β-GALLIUM OXIDE SUBSTRATION PROCESS

Abstract

A β-gallium oxide substrate manufacturing process for producing a substrate from a workpiece formed from β-gallium oxide includes a separation layer formation step with the application of a laser beam of such a wavelength that it is transmitted through the β-gallium oxide to the workpiece, wherein a focal point of the laser beam is positioned from a front surface of the workpiece at a predetermined depth in order to form a separation layer within the workpiece which has a modified part and a crack extending from the modified part, and after the separation layer formation step a separation step in which an external force is applied to the workpiece in order to separate the substrate from the workpiece with the separation layer as the starting point.

Description

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0001] The present invention relates to a β-gallium oxide substrate manufacturing method for manufacturing a substrate from a workpiece formed of β-gallium oxide. DESCRIPTION OF THE RELATED PRIOR ART

[0002] In gallium oxide (Ga2O3), which exhibits crystal polymorphism, the monoclinic β-phase (β-gallium oxide: β-Ga2O3) is the most stable phase. β-gallium oxide is a wide-gap semiconductor with a gap of approximately 4.8 eV (see, for example, Japanese Patent Application Laid-Open No. 2007-254174 A). Therefore, β-gallium oxide is intended as a raw material for semiconductor devices, such as power components.

[0003] Generally, semiconductor devices are formed using a disk-shaped substrate. The substrate is manufactured, for example, by cutting a workpiece, such as a cylindrical block called an ingot, so that a portion of a predetermined thickness contained within the workpiece is separated from the workpiece using a wire saw (see, for example, Japanese Unexamined Patent Application Laid-Open No. 2016-13929 A). SUMMARY OF THE INVENTION

[0004] For example, for the formation of semiconductor devices, a substrate with a thickness of approximately 150 μm is used. Furthermore, the thickness of the wire saw is approximately 300 μm. Therefore, when the substrate is produced from the workpiece using the wire saw, 60% to 70% of the workpiece is discarded as cutting allowance, resulting in low productivity.

[0005] Against this background, it is an object of the present invention to provide a manufacturing method for β-gallium oxide substrates with which the productivity in manufacturing a substrate from a workpiece formed of β-gallium oxide can be improved.

[0006] According to one aspect of the present invention, there is provided a β-gallium oxide substrate manufacturing method for manufacturing a substrate from a workpiece formed of β-gallium oxide. The method includes a separation layer forming step in which a laser beam having a wavelength such that it is transmitted through the β-gallium oxide to the workpiece is applied in a state where a focal point at which the laser beam is converged is positioned at a predetermined depth from a front surface of the workpiece to form a separation layer having a modified part and a crack extending from the modified part within the workpiece, and, after the separation layer forming step, a separation step in which an external force is applied to the workpiece to thereby separate the substrate from the workpiece with the separation layer as a starting point.

[0007] In the present invention, it is further preferable that the workpiece is manufactured such that a crystal plane {001} of β-gallium oxide is exposed on the front surface, and that in the separation layer forming step, the application of the laser beam to the workpiece while the workpiece and the focal point are moved relative to each other in a predetermined direction forming an angle of not more than 35° relative to a straight line parallel to a crystal orientation

[100] of β-gallium oxide, and the relative movement of the workpiece and a position at which the focal point is formed in a direction perpendicular to the predetermined direction are alternately repeated.In addition, it is preferable that the method for producing β-gallium oxide substrates of the present invention further includes a preliminary release layer forming step of applying the laser beam to the workpiece so that the focal point is positioned at the predetermined depth from the front surface of the workpiece, to thereby form a preliminary release layer having a preliminary modified part and a preliminary crack extending from the preliminary modified part inside the workpiece, and after the preliminary release layer forming step but before the release layer forming step, a specifying step of referring to an extending direction of the preliminary crack to thereby specify the predetermined direction.

[0008] In the present invention, after the release layer including the modified portion and the crack extending from the modified portion is formed within the workpiece, the substrate is separated from the workpiece using the release layer as a starting point. As a result, the productivity of the substrate can be improved compared to the case of manufacturing the substrate from the workpiece using a wire saw.

[0009] The above and other objects, features and advantages of the present invention, as well as the modes for carrying them out, will become more apparent and the invention itself will be best understood by studying the following description and the appended claims with reference to the attached drawings which show a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a perspective view schematically illustrating an example of an ingot formed of β-gallium oxide; Fig. 1B is a side view showing the Fig. 1A schematically represents the ingot shown; Fig. 2 is a flow chart showing an example of a β-gallium oxide substrate manufacturing process for producing a substrate from the material described in Fig. 1A and Fig. 1B schematically shows the ingot shown; Fig. Fig. 3 is a perspective view schematically illustrating the manner of a separation layer forming step shown in Fig. 2 is shown; Fig. 4 is a diagram illustrating a relationship between an angle formed by a scanning direction of a laser beam relative to a straight line parallel to a crystal orientation

[100] of β-gallium oxide and a width of a crack in a direction perpendicular to the scanning direction of the laser beam; Fig. 5A is a side view showing one way of Fig. schematically shows the separation step shown in Figure 2; Fig. Figure 5B is a side view showing the manner in Fig. 2 schematically illustrates the separation step; and Fig. 6 is a flowchart schematically illustrating an example of a β-gallium oxide substrate manufacturing process for producing a substrate from an ingot whose precise crystal orientations are not previously detected. DETAILED EXPLANATION OF THE PREFERRED EMBODIMENT

[0010] An embodiment of the present invention will be described with reference to the attached drawings. Fig. Figure 1A is a perspective view schematically illustrating an example of an ingot formed from β-gallium oxide. Fig. 1B is a side view showing the Fig. 1A. It should be noted that in the Fig. 1A and Fig. 1B also shows the crystal planes of the β-gallium oxide belonging to the ingot. In addition, Fig. 1B also shows the crystal orientations of β-gallium oxide.

[0011] The crystal structure of β-gallium oxide is a monoclinic, in which the angle formed between a crystal orientation

[100] (a-axis) and a crystal orientation

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

[010] (b-axis) and the respective crystal orientation

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

[001] (c-axis) is 90°. Fig. 1A and Fig. The ingot 11 shown in Fig. 1B has a front surface 11a and a back surface 11b that are parallel to each other, and a crystal plane {001} is exposed on the front surface 11a and the back surface 11b, respectively (for the sake of simplicity, the plane exposed on the front surface 11a is made the crystal plane (001) here).

[0012] It should be noted that although the ingot 11 is manufactured with the crystal plane {001} exposed on the front surface 11a or the back surface 11b, respectively, a plane slightly inclined with respect to the crystal plane {001} may be exposed on the front surface 11a or the back surface 11b due to a processing error or the like during manufacturing. Specifically, a plane having an angle of no more than 1° to the crystal plane {001} may be exposed on the front surface 11a or the back surface 11b of the ingot 11.

[0013] In addition, a side surface 11c of the ingot 11 is formed with two flat parts, namely a primary alignment plane 13 and a secondary alignment plane 15, which indicate crystal orientations of the β-gallium oxide. The primary alignment plane 13 is longer than the secondary alignment plane 15 and is formed to be positioned in the crystal orientation

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

[0014] Furthermore, the secondary alignment plane 15 is formed to be positioned in the crystal orientation

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

[0015] It should be noted that one or both of the primary alignment plane 13 and the secondary alignment plane 15 may not be formed in the side surface 11c of the ingot 11. Furthermore, instead of the primary alignment plane 13 and the secondary alignment plane 15, the side surface 11c of the ingot 11 may be formed with one or more notches indicating the crystal orientation or orientations of the β-gallium oxide.

[0016] Fig. Figure 2 is a flowchart schematically illustrating an example of the β-gallium oxide substrate manufacturing process for manufacturing a substrate from the ingot 11, which is the workpiece. In this process, first, a release layer having a modified portion and a crack extending from the modified portion is formed within the ingot 11 (release layer forming step S1).

[0017] Fig. Fig. 3 is a perspective view schematically illustrating a manner of the separation layer forming step S1. Note that an X-axis direction and a Y-axis direction shown in Fig. 3 are directions perpendicular to each other in a horizontal plane, and that a Z-axis direction is a direction (vertical direction) perpendicular to both the X-axis direction and the Y-axis direction.

[0018] The separation layer formation 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 substantially parallel to a horizontal plane and capable of holding the ingot 11 on the holding surface.

[0019] The chuck table 4 is connected to a suction mechanism (not shown). The suction mechanism includes, for example, an ejector or the like. When the suction mechanism is actuated, a suction force acts in a space surrounding the holding surface of the chuck table 4. Thus, when the suction mechanism is actuated in a state where the ingot 11 is placed on the holding surface, the ingot 11 is held on the holding surface of the chuck table 4.

[0020] In addition, the chuck table 4 is connected to a rotation mechanism (not shown). The rotation mechanism includes, for example, a disk, a motor, or the like. When the rotation mechanism is actuated, the chuck table 4 is rotated, with a straight line passing through the center of the holding surface and extending along the Z-axis direction as the rotation axis. For example, the rotation mechanism rotates the chuck table 4 so that the secondary alignment plane 15 of the ingot 11 held on the holding surface of the chuck table 4 becomes parallel to the X-axis direction.

[0021] On the upper side of the chuck table 4, a head 8 of a laser beam application unit 6 is provided. The head 8 is provided at a head portion of a cylindrical housing 10 extending in the Y-axis direction. Note that 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, while the housing 10 houses an optical system such as a mirror and / or a lens.

[0022] A base end portion of the housing 10 is connected to a moving mechanism. The moving mechanism includes, for example, a ball screw, a motor, and the like. When the moving mechanism is actuated, the housing 10 is moved along the X-axis direction, the Y-axis direction, and / or the Z-axis direction. Furthermore, the laser beam application unit 6 includes, for example, an unillustrated laser oscillator using Nd:YAG or the like as the laser medium.

[0023] The laser oscillator generates a pulsed laser beam with a wavelength (e.g., 1064 nm) that is transmitted through the β-gallium oxide (e.g., a pulsed laser beam with a frequency of 30 kHz and a pulse width of 4 ns). The laser beam's output (power) is adjusted by an attenuator and is then emitted directly downward from the head 8 through the optical systems housed in the housing 10 and the head 8.

[0024] Furthermore, an imaging unit 12 is provided on a side part of the housing 10, which is capable of imaging an area directly below the imaging unit 12. The imaging unit 12 includes, for example, a light source, such as a light-emitting diode (LED), which emits light of a wavelength such that it is transmitted through the β-gallium oxide (for example, visible light), a lens, and an imaging element, such as a charge-coupled device image sensor (CCD) and a complementary metal oxide semiconductor image sensor (CMOS).

[0025] When the laser processing apparatus 2 performs the separation layer formation step S1, the ingot 11 is first placed on the support surface of the chuck table 4 with the front surface 11a facing upward. Subsequently, the suction mechanism is actuated so that the ingot 11 is held by the chuck table 4. Subsequently, the imaging unit 12 is actuated to form an image of the front surface 11a of the ingot 11.

[0026] Referring to this figure, the rotation mechanism rotates the chuck table 4 so that, for example, the secondary alignment plane 15 becomes parallel to the X-axis direction. In other words, the rotation mechanism rotates the chuck table 4 so that the

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

[010] crystal orientation becomes parallel to the Y-axis direction.

[0027] Next, the moving mechanism moves the housing 10 along the X-axis direction and / or the Y-axis direction in such a manner that a portion of the ingot 11 slightly spaced inward from the secondary alignment plane 15 is positioned in the X-axis direction in the plan view of the head 8.

[0028] Subsequently, the moving mechanism moves the housing 10 along the Z-axis direction so that the focal point onto which the laser beam emitted by the head 8 is focused is positioned at a predetermined depth from the front surface 11a of the ingot 11. Note that the predetermined depth corresponds, for example, to the thickness of the substrate to be manufactured from the ingot 11.

[0029] Next, while the laser beam is emitted from the head 8, the moving mechanism moves the housing 10 along the X-axis direction in such a way that the focal point where the laser beam is converged moves from one end to the other in the X-axis direction of the ingot 11 at a predetermined speed (for example, 450 mm / s). In other words, the laser beam is applied to the ingot 11 in a direction along a straight line parallel to the

[100] crystal orientation of β-gallium oxide, which represents a scanning direction of the laser beam.

[0030] As a result, a modified portion 17 is formed inside the ingot 11, in which the crystal structure of β-gallium oxide is disordered, with the focal point onto which the laser beam is focused forming a center. Furthermore, 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. The internal stress is relieved by the expansion of a crack from the modified portion 17.

[0031] It should be noted that in β-gallium oxide, the crystal plane (100) is the most easily cleaved, and the crystal plane (001) is the second most easily cleaved. Therefore, when the modified portion 17 is formed inside the ingot 11, many cracks extending 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 (particularly in a straight line along the crystal orientation

[100] of β-gallium oxide).

[0032] Next, the moving mechanism moves the housing 10 by a predetermined adjustment amount (for example, 0.2 mm) along the Y-axis direction in such a manner that the head 8 is positioned in the plan view in the X-axis direction from an area slightly farther from the secondary alignment plane 15 than an area that has already been irradiated with the laser beam.

[0033] Subsequently, the laser beam is applied to the ingot 11 as described above, with the scanning direction of the laser beam opposite to the X-axis direction. Furthermore, the above-mentioned operations are repeated until the laser beam is applied to a region of the ingot 11 farthest from the secondary alignment plane 15 is completed.

[0034] In other words, the relative movement of the ingot 11 and the position for forming the focus position where the laser beam is converged (specifically, the movement of the housing 10) along the Y-axis direction and the application of the laser beam to the ingot 11 with the X-axis direction or the direction opposite to the X-axis direction as the scanning direction of the laser beam are alternately repeated. As a result, the separation layer formation step S1 is completed.

[0035] It should be noted that in the above-described separation layer forming step S1, the direction parallel to the crystal orientation

[100] of the β-gallium oxide (the X-axis direction or the direction opposite to the X-axis direction) is set as the scanning direction of the laser beam, but a direction non-parallel to the crystal orientation

[100] may be set as the scanning direction of the laser beam.

[0036] However, it should be noted that when the scanning direction of the laser beam is parallel to the crystal orientation

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

[010] may increase. In the case where 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 of manufacturing the substrate from the ingot 11 decreases.

[0037] Furthermore, in this case, the proportion of cracks extending along the crystal plane (001), that is, the cracks extending parallel to the front surface 11a of the ingot 11, decreases, and thus the width of the separation layer (the length of the separation layer in a direction perpendicular to both the thickness direction of the ingot 11 and the scanning direction of the laser beam) formed inside the ingot 11 is reduced. Therefore, in this case, the above-mentioned angle should be reduced, and the throughput in the laser processing apparatus 2 is reduced.

[0038] Taking these points into consideration, in order to increase the productivity and throughput in the production of the substrate from the ingot 11, it is preferable to adjust the scanning direction of the laser beam so that the angle formed relative to a straight line parallel to the crystal orientation

[010] of the β-gallium oxide is increased, that is, the angle formed relative to a straight line parallel to the crystal orientation

[100] is decreased.

[0039] Fig. Figure 4 is a diagram illustrating the widths of the separation layers formed when the laser beam is applied under several conditions different in the scanning direction relative to a workpiece formed of β-gallium oxide, which is manufactured such that the crystal plane (001) is exposed on the front surface. In particular, in Fig. 4 shows a relationship between the angle formed by the scanning direction of the laser beam relative to a straight line parallel to the crystal orientation

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

[0040] As in Fig. As shown in Figure 4, the width of the separation layer is increased when the angle formed by the scanning direction of the laser beam relative to a straight line parallel to the crystal orientation

[100] of the β-gallium oxide is not more than 35°. Therefore, in the separation layer forming step S1, it is preferable to adjust the scanning direction of the laser beam so that the angle is not more than 35°. Referring to Fig. 4, it is even more preferable to set the scanning direction of the laser beam so that the angle is not more than 10°, and most preferably, the scanning direction of the laser beam is set so that the angle is not more than 5°.

[0041] Furthermore, in the separation layer forming step S1, the laser beam may be applied to the ingot 11 only along one direction (for example, the X-axis direction). In other words, in the separation layer forming step S1, the laser beam may be applied to the ingot 11 repeatedly with the one direction as the scanning direction of the laser beam, without assuming 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.

[0042] After the separation layer formation step S1, the substrate is separated from the ingot 11, with the separation layer serving as the starting point (separation step S2). Fig. 5A and Fig. 5B are side views schematically illustrating a manner of the separating step S2. The separating step S2 is performed by a separating device 14. The separating device 14 includes a clamping table 16 having a similar structure to that shown in Fig. 3 shown clamping table 4.

[0043] 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 or the like. When the table-side suction mechanism is actuated, a suction force acts in a space near a holding surface of the chuck table 16. Consequently, when the table-side suction mechanism is actuated in a state where the ingot 11 is placed on the holding surface, the ingot 11 is held on the holding surface of the chuck table 16.

[0044] A separating unit 18 is provided on the upper side of the clamping table 16. The separating unit 18 has a suction plate 20, the lower surface of which is formed with a plurality of suction ports. The plurality of suction ports communicate with a separating unit-side suction mechanism, such as a vacuum pump, via a suction channel formed within the suction plate 20. When the separating unit-side suction mechanism is actuated, a suction force acts in a space near the lower surface of the suction plate 20.

[0045] In addition, a vertical movement mechanism 22 is connected to an upper surface of the suction plate 20. The vertical movement mechanism 22 includes, for example, a ball screw, a motor, and the like. When the vertical movement mechanism 22 is actuated, the suction plate 20 is moved in the vertical direction.

[0046] When the separating device 14 performs the separation step S2, first, in a state where the chuck table 16 and the suction plate 20 are sufficiently spaced apart from each other, the ingot 11 with a separation layer 19 formed inside it is placed on the holding surface of the chuck table 16 so that the front surface 11a of the ingot 11 faces upward. Subsequently, the table-side suction mechanism is actuated so that the ingot 11 is held by the chuck table 16.

[0047] Next, the vertical movement mechanism lowers the suction plate 20 so that the lower surface of the suction plate 20 is brought into contact with the front surface 11a of the ingot 11 (see Fig. 5A). Subsequently, the separating unit-side suction mechanism is actuated so that the front surface 11a of the ingot 11 is sucked upward. Next, the vertical movement mechanism lifts the suction plate 20 so that the suction plate 20 is spaced from the clamping table 16 (see Fig. 5B).

[0048] As a result, such an external force that separates the front surface 11a and the rear surface 11b of the ingot 11 is exerted on the ingot 11, causing the cracks contained in the separation layer 19 to further extend. As a result, the ingot 11 is separated at the separation layer 19, and a substrate 21 is produced. Through these processes, the separation step S2, that is, the Fig. 2, the substrate manufacturing process is completed.

[0049] In the Fig. In the substrate manufacturing method illustrated in Figure 2, after the separation layer 19 including the modified portion 17 and the cracks extending from the modified portion 17 is formed within the ingot 11, 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 of manufacturing the substrate 21 from the ingot 11 using a wire saw.

[0050] It should be noted that the content of the present description represents an embodiment of the present invention, and the present invention is not limited to the content of the present description. For example, in the separation layer formation step S1, it is sufficient if the ingot 11 and the focal point where the laser beam is focused can be moved relative to each other, and the structure thereof is not limited in any way.

[0051] In particular, the separation layer forming step S1 may be performed by a laser processing apparatus provided with moving mechanisms for moving the chuck table 4 in the X-axis direction, the Y-axis direction and / or the Z-axis direction.

[0052] Alternatively, the separation layer forming step S1 may be performed by using a laser processing apparatus having a laser beam application unit 6 provided with an optical scanning system capable of changing the direction of a laser beam emitted from a head 8. Note that the optical scanning system includes, for example, a galvano scanner, an acousto-optic device (AOD), a polygon mirror, and / or the like.

[0053] Furthermore, in the separation step S2, an ultrasonic vibration may be applied to the ingot 11 as an external force for forming the substrate 21. In other words, in the separation step S2, the ultrasonic vibration may be applied to the front surface 11a side of the ingot 11 instead of or before applying such an external force that separates the front surface 11a side and the back surface 11b side of the ingot 11 from each other.

[0054] In addition, the workpiece used for the preparation of the β-gallium oxide substrate may be an ingot prepared such that a crystal plane other than the {001} crystal plane (for example, the (100) crystal plane) of the β-gallium oxide is exposed on the front surface.

[0055] Furthermore, the workpiece to be used for producing the β-gallium oxide substrate can be, for example, a bare wafer having a thickness of 2 to 5 times the thickness of the substrate to be produced. It should be noted that the bare wafer is produced by separating it from the ingot 11, for example, by a process similar to the process described above. In this case, the substrate can be said to be produced by repeating the process described above twice.

[0056] Furthermore, the workpiece used for fabricating the β-gallium oxide substrate may be a device wafer fabricated by forming semiconductor devices on a surface of the bare wafer. In this case, the laser beam is preferably applied to the device wafer from a side of the device wafer on which the semiconductor devices are not formed to prevent the laser beam from adversely affecting the semiconductor devices.

[0057] In addition, the workpiece to be used for the preparation of the β-gallium oxide substrate may be an ingot manufactured with the crystal plane {001} of the β-gallium oxide exposed on the front surface, but whose precise crystal orientations are not known in advance. Fig.6 is a flowchart schematically illustrating an example of a β-gallium oxide substrate manufacturing process for manufacturing a substrate from such a workpiece as mentioned above.

[0058] In this method, first, a preliminary separation layer including a preliminary modified portion and preliminary cracks extending from the preliminary modified portion is formed inside the ingot (preliminary separation layer formation step S3). The preliminary separation layer formation step S3 is performed, for example, using the laser processing apparatus 2 described above.

[0059] When the laser processing apparatus 2 performs the preliminary separation layer formation step S3, the ingot is first placed on the holding surface of the chuck table 4 with the front surface of the ingot facing upward. Subsequently, the suction mechanism is actuated so that the ingot is held by the chuck table 4. Subsequently, the moving mechanism moves the housing 10 along the X-axis direction and / or in the Y-axis direction so that the head 8 is positioned directly above the ingot.

[0060] Next, the moving mechanism moves the housing 10 along the Z-axis direction so that the focal point onto which the laser beam emitted by the head 8 is focused is positioned at a predetermined depth from the front surface of the ingot. Note that the predetermined depth corresponds to the thickness of the substrate to be fabricated from the ingot.

[0061] The laser beam is then emitted from the head 8. In this case, the movement mechanism can move the housing 10 so that the focal point where the laser beam is focused is moved or not. As a result, the preliminary modified part, in which the crystal structure of β-gallium oxide is disordered, is formed inside the ingot, with the focal point where the laser beam is focused at the center.

[0062] In addition, when the preliminarily modified part is formed inside the ingot, preliminarily cracks extend from the preliminarily modified part. In this case, the crystal plane (100) of β-gallium oxide is the easiest to cleave. Therefore, the preliminarily cracks extend mainly along the crystal plane (100). As a result, the preliminarily separation layer, which includes the preliminarily modified part and the preliminarily cracks extending from the preliminarily modified part, is formed inside the ingot.

[0063] After the preliminary separation layer forming step S3, but before the separation layer forming step S1, the extension direction of the preliminary cracks is referenced, and the scanning direction of the laser beam in the separation layer forming step S1 is specified (specifying step S4). In the specifying step S4, the moving mechanism first moves the housing 10 along the X-axis direction and / or the Y-axis direction in such a way that the imaging unit 12 is positioned directly above the preliminary separation layer.

[0064] Next, the imaging unit 12 is operated to form an image of the preliminary separation layer. In other words, the preliminary separation layer is imaged from a direction perpendicular to the crystal plane (001) of β-gallium oxide. If the cracks contained in the preliminary separation layer extend along the crystal plane (100), the preliminary cracks are included in the image mainly as cracks extending parallel to the crystal orientation

[010] .

[0065] Subsequently, referring to the extension direction of the preliminary cracks in this image, a direction perpendicular to the extension direction is set as the scanning direction of the laser beam in the separation layer formation step S1. Consequently, a direction having an angle of no more than 35° relative to a straight line parallel to the

[100] crystal orientation of β-gallium oxide can be set as the scanning direction of the laser beam.

[0066] Apart from the above points, structures, methods and the like relating to the above-described embodiment may be modified as necessary in carrying out the present invention, provided that the modifications do not depart from the scope of the subject invention.

[0067] The present invention is not limited to the details of the preferred embodiment described above. The scope of the invention is defined by the appended claims, and all changes and modifications that fall within the equivalent scope of the claims are therefore encompassed by the invention. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2007- 254 174 A

[0002] JP 2016-13 929 A

[0003]

Claims

[1] A β-gallium oxide substrate manufacturing method for manufacturing a substrate from a workpiece formed of β-gallium oxide, the β-gallium oxide substrate manufacturing method comprising: a separation layer forming step comprising applying a laser beam of such a wavelength that it is transmitted through the β-gallium oxide to the workpiece in a state where a focal point at which the laser beam is converged is positioned at a predetermined depth from a front surface of the workpiece, to form, within the workpiece, a separation layer having a modified part and a crack extending from the modified part; and after the separation layer forming step, a separation step in which an external force is applied to the workpiece to thereby separate the substrate from the workpiece, with the separation layer serving as a starting point. [2] A β-gallium oxide substrate manufacturing method according to claim 1, wherein the workpiece is manufactured such that a crystal plane {001} of the β-gallium oxide is exposed on the front surface, and, in the separation layer forming step, applying the laser beam to the workpiece while moving the workpiece and the focal point relative to each other in a predetermined direction forming an angle of not more than 35° relative to a straight line parallel to a crystal orientation [100] of the β-gallium oxide, and alternately repeating the relative movement of the workpiece and a position at which the focal point is formed in a direction perpendicular to the predetermined direction. [3] The β-gallium oxide substrate manufacturing method according to claim 2, further comprising: a preliminary separation layer forming step of applying the laser beam to the workpiece in such a manner that the focal point is positioned at the predetermined depth from the front surface of the workpiece, to thereby form within the workpiece a preliminary separation layer including a preliminary modified part and a preliminary crack extending from the preliminary modified part; and after the preliminary separation layer forming step but before the separation layer forming step, a specifying step of referring to an extending direction of the preliminary crack to thereby specify the predetermined direction.

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