Preparation method of silicon carbide single crystal and silicon carbide single crystal

Abstract

The invention provides a silicon carbide single crystal preparation method and a silicon carbide single crystal. In the preparation method disclosed by the invention, the surface of the obtained spliced seed crystal has different step flow directions through a special SiC seed crystal cutting and splicing method, so that anti-parallel flow on the surface of the whole seed crystal can be realized on the premise that the spliced seed crystal is concentric with the circle center of a crucible. The preparation method provided by the invention can reduce the SiC single crystal growth micro step height, inhibit step aggregation and improve the interface stability, and finally obtains the high-quality silicon carbide single crystal.

Description

Technical Field

[0001] The invention relates to a method for preparing a silicon carbide single crystal and the silicon carbide single crystal, and belongs to the technical field of silicon carbide crystal preparation. Background Art

[0002] The SiC liquid phase method is a growth technology for preparing high-quality SiC. However, the solvent inclusion caused by step aggregation is the main reason that limits its development. Since CVD epitaxy usually uses 4° off-axis epitaxy, a 4° off-axis seed crystal is usually selected when preparing SiC substrates. Direction, off-axis growth has good crystal stability, because the off-axis seed crystal carries the initial crystal stacking genetic information, which can expand the crystal stacking order along the step flow direction. In the process of preparing silicon carbide by liquid phase method, necessary seed crystal rotation is usually introduced to drive the convection of solute and regulate the temperature distribution. The centrifugal force generated by the rotation of the seed crystal makes the convection in the solution diverge from the inside to the outside, so it can be based on the solution convection direction and the initial step flow direction. The orientation relationship of the seed crystal surface is divided into two regions, namely solution convection and Parallel flow regions in the same direction, as well as solution convection and The antiparallel flow region in the opposite direction. Step coalescence is often observed in the parallel flow region, which leads to the formation of gully-type defects on the macroscopic steps, and finally induces the solvent wrapping and deteriorates the crystal quality. On the contrary, in the parallel flow region, the growth steps are fine and dense, the growth surface is smooth and presents a crystal face, and the crystal quality is better than that in the parallel flow region (such as Figure 1 Therefore, achieving an antiparallel flow region on the entire seed crystal surface is an effective way to improve crystal quality.

[0003] In order to realize the antiparallel flow region on the entire seed crystal surface, reference 1 provides that the small-sized crystal is placed away from the center of the crucible, and only the crucible rotates to drive the tangential unidirectional convection. By placing the direction in the opposite direction of convection, antiparallel flow can be achieved on the entire surface, thereby improving the crystal quality. However, this method is subject to the problems of excessive crucible size and asymmetric temperature distribution on the seed crystal surface for large-sized crystals.

[0004] It can be seen that although the art has conducted certain explorations on methods for improving the quality of silicon carbide crystals by achieving antiparallel flow regions on the entire seed crystal surface, there is still room for further improvement.

[0005] References:

[0006] Cited literature 1: Can Zhu, Shunta Harada, Kazuaki Seki, et al. Influence of Solution Flow on Step Bunching in Solution Growth of SiC Crystals[J]. Cryst. Growth Des. 2013, 13, 3691-3696. Summary of the invention

[0007] Problem that the invention aims to solve

[0008] In view of the above situation, it is necessary to provide a method for placing the seed crystal concentrically with the center of the crucible and achieving antiparallel flow on the entire seed crystal surface, so as to improve the quality of liquid phase grown silicon carbide crystals.

[0009] Solutions for solving problems

[0010] In order to solve the above problems, the present inventors have studied and discovered a special seed crystal cutting and splicing method, which makes the surface of the spliced ​​seed crystal have different step flow directions, so that the anti-parallel flow of the entire seed crystal surface can be achieved under the premise of being concentric with the center of the crucible.

[0011] The present invention first provides a method for preparing a silicon carbide single crystal, which comprises the following steps:

[0012] Step S1: providing a θ off-axis seed crystal and a -θ off-axis seed crystal each having an antiparallel flow region and a parallel flow region, wherein the step flow direction of the θ off-axis seed crystal is direction, the step flow direction of -θ off-axis seed crystal is

[0013] Step S2: Place the θ off-axis seed crystal and the -θ off-axis seed crystal along Cutting in half in the diameter direction to obtain a half portion with an antiparallel flow region and a half portion with a parallel flow region of a θ off-axis seed crystal and a half portion with a parallel flow region and a half portion with an antiparallel flow region of a -θ off-axis seed crystal, splicing the half portion with an antiparallel flow region of the θ off-axis seed crystal and the half portion with an antiparallel flow region of the -θ off-axis seed crystal to the gap to obtain a spliced ​​seed crystal;

[0014] Step S3: putting silicon, transition metal element and aluminum element as raw materials into a graphite crucible and heating them to melt the raw materials to form a mixed solution, contacting the spliced ​​seed crystal with the liquid surface of the mixed solution, and rotating and pulling the spliced ​​seed crystal to grow a crystal;

[0015] Step S4: Pull the crystal upward so that the crystal growth interface is separated from the liquid surface, thereby obtaining a silicon carbide single crystal.

[0016] According to the preparation method of the present invention, in step S1, the positive-axis silicon carbide single crystal is oriented with the

[0001] crystal direction facing upward. Direction is horizontal to the left,

[0001] crystal axis is The directions are tilted, and the tilt angles are θ and -θ respectively. The normal-axis silicon carbide single crystal is cut along the direction parallel to the (0001) plane to obtain θ off-axis seed crystal and -θ off-axis seed crystal.

[0017] According to the preparation method of the present invention, wherein the angle θ is 0 to 12°.

[0018] According to the preparation method of the present invention, in step S3, the transition metal element is selected from one or more of chromium, titanium, iron, lanthanum, cerium, yttrium, cobalt, nickel, tin, neodymium, praseodymium, copper, vanadium, zirconium and niobium.

[0019] According to the preparation method of the present invention, in step S3, the concentration of the aluminum element in the mixed solution is 4 mol.%-20 mol.%; and / or,

[0020] The concentration of the transition metal element in the mixed solution is 40 mol.%-60 mol.%; and / or,

[0021] The concentration of silicon in the mixed solution is 30 mol.% to 50 mol.%.

[0022] According to the preparation method of the present invention, in step S3, the temperature of heating the raw material is 1800-1900° C., and the power of the heating coil is 5-12 kW.

[0023] According to the preparation method of the present invention, in step S3, the rotation speed of rotating and pulling the spliced ​​seed crystal is 50-200 rpm, and the pulling speed is 50-200 μm / h.

[0024] According to the preparation method of the present invention, in step S3, the temperature gradient during crystal growth is 1-20° C. / cm, and the crystal growth time is 40-200 h.

[0025] According to the preparation method of the present invention, in step S4, the speed of pulling the crystal upward is 800-1200 mm / h; after the crystal growth interface is separated from the liquid surface, the power is linearly reduced to 0 kW within 10 hours.

[0026] In addition, the present invention also provides a silicon carbide single crystal, wherein the silicon carbide single crystal is prepared according to the preparation method of the present invention.

[0027] Effects of the Invention

[0028] Through the above technical solution, the present invention achieves the following beneficial effects:

[0029] The method for preparing a silicon carbide single crystal provided by the present invention helps to reduce the height of the growing microscopic steps, inhibit step aggregation and improve interface stability, and ultimately obtain high-quality silicon carbide single crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A photograph of a silicon carbide single crystal obtained by a conventional liquid phase method (Comparative Example 1) is shown;

[0031] Figure 2 A schematic diagram showing the relationship between the solution flow direction and the step flow direction in the antiparallel flow region and the parallel flow region on the seed crystal surface;

[0032] Figure 3 A schematic diagram showing the relationship between the solution flow direction and the step flow direction in the antiparallel flow region and the parallel flow region;

[0033] Figure 4 A schematic diagram showing seed crystal cutting in the method for growing silicon carbide single crystal by a liquid phase method provided by the present invention is shown;

[0034] Figure 5 A photograph of the silicon carbide single crystal obtained in Example 1 is shown. DETAILED DESCRIPTION

[0035] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0036] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0037] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0038] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0039] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0040] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0041] In this specification, the term "parallel flow region" refers to the region on the seed crystal surface where the angle between the direction of the solution convection diverging from the inside to the outside due to the centrifugal force generated by the rotation of the seed crystal and the direction of the initial step flow of the seed crystal is α, where 0≤α<90° (e.g. Figure 2 In this region, the flow direction of the fluid and the step flow are roughly the same, and the solute atoms move and diffuse away from the kink region (as shown in the parallel flow region in Figure 1). Figure 3 b); the “antiparallel flow region” refers to the region on the seed crystal surface where the angle between the direction of the solution convection diverging from the inside to the outside due to the centrifugal force generated by the rotation of the seed crystal and the direction of the initial step flow of the seed crystal is β, where 90°≤β<180° (as shown in FIG. Figure 2 In this region, the fluid flow direction and the step flow direction are roughly opposite, and the solute atoms move and diffuse toward the kink region (as shown in the antiparallel flow region in FIG. Figure 3 a).

[0042] <First aspect>

[0043] The method for preparing a silicon carbide single crystal of the present invention comprises the following steps:

[0044] Step S1: providing a θ off-axis seed crystal and a -θ off-axis seed crystal each having an antiparallel flow region and a parallel flow region, wherein the step flow direction of the θ off-axis seed crystal is direction, the step flow direction of -θ off-axis seed crystal is

[0045] Step S2: Place the θ off-axis seed crystal and the -θ off-axis seed crystal along Cutting in half in the diameter direction to obtain a half portion with an antiparallel flow region and a half portion with a parallel flow region of a θ off-axis seed crystal and a half portion with a parallel flow region and a half portion with an antiparallel flow region of a -θ off-axis seed crystal, splicing the half portion with an antiparallel flow region of the θ off-axis seed crystal and the half portion with an antiparallel flow region of the -θ off-axis seed crystal to the gap to obtain a spliced ​​seed crystal;

[0046] Step S3: putting silicon, transition metal element and aluminum element as raw materials into a graphite crucible and heating them to melt the raw materials to form a mixed solution, contacting the spliced ​​seed crystal with the liquid surface of the mixed solution, and rotating and pulling the spliced ​​seed crystal to grow a crystal;

[0047] Step S4: Pull the crystal upward so that the crystal growth interface is separated from the liquid surface, thereby obtaining a silicon carbide single crystal.

[0048] Each step is described in detail below with reference to the accompanying drawings.

[0049] Step S1

[0050] In step S1, if Figure 4 As shown, the positive-axis silicon carbide single crystal is bonded to a polymer tooling (also called a "mold", not shown in the figure), the mold is parallel to the (0001) plane (i.e., the horizontal plane), and the positive-axis silicon carbide single crystal

[0001] is oriented upward. Direction is horizontal to the left,

[0001] crystal axis is The directions are tilted, and the tilt angles are θ and -θ respectively. The positive axis silicon carbide single crystal is cut along the direction parallel to the (0001) plane (i.e., the horizontal direction) to obtain θ off-axis seed crystals ( Figure 4 The first cut results in a step flow direction of Direction seed crystal) and -θ off-axis seed crystal ( Figure 4 The first cut results in a step flow direction of The θ off-axis seed crystal and the -θ off-axis seed crystal include an anti-parallel flow region and a parallel flow region, respectively.

[0051] In some specific embodiments, the θ may be 0 to 12°, such as 2°, 4°, 6°, 8°, 10°, etc.

[0052] Step S2

[0053] In step S2, if Figure 4 As shown, the θ off-axis seed crystal and the -θ off-axis seed crystal are placed along The diameter direction is cut to obtain the part of the θ off-axis seed crystal with anti-parallel flow region ( Figure 4 A) and the portion of the θ off-axis seed crystal with parallel flow region ( Figure 4 B) and the portion of the -θ off-axis seed crystal with parallel flow region ( Figure 4 C) and the portion of the -θ off-axis seed crystal with antiparallel flow region ( Figure 4 D), the portion of the θ off-axis seed crystal with the antiparallel flow region ( Figure 4A) and the portion of the -θ off-axis seed crystal with an antiparallel flow region ( Figure 4 D) is spliced ​​to the gap to obtain a spliced ​​seed crystal ( Figure 4 The seed crystal obtained by splicing A and D in the figure).

[0054] Step S3

[0055] In step S3, the spliced ​​seed crystal obtained in step S2 is bonded to a graphite holder, and a water-cooled stainless steel seed crystal rod is connected through a graphite seed crystal rod. A graphite crucible is placed in an induction heating single crystal furnace, and a heat preservation layer is wrapped around the graphite crucible. Silicon, transition metal single substance and aluminum single substance as raw materials are placed in the graphite crucible, and an induction heating coil is used to heat the raw materials to melt the raw materials to form a silicon-transition metal single substance-aluminum single substance high-temperature mixed solution. After all the raw materials are melted, the spliced ​​seed crystal is contacted with the liquid surface of the mixed solution, and then the spliced ​​seed crystal is rotated and pulled to grow the crystal.

[0056] There is no particular limitation on the method of bonding the spliced ​​seed crystal to the graphite holder, and the method can be selected as needed. In some specific implementation schemes, the spliced ​​seed crystal can be bonded to the graphite holder by hot pressing with high-temperature glue.

[0057] In the present invention, the transition metal element can be selected from one or more of chromium, titanium, iron, lanthanum, cerium, yttrium, cobalt, nickel, tin, neodymium, praseodymium, copper, vanadium, zirconium and niobium.

[0058] In a mixed solution of silicon-transition metal element-aluminum element, the concentration of aluminum may be 4 mol.%-20 mol.%, for example, 6 mol.%, 8 mol.%, 10 mol.%, 12 mol.%, 15 mol.%, 18 mol.%, etc. In a mixed solution of silicon-transition metal element-aluminum element, the concentration of transition metal element may be 40 mol.%-60 mol.%, for example, 45 mol.%, 48 mol.%, 50 mol.%, 52 mol.%, 55 mol.%, 58 mol.%, etc. In a mixed solution of silicon-transition metal element-aluminum element, the concentration of silicon may be 30 mol.%-50 mol.%, for example, 35 mol.%, 38 mol.%, 40 mol.%, 42 mol.%, 45 mol.%, 48 mol.%, etc.

[0059] The power of the induction coil during heating can be 5 to 12 kW. The temperature of heating the silicon-transition metal element-aluminum element mixed solution is 1800 to 1900° C., for example, 1810° C., 1820° C., 1830° C., 1840° C., 1850° C., 1860° C., 1870° C., 1880° C., 1890° C., etc.

[0060] When the spliced ​​seed crystal is rotated and pulled as mentioned above, the rotation speed can be 50-200rpm, for example, 80rpm, 100rpm, 120rpm, 150rpm, 180rpm, etc.; the pulling speed can be 50-200μm / h, for example, 70μm / h, 90μm / h, 100μm / h, 120μm / h, 150μm / h, 180μm / h, etc.

[0061] In step S3, the temperature gradient during crystal growth is 1 to 20°C / cm, for example, it can be 5°C / cm, 8°C / cm, 10°C / cm, 12°C / cm, 15°C / cm, 18°C / cm, etc.; the crystal growth time is 40 to 200h, for example, it can be 50h, 80h, 100h, 120h, 150h, 180h, etc.

[0062] In step S3, the spliced ​​seed crystal and the crucible are rotated in a manner of simultaneous periodic reciprocating rotation (accelerated crucible rotation method, ACRT) or independent periodic reciprocating rotation (switching flow).

[0063] Step S4

[0064] In step S4, after 40 to 200 hours of growth, the crystal is pulled upward at a speed of 800-1200 mm / h to separate the growth interface from the liquid to end the crystal growth. Finally, the power of the induction coil is linearly reduced to 0 kW within 10 hours to allow the crystal to slowly cool and release stress. Thus, a silicon carbide single crystal is obtained.

[0065] <Second Aspect>

[0066] A second aspect of the present invention provides a silicon carbide single crystal, which is obtained according to the preparation method described in the first aspect.

[0067] Example

[0068] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0069] Example 1

[0070] Step S1: Place the positive-axis silicon carbide single crystal with the

[0001] crystal direction facing upwards. Direction is horizontal to the left,

[0001] crystal axis is The directions are tilted, and the tilt angles are 4° and -4°. The normal-axis silicon carbide single crystal is cut along a direction parallel to the (0001) plane to obtain 4° off-axis seed crystals and -4° off-axis seed crystals.

[0071] Step S2: Place the 4° off-axis seed crystal and the -4° off-axis seed crystal along Secondary cutting is performed in the diameter direction to obtain four semicircular seed crystals, namely, the half with antiparallel flow area and the half with parallel flow area of ​​the 4° off-axis seed crystal and the half with antiparallel flow area and the half with parallel flow area of ​​the -4° off-axis seed crystal. Among them, the half with antiparallel flow area of ​​the 4° off-axis seed crystal and the half with antiparallel flow area of ​​the -4° off-axis seed crystal are spliced ​​until the gaps are merged to obtain a spliced ​​seed crystal.

[0072] Step S3: Bond the spliced ​​seed crystal to the graphite holder, and connect the water-cooled stainless steel seed crystal rod through the graphite seed crystal rod. Place the graphite crucible in an induction heating single crystal furnace, and wrap the graphite crucible with an insulation layer. Place silicon, transition metal chromium, and aluminum raw materials in the graphite crucible to prepare Si 40 Cr 50 Al 10 The coil heats and melts the raw materials at 7kW power. After all the raw materials are melted, the liquid temperature reaches 1850℃, the spliced ​​seed crystal is lowered to contact the liquid surface, and the rotation and pulling at 150rpm begins. The crucible rotates at -20rpm. After 30min, the seed crystal is decelerated to 0rpm in 1min and reversely accelerated to -150rpm for rotation and pulling. The crucible is decelerated to 0rpm in 1min and reversely accelerated to 20rpm for rotation. The seed crystal crucible is rotated in this 30min cycle. The growth temperature gradient is controlled at 10℃ / cm. The spliced ​​seed crystal is pulled at a speed of 100 microns per hour.

[0073] Step S4: After 100 hours of growth, the crystal is pulled upward at a speed of 1000 mm / h, so that the growth interface is separated from the liquid surface to end the crystal growth, and finally the power is linearly reduced to 0 kW within 10 hours. The photo of the obtained silicon carbide single crystal is shown in Figure 5 As shown. Figure 5 It can be seen that the crystals prepared by the method of the present invention have smooth surfaces, fine growth steps, and pure interiors.

[0074] Example 2

[0075] Step S1: Place the positive-axis silicon carbide single crystal with the

[0001] crystal direction facing upwards. Direction is horizontal to the left,

[0001] crystal axis is The direction is tilted, and the tilt angles are 1° and -1°. The normal-axis silicon carbide single crystal is cut along a direction parallel to the (0001) plane to obtain 1° off-axis seed crystals and -1° off-axis seed crystals after cutting.

[0076] Step S2: Place the 1° off-axis seed crystal and the -1° off-axis seed crystal along A second cutting is performed in the diameter direction to obtain four semicircular seed crystals, namely the half with antiparallel flow area and the half with parallel flow area of ​​the 1° off-axis seed crystal and the half with antiparallel flow area and the half with parallel flow area of ​​the -1° off-axis seed crystal. Among them, the half with antiparallel flow area of ​​the 1° off-axis seed crystal and the half with antiparallel flow area of ​​the -1° off-axis seed crystal are spliced ​​until the gaps are merged to obtain a spliced ​​seed crystal.

[0077] Step S3: Bond the spliced ​​seed crystal to the graphite holder, and connect the water-cooled stainless steel seed crystal rod through the graphite seed crystal rod. Place the graphite crucible in an induction heating single crystal furnace, and wrap the graphite crucible with an insulation layer. Place silicon, transition metal chromium, and aluminum raw materials in the graphite crucible to prepare Si 40 Cr 50 Al 10 The coil heats and melts the raw materials at 7kW power. After all the raw materials are melted, the liquid temperature reaches 1850℃, the spliced ​​seed crystal is lowered to contact the liquid surface, and the rotation and pulling at 150rpm begins. The crucible rotates at -20rpm. After 30min, the seed crystal is decelerated to 0rpm in 1min and reversely accelerated to -150rpm for rotation and pulling. The crucible is decelerated to 0rpm in 1min and reversely accelerated to 20rpm for rotation. The seed crystal crucible is rotated in this 30min cycle. The growth temperature gradient is controlled at 10℃ / cm. The spliced ​​seed crystal is pulled at a speed of 100 microns per hour.

[0078] Step S4: After 100 hours of growth, the crystal is pulled upward at a speed of 1000 mm / h so that the growth interface is separated from the liquid surface to end the crystal growth. Finally, the power is linearly reduced to 0 kW within 10 hours.

[0079] Comparative Example 1

[0080] Step S1: Place the positive-axis silicon carbide single crystal with the

[0001] crystal direction facing upwards. Direction is horizontal to the left,

[0001] crystal axis is The direction is tilted, the tilt angle is 4°, and the normal-axis silicon carbide single crystal is cut along a direction parallel to the (0001) plane to obtain a 4° off-axis seed crystal.

[0081] Step S2: Glue the 4° off-axis seed crystal to the graphite holder, and connect the water-cooled stainless steel seed crystal rod through the graphite seed crystal rod. Place the graphite crucible in an induction heating single crystal furnace, and wrap the graphite crucible with an insulation layer. Place silicon, transition metal chromium, and aluminum raw materials in the graphite crucible to prepare Si 40 Cr 50 Al 10 The coil heats and melts the raw materials at 7kW power. After all the raw materials are melted, the liquid temperature reaches 1850℃, the spliced ​​seed crystal is lowered to contact the liquid surface, and the rotation and pulling at 150rpm begins. The crucible rotates at -20rpm. After 30min, the seed crystal is decelerated to 0rpm in 1min and reversely accelerated to -150rpm for rotation and pulling. The crucible is decelerated to 0rpm in 1min and reversely accelerated to 20rpm for rotation. The seed crystal crucible is rotated in this 30min cycle. The growth temperature gradient is controlled at 10℃ / cm. The spliced ​​seed crystal is pulled at a speed of 100 microns per hour.

[0082] Step S3: After 60 hours of growth, the crystal is pulled upward at a speed of 1000 mm / h to separate the growth interface from the liquid surface to end the crystal growth. Finally, the power is linearly reduced to 0 kW within 10 hours. The photo of the obtained silicon carbide single crystal is shown in Figure 1 As shown. Figure 1 It can be seen that the surface of the crystals prepared by the traditional method is rough and there are co-solvent encapsulation defects inside the crystals.

[0083] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0084] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing a silicon carbide single crystal, characterized in that: The following steps are involved: Step S1: providing a θ off-axis seed crystal and a -θ off-axis seed crystal, each having an antiparallel flow region and a parallel flow region, wherein the step flow direction of the θ off-axis seed crystal is direction, the step flow direction of -θ off-axis seed crystal is Step S2: Place the θ off-axis seed crystal and the -θ off-axis seed crystal along [ _ 1100] Cutting in half in the diameter direction to obtain a half portion with an antiparallel flow region and a half portion with a parallel flow region of a θ off-axis seed crystal and a half portion with a parallel flow region and a half portion with an antiparallel flow region of a -θ off-axis seed crystal, splicing the half portion with an antiparallel flow region of the θ off-axis seed crystal and the half portion with an antiparallel flow region of the -θ off-axis seed crystal to the gap to obtain a spliced ​​seed crystal; Step S3: putting silicon, transition metal element and aluminum element as raw materials into a graphite crucible and heating them to melt the raw materials to form a mixed solution, contacting the spliced ​​seed crystal with the liquid surface of the mixed solution, and rotating and pulling the spliced ​​seed crystal to grow a crystal; Step S4: Pull the crystal upward so that the crystal growth interface is separated from the liquid surface, thereby obtaining a silicon carbide single crystal.

2. The preparation method according to claim 1, characterized in that: In step S1, the positive-axis silicon carbide single crystal is oriented with the [0001] crystal direction facing upward. Direction is horizontal to the left, [0001] crystal axis is The directions are tilted, and the tilt angles are θ and -θ respectively. The normal-axis silicon carbide single crystal is cut along the direction parallel to the (0001) plane to obtain θ off-axis seed crystal and -θ off-axis seed crystal.

3. The preparation method according to claim 1 or 2, characterized in that: The θ is 0 to 12°.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In step S3, the transition metal element is selected from one or more of chromium, titanium, iron, lanthanum, cerium, yttrium, cobalt, nickel, tin, neodymium, praseodymium, copper, vanadium, zirconium and niobium.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step S3, the concentration of the aluminum element in the mixed solution is 4 mol.%-20 mol.%; and / or, The concentration of the transition metal element in the mixed solution is 40 mol.%-60 mol.%; and / or, The concentration of silicon in the mixed solution is 30 mol.% to 50 mol.%.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step S3, the raw material is heated to a temperature of 1800-1900°C, and the power of the heating coil is 5-12 kW.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In step S3, the spliced ​​seed crystal is rotated and pulled at a rotation speed of 50 to 200 rpm, and the pulling speed is 50 to 200 μm / h.

8. The preparation method according to any one of claims 1 to 7, characterized in that: In step S3, the temperature gradient during crystal growth is 1-20°C / cm, and the crystal growth time is 40-200h.

9. The preparation method according to any one of claims 1 to 8, characterized in that: In step S4, the crystal is pulled upward at a speed of 800-1200 mm / h; after the crystal growth interface is separated from the liquid surface, the power is linearly reduced to 0 kW within 10 hours.

10. A silicon carbide single crystal, characterized in that: The silicon carbide single crystal is prepared according to the preparation method according to any one of claims 1 to 9.

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