Silicon carbide raw material as well as preparation method and application thereof

Abstract

The invention provides a silicon carbide raw material and a preparation method and application thereof, and relates to the technical field of silicon carbide crystals. The preparation method of the silicon carbide raw material comprises the following steps: doping impurity elements into silicon powder and carbon powder, and carrying out first heat preservation treatment to obtain primary powder; silicon powder, carbon powder, impurity elements and the primary powder are mixed and subjected to second-time heat preservation treatment, medium-grade powder is obtained, silicon powder, carbon powder, impurity elements and medium-grade powder are mixed and subjected to third-time heat preservation treatment, and particle raw materials are obtained. And regulating and controlling the impurity addition amount, the synthesis temperature gradient and the powder particle size distribution in each stage to form a particle raw material with a gradient structure in which the impurity concentration is continuously reduced from the core to the surface layer. When silicon carbide crystals are grown by the PVT method, the raw material can dynamically compensate the impurity concentration of a growth interface and reduce impurity concentration fluctuation. The silicon carbide raw material prepared by the method is applicable to preparation of large-size uniformly-doped silicon carbide single crystals, and the prepared silicon carbide crystals are uniform in doping, single in crystalline phase and free of polymorphic appearance.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide crystals, and in particular to a silicon carbide raw material and a preparation method and application thereof. Background Art

[0002] As a third-generation semiconductor material, silicon carbide (SiC) crystals have important applications in the field of high-temperature and high-frequency devices, but the precise control of the impurity concentration distribution during the growth of single crystals has always been a technical difficulty. The traditional PVT method (physical vapor transport method) usually uses raw materials with a single impurity concentration, which leads to significant fluctuations in the impurity concentration at the growth interface (usually exceeding ±30%), affecting the uniformity of the electrical properties of the crystal. For example, patent CN103320862A / B discloses a method for optimizing the crystal form by doping elements (such as aluminum and boron), but it is still difficult to overcome the problem of uneven impurity diffusion, especially in the context of large-scale crystal growth. This problem becomes increasingly prominent, greatly limiting the further improvement of silicon carbide crystal performance and large-scale application. CN117305983A discloses a method for maintaining the stability of Al doping, but due to the movement of the interface before, during and after crystal growth, the axial temperature gradient and axial concentration gradient are difficult to control. The existing raw material synthesis process mostly relies on a single high-temperature synthesis, and the impurity distribution of the powder is discrete and cannot form a continuous gradient, which further aggravates the concentration instability of the growth interface. The obtained silicon carbide crystals are prone to multiple crystal forms, reducing the consistency of the single crystal. Summary of the Invention

[0003] In view of the above problems existing in the prior art, the present invention provides a silicon carbide raw material and a preparation method and application thereof, so as to improve the problem that silicon carbide crystals are prone to multiple crystal forms.

[0004] To achieve the above-mentioned and other related purposes, the present invention provides a method for preparing a silicon carbide raw material in a first aspect, comprising the following steps:

[0005] Mixing carbon powder and silicon powder uniformly to obtain a first mixture, mixing the first mixture and impurity elements uniformly to obtain a second mixture, and maintaining the second mixture at a temperature T1 for a time Δt1 to obtain a primary powder;

[0006] Mixing carbon powder and silicon powder uniformly to obtain a third mixture, and uniformly mixing the third mixture with the impurity element to obtain a fourth mixture; uniformly mixing the primary powder with the fourth mixture to obtain a fifth mixture, and maintaining the fifth mixture at a temperature of T2 for a time of Δt2 to obtain an intermediate powder;

[0007] The carbon powder and the silicon powder are evenly mixed to obtain a sixth mixture, the sixth mixture is evenly mixed with the impurity elements to obtain a seventh mixture, the intermediate powder is evenly mixed with the seventh mixture to obtain an eighth mixture; the eighth mixture is maintained at a temperature of T3 for a time of Δt3 to obtain a granular raw material.

[0008] In one embodiment of the present invention, in the first mixture, the third mixture, and the sixth mixture, the molar ratio of the carbon powder to the silicon powder is (0.85-1.25):1, the mass ratio of the first mixture to the impurity element is 1:(0.001-0.005), the mass ratio of the third mixture to the impurity element is 1:(0.0005-0.0025), and the mass ratio of the sixth mixture to the impurity element is 1:(0.00025-0.00125); when preparing the intermediate powder, the mass ratio of the fourth mixture to the primary powder is 1:(0.15-0.85); when preparing the granular raw material, the mass ratio of the seventh mixture to the intermediate powder is 1:(0.1-0.9).

[0009] In one embodiment of the present invention, TI is 1100-1600°C, T2 is 1300-2000°C, T3 is 1800-2300°C, Δt1, Δt2, and Δt3 are 1-25h, and Δt1, Δt2, and Δt3 increase by 10-50% respectively; the heating rate when preparing the primary powder is 5-10°C / min, the heating rate when preparing the intermediate powder is 10-15°C / min, and the heating rate when preparing the granular raw material is 15-30°C / min.

[0010] In one embodiment of the present invention, along the axial direction of the filler, the temperature gradient of the second mixture when preparing the primary powder is 2 to 3°C / cm; the temperature gradient of the fifth mixture when preparing the intermediate powder is 3 to 5°C / cm; and the temperature gradient of the eighth mixture when preparing the granular raw material is 5 to 10°C / cm.

[0011] In one embodiment of the present invention, the impurity element is any one or more of aluminum, cerium, phosphorus, boron, chromium, vanadium, and oxides or carbides corresponding to aluminum, cerium, phosphorus, boron, chromium, and vanadium.

[0012] A second aspect of the present invention provides a silicon carbide raw material, which includes a granular raw material produced by the above preparation method.

[0013] In one embodiment of the present invention, the granular raw material includes a spherical core, a first coating layer and a second coating layer, the first coating layer is coated on the outside of the spherical core, the second coating layer is coated on the outside of the first coating layer, the diameter ratio of the spherical core, the first coating layer and the second coating layer is 1: (1.5 to 8): (5 to 20), the impurity content in the spherical core, the first coating layer and the second coating layer is distributed in a gradient, and the gradient of the impurity content is 0.1 to 5 g / cm 3 / mm.

[0014] In one embodiment of the present invention, along the radial direction of the granular raw material, the impurity concentration decreases continuously from the center to the edge of the granular raw material, and the change rate of the impurity concentration is ≥5at% / mm.

[0015] In one embodiment of the present invention, the silicon carbide raw material further includes primary powder and intermediate powder, and the mass ratio of the primary powder, the intermediate powder and the granular raw material is (0-1):(1-0):1.

[0016] The third aspect of the present invention provides an application of a silicon carbide raw material, wherein the silicon carbide raw material is used to prepare silicon carbide crystals by a PVT method, and the impurity concentration at the growth interface of the silicon carbide crystals is 1×10 14 ~5×10 20 at / cm 3 , and the concentration fluctuation is ≤±10%.

[0017] The present invention discloses a method for preparing silicon carbide raw material. The method comprises doping silicon powder and carbon powder with impurity elements and subjecting them to a first heat preservation treatment to obtain a primary powder. The silicon powder, carbon powder, impurity elements, and primary powder are mixed and subjected to a second heat preservation treatment to obtain an intermediate powder. The silicon powder, carbon powder, impurity elements, and intermediate powder are mixed and subjected to a third heat preservation treatment to obtain a granular raw material. By regulating the amount of impurity added at each stage, the synthesis temperature gradient, and the powder particle size distribution, a granular raw material with a gradient structure having a continuously decreasing impurity concentration from the core to the surface is formed. The silicon carbide raw material based on a multi-layer impurity concentration gradient structure proposed by the present invention forms a continuously decreasing impurity concentration gradient (gradient change rate ≥ 5at% / mm) from the core to the surface through a staged synthesis process (low temperature to high temperature layer by layer), thereby dynamically compensating for the interface impurity concentration during the PVT growth process and controlling the fluctuation range within ±10%. The silicon carbide raw material prepared by the present invention is particularly suitable for the industrial preparation of large-scale, uniformly doped silicon carbide single crystals. The obtained silicon carbide crystals are uniformly doped, have a single crystal phase, and are free of polymorphs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 is a flow chart for preparing silicon carbide raw materials in one embodiment of the present invention;

[0020] Figure 2 A schematic diagram of heating and constant temperature during the preparation process of silicon carbide raw material in one embodiment of the present invention;

[0021] Figure 3 A schematic diagram of the axial temperature gradient of a preparation process of silicon carbide raw material in one embodiment of the present invention;

[0022] Figure 4 is a schematic cross-sectional view of a granular powder of silicon carbide raw material in one embodiment of the present invention;

[0023] Figure 5 A silicon carbide crystal growth apparatus according to an embodiment of the present invention;

[0024] Figure 6 Schematic diagram of the raw material arrangement for preparing silicon carbide crystals in one embodiment of the present invention;

[0025] Figure 7 This is a photograph of the silicon carbide crystal prepared in Example 1 of the present invention;

[0026] Figure 8 This is a photograph of the silicon carbide crystal prepared in Example 2 of the present invention;

[0027] Figure 9 This is a photograph of the silicon carbide crystal prepared in Example 3 of the present invention;

[0028] Figure 10 This is a photograph of the silicon carbide crystal prepared in Example 4 of the present invention;

[0029] Figure 11 A schematic diagram of the raw material arrangement for preparing silicon carbide crystals in a comparative example of the present invention;

[0030] Figure 12 This is a photograph of the silicon carbide crystal prepared in Comparative Example 1 of the present invention;

[0031] Figure 13 This is a photograph of the silicon carbide crystal prepared in Comparative Example 2 of the present invention.

[0032] Component number description:

[0033] 100, granular raw material; 110, spherical core; 120, first coating layer; 130, second coating layer; 200, growth device; 210, seed crystal cover; 220, crucible barrel; 221, receiving chamber; 230, graphite ring; 240, seed crystal. DETAILED DESCRIPTION

[0034] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following examples and the features in the examples can be combined with each other unless they conflict. It should also be understood that the terms used in the examples of the present invention are for the purpose of describing specific embodiments, not for the purpose of limiting the scope of protection of the present invention. The test methods for which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under the conditions recommended by the manufacturers.

[0035] When numerical ranges are given in the examples, it should be understood that unless otherwise specified herein, both endpoints of each numerical range and any value between the two endpoints may be used. Unless otherwise defined, all technical and scientific terms used herein are consistent with the prior art as understood by those skilled in the art and the description of the present invention. Any prior art methods, devices, and materials similar or equivalent to those in the examples of the present invention may also be used to implement the present invention.

[0036] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0037] See also Figure 1 The present invention provides a method for preparing silicon carbide raw materials, comprising the following steps:

[0038] S1. Evenly mix carbon powder and silicon powder to obtain a first mixture, evenly mix the first mixture with impurity elements to obtain a second mixture, and maintain the second mixture at a temperature of T1 for a time of Δt1 to obtain a primary powder;

[0039] S2. Evenly mix the carbon powder and the silicon powder to obtain a third mixture, evenly mix the third mixture with impurity elements to obtain a fourth mixture; evenly mix the primary powder and the fourth mixture to obtain a fifth mixture, and maintain the fifth mixture at a temperature of T2 for a time of Δt2 to obtain an intermediate powder;

[0040] S3. Evenly mix the carbon powder and silicon powder to obtain a sixth mixture, evenly mix the sixth mixture with impurity elements to obtain a seventh mixture, evenly mix the intermediate powder and the seventh mixture to obtain an eighth mixture; maintain the eighth mixture at a temperature of T3 for a time of Δt3 to obtain a granular raw material.

[0041] In step S1, the molar ratio of carbon powder to silicon powder is (0.85-1.25):1, and the mass ratio of the first mixture to the impurity element is 1:(0.001-0.005). TI is 1100-1600°C, and Δt1 is 1-25h. When the second mixture is heated, the heating rate is 5-10°C / min, and the temperature gradient of the second mixture during heating is 2-3°C / min along the axial direction of the filler. In some embodiments, after the second mixture is heat-insulated, the preparation of the primary powder further includes screening the obtained primary powder, and the particle size of the primary powder after screening is 0.4-1mm. In the present application, the crystal phase of the primary powder is 3C phase.

[0042] In step S2, the molar ratio of carbon powder to silicon powder is (0.85-1.25):1, the mass ratio of the third mixture to the impurity elements is 1:(0.0005-0.0025), and the mass ratio of the fourth mixture to the primary powder is 1:(0.15-0.85). When the fifth mixture is heated, the heating rate is 10-15°C / min, and the temperature gradient of the fifth mixture during heating is 3-5°C / cm along the axial direction of the filler. In some embodiments, after the fifth mixture is heat-insulated, the preparation of the intermediate powder further includes screening the obtained intermediate powder, and the particle size of the intermediate powder after screening is 0.6-3 mm. In the present application, the crystal phase of the intermediate powder is α phase.

[0043] In step S3, the molar ratio of carbon powder to silicon powder is (0.85-1.25):1, the mass ratio of the sixth mixture to the impurity elements is 1:(0.00025-0.00125), and the mass ratio of the seventh mixture to the intermediate powder is 1:(0.1-0.9). T3 is 1800-2300°C, and Δt3 is 1-25h. When the eighth mixture is heated, the heating rate is 15-30°C / min, and the temperature gradient of the eighth mixture during heating is 5-10°C / cm along the axial direction of the filler. In some embodiments, after the eighth mixture is heat-insulated, the preparation of the granular raw material also includes screening the obtained granular raw material, and the diameter of the sieved granular raw material is 2-8 mm. In the present application, the crystal phase of the silicon carbide particles is α phase.

[0044] The cross-sectional view of the granular raw material 100 is as follows: Figure 4As shown, the granular raw material 100 includes a spherical core 110, a first coating layer 120 and a second coating layer 130. The first coating layer 120 is coated on the outside of the spherical core 110 and is roughly spherical. The second coating layer 130 is coated on the outside of the first coating layer 120 and is roughly spherical. The diameter D1 of the spherical core 110, the diameter D2 of the first coating layer 120 and the diameter D3 of the second coating layer 130 are in the ratio of D1:D2:D3=1:(1.5-8):(5-20). The impurity content in the spherical core 110, the first coating layer 120 and the second coating layer 130 is distributed in a gradient, and the gradient of the impurity content is 0.1-5 g / cm 3 / mm.

[0045] See also Figure 2 In some embodiments, TI is 1100-1600° C., T2 is 1300-2000° C., T3 is 1800-2300° C., Δt1, Δt2, and Δt3 are 1-25 h, and Δt1, Δt2, and Δt3 increase by 10-50% sequentially.

[0046] See also Figure 3 In some embodiments, along the axial direction of the filler, the temperature gradient of the second mixture when preparing the primary powder is 2 to 3°C / cm; the temperature gradient of the fifth mixture when preparing the intermediate powder is 3 to 5°C / cm; and the temperature gradient of the eighth mixture when preparing the granular raw material 100 is 5 to 10°C / cm.

[0047] In some embodiments, the impurity element is any one or more of aluminum, cerium, phosphorus, boron, chromium, vanadium, and oxides or carbides corresponding to aluminum, cerium, phosphorus, boron, chromium, and vanadium.

[0048] The present invention also provides a silicon carbide raw material, which includes the granular raw material 100 prepared by the above preparation method.

[0049] The present invention relates to a method for preparing silicon carbide raw material. The method involves doping silicon powder and carbon powder with impurity elements and subjecting them to a first heat preservation treatment to obtain a primary powder. The silicon powder, carbon powder, impurity elements, and primary powder are mixed and subjected to a second heat preservation treatment to obtain an intermediate powder. The silicon powder, carbon powder, impurity elements, and intermediate powder are mixed and subjected to a third heat preservation treatment to obtain a granular raw material 100. By regulating the amount of impurity added at each stage, the synthesis temperature gradient, and the powder particle size distribution, a granular raw material 100 having a gradient structure with a continuously decreasing impurity concentration from the core to the surface is formed. When growing silicon carbide crystals using the PVT method, this raw material can dynamically compensate for the impurity concentration at the growth interface, ensuring that the impurity concentration fluctuates within a range of ≤±10%. The silicon carbide raw material prepared by the present invention is particularly suitable for the industrial production of large-scale, uniformly doped silicon carbide single crystals.

[0050] In one embodiment, the silicon carbide raw material further includes primary powder and intermediate powder. Exemplarily, the mass ratio of the primary powder, the intermediate powder and the granular raw material 100 is (0-1):(1-0):1.

[0051] See also Figure 5 In some embodiments, a growth apparatus 200 for producing silicon carbide crystals includes a seed crystal cover 210, a crucible barrel 220, a graphite ring 230, and a seed crystal 240. The seed crystal 240 is fixedly mounted on the side of the seed crystal cover 210 facing the crucible barrel 220. The seed crystal 240 provides a lattice structure template for crystal growth, allowing substances in the gas phase to deposit and grow in an orderly manner according to the lattice arrangement of the seed crystal 240, thereby ensuring the consistency of the crystal structure. The graphite ring 230 is located at one end of the crucible barrel 220 near the seed crystal cover 210, with the outer wall of the graphite ring 230 aligned with the inner wall of the crucible barrel 220. The crucible barrel 220 is provided with a receiving cavity 221 for placing silicon carbide raw material. When producing silicon carbide crystals, the silicon carbide raw material is placed in the receiving cavity 221, and the seed crystal cover 210, with the seed crystal 240 bonded thereto, is fixedly connected to the crucible barrel 220 via threads. The growth device 200 is placed in a growth device, and the temperature and pressure of the growth device are adjusted to grow a silicon carbide crystal. In this application, there is no limitation on the crystal form of the seed crystal 240, and it can be selected according to actual needs. Exemplarily, the crystal form of the seed crystal 240 is either 4H-SiC or 6H-SiC.

[0052] The technical solutions of the present invention are described in detail below through several specific examples. Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the examples are all commercially available.

[0053] S1: High-purity carbon powder and silicon powder were mixed in a molar ratio of 1.1:1 to obtain 10 kg of a first mixture. This first mixture was then mixed with 15 g of CeO to obtain a second mixture. The second mixture was placed in a crucible and heated to 1350°C at a heating rate of 5°C / min and held for 4.7 hours to obtain a primary powder. The resulting primary powder was sieved to obtain 8 kg of primary powder with a particle size of 0.4-0.6 mm for later use. The temperature gradient of the second mixture along the axial direction of the crucible was 2°C / cm.

[0054] S2: Mix high-purity carbon powder and silicon powder in a molar ratio of 1.1:1 to obtain 7kg of the third mixture, and mix 7kg of the third mixture with 5gCeO to obtain the fourth mixture. Mix the fourth mixture with 3kg of primary powder to obtain the fifth mixture. Place the fifth mixture in a crucible, and heat it to 1800℃ at a heating rate of 15℃ / min and keep it for 7.3h to synthesize α-phase silicon carbide intermediate powder. The obtained intermediate powder is sieved to obtain 6kg of intermediate powder with a particle size of 1.5-2.5mm for standby use. Among them, the temperature gradient of the fifth mixture along the axial direction of the crucible is 3℃ / cm,

[0055] S3: Mix high-purity carbon powder and silicon powder in a molar ratio of 1.1:1 to obtain 5kg of the sixth mixture, mix the sixth mixture with 3g of CeO to obtain the seventh mixture, mix the seventh mixture with 5kg of intermediate powder to obtain the eighth mixture, place the eighth mixture in a crucible, heat the eighth mixture to 2240℃ at a heating rate of 20℃ / min and maintain for 11h to obtain α-phase silicon carbide granular raw material 100. The obtained granular raw material 100 is sieved to obtain 5kg of granular raw material 100 with a particle size of 3-8mm and 2kg of granular raw material 100 with a particle size of 2-3mm. The granular raw materials 100 of the two particle sizes are mixed for use. Among them, the temperature gradient of the eighth mixture along the axial direction of the crucible is 5℃ / cm. The cross-sectional view of the granular raw material 100 obtained in this embodiment is as shown in FIG. Figure 4 As shown, the diameter ratio of the spherical core 110, the first cladding layer 120 and the second cladding layer 130 is 1:3:12, the aluminum concentration of the spherical core 110 is 15at%, the aluminum concentration of the first cladding layer 120 is 7.5at%, and the aluminum concentration of the second cladding layer 130 is 3.75at%. The concentrations show a continuously decreasing change and exceed 5at% / mm.

[0056] In this embodiment, the method for growing silicon carbide crystals is as follows: Figure 5 Assemble the growth device 200: Place the graphite ring 230 on the seed crystal cover 210, place the silicon carbide raw material in the receiving chamber 221, and screw the seed crystal cover 210 with the seed crystal 240 bonded to the crucible barrel 220. Place the growth device 200 in the growth equipment. Crystal growth: Adjust the position of the growth device 200 relative to the heater so that the seed crystal cover 210 is located at a position -30mm below the heater plane, so that the seed crystal cover 210 is in the low temperature zone; Heating: Evacuate the temperature to 10 -3 Pa and below, heat to 1000℃ and continue to vacuum to 10 -3Pa, then fill with argon to 300mbar, and heat to 2100℃ under this pressure; decompression growth: set the pressure to be reduced to the preset crystal growth pressure of 1mbar in 20h, and heat to the preset crystal growth temperature of 2250℃, continue to grow for the preset time of 150h until the temperature reaches 2300℃, and cool to room temperature.

[0057] In this embodiment, the silicon carbide raw material is placed as follows: Figure 6 As shown, 2 kg of granular raw material 100 is placed in the center of the crucible, 3 kg of a mixture of intermediate powder and granular raw material 100 is placed on the periphery of the granular raw material 100, the mass ratio of the intermediate powder to the granular raw material 100 is 1:1, and 2 kg of primary powder is placed on top of the granular raw material 100 and the mixture. The silicon carbide crystals prepared in this embodiment are as follows. Figure 7 As shown, during the growth process of silicon carbide crystals, the Ce ion concentration at the crystal interface remains stable as the raw materials are released, and the resulting silicon carbide crystals have a single crystal form without polymorphism.

[0058] Example 2

[0059] The preparation method of silicon carbide raw material in this application is as follows:

[0060] S1: High-purity carbon powder and silicon powder are mixed in a molar ratio of 1.1:1 to obtain 10kg of the first mixture. The first mixture is mixed with 30g of Al2O3 to obtain a second mixture. The second mixture is placed in a crucible and heated to 1400℃ at a heating rate of 5℃ / min and maintained for 5.3h to generate 3C phase silicon carbide primary powder. The obtained primary powder is sieved to obtain 7kg of primary powder with a particle size of 0.4mm-0.6mm for standby use. The temperature gradient of the second mixture along the axial direction of the crucible is 2.5℃ / cm.

[0061] S2: High-purity carbon powder and silicon powder are mixed uniformly in a molar ratio of 1.1:1 to obtain 7 kg of a third mixture. The third mixture is mixed uniformly with 15 g of Al2O3 to obtain a fourth mixture. The fourth mixture is mixed uniformly with 3 kg of primary powder to obtain a fifth mixture. The fifth mixture is placed in a crucible and heated to 2000°C at a heating rate of 10°C / min and maintained for 8 hours to synthesize α-phase silicon carbide intermediate powder. The obtained intermediate powder is sieved to obtain 5 kg of powder with a particle size of 1.5 mm to 2.5 mm for standby use. The temperature gradient of the fifth mixture along the axial direction of the crucible is 3.5°C / cm.

[0062] S3: Mix high-purity carbon powder and silicon powder in a molar ratio of 1.1:1 to obtain 10kg of the sixth mixture, mix the sixth mixture with 10g of Al2O3 to obtain the seventh mixture, mix the seventh mixture with 1kg of intermediate powder to obtain the eighth mixture, place the eighth mixture in a crucible, and heat the eighth mixture to 2280℃ at a heating rate of 25℃ / min and keep it for 12h to synthesize α-phase silicon carbide granular raw material 100, screen the obtained granular raw material 100, and obtain granular raw material 100 with a particle size of 3-8mm with a mass of 5.5kg and granular raw material 100 with a particle size of 2-3mm with a mass of 2.2kg. Mix the granular raw materials 100 of the two particle sizes for later use. Along the axial direction of the crucible, the temperature gradient of the eighth mixture is 5℃ / cm. The cross-sectional view of the granular raw material 100 obtained in this embodiment is shown in FIG. Figure 4 As shown, the diameter ratio of the spherical core 110, the first cladding layer 120 and the second cladding layer 130 is 1:6:10, the aluminum concentration of the spherical core 110 is 15at%, the aluminum concentration of the first cladding layer 120 is 5at%, and the aluminum concentration of the second cladding layer 130 is 0.5at%. The concentrations show a continuously decreasing change and exceed 5at% / mm.

[0063] In this embodiment, the method for growing silicon carbide crystals is as follows: Figure 5 Assemble the growth device 200. The growth device 200 of this embodiment is the same as that of embodiment 1. Crystal growth: Adjust the position of the growth device 200 relative to the heater so that the seed crystal cover 210 is located at a position -30 mm below the heater plane, so that the seed crystal cover 210 is in the low temperature zone; vacuumize to 10 -3 Pa and below, heat to 1000℃ and continue to vacuum to 10 -3 Pa, then fill with argon to 300mbar, and heat to 2100℃ under this pressure; set the pressure to drop to the preset crystal growth pressure of 1mbar in 20h, and heat to the preset crystal growth temperature of 2250℃, continue to grow for the preset time of 150h, and then the temperature reaches 2300℃, and cool to room temperature.

[0064] In this embodiment, the silicon carbide raw material is placed as follows: Figure 6 As shown, 2 kg of granular raw material 100 is placed in the center of the crucible, 3 kg of a mixture of intermediate powder and granular raw material 100 is placed on the periphery of the granular raw material 100, the mass ratio of the intermediate powder to the granular raw material 100 is 1:1, and 2 kg of primary powder is placed on top of the granular raw material 100 and the mixture. The silicon carbide crystals prepared in this embodiment are as follows. Figure 8 As shown, during the growth process of silicon carbide crystals, the Al ion concentration at the crystal interface remains stable as the raw materials are released, and the resulting silicon carbide crystals have a single crystal form without polymorphism.

[0065] Example 3

[0066] The preparation method of silicon carbide raw material in this application is as follows:

[0067] S1: High-purity carbon powder and silicon powder are mixed evenly in a molar ratio of 0.85:1 to obtain 10kg of the first mixture, and the first mixture is mixed evenly with 50g of metal aluminum to obtain a second mixture. The second mixture is placed in a crucible, and the temperature is raised to 1100℃ at a heating rate of 10℃ / min and maintained for 20.6h to generate 3C phase silicon carbide primary powder. The obtained primary powder is sieved to obtain 7kg of primary powder with a particle size of 0.4-0.6mm for standby use. Among them, the temperature gradient of the second mixture along the axial direction of the crucible is 3℃ / cm.

[0068] S2: High-purity carbon powder and silicon powder are mixed evenly in a molar ratio of 1.25:1 to obtain 8 kg of a third mixture. The third mixture is mixed evenly with 20 g of metallic aluminum to obtain a fourth mixture. The fourth mixture is mixed evenly with 6.8 kg of primary powder to obtain a fifth mixture. The fifth mixture is placed in a crucible and heated to 1500°C at a heating rate of 13°C / min and maintained for 22.7 hours to synthesize α-phase silicon carbide intermediate powder. The obtained intermediate powder is sieved to obtain 5 kg of powder with a particle size of 1.5 to 2.5 mm for standby use. The temperature gradient of the fifth mixture along the axial direction of the crucible is 5°C / cm.

[0069] S3: Mix high-purity carbon powder and silicon powder in a molar ratio of 1:1 to obtain 6 kg of the sixth mixture, mix the sixth mixture with 1.5 g of metal aluminum to obtain the seventh mixture, mix the seventh mixture with 3.6 kg of intermediate powder to obtain the eighth mixture, place the eighth mixture in a crucible, and heat the eighth mixture to 1800 ° C at a heating rate of 30 ° C / min and keep it for 25 hours to synthesize α-phase silicon carbide granular raw material 100, screen the obtained granular raw material 100, and obtain granular raw material 100 with a particle size of 3 to 8 mm and a mass of 3.6 kg, and granular raw material 100 with a particle size of 2 to 3 mm and a mass of 4.8 kg. The granular raw materials 100 of the two particle sizes are mixed for use. Along the axial direction of the crucible, the temperature gradient of the eighth mixture is 8 ° C / cm. The cross-sectional view of the granular raw material 100 obtained in this embodiment is shown as follows Figure 4 As shown, the diameter ratio of the spherical core 110, the first cladding layer 120 and the second cladding layer 130 is 1:5.5:15, the aluminum concentration of the spherical core 110 is 12at%, the aluminum concentration of the first cladding layer 120 is 6at%, and the aluminum concentration of the second cladding layer 130 is 3at%. The concentration shows a continuously decreasing change and exceeds 5at% / mm.

[0070] In this embodiment, the growth method of silicon carbide crystals is the same as that in Example 1. The silicon carbide crystals prepared in this embodiment are as follows: Figure 9 As shown, during the growth process of silicon carbide crystals, the aluminum ion concentration at the crystal interface remains stable as the raw materials are released, and the resulting silicon carbide crystals have a single crystal form without polymorphism.

[0071] Example 4

[0072] The preparation method of silicon carbide raw material in this application is as follows:

[0073] S1: High-purity carbon powder and silicon powder are mixed evenly in a molar ratio of 1.25:1 to obtain 10kg of the first mixture. The first mixture is mixed evenly with 10g of V2O5 to obtain a second mixture. The second mixture is placed in a crucible and heated to 1600℃ at a heating rate of 8℃ / min and maintained for 1h to generate 3C phase silicon carbide primary powder. The obtained primary powder is sieved to obtain 7kg of primary powder with a particle size of 0.4-0.6mm for standby use. The temperature gradient of the second mixture along the axial direction of the crucible is 3℃ / cm.

[0074] S2: High-purity carbon powder and silicon powder were mixed in a molar ratio of 0.85:1 to obtain 8 kg of a third mixture. The third mixture was mixed with 4 g of V2O5 to obtain a fourth mixture. The fourth mixture was mixed with 1.2 kg of primary powder to obtain a fifth mixture. The fifth mixture was placed in a crucible and heated to 1300°C at a heating rate of 10°C / min and maintained for 1.5 hours to synthesize α-phase silicon carbide intermediate powder. The obtained intermediate powder was sieved to obtain 5 kg of powder with a particle size of 1.5 to 2.5 mm for later use. The temperature gradient of the fifth mixture along the axial direction of the crucible was 4°C / cm.

[0075] S3: Mix high-purity carbon powder and silicon powder in a molar ratio of 0.85:1 to obtain 5kg of the sixth mixture, mix the sixth mixture with 6.25g of V2O5 to obtain the seventh mixture, mix the seventh mixture with 4.5kg of intermediate powder to obtain the eighth mixture, place the eighth mixture in a crucible, and heat the eighth mixture to 2300℃ at a heating rate of 15℃ / min and keep it for 2.25h to synthesize α-phase silicon carbide granular raw material 100, sieve the obtained granular raw material 100 to obtain 4kg of granular raw material 100 with a particle size of 3-8mm and 4kg of granular raw material 100 with a particle size of 2-3mm, and mix the granular raw materials 100 of the two particle sizes for later use. Along the axial direction of the crucible, the temperature gradient of the eighth mixture is 10℃ / cm. The cross-sectional view of the granular raw material 100 obtained in this embodiment is shown in FIG. Figure 4As shown, the diameter ratio of the spherical core 110, the first cladding layer 120 and the second cladding layer 130 is 1:5:15, the aluminum concentration of the spherical core 110 is 25at%, the aluminum concentration of the first cladding layer 120 is 15at%, and the aluminum concentration of the second cladding layer 130 is at5%, and the concentrations show a continuously decreasing change and exceed 5at% / mm.

[0076] In this embodiment, the growth method of silicon carbide crystals is the same as that in Example 1. The silicon carbide crystals prepared in this embodiment are as follows: Figure 10 As shown, during the growth process of silicon carbide crystals, the aluminum ion concentration at the crystal interface remains stable as the raw materials are released, and the resulting silicon carbide crystals have a single crystal form without polymorphism.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that the raw material for preparing silicon carbide in this comparative example is 10 kg of silicon carbide powder, 2.5 g of cerium oxide powder is added to the silicon carbide powder, and the mass ratio of silicon carbide powder to cerium oxide powder is 1:0.00025. The silicon carbide powder in this comparative example is placed as follows Figure 11 As shown, the growth conditions of the silicon carbide crystal are the same as those in Example 1. The seed crystal of this comparative example is 4H crystal type. Figure 12 As shown, it can be seen that there are a large number of 6H phase transitions, which is related to the depletion of the crystal inhibitory element Ce in the later stage.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 2 is that the raw material for preparing silicon carbide in this comparative example is 10 kg of silicon carbide powder, the aluminum oxide content in the silicon carbide powder is 3 g, and the mass ratio of silicon carbide powder to aluminum oxide powder is 1:0.0003. Figure 11 As shown, the growth conditions of the silicon carbide crystal are the same as those in Example 2. The silicon carbide crystal prepared in this comparative example is as follows Figure 13 As shown, it can be seen that the color of the silicon carbide crystals prepared in this comparative example is obviously stratified. The reason is that in the initial stage of silicon nitride crystal growth, the alumina in the powder decomposition area decomposes violently and the color is dark. In the middle stage, the alumina is exhausted and the color is gone. In the later stage, the temperature continues to rise, resulting in the powder that did not decompose in the early stage and absorbed alumina in the area began to decompose, and the crystal showed color, resulting in uneven color distribution.

[0081] from Figures 7 to 10 It can be seen that the silicon carbide crystals prepared in Examples 1 to 4 have a single crystal form and uniform color distribution. Figure 12 and Figure 13 It can be seen that the silicon carbide crystals prepared in Comparative Examples 1 and 2 have problems with polymorphism and uniform color distribution.

[0082] The present invention relates to a method for preparing silicon carbide raw materials. The method comprises doping silicon powder and carbon powder with impurity elements and subjecting them to a first heat preservation treatment to obtain a primary powder. The silicon powder, carbon powder, impurity elements, and primary powder are mixed and subjected to a second heat preservation treatment to obtain an intermediate powder. The silicon powder, carbon powder, impurity elements, and intermediate powder are mixed and subjected to a third heat preservation treatment to obtain a granular raw material. By regulating the amount of impurity added at each stage, the synthesis temperature gradient, and the powder particle size distribution, a granular raw material having a gradient structure with a continuously decreasing impurity concentration from the core to the surface is formed. When silicon carbide crystals are grown using a PVT method, this raw material can dynamically compensate for the impurity concentration at the growth interface, ensuring that the impurity concentration fluctuates within a range of ≤±10%. The silicon carbide raw material prepared by the present invention is particularly suitable for the industrial production of large-scale, uniformly doped silicon carbide single crystals. The resulting silicon carbide crystals are uniformly doped, have a single crystal phase, and are free of polymorphic forms. Therefore, the present invention effectively overcomes some practical problems in the prior art and thus has high utilization value and practical significance.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing silicon carbide raw material, characterized in that: The steps include: Mixing carbon powder and silicon powder uniformly to obtain a first mixture, mixing the first mixture and impurity elements uniformly to obtain a second mixture, and maintaining the second mixture at a temperature T1 for a time Δt1 to obtain a primary powder; Mixing carbon powder and silicon powder uniformly to obtain a third mixture, and uniformly mixing the third mixture with impurity elements to obtain a fourth mixture; uniformly mixing the primary powder and the fourth mixture to obtain a fifth mixture, and maintaining the fifth mixture at a temperature of T2 for a time of Δt2 to obtain an intermediate powder; The carbon powder and the silicon powder are evenly mixed to obtain a sixth mixture, the sixth mixture is evenly mixed with impurity elements to obtain a seventh mixture, the intermediate powder is evenly mixed with the seventh mixture to obtain an eighth mixture; the eighth mixture is maintained at a temperature of T3 for a time of Δt3 to obtain a granular raw material.

2. The preparation method according to claim 1, characterized in that In the first mixture, the third mixture, and the sixth mixture, the molar ratio of the carbon powder to the silicon powder is (0.85-1.25):1, the mass ratio of the first mixture to the impurity element is 1:(0.001-0.005), the mass ratio of the third mixture to the impurity element is 1:(0.0005-0.0025), and the mass ratio of the sixth mixture to the impurity element is 1:(0.00025-0.00125); when preparing the intermediate powder, the mass ratio of the fourth mixture to the primary powder is 1:(0.15-0.85); when preparing the granular raw material, the mass ratio of the seventh mixture to the intermediate powder is 1:(0.1-0.9).

3. The preparation method according to claim 1, characterized in that TI is 1100-1600°C, T2 is 1300-2000°C, T3 is 1800-2300°C, Δt1, Δt2, and Δt3 are 1-25h, and Δt1, Δt2, and Δt3 increase successively by 10-50%; the heating rate when preparing the primary powder is 5-10°C / min, the heating rate when preparing the intermediate powder is 10-15°C / min, and the heating rate when preparing the granular raw material is 15-30°C / min.

4. The preparation method according to claim 1, characterized in that Along the axial direction of the filler, the temperature gradient of the second mixture when preparing the primary powder is 2 to 3°C / cm; the temperature gradient of the fifth mixture when preparing the intermediate powder is 3 to 5°C / cm; and the temperature gradient of the eighth mixture when preparing the granular raw material is 5 to 10°C / cm.

5. The preparation method according to claim 1, characterized in that The impurity elements are any one or more of aluminum, cerium, phosphorus, boron, chromium, vanadium, and their corresponding oxides or carbides.

6. A silicon carbide raw material, characterized in that: The invention comprises a granular raw material prepared by the preparation method according to any one of claims 1 to 5.

7. The silicon carbide raw material according to claim 6, characterized in that: The particle raw material includes a spherical core, a first coating layer and a second coating layer, wherein the first coating layer is coated on the outside of the spherical core, and the second coating layer is coated on the outside of the first coating layer, and the diameter ratio of the spherical core, the first coating layer and the second coating layer is 1:(1.5-8):(5-20), and the impurity content in the spherical core, the first coating layer and the second coating layer is distributed in a gradient, and the gradient of the impurity content is 0.1-5 g / cm 3 / mm.

8. The silicon carbide raw material according to claim 6, characterized in that Along the radial direction of the particle raw material, the impurity concentration decreases continuously from the center to the edge of the particle raw material, and the change rate of the impurity concentration is ≥5at% / mm.

9. The silicon carbide raw material according to claim 6, characterized in that The silicon carbide raw material also includes primary powder and intermediate powder, and the mass ratio of the primary powder, the intermediate powder and the granular raw material is (0-1):(1-0):

1.

10. Use of the silicon carbide raw material according to any one of claims 6 to 9, characterized in that: The silicon carbide raw material is used to prepare silicon carbide crystals by PVT method, and the impurity concentration at the growth interface of the silicon carbide crystals is 1×10 14 ~5×10 20 at / cm 3 , and the concentration fluctuation is ≤±10%.

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