Method for cutting silicon carbide singly crystal ingot, method for manufacturing silicon carbide singly crystal substrate, and silicon carbide singly crystal substrate

Abstract

To provide a method for cutting a silicon carbide single crystal ingot which brings a fixed abrasive grain wire into contact with a columnar ingot composed of a silicon carbide single crystal using a multi wire saw, and can cut a disk-like substrate with small waviness and warpage while suppressing a used amount of the fixed abrasive grain wire.SOLUTION: A method for cutting a silicon carbide single crystal ingot includes a cutting step of bringing a fixed abrasive grain wire into contact with a columnar ingot composed of a silicon carbide single crystal using a multi wire saw, and cutting a substrate with a diameter of 6 inches or 8 inches and a plate thickness of 340 μm or more and 600 μm or less, from the ingot, wherein in the cutting step, a new wire supply amount from start of cutting to end of cutting is set to be 1.7 m / min or more, and a new wire supply amount when a central part in a cross-sectional view of the ingot is cut is set to be larger than that when a peripheral edge part in the cross-sectional view of the ingot is cut.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for cutting a silicon carbide single crystal ingot, a method for manufacturing a silicon carbide single crystal substrate, and a silicon carbide single crystal substrate. [Background technology]

[0002] In recent years, substrates made of silicon carbide single crystals have been attracting attention as materials for semiconductor devices. When manufacturing substrates made of silicon carbide single crystals, a cutting process is performed to cut out disk-shaped substrates from a cylindrical ingot made of silicon carbide single crystals. Methods for cutting out substrates from an ingot include a method for cutting out substrates one by one from an ingot and a method for cutting out multiple substrates simultaneously from an ingot.

[0003] As a method for simultaneously cutting out a plurality of substrates from an ingot, a processing technique using a multi-wire saw has been developed and put to practical use. The multi-wire saw has a pair of guide rollers and a number of wires that run parallel to each other at a predetermined interval between the pair of guide rollers. The number of wires installed between the pair of guide rollers corresponds to the number of substrates to be cut from an ingot. By bringing the ingot into contact with the multiple wires running between the guide rollers, multiple substrates can be cut from the ingot at the same time.

[0004] Known methods for cutting out a disk-shaped substrate from a cylindrical ingot made of silicon carbide single crystal using a multi-wire saw include a free abrasive method in which abrasive grains are supplied to the sliding portion between the ingot and the wire, and a fixed abrasive method in which a fixed abrasive wire with abrasive grains fixed to its surface is used. By using the fixed abrasive method, it is possible to cut out a substrate from the ingot in a shorter time than by using the free abrasive method. As a method for cutting out a substrate from an ingot made of silicon carbide single crystal using a multi-wire saw with a fixed abrasive grain system, there are techniques described in, for example, Patent Documents 1 and 2.

[0005] Patent Document 1 describes a multi-wire machining method in which, when the traveling direction of the saw wire is the X direction, the saw wire cutting direction in which the saw wire cuts the workpiece is the Z direction, and the direction perpendicular to the XZ plane is the Y direction, when cutting the workpiece, the workpiece is moved in a direction that reduces the Y-direction displacement amount in accordance with information on change in displacement amount of the Y-direction displacement component of the deflection of the saw wire that occurs during multi-wire machining.

[0006] Patent Document 2 describes a method for cutting a high-hardness material with a multi-wire saw, in which an ingot of a high-hardness material is cut at multiple locations simultaneously with a multi-wire saw to cut out multiple wafers. Patent Document 2 also describes a method for cutting a high-hardness material with a multi-wire saw, in which, when the ingot is projected onto the wire from the direction in which the ingot is cut, the sum of the projected lengths of the ingot at the multiple locations to be cut is the maximum total contact length a, the continuous wire travel distance is b, and c1 = b / a, where c1 ≧ 20, unit travels in which the wire is reciprocated are repeated, and where the amount of new wire payout in each unit travel is d, and c2 = d / a, where 0.35 ≦ c2 ≦ 1.55. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2015-47673 A [Patent Document 2] JP 2015-134390 A Summary of the Invention [Problem to be solved by the invention]

[0008] When manufacturing electronic devices using a substrate made of silicon carbide single crystal, a thin epitaxial film is usually formed on the substrate. The epitaxial film is formed by placing the substrate on a heating element called a susceptor and heating the substrate to a high temperature in a growth chamber where the atmospheric gas is controlled. If the substrate made of silicon carbide single crystal cut from an ingot is significantly warped, the contact (adhesion) between the substrate placed on the susceptor and the susceptor becomes uneven, and a high-quality epitaxial film cannot be obtained.

[0009] Furthermore, the substrate made of silicon carbide single crystal cut from the ingot is used after undergoing flattening, grinding, and polishing processes as post-processes. Silicon carbide single crystal is a high-hardness material, and the substrate made of silicon carbide single crystal has high rigidity. For this reason, it is difficult to correct the undulation and warpage of the substrate made of silicon carbide single crystal cut from the ingot in the post-processes. For this reason, when cutting a substrate from an ingot made of silicon carbide single crystal, it is preferable to use a cutting method that can cut out a substrate with small undulation and warpage.

[0010] One method for cutting out a substrate with minimal waviness and warpage from an ingot made of silicon carbide single crystal using a multi-wire saw with a fixed abrasive method is to increase the amount (length) of the fixed abrasive wire used for cutting. However, fixed abrasive wire is expensive, with abrasive grains such as diamonds fixed to the outer surface of the core material. Therefore, it is not preferable to use a large amount of fixed abrasive wire.

[0011] The present invention has been made in consideration of the above circumstances, and has an object to provide a method for cutting a silicon carbide single crystal ingot, which is capable of cutting out a disk-shaped substrate with little waviness and warping by using a multi-wire saw to bring a fixed abrasive wire into contact with a cylindrical ingot made of silicon carbide single crystal while limiting the amount of fixed abrasive wire used, a method for manufacturing a silicon carbide single crystal substrate, and a silicon carbide single crystal substrate. [Means for solving the problem]

[0012] [1] A cutting process comprising: bringing a fixed abrasive wire into contact with a cylindrical ingot made of a silicon carbide single crystal using a multi-wire saw; and cutting out a disk-shaped substrate from the ingot; The method for cutting a silicon carbide single crystal ingot, wherein, in the cutting step, an amount of new wire supplied when cutting a central portion in a cross-sectional view of the ingot is made larger than an amount of new wire supplied when cutting a peripheral portion in a cross-sectional view of the ingot.

[0013] [2] The method for slicing a silicon carbide single crystal ingot according to [1], wherein the amount of new wire supply is changed in proportion to a contact length between the ingot and the fixed abrasive wire during slicing.

[0014] [3] The method for slicing a silicon carbide single crystal ingot according to [1] or [2], wherein the length of the fixed abrasive wire used to slice one of the substrates satisfies formula (1). A≧S×13700 Formula (1) In formula (1), A is the length (m) of the fixed abrasive wire used to cut one substrate. S is the planar area (m 2 )

[0015] [4] The method for slicing a silicon carbide single crystal ingot according to [1] or [2], wherein the length of the fixed abrasive wire used to slice into one of the substrates satisfies formula (2). S×15100≧A≧S×13700 Formula (2) In formula (2), A is the length (m) of the fixed abrasive wire used to cut one substrate. S is the planar area (m 2 )

[0016] [5] The method for slicing a silicon carbide single crystal ingot according to any one of [1] to [4], wherein the amount of new wire supplied is 11 times or more the contact length between the ingot and the fixed abrasive wire during slicing.

[0017] [6] The method for cutting a silicon carbide single crystal ingot according to any one of [1] to [5], wherein the ingot has a diameter of 3 inches to 8 inches. [7] The method for cutting a silicon carbide single crystal ingot according to any one of [1] to [5], wherein the ingot has a diameter of 6 inches.

[0018] [8] In the cutting process, a running cycle including a first running step of running the fixed abrasive wire in a first direction while contacting the ingot, and a second running step of running the fixed abrasive wire run in the first running step in a second direction opposite to the first direction while contacting the ingot is repeated multiple times; The method for slicing a silicon carbide single crystal ingot according to any one of [1] to [7], wherein the amount of new wire supplied is changed for each running cycle. [9] The amount of new wire supplied is changed by changing a ratio of a time for performing the first traveling step to a time for performing the second traveling step for each traveling cycle. The method for cutting a silicon carbide single crystal ingot according to [8]. Effect of the Invention

[0019] The method for cutting a silicon carbide single crystal ingot of the present invention includes a cutting step in which a fixed abrasive wire is brought into contact with a cylindrical ingot made of a silicon carbide single crystal using a multi-wire saw to cut out a disk-shaped substrate from the ingot. In the cutting step, the amount of new wire supplied when cutting the central portion of the ingot in cross section is made larger than that when cutting the peripheral portion of the ingot in cross section. This makes it possible to reduce the amount of fixed abrasive wire used compared to the case where the amount of new wire supplied in the cutting step is constant according to the optimal amount when cutting the central portion of the ingot in cross section. Moreover, it is possible to cut out a substrate with small waviness and warpage to the same extent as the case where the amount of new wire supplied in the cutting step is constant according to the optimal amount when cutting the central portion of the ingot in cross section. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic configuration diagram for explaining an example of a multi-wire saw used in a method for slicing a silicon carbide single crystal ingot according to the present embodiment. [Diagram 2] FIG. 2 is an enlarged perspective view for explaining a cutting step of cutting out substrates from an ingot using the multi-wire saw shown in FIG. [Diagram 3] FIG. 3 is a schematic diagram for explaining a contact state between the ingot and the fixed abrasive wire during slicing. [Figure 4] FIG. 4 is a graph showing the bow of the substrates cut out in Test Examples 1 to 6. [Diagram 5] Figures 5(a) to 5(c) are graphs showing the evaluation results of the fourth substrate when the multiple substrates cut out in Test Example 7 were arranged in order from the end (first end) where a new line of the fixed abrasive wire 4 was supplied. [Figure 6] Figures 6(a) to 6(c) are graphs showing the evaluation results of the third substrate when the multiple substrates cut out in Test Example 7 were arranged in order from the end (first end) where a new line of the fixed abrasive wire 4 was supplied. [Figure 7] Figures 7(a) and 7(b) are graphs showing the evaluation results of the fourth substrate when the multiple substrates cut out in Test Example 8 were arranged in order from the end (first end) where a new line of the fixed abrasive wire 4 was supplied. [Figure 8] Figures 8(a) and 8(b) are graphs showing the evaluation results of the fifth substrate when the multiple substrates cut out in Test Example 8 were arranged in order from the end (first end) where a new line of the fixed abrasive wire 4 was supplied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] In order to solve the above problems, the present inventors have focused on the relationship between the cutting position in a cross-sectional view of a cylindrical ingot made of silicon carbide single crystal being cut using a multi-wire saw and the amount of new wire supply, and have conducted extensive research. As a result, they discovered that by supplying more new wire when cutting the central part of the ingot in cross section than when cutting the peripheral part of the ingot in cross section, it is possible to cut out a disk-shaped substrate with little waviness and warping while reducing the amount of fixed abrasive wire used, and thus arrived at the present invention.

[0022] In this specification, the "new wire supply rate" refers to the length per unit time of the fixed abrasive wire used to cut an ingot that first comes into contact with the ingot. For example, in a cutting process, a running cycle consisting of a first running step in which the fixed abrasive wire is brought into contact with the ingot while running in a first direction, and a second running step in which the fixed abrasive wire run in the first running step is brought into contact with the ingot while running in a second direction opposite to the first direction, is repeated multiple times, and the amount of new wire supply is changed for each running cycle, the "amount of new wire supply" in each running cycle is the numerical value shown below.

[0023] The fixed abrasive wire running in the first direction in the first running process is a new wire used for the first time to cut an ingot. The fixed abrasive wire running in the second direction in the second running process is an old wire, not a new wire used for the first time to cut an ingot. Therefore, the "new wire supply amount" in each running cycle is the length of the fixed abrasive wire running in the first direction in the first running process minus the length of the fixed abrasive wire running in the second direction in the second running process divided by the time of the running cycle.

[0024] The method for cutting a silicon carbide single crystal ingot according to the present invention will be described in detail below with reference to the drawings. The drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to easily explain the characteristics, and the dimensional ratios of each component are not necessarily the same as in reality. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately modified and implemented within the scope of the present invention.

[0025] [Multi-wire saw] FIG. 1 is a schematic configuration diagram for explaining an example of a multi-wire saw used in a method for slicing a silicon carbide single crystal ingot according to the present embodiment. In FIG. 1, reference numeral 1 denotes a multi-wire saw, reference numeral 3 denotes an ingot, reference numeral 21 denotes a first guide roller, reference numeral 22 denotes a second guide roller, and reference numeral 4 denotes a fixed abrasive wire.

[0026] The multi-wire saw 1 shown in FIG. 1 includes a pair of guide rollers, a first guide roller 21 and a second guide roller 22. The rotation axis of the first guide roller 21 is arranged parallel to the rotation axis of the second guide roller 22. A single continuous fixed abrasive wire 4 is wound multiple times between the first guide roller 21 and the second guide roller 22. The fixed abrasive wire 4 travels in a predetermined direction at a predetermined travel speed by rotating the first guide roller 21 and the second guide roller 22 at a predetermined rotation speed in the same direction.

[0027] The first guide roller 21 and the second guide roller 22 each have a plurality of equally spaced grooves on their side surfaces for holding the fixed abrasive wire 4. The fixed abrasive wire 4 is wound around each of the grooves provided in the first guide roller 21 and the second guide roller 22, so that a plurality of fixed abrasive wires 4 are disposed in parallel between the first guide roller 21 and the second guide roller 22 at predetermined intervals in plan view.

[0028] The pitch of the multiple grooves provided in the first guide roller 21 and the second guide roller 22 (in other words, the pitch of the multiple fixed abrasive wires 4 arranged between the first guide roller 21 and the second guide roller 22) can be, for example, 600 μm to 875 μm, and can be determined depending on the diameter of the ingot 3, the thickness of the substrate cut from the ingot 3, the thickness of the fixed abrasive wire 4, etc. The number of fixed abrasive wires 4 arranged in parallel between first guide roller 21 and second guide roller 22 corresponds to the number of substrates cut out from ingot 3.

[0029] For example, a core material having abrasive grains fixed to the outer surface thereof can be used as the fixed abrasive wire 4. The abrasive grains are preferably electrodeposited onto the outer surface of the core material. The abrasive grains used have a Mohs hardness greater than that of the ingot 3. Specifically, it is preferable to use diamond as the abrasive grains.

[0030] The grain size of the abrasive grains fixed to the fixed abrasive wire 4 is preferably 20 μm to 40 μm, and more preferably 30 μm to 40 μm. When the grain size of the abrasive grains is 20 μm or more, the ingot 3 can be cut efficiently in a short time. When the grain size of the abrasive grains is 40 μm or less, damage caused by cutting the ingot 3 on the surface of the cut substrate can be suppressed, which is preferable. The grain size of the abrasive grains can be determined depending on the diameter of the ingot 3, the hardness of the abrasive grains, the average running speed of the fixed abrasive wire 4, etc. The diameter of the fixed abrasive wire 4 can be, for example, 120 μm to 180 μm, and can be determined depending on the diameter of the ingot 3, the particle size of the abrasive grains fixed to the outer surface of the fixed abrasive wire 4, the average running speed of the fixed abrasive wire 4, etc.

[0031] A first end of the fixed abrasive wire 4 wound between the first guide roller 21 and the second guide roller 22 is wound around a first bobbin (not shown). The first bobbin either sends the fixed abrasive wire 4 to the first guide roller 21 or takes up the fixed abrasive wire 4 sent from the first guide roller 21, depending on the running direction of the fixed abrasive wire 4. A second end of the fixed abrasive wire 4 opposite to the first end is wound around a second bobbin (not shown). The second bobbin either delivers the fixed abrasive wire 4 to the second guide roller 22 or takes up the fixed abrasive wire 4 delivered from the second guide roller 22, depending on the running direction of the fixed abrasive wire 4.

[0032] The arrangement of the first bobbin and the second bobbin is not particularly limited. For example, the first bobbin may be placed near the first guide roller 21 and the second bobbin may be placed near the second guide roller 22, or both the first bobbin and the second bobbin may be placed near the first guide roller 21, or both the first bobbin and the second bobbin may be placed near the second guide roller 22.

[0033] The multi-wire saw 1 may be provided with other guide rollers in addition to the first guide roller 21 and the second guide roller 22. Furthermore, a pulley or the like may be provided between the first guide roller 21 and the bobbin and / or between the second guide roller 22 and the bobbin.

[0034] 1 includes a first coolant supply unit 61 that supplies coolant liquid from the side of the first guide roller 21, and a second coolant supply unit 62 that supplies coolant liquid from the side of the second guide roller 22. The positions and number of the coolant supply units are not particularly limited, and can be appropriately determined depending on the diameter and length in the central axis direction of the cylindrical ingot 3, the thickness and number of substrates cut from the ingot 3, the amount of coolant liquid supplied, etc. As the coolant, a known coolant that can be used when cutting out a substrate from an ingot 3 made of silicon carbide single crystal can be used, and it is preferable to use a water-soluble cutting oil.

[0035] The multi-wire saw 1 shown in FIG. 1 includes a control means (not shown) for controlling the amount of new wire supply. The control means in this embodiment includes a CPU and various memories (storage devices). The control means controls the operation of the first guide roller 21, the second guide roller 22, the first bobbin, and the second bobbin during cutting of the ingot 3 according to a program stored in the storage device in response to vertical position information of the ingot 3 and the fixed abrasive wire 4. The control means preferably controls the amount of new wire supply for each predetermined unit time, and more preferably controls the amount of new wire supply for each travel cycle. When controlling the amount of new wire supply for each travel cycle, the control means controls the amount of new wire supply by changing the ratio of the time for performing the first travel step to the time for performing the second travel step.

[0036] [Method of cutting silicon carbide single crystal ingot] Next, a method of cutting an ingot 3 made of a silicon carbide single crystal using the multi-wire saw 1 shown in Fig. 1 will be described. Fig. 2 is an enlarged perspective view for explaining a cutting step of cutting out substrates from the ingot using the multi-wire saw shown in Fig. 1. As shown in FIG. 2, in the method for cutting a silicon carbide single crystal ingot of this embodiment, a plurality of fixed abrasive wires 4 arranged in parallel at a predetermined interval are simultaneously brought into contact with a cylindrical ingot 3 made of a silicon carbide single crystal, and a plurality of disk-shaped substrates are simultaneously cut out from the ingot 3 (cutting process).

[0037] The ingot 3 cut in this embodiment is made of silicon carbide single crystal and has a hexagonal crystal structure. The cutting direction of the ingot 3 (in other words, the running direction of the fixed abrasive wire 4) is, for example, a direction parallel to the <11-20> direction of the silicon carbide single crystal. As shown in FIG. 2, the ingot 3 cut in this embodiment is cylindrical. The length of the ingot 3 in the central axis direction (thickness of the ingot 3) can be, for example, 1 mm to 60 mm, and is preferably 5 mm to 60 mm. When the length of the ingot 3 in the central axis direction is 1 mm or more, the effect of cutting out a plurality of substrates from the ingot 3 using the multi-wire saw 1 can be obtained. In addition, when the length of the ingot 3 in the central axis direction is 5 mm or more, a sufficient number of substrates can be obtained from one ingot 3, which is preferable. When the length of the ingot 3 in the central axis direction is 60 mm or less, the maximum number of substrates that can be obtained from the ingot 3 can be cut out by performing the cutting step only once using the multi-wire saw 1. Therefore, if the length of the ingot 3 in the central axial direction is 60 mm or less, the substrates can be cut out from the ingot 3 efficiently.

[0038] The ingot 3 preferably has a diameter of 3 to 8 inches, and more preferably has a diameter of 6 inches.

[0039] In this embodiment, the thickness of the substrate cut from the ingot 3 can be appropriately determined depending on the application of the substrate. The thickness of the substrate cut from the ingot 3 can be, for example, 340 μm to 600 μm, and is preferably 400 μm to 475 μm. When the thickness of the substrate cut from the ingot 3 is 600 μm or less, a sufficient number of substrates can be obtained from one ingot 3. When the thickness of the substrate cut from the ingot 3 is 340 μm or more, a substrate with a uniform thickness and less waviness and warpage can be cut out. In addition, when the thickness of the substrate cut from the ingot 3 is 400 μm or more, even if damage to the substrate surface is removed by performing a subsequent process such as a flattening process, a grinding process, or a polishing process, a sufficient thickness is easily obtained to ensure the performance of laminating a thin film on the substrate, which is preferable.

[0040] As a method for contacting the ingot 3 with the fixed abrasive wire 4, for example, a method can be used in which the ingot 3 supported by a goniostage 5 is pressed down toward the fixed abrasive wire 4 using a known lifting device. In this embodiment, the goniostage 5 continuously or intermittently detects the vertical movement amount of the ingot 3, and continuously or intermittently detects the vertical position of the fixed abrasive wire 4 in contact with the ingot 3. The detected vertical position information of the ingot 3 and the fixed abrasive wire 4 is sent to a control means that controls the amount of new wire supply. As the goniostage 5, a known one can be used.

[0041] In this embodiment, in the cutting process, the ingot 3 is cut by moving the ingot 3 downward at a predetermined descending speed while bringing the ingot 3 into contact with the fixed abrasive wire 4 running between the first guide roller 21 and the second guide roller 22. In this embodiment, the fixed abrasive wire 4 and the ingot 3 are brought into contact with each other while supplying coolant between them from the first coolant supply unit 61 and the second coolant supply unit 62. This makes it possible to remove heat generated by the contact between the fixed abrasive wire 4 and the ingot 3. In addition, sludge generated by cutting the ingot 3 can be removed from between the cut surfaces during cutting. The amounts of coolant supplied from the first coolant supply unit 61 and the second coolant supply unit 62 can be determined according to the diameter of the fixed abrasive wire 4, the hardness of the abrasive grains fixed to the outer surface of the fixed abrasive wire 4, the average running speed of the fixed abrasive wire 4, and the like.

[0042] In this embodiment, in the cutting step, a traveling cycle consisting of a first traveling step and a second traveling step is repeated a plurality of times. In the first running step, the first guide roller 21 and the second guide roller 22 are rotated at a predetermined rotation speed in the direction shown by the arrow in Fig. 1. As a result, a new wire of the fixed abrasive wire 4 is supplied from the first end side of the fixed abrasive wire 4 and wound between the first guide roller 21 and the second guide roller 22. When viewed from the ingot 3 pressed down toward the fixed abrasive wire 4, the wound new wire comes into contact with the ingot 3 while running between the first guide roller 21 and the second guide roller 22 in a first direction, which is a direction from the first guide roller 21 to the second guide roller 22, as shown by the arrow in Fig. 1.

[0043] In the second traveling step, the first guide roller 21 and the second guide roller 22 are rotated at a predetermined rotation speed in a direction opposite to the direction indicated by the arrow in Fig. 1. As a result, the (old wire) of the fixed abrasive wire 4 that has come into contact with the ingot 3 and then been wound is supplied from the second end side opposite to the first end of the fixed abrasive wire 4, and is wound between the first guide roller 21 and the second guide roller 22. When viewed from the ingot 3 that is pressed down toward the fixed abrasive wire 4, the wound old wire comes into contact with the ingot 3 while traveling between the first guide roller 21 and the second guide roller 22 in a second direction (opposite to the first direction) that is a direction from the second guide roller 22 toward the first guide roller 21. Therefore, in this embodiment, the fixed abrasive wire 4 moves back and forth between the first guide roller 21 and the second guide roller 22 in the cutting process.

[0044] The time for one travel cycle can be, for example, 1 minute to 5 minutes. If the time for one travel cycle is 5 minutes or less, the variation in the cutting speed for each travel cycle can be suppressed, which is preferable. If the time for one travel cycle is 1 minute or more, the number of travel cycles is reduced. Therefore, if the time for one travel cycle is 1 minute or more, the time required to change the rotation direction of the first guide roller 21 and the second guide roller 22 is reduced, and the cutting speed of the ingot 3 can be prevented from decreasing. The travel cycle time may be the same for all travel cycles, may be different for each travel cycle, or may be the same for only some of the travel cycles. It is preferable that the travel cycle time is the same for all travel cycles, since this reduces the variation in cutting speed for each travel cycle.

[0045] In this embodiment, the amount of new wire supply is changed in the cutting process. The amount of new wire supply is preferably changed every predetermined unit time, and preferably every travel cycle. Specifically, the amount of new wire supply is preferably changed by changing the ratio of the time for performing the first travel step to the time for performing the second travel step for each travel cycle according to the vertical position information of the ingot 3 and the fixed abrasive wire 4 by the control means. At this time, it is preferable to make the average travel speed of the fixed abrasive wire 4 in the first travel step and the second travel step, and the ratio of the descending speed of the ingot 3 to the length (contact length) of the fixed abrasive wire 4 in contact with the ingot 3, the same in each travel cycle.

[0046] The new wire supply amount in this embodiment is the length per unit time of the fixed abrasive wire 4 used to cut the ingot 3 in one running cycle that first comes into contact with the ingot. Therefore, the new wire supply amount in this embodiment is calculated by subtracting the length (m) of the fixed abrasive wire 4 (old wire) used in the second running step from the length (m) of the fixed abrasive wire 4 (new wire) used in the first running step, and dividing the result by the time (min) of one running cycle. For example, if the duration of one running cycle is one minute, the amount of new wire supplied in each running cycle is the length (m / min) of the fixed abrasive wire 4 (new wire) used in the first running process minus the length (m) of the fixed abrasive wire 4 (old wire) used in the second running process.

[0047] Furthermore, when the average running speed of the fixed abrasive wire 4 is the same in the first running step and the second running step, the "new wire supply amount" in each running cycle is a value calculated by the following formula (I). Y=X1{1-(T2 / T1)} / (T2+T1) (In formula (I), Y is the amount of new wire supplied. X1 is the length of the fixed abrasive wire used in the first running step. T1 is the time it takes to perform the first running step. T2 is the time it takes to perform the second running step.)

[0048] In this embodiment, "the length of the fixed abrasive wire 4 used to cut the substrate" refers to the length of a new wire of the fixed abrasive wire 4 used to cut the ingot 3. In other words, it refers to the total length (m) of the fixed abrasive wire 4 (new wire) used in the first running step of all running cycles.

[0049] The length (m) of the fixed abrasive wire 4 (new wire) used in the first running step and the length (m) of the fixed abrasive wire 4 (old wire) used in the second running step can be detected, for example, from the rotation direction and rotation speed of the first guide roller 21 and / or the second guide roller 22. The length (m) of the fixed abrasive wire 4 (new wire) used in the first running step and the length (m) of the fixed abrasive wire 4 (old wire) used in the second running step may also be detected from the rotation direction and rotation speed of the first bobbin and / or the second bobbin.

[0050] FIG. 3 is a schematic diagram for explaining the contact state between the ingot 3 and the fixed abrasive wire 4 during cutting. The contact length of the fixed abrasive wire 4 on the cut surface of the ingot 3 changes continuously during the cutting process of the ingot 3. As shown in FIG. 3, the length (contact length) of the fixed abrasive wire 4 in contact with the ingot 3 is the length of the chord on the circular cut surface of the ingot 3. The contact length is determined by the vertical position (up and down direction in FIG. 3) of the fixed abrasive wire 4 extending in contact with the ingot 3. Therefore, after the cutting of the ingot 3 starts, the contact length gradually increases as the cutting of the ingot 3 progresses. The contact length becomes the maximum length, which is the diameter of the ingot 3, when the vertical position of the fixed abrasive wire 4 coincides with the central axis of the ingot 3. After reaching the diameter of the ingot 3, the contact length gradually decreases as the cutting of the ingot 3 progresses until the cutting is completed.

[0051] As shown in FIG. 3, the contact length between the fixed abrasive wire 41 and the ingot 3 is short when cutting the peripheral portion of the ingot 3 in cross section. In contrast, the contact length between the fixed abrasive wire 42 and the ingot 3 is long when cutting the central portion of the ingot 3 in cross section. The abrasive grains fixed to the fixed abrasive wire 4 are worn more as the contact length between the ingot 3 and the fixed abrasive wire 4 increases. When the abrasive grains fixed to the fixed abrasive wire 4 are worn, the cutting performance becomes poor and the load on the ingot 3 during cutting increases. When the load applied to the ingot 3 during cutting is large, the waviness and warpage of the cut-out substrate increases.

[0052] In this embodiment, in the cutting process, the amount of new wire supplied when cutting the central portion of the ingot 3 in cross section is greater than the amount of new wire supplied when cutting the peripheral portion of the ingot 3 in cross section. The load on the ingot 3 during cutting, which is in contact with the new wire of the fixed abrasive wire 4, is smaller than when the ingot 3 is in contact with the old wire with worn abrasive grains. Therefore, by using the above-mentioned amount of new wire supply, the load on the ingot 3 caused by the contact between the old wire with worn abrasive grains and the ingot 3 when cutting the central portion of the ingot 3 in cross section can be suppressed.

[0053] Therefore, for example, by setting the amount of new wire supply when cutting the central portion of ingot 3 in a cross-sectional view to the optimal amount when cutting the central portion of ingot 3 in a cross-sectional view, it is possible to cut out a substrate with as little waviness and warping as when the amount of new wire supply is constant and set to the optimal amount when cutting the central portion of ingot 3 in a cross-sectional view. Moreover, by making the amount of new wire supplied when cutting the central portion of the ingot 3 in cross section larger than the amount of new wire supplied when cutting the peripheral portion of the ingot 3 in cross section, it is possible to suppress the amount of new wire supplied when cutting the peripheral portion of the ingot 3 in cross section. Therefore, the amount of fixed abrasive wire 4 used when cutting out the substrate can be reduced compared to the case where the amount of new wire supplied is constant according to the optimal amount when cutting the central portion of the ingot 3 in cross section, for example.

[0054] In this embodiment, it is preferable to change the amount of new wire supplied in the slicing process in proportion to the contact length between the ingot 3 being slicing and the fixed abrasive wire 4. In this case, the load on the ingot 3 being slicing can be further equalized. Therefore, it is possible to cut out a disk-shaped substrate with little waviness and warping while effectively suppressing the amount of fixed abrasive wire used.

[0055] In this embodiment, when the amount of new wire supply in the cutting process is controlled for each travel cycle, the amount of new wire supply during cutting can be expressed by the following formula (3). Bi = Bm × ai / am (3) (In formula (3), Bi is the new wire supply rate Bi (m / min) in the i-th traveling cycle during slicing. Bm is the new wire supply rate (m / min) when the contact length between the ingot 3 and the fixed abrasive wire 4 is maximum (the diameter (m) of the ingot 3 being slicing). ai is the contact length (m) between the ingot 3 and the fixed abrasive wire 4 during slicing. am is the diameter (m) of the ingot 3 being slicing.)

[0056] As a result of the study by the present inventors, it was found that when the diameter of the ingot 3 being cut is 6 inches, in order to cut out a substrate with small waviness and warpage, it is preferable that Bm in formula (3) is 1.7 m / min or more. From this, in order to cut out a substrate with small waviness and warpage when the diameter of the ingot 3 being cut is 6 inches, it is preferable that the new wire supply amount Bi in the i-th traveling cycle during cutting satisfies the following formula (4). Bi≧11×ai (4) (In formula (4), ai is the contact length (m) between the ingot 3 and the fixed abrasive wire 4 during cutting.)

[0057] As shown in formula (4), in this embodiment, when the diameter of the ingot 3 being cut is 6 inches, it is preferable to set the amount of new wire supply in the cutting process to 11 times or more the contact length between the ingot 3 being cut and the fixed abrasive wire 4. When the amount of new wire supply is 11 times or more the contact length, the load on the ingot 3 being cut is sufficiently suppressed, and a substrate with even less waviness and warpage is cut out.

[0058] However, if the amount of new wire supplied in the cutting process is too large, the width of the groove formed between the cut surfaces of the ingot 3 being cut may become wider, and the thickness of the cut substrate may become locally thin. Also, if the width of the groove formed between the cut surfaces of the ingot 3 being cut becomes wider, the fixed abrasive wire 4 running between the cut surfaces of the ingot 3 may become unstable, causing undulations in the cut substrate. Also, if the amount of new wire supplied is too large, the difference in depth of the process-affected layer introduced into the ingot 3 being cut becomes large between the first end of the fixed abrasive wire 4 to which the new wire is supplied and the second end of the fixed abrasive wire 4 to which the old wire is supplied. As a result, the Twyman effect becomes more pronounced, and a substrate with a large warp may be cut out. Furthermore, the more the amount of new wire supplied, the more the amount of fixed abrasive wire used, which is not preferable.

[0059] In this embodiment, it is preferable that the amount of new wire supplied in the cutting process is 12 times or less the contact length between the ingot 3 being cut and the fixed abrasive wire 4. When the amount of new wire supplied is 12 times or less the contact length, the amount of fixed abrasive wire used is effectively reduced, and a substrate having a uniform thickness and less waviness and warpage is cut out.

[0060] In this embodiment, the average running speed of the fixed abrasive wire 4 in the first running step and the second running step is preferably, for example, 1200 m / min to 3000 m / min. When the average running speed of the fixed abrasive wire 4 is 1200 m / min or more, the ingot 3 can be cut efficiently in a short time. When the average running speed of the fixed abrasive wire 4 is 3000 m / min or less, breakage of the fixed abrasive wire 4 can be prevented. Furthermore, when the average running speed of the fixed abrasive wire 4 is 3000 m / min or less, heat generation due to contact between the fixed abrasive wire 4 and the ingot 3 can be suppressed.

[0061] In this embodiment, the length of the fixed abrasive wire 4 (new wire) used to cut out one substrate preferably satisfies formula (1), and more preferably satisfies formula (2). A≧S×13700 Formula (1) In formula (1), A is the length (m) of the fixed abrasive wire (new wire) used to cut one substrate. S is the planar area (m 2 ) S×15100≧A≧S×13700 Formula (2) In formula (2), A is the length (m) of the fixed abrasive wire (new wire) used to cut one substrate. S is the planar area (m 2 )

[0062] When the length of the fixed abrasive wire 4 used to slice one substrate satisfies formula (1), the load on the ingot 3 during slicing can be sufficiently suppressed, resulting in a substrate with even less waviness and warping. Furthermore, when the length of the fixed abrasive wire 4 used to cut out one substrate satisfies formula (2), the same effect can be obtained as when formula (1) is satisfied, and since the amount of new wire supplied is not too large, the amount of fixed abrasive wire 4 used can be reduced, and a substrate with a uniform thickness and less waviness and warping can be cut out.

[0063] In this embodiment, the rocking speed in the cutting step is preferably 600 deg / min or more. When the rocking speed is 600 deg / min or more, the load from the fixed abrasive wire 4 to the ingot 3 due to the presence of a portion of the ingot 3 that is difficult to cut can be suppressed. As a result, a substrate with even less waviness and warpage can be cut out. Furthermore, the oscillation angle in the slicing step is preferably ±3° to ±8°. If the oscillation angle is ±3° or more, coolant liquid can easily enter between the cut surfaces during slicing, and sludge generated by slicing the ingot 3 can easily be removed from between the cut surfaces during slicing. If the oscillation angle is ±8° or less, the amount of coolant liquid that flows away without contacting the fixed abrasive wire 4 is suppressed. Therefore, heat generated by contact between the fixed abrasive wire 4 and the ingot 3 is efficiently removed, which is preferable.

[0064] "Other examples" In the method for cutting a silicon carbide single crystal ingot according to the present embodiment, the ingot 3 is brought into contact with the fixed abrasive wire 4 by pushing down the ingot 3, but the ingot 3 may be brought into contact with the fixed abrasive wire 4 by pushing up the ingot 3. Also, the ingot 3 may be brought into contact with the fixed abrasive wire 4 by pushing down or pushing up the fixed abrasive wire 4. In the method for cutting a silicon carbide single crystal ingot of this embodiment, it is preferable to change the amount of new wire supply for each running cycle, but it is only necessary that the amount of new wire supply when cutting the central portion of the ingot in cross section is greater than that when cutting the peripheral portion of the ingot in cross section, and the method is not limited to changing the amount of new wire supply for each running cycle.

[0065] The method for cutting a silicon carbide single crystal ingot of this embodiment has been described taking as an example a case in which a substrate is cut out from an ingot made of silicon carbide single crystal, but the cutting method of this embodiment can also be used as a method for cutting an ingot made of silicon instead of an ingot made of silicon carbide single crystal, or can be used as a method for cutting an ingot made of a high-hardness material such as sapphire, gallium nitride, diamond, or boron nitride. EXAMPLES

[0066] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0067] (Test Example 1) Using a multi-wire saw 1 shown in FIG. 1, a fixed abrasive wire 4 is brought into contact with an ingot 3 to cut a disk-shaped slab with a planar area of ​​0.0177 mm from the ingot 3. 2 A cutting process was then carried out to simultaneously cut out multiple substrates with a thickness of 415 μm. A cylindrical ingot 3 made of silicon carbide single crystal and having a diameter of 6 inches and a thickness of 7 mm was used as the ingot 3. The cutting direction of the ingot 3 was parallel to the <11-20> direction of the silicon carbide single crystal. The fixed abrasive wire 4 used had a diameter of 120 μm and was made of a core material with abrasive grains of diamond having a particle size of 30 to 40 μm electrodeposited on the outer surface (product name: electrodeposited diamond wire, manufactured by Asahi Diamond Industrial Co., Ltd.).

[0068] The ingot 3 was cut by pressing the ingot 3 supported by the goniostage 5 down toward the fixed abrasive wire 4 using a lifting device. The fixed abrasive wire 4 and the ingot 3 were brought into contact with each other while a water-soluble coolant (product name: Noritake Cool, manufactured by Noritake Co., Limited) was supplied between the fixed abrasive wire 4 and the ingot 3 from a first coolant supply unit 61 and a second coolant supply unit 62, respectively.

[0069] In the cutting process, a running cycle consisting of a first running step and a second running step was repeated multiple times. In all running cycles, the time for one running cycle was one minute. In all running cycles, the average running speed of the fixed abrasive wire 4 was 1200 m / min and the average descending speed of the ingot 3 was 0.088 mm / min in the first and second running steps. The cutting process was performed by keeping the ratio of the time spent on the first running process to the time spent on the second running process constant from the start to the end of cutting, keeping the new wire supply rate constant at 1.7 m / min, and setting the ratio of the time spent on the first running process to the time spent on the second running process so that the length of the fixed abrasive wire (new wire) used to cut out one substrate was 280 m.

[0070] (Test Examples 2 to 6) The ingot 3 was a cylindrical ingot made of silicon carbide single crystal with a diameter of 6 inches and a thickness of 5 to 7 mm.The ratio of the time for the first running step to the time for the second running step from the start to end of cutting was kept constant, the amount of new wire supply was kept constant at the value below, and the ratio of the time for the first running step to the time for the second running step was set so that the fixed abrasive wire (new wire) used to cut out one substrate had the length shown below.Except for this, multiple disk-shaped substrates were simultaneously cut out from the ingot 3 in the same manner as in test example 1.

[0071] The new wire supply rates were kept constant at 1.9 m / min (Test Example 2), 2.0 m / min (Test Example 3), 2.7 m / min (Test Example 4), 1.7 m / min (Test Example 5), and 1.8 m / min (Test Example 6). The lengths of the fixed abrasive wire (new wire) used to cut out one substrate were 310 m (Test Example 2), 320 m (Test Example 3), 330 m (Test Example 4), 340 m (Test Example 5), and 350 m (Test Example 6).

[0072] The substrates obtained in Test Examples 1 to 6 were evaluated by the methods described below, and the results are shown in FIG. (Evaluation method) The surface located at the end (first end) where a new wire of the fixed abrasive wire 4 is supplied in the cutting process was defined as the upper surface, and the plane connecting three points set at 120° intervals from the center on a circumference excluding a region of 3 mm from the outermost periphery of the upper surface of the substrate was defined as the reference plane. The maximum distance (bow) from the reference plane at the center excluding a region of 3 mm from the outermost periphery of the substrate was measured and evaluated.

[0073] The maximum distance (bow) from the reference plane was measured using a FlatMaster Wafer manufactured by Tlopel. If the bow is less than -70 μm, the cut-out substrate has a large warp due to the Twyman effect. If the bow is more than 0 μm, the cut-out substrate has a deformation due to factors other than the Twyman effect.

[0074] Fig. 4 is a graph showing the bow of the substrates cut out in Test Examples 1 to 6. The vertical axis in Fig. 4 is bow (μm). In Fig. 4, the numbers written on the horizontal axis are the numbers when the substrates obtained in Test Examples 1 to 6 are arranged in order from the end (first end) side where a new line of the fixed abrasive wire 4 is supplied.

[0075] As shown in FIG. 4, when the length of the fixed abrasive wire (new wire) used to cut out one substrate was set to 310 m (Test Example 2) to 340 m (Test Example 5), the bow value was in the range of -70 μm to 0 μm for all the substrates evaluated, and the amount of warping was small. In contrast, when the length of the fixed abrasive wire (new wire) used to cut out one substrate was 350 m (Test Example 6), the bow values ​​of the first to third substrates arranged in order from the end (first end) where the new wire of the fixed abrasive wire 4 is supplied were -100 μm or less, and significant warping occurred. In addition, the second and third substrates arranged in order from the end (first end) where the new wire of the fixed abrasive wire 4 is supplied had cracks. This is presumably because the length of the fixed abrasive wire (new wire) used to cut out one substrate in Test Example 6 was too long.

[0076] In addition, when the length of the fixed abrasive wire (new wire) used to cut out one substrate was 280 m (Test Example 1), the bow value was in the range of 0 μm to 40 μm, and the surface shape was confirmed to have undulations. This is presumably because the length of the fixed abrasive wire (new wire) used to cut out one substrate in Test Example 1 was insufficient. From the results of Test Examples 1 to 6, it was confirmed that under the above conditions, by setting the length of the fixed abrasive wire (new wire) used to cut out one substrate to 310 m (Test Example 2) to 340 m (Test Example 5), it is possible to cut out a substrate with little waviness and warping.

[0077] In addition, the plane area of ​​the substrate cut out in Test Examples 1 to 6 was 0.0177 mm 2 Therefore, the range of length A of the fixed abrasive wire 4 (new wire) used to cut out one substrate and satisfy the above-mentioned formula (2) is 242 m to 267 m.

[0078] (Test Example 7) A plurality of disk-shaped substrates were simultaneously cut out from the ingot 3 in the same manner as in Test Example 2, except that the supply rate of new wire from the start to the end of cutting was kept constant at 1.5 m / min. (Test Example 8) A plurality of disk-shaped substrates were simultaneously cut out from the ingot 3 in the same manner as in Test Example 2, except that the supply rate of new wire from the start to the end of cutting was kept constant at 1.7 m / min.

[0079] The substrates obtained in Test Examples 7 and 8 were evaluated by the methods described below. (Evaluation method) The surface located at the end (first end) side where the new wire of the fixed abrasive wire 4 is supplied in the cutting process was defined as the upper surface, and a plane connecting three points set at 120° intervals from the center on a circumference excluding a region of 3 mm from the outermost periphery of the upper surface of the substrate was defined as a reference plane. The height of the center part excluding a region of 3 mm from the outermost periphery of the substrate relative to the reference plane was measured and evaluated. The height relative to the reference plane was measured using a FlatMaster Wafer manufactured by Tlopel. The results are shown in Figs. 5 to 8.

[0080] Figures 5(a) to 5(c) are graphs showing the evaluation results of the fourth substrate when the multiple substrates cut out in Test Example 7 were arranged in order from the end (first end) where a new line of the fixed abrasive wire 4 was supplied. Figures 6(a) to 6(c) are graphs showing the evaluation results of the third substrate when the multiple substrates cut out in Test Example 7 were arranged in order from the end (first end) where a new line of the fixed abrasive wire 4 was supplied. Figures 5(a) and 6(a) are contour maps of the substrate viewed from above. Figure 5(b) is a graph showing the height distribution from a reference plane in the X direction of the substrate shown in Figure 5(a). Figure 6(b) is a graph showing the height distribution from a reference plane in the X direction of the substrate shown in Figure 6(a). Figures 5(c) and 6(c) are perspective views showing the height of the substrate from the reference plane.

[0081] Figures 7(a) and 7(b) are graphs showing the evaluation results of the fourth substrate when the multiple substrates cut out in Test Example 8 were arranged in order from the end (first end) where a new line of the fixed abrasive wire 4 was supplied. Figures 8(a) and 8(b) are graphs showing the evaluation results of the fifth substrate when the multiple substrates cut out in Test Example 8 were arranged in order from the end (first end) where a new line of the fixed abrasive wire 4 was supplied. Figures 7(a) and 8(a) are contour maps of the substrate viewed from above. Figure 7(b) is a graph showing the height distribution from a reference plane in the X direction of the substrate shown in Figure 7(a). Figure 8(b) is a graph showing the height distribution from a reference plane in the X direction of the substrate shown in Figure 8(a).

[0082] As shown in Figures 5 and 6, in Test Example 7, in which the new wire feed rate was constant at 1.5 m / min, large undulations were formed on the board. This is presumably due to an insufficient new wire feed rate. As shown in Figures 7(b) and 8(b), in Test Example 8, where the new wire supply rate was constant at 1.7 m / min, the height from the reference plane was less than 0 μm. In Test Example 8, as shown in Figures 7(a), 7(b) and 8(a), 8(b), although warping occurred in the cut-out substrate due to the Twyman effect, the cut-out substrate had little waviness or warping. From this, it was found that by setting the amount of new wire supplied from the start to the end of cutting to 1.7 m / min or more under the above conditions, it is possible to cut out a board with little waviness and warping. [Explanation of symbols]

[0083] 1...multi-wire saw, 3...ingot, 4...fixed abrasive wire, 5...goniostage, 21...first guide roller, 22...second guide roller, 61...first coolant supply unit, 62...second coolant supply unit.

Claims

1. a cutting step of contacting a fixed abrasive wire with a cylindrical ingot made of a silicon carbide single crystal using a multi-wire saw to cut out a substrate having a diameter of 6 inches or 8 inches and a thickness of 340 μm to 600 μm from the ingot; a cutting step for cutting a silicon carbide single crystal ingot, the cutting step being performed with a new wire supply rate of 1.7 m / min or more from the start to the end of cutting, and the new wire supply rate when cutting a central portion of the ingot in a cross-sectional view is greater than the rate when cutting a peripheral portion of the ingot in a cross-sectional view.

2. 2. The method for slicing a silicon carbide single crystal ingot according to claim 1, wherein a length of a new line of the fixed abrasive wire used to slice one of the substrates is set to be not less than 310 m and not more than 340 m.

3. In the cutting step, a running cycle including a first running step of contacting the fixed abrasive wire with the ingot while running the fixed abrasive wire in a first direction and a second running step of contacting the fixed abrasive wire run in the first running step with the ingot while running the fixed abrasive wire in a second direction opposite to the first direction is repeated a plurality of times; 3. The method for slicing a silicon carbide single crystal ingot according to claim 1, wherein an average running speed of the fixed abrasive wire in the first running step and the second running step is 1200 m / min or more and 3000 m / min or less.

4. In the cutting step, the fixed abrasive wire is caused to travel by rotating a first guide roller and a second guide roller; 4. The method for cutting a silicon carbide single crystal ingot according to claim 1, wherein the first guide roller and the second guide roller are oscillated at a speed of 600 deg / min or more.

5. 5. The method for slicing a silicon carbide single crystal ingot according to claim 1, wherein the amount of new wire supplied is set to 11 times or more the contact length between the ingot and the fixed abrasive wire during slicing.

6. The method for slicing a silicon carbide single crystal ingot according to any one of claims 1 to 5, wherein the amount of new wire supplied is set to 12 times or less a contact length between the ingot and the fixed abrasive wire during slicing.

7. a cutting step of contacting a fixed abrasive wire with a cylindrical ingot made of a silicon carbide single crystal using a multi-wire saw to cut out a substrate having a diameter of 6 inches or 8 inches and a thickness of 340 μm to 600 μm from the ingot; a cutting step of cutting a silicon carbide single crystal substrate by cutting the ingot at a cutting rate of 1.7 m / min or more, and cutting the ingot at a central portion in a cross-sectional view of the ingot at a cutting rate of 1.7 m / min or more, and cutting the ingot at a peripheral portion in a cross-sectional view of the ingot at a cutting rate of 1.7 m / min or more.

8. A substrate having a diameter of 6 or 8 inches and a thickness of 340 μm to 600 μm, a plane connecting three points set at 120° intervals from a center on a circumference excluding a region of 3 mm from the outermost periphery of the top surface of the substrate is defined as a reference plane, the minimum value of the height with respect to the reference plane is within a region of 18.36 mm from the radial center of the substrate, A silicon carbide single crystal substrate, wherein the value of the maximum distance from the reference plane of a central portion excluding a region of 3 mm from the outermost periphery of the substrate is in the range of -44 μm or more and less than 0 μm.

9. 9. The silicon carbide single crystal substrate according to claim 8, wherein a value of a maximum distance from said reference plane to a central portion excluding a region of 3 mm from an outermost periphery of said substrate is in a range of not less than −44 μm and not more than −14 μm.

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