High Quality SiC Crystals Grown by the Physical Vapor Transport Method with a New Crucible Design

We investigated the effects of hydrogen addition to the growth process of SiC single crystal using sublimation physical vapor transport (PVT) techniques. Hydrogen was periodically added to an inert gas for the growth ambient during the SiC bulk growth. Grown 2”-SiC single crystals were proven to be the polytype of 6H-SiC and carrier concentration levels of about 1017/cm3 was determined from Hall measurements. As compared to the characteristics of SiC crystal grown without using hydrogen addition, the SiC crystal grown with periodically modulated hydrogen addition definitely exhibited lower carrier concentration and lower micropipe density as well as reduced growth rate.

Two SiC single crystal ingots were prepared using sublimation PVT techniques through the different process procedure and then their crystal quality was systematically compared, because the present research was focused to improve the quality of SiC crystal by modifying the initial stage of the PVT growth. Before the main growth step for growing SiC bulk crystal, initial stage period where growth rate was kept to relatively low rate of <10μm/h was introduced to conventional process procedure. N-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC was successfully fabricated. As compared to the characteristics of SiC crystal grown using the conventional schedule, the quality of SiC crystal grown with modifying the initial stage was significantly improved, exhibiting decrease of defect formation such as micropipe and polytype formation.

SiC crystal boules with different shapes were prepared using sublimation physical vapor transport technique (PVT) and then their crystal quality was systematically investigated. The temperature distribution in the growth system and the crystal shape were controlled by modification of crucible and insulation felt design, which was successfully simulated using “Virtual Reactor” for flat structure design and concave structure design. The SiC polytype proved to be the n-type 6H-SiC from the typical absorption spectrum of SiC crystal. The defect density of SiC crystal boules with concave structure was slightly lower than that of flat structure and the crystal quality of SiC crystal boules with both flat structure and concave structure was significantly improved as the SiC crystal grows during the PVT methods.

A recent study reported the rapid growth of SiC single crystals of ~1.5 mm/h using high-purity SiC sources obtained by recycling CVD-SiC blocks used as materials in semiconductor processes. This method has gained attention as a way to improve the productivity of the physical vapor transport (PVT) method, widely used for manufacturing single crystal substrates for power semiconductors. When recycling CVD-SiC blocks by crushing them for use as sources for growing SiC single crystals, the properties and the particle size distribution of the material differ from those of conventional commercial SiC powders, making it necessary to study their effects. Therefore, in this study, SiC single crystals were grown using the PVT method with crushed CVD-SiC blocks of various sizes as the source material, and the growth behavior was analyzed. Simulation results of the temperature distribution in the PVT system confirmed that using large, crushed blocks as the SiC source material generates a greater temperature gradient within the source compared to conventional commercial SiC powder, making it advantageous for rapid growth processes. Additionally, when the large, crushed blocks were vertically aligned, good crystal quality was experimentally achieved at high growth rates, even under non-optimized growth conditions.

Silicon carbide (SiC) has important application prospects in power and radio frequency devices. Obtaining SiC crystals with large diameters and high quality is still a challenge. In this work, the temperature field during SiC crystal growth is investigated through the physical vapor transport (PVT) method. Based on the numerical simulated results, an improved growing system is designed and perfect SiC crystals without any edge defects are successfully obtained. Furthermore, the X‐ray rocking curve, electrical resistivity, and dislocation density of the obtaining SiC crystals are evaluated.

A sublimation method using the SiC seed crystal and SiC powder as the source material is commonly adopted to grow SiC bulk single crystal. However, it has proved to be difficult to achieve the high quality crystal and the process reliability because SiC single crystal should be grown at very high temperature in closed system. In this study, SiC crystal boules were prepared with different angles in trapezoid-shaped graphite seed holders using sublimation physical vapor transport technique (PVT) and then their crystal quality was systematically investigated. The temperature distribution in the growth system and the crystal shape were varied with angles in trapezoid-shaped graphite seed holders, which was successfully simulated using 'Virtual Reactor'. The SiC polytype proved to be the n-type 6H-SiC from the typical absorption spectrum of SiC crystal. The micropipe densities of SiC wafers in this study were measured to be < <TEX>$100/cm^2$</TEX>. Consequently, SiC single crystal with large diameter was successfully achieved with changing angle in trapezoid-shaped graphite seed holders.

Aluminum nitride (AlN) bulk crystals, approximately 50.8mm in diameter and up to 5mm thickness, were grown by a physical vapor transport (PVT) method in a tantalum crucible. To investigate the effect of crucible materials, various crucible materials, a graphite and TaC-coated graphite and tantalum crucible were used for the AlN growth. XRD pattern of AlN crystal grown on SiC seed in the Ta-crucible exhibited only (00l) peaks, indicating that AlN single crystal was successfully grown on SiC seed. The interface structure between AlN and SiC crystals was observed by a high resolution TEM.

Growth of cubic SiC single crystals by the physical vapor transport technique

The growth of p-type SiC crystals with low resistivities should be investigated due to its application inn-channel Insulated Gate Bipolar Transistor (IGBT) fabrication. In this paper, the growth of 2 inch p-type 4H-SiC single crystals was carried out by conventional physical vapor transport (PVT) method with Al 4 C 3 as Al dopant source. Results showed that the aluminum atoms can be effectively incorporated into SiC crystals and the color of Al-doped 4H-SiCcrystals was blue. With the increase of aluminum content in SiC crystals, the color of Al-doped SiC became darker and eventually opaque. At heavy Al doping condition, the polytype of 4H-SiC was not stable and the grown crystals easily turned to 6H-SiC polytype. In addition, by adopting Al-N co-doping technique, p-type SiC single crystals with stable 4H-SiC polytype were grown. However, due to the difficulty in controlling the release of Al, Al-N co-doped single crystals turned to n-p-n type conduction crystals. Noncontact resistivity measurement showed the minimum resistivity of p-type 4H-SiC wafers was about 4149 mfi-cm.

The physical vapor transport (PVT) method is the most commonly applied growth technique for bulk SiC single crystals. Nowadays, the increasing demand of SiC substrates inevitably requires the adaption of PVT reactors to larger boule diameters. Since the boule quality and the single-crystal yield are primarily dependent on the thermal field inside the growth chamber and its stability, the control and optimization of the thermal conditions are the most crucial aspects to address. In this respect, the temperature difference along the seed, in the source and between source and seed, in addition to the growth temperature, are of particular interest. Due to the quasi-closed nature of the PVT system, in-situ measurements are hardly feasible, making numerical simulations the primary tool for analyzing the thermal field. But, since the high computational demand of these simulations restricts the number of cases that can be practically evaluated, numerical in-depth investigations are constrained. Attributed to this, the present study demonstrates an efficient way for constrained multi-objective optimization of the thermal field of PVT simulations by leveraging the correlation within the data through singular value decomposition (SVD). A 6-inch inductively heated PVT reactor is taken as a representative example and is optimized by combining machine learning models with numerical simulation data and optimization algorithms. In general, this approach enables the identification of optimal process parameters and reactor configurations, while revealing inherent tradeoffs between objectives and operational limitations, regardless of the PVT furnace operation principle (resistive or inductive) or seed crystal diameter (6-inch, 8-inch, etc.). Furthermore, it allows for an in-depth analysis of optimal settings, parameter sensitivities, interdependencies and solution robustness. • Machine learning model for thermal profile and thermal field prediction. • Machine learning model for growth rate prediction. • Constrained two- and three-objective optimization. • Evaluation of constrained multi-objective optimization results. • Sensitivity and uncertainty analysis.

Growth of SiC by PVT method with different sources for doping by a cerium impurity, CeO2 or CeSi2

The nucleation and growth of SiC polycrystals around seed crystals restrain the growth of SiC single crystals in the radial direction fabricated by physical vapor transport method in which the ordinary graphite is used as the crucible lid. Therefore, it is necessary to reduce the nucleation and growth of SiC polycrystals around the seed crystals. In order to effectively enlarge SiC single crystals, the authors propose the use of a graphite paper instead of graphite as the lid to restrain the nucleation of SiC polycrystals on the lid. The micrographs of SiC polycrystals on the graphite paper and graphite at the different growth stages show that the nucleation of SiC polycrystals on the graphite paper is more difficult than that on graphite. X-ray diffraction and scanning electron microscope investigations show that the graphite paper possesses high-macroscopic anisotropy, which induced that polycrystals can only grow on the surface of graphite paper and be easily removed.

A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method. The composite structure of the growing SiC crystal and graphite lid is considered in the model. The thermal expansion match between the crucible lid and SiC crystal is studied for the first time. The influence of thermal stress on the dislocation density and crystal quality is discussed.

In this paper, several new powder packing methods are proposed, and the COMSOL software is used to simulate the temperature distribution under different conditions. The influence of powder packing on the growth of SiC single crystal by physical vapor transport (PVT) is studied. The results show that the heat flux of the top region of the powder is increased by trapezoid graphite and graphite ring, the radial temperature gradient of the powder is reduced, which contributes to the improve the powder utilization rate. By covering the surface of the powder with a layer of porous graphite filter, the recrystallization on the surface of the powder is inhibited, the defects of carbon inclusion and thermal stress in the SiC crystal are reduced, and the growth quality and growth rate of the SiC crystal are obviously improved. The simulation results were verified by experiment, and the results agrees well with experiment.

Undoped and V-doped 6H—SiC single crystals have been grown by the physical vapor transport method. The V concentration is determined to be 3.76 × 1017 at/cm3 and 6.14 × 1017 at/cm3 by secondary ion mass spectrometry for low V-doped and high V-doped SiC samples, respectively. The undoped 6H—SiC shows diamagnetism, while the V-doped 6H—SiC exhibits weak ferromagnetism. The lower V-doped sample shows stronger ferromagnetism compared to that of the higher V-doped sample. However, the structural characterization indicates that the lower V-doped SiC has a relative poor crystalline quality. It is found that both V dopants and defects are essential for introducing ferromagnetic exchange in V-doped SiC single crystals.