Silicon carbide substrate with stress distributed in a stepwise manner

Abstract

This application discloses a silicon carbide substrate in which stress is distributed in a stepped manner, and belongs to the field of silicon carbide manufacturing and processing technology. The silicon carbide substrate includes a first main surface and a second main surface. The first main surface has a first-level stress section, a second-level stress section surrounding the first-level stress section, and a third-level stress section surrounding the second-level stress section. The width of the third-level stress section extending inward from the edge of the substrate is 2.5 to 30 mm, and the width of the second-level stress section extending inward from the edge of the third-level stress section is 10 to 50 mm. The internal relative stress in the first-level stress section is greater than or equal to the internal relative stress in the second-level stress section, and less than the internal relative stress in the third-level stress section. By uniformly transitioning the internal relative stress in each section of the silicon carbide substrate and realizing a stepped distribution, the quality of the silicon carbide substrate is improved, and the range of applications for the substrate is expanded.

Description

Technical Field

[0001] This application relates to the technical field of silicon carbide manufacturing and processing, and particularly to a silicon carbide substrate with a stepped stress distribution.

[0002] This application claims the priority of a Chinese patent application filed with the China National Intellectual Property Administration on July 7, 2023, with the application number 202310837065.0 and the application title "Silicon Carbide Substrate with Stepped Stress Distribution", and all its contents are incorporated herein by reference.

Background Art

[0003] Silicon carbide (SiC) single crystal substrates have excellent physical properties such as a wide bandgap, high resistivity and thermal conductivity, and high breakdown electric field strength, and thus are the optimal semiconductor materials in the manufacture of gallium nitride (GaN)-based high-frequency microwave devices. With the continuous development of 5G technology, the demand for silicon carbide single crystal substrates in the market is expanding, and with the progress of mass production and commercialization, the quality requirements for silicon carbide single crystal substrates are also becoming more sophisticated.

[0004] In the process of growing silicon carbide crystals, due to imbalances in the Si / C ratio, introduction of impurities, and changes in temperature gradients, various defects such as polycrystals, polymorphs, micropipes, and dislocations are easily introduced into the crystals. The defects cause lattice strain, and more seriously, the crystal form is transformed, for example, polymorph co-occurrences such as 4H, 6H, 3C, 15R, etc. occur. The lattice strain releases stress by generating defects, that is, internal stress is introduced into SiC, thereby degrading the quality of the SiC crystal, restricting the use range of the crystal, and reducing the yield rate of the product. Furthermore, the internal stress of the silicon carbide substrate is likely to cause non-uniform stress distribution due to the temperature field and the presence of defects, which affects the manufacturing and processing of downstream products.

Summary of the Invention

Problems to be Solved by the Invention

[0005] To solve the above problems, a silicon carbide substrate is provided in which stress is distributed in a stepped manner. This substrate is divided into a first-level stress section, a second-level stress section, and a third-level stress section, and the stress within each section is uniformly distributed, achieving a stepped distribution. This improves the quality of the silicon carbide substrate and expands the range of applications for the substrate. This substrate can be used to obtain epitaxial wafers through processing, or as a seed crystal for crystal growth. By reducing the stress in the epitaxial wafer or crystal, high-quality epitaxial wafers or crystals can be obtained. [Means for solving the problem]

[0006] According to one aspect of this application, a silicon carbide substrate is provided in which stress is distributed in a stepped manner, wherein the diameter of the silicon carbide substrate exceeds 150 mm, and the silicon carbide substrate includes a first main surface and a second main surface. The first main surface has a first-level stress section, a second-level stress section surrounding the first-level stress section, and a third-level stress section surrounding the second-level stress section, the width of the third-level stress section extending inward from the edge of the substrate is 2.5 to 30 mm, and the width of the second-level stress section extending inward from the edge of the third-level stress section is 10 to 50 mm. The internal relative stress in the first-level stress interval is greater than or equal to the internal relative stress in the second-level stress interval, and less than the internal relative stress in the third-level stress interval. The internal relative stress is the stress value measured at a position where the silicon carbide substrate is extended at least 3 μm perpendicularly from the first or second main surface.

[0007] The internal relative stress is smallest in the second-level stress zone and largest in the third-level stress zone. Therefore, the wider the second-level stress zone extends inward from the edge of the third-level stress zone, the greater the proportion of the silicon carbide substrate where the internal relative stress is relatively small.

[0008] Since silicon carbide crystals grow in a crucible, their outer periphery comes into contact with the graphite crucible. In the high-temperature environment during crystal growth, the graphite crucible expands due to heat, compressing the edges of the silicon carbide crystals and generating edge stress, which easily leads to lattice strain and stress. In silicon carbide substrates obtained by processing silicon carbide crystals, the stress is greatest in the third-level stress zone of the substrate, while the first-level stress zone is in the center of the crystal. A radial temperature gradient exists during SiC crystal growth, and this radial temperature gradient increases from the center to the edge. Therefore, the overall relative stress gradually increases from the center to the edge, and the stress also tends to increase from the center to the edge, with the stress in the first-level stress zone being greater than that in the second-level stress zone.

[0009] Selectively, the internal absolute stress in the second-level stress interval is greater than or equal to the internal absolute stress in the first-level stress interval, and less than the internal absolute stress in the third-level stress interval. The internal absolute stress is the stress value measured at a position where the silicon carbide substrate is extended at least 3 μm perpendicularly from the first or second main surface. Because the processing conditions of the SiC substrates differ, the internal absolute stress and internal relative stress are stress values ​​measured at a position at least 3 μm perpendicular to the interior of the SiC substrate from the first or second main surface. This ensures that the obtained stress values ​​are the internal stress values ​​of the SiC substrate, and allows for the removal of stresses introduced during processes such as cutting, grinding, and polishing of the SiC substrate.

[0010] Selectively, in any plane parallel to the first principal surface and / or the second principal surface, the internal absolute stress in the radial direction of the first-level stress interval is -20 to 5 MPa, the internal absolute stress in the radial direction of the second-level stress interval is 5 to 15 MPa, and the internal absolute stress in the radial direction of the third-level stress interval is 15.2 to 50 MPa. Selectively, in any plane parallel to the first principal surface and / or the second principal surface, the internal absolute stress in the radial direction of the first-level stress zone is -5 to 5 MPa, the internal absolute stress in the radial direction of the second-level stress zone is 5 to 10 MPa, and the internal absolute stress in the radial direction of the third-level stress zone is 15.2 to 20 MPa.

[0011] When the interior of a silicon carbide substrate is subjected to tensile and compressive stress, tensile and shrinkage changes corresponding to the interplanar spacing d occur. Therefore, when stress is measured by Raman spectroscopy, the Raman peak intensity may shift to a lower or higher frequency. When the interior of the substrate is subjected to tensile stress, the Raman peak position shifts to a lower frequency, and the obtained stress value is positive. When the interior of the substrate is subjected to compressive stress, the Raman peak position shifts to a higher frequency, and the obtained stress value is negative. Therefore, in this application, the sign before the stress value indicates the direction of stress inside the substrate, and the absolute value of the value indicates the magnitude of the stress. For example, if the average internal absolute stress in the first layer of a silicon carbide substrate is -3 MPa and the average internal absolute stress in the second layer is 5 MPa, then the internal absolute stress in the first-layer stress interval indicates compressive stress, and the internal absolute stress in the second-layer stress interval indicates tensile stress. Furthermore, the internal absolute pressure in the radial direction of the first-layer stress interval is smaller than the internal absolute pressure in the radial direction of the second-layer stress interval.

[0012] As can be seen from the internal absolute stress values ​​in the radial direction for the first, second, and third stress levels described above, the first stress level is a transition region between compressive and tensile stress, and both the second and third stress levels are tensile stress regions. The closer the values ​​in the first or third stress level are to those in the second stress level, the more uniform the internal stress distribution in the radial direction of the silicon carbide substrate is.

[0013] Selectively, measurements are taken in the axial direction extending perpendicularly into the silicon carbide substrate from any point on the first main surface. The absolute stress in the axial direction of the first stress level is -30 to 10 MPa, the absolute stress in the axial direction of the second stress level is 10 to 30 MPa, and the absolute stress in the axial direction of the third stress level is 30.2 to 50 MPa.

[0014] In this application, the reference value for absolute stress is the reference stress calculated from the standard Raman peak position obtained based on the SiC complete crystal lattice parameters, and is denoted as 0.

[0015] Selectively, in any plane parallel to the first principal surface and / or the second principal surface, the radial relative internal stress in the first-level stress zone is -15 to 15 MPa, the radial relative internal stress in the second-level stress zone is -10 to 10 MPa, and the radial relative internal stress in the third-level stress zone is -24.8 to 24.8 MPa.

[0016] Selectively, the internal relative stress in the radial direction of the first-level stress zone is -14.3 to 14.5 MPa, and the internal relative stress in the radial direction of the second-level stress zone is -9.4 to 10.0 MPa.

[0017] The absolute internal stress in the radial direction described above reflects the difference between a substrate and a substrate without internal residual stress (i.e., a perfect crystal), while the relative internal stress in the radial direction reflects the uniformity and regularity of the distribution of the substrate in the radial direction.

[0018] Selectively, in any plane parallel to the first principal plane and / or the second principal plane, Smax1 represents the maximum absolute value of the internal relative stress in the radial direction within the first-level stress interval, Smax2 represents the maximum absolute value of the internal relative stress in the radial direction within the second-level stress interval, and Smax3 represents the maximum absolute value of the relative stress in the radial direction within the third-level stress interval. △S1 = Smax1 - Smax2, △S2 = Smax3 - Smax1, △S1 ≤ △S2, Selectively, 0MPa ≤ △S1 ≤ 10MPa and 0MPa ≤ △S2 ≤ 22MPa.

[0019] Selectively, 0.2 MPa ≤ △S1 ≤ 9.8 MPa and 0.3 MPa ≤ △S2 ≤ 21.4 MPa.

[0020] Selectively, in any plane parallel to the first principal plane and / or the second principal plane, Smin1 represents the minimum absolute value of the internal relative stress in the radial direction within the first-level stress interval, Smin2 represents the minimum absolute value of the internal relative stress in the radial direction within the second-level stress interval, and Smin3 represents the minimum absolute value of the relative stress in the radial direction within the third-level stress interval. △S3 = Smin1 - Smin2, △S4 = Smin3 - Smin1, △S3 ≤ △S4, Selectively, 0MPa ≤ ΔS3 ≤ 5MPa and 0MPa ≤ ΔS4 ≤ 20MPa.

[0021] Selectively, 0.2 MPa ≤ △S3 ≤ 4.7 MPa and 0.3 MPa ≤ △S4 ≤ 19.6 MPa.

[0022] The absolute value of the internal relative stress in the radial direction represents the magnitude of the relative stress within each region, and △S1 and △S3 represent the difference in internal relative stress in the radial direction between the second-level stress section and the first-level stress section. The smaller the values ​​of △S1 and △S3, the closer the internal relative stress in the radial direction is between the second-level stress section and the first-level stress section. △S2 and △S4 represent the difference in internal relative stress in the radial direction between the third-level stress section and the first-level stress section. The smaller the values ​​of △S2 and △S4, the closer the internal relative stress in the radial direction is between the third-level stress section and the first-level stress section. "△S1≦△S2" and "△S3≦△S4" indicate that the difference in internal relative stress in the radial direction between the second-level stress section and the first-level stress section of this silicon carbide substrate is smaller than the difference between the third-level stress section and the first-level stress section.

[0023] Optionally, in any plane parallel to the first major surface and / or the second major surface, S1 represents the average value of the absolute value of the internal relative stress in the radial direction within the first stress layer interval, S2 represents the average value of the absolute value of the internal relative stress in the radial direction within the second stress layer interval, and S3 represents the average value of the absolute value of the relative stress in the radial direction within the third stress layer interval. 0 MPa ≤ S1 - S2 ≤ 14.5 MPa, 0 MPa ≤ S3 - S1 ≤ 22.5 MPa.

[0024] Optionally, 0 MPa ≤ S3 - S1 ≤ 22.4 MPa.

[0025] Multi-point stress measurement is performed on the silicon carbide substrate, and the average value of the absolute value refers to the value obtained by dividing the sum of the absolute values of the stresses at all measurement points within the region by the number of measurement points. This multi-point measurement is to select and measure a plurality of different positions within the region or to perform mapping measurement on the substrate.

[0026] Optionally, 0 MPa ≤ S1 - S2 ≤ 8 MPa, 0 MPa ≤ S3 - S1 ≤ 10 MPa.

[0027] Optionally, measurement is performed in the axial direction extending perpendicularly from an arbitrary point on the first major surface into the silicon carbide substrate. The relative stress in the axial direction within the first stress layer interval is -20 to 20 MPa, the relative stress in the axial direction within the second stress layer interval is -16 to 16 MPa, and the relative stress in the axial direction within the third stress layer interval is -25 to 25 MPa.

[0028] Optionally, the relative stress in the axial direction within the first stress layer interval is -19.3 to 19.7 MPa, the relative stress in the axial direction within the second stress layer interval is -15.7 to 15.2 MPa, and the relative stress in the axial direction within the third stress layer interval is -24.3 to 24.7 MPa.

[0029] The absolute stress in this axial direction reflects the difference between the substrate and a substrate without internal stress, and the relative stress in the axial direction reflects the uniformity of the substrate in the axial direction.

[0030] In this application, the internal relative stress in the radial direction of the first-level stress interval is calculated by taking a reference value from the entire first-level region, and performing a related numerical calculation on the values ​​at each measurement point to obtain the relative stress value at that measurement point. The reference value includes, but is not limited to, the median, mean, mode, or other statistical function calculation result of the total stress values ​​in the entire measurement region. Similarly, the same calculation method is used for the internal relative stress in the radial direction of the second-level stress interval and the third-level stress interval.

[0031] The reference value for the radial internal absolute stress in the first, second, and third stress levels is the reference stress calculated from the standard Raman peak position obtained based on the SiC complete crystal lattice parameters, and is denoted as 0.

[0032] Selectively, measurements are taken in the axial direction extending perpendicularly within the silicon carbide substrate from any point on the first main surface. Smax5 represents the maximum value of the internal relative stress in the axial direction of the first-level stress interval, and Smin5 represents the minimum value of the internal relative stress in the axial direction of the first-level stress interval. △S5 = Smax5 - Smin5, 0MPa ≤ △S5 ≤ 10MPa.

[0033] Selectively, 0 MPa ≤ ΔS5 ≤ 9.6 MPa.

[0034] Smax6 is the maximum value of the internal relative stress in the axial direction within the second-level stress interval, and Smin6 is the minimum value of the internal relative stress in the axial direction within the second-level stress interval. △S6 = Smax6 - Smin6, 0MPa ≤ △S6 ≤ 10MPa.

[0035] Selectively, 0 MPa ≤ ΔS6 ≤ 9.2 MPa.

[0036] Smax7 is the maximum value of the internal relative stress in the axial direction within the third-level stress interval, and Smin7 is the minimum value of the internal relative stress in the axial direction within the third-level stress interval. △S7 = Smax7 - Smin7, 0MPa ≤ △S7 ≤ 10MPa.

[0037] Selectively, 0 MPa ≤ ΔS7 ≤ 9.9 MPa.

[0038] The maximum and minimum values ​​of the internal relative stress in the axial direction mentioned above represent the true values ​​of the internal relative stress in the axial direction, distinguishing between compressive and tensile stress in the axial direction. For example, if the internal relative stress in the axial direction of the first-level stress interval is -5 to 1 MPa along an arbitrary axis, the maximum value of the internal relative stress in the axial direction is 1 MPa, and the minimum value of the internal relative stress in the axial direction is -5 MPa. △S5 is 6 MPa. These △S5, △S6, and △S7 represent the degree of change in the interplane spacing of the crystals in the axial direction of the substrate at a microscopic level. The smaller the values ​​of △S5, △S6, and △S7, the smaller the change in the interplane spacing of the crystals in the axial direction of the substrate.

[0039] Selectively, 0MPa ≤ △S5 ≤ 5.2MPa, 0MPa ≤ △S6 ≤ 3.9MPa, and 0MPa ≤ △S7 ≤ 6.1MPa.

[0040] Selectively, the silicon carbide substrate has a diameter exceeding 200 mm, the third-level stress zone has a width of 21-30 mm extending inward from the substrate edge, the second-level stress zone has a width of 10-39 mm extending inward from the edge of the third-level stress zone, and / or The thickness of the silicon carbide substrate is greater than or equal to 0.1 mm.

[0041] Selectively, the off-angle of the first principal surface and / or the second principal surface with respect to the {0001} plane is 4° or less.

[0042] Selectively, the curvature of the silicon carbide substrate is between -50 μm and 50 μm.

[0043] Selectively, the curvature of the silicon carbide substrate is -20 μm to 20 μm.

[0044] Selectively, the curvature of the silicon carbide substrate is -10 μm to 10 μm.

[0045] Selectively, the crystal form of the silicon carbide substrate is one of 2H-SiC, 4H-SiC, 6H-SiC, 3C-SiC, or 15R-SiC.

[0046] Selectively, the crystal form of the silicon carbide substrate is 4H-SiC.

[0047] Selectively, the silicon carbide substrate is either a semi-insulating silicon carbide substrate or a conductive silicon carbide substrate.

[0048] Selectively, the local thickness deviation in the first-level stress zone is 0.1 to 0.3 μm, the local thickness deviation in the second-level stress zone is 0.3 to 0.7 μm, and the local thickness deviation in the third-level stress zone is 0.7 to 2 μm.

[0049] The silicon carbide substrate described in any of the above sections is manufactured by processing a silicon carbide single crystal, and according to another aspect of this application, a method for manufacturing a silicon carbide single crystal is provided, comprising the following steps: (1) Add silicon carbide powder to a graphite crucible, (2) After evacuating the furnace to 10⁻⁶ mbar or less, introduce high-purity inert gas to 300-500 mbar, repeat this process 2-3 times, and finally evacuate the furnace to 10 mbar or less. (3) Introduce high-purity inert gas into the furnace and raise the pressure to 10-100 mbar in 1-3 hours, then continue introducing high-purity inert gas to maintain a constant pressure. (4) During the crystal growth stage, if the pressure is kept constant, the temperature inside the furnace will rise to the single crystal growth temperature of 2200K to 2800K in 3 to 5 hours, and the growth time will be 30 to 150 hours. (5) After the single crystal growth is complete, the furnace body can be opened and the graphite crucible removed to obtain the silicon carbide single crystal.

[0050] Selectively, the graphite crucible is coated with a composite coating, the composite coating comprising: TaxCy permeable layer. The TaxCy permeable layer is deposited on a graphite substrate, where 0 <x<1,0<y<1、 TaC coating. The TaC coating is applied on top of the TaxCy impregnation layer.

[0051] The TaxCy permeation layer is formed on the surface and inside the graphite substrate. The TaxCy permeation layer is uniformly distributed on the surface of the graphite substrate, exhibits excellent density, improves environmental stability during the growth process of silicon carbide crystals, and reduces thermal expansion of the graphite substrate.

[0052] Selectively, each TaxCy crystal grain in the TaxCy infiltration layer grows anisotropically, and the TaC crystal grains in the TaC coating grow oriented along the "200" and "220" directions. The TaxCy crystal grains in the TaxCy infiltration layer and the TaC crystal grains in the TaC coating are arranged alternately. The TaxCy crystal grains in the TaxCy infiltration layer are arranged alternately, and the size of the TaxCy crystal grains is 5 to 30 μm, while the TaC crystal grains in the TaC coating are arranged in a stacking fault row manner, and the size of the TaC crystal grains is 15 to 40 μm.

[0053] The size of the TaxCy crystal grains reduces stress in the TaxCy permeation layer, avoids the formation of prominent grain boundaries in the TaxCy permeation layer, and prevents crack initiation within the TaxCy permeation layer, thereby avoiding crystal compression by the graphite substrate.

[0054] TaC crystal grains in the TaC coating grow oriented in the "200" and "220" directions, thereby improving the density of the TaC coating. As a result, the bonding strength between the composite coating and the graphite substrate, as well as the temperature resistance and thermal chemical corrosion resistance of the composite coating, are improved, and interference from the graphite substrate during the crystal growth process is reduced, thereby contributing to the production of silicon carbide crystals of uniform quality.

[0055] Selectively, the thickness of the TaxCy permeation layer is 10 to 450 μm, the thickness of the TaC coating is 30 to 400 μm, and the total thickness of the TaxCy permeation layer and the TaC coating is 40 to 500 μm. [Effects of the Invention]

[0056] The beneficial effects of this application include, but are not limited to, the following:

[0057] 1. In the silicon carbide crystal growth process, the stress introduced by changes in the temperature gradient or the crystal growth environment is the internal stress of the silicon carbide substrate. In the silicon carbide substrate according to this application, the first-level stress interval is a compressive stress region, the second-level stress interval is a stress transition region, and the third-level stress interval is a tensile stress region, thereby obtaining a silicon carbide substrate in which the stress is distributed in a stepwise manner.

[0058] 2. The silicon carbide substrate according to this application exhibits low internal stress in both the radial and axial directions in the first, second, and third stress levels, and the stress distribution is uniform within these regions, allowing for uniform stress transfer at the joint locations of the regions. This demonstrates the excellent uniformity of the silicon carbide substrate, enabling its use as an epitaxial substrate or seed crystal, thereby contributing to improved production quality of downstream products.

[0059] 3. The silicon carbide substrate according to this application allows for the understanding of changes in the lattice structure in each region based on stress values ​​measured in different regions, and enables the analysis of microscopic unit cell parameters of the substrate from the stress values. Because it exhibits a certain feedback effect, it is possible to easily realize mass production of high-quality silicon carbide substrates.

[0060] 4. By utilizing a composite coating formed on the crucible surface, this application can improve the resistance of the graphite crucible and reduce its influence on the crystal growth process. This improves the stability of the crystal environment and the uniformity of the temperature distribution, and reduces the number of defects and impurity content in the crystal, thereby enabling the production of high-quality silicon carbide crystals with a stepped stress distribution.

[0061] 5. The stress distribution in each region of the silicon carbide substrate according to this application can be adjusted based on the process parameters of each step in crystal growth, enabling the manufacture of high-quality silicon carbide substrates. Furthermore, the stress measured by the quantitative measurement method according to this application includes stresses that have not been released as defects due to lattice strain present in the substrate. This improves the accuracy of stress measurement within the silicon carbide substrate and reflects stress information for the entire substrate. [Brief explanation of the drawing]

[0062] To more clearly illustrate the embodiments of this application or the technical concepts in the prior art, the following briefly describes the drawings that may be used in the embodiments or prior art descriptions. It is obvious that the drawings in the following description are only some of the embodiments described in this application, and those skilled in the art can obtain other drawings based on the structures shown in these drawings without expending any creative effort. [Figure 1] This is a schematic diagram of the internal stress of the substrate obtained by Raman equidistant focus testing according to Example 4 of this application. [Figure 2] This is a schematic diagram of the measurement of internal substrate stress by Raman equifocal plane testing according to Example 4 of this application. [Figure 3] This is an SEM image of the surface of crucible 1# according to Example 5 of this application. [Modes for carrying out the invention]

[0063] The embodiments of this application provide a silicon carbide substrate in which stress is distributed in a stepwise manner.

[0064] To enable those skilled in the art to better understand the technical concept of this application, the technical concept in the embodiments of this application is described below clearly and completely with reference to the drawings of the embodiments. Clearly, the embodiments described are only a selection of embodiments of this application, not all of them. All other embodiments derived from the embodiments of this application without creative effort by those skilled in the art should also fall within the scope of protection of this application.

[0065] The present application will be described in detail below based on the embodiments. However, the present application is not limited to these embodiments.

[0066] Unless otherwise specified, all raw materials in the embodiments of this application are purchased through commercial means.

[0067] In the following examples, the principle of stress measurement of the substrate by Raman spectroscopy employed is as follows: A Raman spectrometer focuses a monochromatic laser of a specific wavelength through a series of optical paths using an objective lens and irradiates the substrate surface. Photon scattering occurs when the laser photons interact with the crystal lattice of the substrate. The occurrence of Raman scattering is related to the lattice vibrations of the substrate itself. If residual stress is present in the sample, tensile stress and compressive stress elongate or shorten the atomic bond length, respectively, which decreases or increases the vibration frequency of the atoms. In the Raman spectrum, the characteristic peak position of the substrate shifts to a lower or higher frequency, i.e., a peak position offset appears.

[0068] <Example 1> Quantitative measurement method for substrate stress (1) Calculation of the peak position offset and stress transformation coefficient First, a silicon carbide substrate is measured using a single-crystal XRD diffractometer, and the substrate is analyzed by reciprocal lattice space analysis. The parameters of the standard sample, a 4H-silicon carbide substrate, are calculated and compared with the standard parameters. Next, the θ and d of different substrates are measured based on the Bragg diffraction formula: 2dsinθ=nλ (where d is the interplanar spacing, θ is the diffraction half-angle, n is the diffraction order, and λ is the wavelength). This shows that tensile and compressive stresses within the crystal cause tensile and shrinkage changes corresponding to the interplanar spacing d. Based on the different interplanar spacings d0 and dx, dx is classified into d1 and d2. Here, d0 is the theoretical interplanar spacing, d1 is the interplanar spacing after tensile stress (d1 is greater than d0), and d2 is the interplanar spacing after compressive stress (d2 is less than d0). The difference in interplanar spacing △d at different positions is calculated as △d=d1-d0 or △d=d0-d2.

[0069] The actual peak position of the substrate obtained by Raman measurement is compared with the reference peak position, and the peak position offset amount △v at each measurement point is calculated. The stress value σ of the silicon carbide substrate at each measurement point is calculated using Hooke's Law or the stress-strain formula. The ratio of the peak position offset to the stress value at each measurement point is the peak position offset to the stress transformation coefficient μ, and its range is -125 to -2500.

[0070] The formula for Hooke's Law is σ / S = E × (△d / d0), where S is the area over which σ acts and is a fixed value. When Hooke's Law is applied to microscopic calculations, S is the microscopic area (which can be considered as having a unit of 1), E is the Young's modulus of the substrate and a fixed parameter of the substrate, △d is the difference in interplanar spacing at different locations, and d0 is the theoretical interplanar spacing. σ is the stress value being calculated.

[0071] The formula for calculating stress and strain is σ = E × △d. Here, E is the Young's modulus of the substrate and is a fixed parameter of the substrate. △d is the difference in interplane distance at different locations, and σ is the stress value that needs to be calculated.

[0072] (2) Method for quantitative measurement of substrate stress First, Raman measurement points are set, and single-point measurements may be performed, or mapping scans may be performed on the entire substrate. Therefore, single-point measurements involve setting sporadic coordinate points, while mapping scans cover 10×10 to 50×50 or more points, allowing for the selection of an appropriate measurement method according to the properties of the substrate and the determination of Raman measurement coordinates for silicon carbide substrates.

[0073] Subsequently, the measurement results are output. These results include, but are not limited to, editable peak locations, peak intensity data, and mapping.

[0074] Next, the output data is fitted to the peak position. The fitting function includes, but is not limited to, Gaussian, Lorentz, GaussLor, AGauss, Aloren, and AGaussLor. This yields accurate peak position values ​​and peak position offsets, with the peak position being accurate to more than one decimal place.

[0075] Finally, the stress value of silicon carbide is calculated based on the peak position offset amount and stress transformation coefficient μ calculated in (1), and the peak position offset amount △v obtained from the Raman measurement. The calculation formula is σ(MPa) = μ × △v(cm -1 ) and finally output a stress measurement image of the substrate.

[0076] <Example 2> Measurement of curvature of substrate surface During the process of obtaining a SiC wafer from a crystal through a series of processing steps, the surface is subjected to a large amount of external mechanical stress, making it difficult to guarantee that the surface is perfectly horizontal; in other words, a certain degree of curvature or warping exists. To eliminate the influence of the curvature of the substrate surface on the measurement of substrate surface stress and internal stress, it is necessary to first measure the curvature of the substrate. Based on this curvature, equifocal measurement is selected for substrate surface stress, and equifocal measurement or equifocal plane measurement is selected for substrate internal stress.

[0077] After measuring the curvature, the measuring device needs to be calibrated using single-crystal silicon. First, a Z-axis mapping measurement is performed on the single-crystal Si to confirm that it has a Gaussian distribution. The surface of the single-crystal Si substrate is set as the zero point, and an axial mapping measurement is performed from -100 μm inside the single-crystal Si substrate to +20 μm at the top of the single-crystal Si substrate. The change in Raman signal intensity is analyzed, and since the single-crystal Si substrate is an opaque material, its peak intensity shows a Gaussian distribution, with the surface zero point as the axis of symmetry. Subsequently, a surface-focused single-point measurement is performed on the single-crystal Si, and the Raman peak position of the single-crystal Si is set to 520.70 cm using the calibration device. -1 Adjust to this value. This indicates that the optical path calibration of the device is complete.

[0078] Measurements were performed on a 4H-SiC substrate in the Z-axis direction using a calibrated measuring device. The Raman laser was irradiated from -100 μm inside the 4H-SiC substrate to +20 μm above the 4H-SiC substrate. Because 4H-SiC substrates and other silicon carbides have the characteristics of transparent materials, the Raman laser can be incident into the substrate, and the feedback signal gradually weakens as the incident depth increases. Other silicon carbides include semi-insulating, conductive, 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 depth to which the Raman laser is incident into the substrate increases.

[0079] The Raman spectrometer's autofocus function automatically sets the device to detect the peak with the strongest measurement signal on the substrate surface, and this function can be used to measure the curvature of the substrate surface. The specific method is as follows: S1: First, ensure the horizontal position of the measurement platform, select a fixed origin (0,0) on the platform, and mark this point as the three-dimensional coordinate (0,0,0). S2: Raise the objective lens to a height that does not touch the substrate according to the thickness of the substrate, perform automatic focus adjustment at an arbitrary point, identify the position on the substrate surface where the measurement signal is strongest, and mark this position as (a,b,c). Then, move the Raman laser downward by a distance H, and adjust the focal position to (a,b,cH). S3: The measurement position of the Raman laser is adjusted to (0,0,cH), and an isofocal plane measurement is performed. This obtains a two-dimensional peak intensity distribution map of the substrate surface. Based on the relationship between the peak intensity distribution of the silicon carbide substrate and the two-dimensional peak intensity distribution map of the substrate surface, the distance between the focal plane of the Raman laser and the silicon carbide substrate surface can be calculated. This allows for an understanding of the curvature within the substrate surface and provides a diagram of the curvature distribution within the substrate surface.

[0080] <Example 3> Distinction between substrate surface stress and internal stress by measurement in the axial direction During the crystal growth process, the substrate is affected by the temperature field and the introduction of inclusions, resulting in the presence of thermal stress and residual stress within the crystal. Furthermore, the crystal undergoes a series of cutting, grinding, and polishing processes to obtain the substrate. In the processing steps that form the substrate from the crystal, lattice distortion occurs on the surface, generating surface stress. To further distinguish between surface stress and internal stress in the substrate, axial measurements (Z-direction mapping) are performed on the substrate based on the permeability characteristics of silicon carbide. The substrate surface is used as the reference point (zero point), and the axial measurement range is from a position of -150 μm to -30 μm inside the substrate to above the substrate surface.

[0081] During the measurement process, the laser beam spot was gradually focused from the inside of the substrate to the damaged stress stretching layer, then to the surface damaged layer, and finally to air. The thickness of the substrate surface damaged layer and the damaged stress stretching layer was then measured. With the substrate surface as the zero point, the measurement range in the axial direction was gradually moved from a position of -100 μm inside the substrate to a position of 30 μm above the substrate surface. Tests were performed at five locations on the substrate (top, bottom, left, right, and center). The trend was the same at all five locations on the substrate, with differences only in the negative stress maximum value at the surface damaged areas.

[0082] As the laser beam spot gradually moves from -100 μm to -30 μm inside the substrate, the stress curve fluctuates up and down along the horizontal line, indicating that the internal stress is uniform. When the laser beam spot focuses on the damaged stress stretching layer, the stress curve begins to show a downward trend at the -30 μm position, and this downward trend in stress gradually increases, reaching a maximum value of negative stress as it approaches the zero point on the substrate surface, at which point it is shown as the stress value of the surface damaged layer. Finally, as the laser beam spot rises further and moves away from the substrate surface into the air, the stress rapidly increases to a turbulent fluctuation. Therefore, based on the measurement results in the axial direction of the substrate, the thickness of the surface damaged layer and the damaged stress stretching layer of the substrate can be determined, thereby separating the stress within the substrate into surface stress and internal stress. This provides a theoretical basis for quantitative measurement of surface stress and internal stress within the substrate.

[0083] <Example 4> Quantitative measurement of internal stress in a substrate During the crystal growth process by the PVT method, silicon carbide experiences residual stress within the crystal due to temperature gradient changes and the intrusion of inclusions. Unlike surface processing stress, internal stress is located at a certain depth from the surface and reflects both thermal stress and residual stress during crystal growth. Furthermore, since silicon carbide is subjected to a large amount of external mechanical stress during the manufacturing process of a substrate from a crystal through a series of processing steps, it is difficult to guarantee that the surface is perfectly horizontal; in other words, a certain degree of curvature or warping exists on the substrate surface. Based on the substrate surface curvature measurement method obtained by Raman measurement in Example 2, this example relates to a method for quantitatively evaluating internal stress without being affected by surface curvature or warping, taking into account the physical properties and characteristics of silicon carbide.

[0084] Based on the physical properties of silicon carbide, specifically its light transmittance, quantitative evaluation methods for internal substrate stress using the Raman method are classified into equifocal measurement and equifocal plane measurement. Specifically, these are as follows: 1.Equidistant focus measurement The principle of equally spaced focusing measurement is as shown in Figure 1. Figure 1(b) shows the focal position of the Raman laser inside the substrate, and Figure 1(a) is a diagram of the measurement principle. In this measurement method, the depth of focus (d) of the Raman laser focused inside the substrate at different measurement points is kept constant. First, the transmission depth (Dp) of the Raman laser is calculated based on the following formula.

number

[0085] Then, the spot diameter (D) of the Raman laser is calculated based on the following formula,

number

[0086] This spot diameter (D) is the diameter of the short axis of the laser spot. The larger this value, the stronger the Raman peak intensity at each measurement position, and the more impurity peaks there are, thus affecting the accuracy of the Raman measurement. When λ is determined, a large Na value results in weaker peak intensity, which also affects the accuracy of the Raman measurement. Therefore, it is necessary to select appropriate λ and Na values, thereby improving the accuracy of the measurement method.

[0087] Based on the properties of silicon carbide, the peak intensity is strongest when the laser is focused on the substrate surface. Therefore, the laser can be focused on the substrate surface using the autofocus function of the Raman measurement device, and then, based on the determined depth of focus (d) above, equally spaced focal measurements can be performed at different positions on the substrate. That is, the distance between the focal plane and the substrate surface is always kept equal. This method is unaffected by curvature or warping of the substrate surface, and the obtained Raman peak intensity is always maintained at the maximum value in the axial direction of the measurement point, and a diagram of the internal stress distribution of the substrate is obtained based on the stress quantitative measurement method of Example 1.

[0088] 2. Isofocal plane measurement The principle of isofocal plane measurement is shown in Figure 2. Figure 2(b) shows the focal position of the Raman laser inside the substrate, and Figure 2(a) is a diagram of the measurement principle. In this measurement method, the depth of focus (d) at which the Raman laser spot is focused inside the substrate changes at different measurement points. The laser spot is focused at a coplanar position inside the substrate at each measurement point. The transmission depth (Dp) of the Raman laser is calculated using the same formula as in equidistant focus measurement, and an appropriate depth of focus (d) is selected using the same selection method.

[0089] In this measurement method, since the focal plane is constant, taking into account the properties of silicon carbide, the peak intensity is strongest when the laser is focused on the substrate surface, and the signal gradually weakens as the depth of focus increases. Furthermore, from the effective S / N ratio measurement results using a Raman measurement device, it was found that the effective S / N ratio is inversely correlated with the depth of focus (d) of the Raman laser. Therefore, in this measurement method, the depth of focus (d) at different measurement points takes into account the curvature of the substrate, and by calculating an effective peak position offset amount using the stress quantitative measurement method of Example 1, the error in internal stress measurement is reduced. This measurement method yields a diagram of the internal stress measurement results of the substrate.

[0090] Using the two measurement methods described above—equally spaced focal point measurement and equifocal plane measurement—the peak position offset within the substrate was obtained, and the internal stress distribution of the substrate was calculated. The difference between the internal stress values ​​of the substrate calculated by the two methods—equally spaced focal point measurement and equifocal plane measurement—is less than or equal to 0.2 MPa, and the difference between the peak position values ​​obtained by the equally spaced focal point measurement and equifocal plane measurement is less than 0.0005 cm⁻¹. The above two methods can verify the accuracy of the quantitative measurement method of this application, and the accuracy of this measurement method can be further improved by setting the focal depth and spot diameter.

[0091] The internal stress in question includes both absolute and relative internal stress. Using 4H-SiC as an example, The internal absolute stress is calculated by subtracting the standard peak position from the 4H-SiC peak position measured at the determined reduced wave vector peak. For example, the formula for calculating the internal absolute stress of FTO(2 / 4) is as follows: σ Absolute = μ × (v Actual - VFTO(2 / 4)), where σ is in MPa, and v Actual and VFTO(2 / 4) are in cm. -1 Here, v actually represents the actual FTO(2 / 4) peak position at the substrate measurement point, and VFTO(2 / 4) represents the standard FTO(2 / 4) peak position of the substrate. The internal relative stress is calculated by taking the difference between the actual measured values ​​of the same reduced wave vector peak positions at any two points on the SiC substrate surface, for example, the FTO(2 / 4) peak position, and the formula for calculating the internal absolute stress is as follows: σ relative = μ × (V(x1,y1) - V(x2,y2)), where σ is in MPa, and V(x1,y1) and V(x2,y2) are in cm, where V(x1,y1) is the actual FTO(2 / 4) peak position at the substrate measurement point, and V(x2,y2) is the actual FTO(2 / 4) peak position at the relative point on the substrate. The relative stress value at the measurement point is calculated based on the above formula. If the σ relative value is positive, the stress at the relative point of the measurement point is tensile stress, and if the σ relative value is negative, the stress at the relative point of the measurement point is compressive stress.

[0092] <Example 5> This embodiment relates to a method for producing a graphite crucible for silicon carbide growth, and includes the following steps: Step (1): The graphite substrate is immersed in a tantalum pentachloride solution, with a concentration of tantalum pentachloride of 5% to 95% and a porosity of the graphite substrate of 5% to 55%. Gas pressurization is performed at a gas pressure of 1 to 2 MPa for a pressurization time of 0.5 to 1 hour. After immersion, the graphite substrate is dried and sintered to obtain a graphite substrate having a TaxCy permeation layer. Step (2): Prepare a slurry containing TaC, the slurry comprising 25-40 parts TaC powder, 20-35 parts solvent, 15-25 parts co-solvent, 1-3 parts defoamer, 2-5 parts thickener, 5-15 parts linear saturated aliphatic hydrocarbon, and 1-3 parts carbon powder. The slurry is applied to the surface of a graphite substrate having a TaxCy permeable layer, dried, and then sintered. The sintering is performed in an inert gas environment: sintering is carried out at 700-900 mbar and 500-700°C for 3-5 hours, then the pressure is increased to 1000-1100 mbar and the temperature to 1600-1800°C for 8-10 hours, and finally the pressure is increased to 145-155 kPa and the temperature to 2200-2400°C for 14-16 hours, and then the mixture is cooled to room temperature and atmospheric pressure over 15-25 hours to obtain the graphite crucible.

[0093] Selectively, the sintering in step (1) is carried out in an inert gas environment, and the dried graphite substrate is placed in a vacuum furnace and subjected to stepwise heating and stepwise cooling. Stepwise heating means raising the temperature to 250-350°C and sintering for 4-6 hours, then raising the temperature to 850-950°C and sintering for 2.5-3.5 hours, and finally raising the temperature to 1200-1300°C and sintering for 3-5 hours. Stepwise cooling involves lowering the temperature to 900-1100°C, holding it for 0.5-2 hours, then lowering it to 750-850°C, holding it for 0.5-1 hour, and finally lowering it to room temperature at a rate of 15-25°C / h.

[0094] Selectively, the pressure inside the vacuum furnace during the sintering process is set to 800-1000 mbar.

[0095] Based on the above manufacturing method, crucibles 1# to 6# and control crucibles D1# to D3# are obtained. Specifically, the process is as follows: Crucible 1# Step (1): Place the graphite substrate in a tantalum pentachloride n-butanol solution in a container. The tantalum pentachloride concentration in the solution is 70%, and the porosity of the graphite substrate is 45%. Place the container in a pressure chamber and pressurize it at a pressurization rate of 0.1 MPa / min. When the pressure in the pressure chamber reaches 1 MPa, maintain this pressure for 1 hour, then reduce the pressure. Place the immersed graphite substrate in a vacuum furnace and dry it at 60°C for 7 hours. Then, introduce argon gas into the vacuum furnace and sinter it while maintaining the furnace pressure at 900 mbar. After that, gradually increase the temperature, raising it to 300°C in 1 hour and sintering for 5 hours, then raising it to 900°C in 2 hours and sintering for 3 hours, and finally raising it to 1250°C in 1 hour and sintering for 4 hours. Subsequently, the temperature was gradually lowered, reaching 1000°C in 1 hour and maintaining it for 1 hour, then lowering to 800°C in 1 hour and maintaining it for 1 hour, and finally lowering to room temperature at a rate of 20°C / h to obtain a graphite substrate having a TaxCy permeation layer. Step (2): Dissolve 4N grade TaC in an organic solvent to prepare a TaC-containing slurry. The slurry contains 32.7 parts TaC powder, 25 parts ethanol, 20 parts tetrahydrofuran, 1.5 parts BYK defoamer, 3.5 parts cellulose ether, 10 parts linear saturated aliphatic hydrocarbon, and 1.3 parts carbon powder. Mix the above components and stir for 2.5 hours. Then, apply the mixture to the surface of a graphite substrate having a TaxCy permeable layer using a spray device. Place the coated graphite substrate in a heating furnace, raise the temperature to 200°C in an air environment and dry for 10 hours. After that, introduce argon gas into the heating furnace and sinter at 800 mbar and 600°C for 4 hours. Subsequently, increase the pressure to 1000 mbar and raise the temperature to 1700°C for 9 hours. Finally, increase the pressure to 150 kPa and raise the temperature to 2300°C for 15 hours. Finally, cool to room temperature and atmospheric pressure over 20 hours to obtain crucible #1.

[0096] Crucible 2# Step (1): Place the graphite substrate in a tantalum pentachloride n-butanol solution in a container. The tantalum pentachloride concentration in the solution is 70%, and the porosity of the graphite substrate is 45%. Place the container in a pressure chamber and pressurize it at a pressurization rate of 0.2 MPa / min. When the pressure in the pressure chamber reaches 1 MPa, maintain this pressure for 1 hour, then reduce the pressure. Place the immersed graphite substrate in a vacuum furnace and dry it at 80°C for 5 hours. Then, introduce argon gas into the vacuum furnace and sinter it while maintaining the furnace pressure at 800 mbar. After that, gradually increase the temperature, raising it to 250°C in 1 hour and sintering for 6 hours, then raising it to 850°C in 2 hours and sintering for 3.5 hours, and finally raising it to 1200°C in 1 hour and sintering for 5 hours. Subsequently, the temperature was gradually lowered, reaching 900°C in 1 hour and maintaining it for 2 hours, then lowering to 750°C in 1 hour and maintaining it for 1 hour, and finally lowering to room temperature at a rate of 15°C / h to obtain a graphite substrate having a TaxCy permeation layer. Step (2): Dissolve 4N grade TaC in an organic solvent to prepare a TaC-containing slurry. The slurry contains 25 parts TaC powder, 20 parts ethanol, 25 parts tetrahydrofuran, 3 parts BYK defoamer, 2 parts cellulose ether, 15 parts linear saturated aliphatic hydrocarbon, and 3 parts carbon powder. Mix the above components and stir for 2.5 hours. Then, apply the mixture to the surface of a graphite substrate having a TaxCy permeable layer using a spray device. Place the coated graphite substrate in a heating furnace, raise the temperature to 180°C in an air environment, and dry for 12 hours. After that, introduce hydrogen into the heating furnace and sinter at 700 mbar and 700°C for 3 hours. Subsequently, increase the pressure to 1000 mbar and raise the temperature to 1800°C for 8 hours. Finally, increase the pressure to 145 kPa and raise the temperature to 2400°C for 16 hours. Finally, cool to room temperature and atmospheric pressure over 25 hours to obtain crucible #2.

[0097] Crucible 3# Step (1): Place the graphite substrate in a tantalum pentachloride n-butanol solution in a container. The tantalum pentachloride concentration in the solution is 70%, and the porosity of the graphite substrate is 45%. Place the container in a pressure chamber and pressurize it at a pressurization rate of 0.05 MPa / min. When the pressure in the pressure chamber reaches 2 MPa, maintain this pressure for 0.5 hours, then reduce the pressure. Place the immersed graphite substrate in a vacuum furnace and dry it at 60°C for 7 hours. Then, introduce hydrogen into the vacuum furnace and sinter it while maintaining the furnace pressure at 1000 mbar. After that, gradually increase the temperature, raising it to 350°C in 1 hour and sintering for 4 hours, then raising it to 950°C in 2 hours and sintering for 2.5 hours, and finally raising it to 1300°C in 1 hour and sintering for 3 hours. Subsequently, the temperature was gradually lowered to 1100°C in 1 hour and maintained for 0.5 hours, then lowered to 850°C in 1 hour and maintained for 0.5 hours, and finally lowered to room temperature at a rate of 25°C / h to obtain a graphite substrate having a TaxCy permeation layer. Step (2): Dissolve 4N grade TaC in an organic solvent to prepare a TaC-containing slurry. The slurry contains 40 parts TaC powder, 35 parts ethanol, 15 parts tetrahydrofuran, 1 part BYK defoamer, 5 parts cellulose ether, 5 parts linear saturated aliphatic hydrocarbon, and 1 part carbon powder. Mix the above components and stir for 2.5 hours. Then, apply the mixture to the surface of a graphite substrate having a TaxCy permeation layer using a spray device. Place the coated graphite substrate in a heating furnace, raise the temperature to 220°C in an air environment and dry for 8 hours. After that, introduce argon gas into the heating furnace and sinter at 900 mbar and 500°C for 5 hours. Subsequently, increase the pressure to 1100 mbar and raise the temperature to 1600°C for 10 hours. Finally, increase the pressure to 155 kPa and raise the temperature to 2200°C for 14 hours. Finally, cool to room temperature and atmospheric pressure over 15 hours to obtain composite coating crucible 3#.

[0098] Crucible 4# The difference between this embodiment and crucible 1# is that in step (1), gas pressurization is not performed when immersing the graphite substrate in the tantalum pentachloride n-butanol solution. Instead, it is immersed at room temperature and pressure for 1 hour, followed by drying and calcination. Other conditions are the same as for crucible 1# to obtain crucible 4#.

[0099] Crucible 5# This embodiment differs from crucible 1# in that, in step (1), the process of firing the graphite substrate in a vacuum furnace after immersion drying is as follows: the furnace pressure is maintained at 900 mbar, sintered at 700°C for 7 hours, then sintered at 1200°C for 5 hours, after which the temperature is gradually lowered. Other conditions are the same as for crucible 1# to obtain composite coated crucible 5#.

[0100] Crucible 6# The difference between this embodiment and crucible 1# is that in step (2), the process of sintering the graphite substrate, which has been sprayed with slurry and dried, in a heating furnace is as follows: Sintering at 1000 mbar and 1200°C for 12 hours, then increasing the pressure to 140 kPa, increasing the temperature to 2300°C, sintering for 20 hours, and finally cooling to room temperature and atmospheric pressure over 20 hours. The other conditions are the same as for crucible 1# to obtain crucible 6#.

[0101] Control crucible D1# This control example is compared to Example 1, with step (1) being the same, and step (2) employing the CVD method. Specifically, Step (2): A graphite substrate having a TaxCy permeation layer is placed in a chemical vapor deposition furnace, vacuumed to below 50 Pa, and then heated to 1200°C. A mixed gas consisting of ethane, TaCl5, H2, and hydrogen as a carrier gas is introduced, and the mixed gas is allowed to flow into the deposition furnace at a stable flow rate. The furnace pressure is maintained at 5000 Pa. First, the molar ratio of TaCl5 to ethane gas is controlled to 1.2:1 to form a transition layer with a thickness of 50 μm. Next, the molar ratio of TaCl5 to ethane gas is controlled to 3:1 to form a TaC coating with a thickness of 60 μm, thereby obtaining a control crucible D1#.

[0102] Control crucible D2# In this control example, compared to the control crucible D1#, step (1) is omitted, and only step (2) is performed on the graphite substrate. In step (2), a transition layer and a TaC coating are formed on the graphite substrate using the CVD method, and the specific CVD method conditions are the same as those for the control crucible D1#, thereby obtaining the control crucible D2#.

[0103] Control crucible D3# In this control example, step (1) is omitted compared to Example 1, and only step (2) is performed on the graphite substrate, with the operating conditions for step (2) being the same as in Example 1, thereby obtaining a control crucible D3#.

[0104] High-temperature erosion and thermochemical erosion experiments were performed on crucibles 1# to 6# and control crucibles D1# to D3# manufactured as described above. The growth environment for silicon carbide crystals, a third-generation semiconductor, using the PVT method was simulated. Crucibles 1# to 6# and control crucibles D1# to D3# were maintained in a silicon carbide atmosphere erosion environment at 2300°C for 100 hours, and the test results are shown in Table 1.

[0105] [Table 1]

[0106] In Table 1, the weight loss rate due to erosion = [(weight before experiment - weight after experiment) / weight before experiment] × 100%. The above high-temperature erosion and thermochemical erosion experiments demonstrated that the TaC coating of this embodiment improves the protective performance against graphite substrates, enhances the durability and corrosion resistance of the TaC coating, and consequently extends the life of the crucible. Crucible 1# was subjected to SEM testing after several uses, and the results are shown in Figure 3. Figure 3(a) is a test diagram of the localized composite coating on crucible 1#, and Figures 3(b) and 3(c) are magnified views of the cracks in Figure 3(a2). As can be seen from these, although crucible 1# manufactured in this embodiment developed cracks during multiple uses, the crack width could be controlled to within 1 μm, and it did not form through cracks, so it can still be used for the production of high-quality silicon carbide crystals. EDS mapping analysis of the TaxCy permeation layer of the crucible described above revealed that the TaxCy permeation layer was formed inside and on the surface of the graphite substrate and penetrated into the graphite substrate, resulting in a strong bond with the graphite substrate and improving the durability of the crucible. XRD tests were performed on the TaxCy permeation layer, TaC coating, and TaC in crucible 1# of this application. The TaxCy crystal grains in the TaxCy permeation layer showed anisotropic growth, and the TaC crystal grains in the TaC coating grew oriented in the

[0200] and

[0220] directions.

[0107] By depositing the composite coating prepared in this embodiment onto the surface of a graphite substrate, the graphite substrate can be protected, and its heat resistance and corrosion resistance can be improved. This reduces the interference that the graphite substrate exerts on the crystal growth environment, thereby improving the stability of the crystal environment. The firing and sintering processes control the orientation and growth of crystal grains in the TaxCy infiltration layer and the TaC coating, increasing the density of this composite coating, which can then be used to produce high-quality silicon carbide crystals.

[0108] <Example 6> This embodiment relates to a method for producing a silicon carbide single crystal with a diameter of 150 mm, and includes the following steps: (1) Add silicon carbide powder to the graphite crucible. (2) After evacuating the furnace to below 10 mbar, introduce high-purity inert gas to 300-500 mbar, repeat this process 2-3 times, and finally evacuate the furnace to below 10 mbar. (3) Introduce high-purity inert gas into the furnace and raise the pressure to 10-100 mbar in 1-3 hours, then continue introducing high-purity inert gas to maintain a constant pressure. (4) During the crystal growth stage, if the pressure is kept constant, the temperature inside the furnace is raised to the single crystal growth temperature of 2200K to 2800K in 3 to 5 hours, and the growth time is 30 to 150 hours. (5) After the single crystal growth is complete, the furnace body can be opened and the graphite crucible removed to obtain the silicon carbide single crystal.

[0109] Equal amounts of silicon carbide powder were added to crucibles 1# to 3# and control crucibles D1# to D3#, respectively, prepared in Example 6. The furnace was then evacuated to below 10⁻⁶ mbar, and high-purity inert gas was introduced up to 300 mbar. This process was repeated three times, and finally the furnace was evacuated to below 10⁻⁶ mbar, high-purity inert gas was introduced into the furnace, and the pressure was increased to 30 mbar in 1 hour. The high-purity inert gas was then continuously introduced to maintain a constant pressure. As a crystal growth stage, the temperature inside the furnace was raised to the single-crystal growth temperature of 2500 K in 3 hours while maintaining a constant pressure. The growth time was 70 hours. After the single-crystal growth was complete, the furnace body was opened, and the graphite crucibles were removed to obtain silicon carbide single crystals 1# to 3# and control silicon carbide single crystals D1# to D3#, respectively.

[0110] The silicon carbide single crystals 1# to 3# and control silicon carbide single crystals D1# to D3# were subjected to the same cutting, grinding, mechanical polishing, and chemical polishing processes to obtain silicon carbide substrates 1# to 3# and control silicon carbide substrates D1# to D3#, and internal stress tests were performed using the methods of Examples 1 to 4. The results are shown in Tables 2 and 3.

[0111] [Table 2]

[0112] [Table 3]

[0113] Upon inspection of the surface shape of the silicon carbide substrates 1# to 3#, it was found that the range of local thickness deviation in the first-level stress zone of silicon carbide substrates 1# to 3# was 0.1 to 0.3 μm, the range of local thickness deviation in the second-level stress zone was 0.3 to 0.7 μm, and the range of local thickness deviation in the third-level stress zone was 0.7 to 2 μm.

[0114] The stress values ​​in Tables 2 and 3 all refer to relative stress values. In this application, the sign of the stress value indicates whether the stress on the substrate is tensile or compressive. In conventional art, when describing and evaluating the stress state of a substrate, the difference obtained by subtracting the minimum value from the maximum value of the above-mentioned stress value is often used to reflect the stress state of the substrate. For example, if the internal relative stress in the axial direction of the first-level stress interval of SiC substrate 1# is -13.3 to 15.7, in this field, when generally indicating the internal relative stress in the axial direction of the first-level stress interval of this SiC substrate 1#, the stress value can also be described as 29 MPa.

[0115] The data in Tables 2-3 shows only the substrates obtained from crucibles 1#-3# and control crucibles D1#-D3# manufactured in Example 5. When SiC substrates are manufactured using crucibles 4#-8# employing the same crystal growth and processing methods as in Example 6, and when the parameters in Tables 2-3 are characterized using absolute stress, the following requirements are met: The third stress hierarchy section has a width of 2.5-30 mm extending inward from the substrate edge, the second stress hierarchy section has a width of 10-50 mm extending inward from the edge of the third stress hierarchy section, the internal relative stress in the first stress hierarchy section is greater than or equal to the internal relative stress in the second stress hierarchy section, and less than the internal relative stress in the third stress hierarchy section, the radial internal relative stress in the first stress hierarchy section is -15-15 MPa, the radial internal relative stress in the second stress hierarchy section is -10-10 MPa, and the radial internal relative stress in the third stress hierarchy section is -24.8-24.8 MPa. △S1≦△S2. 0MPa≦△S1≦10MPa, 0MPa≦△S2≦22MPa. △S3≦△S4. 0MPa≦△S3≦5MPa, 10MPa≦△S4≦20MPa. 0MPa≦S1-S2≦14.5MPa, 0MPa≦S3-S1≦22.5MPa. The internal relative stress in the axial direction of the first-level stress interval is -20 to 20MPa, the internal relative stress in the axial direction of the second-level stress interval is -16 to 16MPa, and the internal relative stress in the axial direction of the third-level stress interval is -25 to 25MPa. 0MPa≦△S5≦10MPa, 0MPa≦△S6≦10MPa, 0MPa≦△S7≦10MPa. The absolute internal stress in the second-level stress zone is greater than or equal to the absolute internal stress in the first-level stress zone, and less than the absolute internal stress in the third-level stress zone. The absolute internal stress in the radial direction of the first-level stress zone is -20 to 5 MPa, the absolute internal stress in the radial direction of the second-level stress zone is 5 to 15 MPa, and the absolute internal stress in the radial direction of the third-level stress zone is 15.2 to 50 MPa. The absolute stress in the axial direction of the first-level stress zone is -30 to 10 MPa, the absolute stress in the axial direction of the second-level stress zone is 10 to 30 MPa, and the absolute stress in the axial direction of the third-level stress zone is 30.2 to 50 MPa.

[0116] Each embodiment in this application is described in a progressive manner, and parts that are identical or similar between embodiments can be referenced to one another. Each embodiment focuses on explaining the differences from the other embodiments. In particular, the embodiments of apparatus, equipment, and non-volatile computer storage media are basically similar to the embodiments of methods, so the explanations are relatively simplified, and relevant parts can be found by referring to the descriptions of some parts of the embodiments of methods.

[0117] Finally, it should be understood that the embodiments described above in this application are merely for illustrating the technical concepts of the present invention and do not limit them. Although the present invention has been described in detail with reference to the embodiments described above, it should be understood by those skilled in the art that it is still possible to modify the technical concepts described in the embodiments described above, or to replace some of the technical features thereof, and such modifications or replacements do not cause the essence of the relevant technical concept to deviate from the spirit and scope of the technical concepts of each embodiment of the present invention.

Claims

1. A silicon carbide substrate in which stress is distributed in a stepwise manner, wherein the diameter of the silicon carbide substrate exceeds 150 mm, the silicon carbide substrate includes a first main surface and a second main surface, the first main surface has a first-level stress section, a second-level stress section surrounding the first-level stress section, and a third-level stress section surrounding the second-level stress section, the width of the third-level stress section extending inward from the edge of the substrate is 2.5 to 30 mm, and the width of the second-level stress section extending inward from the edge of the third-level stress section is 10 to 50 mm. The internal relative stress in the first-level stress interval is greater than or equal to the internal relative stress in the second-level stress interval, and less than the internal relative stress in the third-level stress interval. The internal relative stress is the stress value measured at a position where the silicon carbide substrate is extended perpendicularly by at least 3 μm from the first or second main surface.

2. The internal absolute stress in the second-level stress interval is greater than or equal to the internal absolute stress in the first-level stress interval, and less than the internal absolute stress in the third-level stress interval, and the internal absolute stress is the stress value measured at a position where the silicon carbide substrate is extended at least 3 μm perpendicularly from the first or second main surface, and / or A silicon carbide substrate in which stress is distributed in a stepwise manner, according to claim 1, wherein in any plane parallel to the first main surface and / or the second main surface, the internal absolute stress in the radial direction of the first-level stress interval is -20 to 5 MPa, the internal absolute stress in the radial direction of the second-level stress interval is 5 to 15 MPa, and the internal absolute stress in the radial direction of the third-level stress interval is 15.2 to 50 MPa.

3. A silicon carbide substrate in which stress is distributed in a stepwise manner, as described in claim 2, wherein measurements are taken in the axial direction from an arbitrary point on the first main surface, extending perpendicularly into the silicon carbide substrate, and the absolute stress in the axial direction of the first-level stress section is -30 to 10 MPa, the absolute stress in the axial direction of the second-level stress section is 10 to 30 MPa, and the absolute stress in the axial direction of the third-level stress section is 30.2 to 50 MPa.

4. A silicon carbide substrate in which stress is distributed in a stepwise manner, according to claim 1, wherein in any plane parallel to the first principal surface and / or the second principal surface, the internal relative stress in the radial direction of the first-level stress interval is -15 to 15 MPa, the internal relative stress in the radial direction of the second-level stress interval is -10 to 10 MPa, and the internal relative stress in the radial direction of the third-level stress interval is -24.8 to 24.8 MPa.

5. In any plane parallel to the first principal surface and / or the second principal surface, Smax1 represents the maximum value of the absolute value of the internal relative stress in the radial direction within the first-level stress interval, Smax2 represents the maximum value of the absolute value of the internal relative stress in the radial direction within the second-level stress interval, Smax3 represents the maximum value of the absolute value of the relative stress in the radial direction within the third-level stress interval, and △S1 = Smax1 - Smax2, △S2 = Smax3 - Smax1, △S1 ≤ △S2, the silicon carbide substrate in which stress is distributed in a stepwise manner according to claim 1.

6. A silicon carbide substrate in which the stress is distributed in a stepwise manner, as described in claim 5, wherein 0 MPa ≤ ΔS1 ≤ 10 MPa and 0 MPa ≤ ΔS2 ≤ 22 MPa.

7. In any plane parallel to the first principal surface and / or the second principal surface, Smin1 represents the minimum absolute value of the internal relative stress in the radial direction within the first-level stress interval, Smin2 represents the minimum absolute value of the internal relative stress in the radial direction within the second-level stress interval, Smin3 represents the minimum absolute value of the relative stress in the radial direction within the third-level stress interval, and △S3 = Smax1 - Smax2, △S4 = Smax3 - Smax1, △S3 ≤ △S4, as described in claim 1, the silicon carbide substrate in which the stress is distributed in a stepwise manner.

8. A silicon carbide substrate in which the stress is distributed in a stepwise manner, as described in claim 7, wherein 0 MPa ≤ ΔS3 ≤ 5 MPa and 10 MPa ≤ ΔS4 ≤ 20 MPa.

9. In any plane parallel to the first principal surface and / or the second principal surface, S1 represents the average value of the absolute values ​​of the internal relative stress in the radial direction within the first-level stress interval, S2 represents the average value of the absolute values ​​of the internal relative stress in the radial direction within the second-level stress interval, and S3 represents the average value of the absolute values ​​of the relative stress in the radial direction within the third-level stress interval, with 0 MPa ≤ S1 - S2 ≤ 14.5 MPa and 0 MPa ≤ S3 - S1 ≤ 22.5 MPa, the silicon carbide substrate in which the stress is distributed in a stepwise manner according to claim 1.

10. A silicon carbide substrate in which stress is distributed in a stepwise manner, as described in claim 1, wherein measurements are taken in the axial direction extending perpendicularly within the silicon carbide substrate from any point on the first main surface, and the internal relative stress in the axial direction of the first-level stress section is -20 to 20 MPa, the internal relative stress in the axial direction of the second-level stress section is -16 to 16 MPa, and the internal relative stress in the axial direction of the third-level stress section is -25 to 25 MPa.

11. Measurements are taken in the axial direction extending perpendicularly within the silicon carbide substrate from any point on the first main surface, where Smax5 represents the maximum internal relative stress in the axial direction of the first-level stress zone, Smin5 represents the minimum internal relative stress in the axial direction of the first-level stress zone, and ΔS5 = Smax5 - Smin5, 0 MPa ≤ ΔS5 ≤ 10 MPa. Smax6 is the maximum internal relative stress in the axial direction of the second-level stress interval, Smin6 is the minimum internal relative stress in the axial direction of the second-level stress interval, and S6 = Smax6 - Smin6, 0 MPa ≤ ΔS6 ≤ 10 MPa. Smax7 is the maximum value of the internal relative stress in the axial direction of the third-level stress interval, and Smin7 is the minimum value of the internal relative stress in the axial direction of the third-level stress interval. △S7 = Smax7 - Smin7, 0 MPa ≤ △S7 ≤ 10 MPa.

12. A silicon carbide substrate in which stress is distributed in a stepwise manner, according to claim 1, wherein the diameter of the silicon carbide substrate exceeds 200 mm, the width of the third-level stress section extending inward from the edge of the substrate is 21 to 30 mm, the width of the second-level stress section extending inward from the edge of the third-level stress section is 10 to 39 mm, and / or the thickness of the silicon carbide substrate is greater than or equal to 0.1 mm.

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