Growth method of silicon carbide crystal

Abstract

The invention provides a growth method of silicon carbide crystals. In the growth process, sublimated silicon carbide raw materials can pass through the porous silicon to reach the surface of a seed crystal, rich capillary channels of the porous silicon can filter carbon particles in airflow, prevent the carbon particles from being attached to the surface of the seed crystal and reduce formation of carbon particle inclusions in silicon carbide single crystals, and the filtered carbon particles can react with the porous silicon firstly to form SiC and then react with the porous silicon to form SiC. Along with the increase of the growth temperature, the material is decomposed into Si and C as a raw material. Moreover, the porous silicon can serve as a Si source in the growth process, the carbon-silicon ratio in a gas phase is balanced, excessive carbon is prevented from being separated out into carbon particles on the surface of the seed crystal, and formation of carbon particle inclusions and microtubules and dislocations evolved by the carbon particle inclusions are avoided.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor technology, and in particular relates to a method for growing silicon carbide crystals. Background Art

[0002] Silicon carbide belongs to the third generation of semiconductor materials and has the advantages of wide bandgap, high thermal conductivity, high critical breakdown field strength, and high electron saturation drift rate. Therefore, it has great application prospects in the field of semiconductor manufacturing.

[0003] The industrial growth of silicon carbide mainly uses the physical vapor transport (PVT) method, and the growth conditions are harsh. During the growth process, the raw materials gradually decompose. Due to the nature of Si, Si is lost very quickly, and the carbon-silicon ratio gradually increases, making the entire gas phase carbon-rich, and it is easy to precipitate carbon inclusion defects on the surface of the seed crystal. In addition, the commonly used filter layers currently use graphite products, which will sublimate during the growth process, further making the gas phase carbon-rich and forming more carbon particle inclusions; and as the growth process progresses, the silicon carbide raw materials are very brittle after graphitization and easily form carbon particles. As the airflow rises to the surface of the seed crystal, the number of carbon inclusions increases further. Carbon inclusions can also become the source of microtubes and dislocations, which increases the defect density in silicon carbide single crystals. These defects limit the improvement and progress of SiC device performance and hinder its industrial application and development.

[0004] Therefore, it is urgent to find a method to effectively reduce defects such as carbon inclusions, microtubes and dislocations in silicon carbide single crystals. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for growing silicon carbide crystals. The method for growing silicon carbide crystals provided by the present invention can effectively reduce defects such as carbon inclusions, microtubes and dislocations in silicon carbide single crystals.

[0006] The present invention provides a method for growing a silicon carbide crystal, comprising the following steps:

[0007] A) charging silicon carbide raw material into a growth crucible;

[0008] B) placing the porous silicon in a growth crucible, with the lower surface of the porous silicon being in contact with the upper surface of the loaded silicon carbide raw material;

[0009] C) growing silicon carbide crystals to obtain silicon carbide crystals.

[0010] Preferably, the porous silicon has a purity greater than 99.99%, a pore size of 100 to 300 μm, a porosity of 30 to 70%, and a thickness of 5 to 20 mm;

[0011] The dimension of the porous silicon in the plane direction is smaller than the cross-sectional dimension of the growth crucible by d, 0<d≤0.5mm.

[0012] Preferably, the pores of the porous silicon are three-dimensional through-holes, and the direction of the pores is parallel to the axis in the vertical direction of the growth crucible.

[0013] Preferably, the upper surface of the silicon carbide raw material is a plane, and the lower surface of the porous silicon is a plane.

[0014] Preferably, the upper surface of the silicon carbide raw material is conical, and the lower surface of the porous silicon is concave inwardly to form a cone and its size matches the cone formed by the upper surface of the silicon carbide raw material;

[0015] The angle between the cone and the horizontal plane is θ, 0<θ≤30°.

[0016] Preferably, the pores of the porous silicon are arranged obliquely around the axis in the vertical direction of the growth crucible, and the angle between the pores and the axis in the vertical direction of the growth crucible is γ, 0<γ≤60°, and the inclination direction of the pores is from top to bottom, extending from the axis in the vertical direction of the growth crucible to the inner wall of the growth crucible.

[0017] Preferably, the upper surface of the silicon carbide raw material is a plane, and the lower surface of the porous silicon is a plane.

[0018] Preferably, the upper surface of the silicon carbide raw material is conical, and the lower surface of the porous silicon is concave inwardly to form a cone and its size matches the cone formed by the upper surface of the silicon carbide raw material;

[0019] The angle between the cone and the plane direction is θ, 0<θ≤30°

[0020] Preferably, the inner side of the growth crucible is cylindrical, and the porous silicon is cylindrical.

[0021] Preferably, the growth temperature is 2100-2400° C. and the growth time is 100-200 h.

[0022] Compared with the prior art, the present invention provides a method for growing silicon carbide crystals, comprising the following steps: A) loading silicon carbide raw materials into a growth crucible; B) placing porous silicon in the growth crucible, and the lower surface of the porous silicon is in contact with the upper surface of the loaded silicon carbide raw materials; C) growing silicon carbide crystals to obtain silicon carbide crystals. During the growth process, the sublimated silicon carbide raw materials will pass through the porous silicon to reach the surface of the seed crystal. The abundant capillary channels of the porous silicon can filter the carbon particles in the airflow, prevent the carbon particles from adhering to the surface of the seed crystal, and reduce the formation of carbon particle inclusions in the silicon carbide single crystal. The filtered carbon particles will first react with the porous silicon to form SiC, and as the growth temperature increases, they will decompose into Si and C as raw materials. In addition, the porous silicon will act as a Si source during the growth process, balance the carbon-silicon ratio in the gas phase, prevent excessive carbon from precipitating as carbon particles on the surface of the seed crystal, and avoid the formation of carbon particle inclusions, as well as microtubes and dislocations evolved from the carbon particle inclusions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of assembling raw materials for growing silicon carbide crystals provided in Example 1;

[0024] Figure 2 A schematic diagram of the raw material assembly for growing silicon carbide crystals provided in Example 2;

[0025] Figure 3 A schematic diagram of the raw material assembly for growing silicon carbide crystals provided in Example 3;

[0026] Figure 4 Schematic diagram of the raw material assembly for the growth of silicon carbide crystal provided in Example 4. DETAILED DESCRIPTION

[0027] The present invention provides a method for growing a silicon carbide crystal, comprising the following steps:

[0028] A) charging silicon carbide raw material into a growth crucible;

[0029] B) placing the porous silicon in a growth crucible, with the lower surface of the porous silicon being in contact with the upper surface of the loaded silicon carbide raw material;

[0030] C) growing silicon carbide crystals to obtain silicon carbide crystals.

[0031] The present invention first prepares a growth crucible for growing silicon carbide crystals. In the present invention, there is no special limitation on the growth crucible. Preferably, a graphite crucible is used.

[0032] Then, a raw material is loaded into the growth crucible, wherein the raw material is a silicon carbide raw material, and the silicon carbide is high-purity silicon carbide.

[0033] Next, the porous silicon carbide is cut to fit the inner wall size of the crucible. Preferably, the size of the porous silicon in the plane direction is smaller than the cross-sectional size of the growth crucible by d, 0<d≤0.5 mm, and can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any value between 0 and 0.5 mm.

[0034] In some preferred embodiments of the present invention, the inner wall of the growth crucible is cylindrical, and the inner diameter of the growth crucible is D1. Therefore, the porous silicon is also cut into a cylindrical shape, and the diameter of the porous silicon is D2, where D2=D1-d.

[0035] In the present invention, the purity of the porous silicon is greater than 99.99%, the pore size is 100 to 300 μm, the porosity is 30 to 70%, and the thickness is 5 to 20 mm. The pore size of the porous silicon can be 100, 150, 200, 250, 300, or any value between 100 and 300 μm; the porosity can be 30%, 40%, 50%, 60%, 70%, or any value between 30 and 70%; the thickness can be 5, 10, 15, 20, or any value between 5 and 20 mm. In some preferred embodiments of the present invention, the purity of the porous silicon is greater than 99.99%, the pore size is 180 μm, the porosity is 50%, and the thickness is 10 mm.

[0036] In some specific embodiments of the present invention, the pores of the porous silicon are three-dimensional through-holes, and the direction of the pores is parallel to the axis in the vertical direction of the growth crucible.

[0037] When the direction of the pores of the porous silicon is parallel to the axis in the vertical direction of the growth crucible, the upper surface of the silicon carbide raw material is a plane, and the lower surface of the porous silicon is a plane.

[0038] When the direction of the pores of the porous silicon is parallel to the axis in the vertical direction of the growth crucible, the upper surface of the silicon carbide raw material can also be conical, then the lower surface of the porous silicon is concave inwardly to be conical and its size matches the cone formed by the upper surface of the silicon carbide raw material; the angle between the cone and the plane direction is θ, 0<θ≤30°, which can be 1°, 5°, 10°, 15°, 20°, 25°, 30°, or any value between 0 and 30°. The above-mentioned arrangement of porous silicon and silicon carbide raw materials can solve the problem that the raw materials close to the side wall of the crucible will sublimate preferentially, and its sublimation gas flow will flow along the crucible wall, causing serious corrosion to the edge of the porous silicon.

[0039] In some specific embodiments of the present invention, the pores of the porous silicon are arranged obliquely around the axis in the vertical direction of the growth crucible, and the angle between the pores and the axis in the vertical direction of the growth crucible is γ, 0<γ≤60°, and can be 1°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any value between 0 and 60°, and the inclination direction of the pores is from top to bottom from the axis in the vertical direction of the growth crucible to the inner wall of the growth crucible. The above-mentioned arrangement of the porous silicon pores can solve the problem that the raw materials near the side wall of the crucible will be preferentially sublimated, and its gas flow also flows along the crucible wall, resulting in uneven supply of raw materials in the radial direction of the seed crystal, less raw materials in the center, more raw materials at the edge, and a concave-convex interface in the growth, which leads to insufficient effective thickness of the crystal and the formation of internal stress in the crystal. Excessive internal stress can cause the crystal to crack.

[0040] The inclined setting of the pores of the porous silicon can transport the raw materials close to the side wall of the crucible to the center of the seed crystal through the pores of the porous silicon, thereby balancing the growth rate of the crystal in the radial direction.

[0041] When the pores of the porous silicon are arranged obliquely around the axis in the vertical direction of the growth crucible, the upper surface of the silicon carbide raw material is a plane, and the lower surface of the porous silicon is a plane.

[0042] When the pores of the porous silicon are arranged obliquely around the axis in the vertical direction of the growth crucible, the upper surface of the silicon carbide raw material can also be conical, then the lower surface of the porous silicon is concave inwardly to be conical and its size matches the cone formed by the upper surface of the silicon carbide raw material; the angle between the cone and the plane direction is θ, 0<θ≤30°, which can be 1°, 5°, 10°, 15°, 20°, 25°, 30°, or any value between 0 and 30°. The above-mentioned arrangement of porous silicon and silicon carbide raw materials can further optimize the transport uniformity of raw materials and reduce carbon particle encapsulation.

[0043] After the silicon carbide raw material and the porous silicon are placed, the silicon carbide crystal is grown to obtain the silicon carbide crystal.

[0044] The present invention has no special restrictions on the growth conditions of the silicon carbide crystal, and the growth conditions for growing silicon carbide crystals by the PVT method well known to those skilled in the art can be used.

[0045] During the growth of silicon carbide crystals, the ratio of Si to C elements in SiC raw material particles is 1: 1. The method of the present invention can obtain silicon carbide single crystals with low carbon inclusions, microtubes and dislocation defects only by a growth method consistent with normal crystals, effectively improving the quality of silicon carbide substrates.

[0046] During the growth process, the sublimated silicon carbide raw material will pass through the porous silicon to reach the surface of the seed crystal. The rich capillary channels of the porous silicon can filter the carbon particles in the airflow, prevent the carbon particles from adhering to the surface of the seed crystal, and reduce the formation of carbon particle inclusions in the silicon carbide single crystal. The filtered carbon particles will first react with the porous silicon to form SiC, and then decompose into Si and C as the growth temperature increases. In addition, the porous silicon will act as a Si source during the growth process, balancing the carbon-silicon ratio in the gas phase, preventing excessive carbon from precipitating as carbon particles on the surface of the seed crystal, avoiding the formation of carbon particle inclusions, and microtubes and dislocations evolved from the carbon particle inclusions.

[0047] In order to further understand the present invention, the growth method of silicon carbide crystal provided by the present invention is described below in conjunction with embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0048] Embodiment 1:

[0049] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0050] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 50%, and a thickness of 10 mm, and carefully cut the porous silicon into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm);

[0051] (3) placing the porous silicon processed in step (2) into the crucible loaded with silicon carbide raw material in step (1) and placing it close to the raw material; the pores of the porous silicon are three-dimensional through-holes, and the direction of the pores is parallel to the axis in the vertical direction of the growth crucible; Figure 1 , Figure 1 Schematic diagram of the raw material assembly for the growth of silicon carbide crystal provided in Example 1.

[0052] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0053] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1 / cm 2 .

[0054] Embodiment 2:

[0055] (1) Select a graphite crucible to be used for growth, with an inner diameter of D1, and load it with high-purity silicon carbide raw materials used for normal growth, so that the surface forms a cone, and the angle between the cone and the horizontal plane is θ=15°;

[0056] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 50%, and a thickness of 10 mm, and carefully cut it into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm), and then make it into a cylinder with one side concave inwardly concave, and the angle between the concave cone and the horizontal plane is 15°; so that the concave part of the porous silicon can just fit with the conical silicon carbide raw material below;

[0057] (3) placing the porous silicon processed in step (2) into the crucible loaded with silicon carbide raw material in step (1) and placing it close to the raw material; the pores of the porous silicon are three-dimensional through-holes, and the direction of the pores is parallel to the axis in the vertical direction of the growth crucible; Figure 2 , Figure 2 Schematic diagram of the raw material assembly for the growth of silicon carbide crystal provided in Example 2.

[0058] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0059] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 0.6 / cm 2 .

[0060] Embodiment 3:

[0061] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0062] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 50%, and a thickness of 10 mm, and carefully cut it into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm), and ensure that the direction of the hole is toward the axis of the cylindrical porous silicon, and the angle between the hole and the axis in the vertical direction of the growth crucible is γ = 30°;

[0063] (3) Place the porous silicon treated in step (2) into the crucible containing the silicon carbide raw material in step (1) and place it close to the raw material; Figure 3 , Figure 3 Schematic diagram of the raw material assembly for the growth of silicon carbide crystal provided in Example 3.

[0064] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 0.6 / cm 2 .

[0065] Embodiment 4:

[0066] (1) Select a graphite crucible to be used for growth, with an inner diameter of D1, and load it with high-purity silicon carbide raw materials used for normal growth, so that the surface forms a cone, and the angle between the cone and the horizontal plane is θ=15°;

[0067] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 50%, and a thickness of 10 mm, and carefully cut it into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm), ensure that the direction of the hole is toward the axis of the cylindrical porous silicon, and the angle between the hole and the axis in the vertical direction of the growth crucible is 30°, and then make it into a cylinder with a concave inward, and the angle between the concave cone and the horizontal plane is θ = 30°; so that the concave part of the porous silicon can just fit with the conical silicon carbide raw material below;

[0068] (3) Place the treated porous silicon into the crucible containing the silicon carbide raw material in step 1 and place it close to the raw material; Figure 4 , Figure 4 Schematic diagram of the raw material assembly for the growth of silicon carbide crystal provided in Example 4.

[0069] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0070] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 0.4 / cm 2 .

[0071] Embodiment 5:

[0072] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0073] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 300 μm, a porosity of 70%, and a thickness of 10 mm, and carefully cut the porous silicon into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm);

[0074] (3) placing the porous silicon processed in step (2) into the crucible loaded with silicon carbide raw material in step (1) and placing it close to the raw material; the pores of the porous silicon are three-dimensional through-holes, and the direction of the pores is parallel to the axis in the vertical direction of the growth crucible.

[0075] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0076] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1.1 / cm 2 .

[0077] Embodiment 6:

[0078] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0079] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 100 μm, a porosity of 30%, and a thickness of 10 mm, and carefully cut the porous silicon into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm);

[0080] (3) placing the porous silicon processed in step (2) into the crucible loaded with silicon carbide raw material in step (1) and placing it close to the raw material; the pores of the porous silicon are three-dimensional through-holes, and the direction of the pores is parallel to the axis in the vertical direction of the growth crucible.

[0081] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0082] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1 / cm 2 .

[0083] Embodiment 7:

[0084] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0085] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 50%, and a thickness of 20 mm, and carefully cut the porous silicon into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm);

[0086] (3) placing the porous silicon processed in step (2) into the crucible loaded with silicon carbide raw material in step (1) and placing it close to the raw material; the pores of the porous silicon are three-dimensional through-holes, and the direction of the pores is parallel to the axis in the vertical direction of the growth crucible.

[0087] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0088] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1 / cm 2 .

[0089] Embodiment 8:

[0090] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0091] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 50%, and a thickness of 5 mm, and carefully cut the porous silicon into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm);

[0092] (3) placing the porous silicon processed in step (2) into the crucible loaded with silicon carbide raw material in step (1) and placing it close to the raw material; the pores of the porous silicon are three-dimensional through-holes, and the direction of the pores is parallel to the axis in the vertical direction of the growth crucible.

[0093] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0094] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1.1 / cm 2 .

[0095] Comparative Example 1:

[0096] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0097] (2) The porous silicon of Experimental Example 1 was replaced with the high-purity silicon carbide raw material used for normal growth, and the surface was leveled;

[0098] (3) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0099] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 2 / cm 2 .

[0100] Comparative Example 2:

[0101] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0102] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 500 μm, a porosity of 50%, and a thickness of 10 mm, and carefully cut the porous silicon into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm);

[0103] (3) placing the porous silicon processed in step (2) into the crucible containing the silicon carbide raw material in step (1) and placing it close to the raw material;

[0104] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0105] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1.6 / cm 2 .

[0106] Comparative Example 3:

[0107] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0108] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 80%, and a thickness of 10 mm, and carefully cut the porous silicon into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm);

[0109] (3) placing the porous silicon processed in step (2) into the crucible containing the silicon carbide raw material in step (1) and placing it close to the raw material;

[0110] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0111] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1.4 / cm 2 .

[0112] Comparative Example 4:

[0113] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0114] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 50%, and a thickness of 10 mm, and carefully cut it into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm), and ensure that the direction of the hole is toward the axis of the cylindrical porous silicon, and the angle between the hole and the axis in the vertical direction of the growth crucible is 80°;

[0115] (3) Place the porous silicon processed in step (2) into the crucible containing the silicon carbide raw material in step (1) and place it close to the raw material.

[0116] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1.2 / cm 2 .

[0117] Comparative Example 5:

[0118] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0119] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 180 μm, a porosity of 50%, and a thickness of 10 mm, and carefully cut it into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm), and ensure that the direction of the pores is perpendicular to the axis of the cylindrical porous silicon, the inclination angle of the pores is γ = 150°, and the pores are arranged in a V-shape;

[0120] (3) Place the porous silicon processed in step (2) into the crucible containing the silicon carbide raw material in step (1) and place it close to the raw material.

[0121] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1.2 / cm 2 .

[0122] Comparative Example 6

[0123] (1) Select a graphite crucible with an inner diameter of D1 to be used for growth, fill it with high-purity silicon carbide raw materials used for normal growth, and flatten the surface;

[0124] (2) Select porous silicon with a purity greater than 99.99%, a pore size of 50 μm, a porosity of 20%, and a thickness of 10 mm, and carefully cut the porous silicon into a cylindrical shape with a diameter of D2 = D1-d mm (d is about 0.3 mm);

[0125] (3) placing the porous silicon processed in step (2) into the crucible containing the silicon carbide raw material in step (1) and placing it close to the raw material;

[0126] (4) Use normal growth process and inspect the crystals for defects such as inclusions, micropipes, and dislocations after they are taken out of the furnace.

[0127] Results: After annealing, rounding, cutting, grinding and polishing, the prepared silicon carbide crystals were subjected to microscope analysis and testing. Multiple tests showed that the density of carbon inclusion defects was about 1.6 / cm 2 .

[0128] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for growing silicon carbide crystals, characterized in that: The following steps are involved: A) charging silicon carbide raw material into a growth crucible; B) placing the porous silicon in a growth crucible, with the lower surface of the porous silicon being in contact with the upper surface of the loaded silicon carbide raw material; C) growing silicon carbide crystals to obtain silicon carbide crystals.

2. The growth method according to claim 1, characterized in that The porous silicon has a purity greater than 99.99%, a pore size of 100 to 300 μm, a porosity of 30 to 70%, and a thickness of 5 to 20 mm; The dimension of the porous silicon in the plane direction is smaller than the cross-sectional dimension of the growth crucible by d, 0<d≤0.5mm.

3. The growth method according to claim 1, characterized in that: The pores of the porous silicon are three-dimensional penetrating pores, and the directions of the pores are parallel to the axis in the vertical direction of the growth crucible.

4. The growth method according to claim 3, characterized in that: The upper surface of the silicon carbide raw material is a plane, and the lower surface of the porous silicon is a plane.

5. The growth method according to claim 3, characterized in that: The upper surface of the silicon carbide raw material is conical, and the lower surface of the porous silicon is concave inwardly to form a conical shape and its size matches the conical shape formed by the upper surface of the silicon carbide raw material; The angle between the cone and the horizontal plane is θ, 0<θ≤30°.

6. The growth method according to claim 1, characterized in that: The pores of the porous silicon are arranged obliquely around the axis in the vertical direction of the growth crucible, and the angle between the pores and the axis in the vertical direction of the growth crucible is γ, 0<γ≤60°, and the inclination direction of the pores is from top to bottom, extending from the axis in the vertical direction of the growth crucible to the inner wall of the growth crucible.

7. The growth method according to claim 6, characterized in that: The upper surface of the silicon carbide raw material is a plane, and the lower surface of the porous silicon is a plane.

8. The growth method according to claim 6, characterized in that: The upper surface of the silicon carbide raw material is conical, and the lower surface of the porous silicon is concave inwardly to form a cone and its size matches the cone formed by the upper surface of the silicon carbide raw material; The angle between the cone and the plane direction is θ, 0<θ≤30°.

9. The growth method according to claim 1, characterized in that: The inner side of the growth crucible is cylindrical, and the porous silicon is cylindrical.

10. The growth method according to claim 1, characterized in that: The growth temperature is 2100-2400° C. and the growth time is 100-200 hours.

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