A method of reducing defects in silicon carbide crystals

Abstract

This application discloses a method for reducing defects in silicon carbide crystals, comprising: dividing the interior of a crucible into sequentially adjacent regions A, B, and C using graphite paper rings; adding pretreated silicon carbide raw materials to each region; fixing a seed crystal at the top of the crucible; and performing physical vapor transport growth, annealing, and cooling. The silicon carbide raw material is added in a manner that is high at the center and low at the edges. This method utilizes a flow channel formed by adding graphite paper rings into the crucible, and a stepped loading method to create a loading pattern with low edges and a high center, guiding the orderly volatilization of the airflow. Simultaneously, it ensures that the remaining material does not skew or collapse during the growth process, suppressing and reducing phase transitions and inclusion formation at the source, thereby obtaining high-quality, low-defect silicon carbide crystals.

Description

Technical Field

[0001] This application relates to the field of semiconductor material preparation technology, and in particular to a method for reducing defects in silicon carbide crystals. Background Technology

[0002] Inclusions are heterogeneous phases or voids in SiC crystals that deviate from the stoichiometry, composition, and structure of the matrix. They belong to the category of bulk defects and are one of the most common and harmful defects in SiC single crystals grown by PVT (physical vapor transport), directly affecting the breakdown voltage, leakage current, yield, and reliability of devices.

[0003] Therefore, developing a method to reduce defects in silicon carbide crystals is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, this application provides a method for reducing defects in silicon carbide crystals. By modifying the internal structure of the crucible and optimizing relevant crystal growth process parameters, defects such as phase transitions and inclusions in silicon carbide crystals can be effectively reduced.

[0005] This application provides a method for reducing defects in silicon carbide crystals, including: The crucible interior is divided into three adjacent regions, A, B and C, using graphite paper rings. Pretreated silicon carbide raw materials are added to each region, and seed crystals are fixed at the top of the crucible for physical vapor transport growth, annealing and cooling. The silicon carbide raw material is added in a way that is high at the center and low at the edges.

[0006] In some specific implementations, the pretreated silicon carbide raw material added to region A has a mesh size of 50 to 65 mesh; The pretreated silicon carbide raw material added to Zone B has a mesh size of 35 to 50 mesh; The pretreated silicon carbide raw material added to the C zone has a mesh size of 15 to 35 mesh; The height difference between the center and the edge of the silicon carbide raw material added is 8cm to 15cm.

[0007] In some specific implementations, the mass of the pretreated silicon carbide raw material added to area A is 20% to 30% of the total amount of pretreated silicon carbide raw material added; The mass of the pretreated silicon carbide raw material added to Zone B is 40% to 50% of the total amount of pretreated silicon carbide raw material added. The mass of the pretreated silicon carbide raw material added to Zone C is 20% to 30% of the total amount of pretreated silicon carbide raw material added.

[0008] In some specific implementations, the method for preparing the pretreated silicon carbide raw material includes: subjecting the silicon carbide raw material to vacuum high-temperature pretreatment; The temperature of the vacuum high-temperature pretreatment is 250°C to 350°C; The vacuum high-temperature pretreatment time is 3 to 5 hours. The pretreated silicon carbide raw material has a mesh size of 15 to 65 mesh.

[0009] In some specific implementations, the physical vapor transport growth method includes heating to a first temperature at a first heating rate for a first holding, and heating to a second temperature at a second heating rate for a second holding and growth.

[0010] In some specific implementations, the first heating rate is 10°C / min to 15°C / min; The first temperature is 2000℃ to 2200℃; The first heat preservation time is 30 to 60 minutes.

[0011] In some specific implementations, the second heating rate is 5°C / min to 8°C / min; The second temperature is 2200℃ to 2400℃; The second heat preservation time is 0.5h to 3h; The axial temperature gradient formed between the seed crystal and the source region during the second heating is 15℃ / min to 30℃ / min.

[0012] In some specific implementations, the physical vapor transport method growth is carried out under the protection of an inert gas. The inert gas includes argon and / or nitrogen; The crucible pressure is between 5 mbar and 30 mbar.

[0013] In some specific implementations, the growth includes the initial growth stage and stable growth; The growth rate during the initial growth stage is 50 μm / h to 150 μm / h; The initial growth phase refers to the first 2 to 5 hours after the start of growth. The stable growth rate is 200 μm / h to 400 μm / h; Adjust the pressure value to 18 mbar to 22 mbar so that the C / Si gas phase ratio is 1.0 to 1.2 during stable growth.

[0014] In some specific implementations, the annealing temperature is between 2100°C and 2250°C; The annealing time is 1 hour to 3 hours; After annealing, the temperature is reduced to room temperature at a rate of 1°C / min to 3°C / min.

[0015] This application provides a method for effectively reducing phase transitions and inclusion defects in silicon carbide crystals. The method involves adding a flow channel made of graphite paper rings into the crucible and using a stepped loading method to create a loading pattern with lower edges and higher centers, guiding the orderly volatilization of the airflow. Simultaneously, it ensures that the remaining material does not skew or collapse during growth, suppressing and reducing phase transitions and inclusion formation at the source, thereby obtaining high-quality, low-defect silicon carbide crystals. Attached Figure Description

[0016] Figure 1 A diagram of the growth apparatus for the method of reducing silicon carbide crystal defects provided in Embodiment 1 of this application; Figure 2 This is a crystal side view of the method for reducing silicon carbide crystal defects provided in Embodiment 1 of this application. Detailed Implementation

[0017] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0018] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0019] It should be understood that the order of steps or the sequence of actions is not important as long as this application remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0020] The use of any and all instances or exemplary language such as “e.g.” or “include” in this document is intended merely to better illustrate the application and does not constitute a limitation on the scope of the application. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of this application.

[0021] Furthermore, the numerical ranges and parameters used to define this application are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any numerical value inevitably contains standard deviations due to individual test methods. Therefore, unless otherwise explicitly stated, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately." Here, "approximately" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range.

[0022] This application provides a method for reducing defects in silicon carbide crystals, including: The crucible interior is divided into three adjacent regions, A, B and C, using graphite paper rings. Pretreated silicon carbide raw materials are added to each region, and seed crystals are fixed at the top of the crucible for physical vapor transport growth, annealing and cooling. The silicon carbide raw material is added in a way that is high at the center and low at the edges.

[0023] This application optimizes and studies the growth process of silicon carbide crystals to improve their growth quality and process stability, belonging to the field of semiconductor crystal growth technology. The method employs the physical vapor transport (PVT) method. This involves structurally modifying the crucible's interior (by adding a flow channel made of graphite paper rings), and then loading pre-fired silicon carbide raw materials with a specific mesh size ratio. The mesh size of the material loaded in the central region of the crucible is 50-35 mesh, while the mesh sizes on the sides are 65-50 mesh and 35-15 mesh, respectively. The raw materials are loaded in a manner that is higher at the center and lower at the edges, following the flow channel structure. Furthermore, through multi-stage precise temperature control, optimization of the temperature field distribution within the furnace cavity, staged control of the crystal growth rate, and dynamic adjustment of the vapor phase stoichiometry, the formation of crystal phase transitions and carbon particle inclusion defects can be effectively suppressed. This invention can significantly reduce crystal phase transformation and the formation of inclusions on the crystal surface from the source, which can significantly improve crystal quality and raw material utilization. It has good process repeatability and is suitable for industrial production of high-quality, large-size silicon carbide crystals.

[0024] This application first uses graphite paper rings to divide the interior of the crucible into sequentially adjacent regions A, B, and C. In some specific implementations, the parameters of the graphite paper rings include: a weight of 45g to 55g, preferably 50g, and a density of 1.2 g / cm³. 3 Up to 1.6 g / cm 3 The preferred value is 1.4 g / cm³. 3The thickness is 0.4mm to 0.8mm, preferably 0.5mm. By modifying the internal structure of the crucible and adding a flow channel made of graphite paper rings, the silicon carbide particles are separated, and a transport channel for silicon carbide gas phase flow is formed between the silicon carbide particles and between the silicon carbide particles and the graphite rings. The graphite paper rings are not only inexpensive and achieve the same effect as graphite columns, but they are also reusable, reducing the increased costs associated with replacing custom crucibles, making them suitable for large-scale application. Under high-temperature conditions, the graphite paper rings exhibit higher stability and will not cause defects in the inclusions due to wear and tear of the graphite components caused by high temperatures. In the actual research and development process, this application optimizes the growth process, combines a large number of experiments to determine the mesh size range and changes in the raw material stacking method, and improves the raw material volatilization path; the introduction of graphite paper ring guide channel can effectively ensure the stability of airflow volatilization, and together with the screening of raw material mesh size range and the raw material stacking method, it can effectively improve and avoid the collapse and skewing of residual material in the later stage, which would lead to insufficient supply of silicon carbide raw materials in the later stage.

[0025] This application then adds pretreated silicon carbide raw materials to regions A, B, and C respectively, fixes a seed crystal on the top of the crucible, and performs physical vapor transport growth. In some specific implementations, the mesh size of the pretreated silicon carbide raw material added to region A is 50 to 65 mesh; the mesh size of the pretreated silicon carbide raw material added to region B is 35 to 50 mesh; and the mesh size of the pretreated silicon carbide raw material added to region C is 15 to 35 mesh. The height difference between the center and the edge of the added silicon carbide raw material is 8 cm to 15 cm, preferably 10 cm. This setting aims to create a stable airflow path with a higher center and lower edge, ensuring the growth quality of the crystal in the later stages and changing the volatilization path of the raw material. Since the crystal grows in a spiral manner, changes in the stacking method have a significant impact on the growth. In some specific implementations, the mass of the pretreated silicon carbide raw material added to region A is 20% to 30% of the total amount of pretreated silicon carbide raw material added; the mass of the pretreated silicon carbide raw material added to region B is 40% to 50% of the total amount of pretreated silicon carbide raw material added; and the mass of the pretreated silicon carbide raw material added to region C is 20% to 30% of the total amount of pretreated silicon carbide raw material added. In some specific implementations, the preparation method of the pretreated silicon carbide raw material includes: subjecting the silicon carbide raw material to vacuum high-temperature pretreatment; the temperature of the vacuum high-temperature pretreatment is 250°C to 350°C; the time of the vacuum high-temperature pretreatment is 3 hours to 5 hours, preferably 4 hours; and the mesh size of the pretreated silicon carbide raw material is 15 mesh to 65 mesh. Adding pretreatment to the raw material allows small particles and fine particles to be removed at high temperatures, preventing these factors from affecting the crystal growth process. High-temperature pretreatment directly affects inclusion defects in the crystal; it can remove fine particulate dust from the raw material, reducing inclusion defects by 40%.

[0026] This application improves the temperature field structure by loading pre-fired silicon carbide raw materials with a specific mesh size ratio at high temperature. The raw materials are loaded in a way that is high in the center and low at the edges according to the flow channel structure. In addition, the mesh size range is controlled to improve the growth quality of crystals. Through repeated experiments, the airflow transport path can be effectively improved.

[0027] This application then performs physical vapor transport (PVT) growth, annealing, and cooling. In some specific implementations, the PVT growth includes heating to a first temperature at a first heating rate, holding at that temperature for the first time, and heating to a second temperature at a second heating rate for the second holding and growth. In some specific implementations, the first heating rate is 10°C / min to 15°C / min, preferably 12°C / min; the first temperature is 2000°C to 2200°C, preferably 2100°C; and the first holding time is 30 min to 60 min, preferably 40 min to 50 min. The growth chamber is heated to 2000-2200°C at the first heating rate (10-15°C / min) and held for 30-60 min to allow the raw material to fully sublimate and stabilize, while ensuring uniform heating of the seed crystal. In some specific implementations, the second heating rate is 5℃ / min to 8℃ / min, preferably 6℃ / min; the second temperature is 2200℃ to 2400℃, preferably 2350℃; the second holding time is 0.5h to 3h, preferably 1h; the axial temperature gradient formed between the seed crystal and the source region during the second heating is 15℃ / min to 30℃ / min, preferably 23℃ / min. The temperature of the heat source region is raised to the crystal growth temperature (2200-2400℃) at the second heating rate (5-8℃ / min), while the temperature at the seed crystal location is controlled to form the required axial temperature gradient (15-35℃ / cm) between the seed crystal and the source region. During this stage, the radial temperature distribution is optimized by adjusting the position and power of the induction coil to make it as flat as possible, with the radial temperature difference controlled within ±2℃. In some specific implementations, the seed crystal temperature is set to 2000℃ to 2200℃, preferably 2120℃. In some specific implementations, the physical vapor transport growth is carried out under an inert gas atmosphere; the inert gas includes, but is not limited to, argon and / or nitrogen, and this application does not have specific requirements for the selection of the inert gas; the crucible pressure is 5 mbar to 30 mbar, preferably 18 mbar to 22 mbar. In some specific implementations, the growth includes an initial growth phase and a stable growth phase; the growth rate in the initial growth phase is 50 μm / h to 150 μm / h, preferably 100 μm / h; the initial growth phase is the first 2 to 5 hours of growth, preferably the first 3 hours; in the initial growth phase (first 2-5 hours), the growth rate is controlled at a low level (50-150 μm / h) to ensure atomically flat growth interfaces, laying the foundation for subsequent high-quality growth, ensuring the stability of the crystal growth rate to a certain extent, and simultaneously reducing the generation of crystal color inhomogeneity defects.The stable growth rate is 200 μm / h to 400 μm / h, preferably 300 μm / h; the pressure is adjusted to 18 mbar to 22 mbar to achieve a C / Si vapor phase ratio of 1.0 to 1.2, preferably 1.05, during stable growth. The C / Si vapor phase ratio is maintained around 1.0-1.2 by fine-tuning the source region temperature or cavity pressure to avoid the precipitation of encapsulated particles due to silicon-rich or carbon-rich conditions. In some specific implementations, growth continues for 50 to 80 hours, preferably 60 hours, after adjusting the pressure. In some specific implementations, the annealing temperature is 2100℃ to 2250℃, preferably 2150℃; the annealing time is 1 hour to 3 hours, preferably 2 hours; and the temperature is lowered to room temperature at 1℃ / min to 3℃ / min after annealing. After growth, in-situ annealing is first performed at 2100-2250℃ for 1-3 hours under an inert atmosphere to eliminate internal stress in the crystal. Then, the temperature is slowly reduced to room temperature at a stable growth rate (1-3 °C / min) to prevent crystal cracking due to thermal stress.

[0028] This application involves loading high-purity silicon carbide powder with a specific mesh size ratio into a crucible containing graphite paper rings. The addition of flow channels made from the graphite paper rings significantly improves the airflow direction, ensuring the stability of the Si-C stacking sequence during crystal growth and greatly reducing the probability of crystal phase transitions. Simultaneously, multi-stage precise temperature control is employed, with specific heating curves and temperature field adjustment methods designed to ensure the stability of the furnace temperature field. The addition of the graphite paper ring flow channels inside the crucible results in a loading pattern that is higher at the center and lower at the edges, which to some extent ensures the orderliness of raw material sublimation and gas phase transport, avoiding the formation of inclusions caused by localized Si / C oversaturation in the later stages of growth, and effectively reducing the formation of crystal inclusions.

[0029] The present application is further illustrated below with reference to embodiments. The scope of protection of the present application is not limited to the following embodiments.

[0030] Example 1

[0031] This embodiment provides a growth apparatus for reducing defects in silicon carbide crystals. See [link to relevant documentation]. Figure 1 ,include: The crucible body is used to fill silicon carbide granular raw materials; Multiple coils are symmetrically arranged on the outside of the crucible body; Graphite paper rings are disposed within the crucible body, with two rings spaced apart and inserted into the silicon carbide granular raw material to separate the granules and create transport channels for silicon carbide gas phase flow between the granules and between the granules and the outer wall of the graphite rings. A seed crystal is located at the top of the crucible body.

[0032] This embodiment provides a method for reducing defects in silicon carbide crystals, including: Raw materials with a specific mesh ratio (65~50 mesh: 50~35 mesh: 35~15 mesh = 0.25:0.5:0.25, with 65~50 mesh placed on the left side of the apparatus, 50~35 mesh in the middle, and 35~15 mesh on the right side) were pretreated at 300 °C under high vacuum for 1 hour. The system was then evacuated to... Then, high-purity Ar gas was introduced to a pressure of 20 mbar. The graphite paper ring weighed 50g and had a density of 1.4g / cm³. 3 The crucible has a thickness of 0.5 mm and a height difference of 10 cm between the center and edge. The temperature is increased to 2100 °C at 12 °C / min and held for 4 hours. Then, the temperature is increased to the source region temperature of 2350 °C at 6 °C / min, with the seed crystal temperature set at 2120 °C, creating an axial temperature gradient of approximately 23 °C / cm. By controlling the airflow in the furnace cavity through the graphite paper ring guide grooves inside the crucible, the radial temperature difference can be controlled within ±1.5 °C, effectively reducing the formation of crystal phase transformation defects. In the initial growth stage (first 3 hours), the growth rate is controlled at 100 μm / h. After entering steady-state growth, the growth rate is increased to 300 μm / h, and the C / Si ratio is maintained at approximately 1.05 by fine-tuning the pressure (range 18-22 mbar), continuing growth for 60 hours. After growth, the crucible is annealed in situ at 2150 °C for 2 hours, and then slowly cooled to room temperature at a rate of 2 °C / min. The silicon carbide crystal gained 3000g in weight, exhibited no phase transition, and showed no inclusion defects on the crystal surface. The crystal side view of the method for reducing defects in silicon carbide crystals provided in Example 1 is shown below. Figure 2 As shown.

[0033] Example 2

[0034] This embodiment provides a method for reducing defects in silicon carbide crystals, including: Raw materials with a specific mesh ratio (65~50 mesh: 50~35 mesh: 35~15 mesh = 0.25:0.5:0.25, with 65~50 mesh placed on the left side of the apparatus, 50~35 mesh in the middle, and 35~15 mesh on the right side) were pretreated at 300 ℃ under high vacuum for 1 hour. After growth, the material was annealed in situ at 2150 ℃ for 2 hours, and then slowly cooled to room temperature at a rate of 2 ℃ / min. With increasing use of the crucible, the entire crucible suffered severe high-temperature erosion, resulting in significant carbon powder precipitation. Using a flow channel made of graphite paper rings, compared to internal crucible modifications, offered advantages such as low cost and fewer subsequent defects. The silicon carbide crystal gained 3000g in weight, exhibited no phase transformation, and showed no surface defects.

[0035] Example 3

[0036] This embodiment provides a method for reducing defects in silicon carbide crystals, including: Raw materials with a specific mesh ratio (65~50 mesh: 50~35 mesh: 35~15 mesh = 0.25:0.5:0.25, with 65~50 mesh placed on the left side of the apparatus, 50~35 mesh in the middle, and 35~15 mesh on the right side) were pretreated at 300 °C under high vacuum for 1 hour. The system was then evacuated to... Then, high-purity Ar gas was introduced to a pressure of 20 mbar. The graphite paper ring weighed 50g and had a density of 1.4g / cm³. 3 The silicon carbide crystal was 0.5 mm thick, with a height difference of 10 cm between the center and edge inside the crucible. During the initial growth phase (first 3 hours), the growth rate was controlled at 100 μm / h. After reaching steady-state growth, the growth rate was increased to 300 μm / h, and the C / Si ratio was maintained at approximately 1.05 by fine-tuning the pressure (range 18-22 mbar), continuing growth for 80 hours. After growth, it was annealed in situ at 2150℃ for 2 hours, and then slowly cooled to room temperature at a rate of 2℃ / min. The silicon carbide crystal gained 3200 g in weight, exhibited a late-stage phase transition, and showed no inclusion defects. (This example involves extending the crystal growth time.)

[0037] Example 4

[0038] This embodiment provides a method for reducing defects in silicon carbide crystals, including: Raw materials with a specific mesh size ratio (65~50 mesh: 50~35 mesh: 35~15 mesh = 1:1:1, with 65~50 mesh placed on the left side of the apparatus, 50~35 mesh in the middle, and 35~15 mesh on the right side) were pretreated at 300 ℃ under high vacuum for 1 hour. The system was then evacuated to... Then, high-purity Ar gas was introduced to a pressure of 20 mbar. The graphite paper ring weighed 50g and had a density of 1.4g / cm³. 3 The silicon carbide crystal was 0.5 mm thick, with a height difference of 10 cm between the center and edge of the crucible. During the initial growth phase (first 3 hours), the growth rate was controlled at 100 μm / h. After reaching steady-state growth, the growth rate was increased to 300 μm / h, and the C / Si ratio was maintained at approximately 1.05 by fine-tuning the pressure (range 18-22 mbar), continuing growth for 80 hours. After growth, it was annealed in situ at 2150℃ for 2 hours, and then slowly cooled to room temperature at a rate of 2℃ / min. The silicon carbide crystal gained 2200 g in weight, exhibiting an initial phase transition and moderate inclusion defects.

[0039] Example 5

[0040] This embodiment provides a method for reducing defects in silicon carbide crystals, including: The raw materials were prepared with a specific mesh ratio (65~50 mesh: 50~35 mesh: 35~15 mesh = 0.25:0.5:0.25, with the 65~50 mesh placed on the left side of the apparatus, the 50~35 mesh in the middle, and the 35~15 mesh on the right side). The graphite paper ring weighed 50g and had a density of 1.4g / cm³. 3 The silicon carbide crystal was 0.5 mm thick, with a height difference of 15 cm between the center and edge of the crucible. After entering steady-state growth, the growth rate was increased to 300 μm / h, and the C / Si ratio was maintained at approximately 1.05 by fine-tuning the pressure (range 18-22 mbar), and growth continued for 60 h. After growth, it was annealed in situ at 2150 °C for 2 h, and then slowly cooled to room temperature at a rate of 2 °C / min. The silicon carbide crystal gained 3100 g in weight, exhibited a phase transition in the middle stage of crystal formation, edge collapse on the crystal surface, insufficient raw material supply, and a small number of inclusion defects on the crystal surface.

[0041] Comparative Example 1

[0042] This comparative example uses a conventional PVT process. The difference from Example 1 is that no high-temperature pretreatment of the raw materials was performed, no graphite paper ring guide groove was added to the internal structure of the crucible, no segmented heat preservation was used during the heating process, and a constant growth rate was used from the initial growth stage. The C / Si gas phase ratio was not actively controlled. The final silicon carbide crystal had a weight gain of 2300g, the crystal surface contained moderate inclusions, and a phase transition occurred at 5mm.

[0043] Comparative Example 2

[0044] This comparative example uses a conventional PVT process with a single variable approach. The difference from Example 1 is that no silicon carbide raw material with a specific mesh size ratio was added, and growth was performed at a constant rate from the initial stage. The C / Si gas phase ratio was not actively controlled. The final silicon carbide crystal had a weight gain of 2380g, with moderate inclusions on the crystal surface and the formation of phase transition defects. The phase transition occurred at 11mm.

[0045] Comparative Example 3

[0046] This comparative example uses a conventional PVT process with a single variable method. The difference from Example 1 is that no graphite paper ring channel was added to the crucible, and a constant growth rate was used in the initial stage of growth. In contrast to the addition of the graphite channel, the channel improves the stability of the raw material gas flow evaporation and ensures the stability of the raw material stacking order during growth. The final silicon carbide crystal showed a weight gain of 2410g, with moderate inclusions on the crystal surface, and a phase transition occurred at 12mm.

[0047] Comparative Example 4

[0048] This comparative example uses a conventional PVT process with a single variable approach. The difference from Example 1 is that the C / SI gas ratio within the furnace cavity was not controlled. The final silicon carbide crystal showed a weight gain of 2190g, with moderate inclusions on the crystal surface, and a phase transition occurred at a depth of 9.5mm.

[0049] Comparative Example 5

[0050] The difference between this comparative example and Example 1 is that the raw material mesh size ratio is 10-20:20-30:30-40:40-50:50-60:60-70:70-80, and the mass ratio is 35%:15%:5%:5%:15%:25%.

[0051] Compared with Comparative Example 5, the mesh ratio of this application is significantly different. This application, combined with the current mesh ratio and loading method, can significantly improve the airflow path. By loading according to the internal structure of the crucible, the crystal exhibits defects in the initial phase transition.

[0052] This application effectively solves the crystal phase transition problem through optimized experiments on the mesh size range and combined with the charging method. (Different mesh sizes, different temperature field structures, and volatilization paths all have a significant impact on crystal growth).

[0053] Comparative Example 6

[0054] The difference between this comparative example and Example 1 is that the raw material mesh ratio was not screened in a specific way; raw materials of 10-80 mesh were randomly selected and loaded into the crucible in a ratio of 15-25:25-35:35-45:45-55:55-65 mesh in 1:1:1:1. Pretreatment was performed at 300 °C under high vacuum for 1 hour. After growth, in-situ annealing was carried out at 2150 °C for 2 hours, followed by slow cooling to room temperature at a rate of 2 °C / min. This example did not screen or optimize the raw material mesh, resulting in numerous phase transition defects in the crystals produced by repeated growth. The silicon carbide crystal gained 2400g, exhibited an initial phase transition, and showed a small number of inclusion defects on the crystal surface.

[0055] Comparative Example 7

[0056] Raw materials with a specific mesh ratio (65~50 mesh: 50~35 mesh: 35~15 mesh = 0.25:0.5:0.25, with 65~50 mesh placed on the left side of the apparatus, 50~35 mesh in the middle, and 35~15 mesh on the right side) were pretreated at 300 ℃ under high vacuum for 1 hour. The system was then evacuated to 5×1 After Pa, high-purity Ar gas was introduced to a pressure of 20 mbar. The graphite paper ring weighed 50 g and had a density of 1.4 g / cm³. 3The silicon carbide crystal was 0.5 mm thick, with a height difference of 0 cm between the center and edge inside the crucible. During the initial growth phase (first 3 hours), the growth rate was controlled at 100 μm / h. After reaching steady-state growth, the growth rate was increased to 300 μm / h, and the C / Si ratio was maintained at approximately 1.05 by fine-tuning the pressure (range 18-22 mbar), continuing growth for 60 hours. After growth, it was annealed in situ at 2150℃ for 2 hours, and then slowly cooled to room temperature at a rate of 2℃ / min. The silicon carbide crystal gained 2800 g in weight, exhibited a mid-phase phase transition, and showed inclusion defects on the crystal surface.

[0057] After cutting, grinding, and polishing the silicon carbide ingots grown in Examples 1-2 and Comparative Examples 1-7, defects were observed using a polarizing microscope or similar instruments.

[0058] Comparative Example 1 Crystal: A large number of hazy-like scattering points (encapsulations) were observed on the crystal surface, indicating that the crystal was undergoing a mid-term phase transition.

[0059] Comparative Example 2 Crystal: The silicon carbide raw material was not subjected to high-temperature pretreatment, and the crystal underwent a mid-term phase transition and encapsulation.

[0060] Example 1 Crystal: After repeated experiments, local inclusions were observed only in a very small number of areas. The inclusion density was reduced by more than 60% compared with Comparative Example 1. At the same time, the probability of phase transition in the crystal was also reduced by 50%, which effectively improved the growth quality of silicon carbide crystal.

[0061] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and application concept of this application, should be included within the scope of protection of this application.

Claims

1. A method for reducing defects in silicon carbide crystals, characterized in that, include: The crucible interior is divided into adjacent regions A, B and C using graphite paper rings. Pretreated silicon carbide raw materials are added to each region, and seed crystals are fixed at the top of the crucible for physical vapor transport growth, annealing and cooling. The silicon carbide raw material is added in a way that is high at the center and low at the edges.

2. The method according to claim 1, characterized in that, The pretreated silicon carbide raw material added to area A has a mesh size of 50 to 65 mesh; The pretreated silicon carbide raw material added to Zone B has a mesh size of 35 to 50 mesh; The pretreated silicon carbide raw material added to the C zone has a mesh size of 15 to 35 mesh; The height difference between the center and the edge of the silicon carbide raw material added is 8cm to 15cm.

3. The method according to claim 1, characterized in that, The mass of the pretreated silicon carbide raw material added to Zone A is 20% to 30% of the total amount of pretreated silicon carbide raw material added. The mass of the pretreated silicon carbide raw material added to Zone B is 40% to 50% of the total amount of pretreated silicon carbide raw material added. The mass of the pretreated silicon carbide raw material added to Zone C is 20% to 30% of the total amount of pretreated silicon carbide raw material added.

4. The method according to claim 1, characterized in that, The method for preparing the pretreated silicon carbide raw material includes: subjecting the silicon carbide raw material to vacuum high-temperature pretreatment; The temperature of the vacuum high-temperature pretreatment is 250°C to 350°C; The vacuum high-temperature pretreatment time is 3 to 5 hours. The pretreated silicon carbide raw material has a mesh size of 15 to 65 mesh.

5. The method according to claim 1, characterized in that, The physical vapor transport growth method includes heating to a first temperature at a first heating rate for a first holding, and heating to a second temperature at a second heating rate for a second holding and growth.

6. The method according to claim 5, characterized in that, The first heating rate is 10°C / min to 15°C / min; The first temperature is 2000℃ to 2200℃; The first heat preservation time is 30 to 60 minutes.

7. The method according to claim 5, characterized in that, The second heating rate is 5°C / min to 8°C / min; The second temperature is 2200℃ to 2400℃; The second heat preservation time is 0.5h to 3h; The axial temperature gradient formed between the seed crystal and the source region during the second heating is 15℃ / min to 30℃ / min.

8. The method according to claim 1, characterized in that, The physical vapor transport method is used for growth under inert gas protection. The inert gas includes argon and / or nitrogen; The crucible pressure is between 5 mbar and 30 mbar.

9. The method according to claim 5, characterized in that, The growth includes the initial growth stage and stable growth; The growth rate during the initial growth stage is 50 μm / h to 150 μm / h; The initial growth phase refers to the first 2 to 5 hours after the start of growth. The stable growth rate is 200 μm / h to 400 μm / h; Adjust the pressure value to 18 mbar to 22 mbar so that the C / Si gas phase ratio is 1.0 to 1.2 during stable growth.

10. The method according to claim 1, characterized in that, The annealing temperature is from 2100°C to 2250°C; The annealing time is 1 hour to 3 hours; After annealing, the temperature is reduced to room temperature at a rate of 1°C / min to 3°C / min.

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