A double-induction heating growth device and growth method for large-diameter silicon carbide single crystals

Abstract

This invention belongs to the field of crystal growth technology, specifically relating to a dual-induction heating growth apparatus and method for large-diameter silicon carbide single crystals. The dual-induction heating growth apparatus includes a graphite crucible, a first induction heating coil, and a second induction heating coil; the first and second induction heating coils are disposed on the outer periphery of the graphite crucible; the first induction heating coil is located above the second induction heating coil; the first and second induction heating coils do not overlap; the induction power supply frequency corresponding to the first induction heating coil is 30–100 kHz, and the induction power supply frequency corresponding to the second induction heating coil is 1–10 kHz. This invention employs the mutual coupling of induction heating coils of different frequencies, effectively improving the radial temperature gradient at the silicon carbide seed crystal while maintaining a low heating power, thus improving the growth quality of large-diameter silicon carbide single crystals and reducing production costs.

Description

Technical Field

[0001] This invention belongs to the field of crystal growth technology, specifically relating to a dual induction heating growth device and method for large-diameter silicon carbide single crystals. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Silicon carbide (SiC) is a third-generation semiconductor material with advantages such as high temperature resistance, radiation resistance, high thermal conductivity, large bandgap, high electron saturation drift velocity, and high breakdown voltage. It is widely used in electric vehicles, rail transportation, 5G communication, high voltage power transmission and transformation and other fields, and is an important semiconductor material.

[0004] Currently, the most mature method for growing silicon carbide single crystals is the physical vapor transport (PVT) method. In PVT, the powder is placed at the bottom of the crucible, and the seed crystal is placed on the top of the crucible. When the powder is heated, it sublimates and decomposes, transporting the powder to the silicon carbide seed crystal to deposit and form a silicon carbide single crystal. The sublimation of the silicon carbide powder and the recrystallization of the silicon carbide seed crystal growth surface are two core processes in single crystal growth, which are closely related to the temperature field of the growth system. Induction heating is currently the most common heating method. In induction heating, the graphite crucible acts as the heating element, and heat is generated by the crucible wall and transferred to the center of the crucible. The higher the frequency of the induction power supply, the stronger the skin effect of the induced current, and the greater the temperature difference between the crucible wall and the center of the crucible, which amplifies both the axial and radial temperature gradients inside the crucible. If the radial temperature gradient at the seed crystal is too large, it will lead to greater thermal stress in the grown crystal, which will then cause a large number of dislocation defects, and in severe cases, even crystal cracking. In addition, an excessively large radial temperature gradient will also lead to excessive convexity of the crystal, affecting the crystal utilization rate. If the axial temperature gradient in silicon carbide powder is too large, it can easily lead to recrystallization of the growth components on the surface of the material, hindering the transport of the growth components to the growth surface of the silicon carbide seed crystal and affecting single crystal growth. Currently, the diameter of silicon carbide single crystals is getting larger and larger, and correspondingly, the size of the crucible also needs to be larger, resulting in an increase in the radial temperature gradient on the seed crystal surface. When using induction heating, the crucible itself is the heating element. Due to the limitations of the induction heating principle, the radial and axial temperature gradients within the crucible are coupled, making it difficult to adjust one of the temperature gradients independently. Resistance heating is considered a possible heating method for growing low-stress, large-diameter silicon carbide single crystals. When growing silicon carbide single crystals using the physical vapor transport method, the crystal grows under high temperature and low pressure (>2000℃, <100mbar). Under this condition, the resistance heater is very prone to increased current and voltage, which can cause secondary gas ionization and lead to glow discharge, electrode arcing, and other phenomena, resulting in a high probability of heater damage (refer to US patent document US0092288274B2). In addition, the energy required to grow silicon carbide single crystals using resistance heating is much greater than that of induction heating, which leads to a sharp increase in the cost of single crystal growth.

[0005] Chinese patent document CN 110359087 B discloses a growth apparatus for silicon carbide single crystals and a method for manufacturing silicon carbide single crystals. This method uses two independent coaxial induction heating coils of different diameters to heat a graphite crucible. A second induction coil, employing high-frequency heating, is positioned near the bottom of the crucible and surrounds a first induction coil employing medium-frequency heating. This allows for fine-tuning of the temperature gradient at the silicon carbide powder during crystal growth. While this method can fine-tune the temperature gradient at the crucible powder, because the second induction coil is located at the bottom of the crucible, its influence on the temperature field at the seed crystal during the growth of large-size silicon carbide is limited. Therefore, it cannot adjust the temperature of the seed crystal growth surface, and consequently, cannot reduce the thermal stress within the large-size silicon carbide single crystal. Furthermore, although the two sets of coils in this method are placed coaxially, they have different diameters. In addition, since the efficiency of induction heating decreases as the distance between the induction coil and the heating element increases, the larger diameter induction heating coil will result in lower coupling efficiency. In particular, the second induction coil is located at the silicon carbide powder, where the temperature is the highest in the reaction crucible. High-frequency induction heating will lead to a more severe skin effect of the current, resulting in a large power consumption for silicon carbide single crystal growth.

[0006] Chinese patent document CN 108286074 B discloses a growth apparatus and its operating method for growing large-size silicon carbide single crystals. This method first heats the growth chamber to a preset temperature using a constant frequency and constant intensity current heating mode. Then, it uses the constant frequency from the first heating step as the center frequency for multi-frequency heating, while simultaneously adjusting the intensity of the heating current to reduce the radial temperature gradient at the crystal growth surface and improve crystal quality. Although this method can reduce the radial temperature gradient at the crystal growth interface, it only has one set of coils, making it impossible to individually adjust the temperature field at the growth interface between the silicon carbide powder and the silicon carbide seed crystal. Furthermore, in this invention, the induction power supply's frequency changes continuously during use, requiring the induction heating power supply to be a frequency converter. Referring to Chinese patent document CN108064095B, ​​current methods for changing the induction heating resonant frequency mainly involve changing the number of capacitor pillars in the resonant capacitor to change its capacitance. However, adjusting each capacitor pillar causes a significant frequency change, resulting in low precision and large fluctuations. This increases the difficulty and cost of manufacturing the frequency conversion induction heating system, indirectly increasing the cost of silicon carbide single crystal growth.

[0007] Chinese patent document CN 217077865 U discloses a high-frequency dual-coil induction heating silicon carbide single crystal growth apparatus. This method uses two sets of coils, one above the other, to heat the crucible powder and the other the seed crystal. During growth, the power and position of the two sets of coils are adjusted in real time based on the temperature difference between the upper and lower measuring points and the set temperature, thereby precisely controlling the radial and axial temperature gradients at the top of the crucible. While this method breaks the coupling between the radial and axial temperature gradients, the adjustment of the two sets of coil positions is based on the temperatures measured at the upper and lower points. Currently, the pyrometers used for temperature measurement are generally infrared pyrometers, which have drawbacks such as poor accuracy. Furthermore, component volatilization during the growth process can easily lead to dirt accumulation in the measuring windows and even blockage of the measuring orifices. If inaccurate temperature measurements occur, the vertical movement of the two sets of coils cannot be controlled, and the system may even control the coil movement based on erroneous temperature data, severely negatively impacting the stability of crystal growth. Even with improvements to the temperature measuring mechanism, the method remains complex and costly. In addition, this method uses high-frequency induction heating, which has a stronger skin effect than medium-frequency and low-frequency induction heating, requires higher heating power, and has higher growth power consumption, which is not conducive to reducing the cost of silicon carbide single crystal growth. Furthermore, when heating at high frequency, the internal axial ladder of the powder is too large and the radial temperature gradient inside the material is too small, which causes the gas phase components to be transported vertically upward to the powder surface for crystallization, hindering the subsequent powder transport and affecting crystal growth. Summary of the Invention

[0008] In view of the technical problems of high stress cracking, many defects, and inability to independently adjust the temperature field of the seed crystal growth interface and the temperature field of silicon carbide powder in the existing technology for growing large-diameter silicon carbide single crystals, the purpose of this invention is to provide a dual induction heating growth device and growth method for large-diameter silicon carbide single crystals.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0010] In a first aspect, a dual induction heating growth apparatus for large-diameter silicon carbide single crystals includes a graphite crucible, a first induction heating coil, and a second induction heating coil; the first induction heating coil and the second induction heating coil are disposed on the outer periphery of the graphite crucible; the first induction heating coil is located above the second induction heating coil; the first induction heating coil and the second induction heating coil do not overlap; the induction power supply frequency corresponding to the first induction heating coil is 30 to 100 kHz, and the induction power supply frequency corresponding to the second induction heating coil is 1 to 10 kHz.

[0011] Preferably, when in use, the graphite crucible has a silicon carbide seed crystal bonded to the top and silicon carbide powder placed at the bottom; the graphite crucible is wrapped with insulation material.

[0012] Preferably, the lower end of the first induction heating coil is located below the growth surface of the silicon carbide seed crystal, the upper end of the second induction heating coil is located above the silicon carbide powder, and the interval between the first induction heating coil and the second induction heating coil is 20-50 mm.

[0013] Preferably, the axes of symmetry of the first induction heating coil and the second induction heating coil coincide with the axis of symmetry of the graphite crucible.

[0014] Preferably, the length of the first induction heating coil is 1 to 1.5 times the distance between the surface of the silicon carbide powder and the silicon carbide seed crystal, and the length of the second induction heating coil is 1.5 to 3 times the height of the silicon carbide powder.

[0015] Preferably, the length of the first induction heating coil is less than the length of the second induction heating coil.

[0016] Preferably, the turn spacing between the first induction heating coil and the second induction heating coil is 5 to 20 mm.

[0017] Preferably, it also includes a temperature control device for detecting and adjusting the internal temperature of the heating system.

[0018] Preferably, it further includes an adjustment device for adjusting the power and / or position of the first induction heating coil or the second induction heating coil.

[0019] When the silicon carbide growth interface is concave, the power of the first induction heating coil should be reduced; when the silicon carbide single crystal growth interface is relatively convex, the power of the first induction heating coil should be increased. By adjusting the position and power of the first induction heating coil, a near-flat, slightly convex silicon carbide single crystal growth interface can be obtained, reducing stress in the silicon carbide single crystal and improving its quality. When the silicon carbide single crystal growth rate is too slow, the power of the second induction heating coil should be increased or / and the second induction heating coil should be moved downwards; when the silicon carbide single crystal growth rate is too fast, the power of the second induction heating coil should be decreased or / and the second induction heating coil should be moved upwards. By adjusting the power and position of the second induction heating coil, a suitable single crystal growth rate can be obtained.

[0020] In a second aspect, a method for growing large-size silicon carbide single crystals, using the dual induction heating growth apparatus described in the first aspect, includes the following steps:

[0021] S1. Spread the silicon carbide powder evenly on the bottom of the graphite crucible, attach the silicon carbide seed crystal to the top of the graphite crucible, and tighten the top cover.

[0022] S2. After placing the graphite crucible into the growth device, seal the growth device and perform a vacuum treatment inside the growth device.

[0023] S3. Carrier gas is introduced into the growth apparatus, and the first induction heating coil and the second induction heating coil are controlled to heat the inside of the growth apparatus to the set temperature. After the temperature is reached, the growth apparatus is kept warm to grow crystals.

[0024] S4. After growth is completed, the location of the high-temperature zone is determined according to the shape of the remaining powder in the graphite crucible, and the location and power of the first induction heating coil and the second induction heating coil are evaluated according to the crystal growth shape and single crystal growth rate.

[0025] S5. Reload and evacuate according to S1 and S2. Adjust the power of the first induction heating coil and the second induction heating coil according to the position of the high temperature zone, the crystal growth shape and the single crystal growth rate. At the same time, adjust the relative position of the first induction heating coil, the second induction heating coil and the crucible. Perform crystal growth according to S3.

[0026] S6. After the crystal growth is completed, the inside of the single crystal growth equipment is cooled down to allow the crystal to cool naturally, thus obtaining a large-size silicon carbide single crystal.

[0027] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0028] (1) This invention sets up a first induction heating coil and a second induction heating coil for the growth of large-diameter silicon carbide single crystals. It cleverly utilizes the "skin effect" of induction heating. By making full use of the different skin depths of heating at different induction frequencies, the first induction heating coil with a higher frequency is used at the growth interface of silicon carbide seed crystal. It takes advantage of the characteristic of high-frequency induction heating to flatten the temperature field at the seed crystal at the top of the crucible, which greatly reduces the radial temperature gradient at the growth interface of silicon carbide seed crystal, reduces the stress in the crystal and improves the quality of large-diameter crystals. The second induction heating coil with a lower frequency heats the silicon carbide powder. It makes full use of the advantage of the high temperature of the crucible wall brought by induction heating, and realizes the preferential sublimation and decomposition of silicon carbide powder near the crucible wall. It effectively reduces the axial temperature gradient in the silicon carbide powder, avoids the crystallization of growth components on the surface of the material, and ensures the growth rate of silicon carbide single crystals.

[0029] (2) This invention divides the induction heating coils into two groups and differentiates the heating frequencies between the different groups of coils. Low-frequency heating is used at the powder where the temperature is highest in the growth system, effectively reducing energy consumption; while high-frequency heating is used at the silicon carbide seed crystal where the temperature is lowest in the growth system, achieving a flattened seed crystal growth interface without significantly increasing energy consumption. Compared with the method of using high-frequency heating for all coils, the single crystal growth in this invention has low energy consumption and no surface crystallization problem; compared with the method of using medium-frequency heating for all coils, the method in this invention produces silicon carbide single crystals with low stress and high quality.

[0030] (3) By maintaining a specific distance between two sets of induction heating coils of different frequencies, this invention achieves the adjustment of the radial temperature gradient of the seed crystal by the first induction coil and the adjustment of the temperature gradient of the hot zone of the powder by the second induction heating coil. This enables the separate adjustment of the radial and axial temperature gradients in the crucible, improves the flexibility of temperature gradient adjustment in the crucible, realizes "axis-radius separation" in the growth crucible, effectively improves the mutual coupling phenomenon of radial and axial temperature gradients in the crucible, and reduces the technical difficulty of silicon carbide single crystal growth.

[0031] (4) The present invention has made a clever design for the induction heating coil, which is compatible with the current growth process and is easy to promote and use.

[0032] (5) The growth apparatus with different frequencies of induction heating in this invention is also applicable to the growth of single crystals such as aluminum nitride and other physical vapor transport growth, and has reference value for improving the quality of single crystals. Attached Figure Description

[0033] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0034] Figure 1 This is a schematic diagram of the dual induction heating growth device for large-diameter silicon carbide single crystals in this invention.

[0035] Figure 2 The stress diagram is shown for the silicon carbide substrate obtained by cutting, grinding, and polishing the grown silicon carbide single crystal in Example 1.

[0036] Figure 3 This is a side view photograph of the silicon carbide single crystal in Example 1;

[0037] Figure 4 The stress diagram is shown for the silicon carbide substrate obtained by cutting, grinding and polishing the grown silicon carbide single crystal in Comparative Example 1.

[0038] Figure 5 A side view of the silicon carbide single crystal in Comparative Example 1;

[0039] Wherein, 1 is the first induction heating coil, 2 is the second induction heating coil, 3 is the graphite crucible, 4 is the insulation material, 5 is the silicon carbide seed crystal, 6 is the silicon carbide crystal, 7 is the silicon carbide powder, L represents the distance between the surface of the silicon carbide powder and the surface of the seed crystal, and H represents the loading height of the silicon carbide powder. Detailed Implementation

[0040] Terminology Explanation:

[0041] Source-to-crystal distance: In this invention, it refers to the distance between the surface of silicon carbide powder and the silicon carbide seed crystal, denoted by L, and is between 50 and 100 mm.

[0042] Powder height: In this invention, it refers to the loading height of silicon carbide powder, denoted by H, which is between 50 and 100 mm.

[0043] Large-size silicon carbide single crystal: In this invention, it refers to silicon carbide single crystals with a diameter greater than or equal to 6 inches.

[0044] Radial temperature gradient of the seed crystal surface: In this invention, this refers to the temperature difference between the center and the edge of the silicon carbide seed crystal surface, the difference per unit length. A larger gradient increases the thermal stress, dislocation density, and convexity of the grown crystal. From the perspective of crystal growth, a smaller radial temperature gradient is better.

[0045] Convexity: In this invention, convexity refers to the thickness difference between the center (thickest part) and the edge (thinnest part) of a silicon carbide crystal. A greater convexity results in a larger thickness difference between the center and the edge, leading to increased internal thermal stress, increased susceptibility to crystal cracking, and reduced utilization. Therefore, from the perspective of crystal growth, a smaller convexity is more ideal.

[0046] Location of high-temperature zone: In this invention, it refers to the location of the area with a high internal temperature in the powder during the growth process.

[0047] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0048] Example 1

[0049] like Figure 1 As shown, the dual induction heating growth apparatus for large-diameter silicon carbide single crystals includes a graphite crucible 3, a first induction heating coil 1, and a second induction heating coil 2. The first and second induction heating coils 1 and 2 are positioned on the outer periphery of the graphite crucible 3; the first induction heating coil 1 is located above the second induction heating coil 2; the first and second induction heating coils 1 and 2 do not overlap. During use, a silicon carbide seed crystal 5 is bonded to the top of the graphite crucible 3, and the silicon carbide single crystal 6 grows on the surface of the silicon carbide seed crystal 5. Silicon carbide powder 7 is placed at the bottom of the graphite crucible 3. The graphite crucible is wrapped with insulation material 4. The axes of symmetry of the first and second induction heating coils 1 and 2 coincide with the axis of symmetry of the graphite crucible 3. The lower end of the first induction heating coil 1 is below the growth surface of the silicon carbide seed crystal 5, and the upper end of the second induction heating coil 2 is above the silicon carbide powder 7.

[0050] The length of the first induction heating coil is set to 1.0 times the source crystal pitch, and the length of the second induction heating coil is set to 1.5 times the height of the silicon carbide powder. The spacing between the two sets of induction heating coils is 20 mm, and the coil turn spacing is 5 mm. The induction power supply frequency corresponding to the first induction heating coil is 30 kHz, and the induction power supply frequency corresponding to the second induction heating coil is 1 kHz. Large-diameter silicon carbide single crystals are grown through the following steps:

[0051] S1. Spread the silicon carbide powder evenly on the bottom of the graphite crucible, attach the silicon carbide seed crystal to the top of the graphite crucible, and tighten the top cover.

[0052] S2. After placing the graphite crucible into the growth device, seal the growth device and perform a vacuum treatment inside the growth device.

[0053] S3. Carrier gas is introduced into the growth apparatus, and the first induction heating coil and the second induction heating coil are controlled to heat the inside of the growth apparatus to the set temperature. After the temperature is reached, the growth apparatus is kept warm to grow crystals.

[0054] S4. After growth is completed, the location of the high-temperature zone is determined according to the shape of the remaining powder in the graphite crucible, and the location and power of the first induction heating coil and the second induction heating coil are evaluated according to the crystal growth shape and single crystal growth rate.

[0055] S5. Reload and evacuate according to S1 and S2. Adjust the power of the first induction heating coil and the second induction heating coil according to the position of the high temperature zone, the crystal growth shape and the single crystal growth rate. At the same time, adjust the relative position of the first induction heating coil, the second induction heating coil and the crucible. Perform crystal growth according to S3.

[0056] S6. After the crystal growth is completed, the inside of the single crystal growth equipment is cooled down to allow the crystal to cool naturally, thus obtaining a large-size silicon carbide single crystal.

[0057] The stress diagram of the silicon carbide substrate obtained by cutting, grinding, and polishing the large-size silicon carbide single crystal in this embodiment is shown below. Figure 2 As shown in the image, the entire wafer is dark in color with no stress spots, indicating low thermal stress. Figure 3 As shown, the maximum thickness of the silicon carbide single crystal, measured with vernier calipers, is 29.5 mm, the minimum thickness is 27.8 mm, and the convexity is 1.7 mm. This indicates that the silicon carbide single crystal grown using the growth apparatus and method of this invention has low convexity and low thermal stress.

[0058] Example 2

[0059] Unlike Example 1, the length of the first induction heating coil is 1.25 times the source crystal distance, and the length of the second induction heating coil is 2.25 times the powder height. The group spacing between the first and second induction heating coils is 35 mm, and the coil turn spacing is 15 mm. The induction power supply frequency corresponding to the first induction heating coil is 65 kHz, and the induction power supply frequency corresponding to the second induction heating coil is 5 kHz. Using vernier calipers, the maximum thickness of the silicon carbide single crystal was measured to be 27.3 mm, the minimum thickness was 26.1 mm, and the convexity was 1.2 mm. This indicates that the silicon carbide single crystal grown using the growth apparatus and method of the present invention has low convexity and low thermal stress.

[0060] Example 3

[0061] Unlike Example 1, the length of the first induction heating coil is 1.25 times the source crystal distance, and the length of the second induction heating coil is 2.25 times the powder height. The spacing between the two sets of induction heating coils is 35 mm, and the coil turn spacing is 15 mm. The induction power supply frequency corresponding to the first induction heating coil is 100 kHz, and the induction power supply frequency corresponding to the second induction heating coil is 10 kHz. Using vernier calipers, the maximum thickness of the silicon carbide single crystal was measured to be 25.6 mm, the minimum thickness was 23.5 mm, and the convexity was 2.1 mm. This indicates that the silicon carbide single crystal grown using the growth apparatus and method of the present invention has low convexity and low thermal stress.

[0062] Comparative Example 1

[0063] Unlike Example 1, the induction power supply frequencies corresponding to both the first and second induction heating coils were set to 3 kHz. The stress diagram of the silicon carbide substrate obtained by cutting, grinding, and polishing the large-size silicon carbide single crystal is shown below. Figure 4 As shown in the figure, there are large bright areas and obvious stress spots in some areas, indicating high thermal stress. Figure 5 As shown, the maximum thickness of the silicon carbide single crystal, measured with vernier calipers, was 28.1 mm, the minimum thickness was 15.3 mm, and the convexity was 12.8 mm. The total heating power during the growth process was only 10,000 W, lower than the total heating power of 13,900 W in Example 1. This indicates that although the first induction heating coil uses low-frequency heating, which consumes less energy during the growth process, the grown silicon carbide single crystal has a larger convexity and higher thermal stress.

[0064] Comparative Example 2

[0065] Unlike Example 1, the induction power supply frequency for both the first and second induction heating coils was set to 100kHz. Using calipers, the maximum thickness of the silicon carbide single crystal was measured to be only 16.8mm, the minimum thickness to be 14.9mm, and the convexity to be 1.9mm. The total heating power during the growth process was 29800W, while the total heating power for silicon carbide single crystal growth in Example 1 was only 13900W. Furthermore, after growth, severe crystallization was observed on the powder surface. This was due to high-frequency heating at the powder level, resulting in a smaller internal diameter gradient and a larger axial gradient. The powder was transported vertically upwards to the powder surface, where crystallization blocked the subsequent transport of gaseous components, leading to a slower growth rate. Although the grown silicon carbide crystals had lower convexity and lower thermal stress due to high-frequency heating of both the first and second induction heating coils, severe surface crystallization resulted in higher energy consumption.

[0066] Comparative Example 3

[0067] Unlike Example 1, the frequency of the induction power supply corresponding to the first induction heating coil was set to 3kHz, and the frequency of the induction power supply corresponding to the second induction heating coil was set to 100kHz. Using vernier calipers, the maximum thickness of the silicon carbide single crystal was measured to be 20.5mm, and the minimum thickness was only 10.4mm, with a convexity of 10.1mm. After growth, severe crystallization was found on the powder surface. This was due to high-frequency heating at the powder level, resulting in a smaller internal diameter gradient and a larger axial gradient. The powder was transported vertically upwards to the powder surface, crystallizing and blocking the subsequent transport of gas phase components, leading to a slower growth rate. After the crystal was cut, ground, and polished into wafers, its stress was tested, revealing high stress in the wafers. This indicates that changing the first induction heating coil to a low frequency leads to a larger radial temperature gradient on the surface of the silicon carbide seed crystal, resulting in greater convexity and higher thermal stress in the grown silicon carbide crystal; changing the second induction heating coil to a high frequency leads to a larger axial temperature gradient in the silicon carbide powder, causing severe surface crystallization and affecting the single crystal growth rate.

[0068] Comparative Example 4

[0069] Unlike Example 1, the spacing between the first and second induction heating coils was set to 5 mm. Using vernier calipers, the maximum thickness of the silicon carbide single crystal was measured to be 23.6 mm, the minimum thickness to be 16.8 mm, and the convexity to be 6.8 mm. Due to the small coil spacing, the coils' ability to level the temperature field was limited, resulting in a larger convexity and higher thermal stress in the grown silicon carbide single crystal.

[0070] Comparative Example 5

[0071] Unlike Example 1, the spacing between the first and second induction heating coils was set to 70 mm. Using vernier calipers, the maximum thickness of the silicon carbide single crystal was only 15.3 mm, the minimum thickness was 13.2 mm, and the convexity was 2.1 mm. The total heating power during the growth process was 29800 W, compared to 13900 W in Example 1. Although the silicon carbide crystal grown in this comparative example had lower convexity and lower thermal stress, the excessive spacing between the two coil groups resulted in an excessively large axial ladder within the material, leading to severe crystallization on the powder surface and affecting crystal growth. Furthermore, because most of the coils were located axially outside the crucible, the energy utilization rate was low, resulting in higher energy consumption.

[0072] Comparative Example 6

[0073] Unlike Example 1, the length of the first induction heating coil was set to 2.0 times the source crystal distance, and the length of the second induction heating coil was set to 4.0 times the height of the silicon carbide powder. Using vernier calipers, the maximum thickness of the silicon carbide single crystal was measured to be 26.8 mm, the minimum thickness to be 25.1 mm, and the convexity to be 1.7 mm. The total heating power during the growth process was 31100 W, while the total heating power for silicon carbide single crystal growth in Example 1 was only 13900 W. Although the silicon carbide crystal grown in this comparative example has lower convexity and lower thermal stress, the energy utilization rate is low and the energy consumption is high due to the excessively long induction heating coil.

[0074] Comparative Example 7

[0075] Unlike Example 1, the length of the first induction heating coil was set to 0.5 times the source crystal distance, and the length of the second induction heating coil was set to 1.0 times the height of the silicon carbide powder. Using vernier calipers, the maximum thickness of the silicon carbide single crystal was measured to be 27.4 mm, the minimum thickness to be 20.7 mm, and the convexity to be 6.7 mm. The total heating power during the growth process was only 12600 W, lower than the 13900 W in Example 1. Although less energy was consumed during the growth process in this comparative example, the shorter coil resulted in a larger convexity and higher thermal stress in the grown silicon carbide single crystal.

[0076] Comparative Example 8

[0077] Unlike Example 1, the turn spacing of both the first and second induction heating coils was set to 30 mm. Using vernier calipers, the maximum thickness of the silicon carbide single crystal was measured to be 25.2 mm, the minimum thickness to be 17.9 mm, and the convexity to be 7.3 mm. The total heating power during the growth process was 18300 W, while the total heating power for silicon carbide single crystal growth in Example 1 was only 13900 W. This indicates that due to the excessively large coil spacing, the energy consumption during growth was higher, and the grown silicon carbide single crystal had greater convexity and higher thermal stress.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual induction heating growth apparatus for large-diameter silicon carbide single crystals, characterized in that, It includes a graphite crucible, a first induction heating coil, and a second induction heating coil; the first induction heating coil and the second induction heating coil are disposed on the outer periphery of the graphite crucible; the first induction heating coil is located above the second induction heating coil; the first induction heating coil and the second induction heating coil do not overlap; the induction power frequency corresponding to the first induction heating coil is 30~100kHz, and the induction power frequency corresponding to the second induction heating coil is 1~10kHz; The lower end of the first induction heating coil is located below the growth surface of the silicon carbide seed crystal, and the upper end of the second induction heating coil is located above the silicon carbide powder. The distance between the first induction heating coil and the second induction heating coil is 20~50mm. The length of the first induction heating coil is 1 to 1.5 times the distance between the surface of the silicon carbide powder and the silicon carbide seed crystal, and the length of the second induction heating coil is 1.5 to 3 times the height of the silicon carbide powder; The turn spacing between the first induction heating coil and the second induction heating coil is 5~20 mm.

2. The dual induction heating growth apparatus as described in claim 1, characterized in that, When in use, the graphite crucible has a silicon carbide seed crystal bonded to the top and silicon carbide powder placed at the bottom; the graphite crucible is wrapped with insulation material.

3. The dual induction heating growth apparatus as described in claim 1, characterized in that, The axes of symmetry of the first induction heating coil and the second induction heating coil coincide with the axis of symmetry of the graphite crucible.

4. The dual induction heating growth apparatus as described in claim 1, characterized in that, The length of the first induction heating coil is less than the length of the second induction heating coil.

5. The dual induction heating growth apparatus as described in claim 1, characterized in that, It also includes a temperature control device for detecting and adjusting the internal temperature of the heating system.

6. The dual induction heating growth apparatus as described in claim 1, characterized in that, It also includes an adjustment device for adjusting the power and / or position of the first induction heating coil or the second induction heating coil.

7. A method for growing large-size silicon carbide single crystals, characterized in that, Using the dual induction heating growth apparatus according to any one of claims 1-6 includes the following steps: S1. Spread the silicon carbide powder evenly on the bottom of the graphite crucible, attach the silicon carbide seed crystal to the top of the graphite crucible, and tighten the top cover. S2. After placing the graphite crucible into the growth device, seal the growth device and perform a vacuum treatment inside the growth device. S3. Carrier gas is introduced into the growth apparatus, and the first induction heating coil and the second induction heating coil are controlled to heat the inside of the growth apparatus to the set temperature. After the temperature is reached, the growth apparatus is kept warm to grow crystals. S4. After growth is completed, the location of the high-temperature zone is determined according to the shape of the remaining powder in the graphite crucible, and the location and power of the first induction heating coil and the second induction heating coil are evaluated according to the crystal growth shape and single crystal growth rate. S5. Reload and evacuate according to S1 and S2. Adjust the power of the first and second induction heating coils according to the position of the high-temperature zone, the crystal growth shape, and the single crystal growth rate. At the same time, adjust the relative positions of the first and second induction heating coils and the crucible. Perform crystal growth according to S3. S6. After the crystal growth is completed, the inside of the single crystal growth equipment is cooled down to allow the crystal to cool naturally, thus obtaining a large-size silicon carbide single crystal.

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