Diamond substrate manufacturing method

Abstract

To reduce an amount of single crystal diamond lost when processed to obtain a diamond substrate.SOLUTION: A diamond substrate manufacturing method includes: a step of arranging a laser beam condensing part 190 for condensing laser beam B opposite to an upper face 10a of a block 10 of a single crystal diamond; a step of forming a modified layer 20 including a processing trace 21 of a graphite along a face (111) of the single crystal diamond and a crack 22 extending the face (111) from the processing trace 21 at predetermined depth from the upper face 10a of the block 10 in some areas of the block 10 by radiating the laser beam B to the upper face 10a of the block 10 from the laser beam condensing part 190; and a step of forming a cleavage surface 25 by voluntarily propagating a cleavage at predetermined depth of a remaining area of the upper face 10a of the block 10 from the modified layer 20.SELECTED DRAWING: Figure 5B

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a diamond substrate, and more particularly to a method for manufacturing a diamond substrate by processing a single crystal diamond using a laser beam. [Background technology]

[0002] Conventionally, silicon carbide (SiC) and gallium nitride (GaN) have replaced silicon (Si) as semiconductor materials suitable for power devices, but diamond semiconductors have attracted attention as a next-generation material because they have a higher breakdown field, a higher power control index, and the highest thermal conductivity compared to these semiconductor materials, and research and development is underway to put them to practical use. In addition, nitrogen-vacancy centers (NV centers) in diamond are capable of highly sensitive magnetic detection at room temperature, so there is hope for their application in magnetic sensors, and research in this area is also being conducted (see Patent Document 1).

[0003] Single-crystal diamond, which is expected to be applied to these semiconductors, is synthesized by the high-pressure, high-temperature (HPHT) method or homoepicapital growth, but these synthesis methods are considered difficult to produce large-area bulk substrates of single-crystal diamond for use in semiconductor processes. Therefore, the chemical vapor deposition (CVD) method, which uses single-crystal magnesium oxide (MgO) as a base crystal to grow single-crystal diamond heteroepicapically, has been adopted as it has an advantage in producing large-area substrates.

[0004] Heteroepicapital growth using this CVD method produces bulk single-crystal diamond crystals that grow in the same orientation as the underlying MgO crystal. That is, if the underlying MgO crystal has a crystal orientation of

[0100] , a bulk diamond crystal with a crystal orientation of

[0100] is obtained, and if the underlying MgO crystal has a crystal orientation of

[0111] , a bulk diamond crystal with a crystal orientation of

[0111] is obtained. For the application of single-crystal diamond to magnetic sensors, it is necessary to form high-density NV centers and align the orientation axes of the NV centers. Because technology for orienting high-density NV centers in the

[0111] direction using the CVD method has been established, there is an increasing need for (111) bulk single-crystal diamond crystals with the (111) plane as the main surface (see Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 107907 [Patent Document 2] International Publication No. 2015 / 046294 [Patent Document 3] Patent Publication No. 2021-080153 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, bulk single-crystal diamond obtained by heteroepicapillary growth is sliced ​​and processed into plate-shaped substrates, but diamond is very hard and difficult to process. Smart-cut technology is used to slice the substrate, introducing a defect layer through ion implantation and then removing it by etching, resulting in separation. However, this requires equipment in a high-vacuum environment, which results in long processing times. Furthermore, while separation is possible at thicknesses of several micrometers, there have been no examples of separation at thicknesses of several hundred micrometers.

[0007] Other methods for processing single-crystal diamond into substrates include polishing the bulk single-crystal diamond separated from the base crystal to the desired thickness or chemical mechanical polishing (CMP). Conventional HPHT single-crystal diamond is processed by slicing substrates from ingots or blocks cut from ingots to a specific length, but this results in loss of kerf. Because bulk single-crystal diamond with a

[0111] orientation is particularly difficult to polish, there is a need for a manufacturing method for obtaining (111) substrates.

[0008] As described above, there is a need for a manufacturing method that can slice bulk crystals, ingots, or blocks of (111) single-crystal diamond, which is expected to be applied to high-precision magnetic sensors, into substrates in a relatively simple manner while reducing processing losses due to kerfs.

[0009] This invention has been proposed in light of the above-mentioned circumstances, and aims to provide a diamond substrate manufacturing method for producing (111) substrates with minimal processing loss from bulk crystals of single-crystal diamond with a

[0111] orientation grown heteroepicapically by the CVD method, and from ingots or blocks of single-crystal diamond obtained by the HTHP method. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the diamond substrate manufacturing method according to this application comprises the steps of: arranging a laser focusing unit that focuses laser light so as to face the top surface of a block of single crystal diamond; irradiating laser light from the laser focusing unit onto the top surface of the block and focusing the laser light inside the block while moving the laser focusing unit and the block relative to each other in two dimensions, thereby forming a modified layer that includes graphite processing marks along the (111) plane of the single crystal diamond to a predetermined depth from the top surface in a partial region of the top surface of the block and cracks extending from the processing marks to the periphery along the (111) plane; and forming a cleavage plane by spontaneously propagating cleavage from the modified layer formed at the predetermined depth in a partial region of the top surface of the block to a predetermined depth in the remaining region of the top surface of the block.

[0011] The method may further include a step of spontaneously separating a portion of the block from the top surface to a depth reaching the modified layer or cleavage plane, and a portion deeper than the modified layer or cleavage plane. The block may have a plate-like shape with the top surface being the (111) plane of the single crystal diamond.

[0012] The process of forming the modified layer may include a process of moving the laser focusing unit and the block relatively in a predetermined scanning direction, and a process of moving the laser focusing unit and the block relatively over a predetermined distance in a direction perpendicular to the scanning direction.

[0013] The laser beam may be a pulsed laser beam, and the graphite in the processed mark may be formed by the laser beam reflected by a crack extending from another processed mark adjacent to the laser beam in at least one of the scanning direction and a direction perpendicular to the scanning direction. The pulse width of the laser beam may be in the range of several nanoseconds to several hundred nanoseconds. [Effects of the Invention]

[0014] According to this invention, it is possible to produce (111) substrates with minimal processing loss from bulk crystals of single crystal diamond with a

[0111] orientation and from single crystal diamond ingots or blocks obtained by the HTHP method, thereby improving the yield when manufacturing diamond substrates. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a perspective view showing a schematic configuration of a processing device. [Figure 2] FIG. 1 is a perspective view illustrating the crystal structure of diamond. [Figure 3] FIG. 1 is a plan view of a block of single crystal diamond illustrating scanning of laser light. [Figure 4A] FIG. 1 is a plan view illustrating the formation of a modified layer on a block of single crystal diamond. [Figure 4B] FIG. 1 is a plan view illustrating the formation of a modified layer on a block of single crystal diamond. [Figure 5A] FIG. 1 is a cross-sectional view illustrating the formation of a modified layer on a block of single crystal diamond. [Figure 5B] FIG. 1 is a cross-sectional view illustrating the formation of a modified layer on a block of single crystal diamond. [Figure 6] 1 is a photograph showing the exfoliated surface of a block of single crystal diamond exfoliated at a modified layer or cleavage plane. [Figure 7] 1A to 1C are cross-sectional views illustrating a method for producing multiple diamond substrates from a block of single crystal diamond. DETAILED DESCRIPTION OF THE INVENTION

[0016] Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are designated by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc., may differ from the actual ones. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. Furthermore, it goes without saying that the drawings may include parts with different dimensional relationships and ratios.

[0017] Furthermore, the embodiments shown below are merely examples of devices and methods for embodying the technical ideas of this invention, and the materials, shapes, structures, arrangements, etc. of the components of the embodiments of this invention are not limited to those described below. Various modifications can be made to the embodiments of this invention within the scope of the claims.

[0018] 1 is a perspective view showing the general configuration of a processing apparatus 100. The processing apparatus 100 has a stage 110 on which a block 10 of single crystal diamond is placed, a stage support 120 that supports the stage 110 so that it can move in the X and Y directions in a horizontal plane, and a fixture 130 that secures the block 10 of single crystal diamond. The fixture 130 can be an adhesive layer, a mechanical chuck, an electrostatic chuck, a vacuum chuck, or the like.

[0019] A plate-like block 10 having a rectangular periphery, obtained by cutting a single crystal diamond ingot to a predetermined length, is fixed on the stage 110 as the workpiece, with its main surface, the (111) plane with an off-angle of 0°, as its upper surface 10a. The shape of the workpiece is not limited to this, and it may be, for example, a single crystal diamond ingot or a disk-shaped wafer, or a bulk crystal of single crystal diamond, as long as its upper surface 10a is the (111) plane.

[0020] The processing apparatus 100 also has a laser light source 160 that generates pulsed laser light, and a laser focusing unit 190 that includes an objective lens 170 and an aberration adjustment unit 180, and irradiates laser light B emitted from the laser light source 160 via the laser focusing unit 190 toward the (111) plane on the top surface of the single-crystal diamond block 10.

[0021] Fig. 2 is a perspective view illustrating the crystal structure of diamond. As shown in Fig. 2(a), in a diamond crystal, the carbon atoms indicated by the white circles have sp ions extending in the directions of the four vertices of a regular tetrahedron centered on the carbon atom. 3 The carbon atoms are covalently bonded to adjacent carbon atoms through the arms of the hybrid orbitals. The covalent bonds are shown as solid lines. Carbon atoms covalently bonded to their four neighboring carbon atoms in this way form a body-centered cubic lattice called the diamond structure.

[0022] Figure 2(b) shows the (111) plane in the diamond structure. In the diamond structure, carbon atoms form covalent bonds with the carbon atoms on all four sides, making single-crystal diamonds very hard. However, the carbon atoms <111> In the direction, there is one adjacent carbon atom and sp 3 It is covalently bonded by only one hybrid orbital arm. <111> In the (111) plane direction perpendicular to the cleavage direction, it can be separated relatively easily by simply cutting the covalent bond of one arm, and this (111) plane becomes the cleavage plane.

[0023] Fig. 3 is a plan view of a single crystal diamond block 10 illustrating the scanning of laser light B. The single crystal diamond block 10, which is placed on the stage 110 of the processing apparatus 100 in Fig. 1 and has a (111) plane of the main surface with an off-angle of 0° as its upper surface 10a, is moved two-dimensionally in the X and Y directions in a horizontal plane relative to the laser focusing unit 190 so that the laser light B emitted from the laser focusing unit 190 is directed toward a predetermined position on the upper surface 10a of the single crystal diamond block 10.

[0024] The scanning line 31 of the laser beam B is first scanned in the [-1-12] direction at a dot pitch dp, then shifted by a line pitch d in the [1-10] direction perpendicular to the [-1-12] direction, and the laser beam B is then scanned in the [11-2] direction at a dot pitch dp to form a new scanning line 31. By repeating the formation of such scanning lines 31, a modified layer 20 is continuously formed along the (111) plane inside the single-crystal diamond block 10. Note that, due to limitations on the characters that can be used in this specification, for convenience, the overscores attached to the numbers in the Miller indices will be replaced with a minus sign "-" before the numbers. The same applies hereinafter.

[0025] Inside the single-crystal diamond block 10, laser light B is focused at a predetermined depth from the top surface 10a, leaving traces of graphite processing and cracks extending along the (111) plane around the traces. The traces of graphite processing are formed when laser light B of a nanosecond pulse laser emitted from the laser light source 160 is reflected by cracks formed along the (111) plane of the cleavage plane, causing the diamond to thermally decompose. Here, a nanosecond pulse laser refers to a laser whose pulse width, i.e., pulse duration, is in the range of several nanoseconds to several hundred nanoseconds, specifically in the range of 1 nanosecond or more and less than 1 μs.

[0026] Figures 4A and 4B are plan views illustrating the formation of a modified layer 20 on a block 10 of single-crystal diamond. Figures 5A and 5B are cross-sectional views illustrating the formation of a modified layer 20 on a block 10 of single-crystal diamond. (a) and (b) of Figure 5A and (c) and (d) of Figure 5B correspond to the cross sections taken along the cutting lines in (a) and (b) of Figure 4A and (c) and (d) of Figure 4B, respectively.

[0027] 4A(a) and 5(a), the first scan line 31 is directed in the [-1-12] direction, forming a processing mark 21a directed toward the lower surface 10b opposite the upper surface 10a in the single-crystal diamond block 10, and cleavage from the processing mark 21a forms cracks 22a extending in the [-110] direction along the (111) plane and cracks 22bi extending in the [1-10] direction, forming a modified layer 20 including the processing mark 21a, cracks 22a, and cracks 22bi around the first scan line 31. The processing mark 21a is formed by pyrolyzing the diamond into graphite by the focused laser light B, and has a conical shape with the vicinity of the cracks 22a and 22bi as the base and the apex in the direction of the lower surface 10b. Here, the length 22biL of the crack 22bi extending in the [1-10] direction is adjusted by the energy of the laser light B at the focal point, the dot pitch dp of irradiation, and the expansion of the processing mark 21a controlled by the focal depth.

[0028] 4A(b) and 5(b), the second scanning line 31 is performed after the laser focusing unit 190 is two-dimensionally moved relative to the first scanning line 31 by a line pitch d in the [1-10] direction perpendicular to the scanning direction of the first scanning line 31. At this time, the line pitch d is set so that the focus of the laser light B is on the crack 22bi. In other words, the relationship between the line pitch d and the length 22biL of the crack 22bi is length 22biL > line pitch d.

[0029] The second scan line 31 is directed in the [11-2] direction, forming processing marks 21b directed toward the top surface 10a, and cleavage from the processing marks 21b forms cracks 22b extending in the [1-10] direction along the (111) plane, forming a modified layer 20 including the processing marks 21b and cracks 22b and 22bi around the second scan line 31. The processing marks 21b are formed by pyrolyzing diamond into graphite by the focused laser light B, and have a conical shape with the vicinity of the cracks 22bi and 22b as the base and the apex directed toward the top surface 10a.

[0030] Here, the expansion of the processing marks 21b causes cleavage of length 22bL in the [1-10] direction along the (111) plane in the crack 22b, expanding the modified layer 20. At this time, the cleavage also advances in the crack 22bi and the crack 22a due to the expansion action of the processing marks 21b, and as a result, continuous cleavage planes are formed in the crack 22a, the crack 22bi, and the crack 22b.

[0031] The scanning directions of the laser light B of the first scanning line 31 and the second scanning line 31 are not limited to the [-1-12] direction and the [11-2] direction, respectively, and may be opposite directions, or scanning may be performed in only one direction. However, from the viewpoint of efficiency in moving the laser focusing unit 190 and the single-crystal diamond block 10 relative to each other, a scanning direction that results in a reciprocating motion is preferred.

[0032] 4B(c) and 5B(c), the third scan line 31 is performed after the laser focusing unit 190 is two-dimensionally moved relatively from the second scan line 31 by a line pitch d in the [1-10] direction perpendicular to the second scan line 31. At this time, the relationship between the line pitch d and the crack length 22bL is length 22bL>line pitch d so that the focus of the laser light B is on the crack 22b where cleavage has occurred.

[0033] The third scan line 31 is directed in the [-1-12] direction, forming a processed mark 21b directed toward the top surface 10a, and cleavage from the processed mark 21b forms a crack 22b extending in the [1-10] direction along the (111) plane, forming a modified layer 20 including the processed mark 21b and the crack 22b around the third scan line 31. The processed mark 21b is formed by pyrolyzing diamond into graphite by the focused laser light B, and has a conical shape with its base near the crack 22bi and its apex directed toward the top surface 10a. The expansion of the processed mark 21b causes cleavage in the crack 22b along the (111) plane in the [1-10] direction with a length 22bL, expanding the modified layer 20.

[0034] 4B(d) and 5B(d), similar operations are repeated for the fourth and subsequent scan lines 31 toward the end face of the block 10 up to the nth scan line 31. When the effect of the graphitized processing marks 21b in the nth scan line 31 exceeds a threshold, cleavage propagates from the processing marks 21b of the nth scan line 31 to the end face of the block 10. As a result, a modified layer 20 cleaved along the (111) plane along the cracks 22b is formed over the entire interior of the block 10.

[0035] Large internal stresses accumulate in the modified layer 20 due to the sudden temperature changes that occur when the processing marks 21b are formed and the change in crystal structure from diamond to graphite. To release this internal stress, the modified layer 20 spontaneously splits along the (111) plane of the cleavage plane. Therefore, the single-crystal diamond block 10 spontaneously peels off into a first portion 11 extending from the upper surface 10a to the modified layer 20, and a second portion 12 extending from the modified layer 20 to the lower surface 10b. At least one of the peeled first portion 11 and second portion 12 may be used as a single-crystal diamond substrate. This substrate may include a wafer.

[0036] Here, since there are no processing marks 21b caused by irradiation with laser light B and the cleaved surface accounts for most of the entire surface, processes such as surface polishing of the peeled substrate are simplified and a peeled surface is obtained that is not damaged by irradiation with laser light B. Furthermore, since the time required for scanning the scan line 31 can be shortened, productivity is greatly improved by shortening the processing time.

[0037] In the single-crystal diamond block 10 that has been separated into the first portion 11 and the second portion 12, the modified layer 20 corresponds to the "kerf loss" lost during processing. The thickness of the modified layer 20 is approximately the height of the roughly conical graphite processing marks 21b, and can be set to a range of several μm or less. This reduces the amount of single-crystal diamond lost when processing the single-crystal diamond block 10 to produce diamond substrates. This in turn improves the yield when processing the single-crystal diamond block 10 to produce diamond substrates. [Example]

[0038] In the processing apparatus 100 shown in Fig. 1, a nanosecond laser with the specifications shown in Table 1 was used as the laser light source 160. Furthermore, as shown in Table 2, the single crystal diamond block 10 was moved two-dimensionally relative to the laser focusing unit 190, and laser light B was irradiated toward the upper surface 10a, which is the (111) plane, to form a modified layer 20 to a predetermined depth in a partial region of the upper surface 10a. In this example, a type Ib diamond was used by the HPHT method.

[0039] [Table 1]

[0040] [Table 2]

[0041] The laser light source 160 and irradiation conditions described above are set to promote graphitization by heat accumulation at the focused portion of the laser beam B, and to increase the density of this graphitization, thereby promoting cleavage along the (111) plane due to the expansion of the processing marks 21b. In the above example, by setting the dot pitch dp to 0.05 μm and the line pitch d to 30 μm, the density of the graphitized processing marks increases, and the stress in the cracks 22b promotes cleavage along the (111) plane. As a result, laser irradiation with 10 scan lines, i.e., the formation of processing marks 21b within a range of 300 μm from the edge of the diamond block, enables cleavage along the (111) plane.

[0042] Regarding the size of the processing marks 21b, it is necessary to control the growth of the processing marks 21b, i.e., the graphitized portion, in order to reduce loss after peeling. The conditions were set taking into consideration the need to keep the depth (growth height) of the processing marks 21b formed in the single-crystal diamond block 10 to a maximum of 30 μm or less.

[0043] Thus, the conditions obtained by taking into consideration the length of the cracks 22b and the size of the processing marks 21b were that the appropriate range for the dot pitch dp was 0.01 μm to 0.5 μm at a laser output of 1 W and an oscillation frequency of 20 kHz, and the range for the line pitch d at this time was 10 μm to 50 μm. Since it is difficult to actually measure the length of the cracks 22b, it is considered that the range of the line pitch d is 100 μm to 150 μm, which can be estimated from the range of the line pitch d. Tables 1 and 2 were set based on such considerations.

[0044] Under the conditions shown in Tables 1 and 2, a predetermined vertical range of the top surface 10a of a single-crystal diamond block 10 was scanned with 10 scanning lines 31, and a modified layer 20 was formed in this region to a predetermined depth from the top surface 10a. As a result, starting from the modified layer 20, spontaneous cleavage propagated along the (111) plane of the cleavage surface to the same predetermined depth as the modified layer 20, and a cleavage surface 25 was formed at the predetermined depth over the entire surface of the remaining region except for the portion where the modified layer 20 was formed. The single-crystal diamond block 10 then spontaneously peeled off at the modified layer 20 or cleavage surface 25, resulting in a first portion 11 extending from the top surface 10a to the modified layer 20 or cleavage surface 25, and a second portion 12 deeper than the modified layer 20 or cleavage surface 25.

[0045] Figure 6 is a photograph showing the peeled surface of a block 10 of single crystal diamond peeled at the modified layer 20 or cleavage plane 25. On the peeled surface, graphite processing marks 21 formed along ten scan lines 31 can be observed. In the part of the peeled surface other than the processing marks 21, the cleavage plane 25, which is the (111) plane, can be observed to form a smooth surface.

[0046] In the above example, by setting the dot pitch dp to 0.05 μm and the line pitch d to 30 μm, the density of the graphitized processing marks increases, and the stress in the cracks 22b causes cleavage along the (111) plane. As a result, laser irradiation with 10 scan lines, i.e., the formation of processing marks 21b within a range of 300 μm from the edge of the diamond block, enables cleavage along the (111) plane. Since the outer dimension of the single-crystal diamond block 10 used in this example is 2.5 mm in the [1-10] direction, approximately 90% of the surface of the diamond substrate obtained by peeling is formed by cleavage planes of the (111) plane, which do not have processing marks 21b. The resulting cleavage planes are smooth, which has the great advantage of greatly simplifying subsequent processing steps such as polishing and etching.

[0047] Figure 7 is a cross-sectional view illustrating a method for producing multiple diamond substrates from a single-crystal diamond block 10. Figure 7(a) shows the single-crystal diamond block 10 with the modified layer 20 formed thereon before peeling, and Figure 7(b) shows the second portion 12 peeled from the single-crystal diamond block 10 using the modified layer 20 as the cleavage plane. The upper surface 12a of the second portion 12 corresponds to the cleavage plane in the single-crystal diamond block 10, and the lower surface 12a of the second portion 12 corresponds to the lower surface 10b of the single-crystal diamond block 10.

[0048] A new diamond substrate can be manufactured by irradiating the upper surface 12a of the second portion 12 with laser light B in accordance with Tables 1 and 2 to form a modified layer 20 on the second portion 12, and then peeling off the modified layer 20 as a cleavage plane. Repeating this process has the great advantage of enabling the manufacture of diamond, a difficult-to-cut material, by an extremely efficient and simple method with greatly reduced processing loss. [Industrial Applicability]

[0049] The present invention can be utilized in the manufacture of power devices and magnetic sensors that use diamond substrates. [Explanation of symbols]

[0050] 10 blocks 10a top surface 20 Modified layer 21 Machining marks 22 Crack 25 Cleavage plane 100 Processing equipment 190 Laser focusing unit

Claims

1. a step of positioning a laser focusing unit that focuses laser light so as to face the upper surface, which is the main surface of a block of single crystal diamond, the main surface of which is a (111) plane; a step of irradiating a laser beam from the laser focusing unit onto the top surface of the block, and two-dimensionally moving the laser focusing unit and the block relative to each other while focusing the laser beam inside the block, thereby forming a modified layer including processing marks of graphite along the (111) plane of the single crystal diamond to a predetermined depth from the top surface in a partial region of the top surface of the block and cracks extending from the processing marks to the periphery along the (111) plane; spontaneously propagating a cleave from the modified layer to the predetermined depth in the remaining region of the top surface of the block to form a cleave plane; Including, The step of forming the modified layer includes a step of relatively moving the laser focusing unit and the block in a predetermined scanning direction, and a step of relatively moving the laser focusing unit and the block in a direction perpendicular to the scanning direction at a line pitch d, and the line pitch d satisfies the relationship between the length L of the crack extending from the processing mark along the (111) plane of the crack and the length L of the crack > the line pitch d. Diamond substrate manufacturing method.

2. 2. A method for manufacturing a diamond substrate as described in claim 1, further comprising a step of spontaneously peeling off a portion of the block from the top surface to a depth reaching the modified layer or the cleavage surface, and a portion deeper than the modified layer or the cleavage surface.

3. 3. The method for producing a diamond substrate according to claim 1, wherein the block has a plate-like shape with the upper surface thereof being a (111) plane of the single crystal diamond.

4. 4. A method for manufacturing a diamond substrate according to claim 1, wherein in the step of forming the modified layer, the scanning direction is the [-1-12] direction or the [11-2] direction, and the direction perpendicular to the scanning direction is the [-110] direction or the [1-10] direction.

5. 5. A method for manufacturing a diamond substrate according to claim 1, wherein the laser light is a pulsed laser light, and the graphite in the processing mark is formed by laser light reflected by a crack extending from another processing mark adjacent to the scanning direction and at least one of the scanning direction and a direction perpendicular to the scanning direction.

6. 6. The method for producing a diamond substrate according to claim 1, wherein the laser light has a pulse width in the range of several nanoseconds to several hundred nanoseconds.

7. A method for manufacturing a diamond substrate described in any one of claims 1 to 6, wherein in the step of forming the modified layer, the line pitch is 10 μm to 50 μm.

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