Thermal field structure capable of dynamically adjusting temperature gradient distribution for silicon carbide crystal growth

Abstract

The invention relates to the technical field of silicon carbide crystal growth, in particular to a silicon carbide crystal growth thermal field structure capable of dynamically adjusting temperature gradient distribution, which comprises a multi-layer thermal insulation component, a crucible and a dynamic adjusting mechanism. The thermal insulation cylinder adopts a double-layer design, an outer sleeve can move axially, the diameters of the upper and lower parts of an inner cylinder are gradually changed, and the temperature gradient is accurately controlled by combining a thermal field lifting function. Thermal field parameters are optimized by introducing a temperature gradient mathematical model, the sleeve position and lifting parameters are dynamically adjusted to meet the requirements of different growth stages, and the edge defects of the seed crystal are effectively inhibited. The crystal growth quality and efficiency are improved, the equipment structure is simplified, the manufacturing cost is reduced, the device is suitable for growth of silicon carbide crystals of various specifications, and the requirement for high-performance materials is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material preparation, and in particular relates to a thermal field structure for silicon carbide crystal growth capable of dynamically adjusting temperature gradient distribution. Background Art

[0002] Silicon carbide (SiC) crystals, as third-generation wide-bandgap semiconductor materials, have broad application prospects in high-voltage, high-current, and high-temperature power devices due to their excellent performance. However, during the physical vapor transport (PVT) growth of SiC crystals, precise control of the thermal field temperature gradient distribution has always been a key factor affecting crystal quality. Traditional fixed thermal field structures have difficulty dynamically adjusting the temperature gradient distribution. Especially in the early and late stages of crystal growth, defects such as polymorphism, polycrystalline, and stress are prone to appear at the edges of the seed crystal, limiting the overall quality and yield of the crystal.

[0003] In the prior art, patent publication number CN102877133B proposes a technical solution for controlling the radial temperature gradient within a crucible by matching and moving a coil and an insulating sleeve. This solution optimizes the pressure and temperature distribution within the furnace, thereby reducing the defect density in the crystal. However, the limited range of movement of the coil and insulating sleeve in this solution makes it difficult to dynamically adjust the temperature gradient distribution. This is particularly true in the later stages of crystal growth, when changes in the temperature distribution within the crucible can cause rapid growth at the edge and lead to flanging problems, affecting the crystallization quality. Furthermore, this solution requires a high degree of complexity in the thermal field structure, which may increase equipment costs and maintenance difficulties.

[0004] Another existing technology, patented with publication number CN113122917B, achieves precise control of the crucible's axial and radial temperatures by providing a temperature control structure and a temperature measuring mechanism, while reducing the crucible's radial temperature gradient, thereby reducing the stress gradient and defect density during crystal growth. However, this technical solution mainly relies on a static temperature control structure and lacks the ability to dynamically adjust the temperature gradient distribution, making it difficult to adapt to the thermal field requirements of different stages during crystal growth. In addition, the design of the temperature control structure is relatively complex, which may increase the difficulty of equipment manufacturing and operation, and has high requirements for the stability of process parameters, which may affect production flexibility and efficiency.

[0005] The above problems show that the existing thermal field structure for silicon carbide crystal growth still has certain deficiencies in terms of dynamically adjusting the temperature gradient distribution, adapting to the requirements of each stage of crystal growth, and simplifying the equipment structure. Therefore, there is an urgent need for a thermal field structure that can dynamically adjust the temperature gradient distribution to suppress the generation of crystal edge defects, improve the quality of crystal growth and the yield rate, and meet the needs of modern industry for high-efficiency, high-quality silicon carbide crystals. The present invention is precisely aimed at this technical difficulty and proposes a thermal field structure for silicon carbide crystal growth that can dynamically adjust the temperature gradient distribution. The invention aims to achieve precise dynamic control of the temperature gradient distribution by combining the thermal field combination structure with the pulling and lifting movement functions of the growth furnace, thereby optimizing the thermal field conditions during the crystal growth process and improving the crystallization quality of the crystal. Summary of the Invention

[0006] A thermal field structure for silicon carbide crystal growth that can dynamically adjust the temperature gradient distribution achieves precise control of the temperature gradient distribution in the crucible by optimizing the combined design of key components inside the thermal field and the dynamic adjustment mechanism. The thermal field structure consists of a multi-layer insulation component, a crucible, and a dynamic adjustment mechanism, wherein the insulation component includes an insulation cylinder, an insulation cover, and an insulation base, while the dynamic adjustment mechanism combines the up and down moving sleeve with the overall thermal field lifting function. Specifically, the insulation cylinder adopts a double-layer structure design, and its outer sleeve can be moved axially by program control, with a moving range of 0-300mm and a moving speed set between 0.1-10mm / h; the inner cylinder is divided into two parts, the upper part is 10-30mm smaller in diameter than the lower part, to form a gradual thermal field distribution. The present invention proposes a crystal growth method based on dynamic thermal field regulation, which is optimized and calculated by introducing a mathematical model of temperature gradient distribution. The model formula is as follows:

[0007]

[0008] Where T(r,z,t) represents the temperature value at any position (r,z) in the thermal field at time t, T0 is the initial temperature, △T is the temperature gradient change amplitude, σ r and σ z are the radial and axial thermal diffusivities, respectively, which are determined by thermal field calibration experiments, with typical values ​​ranging from r =40-60mm, σ z =80-120mm, k is the time correlation coefficient, the value range is 0.0005-0.002h-1, and σ can be changed dynamically r and σ z This algorithm can optimize the thermal field conditions in real time according to the different requirements of the crystal growth stage, ensuring that the temperature gradient at the edge of the seed crystal is always within the optimal range.

[0009] During the crystal growth process, the outer sleeve of the insulation cylinder is moved up and down by a lifting mechanism, and the dynamic adjustment of the temperature gradient is completed in conjunction with the overall lifting function of the thermal field. During the heating stage (2-10 hours), the sleeve position is raised to 5-20mm above the back of the seed crystal holder to reduce the heat accumulation in the edge area of ​​the seed crystal; during the pressure reduction stage (0.5-30 hours), the sleeve is gradually lowered to 5-10mm below the seed crystal, and the heating power is reduced by 50-500W to maintain the overall temperature stability of the thermal field. During the crystal growth stage (100-200 hours), the sleeve continues to slowly descend or maintain a fixed position, and at the same time, the temperature gradient distribution of the raw material area inside the crucible is adjusted by the thermal field lifting function. The thermal field lifting function is realized by a servo motor driving the screw mechanism, with a lifting stroke of 0-200mm, a speed of 0.5-5mm / min, and a position feedback accuracy of ±0.1mm to avoid defects caused by excessive growth of the crystal edge. During the cooling phase (5-20 hours), the sleeve is raised again by 5-20 mm to relieve thermal stress and prevent the crystal from cracking.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] The thermal field structure of the present invention and its dynamic adjustment method significantly improve the quality and efficiency of silicon carbide crystal growth. By dynamically adjusting the relative position of the insulation tube sleeve and the inner tube, and combining the thermal field lifting function, precise control of the temperature gradient distribution inside the crucible is achieved, effectively suppressing the edge defects of the seed crystal. After comparative experimental verification (test standard: SEMIMF1818-2020), after using this method in the crystal growth stage, the polycrystalline defect rate is reduced to ≤3%, which is 40% lower than the control example (CN102877133B solution); the flanging incidence rate is ≤1%, which is 35% lower than the control example. In addition, this technical solution simplifies the equipment structure, reduces manufacturing and maintenance costs, and has good process adaptability, which is suitable for the efficient growth of silicon carbide crystals of different specifications. This method not only improves the crystallization quality of crystals, but also provides reliable technical support for the demand of modern industry for high-performance silicon carbide materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic cross-sectional view of the overall thermal field structure of the present invention;

[0013] Figure 2 This is a schematic diagram of the double-layer structure design of the insulation cylinder;

[0014] Figure 3 Schematic diagram of the working principle of the dynamic adjustment mechanism;

[0015] Figure 4 Calibrate the experimental setup for thermal diffusivity;

[0016] Figure 5 Schematic diagram of the thermal field lifting mechanism. DETAILED DESCRIPTION

[0017] The present invention provides a thermal field structure for silicon carbide crystal growth that can dynamically adjust the temperature gradient distribution. The core of the structure is to achieve precise control of the temperature gradient distribution in the crucible by optimizing the combined design of key components inside the thermal field and the dynamic adjustment mechanism. Figure 1 To the attached Figure 5 The specific embodiments of the present invention are described in detail.

[0018] As attached Figure 1 As shown, the thermal field structure of the present invention is composed of a multi-layer thermal insulation component, a crucible and a dynamic adjustment mechanism. Among them, the thermal insulation component includes a thermal insulation cylinder, a thermal insulation cover 2 and a thermal insulation base 3, and the dynamic adjustment mechanism combines the up and down moving sleeve 4 with the overall thermal field lifting function. The thermal insulation cylinder adopts a double-layer structure design, and its up and down moving sleeve 4 can be moved axially by program control, with a moving range of 0-300mm and a moving speed set between 0.1-10mm / h; the inner cylinder 6 is divided into two parts, the upper part has a diameter 10-30mm smaller than the lower part, so as to form a gradual thermal field distribution. Appendix Figure 2 The double-layer structure of the heat preservation tube is further demonstrated, where the relative positions and size differences of the upper and lower movable sleeve 4 and inner tube 6 are clearly visible. This design can effectively regulate the radial and axial thermal diffusivity, thereby achieving precise control of the temperature gradient distribution. Figure 4 The sleeve position is established by synchronous monitoring with the infrared thermal imager 12 using a multi-position thermocouple, which includes a radial monitoring point 14 and a multi-position thermocouple 13.

[0019] This paper proposes a crystal growth method based on dynamic thermal field regulation, which optimizes the calculation by introducing a mathematical model of temperature gradient distribution. The model formula is as follows:

[0020]

[0021] Where T(r,z,t) represents the temperature value at any position (r,z) in the thermal field at time t, T0 is the initial temperature, △T is the temperature gradient change amplitude, σ r and σ z are the radial and axial thermal diffusivities, respectively, which are determined by thermal field calibration experiments. Figure 4 The device is heated to 1500℃ at 20℃ / min in an argon atmosphere. The temperature data is collected synchronously by 8 sets of radial monitoring points 14 (with a spacing of 15mm) and axial thermocouples 13 (with a spacing of 20mm). Combined with the infrared thermal imager 12 scanning, the typical value range is σ r =40-60mm, σ z=80-120mm, k is the time correlation coefficient, ranging from 0.0005-0.002h-1, and is dynamically adjusted based on the crystal growth stage. By adjusting the position of the up and down moving sleeve 4 and the thermal field lifting parameters, σ can be dynamically changed. r and σ z This algorithm can optimize the thermal field conditions in real time according to the different requirements of the crystal growth stage, ensuring that the temperature gradient at the edge of the seed crystal is always within the optimal range.

[0022] Mathematical model Feasibility is based on the following core verifications:

[0023] The physical meaning is clear:

[0024] σ r (Radial thermal diffusivity) is directly related to the insulation tube structure:

[0025] Moving sleeve 4 upward → insulation gap increases → radial heat loss increases → σ r Increase (typical value 40→60mm),

[0026] Sleeve moves down → thermal field tightness is enhanced → σ r Reduce,

[0027] σ z (Axial thermal diffusivity) is controlled by the overall rise and fall of the thermal field:

[0028] Thermal field rises → Crucible 1 moves away from the heat source → Axial gradient σ z Increase (typical value 80→120mm).

[0029] Parameter calibration experiment support

[0030] The temperature field distribution at different sleeve positions was measured by a thermal imager:

[0031] When the sleeve is raised 20mm: σ r =58±2mm (radial gradient expanded by 15%),

[0032] When the sleeve moves down 10mm: σ z =85±3mm (axial gradient compression 12%),

[0033] Time correlation coefficient

[0034] k=0.0012h -1 Determined by inversion optimization of crystal growth defect rate (k>0.002 leads to a doubling of dislocation density).

[0035] Real-time control algorithm guarantee

[0036] Temperature sensors (such as tungsten-rhenium thermocouples) provide feedback at a sampling frequency of 10 Hz → a control cycle of ≤ 6 seconds → meeting the sub-millimeter interface stability requirements for crystal growth.

[0037] During the actual operation, the up and down movement sleeve 4 of the heat preservation cylinder is realized by the lifting mechanism 7. Figure 5 The lifting mechanism 7 shown includes a precision motor 11 and a screw 10, which cooperate with the overall lifting function of the thermal field to achieve dynamic adjustment of the temperature gradient. Figure 3 The working principle of the dynamic adjustment mechanism is demonstrated, focusing on the range of axial movement of the up-and-down movable sleeve 4 and its connection with the pulling mechanism 7. During the heating stage (2-10 hours), the position of the up-and-down movable sleeve 4 is raised to 5-20 mm above the back of the seed crystal holder 8 to reduce heat accumulation in the edge area of ​​the seed crystal. During the depressurization stage (0.5-30 hours), the up-and-down movable sleeve 4 gradually descends to 5-10 mm below the seed crystal 9, and the heating power is reduced by 50-500 W to maintain the overall temperature stability of the thermal field. During the crystal growth stage (100-200 hours), the up-and-down movable sleeve 4 continues to slowly descend or maintain a fixed position, while adjusting the temperature gradient distribution of the raw material area inside the crucible 1 through the thermal field lifting function to avoid defects caused by excessive growth of the crystal edge. The process of the thermal field lifting function in the crystal growth stage cooperating with the adjustment of the up-and-down movable sleeve 4 shows the dynamic change process of the temperature gradient distribution of the raw material area inside the crucible 1. During the cooling phase (5-20 hours), the sleeve 4 is moved up and down again by 5-20 mm to relieve thermal stress and prevent crystal cracking.

[0038]

[0039]

[0040] Workflow:

[0041] During the crystal growth stage, it is necessary to coordinate the sleeve displacement and the rise and fall of the thermal field:

[0042] Sleeve 4 downward movement rate v c =0.5mm / h→compression radial gradient (σ r decline),

[0043] Thermal field synchronous decline v f =2mm / h→increase axial gradient (σ z rise),

[0044] Dynamic balance formula: Δσ r / Δv f =0.6mm / mm (calibration data).

[0045] During the specific implementation process, the crucible 1 needs to be placed on the insulation base 3 first, and the silicon carbide raw material 5 needs to be loaded into the crucible 1. Subsequently, the insulation tube is installed in place to ensure that the relative position between the up and down movable sleeve 4 and the inner tube 6 meets the design requirements. The insulation cover 2 covers the top of the insulation tube to form a complete thermal field structure. The pulling mechanism 7 in the dynamic adjustment mechanism is driven by a precision motor and can achieve precise control of the up and down movable sleeve 4. During the heating stage, the pulling mechanism 7 raises the up and down movable sleeve 4 to a position 5-20mm above the back of the seed crystal holder 8 to reduce heat accumulation in the edge area of ​​the seed crystal. At this time, the heating power is set to 1000-2000W, so that the temperature in the thermal field gradually increases to the target value. The temperature distribution in the thermal field is monitored in real time by a temperature sensor, and the data is fed back to the control system. The control system calculates the optimal up and down movable sleeve 4 position and heating power parameters according to the mathematical model, thereby achieving precise control of the temperature gradient distribution.

[0046] After entering the depressurization stage, the pulling mechanism 7 gradually lowers the up and down movable sleeve 4 to a position 95-10mm below the seed crystal, and at the same time reduces the heating power by 50-500W to maintain the overall temperature stability of the thermal field. During this process, the control system dynamically adjusts the position and heating power of the up and down movable sleeve 4 according to the real-time monitored temperature data to ensure that the temperature gradient distribution in the thermal field always remains within the optimal range. The crystal growth stage is the most critical link in the entire crystal growth process, and the position of the up and down movable sleeve 4 and the thermal field lifting function need to be finely adjusted. According to the instructions of the control system, the pulling mechanism 7 slowly lowers the up and down movable sleeve 4 or keeps it in a fixed position, and at the same time adjusts the temperature gradient distribution of the raw material area inside the crucible 1 through the thermal field lifting function to avoid defects caused by excessive growth of the crystal edge. At this stage, the heating power is usually set to 500-1500W, and the specific value is adjusted according to the actual needs of crystal growth.

[0047] The cooling stage is the last step of crystal growth and an important step in ensuring crystal quality. The pulling mechanism 7 raises the up-and-down movable sleeve 4 by 5-20 mm again to relieve thermal stress and prevent the crystal from cracking. At this point, the heating power is gradually reduced to 100-500 W, so that the temperature in the thermal field slowly drops to room temperature. During the entire cooling process, the control system dynamically adjusts the position and heating power of the up-and-down movable sleeve 4 according to the real-time monitored temperature data to ensure that the temperature gradient distribution in the thermal field is always maintained within the optimal range. Through the above steps, the thermal field structure of the present invention and its dynamic adjustment method can significantly improve the quality and efficiency of silicon carbide crystal growth.

[0048] The thermal field structure and dynamic adjustment method of the present invention dynamically adjust the relative positions of the up and down movable sleeve 4 and the inner cylinder 6 of the insulation cylinder, and combine the thermal field lifting function to achieve precise control of the temperature gradient distribution inside the crucible 1, effectively suppressing defects such as polymorphism, polycrystalline and flanging in the edge area of ​​the seed crystal. In addition, this technical solution simplifies the equipment structure, reduces manufacturing and maintenance costs, and has good process adaptability, making it suitable for the efficient growth of silicon carbide crystals of different specifications. This method not only improves the crystallization quality of the crystal, but also provides reliable technical support for the demand of modern industry for high-performance silicon carbide materials. Parameter-effect causal chain (experimental verification data)

[0049] Correlation between key operating parameters and crystal quality:

[0050]

[0051]

[0052] Engineering convergence of mathematical models:

[0053] Boundary condition settings:

[0054] T(r crucible,z max ,t)=T 坩埚壁 (Constant temperature 1650℃)

[0055] (Seed crystal interface)

[0056] Iterative convergence: The finite difference method (FDM) was used for solution, with a spatial grid of 2 mm × 2 mm. The temperature field prediction error was < ±3°C.

Claims

1. A thermal field structure for silicon carbide crystal growth capable of dynamically adjusting temperature gradient distribution, characterized in that The invention comprises a multi-layer heat-insulating component, a crucible and a dynamic adjustment mechanism. The multi-layer heat-insulating component comprises a heat-insulating cylinder, a heat-insulating cover (2) and a heat-insulating base (3). The dynamic adjustment mechanism comprises an up-and-down movable sleeve (4) and an overall heat field lifting function. The heat-insulating cylinder is a double-layer structure, comprising an up-and-down movable sleeve (4) and an inner cylinder (6). The up-and-down movable sleeve (4) is movable in the axial direction, with a moving range of 0 to 300 mm and a moving speed of 0.1 to 10 mm per hour. The inner cylinder (6) is divided into an upper and a lower part, and the diameter of the upper part is 10 to 30 mm smaller than that of the lower part.

2. The thermal field structure for silicon carbide crystal growth capable of dynamically adjusting temperature gradient distribution according to claim 1, characterized in that The vertically movable sleeve (4) is moved up and down by a lifting mechanism (7). The lifting mechanism (7) comprises a precision motor (11) and a screw rod (10) for controlling the position of the vertically movable sleeve (4).

3. A thermal field structure for silicon carbide crystal growth capable of dynamically adjusting temperature gradient distribution according to claim 1 or 2, characterized in that The dynamic adjustment mechanism also includes a thermal field lifting function, which is achieved by a servo motor driving a lead screw mechanism, with a lifting stroke of 0-200 mm, a speed of 0.5-5 mm / min, and a position feedback accuracy of ±0.1 mm, and is used to adjust the temperature gradient distribution of the raw material area inside the crucible (1).

4. The thermal field structure for silicon carbide crystal growth capable of dynamically adjusting temperature gradient distribution according to claim 1, characterized in that The crucible (1) is placed on a heat-insulating base (3), and the heat-insulating cover (2) covers the heat-insulating cylinder to form a complete heat field structure.

5. A method for growing silicon carbide crystals based on the thermal field structure according to any one of claims 1 to 4, characterized in that The method comprises a heating stage, a pressure reduction stage, a crystal growth stage and a cooling stage. In the heating stage, the upward and downward moving sleeve (4) is raised to a height 5 to 20 mm above the back of the seed crystal holder (8), and the heating power is set to 1000 to 2000 watts. In the pressure reduction stage, the upward and downward moving sleeve (4) is lowered to a height 5 to 10 mm below the seed crystal (9), and the heating power is reduced by 50 to 500 watts.

6. The method for growing silicon carbide crystals with a thermal field structure according to claim 5, characterized in that During the crystal growth stage, the upward and downward moving sleeve (4) continues to slowly descend or maintains a fixed position, and the temperature gradient distribution of the raw material area inside the crucible (1) is adjusted by the thermal field lifting function, and the heating power is set to 500 to 1500 watts.

7. The method according to claim 5, characterized in that During the cooling stage, the up-and-down moving sleeve (4) is raised again by 5 to 20 mm, and the heating power is gradually reduced to 100 to 500 watts, so that the temperature in the thermal field slowly drops to room temperature.

8. The method for growing silicon carbide crystals in a thermal field structure according to any one of claims 5 to 7, characterized in that The temperature distribution in the thermal field is monitored in real time by a temperature sensor, and the data is fed back to a control system, which calculates the optimal position of the up-and-down moving sleeve (4) and heating power parameters according to a mathematical model.

9. The method for growing silicon carbide crystals with a thermal field structure according to claim 8, wherein The mathematical model is the formula Where T(r,z,t) represents the temperature value at any position (r,z) in the thermal field at time t, T0 is the initial temperature, △T is the temperature gradient change amplitude, σ r and σ z are the radial and axial thermal diffusivities, respectively, and k is the time-dependent coefficient.

10. The method for growing silicon carbide crystals of a thermal field structure according to claim 9, characterized in that By adjusting the position of the up-and-down moving sleeve (4) and the thermal field lifting parameters, the values ​​of the radial thermal diffusion coefficient σr and the axial thermal diffusion coefficient σz are dynamically changed, thereby achieving precise control of the temperature gradient distribution.

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