Method for producing silicon carbide powder containing nitrogen and method for growing silicon carbide crystal
By preparing silicon carbide powder with appropriate nitrogen content and combining it with graphite ring design, the problem of poor resistivity uniformity during silicon carbide crystal growth was solved, and higher quality crystal growth was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING NAURA MICROELECTRONICS EQUIP CO LTD
- Filing Date
- 2022-11-25
- Publication Date
- 2026-07-24
AI Technical Summary
In the current silicon carbide crystal growth process, the resistivity uniformity is poor, leading to defects such as polycrystalline, microtube and hexagonal defects, which seriously reduces the production efficiency.
Using silicon carbide powder with a relatively high nitrogen content, silicon carbide powder with a nitrogen content of 80ppm to 450ppm was prepared by controlling the nitrogen flow rate and protective gas composition during the growth process. Sufficient nitrogen composition was ensured during crystal formation. Combined with graphite ring design to isolate powder regions with different nitrogen contents, sufficient nitrogen composition was ensured on the crystal surface.
It effectively alleviates the problem of increased resistivity caused by insufficient nitrogen content, improves the uniformity of crystal resistivity, reduces defects, and enhances the quality of silicon carbide crystals.
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Figure CN118083983B_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of silicon carbide crystal preparation technology, specifically relating to a method for preparing nitrogen-containing silicon carbide powder and a method for growing silicon carbide crystals. Background Technology
[0002] With the expanding applications of third-generation semiconductor materials, silicon carbide (SiC) single crystals, as representative materials of third-generation semiconductors, have broad application prospects in multiple fields due to their large bandgap, high thermal conductivity, high saturated electron drift velocity, and high breakdown field strength. They are particularly growing rapidly in the fields of electric vehicles (xEVs), rail transportation, and motor driving, with their market share gradually increasing. Currently, with the continuous expansion of the silicon carbide (SiC) market, the demand for SiC substrates is increasing dramatically, but in terms of market share, China only accounts for about 3% of the global market. The technical difficulties and cost distribution of SiC devices are mainly in the substrate and epitaxial parts, accounting for more than 50% of the cost. The main issue with SiC substrates is the low yield rate of SiC single crystals, with defects such as microtubes caused by uneven nitrogen doping concentration. n-type 4H-SiC is mainly used as a substrate material in semiconductor lighting and power electronic devices, and the resistivity and uniformity of the substrate material have a significant impact on device performance.
[0003] Currently, the industry uses physical vapor transport (PVT) to grow silicon carbide crystals. For example, this involves using medium-frequency induction heating. The silicon carbide raw material is placed at the bottom of a graphite crucible, while the silicon carbide seed crystal is at the top. The temperature gradient is adjusted by regulating the holding temperature, resulting in a higher temperature at the silicon carbide raw material and a lower temperature at the seed crystal. The silicon carbide raw material at the high temperature sublimates and decomposes into gaseous substances, which are then transported to the lower-temperature seed crystal, crystallizing to form silicon carbide crystals. Specifically, n-type 4H-SiC is obtained by introducing nitrogen gas, using argon as the carrier gas.
[0004] Currently, silicon carbide crystal growth commonly employs the PVT (Polymer Transformation) method. Silicon carbide powder sublimates upon heating, and various gaseous components are transferred to a seed crystal via mass transfer for crystallization. To achieve effective conductivity, nitrogen is introduced during growth, especially for preparing n-type conductive silicon carbide wafers. Nitrogen gas is introduced during growth to neutralize holes generated by boron and aluminum (i.e., compensation), while the remaining free electrons allow silicon carbide to exhibit n-type conductivity. Currently, theoretical and practical studies have shown that micro-convex interface crystals have better quality. Therefore, to obtain micro-convex interface crystals during silicon carbide crystal growth, a radial temperature gradient is generally required, i.e., a lower temperature at the center and a higher temperature at the periphery. However, current technology achieves this radial temperature gradient by using an induction coil to heat a graphite crucible. The radial temperature gradient is generated by the distance between the graphite center and the induction coil. However, as the peripheral growth temperature increases, the Si in the silicon carbide component on the crystal surface sublimates, while the remaining C component and nitrogen bind less to the crystal surface, leading to increased resistivity. This causes the resistivity difference Δρ between the central region and the edge region to gradually increase, resulting in poor resistivity uniformity of the crystal and causing defects such as polycrystalline, microtube, and hexagonal defects, which severely reduces production efficiency. Summary of the Invention
[0005] The purpose of this application is to provide a method for preparing nitrogen-containing silicon carbide powder and a method for growing silicon carbide crystals, which can at least solve the problem of defects caused by poor resistivity uniformity of current silicon carbide crystals.
[0006] To solve the above-mentioned technical problems, this application is implemented as follows:
[0007] This application provides a method for preparing nitrogen-containing silicon carbide powder, which is used for silicon carbide crystal growth. The preparation method includes:
[0008] Silicon and carbon raw materials are thoroughly mixed at a preset molar ratio to obtain a mixture raw material;
[0009] Place the heating container containing the mixture of raw materials into the reaction equipment;
[0010] The reaction equipment is evacuated and heated;
[0011] A protective gas and nitrogen are introduced into the reaction equipment, and the temperature inside the reaction equipment is continuously increased by heating to cause the carbon raw material and the silicon raw material to react. After cooling, the nitrogen-containing silicon carbide powder is obtained.
[0012] This application embodiment also provides a method for growing silicon carbide crystals. The growth method includes: placing nitrogen-containing silicon carbide powder prepared by the above-mentioned method for preparing nitrogen-containing silicon carbide powder in a heating container and heating it, so that the nitrogen-containing silicon carbide powder in the heating container sublimates and crystallizes at the silicon carbide seed crystal at the top of the heating container to obtain silicon carbide crystals.
[0013] In this embodiment, a nitrogen-containing silicon carbide powder with a relatively high nitrogen content is prepared by using a method for preparing nitrogen-containing silicon carbide powder. When this nitrogen-containing silicon carbide powder is applied to the growth process of silicon carbide crystals, compared with ordinary silicon carbide powder, sufficient nitrogen components can be ensured on the crystal surface during crystal formation, thereby alleviating the problem of increased nitrogen content in the outer region of the crystal due to reduced nitrogen component bonding on the crystal surface.
[0014] Furthermore, the silicon carbide crystal growth method in this application uses nitrogen-containing silicon carbide powder with a higher nitrogen content, which is more suitable for the growth of n-type silicon carbide crystals. During the heating process, as the temperature rises, although the silicon component in the silicon carbide component on the crystal surface sublimates and the remaining carbon component reduces the amount of nitrogen bound to the crystal surface, the relatively high nitrogen content of the nitrogen-containing silicon carbide powder ensures sufficient nitrogen content on the crystal surface. This alleviates the problem of increased resistivity caused by reduced nitrogen binding on the crystal surface, resulting in a relatively small resistivity difference in the crystal. Therefore, it can ensure the uniformity of crystal resistivity and alleviate the problem of defects. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the structure of the single crystal furnace for preparing nitrogen-containing silicon carbide powder as disclosed in the embodiments of this application;
[0016] Figure 2 This is a schematic diagram of the structure of a single crystal furnace filled with silicon carbide powder of a first nitrogen content and silicon carbide powder of a second nitrogen content, as disclosed in an embodiment of this application.
[0017] Figure 3 This is a schematic diagram of the graphite ring structure disclosed in the embodiments of this application;
[0018] Figure 4 This is a cross-sectional schematic diagram of a heating container filled with silicon carbide powder containing a first nitrogen content and silicon carbide powder containing a second nitrogen content, as disclosed in an embodiment of this application.
[0019] Figure 5 This is a process flow diagram of the preparation process of nitrogen-containing silicon carbide powder disclosed in the embodiments of this application;
[0020] Figure 6 This is a schematic diagram of the resistivity distribution of crystals under different filling methods disclosed in the embodiments of this application.
[0021] Explanation of reference numerals in the attached figures:
[0022] 1-Crucible; 2-Silicon carbide seed crystal; 3-Graphite ring; 31-Central through-hole area; 32-Outer edge area; 321-Ventilation hole; 4-Insulation cylinder; 51-Upper insulation structure; 52-Lower insulation structure; 61-Upper temperature measuring component; 62-Lower temperature measuring component; 71-Silicon carbide powder with first nitrogen content; 72-Silicon carbide powder with second nitrogen content; 8-Induction coil. Detailed Implementation
[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0024] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.
[0025] The embodiments of this application will be described in detail below with reference to the accompanying drawings and specific examples and application scenarios.
[0026] refer to Figures 1 to 6 This application discloses a method for preparing nitrogen-containing silicon carbide powder, which can produce nitrogen-containing silicon carbide powder that can be used for silicon carbide crystal growth. The disclosed method for preparing nitrogen-containing silicon carbide powder includes:
[0027] Silicon and carbon raw materials are thoroughly mixed at a preset molar ratio to obtain a mixture raw material;
[0028] Place the heating container (which may be crucible 1) containing the mixed raw materials into the reaction equipment; wherein, the reaction equipment may be a single crystal furnace, or other equipment, which is not limited thereto;
[0029] The reaction equipment is evacuated and heated; a vacuum pump can be used to evacuate the equipment to ensure a certain degree of vacuum inside to meet process requirements.
[0030] A protective gas and nitrogen are introduced into the reaction equipment, and the temperature inside the reaction equipment is continued to rise, causing the carbon and silicon raw materials to react. After cooling, nitrogen-containing silicon carbide powder is obtained.
[0031] By implementing the above steps, carbon and silicon raw materials can react in a nitrogen environment. Compared with ordinary processes, the silicon carbide powder prepared in this application has a relatively high nitrogen content, so as to ensure sufficient nitrogen components in the subsequent silicon carbide crystal growth process. This can effectively alleviate the impact of insufficient nitrogen components on crystal resistivity, thereby improving the uniformity of crystal resistivity and ensuring that the silicon carbide crystal is defect-free.
[0032] For example, the nitrogen content in the nitrogen-containing silicon carbide powder generated by performing the above steps is not less than 50 ppm to ensure sufficient nitrogen content. More preferably, the nitrogen content of the nitrogen-containing silicon carbide powder can be 80 ppm to 450 ppm, including 80 ppm, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 400 ppm, 450 ppm, etc. Of course, other values within this range can also be included. This application embodiment does not specifically limit this, as long as the process requirements are met.
[0033] In this embodiment, a nitrogen-containing silicon carbide powder with a relatively high nitrogen content is prepared by a method for preparing nitrogen-containing silicon carbide powder. When this nitrogen-containing silicon carbide powder is applied to the growth process of silicon carbide crystals, compared with ordinary silicon carbide powder, sufficient nitrogen components can be ensured on the crystal surface during crystal formation, thereby alleviating the problem of increased resistivity in the outer region due to reduced nitrogen component bonding on the crystal surface.
[0034] To control the nitrogen content of nitrogen-containing silicon carbide powder, the flow rate of nitrogen gas introduced into the reaction equipment can be controlled. A higher nitrogen flow rate can increase the nitrogen content of the powder to some extent, while a lower flow rate can decrease it. Furthermore, to more precisely control the nitrogen content and meet process requirements, in some embodiments, the nitrogen flow rate can be in the range of 5 sccm to 70 sccm. More specifically, the flow rate can be in the range of 10 sccm to 50 sccm, including 10 sccm, 15 sccm, 20 sccm, 25 sccm, 30 sccm, 40 sccm, 50 sccm, etc. Of course, other values are also possible, and this application does not specifically limit these values, as long as the process requirements are met.
[0035] By controlling the flow rate of nitrogen gas introduced into the reaction equipment within the range of 10 sccm to 50 sccm, the nitrogen content of the nitrogen-containing silicon carbide powder obtained by the process can be controlled within the range of 80 ppm to 450 ppm, so as to meet the process requirements of subsequent silicon carbide crystal growth.
[0036] In some embodiments, the protective gas may include at least one of argon, helium, or neon, which is introduced into the reaction apparatus as a carrier gas, wherein the volume fraction of the protective gas may be greater than or equal to 99.99%, that is, above 99.999% (inclusive of the critical value). Exemplarily, high-purity argon may be used as the carrier gas (protective gas), with a volume fraction greater than or equal to 99.999%.
[0037] In some embodiments, silicon powder can be used as the silicon raw material, and carbon powder can be used as the carbon raw material, so that the silicon powder and carbon powder can react in a heating container (specifically, crucible 1) to produce silicon carbide powder. In order to obtain nitrogen-containing silicon carbide powder that meets the process requirements, the proportions of silicon powder and carbon powder can be controlled. Optionally, the molar ratio of silicon powder to carbon powder can be controlled in the range of 0.9:1 to 1.1:1, specifically 0.9:1, 1:1, 1.1:1, etc. Of course, other molar ratios are also possible. This application does not specifically limit this, as long as the process requirements are met.
[0038] In some embodiments, the reaction apparatus is evacuated to a vacuum level below 1 × 10⁻⁶. -4 Pa, heating raises the temperature inside the reaction equipment to a first temperature, wherein the first temperature can be 900℃~1200℃, including 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, etc.
[0039] For example, the growth chamber of the single crystal furnace is evacuated to a vacuum level below 1×10⁻⁶. -4 Pa, after 30 to 90 minutes, or about 60 minutes, continue heating to raise the temperature to 1000℃.
[0040] A protective gas and nitrogen are introduced into the reaction apparatus at the first temperature to facilitate subsequent heating so that the nitrogen reacts with the silicon and carbon raw materials at a higher temperature.
[0041] After the protective gas and nitrogen are introduced into the reaction equipment, the temperature inside the reaction equipment is further increased by heating until it reaches a second temperature. For example, the range of the second temperature can be 1900℃ to 2000℃, so that the silicon raw material and the carbon raw material can react in the atmosphere of protective gas and nitrogen and in a high-temperature environment to synthesize nitrogen-containing silicon carbide powder.
[0042] In addition, the synthesis time can be controlled. Specifically, the reaction time between carbon and silicon raw materials can be controlled between 8 and 15 hours. For example, it can be controlled to about 10 hours to ensure that the carbon and silicon raw materials have enough time to react, thereby making the reaction more complete.
[0043] For example, such as Figure 5 As shown, the preparation steps for nitrogen-containing silicon carbide powder are as follows:
[0044] 1) Preparation of toner and silicon powder: Weigh the toner and silicon powder in a molar ratio of 1:1, put them into a container, and mix them thoroughly.
[0045] 2) Mixed powder equipment: The mixed powder formed by the well mixed carbon powder and silicon powder is placed into a crucible 1 of high-purity graphite. The crucible 1 is placed in the synthesis process hot field system and then placed in a single crystal furnace with medium frequency induction heating. Induction heating is achieved through induction coil 8.
[0046] 3) Synthesis process: The growth chamber of the single crystal furnace is evacuated to below 1×10⁻⁶. -4 After about 60 minutes, the temperature is raised to about 1000℃. High-purity argon gas (volume fraction greater than or equal to 99.999%) is introduced into the growth chamber of the single crystal furnace. The nitrogen flow rate is controlled at 10 sccm to 50 sccm. At the same time, the temperature is raised to 1900℃ to 2000℃, and the synthesis time is controlled at about 10 hours.
[0047] 4) Formation of nitrogen-containing silicon carbide powder: By cooling to room temperature, nitrogen-containing silicon carbide powder can be obtained.
[0048] This application also discloses a method for growing silicon carbide crystals, the disclosed growth method including:
[0049] The nitrogen-containing silicon carbide powder prepared by the above-mentioned method is placed in a heating container (specifically, crucible 1) and heated. After the nitrogen-containing silicon carbide powder in the heating container sublimates, it crystallizes at the silicon carbide seed crystal 2 at the top of the heating container to obtain silicon carbide crystal.
[0050] The silicon carbide crystal growth method in this application uses nitrogen-containing silicon carbide powder with a higher nitrogen content, which is more suitable for the growth of n-type silicon carbide crystals. During the heating process, although the silicon component in the silicon carbide component on the crystal surface sublimates and the remaining carbon component reduces the amount of nitrogen bound to the crystal surface as the temperature rises, the relatively high nitrogen content of the nitrogen-containing silicon carbide powder ensures sufficient nitrogen component on the crystal surface. This alleviates the problem of increased resistivity caused by reduced nitrogen binding on the crystal surface, resulting in a relatively small difference in crystal resistivity. Therefore, it can ensure the uniformity of crystal resistivity and alleviate the problem of defects.
[0051] To further improve the uniformity of crystal resistivity, the growth method of silicon carbide crystals may also include:
[0052] The powder filling area inside the heating container is divided into a first filling area and a second filling area, with the first filling area located outside the second filling area.
[0053] A silicon carbide powder 71 with a first nitrogen content is loaded into a first loading zone, and a silicon carbide powder 72 with a second nitrogen content is loaded into a second loading zone, wherein the second nitrogen content is much lower than the first nitrogen content. A graphite ring 3 is used to isolate the silicon carbide seed crystal 2 from the silicon carbide powder 71 and the silicon carbide powder 72 with the first and second nitrogen contents, respectively. After heating, the silicon carbide powders 71 and 72 sublimate and crystallize at the silicon carbide seed crystal 2 to obtain silicon carbide crystals. It should be noted that the silicon carbide powder 71 with the first nitrogen content is the aforementioned nitrogen-containing silicon carbide powder. For example, the nitrogen content of the silicon carbide powder 71 with the first nitrogen content can be no less than 50 ppm, and the nitrogen content of the silicon carbide powder 72 with the second nitrogen content can be 0.
[0054] Optionally, the second filling area can be located in a cylindrical region with a circular cross-section formed around the axis of the crucible 1, that is, the second filling area is located in the middle region of the crucible 1, while the first filling area can be arranged around the second filling area, that is, the first filling area can be a cylindrical region with an annular cross-section. Furthermore, considering that the heating method involves heating the crucible 1 using an induction coil 8 surrounding it, resulting in a higher temperature at the periphery and a lower temperature at the center, after loading silicon carbide powder 71 with a first nitrogen content and silicon carbide powder 72 with a second nitrogen content, the second nitrogen content silicon carbide powder 72 can be located in the central region of the crucible 1, while the first nitrogen content silicon carbide powder 71 can be located in the outer region of the crucible 1. This allows the first nitrogen content silicon carbide powder 71 to surround the second nitrogen content silicon carbide powder 72. Consequently, during the silicon carbide growth process, the amount of nitrogen adsorbed on the surface of the silicon carbide crystal during sublimation can differ between the first nitrogen content silicon carbide powder 71 in the outer region of the crucible 1 and the second nitrogen content silicon carbide powder 72 in the central region, thereby improving the uniformity of the resistivity of the subsequently formed crystal.
[0055] In this embodiment, by combining silicon carbide powder 71 with a higher nitrogen content (first nitrogen content) and silicon carbide powder 72 with a lower nitrogen content or even zero nitrogen content, the first nitrogen content silicon carbide powder 71 is filled in the outer region of the crucible 1 (i.e., the first filling region), while the second nitrogen content silicon carbide powder 72 is filled in the inner region of the crucible 1 (i.e., the second filling region). During heating, as the temperature of the outer region increases, although the silicon component in the silicon carbide composition on the crystal surface sublimates, the remaining carbon component reduces the nitrogen binding on the crystal surface. However, because the first nitrogen content silicon carbide powder 71 in the outer region has a relatively high nitrogen content, the nitrogen component on the crystal surface is not too low. This alleviates the problem of increased resistivity in the outer region, making the resistivity difference between the outer and inner regions relatively small. Therefore, good resistivity uniformity can be maintained to avoid defects.
[0056] In this embodiment, the shape and size of the graphite ring 3 are designed according to the shape and size of the upper surface of each of the two silicon carbide powders. Specifically, the graphite ring 3 may have a central through-hole region 31 and an outer edge region 32. The diameter of the central through-hole region 31 is adapted to the diameter of the second filling region, and the outer diameter of the outer edge region 32 is adapted to the outer diameter of the first filling region. This allows the silicon carbide seed crystal 2 at the top of the crucible 1 to communicate with the silicon carbide powder 72 with the second nitrogen content in the central region through the central through-hole region 31. The silicon carbide seed crystal 2 and the silicon carbide powder 71 with the first nitrogen content in the outer edge region 32 are separated by the outer edge region 32 to provide a certain barrier effect. At the same time, the outer edge region 32 also allows the silicon carbide powder 71 with the first nitrogen content to sublimate and contact the silicon carbide seed crystal 2 at the top of the crucible 1 to achieve crystallization.
[0057] Furthermore, the outer edge region 32 may be provided with a plurality of vent holes 321. For example, the plurality of vent holes 321 may be evenly arranged along the circumference of the outer edge region 32 so as to make the gas passing through the vent holes 321 at various positions of the outer edge region 32 more uniform.
[0058] Furthermore, the width of the outer edge region 32 of the graphite ring 3 can be designed according to the width of the silicon carbide powder 71 with the first nitrogen content, which mainly serves to filter out carbon impurities generated in the silicon carbide powder 71 with the first nitrogen content.
[0059] Based on the above settings, the outer edge region 32 of the graphite ring 3 in this embodiment adopts a hollow design, which can facilitate the smooth flow of gas generated during the sublimation of powder and improve the quality of the generated silicon carbide crystals to a certain extent.
[0060] In addition, the thickness of the graphite ring 3 can be in the range of 3mm to 7mm, specifically including 3mm, 4mm, 5mm, 6mm, 7mm, etc. Of course, it can also be other thickness values, and this application embodiment does not specifically limit it.
[0061] In some embodiments, the graphite ring 3 may be attached to the upper surface of the first nitrogen-containing silicon carbide powder 71 and the second nitrogen-containing silicon carbide powder 72, or there may be a gap between the graphite ring 3 and the upper surface of the first nitrogen-containing silicon carbide powder 71 and the second nitrogen-containing silicon carbide powder 72.
[0062] To prevent heat dissipation within the crucible 1, an upper insulation structure 51 can be provided on the upper outer side of the crucible 1 to insulate the upper part of the crucible 1 and reduce heat dissipation from the upper part. Similarly, a lower insulation structure 52 can be provided on the lower outer side of the crucible 1 to insulate the lower part of the crucible 1 and reduce heat dissipation from the lower part. For example, both the upper insulation structure 51 and the lower insulation structure 52 can be insulation layers, insulation pads, or other structures.
[0063] To further enhance heat preservation, an insulation cylinder 4 can be installed on the outside of the crucible 1. The insulation cylinder 4 can cover the outside of the crucible 1 to minimize heat loss.
[0064] Additionally, an upper temperature measuring component 61 can be provided on the upper outer side of the crucible 1 to monitor the temperature of the upper part of the crucible 1 in real time, so as to facilitate precise control of the upper temperature; similarly, a lower temperature measuring component 62 can be provided on the lower outer side of the crucible 1 to monitor the temperature of the lower part of the crucible 1 in real time, so as to facilitate precise control of the lower temperature. Exemplarily, both the upper temperature measuring component 61 and the lower temperature measuring component 62 can be temperature sensors.
[0065] In this embodiment, in addition to normal nitrogen purging during the process, nitrogen gas is also incorporated into the synthesis of silicon carbide with a high nitrogen content. This combines silicon carbide powder 71 with a first nitrogen content and silicon carbide powder 72 with a second nitrogen content into the crystal growth powder. The first nitrogen content silicon carbide powder 71 is filled on the periphery, and the second nitrogen content silicon carbide powder 72 is filled in the center. This filling method is mainly to alleviate the problem of high resistivity in the surrounding area of the crystal. Specifically, by using the first nitrogen content silicon carbide powder 71 on the periphery, the nitrogen content around the crystal is increased. Furthermore, graphite rings 3 with vent holes 321 are installed on the upper surfaces of the first nitrogen content silicon carbide powder 71 and the second nitrogen content silicon carbide powder 72, making both the central vented area 31 and the outer edge area 32 hollowed out. The diameter is equal to the diameter of the region of silicon carbide powder 72 with the second nitrogen content. The outer edge region 32 of the graphite ring 3 is provided with multiple vent holes 321. These vent holes 321 can facilitate the flow of gas at high temperature. As the nitrogen content in the silicon carbide powder 71 with the first nitrogen content in the outer region increases, and the nitrogen flow rate during the synthesis process is 10 sccm to 50 sccm, the nitrogen content in the silicon carbide powder 71 with the first nitrogen content obtained reaches about 80 to 450 ppm. During the high-temperature sublimation process, nitrogen atoms in the powder will decompose. The more nitrogen adsorbed on the growth surface of the silicon carbide crystal, the more nitrogen enters the outer silicon carbide crystal in proportion due to the different charging structure and the role of the graphite ring 3, so that the resistivity of the silicon carbide crystal is more uniform, which can ensure the uniformity of the resistivity of the subsequently formed wafer.
[0066] like Figure 6As shown in the figure, experiments revealed that the resistivity difference was 0.0117 for the conventional loading method; 0.0045 for the loading method using all silicon carbide powder 71 with the first nitrogen content; and 0.003 for the partitioned loading method using silicon carbide powder 71 with the first nitrogen content and silicon carbide powder 72 with the second nitrogen content. This demonstrates that both the loading method using all silicon carbide powder 71 with the first nitrogen content and the partitioned loading method using silicon carbide powder 71 with the first nitrogen content and silicon carbide powder 72 with the second nitrogen content improve the resistivity difference during silicon carbide crystal growth, thus enhancing the uniformity of crystal resistivity and resulting in superior silicon carbide crystal quality.
[0067] In summary, in this embodiment of the application, by incorporating an appropriate amount of nitrogen during the synthesis of silicon carbide powder, a first nitrogen-content silicon carbide powder 71 with a high nitrogen content, which is more suitable for the growth of n-type silicon carbide crystals, can be obtained. Furthermore, by analyzing the resistivity distribution during crystal growth, a graphite ring 3 with ventilation holes 321 is designed during the growth process, and the positions of the first nitrogen-content silicon carbide powder 71 and the second nitrogen-content silicon carbide powder 72 are effectively distributed. This allows for effective control of nitrogen incorporation during the growth process, thereby improving the crystallization quality of silicon carbide crystals while reducing their resistivity.
[0068] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.
Claims
1. A method for growing silicon carbide crystals, characterized in that, include: Silicon and carbon raw materials are thoroughly mixed at a preset molar ratio to obtain a mixture raw material; Place the heating container containing the mixture of raw materials into the reaction equipment; The reaction equipment is evacuated and heated; A protective gas and nitrogen are introduced into the reaction equipment, and the temperature inside the reaction equipment is continued to rise, so that the carbon raw material and the silicon raw material react. The temperature is then lowered to obtain nitrogen-containing silicon carbide powder. The nitrogen-containing silicon carbide powder is placed in a heating container and heated, causing the nitrogen-containing silicon carbide powder in the heating container to sublimate and crystallize at the silicon carbide seed crystal at the top of the heating container, thereby obtaining silicon carbide crystals, including: The powder filling area inside the heating container is divided into a first filling area and a second filling area, with the first filling area surrounding the outside of the second filling area. Silicon carbide powder with a first nitrogen content is loaded into the first loading area, and silicon carbide powder with a second nitrogen content is loaded into the second loading area. The first nitrogen content is not less than 50 ppm, and the second nitrogen content is 0.
2. The method for growing silicon carbide crystals according to claim 1, characterized in that, The flow rate of the nitrogen gas is in the range of 10 sccm to 50 sccm; And / or, the protective gas includes at least one of argon, helium or neon, and the volume fraction of the protective gas is greater than or equal to 99.999%.
3. The method for growing silicon carbide crystals according to claim 1, characterized in that, The silicon raw material is silicon powder, the carbon raw material is carbon powder, and the molar ratio of silicon powder to carbon powder is in the range of 0.9:1 to 1.1:
1.
4. The method for growing silicon carbide crystals according to claim 1, characterized in that, The reaction equipment is evacuated until the vacuum level inside the reaction equipment is less than 1×10⁻⁶. -4 Pa, heating raises the temperature inside the reaction apparatus to a first temperature; A protective gas and nitrogen are introduced into the reaction apparatus at the first temperature; Continue heating to raise the temperature inside the reaction apparatus to the second temperature; The reaction time of the carbon raw material and the silicon raw material at the second temperature is 8h to 15h.
5. The method for growing silicon carbide crystals according to any one of claims 1 to 4, characterized in that, The first nitrogen content is 80ppm to 450ppm.
6. The method for growing silicon carbide crystals according to any one of claims 1 to 5, characterized in that, The growth method further includes: The silicon carbide seed crystal is isolated from the first and second nitrogen-containing silicon carbide powders by using a graphite ring. After heating, the first and second nitrogen-containing silicon carbide powders sublimate and crystallize at the silicon carbide seed crystal to obtain silicon carbide crystals.
7. The method for growing silicon carbide crystals according to claim 6, characterized in that, The graphite ring has a central through-hole region and an outer edge region. The diameter of the central through-hole region is adapted to the diameter of the second filling region, and the outer diameter of the outer edge region is adapted to the outer diameter of the first filling region.
8. The method for growing silicon carbide crystals according to claim 7, characterized in that, The outer edge region is provided with multiple ventilation holes; And / or, the thickness of the graphite ring is in the range of 3 mm to 7 mm; And / or, the graphite ring is attached to the upper surface of the first nitrogen-containing silicon carbide powder and the second nitrogen-containing silicon carbide powder, or there is a gap between the graphite ring and the respective upper surfaces of the first nitrogen-containing silicon carbide powder and the second nitrogen-containing silicon carbide powder.