SiC single crystal substrate, SiC single crystal production method, and SiC single crystal production device

Abstract

The technical problem to be solved by the present invention is to provide a high-quality SiC single crystal which suppresses the generation of thermal strain during the crystal growth process and which has a small crystal defect density. [Solution] A SiC single crystal substrate having a first main surface and a second main surface positioned on the opposite side of the first main surface is used, and the first main surface is a surface inclined at an off-angle of 0-8 DEG with respect to a {0001} surface. Wherein, in a distribution of phase differences obtained by causing incident light having two polarization components orthogonal to each other and having a wavelength of 520 nm to be incident on the first main surface and measuring a phase difference between first and second emitted light emitted from the second main surface, the average value of the phase differences is 10 nm or less, and the maximum value of the phase differences is 70 nm or less.

Description

Technical Field

[0001] This invention relates to SiC (silicon carbide) single crystal substrates, methods for manufacturing SiC single crystals, and apparatus for manufacturing SiC single crystals, such as techniques for manufacturing SiC single crystals using a melt method. Background Technology

[0002] SiC single crystals exhibit highly stable thermal and chemical properties, along with excellent mechanical strength, radiation resistance, and higher dielectric breakdown voltage and thermal conductivity than Si (silicon) single crystals, demonstrating superior physical properties. Semiconductor devices made from SiC single crystals can achieve high power, high frequency, high voltage withstand, and environmental resistance—features unattainable with existing semiconductor materials like Si single crystals. Therefore, SiC single crystals hold promise as a next-generation semiconductor material for various fields.

[0003] Patent Document 1 (Japanese Patent Application Publication No. 2021-4173) discloses the evaluation of crystal defects in compound semiconductor substrates using a photoelastic method. Patent Document 2 (Japanese Patent Application Publication No. 2022-18072) discloses the fabrication of SiC single-crystal substrates using a vapor phase method. In Non-Patent Document 1, regarding the growth of SiC single crystals using a melt method, it is disclosed that the crystal growth conditions are optimized through simulation. The purpose of this optimization is to suppress the formation of polycrystalline SiC, known as impurities, within the melt. Non-Patent Document 2 discloses that the sublimation recrystallization method is used as the growth method for SiC single crystals.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2021-4173 Patent Document 2: Japanese Patent Application Publication No. 2022-18072 Non-patent literature Non-patent literature 1: K. Kusunoki et al., Mater. Sci. Forum Vol. 963 (2018) pp85-88 Non-patent literature 2: H. Tsuge et al, Mater. Sci. Forum Vol. 740-742 (2013) pp7-10 Summary of the Invention

[0005] The problem that the invention aims to solve As described in Non-Patent Document 1, it is known to optimize crystal growth conditions through simulation to suppress the formation of impurities. However, there is currently no method to optimize crystal growth conditions through simulation with an aim of reducing the thermal strain of SiC single crystals.

[0006] In view of the above facts, the object of the present invention is to realize a high-quality SiC single crystal that suppresses thermal strain during crystal growth and has a low crystal defect density.

[0007] Technical solutions for solving the problem One embodiment of the SiC single-crystal substrate has a first main surface and a second main surface located opposite to the first main surface. The first main surface is inclined at an angle of 0° to 8° relative to the {0001} surface. In a phase difference distribution obtained by incident light with two orthogonal polarization components and a wavelength of 520 nm onto the first main surface and measuring the phase difference between the first and second emitted light emitted from the second main surface, the average value of the phase difference is 10 nm or less, and the maximum value of the phase difference is 70 nm or less.

[0008] One embodiment of a method for manufacturing a SiC single crystal includes: (a) a step of contacting the lower surface of a seed substrate with a molten phase containing Si (silicon) and C (carbon) to grow a SiC single crystal. In step (a), the SiC single crystal is grown under the following conditions: the in-plane temperature difference at the interface between the lower surface of the seed substrate and the molten phase is set to 4.0°C or less, and the upward temperature gradient from the upper surface of the seed substrate located on the opposite side of the lower surface is set to 9°C / cm or more and 25°C / cm or less.

[0009] One embodiment of a SiC single crystal manufacturing apparatus includes: a seed crystal holding shaft having a cylindrical portion and capable of holding a seed crystal substrate below the cylindrical portion; a side heat insulation material disposed within the cylindrical portion; and an upper surface heat insulation material disposed within the cylindrical portion. The seed crystal substrate has a lower surface capable of contacting molten material contained in a crucible, and an upper surface located opposite the lower surface. The molten material contains Si and C. The inner diameter of the cylindrical portion is greater than or equal to the diameter of the seed crystal substrate. The side heat insulation material has a length such that, when the lower surface of the seed crystal substrate contacts the molten material, a portion of the side heat insulation material can be positioned above the upper end of the crucible. The upper surface heat insulation material is disposed at a position spaced above the upper surface of the seed crystal substrate.

[0010] Invention Effects According to one embodiment, thermal strain generated during crystal growth can be suppressed, resulting in high-quality SiC single crystals with low crystal defect density. Attached Figure Description

[0011] Figure 1 This is a cross-sectional view showing the single crystal manufacturing apparatus of Examples 1 to 4.

[0012] Figure 2 This is a cross-sectional view showing a portion of the single crystal manufacturing apparatus of Examples 1 to 4.

[0013] Figure 3 This is a cross-sectional view of the single crystal manufacturing apparatus of Comparative Example 1.

[0014] Figure 4 This is a cross-sectional view of the single crystal manufacturing apparatus of Comparative Example 2.

[0015] Figure 5 This is a cross-sectional view of the single crystal manufacturing apparatus of Comparative Example 3.

[0016] Figure 6 This is a cross-sectional view showing a portion of the single crystal manufacturing apparatus of Comparative Example 3.

[0017] Figure 7 This is a cross-sectional view of the single crystal manufacturing apparatus for Comparative Example 4.

[0018] Figure 8 This is a cross-sectional view of the single crystal manufacturing apparatus for Comparative Example 4.

[0019] Figure 9 This is a table showing the evaluation results of the embodiments and comparative examples.

[0020] Figure 10 A graph showing the relationship between the position of the seed substrate and the temperature difference.

[0021] Figure 11 This is a graph showing the relationship between the distance above the seed substrate and the temperature in Example 3.

[0022] Figure 12 This is an enlarged cross-sectional view showing the single crystal manufacturing apparatus of Example 3.

[0023] Figure 13 A graph showing the relationship between the distance above the seed crystal surface and temperature in Comparative Example 4.

[0024] Figure 14 This is an enlarged cross-sectional view of the single crystal manufacturing apparatus of Comparative Example 4.

[0025] Figure 15 This is a cross-sectional view of the single crystal manufacturing apparatus for Modified Example 1.

[0026] Figure 16 This is a cross-sectional view of the single crystal manufacturing apparatus for Modified Example 2.

[0027] Figure 17 This is a cross-sectional view of the single crystal manufacturing apparatus for modified example 3.

[0028] Figure 18This is a cross-sectional view of the single crystal manufacturing apparatus for variation example 4.

[0029] Symbol Explanation 10a, 10b, 10c, 13a, 13b, 13c: Thermal insulation materials; 10b1: Thermal insulation materials; 10b2: Thermal insulation materials; 10b3: Thermal insulation materials; 11: Coil; 12: Crucible; 14: Seed substrate; 14a: Upper surface; 16, 16a, 16b: Seed crystal holding axes; 16c: Finned component; 18: Crucible retaining shaft; 20: Si-C melt. Detailed Implementation

[0030] In all the accompanying drawings used to illustrate the embodiments, the same symbol is generally used to label the same component, and repeated descriptions are omitted. In addition, to make the drawings easier to understand, sometimes even plan views are given shaded lines.

[0031] (Implementation Method 1) The following explains how, when growing SiC single crystals using the melt method, the phase difference of the SiC single crystal can be reduced by adjusting the growth conditions, thereby producing high-quality SiC single crystals with small thermal strain.

[0032] <Aspects for Improvement> The growth methods for SiC single crystals can be broadly classified into gas-phase methods and liquid-phase methods. The former includes sublimation recrystallization and high-temperature gas methods, while the latter includes melt methods.

[0033] Sublimation recrystallization, a vapor-phase method, involves heating a solid raw material, including powdered SiC, at a high temperature to sublimate it. This sublimation then contacts a low-temperature seed substrate and recrystallizes, resulting in the growth of SiC single crystals. Sublimation recrystallization has several drawbacks, including the potential for hollow, through-type defects, lattice defects, or polymorphisms in the grown single crystal. However, it offers a fast crystal growth rate. Therefore, sublimation recrystallization is the most commonly used method for manufacturing SiC single crystals.

[0034] The high-temperature gas method, another gas-phase method, involves supplying a raw material gas and a carrier gas into a high-temperature furnace. The Si gas and Si₂C gas, which are seed molecules generated by the reaction of the raw material gas in the furnace, come into contact with the seed substrate and crystallize, thereby growing SiC single crystals. Because it uses high-temperature gases, the high-temperature gas method, compared to sublimation recrystallization, can not only obtain high-purity crystals but also expects high growth yields. However, the high-temperature gas method faces technical challenges in reducing crystal defects.

[0035] On the other hand, the melt method, a type of liquid-phase method, involves melting Si (silicon) or Si and its alloys in a graphite crucible, causing C (carbon) to dissolve from the crucible into the melt, and then growing SiC single crystals on the lower surface of a seed substrate. Compared to the sublimation recrystallization method or the high-temperature gas method mentioned above, the melt method can be expected to reduce crystal defects because crystal growth is carried out in a state close to thermal equilibrium.

[0036] However, in the melt method, when the temperature difference within the melt increases, polycrystalline SiC, known as impurities, forms within the melt and on the inner wall of the crucible in contact with the melt. These impurities float around the seed crystal and adhere to the seed crystal substrate, hindering single crystal growth and thus being undesirable. An effective method to suppress impurity formation is to homogenize the temperature distribution within the melt. However, while homogenizing the melt temperature suppresses impurity formation, it can sometimes prevent single crystal growth beneath the seed crystal substrate. Therefore, a solution is needed that can both homogenize the melt temperature distribution and facilitate crystal growth.

[0037] Therefore, the inventors of this invention explored the placement of a heat-insulating material on at least a portion of the side surface of the seed crystal holding axis. The inventors discovered that by placing the heat-insulating material in this manner, a heat dissipation path in the vertical direction of the seed crystal holding axis can be formed, enabling a more uniform temperature distribution within the melt while locally reducing the temperature around the seed crystal substrate. However, the inventors also discovered that if the heat-insulating material is only placed on the side surface of the seed crystal holding axis, residual thermal strain remains in the grown crystal because the temperature of the upper surface of the seed crystal substrate (the back surface of the seed crystal) remains high.

[0038] Thermal strain can cause crystal defects. An example of a crystal defect is a basal plane dislocation (BPD). The density of basal plane dislocations within a SiC single crystal is proportional to the value of the thermal strain within the SiC single crystal. Therefore, in order to fabricate SiC single crystals with fewer crystal defects, crystal growth simulations are performed to optimize crystal growth conditions with an eye toward reducing thermal strain. However, it is difficult to determine the thermal strain within a SiC single crystal through simulation and experiments.

[0039] In summary, from the perspective of controlling the generation of crystal defects, in the manufacturing of SiC single crystals, it is necessary to control the thermal strain generated within the SiC single crystal and reduce the stress within the SiC single crystal substrate obtained from the SiC single crystal.

[0040] <Evaluation of Crystal Defects> Next, the results of the inventor's research on the evaluation method for reducing crystal defects will be explained.

[0041] The inventors discovered that the magnitude of thermal strain within a SiC single crystal is substantially proportional to the phase difference between the two refracted beams of light transmitted through the SiC single crystal substrate due to birefringence when light shines on the substrate. In other words, by evaluating the phase difference, the thermal strain that causes crystal defects can be indirectly evaluated.

[0042] First, let's explain birefringence. Besides amplitude (brightness) and wavelength (color), light also possesses polarization (direction of vibration). The polarization of light can be decomposed into two mutually perpendicular polarization components. For example, incident light on an object has a first polarization component and a second polarization component with different planes of vibration. The first polarization component is, for example, the x-component vibrating along the x-axis, which is perpendicular to the direction of propagation of the incident light. The second polarization component is, for example, the y-component vibrating along the y-axis, which is perpendicular to the direction of propagation of the incident light. The x-axis and y-axis are orthogonal to each other.

[0043] When light passes through an object, the greater the object's refractive index, the longer it takes for the light to travel. In contrast, birefringence refers to the difference in propagation speed of light as it passes through an object due to the different orientations of its planes of vibration. When the incident light has a first polarization component and a second polarization component, for example, the first polarization component travels through the object more slowly than the second. As a result, a phase difference corresponding to the difference in travel speed occurs between the first outgoing light containing the first polarization component and the second outgoing light containing the second polarization component. Furthermore, due to birefringence, when the incident light enters the object, the first and second polarization components are refracted with different refractive indices. Therefore, two beams of light with different angles of incidence emerge from the object.

[0044] When light passes through an object that causes birefringence, the polarization state of the light changes due to the photoelastic effect. In other words, a phase difference is generated, which means that the polarization state changes. Therefore, birefringence can be evaluated by comparing the polarization state of light before and after it passes through the object.

[0045] Birefringence arises from the material of an object or the stress present within it. For example, when light passes through an object, birefringence does not occur when the stress in that object is zero, but it does occur when the object is under stress. The greater the stress within the object through which the light passes, the greater the phase difference of the polarization components caused by birefringence. The magnitude of the resulting phase difference is proportional to the stress, and its proportionality constant (photoelastic coefficient) is a fixed value for each material.

[0046] The distribution of birefringence in an object can be quantitatively quantified and visualized using a polarized image sensor and computational and image processing software. In other words, a polarized image sensor incorporating a photonic crystal filter can capture polarization information invisible to the naked eye in image form. By illuminating multiple parts of the object with light, and analyzing the resulting image containing multiple polarization information using computational and image processing software, the distribution of birefringence can be quantitatively quantified and visualized.

[0047] Birefringence is substantially proportional to the phase difference. Therefore, the phase difference can be used as a parameter to represent the degree of residual stress in an object. In other words, the phase difference value is proportional to the strain value of the object. Especially when the object is formed of a material that is substantially uniform in thickness, such as SiC single crystal, and the thickness of the object is substantially homogeneous, the reliability of the phase difference as a parameter for understanding the strain of the object becomes higher.

[0048] The sublimation recrystallization method described above can only produce crystals with large temperature gradients and distributions during crystal growth, as well as large residual strain. As a result, it is difficult to obtain high-quality SiC single-crystal substrates with an average phase difference of less than 15 nm using the sublimation recrystallization method.

[0049] The inventors focused on the correlation between the phase difference caused by birefringence when light shines on a SiC single crystal and the stress within the SiC single crystal, and discovered a method to evaluate the degree of crystal defects in a SiC single crystal using the value and distribution of the phase difference. The inventors also discovered that when light is shone onto a SiC single crystal and the phase difference between the two beams of light transmitted through the SiC single crystal is measured at multiple locations, SiC single crystals with fewer crystal defects can be obtained by reducing the average and maximum values ​​of the phase difference, respectively.

[0050] <On the use of the melt method to manufacture SiC single crystals> Using the aforementioned phase difference as an evaluation index, the inventors studied a method for manufacturing 4H polytype SiC single crystal substrates with fewer crystal defects. During this research, the inventors explored the use of a melt method for SiC single crystal growth.

[0051] At this point, the inventors discovered that by placing heat-insulating material not only inside the side portion of the seed crystal holding axis, but also on at least a portion of the upper surface of the seed crystal substrate, the temperature difference within the crystal plane can be kept below 4.0°C. The inventors also discovered that by setting the temperature gradient in the vertical direction (above) from the upper surface of the seed crystal substrate, which will become the driving force for crystal growth, to be between 9°C / cm and 25°C / cm, sufficient crystal growth driving force for obtaining bulk crystals can be ensured. As a result, SiC single-crystal substrates with an average phase difference of less than 10 nm can be obtained.

[0052] In this specification, the molten liquid containing Si (silicon) and C (carbon) is sometimes referred to as Si-C molten liquid. In addition, the SiC single crystal grown on the lower surface of the seed substrate, that is, on the surface of the seed substrate on the Si-C molten liquid side, is referred to as a grown crystal.

[0053] <Crystal Growth Simulation and Evaluation of SiC Single Crystal Substrates> The inventors fabricated various analytical models of single-crystal growth apparatuses and used these models to simulate the crystal growth of SiC single crystals under various manufacturing conditions. The inventors also fabricated a single-crystal manufacturing apparatus with the same structure as the analytical models used in the various crystal growth simulations, and used this apparatus to conduct SiC single-crystal growth experiments and manufacture SiC single-crystal substrates. The inventors evaluated the temperature distribution within the single-crystal manufacturing apparatus using crystal growth simulations and evaluated the phase difference using SiC single-crystal substrates obtained from the growth experiments. The following describes the inventors' simulations of SiC single-crystal growth under various manufacturing conditions, the SiC single-crystal growth experiments, the manufacture of SiC single-crystal substrates, and the evaluation of SiC single-crystal substrates. In other words, the following embodiments and comparative examples will be described sequentially.

[0054] Figures 1 to 8 This shows the structure of the single crystal manufacturing apparatus used in the SiC single crystal growth simulation and growth experiment. Figure 1 This is a cross-sectional view showing the single crystal manufacturing apparatus commonly used in Examples 1 to 4. Figure 2 This is a cross-sectional view showing a portion of the single crystal manufacturing apparatus commonly used in Examples 1 to 4. Figure 3 This is a cross-sectional view of the single crystal manufacturing apparatus used in Comparative Example 1. Figure 4 This is a cross-sectional view of the single crystal manufacturing apparatus used in Comparative Example 2. Figure 5 This is a cross-sectional view of the single crystal manufacturing apparatus used in Comparative Example 3. Figure 6 This is a cross-sectional view showing a portion of the single crystal manufacturing apparatus used in Comparative Example 3. Figure 7 and Figure 8 This is a cross-sectional view of the single crystal manufacturing apparatus used in Comparative Example 4. Figure 9This is a table showing the evaluation results of the embodiments and comparative examples.

[0055] (General conditions) First, the general conditions (structure of the manufacturing apparatus and manufacturing conditions) for each embodiment and comparative example described below will be explained.

[0056] The inventors used CGSim (a melt-based bulk crystal growth simulation software, manufactured by STR Japan, Ver. 20.1) to simulate the temperature distribution inside the crystal growth furnace and within the melt during SiC single crystal growth using the melt method. When performing the crystal growth simulation, the inventors fabricated a... Figures 1 to 8 The analytical model of the single crystal manufacturing apparatus shown is illustrated. The inventors also fabricated a single crystal manufacturing apparatus with the same structure as the analytical model used in crystal growth simulation, and conducted SiC single crystal growth experiments using this apparatus.

[0057] Next, the structure of the single crystal manufacturing apparatus common to each embodiment and comparative example will be described.

[0058] For example Figure 1 As shown, the single crystal manufacturing apparatus includes a heat-insulating material 13b constituting the hot zone. The heat-insulating material 13b is a cylindrical molded heat-insulating material. The outer diameter of the heat-insulating material 13b is 530 mm, the inner diameter is 390 mm, and the height is 420 mm. The upper opening of the heat-insulating material 13b is connected to a circular plate-shaped heat-insulating material 13c with a central opening. Furthermore, the lower opening of the heat-insulating material 13b is connected to a circular plate-shaped heat-insulating material 13a with a central opening.

[0059] A graphite crucible 12 is disposed within a cylindrical heat-insulating material 13b. The crucible 12 includes a cylindrical portion forming the sidewalls and a circular plate-shaped portion forming the bottom. The crucible 12 has an outer diameter of 270 mm, an inner diameter of 240 mm, and a height of 250 mm. A curvature of R50 is provided at the inner bottom corner of the crucible 12. However, in Comparative Example 4, the inner bottom corner of the crucible 12 does not have this curvature. Molten Si-C is disposed (contained) within the crucible 12. The interior of the single crystal manufacturing apparatus is set with an argon atmosphere. As a heating device, a five-turn coil (high-frequency coil) 11 with a diameter of 600 mm and a height of 90 mm is disposed around the crucible 12 in the horizontal direction, separated by the shaped heat-insulating material (heat-insulating material 13b). The coils 11 are arranged in a vertical row at a horizontal distance of 165 mm from the side of the crucible 12, and the middle height of the coils 11 in the vertical direction coincides with a height of 50 mm from the bottom surface of the crucible 12.

[0060] Next, the general method for forming Si-C melt for each embodiment and comparative example will be described.

[0061] First, a Si-C melt is formed in crucible 12. Here, crucible 12 contains Si (silicon) / Cr (chromium) / Mo (molybdenum) in an atomic composition percentage of 55:40:5 as the melt raw material. Next, an energizer 11 positioned around crucible 12 is applied, melting the raw material in crucible 12 by heating to form a Si / Cr / Mo alloy melt. Then, a sufficient amount of C is melted from crucible 12 into the Si / Cr / Mo alloy melt, forming a Si-C melt 20 with a height of approximately 50 mm. The growth temperature is confirmed separately from the growth experiment by inserting a thermocouple made of zirconia-coated tungsten-rhenium wire placed in a graphite protective tube into the seed crystal holding shaft, and measuring the surface temperature of the Si-C melt 20 under the same conditions as in the growth experiment.

[0062] Next, the SiC single crystal substrate and its evaluation method will be explained.

[0063] In the SiC single crystal growth experiment, crystal growth was performed using the melt method. A substrate was then cut from the grown crystal. Next, the first main surface of the substrate and the second main surface opposite to the first main surface were planar ground, followed by polishing. This yielded a 4H-SiC single crystal substrate (wafer) with a 4° off-center surface.

[0064] The SiC single-crystal substrate has a first main surface and a second main surface located on the opposite side of the first main surface, and is formed of polytype 4H SiC. The first main surface is a surface inclined at an angle relative to the {0001} surface. The angle can be, for example, 0° or more and 8° or less. The angle is preferably, for example, greater than 0° and 4.5° or less, and more preferably, for example, 2° or more and 4° or less.

[0065] The first principal surface of the SiC single crystal substrate is the so-called Si surface, mainly composed of Si (silicon) atoms, and the second principal surface is the so-called C surface, mainly composed of C (carbon) atoms. The thickness direction of the SiC single crystal substrate is from the first principal surface to the second principal surface. The maximum diameter of the first principal surface is 140 mm or more. Preferably, the maximum diameter of the first principal surface is 150 mm or more, more preferably 190 mm or more, and even more preferably 200 mm or more.

[0066] The inventors obtained the phase difference distribution of the SiC single-crystal substrate (details to be described later). First, the inventors moved along the first principal surface of the SiC single-crystal substrate... <0001> The direction (c-axis) is illuminated by incident light with a wavelength of 520nm. <0001> The direction is perpendicular to the {0001} plane. The incident light has a first polarization component and a second polarization component. The first polarization component is, for example, a polarization component that vibrates along a first direction perpendicular to the propagation direction of the incident light. The second polarization component is, for example, a polarization component that vibrates along a second direction perpendicular to the propagation direction of the incident light. The first direction and the second direction are orthogonal to each other. The phase difference between the first polarization component and the second polarization component contained in the incident light is, for example, zero. Next, the inventors measured the phase difference, i.e., the phase difference between the phase of the first emitted light containing the first polarization component and the phase of the second emitted light containing the second polarization component, emitted from the second main surface through the SiC single crystal substrate.

[0067] This phase difference measurement can be performed at multiple measurement points on the first principal surface of a SiC single-crystal substrate to obtain the phase difference distribution. For example, the number of measurement points on the first principal surface is set to 10. The more measurement points, the more accurate the phase difference distribution can be obtained; therefore, a larger number of measurement points is preferred, and more preferably, the phase difference measurement is performed on the entire surface of the SiC single-crystal substrate. For example, by using an image with millions of pixels to perform phase difference measurement on the entire surface of the SiC single-crystal substrate, an accurate phase difference distribution of the SiC single-crystal substrate can be obtained. In other words, by dividing the first principal surface of the SiC single-crystal substrate into rows and columns and measuring the phase difference at millions of points, an accurate phase difference distribution of the SiC single-crystal substrate can be obtained. The inventors obtained the phase difference distribution of the SiC single-crystal substrate by performing phase difference measurement on the entire surface of the SiC single-crystal substrate, and measured the average and maximum values ​​of the phase difference values ​​in the phase difference distribution.

[0068] The phase difference distribution of the SiC single crystal substrate was quantified and visualized using a two-dimensional birefringence evaluation system, WPA300L, manufactured by Photonic Lattice Co., Ltd. In the phase difference measurement of the SiC single crystal substrate obtained in this growth experiment, the phase difference distribution of the SiC single crystal substrate was quantified and visualized using the WPA300L two-dimensional birefringence evaluation system.

[0069] Next, the physical properties of the melt and the various components introduced into the single crystal growth apparatus are explained. Regarding Si-C melt 20 at 2000℃, the density is 3948 kg / m³. ﹣3 Viscosity = 2.49 × 10 ﹣3 Pas, conductivity = 1.23 × 10 6 Sm ﹣1 Thermal conductivity = 66.5 W / (m·K), specific heat = 791 J / kg ﹣1 K﹣1 The emissivity is 0.3. Regarding crucible 12 and the seed crystal holding shaft, the material is graphite, with a thermal conductivity of 36 W / (m·K) and an electrical conductivity of 9.14 × 10⁻⁶ at 2000℃. 4 Sm ﹣1 Emissivity = 0.8. For molded thermal insulation materials, density = 0.13 g / cm³. 3 The conductivity at 2000℃ is 8.08 × 10⁻⁶. 2 Sm ﹣1 Thermal conductivity = 0.47 W / (m·K), emissivity = 0.6. Regarding the felt described later, its electrical conductivity at 2000℃ = 0 Sm. ﹣1 The thermal conductivity is 0.40 W / (m·K). For argon, the thermal conductivity at 2000℃ is 0.06 W / (m·K). The temperature of coil 11 is 300 K. The oscillation frequency of the high-frequency heating using coil 11 is 2 kHz.

[0070] Next, the explanation Figures 1 to 8 The specific conditions of the various embodiments and comparative examples shown are illustrated. Furthermore, the evaluation results of each embodiment and comparative example are described below.

[0071] (Example 1) The following is an explanation Figure 1 The specific conditions of Example 1 are shown. In Example 1, the seed crystal holding shaft 16 is a graphite shaft. The seed crystal holding shaft 16 has a cylindrical portion (inner diameter 200 mm) and a circular plate portion connected to the front end of the cylinder in a manner that closes the opening of the cylinder. The diameter of the cylindrical portion is 210 mm and the length is 296 mm. The thickness of the circular plate portion is 10 mm and the diameter is 146 mm. The seed crystal substrate 14 is a circular plate-shaped 4H-SiC single crystal with a thickness of 0.8 mm and a diameter of 150 mm. The seed crystal substrate 14 is a circular plate-shaped 4H-SiC single crystal with an offset angle of 4°, which is produced by sublimation. The seed crystal substrate 14 is bonded to the front end of the seed crystal holding shaft 16 with carbon adhesive, with a 146 mm diameter and 10 mm thickness circular plate-shaped graphite component as a buffer. In addition, the inner diameter of the cylindrical portion of the seed crystal holding shaft 16 is a dimension greater than or equal to the diameter of the seed crystal substrate 14. Figure 1 In this context, the graphite component and the seed crystal holding shaft 16 are represented as a whole.

[0072] The lower surface of the seed substrate 14 is a {000-1} surface, and the {0001} surface, which is the upper surface of the seed substrate 14, is engaged with approximately the center of the lower surface of the seed holding shaft 16. The lower surface of the seed substrate 14 is a surface that can contact the Si-C molten liquid 20. The upper surface of the seed substrate 14 is held at the center of the lower surface of the seed holding shaft 16, which is movable in the vertical direction.

[0073] The seed crystal holding shaft 16 and the seed crystal substrate 14 pass through an opening in a circular plate-shaped heat-insulating material 13c disposed on the upper part of the crucible 12, and are disposed inside the heat-insulating material 13b. The diameter of the opening is 220 mm. The gap between the heat-insulating material 13c and the seed crystal holding shaft 16 in the opening is 5 mm.

[0074] The crucible 12 is connected to a cylindrical crucible holding shaft 18 that holds the crucible 12. This crucible holding shaft 18 is configured to move vertically. Furthermore, the crucible holding shaft 18 is rotatably supported on its cylindrical axis. Thus, the crucible 12 mounted on the crucible holding shaft 18 can move vertically in opposite directions via the crucible holding shaft 18, and can rotate horizontally. Additionally, the interior of the crucible holding shaft 18 is hollow, allowing the insertion of thermocouples or radiation thermometers for temperature measurement.

[0075] In Example 1, a heat-insulating material (side heat-insulating material) 10b with an outer diameter of 200 mm, a thickness of 20 mm, and a height of 275 mm is inserted into the interior of the cylindrical portion (side portion) of the seed crystal holding shaft 16. Here, the heat-insulating material 10b is disposed between the outer wall and the inner wall of the cylindrical portion; however, the heat-insulating material 10b may also be disposed further inward than the inner wall of the cylindrical portion, i.e., inside the cylindrical portion. Alternatively, the inner wall of the cylindrical portion may be omitted. In addition, a heat-insulating material (molded heat-insulating material, upper surface heat-insulating material) 10a with a diameter of 150 mm and a thickness of 10 mm is disposed inside the seed crystal holding shaft 16 and at the front end (lower end) of the seed crystal holding shaft 16. The heat-insulating material 10b has a length such that when the lower surface of the seed crystal substrate 14 is in contact with the Si-C melt 20, a portion of the heat-insulating material 10b can be disposed above the upper end of the crucible 12. Furthermore, when the lower surface of the seed substrate 14 comes into contact with the Si-C melt 20, a portion of the heat insulation material 10b is located at the same height as the heat insulation material 13c. Between the heat insulation material 10a and the seed holding shaft 16, there is a circular plate portion of the seed holding shaft 16.

[0076] Thermal insulation materials 10a, 10b, 13a, 13b, and 13c are made of nonwoven fabric woven from pitch-based carbon fibers. The nonwoven fabric is a carbonaceous or graphitic felt. Furthermore, as materials for thermal insulation materials 10a, 10b, 13a, 13b, and 13c, molded thermal insulation materials can also be used, which are obtained by impregnating pitch-based carbon fibers with a resin that has a high carbonization rate, and then undergoing molding, curing, carbonization, and graphitization treatments. When a felt is used for thermal insulation material 10b, a felt with a bulk density of approximately 0.1 g / cm³ can be used. 3 The material. When a molded thermal insulation material is used in thermal insulation material 10a, the molded thermal insulation material has a bulk density of approximately 0.13 g / cm³. 3 ~0.16g / cm3 The material is molded thermal insulation material with a coefficient of thermal expansion of 2.2 × 10⁻⁶. ﹣6 / K. Molded insulation is stiffer than felt, so it is easier to maintain its shape and easier to use.

[0077] The heat insulation materials 10a and 10b are configured such that the direction of their carbon fibers is orthogonal to the heat insulation direction. The purpose of heat insulation material 10a is to achieve heat insulation in a direction perpendicular to the lower surface of the seed crystal holding axis 16. The purpose of heat insulation material 10b is to achieve heat insulation in a direction perpendicular to the side surface of the seed crystal holding axis 16. The bottom surface of heat insulation material 10a is circular, and this bottom surface is opposite to the upper surface of the seed crystal substrate 14. The cylindrical heat insulation material 10b is opposite to the inner wall of the cylindrical portion constituting the seed crystal holding axis 16. Figure 2 As shown, the fibers constituting the heat insulation material 10a extend in the direction along the upper surface of the seed crystal. The extending direction of the fibers constituting the heat insulation material 10a can be the circumferential direction of the disc-shaped heat insulation material 10a or radial direction. In addition, the fibers constituting the heat insulation material 10b extend along the central axis of the cylindrical portion constituting the seed crystal holding axis 16.

[0078] In Example 1, the heat insulation material 10a disposed inside the cylindrical seed crystal holding shaft 16 has a bulk density of 0.16 g / cm³. 3 A 10mm thick circular plate-shaped heat insulation material. The heat insulation material 10a is disposed 15mm above the upper surface of the seed crystal, separated from the graphite component.

[0079] Next, the operation of the single crystal manufacturing apparatus of Example 1, or in other words, the crystal growth process of Example 1, will be described.

[0080] In the crystal growth process using the single crystal manufacturing apparatus of Example 1, firstly, the seed crystal holding axis 16 is moved downwards. As a result, the lower surface of the seed crystal substrate 14, held by the seed crystal holding axis 16, coincides with the upper surface of the Si-C melt 20. At this time, the entire lower surface of the seed crystal substrate 14 is wetted by the Si-C melt 20. Then, at a temperature of 2100°C for 40 hours, while lifting the seed crystal holding axis 16 upwards, SiC single crystals are grown on the lower surface side of the seed crystal substrate 14, starting from the seed crystal substrate 14. During the crystal growth process, the crucible 12 is rotated at 5 rpm around the central axis of the seed crystal holding axis 16. The downward and upward movements of the seed crystal holding axis 16 are performed automatically, for example, by a power controlled by a control unit (not shown).

[0081] After crystal growth, the substrate from which the molten growth portion was cut from the grown crystal is planar ground, followed by polishing. This yields a SiC single-crystal substrate. The inventors used crystal growth simulation to obtain the temperature distribution within the single-crystal manufacturing apparatus and used the SiC single-crystal substrate to measure the phase difference.

[0082] (Example 2) Next, the explanation Figure 2 The specific conditions of Example 2 are shown. Furthermore, even if a matter is not described in the (General Conditions) section above, if it is a condition common to Example 1, this is stated and repeated descriptions are omitted. The same applies to Examples 3, 4, Comparative Example 1, Comparative Example 2, and Comparative Example 3 described later.

[0083] In Example 2, using Figure 1 and Figure 2 The single crystal manufacturing apparatus shown performs crystal growth. The configuration of the single crystal manufacturing apparatus in Example 2 is the same as that in Example 1.

[0084] The crystal growth in Example 2 was carried out under the same conditions as in Example 1, except that the temperature during crystal growth was set to 2000°C.

[0085] In addition, similar to Example 1, the temperature distribution within the single crystal manufacturing apparatus was obtained using crystal growth simulation, and the phase difference was measured using a SiC single crystal substrate.

[0086] (Example 3) In Example 3, using Figure 1 and Figure 2 The single crystal manufacturing apparatus shown performs crystal growth. The configuration of the single crystal manufacturing apparatus in Example 3 is the same as that in Example 1, except that the thickness of the heat insulation material 10a is set to 5 mm.

[0087] Using the single crystal manufacturing apparatus described above, the crystal growth of Example 3 was performed under the same conditions as in Example 1. Therefore, repeated descriptions are omitted.

[0088] In addition, similar to Example 1, the temperature distribution within the single crystal manufacturing apparatus was obtained using crystal growth simulation, and the phase difference was measured using a SiC single crystal substrate.

[0089] (Example 4) In Example 4, using Figure 1 and Figure 2 The single crystal manufacturing apparatus shown performs crystal growth. The configuration of the single crystal manufacturing apparatus in Example 4 is the same as that in Example 1.

[0090] The crystal growth in Example 4 was carried out under the same conditions as in Example 3, except that the crystal growth temperature was set to 2000°C. Therefore, repeated descriptions are omitted.

[0091] In addition, similar to Example 1, the temperature distribution within the single crystal manufacturing apparatus was obtained using crystal growth simulation, and the phase difference was measured using a SiC single crystal substrate.

[0092] (Comparative Example 1) In Comparative Example 1, using Figure 3 The single crystal manufacturing apparatus shown performs crystal growth. The configuration of the single crystal manufacturing apparatus of Comparative Example 1 is the same as that of the single crystal manufacturing apparatus of Example 1, except that the cylindrical heat insulation material 10b and the circular plate heat insulation material 10a are not inserted inside the cylindrical seed crystal holding shaft 16.

[0093] Using the single crystal manufacturing apparatus described above, the crystal growth of Comparative Example 1 was performed under the same conditions as in Example 1; therefore, repeated descriptions are omitted.

[0094] In addition, similar to Example 1, the temperature distribution within the single crystal manufacturing apparatus was obtained using crystal growth simulation, and the phase difference was measured using a SiC single crystal substrate.

[0095] (Comparative Example 2) In Comparative Example 2, using Figure 4 The single crystal manufacturing apparatus shown performs crystal growth. The configuration of the single crystal manufacturing apparatus of Comparative Example 2 is the same as that of the single crystal manufacturing apparatus of Example 1, except that a circular plate-shaped heat insulation material 10a is not inserted inside the cylindrical seed crystal holding shaft 16.

[0096] Using the single crystal manufacturing apparatus described above, crystal growth for Comparative Example 2 was performed under the same conditions as in Example 1; therefore, repeated descriptions are omitted.

[0097] Furthermore, similar to Example 1, crystal growth simulation was used to obtain the temperature distribution within the single crystal manufacturing apparatus. However, in this example, SiC single crystal growth was not possible, and the phase difference of the SiC single crystal substrate could not be measured.

[0098] (Comparative Example 3) In Comparative Example 3, using Figure 5 and Figure 6 The single crystal manufacturing apparatus shown performs crystal growth. The single crystal manufacturing apparatus of Comparative Example 3 differs from that of Example 1 in that it has a short vertically oriented heat insulation material 10c instead of heat insulation material 10b, and a short cylindrical seed crystal holding axis 16a. Specifically, as... Figure 5As shown, the seed crystal holding shaft 16a consists of a solid cylindrical portion (thin shaft portion) connected to a cylindrical portion (thick shaft portion), and the front end of the cylindrical portion has a graphite shaft with a circular plate portion. The cylindrical portion has a diameter of 26 mm and a length of 227 mm. The cylindrical portion has a diameter of 210 mm, a length of 156 mm, and an inner diameter of 200 mm. The circular plate portion has a thickness of 10 mm and a diameter of 146 mm. A heat-insulating material 10c is disposed inside the cylindrical portion of the seed crystal holding shaft 16a.

[0099] like Figure 6 As shown, the fibers constituting the heat insulation material 10a extend in a direction along the upper surface of the seed crystal substrate 14. The extending direction of the fibers constituting the heat insulation material 10a can be the circumferential direction of the disc-shaped heat insulation material 10a or radial direction. In addition, the fibers constituting the heat insulation material 10b extend along the central axis of the cylindrical portion constituting the seed crystal holding axis 16.

[0100] The seed crystal holding shaft 16a and the seed crystal substrate 14 are configured such that the thin shaft portion of the seed crystal holding shaft 16a passes through an opening in a circular plate-shaped heat-insulating material 13c disposed on the upper part of the crucible 12. The diameter of this opening is 70 mm. The gap between the heat-insulating material in the opening and the thin shaft portion of the seed crystal holding shaft 16a is 10 mm. The length of the cylindrical portion of the seed crystal holding shaft 16a is shorter than the length of the cylindrical portion of the seed crystal holding shaft 16 in Example 1. Therefore, the length of the heat-insulating material 10b inside the seed crystal holding shaft 16a is also about 140 mm shorter than the length of the heat-insulating material 10b in Example 1.

[0101] Using the single crystal manufacturing apparatus described above, crystal growth in Comparative Example 3 was performed under the same conditions as in Example 1. Therefore, repeated descriptions are omitted.

[0102] Furthermore, similar to Example 1, crystal growth simulation was used to obtain the temperature distribution within the single crystal manufacturing apparatus. However, in this example, SiC single crystal growth was not possible, and the phase difference of the SiC single crystal substrate could not be measured.

[0103] (Comparative Example 4) Used in Comparative Example 4 Figure 7 and Figure 8 The single crystal manufacturing apparatus shown is used for crystal growth.

[0104] The seed crystal retaining axis 16b used in Comparative Example 4 is as follows: Figure 7As shown, the structure has a graphite circular plate portion mounted on the front end of a graphite cylindrical rod. The cylindrical rod has a diameter of 26 mm and a length of 282 mm. The circular plate portion has a diameter of 146 mm and a thickness of 10 mm. The seed crystal substrate 14 is a circular plate-shaped 4H-SiC single crystal with a thickness of 0.8 mm and a diameter of 150 mm. The upper surface of the seed crystal substrate 14 is held at the center of the lower surface of the seed crystal holding axis 16b. Figure 7 The base is held between the crucible 12 and the crucible holding shaft 18, and is held by the crucible holding shaft 18. The seed crystal holding shaft 16b has a plurality of fin members 16c that are assembled intersecting the extending direction (vertical direction) of the seed crystal holding shaft 16.

[0105] like Figure 8 As shown, the fibers constituting the heat insulation materials 13a and 13c along the upper surface of the seed crystal substrate 14 extend in the direction along the upper surface of the seed crystal substrate 14. Furthermore, the fibers constituting the cylindrical heat insulation material 13b surrounding the crucible 12 extend along the central axis of the cylinder. This is also true in other embodiments and comparative examples.

[0106] Using the single crystal manufacturing apparatus described above, crystal growth in Comparative Example 4 was performed under the same conditions as in Example 1. Therefore, repeated descriptions are omitted.

[0107] Furthermore, similar to Example 1, crystal growth simulation was used to obtain the temperature distribution within the single crystal manufacturing apparatus. However, in this example, SiC single crystal growth was not possible, and the phase difference of the SiC single crystal substrate could not be measured.

[0108] <Evaluation Results> Next, using Figure 9 The evaluation results of Examples 1, 2, 3, 4, Comparative Examples 1, 2, 3, 4, and Reference Examples 1 and 2 will be explained. In Reference Examples 1 and 2, commercially available 6-inch diameter SiC single crystal substrates manufactured using the sublimation recrystallization method were evaluated.

[0109] In the evaluation project, the in-plane temperature difference is the in-plane temperature difference at the interface where the lower surface of the seed substrate 14 contacts the Si-C melt 20. The in-plane temperature difference of the lower surface of the seed holding axis 16 is quantified by calculating a temperature profile within 75 mm from the center of the circular lower surface.

[0110] Figure 10 A graph showing the relationship between the position of the seed substrate and the temperature difference. Figure 10 The horizontal axis represents the distance from the center of the seed substrate 14, and the vertical axis represents the temperature difference within the upper surface of the seed substrate 14. Figure 10In the diagram, solid lines represent the curve of Example 1, thicker dashed lines represent the curve of Example 2, thinner dashed lines represent the curve of Comparative Example 1, single-dot-dash lines represent the curve of Comparative Example 2, thinner double-dot-dash lines represent the curve of Comparative Example 3, and thicker double-dot-dash lines represent the curve of Comparative Example 4. Figure 10 As shown, in Examples 1, 2, Comparative Examples 3 and 4, the in-plane temperature difference at the interface between the lower surface of the seed substrate 14 and the Si-C melt 20 is less than 4.0°C. However, in Comparative Examples 3 and 4, due to the small temperature difference, crystals do not grow.

[0111] In the evaluation project, the temperature gradient is: the temperature curves in the vertical direction of the upper surface of the seed crystal substrate 14 are calculated at the center of the lower surface of the seed crystal holding axis 16 and at every 10 mm interval within 60 mm from the center, and the temperature gradient within 10 mm in the vertical direction from the upper surface of the seed crystal substrate 14 is quantified.

[0112] Figure 11 This is a graph showing the relationship between the distance above the upper surface of the seed substrate 14 and the temperature in Example 3. Figure 11 The horizontal axis represents temperature, and the vertical axis represents the distance above (vertically) from the upper surface of the seed substrate 14. Figure 11 In the middle, from the upper surface 14a of the circular seed substrate 14 (refer to) Figure 12 The temperature change curves were created above seven points at their centers: 0mm, 10mm, 20mm, 30mm, 40mm, 50mm, and 60mm. Figure 12 This is a magnified cross-sectional view of a single crystal manufacturing apparatus. The measurement locations of these seven points are as follows: Figure 12 As shown by the arrow.

[0113] exist Figure 11 In the diagram, curves at distances of 0mm, 10mm, 20mm, 30mm, 40mm, 50mm, and 60mm from the center of the upper surface 14a are represented by thinner dashed lines, thinner single-dot dashed lines, double-dot dashed lines, thinner solid lines, thicker solid lines, thicker dashed lines, and thicker single-dot dashed lines, respectively. Figure 11 In the figure, the curves at distances of 0 mm, 10 mm, 20 mm, and 30 mm from the center of the upper surface 14a basically overlap. At the 0 mm position, the temperature gradient is 9.6 ℃ / cm, and at the 60 mm position, the temperature gradient is 24.2 ℃ / cm.

[0114] Figure 13 A graph showing the relationship between the distance above the upper surface of the seed substrate 14 and the temperature in Comparative Example 4. Figure 13The horizontal axis represents temperature, and the vertical axis represents the distance above (vertically) from the upper surface of the seed substrate 14. Figure 13 In the middle, from the upper surface 14a of the circular seed substrate 14 (refer to) Figure 12 The temperature changes above seven points (0mm, 10mm, 20mm, 30mm, 40mm, 50mm, and 60mm) are plotted as curves. Figure 14 This is an enlarged cross-sectional view of the single crystal manufacturing apparatus of Comparative Example 4. The measurement positions of the seven points are shown below. Figure 14 As shown by the arrow.

[0115] exist Figure 13 In the diagram, the curves at distances of 0 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, and 60 mm from the center of the upper surface 14a are represented by thinner dashed lines, thinner single-dot dashed lines, double-dot dashed lines, thinner solid lines, thicker solid lines, thicker dashed lines, and thicker single-dot dashed lines, respectively. At the 0 mm position, the temperature gradient is 0.7℃ / cm, and at the 60 mm position, the temperature gradient is 0.8℃ / cm. With such small temperature gradients, the temperature difference that drives crystal growth disappears, and therefore, crystal growth does not occur.

[0116] In the evaluation project, regarding the phase difference, for the entire first principal surface of the SiC single crystal substrate obtained by crystal growth through each embodiment and each comparative example, the wavelength of light along the 520nm path... <0001> The phase difference of birefringence caused by photoelasticity was measured by observing the direction of light transmission. Birefringence arises from strain caused by crystal defects or residual stress within the crystal. The inventors determined the average and maximum values ​​of the phase difference distribution in the SiC single-crystal substrate. The measurements were performed using the WPA300L two-dimensional birefringence evaluation system manufactured by Photonic Lattice Co., Ltd.

[0117] As a comprehensive evaluation of each embodiment and each comparative example, the case where the average phase difference is less than 10 nm is evaluated as acceptable (circle (〇)). The case where the average phase difference is less than 10 nm and the maximum phase difference is less than 25 nm is evaluated as a more preferred case among the acceptable cases (double circle (◎)).

[0118] like Figure 9 As shown, in Examples 1-4, the in-plane temperature difference is below 4.0°C, the average phase difference is below 10 nm, and the maximum phase difference is below 70 nm. Furthermore, in Examples 3 and 4, the temperature gradient is above 9°C / cm and below 25°C / cm, and the maximum phase difference is below 40 nm. As mentioned above, a small phase difference indicates a small strain on the object.

[0119] <Effects of the Implementation Method> In this embodiment, by making the thermal strain during crystal growth less than that generated in the sublimation recrystallization method, a SiC single-crystal substrate with less crystal distortion and a lower crystal defect density can be obtained. As a means, this embodiment utilizes a melt method to grow SiC single crystals. In the melt method, where SiC is melted in a metal solvent and grown from a supercooled liquid phase, the growth temperature can be lowered compared to the sublimation recrystallization method. Therefore, the thermal strain of the SiC single crystal can be reduced. This addresses the aforementioned improvement potential that makes SiC single crystals grown by the vapor phase method prone to internal defects.

[0120] Furthermore, by setting the in-plane temperature difference at the interface between the lower surface of the seed substrate and the Si-C molten phase to 4.0°C or less, it is possible to manufacture SiC single crystals and SiC single crystal substrates with an average phase difference of less than 10 nm and a maximum phase difference of 70 nm or less. In addition, by setting the vertical temperature gradient of the upper surface of the seed substrate to 9°C / cm or more and 25°C / cm or less, it is possible to further reduce the average and maximum phase differences. The maximum phase difference is 70 nm or less in Example 1, but more preferably 50 nm or less, and even more preferably 25 nm or less as shown in Examples 3 and 4.

[0121] However, it is believed that when pursuing uniform temperature distribution to reduce the in-plane temperature difference at the interface between the lower surface of the seed substrate and the Si-C molten phase to below 4.0°C, the vertical temperature gradient of the upper surface of the seed substrate simultaneously decreases to below 1°C / cm, and the temperature difference, which is the driving force for crystal growth, disappears. In Comparative Examples 3 and 4, this temperature gradient becomes extremely small, resulting in the inability to obtain SiC single crystals, making it impossible to measure the phase difference or evaluate whether the crystals are qualified.

[0122] In contrast, in Examples 1 to 4 of this embodiment, the in-plane temperature difference at the interface between the lower surface of the seed substrate 14 and the Si-C melt 20 is 4.0°C or less, and the vertical temperature gradient of the upper surface of the seed substrate 14, which serves as the driving force for crystal growth, is greater than in Comparative Examples 3 and 4. In this embodiment, heat-insulating material 10b is used as a component to maintain the temperature difference within the upper surface of the seed substrate 14 at 4.0°C or less. Furthermore, heat-insulating material 10a is used as a component to maintain the vertical temperature distribution from the upper surface of the seed substrate 14 at a rate of 9°C / cm to 25°C / cm or less. In other words, in this embodiment, heat-insulating material is disposed at least in a portion of the space above the upper surface of the seed substrate 14. Here, a seed holding shaft 16 with an inner diameter equal to or greater than the diameter of the seed substrate 14 is used, and heat-insulating materials 10a and 10b are disposed within the cylindrical portion of the seed holding shaft 16 to achieve the aforementioned temperature. In addition, to achieve heat insulation on the side of the seed crystal holding shaft 16, heat insulation material 10b is disposed on at least a portion of the side of the seed crystal holding shaft 16. Furthermore, as a heat-insulating component, heat insulation material 10a is disposed to cover at least a portion of the upper surface of the seed crystal substrate 14.

[0123] Heat dissipation in the vertical direction on the upper surface of the seed substrate 14 is suppressed by the provision of heat-insulating materials 10a and 10b, thereby achieving temperature uniformity within the upper surface of the seed substrate 14. The thicker the heat-insulating materials 10a and 10b, the more significant their heat-insulating effect. Furthermore, the closer the heat-insulating materials 10a and 10b are positioned to the upper surface of the seed substrate 14, the more significant their heat-insulating effect.

[0124] As a result, the temperature distribution within the upper surface of the seed substrate 14 is homogenized. However, when the heat insulation materials 10a and 10b are too thick or too close to the upper surface of the seed substrate 14, the vertical heat dissipation of the upper surface of the seed substrate 14 decreases. Therefore, the temperature difference (temperature gradient) that drives crystal growth becomes smaller. Furthermore, when the heat insulation materials 10a and 10b are excessively far from the upper surface of the seed substrate 14, the effect of homogenizing the temperature distribution on the upper surface of the seed substrate 14 disappears. When the heat insulation material 10a is a molded heat insulation material, the thickness of the heat insulation material 10a, which is capable of homogenizing the in-plane temperature distribution at the interface where the seed substrate 14 contacts the Si-C melt 20 and ensuring the temperature difference that drives crystal growth, is preferably 3 mm to 25 mm, more preferably 5 mm to 15 mm. The position of the heat insulation material 10a is 3 mm to 50 mm from the upper surface of the seed substrate 14, more preferably 10 mm to 30 mm.

[0125] When it is difficult to directly attach the heat insulation material 10a to the seed crystal substrate 14, the heat insulation material 10a can be placed inside the graphite hollow clamp, and the seed crystal substrate 14 can be attached to the hollow clamp.

[0126] As described above, high-quality SiC single crystals with low crystal defect density and suppressed thermal strain during crystal growth can be achieved. The SiC single crystal substrate can be used as a substrate for providing an epitaxial layer for device formation on a first or second main surface. n SiC single crystal substrates of this embodiment can be prepared, and a wafer group (n is, for example, 12 or more, preferably 100 or more) can be formed using these n SiC single crystal substrates.

[0127] The invention described above is based on its implementation methods, but the invention is not limited to the above implementation methods. It goes without saying that changes can be made without departing from the essence of the invention.

[0128] The following describes variations of the implementation method.

[0129] <Variation Example 1> Figure 15 This is a cross-sectional view of the single crystal manufacturing apparatus for Modified Example 1.

[0130] exist Figure 1 In the single-crystal manufacturing apparatus shown, the heat insulation material 10a does not contact the heat insulation material 10b. In contrast, in... Figure 15 In the modified example 1 shown, the heat insulation material 10a is in contact with the heat insulation material 10b. For example, the heat insulation material 10a and the heat insulation material 10b can also be integrated. Thus, the technical concept of the present invention can be applied regardless of whether the heat insulation material 10a and the heat insulation material 10b are in contact.

[0131] <Variation Example 2> Figure 16 This is a cross-sectional view of the single crystal manufacturing apparatus for Modified Example 2.

[0132] In Modification 2, the thermal insulation material 10b is composed of thermal insulation material 10b1 and thermal insulation material 10b2. Thermal insulation material 10b2 is disposed inside thermal insulation material 10b1. Thermal insulation material 10b2 is in contact with thermal insulation material 10b1. Thermal insulation material 10b2 is in contact with thermal insulation material 10a.

[0133] Thermal insulation material 10b1 and thermal insulation material 10b2 can be made of the same material. Alternatively, thermal insulation material 10b1 and thermal insulation material 10b2 can also be made of different materials. When thermal insulation material 10b1 and thermal insulation material 10b2 are made of different materials, for example, a combination of molded thermal insulation material and felt thermal insulation material can be used. When thermal insulation material 10b1 and thermal insulation material 10b2 are made of different materials, for example, a combination of thermal insulation materials with different densities can also be used.

[0134] <Variation Example 3> Figure 17 This is a cross-sectional view of the single crystal manufacturing apparatus for modified example 3.

[0135] In Modification 3, the thermal insulation material 10b is composed of thermal insulation material 10b1, thermal insulation material 10b2, and thermal insulation material 10b3. Thermal insulation material 10b2 is disposed inside thermal insulation material 10b1. Thermal insulation material 10b3 is disposed inside thermal insulation material 10b2. Thermal insulation material 10b2 is in contact with thermal insulation material 10b1. Thermal insulation material 10b2 is in contact with thermal insulation material 10b3. Thermal insulation material 10b3 is in contact with thermal insulation material 10a.

[0136] Thermal insulation materials 10b1, 10b2, and 10b3 can be made of the same material. Alternatively, they can be made of different materials. When thermal insulation materials 10b1, 10b2, and 10b3 are made of different materials, examples include combinations of molded thermal insulation materials and felt thermal insulation materials. Furthermore, when thermal insulation materials 10b1, 10b2, and 10b3 are made of different materials, combinations of thermal insulation materials with different densities can also be used.

[0137] <Variation Example 4> Figure 18 This is a cross-sectional view of the single crystal manufacturing apparatus for variation example 4.

[0138] The cross-sectional shape of the insulation material 10b in variation example 4 can also be the same as... Figure 1 The insulation material 10b shown has different cross-sectional shapes. For example... Figure 18 As shown, in the cross-sectional shape of the heat insulation material 10b in Modified Example 4, the radial (transverse) thickness of the seed crystal retaining axis 16 is greater than that of the heat insulation material 10b in Modified Example 4. Figure 1 The thickness of the heat insulation material 10b shown. On the other hand, in the cross-sectional shape of the heat insulation material 10b in Modified Example 4, the length in the longitudinal direction (longitudinal direction) of the seed crystal holding axis 16 is less than Figure 1The length of the heat insulation material 10b shown. In Modification 4, the heat insulation material 10b is in contact with the heat insulation material 10a. Furthermore, from the perspective of realizing the technical concept of the present invention, in the cross-sectional shape of the heat insulation material 10b in Modification 4, it is preferable that the upper surface of the heat insulation material 10b is positioned above the upper surface of the crucible 12. For example, Figure 18 The diagram shows an example in which the position of the upper surface of the heat insulation material 10b in the cross-sectional shape of the heat insulation material 10b coincides with the position of the upper surface of the crucible 12.

Claims

1. A SiC single-crystal substrate, characterized in that: It has a first main surface and a second main surface located on the opposite side of the first main surface. The first main surface is a surface inclined at an angle of 0° to 8° relative to the {0001} surface. In the distribution of phase difference obtained by incident light with two orthogonal polarization components and a wavelength of 520 nm onto the first principal surface and measuring the phase difference between the first and second emitted light emitted from the second principal surface, The average value of the phase difference is less than 10 nm. The maximum value of the phase difference is below 70 nm.

2. The SiC single-crystal substrate as described in claim 1, characterized in that: The maximum value of the phase difference is less than 50 nm.

3. The SiC single-crystal substrate as described in claim 1, characterized in that: The maximum value of the phase difference is less than 25 nm.

4. The SiC single-crystal substrate as described in claim 1, characterized in that: The maximum diameter of the first main surface is 140 mm or more.

5. The SiC single-crystal substrate as described in claim 1, characterized in that: An epitaxial layer for device formation is disposed on the first main surface or on the second main surface.

6. The SiC single-crystal substrate as described in claim 1, characterized in that: n SiC single crystal substrates constitute a wafer group, wherein n is 12 or more.

7. A method for manufacturing SiC single crystals, characterized in that: This includes (a) a process of bringing the lower surface of a seed substrate into contact with a molten solution containing Si and C to grow SiC single crystals. In step (a), the SiC single crystal is grown under the following conditions: the in-plane temperature difference at the interface between the lower surface of the seed crystal substrate and the molten phase is set to 4.0°C or less, and the temperature gradient from the upper surface of the seed crystal substrate located on the opposite side of the lower surface upwards is set to 9°C / cm or more and 25°C / cm or less.

8. An apparatus for manufacturing SiC single crystals, characterized in that, include: A seed holding shaft having a cylindrical portion and capable of holding a seed substrate below the cylindrical portion; Side insulation material provided within the cylindrical portion; and Thermal insulation material is provided on the upper surface inside the cylindrical portion. The seed crystal substrate has a lower surface that can contact the molten phase contained in the crucible, and an upper surface located on the opposite side of the lower surface. The melt contains Si and C. The inner diameter of the cylindrical portion is greater than or equal to the diameter of the seed crystal substrate. The side insulating material has a length such that, when the lower surface of the seed substrate comes into contact with the molten metal, a portion of the side insulating material can be positioned above the upper end of the crucible. The upper surface heat insulation material is disposed at a position spaced above the upper surface of the seed crystal substrate.

9. The SiC single crystal manufacturing apparatus as described in claim 8, characterized in that: The side insulation material is a component that ensures the in-plane temperature difference at the interface between the lower surface of the seed substrate and the molten phase is below 4.0°C. The upper surface heat insulation material is a component that ensures that the temperature gradient from the upper surface of the seed crystal substrate upwards is above 9°C / cm and below 25°C / cm.

10. The SiC single crystal manufacturing apparatus as described in claim 8, characterized in that: The side insulation material is in contact with the upper surface insulation material.

11. The SiC single crystal manufacturing apparatus as described in claim 8, characterized in that: The side insulation material does not come into contact with the upper surface insulation material.

12. The SiC single crystal manufacturing apparatus as described in claim 8, characterized in that: The side insulation material includes a first side insulation material and a second side insulation material in contact with the first side insulation material.

13. The SiC single crystal manufacturing apparatus as described in claim 12, characterized in that: The side insulation material also includes a third side insulation material that is in contact with the second side insulation material.

14. The SiC single crystal manufacturing apparatus as described in claim 8, characterized in that: In cross-section, the upper surface of the side insulation material is positioned above the upper surface of the crucible.

15. The SiC single crystal manufacturing apparatus as described in claim 14, characterized in that: In cross-section, the upper surface of the side insulation material is positioned at the same level as the upper surface of the crucible.

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