Method for producing cubic silicon carbide single crystals

Abstract

The application provides a preparation method of cubic silicon carbide single crystal, which comprises the following steps: (1) placing a cosolvent in a graphite crucible, vacuumizing a growth furnace, and then introducing a gas to control the air pressure in the growth furnace; (2) heating the graphite crucible to completely melt the cosolvent to form a melt, and reaching a growth temperature of SiC; (3) pushing down a graphite pulling rod in the growth furnace to make a seed crystal contact with the melt, and then growing a 3C-SiC single crystal; wherein the cosolvent comprises Si, Cr, a compound containing an N element, and a metal M; and the metal M is selected from one or more of V, Co, Mn, Ti, Zr, Cu, Mo, Ag, Au and B. By introducing a specific metal element M into the cosolvent system, the application greatly improves the transport rate of Si and C solutes in the melt. In addition, the application introduces a compound containing an N element into the cosolvent, effectively inhibits the generation of other crystal forms such as 4H-SiC, and can stably prepare high-quality 3C-SiC crystals.

Description

Technical Field

[0001] This invention belongs to the field of SiC single crystal liquid phase growth technology. Specifically, this invention relates to a method for preparing cubic silicon carbide single crystals. Background Technology

[0002] Silicon carbide (SiC), a wide-bandgap compound semiconductor, possesses excellent properties such as high breakdown field strength (approximately 10 times that of silicon), high saturated electron drift velocity (approximately twice that of silicon), and high thermal conductivity (approximately 3 times that of silicon and 10 times that of gallium arsenide). Compared with corresponding silicon-based devices, SiC devices have advantages such as high temperature resistance, high voltage resistance, good high-frequency characteristics, high energy conversion efficiency, small size, and light weight. Therefore, they have wide applications in electric vehicles, rail transportation, high-voltage power transmission and transformation, photovoltaic power generation, 5G communication, AR glasses, and AI data centers.

[0003] Currently, over 250 known SiC crystal forms exist, primarily divided into hexagonal (α-SiC) and cubic (β-SiC) systems. Common α-SiC crystal forms include 4H-SiC and 6H-SiC, while β-SiC has only one crystal form: cubic silicon carbide (3C-SiC). Through the industrialized Physical Vapor Transport (PVT) method, 12-inch 4H-SiC single crystals can now be grown. 4H-SiC single crystals are a key material for fabricating SiC-based metal-oxide-semiconductor field-effect transistors (MOSFETs), widely used in new energy vehicles, new energy power generation and storage, photovoltaic inverters, rail transportation, and smart grids. However, 4H-MOSFET devices suffer from high-density interface defect states, leading to low channel carrier mobility, poor device reliability, insufficient stability, and short lifespan. Currently, 90% of the main driver MOSFET devices in China still rely on imports, highlighting the urgent need to overcome the technological limitations of SiC-MOSFET devices at the material level.

[0004] Compared to the widely used 4H-SiC, 3C-SiC exhibits higher carrier mobility (2 to 4 times higher), lower defect state density (two orders of magnitude lower), and higher electron affinity (3.7 eV). Using 3C-SiC to fabricate field-effect transistors (FETs) holds promise for solving the problems of poor reliability, low stability, and short lifetime in MOSFET devices caused by excessive gate oxide interface defects. Therefore, 3C-SiC is considered the "champion" material in the field of power devices. Researchers both domestically and internationally have explored various methods to grow 3C-SiC single crystals, aiming to lay the material foundation for its application in high-performance SiC-based MOSFET power devices.

[0005] Currently, the industrial-scale PVT growth temperature is approximately 2200°C. During this process, SiC powder sublimates and decomposes into gaseous substances such as Si, Si₂C, and SiC₂. Since multiple crystal forms, including 4H, 6H, 15R, and 3C, can stably exist within the temperature range of 1800–2200°C, polymorphisms are prone to coexistence in the grown crystal. To suppress phase transitions and achieve the growth of a single 3C-SiC crystal form, researchers have developed a near-space PVT method, which shortens the distance between the SiC powder source and the seed crystal to 1–2 mm to increase supersaturation (exceeding 5 × 10⁻⁶). 3 The ratio of Si / C is relatively small. However, due to the extremely small distance between the source and the seed crystal, the thickness of the grown 3C-SiC crystal is usually less than 2 mm, and it suffers from problems such as large warpage and many crystal defects, which limits its industrial application.

[0006] To obtain high-quality 3C-SiC materials, 14 teams from seven European countries jointly launched the "Challenger Program" (CHALLENGE: 3C-SiC Hetero-Epitaxially Grown on Silicon Compliance Substrates and New 3C-SiC Substrates for Sustainable Wide-Band-Gap Power Devices). The aim is to provide material support for high-performance MOSFET devices that meet the needs of electric vehicles by epitaxially growing high-quality 3C-SiC on silicon substrates. However, due to approximately 19.7% lattice mismatch between Si and 3C-SiC (lattice constants of 5.43 Å and 4.36 Å, respectively) and approximately 8% thermal expansion coefficient mismatch, the epitaxially grown 3C-SiC contains high-density structural defects, such as stacking faults (density up to 10⁻⁶). 3 -10 4 cm -2 Furthermore, the grown 3C-SiC also suffers from problems such as large warpage and easy cracking, making it difficult to meet the fabrication requirements of high-performance power devices.

[0007] Currently, when growing 3C-SiC single crystals using the liquid-phase method, the solute elements C and Si need to be transported through the melt from the high-temperature zone at the bottom of the graphite crucible to the growth interface (i.e., the SiC seed crystal surface) in the low-temperature zone. In addition to structural units such as Si-C, the high-temperature melt also contains structural units formed by other fluxing elements. However, the fluxing systems currently used often form structural units that are detrimental to the transport of Si and C, thus limiting the growth rate of 3C-SiC single crystals. Therefore, to achieve a higher growth rate, while maintaining the solubility of C in the high-temperature flux, it is necessary to increase the transport rate of C and Si in the high-temperature melt, thereby effectively improving the growth rate of 3C-SiC single crystals.

[0008] In addition, when preparing 3C-SiC single crystals, it is also necessary to suppress the formation of other crystal forms such as 4H-SiC single crystals.

[0009] Therefore, there is an urgent need to develop a growth method that can rapidly and stably produce high-quality 3C-SiC single crystals. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing cubic silicon carbide (3C-SiC) single crystals. This method not only achieves a significant leap in growth rate, making it a highly efficient and practical technical solution, but also changes the surface tension of the melt by controlling the nitrogen element (the flux contains nitrogen-containing compounds), so that the solid-liquid interface energy between 3C-SiC and the melt is lower than that between 4H-SiC and the melt. This allows for stable growth of wafer-level 3C-SiC single crystals through heterogeneous nucleation, which is superior to homogeneous nucleation, to meet the needs of industrial applications.

[0011] The above-mentioned objective of the present invention is achieved through the following technical solution.

[0012] This invention provides a method for preparing 3C-SiC single crystals, which includes the following steps:

[0013] (1) Place the flux in a graphite crucible and evacuate the growth furnace, then introduce gas to control the gas pressure inside the growth furnace;

[0014] (2) Heat the graphite crucible until the flux is completely melted to form a melt and reach the growth temperature of SiC;

[0015] (3) Pushing down the graphite pull rod in the growth furnace makes the seed crystal come into contact with the melt, thereby growing 3C-SiC single crystal;

[0016] in,

[0017] The co-solvent contains Si, Cr, a nitrogen-containing compound, and metal M; and

[0018] The metal M is selected from one or more of V, Co, Mn, Ti, Zr, Cu, Mo, Ag, Au, and B.

[0019] The inventors of this application unexpectedly discovered that adding a nitrogen-containing compound to the flux can stably produce 3C-SiC single crystals and suppress the formation of other crystal forms, such as 4H-SiC single crystals. Not wanting to be bound by theory, this is likely because the addition of a nitrogen-containing compound can alter the melt surface tension by controlling the nitrogen element (e.g., the source and amount of nitrogen), resulting in a lower solid-liquid interface energy between 3C-SiC and the melt compared to that between 4H-SiC and the melt. This allows for stable growth of 3C-SiC single crystals through heterogeneous nucleation, which is superior to homogeneous nucleation.

[0020] The inventors of this application also unexpectedly discovered that adding metal M to the flux can alter the microstructure of the melt without reducing carbon solubility, thereby accelerating solute transport and achieving a significant leap in growth rate. In other words, during the high-temperature liquid-phase growth of 3C-SiC single crystals, by designing the composition and ratio of the flux, without reducing the flux's carbon-solubility, the types and lengths of structural units in the flux are changed, the viscosity of the melt is reduced, and the transport rate of Si and C in the melt is increased, thus improving the growth rate of 3C-SiC single crystals. Furthermore, when metal M is added to the flux, no phase transition occurs or interface instability is caused, resulting in improved crystal quality and surface morphology.

[0021] Preferably, in the preparation method of the present invention, the N-containing compound is selected from Mg3N2, Li3N, Ba3N2, and Fe. x One or more of N, Si3N4, GaN and Ca3N2; where x is 2, 3 or 4.

[0022] Preferably, in the preparation method of the present invention, the molar ratio of Si, Cr, N-containing compound and metal M in the co-solvent is (20-70): (20-70): (0.1-10): (0.1-10); wherein the molar amount of the N-containing compound is calculated based on the molar amount of N element it contains.

[0023] Preferably, in the preparation method of the present invention, the co-solvent further contains Ce to inhibit the co-solvent from adhering to the graphite seed crystal holder.

[0024] Preferably, in the preparation method of the present invention, the molar ratio of Si, Cr, N-containing compound, metal M and Ce in the co-solvent is (20-70): (20-70): (0.1-10): (0.1-10): (0.1-10); wherein, the molar amount of the N-containing compound is calculated based on the molar amount of N element it contains.

[0025] Preferably, in the preparation method of the present invention, the vacuuming of the growth furnace in step (1) is to vacuum the growth furnace to a level less than or equal to 5 × 10⁻⁶. -4 Pa.

[0026] Preferably, in the preparation method of the present invention, the gas is selected from one or more of nitrogen, argon and helium.

[0027] Preferably, in the preparation method of the present invention, the control of the gas pressure in the growth furnace in step (1) is carried out under the condition that the gas pressure in the growth furnace is controlled to be 0.1 to 2.0 atm, more preferably 0.2 to 1.2 atm.

[0028] Preferably, in the preparation method of the present invention, the graphite crucible is made of high-quality graphite.

[0029] Preferably, in the preparation method of the present invention, the inner diameter of the graphite crucible is 10 to 150 mm larger than the diameter of the seed crystal.

[0030] Preferably, in the preparation method of the present invention, the wall thickness of the graphite crucible is greater than or equal to 10 mm.

[0031] Preferably, in the preparation method of the present invention, the seed crystal is a 2-8 inch 4H-SiC single crystal with a positive crystal orientation or an off-center angle of 4° or 8°, or the seed crystal is a 2-8 inch 3C-SiC single crystal with a positive crystal orientation or an off-center angle of 4° or 8°.

[0032] Preferably, in the preparation method of the present invention, the growth of 3C-SiC single crystal in step (3) is carried out under a method including the following steps:

[0033] (i) Control the temperature during the growth of 3C-SiC single crystals so that the temperature at the seed crystal is 1700℃~1900℃, the melt gradually heats up from the surface near the seed crystal to the bottom of the graphite crucible with a temperature gradient of 2~20℃ / cm, and the temperature of the melt at the bottom of the graphite crucible is 1800~2200℃.

[0034] (ii) The seed crystal and the graphite crucible are periodically accelerated and decelerated while the seed crystal is slowly pulled up.

[0035] Preferably, in the preparation method of the present invention, the periodic acceleration and deceleration rotation is carried out under the following conditions: the seed crystal and the graphite crucible are periodically accelerated and decelerated in opposite directions.

[0036] Preferably, in the preparation method of the present invention, the rotational speeds of the seed crystal and the graphite crucible are ±0~200 r / min and ±0~50 r / min, respectively.

[0037] Preferably, in the preparation method of the present invention, the lifting is performed at a rate of 1 to 3000 μm / h.

[0038] In some specific embodiments of the present invention, the preparation method of the present invention includes the following steps:

[0039] (1) Fix the SiC seed crystal on the graphite seed crystal rod and place the flux in the graphite crucible;

[0040] (2) Place the graphite seed crystal rod and graphite crucible in the crystal growth furnace, then evacuate the growth furnace. After the vacuum level reaches the predetermined value, fill it with high-purity inert gas and control the pressure inside the growth furnace.

[0041] (3) Heating the graphite crucible completely melts the flux metal raw material, dissolves C in the graphite crucible in the high-temperature zone of the graphite crucible, and forms a high-temperature melt composed of flux and C;

[0042] (4) Lower the SiC seed crystal so that it comes into contact with the high-temperature melt and grow 3C-SiC single crystal.

[0043] (5) During the crystal growth process, the SiC seed crystal and the graphite crucible are periodically accelerated and decelerated and rotated, while the SiC seed crystal is slowly pulled up.

[0044] The present invention has the following beneficial effects:

[0045] 1. Significantly increases growth rate:

[0046] By introducing a specific metal element M into the flux system, the microstructure of the high-temperature melt was effectively controlled without reducing carbon solubility. This reduced the length of structural units and the viscosity of the melt, thereby significantly improving the transport rate of Si and C solutes in the melt. Ultimately, the growth rate of 3C-SiC single crystals was increased from a maximum of 44.4 µm / h to a maximum of 80.6 µm / h, nearly doubling the efficiency and effectively reducing the cost per unit growth time.

[0047] 2. To stably obtain pure-phase 3C-SiC crystals and suppress the formation of impurity phases:

[0048] Introducing nitrogen-containing compounds into the flux can regulate the surface tension of the melt, resulting in a lower solid-liquid interface energy between 3C-SiC and the melt compared to other crystal forms (such as 4H-SiC). While this is not intended to be theoretically rigorous, the underlying mechanism is speculated to be that these thermodynamic conditions preferentially promote the growth of 3C-SiC on seed crystals via heterogeneous nucleation compared to other crystal forms. This allows for the stable and selective preparation of pure-phase 3C-SiC single crystals, effectively suppressing the formation of other crystal forms such as 4H-SiC.

[0049] 3. Comprehensive improvement of crystal quality and morphology:

[0050] The addition of element M not only increases the growth rate, but also helps to improve the crystallization quality of the crystal, avoid defects such as macroscopic grooves caused by interface instability, and obtain high-quality crystals with bright surfaces and low defect density.

[0051] 4. The process is simple and has broad prospects for industrialization:

[0052] This method is easy to implement, can grow crystals of different sizes from 4 to 8 inches, and can achieve different doping types. It significantly reduces the overall cost while improving the growth rate and quality, making it very suitable for large-scale industrial applications. Attached Figure Description

[0053] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0054] Figure 1 This is a photograph of a 3C-SiC ingot grown using Example 1.

[0055] Figure 2 This is a photograph of a 3C-SiC ingot obtained using Comparative Example 1.

[0056] Figure 3 This is a photograph of a 3C-SiC ingot grown using Example 2.

[0057] Figure 4 This is a photograph of a 3C-SiC ingot obtained using Comparative Example 2.

[0058] Figure 5 This is a photograph of a 3C-SiC ingot grown using Example 3.

[0059] Figure 6 This is a photograph of a 3C-SiC ingot obtained using the growth method described in Comparative Example 3.

[0060] Figure 7 This is a photograph of a 3C-SiC ingot grown using Example 4.

[0061] Figure 8This is a photograph of a 3C-SiC ingot obtained using Comparative Example 4.

[0062] Figure 9 This is a photograph of a 3C-SiC ingot grown using Example 5.

[0063] Figure 10 This is a photograph of a 3C-SiC ingot obtained using Comparative Example 5.

[0064] Figure 11 This is a photograph of a 3C-SiC ingot grown using Example 6.

[0065] Figure 12 This is a photograph of a 3C-SiC ingot obtained using Comparative Example 6.

[0066] Figure 13 The results are Raman test results for SiC crystals grown using Examples 1 to 6 and Comparative Examples 1 to 6.

[0067] Figure 14 The growth rate of 3C-SiC crystals obtained by the examples and comparative examples is statistically distributed. The growth rate of 3C-SiC single crystals increased from a maximum of 44.4 µm / h to a maximum of 80.6 µm / h.

[0068] Figure 15 The Raman plot of the crystal obtained using Comparative Example 8 shows that the crystal form of the grown crystal is 4H-SiC.

[0069] Figure 16 The Raman plot of the crystal obtained using Comparative Example 9 shows that the crystal form of the grown crystal is 4H-SiC.

[0070] Figure 17 The Raman plot of the crystal obtained using Comparative Example 10 shows that the crystal form of the grown crystal is 4H-SiC. Detailed Implementation

[0071] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0072] Example 1

[0073] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 150 mm; the seed crystal is a 4-inch (0001) positive orientation semi-insulating 4H-SiC single crystal with a silicon surface as the growth surface; the raw materials are high-purity Si blocks, Cr blocks, Co blocks and Mg3N2; the flux ratio is Si:Cr:Co:Mg3N2=35:50:10:5, and the height of the melt after the solution melts in the crucible is 30 mm.

[0074] A SiC seed crystal is fixed on a graphite seed crystal rod, and a flux is placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5 The pressure was increased to 0.9 atm by introducing 10 kPa of high-purity nitrogen and 40 kPa of high-purity argon into the furnace cavity. The crucible was heated to 1900 °C at the surface of the flux, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 10 °C / cm within the melt. The mixture was held at this temperature for 2 h. During growth, the seed crystal was rotated clockwise at 30 r / min, and the crucible was rotated counterclockwise at 10 r / min. The pulling speeds of the seed crystal and the crucible were 30 μm / h and 120 μm / h, respectively. After 72 h of growth, the crystal was pulled upwards at 1000 µm / h for in-situ annealing, followed by a slow cooling period of 24 h. After cooling to room temperature, the grown 3C-SiC single crystal was obtained.

[0075] Implementation Results and Analysis:

[0076] Figure 1 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Example 1. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 3.0 mm, representing a growth rate of 41.7 μm / h over 72 h.

[0077] Comparative Example 1

[0078] The preparation method of this comparative example is the same as that of Example 1, except that the ratio of the co-solvent used is Si:Cr:Mg3N2=35:60:5.

[0079] Implementation Results and Analysis:

[0080] Figure 2 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Comparative Example 1. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 1.5 mm, representing a growth rate of 20.8 μm / h over 72 h.

[0081] As can be seen from Example 1 and Comparative Example 1, the growth rate of 3C-SiC single crystals increased by 2.0 times after adding Co to the co-solvent, while other growth conditions remained unchanged.

[0082] Example 2

[0083] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 150 mm; a 4-inch (111) 3C-SiC single crystal substrate is used as the seed crystal, and the growth surface is the silicon surface; the raw materials are high-purity Si blocks, Cr blocks, Ce blocks, Cu blocks and Ba3N2; the ratio of the flux used is Si:Cr:Ce:Cu:Ba3N2=35:50:5:5:5, and the height of the melt after the solution melts in the crucible is 20 mm.

[0084] A SiC seed crystal is fixed on a graphite seed crystal rod, and a flux is placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5 The pressure was increased to 0.2 atm by introducing 10 kPa of high-purity nitrogen and 40 kPa of high-purity argon into the furnace cavity. The crucible was heated to 1900 °C at the surface of the flux, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 10 °C / cm within the melt. The mixture was held at this temperature for 2 h. During growth, the seed crystal was rotated clockwise at 30 r / min, and the crucible was rotated counterclockwise at 10 r / min. The pulling speeds of the seed crystal and the crucible were 30 μm / h and 120 μm / h, respectively. After 48 h of growth, the crystal was pulled upwards at 2000 µm / h for in-situ annealing, followed by a slow cooling period of 24 h. After cooling to room temperature, the grown 3C-SiC single crystal was obtained.

[0085] Implementation Results and Analysis:

[0086] Figure 3 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Example 2. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 2.5 mm, representing a growth rate of 52.1 μm / h over 48 h.

[0087] Comparative Example 2

[0088] The preparation method of this comparative example is the same as that of Example 2, except that the ratio of the co-solvent used is Si:Cr:Ce:Ba3N2=35:55:5:5.

[0089] Implementation Results and Analysis:

[0090] Figure 4The image shows a photograph of a 4-inch 3C-SiC ingot grown using Comparative Example 2. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 1.3 mm, representing a growth rate of 27.1 μm / h over 48 h.

[0091] As can be seen from Example 2 and Comparative Example 2, when Cu is added to the flux, the growth rate of 3C-SiC single crystal is increased by 1.9 times under the condition that other growth conditions remain unchanged.

[0092] Example 3

[0093] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 150 mm; a 4-inch (111) 3C-SiC single crystal substrate is used as the seed crystal, and the growth surface is the silicon surface; the raw materials are high-purity Si blocks, Cr blocks, Ce blocks, Zr blocks and Li3N blocks; the ratio of the flux used is Si:Cr:Ce:Zr:Li3N=65:20:5:5:5, and the height of the melt after the flux melts in the crucible is 40 mm.

[0094] A SiC seed crystal is fixed on a graphite seed crystal rod, and a flux is placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5 The pressure was increased to 0.9 atm by introducing 30 kPa of high-purity nitrogen and 20 kPa of N2 into the furnace cavity. The crucible was heated to 1850 °C at the surface of the flux, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 10 °C / cm within the melt. The mixture was held at this temperature for 2 h. During growth, the seed crystal rotated clockwise at 10 r / min, and the crucible rotated counterclockwise at 10 r / min; the pulling speeds of the seed crystal and the crucible were 100 μm / h and 120 μm / h, respectively. After 36 h of growth, the crystal was pulled upwards at 1000 µm / h for in-situ annealing, with a slow cooling time of 24 h. After cooling to room temperature, the grown 3C-SiC single crystal was obtained.

[0095] Implementation Results and Analysis:

[0096] Figure 5 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Example 3. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 2.2 mm, representing a growth rate of 61.1 μm / h over 36 h.

[0097] Comparative Example 3

[0098] The preparation method of this comparative example is the same as that of Example 3, except that the ratio of the co-solvent used is Si:Cr:Ce:Li3N=65:25:5:5.

[0099] Implementation Results and Analysis:

[0100] Figure 6 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Comparative Example 3. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 1.3 mm, representing a growth rate of 36.1 μm / h over 36 h.

[0101] As can be seen from Example 3 and Comparative Example 3, the growth rate of 3C-SiC single crystals increased by 1.7 times after adding Zr to the co-solvent, while other growth conditions remained unchanged.

[0102] Example 4

[0103] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 150 mm; the seed crystal is a 4-inch (0001)n-type conductive 4H-SiC single crystal with a deviation of 4 degrees, and the growth surface is the silicon surface; the raw materials are high-purity Si blocks, Cr blocks, Ce blocks, Ti blocks and Li3N blocks; the ratio of the flux used is Si:Cr:Ce:Ti:Li3N=55:30:5:5:5, and the height of the melt after the flux melts in the crucible is 20 mm.

[0104] A SiC seed crystal is fixed on a graphite seed crystal rod, and a flux is placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5 The pressure was increased to 0.8 atm by introducing 30 kPa of high-purity nitrogen and 20 kPa of N2 into the furnace cavity. The crucible was heated to 1800 °C at the surface of the flux, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 10 °C / cm within the melt. The mixture was held at this temperature for 2 h. During growth, the seed crystal rotated clockwise at 30 r / min, and the crucible rotated counterclockwise at 10 r / min; the pulling speeds of the seed crystal and the crucible were 300 μm / h and 240 μm / h, respectively. After 36 h of growth, the crystal was pulled upwards at 1000 µm / h for in-situ annealing, with a slow cooling time of 12 h. After cooling to room temperature, the grown 3C-SiC single crystal was obtained.

[0105] Implementation Results and Analysis:

[0106] Figure 7The image shows a photograph of a 4-inch 3C-SiC ingot grown using Example 4. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 2.9 mm, representing a growth rate of 80.6 μm / h over 36 h.

[0107] Comparative Example 4

[0108] The preparation method of this comparative example is the same as that of Example 4, except that the ratio of the co-solvent used is Si:Cr:Ce:Li3N=55:35:5:5.

[0109] Implementation Results and Analysis:

[0110] Figure 8 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Comparative Example 4. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 1.6 mm, representing a growth rate of 44.4 μm / h over 36 h.

[0111] As can be seen from Example 4 and Comparative Example 4, when Ti is added to the co-solvent, the growth rate of 3C-SiC single crystal is increased by 1.8 times under the condition that other growth conditions remain unchanged.

[0112] Example 5

[0113] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 150 mm; the seed crystal is a 4-inch (0001) positive orientation semi-insulating 4H-SiC single crystal with a silicon surface as the growth surface; the raw materials are high-purity Si blocks, Cr blocks, Ce blocks, Mn blocks and Li3N blocks; the ratio of the flux used is Si:Cr:Ce:Mn:Li3N=40:40:10:5:5, and the height of the melt after the solution melts in the crucible is 30 mm.

[0114] A SiC seed crystal is fixed on a graphite seed crystal rod, and a flux is placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5The pressure was increased to 0.9 atm by introducing 40 kPa of high-purity nitrogen and 10 kPa of high-purity argon into the furnace cavity. The crucible was heated to 1900 °C at the surface of the flux, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 10 °C / cm within the melt. The mixture was held at this temperature for 2 h. During growth, the seed crystal rotated clockwise at 30 r / min, and the crucible rotated counterclockwise at 10 r / min; the pulling speeds of the seed crystal and the crucible were 30 μm / h and 120 μm / h, respectively. After 96 h of growth, the crystal was pulled upwards at a speed of 3000 µm / h for in-situ annealing, followed by a slow cooling period of 24 h. After cooling to room temperature, the grown 3C-SiC single crystal was obtained.

[0115] Implementation Results and Analysis:

[0116] Figure 9 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Example 5. It can be seen that this flux system can successfully grow 3C-SiC crystals with a thickness of 5.2 mm, representing a growth rate of 54.2 μm / h over 96 h.

[0117] Comparative Example 5

[0118] The preparation method of this comparative example is the same as that of Example 5, except that the ratio of the co-solvent used is Si:Cr:Ce:Li3N=40:45:10:5.

[0119] Implementation Results and Analysis:

[0120] Figure 10 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Comparative Example 5. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 2.8 mm, representing a growth rate of 29.2 μm / h over 96 h.

[0121] As can be seen from Example 5 and Comparative Example 5, when Mn is added to the co-solvent, the growth rate of 3C-SiC single crystal is increased by 1.9 times under the condition that other growth conditions remain unchanged.

[0122] Example 6

[0123] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 150 mm; the seed crystal is a 4-inch (0001) positive orientation semi-insulating 4H-SiC single crystal with a silicon surface as the growth surface; the raw materials are high-purity Si blocks, Cr blocks, Ce blocks, Ag blocks and Li3N blocks; the ratio of the flux used is Si:Cr:Ce:Ag:Li3N=35:45:10:5:5, and the height of the melt after the solution melts in the crucible is 40 mm.

[0124] A SiC seed crystal is fixed on a graphite seed crystal rod, and a flux is placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5 The pressure was increased to 0.5 atm by introducing 20 kPa of high-purity nitrogen and 30 kPa of high-purity argon into the furnace cavity, and then the gas introduction was stopped. The crucible was heated to 1900 ℃ at the surface of the flux, while maintaining the temperature at the bottom of the melt higher than that at the surface. The temperature gradient in the melt was controlled at 10 ℃ / cm, and the mixture was kept at this temperature for 2 h. During the growth process, the seed crystal was rotated clockwise at 30 r / min, and the crucible was rotated counterclockwise at 10 r / min. The pulling speeds of the seed crystal and the crucible were 30 μm / h and 120 μm / h, respectively. After 48 h of growth, the crystal was pulled upwards at a speed of 1000 µm / h for in-situ annealing, and the temperature was slowly lowered for 24 h. After cooling to room temperature, the grown 3C-SiC single crystal was obtained.

[0125] Implementation Results and Analysis:

[0126] Figure 11 The image shows a photograph of a 4-inch 3C-SiC ingot grown using Example 6. The crystal surface is bright and free of macroscopic trench defects visible to the naked eye. It can be seen that this flux system can successfully grow 3C-SiC crystals with a thickness of 2.4 mm, i.e., a growth rate of 50.0 μm / h over 48 h.

[0127] Comparative Example 6

[0128] The preparation method of this comparative example is the same as that of Example 6, except that the ratio of the co-solvent used is Si:Cr:Ce:Li3N=35:50:10:5.

[0129] Implementation Results and Analysis:

[0130] Figure 12The image shows a photograph of a 4-inch 3C-SiC ingot grown using Comparative Example 6. Macroscopic groove defects are visible on the crystal surface. It can be observed that this flux system can successfully grow 3C-SiC crystals with a thickness of 1.0 mm, representing a growth rate of 20.8 μm / h over 48 h.

[0131] As can be seen from Example 6 and Comparative Example 6, adding Ag to the flux increased the growth rate of 3C-SiC single crystals by 2.4 times under otherwise unchanged growth conditions. Furthermore, the addition of Ag also facilitated the removal of macroscopic trench defects.

[0132] Figure 13 The Raman diagrams of SiC single crystals obtained using Examples 1-6 and Comparative Examples 1-6 are shown. The Raman test results show that the crystal form of the crystals grown before and after adding metal M to the flux is 3C-SiC.

[0133] Figure 14 The statistical distribution of the growth rate of 3C-SiC crystals obtained by the examples and comparative examples shows that the growth rate of 3C-SiC single crystals is significantly improved after adding metal M to the flux, increasing from a maximum of 44.4 µm / h to a maximum of 80.6 µm / h.

[0134] Example 7

[0135] The crucible used in this embodiment is a graphite crucible with an inner diameter of 150 mm and a height of 150 mm; the seed crystal is a 4-inch (0001) positive orientation semi-insulating 4H-SiC single crystal with a silicon surface as the growth surface; the raw materials are high-purity Si blocks, Cr blocks, Ce blocks, Mo blocks and Mg3N2 blocks; the ratio of the flux used is Si:Cr:Ce:Mo:Mg3N2=35:50:5:5:5, and the height of the melt after the solution melts in the crucible is 40 mm.

[0136] A SiC seed crystal is fixed on a graphite seed crystal rod, and a flux is placed in a graphite crucible. The graphite seed crystal rod and the graphite crucible are placed in a crystal growth furnace, and then the growth furnace is evacuated. The vacuum level in the growth chamber is evacuated to 10... -5The pressure was increased to 0.9 atm by introducing 50 kPa of high-purity argon gas into the furnace cavity. The crucible was heated to 1900 °C at the surface of the flux, maintaining the bottom temperature of the melt higher than the surface temperature, with a temperature gradient of 10 °C / cm within the melt. The mixture was held at this temperature for 2 hours. During growth, the seed crystal rotated clockwise at 30 r / min, and the crucible rotated counterclockwise at 10 r / min. The pulling speeds of the seed crystal and the crucible were 30 μm / h and 120 μm / h, respectively. After 48 hours of growth, the crystal was pulled upwards at 1000 µm / h for in-situ annealing, followed by a slow cooling period of 24 hours. After cooling to room temperature, the grown 3C-SiC single crystal was obtained. In this example, the growth rate of the single crystal was 80 μm / h.

[0137] Comparative Example 7

[0138] The preparation method of this comparative example is the same as that of Example 7, except that the ratio of the co-solvent used is Si:Cr:Ce:Mg3N2=35:55:5:5.

[0139] Results and Analysis: 3C-SiC single crystals were obtained with a growth rate of 40 μm / h. As can be seen from Example 7 and Comparative Example 7, adding Mo to the flux increased the growth rate of 3C-SiC single crystals by a factor of two, while keeping other growth conditions unchanged.

[0140] Comparative Example 8

[0141] The preparation method of this comparative example is the same as that of Example 7, except that the ratio of the co-solvent used is Si:Cr:Ce:Mo=35:55:5:5.

[0142] Implementation Results and Analysis:

[0143] Figure 15 The Raman plot of the crystal obtained using Comparative Example 8 shows that the crystal form of the grown crystal is 4H-SiC.

[0144] As can be seen from Example 7 and Comparative Example 8, 3C-SiC can be accurately prepared by adding the nitrogen-containing compound Mg3N2 to the co-solvent while keeping other growth conditions unchanged.

[0145] Comparative Example 9

[0146] The preparation method of this comparative example is the same as that of Example 2, except that the ratio of the co-solvent used is Si:Cr:Ce:Cu=35:55:5:5.

[0147] Implementation Results and Analysis:

[0148] Figure 16 The Raman plot of the crystal obtained using Comparative Example 9 shows that the crystal form of the grown crystal is 4H-SiC.

[0149] As can be seen from Example 2 and Comparative Example 9, 3C-SiC can be accurately prepared by adding the nitrogen-containing compound Ba3N2 to the co-solvent while keeping other growth conditions unchanged.

[0150] Comparative Example 10

[0151] The preparation method of this comparative example is the same as that of Example 3, except that the ratio of the co-solvent used is Si:Cr:Ce:Zr=65:25:5:5.

[0152] Implementation Results and Analysis:

[0153] Figure 17 The Raman plot of the crystal obtained using Comparative Example 10 shows that the crystal form of the grown crystal is 4H-SiC.

[0154] As can be seen from Example 3 and Comparative Example 10, 3C-SiC can be accurately prepared by adding a nitrogen-containing compound Li3N to the co-solvent while keeping other growth conditions unchanged.

Claims

1. A method for preparing cubic silicon carbide single crystals, comprising the following steps: (1) Place the flux in a graphite crucible and evacuate the growth furnace, then introduce gas to control the gas pressure inside the growth furnace; (2) Heat the graphite crucible until the flux is completely melted to form a melt and reach the growth temperature of SiC; (3) Pushing down the graphite pull rod in the growth furnace makes the seed crystal come into contact with the melt, thereby growing 3C-SiC single crystal; in, The co-solvent comprises: Si, Cr, N-containing compounds, and metal M; The metal M is selected from one or more of V, Co, Mn, Ti, Zr, Cu, Mo, Ag, and Au; The N-containing compound is selected from one or more of Mg3N2, Li3N, Ba3N2 and Ca3N2; The molar ratio of Si, Cr, N-containing compound, and metal M in the cosolvent is (20-70): (20-70): (0.1-10): (0.1-10); wherein the molar amount of the N-containing compound is based on the molar amount of N it contains.

2. The preparation method according to claim 1, wherein, The co-solvent also contains Ce.

3. The preparation method according to claim 2, wherein, The molar ratio of Si, Cr, N-containing compound, metal M and Ce in the cosolvent is (20-70): (20-70): (0.1-10): (0.1-10): (0.1-10); wherein the molar amount of the N-containing compound is based on the molar amount of N element it contains.

4. The preparation method according to claim 1, wherein, The vacuuming of the growth furnace in step (1) involves evacuating the growth furnace to a level less than or equal to 5 × 10⁻⁶. -4 Pa.

5. The preparation method according to claim 1, wherein, The gas is selected from one or more of nitrogen, argon and helium.

6. The preparation method according to claim 1, wherein, The control of gas pressure in the growth furnace in step (1) is carried out under the condition that the gas pressure in the growth furnace is controlled to be 0.1 to 2.0 atm.

7. The preparation method according to claim 6, wherein, The control of gas pressure in the growth furnace in step (1) is carried out under the condition that the gas pressure in the growth furnace is controlled to be 0.2 to 1.2 atm.

8. The preparation method according to claim 1, wherein, The graphite crucible is made of high-quality graphite.

9. The preparation method according to claim 1, wherein, The inner diameter of the graphite crucible is 10 to 150 mm larger than the diameter of the seed crystal.

10. The preparation method according to claim 1, wherein, The graphite crucible has a wall thickness of 10 mm or more.

11. The preparation method according to claim 1, wherein, The seed crystal is a 2-8 inch 4H-SiC single crystal with a positive crystal orientation or an off-center angle of 4° or 8°, or the seed crystal is a 2-8 inch 3C-SiC single crystal with a positive crystal orientation or an off-center angle of 4° or 8°.

12. The preparation method according to claim 1, wherein, The growth of 3C-SiC single crystals in step (3) is carried out by a method including the following steps: (i) Control the temperature during the growth of 3C-SiC single crystals so that the temperature at the seed crystal is 1700°C to 1900°C, the melt gradually heats up from the surface near the seed crystal to the bottom of the graphite crucible with a temperature gradient of 2 to 20°C / cm, and the temperature of the melt at the bottom of the graphite crucible is 1800 to 2200°C. (ii) The seed crystal and the graphite crucible are periodically accelerated and decelerated while the seed crystal is slowly pulled up.

13. The preparation method according to claim 12, wherein, The periodic acceleration and deceleration rotation is carried out under the following conditions: the seed crystal and the graphite crucible rotate in opposite directions with periodic acceleration and deceleration, and the rotation speeds of the seed crystal and the graphite crucible are ±0~200 r / min and ±0~50 r / min, respectively.

14. The preparation method according to claim 12, wherein, The lifting was performed at a rate of 1–3000 μm / h.

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