Silicon carbide crystal growth system and silicon carbide crystal growth method

Abstract

The application discloses a silicon carbide crystal growth system and a silicon carbide growth method, and relates to a silicon carbide growth technology. The silicon carbide crystal growth system comprises a powder cylinder, a matching piece and a seed crystal cover. The upper end of the powder cylinder is open, and the powder cylinder is provided with a powder bin inside. The matching piece is connected to the powder cylinder, and is arranged to position a graphite paper above the powder bin and to be detached after a predetermined condition is reached. The seed crystal cover is arranged above the opening, the lower surface of the seed crystal cover is formed as a crystal growth base, and the seed crystal cover is higher than the graphite paper. According to the silicon carbide crystal growth system provided by the embodiment of the application, the graphite paper is positioned between the seed crystal cover and the powder in the powder bin. The crystal can be grown on the graphite paper first. After the graphite paper is detached, the part with high nitrogen impurity in the initial stage of crystal growth is fixed by the crystallization on the graphite paper. When the crystal is grown on the crystal growth base, the purity is higher, so that the crystal quality is improved.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide crystal growth technology, and particularly to a silicon carbide crystal growth system and a silicon carbide crystal growth method. Background Technology

[0002] The physical vapor transport (PVT) method for growing high-purity silicon carbide crystals typically involves controlling material purity, equipment vacuum, furnace cleaning, desorption of adsorbed gases (hydrogen), and high-temperature, high-speed growth to remove nitrogen from the reaction chamber. However, because it is difficult to operate and preserve graphite parts, insulation felts, and powder loading in a vacuum environment, nitrogen doping usually occurs for a period during the initial stage of crystal growth, affecting crystal purity and optical properties. Typically, during the initial stage of crystal growth, as the temperature rises, residual nitrogen in the insulation felt and crucible is released, resulting in doping at the seed crystal growth interface. This leads to the initial crystal growth (approximately 5-6 mm) having insufficient purity to meet the requirements for high-purity or optical crystals, causing high nitrogen impurity content in the early stages of silicon carbide crystal growth due to nitrogen adsorption. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, one objective of this invention is to provide a silicon carbide crystal growth system with a mating component. The mating component can be used to position graphite paper at the opening of a powder cylinder. During crystal growth, growth can begin on the graphite paper. After the graphite paper detaches, the portion of the crystal with higher nitrogen impurity content in the early stage of growth is fixed by the crystals on the graphite paper. At this point, the growth temperature and nitrogen impurity content are more favorable for improving crystal purity compared to the nitrogen impurity desorption stage. The sublimated gaseous components begin to grow on the crystal growth substrate with higher purity, thereby improving crystal quality.

[0004] A silicon carbide crystal growth system according to an embodiment of the present invention includes: a powder cylinder, a fitting component, and a seed crystal cover. The powder cylinder has an opening at its upper end and a powder hopper inside. The fitting component is connected to the powder cylinder and is configured to position graphite paper located above the powder hopper and detaching after a predetermined condition is met. The seed crystal cover is disposed above the opening, and its lower surface is formed as a crystal growth base. The seed crystal cover is higher than the graphite paper.

[0005] According to the silicon carbide crystal growth system of the present invention, by connecting a fitting for positioning graphite paper to the powder cylinder, the graphite paper can be located between the seed crystal cover and the powder in the powder hopper. This avoids the crystal growing directly on the crystal growth base located on the seed crystal cover in the early stage of crystal growth. Instead, the crystal grows on the graphite paper first. After the graphite paper falls off, the part of the crystal with high nitrogen impurity content in the early stage of crystal growth is fixed by the crystal on the graphite paper. At this time, the growth temperature and nitrogen impurity content are more conducive to improving crystal purity than in the nitrogen impurity desorption stage. The sublimated gas phase component begins to grow on the crystal growth base with high purity, thereby improving crystal quality.

[0006] In addition, the silicon carbide crystal growth system according to the above embodiments of the present invention may also have the following additional technical features: In some embodiments of the present invention, the predetermined condition is that the graphite paper falls off after reaching a predetermined weight.

[0007] In some embodiments of the present invention, the mating member is disposed at the upper end of the powder cylinder, the mating member is opposite to the periphery of the opening of the powder cylinder in the vertical direction, and the mating member and the periphery of the opening of the powder cylinder are adapted to clamp and position the graphite paper.

[0008] In some embodiments of the present invention, a first guide tube is provided on the inner side of the periphery of the opening, and the first guide tube and the mating component are opposite each other in the vertical direction. The graphite paper is disposed between the first guide tube and the mating component, and the projection of the inner sidewall of the mating component in the vertical direction protrudes beyond the projection of the inner sidewall of the first guide tube in the vertical direction.

[0009] In some embodiments of the present invention, in the vertical direction, the minimum horizontal distance between the inner sidewalls of the mating component and the inner sidewalls of the first guide tube is L, satisfying 0.4mm ≤ L ≤ 0.6mm; and / or The inner diameter of the first guide tube gradually decreases from bottom to top.

[0010] In some embodiments of the present invention, the silicon carbide crystal growth system includes a sealing element, the upper end of which is sealed to the seed crystal cap, and the lower end of which is sealed to the mating element.

[0011] In some embodiments of the present invention, the silicon carbide crystal growth system includes a second flow guide tube, which is higher than the mating component, and the inner space of the second flow guide tube is opposite to the inner space of the mating component in the vertical direction; the sealing component includes a support portion extending in the vertical direction and a support portion extending in the horizontal direction, the support portion being sealed to the seed crystal cover, the support portion being sealed to the mating component, and the support portion supporting the second flow guide tube in the vertical direction.

[0012] In some embodiments of the present invention, the silicon carbide crystal growth system includes a graphite plate located between the seed crystal cover and the graphite paper, the support portion supporting the graphite plate, and the graphite plate supporting the second guide tube.

[0013] In some embodiments of the present invention, the silicon carbide crystal growth system includes a positioning block disposed horizontally between the support portion and the second guide tube.

[0014] In some embodiments of the present invention, the silicon carbide crystal growth system includes: a growth container, a heat insulation layer and a carbon-based barrier layer, wherein the powder cylinder is disposed inside the growth container; the heat insulation layer covers the outer side of the growth container; and the carbon-based barrier layer is disposed between the outer side of the growth container and the heat insulation layer.

[0015] In some embodiments of the present invention, the carbon-based barrier layer is graphite paper or carbon cloth.

[0016] According to an embodiment of the present invention, a method for growing silicon carbide crystals employs a silicon carbide crystal growth system as described above. The crystal growth method includes: positioning the graphite paper above the powder hopper and between the mating component; heating the powder hopper to cause the sublimated gaseous components of the powder in the powder cylinder to converge towards the graphite paper, thereby growing a polycrystalline structure on the graphite paper until the graphite paper falls off into the powder hopper; and continuing to heat the powder hopper to cause the sublimated gaseous components of the powder in the powder cylinder to converge towards the crystal growth base, thereby growing a crystal on the crystal growth base.

[0017] According to the silicon carbide crystal growth method of this invention, in the initial stage of crystal growth, the sublimated component does not participate in the crystal growth process. Instead, it crystallizes in a polycrystalline form on the top of the powder, i.e., on the graphite paper. Due to the high initial temperature, nitrogen impurities are easily incorporated into the crystal. Therefore, in the initial stage, this sublimated gaseous component crystallizes in a polycrystalline form on the powder surface, as described above. After crystallization, it is beneficial for some of the residual nitrogen impurities in the initial stage to be crystallized and fixed. When the graphite paper falls into the powder hopper, the polycrystalline component falls with the graphite paper and is placed on the powder surface. As the crystal grows and the temperature continues to increase, the later part of the polycrystalline silicon carbide powder with higher nitrogen content becomes more difficult to participate in the crystal growth process due to the high temperature and the principle of high-temperature nitrogen removal. Therefore, the gaseous component can continue to sublimate and accumulate on the crystal growth base. At this time, the grown crystal has a high purity. Therefore, the final crystal obtained by the growth method of this application does not contain the part with high nitrogen impurities in the initial stage of crystal growth, and a crystal with high overall purity can be obtained directly, thereby improving the crystal quality.

[0018] In some embodiments of the present invention, before positioning the graphite paper, the growth method further includes: placing the powder from bottom to top at the bottom of the powder hopper, wherein the particle size of the powder located in the lower layer of the powder hopper is larger than the particle size of the powder located in the upper layer of the powder hopper. Attached Figure Description

[0019] Figure 1 This is a partial structural schematic diagram of the silicon carbide crystal growth system in some embodiments of the present invention (showing the state in which the mating component positions the graphite paper above the powder hopper). Figure 2 This is a magnified view of a partial structure of the silicon carbide crystal growth system in some embodiments of the present invention (a magnified view of the partial thermal field of silicon carbide crystal growth). Figure 3 This is a partial structural schematic diagram of the silicon carbide crystal growth system in some embodiments of the present invention (showing the state after the graphite paper has fallen off). Figure 4 This is a partial structural schematic diagram of a silicon carbide crystal growth system in some embodiments of the present invention (showing the powder cylinder placed inside the pot or showing the silicon carbide crystal growth thermal field). Figure 5 This is a schematic diagram of the structure of the silicon carbide crystal growth system in some embodiments of the present invention; Figure 6 A schematic diagram of the crystal structure in the related technology is shown.

[0020] Figure label: 100. Growth system; 10a. Graphite paper; 11. Powder cylinder; 101. Powder hopper; 12. Fitting parts; 13. Seed crystal cover; 103. Vent hole; 14. First guide tube; 15. Sealing element; 16. Second guide tube; 161. Support part; 162. Support part; 17. Graphite plate; 18. Positioning block; 19. Support plate; 10b. Crystal growth base; 10c. Polycrystalline; 10d. First powder; 10e. Second powder; 110. First sealed chamber; 120. Second sealed chamber; 20. Growth container; 21. Pot body; 211. Mounting base; 212. Support component; 22. Insulation layer; 23. Cover; 24. Carbon-based barrier layer; 31. Quartz tube; 32. Upper flange; 33. Stage; 34. Temperature measuring window; 301. Temperature measuring hole; 35. Induction coil; A. Upper part; B. Lower part. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] Combination Figure 1 and Figure 4 According to an embodiment of the present invention, a silicon carbide crystal growth system 100 includes: a powder cylinder 11, a mating member 12, and a seed crystal cover 13. The powder cylinder 11 has an opening at its upper end and a powder hopper 101 inside, where powder can be placed. The mating member 12 is connected to the powder cylinder 11 and is configured to position a graphite paper 10a located above the powder hopper 101 and detaching after a predetermined condition is met. The seed crystal cover 13 is located above the opening, and its lower surface is formed as a crystal growth base 10b. The seed crystal cover 13 is higher than the graphite paper 10a.

[0023] Specifically, optical crystals simply require high crystal purity and low impurities. In the early stages of crystal growth, impurities such as nitrogen are in the process of desorption and removal, so the crystal purity generally cannot meet the standards.

[0024] During the silicon carbide crystal growth process, a certain amount of nitrogen gas is adsorbed into the powder. As the temperature gradually increases, after desorption, it participates in the initial crystal growth process, generally showing a gradual change from dark green to light green, and then to pale green / pale yellow. This part has a high nitrogen impurity content, causing the initial purity of the crystal to not meet the requirements for high-purity or optical crystals. Therefore, by placing graphite paper 10a between the crystal growth substrate 10b and the powder, the crystal can grow on the graphite paper 10a in the initial stage of crystal growth. After reaching the predetermined conditions, the graphite paper 10a detaches (see...). Figure 3 The crystals or polycrystalline materials 10c grown on the graphite paper 10a, after falling into the powder container 11, avoid the poor crystal purity caused by the nitrogen release stage participating in crystal growth. After the graphite paper 10a falls off, the gaseous components can converge towards the crystal growth base 10b. At this time, the growth temperature and nitrogen impurity content are more conducive to improving crystal purity compared to the nitrogen impurity desorption stage, and the crystal begins to grow on the crystal growth base 10b. Thus, crystals with less nitrogen impurities and higher purity can be formed on the seed crystal cover 13.

[0025] Specifically, graphite paper 10a can be placed above powder cylinder 11 and positioned using mating part 12 to achieve assembly and replacement of graphite paper 10a. In the early stages of crystal growth, nitrogen is present in the atmosphere. If it directly participates in the growth at the crystal growth base 10b, the initial crystal will contain nitrogen impurities and have a greenish tint. Therefore, it is desirable that this initial sublimation component not be incorporated into crystal growth, but rather crystallizes as polycrystalline 10c on the graphite paper 10a at the top of the powder. Due to the higher initial temperature, nitrogen impurities are more easily incorporated into the crystal. Therefore, this initial sublimation gas phase component can crystallize as polycrystalline 10c on the surface of graphite paper 10a. After crystallization, it is beneficial for the initial residual nitrogen impurities to be fixed. After the graphite paper 10a detaches, this crystallization remains on the powder surface. As crystal growth and temperature increase, this later part of the polycrystalline 10c / silicon carbide powder with higher nitrogen content becomes more difficult to participate in the crystal growth process due to the higher temperature, utilizing the principle of high-temperature nitrogen removal.

[0026] According to the silicon carbide crystal growth system 100 of the present invention, by connecting a fitting 12 for positioning graphite paper 10a to the powder cylinder 11, the graphite paper 10a can be located between the seed crystal cover 13 and the powder in the powder hopper 101. This avoids the crystal growing directly on the crystal growth base 10b located on the seed crystal cover 13 in the early stage of crystal growth. Instead, the crystal grows on the graphite paper 10a first. After the graphite paper 10a falls off, the part with higher nitrogen impurity content in the early stage of crystal growth is fixed by the crystal on the graphite paper 10a. At this time, the growth temperature and nitrogen impurity content are more conducive to improving crystal purity than in the nitrogen impurity desorption stage. The sublimated gas phase component begins to grow on the crystal growth base 10b with higher purity, thereby improving crystal quality.

[0027] In some examples, a crystal growth space is formed below the seed crystal cover 13 and the powder cylinder 11. An initial crystal growth space can be formed between the powder cylinder 11 and the graphite paper 10a.

[0028] Combination Figure 4 In some examples, the seed crystal cover 13 can be made of purified graphite, and the edge of the seed crystal cover 13 is provided with vent holes 103 to facilitate venting. The crystal growth base 10b can be fixed to the surface of the seed crystal cover 13 by adhesive bonding. The crystal growth base 10b can be a seed crystal, with the carbon surface of the seed crystal facing the powder side.

[0029] In some embodiments of the present invention, the predetermined condition can be that the graphite paper 10a detaches after reaching a predetermined weight. In actual operation, this can be achieved by controlling the stability of the positioning of the graphite paper 10a by the mating member 12, so that the graphite paper 10a detaches from the mating member 12 and the powder cylinder 11 when the predetermined weight is reached. For example, in practical applications, the predetermined weight is selected based on information such as the thickness or weight of the crystal in the initial growth stage, according to the size of the growth system 100 or the size of the crystal after growth. For example, the contact area between the graphite paper 10a and the mating member 12 can be adjusted according to the size of the growth system 100 or the predetermined weight, so that the graphite paper 10a detaches from the mating member 12 when the predetermined weight is reached.

[0030] In some embodiments, the predetermined condition may also be that the graphite paper 10a falls off after a predetermined time has elapsed.

[0031] In some examples, the thickness of the graphite paper 10a is t, satisfying 0.2mm ≤ t ≤ 0.4mm. By setting a suitable thickness for the graphite paper 10a, it can be used to support crystal growth and allow it to detach under predetermined conditions. In practical applications, the thickness can also be set according to the actual dimensions of the silicon carbide crystal growth system 100. For example, the thickness of the graphite paper 10a can be set based on the dimensions of the powder cylinder 11 and the seed crystal cover 13.

[0032] Combination Figure 1 In some embodiments of the present invention, the mating member 12 is disposed at the upper end of the powder cylinder 11, which facilitates the installation of graphite paper 10a above the powder cylinder 11. The mating member 12 and the periphery of the opening of the powder cylinder 11 are opposite each other in the vertical direction. In this way, after the graphite paper 10a is installed, a portion of the graphite paper 10a can be located between the periphery of the opening of the powder cylinder 11 and the mating member 12, and a portion of the edge of the graphite paper 10a can be supported by the periphery of the opening of the powder cylinder 11. The powder cylinder 11 can support the graphite paper 10a, which helps to improve the stability of the graphite paper 10a after assembly. The mating member 12 and the periphery of the opening of the powder cylinder 11 are suitable for clamping and positioning the graphite paper 10a. After the mating part 12 is installed above the powder cylinder 11, a clamping force is generated between the mating part 12 and the opening of the powder cylinder 11, which can improve the positioning effect of the graphite paper 10a, improve the stability of the graphite paper 10a after installation, and prevent the graphite paper 10a from falling off before the predetermined conditions are met, thus affecting the growth quality of the crystal.

[0033] Combination Figure 4The mating component 12, powder cylinder 11, and graphite paper 10a can construct a first sealed chamber 110 facing the powder. During the initial stage of crystal growth, the crystal can grow within this first sealed chamber 110. Specifically, the gaseous components generated by the heating and sublimation of the powder in the powder cylinder 11 can converge upwards onto the graphite paper 10a, where they crystallize or grow into polycrystalline forms 10c. During the initial growth of the silicon carbide crystal, the nitrogen adsorbed in the graphite components, insulation components, and silicon carbide powder, after desorption as the temperature rises, participates in the crystal growth process within the first sealed chamber 110, i.e., in the crystallization on the graphite paper 10a. This significantly reduces the nitrogen impurity content of the crystal ultimately grown on the crystal growth substrate 10b, thus improving the purity of the final product crystal.

[0034] In some embodiments of the present invention, a first guide tube 14 is provided on the inner side of the periphery of the opening, and the first guide tube 14 and the mating member 12 are opposite each other in the vertical direction. Graphite paper 10a is disposed between the first guide tube 14 and the mating member 12, and the projection of the inner sidewall of the mating member 12 in the vertical direction protrudes beyond the projection of the inner sidewall of the first guide tube 14 in the vertical direction.

[0035] Specifically, the first guide tube 14 can guide the gas phase components to flow in the direction of the graphite paper 10a. In the vertical direction, the mating part 12 extends beyond the inner side of the first guide tube 14, resulting in a higher temperature on the horizontal direction facing the powder side of the graphite paper 10a due to the presence of the mating part 12 or the influence of the part of the mating part 12 protruding from the first guide tube 14. This inhibits or decomposes the local polycrystalline 10c, causing a decrease in the adhesion of the graphite paper 10a at the edge. As a result, after a period of crystal growth, the load-bearing capacity of the graphite paper 10a decreases, and the graphite paper 10a will fall off. After the graphite paper 10a fails, the sublimated gas phase components converge on the surface of the crystal growth base 10b on the seed crystal cover 13, and crystal growth begins.

[0036] Combination Figure 2 In the vertical direction, the minimum horizontal distance between the inner walls of the mating part 12 and the inner walls of the first guide tube 14 is L, satisfying 0.4mm≤L≤0.6mm. Specifically, the portion of the mating part 12 protruding from the first guide tube 14 should only slightly protrude from the first guide tube 14, thereby promoting a higher temperature at the edge of the graphite paper 10a, which facilitates the automatic detachment of the graphite paper 10a after the crystals have grown to a certain extent.

[0037] In some examples, L can be 0.45mm, 0.5mm, 0.55mm, etc.

[0038] For example, in a specific embodiment of the present invention, if the inner diameter of the mating component is 234 mm, then the inner diameter at the thickest point of the inner wall of the first guide tube 14 is 233 mm. The technical effect of this structural design is that, in the vertical direction of the cross-sectional view, the mating component 12 extends 0.5 mm beyond the thickest point of the inner wall of the guide tube.

[0039] Combination Figure 1 and Figure 2 In some embodiments of the present invention, the inner diameter of the first guide tube 14 gradually decreases in the upward direction. Thus, the first guide tube 14 can be in a gradually contracting form from bottom to top, which can optimize the gas flow field and temperature field, facilitating more precise control of the crystal growth profile. Consequently, after being guided by the first guide tube 14, the crystal is less likely to grow at the edge of the graphite paper 10a, and is less likely to affect the detachment of the graphite paper 10a under predetermined conditions.

[0040] Specifically, in combination Figure 2 The powder cylinder 11 has a notch on the inner periphery of the opening. The first guide cylinder 14 can be inserted into the notch, which facilitates the assembly of the first guide cylinder 14 and reduces the space occupied by the first guide cylinder 14 in the powder cylinder 11. It also facilitates the setting of the dimensional relationship between the inner wall of the first guide cylinder 14 and the inner wall of the powder cylinder 11 or the inner wall of the mating part 12.

[0041] Combination Figure 4 In some examples, the inner diameter of the mating part 12 is R1, and the maximum inner diameter of the first guide tube 14 is R2, satisfying 0.8mm≤R2-R1≤1.2mm. The inner diameter of the mating part 12 can be 0.9mm, 1mm, or 1.1mm larger than the maximum inner diameter of the first guide tube 14.

[0042] Combination Figure 4 In some embodiments of the present invention, the silicon carbide crystal growth system 100 includes a sealing member 15, the upper end of which is sealed to the seed crystal cover 13, and the lower end of which is sealed to the mating member 12.

[0043] Specifically, the sealing element 15 is sealed between the seed crystal cover 13 and the upper end of the mating element 12, so that a relatively closed crystal growth space can be formed between the powder cylinder 11, the mating element 12, the sealing element 15, and the seed crystal cover 13. Normally, the seed crystal cover 13 can be directly connected to the powder cylinder 11. However, in this application, a mating element 12 for positioning the graphite paper 10a is provided between the seed crystal cover 13 and the powder cylinder 11. Therefore, by providing the sealing element 15, the assembly of the graphite paper 10a can be facilitated. Since the sealing element 15 is provided between the mating element 12 and the seed crystal cover 13, the vertical dimension of the mating element 12 does not need to be too large, which facilitates control over the positioning effect on the graphite paper 10a and also facilitates assembly, thereby preventing damage to the graphite paper 10a during assembly due to excessive height of the mating element 12.

[0044] Combination Figure 4 In some embodiments of the present invention, the silicon carbide crystal growth system 100 includes a second guide tube 16, which is higher than the mating member 12. The inner space of the second guide tube 16 is opposite to the inner space of the mating member 12 in the vertical direction. After the graphite paper 10a falls off, the gas phase component can continue to grow upward on the crystal growth base 10b. During the process of the gas phase component reaching the crystal growth base 10b located on the seed crystal cover 13, it first passes through the mating member 12 and the second guide tube 16. Due to the fall off of the graphite paper 10a, the gas phase component can reach the inner side of the second guide tube 16 through the mating member 12. After being guided by the second guide tube 16, it gathers on the crystal growth base 10b for growth.

[0045] Combination Figure 4 The sealing element 15 includes a support portion 161 extending in the vertical direction and a support portion 162 extending in the horizontal direction. The support portion 162 is connected to the lower end of the support portion 161. The support portion 161 is sealed to the seed crystal cover 13. The support portion 162 is sealed to the mating part 12. The support portion 162 can support the second guide tube 16 in the vertical direction.

[0046] Specifically, one end of the second guide tube 16 is connected to the support portion 162 and extends axially toward the seed crystal cover 13. Axially, the inner wall of the second guide tube 16 extends inwardly at an angle, and its inner diameter gradually decreases toward the seed crystal cover 13. Thus, the second guide tube 16 can be designed to gradually taper upwards, optimizing the gas flow field and temperature field, facilitating more precise control of the crystal growth profile. Consequently, with the guidance of the second guide tube 16, the crystal is less likely to grow at the edge of the graphite paper 10a, promoting the formation of a micro-convex interface and improving crystal quality.

[0047] Combination Figure 2In some embodiments of the present invention, the silicon carbide crystal growth system 100 includes a support plate 19 connected to the upper opening of the powder cylinder 11. The outer periphery of the graphite paper 10a is placed on the support plate 19. Thus, the support plate 19 can support the graphite paper 10a and create a buffer plane between the powder cylinder 11 and the mating component 12, which helps improve the stability of the graphite paper 10a after installation. Specifically, the support plate 19 can be a graphite sheet or an annular graphite plate 17, which can support the edge of the graphite paper 10a. In some embodiments of the present invention, the silicon carbide crystal growth system 100 includes a graphite plate 17 located between the seed cover 13 and the graphite paper 10a. A support portion 162 supports the graphite plate 17, and the graphite plate 17 supports the second guide tube 16. Specifically, the sublimated gaseous components can pass through the graphite plate 17 and enter the crystal growth space located below the seed cover 13. After the graphite paper 10a falls off, the sublimated gaseous components begin to pass through the graphite plate 17 and converge towards the surface of the crystal growth base 10b, and crystal growth begins. The graphite plate 17 can play a role in "filtering" and "homogenizing" to improve crystal quality and raw material utilization.

[0048] The graphite plate 17 can be a porous graphite plate. At high temperatures, tiny carbon particles in the SiC raw material will rise with the airflow. The porous structure of the porous graphite plate 17 can physically trap these carbon particles, preventing them from reaching the growth interface. In addition, its porous structure allows the gaseous substances sublimated from the powder to pass through more uniformly, avoiding excessively fast local airflow or turbulence. At the same time, it can also participate in thermal field regulation, making the temperature distribution in the raw material area more uniform.

[0049] In conjunction with the foregoing, the sealing element 15 can also provide support for the graphite plate 17, thereby facilitating the installation of the graphite plate 17. Therefore, there is no need to set up a structure for installing the graphite plate 17 inside the powder cylinder 11, which simplifies the structure of the powder cylinder 11. Since the graphite paper 10a can divide the growth system 100 into two crystal growth spaces during the crystal growth process, by setting the sealing element 15, the growth space between the upper end of the powder cylinder 11 and the seed crystal cover 13 can be sealed, and the installation of the second guide cylinder 16 and the graphite plate 17, which are conducive to crystal growth, can also be facilitated.

[0050] In some examples, the porosity of the graphite plate 17 (i.e., the percentage of the volume of pores (i.e., voids) inside the graphite plate to the total volume) is between 45% and 48% (which may include 45% and 48%), thereby achieving the technical effect of filtering carbon encapsulation.

[0051] Combination Figure 4In some embodiments of the present invention, the silicon carbide crystal growth system 100 includes a positioning block 18, which is horizontally disposed between the support portion 161 and the second guide tube 16. The positioning block 18 can define and position the position of the second guide tube 16, and facilitates holding the second guide tube 16 in a predetermined position. One end face of the positioning block 18 can be connected to the support portion 162. In the radial direction, one end of the positioning block 18 abuts against the support portion 161 and the other end abuts against the second guide tube 16.

[0052] In practical applications, the size of the positioning block 18 can be set according to the actual size of the seal 15 and the second guide tube 16 so that the second guide tube 16 is stably connected to the predetermined position of the support part 162 of the seal 15, and the structure is simple and easy to construct.

[0053] Specifically, the positioning block 18 can be made of graphite, and the positioning block 18 can be annular, or multiple positioning blocks 18 can be arranged circumferentially to be positioned between the seal 15 and the second guide tube 16.

[0054] Combination Figure 4 In the vertical direction, the support portion 162 is located at the upper end of the mating part 12, and a portion of the lower end face of the support portion 162 is connected to the upper end face of the mating part 12, which can improve the sealing effect and structural stability. The edge of the graphite plate 17 is stacked and connected to the upper end face of the support portion 162, and the positioning block 18 and the second guide tube 16 are stacked and connected to the graphite plate 17, resulting in a compact structure and strong stability. In the horizontal direction, the positioning block is located between the outer wall surfaces of the support portion 161 and the second guide tube 16, which can be used to adjust the installation position of the second guide tube 16. For example, it can control the positional relationship between the inner side wall of the upper end of the second guide tube 16 and the crystal growth base 10b.

[0055] In some examples, combined Figure 4 A second sealed chamber 120 can be constructed between the seed crystal cover 13, the sealing element 15, and the graphite plate 17. During the later stages of crystal growth, the crystal can grow within the second sealed chamber 120. Specifically, after the graphite paper 10a and the polycrystals 10c on it fall off, the growth temperature and nitrogen impurity content are more favorable for improving crystal purity compared to the nitrogen impurity desorption stage. The sublimated gaseous components begin to pass through the graphite plate 17, enter the second sealed chamber 120, and converge towards the surface of the crystal growth base 10b, thus initiating crystal growth.

[0056] Combination Figure 4 In some embodiments of the present invention, the silicon carbide crystal growth system 100 includes a growth container 20, which includes a pot body 21 and a cover body 23. A powder cylinder 11 is disposed inside the pot body 21, and the cover body 23 covers the pot body 21.

[0057] Specifically, the pot body 21 can be a crucible. By placing the powder cylinder 11 inside the pot body 21, compared to directly placing the powder inside the crucible, the spatial structure is more complex and can be divided into different areas, which is beneficial for optimizing the airflow channels. In addition, by adjusting the thermal field through the built-in graphite components, the radial temperature gradient of the powder layer can be effectively reduced, making the heat distribution more uniform, which is beneficial for improving crystal quality, making powder consumption more uniform, and improving growth efficiency and raw material utilization.

[0058] The silicon carbide crystal growth system 100 also includes a heat insulation layer 22 and a carbon-based barrier layer 24. The heat insulation layer 22 wraps around the outer surface of the growth container 20, providing a heat insulation effect. The heat insulation felt is generally made of graphite, such as graphite felt. During heating, the continuous release of nitrogen from the graphite felt is a significant source of impurities. Therefore, placing the carbon-based barrier layer 24 between the growth container 20 and the heat insulation layer 22 can effectively prevent nitrogen from entering the growth container 20. Simultaneously, the carbon-based barrier layer 24 can also prevent external atmospheric impurities from accumulating inside the container.

[0059] Specifically, the pot body 21 and the lid 23 can be a crucible and a crucible lid. By arranging a layer of high-purity graphite paper 10a or carbon cloth between the crucible and the graphite felt, external atmospheric impurities can be blocked from accumulating into the crucible, thereby reducing the nitrogen impurity content in the growth container and improving the crystal growth quality.

[0060] Combination Figure 4 The sidewalls of the pot body 21 can have a certain thickness to provide insulation. An inner space is constructed within the pot body 21, and the powder cylinder 11 is housed within this space. A gap exists between the outer wall of the powder cylinder 11 and the inner wall of the pot body 21 to reduce heat loss. The bottom wall of the pot body 21 has a recessed mounting base 211, within which the bottom of the powder cylinder 11 is installed. This facilitates positioning and assembly of the powder cylinder 11, improving the structural stability after assembly.

[0061] The upper end of the pot body 21 is open, and an annular recess is provided on the outer periphery of the opening of the pot body 21. The lid 23 includes a top cover extending horizontally and a side cover extending vertically. During assembly, the top cover is placed on the upper end of the opening of the pot body 21, and the side cover extends into the annular recess on the periphery of the opening of the pot body 21. The inner side of the side cover of the lid 23 is threaded, and the outer side of the annular recess is threaded. Thus, the lid 23 can be fixedly connected to the pot body 21 and has a certain degree of sealing. After installation, the lid 23 is flush with the pot body 21 in the vertical direction, which is beneficial for space arrangement.

[0062] When the carbon-based barrier layer 24 is wrapped, the carbon-based barrier layer 24 can be adhered to the outer surface of the growth container 20. For example, the carbon-based barrier layer 24 can wrap the bottom and side walls of the pot body 21 and the side walls of the lid 23. That is, the connection between the lid 23 and the pot body 21 can be wrapped in the carbon-based barrier layer 24, thereby further reducing the possibility of external nitrogen impurities entering the growth container 20 and improving the effect of blocking nitrogen impurities from entering the growth container 20.

[0063] In addition, the side cover of the lid 23 can also serve to keep the pot body 21 warm.

[0064] Combination Figure 4 The pot body 23 may be provided with a support member 212, which is connected to the inner wall of the pot body 21. The seed crystal cover 13 extends horizontally, and the periphery of the seed crystal cover 13 can abut against the upper end of the support member 212 in the vertical direction, which helps to improve the stability of the seed crystal cover 13 after installation and improve the tightness of the fit between the seed crystal cover 13 and the growth container 20.

[0065] In some examples, the carbon-based barrier layer 24 can be graphite paper, carbon paper, or carbon cloth. The thickness and other dimensions of the carbon cloth can be t, satisfying 1mm ≤ t ≤ 1.5mm. By selecting a suitable thickness of carbon paper, it is beneficial to maintain structural stability and to maintain appropriate filtration and uniform gas phase effects.

[0066] Specifically, wrapping the outside of the pot body 21 with high-purity carbon paper / carbon cloth essentially creates an external nitrogen source (graphite felt / furnace atmosphere). crucible wall Between the growth chambers, a carbon-based barrier layer 24 is added. Through four mechanisms—physical barrier, adsorption and retention, chemical reaction consumption, and extension of the diffusion path—it significantly inhibits the diffusion of external nitrogen impurities into the crystal and reduces nitrogen impurities in the crystal. The typical temperature for SiC crystal growth (PVT) is 2100–2400℃, and the main body of the thermal field is composed of graphite / carbon felt.

[0067] Therefore, nitrogen impurities mainly originate from: 1. Residual atmosphere: N2 adsorbed in the furnace cavity and the pores of the insulation layer (residual air, graphite / carbon felt adsorption); 2. Graphite crucible / insulation material: carbon materials themselves adsorb N, which desorbs at high temperatures, becoming N2 or active N atoms that diffuse inwards; 3. External leakage: minor leaks in the furnace body allow N2 to penetrate into the thermal field. Nitrogen exists at high temperatures as N2 molecules, N atoms, CN, and NH4+. x In the form of these substances, they diffuse through the pores into the crucible and then into the growth region, entering the SiC crystal as shallow donor impurities, affecting semi-insulation, resistivity, and optical properties.

[0068] Therefore, this application uses a layer of high-purity carbon cloth / graphite paper bonded between the crucible and the graphite felt to block nitrogen diffusion. The mechanism is as follows: 1. The carbon paper / carbon cloth has high purity, is free of binders, is heat resistant (>2500℃), has three-dimensional porosity, and features interwoven carbon fibers; 2. Encased in the outer wall of the crucible (or between the crucible and the insulation layer 22), forming an "outer garment," it can create a physical barrier and simultaneously extend the diffusion path of nitrogen impurities. The carbon cloth / carbon paper has a high density, with tortuous channels and interwoven multiple layers of fibers, resulting in a labyrinthine, non-straight-through pore structure. For nitrogen impurity atoms to diffuse from the outside to the inside, they must flow and collide multiple times within the fiber gaps, significantly lengthening the diffusion path. Compared to direct contact with the insulation layer 22, where the diffusion was originally "straight-through," it now involves "tortuous paths + multiple layers of obstruction," resulting in a substantial decrease in diffusion flux. 3. Adsorption and retention: Carbon surfaces strongly adsorb nitrogen species. High-temperature carbon surfaces have strong physical adsorption of N2, N atoms, and CNx. Nitrogen species that diffuse in from the outer layer are preferentially captured and retained by the carbon paper / carbon cloth surface and are not easy to continue to penetrate inward. 4. Most importantly, the outermost layer of carbon cloth / paper, in addition to its strong adsorption effect, also involves chemical reaction consumption: carbon reacts with active nitrogen, consuming N. At temperatures >1800℃ under hydrogen conditions, carbon reacts with active nitrogen (N atoms, CN, NH): C + N → CN (cyano group) and 2C + N2 → C2N2 (cyanide gas). These carbon-nitrogen compounds have low boiling points and are highly volatile, diffusing outwards and being carried away by argon gas, rather than entering the crucible inwards. Therefore, the outer carbon cloth / paper can actively consume the inwardly diffusing active nitrogen, converting harmful N into expellable gaseous CN / C2N2.

[0069] Carbon paper / carbon cloth has moderate thermal conductivity and provides insulation and buffering, making the temperature of the outer wall of the crucible more uniform and reducing local high-temperature desorption of N. With the outer layer of N blocked / consumed, the nitrogen partial pressure at the inner wall of the crucible is significantly reduced. According to Fick's diffusion law, the concentration difference between the inside and outside decreases, and the driving force for inward diffusion weakens.

[0070] Therefore, the material selection criteria for high-purity carbon paper / carbon cloth / graphite paper in this application are as follows: 1. High purity (below 5ppm), extremely low inherent impurities (B, N, O), and no additional nitrogen is introduced.

[0071] 2. Dense and thin-layered: Carbon paper / carbon cloth fibers are fine and densely interwoven, resulting in a significantly higher barrier efficiency than loose carbon felt. The manufacturing process of carbon paper / cloth is also more compact; rigid felt is made by weaving and pressing graphite fibers. Specific densities can reflect this. For example, dense graphite paper can achieve a density of 1.05 g / cm³, while the density of graphite felt is typically 0.05–0.08 g / cm³ (inclusive).

[0072] 3. Flexible fit, tightly wrapping the outer wall of the crucible without gaps, avoiding "bypass nitrogen leakage".

[0073] In practical applications, a layer of high-purity graphite paper, carbon cloth, or carbon paper can be placed between the pot body 21 and the insulation layer 22 before loading the furnace to prevent external atmospheric impurities from accumulating inside the crucible.

[0074] Combination Figure 5 The silicon carbide crystal growth system 100 also includes a furnace body, a furnace cover, an induction coil 35, and a stage 33. The furnace body includes a quartz tube 31 and a lower flange, with the lower flange located at the lower end of the quartz tube 31. The furnace cover can be an upper flange 32, located at the upper end of the quartz tube 31. The crucible body 21 is located inside the quartz tube 31, and the induction coil 35 surrounds the outside of the quartz tube 31. The upper flange 32 has a temperature measuring window 34, and the top of the cover 23 has a temperature measuring hole 301 opposite to the temperature measuring window 34. When it is necessary to measure the temperature of the crucible (i.e., the crucible body 21 and the cover 23), the thermometer can be mounted on the upper flange 32 via a bracket and arranged opposite to the temperature measuring window 34.

[0075] Combination Figures 1 to 4 The present invention also proposes a crystal growth method using the aforementioned silicon carbide crystal growth system 100. The crystal growth method includes: positioning graphite paper 10a above the powder hopper 101 and between the mating component 12; heating the powder hopper 101 to cause the sublimated gaseous components of the powder in the powder cylinder 11 to converge towards the graphite paper 10a, and growing polycrystalline material 10c on the graphite paper 10a until the graphite paper 10a falls off into the powder hopper 101; continuing to heat the powder hopper 101 to cause the sublimated gaseous components of the powder in the powder cylinder 11 to converge towards the crystal growth base 10b, and growing crystals on the crystal growth base 10b.

[0076] In the crystal growth method of this application, the sublimation component in the early stage of crystal growth will not be involved in the crystal growth, but will crystallize on the top of the powder, i.e., on the graphite paper 10a, in the form of polycrystalline 10c. Due to the high initial temperature, nitrogen impurities are also easily incorporated into the crystal. Therefore, the sublimation gas phase component in the early stage, as described above, crystallizes on the powder surface in the form of polycrystalline 10c. After crystallization, it is beneficial for some of the residual nitrogen impurities in the early stage to be crystallized and fixed. When the graphite paper 10a falls into the powder hopper 101, the polycrystalline 10c falls with the graphite paper 10a and is placed on the powder surface. As the crystal grows and the temperature continues to increase, the later part of the polycrystalline 10c / silicon carbide powder with higher nitrogen content will be more difficult to participate in the crystal growth process due to the high temperature and the principle of high-temperature nitrogen removal. Therefore, the gas phase components can continue to sublimate and accumulate on the crystal growth base 10b. At this time, the grown crystal has a high purity. Thus, the final crystal obtained by the growth method of this application does not contain the part with high nitrogen impurities in the early stage of crystal growth in related technologies. A crystal with high overall purity can be obtained directly, which is beneficial to improving the crystal quality.

[0077] In other words, the graphite paper 10a is connected to the mating component 12 and the powder cylinder 11 during crystal growth. After crystal growth is complete, the graphite paper 10a separates from the powder cylinder 11 and the mating component 12 and falls into the powder hopper 101. The graphite paper 10a can be a replaceable component in the crystal growth process. A new graphite paper 10a can be replaced for the next crystal growth. Before operation, the graphite paper 10a can be positioned between the powder cylinder 11 and the mating component 12 so that it can participate in the early stages of crystal growth.

[0078] Combination Figure 1 In some embodiments of the present invention, before positioning the graphite paper 10a, the growth method further includes: placing powder from bottom to top at the bottom of the powder hopper 101, wherein the particle size of the powder in the lower layer of the powder hopper 101 is larger than the particle size of the powder in the upper layer of the powder hopper 101.

[0079] Due to prolonged exposure to high temperatures, the powder undergoes recrystallization and sintering, leading to particle adhesion and reduced porosity. According to the powder arrangement method in this application, the larger particles have larger pores, ensuring unobstructed main transport channels for sublimation gas even during partial sintering under prolonged high temperatures. As a support layer, they are not easily blocked, ensuring stable upward transport of gas from the bottom. The smaller particles have high packing density and large specific surface area, providing ample sublimation area in the early stages of growth. Over time, the upper-layer smaller particles preferentially sinter and densify. However, because the lower-layer larger particles maintain good permeability, gaseous substances can bypass the sintered upper region and continue to be transported upwards laterally or through the gaps between the larger particles. This structure effectively confines the effects of aging primarily to the upper layer, protecting the gas channels of the lower powder layer, thereby extending the effective lifespan of the entire powder source and allowing for a more gradual decline in the sublimation rate during later growth. In the early stages of crystal growth, the reduced sublimation rate of the powder helps to lower the nitrogen impurity content in the initial crystal formation phase.

[0080] like Figure 1 The arrangement of silicon carbide powder in the powder container 11 is shown. The powder in the upper layer can be the first powder 10d, and the powder in the lower layer can be the second powder 10e. The bottom silicon carbide powder has a particle size of 3-8 mesh (including 3 mesh and 8 mesh), with larger particles; the top silicon carbide powder has a particle size of 8-20 mesh (including 8 mesh and 20 mesh), with smaller particles. This arrangement of powder can reduce the sublimation rate of the powder during the heating process or the early stage of growth (during nitrogen desorption), thereby reducing the portion with high nitrogen impurity content in the early stage of crystal formation.

[0081] The following describes a specific embodiment of the silicon carbide crystal growth system 100 and growth method of the present invention with reference to the accompanying drawings.

[0082] The core of high-purity silicon carbide crystal growth lies in substrate purity and impurity control, stable semi-insulating electrical properties, and optical performance meeting technical requirements. Its growth difficulty, yield, and cost are far higher than those of N-type conductive silicon carbide crystals. Currently, the core technical challenges in high-purity silicon carbide crystal growth are concentrated in the following areas: 1. Controlling impurities in SiC powder requires a purity of 6N to 8N, especially for nitrogen (N), which must be less than 1 × 10¹⁵ atoms / cm³. Furthermore, the content of light impurities such as boron (B), aluminum (Al), and phosphorus (P) must also be extremely low. Simultaneously, the raw material (SiC powder) readily adsorbs N₂ from the air; therefore, nitrogen gas is inevitably introduced into the reaction chamber during production. The graphite crucible / insulation material also adsorbs nitrogen gas from the air during loading and unloading, and continuously releases N impurities during the growth process.

[0083] 2. Background impurities in the environment, including volatilization of graphite components (a general term for all graphite components, such as crucibles, flow tubes, seed crystal caps, etc.), vacuum leakage, and impure gas sources, will continuously contaminate the crystal. Therefore, strict requirements must be placed on the background vacuum and leakage rate of crystal growth equipment.

[0084] 3. In terms of process, high-temperature and high-speed growth is employed. The high temperature (typically above 2200℃) exceeds the growth rate of N-type conductive silicon carbide crystals, accelerating the desorption and removal of nitrogen from the graphite parts, insulation felt, and powder in the initial stages. However, even with high-temperature nitrogen removal, nitrogen impurities still participate in crystal growth for a period before and during the growth process. Specifically, for example… Figure 2 As shown, after crystal growth is complete, there will be an initial 5-6 mm portion with high nitrogen content, which leads to a reduction in effective thickness.

[0085] Therefore, in view of the above problems, this application proposes a silicon carbide crystal growth system 100 and method with low nitrogen impurity content, which can improve the purity of silicon carbide crystals and avoid the problem of high nitrogen impurity content in the early stage of silicon carbide crystal growth due to nitrogen adsorption.

[0086] By applying the silicon carbide crystal growth system of this invention, the following technical effects can be achieved: 1. A high-purity carbon paper or carbon cloth is provided on the outer wall of the crucible to prevent external impurities (nitrogen atmosphere) from accumulating inside the crucible, such as those from external graphite felt or vacuum furnace chambers. Because graphite felt (soft or hard felt) is affected by processing technology, purification process, and nitrogen adsorption, the continuous release of nitrogen from the graphite felt after heating is a significant source of impurities for a period of time. Therefore, in this application, a layer of high-purity graphite paper or carbon cloth is placed between the crucible and the graphite felt before loading into the furnace to prevent external atmospheric impurities from accumulating inside the crucible. 2. By designing the powder and thermal field, crystal growth during the early nitrogen release stage is suppressed, and the participation of nitrogen desorption in the early nitrogen desorption stage during crystal growth is avoided, thus completely preventing the problem of high nitrogen impurity content in the initial crystals. The thermal field design involves setting up a first sealed chamber near the powder and a second sealed chamber near the seed crystal cover. During the early nitrogen release stage, the crystal grows in the first sealed chamber, avoiding the participation of nitrogen release in crystal growth. After the graphite paper 10a in the first sealed chamber falls off, the gaseous components can enter the second sealed chamber, converge towards the seed crystal, and grow the crystal.

[0087] Combination Figure 5 The silicon carbide crystal growth system 100 mainly consists of: a quartz tube 31, an induction coil 35, an upper flange 32, a lower flange, a temperature measuring device, a water cooling device, a vacuum device, and process gas paths. The main components of a crystal growth thermal field include insulating felt, crucible, crucible lid, seed crystal, silicon carbide powder, stage, and temperature measuring hole.

[0088] Combination Figure 6 In related technologies, if the gaseous components of the sublimated powder grow directly on the seed crystal, the nitrogen adsorbed in the insulation felt, graphite parts (graphite parts can include crucibles, flow guides, seed crystal covers 13, and all other graphite components), and SiC powder will, as the temperature gradually increases, undergo desorption and be discharged from the reaction chamber through a vacuum system, while simultaneously participating in the initial crystal growth process. This will result in a crystal consisting of two parts: the upper part A is green and contains nitrogen doping, while the lower part B is a high-purity part. The thickness of the upper part A is approximately 5-6 mm. After taking a section of this substrate for testing, it was found that its nitrogen impurity content is high. The data is shown in the table below, with wafer number A7048G261K22. The last two digits, 22, indicate that the wafer was taken from the initial growth position 3-5 mm from the seed crystal end (i.e., part A, 3-5 mm from the seed crystal).

[0089]

[0090] Table 1. Secondary ion mass spectrometry (SIMS) analysis data of the comparative example A7048G261K22 high-purity substrate. Where ppm at represents parts per million atoms, and ppm wt represents parts per million gravimetric units (mass).

[0091] The above data shows that, Figure 6 The nitrogen impurity content of the substrate sheet in the early stage of crystal growth is on the order of E+16, which is relatively high. In addition, its related resistivity and optical parameters are shown below. Specifically, they are shown in Tables 2 and 3.

[0092]

[0093] Table 2. Resistivity analysis data of the comparative example A7048G261K22 high-purity substrate (measured by Napson sheet resistance meter). GΩ·cm is the unit of resistivity, read as "gigaohm-centimeter". It is a key physical quantity for measuring the insulating or semi-insulating properties of a material. Generally, the higher the GΩ·cm value, the higher the purity.

[0094] The above data shows that, Figure 6 The average resistivity of the substrate in the early stage of crystal growth is 2.406723. The value is on the order of E+10 Ω·cm (see the average value of 24.06723 in the table above; 24.06723 GΩ·cm can be converted to 2.406723 Ω·cm). Compared to the average substrate resistivity at the same location in the examples below, this indicates that the nitrogen impurity content is relatively high.

[0095] Table 3 shows the data for several optical parameters of the tested wafer. Figure 6 The data for the substrate in the early stage of crystal growth are as follows: at a wavelength of 460 nm, the absorptivity is 1.180574415; at a wavelength of 520 nm, the absorptivity is 1.230077745; and at a wavelength of 620 nm, the absorptivity is 0.682228085. The data are relatively poor and do not meet the technical requirements for optical waveguide-grade substrates.

[0096]

[0097] Table 3 Optical analysis data of comparative example A7048G261K22 high-purity substrate Combination Figure 4 According to the silicon carbide crystal growth system 100 of the present invention, a growth thermal field for silicon carbide crystals is formed inside the quartz tube 31. The growth thermal field for silicon carbide crystals mainly includes a growth container 20 and a powder cylinder 11 disposed inside the growth container 20, specifically comprising: 1. The lid 23 (such as a crucible lid) is made of purified graphite. It is connected to the pot body 21 (crucible body) by threads to achieve a sealing function. At the same time, it serves as the main part of the induction furnace that is heated and provides the thermal field temperature. 2. The pot body 21 (such as the crucible body) is made of purified graphite material. It is connected to the lid 23 (crucible body) by threads to achieve a sealing function. At the same time, it serves as the main part of the induction furnace that is heated and provides the thermal field temperature. 3. Carbon-based barrier layer 24 (graphite paper or carbon cloth), with purification requirements, impurity content of 5 ppm or less, is a technical means of this application to inhibit or isolate the external environment and nitrogen impurities in graphite felt from accumulating into the crucible, thereby improving the purity in the crystal growth chamber; 4. Seed crystal cap 13, made of purified graphite, with ventilation holes 103 arranged on the edge to release air. At the same time, the seed crystal is fixed on its surface by adhesive bonding, with the carbon side of the seed crystal facing the powder side. 5. The second guide tube 16, the sealing element 15, the graphite plate 17 and the positioning block 18 can all be made of purified graphite. The four components work together to form a sealed chamber for crystal growth (second sealed chamber 120). The sealing element 15 positions the second guide tube 16 and the graphite plate 17 through a snap-fit ​​stepped structure and the positioning block 18 (ring structure). 6. The mating part 12, powder cylinder 11, first guide cylinder 14 and graphite paper 10a can all be made of purified graphite. The four parts cooperate with each other to form a sealed chamber facing the powder (first sealed chamber 110). The thickness of graphite paper 10a can be selected as 0.3mm. The edge of graphite paper 10a is squeezed and fixed by the top of powder cylinder 11 and mating part 12.

[0098] Specifically, such as Figure 4 The silicon carbide powder in the powder container 11 is arranged such that the bottom silicon carbide powder has a particle size of 3-8 mesh (larger particles), while the top silicon carbide powder has a particle size of 8-20 mesh (smaller particles). This arrangement reduces the rate of powder sublimation during heating or the early growth stage (nitrogen desorption process), thereby reducing the portion with higher nitrogen impurity content in the initial crystal formation stage. Furthermore, as... Figure 4 The powder cylinder 11 is structurally arranged with the mating part 12, the powder cylinder 11, the guide cylinder 2, and the graphite paper 10a. These four components work together to form a sealed chamber facing the powder. The thickness of the graphite paper 10a is 0.3mm, and the edge of the graphite paper 10a is squeezed and fixed by the top of the powder cylinder 11 and the mating part 12.

[0099] It should be noted that the inner diameter of mating part 12 is 1mm smaller than the inner diameter of guide tube 2. That is, after assembly, if... Figure 2As shown in the enlarged view, the mating part 12 extends 0.5 mm beyond the thickest part of the top of the first guide tube 14 on one side. For example, if the inner diameter of the mating part 12 is 234 mm, then the inner diameter at the thickest part of the upper wall of the first guide tube 14 is 233 mm. The technical effect of this structural design is that, in the vertical direction of the cross-sectional view, since the mating part 12 extends 0.5mm beyond the thickest part of the top wall of the guide tube, at the edge of the graphite paper 10a facing the powder, the local temperature at the edge of the edge is too high and the local supercooling is insufficient, resulting in a very low spontaneous nucleation rate of polycrystalline 10c. It is difficult for stable polycrystalline 10c to grow at the edge, which reduces the adhesion of the graphite paper 10a at the edge. After the polycrystalline 10c grows on the interface of the graphite paper 10a for a period of time, the load-bearing capacity of the edge of the graphite paper 10a decreases. When the weight of the polycrystalline 10c is about 0.8 to 1kg (which can include 0.8 and 1kg), the graphite paper 10a and the polycrystalline 10c fall off together. At this time, the growth temperature and nitrogen impurity content are more conducive to improving crystal purity than in the nitrogen impurity desorption stage. The sublimated gas phase components begin to converge towards the surface of the seed crystal through the graphite plate 17, and the crystal begins to grow.

[0100] Wrapping the crucible with high-purity carbon paper / carbon cloth essentially adds a carbon-based barrier layer between the external nitrogen source (graphite felt / furnace atmosphere), the crucible wall, and the growth chamber. Through four mechanisms—physical barrier, adsorption and retention, chemical reaction consumption, and extended diffusion path—it significantly inhibits the inward diffusion of external nitrogen impurities, thereby reducing nitrogen impurities in the crystals. Therefore, this application uses a layer of high-purity carbon cloth / graphite paper to block nitrogen diffusion between the crucible and the graphite felt. The mechanism is as follows: 1. The carbon paper / carbon cloth has high purity, is free of binders, is heat resistant (>2500℃), has three-dimensional porosity, and features interwoven carbon fibers; 2. Encased in the outer wall of the crucible (or between the crucible and the insulation layer 22), forming an "outer garment," it can create a physical barrier and simultaneously extend the diffusion path of nitrogen impurities. The carbon cloth / carbon paper has a high density, with tortuous channels and interwoven multiple layers of fibers, resulting in a labyrinthine, non-straight-through pore structure. For nitrogen impurity atoms to diffuse from the outside to the inside, they must flow and collide multiple times within the fiber gaps, significantly lengthening the diffusion path. Compared to direct contact with the insulation layer 22, where the diffusion was originally "straight-through," it now involves "tortuous paths + multiple layers of obstruction," resulting in a substantial decrease in diffusion flux. 3. Adsorption and retention: Carbon surfaces strongly adsorb nitrogen species. High-temperature carbon surfaces have strong physical adsorption of N2, N atoms, and CNx. Nitrogen species that diffuse in from the outer layer are preferentially captured and retained by the carbon paper / carbon cloth surface and are not easy to continue to penetrate inward. 4. Most importantly, the outermost layer of carbon cloth / paper, in addition to its strong adsorption effect, also involves chemical reaction consumption: carbon reacts with active nitrogen, consuming N. At temperatures >1800℃ under hydrogen conditions, carbon reacts with active nitrogen (N atoms, CN, NH): C + N → CN (cyano group) and 2C + N2 → C2N2 (cyanide gas). These carbon-nitrogen compounds have low boiling points and are highly volatile, diffusing outwards and being carried away by argon gas, rather than entering the crucible inwards. Therefore, the outer carbon cloth / paper can actively consume the inwardly diffusing active nitrogen, converting harmful N into expellable gaseous CN / C2N2.

[0101] Carbon paper / carbon cloth has moderate thermal conductivity and provides insulation and buffering, making the temperature of the outer wall of the crucible more uniform and reducing local high-temperature desorption of N. With the outer layer of N blocked / consumed, the nitrogen partial pressure at the inner wall of the crucible is significantly reduced. According to Fick's diffusion law, the concentration difference between the inside and outside decreases, and the driving force for inward diffusion weakens.

[0102] By comparing the crystal growth base 10b on the seed cover 13 or the crystal on the seed crystal with the wafer at the same position in the related art, the data in the table below can be obtained through the technical solution of this application.

[0103] According to the silicon carbide growth system 100 and growth method of the present invention, the crystal can be grown on graphite paper 10a and then fall into the powder cylinder 11. The crystal grown on the crystal growth base 10b can remove the part of the crystal with a high nitrogen impurity content near the seed crystal end.

[0104] After the crystal is grown according to the silicon carbide growth system 100 and growth method embodiment of the present invention, a position of 3-5 mm near the initial growth of the crystal seed is selected. After testing this part of the substrate, it is confirmed that its nitrogen impurity content is low. The data is shown in Table 4, wafer number A7048G261L22. The last two digits of the wafer number 22 indicate that the 3-5 mm position near the initial growth of the seed is taken for the comparative example.

[0105]

[0106] Table 4. Secondary ion mass spectrometry (SIMS) analysis data of high-purity substrate A7048G261L22 in Example 1 The above data indicates that the nitrogen impurity content of the substrate sheet during the early stage of crystal growth is on the order of E+15, which is one order of magnitude lower than the nitrogen impurity content of the comparative example (measurement data in Part A of the related art). Furthermore, its related resistivity and optical parameters are shown below, specifically in Tables 5 and 6.

[0107]

[0108] Table 5 Resistivity analysis data of high-purity substrate A7048G261L22 in Example (measured with a Napson sheet resistance meter) The above data shows that the average resistivity of the substrate during the early stage of crystal growth in this application embodiment is 1.211765. The E+11 order of magnitude, compared to the average substrate resistivity at the same location in the aforementioned comparative example (related technology solutions), indicates that its nitrogen impurity content is low.

[0109] Table 6 shows the data of several optical parameters of the test wafer in the embodiment. The data of the substrate in the early stage of crystal growth in this application embodiment are as follows: at a wavelength of 460nm, the absorptivity is 0.27551; at a wavelength of 520nm, the absorptivity is 0.26599; and at a wavelength of 620nm, the absorptivity is 0.21823. The data are relatively good and can meet the technical requirements of optical waveguide-level substrate.

[0110]

[0111] Table 6 Optical analysis data of comparative example A7048G261K22 high-purity substrate As can be seen, the crystal obtained by the silicon carbide growth system 100 of this application has a significantly lower absorption rate compared with the comparative example (i.e., the scheme in the related art), i.e., compared with the data in Table 3. For high-purity semi-insulating SiC wafers, generally speaking, the lower the absorption rate (i.e., the more transparent), the lower the content of metal / nitrogen impurities, and the higher the purity and quality of the crystal; conversely, the higher the absorption rate, the more impurities or defects there are.

[0112] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0113] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0114] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0115] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0116] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0117] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A silicon carbide crystal growth system (100), characterized in that, include: A powder cylinder (11) has an opening at its upper end and a powder hopper (101) inside the powder cylinder (11); A fitting (12) is connected to the powder cylinder (11), and the fitting (12) is configured to position a graphite paper (10a) located above the powder hopper (101) and falling off after a predetermined condition is met; Seed crystal cover (13) is disposed above the opening, and the lower surface of the seed crystal cover (13) is formed as a crystal growth base (10b). The seed crystal cover (13) is higher than the graphite paper (10a).

2. The silicon carbide crystal growth system (100) according to claim 1, characterized in that, The predetermined condition is that the graphite paper (10a) falls off after reaching a predetermined weight.

3. The silicon carbide crystal growth system (100) according to claim 1, characterized in that, The fitting member (12) is located at the upper end of the powder cylinder (11). The fitting member (12) and the opening periphery of the powder cylinder (11) are opposite each other in the vertical direction. The fitting member (12) and the opening periphery of the powder cylinder (11) are suitable for clamping and positioning the graphite paper (10a).

4. The silicon carbide crystal growth system (100) according to claim 1, characterized in that, A first guide tube (14) is provided on the inner side of the periphery of the opening, and the first guide tube (14) and the mating part (12) are opposite each other in the vertical direction. The graphite paper (10a) is disposed between the first guide tube (14) and the mating part (12). The projection of the inner wall of the mating part (12) in the vertical direction protrudes beyond the projection of the inner wall of the first guide tube (14) in the vertical direction.

5. The silicon carbide crystal growth system (100) according to claim 4, characterized in that, In the vertical direction, the minimum horizontal distance between the inner wall of the mating part (12) and the inner wall of the first guide tube (14) is L, satisfying 0.4mm≤L≤0.6mm; and / or The inner diameter of the first guide tube (14) gradually decreases in the direction from bottom to top.

6. The silicon carbide crystal growth system (100) according to claim 1, characterized in that, It includes a sealing element (15), the upper end of which is sealed to the seed crystal cover (13), and the lower end of which is sealed to the mating part (12).

7. The silicon carbide crystal growth system (100) according to claim 6, characterized in that, The system includes a second guide tube (16), which is higher than the mating member (12). The inner space of the second guide tube (16) is opposite to the inner space of the mating member (12) in the vertical direction. The sealing member (15) includes a support portion (161) extending in the vertical direction and a support portion (162) extending in the horizontal direction. The support portion (161) is sealed to the seed crystal cover (13), and the support portion (162) is sealed to the mating member (12). The support portion (162) supports the second guide tube (16) in the vertical direction.

8. The silicon carbide crystal growth system (100) according to claim 7, characterized in that, The growth system (100) includes a graphite plate (17) located between the seed crystal cover (13) and the graphite paper (10a), the support portion (162) supporting the graphite plate (17), and the graphite plate (17) supporting the second guide tube (16); and / or The growth system (100) includes a positioning block (18) which is horizontally disposed between the support (161) and the second guide tube (16).

9. The silicon carbide crystal growth system (100) according to claim 1, characterized in that, include: Growth container (20), the powder cylinder (11) is disposed inside the growth container (20); A heat insulation layer (22) is provided, which covers the outer surface of the growth container; A carbon-based barrier layer (24) is disposed between the outer side of the growth container and the insulation layer (22).

10. The silicon carbide crystal growth system (100) according to claim 9, characterized in that, The carbon-based barrier layer (24) is graphite paper or carbon cloth.

11. A method for growing silicon carbide crystals, characterized in that, The crystal growth method employs the silicon carbide crystal growth system (100) as described in any one of claims 1-10, wherein the crystal growth method comprises: Position the graphite paper (10a) above the powder hopper (101) and between the mating component (12); Heating the powder hopper (101) causes the gaseous components of the powder sublimation in the powder cylinder (11) to converge toward the graphite paper (10a), where polycrystalline material (10c) grows and forms on the graphite paper (10a) until the graphite paper (10a) falls off into the powder hopper (101). The powder hopper (101) is heated, causing the gaseous components of the powder sublimated in the powder cylinder (11) to converge toward the crystal growth base (10b), where crystals are grown.

12. The method for growing silicon carbide crystals according to claim 11, characterized in that, Before positioning the graphite paper (10a), the growth method further includes placing the powder from bottom to top at the bottom of the powder hopper (101), wherein the particle size of the powder located in the lower layer of the powder hopper (101) is larger than the particle size of the powder located in the upper layer of the powder hopper (101).

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