SiC crystal, SiC crystal bar, and method for producing SiC crystal

Abstract

The purpose of the present invention is to provide a SiC crystal, a SiC crystal bar, and a method for producing a SiC crystal, wherein defects do not easily occur when a bonded body obtained by bonding crystals is cut using a multi-wire saw. A SiC crystal according to an embodiment of the present invention has a first surface that is one surface in a lamination direction, and when a waviness curve of the first surface is measured along a first measurement line that passes through the center of the first surface and extends in a < 1-100 > direction, the lowest point of the waviness curve in the first measurement line is located at a position offset from the center.

Description

Technical Field

[0001] This invention relates to SiC crystals, SiC crystal rods, and methods for manufacturing SiC crystals.

[0002] This application claims priority based on Japan Patent Application No. 2024-171181 filed on September 30, 2024, the contents of which are incorporated herein by reference. Background Technology

[0003] Compared to silicon (Si), silicon carbide (SiC) has an insulation breaking electric field that is one order of magnitude larger and a band gap that is three times larger. Furthermore, SiC has approximately three times the thermal conductivity of silicon (Si). Therefore, SiC is expected to be used in power devices, high-frequency devices, and high-temperature operating devices. In recent years, SiC epitaxial wafers have begun to be used in such semiconductor devices.

[0004] SiC epitaxial wafers are obtained by stacking SiC epitaxial layers on the surface of a SiC substrate. The SiC substrate is cut from a SiC ingot. The SiC ingot is a SiC crystal that has been processed into a cylindrical shape.

[0005] SiC ingots are sometimes surface-ground before being shipped. For example, Patent Document 1 discloses a grinding apparatus for semiconductor wafers.

[0006] Prior art literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2023-000307 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] Multi-wire saws are used to cut SiC substrates from SiC ingots. Because multi-wire saws have blades spaced at intervals, multiple SiC substrates can be cut from a SiC ingot in a single pass. Furthermore, to improve processing efficiency using multi-wire saws, multiple SiC ingots are sometimes joined together with adhesives. However, when multiple SiC ingots are joined together, poor cutting can sometimes occur.

[0010] The present invention was made in view of the above-mentioned problems, and its object is to provide a SiC crystal that is less prone to defects when using a multi-wire saw to cut a bonded body formed by joining crystals together. The invention also includes a method for manufacturing the same.

[0011] Methods for solving problems

[0012] Through in-depth research, the inventors discovered that the aforementioned problem stems from poor bonding when joining multiple SiC crystals. Furthermore, they found that the surface condition of the first surface of the SiC crystal, which serves as the bonding surface, significantly affects the adhesion when joining multiple SiC crystals. This disclosure provides the following technical means to solve the above-mentioned problems.

[0013] (1) The first technical solution relates to a SiC crystal having a first surface as a stacking direction, wherein when the waviness curve of the first surface is measured along a first measuring line extending through the center of the first surface in the <1-100> direction, the lowest point of the waviness curve in the first measuring line is located at a position off from the center.

[0014] (2) According to the SiC crystal involved in the above technical solution, when the waviness curve of the first surface is measured along the second measuring line that passes through the center of the first surface and extends in the direction of <11-20>, the lowest point of the waviness curve in the second measuring line can be located at a position away from the center.

[0015] (3) According to the SiC crystal involved in the above technical solution, the surface roughness Ra of the first surface measured along the first measurement line can be less than 20 nm.

[0016] (4) According to the SiC crystal involved in the above technical solution, the surface roughness Ra of the first surface, measured along the second measuring line that passes through the center of the first surface and extends in the direction of <11-20>, can be less than 30 nm.

[0017] (5) According to the SiC crystal involved in the above technical solution, the first surface may have abrasive grain tracks. The intersection point where the abrasive grain tracks overlap the most may be off-center.

[0018] (6) According to the SiC crystal involved in the above technical solution, the difference between the highest point and the lowest point of the waviness curve in the first measurement line can be less than 3.5 μm.

[0019] (7) According to the SiC crystal involved in the above technical solution, the difference between the highest point and the lowest point of the waviness curve in the second measurement line can be less than 3.5 μm.

[0020] (8) The second technical solution relates to a SiC crystal having a first surface as a stacking direction, wherein when the waviness curve of the first surface is measured along a first measuring line extending through the center of the first surface in the <1-100> direction, the difference between the highest point and the lowest point of the waviness curve in the first measuring line is less than 3.5 μm.

[0021] (9) According to the SiC crystal involved in the above technical solution, when the waviness curve of the first surface is measured along the second measuring line that passes through the center of the first surface and extends in the direction of <11-20>, the difference between the highest point and the lowest point of the waviness curve in the second measuring line can be less than 3.5 μm.

[0022] (10) According to the SiC crystal involved in the above technical solution, the surface roughness Ra of the first surface measured along the first measurement line can be less than 20 nm.

[0023] (11) According to the SiC crystal involved in the above technical solution, the surface roughness Ra of the first surface, measured along the second measuring line that passes through the center of the first surface and extends in the direction of <11-20>, can be less than 30 nm.

[0024] (12) According to the SiC crystal involved in the above technical solution, the first surface may have abrasive grain tracks. The intersection point where the abrasive grain tracks overlap the most may be off-center.

[0025] (13) According to the SiC crystal involved in the above technical solution, the lowest point of the waviness curve in the first measurement line can be located at a position away from the center.

[0026] (14) According to the SiC crystal involved in the above technical solution, the lowest point of the waviness curve in the second measurement line can be located at a position away from the center.

[0027] (15) The third technical solution relates to a SiC crystal rod having a first surface as a stacking direction, wherein when the waviness curve of the first surface is measured along a first measuring line extending through the center of the first surface in the <1-100> direction, the lowest point of the waviness curve in the first measuring line is located at a position off from the center.

[0028] (16) The fourth technical solution relates to a method for manufacturing SiC crystals, comprising the following steps: a step of placing a workpiece made of SiC crystals on a support table; and a step of contacting the workpiece placed on the support table rotating along a first direction with a grinding machine rotating along a second direction, wherein the second direction is opposite to the first direction. The grinding machine is positioned opposite to the support table such that the center of the grinding machine is not aligned with the center of the support table. The center of the workpiece is located at a position offset from the center of the support table.

[0029] (17) According to the manufacturing method of SiC crystal involved in the above technical solution, the distance between the center of the workpiece and the center of the support stage can be greater than the radius of the workpiece.

[0030] (18) According to the manufacturing method of SiC crystal involved in the above technical solution, the distance between the center of the workpiece and the center of the support stage can be consistent with the radius of the workpiece.

[0031] (19) According to the manufacturing method of SiC crystal involved in the above technical solution, the diameter of the processed body can be 149 mm or more.

[0032] (20) According to the SiC crystal manufacturing method involved in the above technical solution, when the distance between the center of the workpiece and the center of the support stage is set as x, and the rotational speed of the support stage is set as n, the circumferential speed of the support stage at the workpiece setting position is 2πxn, and the speed at which the grinding machine approaches the workpiece is set as f, the ratio of the circumferential speed to the cutting speed, 2πxn / f, can satisfy 2πxn / f ≤ 1.03 × 10 6 .

[0033] The effects of the invention

[0034] The SiC crystals or SiC crystal rods involved in the above-mentioned technical solutions are less prone to defects when the composite formed by cutting the crystals together using a multi-wire saw. Furthermore, the SiC crystal manufacturing method involved in the above-mentioned technical solutions can produce SiC crystals that are less prone to defects when the composite formed by cutting the crystals together using a multi-wire saw. Attached Figure Description

[0035] Figure 1 This is a three-dimensional view of the SiC crystal according to the first embodiment.

[0036] Figure 2 This is a top view of the first side of the SiC crystal according to the first embodiment.

[0037] Figure 3 It is the waviness curve when measuring the first surface of the SiC crystal according to the first embodiment along the first measurement line.

[0038] Figure 4 It is the waviness curve when measuring the first surface of the SiC crystal according to the first embodiment along the second measurement line.

[0039] Figure 5 This is a top view of the first side of the SiC crystal according to the first embodiment.

[0040] Figure 6 This is a schematic diagram of a grinding apparatus used in the fabrication of the SiC crystal according to the first embodiment.

[0041] Figure 7This is a top view of the grinding apparatus used in manufacturing the SiC crystal according to the first embodiment.

[0042] Figure 8 The measurement results show the waviness curve of the first surface of the SiC crystal in Example 1.

[0043] Figure 9 The measurement results show the waviness curve of the first surface of the SiC crystal in Example 2.

[0044] Figure 10 The measurement results show the waviness curve of the first surface of the SiC crystal in Example 3.

[0045] Figure 11 The results of the measurement of the waviness curve of the first surface of the SiC crystal in Comparative Example 1 are shown.

[0046] Figure 12 The measurement results show the waviness curve of the first surface of the SiC crystal in Example 7.

[0047] Explanation of reference numerals in the attached figures

[0048] 1 SiC crystal

[0049] 1A Page 1

[0050] 1B Page 2

[0051] 1C Side View

[0052] 2. Abrasive particle trajectory

[0053] 10 Grinding equipment

[0054] 11 Workpiece

[0055] 12 boards

[0056] 13 Workpieces

[0057] 14 Support platform

[0058] 15 Grinding Machine

[0059] 21 intersections

[0060] C, C11, C13, C14, C15 Center

[0061] C1 Central Department

[0062] L1 First Measurement Line

[0063] L2 Second Measurement Line

[0064] P1, P3 Lowest points

[0065] P2, P4 highest points Detailed Implementation

[0066] Hereinafter, this embodiment will be described in detail with appropriate reference to the accompanying drawings. In the drawings used in the following description, feature parts are sometimes shown enlarged to facilitate understanding of the features of this embodiment, and the size ratios of each component may sometimes differ from the actual dimensions. The materials, dimensions, etc., illustrated in the following description are merely examples, and this disclosure is not limited thereto; appropriate modifications can be made to implement it without changing its spirit.

[0067] In this specification, [] represents individual orientations, <> represents aggregate orientations, () represents individual surfaces, and {} represents aggregate surfaces. Regarding negative exponents, in crystallography, a "-" (bar) is added before the number; in this specification, a negative sign is added before the number.

[0068] First, the directions are defined. The stacking direction (crystal growth direction) of the SiC single crystal is defined as the Z direction. The Z direction can be the <0001> direction, or it can be tilted or offset relative to the <0001> direction. A direction of a plane orthogonal to the Z direction is defined as the X direction. The X direction is, for example, the <1-100> direction. The Y direction is, for example, the <11-20> direction.

[0069] Figure 1 This is a perspective view of the SiC crystal 1 according to this embodiment. The SiC crystal 1 can be a SiC crystal rod, a seed crystal used in the fabrication of a SiC crystal rod, or a SiC substrate. A SiC crystal rod is also called a SiC ingot. The SiC crystal 1 is, for example, composed of n-type SiC. There are no particular limitations on the polymorphism of the SiC crystal 1; it can be any of 2H, 3C, 4H, or 6H. For example, the SiC crystal 1 is 4H-SiC.

[0070] SiC crystal 1 is a cylindrical columnar body. SiC crystal 1 has a first face 1A, a second face 1B, and a side face 1C. The first face 1A and the second face 1B are the end faces of SiC crystal 1 in the Z direction, respectively. The first face 1A is opposite to the second face 1B. The first face 1A can be a Si face or a C face. The side face 1C connects the first face 1A and the second face.

[0071] The first surface 1A and the second surface 1B may have a portion with an offset angle relative to the (0004) surface in the <11-20> direction, or they may not have such a portion. The offset angle is the angle between the surface orthogonal to the thickness direction of SiC crystal 1, i.e., the Z direction, and the (0004) surface. The offset angle is, for example, greater than 0° and less than 10°, preferably more than 0.1° and less than 8°, more preferably more than 3.5° and less than 4.5°, and even more preferably 4°. Without the offset angle, SiC crystal 1 is grown in a unidirectional plane.

[0072] The thickness T in the Z direction of the SiC crystal 1 is preferably 30 mm or more, more preferably 40 mm or more, and particularly preferably 50 mm or more. If the thickness T of the SiC crystal 1 is sufficiently thick, the effects of warpage and the like on the SiC crystal 1 can be ignored when measuring the waviness curve described later. The thickness T in the Z direction of the SiC crystal 1 is preferably 300 mm or less, for example. Alternatively, the thickness T of the SiC crystal 1 can be less than 30 mm, less than 20 mm, or less than 10 mm. When the thickness T of the SiC crystal 1 is thin, the waviness curve is measured by adsorbing the SiC crystal 1 onto a flat surface. By adsorbing the SiC crystal 1 onto a flat surface, the effects of warpage and the like on the SiC crystal 1 can be ignored.

[0073] Figure 2 This is a top view of the first surface 1A of the SiC crystal 1 according to this embodiment, viewed from the Z direction. The top view shape of the SiC crystal 1 is approximately circular.

[0074] The diameter d of the SiC crystal 1 is, for example, 145 mm or more, preferably 149 mm or more. Furthermore, the diameter d of the SiC crystal 1 is preferably 155 mm or less, more preferably 151 mm or less. Additionally, the diameter d of the SiC crystal 1 can be, for example, 195 mm or more, preferably 199 mm or more. Furthermore, the diameter d of the SiC crystal 1 is preferably 205 mm or less, more preferably 201 mm or less. The diameter d of the SiC crystal 1 can be 295 mm or more, preferably 299 mm or more. The diameter d of the SiC crystal 1 can be 305 mm or less, preferably 301 mm or less. Here, the diameter d of the SiC crystal 1 is the minimum diameter of the SiC crystal 1. For example, when the SiC crystal 1 is a SiC crystal rod, the minimum diameter of the obtainable SiC substrate corresponds to the minimum diameter of the SiC crystal 1. For example, when the diameter of the SiC crystal 1 varies depending on its position in the Z direction, the diameter at the height position with the smallest diameter corresponds to the diameter d.

[0075] The first face 1A of the SiC crystal 1 is ground. The surface of the first face 1A is slightly curved and fluctuates as it is ground. Figure 3 It is the waviness curve of the first surface 1A of SiC crystal 1 measured along the first measurement line L1. Figure 4 This is the waviness curve of the first face 1A of SiC crystal 1 measured along the second measurement line L2. The first measurement line L1 is a line that passes through the center C and extends in the <1-100> direction when viewed from above the first face 1A from the Z direction. The second measurement line L2 is a line that passes through the center C and extends in the <11-20> direction when viewed from above the first face 1A from the Z direction. The center C is defined as the center of the circumcircle of the SiC crystal 1 viewed from above.

[0076] When the thickness of SiC crystal 1 is 30 mm or more, the waviness profile of the first surface 1A is measured by placing SiC crystal 1 on a flat surface. When the thickness of SiC crystal 1 is less than 30 mm, the waviness profile of the first surface 1A is measured by adsorbing SiC crystal 1 onto a flat surface. By making the thickness of SiC crystal 1 sufficiently thick, or by adsorbing SiC crystal 1 onto a flat surface, the effects of warping of the first surface 1A caused by factors other than bending fluctuations accompanying grinding can be ignored.

[0077] The waviness profile was measured, for example, using a SURFCOM NEX 001 DX22 from Tokyo Seimitsu Co., Ltd. The peripheral region, including the area outside the device acquisition area, was not included in the waviness profile measurement range. The peripheral region is defined as a 4 mm range from the outer edge. For example, in the case of a SiC crystal 1 with a diameter of 6 inches (approximately 150 mm), the 4 mm range from the outer edge is considered outside the measurement area, and the measurement length is 142 mm. The measurement speed was 3.0 mm / s, the measurement range was ±500 mm, the calculation specification was JIS-'01 / 13, shape removal with a least-squares straight line equivalent to tilt correction was performed, the cutoff type was Gaussian, the cutoff wavelength was 2.5 mm, and the measurement type was filtered waviness profile. The filtered waviness profile is obtained by removing the roughness component with a shorter wavelength from the cross-sectional curve obtained by tracing the surface of the measurement surface with a probe. The cutoff wavelength indicates the range of the roughness component removed.

[0078] like Figure 3 As shown, the first surface 1A of the SiC crystal 1, measured along the first measurement line L1, is wavy. (As...) Figure 3 As shown, for example, the lowest point P1 of the waviness curve is located off-center from the center C. The lowest point P1 of the waviness curve is preferably located off-center from the central portion C1, which is within 4% of the diameter from the center C. For example, the central portion C1 is a region within a radius of 3 mm from the center C. The lowest point P1 is preferably located outside the range within 5% of the diameter from the center C, more preferably outside the range within 10% of the diameter from the center C.

[0079] In addition, such as Figure 4 As shown, the first surface 1A of the SiC crystal 1, measured along the second measurement line L2, is curved. (As...) Figure 4 As shown, for example, the lowest point P3 of the waviness curve is located off-center from the center C. The lowest point P3 of the waviness curve is preferably located off-center from the central portion C1, within 4% of the diameter from the center C. The lowest point P3 is preferably located outside the range within 5% of the diameter from the center C, and more preferably outside the range within 10% of the diameter from the center C.

[0080] If the lowest point P1 or P3 of the waviness curve is deviated from the center C, then even when cutting the joint formed by joining SiC crystals 1 together with a multi-wire saw, it is less likely to cause defects. The multi-wire saw has a blade extending in the Y direction, and cuts the SiC crystal 1 by moving the joint relative to this blade in the X direction. When cutting the SiC crystal 1 with a multi-wire saw, the following stresses act: stress that causes the cut portion of the SiC crystal 1 to deviate in the X or Y direction; stress that causes the cut portion of the SiC crystal 1 to rotate in the XY plane with the center C as a reference; and stress that causes the cut portion of the SiC crystal 1 to tilt in the Z direction. These stresses are strongly applied at the center C and central portion C1 of the first surface 1A.

[0081] When SiC crystals 1 are bonded together, the adhesive fills the space between the lowest points P1 and P3 of the waviness curve and the adjacent SiC crystals 1. When the lowest point P1 or P3 coincides with the center C, the center C, which experiences strong stress, is easily affected by the adhesive. As a result, the bonded SiC crystals 1 may sometimes shift at the bonding interface. When the lowest point P1 or P3 deviates from the center C, the location susceptible to stress deviates from the location where stress is most likely to occur. Therefore, compared to the case where the lowest point P1 or P3 coincides with the center C, poor bonding of the SiC crystals 1 can be suppressed.

[0082] The height difference h1 in the Z direction between the lowest point P1 and the highest point P2 of the waviness curve (refer to...) Figure 3 For example, it is 3.5 μm or less. The height difference h1 in the Z direction between the lowest point P1 and the highest point P2 of the waviness curve is preferably 2.5 μm or less, more preferably 2.0 μm or less, even more preferably 1.7 μm or less, even more preferably 1.2 μm or less, and particularly preferably 1.0 μm or less.

[0083] Similarly, the height difference h2 in the Z direction between the lowest point P3 and the highest point P4 of the waviness curve (refer to...) Figure 4 For example, it is 3.5 μm or less. The height difference h2 in the Z direction between the lowest point P3 and the highest point P4 of the waviness curve is preferably 2.5 μm or less, more preferably 2.0 μm or less, even more preferably 1.7 μm or less, even more preferably 1.2 μm or less, and particularly preferably 1.0 μm or less.

[0084] If the difference between the lowest and highest points of the waviness curve is large, the depth of the adhesive-filled portion increases. When the adhesive-filled portion is deep, it is more susceptible to stress during the cutting of SiC crystal 1. Furthermore, a large difference between the lowest and highest points of the waviness curve increases the likelihood of thickness deviations in the cut SiC substrate. Conversely, a sufficiently small difference between the lowest and highest points of the waviness curve reduces the probability of poor cutting of the SiC crystal 1 bond.

[0085] The surface roughness Ra of the first surface 1A measured along the first measurement line L1 is preferably 20 nm or less, more preferably 17 nm or less, even more preferably 16 nm or less, and particularly preferably 13 nm or less.

[0086] Furthermore, the surface roughness Ra of the first surface 1A measured along the second measurement line L2 is preferably 30 nm or less, more preferably 29 nm or less, even more preferably 14 nm or less, and particularly preferably 13 nm or less.

[0087] The smaller the surface roughness Ra of the first surface 1A, the larger the bonding area between SiC crystals 1, and the more difficult it is for poor cutting of the SiC crystal 1 bonding body to occur.

[0088] In addition, such as Figure 5 As shown, abrasive grain tracks 2 are sometimes observed on the first surface 1A of the SiC crystal 1. Abrasive grain tracks 2 are grinding marks left after grinding the SiC crystal 1. Since abrasive grain tracks 2 are grinding marks, they can be grinding tracks. Abrasive grains can be contained within the grinding stone used for grinding. Abrasive grain tracks 2 are formed during grinding by the rotating SiC crystal 1 and the rotating grinding machine. Abrasive grain tracks 2 depict a pattern. Abrasive grain tracks 2 are, for example, part of a non-uniform topography curve. Abrasive grain tracks 2 are faintly visible as white lines on the mirror-like first surface 1A. There are multiple abrasive grain tracks 2 on the first surface 1A, and the intersection points 21 where the abrasive grain tracks 2 intersect each other can be identified. The intersection point 21 where the abrasive grain tracks 2 overlap the most is, for example, located at a position offset from the center C of the first surface 1A. The areas with abrasive grain tracks 2 are sometimes dug deeper than the areas without abrasive grain tracks 2; if the intersection point 21 is offset from the center C, poor bonding between the SiC crystals 1 can be suppressed. In addition, the intersection point 21 where the abrasive grain trajectories 2 overlap the most is preferably located at a position offset from the central part C1 of the first surface 1A.

[0089] Furthermore, the relationship in the first face 1A of the SiC crystal 1 can also be satisfied in the second face 1B. If the second face 1B satisfies the same relationship as the first face 1A, then it is less likely to cause cutting defects when multiple SiC crystals 1 are joined together and then cut.

[0090] For example, the lowest point of the waviness curve of the second surface 1B is measured along the third measuring line, preferably at a position offset from the center of the second surface 1B, and more preferably at a position offset from the central portion within 4% of the diameter from the center of the second surface 1B. The third measuring line is a line that passes through the center of the second surface 1B when viewed from above in the Z direction and extends in the <1-100> direction. The center and central portion of the second surface 1B are defined in the same way as the center and central portion of the first surface 1A.

[0091] Additionally, for example, the lowest point of the waviness curve of the second surface 1B is measured along the fourth measuring line, preferably at a position offset from the center of the second surface 1B, and more preferably at a position offset from the center portion within 4% of the diameter from the center of the second surface 1B. The fourth measuring line is a line that passes through the center of the second surface 1B when viewed from above in the Z direction and extends in the <11-20> direction.

[0092] In addition, the height difference in the Z direction between the lowest and highest points of the waviness curve of the second surface 1B along the third measuring line is preferably 3.5 μm or less, more preferably 2.5 μm or less, even more preferably 2.0 μm or less, more preferably 1.7 μm or less, even more preferably 1.2 μm or less, and particularly preferably 1.0 μm or less.

[0093] In addition, the height difference in the Z direction between the lowest and highest points of the waviness curve of the second surface 1B along the fourth measuring line is preferably 3.5 μm or less, more preferably 2.5 μm or less, even more preferably 2.0 μm or less, more preferably 1.7 μm or less, even more preferably 1.2 μm or less, and particularly preferably 1.0 μm or less.

[0094] Furthermore, the surface roughness Ra of the second surface 1B measured along the third measurement line is preferably 20 nm or less, more preferably 17 nm or less, even more preferably 16 nm or less, and particularly preferably 13 nm or less.

[0095] Furthermore, the surface roughness Ra of the second surface 1B measured along the fourth measurement line is preferably 30 nm or less, more preferably 29 nm or less, even more preferably 14 nm or less, and particularly preferably 13 nm or less.

[0096] Furthermore, in the second surface 1B, the intersection point where the abrasive grain trajectories overlap the most is preferably located at a position offset from the center of the second surface 1B.

[0097] Next, the manufacturing method of the SiC crystal 1 according to the first embodiment will be described. The manufacturing method of the SiC crystal 1 includes a preparation step and a grinding step. Figure 6 This is a schematic diagram of a grinding apparatus 10 used in manufacturing the SiC crystal 1 according to the first embodiment.

[0098] In the preparation process, a workpiece 13, which is a workpiece 11 made of SiC crystal, is placed on a support table 14. Here, an example of placing the workpiece 13 on the support table 14 is shown, but the workpiece 11 can also be placed directly on the support table 14.

[0099] The workpiece 11 is the state of the SiC crystal 1 before grinding, and has the same structure as the SiC crystal 1 except for the surface state of the first surface 1A. For example, the diameter of the workpiece 11 is the same as the diameter d of the SiC crystal 1, for example, 149 mm or more.

[0100] The workpiece 13 has a workpiece 11 and a plate 12. The plate 12 is used to improve the flatness of the machined surface of the workpiece 11. The plate 12 is, for example, stainless steel (SUS). If the workpiece 11 is directly mounted on the support table 14, the plate 12 is not required.

[0101] A grinding machine 15 is positioned opposite the support table 14. The grinding machine 15 has, for example, a plurality of grinding wheels arranged in a ring along the outer periphery of the grinding machine 15.

[0102] Figure 7 This is a top view of the grinding apparatus 10 used in manufacturing the SiC crystal 1 according to the first embodiment.

[0103] The center C15 of the grinding machine 15 is located at a position offset from the center C14 of the support table 14. For example... Figure 7 As shown, the outer periphery of the grinding machine 15 can be configured to pass through the center C14 of the support table 14. If the outer periphery of the grinding machine 15 is configured to pass through the center C14 of the support table 14, the height difference h1 in the Z direction between the lowest point P1 and the highest point P2 of the waviness curve, and the height difference h2 in the Z direction between the lowest point P3 and the highest point P4 of the waviness curve, become 2.0 μm or less. The diameter of the grinding machine 15 is preferably longer than, for example, the longest length between the center C14 and the outer periphery of the workpiece 11. The radial length of the grinding wheel configured in an annular shape in the grinding machine 15 is preferably greater than, for example, the diameter of the workpiece 11.

[0104] The workpiece 11 is positioned on the support table 14 such that its center C11 is not aligned with the center C14 of the support table 14. The center C11 of the workpiece 11 is located at a position offset from the center C14 of the support table 14. The center C11 of the workpiece 11 is substantially aligned with the center C13 of the workpiece 13. Alternatively, the center C11 of the workpiece 11 may be offset from the center C13 of the workpiece 13. The distance x between the center C14 and the center C11 is preferably, for example, greater than or equal to the radius of the workpiece 11, and more preferably equal to the radius of the workpiece 11.

[0105] For example, when the diameter of the workpiece 11 is 150 mm (6 inches), the distance x between the center C14 and the center C11 is preferably 50 mm or more and 200 mm or less, more preferably 50 mm or more and 150 mm or less, even more preferably 50 mm or more and 100 mm or less, and particularly preferably 75 mm or more and 100 mm or less.

[0106] Next, a grinding process is performed. In the grinding process, the workpiece 11, which is placed on a support table 14 rotating in a first direction R1, is brought into contact with a grinding machine 15 rotating in a second direction R2, and the first surface of the workpiece 11 is ground. The second direction R2 is the opposite direction to the first direction R1. The grinding machine 15 is capable of moving in the Z direction. By lowering the grinding machine 15 toward the workpiece 11, the workpiece 11 is brought into contact with the grinding machine 15.

[0107] When the distance between the center C11 of the workpiece and the center C14 of the support table 14 is set as x, and the rotational speed of the support table 14 is set as n, the circumferential speed of the support table 14 at the setting position of the workpiece 11 is 2πxn. When the speed at which the grinding machine 15 approaches the workpiece 11 (cutting speed) is set as f, the ratio of the circumferential speed of the workpiece 13 to the cutting speed is expressed as 2πxn / f. Preferably, 2πxn / f satisfies 2πxn / f ≤ 1.03 × 10⁻⁶. 6 If this condition is met, the load on the grinding machine 15 and the workpiece 11 can be reduced, and damage to the grinding wheel of the grinding machine 15 and the workpiece 11 can be suppressed.

[0108] The SiC crystal 1 according to this embodiment is obtained by grinding the workpiece 11 in a grinding process. By setting the workpiece 11 on the support stage 14 in a manner that the center C11 of the workpiece 11 is not the same as the center C14 of the support stage 14, it is possible to avoid the abrasive grain trajectory 2 being concentrated on the center C11 of the workpiece 11.

[0109] The SiC crystal 1 involved in this embodiment, by deviating the position of the lowest point of the waviness curve from the position of the center C, can make the position that is easily subjected to stress deviate from the position that is easily subjected to stress, thereby suppressing the peeling of the SiC crystal 1 at the bonding interface.

[0110] Furthermore, the SiC crystal 1 described in this embodiment has a small difference between the lowest and highest points of its waviness curve, which reduces the probability of the multi-wire saw blade crossing the interface between the SiC crystal 1 and the adhesive, and suppresses the twisting of the multi-wire saw blade during cutting. As a result, it is possible to suppress thickness deviations in the cut SiC substrate and reduce the probability of poor cutting of the SiC crystal 1 bonding assembly.

[0111] The SiC crystal 1 involved in this embodiment does not necessarily need to simultaneously satisfy the deviation of the lowest point of the waviness curve from the center C, and the small difference between the lowest and highest points of the waviness curve. Even if only one of these conditions is met, it is possible to suppress poor cutting of the bonded structure compared to the case where no countermeasures are taken.

[0112] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to specific embodiments. Various modifications and alterations can be made within the scope of the claims and the spirit of this disclosure.

[0113] Example

[0114] Example 1

[0115] Prepare a SiC crystal (SiC ingot) with a diameter of 150 mm (6 inches) and a thickness of 20 mm. For example... Figure 6 and Figure 7 As shown, a SiC crystal, serving as the workpiece 11, is placed on a support stage 14. The diameter of the support stage 14 is 700 mm. The distance x between the center C14 of the support stage 14 and the center C11 of the workpiece 11 is set to 50 mm. The grinding machine 15 uses a cup-shaped grinding wheel with the grinding wheel arranged in a ring. The outer diameter of the ring on the grinding machine 15 with the grinding wheel is 400 mm, and the inner diameter is 385 mm. During grinding, the grinding machine 15 is configured such that the outer circumference of the ring on the grinding machine 15 with the grinding wheel passes through the center C14 of the support stage 14.

[0116] Next, the support table 14 and the grinding machine 15 are rotated in opposite directions, bringing the workpiece 11 placed on the support table 14 into contact with the grinding machine 15. The rotational speed of the support table 14 is 17 rpm. The rotational speed of the grinding machine 15 is 680 rpm. The speed at which the grinding machine 15 approaches the workpiece 11 is 20 μm / min.

[0117] Then, the workpiece 11 is ground to produce SiC crystal 1. The abrasive grain trajectory 2 can be identified on the first surface 1A of the SiC crystal 1, and the densest intersection point 21 of the abrasive grain trajectory 2 is offset from the center C of the first surface 1A.

[0118] Next, the waviness profile of the first face 1A of the SiC crystal 1 was measured. The waviness profile was measured in both the <1-100> and <11-20> directions. The waviness profile was measured using a SURFCOM NEX 001 DX22 from Tokyo Seimitsu Corporation. The waviness profile was measured only for the portion excluding the outer perimeter. The measurement length was 142 mm, calculated by subtracting 4 mm from each end from a diameter of 150 mm.

[0119] Figure 8 The measurement results show the waviness curve of the first surface of the SiC crystal in Example 1. Figure 8 The top image shows the results of measuring the first facet along the <11-20> direction, and the bottom image shows the results of measuring the first facet along the <1-100> direction. The horizontal axis represents the radial measurement position of the SiC crystal. The measurement start point (0mm) is taken from the outer periphery of one side and extends 4mm inward from the outer periphery of the other side, which is the measurement end point (142mm). The 71mm position is the center of the SiC crystal. The vertical axis represents the height position of the first facet at various points in the radial direction of the SiC crystal.

[0120] like Figure 8 As shown, the lowest point of the waviness curve in Example 1 deviates from the center C in either the <11-20> direction or the <1-100> direction. The height difference between the highest and lowest points of the waviness curve measured along the <11-20> direction is 2.4665 μm. The height difference between the highest and lowest points of the waviness curve measured along the <1-100> direction is 3.2912 μm. The surface roughness Ra of the first surface measured along the <11-20> direction is 14.2 nm. The surface roughness Ra of the first surface measured along the <1-100> direction is 16.2 nm.

[0121] Example 2

[0122] The difference between Example 2 and Example 1 is that the distance x between the center C14 of the support stage 14 and the center C11 of the workpiece 11 is set to 100 mm. All other conditions are the same as in Example 1, and the SiC crystal of Example 2 is evaluated.

[0123] Abrasive grain tracks 2 were also observed on the first surface 1A of the SiC crystal 1 in Example 2. The densest position of the abrasive grain tracks 2 is offset from the center C of the first surface 1A.

[0124] Figure 9 The measurement results show the waviness curve of the first surface of the SiC crystal in Example 2. Figure 9 The top image shows the results of measuring the first facet along the <11-20> direction, and the bottom image shows the results of measuring the first facet along the <1-100> direction. The horizontal axis represents the radial measurement position of the SiC crystal. The measurement start point (0mm) is taken from the outer periphery of one side and extends 4mm inward from the outer periphery of the other side, which is the measurement end point (142mm). The 71mm position is the center of the SiC crystal. The vertical axis represents the height position of the first facet at various points in the radial direction of the SiC crystal.

[0125] like Figure 9As shown, the lowest point of the waviness curve in Example 2 deviates from the center C in either the <11-20> direction or the <1-100> direction. The height difference between the highest and lowest points of the waviness curve measured along the <11-20> direction is 0.9233 μm. The height difference between the highest and lowest points of the waviness curve measured along the <1-100> direction is 1.6252 μm. The surface roughness Ra of the first surface measured along the <11-20> direction is 12.6 nm. The surface roughness Ra of the first surface measured along the <1-100> direction is 12.2 nm.

[0126] Example 3

[0127] The difference between Example 3 and Example 1 is that the distance x between the center C14 of the support stage 14 and the center C11 of the workpiece 11 is set to 200 mm. Other conditions are the same as in Example 1, and the SiC crystal of Example 3 is evaluated.

[0128] Abrasive grain tracks 2 were also observed on the first surface 1A of the SiC crystal 1 in Example 3. The densest position of the abrasive grain tracks 2 is offset from the center C of the first surface 1A.

[0129] Figure 10 The measurement results show the waviness curve of the first surface of the SiC crystal in Example 3. Figure 10 The top image shows the results of measuring the first facet along the <11-20> direction, and the bottom image shows the results of measuring the first facet along the <1-100> direction. The horizontal axis represents the radial measurement position of the SiC crystal. The measurement start point (0mm) is taken from the outer periphery of one side and extends 4mm inward from the outer periphery of the other side, which is the measurement end point (142mm). The 71mm position is the center of the SiC crystal. The vertical axis represents the height position of the first facet at various points in the radial direction of the SiC crystal.

[0130] like Figure 10 As shown, the lowest point of the waviness curve in Example 3 deviates from the center C in either the <11-20> direction or the <1-100> direction. The height difference between the highest and lowest points of the waviness curve measured along the <11-20> direction is 1.5813 μm. The height difference between the highest and lowest points of the waviness curve measured along the <1-100> direction is 1.1651 μm. The surface roughness Ra of the first surface measured along the <11-20> direction is 29.3 nm. The surface roughness Ra of the first surface measured along the <1-100> direction is 17.4 nm.

[0131] Comparative Example 1

[0132] The difference between Comparative Example 1 and Example 1 is that the distance x between the center C14 of the support stage 14 and the center C11 of the workpiece 11 is set to 0 mm. That is, in Comparative Example 1, the center C14 of the support stage 14 and the center C11 of the workpiece 11 are at the same position. Other conditions are the same as in Example 1, and the SiC crystal of Comparative Example 1 is evaluated.

[0133] Abrasive grain tracks 2 were also observed on the first surface 1A of the SiC crystal 1 in Comparative Example 1. The densest position of abrasive grain tracks 2 is located in the central part C1 of the first surface 1A.

[0134] Figure 11 The results of the measurement of the waviness curve of the first surface of the SiC crystal in Comparative Example 1 are shown. Figure 11 The top image shows the results of measuring the first facet along the <11-20> direction, and the bottom image shows the results of measuring the first facet along the <1-100> direction. The horizontal axis represents the radial measurement position of the SiC crystal. The measurement start point (0mm) is taken from the outer periphery of one side and extends 4mm inward from the outer periphery of the other side, which is the measurement end point (142mm). The 71mm position is the center of the SiC crystal. The vertical axis represents the height position of the first facet at various points in the radial direction of the SiC crystal.

[0135] like Figure 11 As shown, the lowest point of the waviness curve in Comparative Example 1 deviates from the center C in either the <11-20> direction or the <1-100> direction. The height difference between the highest and lowest points of the waviness curve measured along the <11-20> direction is 2.7245 μm. The height difference between the highest and lowest points of the waviness curve measured along the <1-100> direction is 3.8233 μm. The surface roughness Ra of the first surface measured along the <11-20> direction is 17.3 nm. The surface roughness Ra of the first surface measured along the <1-100> direction is 12.0 nm.

[0136] In the SiC crystals of Examples 1-3, the lowest point of the first facet is offset from the center C of the first facet. In contrast, in the SiC crystal of Comparative Example 1, the lowest point of the first facet is aligned with the center C of the first facet. Compared to the joint formed using the SiC crystal of Comparative Example 1, the joint interface of the joint formed using the SiC crystals of Examples 1-3 is less prone to shifting even when cut with a multi-wire saw.

[0137] Furthermore, the difference between the highest and lowest points of the first surface of the SiC crystals in Examples 1-3 is smaller than that of the SiC crystal in Comparative Example 1. Compared with the SiC crystal formed in Comparative Example 1, the thickness of the SiC substrate formed using the SiC crystals in Examples 1-3 is less prone to deviation.

[0138] Examples 4-6

[0139] The difference between Examples 4-6 and Examples 1-3 is that the thickness of the SiC crystal (SiC ingot) is 30 mm. Other conditions are the same as in Examples 1-3.

[0140] In the SiC crystals of Examples 4-6, the lowest point of the first surface deviates from the center C of the first surface. Furthermore, in the SiC crystals of Examples 4-6, the difference between the highest and lowest points of the first surface is less than 3.5 μm. In Examples 4-6, no issues were found regarding the offset of the bonding interface during the cutting of the bond, or the thickness deviation of the SiC substrate after cutting. It can be confirmed that the same results can be obtained even when the SiC crystal is relatively thick.

[0141] Examples 7-9

[0142] The difference between Examples 7-9 and Examples 1-3 is that the thickness of the SiC crystal (SiC ingot) is 3 mm. Other conditions are the same as in Examples 1-3.

[0143] In the SiC crystals of Examples 7-9, the lowest point of the first surface deviates from the center C of the first surface. Furthermore, in the SiC crystals of Examples 7-9, the difference between the highest and lowest points of the first surface is less than 3.5 μm. In Examples 7-9, no issues were found regarding the offset of the bonding interface during the cutting of the bond, or the thickness deviation of the SiC substrate after cutting. It can be confirmed that the same results can be obtained even when the SiC crystal is relatively thin.

[0144] Figure 12 The measurement results show the waviness curve of the first surface of the SiC crystal in Example 7 (SiC crystal (SiC ingot) with a thickness of 3 mm and a distance x of 50 mm). Figure 12 The top image shows the results of measuring the first facet along the <11-20> direction, and the bottom image shows the results of measuring the first facet along the <1-100> direction. The horizontal axis represents the radial measurement position of the SiC crystal. The measurement start point (0mm) is taken from the outer periphery of one side and extends 4mm inward from the outer periphery of the other side, which is the measurement end point (142mm). The 71mm position is the center of the SiC crystal. The vertical axis represents the height position of the first facet at various points in the radial direction of the SiC crystal.

[0145] like Figure 12As shown, the lowest point of the waviness curve in Example 7 deviates from the center C in either the <11-20> direction or the <1-100> direction. The height difference between the highest and lowest points of the waviness curve measured along the <11-20> direction is 1.3538 μm. The height difference between the highest and lowest points of the waviness curve measured along the <1-100> direction is 1.5171 μm. The surface roughness Ra of the first surface measured along the <11-20> direction is 12.5 nm. The surface roughness Ra of the first surface measured along the <1-100> direction is 12.7 nm.

[0146] Furthermore, the results obtained using SiC crystals (SiC ingots) with a diameter of 150 mm (6 inches) have been shown so far, but the same study was also conducted on SiC crystals (SiC ingots) with a diameter of 200 mm (8 inches). In the case of an 8-inch diameter, the same trend as in the case of a 6-inch diameter was also confirmed.

Claims

1. A SiC crystal having a first face as one face in a stacking direction, when a waviness curve of the first face is measured along a first measurement line passing through a center of the first face and extending in a <1-100> direction, a lowest point of the waviness curve in the first measurement line is located at a position deviated from the center.

2. The SiC crystal according to claim 1, when a waviness curve of the first face is measured along a second measurement line passing through a center of the first face and extending in a <11-20> direction, a lowest point of the waviness curve in the second measurement line is located at a position deviated from the center.

3. The SiC crystal according to claim 1, a surface roughness Ra of the first face measured along the first measurement line is 20 nm or less.

4. The SiC crystal according to claim 1, a surface roughness Ra of the first face measured along a second measurement line passing through a center of the first face and extending in a <11-20> direction is 30 nm or less.

5. The SiC crystal according to claim 1, the first face has abrasive grain traces, an intersection at which the abrasive grain traces overlap the most is deviated from the center.

6. The SiC crystal according to claim 1, a difference between a highest point and a lowest point of the waviness curve in the first measurement line is 3.5 μm or less.

7. The SiC crystal according to claim 2, a difference between a highest point and a lowest point of the waviness curve in the second measurement line is 3.5 μm or less.

8. The SiC crystal according to claim 1, a diameter is 145 mm or more.

9. A SiC crystal having a first face as one face in a stacking direction, when a waviness curve of the first face is measured along a first measurement line passing through a center of the first face and extending in a <1-100> direction, a difference between a highest point and a lowest point of the waviness curve in the first measurement line is 3.5 μm or less.

10. The SiC crystal according to claim 9, when a waviness curve of the first face is measured along a second measurement line passing through a center of the first face and extending in a <11-20> direction, a difference between a highest point and a lowest point of the waviness curve in the second measurement line is 3.5 μm or less.

11. The SiC crystal according to claim 9, a surface roughness Ra of the first face measured along the first measurement line is 20 nm or less.

12. The SiC crystal according to claim 9, a surface roughness Ra of the first face measured along a second measurement line passing through a center of the first face and extending in a <11-20> direction is 30 nm or less.

13. The SiC crystal according to claim 9, the first face has abrasive grain traces, an intersection at which the abrasive grain traces overlap the most is deviated from the center.

14. The SiC crystal according to claim 9, a lowest point of the waviness curve in the first measurement line is located at a position deviated from the center.

15. The SiC crystal according to claim 10, The lowest point of the waviness curve in the second measurement line is located off the center.

16. The SiC crystal of claim 9, The diameter is 145 mm or more.

17. An SiC crystal ingot having a first face as one face of a stacking direction, When a waviness curve of the first face is measured along a first measurement line passing through the center of the first face and extending in the direction of <1-100>, the lowest point of the waviness curve in the first measurement line is located off the center.

18. A method of manufacturing an SiC crystal, comprising the steps of: a step of placing a workpiece composed of an SiC crystal on a support table; and a step of grinding a first face of the workpiece by bringing the workpiece placed on the support table rotating in a first direction into contact with a grinding machine rotating in a second direction opposite to the first direction, the grinding machine is disposed at a position opposite to the support table, and the center of the grinding machine is not aligned with the center of the support table, the center of the workpiece is located off the center of the support table.

19. The method of manufacturing an SiC crystal according to claim 18, the distance between the center of the workpiece and the center of the support table is the radius of the workpiece or more.

20. The method of manufacturing an SiC crystal according to claim 18, the distance between the center of the workpiece and the center of the support table is the same as the radius of the workpiece.

21. The method of manufacturing an SiC crystal according to claim 18, the diameter of the workpiece is 149 mm or more.

22. The method of manufacturing an SiC crystal according to claim 18, the distance between the center of the workpiece and the center of the support table is set to x, when the rotational speed of the support table is set to n, the circumferential speed of the support table at the placement position of the workpiece is 2πxn, the speed at which the grinding machine approaches the workpiece is set to f, At this time, the ratio of the circumferential velocity to the cutting-in velocity 2πxn / f satisfies 2πxn / f≤1.03×10 6 .

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