Diamond substrate manufacturing method

Abstract

Provided is a diamond substrate manufacturing method capable of reducing the loss amount when a single crystal diamond is processed into a diamond substrate. The diamond substrate manufacturing method includes: a step of disposing a laser condensing section (190) that condenses laser light (B) so as to face an upper surface (10a) of a single crystal diamond boule (10); and a step of irradiating laser light (B) onto the upper surface (10a) of the boule (10) using the laser condensing section (190) under prescribed irradiation conditions, condensing the laser light (B) inside the boule (10), and relatively moving the laser condensing section (190) and the boule (10) in two dimensions, thereby forming a modified layer (20) including a graphite processing mark (21b) and a crack (22b) extending along a (111) plane of the single crystal diamond from the processing mark (21b) to a prescribed depth from the upper surface (10a) of the boule (10).

Description

Technical Field

[0001] This invention relates to a method for manufacturing diamond substrates, and more specifically, to a method for manufacturing diamond substrates by processing single-crystal diamond using a laser. Background Technology

[0002] Previously, silicon carbide (SiC) and gallium nitride (GaN) have been used as semiconductor materials suitable for power devices to replace silicon (Si). However, diamond semiconductors have a high dielectric breakdown electric field, a high power control index, and the highest thermal conductivity compared to these semiconductor materials, and are therefore attracting attention as a next-generation material, with research and development underway towards practical application. In addition, nitrogen-vacancy centers (NV centers) in diamond can perform highly sensitive magnetic detection at room temperature, so its application in magnetic sensors is anticipated, and research on this is also underway (see Patent Document 1).

[0003] Single-crystal diamonds intended for use in these semiconductors are expected to be synthesized via high-temperature, high-pressure (HPHT) methods and homoepitaxial growth. However, these methods make it difficult to scale up bulk substrates for single-crystal diamonds used in semiconductor processes. In contrast, vapor-phase (CVD) synthesis, which uses single-crystal magnesium oxide (MgO) as the substrate crystal for heteroepitaxial growth of single-crystal diamonds, has advantages in large-area scaling and has therefore remained applicable.

[0004] In heteroepitaxial growth using this CVD method, bulk diamond crystals grown in the same orientation as the MgO crystal of the substrate can be obtained. That is, when the MgO crystal of the substrate is in the orientation

[100] , a bulk diamond crystal with the orientation

[100] is obtained, and when the MgO crystal of the substrate is in the orientation

[111] , a bulk diamond crystal with the orientation

[111] is obtained. When applying single-crystal diamond to magnetic sensors, it is necessary to form high-density NV color centers and align the orientation axes of the NV color centers. Since the technology of orienting high-density NV color centers along the

[111] direction by CVD method has been established, the necessity of forming (111) bulk crystals from single-crystal diamond with the (111) plane as the main surface has increased (see Patent Document 2).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2015 / 107907

[0008] Patent Document 2: International Publication No. 2015 / 046294

[0009] Patent Document 3: Japanese Patent Application Publication No. 2021-080153 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] On the other hand, the bulk crystals of single-crystal diamond obtained through heteroepitaxial growth need to be sliced ​​to form plate-shaped substrates, but diamond is difficult to process due to its high hardness. As a method for slicing substrates, a smart cutting technique can be used, which involves introducing a defect layer through ion implantation and removing it through etching, thereby achieving peeling. However, this technique suffers from the problems of requiring a high-vacuum environment for ion implantation and having a long processing time. Furthermore, while peeling can be performed at thicknesses of a few μm, there are no known examples of peeling at thicknesses of several hundred μm.

[0012] As another method for processing into a substrate, there is a method of grinding or performing chemical mechanical polishing (CMP) on bulk crystals of single-crystal diamond separated from the substrate crystal until the desired thickness is achieved. In addition, for single-crystal diamond obtained by the existing HPHT method, it is necessary to perform processing from the ingot, further cutting the ingot into blocks of fixed length to obtain a substrate, but there is a problem of loss in the form of cutting allowance. Since bulk crystals of single-crystal diamond in the

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

[0013] As described above, for bulk crystals, ingots or blocks of (111) single-crystal diamond intended for use in high-precision magnetic sensors, there is a requirement for a manufacturing method that can slice the substrate by reducing processing losses caused by cutting allowance in a simpler way.

[0014] The present invention is proposed in view of the above circumstances, and its object is to provide a diamond substrate manufacturing method for fabricating (111) substrates with low processing loss by using bulk crystals of

[111] -oriented single crystal diamond grown by heteroepitaxial growth by CVD and ingots and blocks of single crystal diamond obtained by HTHP method.

[0015] Methods for solving problems

[0016] To address the aforementioned issues, the diamond substrate manufacturing method disclosed in this application includes: a step of configuring a laser focusing section for focusing laser light to face the upper surface of a single-crystal diamond block; and a step of irradiating a laser from the laser focusing section toward the upper surface of the block, focusing the laser light into the interior of the block, while simultaneously moving the laser focusing section relative to the block in a two-dimensional manner, thereby forming a modified layer comprising graphite processing marks and cracks extending around the (111) surface from the upper surface of the block to a predetermined depth along the (111) plane of the single-crystal diamond.

[0017] The crystal block can have a plate-like shape with its upper surface serving as the (111) face of a single-crystal diamond. The process of forming the modified layer may further include: a process of moving the laser focusing part and the crystal block relative to each other in a predetermined scanning direction; and a process of moving the laser focusing part and the crystal block relative to each other at a predetermined interval in a direction orthogonal to the aforementioned scanning direction.

[0018] The laser is a pulsed laser, and the graphite of the processing marks can be formed using laser light reflected from cracks in the scanning direction and in directions orthogonal to the scanning direction, the cracks extending from other processing marks adjacent to each other in at least one direction. The process of forming the modified layer can also form the modified layer to a predetermined depth on the entire surface of the upper surface.

[0019] It can further include a process of spontaneously peeling off portions of the crystal block from the top surface up to the depth of the modified layer and portions deeper than the modified layer. The laser pulse width can range from several nanoseconds to hundreds of nanoseconds.

[0020] Invention Effects

[0021] According to the present invention, a (111) substrate can be fabricated from a bulk crystal of single-crystal diamond in the

[111] orientation and a single-crystal diamond ingot or block obtained by the HTHP method with reduced processing loss, thereby improving the yield when manufacturing diamond substrates. Attached Figure Description

[0022] Figure 1 It is a three-dimensional diagram showing the general structure of the processing device.

[0023] Figure 2 It is a three-dimensional diagram illustrating the crystal structure of diamond.

[0024] Figure 3 This is a planar diagram illustrating a single-crystal diamond block scanned by laser.

[0025] Figure 4A This is a planar diagram illustrating the formation of a modified layer in a single-crystal diamond block.

[0026] Figure 4B This is a planar diagram illustrating the formation of a modified layer in a single-crystal diamond block.

[0027] Figure 5A This is a cross-sectional diagram illustrating the formation of a modified layer in a single-crystal diamond ingot.

[0028] Figure 5B This is a cross-sectional diagram illustrating the formation of a modified layer in a single-crystal diamond ingot.

[0029] Figure 6 It is a photograph showing the peeling surface of a single-crystal diamond block that has been peeled off at the modified layer.

[0030] Figure 7 This is a microscopic photograph of the lower surface of the first part of a single-crystal diamond block that has been peeled off at the modified layer.

[0031] Figure 8 This is a microscopic photograph of the upper surface of the second part of a single-crystal diamond block that has been peeled off at the modified layer.

[0032] Figure 9 This is a microscopic photograph of the adhesive tape that was pressed onto the peeling surface of a single-crystal diamond block after being peeled off at the modified layer.

[0033] Symbol Explanation

[0034] 10: Crystal block, 10a: Upper surface, 20: Modified layer, 21: Processing mark, 22: Crack, 100: Processing device, 190: Laser focusing section. Detailed Implementation

[0035] Next, embodiments of the present invention will be described with reference to the accompanying drawings. In the following drawings, identical or similar parts are given the same or similar symbols. However, it should be noted that the drawings are schematic diagrams, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc., may differ from reality. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. Furthermore, it goes without saying that the drawings also include parts with different dimensional relationships and ratios.

[0036] Furthermore, the embodiments shown below exemplify apparatus and methods for embodying the technical concept of the present invention. In the embodiments of the present invention, the material, shape, structure, arrangement, etc., of the constituent components are not specific to these. Various modifications can be made to the embodiments of the present invention within the scope of the claims.

[0037] Figure 1 This is a perspective view showing the schematic structure of the processing apparatus 100. The processing apparatus 100 includes: a base 110 for holding a single-crystal diamond ingot 10, a base support portion 120 supporting the base 110 so as to be movable in the XY direction in the horizontal plane, and a fixture 130 for fixing the single-crystal diamond ingot 10. The fixture 130 can be an adhesive layer, a mechanical chuck, an electrostatic chuck, a vacuum chuck, etc.

[0038] The plate-shaped crystal block 10, which is obtained by cutting a single-crystal diamond ingot into a specified length and has a rectangular outer perimeter, is fixed on the base 110 with the (111) surface, which has an offset angle of 0° as the main surface, as the upper surface 10a. The shape of the object being processed is not limited to this. As long as the upper surface 10a is also the (111) surface, it can be, for example, a single-crystal diamond ingot, a disk-shaped wafer, or a block crystal of single-crystal diamond.

[0039] In addition, the processing apparatus 100 has a laser source 160 that emits pulsed laser light and a laser focusing section 190 that includes an objective lens 170 and an aberration adjustment section 180, and irradiates the (111) surface of the upper surface of the single crystal diamond block 10 with laser light B emitted by the laser source 160 via the laser focusing section 190.

[0040] Figure 2 It is a three-dimensional diagram illustrating the crystal structure of diamond. For example... Figure 2 As shown in (a), in a diamond crystal, carbon atoms, represented by white circles, extend through splines at the four vertices of a regular tetrahedron centered on the carbon atom. 3 The arms of the hybrid orbitals form covalent bonds with adjacent carbon atoms. Covalent bonds are represented by solid lines. These carbon atoms, covalently bonded to four adjacent carbon atoms, form a body-centered cubic lattice known as the diamond structure.

[0041] Figure 2 (b) shows the (111) facet in the diamond structure. It is known that in the diamond structure, single-crystal diamond is very hard because carbon atoms form covalent bonds with their four neighboring carbon atoms. However, carbon atoms in… <111> In the direction, it is connected to an adjacent carbon atom only through sp. 3 One arm of the hybrid orbital forms a covalent bond. Therefore, in conjunction with... <111> In the direction of the orthogonal (111) plane, the covalent bond of only one arm can be cut more easily, and the (111) plane becomes the cracking surface.

[0042] Figure 3 This is a plan view illustrating the scanning of a single-crystal diamond block 10 by laser B. For a crystal block placed on... Figure 1 On the base 110 of the processing apparatus 100, a single crystal diamond block 10 with a (111) surface of 0° offset angle as the main surface as the upper surface 10a is placed, and the block is moved in two dimensions relative to the laser focusing part 190 in the XY direction in the horizontal plane, so that the laser B irradiated from the laser focusing part 190 irradiates a predetermined position on the upper surface 10a of the single crystal diamond block 10.

[0043] The laser B scans line 31 first in the [-1-12] direction with a dot pitch dp. Then, after shifting only with a line pitch d in the [1-10] direction, which is orthogonal to the [-1-12] direction, the laser B scans in the [11-2] direction with a dot pitch dp, forming a new scan line 31. By repeatedly forming such scan lines 31, a modified layer 20 is gradually and continuously formed along the (111) plane inside the single-crystal diamond block 10. It should be noted that the text available in this specification is limited, so for convenience, the underscores of the Miller index are replaced with a minus sign "-" before the number. The same applies below.

[0044] Inside the single-crystal diamond ingot 10, laser B is focused to a predetermined depth starting from the upper surface 10a, forming graphite processing marks and cracks extending along the (111) plane around these processing marks. The graphite processing marks are formed by the thermal decomposition of diamond through reflection of the nanosecond pulsed laser B emitted from the laser source 160 along the cracks formed on the (111) plane of the cracked surface. Here, a nanosecond pulsed laser refers to a laser with a pulse width (i.e., pulse duration) in the range of several ns to hundreds of ns, specifically, a laser in the range of 1 ns or more but less than 1 μs.

[0045] Figure 4A and Figure 4B This is a plan view illustrating the formation of a modified layer 20 in a single-crystal diamond ingot 10. Figure 5A and Figure 5B This is a cross-sectional view illustrating the formation of a modified layer 20 in a single-crystal diamond ingot 10. Figure 5A (a) and (b) in the middle and Figure 5B (c) and (d) in the text correspond to respectively Figure 4A (a) and (b) in the middle and Figure 4B The cross sections along the cutting line in (c) and (d) of the diagram.

[0046] Reference Figure 4A (a) and Figure 5A (a) A first scan line 31 is directed in the [-1-12] direction, forming a processing mark 21a in the single-crystal diamond block 10 facing the lower surface 10b opposite to the upper surface 10a. Simultaneously, cracks 22a extending in the [-110] direction and cracks 22bi extending in the [1-10] direction are formed along the (111) plane by cracking starting from the processing mark 21a. A modified layer 20 including the processing mark 21a, cracks 22a and cracks 22bi is formed around the first scan line 31. The processing mark 21a is formed by thermally decomposing diamond into graphite using a focused laser B, and has a conical shape with the area near cracks 22a and 22bi as the base and the direction of the lower surface 10b as the apex. Here, the length 22biL of the cracks 22bi extending in the [1-10] direction is adjusted by the expansion of the processing mark 21a controlled by the energy of the laser B at the focused point, the irradiated dot pitch dp, and the focal depth.

[0047] Reference Figure 4A (b) and Figure 5A(b) The second scan line 31 is performed after the laser focusing part 190 is moved in a two-dimensional manner in a direction orthogonal to the scanning direction of the first scan line 31 in the [1-10] direction, with only a line spacing d. At this time, the line spacing d is set so that the focal point of the laser B falls on the crack 22bi. That is, the relationship between the line spacing d and the length 22biL of the crack 22bi is that the length 22biL > the line spacing d.

[0048] The second scan line 31, along the [11-2] direction, forms a machining mark 21b towards the upper surface 10a, and simultaneously forms a crack 22b extending in the [1-10] direction along the (111) surface by cracking starting from the machining mark 21b. A modified layer 20, including the machining mark 21b, crack 22b, and 22bi, is formed around the second scan line 31. The machining mark 21b is formed by thermally decomposing diamond into graphite using a focused laser B, and has a conical shape with the area near crack 22bi and crack 22b as its base and the direction of the upper surface 10a as its apex.

[0049] Here, due to the expansion of the processing mark 21b, a crack of length 22bL is generated along the (111) plane in the [1-10] direction at crack 22b, and the modified layer 20 expands. At this time, cracks in cracks 22bi and 22a will also further develop due to the expansion of the processing mark 21b, resulting in the formation of continuous crack surfaces at cracks 22a, 22bi, and 22b.

[0050] It should be noted that the scanning directions of the laser B of the first scan line 31 and the second scan line 31 are not limited to the [-1-12] direction and the [11-2] direction, respectively. They can also be opposite directions, or they can scan in only one direction. However, from the perspective of the efficiency of moving the laser focusing part 190 and the single crystal diamond block 10 relative to each other, the scanning direction for reciprocating motion is preferred.

[0051] Reference Figure 4B (c) and Figure 5B (c) The third scan line 31 is performed after the laser focusing part 190 is moved in a two-dimensional relative position in the [1-10] direction orthogonal to the second scan line 31, with only the line spacing d. At this time, in order to make the focus of the laser B fall on the crack 22b that has been cracked, the relationship between the line spacing d and the crack length 22bL is that the length 22bL > the line spacing d.

[0052] The third scan line 31, along the [-1-12] direction, forms a machining mark 21b towards the upper surface 10a, and simultaneously forms a crack 22b extending in the [1-10] direction along the (111) plane through cracking starting from the machining mark 21b. A modified layer 20, including the machining mark 21b and the crack 22b, is formed around the third scan line 31. The machining mark 21b is formed by thermally decomposing diamond into graphite using a focused laser B, and has a conical shape with the area near the crack 22bb as its base and the direction of the upper surface 10a as its apex. Due to the expansion of the machining mark 21b, a crack of length 22bL is generated at the crack 22b along the (111) plane in the [1-10] direction, and the modified layer 20 expands.

[0053] Reference Figure 4B (d) and Figure 5B (d) The same operation is repeated after the fourth scan line 31 until the nth scan line 31 is reached on the end face of the ingot 10. As a result, a modified layer 20 is formed throughout the interior of the ingot 10, with cracks along the crack 22b on the (111) plane. Due to the rapid temperature change during the formation of the machining mark 21, the change in crystal structure from diamond to graphite, etc., a large internal stress is accumulated in the modified layer 20. In order to release such internal stress, the modified layer 20 spontaneously splits along the (111) plane of the cracked surface. Therefore, the single-crystal diamond ingot 10 spontaneously peels off in the modified layer 20 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 these peeled first portions 11 and second portions 12 can serve as a substrate for the single-crystal diamond. The substrate may also include a wafer.

[0054] In the single-crystal diamond ingot 10 separated into a first part 11 and a second part 12, the modified layer 20 corresponds to the "cutting allowance" lost due to processing. The thickness of the modified layer 20 is approximately equal to the height of the graphite processing mark 21b having a generally conical shape, and can be set to a range of a few μm or less. Therefore, the amount of single-crystal diamond lost when processing the single-crystal diamond ingot 10 to manufacture a diamond substrate can be reduced. This, in turn, can improve the yield when processing the single-crystal diamond ingot 10 to manufacture a diamond substrate.

[0055] Example

[0056] exist Figure 1In the processing apparatus 100 shown, the laser source 160 uses a nanosecond laser with specifications as shown in Table 1. Furthermore, as shown in Table 2, the single-crystal diamond ingot 10 is moved relative to the laser focusing section 190 in a two-dimensional manner, and laser B is irradiated onto the upper surface 10a, which is the (111) plane, forming a modified layer 20 from the upper surface 10a to a predetermined depth. In this embodiment, type Ib diamond produced by the HPHT method is used.

[0057] [Table 1]

[0058] Specifications of laser source

[0059] Types of laser oscillators Hippo 532-11 (Made by Spectra Physics) wavelength 532nm Pulse width 10ns repetition frequency 20kHz Output 1W

[0060] [Table 2]

[0061] Laser irradiation settings

[0062] Scan speed 10mm / s dp 0.5μm Line spacing d 60μm

[0063] The laser source 160 and irradiation conditions described above are set with consideration of the length of the crack 22b and the size of the processing mark 21b. Regarding the length of the crack 22b, graphitization is promoted by the heat storage of the focusing part of the laser B. Therefore, the larger the graphitized processing mark 21b and the narrower the spacing between the dots dp and the lines d, the more difficult it is to control the length of the crack 22b, and the less control it is to control the cracking progress of the (111) surface caused by the expansion of the processing mark 21b. Therefore, conditions are set in a way that can control the cracking of the (111) surface to obtain a stable processing and peeling state.

[0064] Regarding the size of the processing mark 21b, in order to reduce losses after peeling, it is also necessary to control the growth of the processing mark 21b, i.e., the graphitized portion. Considering the need to control the depth (growth height) of the processing mark 21b formed in the single-crystal diamond ingot 10 to a maximum of less than 30 μm, the conditions are set accordingly.

[0065] Taking into account the length of crack 22b and the size of machining mark 21b, the conditions obtained are: at a laser output of 1W and an oscillation frequency of 20kHz, the suitable range for the dot pitch dp is 0.5μm to 1.0μm, and the range for the line spacing d is 50μm to 100μm. Since it is difficult to actually measure the length of crack 22b, the range inferred from the above range of line spacing d is considered to be 100μm to 150μm. Tables 1 and 2 were established through this discussion.

[0066] The entire upper surface 10a of the single-crystal diamond ingot 10 is scanned under the conditions described above, forming a modified layer 20 from the upper surface 10a to a predetermined depth. As a result, the single-crystal diamond ingot 10 spontaneously peels off at the modified layer 20, yielding a first portion 11 extending from the upper surface 10a to the modified layer 20 and a second portion 12 deeper than the modified layer 20.

[0067] Figure 6 This is a photograph showing the peeled surface of the single-crystal diamond block 10 peeled off at the modified layer 20. Figure 6 (a) is a photograph of the lower surface of part 11. Figure 6 (b) is a photograph of the upper surface of the second part 12, showing the peeling surface of the modified layer 20.

[0068] Figure 7 This is a scanning electron microscope (SEM) photograph of the lower surface of the first portion 11 of the single-crystal diamond block 10 that has been peeled off at the modified layer 20. Figure 7 (a) shows the entire lower surface of the first part 11. Figure 7 (b) is to Figure 7 (a) is a further magnified photograph of a portion thereof. Both show the peeling surface of the modified layer 20 on the lower surface of the first portion 11. Figure 7 In (b), it was observed that the processing marks 21 at the peel surface of the modified layer 20 swelled or dented.

[0069] Figure 8 This is a scanning electron microscope (SEM) photograph of the upper surface of the second part 12 of the single-crystal diamond block 10 that has been peeled off at the modified layer 20. Figure 8 (a) shows the entire upper surface of the second part 12. Figure 8 (b) is to Figure 8 (a) is a further magnified photograph of a portion thereof. Both show the peeling surface of the modified layer 20 on the upper surface of the second part 12. Figure 8 In (b), it was observed that the processing marks 21 of the modified layer 20 were very strong.

[0070] Figure 9 This is a microscopic photograph of the adhesive tape after it has been pressed onto the peeling surface of the single-crystal diamond block 10 peeled off at the modified layer 20. Graphite transfer from the peeling surface is observed on the adhesive surface of the adhesive tape. Therefore, it can be seen that on the peeling surface, graphite from the processing marks 21 formed in the modified layer 20 exists in a state that can be easily peeled off through the pressing of the adhesive tape.

[0071] Industrial availability

[0072] This invention can be used in the manufacture of power devices and magnetic sensors using diamond substrates.

Claims

1. A diamond substrate manufacturing method comprising: a step of arranging a laser light condensing section that condenses laser light so as to face an upper surface of a single crystal diamond boule; and a step of irradiating laser light from the laser light condensing section to the upper surface of the boule, condensing the laser light inside the boule, and relatively moving the laser light condensing section and the boule in two dimensions, thereby forming a modified layer containing a graphite processing mark and a crack extending from the processing mark in the surrounding along a (111) plane of single crystal diamond from the upper surface of the boule to a prescribed depth, the step of forming the modified layer includes a step of relatively moving the laser light condensing section and the boule in a prescribed scanning direction, and a step of relatively moving the laser light condensing section and the boule in a direction orthogonal to the scanning direction at a line pitch d, the line pitch d having a relationship of L > d with respect to a length L of the crack, and the line pitch d ranging from 50 μm to 100 μm.

2. The diamond substrate manufacturing method according to claim 1, wherein the boule has a plate shape in which the upper surface is a (111) plane of single crystal diamond.

3. The diamond substrate manufacturing method according to claim 1 or 2, wherein the laser light is laser light of a pulse wave, the graphite of the processing mark is formed using laser light reflected by the crack in the scanning direction and in a direction orthogonal to the scanning direction, and the crack extends from other processing marks adjacent in at least one direction.

4. The diamond substrate manufacturing method according to claim 1 or 2, wherein in the step of forming the modified layer, a modified layer is formed at a prescribed depth over the entire surface of the upper surface.

5. The diamond substrate manufacturing method according to claim 1 or 2, further comprising: a step of spontaneously peeling a portion of the boule from the upper surface to a depth reaching the modified layer and a portion deeper than the modified layer.

6. The diamond substrate manufacturing method according to claim 1 or 2, wherein a pulse width of the laser light ranges from several ns to several hundred ns.

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