A SiC substrate and a SiC crystal with uniform stress distribution in three-dimensional directions

Abstract

The present application discloses a SiC substrate and a SiC crystal with uniform three-dimensional directional stress distribution, belonging to the technical field of SiC production and processing. The SiC substrate includes a first surface layer, a second surface layer and an intermediate layer; on the same axis, at any plane parallel to the first main surface or the second main surface in the first surface layer, Smax1 represents the maximum absolute value of the radial stress in the first surface layer, Smax2 represents the maximum absolute value of the radial stress in the intermediate layer, Smax3 represents the maximum absolute value of the radial stress in the second surface layer, △S1 = Smax2 - Smax1, △S2 = Smax2 - Smax3, -15 MPa ≤ △S1 ≤ 10 MPa, -15 MPa ≤ △S2 ≤ 10 MPa. The radial stress in the SiC substrate in the above first surface layer, second surface layer and intermediate layer is relatively low, and the stress distribution uniformity between each layer is good, which can improve the quality of the SiC substrate, expand the use range of the SiC substrate, and is beneficial to the production and processing of downstream epitaxial wafers and crystals.

Description

Technical Field

[0001] The present application relates to a SiC substrate and a SiC crystal with uniform stress distribution in three-dimensional directions, belonging to the technical field of SiC production and processing. Background Art

[0002] During the growth of SiC crystals, due to the imbalance of Si / C ratio, impurity introduction, temperature gradient change, etc., various defects such as polycrystals, polytypes, microtubes, and dislocations are easily introduced into the crystals. The defects will cause lattice distortion, and more seriously, the crystal form will change, such as the coexistence of multiple polytypes such as 4H, 6H, 3C, 15R, etc. The lattice distortion releases stress by generating defects, that is, internal stress is introduced into SiC, thereby reducing the quality of SiC crystals, restricting the use range of the crystals, affecting the subsequent processing process of SiC crystals, and reducing the yield of products.

[0003] On the other hand, during the processing of SiC substrates, most of them are obtained by mechanical processing, such as laser cutting, wire cutting and other methods from the ingot, and then surface treatment is carried out through mechanical processing processes such as grinding and polishing. During the substrate processing, microcracks will exist on the surface due to mechanical stress, thereby introducing a damaged layer. For SiC, the difference in the thickness of the damaged layer on the C and Si surfaces will affect the surface quality of the substrate, thereby affecting the production and processing of downstream products. Therefore, both internal stress and surface stress exist in the SiC substrate. When the SiC substrate is used for crystal growth or epitaxial layer growth, the stress of the SiC substrate will be inherited into the crystal or epitaxial layer, resulting in an increase in defects in the epitaxial layer and the crystal, easy cracking and uneven quality, and it is difficult to carry out subsequent processing production. Summary of the Invention

[0004] In order to solve the above problems, a SiC substrate and a SiC crystal with uniform stress distribution in three-dimensional directions are provided. The SiC substrate is divided into a first surface layer, a second surface layer and an intermediate layer. The radial stress in the SiC substrate in the above first surface layer, second surface layer and intermediate layer is relatively low, and the stress distribution uniformity between each layer is good, which can improve the quality of the SiC substrate, expand the use range of the SiC substrate, and is beneficial to the production and processing of downstream products. When it is used for crystal or epitaxial layer growth, it can improve the quality of the crystal and the epitaxial layer.

[0005] According to one aspect of the present application, a SiC substrate with uniform stress distribution in three-dimensional directions is provided. The thickness of the SiC substrate is not less than 100 μm. The SiC substrate includes a first main surface and a second main surface. The area of the first main surface facing the second main surface from 10 nm to 30 μm is the first surface layer, and the area of the second main surface facing the first main surface from 10 nm to 30 μm is the second surface layer. The intermediate layer is between the first surface layer and the second surface layer;

[0006] On the same axis, at any plane parallel to the first main surface or the second main surface, Smax1 represents the maximum absolute value of the radial stress in the first surface layer, Smax2 represents the maximum absolute value of the radial stress in the intermediate layer, Smax3 represents the maximum absolute value of the radial stress in the second surface layer, △S1 = Smax2 - Smax1, △S2 = Smax2 - Smax3, -15 MPa ≤ △S1 ≤ 10 MPa, -15 MPa ≤ △S2 ≤ 10 MPa;

[0007] Preferably, -14.9 MPa ≤ △S1 ≤ 7.7 MPa, -14.6 MPa ≤ △S2 ≤ 7.9 MPa.

[0008] The above △S1 represents the difference in the radial stress between the first surface layer and the intermediate layer, and △S2 represents the difference in the radial stress between the second surface layer and the intermediate layer. The closer the value of △S1 is to 0, the better the uniformity of the radial stress distribution between the first surface layer and the intermediate layer, and the better the quality of the substrate. The closer the value of △S2 is to 0, the better the uniformity of the radial stress distribution between the second surface layer and the intermediate layer, and the better the quality of the substrate. If both △S1 and △S2 are close to 0 at the same time, it means that the radial stress distribution of the substrate is uniform along the entire axis, and the quality of the substrate reaches the best.

[0009] Optionally, at any plane parallel to the first main surface in the first surface layer, the radial stress of the SiC substrate is -15 MPa to 15 MPa, and at any plane parallel to the second main surface in the second surface layer, the radial stress of the SiC substrate is -15 MPa to 15 MPa;

[0010] At any plane parallel to the first main surface or the second main surface in the intermediate layer, the radial stress of the SiC substrate is -10 MPa to 10 MPa.

[0011] Since the internal tensile and compressive stresses in the SiC substrate cause corresponding elongation and contraction changes in the crystal plane spacing d, when using Raman to measure stress, the Raman peak intensity will shift to a lower or higher frequency. When the substrate is internally subjected to tensile stress, the Raman peak shifts to a lower frequency, and the obtained stress value is positive. When the substrate is internally subjected to compressive stress, the Raman peak shifts to a higher frequency, and the obtained stress value is negative. Therefore, the positive and negative signs before the stress values in this application represent the internal stress direction of the substrate, and the absolute value of the value represents the magnitude of the stress. For example, when the radial stress in the first surface layer of the SiC substrate is -15 MPa and the radial stress in the second surface layer is -10 MPa, it means that the radial directions in the first surface layer and the second surface layer are compressive stresses, and the radial pressure in the first surface layer is greater than that in the second surface layer.

[0012] The first surface layer and the second surface layer are the surface stresses of the substrate. The thicknesses of the first surface layer and the second surface layer vary with different processing techniques such as substrate cutting, grinding, and polishing. The thinner the thicknesses of the first surface layer and the second surface layer, the smaller the radial stresses of the first surface layer and the second surface layer. The region of the first main surface facing the second main surface from 10 nm to 30 μm is the first surface layer. When the value of the above region is closer to 10 nm, the radial stress of the SiC substrate in the first surface layer is smaller, that is, closer to 0 MPa. When the value of the above region is closer to 30 μm, the radial stress of the SiC substrate in the first surface layer is larger, that is, closer to -15 MPa or 15 MPa. Similarly, the region of the second main surface facing the first main surface from 10 nm to 30 μm is the second surface layer. When the value of the above region is closer to 10 nm, the radial stress of the SiC substrate in the second surface layer is smaller, that is, closer to 0 MPa. When the value of the above region is closer to 30 μm, the radial stress of the SiC substrate in the second surface layer is larger, that is, closer to -15 MPa or 15 MPa.

[0013] Preferably, -5 MPa ≤ Smax3 - Smax1 ≤ 5 MPa. More preferably, -4.9 MPa ≤ Smax3 - Smax1 ≤ 5 MPa. This Smax3 - Smax1 represents the radial stress difference between the first surface layer and the second surface layer. The smaller this value, the better the uniformity of the radial stress distribution of the first surface layer and the second surface layer of the substrate.

[0014] Optionally, the diameter of the SiC substrate is 150 mm or more, preferably 200 mm or more.

[0015] Optionally, the radial stress includes radial absolute stress and radial relative stress;

[0016] At any plane parallel to the first main surface in the first surface layer, the radial absolute stress of the SiC substrate is -15 MPa to 15 MPa, and the radial relative stress of the SiC substrate is -15 MPa to 14.5 MPa, preferably -14.9 MPa to 14.5 MPa;

[0017] At any plane parallel to the second main surface in the second surface layer, the radial absolute stress of the SiC substrate is -15 MPa to 15 MPa, and the radial relative stress of the SiC substrate is -15 MPa to 14.5 MPa, preferably -14.7 MPa to 14.5 MPa;

[0018] At any plane parallel to the first main surface or the second main surface in the intermediate layer, the radial absolute stress of the SiC substrate is -10 MPa to 10 MPa, and the radial relative stress of the SiC substrate is -8 MPa to 8 MPa.

[0019] The absolute stress can reflect the difference between the substrate and a perfect defect-free SiC crystal, and is used to determine the stress level of the SiC substrate. However, since it is difficult to achieve a perfect SiC-free substrate with current technology, the relative stress can be used to judge the relative stress distribution within the substrate plane.

[0020] For example, when the absolute stress of the substrate is large and the relative stress is small, it indicates that there are more in-plane defects, but the stress distribution is uniform, the crystal quality is poor, and the quality uniformity in each region of the substrate is poor; if the absolute stress is small and the relative stress is large, the overall substrate quality is good, but there are abnormal quality deviations locally.

[0021] In this application, the reference value of the absolute stress is the reference stress calculated from the standard Raman peak position obtained according to the perfect lattice parameters of SiC, marked as 0; the relative stress is obtained by taking a reference value on the entire test plane and performing relevant numerical operations on the value of each test point with the reference value to obtain the relative stress value of the test point. The reference value includes, but is not limited to, any one of the average value, median, mode, and results calculated by other statistical functions of all stress values on the entire test plane.

[0022] Optionally, on the same axis, at any plane parallel to the first main surface or the second main surface, Smin1 represents the minimum absolute value of the radial stress in the first surface layer, Smin2 represents the minimum absolute value of the radial stress in the intermediate layer, Smin3 represents the minimum absolute value of the radial stress in the second surface layer, △S3 = Smin2 - Smin1, △S4 = Smin2 - Smin3, -5 MPa ≤ △S3 ≤ 5 MPa, -5 MPa ≤ △S4 ≤ 5 MPa;

[0023] Preferably, -5 MPa ≤ Smin3 - Smin1 ≤ 5 MPa.

[0024] More preferably, -4.8 MPa ≤ △S3 ≤ 5 MPa, -5 MPa ≤ △S4 ≤ 4.8 MPa, -4.5 MPa ≤ Smin3 - Smin1 ≤ 4.4 MPa

[0025] Optionally, an axial test is carried out by extending perpendicularly from any point on the first main surface into the SiC substrate. The axial stress of the SiC substrate in the first surface layer is -10 MPa to 10 MPa, the axial stress of the SiC substrate in the intermediate layer is -10 MPa to 10 MPa, and the axial stress of the SiC substrate in the second surface layer is -10 MPa to 10 MPa.

[0026] Optionally, the axial stress includes axial absolute stress and axial relative stress, and an axial test is carried out by extending perpendicularly from any point on the first main surface into the SiC substrate;

[0027] The axial absolute stress of the SiC substrate in the first surface layer is -10 MPa to 10 MPa, and the axial relative stress of the SiC substrate in the first surface layer is -8 MPa to 8 MPa, preferably -7.8 MPa to 7.9 MPa;

[0028] The axial absolute stress of the SiC substrate in the intermediate layer is -10 MPa to 10 MPa, and the axial relative stress of the SiC substrate in the intermediate layer is -8 MPa to 8 MPa, preferably -8.0 MPa to 7.8 MPa;

[0029] The axial absolute stress of the SiC substrate in the second surface layer is -10 MPa to 10 MPa, and the axial relative stress of the SiC substrate in the second surface layer is -8 MPa to 8 MPa, preferably -7.8 MPa to 8.0 MPa.

[0030] Optionally, an axial test is performed by extending perpendicularly from any point on the first main surface into the SiC substrate. Let S1 be the maximum axial stress in the first surface layer, S2 be the minimum axial stress in the first surface layer, △S5 = S1 - S2, and 0 MPa ≤ △S5 ≤ 15 MPa;

[0031] Let S3 be the maximum axial stress in the intermediate layer, S4 be the minimum axial stress in the intermediate layer, △S6 = S3 - S4, and 0 MPa ≤ △S6 ≤ 10 MPa;

[0032] Let S5 be the maximum axial stress in the second surface layer, S6 be the minimum axial stress in the second surface layer, △S7 = S5 - S6, and 0 MPa ≤ △S7 ≤ 15 MPa.

[0033] The above maximum axial stress and minimum axial stress refer to the true values of the axial stress. Compressive stress and tensile stress are distinguished axially. For example, on any axis, if the axial comprehensive stress in the intermediate layer is -5 - 1 MPa, then the maximum axial stress is 1 MPa, the minimum axial stress is -5 MPa, and △S6 is 6 MPa. The △S5, △S6, and △S7 represent the degree of change in the crystal plane spacing in the axial direction of the substrate in the first surface layer, intermediate layer, and second surface layer at the microscopic level. The smaller the △S5, △S6, and △S7, the smaller the change in the crystal plane spacing of the substrate in the axial direction.

[0034] Preferably, 0 MPa ≤ △S5 ≤ 14.9 MPa, 0 MPa ≤ △S7 ≤ 14.3 MPa.

[0035] Optionally, the crystal form of the SiC substrate is one of 2H-SiC, 4H-SiC, 6H-SiC, 3C-SiC, 15R-SiC, preferably 4H-SiC.

[0036] Optionally, the SiC substrate is a semi-insulating SiC substrate or a conductive SiC substrate.

[0037] Optionally, the curvature of the SiC substrate is -100 μm to 100 μm, preferably -50 μm to 50 μm, more preferably -11 μm to 15 μm.

[0038] Preferably, the deviation angle of the first main surface and / or the second main surface with respect to the {0001} plane is 4° or less.

[0039] According to another aspect of the present application, a SiC crystal with uniform three-dimensional direction stress distribution is provided. The thickness of the SiC crystal is not less than 0.35 mm. The SiC crystal includes an upper surface and a lower surface. In the region from the upper surface to the lower surface, the radial stress at any horizontal plane is -10 MPa to 10 MPa.

[0040] Preferably, the diameter of the SiC crystal is 150 mm or more, preferably 200 mm or more.

[0041] Optionally, when performing an axial test by extending downward from any point on the upper surface of the SiC crystal, the axial stress of the SiC crystal is -10 MPa to 10 MPa.

[0042] Preferably, the axial stress includes axial absolute stress and axial relative stress;

[0043] When performing an axial test by extending downward from any point on the upper surface of the SiC crystal, the axial absolute stress of the SiC crystal is -10 MPa to 10 MPa, and the axial relative stress of the SiC crystal is -8 MPa to 8 MPa, preferably -8 MPa to 7.8 MPa.

[0044] Optionally, the radial stress includes radial absolute stress and radial relative stress;

[0045] In the region from the upper surface to the lower surface of the SiC crystal, the radial absolute stress at any horizontal plane of the SiC crystal is -10 MPa to 10 MPa, and the radial relative stress at any horizontal plane of the SiC crystal is -8 MPa to 8 MPa.

[0046] The above absolute stress and relative stress have the same characteristics as those that can be reflected by the substrate absolute stress and relative stress.

[0047] Optionally, when performing an axial test by extending downward from any point on the upper surface of the SiC crystal, S7 is denoted as the maximum value of the axial stress of the SiC crystal, S8 is denoted as the minimum value of the axial stress of the SiC crystal, △S8 = S7 - S8, and 0 MPa ≤ △S8 ≤ 10 MPa.

[0048] The above maximum axial stress and minimum axial stress refer to the true values of the axial stress, distinguishing compressive stress and tensile stress in the axial direction. For example, on any axis, if the axial stress of the SiC crystal is -5 MPa to 5 MPa, then the maximum axial stress is 5 MPa, the minimum axial stress is -5 MPa, and △S8 is 10 MPa. This △S8 represents the degree of change in the crystal plane spacing of the crystal in the axial direction. The smaller △S8 is, the smaller the change in the crystal plane spacing of the crystal in the axial direction is proven.

[0049] Preferably, 0 MPa ≤ △S8 ≤ 6.3 MPa, and more preferably, 0 MPa ≤ △S8 ≤ 1.1 MPa.

[0050] According to another aspect of the present application, a method for preparing a SiC single crystal is provided, including the following steps:

[0051] (1) Add silicon carbide powder to a graphite crucible;

[0052] (2) Evacuate the inside of the furnace to below 10 -6 mbar, then introduce high-purity inert gas to 300 - 500 mbar, repeat this process 2 - 3 times, and finally evacuate the inside of the furnace to below 10 -6 mbar;

[0053] (3) Introduce high-purity inert gas into the furnace, raise the pressure to 10 - 100 mbar within 1 - 3 h, continuously introduce high-purity inert gas and keep the pressure constant;

[0054] (4) Crystal growth stage: While keeping the pressure constant, raise the temperature inside the furnace to the crystal growth temperature of 2200 K - 2800 K within 3 - 5 h, and the growth time is 30 - 150 h;

[0055] (5) After the crystal growth is completed, open the furnace and take out the graphite crucible to obtain the SiC crystal.

[0056] Optionally, the graphite crucible is coated with a TaC coating. The TaC coating is deposited on the surface of the graphite substrate, and through-holes are uniformly distributed in the TaC coating. The density of the through-holes is 160 - 310 per mm 2 . This TaC coating contains through-holes, which can improve the transmission rate of the silicon carbide raw material atmosphere while improving the uniformity of the temperature field during crystal growth, thereby increasing the crystal growth rate and reducing the internal stress of the crystal, obtaining a high-quality and low-stress silicon carbide crystal.

[0057] Optionally, the aperture of the through-hole is 2-7 μm, preferably 2.3-6.1 μm. This aperture can not only improve the transmission rate of the silicon carbide raw material atmosphere, but also not reduce the protection performance of the graphite substrate, avoid the edge stress generated by the crystal being extruded by the thermal expansion of the graphite substrate in the thermal field, and further reduce the stress in the crystal.

[0058] Optionally, the thickness of the TaC coating is 30-400 μm. The TaC grains in the TaC coating are arranged in a stacking fault arrangement, and the size of the TaC grains is 15-50 μm. The TaC grains in the TaC coating grow along the

[200] and

[220] directions. The growth direction of the TaC grains can improve the temperature resistance and heat chemical erosion resistance of the TaC coating, thereby reducing the interference of the graphite substrate on the crystal growth environment and improving the stability of the crystal environment.

[0059] The beneficial effects of this application include but are not limited to:

[0060] 1. The stress introduced during the SiC crystal growth process due to temperature gradient changes or changes in the crystal growth environment is the stress in the SiC substrate intermediate layer. The stresses in the first surface layer and the second surface layer of the SiC substrate are the stresses generated during the process of processing the SiC crystal into the SiC substrate. The stress distribution in the first surface layer, the second surface layer and the intermediate layer of the SiC substrate of this application is uniform and the stress value is very low, which proves that the quality of the SiC substrate is good and is beneficial to the production and processing of downstream products.

[0061] 2. This application tests the stress quantification of the SiC substrate, distinguishes the surface stress and the in-body stress in the SiC substrate, and can control the stress distribution of the SiC substrate within a reasonable range according to the different downstream products prepared by the SiC substrate, so as to expand the use range of the SiC substrate.

[0062] 3. According to the SiC substrate of this application, the three-dimensional stress distribution in the first surface layer, the second surface layer and the intermediate layer is uniform, which proves that the SiC substrate can be regarded as a stress homogeneous body, and the surface shape of the SiC substrate is also improved.

[0063] 4. This application uses the TaC coating with through-holes formed on the surface of the crucible, which can ensure the transmission of the raw material atmosphere during crystal growth while improving the uniformity of the temperature field, so it can be used to prepare silicon carbide crystals with low stress. The substrate prepared from this crystal can improve the crystal growth quality of the epitaxial wafer and subsequent crystals.

[0064] 5. According to the stress distribution of the SiC substrate in each layer of the present application, it can be adjusted according to the process parameters of crystal growth and / or substrate processing to prepare a high-quality SiC substrate. And through the quantitative test method of the present application, the detected stress also includes the stress in the substrate where lattice distortion exists and has not been released by defects, improving the detection accuracy of the stress in the SiC substrate and reflecting all the stress information of the entire SiC substrate. Description of the Drawings

[0065] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0066] Figure 1 It is a flow chart of Raman test stress related to Embodiment 1 of the present application.

[0067] Figure 2 It is a distribution diagram of axial peak intensities of a 4H-SiC substrate related to Embodiment 2 of the present application.

[0068] Figure 3 It is a schematic diagram of Raman axial test of an SiC substrate and a stress axial distribution diagram related to Embodiment 3 of the present application.

[0069] Figure 4 It is a morphological characterization diagram of the TaC coating in crucible No. 1 related to Embodiment 6 of the present application.

[0070] Figure 5 It is an XRD test diagram of the TaC coating and TaC in crucible No. 1 in Embodiment 6 of the present application. Detailed Embodiments

[0071] The present application will be described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0072] Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels.

[0073] The principle of using Raman to test the stress of the substrate in the following embodiments is as follows: The Raman spectrometer irradiates the surface of the substrate by converging a monochromatic laser of a certain wavelength through a series of optical paths by an objective lens. The interaction between the laser photons and the substrate lattice causes photon scattering. The occurrence of Raman scattering is related to the lattice vibration of the substrate itself. When there is residual stress in the sample, tensile and compressive stresses will cause the atomic bond lengths to elongate or shorten accordingly, resulting in a decrease or increase in the vibration frequency of the atoms, which is reflected in the Raman spectrum as the peak position of the characteristic peak of the substrate shifting to a lower or higher frequency, that is, there is a peak position shift.

[0074] Quantitative Test Method for Substrate Stress in Embodiment 1

[0075] (1) Calculation of Peak Position Offset and Stress Conversion Coefficient

[0076] First, use a single-crystal XRD diffractometer to test the silicon carbide substrate and analyze the substrate according to the reciprocal lattice space. Calculate the parameters of the standard sample 4H-SiC substrate and compare them with the standard parameters. Subsequently, according to Bragg's diffraction equation: 2dsinθ = nλ, where d is the interplanar spacing, θ is the diffraction half-angle, n is the diffraction order, and λ is the wavelength. By testing θ and d of different substrates, it can be known that the tensile and compressive stresses inside the crystal cause corresponding stretching and shrinking changes in the interplanar spacing d. According to different interplanar spacings d0 and d x , d x are divided into d1 and d2, where d0 is the theoretical interplanar spacing, d1 is the interplanar spacing after tensile stress, and d1 is greater than d0. d2 is the interplanar spacing after compressive stress, and d2 is less than d0. Calculate the difference in interplanar spacing △d at different positions, △d = d1 - d0 or △d = d0 - d2.

[0077] Obtain the actual peak position of the substrate through Raman testing, and calculate the peak position offset △v at different test points compared with the standard peak position; combine Hooke's law or the stress-strain formula to calculate the stress value σ of the silicon carbide substrate at different test points. Then, the ratio of the peak position offset to the stress value at different test points is the peak position offset and stress conversion coefficient μ, and its range is -125 to -2500.

[0078] The calculation formula of Hooke's law is σ / S = E×(△d / d0), where S is the area on which σ acts and is a fixed value. When Hooke's law is applicable to microscopic calculations, S is the microscopic area and can be counted as unit 1. E is the Young's modulus of the substrate and is a fixed parameter of the substrate. △d is the difference in interplanar spacing at different positions, d0 is the theoretical interplanar spacing, and σ is the stress value to be calculated.

[0079] The calculation formula of stress-strain is σ = E×△d, where E is the Young's modulus of the substrate and is a fixed parameter of the substrate. △d is the difference in interplanar spacing at different positions, and σ is the stress value to be calculated.

[0080] (2) Quantitative Testing Method for Substrate Stress

[0081] Reference Figure 1 , first set the Raman test points. It can be a single-point test or a Mapping scan of the entire substrate. Therefore, the single-point test is the setting of sporadic coordinate points, and the Mapping scan is from 10x10 to 50x50 and more points, and the appropriate test method can be selected according to the properties of the substrate to determine the Raman test coordinates of the silicon carbide substrate.

[0082] After that, output the test results, which include but are not limited to editable peak positions, peak intensity data, and Mapping.

[0083] Subsequently, peak fitting is performed on the output data. The fitting functions include but are not limited to Gaussian, Lorentz, GaussLor, AGauss, Aloren, and AGaussLor to obtain the precise peak position value and peak position offset. The peak position is accurate to more than 1 digit after the decimal point.

[0084] Finally, based on the peak position offset calculated in (1), the stress conversion coefficient μ, and the peak position offset △v obtained from the Raman test, the stress value of silicon carbide is calculated. The calculation formula is: σ (MPa) = μ × △v (cm -1 ), and finally, the stress test image of the substrate is output.

[0085] Example 2: Flatness Test of the Substrate Surface

[0086] Since a large amount of external mechanical stress acts on SiC during the process of preparing wafers from crystals through a series of processing, it is difficult to ensure that the surface is completely flat, that is, there is a certain degree of bending and warping. In order to eliminate the influence of the substrate surface flatness on the substrate surface stress and in-body stress tests, it is necessary to first perform a flatness test on the substrate. According to this flatness, equal-spacing focused tests are selected for the substrate surface stress, and equal-spacing focused tests or equal-focus plane tests are selected for the substrate in-body stress.

[0087] After the flatness test, it is necessary to use single-crystalline silicon to calibrate the tester. First, perform a Z-direction Mapping test on single-crystalline Si to confirm that it is a Gaussian distribution. Taking the surface of the single-crystalline Si substrate as the zero point, perform an axial Mapping test from -100 μm inside the single-crystalline Si substrate to +20 μm above the single-crystalline Si substrate to analyze the change in Raman signal intensity, the axial peak intensity distribution map of the single-crystalline Si substrate. Since the single-crystalline Si substrate is a non-transparent material, its peak intensity shows a Gaussian distribution with the surface zero point position as the axis of symmetry; then perform a surface focused single-point test on single-crystalline Si to make the Raman peak position of single-crystalline Si 520.70 cm -1 , at this time, it indicates that the instrument optical path has been calibrated.

[0088] Use the calibrated tester to perform a Z-direction axial test on the 4H-SiC substrate. The Raman laser ranges from -100 μm inside the 4H-SiC substrate to +20 μm above the 4H-SiC substrate. Figure 2It is the axial peak intensity distribution diagram of a 4H-SiC substrate. The 4H-SiC substrate and other silicon carbide substrates with transparent materials have the characteristic that Raman laser can penetrate into the interior of the silicon carbide substrate. As the incident depth of the Raman laser increases, the feedback signal gradually weakens. Other silicon carbide substrates include semi-insulating type, conductive type, and silicon carbide substrates with different crystal forms such as 3C, 4H, 15R, and 6H. Therefore, the Raman peak intensity of the silicon carbide substrate gradually decreases as the incident depth of the Raman laser into the interior of the silicon carbide substrate increases.

[0089] Through the autofocus function of the Raman device, the strongest peak of the test signal on the substrate surface can be automatically set and found, so that the curvature of the substrate surface can be measured with the help of this function. The specific method is as follows:

[0090] S1: First, ensure the level of the test platform. Select a fixed origin (0, 0) on the test platform and mark this point as the three-dimensional coordinate (0, 0, 0);

[0091] S2: Raise the objective lens to a height where it does not touch the substrate according to the substrate thickness. Automatically focus on any point to the position with the strongest test signal on the substrate surface and mark this position as (a, b, c). Then adjust the Raman laser to move down by a distance of H, and the focus position is (a, b, c - H);

[0092] S3: Adjust the Raman laser test position to (0, 0, c - H) for an equal-focus plane test to obtain a two-dimensional peak intensity scan map of the substrate surface. According to Figure 2 the peak intensity distribution relationship of the silicon carbide substrate, the distance between the focus plane of the Raman laser and the surface of the silicon carbide substrate can be obtained, so that the in-plane bending condition of the substrate can be obtained, and the in-plane bending distribution map of the substrate can be output.

[0093] Example 3 Axial Test to Distinguish Substrate Surface Stress and Body Stress

[0094] Due to the influence of the temperature field and the introduced inclusions during the crystal growth process of the substrate, there are thermal stress and residual stress inside the crystal. And after the crystal undergoes a series of cutting, grinding, and polishing to obtain the substrate, the above-mentioned processing process of forming the substrate from the crystal will cause surface lattice distortion, thus generating surface stress. In order to further distinguish the surface stress and body stress of the substrate, according to the light transmission characteristics of silicon carbide, an axial test is performed on the substrate, that is, Z-direction Mapping. Taking the substrate surface as the zero point, the test range of the axial test is from -150 μm to -30 μm inside the substrate to above the substrate surface.

[0095] The test principle diagram is as Figure 3As shown in (a), that is, the laser spot gradually focuses upward from within the substrate to the damage stress extension layer, further to the surface damage layer, and then continues to focus upward into the air to determine the thicknesses of the surface damage layer and the damage stress extension layer of the substrate. Taking the substrate surface as the zero point, the test range for axial testing is that the Raman laser spot gradually moves upward from -100 μm inside the substrate to 30 μm above the substrate surface. Figure 3 (b) is the axial stress distribution map of five-point testing on the top, bottom, left, right, and middle of the substrate. The trends of the five points on the substrate are the same, and there are only differences in the maximum negative stress at the surface damage.

[0096] Figure 3 In (b), from -100 μm to -30 μm upward inside the substrate, at this time the stress fluctuates up and down along the horizontal line, representing that the internal stress in the body is in a uniform state; when the laser spot focuses on the damage stress extension layer, the stress curve starts to show a downward trend at -30 μm, and the downward trend of the stress gradually increases. When approaching the zero point of the substrate surface, the maximum negative stress is reached, and at this time it represents the stress value of the surface damage layer; finally, the laser spot continues to move upward and gradually moves away from the substrate surface into the air, and the stress shows a rapid rise to chaotic fluctuations. Therefore, the thicknesses of the surface damage layer and the damage stress extension layer of the substrate can be determined according to the axial test results of the substrate, so as to distinguish the stress in the substrate into surface stress and internal stress, providing a theoretical basis for the subsequent quantitative testing of the surface stress and internal stress in the substrate.

[0097] Example 4 Quantitative Testing of the Internal Stress of the Substrate

[0098] During the PVT crystal growth process of silicon carbide, residual stress exists in the crystal due to the change in temperature gradient and the intrusion of inclusions. Different from the surface processing stress, the internal stress is located at a certain depth from the surface and reflects the thermal stress and residual stress during crystal growth. And during the process of preparing the substrate from the crystal through a series of processing, the silicon carbide has experienced a large amount of external mechanical stress, making it difficult to ensure that the surface is completely flat, that is, there is a certain degree of bending and warping on the substrate surface. According to the method for measuring the surface curvature of the substrate obtained by Raman testing in Example 2, this example combines the physical properties of silicon carbide and involves a method for quantitatively characterizing its internal stress that is not affected by the surface bending and warping.

[0099] According to the physical property of silicon carbide having light transmissibility, the method for quantitatively characterizing the internal stress of the substrate by Raman is divided into equally spaced focusing testing and equal focusing plane testing, as follows:

[0100] 1. Equally Spaced Focusing Testing

[0101] In the equally spaced focusing test mode, the focusing depth (d) of the Raman laser at different test points inside the substrate remains unchanged. First, calculate the penetration depth (Dp) of the Raman laser according to the following formula:

[0102]

[0103] In the above formula, Dp is the penetration depth of Raman excitation in the sample, α is the absorption coefficient, λ is the laser wavelength, and k is the extinction coefficient. The specific value of the penetration depth (Dp) is calculated according to the above formula. To select an appropriate focusing depth (d), the requirement to be satisfied is that the penetration depth (Dp) is greater than the focusing depth (d). And since the internal stress is being tested, the focusing depth d needs to be greater than the thicknesses of the surface damage layer and the damaged stress extension layer obtained in Example 3.

[0104] After that, the spot diameter (D) of the Raman laser is calculated according to the following formula:

[0105] where λ is the laser wavelength and Na is the numerical aperture of the device.

[0106] This spot diameter (D) is the minor-axis diameter of the laser spot. The larger this value is, the stronger the peak intensity of Raman at each test position and the more impurity peaks there are, which affects the detection accuracy of Raman. When λ is determined, if the value of Na is large, the peak intensity is very weak, which also affects the Raman detection accuracy. Therefore, appropriate λ and Na need to be selected to improve the accuracy of this test method.

[0107] According to the characteristics of the silicon carbide material, the peak intensity reaches the strongest when the laser is focused on the substrate surface, as Figure 2 shown. Therefore, using the autofocus function of the Raman tester can achieve laser focusing on the substrate surface. Subsequently, according to the determined focusing depth (d) above, equal-spacing focusing tests can be carried out at different test points on the substrate, that is, the distance between the focusing plane and the substrate surface is always equal. This method is not affected by the bending and warping of the substrate surface, and keeps the obtained Raman peak intensity at the maximum value in the axial direction of the test point. According to the stress quantitative test method of Example 1, the in-body stress test result diagram of the substrate is obtained.

[0108] 2. Equal-focusing plane test

[0109] In the equal-focusing plane test method, the focusing depth (d) at which the Raman laser spot is focused inside the substrate changes at different test points, and the laser spot is focused on the same plane inside the substrate at different test points. The penetration depth (Dp) of the Raman laser is calculated according to the same formula as in the equal-spacing focusing test, and an appropriate focusing depth (d) is selected by the same selection method.

[0110] Since the focal planes are equal in this test method, combined with the characteristics of silicon carbide, when the laser is focused on the substrate surface, the peak intensity reaches the strongest and the signal gradually attenuates as the focal depth increases. And according to the effective signal-to-noise ratio measured by the Raman tester, it is found that the effective signal-to-noise ratio is inversely negatively correlated with the Raman laser focal depth (d). Therefore, in this test method, the focal depth (d) at different test points needs to be combined with the curvature of the substrate to obtain the effective peak position offset through the stress quantitative test method of Example 1, thereby reducing the error of in-vivo stress testing.

[0111] Through the above two test methods of equal-spacing focusing and equal focal plane, the peak position offsets inside the substrate are obtained respectively, and the in-vivo stress distribution of the substrate is calculated. The difference between the in-vivo stress values of the substrate calculated by the two methods of equal-spacing focusing test and equal focal plane test ≤ 0.2 Mpa, and the difference between the peak position values obtained by the two methods of equal-spacing focusing test and equal focal plane test < 0.0005 cm -1 . The above two methods can verify the accuracy of the quantitative detection method of this application, and the accuracy of this test method can be further improved according to the settings of the focal depth and spot diameter.

[0112] This in-vivo stress includes in-vivo absolute stress and in-vivo relative stress. Taking 4H-SiC as an example:

[0113] For the in-vivo absolute stress, the difference between the measured peak position of the 4H-SiC peak at the determined reduced wave vector and the standard peak position is used, such as FTO(2 / 4). The calculation formula for the in-vivo absolute stress is:

[0114] σabsolute = μ × (v 实际 - V FTO(2 / 4) ), where σ is in MPa, and the units of v 实际 and V FTO(2 / 4) are in cm -1 , where v 实际 is the actual FTO(2 / 4) peak position at the substrate test point, and V FTO(2 / 4) is the FTO(2 / 4) standard peak position of the substrate;

[0115] For the in-vivo relative stress, the difference between the measured values of the same reduced wave vector peak positions of any two points in the plane of the SiC substrate, such as the FTO(2 / 4) peak position, is used. The calculation formula for the in-vivo relative stress is:

[0116] σrelative = μ × (v (x1,y1) - V (x2,y2) ), where σ is in MPa, and the units of v (x1,y1) and V (x2,y2) are in cm -1 , where v (x1,y1) is the actual FTO(2 / 4) peak position at the substrate test point, and V (x2,y2)The actual FTO (2 / 4) peak position of the substrate relative point. Calculate the relative stress value of the test point according to the above calculation formula. If the relative value of σ is positive, it indicates that the stress of the test point relative to the relative point is tensile stress. If the relative value of σ is negative, it indicates that the stress of the test point relative to the relative point is compressive stress.

[0117] Example 5 Quantitative testing of the surface stress of the substrate

[0118] According to the axial testing in Example 3, determine the thickness of the surface damaged layer of the substrate. Since the thickness of the surface damaged layer of the substrate is less than the surface curvature of the substrate, there is a situation where the laser spot falls into the interior of the substrate in the equal-focus plane testing method, resulting in errors in the test results of the surface stress of the substrate. Therefore, the equal-spacing focusing testing method is mainly used in the quantitative testing of the surface stress. In this testing method, the focusing depth (d) of the Raman laser at different test points on the surface damaged layer of the substrate remains unchanged.

[0119] First, calculate the penetration depth (Dp) of the Raman laser and the spot diameter (D) of the Raman laser according to the same formula as in Example 4. Select a suitable focusing depth (d), and the requirements to be met are that the penetration depth (Dp) is greater than the focusing depth (d), and the Raman laser spot is located in the surface damaged layer.

[0120] According to the determined focusing depth (d) and spot diameter (D) above, by debugging the parameters of the Raman tester, use the autofocus function to focus the laser on the surface of the substrate, so that the surface damaged layer introduced by processing of the substrate falls within the laser spot range, thereby realizing equal-spacing focusing testing at different test points of the substrate, that is, the distance between the focusing plane and the surface of the substrate is always equal. This method is not affected by the bending and warping of the substrate surface, and keeps the obtained Raman peak intensity at the maximum value in the axial direction of the test point. According to the stress quantitative testing method in Example 1, obtain the test results of the surface stress of the substrate.

[0121] The methods for quantitatively testing the surface stress and in-body stress of the substrate in Example 4 and Example 5 can eliminate the influence of the bending and warping of the substrate surface, realize the quantitative testing of the surface stress and in-body stress of the substrate, and improve the testing accuracy of this testing method; and can play a feedback role in adjusting the process parameters of each process of crystal growth and / or substrate processing, so as to optimize the process parameters of the crystal growth process or substrate processing process to prepare a high-quality substrate.

[0122] Example 6

[0123] This example relates to a method for preparing a TaC coating with a through-hole, including the following steps:

[0124] (1) Prepare the slurry: Mix 25 - 40 parts of TaC powder, 5 - 8 parts of Ta2O5, 20 - 35 parts of solvent, 15 - 25 parts of cosolvent, 1 - 3 parts of air-entraining agent, 2 - 5 parts of thickener, 5 - 15 parts of straight-chain saturated aliphatic hydrocarbon, and 1 - 3 parts of carbon powder, and stir at 700 - 800 r / min for 2 - 3 h to obtain a slurry containing TaC;

[0125] (2) Spray the slurry onto the surface of the graphite substrate, heat up to 60 - 80 °C, maintain for 2 - 4 h for bubble rupture, and then dry at 180 - 220 °C for 8 - 12 h; sinter at 700 - 900 mbar and 500 - 700 °C for 3 - 5 h; then increase the pressure to 1000 - 1100 mbar and the temperature to 1600 - 1800 °C, sinter for 8 - 10 h; then adjust the pressure to 145 - 155 kPa and the temperature to 2200 - 2400 °C, sinter for 14 - 16 h, and finally cool to room temperature and normal pressure within 15 - 25 h to obtain a TaC coating with through-type through holes.

[0126] Prepare crucibles 1# - 8# and comparative crucibles D1# - D3# according to the above preparation method, as follows:

[0127] Crucible 1#

[0128] (1) Prepare the slurry: Mix 32.7 parts of TaC powder, 6 parts of Ta2O5, 25 parts of ethanol, 20 parts of tetrahydrofuran, 1.5 parts of saponin air-entraining agent, 3.5 parts of cellulose ether, 10 parts of straight-chain saturated aliphatic hydrocarbon, and 1.3 parts of carbon powder, and stir at 700 r / min for 2.5 h to obtain a slurry containing TaC;

[0129] (2) Electrostatically spray the slurry in step (1) onto the surface of the graphite substrate, heat up to 70 °C, maintain for 3 h for bubble rupture, dry at 200 °C for 10 h, and then sinter: sinter at 800 mbar and 600 °C for 4 h; then increase the pressure to 1000 mbar and the temperature to 1700 °C, sinter for 9 h; then adjust the pressure to 150 kPa and the temperature to 2300 °C, sinter for 15 h, and finally cool to room temperature and normal pressure within 20 h to obtain crucible 1#.

[0130] Crucible 2#

[0131] (1) Prepare the slurry: Mix 25 parts of TaC powder, 5 parts of Ta2O5, 20 parts of ethanol, 15 parts of tetrahydrofuran, 1 part of saponin air-entraining agent, 2 parts of cellulose ether, 5 parts of straight-chain saturated aliphatic hydrocarbon, and 1 part of carbon powder, and stir at 800 r / min for 2 h to obtain a slurry containing TaC;

[0132] (2) Electrostatically spray the slurry from step (1) onto the surface of the graphite substrate, heat up to 60 °C, maintain for 4 h for bubble bursting, dry at 180 °C for 12 h, and then carry out sintering: sinter at 700 mbar and 500 °C for 5 h; subsequently increase the pressure to 1000 mbar, raise the temperature to 1600 °C, sinter for 10 h; then adjust the pressure to 145 kPa, raise the temperature to 2200 °C, sinter for 16 h, and finally reduce the temperature and pressure to room temperature and atmospheric pressure within 15 h to obtain crucible 2#.

[0133] Crucible 3#

[0134] (1) Prepare the slurry: Mix 40 parts of TaC powder, 8 parts of Ta2O5, 35 parts of ethanol, 25 parts of tetrahydrofuran, 3 parts of saponin-type air-entraining agent, 5 parts of cellulose ether, 15 parts of straight-chain saturated aliphatic hydrocarbon and 3 parts of carbon powder, and stir at 700 r / min for 3 h to obtain a slurry containing TaC;

[0135] (2) Electrostatically spray the slurry from step (1) onto the surface of the graphite substrate, heat up to 80 °C, maintain for 2 h for bubble bursting, dry at 220 °C for 8 h, and then carry out sintering: sinter at 900 mbar and 700 °C for 3 h; subsequently increase the pressure to 1100 mbar, raise the temperature to 1800 °C, sinter for 8 h; then adjust the pressure to 155 kPa, raise the temperature to 2400 °C, sinter for 14 h, and finally reduce the temperature and pressure to room temperature and atmospheric pressure within 25 h to obtain crucible 3#.

[0136] Crucible 4#

[0137] The difference between this example and crucible 1# is that in step (1), after mixing the raw materials, stir at 700 r / min for 5 min, and the other conditions are the same as those of crucible 1# to obtain TaC coating 4#.

[0138] Crucible 5#

[0139] The difference between this example and crucible 1# is that in step (2), electrostatically spray the slurry from step (1) onto the surface of the graphite substrate, heat up to 200 °C, maintain for 13 h for bubble bursting and drying, and then carry out sintering, and the other conditions are the same as those of crucible 1# to obtain crucible 5#.

[0140] Crucible 6#

[0141] The difference between this example and crucible 1# is that in step (2), the sintering is as follows: sinter at 400 mbar and 400 °C for 4 h; subsequently increase the pressure to 1000 mbar, raise the temperature to 1700 °C, sinter for 9 h; then adjust the pressure to 150 kPa, raise the temperature to 2300 °C, sinter for 15 h, and finally reduce the temperature and pressure to room temperature and atmospheric pressure within 20 h, and the other conditions are the same as those of crucible 1# to obtain crucible 6#.

[0142] Crucible 7#

[0143] The difference between this example and Crucible 1# is that in step (2), the sintering is as follows: sintering is carried out at 800 mbar and 600 °C for 4 h; then the pressure is increased to 1000 mbar, the temperature is increased to 1200 °C, and sintering is carried out for 9 h; then the pressure is adjusted to 150 kPa, the temperature is increased to 2300 °C, and sintering is carried out for 15 h. Finally, it is cooled to room temperature and atmospheric pressure within 20 h, and the other conditions are the same as those of Crucible 1#, that is, Crucible 7# is obtained.

[0144] Crucible 8#

[0145] The difference between this example and Crucible 1# is that in step (2), the sintering is as follows: sintering is carried out at 800 mbar and 600 °C for 4 h; then the pressure is increased to 1000 mbar, the temperature is increased to 1700 °C, and sintering is carried out for 9 h; then the pressure is adjusted to 120 kPa, the temperature is increased to 2500 °C, and sintering is carried out for 15 h. Finally, it is cooled to room temperature and atmospheric pressure within 20 h, and the other conditions are the same as those of Crucible 1#, that is, Crucible 8# is obtained.

[0146] Comparative Crucible D1#

[0147] Compared with Crucible 1#, in this comparative example, a TaC coating is prepared by the CVD method, specifically as follows:

[0148] Put the graphite substrate into a chemical vapor deposition furnace, evacuate to below 50 Pa, then heat up to 1200 °C, and introduce a mixed gas composed of ethane, TaCl5, H2, and the carrier gas argon. The mixed gas enters the deposition furnace at a stable flow rate, and the furnace pressure is maintained at 5000 Pa. First, control the molar ratio of TaCl5 to ethane gas to be 1.2:1 to form a transition layer with a thickness of 50 μm; then control the molar ratio of TaCl5 to ethane gas to be 3:1 to form a TaC coating with a thickness of 60 μm, that is, Comparative Crucible D1# is obtained.

[0149] Comparative Crucible D2#

[0150] Compared with Crucible 1#, in this comparative example, the raw materials in the slurry of step (1) are different: BYK defoamer is used to replace the saponin air-entraining agent, and the other conditions are the same as those of Crucible 1#, that is, Comparative Crucible D2# is obtained.

[0151] Comparative Crucible D3#

[0152] Compared with Crucible 1#, in this comparative example, the raw materials in the slurry of step (1) are different: TaCl5 is used to replace Ta2O5, and the other conditions are the same as those of Crucible 1#, that is, Comparative Crucible D3# is obtained.

[0153] Perform cross-sectional SEM testing and EDS energy spectrum analysis on the prepared Crucibles 1# - 8# and Comparative Crucibles D1# - D3#. FromFigure 4 It can be seen from Figure 4 (a) shows the microscopic morphology of a TaC coating with through - holes prepared. The surface is uniformly distributed with holes having similar morphologies and sizes; Figure 4 (b) shows the bubble morphology photographed during the preparation of the TaC coating. It can be clearly seen that the bubble sizes are uniform, so that a TaC coating with a through - hole morphology is obtained during preparation, and its through - holes are also uniformly distributed; Figure 4 (c) shows that the coating is polished until the base graphite is exposed, and holes can still be seen at this time. Therefore, it is proved that the formed holes are through - type through - holes; Figure 4 (d) shows the cross - section SEM and EDS Mapping diagrams of the coating demo. This image can clearly show the distribution of TaC and the penetration of the holes, and it is determined to be a Ta - containing coating by EDS. From Figure 5 it can be seen that the TaC grains of the TaC coating grow along the

[200] and

[220] directions. The thickness of the formed TaC coating, the average pore diameter of the through - type through - holes in the TaC coating, the density, and the size of the TaC grains are measured, and the test results are shown in Table 1;

[0154] Table 1

[0155]

[0156] High - temperature erosion and thermochemical erosion experiments are carried out on the above - prepared crucibles 1# - 8# and the comparative crucibles D1# - D3# to simulate the growth environment of the third - generation semiconductor SiC crystal by the PVT method. The crucibles 1# - 8# and the comparative crucibles D1# - D3# are maintained at 2300 °C and eroded in a SiC atmosphere for 100 h. The test results are shown in Table 2:

[0157] Table 2

[0158] Sample Weight before experiment (g) Weight after experiment (g) Erosion weight loss rate (%) Crucible 1# 753 702 6.8 Crucible 2# 714 639 10.5 Crucible 3# 742 701 5.5 Crucible 4# 747 714 4.4 Crucible 5# 760 721 5.1 Crucible 6# 741 708 4.5 Crucible 7# 755 716 5.2 Crucible 8# 749 698 6.8 Comparative crucible D1# 797 769 3.5 Comparative crucible D2# 761 707 4.1 Comparative crucible D3# 759 704 6.5

[0159] In Table 2, the erosion weight loss rate = [(weight before experiment - weight after experiment) / weight before experiment] × 100%. The above high - temperature erosion and thermochemical erosion experiments prove that the TaC coating of this embodiment can improve the protection performance of the graphite substrate, extend the tolerance and corrosion resistance of the TaC coating, and thus extend the service life of the crucible.

[0160] Example 7

[0161] This embodiment relates to a method for preparing a SiC single - crystal crystal, including the following steps:

[0162] (1) Add silicon carbide powder to the crucible;

[0163] (2) Vacuum the furnace body to 10 -6Below mbar, and then introduce high-purity inert gas to 300 - 500 mbar. Repeat this process 2 - 3 times, and finally evacuate the vacuum in the furnace body to 10 -6 mbar or below;

[0164] (3) Introduce high-purity inert gas into the furnace body, and raise the pressure to 10 - 100 mbar within 1 - 3 h. Continuously introduce high-purity inert gas and keep the pressure constant;

[0165] (4) Crystal growth stage: Without changing the pressure, raise the temperature in the furnace body to the crystal growth temperature of 2200K - 2800K within 3 - 5 h, and the growth time is 30 - 150 h;

[0166] (5) After the single crystal growth is completed, open the furnace body and take out the graphite crucible to obtain the SiC single crystal.

[0167] Add equal amounts of silicon carbide powder to crucibles 1# - 3# prepared in Example 6 and comparative crucibles D1# - D3# respectively; Evacuate the vacuum in the furnace body to 10 -6 mbar or below, then introduce high-purity inert gas to 300 mbar. Repeat this process 3 times, and finally evacuate the vacuum in the furnace body to 10 -6 mbar or below; Introduce high-purity inert gas into the furnace body, raise the pressure to 20 mbar within 1 h, continuously introduce high-purity inert gas and keep the pressure constant; Crystal growth stage: Without changing the pressure, raise the temperature in the furnace body to the single crystal growth temperature of 2300K within 3 h, and the growth time is 80 h; After the single crystal growth is completed, open the furnace body and take out the graphite crucible to obtain SiC single crystals 1# - 3# and comparative SiC single crystals D1# - D3# respectively. Use the testing methods of Examples 1 - 4 to conduct radial and axial stress tests on the SiC single crystals. Since the SiC single crystals are relatively thick, the SiC single crystals can be sliced, and in vivo stress tests are conducted on each SiC substrate slice, so as to know the axial stress differences of the SiC single crystals and the radial stress differences of the SiC single crystals at different axial positions. The test results are shown in Table 3 below:

[0168] Table 3

[0169] Sample Radial stress (MPa) Axial stress (MPa) △S8 (MPa) SiC single crystal 1# -3.1～3.6 -1.3～1.7 0～1.1 SiC single crystal 2# -7.8～8.0 -8.0～7.5 0～6.3 SiC single crystal 3# -8.0～7.9 -7.6～7.8 0～10.0 Comparative SiC single crystal D1# -15.0～15.5 -13.7～14.5 0～15.4 Comparative SiC single crystal D2# -12.6～13.1 -10.2～12.3 0～13.7 Comparative SiC single crystal D3# -7.4～11.8 -6.6～10.4 0～11.2

[0170] Example 8

[0171] This example relates to the preparation of an SiC substrate, including the following steps:

[0172] (1) Cut the SiC single crystal and slice it at a cutting speed of 0.005 mm / s to obtain the cut wafers;

[0173] (2) The cut wafers were passed through a main disk with a rotation speed of 75 r / min, using W10 diamond powder and a load of 0.3 kg / cm 2 grinding to obtain a ground wafer;

[0174] (3) The ground wafer was passed through a main disk with a rotation speed of 80 r / min, using diamond powder with a particle size of W0.5 and a load of 0.5 kg / cm 2 Mechanical polishing and main disk speed 50r / min, ceramic disk speed 35r / min, chemical mechanical polishing liquid as polishing material, polishing pressure 0.15kg / cm 2 The SiC substrate was obtained after chemical polishing.

[0175] The SiC single crystal crystals 1#-3# prepared in Example 7 were subjected to the above steps of cutting, grinding, mechanical polishing and chemical mechanical polishing to obtain SiC substrates 1#-3#, and the SiC single crystal crystal 1# was sliced ​​at a cutting speed of 0.003 mm / s; grinding: main disk speed 69 r / min, W10 particle size diamond powder, load 0.35 kg / cm 2 The ground wafer was passed through a main disk at a speed of 49 r / min, using W0.5 powder size diamond powder and a load of 0.5 kg / cm 2 Mechanical polishing and main disk speed 50r / min, ceramic disk speed 37r / min, chemical mechanical polishing liquid as polishing material, polishing pressure 0.18kg / cm 2 Chemical polishing was performed to obtain SiC substrate 4#, and the above SiC substrates 1#-4# were tested using the methods of Examples 1-5, and the results are shown in Tables 4 and 5. It can be seen from Tables 4 and 5 that the stress of the first surface layer and the second surface layer is basically the same, and the stress distribution of the middle layer is more uniform.

[0176] Table 4

[0177]

[0178] Table 5

[0179]

[0180] The stress values in Table 3-5 all refer to relative stress values. In this application, the positive and negative signs of the stress values represent whether the substrate is subjected to tensile stress or compressive stress. The values of △S1 and △S2 in Table 4 are the results calculated using the relative stress values. When using absolute stress to characterize △S1 and △S2, the requirements of -15MPa ≤ △S1 ≤ 10MPa and -15MPa ≤ △S2 ≤ 10MPa can be met. In the prior art, when describing and evaluating the stress state of a substrate, it is often obtained by subtracting the minimum value from the maximum value among the above stress values to reflect the stress state of the substrate. For example, if the axial stress of the first surface layer of the SiC substrate 1# is -5.2 - 7.8, when generally representing the axial stress of the first surface layer of this SiC substrate 1# in the art, it can also be described as the stress value being 13MPa.

[0181] The data in the above Tables 3-5 are only the SiC substrates and SiC crystals prepared using the crucibles 1#-3# and the comparative crucibles D1#-D3# prepared in Example 6. When using the same crystal growth and processing methods in Examples 7 and 8 and using the crucibles 4#-8# to prepare SiC crystals and SiC substrates, and when using absolute stress to characterize the parameters of the crystals and substrates in Tables 3-5, the crystals can meet the requirements of the axial absolute stress being -10MPa to 10MPa, the axial relative stress being -8MPa to 8MPa; the radial absolute stress at any horizontal plane of the crystal being -10MPa to 10MPa, the radial relative stress being -8MPa to 8MPa; and 0MPa ≤ △S8 ≤ 10MPa.

[0182] The substrate can meet the requirements of -15MPa ≤ △S1 ≤ 10MPa, -15MPa ≤ △S2 ≤ 10MPa; -5MPa ≤ Smax3 - Smax1 ≤ 5MPa; the radial absolute stress of the SiC substrate in the first surface layer being -15MPa to 15MPa, the radial relative stress being -15MPa to 14.5MPa; the radial absolute stress of the SiC substrate in the second surface layer being -15MPa to 15MPa, the radial relative stress being -15MPa to 14.5MPa; the radial absolute stress of the SiC substrate in the intermediate layer being -10MPa to 10MPa, the radial relative stress being -8MPa to 8MPa; -5MPa ≤ △S3 ≤ 5MPa, -5MPa ≤ △S4 ≤ 5MPa, -5MPa ≤ Smin3 - Smin1 ≤ 5MPa; the axial stress of the SiC substrate in the first surface layer being -10MPa to 10MPa, the axial stress of the SiC substrate in the intermediate layer being -10MPa to 10MPa, the axial stress of the SiC substrate in the second surface layer being -10MPa to 10MPa; 0MPa ≤ △S5 ≤ 15MPa, 0MPa ≤ △S6 ≤ 10MPa, 0MPa ≤ △S7 ≤ 15MPa.

[0183] As described above, these are only the embodiments of the present application. The protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A SiC substrate with uniform stress distribution in three-dimensional directions, characterized in that, The thickness of the SiC substrate is not less than 100 μm. The SiC substrate includes a first major surface and a second major surface. The region of the first major surface facing the second major surface with a thickness of 10 nm to 30 μm is the first surface layer. The region of the second major surface facing the first major surface with a thickness of 10 nm to 30 μm is the second surface layer. The layer between the first surface layer and the second surface layer is the intermediate layer; On the same axis, at any plane parallel to the first major surface or the second major surface, Smax1 represents the maximum absolute value of the radial stress in the first surface layer, Smax2 represents the maximum absolute value of the radial stress in the intermediate layer, Smax3 represents the maximum absolute value of the radial stress in the second surface layer, △S1 = Smax2 - Smax1, △S2 = Smax2 - Smax3, -15 MPa ≤ △S1 ≤ 10 MPa, -15 MPa ≤ △S2 ≤ 10 MPa.

2. The SiC substrate according to claim 1, wherein At any plane parallel to the first major surface in the first surface layer, the radial stress of the SiC substrate is -15 MPa to 15 MPa; At any plane parallel to the second major surface in the second surface layer, the radial stress of the SiC substrate is -15 MPa to 15 MPa; At any plane parallel to the first major surface or the second major surface in the intermediate layer, the radial stress of the SiC substrate is -10 MPa to 10 MPa; The diameter of the SiC substrate is more than 150 mm.

3. The SiC substrate according to claim 2, wherein -5 MPa ≤ Smax3 - Smax1 ≤ 5 MPa.

4. The SiC substrate according to claim 1, wherein The radial stress includes the absolute radial stress and the relative radial stress; At any plane parallel to the first major surface in the first surface layer, the absolute radial stress of the SiC substrate is -15 MPa to 15 MPa, and the relative radial stress of the SiC substrate is -15 MPa to 14.5 MPa; At any plane parallel to the second major surface in the second surface layer, the absolute radial stress of the SiC substrate is -15 MPa to 15 MPa, and the relative radial stress of the SiC substrate is -15 MPa to 14.5 MPa; At any plane parallel to the first major surface or the second major surface in the intermediate layer, the absolute radial stress of the SiC substrate is -10 MPa to 10 MPa, and the relative radial stress of the SiC substrate is -8 MPa to 8 MPa.

5. The SiC substrate according to claim 1, wherein, On the same axis, at any plane parallel to the first major surface or the second major surface, Smin1 represents the minimum absolute value of the radial stress in the first surface layer, Smin2 represents the minimum absolute value of the radial stress in the intermediate layer, Smin3 represents the minimum absolute value of the radial stress in the second surface layer, △S3 = Smin2 - Smin1, △S4 = Smin2 - Smin3, -5 MPa ≤ △S3 ≤ 5 MPa, -5 MPa ≤ △S4 ≤ 5 MPa.

6. The SiC substrate according to claim 5, characterized in that, -5 MPa ≤ Smin3 - Smin1 ≤ 5 MPa.

7. The SiC substrate according to claim 1, characterized in that, Axial tests are carried out by extending vertically from any point on the first main surface into the SiC substrate. The axial stress of the SiC substrate in the first surface layer is -10 MPa to 10 MPa, the axial stress of the SiC substrate in the intermediate layer is -10 MPa to 10 MPa, and the axial stress of the SiC substrate in the second surface layer is -10 MPa to 10 MPa.

8. The SiC substrate according to claim 1, wherein Axial tests are carried out by extending vertically from any point on the first main surface into the SiC substrate. Let S1 be the maximum axial stress in the first surface layer, S2 be the minimum axial stress in the first surface layer, and △S5 = S1 - S2, where 0 MPa ≤ △S5 ≤ 15 MPa; Let S3 be the maximum axial stress in the intermediate layer, S4 be the minimum axial stress in the intermediate layer, and △S6 = S3 - S4, where 0 MPa ≤ △S6 ≤ 10 MPa; Let S5 be the maximum axial stress in the second surface layer, S6 be the minimum axial stress in the second surface layer, and △S7 = S5 - S6, where 0 MPa ≤ △S7 ≤ 15 MPa.

9. A SiC crystal with uniform stress distribution in three-dimensional directions, characterized in that, The thickness of the SiC crystal is not less than 0.35 mm. The SiC crystal includes an upper surface and a lower surface. In the region from the upper surface to the lower surface, the radial stress at any horizontal plane is -10 MPa to 10 Mpa.

10. The SiC crystal according to claim 9, wherein, The diameter of the SiC crystal is more than 150 mm.

11. The SiC crystal according to claim 9, wherein, Axial tests are carried out by extending downward from any point on the upper surface of the SiC crystal. The axial stress of the SiC crystal is -10 MPa to 10 MPa.

12. The SiC crystal according to claim 11, wherein The axial stress includes axial absolute stress and axial relative stress; Axial tests are carried out by extending downward from any point on the upper surface of the SiC crystal. The axial absolute stress of the SiC crystal is -10 MPa to 10 MPa, and the axial relative stress of the SiC crystal is -8 MPa to 8 MPa.

13. The SiC crystal according to claim 9, characterized in that, The radial stress includes radial absolute stress and radial relative stress; In the region from the upper surface to the lower surface, the radial absolute stress at any horizontal plane of the SiC crystal is -10 MPa to 10 MPa, and the radial relative stress at any horizontal plane of the SiC crystal is -8 MPa to 8 MPa.

14. The SiC crystal according to claim 9, wherein Axial tests are carried out by extending downward from any point on the upper surface of the SiC crystal. Let S7 be the maximum axial stress of the SiC crystal, S8 be the minimum axial stress of the SiC crystal, and △S8 = S7 - S8, where 0 MPa ≤ △S8 ≤ 10 MPa.

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