Silicon carbide crystal and liquid phase growth method thereof

Abstract

The invention belongs to the technical field of semiconductors, and particularly relates to a silicon carbide crystal and a liquid phase growth method thereof. Compared with the prior art, the liquid phase growth method provided by the invention adopts the seed crystal support with the diameter smaller than that of the seed crystal, and meanwhile, the temperature and the pressure are increased and reduced after crystal growth is finished, so that volatilization of metal on the crystal surface and on the side surface of the seed crystal support is promoted, and cracks caused by different thermal expansion coefficients of the surface metal and silicon carbide in the cooling process are reduced.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, and particularly relates to a silicon carbide crystal and its liquid-phase growth method. Background Technology

[0002] Silicon carbide (SiC) is a representative third-generation wide-bandgap semiconductor material with broad application prospects in new energy vehicles, energy storage and other fields.

[0003] Existing silicon carbide liquid phase crystal growth processes typically use Si x Cr y Al z In solvent systems, when the seed crystal is pulled away from the melt surface after growth, one or more droplets remain on the crystal surface upon detachment. During crystal cooling, the significant difference in thermal expansion coefficients between the metal droplets and silicon carbide easily generates substantial stress, potentially leading to dislocations or even cracks. While seed crystal remelting can eliminate surface contamination and damage before crystal growth begins, this process also results in edge polycrystalline formation on the sides of the seed crystal support, leading to high edge stress during cooling and a tendency for cracks to form at the edges. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a silicon carbide crystal and a liquid phase growth method thereof, which can reduce surface droplets and edge polycrystalline silicon carbide crystals.

[0005] This invention provides a liquid-phase growth method for silicon carbide crystals, comprising the following steps:

[0006] S1) Raw material preparation: Place the crystal growth raw material in a crucible; bond the seed crystal to the seed crystal holder; the diameter of the seed crystal is larger than the diameter of the seed crystal holder;

[0007] S2) Material melting and preheating: Heating in a protective atmosphere melts the crystal growth material to form a crystal growth solution, while preheating the seed crystal on the surface of the crystal growth solution.

[0008] S3) Seed crystal remelting: After preheating, the seed crystal is lowered below the liquid surface for seed crystal remelting;

[0009] S4) Crystal growth: After the seed crystal is melted back, the seed crystal is pulled up to 1~2 mm above the liquid surface, and the seed crystal and crucible are rotated to grow the crystal. During the crystal growth process, the seed crystal and crucible are pulled up at the same time.

[0010] S5) High-temperature volatilization: After growth is completed, the seed crystal rotation rate is reduced and the seed crystal is separated from the liquid surface of the crystal growth solution. Then, the temperature is increased and the pressure is reduced to carry out volatilization treatment.

[0011] S6) Cooling: After the volatilization process is completed, the temperature is lowered to obtain silicon carbide crystals.

[0012] Preferably, the crystal growth raw material includes Si. x Cr y Al z M a Where x, y, z and a are the molar concentrations of elements in the crystal growth raw materials, x is 30%~70%, y is 20%~60%, z is 1%~10%, and a is 0~5%; M is a transition metal element and / or a rare earth element.

[0013] Preferably, the difference between the diameter of the seed crystal and the diameter of the seed crystal holder is 2 to 10 mm.

[0014] Preferably, in step S2), heating is performed under a pressure of 10~90 kPa; during preheating, the distance between the seed crystal and the liquid surface is 20~50 mm; and the preheating time is 40 min~2 h.

[0015] Preferably, in step S2), after heating to 1700℃~1900℃, the seed crystal is preheated on the surface of the crystal growth solution.

[0016] Preferably, in step S3), the seed crystal descends at a rate of 30~600 μm / h; the distance between the seed crystal and the liquid surface during the seed crystal remelting is 0~10 mm; and the seed crystal remelting time is 40 min~2 h.

[0017] Preferably, in step S4), the rotational speed of the seed crystal is 50~200 rpm; the rotational speed of the crucible is 5~100 rpm; the pulling speed of the seed crystal is 5~100 μm / h; and the pulling speed of the crucible is 2~70 μm / h.

[0018] Preferably, in step S5), the rotational speed of the seed crystal is 5~20 rpm when separating the seed crystal from the liquid surface of the crystal growth solution;

[0019] The separation of the seed crystal from the crystal growth solution is achieved by either lifting the seed crystal or lowering the crucible; the lifting rate of the seed crystal is 1500~5000 μm / h; the lowering rate of the crucible is 1500~5000 μm / h.

[0020] The distance from the liquid surface of the seed crystal and the crystal growth solution to the distance between them is 20~50 mm;

[0021] The seed crystal is rotated at a speed of 50-200 rpm during the volatilization process.

[0022] Preferably, the temperature of the volatilization treatment is 5°C to 50°C higher than the crystal growth temperature; the pressure of the volatilization treatment is 6 to 40 kPa; and the volatilization treatment time is 1 to 4 h.

[0023] The present invention also provides a silicon carbide crystal grown by the above-described liquid phase growth method.

[0024] Compared with the prior art, the liquid phase growth method provided by the present invention uses a seed crystal holder with a diameter smaller than the seed crystal, and simultaneously raises the temperature and lowers the pressure after crystal growth to promote the volatilization of metal on the crystal surface and the side of the seed crystal holder, thereby reducing cracks caused by the different thermal expansion coefficients of the surface metal and silicon carbide during the cooling process. Attached Figure Description

[0025] Figure 1 A schematic flowchart of a specific liquid phase growth method for silicon carbide crystals provided by the present invention;

[0026] Figure 2 This is a schematic diagram showing the seed crystal bonded to the seed crystal holder.

[0027] Figure 3 A photograph of the silicon carbide crystal obtained in Example 1 of this invention;

[0028] Figure 4 This is an X-ray diffraction rocking curve of the silicon carbide crystal obtained in Example 1 of the present invention;

[0029] Figure 5 This is a graph showing the resistivity test results of the silicon carbide crystal obtained in Example 1 of the present invention;

[0030] Figure 6 A photograph of the silicon carbide crystal obtained in Example 2 of this invention;

[0031] Figure 7 This is an X-ray diffraction rocking curve of the silicon carbide crystal obtained in Example 2 of the present invention;

[0032] Figure 8 This is a graph showing the resistivity test results of the silicon carbide crystal obtained in Example 2 of the present invention;

[0033] Figure 9 A photograph of the silicon carbide crystal obtained in Comparative Example 1 of this invention;

[0034] Figure 10 This is a photograph of the silicon carbide crystal obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention provides a liquid-phase growth method for silicon carbide crystals, comprising the following steps: S1) Raw material preparation: placing the crystal growth raw material in a crucible; bonding a seed crystal to a seed crystal holder; the diameter of the seed crystal is larger than the diameter of the seed crystal holder; S2) Melting and preheating: heating in a protective atmosphere to melt the crystal growth raw material, forming a crystal growth solution, while preheating the seed crystal on the surface of the crystal growth solution; S3) Seed crystal remelting: after preheating, lowering the seed crystal below the liquid surface for seed crystal remelting; S4) Crystal growth: after seed crystal remelting, lifting the seed crystal 1-2 mm above the liquid surface, rotating the seed crystal and the crucible to grow the crystal, and simultaneously lifting the seed crystal and the crucible during crystal growth; S5) High-temperature volatilization: after growth, reducing the seed crystal rotation rate and separating the seed crystal from the surface of the crystal growth solution, then raising the temperature and lowering the pressure for volatilization treatment; S6) Cooling: after volatilization treatment, cooling to obtain silicon carbide crystals.

[0037] See Figure 1 , Figure 1 This is a schematic flowchart of a specific liquid-phase growth method for silicon carbide crystals provided by the present invention.

[0038] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0039] First, the raw material for crystal growth is placed in a crucible; a seed crystal is then bonded to a seed crystal holder; the diameter of the seed crystal is larger than the diameter of the seed crystal holder; the seed crystal holder is fixed to a seed crystal rod, and the seed crystal rotates by rotating the seed crystal rod. (See also...) Figure 2 , Figure 2 This is a schematic diagram showing the seed crystal bonded to the seed crystal holder. The seed crystal holder can specifically be a graphite holder.

[0040] In one specific embodiment of the present invention, the crystal growth raw material includes Si. x Cr y Al z M a Where x, y, z and a are the molar concentrations of elements in the crystal growth raw materials, x is 30%~70%, y is 20%~60%, z is 1%~10%, and a is 0~5%; M is a transition metal element and / or a rare earth element.

[0041] In one specific embodiment of the present invention, x can optionally be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range between any two of the above values.

[0042] In one specific embodiment of the present invention, optionally, y is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range between any two of the above values.

[0043] In this invention, the value of z can be selected according to the resistivity requirements of the prepared silicon carbide crystal. In a specific embodiment provided by this invention, z can optionally be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any two of the above values.

[0044] In one specific embodiment of the present invention, optionally, a is 0%, 1%, 2%, 3%, 4%, 5%, or a range between any two of the above values.

[0045] In one specific embodiment of the present invention, x is 50%, y is 40%, z is 5%, and a is 5%.

[0046] In one specific embodiment of the present invention, M is preferably one or more of Sc, Ti, Co, Y, Fe, Sn, Nd and Ce.

[0047] In a specific embodiment of the present invention, the difference between the diameter of the seed crystal and the diameter of the seed crystal holder is preferably 2 to 10 mm; optionally, the difference between the diameter of the seed crystal and the diameter of the seed crystal holder is 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or any two of the above values.

[0048] Then, the raw material for crystal growth is heated in a protective atmosphere to melt and form a crystal growth solution, while the seed crystal is preheated on the surface of the crystal growth solution.

[0049] In one specific embodiment of the present invention, the protective atmosphere can be any protective atmosphere known to those skilled in the art, preferably argon and / or helium; the heating is preferably carried out under a pressure of 10 to 90 kPa; optionally, heating is carried out under a pressure of 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa or any two of the above values.

[0050] In one specific embodiment of the present invention, when the heating temperature rises to above 1500°C, the crystal growth raw material begins to melt.

[0051] In one specific embodiment of the present invention, after heating to 1700°C~1900°C in a protective atmosphere, the seed crystal is preheated on the surface of the crystal growth solution; optionally, after heating to 1700°C, 1750°C, 1800°C, 1850°C, 1900°C or any two of the above values ​​in a protective atmosphere, the seed crystal is preheated on the surface of the crystal growth solution.

[0052] In one specific embodiment of the present invention, during preheating, the distance between the seed crystal and the liquid surface is 20~50mm; optionally, during preheating, the distance between the seed crystal and the liquid surface is 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm or any two of the above values.

[0053] In one specific embodiment of the present invention, the preheating time is preferably 40 min to 2 h; optionally, the preheating time is 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min or any two of the above values.

[0054] After preheating, the seed crystal is lowered below the liquid surface for seed crystal remelting.

[0055] In a specific embodiment of the present invention, the seed crystal descent rate is preferably 30~600 μm / h; optionally, the seed crystal descent rate is 30 μm / h, 50 μm / h, 80 μm / h, 100 μm / h, 130 μm / h, 150 μm / h, 180 μm / h, 200 μm / h, 230 μm / h, 250 μm / h, 280 μm / h, 300 μm / h, 330 μm / h, 350 μm / h, 380 μm / h, 400 μm / h, 430 μm / h, 450 μm / h, 480 μm / h, 500 μm / h, 530 μm / h, 550 μm / h, 580 μm / h, 600 μm / h, or any two of the above values.

[0056] In one specific embodiment of the present invention, the distance between the seed crystal and the liquid surface during the remelting of the seed crystal is preferably 0 to 10 mm; optionally, the distance between the seed crystal and the liquid surface during the remelting of the seed crystal is 0 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or any two of the above values.

[0057] In one specific embodiment of the present invention, the remelting time of the seed crystal is preferably 40 min to 2 h; optionally, the remelting time of the seed crystal is 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min or any two of the above values.

[0058] After the seed crystal is melted back, pull the seed crystal up to 1-2 mm above the liquid surface, rotate the seed crystal and crucible to grow the crystal, and simultaneously pull the seed crystal and crucible together during the crystal growth process.

[0059] In one specific embodiment of the present invention, optionally, after the seed crystal remelting is completed, the seed crystal is pulled up to a height of 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, or any two of the above values ​​above, above the liquid surface. Within this range, due to the viscosity and surface tension of the crystal growth solution, the crystal growth solution and the seed crystal adhere to each other, forming a meniscus between them to avoid contact between the crystal growth solution and the side of the seed crystal holder.

[0060] In one specific embodiment of the present invention, the rotation speed of the seed crystal during crystal growth is preferably 50~200 rpm; optionally, the rotation speed of the seed crystal is 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm or any two of the above values.

[0061] In one specific embodiment of the present invention, the rotation speed of the crucible during crystal growth is preferably 5 to 100 rpm; optionally, the rotation speed of the crucible is 5 rpm, 10 rpm, 20 rpm, 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm or any two of the above values.

[0062] Crystals can be grown in a directional manner by pulling seed crystals. However, in order to maintain the stability of the growth interface during the growth process, the distance between the seed crystal and the liquid surface must be kept constant to eliminate changes in temperature gradient.

[0063] In a specific embodiment of the present invention, the seed crystal pulling rate during crystal growth is preferably 5~100 μm / h; optionally, the seed crystal pulling rate during crystal growth is 5 μm / h, 10 μm / h, 15 μm / h, 20 μm / h, 25 μm / h, 30 μm / h, 35 μm / h, 40 μm / h, 45 μm / h, 50 μm / h, 55 μm / h, 60 μm / h, 65 μm / h, 70 μm / h, 75 μm / h, 80 μm / h, 85 μm / h, 90 μm / h, 95 μm / h, 100 μm / h, or any two of the above values.

[0064] In a specific embodiment of the present invention, the preferred pulling rate of the crucible during crystal growth is 2 to 70 μm / h; optionally, the pulling rate of the crucible during crystal growth is 2 μm / h, 5 μm / h, 10 μm / h, 15 μm / h, 20 μm / h, 25 μm / h, 30 μm / h, 35 μm / h, 40 μm / h, 45 μm / h, 50 μm / h, 55 μm / h, 60 μm / h, 65 μm / h, 70 μm / h, or any two of the above values.

[0065] In one specific embodiment of the present invention, the pulling rate of the seed crystal during crystal growth is preferably 10-50 μm / h faster than the pulling rate of the crucible; optionally, the pulling rate of the seed crystal during crystal growth is 10 μm / h, 15 μm / h, 20 μm / h, 25 μm / h, 30 μm / h, 35 μm / h, 40 μm / h, 45 μm / h, 50 μm / h, or any two of the above values ​​faster than the pulling rate of the crucible.

[0066] After growth is complete, reduce the seed crystal rotation rate and separate the seed crystal from the liquid surface of the crystal growth solution to prevent the crystal from sticking to the gradually solidifying liquid during the subsequent cooling process.

[0067] In one specific embodiment of the present invention, the rotation speed of the seed crystal when separating the seed crystal from the liquid surface of the crystal growth solution is preferably 5 to 20 rpm; optionally, the rotation speed of the seed crystal when separating the seed crystal from the liquid surface of the crystal growth solution is 5 rpm, 8 rpm, 10 rpm, 12 rpm, 15 rpm, 18 rpm, 20 rpm or any two of the above values.

[0068] In one specific embodiment of the present invention, the crucible rotation rate is 0 when separating the seed crystal from the liquid surface of the crystal growth solution.

[0069] In one specific embodiment of the present invention, the separation of the seed crystal from the crystal growth solution is achieved by lifting the seed crystal or lowering the crucible; the seed crystal lifting rate is preferably 1500~5000 μm / h; optionally, the seed crystal lifting rate is 1500 μm / h, 2000 μm / h, 2500 μm / h, 3000 μm / h, 3500 μm / h, 4000 μm / h, 4500 μm / h, 5000 μm / h, or any two of the above values; the crucible lowering rate is preferably 1500~5000 μm / h; optionally, the crucible lowering rate is 1500 μm / h, 2000 μm / h, 2500 μm / h, 3000 μm / h, 3500 μm / h, 4000 μm / h, 4500 μm / h, 5000 μm / h, or any two of the above values; μm / h or any two of the above values. Specifically, when separating the seed crystal from the crystal growth liquid surface by lowering the crucible, the seed crystal is preferably kept stationary to avoid significant temperature changes.

[0070] In one specific embodiment of the present invention, the distance between the liquid surface of the seed crystal and the crystal growth solution and the two is preferably 20-50 mm; optionally, the distance between the liquid surface of the seed crystal and the crystal growth melt and the two is 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm or any two of the above values.

[0071] After separating the seed crystal from the liquid surface of the crystal growth solution, the temperature is increased and the pressure is decreased to perform a volatilization treatment. This volatilization treatment allows the liquid or polycrystalline material on the side of the seed crystal support or the crystal surface to gradually evaporate at high temperatures.

[0072] In one specific embodiment of the present invention, the target temperature for heating, i.e. the temperature of the volatilization treatment, is preferably 5°C to 50°C higher than the temperature of crystal growth; optionally, the temperature of the volatilization treatment is 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C or any two of the above values ​​higher than the temperature of crystal growth.

[0073] In one specific embodiment of the present invention, the pressure is reduced while the temperature is increased to facilitate the volatilization of the raw material under high temperature conditions; the target pressure for reducing the pressure, that is, the pressure of the volatilization treatment, is preferably 6~40 kPa; optionally, the pressure of the volatilization treatment is 6 kPa, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, 45 kPa, 40 kPa or any two of the above values.

[0074] In one specific embodiment of the present invention, the volatilization treatment time is preferably 1 to 4 hours; optionally, the volatilization treatment time is 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours or any two of the above values.

[0075] To improve the effectiveness of the volatilization treatment, the rotation speed of the seed crystal is increased during the heating process to reduce the thickness of the surface melt layer using centrifugal force. Specifically, the rotation speed of the seed crystal during the volatilization treatment is preferably 50~200 rpm; optionally, the rotation speed of the seed crystal during the volatilization treatment is 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, or any two of the above values.

[0076] After the volatilization process is completed, the temperature is lowered to obtain silicon carbide crystals.

[0077] In one specific embodiment of the present invention, after the volatilization treatment is completed, heating is preferably stopped, and the material is allowed to cool naturally while maintaining pressure to obtain silicon carbide crystals.

[0078] The liquid phase growth method provided by this invention uses a seed crystal holder with a diameter smaller than the seed crystal, and simultaneously raises the temperature and lowers the pressure after crystal growth to promote the volatilization of metal on the crystal surface and the side of the seed crystal holder, thereby reducing cracks caused by the different thermal expansion coefficients of the surface metal and silicon carbide during the cooling process.

[0079] The present invention also provides a silicon carbide crystal grown by the above-described liquid phase growth method.

[0080] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a silicon carbide crystal and its liquid-phase growth method provided by the present invention.

[0081] All reagents used in the following examples are commercially available.

[0082] Example 1: Growth of 6-inch crystals

[0083] 1.1 Installation of raw materials and seed crystals: The main component of the crystal growth raw material is Si. x Cr y Al z The parameters are x=54, y=40, z=5, and the raw materials also include Fe, with a Fe content of 1%. These raw materials are mixed thoroughly and placed in a crucible. A graphite support smaller than the seed crystal diameter by 5 mm is selected for seed crystal bonding.

[0084] 1.2 High-temperature melting: The pressure inside the chamber is controlled at 60 kPa. When the power is heated to gradually increase the temperature to 1500℃, the polycrystalline silicon and metal raw materials begin to melt.

[0085] 1.3 Seed crystal preheating: The temperature is continuously increased to 1800℃. After the raw materials are melted, the seed crystal is preheated for 100 min at a depth of 30 mm above the liquid surface.

[0086] 1.4 Contacting the Liquid: After preheating, the seed crystal is gradually brought into contact with the liquid surface at a descent speed of 600 μm / h. After the seed crystal contacts the liquid surface, it continues to descend 5 mm for seed crystal remelting, which takes 60 min. Then, the seed crystal is pulled up to 1.5 mm above the liquid surface to form a meniscus, avoiding contact between the melt and the side of the graphite support.

[0087] 1.5 Growth: During the growth process, the pressure in the chamber was kept constant, the rotation speed of the seed crystal was 120 rpm, the rotation speed of the crucible was 20 rpm, the pulling speed of the seed crystal was 80 μm / h, and the pulling speed of the crucible was 50 μm / h, in order to maintain the stability of the meniscus height. The growth time was 40 h.

[0088] 1.6 Crucible Lowering: After growth, the seed crystal rotation speed is reduced to 5 rpm, and the crucible rotation speed is reduced to 0. The crucible is then lowered at a speed of 3000 μm / h, stopping when the liquid surface is 30 mm from the seed crystal. The seed crystal is kept stationary to prevent significant temperature changes. The temperature is then increased by 25°C, with the seed crystal rotation speed accelerated to 120 rpm during the heating process to reduce the surface solution layer thickness using centrifugal force. This high temperature is maintained for 4 hours, allowing the droplets or polycrystals on the seed crystal support side or crystal surface to gradually evaporate at the high temperature.

[0089] 1.7 Reduce pressure: While heating in step 1.6, reduce the pressure in the chamber to 40 kPa to facilitate the volatilization of the raw material under high temperature conditions. Maintain the current temperature and pressure conditions for 4 hours.

[0090] 1.8 Cooling: After the volatilization process is complete, stop heating, maintain the pressure, and begin natural cooling to obtain silicon carbide crystals.

[0091] Figure 3 This is a photograph of the silicon carbide crystal obtained in Example 1. (From...) Figure 3 It can be seen that there is no edge polycrystalline on the side of the crystal, no obvious large droplets on the crystal surface, and no obvious cracks.

[0092] The full width at half maximum (FWHM) of the silicon carbide crystal obtained in Example 1 was measured using an X-ray single-crystal diffractometer, and its X-ray rocking curve is shown below. Figure 4 As shown. By Figure 4It can be seen that the crystal has good crystallinity and a full width at half maximum (FWHM) of 17.28 arcsec.

[0093] The resistivity of the silicon carbide crystal obtained in Example 1 was measured, and the results are as follows: Figure 5 As shown. By Figure 5 It can be seen that the resistivity of silicon carbide crystal is uniform, approximately 85 mΩ.

[0094] Example 2:

[0095] 2.1 Installation of raw materials and seed crystals: The main component of the crystal growth raw material is Si. x Cr y Al z The parameters are x=54, y=40, z=5, and the raw materials also include Fe, with a Fe content of 1%. These raw materials are mixed thoroughly and placed in a crucible. A graphite support smaller than the seed crystal diameter by 5 mm is selected for seed crystal bonding.

[0096] 2.2 High-temperature melting: The pressure inside the chamber is controlled at 60 kPa. When the power is heated to gradually increase the temperature to 1500℃, the polycrystalline silicon and metal raw materials begin to melt.

[0097] 2.3 Seed crystal preheating: The temperature is continuously increased to 1800℃. After the raw materials are melted, the seed crystal is preheated for 100 min at a depth of 30 mm above the liquid surface.

[0098] 2.4 Contacting the Liquid: After preheating, the seed crystal is gradually brought into contact with the liquid surface at a descent speed of 600 μm / h. Once in contact with the liquid surface, the seed crystal is allowed to continue descending 5 mm for remelting over a period of 60 min. The seed crystal is then pulled up to 2 mm above the liquid surface to form a meniscus, preventing the melt from contacting the sides of the graphite support.

[0099] 2.5 Growth: During the growth process, the pressure in the chamber was kept constant, the rotation speed of the seed crystal was 120 rpm, the rotation speed of the crucible was 20 rpm, the pulling speed of the seed crystal was 80 μm / h, and the pulling speed of the crucible was 50 μm / h, in order to maintain the stability of the meniscus height. The growth time was 40 h.

[0100] 2.6 Crucible Lowering: After growth, the seed crystal rotation speed is reduced to 5 rpm, and the crucible rotation speed is reduced to 0. The crucible is then lowered at a speed of 3000 μm / h, stopping when the liquid surface is 30 mm from the seed crystal. The seed crystal is kept stationary to prevent significant temperature changes. The temperature is then increased by 25°C, with the seed crystal rotation speed accelerated to 120 rpm during the heating process to reduce the surface solution layer thickness using centrifugal force. This high temperature is maintained for 4 hours, allowing the droplets or polycrystals on the seed crystal support side or crystal surface to gradually evaporate.

[0101] 2.7 Reduce pressure: While heating in step 1.6, reduce the pressure in the chamber to 40 kPa to facilitate the volatilization of the raw material under high temperature conditions. Maintain the current temperature and pressure conditions for 4 hours.

[0102] 2.8 Cooling: After the volatilization process is complete, stop heating, maintain the pressure, and begin natural cooling to obtain silicon carbide crystals.

[0103] Figure 6 This is a photograph of the silicon carbide crystal obtained in Example 2. (From...) Figure 6 It can be seen that the crystal has no edge polycrystalline structure on the side, no obvious large droplets on the crystal surface, and no obvious cracks. However, due to the slightly high meniscus, the crystal shape is more rounded, with no obvious diameter expansion and possibly even diameter contraction.

[0104] The full width at half maximum (FWHM) of the silicon carbide crystal obtained in Example 2 was measured using an X-ray single-crystal diffractometer, and its X-ray rocking curve is shown below. Figure 7 As shown. By Figure 7 It can be seen that the crystal has good crystallinity, with a full width at half maximum (FWHM) of 16.92 arcsec, and the crystal quality is comparable to that of Example 1.

[0105] The resistivity of the silicon carbide crystal obtained in Example 2 was measured, and the results are as follows: Figure 8 As shown. By Figure 8 It can be seen that the resistivity of silicon carbide crystal is uniform, about 82 mΩ, which is comparable to that of Example 1.

[0106] Comparative Example 1

[0107] 1.1 Installation of raw materials and seed crystals: The main component of the crystal growth raw material is Si. x Cr y Al z The raw materials have x=54, y=40, and z=5, and also include a small amount of Fe, accounting for 1%. These raw materials are mixed thoroughly and placed in a crucible. A graphite support smaller than the seed crystal diameter by 5 mm is selected for seed crystal bonding.

[0108] 1.2 High-temperature melting: The pressure inside the chamber is controlled at 60 kPa. When the power is heated to gradually increase the temperature to 1500℃, the polycrystalline silicon and metal raw materials begin to melt.

[0109] 1.3 Seed crystal preheating: The temperature is continuously increased to 1800℃. After the raw materials are melted, the seed crystal is preheated for 100 min at a depth of 30 mm above the liquid surface.

[0110] 1.4 Contacting the Liquid: After preheating, the seed crystal is gradually brought into contact with the liquid surface at a descent speed of 600 μm / h. After the seed crystal contacts the liquid surface, it continues to descend 5 mm for seed crystal remelting, which takes 60 min. Then, the seed crystal is pulled up to 1.5 mm above the liquid surface to form a meniscus, avoiding contact between the melt and the side of the seed crystal support.

[0111] 1.5 Growth: During the growth process, the pressure in the chamber was kept constant, the rotation speed of the seed crystal was 120 rpm, the rotation speed of the crucible was 20 rpm, the pulling speed of the seed crystal was 80 μm / h, and the pulling speed of the crucible was 50 μm / h, in order to maintain the stability of the meniscus height. The growth time was 40 h.

[0112] 1.6 Lowering the Crucible: After growth is complete, the seed crystal rotation speed is reduced to 5 rpm, and the crucible rotation speed is reduced to 0. The seed crystal is kept stationary to prevent significant temperature changes. At this point, the crucible is lowered at a speed of 3000 μm / h, and the lifting is stopped when the liquid surface is 30 mm away from the seed crystal. The seed crystal rotation speed is then increased to 120 rpm, and centrifugal force is used to thin the surface solution layer.

[0113] 1.7 Cooling: Stop heating, maintain this pressure, and begin natural cooling.

[0114] Figure 9 This is a photograph of the silicon carbide crystal obtained in Comparative Example 1. Figure 9 It can be seen that although Comparative Example 1 controlled the meniscus height to be 1.5 mm, the temperature was not increased and the pressure was not decreased during the growth process and metal volatilization. This resulted in large metal droplets on the crystal surface. During the cooling process, due to the large difference in thermal expansion coefficients between the metal droplets and silicon carbide, significant stress was generated. The crystal cracked after being taken out of the furnace, and the cracks originated from and extended from the metal droplets.

[0115] Comparative Example 2

[0116] 2.1 Installation of raw materials and seed crystals: The main component of the crystal growth raw material is Si. x Cr y Al z The parameters are x=54, y=40, z=5, and the raw materials also include Fe, with a Fe content of 1%. These raw materials are mixed thoroughly and placed in a crucible. A graphite support smaller than the seed crystal diameter by 5 mm is selected for seed crystal bonding.

[0117] 2.2 High-temperature melting: The pressure inside the chamber is controlled at 60 kPa. When the power is heated to gradually increase the temperature to 1500℃, the polycrystalline silicon and metal raw materials begin to melt.

[0118] 2.3 Seed crystal preheating: The temperature is continuously increased to 1800℃. After the raw materials are melted, the seed crystal is preheated for 100 min at a depth of 30 mm above the liquid surface.

[0119] 2.4 Liquid Contact: After preheating, the seed crystal is gradually brought into contact with the liquid surface at a descent speed of 600 μm / h. Once in contact with the liquid surface, the seed crystal continues to descend 5 mm for remelting, which takes 60 min. The seed crystal is then pulled up to 8 mm below the liquid surface for submerged growth.

[0120] 2.5 Growth: During the growth process, the pressure in the chamber was kept constant, the rotation speed of the seed crystal was between 120 rpm, the rotation speed of the crucible was between 20 rpm, the pulling speed of the seed crystal was 80 μm / h, and the pulling speed of the crucible was 50 μm / h, in order to maintain the stability of the meniscus height. The growth time was 40 h.

[0121] 2.6 Crucible Lowering: After growth, the seed crystal rotation speed was reduced to 5 rpm, and the crucible rotation speed was reduced to 0. The crucible was then lowered at a speed of 3000 μm / h, stopping when the liquid surface was 30 mm from the seed crystal. The seed crystal was kept stationary to prevent significant temperature changes. The temperature was then increased by 25°C, with the seed crystal rotation speed accelerated to 120 rpm during the heating process to reduce the surface solution layer thickness using centrifugal force. This high temperature was maintained for 4 hours to facilitate the gradual evaporation of surface droplets.

[0122] 2.7 Cooling: Stop heating, maintain this pressure, and begin natural cooling.

[0123] Figure 10 The image shows a photograph of the silicon carbide crystal obtained in Comparative Example 2. Figure 10 It can be seen that the height of the liquid surface in the growth process of the crystal in Comparative Example 2 was -8mm, and no temperature or pressure was increased or decreased after growth. After growth, it was observed that the side of the graphite support was corroded and still had metallic polycrystalline material, resulting in three obvious cracks near the edge of the crystal; there was a droplet at the center of the crystal, and fine cracks extended from the edge of the droplet.

[0124] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A liquid-phase growth method for silicon carbide crystals, characterized in that, Includes the following steps: S1) Raw material preparation: Place the crystal growth raw material in a crucible; The seed crystal is bonded to the seed crystal holder; the diameter of the seed crystal is larger than the diameter of the seed crystal holder. S2) Material melting and preheating: Heating in a protective atmosphere melts the crystal growth material to form a crystal growth solution, while preheating the seed crystal on the surface of the crystal growth solution. S3) Seed crystal remelting: After preheating, the seed crystal is lowered below the liquid surface for seed crystal remelting; S4) Crystal growth: After the seed crystal is melted back, the seed crystal is pulled up to 1~2 mm above the liquid surface, and the seed crystal and crucible are rotated to grow the crystal. During the crystal growth process, the seed crystal and crucible are pulled up at the same time. S5) High-temperature volatilization: After growth is completed, the seed crystal rotation rate is reduced and the seed crystal is separated from the liquid surface of the crystal growth solution. Then, the temperature is increased and the pressure is reduced to carry out volatilization treatment. S6) Cooling: After the volatilization process is completed, the temperature is lowered to obtain silicon carbide crystals.

2. The liquid-phase growth method according to claim 1, characterized in that, The crystal growth raw material includes Si x Cr y Al z M a Where x, y, z and a are the molar concentrations of elements in the crystal growth raw materials, x is 30%~70%, y is 20%~60%, z is 1%~10%, and a is 0~5%; M is a transition metal element and / or a rare earth element.

3. The liquid-phase growth method according to claim 1, characterized in that, The difference between the diameter of the seed crystal and the diameter of the seed crystal holder is 2~10 mm.

4. The liquid-phase growth method according to claim 1, characterized in that, In step S2), heating is performed under a pressure of 10~90 kPa; during preheating, the distance between the seed crystal and the liquid surface is 20~50 mm; the preheating time is 40 min~2 h.

5. The liquid-phase growth method according to claim 1, characterized in that, In step S2), after heating to 1700℃~1900℃, the seed crystal is preheated on the surface of the crystal growth solution.

6. The liquid-phase growth method according to claim 1, characterized in that, In step S3), the seed crystal descends at a rate of 30-600 μm / h; the distance between the seed crystal and the liquid surface during the remelting process is 0-10 mm; and the remelting time is 40 min-2 h.

7. The liquid-phase growth method according to claim 1, characterized in that, In step S4), the rotational speed of the seed crystal is 50~200 rpm; the rotational speed of the crucible is 5~100 rpm; the pulling speed of the seed crystal is 5~100 μm / h; and the pulling speed of the crucible is 2~70 μm / h.

8. The liquid phase growth method according to claim 1, characterized in that, In step S5), the rotational speed of the seed crystal is 5~20 rpm when separating the seed crystal from the liquid surface of the crystal growth solution. The separation of the seed crystal from the crystal growth solution is achieved by either lifting the seed crystal or lowering the crucible; the lifting rate of the seed crystal is 1500~5000 μm / h; the lowering rate of the crucible is 1500~5000 μm / h. The distance from the liquid surface of the seed crystal and the crystal growth solution to the distance between them is 20~50 mm; The seed crystal is rotated at a speed of 50-200 rpm during the volatilization process.

9. The liquid-phase growth method according to claim 1, characterized in that, The temperature of the volatilization treatment is 5°C to 50°C higher than the crystal growth temperature; the pressure of the volatilization treatment is 6 to 40 kPa; and the volatilization treatment time is 1 to 4 hours.

10. A silicon carbide crystal grown by the liquid phase growth method according to any one of claims 1 to 9.

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