Manufacturing method of β gallium oxide substrate

Abstract

To provide a manufacturing method of a β gallium oxide substrate capable of improving productivity of a substrate when manufacturing the substrate from a workpiece consisting of a β gallium oxide.SOLUTION: A manufacturing method of a β gallium oxide substrate for manufacturing a substrate from a workpiece consisting of a β gallium oxide includes: a separate layer formation step of forming a separate layer including a modified part and a crack extending from the modified part inside of the workpiece by irradiating the workpiece with a laser beam in a state where a light focus point, in which the laser beam of a wavelength transmitted through the β gallium oxide is focused, is positioned in a predetermined depth from a surface of the workpiece; and a separation step of separating the substrate from the workpiece with the separate layer defined as an origin by applying an external force to the workpiece after the separate layer formation step.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing a β-gallium oxide substrate, which produces a substrate from a workpiece made of β-gallium oxide. [Background technology]

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

[0003] Semiconductor devices are generally formed using a disk-shaped substrate, which is manufactured by cutting a workpiece, such as a cylindrical block called an ingot, with a wire saw so as to separate a portion having a predetermined thickness from the workpiece (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-254174 A [Patent Document 2] JP 2016-13929 A Summary of the Invention [Problem to be solved by the invention]

[0005] For example, a substrate having a thickness of about 150 μm is used to form a semiconductor device. Also, the thickness of a wire saw is, for example, about 300 μm. Therefore, when manufacturing a substrate from a workpiece using a wire saw, 60% to 70% of the workpiece is discarded as a cut margin, resulting in low productivity.

[0006] In view of this, an object of the present invention is to provide a method for manufacturing a β-gallium oxide substrate that can improve productivity when manufacturing substrates from a workpiece made of β-gallium oxide. [Means for solving the problem]

[0007] According to the present invention, there is provided a method for producing a β-gallium oxide substrate, which produces a substrate from a workpiece made of β-gallium oxide, comprising: a separation layer formation step of forming a separation layer inside the workpiece, the separation layer including a modified portion and a crack extending from the modified portion, by irradiating the workpiece with a laser beam having a wavelength that transmits the β-gallium oxide while positioning the focal point of the laser beam at a predetermined depth from the surface of the workpiece; and a separation step of separating the substrate from the workpiece, starting from the separation layer, by applying an external force to the workpiece after the separation layer formation step.

[0008] Further, in the present invention, the workpiece is manufactured so that the crystal plane {001} of the β-gallium oxide is exposed on the surface, and in the separation layer forming step, it is preferable that the irradiation of the laser beam on the workpiece while moving the workpiece and the focal point relative to each other along a predetermined direction that forms an angle of 35° or less with a straight line parallel to the crystal orientation

[0100] of the β-gallium oxide, and the relative movement of the workpiece and the position where the focal point is formed along a direction perpendicular to the predetermined direction are alternately repeated. In addition, the manufacturing method of the β-gallium oxide substrate of the present invention preferably further comprises a preliminary separation layer forming step of forming a preliminary separation layer including a preliminary modified part and a preliminary crack extending from the preliminary modified part inside the workpiece by irradiating the workpiece with the laser beam so that the focal point is positioned at the predetermined depth from the surface of the workpiece, and a specifying step of specifying the predetermined direction by referring to the extension direction of the preliminary crack after the preliminary separation layer forming step and before the separation layer forming step. Effect of the Invention

[0009] 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 from the separation layer as a starting point. This improves the productivity of the substrate compared to the case where the substrate is manufactured from the workpiece using a wire saw. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1(A) is a perspective view that shows a schematic example of an ingot made of β-gallium oxide, and FIG. 1(B) is a side view that shows a schematic example of the ingot shown in FIG. 1(A). [Diagram 2] FIG. 2 is a flow chart that illustrates a schematic example of a method for producing a β-gallium oxide substrate from the ingot shown in FIGS. 1(A) and 1(B). [Diagram 3] FIG. 3 is a perspective view that illustrates the separation layer forming step illustrated in FIG. [Figure 4] FIG. 4 is a graph showing the relationship between the angle that the scanning direction of the laser beam makes with respect to a line parallel to the crystal orientation

[0100] of β-gallium oxide, and the width of the crack in a direction perpendicular to the scanning direction of the laser beam. [Diagram 5] 5(A) and 5(B) are side views each showing a schematic view of the separation step shown in FIG. [Figure 6] FIG. 6 is a flow chart that illustrates an example of a method for producing a β-gallium oxide substrate, in which a substrate is produced from an ingot whose exact crystal orientation is not known in advance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1(A) is a perspective view showing an example of an ingot made of β-gallium oxide, and Fig. 1(B) is a side view showing the ingot shown in Fig. 1(A). Note that Fig. 1(A) and Fig. 1(B) also show the crystal plane of β-gallium oxide contained in this ingot. Fig. 1(B) also shows the crystal orientation of this β-gallium oxide.

[0012] The crystal structure of β-gallium oxide is a monoclinic crystal with an angle of 103.7° between the crystal orientation

[0100] (a-axis) and the crystal orientation

[0001] (c-axis) and an angle of 90° between the crystal orientation

[0010] (b-axis) and each of the crystal orientations

[0100] (a-axis) and

[0001] (c-axis). The ingot 11 shown in Figures 1(A) and 1(B) has a front surface 11a and a back surface 11b that are parallel to each other, and a crystal plane {001} is exposed on each of the front surface 11a and the back surface 11b (here, for convenience, the plane exposed on the front surface 11a is referred to as a crystal plane (001)).

[0013] Although the ingot 11 is manufactured so that the crystal plane {001} is exposed on each of the front surface 11a and the back surface 11b, a plane slightly inclined from the crystal plane {001} may be exposed on each of the front surface 11a and the back surface 11b due to processing errors during manufacturing, etc. Specifically, a plane that forms an angle of 1° or less with respect to the crystal plane {001} may be exposed on each of the front surface 11a and the back surface 11b of the ingot 11.

[0014] In addition, two flat portions for indicating the crystal orientation of β-gallium oxide, namely, a primary orientation flat 13 and a secondary orientation flat 15, are formed on a side surface 11c of the ingot 11. The primary orientation flat 13 is longer than the secondary orientation flat 15 and is formed so as to be positioned in the crystal orientation

[0100] when viewed from the center of the ingot 11.

[0015] Moreover, the secondary orientation flat 15 is formed so as to be positioned in the crystal orientation

[0010] when viewed from the center of the ingot 11. In other words, the secondary orientation flat 15 is formed so as to be a plane on which the crystal plane (010) is exposed. Therefore, in the ingot 11, the crystal plane (100) forms an obtuse angle of 103.7° with the front surface 11a or the back surface 11b, and is perpendicular to the secondary orientation flat 15.

[0016] 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. Also, instead of the primary orientation flat 13 and the secondary orientation flat 15, a notch may be formed on the side surface 11c of the ingot 11 to indicate the crystal orientation of β gallium oxide.

[0017] 2 is a flow chart that illustrates an example of a method for producing a β-gallium oxide substrate from a workpiece, that is, an ingot 11. In this method, first, a separation layer including a modified portion and a crack extending from the modified portion is formed inside the ingot 11 (separation layer formation step S1).

[0018] Fig. 3 is a perspective view showing the separation layer forming step S1 in a schematic manner. Note that the X-axis direction and the Y-axis direction shown in Fig. 3 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.

[0019] This separation layer forming step S1 is performed by a laser processing device 2. The laser processing device 2 includes a chuck table 4 having a circular holding surface that is approximately parallel to a horizontal plane and capable of holding an ingot 11 on this holding surface.

[0020] The chuck table 4 is connected to a suction mechanism (not shown). This suction mechanism has, for example, an ejector. When the suction mechanism operates, a suction force acts on the space near the holding surface of the chuck table 4. Therefore, when the suction mechanism operates with the ingot 11 placed on the holding surface, the ingot 11 is held on the holding surface of the chuck table 4.

[0021] The chuck table 4 is also connected to a rotation mechanism (not shown). This rotation mechanism includes, for example, a pulley and a motor. When the rotation mechanism operates, the chuck table 4 rotates about a rotation axis that passes through the center of the holding surface and is aligned along the Z-axis direction. For example, the rotation mechanism rotates the chuck table 4 so that the secondary orientation flat 15 of the ingot 11 held on the holding surface of the chuck table 4 is parallel to the X-axis direction.

[0022] A head 8 of the laser beam irradiation unit 6 is provided above the chuck table 4. This head 8 is provided at the tip of a cylindrical housing 10 extending along the Y-axis direction. The head 8 houses an optical system such as a condenser lens (for example, a condenser lens with a numerical aperture (NA) of 0.85) and a mirror, and the housing 10 houses an optical system such as a mirror and / or a lens.

[0023] The base end of the housing 10 is connected to a moving mechanism. The moving mechanism has, for example, a ball screw and a motor. When the moving mechanism operates, the housing 10 moves along the X-axis direction, the Y-axis direction, and / or the Z-axis direction. The laser beam irradiation unit 6 has, for example, a laser oscillator (not shown) including Nd:YAG or the like as a laser medium.

[0024] This 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) with a wavelength (e.g., 1064 nm) that transmits through β-gallium oxide. Then, after the output (power) of this laser beam is adjusted by an attenuator, it is emitted directly downward from the head 8 via the housing 10 and an optical system contained in the head 8.

[0025] Furthermore, an imaging unit 12 capable of imaging the area directly below is provided on the side of the housing 10. The imaging unit 12 has a light source such as an LED (Light Emitting Diode) that emits light of a wavelength (e.g., visible light) that transmits β-gallium oxide, an objective lens, and an imaging element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

[0026] When performing the separation layer forming step S1 in the laser processing apparatus 2, first, the ingot 11 is placed on the holding surface of the chuck table 4 with the surface 11a facing up. Next, the suction mechanism is operated so that the ingot 11 is held on the chuck table 4. Next, the imaging unit 12 is operated so as to form an image of the surface 11a of the ingot 11.

[0027] Next, with reference to this image, for example, the rotation mechanism rotates the chuck table 4 so that the secondary orientation flat 15 is parallel to the X-axis direction. In other words, the rotation mechanism rotates the chuck table 4 so that the crystal orientation

[0100] of β gallium oxide is parallel to the X-axis direction and the crystal orientation

[0010] is parallel to the Y-axis direction.

[0028] Next, the moving mechanism moves the housing 10 along the X-axis and / or Y-axis directions so that the area of ​​the ingot 11 slightly inside the secondary orientation flat 15 is positioned in the X-axis direction when viewed in a plan view from the head 8.

[0029] Next, the moving mechanism moves the housing 10 along the Z-axis direction so that the focal point at which the laser beam emitted from the head 8 is focused is positioned at a predetermined depth from the surface 11a of the ingot 11. Note that this predetermined depth corresponds to, for example, the thickness of a substrate to be manufactured from the ingot 11.

[0030] Next, while emitting a laser beam from head 8, the moving mechanism moves housing 10 along the X-axis direction so that the focal point at which the laser beam is focused passes from one end to the other end in the X-axis direction of ingot 11 at a predetermined speed (e.g., 450 mm / s). In other words, the laser beam is irradiated onto ingot 11 with the scanning direction of the laser beam being a straight line parallel to the crystal orientation

[0100] of β-gallium oxide.

[0031] As a result, modified portion 17, in which the crystal structure of β-gallium oxide is disturbed, is formed inside ingot 11, centered around the focal point where the laser beam is focused. Furthermore, when modified portion 17 is formed inside ingot 11, the volume of ingot 11 expands, causing internal stress in ingot 11. This internal stress is alleviated by cracks extending from modified portion 17.

[0032] In β-gallium oxide, the crystal plane (100) is most likely to cleave, followed by the crystal plane (001). Therefore, when the modified portion 17 is formed inside the ingot 11, many cracks are formed along the crystal plane (100) and the crystal plane (001). 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, in a linear region along the crystal orientation

[0100] of the β-gallium oxide).

[0033] Next, the moving mechanism moves the housing 10 a predetermined index amount (e.g., 0.2 mm) along the Y-axis direction so that the head 8 is positioned in the X-axis direction when viewed in a plane from an area slightly farther from the secondary orientation flat 15 than the area already irradiated with the laser beam.

[0034] Next, the laser beam is irradiated onto the ingot 11 as described above, with the scanning direction of the laser beam being the opposite direction to the X-axis direction. Furthermore, the above-described operation is repeated until irradiation of the region of the ingot 11 farthest from the secondary orientation flat 15 with the laser beam is completed.

[0035] That is, the relative movement between the ingot 11 along the Y-axis direction and the position where the focal point of the laser beam is formed (specifically, the movement of the housing 10) and the irradiation of the ingot 11 with the laser beam in the X-axis direction or the opposite direction are alternately repeated. This completes the separation layer formation step S1.

[0036] In the above-mentioned separation layer formation process S1, the direction parallel to the crystal orientation

[0100] of β-gallium oxide (the X-axis direction or the opposite direction) is set as the scanning direction of the laser beam, but a direction non-parallel thereto may also be set as the scanning direction of the laser beam.

[0037] However, when the scanning direction of the laser beam becomes parallel to the crystal orientation

[0010] of β-gallium oxide, the ratio of cracks extending along the crystal plane (100) parallel to the crystal orientation

[0010] may increase. If the ratio of cracks extending along the crystal plane (100) increases, the thickness of the separation layer formed inside the ingot 11 increases, and the productivity of manufacturing substrates from the ingot 11 decreases.

[0038] In this case, the ratio of cracks extending along the crystal plane (001), i.e., cracks extending parallel to the surface 11a of the ingot 11, decreases, so that the width of the separation layer formed inside the ingot 11 (the length in the direction perpendicular to the thickness direction of the ingot 11 and the scanning direction of the laser beam) decreases. Therefore, in this case, the index amount has to be reduced, and the throughput of the laser processing device 2 decreases.

[0039] Taking these points into consideration, in order to improve productivity and throughput when manufacturing substrates from ingot 11, it is preferable to set the scanning direction of the laser beam so that it forms a large angle with respect to a line parallel to the crystal orientation

[0010] of β-gallium oxide, i.e., so that it forms a small angle with respect to a line parallel to the crystal orientation

[0100] .

[0040] Fig. 4 is a graph showing the width of the separation layer formed when a workpiece made of β-gallium oxide manufactured so that the crystal plane (001) is exposed on the surface is irradiated with a laser beam under a number of conditions with different scanning directions. Specifically, Fig. 4 shows the relationship between the angle that the scanning direction of the laser beam makes with respect to a line parallel to the crystal orientation

[0100] of β-gallium oxide, and the width of the separation layer.

[0041] As shown in Fig. 4, the width of this separation layer becomes large when the angle that the scanning direction of the laser beam makes with respect to a line parallel to the crystal orientation

[0100] of β-gallium oxide is 35° or less. Therefore, in the separation layer formation step S1, it is preferable that the scanning direction of the laser beam is set so that this angle is 35° or less. Furthermore, referring to Fig. 4, it is more preferable that the scanning direction of the laser beam is set so that it is 10° or less, and most preferably 5° or less.

[0042] In addition, in the separation layer forming step S1, the laser beam may be irradiated onto the ingot 11 only along one direction (for example, the X-axis direction). That is, in the separation layer forming step S1, the laser beam may be repeatedly irradiated onto the ingot 11 in the one direction as the scanning direction of the laser beam, without the opposite direction to the one direction (for example, the opposite direction to the X-axis direction) being the scanning direction of the laser beam.

[0043] After the separation layer forming step S1, the substrate is separated from the ingot 11 starting from the separation layer (separation step S2). Each of Fig. 5(A) and Fig. 5(B) is a side view showing a schematic view of the separation step S2. This separation step S2 is performed in a separation apparatus 14. The separation apparatus 14 includes a chuck table 16 having a structure similar to that of the chuck table 4 shown in Fig. 3.

[0044] The chuck table 16 is connected to a table-side suction mechanism (not shown). This table-side suction mechanism has, for example, a vacuum pump. When this table-side suction mechanism operates, a suction force acts on the space near the holding surface of the chuck table 16. Therefore, when the table-side suction mechanism operates with the ingot 11 placed on the holding surface, the ingot 11 is held on the holding surface of the chuck table 16.

[0045] A separation unit 18 is provided above the chuck table 16. This separation unit 18 has a suction plate 20 having a plurality of suction ports formed on the lower surface thereof. The plurality of suction ports communicate with a separation unit side suction mechanism such as a vacuum pump via suction paths formed inside the suction plate 20. When the separation unit side suction mechanism operates, a suction force acts on the space near the lower surface of the suction plate 20.

[0046] A vertical movement mechanism 22 is connected to the upper surface of the suction plate 20. The vertical movement mechanism 22 has, for example, a ball screw and a motor. When the vertical movement mechanism 22 operates, the suction plate 20 moves in the vertical direction.

[0047] When performing the separation step S2 in the separation device 14, first, the ingot 11 having the separation layer 19 formed therein is placed on the holding surface of the chuck table 16 with the surface 11a facing up, with the chuck table 16 and the suction plate 20 being sufficiently separated from each other. Next, the table-side suction mechanism is operated so that the ingot 11 is held on the chuck table 16.

[0048] Next, the vertical movement 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 FIG. 5(A)). Next, the separation unit side suction mechanism is operated so that the front surface 11a side of the ingot 11 is sucked upward. Next, the vertical movement mechanism raises the suction plate 20 so as to separate the suction plate 20 from the chuck table 16 (see FIG. 5(B)).

[0049] This applies an external force to ingot 11 that separates front surface 11a and back surface 11b of ingot 11, further expanding the cracks contained in separation layer 19. As a result, ingot 11 is separated at separation layer 19 to produce substrate 21. This completes separation step S2, i.e., the method for producing the substrate shown in FIG.

[0050] 2, a separation layer 19 including modified portions 17 and cracks extending from modified portions 17 is formed inside ingot 11, and then substrate 21 is separated from ingot 11 starting from separation layer 19. This improves the productivity of substrate 21 compared to the case where substrate 21 is manufactured from ingot 11 using a wire saw.

[0051] The above is one embodiment of the present invention, and the present invention is not limited to the above. For example, in the separation layer formation step S1, it is sufficient to relatively move the ingot 11 and the focal point where the laser beam is focused, and there is no limitation on the structure for this purpose.

[0052] Specifically, this separation layer forming step S1 may be performed in a laser processing device provided with a moving mechanism for moving the chuck table 4 along each of the X-axis direction, the Y-axis direction, and / or the Z-axis direction.

[0053] Alternatively, the separation layer forming step S1 may be performed using a laser processing apparatus in which a scanning optical system capable of changing the direction of the laser beam emitted from the head 8 is provided in the laser beam irradiation unit 6. Note that this scanning optical system includes, for example, a galvano scanner, an acousto-optical device (AOD), and / or a polygon mirror.

[0054] In addition, in the separation step S2, ultrasonic vibration may be applied to the ingot 11 as an external force for producing the substrate 21. That is, in this separation step S2, ultrasonic vibration may be applied to the front surface 11a side of the ingot 11 instead of or prior to the application of an external force that separates the front surface 11a side and the back surface 11b side of the ingot 11.

[0055] Furthermore, the workpiece used in the manufacture of a β-gallium oxide substrate may be an ingot manufactured so that a crystal face of β-gallium oxide other than the {001} crystal face (for example, the (100) crystal face) is exposed on the surface.

[0056] The workpiece used to manufacture the β-gallium oxide substrate may be, for example, a bare wafer having a thickness between two and five times that of the substrate to be manufactured. The bare wafer is manufactured, for example, by being separated from the ingot 11 by a method similar to the above-mentioned method. In this case, the substrate can also be expressed as being manufactured by repeating the above-mentioned method twice.

[0057] The workpiece used in the manufacture of the β-gallium oxide substrate may be a device wafer manufactured by forming semiconductor devices on one side of the bare wafer. In this case, the laser beam is preferably irradiated onto the device wafer from the side on which the semiconductor devices are not formed, in order to prevent adverse effects on the semiconductor devices.

[0058] In addition, the workpiece used in the manufacture of the β-gallium oxide substrate may be an ingot manufactured so that the crystal plane {001} of β-gallium oxide is exposed on the surface, but the exact crystal orientation of the ingot is not known in advance. Fig. 6 is a flow chart that shows a schematic example of a method for manufacturing a β-gallium oxide substrate, which manufactures a substrate from such a workpiece.

[0059] In this method, first, a preliminary separation layer including a preliminary modified portion and a preliminary crack extending from the preliminary modified portion is formed inside the ingot (preliminary separation layer forming step S3). This preliminary separation layer forming step S3 is performed, for example, in the laser processing device 2 described above.

[0060] When the preliminary separation layer forming step S3 is performed in the laser processing apparatus 2, first, the ingot is placed on the holding surface of the chuck table 4 with its surface facing up. Next, the suction mechanism is operated so that the ingot is held on the chuck table 4. Next, the movement mechanism moves the housing 10 along the X-axis direction and / or Y-axis direction so that the head 8 is positioned directly above the ingot.

[0061] Next, the moving mechanism moves the housing 10 along 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 surface of the ingot. Note that this predetermined depth corresponds to, for example, the thickness of a substrate to be manufactured from the ingot.

[0062] Next, a laser beam is emitted from the head 8. At this time, the moving mechanism may or may not operate the housing 10 to move the focal point where the laser beam is focused. As a result, a pre-modified portion in which the crystal structure of β gallium oxide is disturbed is formed inside the ingot, centered on the focal point where the laser beam is focused.

[0063] Furthermore, when a preliminary reformed region is formed inside the ingot, a preliminary crack propagates from the preliminary reformed region. Here, in β-gallium oxide, the crystal plane (100) is most likely to cleave. Therefore, the preliminary crack propagates mainly along the crystal plane (100). As a result, a preliminary separation layer is formed inside the ingot, which includes the preliminary reformed region and the preliminary crack propagating from the preliminary reformed region.

[0064] 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 specified by referring to the extension direction of the preliminary crack (specifying step S4). In this specifying step S4, first, the moving mechanism moves the housing 10 along the X-axis direction and / or the Y-axis direction so that the imaging unit 12 is positioned directly above the preliminary separation layer.

[0065] 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. Then, if a preliminary crack included in the preliminary separation layer extends along the crystal plane (100), the preliminary crack is included in the image as extending mainly parallel to the crystal orientation

[0010] .

[0066] Next, referring to the extension direction of the preliminary crack in this image, a direction perpendicular to the extension direction is specified as the scanning direction of the laser beam in the separation layer formation step S1. This makes it possible to specify the direction that forms an angle of 35° or less with respect to a line parallel to the crystal orientation

[0100] of β-gallium oxide as the scanning direction of the laser beam.

[0067] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0068] 2: Laser processing equipment 4: Chuck table 6: Laser beam irradiation unit 8: Head 10: Housing 11: Ingot (11a: front surface, 11b: back surface, 11c: side surface) 12: Imaging unit 13: Primary orientation flat 14: Separation device 15: Secondary orientation flat 16: Chuck table 17: Modification section 18: Separation unit 19: Separation layer 20: Suction plate 21: Substrate 22: Vertical movement mechanism

Claims

1. A method for producing a β-gallium oxide substrate, comprising the steps of: producing a substrate from a workpiece made of β-gallium oxide; a separation layer forming step of forming a separation layer including a modified portion and a crack extending from the modified portion inside the workpiece by irradiating the workpiece with a laser beam having a wavelength that transmits the β-gallium oxide while positioning a focal point of the laser beam at a predetermined depth from the surface of the workpiece; a separation step of applying an external force to the workpiece after the separation layer forming step to separate the substrate from the workpiece starting from the separation layer; A method for producing a β-gallium oxide substrate comprising the steps of:

2. The workpiece is manufactured so that the crystal face {001} of the β-gallium oxide is exposed on the surface thereof, 2. The method for manufacturing a β-gallium oxide substrate as described in claim 1, wherein in the separation layer formation step, the following steps are alternately repeated: irradiating the workpiece with the laser beam while moving the workpiece and the focal point relatively along a predetermined direction such that the angle between the workpiece and the focal point is 35° or less with respect to a straight line parallel to the crystal orientation [100] of the β-gallium oxide; and moving the workpiece relative to the position where the focal point is formed along a direction perpendicular to the predetermined direction.

3. a preliminary separation layer forming step of forming a preliminary separation layer including a preliminary modified portion and a preliminary crack extending from the preliminary modified portion inside the workpiece by irradiating the workpiece with the laser beam so as to position the focal point at the predetermined depth from the surface of the workpiece; a step of determining the predetermined direction by referring to the extension direction of the preliminary crack after the preliminary separation layer forming step and before the separation layer forming step; The method for producing a β-gallium oxide substrate according to claim 2 , further comprising:

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