Silicon carbide growth method for rapidly preparing large-diameter crystal

Abstract

The invention relates to the technical field of silicon carbide growth methods for rapidly preparing large-diameter crystals, particularly discloses a silicon carbide growth method for rapidly preparing large-diameter crystals, and aims to solve the problems that a traditional physical vapor transport method is low in diameter expansion efficiency, long in period and high in cost, and defects such as polycrystal wrapping and stacking fault are easily generated. According to the method, a cylindrical silicon carbide seed crystal is adopted, the C surface of the seed crystal is completely shielded, and a gas-phase component is forced to be directionally conveyed to the side surface of the seed crystal along an annular conveying gas channel for radial epitaxial growth; the conveying air channel is jointly defined by porous graphite, a TaC isolation piece, a TaC air channel wall and a TaC porous plate, and the stability and uniformity of a gas-phase mass transfer path are achieved by accurately controlling the sizes, pore structures and assembly matching of all components. By adopting the technical scheme, the diameter of the crystal can be expanded from 150 mm to 310 mm or above through single growth, the diameter expanding efficiency is remarkably improved, meanwhile, microtube defects and polycrystalline nucleation are effectively inhibited, high-quality and large-size 4H type single crystal silicon carbide is obtained, and the method has excellent industrialization prospects.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic materials technology, specifically relating to a high-purity boron-doped silicon carbide powder and its solid-phase synthesis method. Background Technology

[0002] With the rapid development of third-generation semiconductor materials, silicon carbide (SiC) crystals, with their high breakdown electric field, high thermal conductivity, and excellent chemical stability, occupy an irreplaceable position in key fields such as high-voltage power devices, 5G RF front-ends, and sensors for extreme environments. However, due to the unique thermodynamic property of silicon carbide, which has no liquid phase at normal pressure, the industry generally uses the physical vapor transport (PVT) method for single crystal growth. This method has long faced core bottlenecks such as slow growth rate, low diameter expansion efficiency, and high crystal defect density. Especially in the process of evolving towards 8-inch and even 12-inch large-diameter substrates, the traditional diameter expansion process based on sheet-like seed crystals is constrained by the inherent limitations of the C-plane step flow growth mechanism, resulting in insufficient lateral expansion momentum and a high tendency to induce polycrystalline encapsulation and stacking faults in the edge region. This means that the single diameter expansion increment can usually only be maintained in the range of 10–15 mm, which seriously hinders the large-scale, low-cost manufacturing of high-quality, large-size silicon carbide wafers.

[0003] While existing technologies attempt to overcome these limitations through structural or process optimization, they still struggle to balance diameter expansion rate and crystal integrity. For example, CN115142132B proposes using vertically arranged rod-shaped seed crystals in conjunction with a rotational diameter expansion strategy to circumvent the size constraints of sheet-like seed crystals. However, its growth still relies on the surface diffusion mechanism of the top C-face, which not only fails to effectively avoid the formation of microtube defects but also results in low transport efficiency of gas phase components at the C-face edge, restricting the improvement of lateral growth rate. Simultaneously, the strong coupling between the temperature field and concentration field during rotation easily causes instability in the crystal edge morphology, affecting the yield of subsequent cutting, grinding, and polishing. Another approach, such as CN117107345B, constructs a multi-chamber raw material zone and a buffer chamber to directionally guide the gas phase flow to the outer edge of the seed crystal. Although this improves the control of local supersaturation, it still does not escape the inherent constraints of the low-activity growth mode of the C-face. The diameter expansion driving force remains limited, and the complex multi-zone heating system significantly increases the difficulty of controlling the process window, making it difficult to achieve stable and repeatable operation in a mass production environment.

[0004] Therefore, current silicon carbide crystal growth technology urgently needs a fundamental transformation: abandoning the reliance on the highly defect-sensitive C-face, reconstructing the lateral growth path, and simultaneously solving the synergistic challenges of gas phase transport efficiency and interface deposition kinetics. Only in this way can we achieve rapid diameter expansion from 150 mm seed crystals to crystals larger than 300 mm in a single operation, while ensuring the integrity of the single crystal, thus providing a reliable technical path for the efficient fabrication of next-generation ultra-large silicon carbide substrates. Summary of the Invention

[0005] The purpose of this invention is to provide a method for rapidly preparing large-diameter silicon carbide crystals, which can effectively solve the technical problems mentioned in the background art, such as low diameter expansion efficiency, high cost and long cycle due to the need for multiple gradual diameter expansions in the traditional physical vapor transport method during silicon carbide crystal growth, and defects such as polycrystalline encapsulation and stacking faults easily generated at the crystal edges.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A rapid method for preparing large-diameter silicon carbide crystals includes the following specific steps:

[0008] Step 1: Process the silicon carbide seed crystal into a standard cylindrical shape. The thickness of the cylindrical seed crystal is controlled between 10mm and 30mm, and the diameter is controlled between 150mm and 200mm to ensure that its geometric dimensions meet the tight fit requirements of the subsequent growth components.

[0009] Step 2: Set the crystal orientation of the cylindrical seed crystal as follows: <0001> The orientation and deviation range are controlled within ±1° to ensure that the crystal grows laterally along a specific orientation and avoids the limitation of lateral expansion by the C-plane step flow mechanism.

[0010] Step 3: The cylindrical seed crystal is supported by TaC isolators and TaC porous plates. The upper and lower end faces of the cylindrical seed crystal are tightly covered by the TaC isolators and TaC porous plates, so that the growth atmosphere mainly flows through the annular transport channel and acts on the side surface of the seed crystal, thereby blocking the possibility of the C-face as the main growth interface.

[0011] Step 4: Use TaC isolators made of TaC material or composite materials with TaC coating. The material has high temperature stability and anti-graphitization properties, which can effectively prevent silicon carbide vapor from the raw material area from depositing in non-target areas.

[0012] Step 5: Precisely adjust the thickness of the TaC separator according to the thickness of the cylindrical seed crystal, so that the overall thickness of the TaC separator and the cylindrical seed crystal are closely matched with the porous graphite component, ensuring the sealing and mechanical stability of the gas path structure.

[0013] Step 6: Use a TaC porous plate made of porous TaC material or a porous graphite substrate coated with TaC. This porous plate has the function of directionally guiding the diffusion of gas phase components and participates in the construction of a stable gas phase mass transfer path as part of the transport channel.

[0014] Step 7: A closed annular transport channel is formed by the porous graphite, TaC separator, TaC gas channel wall and TaC porous plate. This transport channel is specifically used to directionally transport the sublimated silicon carbide gas phase components to the side area of ​​the cylindrical seed crystal.

[0015] Step 8: The thickness of the porous graphite is set to 1.5mm to 5mm, the outer diameter is consistent with the inner diameter of the growth crucible, and the inner diameter is smaller than the outer diameter of the TaC isolator. During assembly, it is fitted with the TaC isolator without gaps to ensure that the airflow can only flow along the preset channel.

[0016] Step 9: The TaC gas channel wall is made of TaC material or a composite structure with graphite as the substrate and TaC on the surface. Its inner diameter is matched with the outer diameter of the TaC separator. After assembly, the width of the gas delivery channel is equal to the axial thickness of the cylindrical seed crystal, thereby limiting the spatial distribution of vapor deposition.

[0017] Step 10: Set up a graphite internal support, which is made of high-purity graphite, and form a closed cavity with the growth crucible to fill silicon carbide powder as a gas phase source. The support is located in the central area inside the transport channel.

[0018] Step 11: The height of the graphite inner support is determined based on the total thickness of the cylindrical seed crystal and the TaC isolator, ensuring that its top end contacts and is securely connected to the bottom of the TaC isolator. Its outer diameter is smaller than the outer diameter of the TaC isolator but larger than the inner diameter of the porous graphite, maintaining structural stability and clear spatial partitioning.

[0019] Step 12: The crystal growth process is initiated under high temperature and low pressure conditions. The silicon carbide powder is heated and sublimated to generate gaseous components such as Si and SiC2. These components pass through the TaC porous plate and porous graphite into the transport channel. Driven by the concentration gradient, they are uniformly transported along the annular channel to the side surface of the cylindrical seed crystal, and heteroepitaxial deposition occurs on its side surface, realizing one-time rapid radial diameter expansion growth of the crystal, and finally obtaining a complete single crystal with a diameter of more than 300 mm. At the same time, since the growth interface is far away from the C-plane, the formation of microtube defects is significantly suppressed.

[0020] Preferably, the initial diameter of the cylindrical seed crystal is 150 mm and the thickness is 20 mm, and the crystal diameter reaches 310 mm after one growth.

[0021] Preferably, the porosity of the TaC porous plate is 35% to 45%, and the average pore size is 10 μm to 30 μm.

[0022] Preferably, the density of the TaC separator is not less than 12 g / cm³. 3 It has a Vickers hardness greater than 20 GPa and maintains structural integrity at 2300℃.

[0023] Preferably, the thickness tolerance of the TaC separator is within ±0.1mm, and the surface roughness Ra of the mating surface is less than 0.8um.

[0024] Preferably, the cross-section of the transport channel is rectangular, with a width of 20mm and a height of 5mm.

[0025] Preferably, the porous graphite has a pore connectivity greater than 95% and a thermal conductivity of 80 W / (K·m) at room temperature.

[0026] Preferably, the inner surface roughness Ra of the TaC airway wall is less than 0.4 μm.

[0027] Preferably, the silicon carbide powder is an α-type polycrystalline powder with a particle size of 50 μm to 150 μm and a packing density of 1.8 g / cm³. 3 Up to 2.1 g / cm 3 .

[0028] Compared with the prior art, the present invention has the following outstanding differences and beneficial effects:

[0029] (1) For the first time, a large-sized cylindrical seed crystal (diameter 150–200 mm, thickness 10–30 mm) was used and the C-face was completely shielded, forcing the growth interface to transfer to the lateral non-polar surface, breaking through the physical limitation of the C-face step flow on lateral expansion;

[0030] (2) Construct an annular transport channel with a full TaC liner. All four walls are made of highly stable TaC material, which has the triple functions of airflow guidance, anti-parasitic deposition and structural support, significantly improving mass transfer controllability and process stability.

[0031] (3) By uniformly transporting gaseous components in the annular channel and directionally depositing them on the side surface, a one-time large-span diameter expansion from 150mm to 310mm is achieved, with a single diameter expansion amount of 160mm. This completely abandons the traditional step-by-step diameter expansion mode, significantly shortens the cycle and reduces costs.

[0032] (4) Because the growth interface is far from the C plane and is controlled in the TaC environment throughout the process, microtube defects are eliminated in the fundamental way, and polycrystalline and stacking faults are effectively suppressed to obtain high-quality ultra-large single crystals.

[0033] This invention not only solves the industry problem of balancing diameter expansion efficiency and crystal quality, but also provides a new technological paradigm for the large-scale preparation of 4–12 inch silicon carbide single crystals. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall technical solution architecture of a method for rapidly preparing large-diameter crystals of silicon carbide proposed in this invention.

[0035] Figure 2 This is a schematic diagram of the core principle framework of the present invention, which achieves one-time large-size radial diameter expansion by reconstructing the crystal growth interface and mass transfer path.

[0036] Figure 3 This is a flowchart illustrating the logical flow of the cylindrical seed crystal structure design, C-face shielding mechanism, and forced formation of the lateral growth interface in this invention.

[0037] Figure 4 This is a schematic diagram of the multi-level interaction relationship and the data flow of the circumferential uniform transport of gas phase components in the annular transport channel with full TaC lining in this invention.

[0038] Figure 5 This is a schematic diagram of a silicon carbide growth apparatus.

[0039] Figure label:

[0040] 6. Graphite internal support; 7. Porous graphite; 8. TaC isolation component; 9. Gas delivery channel; 10. TaC gas channel wall; 11. TaC porous plate; 12. Cylindrical seed crystal. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1-5 The present invention will be further described in detail below with reference to specific embodiments.

[0042] Currently, in the field of silicon carbide crystal growth, due to its thermodynamic characteristic of having no liquid phase at atmospheric pressure, the industry generally adopts the physical vapor transport method for single crystal preparation. However, this method has long faced core bottlenecks such as slow growth rate, low diameter expansion efficiency, and high crystal defect density. Especially in the evolution towards 8-inch and even 12-inch large-diameter substrates, the traditional diameter expansion process based on sheet-like seed crystals is constrained by the inherent limitations of the C-plane step flow growth mechanism, resulting in insufficient lateral expansion momentum and a high tendency to induce polycrystalline encapsulation and stacking faults in the edge region. Consequently, the single diameter expansion increment can usually only be maintained within the range of 10 to 15 mm, which seriously hinders the large-scale, low-cost manufacturing of high-quality, large-size silicon carbide wafers. To address the above technical problems, this invention proposes to achieve one-time large-size radial diameter expansion by reconstructing the crystal growth interface and mass transfer path, and applies it to a silicon carbide growth method for rapid preparation of large-diameter crystals.

[0043] refer to Figure 1The schematic diagram of the overall technical solution shows that the core of the method described in this invention lies in constructing an integrated growth system with a cylindrical seed crystal 12 as the center, an annular transport channel 9 lined with all-TaC as the main mass transfer mechanism, and the non-polar side surface as the only active growth interface. This system completely breaks away from the traditional C-face-dominated step-flow growth mode by forcibly shielding the upper and lower C-faces of the seed crystal and guiding the gas phase components to be uniformly transported circumferentially to the side surface, thus achieving a one-time rapid diameter expansion from an initial seed crystal of 150mm or more to a complete single crystal of 300mm or more.

[0044] Specifically, in step (1), the silicon carbide seed crystal is processed into a standard cylindrical shape. The thickness of the cylindrical seed crystal is controlled between 10 mm and 30 mm, and the diameter is controlled between 150 mm and 200 mm. This geometric configuration is significantly different from traditional sheet-like seed crystals (usually less than 5 mm thick). Its thickened design not only provides sufficient axial space for the lateral diameter expansion process, avoiding stress concentration and cracking risks caused by excessively rapid growth front advancement, but also meets the structural requirements for tight-fitting assembly with the TaC isolation component 8 and porous graphite 7 components. In a preferred embodiment, the initial diameter of the cylindrical seed crystal is set to 150 mm, and the thickness is 20 mm. After a single growth, the final diameter reaches 310 mm, with a diameter expansion increment of 160 mm, which is more than 10 times the single diameter expansion amount (10 to 15 mm) of the traditional method. The selection of these dimensional parameters is based on thermal field simulation and stress distribution calculations: when the thickness is less than 10 mm, the seed crystal is prone to bending deformation at 2300°C, compromising the flatness of the side surface; when the thickness exceeds 30 mm, it significantly increases material consumption and thermal inertia, prolongs the heating and steady-state establishment time, and reduces process economy. Therefore, a thickness range of 10 to 30 mm represents the optimal balance between mechanical stability, thermal response speed, and material cost.

[0045] Specifically, in step (2), the crystal orientation of the cylindrical seed crystal 12 is set as follows: <0001> The orientation deviation is controlled within ±1°. This crystal orientation setting is a prerequisite for ensuring lateral epitaxial growth of the crystal along a specific orientation, aiming to fundamentally circumvent the limitation of lateral expansion dynamics by the C-plane step flow mechanism. In practice, crystal orientation calibration is completed online using a high-precision X-ray diffractometer, with the actual deviation controlled within ±0.8° to ensure the orientation consistency of the entire side surface epitaxial growth. If the crystal orientation deviation exceeds ±1°, the side surface will exhibit mixed crystal plane characteristics (such as including nonpolar planes like {1-100} and {11-20}), leading to significant differences in growth rates in different regions, causing interface instability and dislocation multiplication. Strict control within ±1° ensures that the side surface is mainly composed of a single type of nonpolar crystal plane, with highly periodic surface atomic arrangement and low surface energy characteristics, which is conducive to the orderly adsorption and migration of Si and C atoms, thereby forming a highly intact epitaxial layer.

[0046] Specifically, in step (3), the cylindrical seed crystal 12 is supported by the TaC isolator 8 and the TaC porous plate 11, so that its upper and lower end faces (i.e., C-faces) are completely shielded and not exposed to the growth atmosphere, thereby forcing the growth behavior to occur only on the side surface of the seed crystal. See Figure 3 The diagram shows the design of the cylindrical seed crystal 12 and the logical flow of the C-face shielding mechanism. This structural feature is key to achieving non-C-face-dominated diameter expansion. The TaC isolator 8 is located below the seed crystal, directly contacting the bottom of the crucible or the lower support structure; the TaC porous plate 11 covers the seed crystal, and the two together hold the seed crystal, forming a physical barrier. Due to the extremely low SiC vapor reactivity and excellent chemical inertness of TaC material at high temperatures, it can effectively block the diffusion path of gaseous components to the C-face, eliminating parasitic deposition on the C-face. At the same time, this shielding mechanism eliminates the possibility of the C-face as a potential nucleation site, fundamentally cutting off the nucleation conditions for microtube defects—microtube defects usually originate from tiny pores or impurity-induced vacancy aggregation on the C-face. In this invention, the C-face is in an inert environment throughout, with no material exchange, so the microtube defect density is below the detection limit.

[0047] Specifically, in step (4), the thickness of the TaC isolator 8 is precisely adjusted according to the thickness of the cylindrical seed crystal 12, so that the overall thickness of the two combined forms a gapless fit with the porous graphite 7 component. This fit ensures the mechanical stability and gas path sealing of the entire growth assembly, preventing bypass airflow from interfering with the lateral growth interface. During assembly, the total height of the seed crystal and the TaC isolator 8 must be strictly matched with the depth of the mounting groove of the porous graphite 7, with the tolerance controlled within ±0.1mm. If there is a gap, the high-temperature airflow may escape from the gap, bypass the preset annular transport channel 9, and directly impact a local area on the side surface of the seed crystal, causing uneven distribution of supersaturation and inducing polycrystalline nucleation or fluctuations in the growth rate. Conversely, if there is an interference fit, excessive compressive stress may be generated during the heating stage due to the difference in thermal expansion coefficients, leading to the breakage of the brittle seed crystal. Therefore, gapless fit is a necessary structural prerequisite for achieving stable and controllable lateral growth.

[0048] Specifically, in step (5), a TaC separator 8 is used, which is made of high-density TaC material or a composite material with a TaC coating covering the entire surface, and has a density of not less than 12 g / cm³. 3 With a Vickers hardness greater than 20 GPa, it maintains structural integrity even at 2300℃, exhibiting both graphitization and corrosion resistance. These performance characteristics ensure that TaC spacers 8 can operate for extended periods in extreme growth environments without deformation, peeling, or chemical corrosion. High density (≥12 g / cm³) 3This effectively suppresses TaC grain coarsening and porosity formation at high temperatures, maintaining a dense microstructure; its high hardness (>20 GPa) endows it with resistance to mechanical shock and thermal shock. Furthermore, TaC's low wettability to SiC vapor makes it difficult for deposits to adhere to its surface, avoiding dimensional drift or blockage of airflow channels due to parasitic layer accumulation. In material preparation, pure TaC bulk materials can be prepared by hot pressing sintering, or a dense TaC coating of 50 to 100 μm thickness can be deposited on a graphite substrate via chemical vapor deposition (CVD), the latter reducing material costs while maintaining performance.

[0049] Specifically, in step (6), a porous TaC plate 11 is constructed from porous TaC material or a porous graphite 7 substrate coated with a dense TaC layer of 50 to 100 μm. The porosity is controlled between 35% and 45%, and the average pore size is 10 to 30 μm. This structural design allows for efficient penetration of gaseous components while effectively blocking particle migration in the raw material region. At the same time, its TaC surface inhibits heterogeneous nucleation, avoiding polycrystalline contamination. A porosity below 35% will significantly increase airflow resistance and reduce transport efficiency; a porosity above 45% will weaken mechanical strength and make it prone to collapse at high temperatures. The average pore size of 10 to 30 μm is based on Knudsen diffusion and molecular flow theory: at this scale, the mean free path of the main gaseous components such as Si and SiC2 is much larger than the pore size, the airflow is mainly viscous, and the pressure drop is controllable; at the same time, the pore size is much smaller than the particle size of the raw material powder (50 to 150 μm), which can effectively filter unsublimated particles and prevent them from entering the growth region and contaminating the crystal surface. The presence of the TaC coating further enhances the surface energy barrier, making it difficult for gaseous components to nucleate on its surface and ensuring that all deposition occurs only on the seed crystal side surface.

[0050] Specifically, in step (7), a closed annular gas transport channel 9 is formed by porous graphite 7, TaC separator 8, TaC gas channel wall 10, and TaC porous plate 11. All four walls of this gas transport channel 9 contain TaC material, thus constructing a gas-phase mass transfer channel with a full TaC lining. See also... Figure 4 The diagram illustrates the multi-level interaction relationship and circumferential uniform transport data flow of gas phase components in the all-TaC-lined annular transport channel 9. This channel significantly improves high-temperature chemical stability and airflow guidance accuracy. In a preferred embodiment, the transport channel 9 has a rectangular cross-section with a width of 20 mm and a height of 5 mm, resulting in a constant flow area of ​​100 square millimeters. This rectangular cross-section, combined with the annular layout, enables circumferential uniform gas supply and effectively suppresses local supersaturation. The channel wall is composed of independent TaC components or TaC-coated graphite, with its inner surface parallel to the seed crystal side surface and a spacing controlled between 1 and 3 mm to form a stable boundary layer flow. The all-TaC lining design eliminates the possibility of graphite reacting with SiC vapor at high temperatures to form a SiC parasitic layer, avoiding airflow attenuation caused by the shrinking of the channel cross-sectional area over time.

[0051] Specifically, in step (8), the inner surface of the TaC gas channel wall 10 is mirror-polished to a roughness Ra of less than 0.4 μm. This surface treatment further reduces gas flow resistance and inhibits polycrystalline nucleation. A rough surface can create local eddies and stagnant zones, causing gaseous components to deposit on the wall surface, which can not only block the channel but also potentially detach and become heterogeneous nucleation nuclei. After mirror polishing, the surface energy is uniformly distributed, and the atomic-level flatness makes it difficult for gaseous molecules to find stable adsorption sites, thereby ensuring that gaseous components are deposited in a controlled manner only at the highly active interface on the seed crystal side surface. The polishing process can use diamond polishing paste for step-by-step polishing, and finally use nano-sized alumina suspension for chemical mechanical polishing (CMP) to achieve the technical requirement of Ra < 0.4 μm.

[0052] Specifically, in step (9), the porous graphite 7 has a thickness of 1.5 to 5 mm, an outer diameter matching the inner diameter of the crucible, and an inner diameter smaller than the outer diameter of the TaC isolator 8. After assembly, it achieves surface contact sealing with the TaC isolator 8, with a fit tolerance of ±0.1 mm and a roughness Ra < 0.8 μm. This sealing structure ensures that the airflow is strictly confined within the preset annular channel, preventing leakage from the radial gap between the porous graphite 7 and the TaC isolator 8. As the outer boundary of the gas passage, the thickness of the porous graphite 7 needs to balance mechanical strength and thermal conductivity: if it is too thin (<1.5 mm), it is prone to deformation at high temperatures, damaging the seal; if it is too thick (>5 mm), it increases thermal resistance and affects the uniformity of the temperature field. The outer diameter fits tightly with the inner wall of the crucible to form the first seal; the inner diameter is slightly smaller than the outer diameter of the TaC isolator 8 to form the second radial seal. This dual sealing mechanism greatly improves the reliability of the gas passage.

[0053] Specifically, in step (10), a high-purity graphite inner support 6 is installed in the central region of the transport channel 9 to support the α-type SiC powder 5. Its height matches the total thickness of the seed crystal-TaC assembly, and its outer diameter is between the inner diameter of the porous graphite 7 and the outer diameter of the TaC separator 8, forming a stepped rigid support structure. This inner support not only provides a platform for supporting the raw material but also serves as a heat source at the center of the thermal field. Its outer diameter design ensures a clear geometric boundary between the raw material area and the transport channel 9, preventing the powder from directly contacting the channel wall. The particle size of the α-type SiC powder 5 is controlled between 50 and 150 μm, and the packing density is 1.8 to 2.1 g / cm³. 3 This particle size range ensures good sublimation kinetics: excessively fine powder is easily carried into the growth zone by the airflow, causing contamination; excessively coarse powder results in a slow sublimation rate, affecting growth efficiency. The packing density is controlled by vibration compaction; too high a density leads to poor internal heat transfer and the formation of a temperature gradient; too low a density results in insufficient gas production per unit volume, making it difficult to maintain the required supersaturation.

[0054] Specifically, in step (11), growth is initiated at 2100 to 2300°C and 10 to 100 Pa. SiC powder 5 sublimates to form gaseous components such as Si and SiC2, which sequentially penetrate the TaC porous plate 11 and porous graphite 7, entering the annular transport channel 9. This temperature and pressure window is the optimal process range determined based on the SiC phase diagram and the equilibrium concentration of the gaseous components. Below 2100°C, the sublimation rate is too low to provide sufficient gaseous flux; above 2300°C, the risk of graphite crucible corrosion and TaC volatilization is aggravated. Below 10 Pa, the mean free path of molecules is too large, and gaseous transport is dominated by free molecular flow, making it difficult to form a stable concentration gradient; above 100 Pa, the frequency of gaseous collisions increases, potentially leading to incomplete decomposition of SiC2 and the introduction of impurity phases. Under these conditions, SiC powder 5 first decomposes into active components such as Si(g), Si2C(g), and SiC2(g), with SiC2 considered the main crystal growth precursor.

[0055] Specifically, in step (12), the gas phase components are uniformly transported circumferentially to the side surface of the cylindrical seed crystal 12 under the drive of the concentration gradient, and heteroepitaxial deposition occurs at the non-polar lateral interface, realizing one-time continuous radial expansion growth of the crystal—this process completely departs from the C-plane growth mechanism, avoids the nucleation conditions of microtube defects, and finally obtains a complete single crystal with a diameter greater than 300 mm. Since the transport channel 9 is annular and has a constant cross-section, the gas phase components are highly uniformly distributed circumferentially, so that the supersaturation difference at each point on the seed crystal side surface is less than 5%, thereby achieving synchronous and uniform radial expansion. On the non-polar side surface, Si and C atoms are epitaxially grown in a two-dimensional island mode or a layered mode. Its growth rate is mainly controlled by surface diffusion and step merging dynamics, rather than the step flow mechanism of the C-plane. This mechanism has a higher tolerance for impurities and defects, and there are no helical dislocation nuclei required for microtube nucleation. Therefore, the obtained crystal is confirmed by Raman spectroscopy to be a single 4H crystal form, and X-ray topological imaging shows that the dislocation density is less than 1×10 4 The microtube defect density per square centimeter is below the detection limit. In 10 out of 12 repeated experiments, single crystals with a diameter greater than 300 mm were successfully obtained, with a success rate of 83.3% and an average diameter expansion rate of 0.8 mm per hour, which is more than 6 times that of traditional methods.

[0056] To further verify the engineering feasibility and industrialization potential of this invention, a specific application example is constructed: a 4H-SiC cylindrical seed crystal 12 with an initial diameter of 150 mm and a thickness of 20 mm, and a crystal orientation deviation of ±0.7° is used; a TaC separator 8 with a thickness of 20 mm and a density of 12.5 g / cm³ is used; a TaC porous plate 11 with a porosity of 40% and an average pore size of 20 μm is used; a transport channel 9 with a cross-section of 20 mm × 5 mm is used; and the raw material is 100 μm α-SiC powder 5 with a packing density of 2.0 g / cm³. The above components are arranged as follows: Figure 1The assembly shown is placed inside an induction heating PVT furnace, and the vacuum level is increased to 10. -3 After Pa, high-purity argon was introduced as the carrier gas. The temperature was increased to 2200°C at a rate of 50°C / min, while the furnace pressure was adjusted to 50 Pa. After holding at this temperature for 120 hours, it was naturally cooled. A complete single-crystal cylinder with a diameter of 312 mm and a thickness of 20 mm was finally obtained. After cutting, grinding, and polishing, a 300 mm diameter wafer was prepared. Its surface showed no visible polycrystalline material, cracks, or pores, and the half-width at half-maximum (FWHM) of the X-ray rocking curve was 35 arcseconds, indicating excellent crystal integrity. This example fully demonstrates that the present invention can operate stably on industrial-grade equipment, achieving efficient preparation of ultra-large-size silicon carbide single crystals.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for rapidly preparing large-diameter silicon carbide crystals, characterized in that: The specific steps include the following: Step 1: Process the silicon carbide seed crystal into a standard cylindrical shape. The thickness of the cylindrical seed crystal is controlled between 10mm and 30mm, and the diameter is controlled between 150mm and 200mm to ensure that its geometric dimensions meet the tight fit requirements of the subsequent growth components. Step 2: Set the crystal orientation of the cylindrical seed crystal as follows: <0001> The orientation and deviation range are controlled within ±1° to ensure that the crystal grows laterally along a specific orientation and avoids the limitation of lateral expansion by the C-plane step flow mechanism. Step 3: The cylindrical seed crystal is supported by TaC isolators and TaC porous plates. The upper and lower end faces of the cylindrical seed crystal are tightly covered by the TaC isolators and TaC porous plates, so that the growth atmosphere mainly flows through the annular transport channel and acts on the side surface of the seed crystal, thereby blocking the possibility of the C-face as the main growth interface. Step 4: Use TaC isolators made of TaC material or composite materials with TaC coating. The material has high temperature stability and anti-graphitization properties, which can effectively prevent silicon carbide vapor from the raw material area from depositing in non-target areas. Step 5: Precisely adjust the thickness of the TaC separator according to the thickness of the cylindrical seed crystal, so that the overall thickness of the TaC separator and the cylindrical seed crystal are closely matched with the porous graphite component, ensuring the sealing and mechanical stability of the gas path structure. Step 6: Use a TaC porous plate made of porous TaC material or a porous graphite substrate coated with TaC. This porous plate has the function of directionally guiding the diffusion of gas phase components and participates in the construction of a stable gas phase mass transfer path as part of the transport channel. Step 7: A closed annular transport channel is formed by the porous graphite, TaC separator, TaC gas channel wall and TaC porous plate. This transport channel is specifically used to directionally transport the sublimated silicon carbide gas phase components to the side area of ​​the cylindrical seed crystal. Step 8: The thickness of the porous graphite is set to 1.5mm to 5mm, the outer diameter is consistent with the inner diameter of the growth crucible, and the inner diameter is smaller than the outer diameter of the TaC isolator. During assembly, it is fitted with the TaC isolator without gaps to ensure that the airflow can only flow along the preset channel. Step 9: The TaC gas channel wall is made of TaC material or a composite structure with graphite as the substrate and TaC on the surface. Its inner diameter is matched with the outer diameter of the TaC separator. After assembly, the width of the gas delivery channel is equal to the axial thickness of the cylindrical seed crystal, thereby limiting the spatial distribution of vapor deposition. Step 10: Set up a graphite internal support, which is made of high-purity graphite, and form a closed cavity with the growth crucible to fill silicon carbide powder as a gas phase source. The support is located in the central area inside the transport channel. Step 11: The height of the graphite inner support is determined based on the total thickness of the cylindrical seed crystal and the TaC isolator, ensuring that its top end contacts and is securely connected to the bottom of the TaC isolator. Its outer diameter is smaller than the outer diameter of the TaC isolator but larger than the inner diameter of the porous graphite, maintaining structural stability and clear spatial partitioning. Step 12: The crystal growth process is initiated under high temperature and low pressure conditions. The silicon carbide powder is heated and sublimated to generate gaseous components such as Si and SiC2. These components pass through the TaC porous plate and porous graphite into the transport channel. Driven by the concentration gradient, they are uniformly transported along the annular channel to the side surface of the cylindrical seed crystal, and heteroepitaxial deposition occurs on its side surface, realizing one-time rapid radial diameter expansion growth of the crystal, and finally obtaining a complete single crystal with a diameter of more than 300 mm. At the same time, since the growth interface is far away from the C-plane, the formation of microtube defects is significantly suppressed.

2. The method for rapidly preparing large-diameter crystals of silicon carbide according to claim 1, characterized in that: The initial diameter of the cylindrical seed crystal is 150 mm and the thickness is 20 mm. After one growth, the crystal diameter reaches 310 mm.

3. The method for rapidly preparing large-diameter crystals of silicon carbide according to claim 1, characterized in that: The porosity of the TaC porous plate is 35% to 45%, and the average pore size is 10 μm to 30 μm.

4. The method for rapidly preparing large-diameter crystals of silicon carbide according to claim 1, characterized in that: The density of the TaC separator is not less than 12 g / cm³. 3 It has a Vickers hardness greater than 20 GPa and maintains structural integrity at 2300℃.

5. The method for rapidly preparing large-diameter crystals of silicon carbide according to claim 1, characterized in that: The thickness tolerance of the TaC separator is within ±0.1mm, and the surface roughness Ra of the mating surface is less than 0.8um.

6. The method for rapidly preparing large-diameter crystals of silicon carbide according to claim 1, characterized in that: The cross-section of the transport channel is rectangular, with a width of 20mm and a height of 5mm.

7. The method for rapidly preparing large-diameter crystals of silicon carbide according to claim 1, characterized in that: The porous graphite has a pore connectivity greater than 95% and a thermal conductivity of 80 W / (K·m) at room temperature.

8. The method for rapidly preparing large-diameter crystals of silicon carbide according to claim 1, characterized in that: The inner surface roughness Ra of the TaC airway wall is less than 0.4 μm.

9. The method for rapidly preparing large-diameter crystals of silicon carbide according to claim 1, characterized in that: The silicon carbide powder is an α-type polycrystalline powder with a particle size of 50 μm to 150 μm and a packing density of 1.8 g / cm³. 3 Up to 2.1 g / cm 3 .

Images