SiC single crystal substrate, method for manufacturing SiC single crystals, and apparatus for manufacturing SiC single crystals

Abstract

This technology suppresses the generation of thermal strain during crystal growth, enabling the realization of high-quality SiC single crystals with a low crystal defect density. [Solution] A SiC single crystal substrate is used, comprising a first main surface and a second main surface located opposite the first main surface, wherein the first main surface is a surface inclined with an off-angle of 0° to 8° with respect to the {0001} plane. Here, incident light having two mutually orthogonal polarization components and a wavelength of 520 nm is incident on the first main surface, and the phase difference between the first emitted light and the second emitted light emitted from the second main surface is measured. In the distribution of phase differences obtained, 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.

Description

[Technical Field]

[0001] The present invention relates to a SiC (silicon carbide) single crystal substrate, a method for manufacturing a SiC single crystal, and an apparatus for manufacturing a SiC single crystal, and more particularly to a SiC single crystal manufacturing technology using a solution method. [Background technology]

[0002] SiC single crystals possess excellent physical properties, including high thermal and chemical stability, superior mechanical strength, strong radiation resistance, and higher dielectric breakdown voltage and thermal conductivity compared to Si (silicon) single crystals. Semiconductor devices using SiC single crystals can achieve high power output, high frequency, high voltage resistance, and environmental resistance that cannot be realized with semiconductor devices using existing semiconductor materials such as Si single crystals. For this reason, SiC single crystals are expected to be the next-generation semiconductor material in various fields.

[0003] Patent Document 1 (Japanese Patent Publication No. 2021-4173) describes evaluating the crystal strain of a compound semiconductor substrate using a photoelastic method. Patent Document 2 (Japanese Patent Publication No. 2022-18072) describes manufacturing a SiC single crystal substrate using a vapor phase method. Non-Patent Document 1 describes optimizing the crystal growth conditions by simulation for the growth of SiC single crystals using a solution method. This optimization is performed to suppress the formation of polycrystalline SiC called miscellaneous crystals in the solution. Non-Patent Document 2 describes using a sublimation recrystallization method as a method for growing SiC single crystals. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-4173 [Patent Document 2] Japanese Patent Publication No. 2022-18072 [Non-patent literature]

[0005] [Non-Patent Document 1] K. Kusunoki et al., Mater. Sci. Forum Vol. 963 (2018) pp 85-88 [Non-Patent Document 2] H. Tsuge et al, Mater. Sci. Forum Vol. 740-742 (2013) pp 7-10. [Overview of the project] [Problems that the invention aims to solve]

[0006] As described in Non-Patent Document 1, it is known that the formation of miscellaneous crystals can be suppressed by optimizing crystal growth conditions through simulation. However, optimization of crystal growth conditions through simulation focusing on reducing the thermal strain of SiC single crystals has not been performed.

[0007] In view of the above circumstances, this disclosure aims to suppress the occurrence of thermal strain during crystal growth and to realize high-quality SiC single crystals with a low crystal defect density. [Means for solving the problem]

[0008] In one embodiment, the SiC single crystal substrate is a SiC single crystal substrate having a first main surface and a second main surface on the opposite side of the first main surface, wherein the first main surface is a surface inclined with respect to the {0001} plane at an off-angle of 0° to 8°. Here, incident light having two mutually orthogonal polarization components and a wavelength of 520 nm is incident on the first main surface, and the phase difference between the first emitted light and the second emitted light emitted from the second main surface is measured. In the distribution of the phase difference obtained, 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.

[0009] A method for manufacturing a SiC single crystal in one embodiment comprises (a) a step of growing a SiC single crystal by bringing the lower surface of a seed crystal substrate into contact with a solution containing Si (silicon) and C (carbon). In step (a), the SiC single crystal is grown under conditions that the in-plane temperature difference at the interface where the lower surface of the seed crystal substrate and the solution are in contact is 4.0°C or less, and the temperature gradient from the upper surface of the seed crystal substrate, which is located on the opposite side of the lower surface, toward the upward direction is 9°C / cm or more and 25°C / cm or less.

[0010] A SiC single crystal manufacturing apparatus in one embodiment comprises a cylindrical portion, a seed crystal holding shaft capable of holding a seed crystal substrate below the cylindrical portion, a side insulating material provided within the cylindrical portion, and an upper insulating material provided within the cylindrical portion. Here, the seed crystal substrate has a lower surface that can come into contact with a solution contained in a crucible, and an upper surface located on the opposite side from the lower surface. The solution 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 crystal substrate is in contact with the solution, a portion of the side insulating material can be positioned further above the upper end of the crucible. The upper insulating material is provided at a position away from the upper surface of the seed crystal substrate in the upward direction. [Effects of the Invention]

[0011] According to one embodiment, it is possible to suppress the occurrence of thermal strain during crystal growth and realize a high-quality SiC single crystal with a low crystal defect density. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view showing the single crystal manufacturing apparatus in Examples 1 to 4. [Figure 2] This is a cross-sectional view showing a part of the single crystal manufacturing apparatus in Examples 1 to 4. [Figure 3] This is a cross-sectional view showing the single crystal manufacturing apparatus in Comparative Example 1. [Figure 4] This is a cross-sectional view showing the single crystal manufacturing apparatus in Comparative Example 2. [Figure 5] It is a cross-sectional view showing a single crystal manufacturing apparatus in Comparative Example 3. [Figure 6] It is a cross-sectional view showing a part of the single crystal manufacturing apparatus in Comparative Example 3. [Figure 7] It is a cross-sectional view showing a single crystal manufacturing apparatus in Comparative Example 4. <了 [Figure 8] It is a cross-sectional view showing a single crystal manufacturing apparatus in Comparative Example 4. [Figure 9] It is a table showing the evaluation results in the examples and comparative examples. [Figure 10] It is a graph showing the relationship between the position of the seed crystal substrate and the temperature difference. [Figure 11] It is a graph showing the relationship between the distance upward from the upper surface of the seed crystal and the temperature in Example 3. [Figure 12] It is an enlarged cross-sectional view showing the single crystal manufacturing apparatus in Example 3. [Figure 13] It is a graph showing the relationship between the distance upward from the upper surface of the seed crystal and the temperature in Comparative Example 4. [Figure 14] It is an enlarged cross-sectional view showing the single crystal manufacturing apparatus in Comparative Example 4. [Figure 15] It is a cross-sectional view showing the single crystal manufacturing apparatus in Modification 1. [Figure 16] It is a cross-sectional view showing the single crystal manufacturing apparatus in Modification 2. [Figure 17] It is a cross-sectional view showing the single crystal manufacturing apparatus in Modification 3. [Figure 18] It is a cross-sectional view showing the single crystal manufacturing apparatus in Modification 4.

Mode for Carrying Out the Invention

[0013] In all the drawings for explaining the embodiments, in principle, the same members are denoted by the same reference numerals, and the repeated description thereof is omitted. Note that, for easy understanding of the drawings, hatching may be added even to a plan view.

[0014] (Embodiment 1) The following describes how to reduce the phase difference of SiC single crystals by adjusting the growth conditions during solution-based SiC single crystal growth, thereby producing high-quality SiC single crystals with low thermal strain.

[0015] <Room for improvement> SiC single crystal growth methods are broadly classified into gas-phase and liquid-phase methods. The former includes sublimation recrystallization and high-temperature gas methods. The latter includes solution methods.

[0016] Sublimation recrystallization, a vapor phase method, involves heating and sublimating a solid raw material consisting of powdered SiC at a high temperature, and then recrystallizing it in contact with a low-temperature seed crystal substrate to grow a SiC single crystal. Sublimation recrystallization has the disadvantage of easily producing crystal defects in the grown single crystal, such as hollow through-defects, lattice defects, or different crystal polymorphs. However, sublimation recrystallization offers a fast crystal growth rate. Therefore, SiC single crystals are often manufactured using sublimation recrystallization.

[0017] Another gas-phase method, the high-temperature gas method, involves supplying a raw material gas and a carrier gas into a high-temperature furnace. SiC single crystals are grown by bringing the molecular species formed by the reaction of the raw material gases in the furnace—Si gas and Si2C gas—into contact with a seed crystal substrate and allowing them to crystallize. The high-temperature gas method allows for the production of crystals of higher purity compared to the sublimation recrystallization method by using high-temperature gas, and also offers the potential for high-yield growth. However, the high-temperature gas method faces challenges in reducing crystal defects.

[0018] On the other hand, the solution method, a type of liquid-phase method, involves melting Si (silicon) or Si and an alloy in a graphite crucible, dissolving C (carbon) from the crucible into the melt, and growing a SiC single crystal on the underside of a seed crystal substrate. Compared to the sublimation recrystallization method and the high-temperature gas method described above, the solution method allows crystal growth to occur in a state closer to thermal equilibrium, thus reducing crystal defects.

[0019] However, in the solution method, if the temperature difference within the solution becomes large, polycrystalline SiC called "miscellaneous crystals" will form within the solution and on the inner wall of the crucible in contact with the solution. The floating of these miscellaneous crystals around the seed crystal and their adhesion to the seed crystal substrate is undesirable because it inhibits single crystal growth. To suppress the formation of miscellaneous crystals, it is effective to homogenize the temperature distribution within the solution. However, while homogenizing the temperature distribution of the solution can suppress the formation of miscellaneous crystals, it may also prevent single crystal growth beneath the seed crystal substrate. Therefore, it is necessary to devise a method that both homogenizes the temperature distribution of the solution and promotes crystal growth.

[0020] Therefore, the inventors considered placing an insulating material on at least a portion of the side surface of the seed crystal holding axis. The inventors found that by arranging the insulating material in this way, a heat dissipation path can be formed in the vertical direction of the seed crystal holding axis, thereby homogenizing the temperature distribution in the solution and locally lowering the temperature around the seed crystal substrate. However, it was also found that simply placing an insulating material on the side surface of the seed crystal holding axis does not prevent thermal strain from remaining in the growing crystal because the temperature of the upper surface of the seed crystal substrate (back of the seed crystal) is still high.

[0021] Thermal strain can cause crystal defects. An example of a crystal defect is basal plane dislocation (BPD). The density of basal plane dislocations in a SiC single crystal is proportional to the value of thermal strain within the SiC single crystal. Therefore, in order to manufacture a SiC single crystal with few crystal defects, it is conceivable to optimize the crystal growth conditions by performing crystal growth simulations that focus on reducing thermal strain. However, measuring thermal strain within a SiC single crystal through simulation or experiment is difficult.

[0022] Therefore, in the manufacturing of SiC single crystals, it is desirable to suppress the thermal strain generated within the SiC single crystal and to reduce the stress within the SiC single crystal substrate obtained from the SiC single crystal, from the viewpoint of suppressing the occurrence of crystal defects.

[0023] <Evaluation of crystal defects> Next, we will explain the results of our investigation into a method for evaluating the effect of reducing crystal defects.

[0024] The inventors have found that the magnitude of thermal strain within a SiC single crystal is approximately proportional to the phase difference that occurs between two refracted beams of light transmitted through a SiC single crystal substrate due to birefringence when light is irradiated onto the substrate. In other words, by evaluating the phase difference, it is possible to indirectly evaluate the thermal strain, which is the cause of crystal defects.

[0025] First, let's explain birefringence. Light has elements other than amplitude (brightness) and wavelength (color), such as polarization (direction of vibration). The polarization of light can be decomposed into two polarization components that are perpendicular to each other. For example, incident light entering an object has a first polarization component and a second polarization component, each with different planes of vibration. The first polarization component is, for example, the x component that vibrates along the x-axis perpendicular to the direction of propagation of the incident light. The second polarization component is, for example, the y component that vibrates along the y-axis perpendicular to the direction of propagation of the incident light. The x-axis and y-axis are orthogonal to each other.

[0026] When light passes through an object, the greater the refractive index of the object, the longer it takes for the light to pass through. In contrast, birefringence refers to the phenomenon where, when light passes through an object, its speed differs depending on the orientation of the plane of vibration. When incident light has a first polarization component and a second polarization component, for example, the first polarization component passes through the object more slowly than the second polarization component. As a result, a phase difference arises between the first emitted light containing the first polarization component and the second emitted light containing the second polarization component, due to the difference in their passing speeds. Furthermore, due to birefringence, the first and second polarization components are refracted at different refractive indices when the incident light hits the object. This results in two emitted beams of light with different angles of illumination being emitted from the object.

[0027] When light passes through an object that exhibits birefringence, the polarization state of the light changes due to the photoelastic effect. In other words, the occurrence of a phase difference means that the polarization state is changed. Therefore, birefringence can be evaluated by comparing the polarization state of light before and after it passes through the object.

[0028] Birefringence occurs due to the material of an object or the stress it experiences. For example, when light is transmitted through an object, birefringence may not occur when the object's stress is zero, but it will occur when the object is under stress. The phase difference of the polarization components caused by birefringence increases with increasing stress within the object through which the light is transmitted. The magnitude of the resulting phase difference is proportional to the stress, and the proportionality constant (photoelastic coefficient) is constant for each material.

[0029] The distribution of birefringence in an object can be quantified and visualized using a polarization image sensor and computational / image processing software. In other words, a polarization image sensor incorporating a photonic crystal filter can capture invisible polarization information as an image. By irradiating multiple points on an object with light and analyzing the resulting images containing multiple polarization information using computational / image processing software, the distribution of birefringence can be quantified and visualized.

[0030] Birefringence is approximately proportional to the phase difference. Therefore, the phase difference can be used as a parameter indicating the degree of residual stress in an object. In other words, the value of the phase difference is proportional to the value of the strain in the object. In particular, when an object is formed from substantially the same material in the thickness direction, such as a SiC single crystal, and the thickness of the object is substantially uniform, the reliability of the phase difference as a parameter for determining the strain of the object increases.

[0031] In the sublimation recrystallization method described above, the temperature gradient and temperature distribution during crystal growth are large, and only crystals with high residual strain can be obtained. 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.

[0032] The inventors focused on the correlation between the phase difference caused by birefringence when light is irradiated onto a SiC single crystal and the stress within the SiC single crystal, and found a method for evaluating the degree of crystal defects in a SiC single crystal using the value of the phase difference and the distribution of the phase difference. Furthermore, the inventors found that by irradiating a SiC single crystal with light and measuring the phase difference between the two emitted rays transmitted through the SiC single crystal at multiple locations, a SiC single crystal with fewer crystal defects can be obtained by reducing both the average value and the maximum value of the phase difference.

[0033] <Regarding the manufacturing of SiC single crystals using solution-based methods> The inventors of the present invention studied a method for manufacturing a 4H polytype SiC single crystal substrate with few crystal defects, using the above-mentioned phase difference as an evaluation index. In the course of this research, the inventors investigated growing SiC single crystals by a solution method.

[0034] Therefore, the inventors found that by placing insulating material within the side surface of the seed crystal holding shaft, and also by placing insulating material on at least a portion of the upper surface of the seed crystal substrate, the temperature difference within the crystal plane can be reduced to 4.0°C or less. In addition, the inventors found that by setting the vertical (upward) temperature gradient from the upper surface of the seed crystal substrate, which serves as the driving force for crystal growth, to 9°C / cm or more and 25°C / cm or less, sufficient crystal growth driving force to obtain a bulk crystal can be secured. As a result, it was found that a SiC single crystal substrate with an average phase difference of less than 10 nm can be obtained.

[0035] In this specification, a solution containing Si (silicon) and C (carbon) may be referred to as a Si-C solution. Furthermore, a SiC single crystal grown on the underside of a seed crystal substrate, that is, on the side of the seed crystal substrate facing the Si-C solution, is referred to as a grown crystal.

[0036] <Crystal growth simulation and evaluation of SiC single-crystal substrates> The inventors created multiple analytical models of single crystal growth apparatuses and used these models to perform crystal growth simulations of SiC single crystals under various manufacturing conditions. Furthermore, the inventors created a single crystal manufacturing apparatus with a structure similar to the analytical models used in the multiple crystal growth simulations, and used it 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 through crystal growth simulations and evaluated the phase difference using SiC single crystal substrates obtained from the growth experiments. The following describes the crystal growth simulations of SiC single crystals under multiple manufacturing conditions, the SiC single crystal growth experiments, the manufacture of SiC single crystal substrates, and the evaluation of SiC single crystal substrates performed by the inventors. Specifically, each example and comparative example described below will be explained in order.

[0037] Figures 1 to 8 show the structure of the single crystal manufacturing apparatus used in the crystal growth simulation and growth experiment of SiC single crystals. Figure 1 is a cross-sectional view of the single crystal manufacturing apparatus used in common to Examples 1 to 4. Figure 2 is a cross-sectional view of a part of the single crystal manufacturing apparatus used in common to Examples 1 to 4. Figure 3 is a cross-sectional view of the single crystal manufacturing apparatus used in Comparative Example 1. Figure 4 is a cross-sectional view of the single crystal manufacturing apparatus used in Comparative Example 2. Figure 5 is a cross-sectional view of the single crystal manufacturing apparatus used in Comparative Example 3. Figure 6 is a cross-sectional view of a part of the single crystal manufacturing apparatus used in Comparative Example 3. Figures 7 and 8 are cross-sectional views of the single crystal manufacturing apparatus used in Comparative Example 4. Figure 9 is a table showing the evaluation results in the examples and comparative examples.

[0038] (Common conditions) First, we will explain the conditions common to each of the examples and comparative examples described later (the structure of the manufacturing equipment and the manufacturing conditions).

[0039] The inventors of this invention simulated the temperature distribution inside the crystal growth furnace and in the solution when growing SiC single crystals using the solution method, using CGSim (Survey software for bulk crystal growth from solution, manufactured by STR Japan, Ver. 20.1). For the crystal growth simulation, the inventors created an analytical model of a single crystal manufacturing apparatus having the configuration shown in Figures 1 to 8. Furthermore, the inventors created a single crystal manufacturing apparatus with a structure similar to the analytical model used in the crystal growth simulation, and conducted SiC single crystal growth experiments using this apparatus.

[0040] Next, the structure of the single crystal manufacturing apparatus common to each example and each comparative example will be described.

[0041] For example, as shown in Figure 1, the single crystal manufacturing apparatus is equipped with an insulating material 13b that constitutes the hot zone. The insulating material 13b is a cylindrical molded insulating material. The outer diameter of the insulating material 13b is 530 mm, the inner diameter is 390 mm, and the height is 420 mm. The opening at the upper end of the insulating material 13b is connected to a disc-shaped insulating material 13c which has an opening in the center. The opening at the lower end of the insulating material 13b is connected to a disc-shaped insulating material 13a which has an opening in the center.

[0042] A graphite crucible 12 is placed inside a cylindrical insulating material 13b. The crucible 12 has a cylindrical portion that forms the side wall and a disc-shaped portion that forms the bottom surface. The outer diameter of the crucible 12 is 270 mm, the inner diameter is 240 mm, and the height is 250 mm. The inner bottom corners of the crucible 12 are provided with a curvature of R50. In Comparative Example 4, no curvature is provided at the inner bottom corners of the crucible 12. A Si-C solution is placed (contained) inside the crucible 12. The inside of the single crystal manufacturing apparatus is maintained in an argon atmosphere. As a heating device, a 5-turn coil (high-frequency coil) 11 with a diameter of 600 mm and a height of 90 mm is placed around the horizontal perimeter of the crucible 12 via a molded insulating material (insulating material 13b). The coils 11 are arranged in a vertical line 165 mm horizontally from the side of the crucible 12, and are positioned so that the midpoint of the vertical height of the coils 11 coincides with a height of 50 mm from the bottom surface inside the crucible 12.

[0043] Next, we will describe the method for forming the Si-C solution, which is common to each example and each comparative example.

[0044] First, a Si-C solution was formed in crucible 12. Here, Si (silicon) / Cr (chromium) / Mo (molybdenum) were placed in crucible 12 as molten raw materials in an atomic composition ratio of 55:40:5. Next, current was passed through coils 11 arranged around crucible 12 to melt the raw materials in crucible 12 by heating, forming a Si / Cr / Mo alloy melt. Then, a sufficient amount of C was dissolved from crucible 12 into the Si / Cr / Mo alloy melt to form a Si-C solution 20 with a height of approximately 50 mm. The growth temperature was confirmed separately from the growth experiment by inserting a thermocouple, consisting of a 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 solution 20 under the same conditions as the growth experiment.

[0045] Next, we will describe the SiC single crystal substrate and its evaluation method.

[0046] In the SiC single crystal growth experiment, crystal growth was performed using a solution method. Subsequently, a substrate was cut from the grown crystal. Next, the first principal surface and the second principal surface opposite the first principal surface of the substrate were planar ground and then polished. This resulted in obtaining a 4H-SiC single crystal substrate (wafer) with a 4° off-plane.

[0047] The SiC single crystal substrate comprises a first principal surface and a second principal surface opposite the first principal surface, and is made of polytype 4H SiC. The first principal surface is a surface inclined at an off-angle with respect to the {0001} plane. The off-angle may be, for example, 0° or more and 8° or less. Preferably, the off-angle is, for example, greater than 0° and 4.5° or less, and more preferably, for example, 2° or more and 4° or less.

[0048] The first principal surface of the SiC single crystal substrate is a so-called Si surface, where mainly Si (silicon) atoms are exposed on the surface, and the second principal surface is a so-called C surface, where mainly C (carbon) atoms are exposed on the surface. The thickness direction of the SiC single crystal substrate is the direction 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.

[0049] The inventors obtained the phase difference distribution (details will be described later) for this SiC single crystal substrate. First, the inventors applied the following to the first main surface of the SiC single crystal substrate: <0001> Incident light with a wavelength of 520 nm was irradiated along the direction (c-axis). <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 direction of propagation of the incident light. The second polarization component is, for example, a polarization component that vibrates along a second direction perpendicular to the direction of propagation of the incident light. The first and second directions 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, which is the 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, among the emitted light that passed through the SiC single crystal substrate and exited from the second main surface.

[0050] The phase difference distribution can be obtained by measuring such phase differences at multiple measurement points on the first main surface of a SiC single crystal substrate, for example. The number of measurement points on the first main surface is, for example, 10. A larger number of measurement points is preferable because a more accurate distribution of phase differences can be obtained. It is even more desirable to measure the phase difference across the entire surface of the SiC single crystal substrate. For example, by measuring the phase difference across the entire surface of the SiC single crystal substrate using an image of several million pixels, an accurate distribution of the phase difference of the SiC single crystal substrate can be obtained. In other words, by measuring the phase difference at each of several million locations obtained by dividing the first main surface of the SiC single crystal substrate into a matrix, an accurate distribution of the phase difference of the SiC single crystal substrate can be obtained. The inventors obtained the distribution of the phase difference of the SiC single crystal substrate by measuring the phase difference across the entire surface of the SiC single crystal substrate and measured the average and maximum values ​​of the phase difference in the distribution.

[0051] The distribution of the phase difference of the SiC single crystal substrate is quantified and visualized using an apparatus such as a two-dimensional birefringence evaluation system WPA300L manufactured by Photonic Lattice Co., Ltd. In the measurement of the phase difference of the SiC single crystal substrate obtained in this growth experiment, the two-dimensional birefringence evaluation system WPA300L was used to quantify and visualize the distribution of the phase difference of the SiC single crystal substrate.

[0052] Next, the physical property values of the solution and the physical property values of each member incorporated in the single crystal growth apparatus will be described. Regarding the Si-C solution 20 at 2000 °C, density = 3948 kgm 3 ,

[0054] , ―1 ,

[0053] , , , , ―1 , 2 , ―1 , , , viscosity = 2.49×10 -3 Pas, electrical conductivity = 1.23×10 6 Sm ―1 , thermal conductivity = 66.5 W / (m·K), specific heat 791 Jkg -1 K -1 , emissivity 0.3. For the crucible 12 and the seed crystal holding shaft, the material is graphite, thermal conductivity at 2000 °C = 36 W / (m·K), electrical conductivity = 9.14×10 <00,00007>Sm ―1 , emissivity = 0.8. The formed heat insulating material has a density = 0.13 g / cm <, 3 , electrical conductivity at 2000 °C = 8.08×10 2 Sm ―1 , thermal conductivity = 0.47 W / (m·K), emissivity = 0.6. The felt described later has an electrical conductivity of 0 Sm at 2000 °C ―1 , thermal conductivity = 0.40 W / (m·K). Argon has a thermal conductivity of 0.06 W / (m·K) at 2000 °C. The temperature of the coil 11 is 300 K. The oscillation frequency of the high-frequency heating by the coil 11 is 2 kHz.

[0053] Next, the specific conditions of a plurality of examples and a plurality of comparative examples shown in FIGS. 1 to 8 will be described. The evaluation results of each example and comparative example will be described later.

[0054] (Example 1) The following describes the specific conditions for Example 1 shown in Figure 1. In Example 1, the seed crystal holding shaft 16 is a graphite shaft. The seed crystal holding shaft 16 comprises a cylindrical portion (inner diameter 200 mm) and a disc portion connected to the tip of the cylinder to close the opening of the cylinder. The diameter of the cylindrical portion is 210 mm and the length is 296 mm. The thickness of the disc portion is 10 mm and the diameter is 146 mm. The seed crystal substrate 14 is a disc-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 disc-shaped 4H-SiC single crystal having a {000-1} plane with an off-angle of 4°, produced by sublimation. Here, the seed crystal substrate 14 is attached to the tip of the seed crystal holding shaft 16 with carbon adhesive via a disc-shaped graphite member with a diameter of 146 mm and a thickness of 10 mm. Furthermore, the inner diameter of the cylindrical portion of the seed crystal holding shaft 16 is greater than or equal to the diameter of the seed crystal substrate 14. In Figure 1, the graphite member is shown integrated with the seed crystal holding shaft 16.

[0055] The seed crystal substrate 14 is positioned so that its lower surface becomes the {000-1} plane, and its upper surface, the {0001} plane, is bonded to approximately the center of the lower surface of the seed crystal holding shaft 16. The lower surface of the seed crystal substrate 14 is a surface that can contact the Si-C solution 20. The upper surface of the seed crystal substrate 14 is held in the center of the lower surface of the seed crystal holding shaft 16, which is movable in the vertical direction.

[0056] The seed crystal holding shaft 16 and the seed crystal substrate 14 are positioned inside the insulating material 13b through an opening in the disc-shaped insulating material 13c, which is located on top of the crucible 12. The diameter of the opening is 220 mm. The gap between the insulating material 13c and the seed crystal holding shaft 16 at the opening is 5 mm.

[0057] 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 be movable in the vertical direction. Furthermore, the crucible holding shaft 18 is supported so as to be rotatable with its cylindrical axis as the axis of rotation. As a result, the crucible 12 attached to the crucible holding shaft 18 can be moved vertically and rotated horizontally by the crucible holding shaft 18. The crucible holding shaft 18 has a hollow structure inside, and is configured so that a thermocouple or radiation thermometer can be inserted to measure the temperature.

[0058] In Example 1, a thermal insulation material (side insulation material) 10b with an outer diameter of 200 mm, a thickness of 20 mm, and a height of 275 mm is inserted inside the cylindrical portion (side portion) of the seed crystal holding shaft 16. Here, the thermal insulation material 10b is placed between the outer and inner walls of the cylindrical portion, but the thermal insulation material 10b may also be placed inside the inner wall of the cylindrical portion, i.e., inside the cylindrical portion. Alternatively, the inner wall of the cylindrical portion may be omitted. Furthermore, a thermal insulation material (molded insulation material, top surface insulation material) 10a with a diameter of 150 mm and a thickness of 10 mm is placed inside the seed crystal holding shaft 16, at the tip (lower end) of the seed crystal holding shaft 16. The thermal insulation material 10b has a length such that when the lower surface of the seed crystal substrate 14 is in contact with the Si-C solution 20, a portion of the thermal insulation material 10b can be positioned even higher than the upper end of the crucible 12. Furthermore, a portion of the thermal insulation material 10b is at the same height as the thermal insulation material 13c when the lower surface of the seed crystal substrate 14 is in contact with the Si-C solution 20. The disc portion of the seed crystal holding shaft 16 is interposed between the thermal insulation material 10a and the seed crystal holding shaft 16.

[0059] The thermal insulation materials 10a, 10b, 13a, 13b, and 13c consist of a nonwoven fabric made by intertwining pitch-based carbon fibers. The nonwoven fabric is a carbonaceous or graphite-based felt. Alternatively, the thermal insulation materials 10a, 10b, 13a, 13b, and 13c may also be molded thermal insulation materials, which are made by impregnating pitch-based carbon fibers with a resin with a high carbonization rate, and then molding, hardening, carbonizing, and graphitizing them. When using felt for thermal insulation material 10b, for example, the felt may have a bulk density of approximately 0.1 g / cm³. 3The following materials are used. When molded insulation material is used for insulation material 10a, the molded insulation material has a bulk density of approximately 0.13 g / cm³. 3 ~0.16 g / cm³ 3 The following materials are used. The thermal expansion coefficient of the molded insulation is 2.2 × 10⁻⁶. -6 It is / K. Molded insulation is more rigid than felt, making it easier to maintain its shape and use.

[0060] The insulating materials 10a and 10b are arranged so that the direction of their carbon fibers is perpendicular to the insulating direction. Insulating material 10a is arranged for insulating in a direction perpendicular to the lower surface of the seed crystal holding shaft 16. Insulating material 10a is arranged for insulating in a direction perpendicular to the side surface of the seed crystal holding shaft 16. The bottom surface of insulating material 10a is circular and faces the upper surface of the seed crystal substrate 14. The cylindrical insulating material 10 faces the inner wall of the cylindrical portion constituting the seed crystal holding shaft 16. As shown in Figure 2, the fibers constituting insulating material 10a extend in a direction along the upper surface of the seed crystal. The direction of extension of the fibers constituting insulating material 10a may be in the circumferential direction of the disc-shaped insulating material 10a or in the radial direction. The fibers constituting insulating material 10b extend along the central axis of the cylindrical portion constituting the seed crystal holding shaft 16.

[0061] In Example 1, the thermal insulation material 10a installed inside the cylindrical seed crystal holding shaft 16 has a bulk density of 0.16 g / cm³. 3 The insulating material is a disc-shaped molded insulating material with a thickness of 10 mm. The insulating material 10a is installed at a position 15 mm above the upper surface of the seed crystal via a graphite member.

[0062] Next, we will describe the operation of the single crystal manufacturing apparatus in Example 1, or in other words, the crystal growth process in Example 1.

[0063] In the crystal growth process using the single crystal manufacturing apparatus according to Example 1, first, the seed crystal holding shaft 16 is moved downward. As a result, the lower surface of the seed crystal substrate 14 held by the seed crystal holding shaft 16 coincides with the upper surface of the Si-C solution 20. At this time, the entire lower surface of the seed crystal substrate 14 is wetted by the Si-C solution 20. Subsequently, at a temperature of 2100°C, a SiC single crystal was grown on the lower surface of the seed crystal substrate 14, starting from the seed crystal substrate 14, over a period of 40 hours while the seed crystal holding shaft 16 was pulled upward. During crystal growth, the crucible 12 was rotated at 5 rpm around the central axis of the seed crystal holding shaft 16. The downward and upward movements of the seed crystal holding shaft 16 described above are performed automatically by power controlled, for example, by a control unit (not shown).

[0064] After crystal growth, the substrate from which the solution-grown portion was cut out from the grown crystal was subjected to surface grinding and then polishing. This resulted in obtaining a SiC single crystal substrate. The inventors obtained the temperature distribution inside the single crystal manufacturing apparatus by crystal growth simulation and measured the phase difference using the SiC single crystal substrate.

[0065] (Example 2) Next, we will explain the specific conditions related to Example 2 shown in Figure 2. Note that even if a condition is not explained in the (Common Conditions) section above, if it is common to Example 1, we will state that fact and omit redundant explanations. The same applies to Examples 3, 4, Comparative Example 1, Comparative Example 2, and Comparative Example 3, which will be described later.

[0066] In Example 2, crystal growth was performed using the single crystal manufacturing apparatus shown in Figures 1 and 2. The configuration of the single crystal manufacturing apparatus in Example 2 is the same as that of the single crystal manufacturing apparatus in Example 1.

[0067] Crystal growth in Example 2 was carried out under the same conditions as in Example 1, except that the temperature during crystal growth was 2000°C.

[0068] Furthermore, similar to Example 1, the temperature distribution inside the single crystal manufacturing apparatus was obtained by crystal growth simulation, and the phase difference was measured using a SiC single crystal substrate.

[0069] (Example 3) In Example 3, crystal growth was performed using the single crystal manufacturing apparatus shown in Figures 1 and 2. Here, the configuration of the single crystal manufacturing apparatus in Example 3 is the same as that of the single crystal manufacturing apparatus in Example 1, except that the thickness of the insulating material 10a is 5 mm.

[0070] Crystal growth in Example 3 was carried out using the single crystal manufacturing apparatus described above, under the same conditions as in Example 1. Therefore, redundant explanations will be omitted.

[0071] Furthermore, similar to Example 1, the temperature distribution inside the single crystal manufacturing apparatus was obtained by crystal growth simulation, and the phase difference was measured using a SiC single crystal substrate.

[0072] (Example 4) In Example 4, crystal growth was performed using the single crystal manufacturing apparatus shown in Figures 1 and 2. The configuration of the single crystal manufacturing apparatus in Example 4 is the same as that of the single crystal manufacturing apparatus in Example 1.

[0073] The crystal growth in Example 4 was carried out under the same conditions as in Example 3, except that the temperature during crystal growth was 2000°C. Therefore, redundant explanations will be omitted.

[0074] Furthermore, similar to Example 1, the temperature distribution inside the single crystal manufacturing apparatus was obtained by crystal growth simulation, and the phase difference was measured using a SiC single crystal substrate.

[0075] (Comparative Example 1) In Comparative Example 1, crystal growth was performed using the single crystal manufacturing apparatus shown in Figure 3. The configuration of the single crystal manufacturing apparatus in Comparative Example 1 is the same as that of the single crystal manufacturing apparatus in Example 1, except that a cylindrical insulating material 10b and a disc-shaped insulating material 10a are not inserted inside the cylindrical seed crystal holding shaft 16.

[0076] The crystal growth in Comparative Example 1 was carried out using the single crystal manufacturing apparatus described above, under the same conditions as in Example 1. Therefore, redundant explanations are omitted.

[0077] Furthermore, similar to Example 1, the temperature distribution inside the single crystal manufacturing apparatus was obtained by crystal growth simulation, and the phase difference was measured using a SiC single crystal substrate.

[0078] (Comparative Example 2) In Comparative Example 2, crystal growth was performed using the single crystal manufacturing apparatus shown in Figure 4. The configuration of the single crystal manufacturing apparatus in Comparative Example 2 is the same as that of the single crystal manufacturing apparatus in Example 1, except that a disc-shaped insulating material 10a is not inserted inside the cylindrical seed crystal holding shaft 16.

[0079] Crystal growth in Comparative Example 2 was carried out using the single crystal manufacturing apparatus described above, under the same conditions as in Example 1. Therefore, redundant explanations will be omitted.

[0080] Furthermore, similar to Example 1, the temperature distribution inside the single crystal manufacturing apparatus was obtained by crystal growth simulation. However, in this case, it was not possible to grow a SiC single crystal, and therefore the phase difference of the SiC single crystal substrate could not be measured.

[0081] (Comparative Example 3) In Comparative Example 3, crystal growth was performed using the single crystal manufacturing apparatus shown in Figures 5 and 6. Unlike the single crystal manufacturing apparatus of Example 1, the single crystal manufacturing apparatus of Comparative Example 3 has a shorter thermal insulation material 10c instead of thermal insulation material 10b, and further has a seed crystal holding shaft 16a with a shorter cylindrical portion. Specifically, as shown in Figure 5, the seed crystal holding shaft 16a is a graphite shaft that connects a solid cylindrical portion (thin shaft portion) and a cylindrical portion (thick shaft portion), with a disc portion at the tip of the cylindrical portion. The diameter of the cylindrical portion is 26 mm and its length is 227 mm. The diameter of the cylindrical portion is 210 mm, its length is 156 mm, and its inner diameter is 200 mm. The thickness of the disc portion is 10 mm and its diameter is 146 mm. Thermal insulation material 10c is placed inside the cylindrical portion of the seed crystal holding shaft 16a.

[0082] As shown in Figure 6, the fibers constituting the thermal insulation material 10a extend in a direction along the upper surface of the seed crystal substrate 14. The direction of extension of the fibers constituting the thermal insulation material 10a may be in the circumferential direction of the disc-shaped thermal insulation material 10a, or it may be in the radial direction. The fibers constituting the thermal insulation material 10b extend along the central axis of the cylindrical portion constituting the seed crystal holding axis 16.

[0083] The seed crystal holding shaft 16a and the seed crystal substrate 14 are positioned through an opening in a disc-shaped insulating material 13c placed on top of the crucible 12, with the slender shaft portion of the seed crystal holding shaft 16a passing through it. The diameter of the opening is 70 mm. The gap between the insulating material and the slender shaft portion of the seed crystal holding shaft 16a in the opening is 10 mm. Since the cylindrical portion of the seed crystal holding shaft 16a is shorter in length than the cylindrical portion of the seed crystal holding shaft 16 in Example 1, the length of the insulating material 10b inside the seed crystal holding shaft 16a is also about 140 mm shorter than the length of the insulating material 10b in Example 1.

[0084] The crystal growth in Comparative Example 3 was carried out using the single crystal manufacturing apparatus described above, under the same conditions as in Example 1. Therefore, redundant explanations will be omitted.

[0085] Furthermore, similar to Example 1, the temperature distribution inside the single crystal manufacturing apparatus was obtained by crystal growth simulation. However, in this case, it was not possible to grow a SiC single crystal, and therefore the phase difference of the SiC single crystal substrate could not be measured.

[0086] (Comparative Example 4) In Comparative Example 4, crystal growth was performed using the single crystal manufacturing apparatus shown in Figures 7 and 8.

[0087] The seed crystal holding shaft 16b used in Comparative Example 4 has a configuration in which a graphite disc portion is attached to the tip of a graphite cylindrical rod, as shown in Figure 7. The diameter of the cylindrical rod is 26 mm and the length is 282 mm. The diameter of the disc portion is 146 mm and the thickness is 10 mm. The seed crystal substrate 14 is a disc-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 in the center of the lower surface of the seed crystal holding shaft 16b. In Figure 7, a base is shown between the crucible 12 and the crucible holding shaft 18, which holds the crucible 12 and is held by the crucible holding shaft 18. The seed crystal holding shaft 16b has a plurality of fin structures 16c attached so as to intersect with the extending direction (vertical direction) of the seed crystal holding shaft 16.

[0088] As shown in Figure 8, the fibers constituting the thermal insulation materials 13a and 13c along the upper surface of the seed crystal substrate 14 extend in a direction along the upper surface of the seed crystal substrate 14. Similarly, the fibers constituting the cylindrical thermal 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.

[0089] The crystal growth in Comparative Example 4 was carried out using the single crystal manufacturing apparatus described above, under the same conditions as in Example 1. Therefore, redundant explanations will be omitted.

[0090] Furthermore, similar to Example 1, the temperature distribution inside the single crystal manufacturing apparatus was obtained by crystal growth simulation. However, in this case, it was not possible to grow a SiC single crystal, and therefore the phase difference of the SiC single crystal substrate could not be measured.

[0091] <Evaluation Results> Next, using Figure 9, the evaluation results of Examples 1, 2, 3, and 4, Comparative Examples 1, 2, 3, and 4, and Reference Examples 1 and 2 described above will be explained. Reference Examples 1 and 2 are evaluations of 6-inch diameter SiC single crystal substrates fabricated by a commercially available sublimation recrystallization method.

[0092] Among the evaluation items, the in-plane temperature difference is the temperature difference at the interface where the lower surface of the seed crystal substrate 14 and the Si-C solution 20 come into contact. The in-plane temperature difference of the lower surface of the seed crystal holding shaft 16 is quantified by determining the temperature profile over a distance of 75 mm from the center of the circular lower surface.

[0093] Figure 10 is a graph showing the relationship between the position of the seed crystal substrate and the temperature difference. In Figure 10, the horizontal axis represents the distance from the center of the seed crystal substrate 14, and the vertical axis represents the temperature difference within the upper surface of the seed crystal substrate 14. In Figure 10, the graph for Example 1 is shown as a solid line, the graph for Example 2 as a relatively thick dashed line, the graph for Comparative Example 1 as a relatively thin dashed line, the graph for Comparative Example 2 as a dashed line, the graph for Comparative Example 3 as a relatively thin double-dotted line, and the graph for Comparative Example 4 as a relatively thick double-dotted line. As shown in Figure 10, in Examples 1 and 2, and Comparative Examples 3 and 4, the in-plane temperature difference at the interface where the lower surface of the seed crystal substrate 14 and the Si-C solution 20 come into contact is 4.0°C or less. However, in Comparative Examples 3 and 4, the temperature difference is small, so the crystal does not grow.

[0094] Among the evaluation items, the temperature gradient is calculated by determining the temperature profile in the vertical direction relative to the upper surface of the seed crystal substrate 14 at the center of the lower surface of the seed crystal holding axis 16 and at 10 mm pitch positions up to a distance of 60 mm from the center, and quantifying the temperature gradient over a 10 mm vertical distance from the upper surface of the seed crystal substrate 14.

[0095] Figure 11 is a graph showing the relationship between the upward distance from the top surface of the seed crystal substrate 14 and the temperature in Example 3. The horizontal axis of Figure 11 represents temperature, and the vertical axis represents the upward (vertical) distance from the top surface of the seed crystal substrate 14. In Figure 11, the temperature change in the upward direction is graphed from seven points at 0 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, and 60 mm from the center of the top surface 14a (see Figure 12) of the circular seed crystal substrate 14. Figure 12 is an enlarged cross-sectional view showing the single crystal manufacturing apparatus. The measurement positions of the seven points are indicated by arrows in Figure 12.

[0096] In Figure 11, the graphs for 0mm, 10mm, 20mm, 30mm, 40mm, 50mm, and 60mm from the center of the top surface 14a are shown by relatively thin dashed lines, relatively thin dotted lines, double dotted lines, relatively thin solid lines, relatively thick solid lines, relatively thick dashed lines, and relatively thick dotted lines, respectively. In Figure 11, the graphs for 0mm, 10mm, 20mm, and 30mm from the center of the top surface 14a almost overlap. At 0mm, the temperature gradient is 9.6℃ / cm, and at 60mm, the temperature gradient is 24.2℃ / cm.

[0097] Figure 13 is a graph showing the relationship between the upward distance from the top surface of the seed crystal substrate 14 and the temperature in Comparative Example 4. The horizontal axis of Figure 13 represents temperature, and the vertical axis represents the upward (vertical) distance from the top surface of the seed crystal substrate 14. In Figure 13, the temperature change in the upward direction is graphed from a total of seven points at 0 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, and 60 mm from the center of the top surface 14a (see Figure 12) of the circular seed crystal substrate 14. Figure 14 is an enlarged cross-sectional view showing the single crystal manufacturing apparatus in Comparative Example 4. The measurement positions of the seven points are as indicated by the arrows in Figure 14.

[0098] In Figure 13, the graphs for 0 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, and 60 mm from the center of the upper surface 14a are shown by relatively thin dashed lines, relatively thin dotted lines, double dotted lines, relatively thin solid lines, relatively thick solid lines, relatively thick dashed lines, and relatively thin thick dotted lines, respectively. At 0 mm, the temperature gradient is 0.7 °C / cm, and at 60 mm, the temperature gradient is 0.8 °C / cm. When the temperature gradient is small in this way, the temperature difference that drives crystal growth is lost, and therefore the crystal does not grow.

[0099] Among the evaluation items, the phase difference is applied to the entire surface of the first main surface of the SiC single crystal substrate obtained by crystal growth in each example and each comparative example. <0001> Light with a wavelength of 520 nm was transmitted along the direction, and the phase difference of birefringence due to the photoelastic effect was measured. Birefringence is caused by strain due to crystal defects or residual stress within the crystal. The inventors determined the average and maximum values ​​of the phase difference in the phase difference distribution of a SiC single crystal substrate. A 2D birefringence evaluation system WPA300L manufactured by Photonic Lattice Co., Ltd. was used for the measurements.

[0100] In the overall evaluation of each example and comparative example, those with an average phase difference of 10 nm or less were evaluated as passing (circle (〇)). Furthermore, those with an average phase difference of 10 nm or less and a maximum phase difference of 25 nm or less were evaluated as more desirable (double circle (◎)) among those that could be evaluated as passing.

[0101] As shown in Figure 9, in Examples 1 to 4, the in-plane temperature difference is 4.0°C or less, the average phase difference is 10 nm or less, and the maximum phase difference is 70 nm or less. In Examples 3 and 4, the temperature gradient is between 9°C / cm and 25°C / cm, and the maximum phase difference is 40 nm or less. As mentioned above, a small phase difference can mean that the distortion of the object is small.

[0102] <Effects of the Embodiment> In this embodiment, by reducing the thermal strain during crystal growth compared to the thermal strain that occurs in the sublimation recrystallization method, it is possible to obtain a SiC single crystal substrate with less crystal strain and a low crystal defect density. As a means to achieve this, in this embodiment, the SiC single crystal is grown using a solution method. In the solution method, in which SiC is dissolved in a metal solvent and a SiC single crystal is 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 eliminates the above-mentioned room for improvement, which is that SiC single crystals grown by the vapor phase method are prone to internal defects.

[0103] Furthermore, by keeping the in-plane temperature difference at the interface where the lower surface of the seed crystal substrate contacts the Si-C solution 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 on the upper surface of the seed crystal substrate to 9°C / cm or more and 25°C / cm or less, the average and maximum phase differences can be further reduced. In Example 1, the maximum phase difference is 70 nm or less, but it is more preferable to have a phase difference of 50 nm or less, and even more preferable to have a phase difference of 25 nm or less, as in Examples 3 and 4.

[0104] However, if the temperature distribution is made uniform in order to reduce the in-plane temperature difference at the interface where the lower surface of the seed crystal substrate and the Si-C solution come into contact to 4.0°C or less, the vertical temperature gradient on the upper surface of the seed crystal substrate will simultaneously become smaller than 1°C / cm, and it is thought that the temperature difference that drives crystal growth will be lost. In Comparative Examples 3 and 4, as a result of this temperature gradient becoming extremely small, it was not possible to obtain SiC single crystals, and therefore the phase difference could not be measured and the pass / fail evaluation could not be performed.

[0105] In contrast, in Examples 1 to 4 of this embodiment, the in-plane temperature difference at the interface where the lower surface of the seed crystal substrate 14 and the Si-C solution 20 come into contact is 4.0°C or less, and the vertical temperature gradient on the upper surface of the seed crystal substrate 14, which is the driving force for crystal growth, is larger than that of Comparative Examples 3 and 4. In this embodiment, a thermal insulation material 10b is used as a component to maintain the temperature difference within the upper surface of the seed crystal substrate 14 at 4.0°C or less. Furthermore, a thermal insulation material 10a is used as a component to maintain the vertical temperature distribution from the upper surface of the seed crystal substrate 14 at 9°C / cm or more and 25°C / cm or less. In other words, in this embodiment, a thermal insulation material is placed at least in part at a position away from the upper surface of the seed crystal substrate 14 in the upward direction. Here, a seed crystal holding shaft 16 having an inner diameter the same as or greater than the diameter of the seed crystal substrate 14 is used, and the above temperatures are achieved by placing thermal insulation materials 10a and 10b inside the cylindrical portion of the seed crystal holding shaft 16. Furthermore, the thermal insulation material 10b is placed on at least a portion of the side surface of the seed crystal holding shaft 16 in order to provide thermal insulation on the side surface of the seed crystal holding shaft 16. In addition, the thermal insulation material 10a is placed to cover at least a portion of the upper surface of the seed crystal substrate 14 as a member with thermal insulation properties.

[0106] Since heat dissipation from the upper surface of the seed crystal substrate 14 from the vertical direction is suppressed by the arrangement of the insulating materials 10a and 10b, the temperature within the upper surface of the seed crystal substrate 14 can be made uniform. The insulating effect of the insulating materials 10a and 10b becomes more pronounced as the thickness of the insulating materials 10a and 10b increases. Furthermore, the insulating effect of the insulating materials 10a and 10b becomes more pronounced as the position of the insulating materials 10a and 10b is closer to the upper surface of the seed crystal substrate 14.

[0107] As a result, the temperature distribution within the upper surface of the seed crystal substrate 14 can be made uniform. However, if the insulating materials 10a and 10b are too thick or too close to the upper surface of the seed crystal substrate 14, the amount of heat removed vertically from the upper surface of the seed crystal substrate 14 will decrease. Therefore, the temperature difference (temperature gradient) that drives crystal growth will become smaller. Also, if the insulating materials 10a and 10b are too far from the upper surface of the seed crystal substrate 14, the effect of uniformizing the temperature distribution on the upper surface of the seed crystal substrate 14 will be lost. When molded insulating material is used for insulating material 10a, the thickness of the insulating material 10a that can ensure a temperature difference that drives crystal growth while uniformizing the in-plane temperature distribution at the interface where the seed crystal substrate 14 and the Si-C solution 20 come into contact is preferably 3 mm to 25 mm, more preferably 5 mm to 15 mm. The placement position of the insulating material 10a is 3 mm to 50 mm from the upper surface of the seed crystal substrate 14, more preferably 10 mm to 30 mm.

[0108] If it is difficult to directly attach the heat insulating material 10a to the seed crystal substrate 14, the heat insulating material 10a can be placed inside a hollow jig made of graphite, and the seed crystal substrate 14 can be attached to the hollow jig.

[0109] As described above, it is possible to suppress the occurrence of thermal strain during crystal growth and realize a high-quality SiC single crystal with a low crystal defect density. The SiC single crystal substrate can be used as a substrate for forming an epitaxial layer for device formation on the first or second main surface. A wafer set (where n is, for example, 12 or more, preferably 100 or more) may be constructed using n SiC single crystal substrates of this embodiment.

[0110] Although the present inventors have described the invention in detail based on its embodiments, it goes without saying that the present invention is not limited to the embodiments described above and can be modified without departing from the spirit of the invention.

[0111] The following describes some modifications of the embodiment.

[0112] <Example 1> Figure 15 is a cross-sectional view showing a single crystal manufacturing apparatus in modified example 1.

[0113] In the single crystal manufacturing apparatus shown in Figure 1, the thermal insulation material 10a and thermal insulation material 10b are not in contact. In contrast, in the modified example 1 shown in Figure 15, the thermal insulation material 10a and thermal insulation material 10b are in contact. For example, the thermal insulation material 10a and thermal insulation material 10b may be integrated. Thus, the technical concept of this disclosure can be applied regardless of whether or not the thermal insulation material 10a and thermal insulation material 10b are in contact.

[0114] <Modification 2> Figure 16 is a cross-sectional view showing a single crystal manufacturing apparatus in modified example 2.

[0115] In modified example 2, the insulation material 10b is composed of insulation material 10b1 and insulation material 10b2. Insulation material 10b2 is placed inside insulation material 10b1. Insulation material 10b2 is in contact with insulation material 10b1. Insulation material 10b2 is in contact with insulation material 10a.

[0116] The insulation material 10b1 and the insulation material 10b2 may be made of the same material. Alternatively, the insulation material 10b1 and the insulation material 10b2 may be made of different materials. When the insulation material 10b1 and the insulation material 10b2 are made of different materials, for example, a combination of molded insulation material and felt insulation material can be used. When the insulation material 10b1 and the insulation material 10b2 are made of different materials, for example, a combination of insulation materials with different densities can be used.

[0117] <Variation 3> Figure 17 is a cross-sectional view showing a single crystal manufacturing apparatus in modified example 3.

[0118] In modified example 3, the insulation material 10b is composed of insulation material 10b1, insulation material 10b2, and insulation material 10b3. Insulation material 10b2 is placed inside insulation material 10b1. Insulation material 10b3 is placed inside insulation material 10b2. Insulation material 10b2 is in contact with insulation material 10b1. Insulation material 10b2 is in contact with insulation material 10b3. Insulation material 10b3 is in contact with insulation material 10a.

[0119] The insulation materials 10b1, 10b2, and 10b3 may be composed of the same material. Alternatively, the insulation materials 10b1, 10b2, and 10b3 may be composed of different materials. When the insulation materials 10b1, 10b2, and 10b3 are composed of different materials, for example, a combination of molded insulation material and felt insulation material can be used. When the insulation materials 10b1, 10b2, and 10b3 are composed of different materials, for example, a combination of insulation materials with different densities can be used.

[0120] <Modification 4> Figure 18 is a cross-sectional view showing a single crystal manufacturing apparatus in modified example 4.

[0121] The cross-sectional shape of the thermal insulation material 10b in Modified Example 4 may be different from the cross-sectional shape of the thermal insulation material 10b shown in Figure 1. For example, as shown in Figure 18, in the cross-sectional shape of the thermal insulation material 10b in Modified Example 4, the radial (lateral) thickness of the seed crystal holding axis 16 is thicker than the thickness of the thermal insulation material 10b shown in Figure 1. On the other hand, in the cross-sectional shape of the thermal insulation material 10b in Modified Example 4, the longitudinal (vertical) length of the seed crystal holding axis 16 is smaller than the length of the thermal insulation material 10b shown in Figure 1. The thermal insulation material 10b in Modified Example 4 is in contact with the thermal insulation material 10a. Furthermore, from the viewpoint of realizing the technical concept of this disclosure, it is desirable that the position of the upper surface of the thermal insulation material 10b in the cross-sectional shape of the thermal insulation material 10b in Modified Example 4 is greater than or equal to the position of the upper surface of the crucible 12. For example, Figure 18 shows an example in the cross-sectional shape of the thermal insulation material 10b in Modified Example 4 where the position of the upper surface of the thermal insulation material 10b coincides with the position of the upper surface of the crucible 12. [Explanation of Symbols]

[0122] 10a, 10b, 10c, 13a, 13b, 13c insulation 10b1 Insulation 10b2 Insulation 10b3 Insulation 11 coils 12 Crucible 14 Seed crystal substrate 14a Top side 16, 16a, 16b Seed crystal holding shaft 16c fin structure 18 Crucible holding shaft 20 Si-C solution

Claims

1. A SiC single crystal substrate having a first main surface and a second main surface on the opposite side of the first main surface, The first main surface is a surface inclined with respect to the {0001} surface at an off-angle of 0° to 8°, In the distribution of phase difference obtained by measuring the phase difference between the first emitted light and the second emitted light emitted from the second main surface, when incident light having two mutually orthogonal polarization components and a wavelength of 520 nm is incident on the first main surface, The average value of the phase difference is 10 nm or less. The maximum value of the aforementioned phase difference is 70 nm or less, in a SiC single crystal substrate.

2. A SiC single crystal substrate according to claim 1, A SiC single crystal substrate in which the maximum value of the aforementioned phase difference is 50 nm or less.

3. A SiC single crystal substrate according to claim 1, A SiC single crystal substrate in which the maximum value of the aforementioned phase difference is 25 nm or less.

4. A SiC single crystal substrate according to claim 1, A SiC single crystal substrate having a maximum diameter of 140 mm or more for the first main surface.

5. A SiC single crystal substrate according to claim 1, A SiC single crystal substrate having an epitaxial layer for device formation provided on the first main surface or the second main surface.

6. A SiC single crystal substrate according to claim 1, The n (where n is 12 or more) SiC single crystal substrates constitute a wafer set.

7. (a) A step of growing a SiC single crystal by bringing the lower surface of a seed crystal substrate into contact with a solution containing Si and C. Equipped with, A method for producing a SiC single crystal, wherein in step (a), the in-plane temperature difference at the interface where the lower surface of the seed crystal substrate and the solution come into contact is 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, toward the upward direction is 9°C / cm or more and 25°C / cm or less, and the SiC single crystal is grown under these conditions.

8. A seed crystal holding shaft having a cylindrical portion and capable of holding a seed crystal substrate below the cylindrical portion, The side insulating material provided within the cylindrical portion, An upper insulating material provided within the cylindrical portion, Equipped with, The seed crystal substrate has a lower surface that can come into contact with the solution contained in the crucible, and an upper surface located on the opposite side from the lower surface. The aforementioned solution 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 crystal substrate is in contact with the solution, a portion of the side insulating material can be positioned further above the upper end of the crucible. The SiC single crystal manufacturing apparatus is provided with the upper insulating material located at a position away from the upper surface of the seed crystal substrate in the upward direction.

9. A SiC single crystal manufacturing apparatus according to claim 8, The aforementioned side insulating material is a component that reduces the in-plane temperature difference at the interface where the lower surface of the seed crystal substrate and the solution come into contact to 4.0°C or less. The above-mentioned upper surface insulating material is a component that causes the temperature distribution of the seed crystal substrate in the upward direction from the upper surface to be between 9°C / cm and 25°C / cm, in a SiC single crystal manufacturing apparatus.

10. A SiC single crystal manufacturing apparatus according to claim 8, The aforementioned side insulation material is in contact with the aforementioned top insulation material in a SiC single crystal manufacturing apparatus.

11. A SiC single crystal manufacturing apparatus according to claim 8, A SiC single crystal manufacturing apparatus in which the side insulation material is not in contact with the top insulation material.

12. A SiC single crystal manufacturing apparatus according to claim 8, The aforementioned side insulation material is First side insulation material and, A second side insulation material in contact with the first side insulation material, A manufacturing apparatus for SiC single crystals, having the following features.

13. A SiC single crystal manufacturing apparatus according to claim 12, The SiC single crystal manufacturing apparatus further comprises a third side insulating material that contacts the second side insulating material.

14. A SiC single crystal manufacturing apparatus according to claim 8, A SiC single crystal manufacturing apparatus, wherein, in a cross-sectional view, the position of the upper surface of the side insulating material is greater than or equal to the position of the upper surface of the crucible.

15. A SiC single crystal manufacturing apparatus according to claim 14, A SiC single crystal manufacturing apparatus, wherein, in a cross-sectional view, the position of the upper surface of the side insulating material coincides with the position of the upper surface of the crucible.

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