Method for producing beta gallium oxide substrate

Abstract

The invention provides a method for manufacturing a beta gallium oxide substrate, which can improve the productivity of a substrate when the substrate is manufactured from a workpiece made of beta gallium oxide. A method for manufacturing a [beta]-gallium oxide substrate, which is for manufacturing a substrate from a workpiece comprising [beta]-gallium oxide, and which comprises: a separation layer formation step for forming a separation layer on a surface of the workpiece in a state in which a focal point where a laser beam having a wavelength that passes through [beta]-gallium oxide converges is positioned at a predetermined depth from the front surface of the workpiece; irradiating a laser beam to the workpiece to form a separation layer including a modified part and cracks extending from the modified part in the workpiece; and a separation step of applying an external force to the workpiece after the separation layer forming step, thereby separating the substrate from the workpiece using the separation layer as a starting point.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a β-gallium oxide substrate for manufacturing a substrate from a workpiece composed of β-gallium oxide. Background Art

[0002] Regarding gallium oxide (Ga2O3) as a crystalline polytype, the monoclinic β phase (β-gallium oxide: β-Ga2O3) is the most stable phase. Moreover, β-gallium oxide is a wide bandgap semiconductor with a bandgap of about 4.8 eV (for example, see Patent Document 1). Therefore, β-gallium oxide is expected to be used as a raw material for semiconductor devices such as power devices.

[0003] Semiconductor devices are generally formed using a disc-shaped substrate, which is manufactured by, for example, cutting a workpiece such as a cylindrical block called an ingot into pieces having a predetermined thickness using a wire saw (see, for example, Patent Document 2).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2007-254174

[0005] Patent Document 2: Japanese Patent Application Publication No. 2016-13929

[0006] Semiconductor devices are formed using, for example, a substrate having a thickness of about 150 μm. In addition, the thickness of a wire saw is, for example, about 300 μm. Therefore, when a substrate is manufactured from a workpiece using a wire saw, 60% to 70% of the workpiece is discarded as cutting loss, resulting in low productivity. Summary of the invention

[0007] In view of this point, an object of the present invention is to provide a method for producing a β-gallium oxide substrate capable of improving the productivity of a substrate when producing a substrate from a workpiece composed of β-gallium oxide.

[0008] According to the present invention, a method for manufacturing a β-gallium oxide substrate is provided, wherein the substrate is manufactured from a workpiece composed of β-gallium oxide, wherein the method for manufacturing the β-gallium oxide substrate comprises the following steps: a separation layer forming step, wherein the laser beam is irradiated onto the workpiece while positioning a focal point of a laser beam having a wavelength that transmits the β-gallium oxide at a predetermined depth from the front surface of the workpiece, thereby forming a separation layer including a modified portion and cracks extending from the modified portion inside the workpiece; and a separation step, wherein, after the separation layer forming step, an external force is applied to the workpiece, thereby separating the substrate from the workpiece with the separation layer as a starting point.

[0009] Furthermore, in the present invention, it is preferred that the workpiece is manufactured in such a manner that the crystal plane {001} of the β-gallium oxide is exposed on the front surface, and in the separation layer forming step, the following operations are alternately repeated: while the workpiece and the light-converging point are relatively moved in a predetermined direction, the workpiece is irradiated with the laser beam; and the workpiece is relatively moved in a direction perpendicular to the predetermined direction and the position where the light-converging point is formed, wherein the angle formed by the predetermined direction and a straight line parallel to the crystal direction

[100] of the β-gallium oxide is 35° or less. Furthermore, it is preferred that the method for manufacturing a β-gallium oxide substrate of the present invention further comprises the following steps: a preliminary separation layer forming step of irradiating the workpiece with the laser beam in such a manner that the light-converging point is positioned at the predetermined depth from the front surface of the workpiece, thereby forming a preliminary separation layer including a preliminary modified portion and a preliminary crack extending from the preliminary modified portion inside the workpiece; and a determination step of determining the predetermined direction with reference to the extension direction of the preliminary crack after the preliminary separation layer forming step and before the separation layer forming step.

[0010] In the present invention, a separation layer including a modified portion and cracks extending from the modified portion is formed inside the workpiece, and then the substrate is separated from the workpiece using the separation layer as a starting point. Thus, the productivity of the substrate can be improved compared to the case where the substrate is manufactured from the workpiece using a wire saw. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 (A) is a perspective view schematically showing an example of an ingot made of β-gallium oxide. Figure 1 (B) is a schematic diagram showing Figure 1 (A) is a side view of the ingot shown.

[0012] Figure 2 It is a schematic diagram showing the Figure 1 (A) and Figure 1 Flow chart of an example of a method for manufacturing a β-gallium oxide substrate for manufacturing an ingot substrate shown in (B).

[0013] Figure 3 It is schematically shown Figure 2 A perspective view showing a separation layer forming step.

[0014] Figure 4 The graph shows the relationship between the angle formed by the scanning direction of the laser beam and a straight line parallel to the crystal direction

[100] of β-gallium oxide, and the width of a crack in a direction perpendicular to the scanning direction of the laser beam.

[0015] Figure 5 (A) and Figure 5 (B) are schematically shown Figure 2 A side view of the separation process is shown.

[0016] Figure 6 This is a flowchart schematically showing an example of a method for manufacturing a β-gallium oxide substrate in which the substrate is manufactured from an ingot whose accurate crystal orientation is not known in advance.

[0017] Description of symbols

[0018] 2: Laser processing device; 4: Chuck worktable; 6: Laser beam irradiation unit; 8: Head; 10: Shell; 11: Ingot (11a: front, 11b: back, 11c: side); 12: Shooting unit; 13: Primary orientation plane; 14: Separation device; 15: Secondary orientation plane; 16: Chuck worktable; 17: Modification section; 18: Separation unit; 19: Separation layer; 20: Suction plate; 21: Substrate; 22: Vertical direction moving mechanism. DETAILED DESCRIPTION

[0019] Embodiments of the present invention will be described with reference to the drawings. Figure 1 (A) is a perspective view schematically showing an example of an ingot made of β-gallium oxide. Figure 1 (B) is a schematic diagram showing Figure 1 The side view of the ingot shown in (A) is shown in FIG. Figure 1 (A) and Figure 1 In (B), the crystal plane of β-gallium oxide contained in the ingot is also shown. Figure 1 (B) also shows the crystal orientation of the β-gallium oxide.

[0020] The crystal structure of β-gallium oxide is a monoclinic crystal in which the angle between the crystal direction

[100] (a-axis) and the crystal direction

[001] (c-axis) is 103.7°, and the angle between the crystal direction

[010] (b-axis) and the crystal direction

[100] (a-axis) and the crystal direction

[001] (c-axis) is 90° respectively. And, Figure 1 (A) and Figure 1 Ingot 11 shown in (B) has parallel front surface 11a and back surface 11b, and crystal plane {001} is exposed on front surface 11a and back surface 11b, respectively (herein, for convenience, the surface exposed on front surface 11a is referred to as crystal plane (001)).

[0021] In addition, in the ingot 11, the crystal plane {001} is manufactured so as to be exposed on the front surface 11a and the back surface 11b, respectively. However, due to processing errors during manufacturing, etc., a surface slightly inclined relative to the crystal plane {001} may be exposed on the front surface 11a and the back surface 11b, respectively. Specifically, a surface having an angle of 1° or less with the crystal plane {001} may be exposed on the front surface 11a and the back surface 11b of the ingot 11, respectively.

[0022] In addition, two flat portions indicating the crystal orientation of β-gallium oxide, namely, a primary orientation plane 13 and a secondary orientation plane 15, are formed on the side surface 11c of the ingot 11. The primary orientation plane 13 is longer than the secondary orientation plane 15 and is formed so as to be located in the crystal orientation

[100] when viewed from the center of the ingot 11.

[0023] In addition, the secondary orientation plane 15 is formed so as to be positioned in the crystal direction

[010] when viewed from the center of the ingot 11. In other words, the secondary orientation plane 15 is formed so as to be a plane where the crystal plane (010) is exposed. Therefore, in the ingot 11, the obtuse angle between the crystal plane (100) and the front surface 11a or the back surface 11b is 103.7°, and the crystal plane (100) is perpendicular to the secondary orientation plane 15.

[0024] In addition, one or both of the primary orientation flat 13 and the secondary orientation flat 15 may not be formed on the side surface 11c of the ingot 11. In addition, instead of the primary orientation flat 13 and the secondary orientation flat 15, a notch (recess) for indicating the crystal orientation of β-gallium oxide may be formed on the side surface 11c of the ingot 11.

[0025] Figure 2 1 is a flowchart schematically showing an example of a method for manufacturing a β-gallium oxide substrate from an ingot 11 as a workpiece. In this method, first, a separation layer including a modified portion and cracks extending from the modified portion is formed inside the ingot 11 (separation layer forming step S1).

[0026] Figure 3 Schematically showing the separation layer forming step S1. Figure 3 The X-axis direction and the Y-axis direction shown are directions perpendicular to each other on a horizontal plane, and the Z-axis direction is a direction (vertical direction) perpendicular to the X-axis direction and the Y-axis direction.

[0027] This separation layer forming step S1 is performed in the laser processing apparatus 2. The laser processing apparatus 2 includes a chuck table 4 having a circular holding surface substantially parallel to a horizontal plane and capable of holding the ingot 11 on the holding surface.

[0028] The chuck table 4 is connected to a suction mechanism (not shown). The suction mechanism includes, for example, an ejector. When the suction mechanism is operated, suction acts on the space near the holding surface of the chuck table 4. Therefore, when the suction mechanism is operated with the ingot 11 placed on the holding surface, the ingot 11 is held on the holding surface of the chuck table 4.

[0029] In addition, the chuck table 4 is connected to a rotating mechanism (not shown). The rotating mechanism includes, for example, a pulley and a motor. When the rotating mechanism is operated, the chuck table 4 rotates with a straight line passing through the center of the holding surface and along the Z-axis direction as the rotation axis. For example, the rotating mechanism rotates the chuck table 4 in such a manner that the secondary orientation plane 15 of the ingot 11 held by the holding surface of the chuck table 4 is parallel to the X-axis direction.

[0030] A head 8 of the laser beam irradiation unit 6 is provided above the chuck table 4. The head 8 is provided at the front end of a cylindrical housing 10 extending in the Y-axis direction. In addition, the head 8 accommodates an optical system such as a condenser lens (e.g., a condenser lens having a numerical aperture (NA) of 0.85) and a reflector, and the housing 10 accommodates an optical system such as a reflector and / or a lens.

[0031] The base end of the housing 10 is connected to a moving mechanism. The moving mechanism includes, for example, a ball screw and a motor. When the moving mechanism is operated, the housing 10 moves along the X-axis direction, the Y-axis direction, and / or the Z-axis direction. In addition, the laser beam irradiation unit 6 includes, for example, a laser oscillator (not shown) containing Nd:YAG or the like as a laser medium.

[0032] The laser oscillator generates a pulsed laser beam (e.g., a pulsed laser beam with a frequency of 30 kHz and a pulse width of 4 ns) of a wavelength (e.g., 1064 nm) that transmits β-gallium oxide. After the output (power) of the laser beam is adjusted by an attenuator, the laser beam is emitted from the head 8 directly downward through an optical system housed in the housing 10 and the head 8.

[0033] Furthermore, a photographing unit 12 capable of photographing the area directly below the housing 10 is provided on the side of the housing 10. The photographing unit 12 includes, for example, a light source such as an LED (Light Emission Diode) that emits light of a wavelength (for example, visible light) that transmits β-gallium oxide, an objective lens, and photographing elements such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

[0034] When the separation layer forming step S1 is performed using the laser processing device 2, first, the ingot 11 is placed on the holding surface of the chuck table 4 with the front surface 11a facing upward. Next, the suction mechanism is operated so as to hold the ingot 11 on the chuck table 4. Next, the imaging unit 12 is operated so as to form an image of the front surface 11a of the ingot 11.

[0035] Next, referring to the image, the rotating mechanism rotates the chuck table 4 so that the secondary orientation plane 15 is parallel to the X-axis direction. That is, the rotating mechanism rotates the chuck table 4 so that the crystal direction

[100] of β-gallium oxide is parallel to the X-axis direction and the crystal direction

[010] is parallel to the Y-axis direction.

[0036] Next, the moving mechanism moves the housing 10 in the X-axis direction and / or the Y-axis direction so that the region slightly inside the secondary orientation plane 15 of the ingot 11 is positioned in the X-axis direction when viewed from the head 8 in a plan view.

[0037] Next, the moving mechanism moves the housing 10 in the Z-axis direction so that the focal point of the laser beam emitted from the head 8 is positioned at a predetermined depth from the front surface 11a of the ingot 11. The predetermined depth corresponds to the thickness of a substrate manufactured from the ingot 11, for example.

[0038] Next, while emitting a laser beam from the head 8, the housing 10 is moved along the X-axis direction so that the focal point where the laser beam converges passes from one end to the other end of the ingot 11 in the X-axis direction at a predetermined speed (e.g., 450 mm / s). That is, the laser beam is irradiated onto the ingot 11 with the direction along a straight line parallel to the crystal direction

[100] of β-gallium oxide as the scanning direction of the laser beam.

[0039] As a result, a modified portion 17 in which the crystal structure of β-gallium oxide is disturbed is formed inside the ingot 11 with the focal point where the laser beam converges as the center. When the modified portion 17 is formed inside the ingot 11, the volume of the ingot 11 expands and internal stress is generated in the ingot 11. Cracks extend from the modified portion 17, so that the internal stress is relaxed.

[0040] In addition, in β-gallium oxide, the crystal plane (100) is most easily cleaved, followed by the crystal plane (001). Therefore, when the modified portion 17 is formed inside the ingot 11, a large number of cracks along the crystal plane (100) and the crystal plane (001) are formed. As a result, a separation layer including the modified portion 17 and the cracks extending from the modified portion 17 is formed inside the ingot 11 (specifically, a linear region along the crystal direction

[100] of β-gallium oxide).

[0041] Next, the moving mechanism moves the housing 10 along the Y-axis direction by a predetermined displacement amount (e.g., 0.2 mm) so that the head 8 is positioned in the X-axis direction when viewed from a region slightly away from the secondary orientation plane 15 than the region already irradiated with the laser beam when viewed from above.

[0042] Next, the laser beam is irradiated to the ingot 11 in the above-mentioned manner, with the direction opposite to the X-axis direction being the scanning direction of the laser beam. The above-mentioned operation is repeated until the laser beam irradiation to the region farthest from the secondary orientation plane 15 in the ingot 11 is completed.

[0043] That is, the relative movement of the ingot 11 along the Y-axis direction and the position of the focal point where the laser beam converges (specifically, the movement of the housing 10) and the irradiation of the laser beam to the ingot 11 with the X-axis direction or the opposite direction as the scanning direction of the laser beam are repeated alternately. Thus, the separation layer forming step S1 is completed.

[0044] In the separation layer forming step S1, a direction parallel to the crystal direction

[100] of β-gallium oxide (X-axis direction or the opposite direction) is set as the scanning direction of the laser beam, but a direction not parallel thereto may be set as the scanning direction of the laser beam.

[0045] However, when the scanning direction of the laser beam is parallel to the crystal direction

[010] of β-gallium oxide, the proportion of cracks extending along the crystal plane (100) parallel to the crystal direction

[010] may increase. In addition, when the proportion of cracks extending along the crystal plane (100) increases, the thickness of the separation layer formed inside the ingot 11 increases, and the productivity when manufacturing the substrate from the ingot 11 decreases.

[0046] In this case, the ratio of cracks extending along the crystal plane (001), that is, cracks extending parallel to the front surface 11a of the ingot 11, is reduced, so the width (length in the direction perpendicular to the thickness direction of the ingot 11 and the scanning direction of the laser beam) of the separation layer formed inside the ingot 11 is reduced. Therefore, in this case, the above-mentioned indexing amount has to be reduced, and the production capacity of the laser processing device 2 is reduced.

[0047] Based on these points, in order to improve the productivity and production capacity when manufacturing a substrate from the ingot 11, it is preferred to set the scanning direction of the laser beam in such a way that the angle formed with a straight line parallel to the crystal direction

[010] of β-gallium oxide becomes larger, that is, the angle formed with a straight line parallel to the crystal direction

[100] becomes smaller.

[0048] Figure 4 1 is a diagram showing the width of the separation layer formed when a workpiece made of β-gallium oxide manufactured in such a way that the crystal plane (001) is exposed on the front side is irradiated with a laser beam under multiple conditions with different scanning directions. Figure 4 , the relationship between the angle between the scanning direction of the laser beam and a straight line parallel to the crystal direction

[100] of β-gallium oxide and the width of the separation layer is shown.

[0049] like Figure 4As shown in FIG. 1 , the width of the separation layer increases when the angle between the scanning direction of the laser beam and the straight line parallel to the crystal direction

[100] of β-gallium oxide is less than 35°. Therefore, in the separation layer forming step S1, it is preferred that the scanning direction of the laser beam is set so that the angle is less than 35°. Figure 4 The scanning direction of the laser beam is more preferably set to an angle of less than 10°, and most preferably set to an angle of less than 5°.

[0050] In addition, in the separation layer forming step S1, the laser beam irradiation to the ingot 11 may be performed only in one direction (for example, the X-axis direction). That is, in the separation layer forming step S1, instead of using the direction opposite to the one direction (for example, the direction opposite to the X-axis direction) as the scanning direction of the laser beam, the laser beam irradiation to the ingot 11 may be repeated with the one direction as the scanning direction of the laser beam.

[0051] After the separation layer forming step S1 , the substrate is separated from the ingot 11 using the separation layer as a starting point (separation step S2 ). Figure 5 (A) and Figure 5 (B) are side views schematically showing the separation step S2. The separation step S2 is implemented in the separation device 14. The separation device 14 has a chuck table 16, and the chuck table 16 has Figure 3 The chuck table 4 shown is of the same construction.

[0052] The chuck table 16 is connected to a table-side suction mechanism (not shown). The table-side suction mechanism includes, for example, a vacuum pump. When the table-side suction mechanism is operated, suction acts on the space near the holding surface of the chuck table 16. Therefore, when the table-side suction mechanism is operated with the ingot 11 placed on the holding surface, the ingot 11 is held on the holding surface of the chuck table 16.

[0053] A separation unit 18 is provided above the chuck table 16. The separation unit 18 has a suction plate 20 having a plurality of suction ports formed on the lower surface. The plurality of suction ports are connected to a separation unit side suction mechanism such as a vacuum pump via a suction path formed inside the suction plate 20. When the separation unit side suction mechanism is operated, suction acts on the space near the lower surface of the suction plate 20.

[0054] In addition, a vertical direction moving mechanism 22 is connected to the upper surface of the suction plate 20. The vertical direction moving mechanism 22 includes, for example, a ball screw and a motor, etc. When the vertical direction moving mechanism 22 is operated, the suction plate 20 moves in the vertical direction.

[0055] When the separation step S2 is performed by the separation device 14, first, in a state where the chuck table 16 and the suction plate 20 are sufficiently separated, the ingot 11 having the separation layer 19 formed therein is placed on the holding surface of the chuck table 16 with the front surface 11a facing upward. Next, the table-side suction mechanism is operated so as to hold the ingot 11 on the chuck table 16.

[0056] Next, the vertical direction moving mechanism lowers the suction plate 20 so that the lower surface of the suction plate 20 contacts the front surface 11a of the ingot 11 (see Figure 5 Next, the suction mechanism on the separation unit side is operated in such a manner that the front surface 11a side of the ingot 11 is sucked upward. Next, the vertical direction moving mechanism raises the suction plate 20 in such a manner that the suction plate 20 is separated from the chuck table 16 (see Figure 5 (B)).

[0057] As a result, an external force is applied to the ingot 11 to pull the front side 11a and the back side 11b of the ingot 11 apart, and the cracks included in the separation layer 19 are further extended. As a result, the ingot 11 is separated at the separation layer 19 to produce the substrate 21. By the above, the separation step S2 is completed. Figure 2 A method for manufacturing the substrate shown.

[0058] exist Figure 2 In the manufacturing method of the substrate shown, a separation layer 19 including a modified portion 17 and cracks extending from the modified portion 17 is formed inside the ingot 11, and then the substrate 21 is separated from the ingot 11 using the separation layer 19 as a starting point. As a result, the productivity of the substrate 21 can be improved compared to the case where the substrate 21 is manufactured from the ingot 11 using a wire saw.

[0059] The above contents are one embodiment of the present invention, and the present invention is not limited to the above contents. For example, in the separation layer forming step S1, as long as the ingot 11 and the focal point where the laser beam converges can be relatively moved, there is no limitation on the structure for achieving the movement.

[0060] Specifically, the separation layer forming step S1 may be performed in a laser processing apparatus provided with a moving mechanism for moving the chuck table 4 in the X-axis direction, the Y-axis direction, and / or the Z-axis direction.

[0061] Alternatively, the separation layer forming step S1 may be performed using a laser processing device in which the laser beam irradiation unit 6 is provided with a scanning optical system capable of changing the direction of the laser beam emitted from the head 8. The scanning optical system includes, for example, an electrical scanner, an acousto-optic device (AOD) and / or a polygon mirror.

[0062] In the separation step S2, ultrasonic vibration may be applied to the ingot 11 as an external force for manufacturing the substrate 21. That is, in the separation step S2, instead of applying an external force such as pulling the front side 11a and the back side 11b of the ingot 11 apart, ultrasonic vibration may be applied to the front side 11a of the ingot 11 in advance.

[0063] Alternatively, the workpiece used for manufacturing the β-gallium oxide substrate may be an ingot manufactured so that a crystal plane other than the crystal plane {001} of β-gallium oxide (for example, the crystal plane (100)) is exposed on the front surface.

[0064] In addition, the workpiece used for manufacturing the β-gallium oxide substrate may be, for example, a bare wafer having a thickness of at least 2 times and not more than 5 times that of the substrate to be manufactured. In addition, the bare wafer is manufactured by, for example, separating from the ingot 11 by the same method as the above method. In this case, it can also be expressed as manufacturing the substrate by repeating the above method twice.

[0065] In addition, the workpiece used for manufacturing the β-gallium oxide substrate may also be a device wafer manufactured by forming a semiconductor device on one surface of the bare wafer. In this case, in order to prevent adverse effects on the semiconductor device, it is preferred to irradiate the device wafer with a laser beam from the side of the device wafer where the semiconductor device is not formed.

[0066] Furthermore, although the workpiece used for manufacturing the β-gallium oxide substrate is manufactured so that the crystal plane {001} of the β-gallium oxide is exposed on the front surface, the workpiece may be an ingot whose accurate crystal orientation is not known in advance. Figure 6 1 is a flowchart schematically showing an example of a method for manufacturing a β-gallium oxide substrate for manufacturing a substrate from such a workpiece.

[0067] In this method, first, a preliminary separation layer including a preliminary reformed portion and preliminary cracks extending from the preliminary reformed portion is formed inside the ingot (preliminary separation layer forming step S3). The preliminary separation layer forming step S3 is performed, for example, in the above-mentioned laser processing device 2.

[0068] When the preliminary separation layer forming step S3 is performed using the laser processing device 2, first, the ingot is placed on the holding surface of the chuck table 4 with the front side facing upward. Next, the suction mechanism is operated so as to hold the ingot on the chuck table 4. Next, the moving mechanism moves the housing 10 in the X-axis direction and / or the Y-axis direction so as to position the head 8 directly above the ingot.

[0069] Next, the moving mechanism moves the housing 10 in the Z-axis direction so that the focal point of the laser beam emitted from the head 8 is positioned at a predetermined depth from the front surface of the ingot. The predetermined depth corresponds to, for example, the thickness of a substrate manufactured from the ingot.

[0070] Next, a laser beam is emitted from the head 8. At this time, the moving mechanism may move the housing 10 to move the focal point where the laser beam converges, or may not move the housing 10. Thus, a preliminary modified portion in which the crystal structure of β-gallium oxide is disturbed is formed inside the ingot with the focal point where the laser beam converges as the center.

[0071] In addition, when the preliminary modified portion is formed inside the ingot, the preliminary crack extends from the preliminary modified portion. Here, in β-gallium oxide, the crystal plane (100) is most easily cleaved. Therefore, the preliminary crack mainly extends along the crystal plane (100). As a result, a preliminary separation layer including the preliminary modified portion and the preliminary crack extending from the preliminary modified portion is formed inside the ingot.

[0072] After the preliminary separation layer forming step S3 and before the separation layer forming step S1, the scanning direction of the laser beam in the separation layer forming step S1 is determined with reference to the extension direction of the preliminary crack (determination step S4). In the determination step S4, first, the moving mechanism moves the housing 10 along the X-axis direction and / or the Y-axis direction so as to position the imaging unit 12 directly above the preliminary separation layer.

[0073] Next, the imaging unit 12 is operated to form an image of the preliminary separation layer. That is, the preliminary separation layer is imaged from a direction perpendicular to the crystal plane (001) of β-gallium oxide. Furthermore, in the case where the preliminary crack included in the preliminary separation layer extends along the crystal plane (100), the preliminary crack is included in the image as a preliminary crack extending mainly parallel to the crystal direction

[010] .

[0074] Next, referring to the extension direction of the preliminary crack in the image, the direction perpendicular to the extension direction is determined as the scanning direction of the laser beam in the separation layer forming step S1. Thus, the direction at which the angle formed by a straight line parallel to the crystal direction

[100] of β-gallium oxide is 35° or less can be determined as the scanning direction of the laser beam.

[0075] In addition, the structure and method etc. which concern on the said embodiment can be implemented with appropriate change unless it deviates from the scope of the objective of this invention.

Claims

1. A method for manufacturing a β-gallium oxide substrate, comprising manufacturing a substrate from a workpiece composed of β-gallium oxide, wherein: The method for manufacturing the β-gallium oxide substrate comprises the following steps: a separation layer forming step of irradiating the workpiece with the laser beam having a wavelength that transmits the β-gallium oxide while positioning a focal point thereof at a predetermined depth from the front surface of the workpiece, thereby forming a separation layer including a modified portion and cracks extending from the modified portion inside the workpiece; as well as The separation step is a step of applying an external force to the workpiece after the separation layer forming step, thereby separating the substrate from the workpiece with the separation layer as a starting point.

2. The method for manufacturing a β-gallium oxide substrate according to claim 1, wherein: The workpiece is manufactured in such a manner that the crystal plane {001} of the β-gallium oxide is exposed on the front surface, In the separation layer forming step, the following operations are repeated alternately: irradiating the object to be processed with the laser beam while relatively moving the object to be processed and the focal point in a predetermined direction; and The workpiece and the position where the focal point is formed are relatively moved along a direction perpendicular to the specified direction, wherein the angle formed by the specified direction and a straight line parallel to the crystal direction [100] of the β-gallium oxide is less than 35°.

3. The method for manufacturing a β-gallium oxide substrate according to claim 2, wherein: The method for manufacturing the β-gallium oxide substrate further comprises the following steps: a preliminary separation layer forming step of irradiating the workpiece with the laser beam in such a manner that the focal point is positioned at the predetermined depth from the front surface of the workpiece, thereby forming a preliminary separation layer including a preliminary modified portion and preliminary cracks extending from the preliminary modified portion inside the workpiece; and The determining step is after the preliminary separation layer forming step and before the separation layer forming step, determining the prescribed direction with reference to the extending direction of the preliminary crack.

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