SiC crystal, SiC boolean, and method for manufacturing SiC crystal

Abstract

The objective is to provide SiC crystals, SiC boules, and methods for manufacturing the same, which are less prone to defects when cutting a bonded structure of joined crystals with a multi-wire saw. [Solution] The SiC crystal according to this embodiment has a first surface which is one surface in the stacking direction, and when the waviness curve of the first surface is measured along a first measurement line which passes through the center of the first surface and extends in the <1-100> direction, the lowest point of the waviness curve on the first measurement line is located at a position offset from the center.

Description

Technical Field

[0001] The present invention relates to SiC crystals, SiC boules, and a method for manufacturing SiC crystals.

Background Art

[0002] Silicon carbide (SiC) has a breakdown electric field that is one order of magnitude larger and a bandgap that is three times larger than that of silicon (Si). In addition, silicon carbide (SiC) has characteristics such as a thermal conductivity that is about three times higher than that of silicon (Si). Therefore, silicon carbide (SiC) is expected to be applied to power devices, high-frequency devices, high-temperature operation devices, etc. In recent years, SiC epitaxial wafers have been used in semiconductor devices as described above.

[0003] An SiC epitaxial wafer is obtained by laminating an SiC epitaxial layer on the surface of an SiC substrate. The SiC substrate is cut out from an SiC ingot. The SiC ingot is a columnar SiC crystal.

[0004] The SiC ingot may be shipped after grinding its surface. For example, Patent Document 1 discloses a grinding apparatus for a semiconductor wafer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] A multi-wire saw is used to cut SiC substrates from SiC ingots. Because the multi-wire saw has blades spaced at regular intervals, multiple SiC substrates can be cut from a single SiC ingot in one pass. Furthermore, to improve the efficiency of processing with a multi-wire saw, multiple SiC ingots are sometimes joined together with adhesive. However, when multiple SiC ingots are joined together, cutting defects can occur.

[0007] This disclosure has been made in view of the above-mentioned problems, and aims to provide a SiC crystal and a method for manufacturing the same that are less prone to defects when a bonded body of crystals is cut with a multi-wire saw. [Means for solving the problem]

[0008] The inventors, after diligent research, have found that the cause of the above-mentioned problems lies in poor bonding when multiple SiC crystals are joined together. They have also found that the surface condition of the first face of the SiC crystal, which is the bonding surface, has a significant effect on the adhesion when multiple SiC crystals are joined together. This disclosure provides the following means to solve the above-mentioned problems.

[0009] (1) The SiC crystal according to the first embodiment has a first surface which is one surface in the stacking direction, and when the waviness curve of the first surface is measured along a first measurement line which passes through the center of the first surface and extends in the <1-100> direction, the lowest point of the waviness curve on the first measurement line is located at a position offset from the center.

[0010] (2) In the SiC crystal according to the above embodiment, when the waviness curve of the first plane is measured along a second measurement line that passes through the center of the first plane and extends in the <11-20> direction, the lowest point of the waviness curve on the second measurement line may be at a position offset from the center.

[0011] (3) The SiC crystal according to the above embodiment may have a surface roughness Ra of 20 nm or less of the first surface measured along the first measurement line.

[0012] (4) The SiC crystal according to the above embodiment may have a surface roughness Ra of 30 nm or less of the first surface, measured along a second measurement line that passes through the center of the first surface and extends in the <11-20> direction.

[0013] (5) In the SiC crystal according to the above embodiment, the first surface may have abrasive trajectories. The intersection where the abrasive trajectories overlap the most may be offset from the center.

[0014] (6) In the SiC crystal according to the above embodiment, the difference between the highest and lowest points of the waviness curve on the first measurement line may be 3.5 μm or less.

[0015] (7) In the SiC crystal according to the above embodiment, the difference between the highest and lowest points of the waviness curve on the second measurement line may be 3.5 μm or less.

[0016] (8) The SiC crystal according to the second embodiment has a first surface which is one surface in the stacking direction, and when the waviness curve of the first surface is measured along a first measurement line which passes through the center of the first surface and extends in the <1-100> direction, the difference between the highest point and the lowest point of the waviness curve on the first measurement line is 3.5 μm or less.

[0017] (9) In the SiC crystal according to the above embodiment, when the waviness curve of the first plane is measured along a second measurement line that passes through the center of the first plane and extends in the <11-20> direction, the difference between the highest point and the lowest point of the waviness curve along the second measurement line may be 3.5 μm or less.

[0018] (10) The SiC crystal according to the above embodiment may have a surface roughness Ra of the first surface measured along the first measurement line of 20 nm or less.

[0019] (11) The SiC crystal according to the above embodiment may have a surface roughness Ra of 30 nm or less of the first surface, measured along a second measurement line that passes through the center of the first surface and extends in the <11-20> direction.

[0020] (12) In the SiC crystal according to the above aspect, the first surface may have abrasive grain traces. The intersection point where the abrasive grain traces overlap the most may be deviated from the center.

[0021] (13) In the SiC crystal according to the above aspect, the lowest point of the undulation curve on the first measurement line may be at a position deviated from the center.

[0022] (14) In the SiC crystal according to the above aspect, the lowest point of the undulation curve on the second measurement line may be at a position deviated from the center.

[0023] (15) The SiC boule according to the third aspect has a first surface which is one surface in the stacking direction. When measuring the undulation curve of the first surface along a first measurement line extending in the <1-100> direction passing through the center of the first surface, the lowest point of the undulation curve on the first measurement line is at a position deviated from the center.

[0024] (16) The method for manufacturing a SiC crystal according to the fourth aspect includes a step of installing a workpiece made of a SiC crystal on a support table, and a step of bringing the workpiece placed on the support table rotating in a first direction into contact with a grinding wheel rotating in a second direction opposite to the first direction, and grinding the first surface of the workpiece. The grinding wheel is arranged at a position facing the support table such that the center of the grinding wheel does not coincide with the center of the support table. The center of the workpiece is at a position deviated from the center of the support table.

[0025] (17) In the method for manufacturing a SiC crystal according to the above aspect, the distance between the center of the workpiece and the center of the support table may be equal to or greater than the radius of the workpiece.

[0026] (18) In the method for manufacturing a SiC crystal according to the above aspect, the distance between the center of the workpiece and the center of the support table may coincide with the radius of the workpiece.

[0027] (19) In the method for producing SiC crystals according to the above embodiment, the diameter of the workpiece may be 149 mm or more.

[0028] (20) In the method for manufacturing SiC crystals according to the above embodiment, when the distance between the center of the workpiece and the center of the support table is x, and the rotational speed of the support table is n, the peripheral speed of the support table at the installation position of the workpiece is 2πxn, and when the speed at which the grinding machine approaches the workpiece is f, the ratio of the cutting speed to the peripheral speed, 2πxn / f, is 2πxn / f ≤ 1.03 × 10 6 It may satisfy the requirement. [Effects of the Invention]

[0029] The SiC crystal or SiC boule according to the above embodiment is less prone to defects when the bonded structure, formed by joining crystals together, is cut with a multi-wire saw. Furthermore, the method for manufacturing the SiC crystal according to the above embodiment can produce a SiC crystal that is less prone to defects when the bonded structure, formed by joining crystals together, is cut with a multi-wire saw. [Brief explanation of the drawing]

[0030] [Figure 1] This is a perspective view of the SiC crystal according to the first embodiment. [Figure 2] This is a plan view of the first surface of the SiC crystal according to the first embodiment. [Figure 3] This is a undulation curve obtained when the first surface of the SiC crystal according to the first embodiment is measured along the first measurement line. [Figure 4] This is the waviness curve obtained when the first surface of the SiC crystal according to the first embodiment is measured along the second measurement line. [Figure 5] This is a plan view of the first surface of the SiC crystal according to the first embodiment. [Figure 6] This is a schematic diagram of a grinding apparatus used in producing SiC crystals according to the first embodiment. [Figure 7] This is a plan view of a grinding apparatus used in producing SiC crystals according to the first embodiment. [Figure 8]The measurement results of the waviness curve of the first face of the SiC crystal in Example 1 are shown. [Figure 9] The measurement results of the waviness curve of the first face of the SiC crystal in Example 2 are shown. [Figure 10] The measurement results of the waviness curve of the first face of the SiC crystal in Example 3 are shown. [Figure 11] The measurement results of the waviness curve of the first face of the SiC crystal of Comparative Example 1 are shown. [Figure 12] The measurement results of the waviness curve of the first face of the SiC crystal in Example 7 are shown. [Modes for carrying out the invention]

[0031] This embodiment will now be described in detail with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience to clearly illustrate the features of this embodiment, and the dimensional ratios of each component may differ from those of the actual components. The materials, dimensions, etc., exemplified in the following description are examples only, and this disclosure is not limited to them. It is possible to modify and implement these examples as appropriate without altering the essence of the invention.

[0032] In this specification, individual orientations are indicated by [], collective orientations by <>, individual planes by () and collective planes by {}. While crystallography dictates that negative exponents are represented by a "-" (bar) above the number, in this specification, the negative sign is placed before the number.

[0033] First, let's define the direction. The stacking direction (crystal growth direction) of a SiC single crystal is defined as the Z direction. The Z direction is: <0001> Direction is also fine, <0001> It may be inclined by an offset angle with respect to the direction. The X direction is defined as one direction of the plane perpendicular to the Z direction. The X direction is, for example, the <1-100> direction. The Y direction is, for example, the <11-20> direction.

[0034] Figure 1 is a perspective view of the SiC crystal 1 according to this embodiment. The SiC crystal 1 may be a SiC boule, a seed crystal used in the production of a SiC boule, or a SiC substrate. A SiC boule is also called a SiC ingot. The SiC crystal 1 is made of, for example, n-type SiC. The polytype of the SiC crystal 1 is not particularly limited and may be any of 2H, 3C, 4H, or 6H. The SiC crystal 1 is, for example, 4H-SiC.

[0035] The SiC crystal 1 is a cylindrical columnar body. The SiC crystal 1 has a first face 1A, a second face 1B, and a side surface 1C. The first face 1A and the second face 1B are the faces at the ends of the SiC crystal 1 in the Z direction. The first face 1A and the second face 1B are opposite each other. The first face 1A may be either a Si face or a C face. The side surface 1C connects the first face 1A and the second face.

[0036] The first surface 1A and the second surface 1B may or may not have a portion having an offset angle with respect to the (0004) plane in the <11-20> direction. The offset angle is the angle between the plane perpendicular to the Z direction, which is the thickness direction of the SiC crystal 1, and the (0004) plane. The offset angle is, for example, greater than 0° and 10° or less, preferably 0.1° or more and 8° or less, more preferably 3.5° or more and 4.5° or less, and even more preferably 4°. If there is no offset angle, the SiC crystal 1 is grown with just-plane growth.

[0037] The thickness T in the Z direction of the SiC crystal 1 is more 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 warping of 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. The thickness T of the SiC crystal 1 may also be less than 30 mm, 20 mm or less, or 10 mm or less. If 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 warping of the SiC crystal 1 can be ignored.

[0038] Figure 2 is a plan view of the first surface 1A of the SiC crystal 1 according to this embodiment, viewed from the Z direction. The plan view shape of the SiC crystal 1 is approximately circular.

[0039] The diameter d of the SiC crystal 1 is, for example, 145 mm or more, preferably 149 mm or more. The diameter d of the SiC crystal 1 is preferably 155 mm or less, more preferably 151 mm or less. The diameter d of the SiC crystal 1 may also be, for example, 195 mm or more, preferably 199 mm or more. The diameter d of the SiC crystal 1 may also be preferably 205 mm or less, more preferably 201 mm or less. The diameter d of the SiC crystal 1 may also be 295 mm or more, preferably 299 mm or more. The diameter d of the SiC crystal 1 may also 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, if the SiC crystal 1 is a SiC Boolean, the minimum obtainable SiC substrate diameter corresponds to the minimum diameter of the SiC crystal 1. For example, if the diameter of the SiC crystal 1 differs depending on the position in the Z direction, the diameter at the height position where the diameter is smallest corresponds to the diameter d.

[0040] The first surface 1A of SiC crystal 1 has been ground. Due to the grinding, the surface of the first surface 1A is slightly undulating. Figure 3 shows the undulation curve of the first surface 1A of SiC crystal 1 measured along the first measurement line L1. Figure 4 shows the undulation curve of the first surface 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 when the first surface 1A is viewed from the Z direction in a plan view and extends in the <1-100> direction. The second measurement line L2 is a line that passes through the center C when the first surface 1A is viewed from the Z direction in a plan view and extends in the <11-20> direction. The center C is the center of the circumscribed circle of SiC crystal 1 when viewed from a plan view.

[0041] If the thickness of the SiC crystal 1 is 30 mm or more, the waviness curve of the first surface 1A is measured by placing the SiC crystal 1 on a flat surface. If the thickness of the SiC crystal 1 is less than 30 mm, the waviness curve of the first surface 1A is measured by adsorbing the SiC crystal 1 onto a flat surface. If the thickness of the SiC crystal 1 is sufficiently thick, or by adsorbing the SiC crystal 1 onto a flat surface, the effects of warping of the first surface 1A caused by factors other than waviness generated during grinding can be ignored.

[0042] The waviness curve is measured using, for example, a SURFCOM NEX 001 DX22 manufactured by Tokyo Seimitsu Co., Ltd. The outer region, including the area outside the device's acquisition range, is not included in the measurement range of the waviness curve. The outer region is a range of 4 mm from the outer edge. For example, if the diameter of SiC crystal 1 is 6 inches (approximately 150 mm), the measurement range is 4 mm on each side from the outer edge, and the measurement length is 142 mm. The measurement speed is 3.0 mm / second, the measurement range is ±500 mm, the calculation standard is JIS-'01 / 13 standard, the least-squares line is used for shape removal corresponding to slope correction, the cutoff type is Gaussian, the cutoff wavelength is 2.5 mm, and the measurement type is filtered waviness curve. The filtered waviness curve is a curve obtained by removing the roughness component with a short wavelength of waviness from the cross-sectional curve obtained by tracing the surface of the measurement surface with a probe. The cutoff wavelength indicates the range of roughness component to be removed.

[0043] As shown in Figure 3, the first surface 1A of the SiC crystal 1 measured along the first measurement line L1 is wavy. As shown in Figure 3, for example, the lowest point P1 of the wavy curve is located offset from the center C. Preferably, the lowest point P1 of the wavy curve is located offset from the central part C1, which is within 4% of the diameter from the center C. For example, the central part C1 is a region with a radius of 3 mm from the center C. Preferably, the lowest point P1 is 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.

[0044] Furthermore, as shown in Figure 4, the first surface 1A of the SiC crystal 1 measured along the second measurement line L2 is wavy. As shown in Figure 4, for example, the lowest point P3 of the wavy curve is located at a position offset from the center C. Preferably, the lowest point P3 of the wavy curve is located at a position offset from the central part C1 within 4% of the diameter from the center C. Preferably, the lowest point P3 is 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.

[0045] If the lowest point P1 or P3 of the undulation curve is offset from the center C, defects are less likely to occur when the joined body of SiC crystals 1 is cut with a multi-wire saw. The multi-wire saw has a blade that extends in the Y direction, and cuts the SiC crystals 1 by moving the joined body in the X direction relative to this blade. When cutting the SiC crystals 1 with a multi-wire saw, stress acts on the cut portion of the SiC crystals 1, causing it to shift in the X or Y direction, stress acts on the cut portion of the SiC crystals 1, causing it to rotate in the XY plane with respect to the center C, and stress acts on the cut portion of the SiC crystals 1, causing it to tilt in the Z direction. The center C and central part C1 of the first surface 1A are strongly subjected to these stresses.

[0046] When two SiC crystals 1 are joined together, adhesive is filled between the lowest points P1 and P3 of the wave curve and the adjacent SiC crystals 1. If the lowest point P1 or P3 coincides with the center C, the center C, where strong stress acts, is joined by the adhesive and becomes susceptible to stress. As a result, the joined SiC crystals 1 may shift at the joining interface. If the position of the lowest point P1 or P3 is offset from the center C, the position susceptible to stress and the position where stress acts are offset, thus suppressing bonding defects in the SiC crystals 1 more effectively than when the lowest point P1 or P3 coincides with the center C.

[0047] The difference in height h1 in the Z direction between the lowest point P1 and the highest point P2 of the undulation curve (see Figure 3) is, for example, 3.5 μm or less. Preferably, the difference in height h1 in the Z direction between the lowest point P1 and the highest point P2 of the undulation curve is 2.5 μm or less, 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.

[0048] Similarly, the difference in height h2 in the Z direction between the lowest point P3 and the highest point P4 of the undulation curve (see Figure 4) is, for example, 3.5 μm or less. The difference in height h2 in the Z direction between the lowest point P3 and the highest point P4 of the undulation curve is preferably 2.5 μm or less, 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.

[0049] A large difference between the lowest and highest points of the waviness curve results in a deeper layer of adhesive. When the layer of adhesive is deep, the SiC crystal 1 is more susceptible to stress during cutting. A large difference between the lowest and highest points of the waviness curve increases the likelihood of variations in the thickness of the SiC substrate after cutting. Conversely, if the difference between the lowest and highest points of the waviness curve is sufficiently small, the probability of cutting defects in the SiC crystal 1 bond can be reduced.

[0050] 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.

[0051] 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.

[0052] The smaller the surface roughness Ra of the first surface 1A, the larger the bonding area between the SiC crystals 1, and the less likely it is that cutting defects will occur in the bonded body of the SiC crystals 1.

[0053] Furthermore, on the first surface 1A of the SiC crystal 1, abrasive trajectories 2 may be observed, as shown in Figure 5. Abrasive trajectories 2 are grinding marks left after grinding the SiC crystal 1. Abrasive trajectories 2 are formed by the rotating SiC crystal 1 and the rotating grinding machine during grinding. Abrasive trajectories 2 form a pattern. For example, abrasive trajectories 2 are part of a rose curve. Abrasive trajectories 2 are faintly visible as white lines on the mirror-like first surface 1A. Multiple abrasive trajectories 2 are present on the first surface 1A, and intersection points 21 where the abrasive trajectories 2 intersect can be observed. The intersection point 21 where the abrasive trajectories 2 overlap the most is, for example, located at a position offset from the center C of the first surface 1A. Areas with abrasive trajectories 2 may be more deeply recessed than areas without abrasive trajectories 2, and if this intersection point 21 is offset from the center C, poor bonding between the SiC crystals 1 can be suppressed. Furthermore, it is preferable that the intersection point 21 where the abrasive grain trajectories 2 overlap the most is located, for example, at a position offset from the central part C1 of the first surface 1A.

[0054] Furthermore, the relationship on the first surface 1A of the SiC crystal 1 may also be satisfied on the second surface 1B. If the second surface 1B satisfies the same relationship as the first surface 1A, cutting defects become less likely when joining and cutting multiple SiC crystals 1.

[0055] For example, the lowest point of the undulation curve measured along the third measurement line on the second surface 1B is preferably located offset from the center of the second surface 1B, and more preferably offset from the central part within 4% of the diameter from the center of the second surface 1B. The third measurement line is a line that passes through the center when the second surface 1B is viewed from the Z direction in a plan view and extends in the <1-100> direction. The center and central part of the second surface 1B are defined the same as the center and central part of the first surface 1A.

[0056] Furthermore, for example, the lowest point of the undulation curve measured along the fourth measurement line on the second surface 1B is preferably located offset from the center of the second surface 1B, and more preferably offset from the center of the second surface 1B by 4% of its diameter. The fourth measurement line is a line that passes through the center of the second surface 1B when viewed from the Z direction in a plan view and extends in the <11-20> direction.

[0057] Furthermore, the difference in height in the Z direction between the lowest and highest points of the waviness curve measured along the third measurement line on the second surface 1B is preferably 3.5 μm or less, more preferably 2.5 μm or less, 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.

[0058] Furthermore, the difference in height in the Z direction between the lowest and highest points of the waviness curve measured along the fourth measurement line on the second surface 1B is preferably 3.5 μm or less, more preferably 2.5 μm or less, 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.

[0059] 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.

[0060] 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.

[0061] Furthermore, on the second surface 1B, it is preferable that the intersection point where the abrasive grain trajectories overlap the most is located, for example, at a position offset from the center of the second surface 1B.

[0062] Next, a method for manufacturing the SiC crystal 1 according to the first embodiment will be described. The method for manufacturing the SiC crystal 1 includes a preparation step and a grinding step. Figure 6 is a schematic diagram of the grinding apparatus 10 used when producing the SiC crystal 1 according to the first embodiment.

[0063] In the preparation step, the workpiece 13, on which the workpiece 11 made of SiC crystal is placed, is placed on the support table 14. Here, an example is shown in which the workpiece 13 is placed on the support table 14, but the workpiece 11 may also be placed directly on the support table 14.

[0064] The workpiece 11 is in the state before grinding of the SiC crystal 1, 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.

[0065] The workpiece 13 comprises 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 made of, for example, stainless steel (SUS). If the workpiece 11 is placed directly on the support table 14, the plate 12 is not necessary.

[0066] 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 shape along the outer circumference of the grinding machine 15.

[0067] Figure 7 is a plan view of the grinding apparatus 10 used when producing the SiC crystal 1 according to the first embodiment.

[0068] The center C15 of the grinding machine 15 is offset from the center C14 of the support table 14. As shown in Figure 7, the outer circumference of the grinding machine 15 may be positioned so as to pass through the center C14 of the support table 14. When the outer circumference of the grinding machine 15 is positioned so as to pass through the center C14 of the support table 14, the difference in height h1 in the Z direction between the lowest point P1 and the highest point P2 of the waviness curve, and the difference in height h2 in the Z direction between the lowest point P3 and the highest point P4 of the waviness curve, are 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 circumference of the workpiece 11. The radial length of the grinding wheel, which is arranged in a ring shape in the grinding machine 15, is preferably larger than, for example, the diameter of the workpiece 11.

[0069] The workpiece 11 is placed on the support table 14 such that the center C11 of the workpiece 11 does not coincide with the center C14 of the support table 14. The center C11 of the workpiece 11 is offset from the center C14 of the support table 14. The center C11 of the workpiece 11 basically coincides with the center C13 of the workpiece 13. 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 greater than or equal to the radius of the workpiece 11, and more preferably coincides with the radius of the workpiece 11.

[0070] For example, if 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.

[0071] Next, a grinding process is performed. In the grinding process, the workpiece 11, which is placed on a support table 14 that rotates in a first direction R1, is brought into contact with a grinding machine 15 that rotates 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 movable in the Z direction. By lowering the grinding machine 15 toward the workpiece 11, the workpiece 11 and the grinding machine 15 come into contact.

[0072] Let x be the distance between the center C11 of the workpiece and the center C14 of the support table 14, and let n be the rotational speed of the support table 14. Then the peripheral speed of the support table 14 at the installation position of the workpiece 11 is 2πxn. Let f be the speed at which the grinding machine 15 approaches the workpiece 11. Then the ratio of the cutting speed to the peripheral speed of the workpiece 13 is expressed as 2πxn / f. 2πxn / f ≤ 1.03 × 10⁻¹⁰ 6 It is preferable that this condition is met. When 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.

[0073] By grinding the workpiece 11 in the grinding process, the SiC crystal 1 according to this embodiment is obtained. By positioning the workpiece 11 on the support table 14 so that the center C11 of the workpiece 11 does not coincide with the center C14 of the support table 14, it is possible to avoid the abrasive grain trajectories 2 becoming densely concentrated at the center C11 of the workpiece 11.

[0074] In this embodiment, the SiC crystal 1 has a displacement between the lowest point of the waviness curve and the center C, which allows for a shift in the position susceptible to stress and the position where stress is most likely to act, thereby suppressing delamination of the SiC crystal 1 bond at the bonding interface.

[0075] Furthermore, in this embodiment, the SiC crystal 1 has a small difference between the lowest and highest points of the waviness curve, which reduces the probability that the blade of the multi-wire saw will pass through the interface between the SiC crystal 1 and the adhesive, thereby suppressing twisting of the multi-wire saw blade during cutting. As a result, variations in the thickness of the SiC substrate after cutting are suppressed, and the probability of cutting defects in the SiC crystal 1 bonded body is reduced.

[0076] In this embodiment, the SiC crystal 1 does not necessarily need to satisfy both the condition that the lowest point of the waviness curve is offset from the center C, and that the difference between the lowest and highest points of the waviness curve is small. Satisfying only one of these conditions can suppress cutting defects in the joined body compared to when no countermeasures are taken.

[0077] While preferred embodiments of this disclosure have been described in detail above, this disclosure is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the gist of this disclosure as described in the claims. [Examples]

[0078] "Example 1" A SiC crystal (SiC ingot) with a diameter of 150 mm (6 inches) and a thickness of 20 mm was prepared. As shown in Figures 6 and 7, the SiC crystal, which is the workpiece 11, was placed on the support table 14. The diameter of the support table 14 was 700 mm. The distance x between the center C14 of the support table 14 and the center C11 of the workpiece 11 was 50 mm. The grinding machine 15 used a cup-type grinding wheel with grinding wheels arranged in a ring shape. The outer diameter of the ring on which the grinding wheel of the grinding machine 15 is arranged was 400 mm, and the inner diameter was 385 mm. During grinding, the grinding machine 15 is positioned so that the outer circumference of the ring on which the grinding wheel of the grinding machine 15 is arranged passes through the center C14 of the support table 14.

[0079] Next, the support table 14 and the grinding machine 15 were rotated in opposite directions, bringing the workpiece 11 placed on the support table 14 into contact with the grinding machine 15. The rotation speed of the support table 14 was set to 17 rpm. The rotation speed of the grinding machine 15 was set to 680 rpm. The speed at which the grinding machine 15 was brought towards the workpiece 11 was set to 20 μm / min.

[0080] Then, the workpiece 11 was ground to produce a SiC crystal 1. Abrasive trajectories 2 were observed on the first surface 1A of the SiC crystal 1, and the intersection 21 where the abrasive trajectories 2 were most densely concentrated was offset from the center C of the first surface 1A.

[0081] Next, the waviness curve of the first face 1A of SiC crystal 1 was measured. The waviness curve was measured in both the <1-100> direction and the <11-20> direction. The waviness curve was measured using a SURFCOM NEX 001 DX22 manufactured by Tokyo Seimitsu Co., Ltd. The waviness curve was measured in the area excluding the outer periphery. The measurement length was set to 142 mm, which is the 150 mm diameter minus 4 mm from each end.

[0082] Figure 8 shows the measurement results of the waviness curve of the first face of the SiC crystal of Example 1. The upper part of Figure 8 shows the measurement results of the first face along the <11-20> direction, and the lower part shows the measurement results of the first face along the <1-100> direction. The horizontal axis indicates the measurement position in the radial direction of the SiC crystal. The measurement started at a position 4 mm inward from one outer edge (0 mm) and ended at a position 4 mm inward from the other outer edge (142 mm), with the center of the SiC crystal being at 71 mm. The vertical axis shows the height position of the first face at each point in the radial direction of the SiC crystal.

[0083] As shown in Figure 8, the lowest point of the waviness curve in Example 1 was offset from the center C in both the <11-20> and <1-100> directions. The difference in height between the highest and lowest points of the waviness curve measured along the <11-20> direction was 2.4665 μm. The difference in height between the highest and lowest points of the waviness curve measured along the <1-100> direction was 3.2912 μm. The surface roughness Ra of the first surface measured along the <11-20> direction was 14.2 nm. The surface roughness Ra of the first surface measured along the <1-100> direction was 16.2 nm.

[0084] Example 2 Example 2 differs from Example 1 in that the distance x between the center C14 of the support table 14 and the center C11 of the workpiece 11 is set to 100 mm. The SiC crystal of Example 2 was evaluated under the same conditions as in Example 1.

[0085] Abrasive trajectories 2 were also observed on the first surface 1A of the SiC crystal 1 in Example 2. The location where the abrasive trajectories 2 were most densely concentrated was offset from the center C of the first surface 1A.

[0086] Figure 9 shows the measurement results of the waviness curve of the first face of the SiC crystal of Example 2. The upper part of Figure 9 shows the measurement results of the first face along the <11-20> direction, and the lower part shows the measurement results of the first face along the <1-100> direction. The horizontal axis indicates the measurement position in the radial direction of the SiC crystal. The measurement started at a position 4 mm inward from one outer edge (0 mm) and ended at a position 4 mm inward from the other outer edge (142 mm), with the center of the SiC crystal being at 71 mm. The vertical axis shows the height position of the first face at each point in the radial direction of the SiC crystal.

[0087] As shown in Figure 9, the lowest point of the waviness curve in Example 2 was offset from the center C in both the <11-20> and <1-100> directions. The difference in height between the highest and lowest points of the waviness curve measured along the <11-20> direction was 0.9233 μm. The difference in height between the highest and lowest points of the waviness curve measured along the <1-100> direction was 1.6252 μm. The surface roughness Ra of the first surface measured along the <11-20> direction was 12.6 nm. The surface roughness Ra of the first surface measured along the <1-100> direction was 12.2 nm.

[0088] "Example 3" Example 3 differs from Example 1 in that the distance x between the center C14 of the support table 14 and the center C11 of the workpiece 11 was set to 200 mm. The SiC crystal of Example 3 was evaluated under the same conditions as in Example 1.

[0089] Abrasive grain trajectories 2 were also observed on the first surface 1A of the SiC crystal 1 in Example 3. The location where the abrasive grain trajectories 2 were most densely concentrated was offset from the center C of the first surface 1A.

[0090] Figure 10 shows the measurement results of the waviness curve of the first face of the SiC crystal of Example 3. The upper part of Figure 10 shows the measurement results of the first face along the <11-20> direction, and the lower part shows the measurement results of the first face along the <1-100> direction. The horizontal axis indicates the measurement position in the radial direction of the SiC crystal. The measurement started at a position 4 mm inward from one outer edge (0 mm) and ended at a position 4 mm inward from the other outer edge (142 mm), with the center of the SiC crystal being at 71 mm. The vertical axis shows the height position of the first face at each point in the radial direction of the SiC crystal.

[0091] As shown in Figure 10, the lowest point of the waviness curve in Example 3 was offset from the center C in both the <11-20> and <1-100> directions. The difference in height between the highest and lowest points of the waviness curve measured along the <11-20> direction was 1.5813 μm. The difference in height between the highest and lowest points of the waviness curve measured along the <1-100> direction was 1.1651 μm. The surface roughness Ra of the first surface measured along the <11-20> direction was 29.3 nm. The surface roughness Ra of the first surface measured along the <1-100> direction was 17.4 nm.

[0092] "Comparative Example 1" Comparative Example 1 differs from Example 1 in that the distance x between the center C14 of the support table 14 and the center C11 of the workpiece 11 is set to 0 mm. In other words, in Comparative Example 1, the positions of the center C14 of the support table 14 and the center C11 of the workpiece 11 coincide. The SiC crystal of Comparative Example 1 was evaluated under the same conditions as in Example 1.

[0093] Abrasive grain trajectories 2 were also observed on the first surface 1A of the SiC crystal 1 in Comparative Example 1. The location where the abrasive grain trajectories 2 were most densely concentrated was within the central part C1 of the first surface 1A.

[0094] Figure 11 shows the measurement results of the waviness curve of the first face of the SiC crystal of Comparative Example 1. The upper part of Figure 11 shows the measurement results of the first face along the <11-20> direction, and the lower part shows the measurement results of the first face along the <1-100> direction. The horizontal axis indicates the measurement position in the radial direction of the SiC crystal. The measurement started at a position 4 mm inward from one outer edge (0 mm) and ended at a position 4 mm inward from the other outer edge (142 mm), with the center of the SiC crystal being at 71 mm. The vertical axis shows the height position of the first face at each point in the radial direction of the SiC crystal.

[0095] As shown in Figure 11, the lowest point of the waviness curve of Comparative Example 1 coincided with the center C in both the <11-20> and <1-100> directions. The difference in height between the highest and lowest points of the waviness curve measured along the <11-20> direction was 2.7245 μm. The difference in height between the highest and lowest points of the waviness curve measured along the <1-100> direction was 3.8233 μm. The surface roughness Ra of the first surface measured along the <11-20> direction was 17.3 nm. The surface roughness Ra of the first surface measured along the <1-100> direction was 12.0 nm.

[0096] In Examples 1-3, the lowest point of the first face of the SiC crystal was offset from the center C of the first face. In contrast, in Comparative Example 1, the lowest point of the first face of the SiC crystal coincided with the center C of the first face. Compared to the SiC crystal joint using the SiC crystals of Examples 1-3, the joint interface of the SiC crystal joint using the SiC crystal of Comparative Example 1 was less prone to misalignment when cut with a multi-wire saw.

[0097] Furthermore, the difference between the highest and lowest points of the first surface of the SiC crystals in Examples 1 to 3 was smaller compared to the SiC crystal in Comparative Example 1. The SiC crystal junctions using the SiC crystals of Examples 1 to 3 showed less variation in the thickness of the SiC substrate compared to the SiC crystal junction using the SiC crystal in Comparative Example 1.

[0098] Examples 4-6 Examples 4-6 differ from Examples 1-3 in that the thickness of the SiC crystal (SiC ingot) was set to 30 mm. All other conditions were the same as in Examples 1-3.

[0099] In Examples 4-6, the lowest point of the first face of the SiC crystals was offset from the center C of the first face. Furthermore, the difference between the highest and lowest points of the first face of the SiC crystals in Examples 4-6 was 3.5 μm or less. In Examples 4-6, no problematic misalignment of the bonding interface during cutting of the bonded material, nor any variation in the thickness of the SiC substrate after cutting, was observed. It was confirmed that similar results can be obtained even when the SiC crystal thickness is high.

[0100] Examples 7-9 Examples 7-9 differ from Examples 1-3 in that the thickness of the SiC crystal (SiC ingot) was set to 3 mm. All other conditions were the same as in Examples 1-3.

[0101] In Examples 7-9, the lowest point of the first face of the SiC crystal was offset from the center C of the first face. Furthermore, the difference between the highest and lowest points of the first face of the SiC crystal in Examples 7-9 was 3.5 μm or less. In Examples 7-9, no problematic misalignment of the bonding interface during cutting of the bonded material, nor any variation in the thickness of the SiC substrate after cutting, was observed. It was confirmed that similar results can be obtained even when the SiC crystal thickness is thin.

[0102] Figure 12 shows the measurement results of the waviness curve of the first face of the SiC crystal in Example 7 (SiC crystal (SiC ingot) thickness of 3 mm, distance x of 50 mm). The upper part of Figure 12 shows the measurement results of the first face along the <11-20> direction, and the lower part shows the measurement results of the first face along the <1-100> direction. The horizontal axis indicates the measurement position in the radial direction of the SiC crystal. The measurement started at a position 4 mm inward from one outer edge (0 mm) and ended at a position 4 mm inward from the other outer edge (142 mm), with the center of the SiC crystal being at 71 mm. The vertical axis shows the height position of the first face at each point in the radial direction of the SiC crystal.

[0103] As shown in Figure 12, the lowest point of the waviness curve in Example 7 was offset from the center C in both the <11-20> and <1-100> directions. The difference in height between the highest and lowest points of the waviness curve measured along the <11-20> direction was 1.3538 μm. The difference in height between the highest and lowest points of the waviness curve measured along the <1-100> direction was 1.5171 μm. The surface roughness Ra of the first surface measured along the <11-20> direction was 12.5 nm. The surface roughness Ra of the first surface measured along the <1-100> direction was 12.7 nm.

[0104] While the results presented so far have been based on SiC crystals (SiC ingots) with a diameter of 150 mm (6 inches), similar studies were also conducted on SiC crystals (SiC ingots) with a diameter of 200 mm (8 inches). The same trend was observed for the 8-inch diameter as for the 6-inch diameter. [Explanation of symbols]

[0105] 1 SiC crystal 1A 1st page 1B 2nd side 1C side 2. Abrasive trajectories 10 Grinding device 11 Workpiece 12 plates 13 Work 14 Support Table 15 Grinding machine 21 intersection C, C11, C13, C14, C15 center C1 central part L1 First measurement line L2 Second measurement line P1, P3 lowest point P2, P4 Highest point

Claims

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

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

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

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

5. The first surface has abrasive grain trajectories, The SiC crystal according to claim 1, wherein the intersection point where the abrasive grain trajectories overlap the most is offset from the center.

6. The SiC crystal according to claim 1, wherein the difference between the highest and lowest points of the undulation curve on the first measurement line is 3.5 μm or less.

7. The SiC crystal according to claim 2, wherein the difference between the highest and lowest points of the undulation curve on the second measurement line is 3.5 μm or less.

8. It has a first surface which is one surface in the stacking direction, A SiC crystal in which, when the waviness curve of the first surface is measured along a first measurement line passing through the center of the first surface and extending in the <1-100> direction, the difference between the highest and lowest points of the waviness curve along the first measurement line is 3.5 μm or less.

9. The SiC crystal according to claim 8, wherein when the waviness curve of the first surface is measured along a second measurement line passing through the center of the first surface and extending in the <11-20> direction, the difference between the highest and lowest points of the waviness curve along the second measurement line is 3.5 μm or less.

10. The SiC crystal according to claim 8, wherein the surface roughness Ra of the first surface measured along the first measurement line is 20 nm or less.

11. The SiC crystal according to claim 8, wherein the surface roughness Ra of the first surface, measured along a second measurement line passing through the center of the first surface and extending in the <11-20> direction, is 30 nm or less.

12. The first surface has abrasive grain trajectories, The SiC crystal according to claim 8, wherein the intersection point where the abrasive grain trajectories overlap the most is offset from the center.

13. The SiC crystal according to claim 8, wherein the lowest point of the undulation curve in the first measurement line is located at a position offset from the center.

14. The SiC crystal according to claim 9, wherein the lowest point of the undulation curve in the second measurement line is located at a position offset from the center.

15. It has a first surface which is one surface in the stacking direction, A SiC Boolean in which, when the waviness curve of the first surface is measured along a first measurement line passing through the center of the first surface and extending in the <1-100> direction, the lowest point of the waviness curve along the first measurement line is offset from the center.

16. A process of placing a workpiece made of SiC crystal on a support table, The process includes bringing into contact a workpiece placed on a support table rotating in a first direction with a grinding machine rotating in a second direction opposite to the first direction, thereby grinding the first surface of the workpiece. The grinding machine is positioned opposite the support table, such that the center of the grinding machine does not coincide with the center of the support table. A method for manufacturing SiC crystals, wherein the center of the workpiece is located at a position offset from the center of the support table.

17. The method for producing a SiC crystal according to claim 16, wherein the distance between the center of the workpiece and the center of the support table is greater than or equal to the radius of the workpiece.

18. The method for producing a SiC crystal according to claim 16, wherein the distance between the center of the workpiece and the center of the support table is equal to the radius of the workpiece.

19. The method for producing SiC crystals according to claim 16, wherein the diameter of the workpiece is 149 mm or more.

20. Let x be the distance between the center of the workpiece and the center of the support table. When the rotational speed of the support table is n, the peripheral speed of the support table at the workpiece installation position is 2π x n. When the speed at which the grinding machine approaches the workpiece is f, The ratio of the cutting speed to the peripheral speed, 2πxn / f, is given by 2πxn / f ≤ 1.03 × 10⁻⁶. ６ A method for producing SiC crystals according to claim 16, satisfying the requirements.

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