-established crystallization technology to produce polycrystalline or quasi-mono crystalline silicon ingots for photovoltaic applications. Before the crystallization process the silica crucible is charged with irregular shaped silicon feedstock typically resulting in a filling degree of 50 to 60%. Hence, the...
Article
The role of various growth and process conditions (Lorentz force, temperature gradients in the melt and the crystal, steady-state crystallization velocity) in directional solidification of multicrystalline silicon in a traveling magnetic field is analyzed for a research-scale furnace (melt size of 22×22×11 cm3). The influence on the melt flow patte...
Article
A new experimental setup containing a GaInSn melt with a square horizontal cross section of 10×10 cm2 and a variable melt height up to 10 cm has been developed. The melt is positioned in the center of a coil system generating a traveling magnetic field (TMF). Using a cooling system at the bottom and a heating system at the top of the melt, a vertic...
Article
Full-text available
Directional solidification is an important process for fabricating large multicrystalline silicon ingots. The complex 3D melt flows during solidification can be influenced by magnetic fields and are usually investigated in model experiments using 1D ultrasound Doppler measurements and extensive sensor traversing. We present a dual-plane, two-compon...
Article
Directional solidification of large multi-crystalline silicon ingots is a distinctly unsteady process with a complex interaction between melt flow, crystallization interface, and species transport. Both the different time-scales and the three-dimensional character make numerical simulations of this process a challenging task. The complexity of such...
Article
Low-temperature model experiments and 3D, time-dependent flow simulations with relevance to the melt motion during directional solidification of multicrystalline silicon under a traveling magnetic field are presented. The influence of the inductor current, the relative inductor–melt position, and the melt height on the flow pattern and velocity is...
Article
Full-text available
In numerical simulations of the floating-zone crystal growth process, the shape of phase boundaries is unknown beforehand and must be obtained as a part of the solution. One of the factors, which may influence the shape of phase boundaries significantly, is convective heat transfer in the molten zone. The present paper offers an analysis based on m...
Article
Full-text available
During the floating zone silicon single crystal growth by the needle-eye technique, the melting of the polycrystalline feed rod is ensured by a high-frequency inductor. It gives rise to electromagnetic (EM) forces in the skin layer at the free surface of the molten zone, which may influence the melt flow very distinctly. In the present paper two ap...
Article
The paper proposes Monte-Carlo method-based 2D and 3D models of vacancies and interstitials in a cubic crystal. The model exploits the concept of lattice gas with covalent bounds between neighbour nodes. Two lattices shifted by half-period serve as nodes for atoms of the main crystal and interstitials. Distribution of particles between both lattice...
Article
A new Monte Carlo 2D model for vacancies and interstitials in a cubic crystal is proposed. These defects are modelled using the concept of the shifted lattice for interstitials in the base lattice and of covalent bonds. It is shown that at higher temperatures this model leads to the liquid structure of the material. Using Monte Carlo simulations th...
Article
Full-text available
Introduction. The floating zone (FZ) process with the needle-eye technique is widely used for the growth of large silicon single crystals for the high-tech electronics industry. The quality of the grown crystals as well as overall stability of the growth process is influenced by the motion of liquid silicon in the molten zone. This paper presents a...

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Projects (2)
Project
*** NEMOCRYS: Next Generation Multiphysical Models for Crystal Growth Processes *** Crystalline materials are indispensable for the contemporary world and silicon crystals in particular have enabled the technological progress from first transistors to quantum computers. Such crystals are produced in high-temperature processes with a permanent demand to improve both material quality and efficiency of mass production. The high complexity of the growth processes involving various physical phenomena from electromagnetism to fluid dynamics as well as the limited possibilities of direct measurements make process optimization very challenging. Numerical simulation is often used, but due to limited accuracy of the models, experimental trial-and-error still dominates in practice as I have directly experienced while developing crystal growth methods both on research and industrial scales for more than a decade. There is a series of fundamental assumptions in multiphysical models that have been used for many crystal growth processes of various materials but have never been thoroughly validated. I propose to build a general experimental platform (MultiValidator) to address these challenges and, for the first time, to consider the complete physical complexity of a real growth process. A unique crystal growth setup will be developed for a model material (e.g., Ga) to enable low working temperatures, relaxed vacuum-sealing requirements and easy experimental access for various measurement techniques simultaneously (e.g., flow velocity and thermal stress fields). In this way, a new level of physical understanding and a new generation of multiphysical models for crystal growth processes will be established. The following paradigm change in the way how we observe, describe and develop crystal growth processes and similar complex multiphysical systems will minimize the necessary experimental cycles and open new horizons for a scientific analysis as well as for smart process control, for example, within the Industry 4.0 initiative.
Project
Si single crystal growth from melt in a Si granulate crucible (Si-GC) is a novel concept to obtain dislocation-free crystals without contamination from a crucible material. The achievable purity depends only on the purity of the fluidized bed granules used as a low-cost feedstock material. We investigate the potential for a stable growth process for large-diameter crystals with a quality similar to Float-Zone Si.