PVT growth system and process for preparing 8-inch low-defect silicon carbide single crystal

Abstract

The invention discloses a PVT growth system and process for preparing 8-inch low-defect silicon carbide single crystals, and relates to the technical field of preparation and growth processes of silicon carbide single crystal materials, and the PVT growth system and process comprises the following steps: constructing a three-dimensional model of a growth device, carrying out space structure design and parameter setting on a heating unit, a heat insulation assembly and an airflow guide device, the thermal field structure is annularly and symmetrically distributed in the radial direction, and has a uniform temperature gradient area in the axial direction. By optimizing the thermal field structure design, matching the thermal expansion performance of the graphite assembly, implementing real-time temperature control and dynamic feedback adjustment, and introducing a gas transport guide and synchronous cooling strategy, the temperature field uniformity and thermal stress distribution in the crystal growth process are effectively controlled, the interface disturbance and crystal warping are inhibited, and the crystal growth quality is improved. The structural integrity and flatness of the silicon carbide single crystal are remarkably improved, the product yield is improved, and the processing difficulty and the manufacturing cost are reduced.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide single crystal material preparation and growth process technology, specifically to a PVT growth system and process for preparing 8-inch low-defect silicon carbide single crystals. Background Technology

[0002] The PVT growth method for preparing 8-inch low-defect silicon carbide single crystals refers to the process of using physical vapor transport (PVT) to vaporize silicon carbide raw materials and transport them to the seed crystal surface through sublimation-condensation under high temperature and controlled atmosphere conditions, thereby depositing and growing them into single-crystal silicon carbide (SiC) crystals. This method is particularly suitable for preparing large-size (e.g., 8-inch) high-quality SiC single crystals. Its core lies in precisely controlling the temperature field distribution, sublimation rate, atmosphere composition, and crystal interface stability, thereby reducing defects such as dislocations and microtubes within the crystal and improving the structural integrity and electrical performance of the single crystal. This process is currently the mainstream method for mass-producing large-size SiC single crystals in industry and is of crucial significance for the manufacture of high-power, high-frequency, and high-temperature electronic devices.

[0003] Existing technologies have the following shortcomings: In the existing PVT method for fabricating 8-inch low-defect silicon carbide single crystals, localized anomalies in the temperature gradient within the growth chamber can cause crystal warping. During high-temperature sublimation and deposition, if the temperature field distribution within the chamber is uneven, or if the thermodynamic stability is compromised due to inconsistent thermal expansion of the graphite structural components, the crystal growth interface will shift, gradually accumulating internal stress and ultimately leading to warping of the entire crystal. This deformation will severely affect subsequent wafer grinding, polishing, and planarization processes, reducing product yield and even causing the entire crystal to be scrapped, significantly increasing manufacturing costs and extending the production cycle. Therefore, controlling the uniformity of the temperature field and the thermal stability of the chamber structure is crucial to ensuring the stable growth of high-quality silicon carbide single crystals using the PVT method.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a PVT growth system and process for preparing 8-inch low-defect silicon carbide single crystals. By optimizing the thermal field structure design, matching the thermal expansion performance of graphite components, implementing real-time temperature control and dynamic feedback adjustment, and introducing gas transport guidance and synchronous cooling strategies, the system effectively controls the temperature field uniformity and thermal stress distribution during crystal growth, suppresses interface disturbances and crystal warping, significantly improves the structural integrity and flatness of silicon carbide single crystals, increases product yield, and reduces processing difficulty and manufacturing costs, thereby solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a PVT growth process for preparing 8-inch low-defect silicon carbide single crystals, comprising the following steps: A three-dimensional model of the growth device was constructed, and the spatial structure design and parameter setting of the heating unit, heat insulation component and airflow guiding device were carried out to make the thermal field structure circumferentially symmetrical in the radial direction and have a uniform temperature gradient region in the axial direction. Based on the thermal field structure, high-purity graphite materials with low thermal expansion coefficient differences are selected. The dimensions of each structural component are corrected and matched by the isothermal thermal expansion curve at the target working temperature to ensure that the thermal deformation of each structural component is coordinated and consistent under high temperature conditions. The sublimation source and seed crystal are respectively installed in the central area of ​​the thermal field structure and connected to their respective independent precision temperature control units. At the same time, independent thermocouples are set at the sublimation end and the crystallization end to collect the actual temperature of each area in real time. During crystal growth, temperature data collected by thermocouples is compared with a preset temperature gradient model, and the power output of the heating unit and the position of the shielding structure are adjusted in real time through a dynamic feedback control system. An inert gas flow is applied inside the growth chamber, and a controlled gas transport path is formed in the axial direction of the chamber by adjusting the gas flow rate and direction. The transport trajectory of the sublimation product is precisely guided by the airflow guiding device. When the silicon carbide single crystal grows to the set thickness, the operating temperature of the sublimation end and the crystallization end is gradually reduced at the same time, and synchronous cooling is carried out while maintaining a constant micro-temperature difference.

[0007] Preferably, in the process of constructing the three-dimensional model of the growth device, the finite element thermal field simulation technology is used to iteratively model and optimize the heating unit, heat insulation components and airflow guiding device. Based on the design constraint that the axial temperature difference fluctuation in the crystal growth region is less than ±3K, a symmetrically distributed isotherm model is constructed. Through heat flux density analysis, it is ensured that the equivalent thermal resistance ratio between the heating and insulation regions of the thermal field model meets the stable temperature difference control range, and that the circumferential thermal uniformity index reaches greater than 90%. Meanwhile, a biomimetic symmetric perturbation control structure is introduced into the three-dimensional structural model to further reduce edge heat loss and ensure that the entire thermal field region forms an axially gradual and radially symmetrical temperature field structure, avoiding the warping trend of the growth interface caused by thermal energy deflection.

[0008] Preferably, in the selection of high-purity graphite materials and the design of structural components, a comprehensive evaluation is conducted based on the material's coefficient of thermal expansion, thermal conductivity, Young's modulus, and thermal shock stability. By constructing a multi-parameter thermodynamic stability matrix, materials with low expansion variability within the working temperature range are selected. During the structural design process, the back-calculation matching method is adopted. Based on the predicted thermal expansion values ​​of each key node and the initial dimensions of the components, the compensation adjustment factor is calculated, and the dimensions of the support frame, heating cylinder wall, and inner liner sealing plate are prestressed. After processing, a high-temperature simulated prestressing loading experiment was conducted to verify the linear fit accuracy of all structural components under high-temperature coupling conditions, ensuring that the overall thermal stability of the assembled components is greater than 95%.

[0009] Preferably, the spatial position between the sublimation source and the seed crystal is precisely aligned and adjusted to ensure that the axial distance is controlled within ±0.5mm. The sublimation source is formed by pressing high-density silicon carbide raw materials and undergoes thermal pretreatment to remove volatile impurities; the seed crystal uses a highly oriented, low-dislocation single crystal wafer, which is double-sided polished and marked with laser to mark the growth initiation surface. In the construction of the temperature control system, miniature thermocouples are embedded in the sublimation source support substrate and the seed crystal carrier, respectively, and the temperature difference stability range of the control loop is set to within 3K. With the help of a high-frequency response PID temperature control algorithm, dynamic temperature difference tracking between the sublimation zone and the crystallization zone is achieved. The thermocouple response position is calibrated by the spatial coplanar method to ensure that the thermal coupling error is controlled within ±0.2K, thereby improving the thermal field symmetry and stability.

[0010] Preferably, the dynamic feedback control system makes decisions and controls by comparing the deviation between the set temperature gradient model and the actual temperature curve in real time, and using a hybrid algorithm that combines a fuzzy control rule base and a neural network prediction algorithm. The heating unit contains multiple sets of independent temperature-controlled resistors, and the power distribution is adjusted according to the regional thermal response coefficient; the shielding structure is driven by an electric linear drive device, and the dynamic micro-displacement of ±1mm in the longitudinal direction is achieved based on the interface speed feedback signal of the crystal growth stage. Temperature field data is automatically collected every 15 minutes during crystal growth, a temperature distribution trend curve is fitted, and the interface stability index is output to the control module. Instantaneous deviations caused by external disturbances are eliminated through exponential smoothing filtering, thereby achieving synchronous and stable control of interface growth rate and morphology.

[0011] Preferably, to verify the correlation between the rationality of the thermal field structure design and the stability of crystal growth, a simulation and evaluation model of the thermal field design parameters is constructed to evaluate the thermal field symmetry and gradient control capability. The specific steps are as follows: The temperature distribution of the target thermal field structure at different radial positions is calculated, and the radial temperature uniformity parameter is constructed based on this. The calculation expression is as follows: In the formula, It is an indicator of radial temperature non-uniformity. It is the maximum temperature among all radial measuring points. It is the minimum temperature among all radial measuring points. It is the arithmetic mean temperature of all radial temperature values. It is a set of temperature values ​​at different "radial positions" in the thermal field; The standard deviation of temperature variation along the axial direction in the crystal growth region is calculated to measure whether there is local non-uniformity in the thermal gradient. The calculation expression is as follows: In the formula, It is the first along the "axial" direction in the crystal growth cavity. Temperature values ​​at each measuring point It is the average value of all axial temperature measurement points. It is the number of axial measuring points. It is the standard deviation of axial temperature; Through fusion and Two indicators are used to construct a thermal field structure stability factor to comprehensively judge the overall stability level of the thermal field structure. The calculation expression is as follows: In the formula, It is a thermal symmetry correction factor. It is the thermal field structure stability factor; by As a criterion, design iteration and optimization are performed; when If the thermal field structure meets the standard for low warp growth of crystals, then the distribution of heat sources, the arrangement of insulation structures and the combination of materials need to be replanned to improve the thermal field symmetry and thermal gradient control capability.

[0012] Preferably, during the establishment of the axial gas transport path, the inert gas inlet pressure and outlet back pressure difference are set to 0.5 kPa-1.2 kPa, and the airflow is guided to a quasi-laminar state by combining the vortex rectifier module. The flow rate control module dynamically adjusts the gas flow rate through a high-precision mass flow meter to maintain the average axial flow rate within the range of 0.3 m / s to 0.8 m / s, ensuring that the sublimation products are transported to the crystallization region along the shortest path above the central axis of the cavity. The airflow guiding device is equipped with a porous buffer diffusion layer and a conical compression channel to uniformize the air pressure field and reduce flow dead zones. The thermal barrier reflective coating technology enhances the local thermal stability of the airflow, reduces the non-uniformity of the deposition rate caused by flow field disturbance, and improves the structural integrity of the crystal growth interface.

[0013] Preferably, in the temperature control of the crystal cooling stage, the sublimation source and the crystallization end are subjected to step cooling operation through a dual-channel independent temperature control system. The entire cooling process is divided into five cooling stages, and the difference in cooling rate between each stage is controlled within 2K / min. The crystal stress formation threshold is estimated by predictive temperature control algorithm, and the target temperature curve for each stage is set accordingly. During the cooling synchronization process, high heat capacity material is used to adjust the delay gradient change of the thermal buffer to maintain the stability of the micro temperature difference and prevent thermal shock. By monitoring the distribution of thermal stress on the crystal surface in real time, the timing of thermal stress release can be accurately determined, and a constant temperature holding procedure can be performed during the final cooling stage to complete the release of residual stress, ensuring that the final yield of the crystal exceeds 95%.

[0014] Preferably, to achieve simultaneous cooling and coordinated release of thermal stress during the later cooling stage of crystal growth, a time function model of thermal stress response is established, and a mathematical coupling analysis method is introduced to ensure optimal control of the cooling process in terms of structural integrity and thermal balance. The specific steps are as follows: By setting the sublimation source and the initial temperature of the crystallization end and Establish a synchronous cooling function group, define the sublimation source temperature and the crystallization end temperature respectively, and calculate the expression as follows: In the formula, It is the source of sublimation in time The actual temperature at that moment, It is the crystallization end in time The actual temperature at that moment, and These are the initial temperatures of the sublimation source and the crystallization end, respectively. and These are the linear cooling rates at the sublimation end and the crystallization end, respectively. Define the temperature difference between the two ends, and calculate it as follows: In the formula, It is the sublimation source and the crystallization end in time The absolute temperature difference; The instantaneous thermal stress response associated with temperature difference is established, and the calculation expression is as follows: In the formula, It is the crystal in time The instantaneous thermal stress experienced at a given moment. It is the Young's modulus of silicon carbide single crystal material in the cooling temperature range. It is the coefficient of thermal expansion of silicon carbide material; The cumulative thermal stress energy is obtained by integrating the thermal stress response, and the calculation expression is as follows: In the formula, It is a crystal from Until time Total thermal stress energy, It is a time variable; when At that time, the cooling process was considered safe, and the crystal was in a low-risk zone of thermal stress. This is the critical threshold for thermal stress failure in crystalline materials.

[0015] A PVT growth system for preparing 8-inch low-defect silicon carbide single crystals includes a thermal field structure modeling module, a thermal expansion matching and structure control module, a precision temperature control and thermal measurement acquisition module, a dynamic feedback control module, a gas transport control module, and a synchronous cooling and stress release module. The thermal field structure modeling module constructs a three-dimensional model of the growth device, performs spatial structure design and parameter setting for the heating unit, heat insulation components and airflow guiding device, so that the thermal field structure is circumferentially symmetrical in the radial direction and has a uniform temperature gradient region in the axial direction. The thermal expansion matching and structural control module, based on the thermal field structure, selects high-purity graphite materials with low thermal expansion coefficient differences, and combines the isothermal thermal expansion curves at the target working temperature to correct and match the dimensions of each structural component, ensuring that the thermal deformation of each structural component is coordinated and consistent under high temperature conditions. The precision temperature control and thermal measurement module installs the sublimation source and seed crystal in the central area of ​​the thermal field structure and connects them to their respective independent precision temperature control units. At the same time, independent thermocouples are set at the sublimation end and the crystallization end to collect the actual temperature of each area in real time. The dynamic feedback control module compares the temperature data collected by thermocouples with the preset temperature gradient model during crystal growth, and adjusts the power output of the heating unit and the position of the shielding structure in real time through the dynamic feedback control system. The gas transport control module applies inert gas flow inside the growth chamber and forms a controlled gas transport path along the axis of the chamber by adjusting the gas flow rate and direction. The airflow guiding device precisely guides the transport trajectory of the sublimation product. The synchronous cooling and stress relief module simultaneously reduces the operating temperature of the sublimation end and the crystallization end as the silicon carbide single crystal grows to the set thickness, performing synchronous cooling while maintaining a constant micro-temperature difference.

[0016] The technical effects and advantages provided by the present invention in the above technical solution are as follows: By introducing a circumferentially symmetrical and axially uniform thermal field structure design during PVT growth, coupled with high-purity graphite components with highly matched thermal expansion properties, and a real-time temperature control and dynamic feedback adjustment mechanism, the thermal stability and temperature control accuracy of the crystal growth environment can be significantly improved. At the same time, by using the directional guidance of the gas transport path and the synchronous cooling strategy under micro-differential temperature conditions, raw material segregation, interface disturbance, and thermal stress accumulation during the cooling stage are effectively suppressed, thereby avoiding structural deformation problems such as crystal warping. This ensures that the obtained silicon carbide single crystal has excellent flatness and integrity, improves wafer yield, and reduces the difficulty of subsequent processing and manufacturing costs. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 This is a flowchart of a PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to the present invention.

[0019] Figure 2 This is a schematic diagram of a PVT growth system for preparing 8-inch low-defect silicon carbide single crystals according to the present invention. Detailed Implementation

[0020] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that the description of this disclosure will be more complete and fully convey the concept of the exemplary embodiments to those skilled in the art.

[0021] This invention provides, for example Figure 1 The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals, as shown, includes the following steps: A three-dimensional model of the growth device was constructed, and the spatial structure design and parameter setting of the heating unit, heat insulation component and airflow guiding device were carried out to make the thermal field structure circumferentially symmetrical in the radial direction and have a uniform temperature gradient region in the axial direction. In the process of constructing the three-dimensional model of the growth device, the finite element thermal field simulation technology is used to iteratively model and optimize the heating unit, heat insulation components and airflow guiding device. Based on the design constraint that the axial temperature difference fluctuation in the crystal growth region is less than ±3K, a symmetrically distributed isotherm model is constructed. Through heat flux density analysis, it is ensured that the equivalent thermal resistance ratio between the heating and insulation regions of the thermal field model meets the stable temperature difference control range, and that the circumferential thermal uniformity index reaches greater than 90%. Meanwhile, a biomimetic symmetric perturbation control structure is introduced into the three-dimensional structural model to further reduce edge heat loss and ensure that the entire thermal field region forms an axially gradual and radially symmetrical temperature field structure, avoiding the warping trend of the growth interface caused by thermal energy deflection.

[0022] The core function of this step is to construct a three-dimensional thermal field model of the growth apparatus and optimize the structural design of the heating unit, insulation components, and airflow guiding device using finite element simulation technology. This ensures that the resulting thermal field exhibits both axial uniformity and radial symmetry in spatial distribution. The technical significance of this structural design lies in its ability to significantly reduce interface disturbances and thermal stress accumulation caused by temperature inhomogeneity during crystal growth, thereby effectively preventing morphological defects such as crystal warping. Using three-dimensional simulation analysis, the impact of different structural arrangements on thermal field uniformity can be assessed in advance, avoiding the waste of time and costs caused by trial and error in actual operations. Furthermore, the introduction of a temperature gradient model with circumferential symmetry and controllable axial temperature difference ensures a highly stable crystal growth environment, which is crucial for the single crystal growth of high-hardness and brittle materials like silicon carbide. This step, through parameter setting and isotherm construction, theoretically ensures the continuity and smooth transition of the thermal field, providing a physical basis for the stable development of the crystal growth interface and contributing to improved repeatability and consistency of the crystal growth process, ultimately leading to increased wafer yield.

[0023] Based on the thermal field structure, high-purity graphite materials with low thermal expansion coefficient differences are selected. The dimensions of each structural component are corrected and matched by the isothermal thermal expansion curve at the target working temperature to ensure that the thermal deformation of each structural component is coordinated and consistent under high temperature environment, thereby maintaining the thermodynamic stability of the growth cavity. In the selection of high-purity graphite materials and the design of structural components, a comprehensive evaluation is conducted based on the material's coefficient of thermal expansion, thermal conductivity, Young's modulus, and thermal shock stability. By constructing a multi-parameter thermodynamic stability matrix, materials with low expansion variability in the working temperature range (2100K-2400K) are selected. During the structural design process, the back-calculation matching method is adopted. Based on the predicted thermal expansion values ​​of each key node and the initial dimensions of the components, the compensation adjustment factor is calculated, and the dimensions of the support frame, heating cylinder wall, and inner liner sealing plate are prestressed. After processing, a high-temperature simulated prestressing loading experiment was conducted to verify the linear fit accuracy of all structural components under high-temperature coupling conditions, ensuring that the overall thermal stability of the assembled components is greater than 95%.

[0024] The main function of this step is to establish a thermally stable support system for the entire growth chamber under high-temperature conditions by selecting high-purity graphite materials based on their physical and thermodynamic properties and designing thermally matched structural components. The temperature involved in the growth of silicon carbide crystals exceeds 2000K. At this temperature, any structural component, due to inconsistent thermal expansion, can generate dimensional stress differences, potentially leading to localized thermal stress concentration points and causing micro-deformation or even cleavage of the crystal structure. Therefore, this step constructs a thermal deformation control matrix using multiple physical parameters such as the coefficient of thermal expansion and Young's modulus to ensure the overall thermal stability of the structure at the material level. The introduction of isothermal thermal expansion curve compensation and pre-stressing processing strategies during manufacturing not only ensures consistency in the direction of thermal deformation between structural components but also minimizes actual manufacturing errors through experimental feedback closed-loop correction. The application of this technology allows the thermal field structure to maintain dimensional accuracy and stress symmetry during long-term high-temperature operation, providing a solid mechanical support foundation for stable crystal growth, effectively extending equipment life and reducing the crystal defect rate caused by thermal instability.

[0025] The sublimation source and seed crystal are respectively installed in the central area of ​​the thermal field structure and connected to their respective independent precision temperature control units. At the same time, independent thermocouples are set at the sublimation end and the crystallization end to collect the actual temperature of each area in real time, so as to realize the control of the small temperature difference between the sublimation end and the crystallization end. The spatial position between the sublimation source and the seed crystal is precisely aligned and adjusted to ensure that the axial distance is controlled within ±0.5mm. The sublimation source is formed by pressing high-density silicon carbide raw materials and undergoes thermal pretreatment to remove volatile impurities; the seed crystal uses a highly oriented, low-dislocation single crystal wafer, which is double-sided polished and marked with laser to mark the growth initiation surface. In the construction of the temperature control system, miniature thermocouples are embedded in the sublimation source support substrate and the seed crystal carrier, respectively, and the temperature difference stability range of the control loop is set to within 3K. With the help of a high-frequency response PID temperature control algorithm, dynamic temperature difference tracking between the sublimation zone and the crystallization zone is achieved. The thermocouple response position is calibrated by the spatial coplanar method to ensure that the thermal coupling error is controlled within ±0.2K, thereby improving the thermal field symmetry and stability.

[0026] This step ensures precise control over the spatial position between the sublimation source and the seed crystal, and establishes a highly sensitive, fast-response temperature detection and control system, providing direct support for micro-temperature management in the crystal growth region. In physical vapor transport (PVT), the temperature difference between the sublimation end and the crystallization end is one of the key factors controlling the crystal growth rate and interface stability. If the temperature difference fluctuation range is too large, unstable fluctuations can easily occur at the crystallization interface, affecting the integrity of the crystal structure. This step, through micro-displacement installation precision control, a dual-region independent temperature control system, and highly sensitive thermocouple embedding technology, enables precise detection and feedback adjustment of minute temperature difference changes within each growth cycle. Especially after the thermocouple position is coplanarly calibrated, temperature feedback lag caused by thermal delay or misalignment is avoided, allowing the control system to respond to temperature difference changes more quickly. At the same time, the pre-calibration of the seed crystal position and state ensures that the crystal growth is in a thermally symmetrical state from the starting face, laying the foundation for low-defect growth of the entire single crystal.

[0027] During crystal growth, the temperature data collected by thermocouples is compared with the preset temperature gradient model. The power output of the heating unit and the position of the shielding structure are adjusted in real time through a dynamic feedback control system, thereby continuously and stably controlling the spatial position and morphology of the crystal growth interface. The dynamic feedback control system makes decisions and controls by comparing the deviation between the set temperature gradient model and the actual temperature curve in real time and using a hybrid algorithm that combines a fuzzy control rule base and a neural network prediction algorithm. The heating unit contains multiple sets of independent temperature-controlled resistors, and the power distribution is adjusted according to the regional thermal response coefficient; the shielding structure is driven by an electric linear drive device, and the dynamic micro-displacement of ±1mm in the longitudinal direction is achieved based on the interface speed feedback signal of the crystal growth stage. Temperature field data is automatically collected every 15 minutes during crystal growth, a temperature distribution trend curve is fitted, and the interface stability index is output to the control module. Instantaneous deviations caused by external disturbances are eliminated through exponential smoothing filtering, thereby achieving synchronous and stable control of interface growth rate and morphology.

[0028] This step introduces a dynamic feedback control system to monitor and adjust the temperature gradient changes during crystal growth in real time, thereby maintaining the spatial stability and morphological consistency of the growth interface. Its core function is to address temperature field deviations caused by unforeseen factors such as environmental disturbances, current fluctuations, and material consumption during the PVT process. By integrating neural network prediction and fuzzy control mechanisms, the control system possesses "learning + adaptation" capabilities, enabling it to predict future temperature field trends based on historical data and make timely adjustments. Furthermore, the displacement adjustment of the shielding structure provides a physical means for rebalancing the spatial thermal field, allowing for fine-tuning of local temperatures without affecting the power output of the main heat source. This multi-dimensional dynamic adjustment strategy avoids over-reliance on heat source power control, thus improving the stability and response efficiency of the system. The implementation of this step results in a smoother interface movement trajectory during crystal growth, effectively reducing crystallization interface collapse, distortion, and local coarsening caused by temperature disturbances, providing a real-time controllable means for obtaining high-quality crystals.

[0029] To verify the correlation between the rationality of the thermal field structure design and the stability of crystal growth, a simulation and evaluation model of the thermal field design parameters was constructed to assess the thermal field symmetry and gradient control capability. The specific steps are as follows: The temperature distribution of the target thermal field structure at different radial positions is calculated, and the radial temperature uniformity parameter is constructed based on this. The calculation expression is as follows: In the formula, This is an index of radial temperature inhomogeneity, expressed as a percentage (%). A smaller value indicates a more uniform thermal field in the circumferential direction, which is beneficial for reducing lateral distortion of the crystal. It is the maximum temperature among all radial measuring points, reflecting the hottest point. It represents the minimum temperature among all radial measurement points, reflecting the coldest point. It is the arithmetic mean temperature of all radial temperature values, reflecting the overall thermal level. It is a set of temperature values ​​at different "radial positions" in the thermal field, with units of Kelvin (K) or degrees Celsius (°C); these values ​​are obtained by arranging multiple thermocouples or thermal field simulation measurement points along the "radial direction" of the crystal growth cavity, and the collected data reflects whether the thermal energy is uniform in the circumferential direction; The standard deviation of temperature variation along the axial direction in the crystal growth region is calculated to measure whether there is local non-uniformity in the thermal gradient. The calculation expression is as follows: In the formula, It is the first along the "axial" direction in the crystal growth cavity. The temperature values ​​at several measuring points, arranged progressively from the sublimation source direction to the seed crystal end direction, reflect the thermal gradient in the depth direction. It is the average value of all axial temperature measurement points, representing the average thermal environment along the entire crystal growth path. The number of axial measuring points typically depends on the simulation accuracy of the equipment or the density of thermocouple placement. It is the axial temperature standard deviation. The smaller the value, the better the linearity of the thermal gradient, which helps to maintain the flatness and stability of the growth interface. This step is used to quantify the thermal uniformity along the entire crystal growth length.

[0030] Through fusion and Two indicators are used to construct a thermal field structure stability factor to comprehensively judge the overall stability level of the thermal field structure. The calculation expression is as follows: In the formula, This is the thermal symmetry correction factor, a dimensionless parameter ranging from 0.85 to 1.15. It is calculated based on a combination of factors, including isothermal symmetry and cavity structure geometric symmetry, in three-dimensional thermal field simulation. This is the thermal field structure stability factor. A larger value indicates a more symmetrical and stable overall thermal field, and it is a comprehensive score of the quality of the thermal field design of a PVT device; it is typically set in engineering. This is a stability limit; values ​​below this limit may lead to crystal instability or warping. by As a criterion, design iteration and optimization are performed; when If the thermal field structure meets the standard for low warp growth of crystals, then the distribution of heat sources, the arrangement of insulation structures and the combination of materials need to be replanned to improve the thermal field symmetry and thermal gradient control capability.

[0031] The core function of this step is to establish a systematic thermal field uniformity evaluation model to guide thermal field structure optimization and provide a quantitative reference standard for temperature control. This is achieved by calculating the radial temperature difference ratio (…). ), standard deviation of axial temperature difference ( Furthermore, by combining the thermal field symmetry correction factor, a comprehensive stability factor Ψ is constructed, which can be used to quantitatively analyze the consistency of the actual temperature distribution of the entire thermal field structure in three-dimensional space. The introduction of this model has two significant technical effects: firstly, it provides a data-driven feedback channel for thermal field design, allowing engineers to... The value can quickly determine whether the structural design meets the requirements for crystal growth stability; on the other hand, it can be obtained through dynamic simulation. and It can provide precise boundary conditions for subsequent temperature control strategies, especially as crystal size increases (e.g., 8 inches), where temperature difference control becomes significantly more difficult, and relying on intuition and experience for design will pose great risks. The setting of the Ψ factor provides a bridge between thermal field design and actual operating conditions, making structural debugging have verifiable quantitative basis, and is a key tool for improving the reliability of crystal growth equipment and crystal consistency.

[0032] An inert gas flow is applied inside the growth chamber, and a controlled gas transport path is formed in the axial direction of the chamber by adjusting the gas flow rate and direction. The transport trajectory of the sublimation product is precisely guided by the airflow guiding device to avoid raw material segregation and disturbance of the crystal growth interface. In the process of establishing the axial gas transport path, the inert gas inlet pressure and outlet back pressure difference are set to 0.5kPa-1.2kPa, and the airflow is guided to a quasi-laminar state by combining the vortex rectification module. The flow rate control module dynamically adjusts the gas flow rate through a high-precision mass flow meter to maintain the average axial flow rate within the range of 0.3 m / s to 0.8 m / s, ensuring that the sublimation products are transported to the crystallization region along the shortest path above the central axis of the cavity. The airflow guiding device is equipped with a porous buffer diffusion layer and a conical compression channel to uniformize the air pressure field and reduce flow dead zones. The thermal barrier reflective coating technology enhances the local thermal stability of the airflow, reduces the non-uniformity of the deposition rate caused by flow field disturbance, and improves the structural integrity of the crystal growth interface.

[0033] This step plays a crucial role in the active control of the atmosphere transport path within the growth chamber. By establishing a controlled inert gas flow system, it addresses the issue of uneven transport of sublimation products within the chamber. The PVT method essentially relies on the gas-phase migration and condensation of sublimated material from the high-temperature region to the low-temperature region; therefore, the gas flow trajectory directly determines the uniformity of material supply and interfacial stability. This step introduces a multi-stage flow management structure, including inlet pressure differential settings, vortex rectifying components, and adjustable conical channels, transforming the random, disordered natural convection into an axially controllable laminar flow mode. This directional flow significantly reduces gas disturbance at the interfacial front, preventing growth instability caused by sublimation product deviation and gas concentration asymmetry. Furthermore, the combination of compression channels and porous diffusion layers helps create a smooth velocity transition region, improving transport efficiency while reducing material fluctuations caused by turbulence. Overall, this step significantly improves gas-phase transport accuracy and material utilization, serving as a crucial guarantee for enhancing PVT growth consistency and crystal quality.

[0034] When silicon carbide single crystal grows to the set thickness, the working temperature of the sublimation end and the crystallization end is gradually reduced at the same time. Synchronous cooling is carried out on the basis of maintaining a constant micro-temperature difference to ensure that the crystal achieves growth termination and complete cooling under low thermal stress, and suppresses structural distortion caused by thermal stress. In the temperature control of the crystal cooling stage, the sublimation source and the crystallization end are subjected to step cooling operation through a dual-channel independent temperature control system. The entire cooling process is divided into five cooling stages, and the difference in cooling rate between each stage is controlled within 2K / min. The crystal stress formation threshold is estimated by predictive temperature control algorithm, and the target temperature curve for each stage is set accordingly. During the cooling synchronization process, high heat capacity material is used to adjust the delay gradient change of the thermal buffer to maintain the stability of the micro temperature difference and prevent thermal shock. By monitoring the distribution of thermal stress on the crystal surface in real time, the timing of thermal stress release can be accurately determined, and a constant temperature holding procedure can be performed during the final cooling stage to complete the release of residual stress, ensuring that the final yield of the crystal exceeds 95%.

[0035] This step aims to address the issues of thermal stress concentration and crystal structure distortion caused by abrupt temperature gradient changes during the cooling stage after silicon carbide crystal growth. A five-stage cooling program is implemented, with each stage controlling the overall thermal contraction of the crystal at an extremely low cooling rate, ensuring that internal stress is released gradually rather than accumulating abruptly. An independent temperature control system precisely controls the temperature of the sublimation source and the crystallization end separately, and thermal inertia is introduced using thermal buffer materials to further delay temperature fluctuations and improve thermal stability. The core of this step is to achieve a dual control strategy of "constant-temperature cooling" and "micro-difference synchronization." A predictive algorithm presets the upper limit of thermal stress and sets a corresponding cooling path, enabling dynamic monitoring and automatic release of residual stress. Simultaneously, a final cooling isothermal hold program ensures that the crystal completes the final stage of stress stabilization on a low-temperature platform, effectively reducing the risk of defects such as lattice dislocation, microcracks, and interface collapse caused by rapid cooling, significantly improving the integrity and yield of the final product.

[0036] To achieve simultaneous cooling and coordinated release of thermal stress during the later stages of crystal growth, a time function model of thermal stress response was established, and a mathematical coupling analysis method was introduced to ensure optimal control of the cooling process in terms of structural integrity and thermodynamic balance. The specific steps are as follows: By setting the sublimation source and the initial temperature of the crystallization end... and Establish a synchronous cooling function group, define the sublimation source temperature and the crystallization end temperature respectively, and calculate the expression as follows: In the formula, It is the source of sublimation in time The actual temperature at any given time, expressed in Kelvin (K). This is a key parameter controlling the cooling rate of the heat source in the sublimation zone. The temperature must decrease slowly and steadily to avoid disturbances to crystal surface growth caused by fluctuations in the sublimation rate. It is the crystallization end in time The actual temperature at any given time, measured in Kelvin (K), represents the temperature variation in the crystal growth region and plays a dominant role in the quality of crystallization termination and interface stability. and These are the initial temperatures of the sublimation source and the crystallization end, respectively, in Kelvin (K). They are typically between 2400K and 2600K, and serve as the initial temperature setpoint for the cooling stage. These values ​​are usually locked immediately after crystal growth and are used for calibrating the starting point of the cooling path. and These are the linear cooling rates of the sublimation end and the crystallization end, respectively, in K / min (Kelvin per minute), with a range of 1K / min to 5K / min. They determine the temperature drop within each unit of time and are the core adjustment parameters for synchronous cooling path control. Define the temperature difference between the two ends, and calculate it as follows: In the formula, It is the sublimation source and the crystallization end in time The absolute temperature difference describes the thermal gradient between the upper and lower ends and is the direct driving factor for the generation of thermal stress during the cooling process of the crystal. The control target is to keep it ≤3K. The smaller the value, the more beneficial it is to the stability of the crystal structure. The unit is K (Kelvin). This temperature difference directly controls the driving force of thermal stress during the cooling process. Exceeding the control threshold (usually set to 3K) will cause cracks or micro-warping in local areas of the crystal.

[0037] The instantaneous thermal stress response associated with temperature difference is established, and the calculation expression is as follows: In the formula, It is the crystal in time The instantaneous thermal stress experienced at a given moment, measured in Pa (Pascal), is used to analyze whether stress accumulation exceeding the material's limits will occur during the cooling process. It is the Young's modulus (elastic modulus) of silicon carbide single crystal material in the cooling temperature range, with the unit being Pa (Pascal). A typical value is approximately... It measures the stiffness of a material under stress and is a proportionality coefficient used in stress calculations. It is the coefficient of thermal expansion of silicon carbide, in units of: (per Kelvin), typical value: It reflects the material’s ability to change size with temperature and is the essential parameter of the heat source that generates stress. The above steps quantify the stress amplitude caused by the thermal gradient on the crystal structure per unit time.

[0038] The cumulative thermal stress energy is obtained by integrating the thermal stress response, and the calculation expression is as follows: In the formula, It is a crystal from Until time Total thermal stress energy, unit: (Pa squared multiplied by seconds) It is a time variable; when At that time, the cooling process was considered safe, and the crystal was in a low-risk zone of thermal stress. This is the critical threshold for thermal stress failure in crystalline materials.

[0039] Therefore, through continuous dynamic adjustment and The ratio, to achieve Keep constant, thus Throughout the cooling process, the temperature is kept below the safety limit to ensure the integrity of the crystal cooling termination process and a low stress level.

[0040] This step aims to establish a complete stress-temperature difference coupled simulation model for the cooling process, used to dynamically control the accumulation of thermal stress in the cooling path of the crystal terminal. This is achieved by setting a synchronous cooling function between the sublimation source and the crystallization end and constructing a micro-temperature difference model. This allows for real-time tracking of instantaneous temperature differences during the cooling process. Instantaneous thermal stress is then introduced based on this. ,Will This is transformed into measurable mechanical response parameters, thereby quantifying the thermal stress evolution process. Furthermore, this is achieved through a square integral function. Characterizing the time-accumulation properties of stress energy, ultimately reaching a critical threshold. As a criterion for judging the cooling process, a closed-loop stress control system is achieved throughout the entire process. The technical significance of this model lies in solving the control challenges faced during the "most crack-prone period" at the end of crystal growth, controlling physical quantities mathematically, and overcoming the limitations of traditional cooling methods that rely on linear cooling. This is achieved by adjusting the cooling rate parameters in real time. and This technology enables the crystal to complete stress release and thermal equilibrium in an environment with a constant micro-temperature difference, ensuring the integrity of the crystal structure and microscopic uniformity. It is a key technology to ensure high-yield production of large-size, low-defect crystals.

[0041] By introducing a circumferentially symmetrical and axially uniform thermal field structure design during PVT growth, coupled with high-purity graphite components with highly matched thermal expansion properties, and a real-time temperature control and dynamic feedback adjustment mechanism, the thermal stability and temperature control accuracy of the crystal growth environment can be significantly improved. At the same time, by using the directional guidance of the gas transport path and the synchronous cooling strategy under micro-differential temperature conditions, raw material segregation, interface disturbance, and thermal stress accumulation during the cooling stage are effectively suppressed, thereby avoiding structural deformation problems such as crystal warping. This ensures that the obtained silicon carbide single crystal has excellent flatness and integrity, improves wafer yield, and reduces the difficulty of subsequent processing and manufacturing costs.

[0042] This invention provides, for example Figure 2 The PVT growth system shown is for preparing 8-inch low-defect silicon carbide single crystals, including a thermal field structure modeling module, a thermal expansion matching and structure control module, a precision temperature control and thermal measurement acquisition module, a dynamic feedback control module, a gas transport control module, and a synchronous cooling and stress release module. The thermal field structure modeling module constructs a three-dimensional model of the growth device, performs spatial structure design and parameter setting for the heating unit, heat insulation components and airflow guiding device, so that the thermal field structure is circumferentially symmetrical in the radial direction and has a uniform temperature gradient region in the axial direction. The thermal expansion matching and structural control module, based on the thermal field structure, selects high-purity graphite materials with low thermal expansion coefficient differences, and combines the isothermal thermal expansion curves at the target working temperature to correct and match the dimensions of each structural component, ensuring that the thermal deformation of each structural component is coordinated and consistent under high temperature conditions. The precision temperature control and thermal measurement module installs the sublimation source and seed crystal in the central area of ​​the thermal field structure and connects them to their respective independent precision temperature control units. At the same time, independent thermocouples are set at the sublimation end and the crystallization end to collect the actual temperature of each area in real time. The dynamic feedback control module compares the temperature data collected by thermocouples with the preset temperature gradient model during crystal growth, and adjusts the power output of the heating unit and the position of the shielding structure in real time through the dynamic feedback control system. The gas transport control module applies inert gas flow inside the growth chamber and forms a controlled gas transport path along the axis of the chamber by adjusting the gas flow rate and direction. The airflow guiding device precisely guides the transport trajectory of the sublimation product. The synchronous cooling and stress relief module simultaneously reduces the operating temperature of the sublimation end and the crystallization end as the silicon carbide single crystal grows to the set thickness, performing synchronous cooling while maintaining a constant micro-temperature difference.

[0043] The present invention provides a PVT growth process for preparing 8-inch low-defect silicon carbide single crystals, which is achieved by the above-mentioned PVT growth system for preparing 8-inch low-defect silicon carbide single crystals. For details of the specific method and process of the PVT growth system for preparing 8-inch low-defect silicon carbide single crystals, please refer to the above-mentioned embodiment of the PVT growth process for preparing 8-inch low-defect silicon carbide single crystals, which will not be repeated here.

[0044] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0045] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

[0046] It should be noted that, in this document, the use of relational terms such as "first" and "second" is merely for distinguishing one entity or operation from another, and does not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0047] It should be understood that in the various embodiments of this application, the order of the above-mentioned processes does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0048] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0049] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0050] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0051] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0052] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0053] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A PVT growth process for preparing 8-inch low-defect silicon carbide single crystals, characterized in that, Includes the following steps: A three-dimensional model of the growth device was constructed, and the spatial structure design and parameter setting of the heating unit, heat insulation component and airflow guiding device were carried out to make the thermal field structure circumferentially symmetrical in the radial direction and have a uniform temperature gradient region in the axial direction. Based on the thermal field structure, high-purity graphite materials with low thermal expansion coefficient differences are selected. The dimensions of each structural component are corrected and matched by the isothermal thermal expansion curve at the target working temperature to ensure that the thermal deformation of each structural component is coordinated and consistent under high temperature conditions. The sublimation source and seed crystal are respectively installed in the central area of ​​the thermal field structure and connected to their respective independent precision temperature control units. At the same time, independent thermocouples are set at the sublimation end and the crystallization end to collect the actual temperature of each area in real time. During crystal growth, temperature data collected by thermocouples is compared with a preset temperature gradient model, and the power output of the heating unit and the position of the shielding structure are adjusted in real time through a dynamic feedback control system. An inert gas flow is applied inside the growth chamber, and a controlled gas transport path is formed in the axial direction of the chamber by adjusting the gas flow rate and direction. The transport trajectory of the sublimation product is precisely guided by the airflow guiding device. When the silicon carbide single crystal grows to the set thickness, the operating temperature of the sublimation end and the crystallization end is gradually reduced at the same time, and synchronous cooling is carried out while maintaining a constant micro-temperature difference.

2. The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to claim 1, characterized in that, In the process of constructing the three-dimensional model of the growth device, the finite element thermal field simulation technology is used to iteratively model and optimize the heating unit, heat insulation components and airflow guiding device. Based on the design constraint that the axial temperature difference fluctuation in the crystal growth region is less than ±3K, a symmetrically distributed isotherm model is constructed. Through heat flux density analysis, it is ensured that the equivalent thermal resistance ratio between the heating and insulation regions of the thermal field model meets the stable temperature difference control range, and that the circumferential thermal uniformity index reaches greater than 90%. Meanwhile, a biomimetic symmetric perturbation control structure is introduced into the three-dimensional structural model to further reduce edge heat loss and ensure that the entire thermal field region forms an axially gradual and radially symmetrical temperature field structure, avoiding the warping trend of the growth interface caused by thermal energy deflection.

3. The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to claim 1, characterized in that, In the selection of high-purity graphite materials and the design of structural components, a comprehensive evaluation is conducted based on the material's coefficient of thermal expansion, thermal conductivity, Young's modulus, and thermal shock stability. By constructing a multi-parameter thermodynamic stability matrix, materials with low expansion variability within the working temperature range are screened. During the structural design process, the back-calculation matching method is adopted. Based on the predicted thermal expansion values ​​of each key node and the initial dimensions of the components, the compensation adjustment factor is calculated, and the dimensions of the support frame, heating cylinder wall, and inner liner sealing plate are prestressed. After processing, a high-temperature simulated prestressing loading experiment was conducted to verify the linear fit accuracy of all structural components under high-temperature coupling conditions, ensuring that the overall thermal stability of the assembled components is greater than 95%.

4. The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to claim 1, characterized in that, The spatial position between the sublimation source and the seed crystal is precisely aligned and adjusted to ensure that the axial distance is controlled within ±0.5mm. The sublimation source is formed by pressing high-density silicon carbide raw materials and undergoes thermal pretreatment to remove volatile impurities; the seed crystal uses a highly oriented, low-dislocation single crystal wafer, which is double-sided polished and marked with laser to mark the growth initiation surface. In the construction of the temperature control system, miniature thermocouples are embedded in the sublimation source support substrate and the seed crystal carrier, respectively, and the temperature difference stability range of the control loop is set to within 3K. With the help of a high-frequency response PID temperature control algorithm, dynamic temperature difference tracking between the sublimation zone and the crystallization zone is achieved. The thermocouple response position is calibrated by the spatial coplanar method to ensure that the thermal coupling error is controlled within ±0.2K, thereby improving the thermal field symmetry and stability.

5. The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to claim 1, characterized in that, The dynamic feedback control system makes decisions and controls by comparing the deviation between the set temperature gradient model and the actual temperature curve in real time and using a hybrid algorithm that combines a fuzzy control rule base and a neural network prediction algorithm. The heating unit contains multiple sets of independent temperature-controlled resistors, and the power distribution is adjusted according to the regional thermal response coefficient; the shielding structure is driven by an electric linear drive device, and the dynamic micro-displacement of ±1mm in the longitudinal direction is achieved based on the interface speed feedback signal of the crystal growth stage. Temperature field data is automatically collected every 15 minutes during crystal growth, a temperature distribution trend curve is fitted, and the interface stability index is output to the control module. Instantaneous deviations caused by external disturbances are eliminated through exponential smoothing filtering, thereby achieving synchronous and stable control of interface growth rate and morphology.

6. The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to claim 1, characterized in that, To verify the correlation between the rationality of the thermal field structure design and the stability of crystal growth, a simulation and evaluation model of the thermal field design parameters was constructed to assess the thermal field symmetry and gradient control capability. The specific steps are as follows: The temperature distribution of the target thermal field structure at different radial positions is calculated, and the radial temperature uniformity parameter is constructed based on this. The calculation expression is as follows: In the formula, It is an indicator of radial temperature non-uniformity. It is the maximum temperature among all radial measuring points. It is the minimum temperature among all radial measuring points. It is the arithmetic mean temperature of all radial temperature values. It is a set of temperature values ​​at different "radial positions" in the thermal field; The standard deviation of temperature variation along the axial direction in the crystal growth region is calculated to measure whether there is local non-uniformity in the thermal gradient. The calculation expression is as follows: In the formula, It is the first along the "axial" direction in the crystal growth cavity. Temperature values ​​at each measuring point It is the average value of all axial temperature measurement points. It is the number of axial measuring points. It is the standard deviation of axial temperature; Through fusion and Two indicators are used to construct a thermal field structure stability factor to comprehensively judge the overall stability level of the thermal field structure. The calculation expression is as follows: In the formula, It is a thermal symmetry correction factor. It is the thermal field structure stability factor; by As a criterion, design iteration and optimization are performed; when If the thermal field structure meets the standard for low warp growth of crystals, then the distribution of heat sources, the arrangement of insulation structures and the combination of materials need to be replanned to improve the thermal field symmetry and thermal gradient control capability.

7. The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to claim 1, characterized in that, In the process of establishing the axial gas transport path, the inert gas inlet pressure and outlet back pressure difference are set to 0.5kPa-1.2kPa, and the airflow is guided to a quasi-laminar state by combining the vortex rectification module. The flow rate control module dynamically adjusts the gas flow rate through a high-precision mass flow meter to maintain the average axial flow rate within the range of 0.3 m / s to 0.8 m / s, ensuring that the sublimation products are transported to the crystallization region along the shortest path above the central axis of the cavity. The airflow guiding device is equipped with a porous buffer diffusion layer and a conical compression channel to uniformize the air pressure field and reduce flow dead zones. The thermal barrier reflective coating technology enhances the local thermal stability of the airflow, reduces the non-uniformity of the deposition rate caused by flow field disturbance, and improves the structural integrity of the crystal growth interface.

8. The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to claim 1, characterized in that, In the temperature control of the crystal cooling stage, the sublimation source and the crystallization end are subjected to step cooling operation through a dual-channel independent temperature control system. The entire cooling process is divided into five cooling stages, and the difference in cooling rate between each stage is controlled within 2K / min. The crystal stress formation threshold is estimated by predictive temperature control algorithm, and the target temperature curve for each stage is set accordingly. During the cooling synchronization process, high heat capacity material is used to adjust the delay gradient change of the thermal buffer to maintain the stability of the micro temperature difference and prevent thermal shock. By monitoring the distribution of thermal stress on the crystal surface in real time, the timing of thermal stress release can be accurately determined, and a constant temperature holding procedure can be performed during the final cooling stage to complete the release of residual stress, ensuring that the final yield of the crystal exceeds 95%.

9. The PVT growth process for preparing 8-inch low-defect silicon carbide single crystals according to claim 1, characterized in that, To achieve simultaneous cooling and coordinated release of thermal stress during the later stages of crystal growth, a time function model of thermal stress response was established, and a mathematical coupling analysis method was introduced to ensure optimal control of the cooling process in terms of structural integrity and thermodynamic balance. The specific steps are as follows: By setting the sublimation source and the initial temperature of the crystallization end and Establish a synchronous cooling function group, define the sublimation source temperature and the crystallization end temperature respectively, and calculate the expression as follows: In the formula, It is the source of sublimation in time The actual temperature at that moment, It is the crystallization end in time The actual temperature at that moment, and These are the initial temperatures of the sublimation source and the crystallization end, respectively. and These are the linear cooling rates at the sublimation end and the crystallization end, respectively. Define the temperature difference between the two ends, and calculate it as follows: In the formula, It is the sublimation source and the crystallization end in time The absolute temperature difference; The instantaneous thermal stress response associated with temperature difference is established, and the calculation expression is as follows: In the formula, It is the crystal in time The instantaneous thermal stress experienced at a given moment. It is the Young's modulus of silicon carbide single crystal material in the cooling temperature range. It is the coefficient of thermal expansion of silicon carbide material; The cumulative thermal stress energy is obtained by integrating the thermal stress response, and the calculation expression is as follows: In the formula, It is a crystal from Until time Total thermal stress energy, It is a time variable; when At that time, the cooling process was considered safe, and the crystal was in a low-risk zone of thermal stress. This is the critical threshold for thermal stress failure in crystalline materials.

10. A PVT growth system for preparing 8-inch low-defect silicon carbide single crystals, used to implement the PVT growth process for preparing 8-inch low-defect silicon carbide single crystals as described in any one of claims 1-9, characterized in that, It includes a thermal field structure modeling module, a thermal expansion matching and structure control module, a precision temperature control and thermal measurement acquisition module, a dynamic feedback control module, a gas transport control module, and a synchronous cooling and stress release module; The thermal field structure modeling module constructs a three-dimensional model of the growth device, performs spatial structure design and parameter setting for the heating unit, heat insulation components and airflow guiding device, so that the thermal field structure is circumferentially symmetrical in the radial direction and has a uniform temperature gradient region in the axial direction. The thermal expansion matching and structural control module, based on the thermal field structure, selects high-purity graphite materials with low thermal expansion coefficient differences, and combines the isothermal thermal expansion curves at the target working temperature to correct and match the dimensions of each structural component, ensuring that the thermal deformation of each structural component is coordinated and consistent under high temperature conditions. The precision temperature control and thermal measurement module installs the sublimation source and seed crystal in the central area of ​​the thermal field structure and connects them to their respective independent precision temperature control units. At the same time, independent thermocouples are set at the sublimation end and the crystallization end to collect the actual temperature of each area in real time. The dynamic feedback control module compares the temperature data collected by thermocouples with the preset temperature gradient model during crystal growth, and adjusts the power output of the heating unit and the position of the shielding structure in real time through the dynamic feedback control system. The gas transport control module applies inert gas flow inside the growth chamber and forms a controlled gas transport path along the axis of the chamber by adjusting the gas flow rate and direction. The airflow guiding device precisely guides the transport trajectory of the sublimation product. The synchronous cooling and stress relief module simultaneously reduces the operating temperature of the sublimation end and the crystallization end as the silicon carbide single crystal grows to the set thickness, performing synchronous cooling while maintaining a constant micro-temperature difference.

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