Manufacturing method of substrate

Abstract

To provide a manufacturing method of a substrate capable of improving productivity of a substrate when manufacturing the substrate, from a workpiece containing gallium oxide as a raw material, which is thinner than the workpiece.SOLUTION: A manufacturing method of a substrate includes: a separate layer forming step of relatively moving a workpiece and a focal point of a laser beam having a wavelength transmittable through gallium oxide and repeating pulse-shaped output so as to be orthogonal to a thickness direction of the workpiece in a state where the focal point is positioned inside of the workpiece, thereby forming a separate layer including a plurality of modified parts aligned in a direction of movement, in which the focal point moves with respect to the workpiece, and cracks extending from the plurality of modified parts inside of the workpiece; and cleavage step of cleaving the workpiece in the separate layer after the separate layer forming step, thereby manufacturing the substrate.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a substrate that manufactures a substrate thinner than a workpiece from a workpiece made of gallium oxide.

Background Art

[0002] Gallium oxide (Ga 2 O 3 ) is a wide-gap semiconductor with a bandgap of about 4.8 eV (see, for example, Patent Document 1). Therefore, gallium oxide is expected to be used as a substrate for forming semiconductor devices such as power devices. This substrate is manufactured, for example, by cutting a columnar workpiece called an ingot using a wire saw (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] For forming a semiconductor device, for example, a substrate having a thickness of about 150 μm is used. Also, the thickness of the 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 waste, and its productivity is low.

[0005] In view of this point, an object of the present invention is to provide a method for manufacturing a substrate capable of improving the productivity of the substrate when manufacturing a substrate thinner than a workpiece from a workpiece made of gallium oxide.

Means for Solving the Problems

[0006] According to the present invention, there is provided a method for manufacturing a substrate by manufacturing a substrate thinner than a workpiece made of gallium oxide from the workpiece, including a separation layer forming step of forming, inside the workpiece, a separation layer including a plurality of modified portions arranged along a moving direction in which the condensing point of a laser beam having a wavelength that penetrates the gallium oxide and repeating a pulsed output moves with respect to the workpiece, and cracks extending from each of the plurality of modified portions, by relatively moving the workpiece and the condensing point in a direction orthogonal to the thickness direction of the workpiece with the condensing point positioned inside the workpiece; and a splitting step of manufacturing the substrate by splitting the workpiece at the separation layer after the separation layer forming step, wherein a value obtained by dividing a center distance between a pair of adjacent modified portions in the moving direction among the plurality of modified portions by lengths of each of one side and the other side of the pair of modified portions in the moving direction is 1.63 or more and 2.73 or less.

[0007] Furthermore, in the present invention, it is preferable that the value is 1.94 or more and 2.43 or less, and more preferably 2.11 or more and 2.33 or less.

[0008] In addition, the method for manufacturing a substrate of the present invention further includes a preliminary modification portion forming step of forming, inside the workpiece, a preliminary modification portion by irradiating the workpiece with the laser beam with the condensing point positioned inside the workpiece so that the laser beam irradiated to the workpiece in the separation layer forming step and the pulse energy are equal; and a measurement step of measuring a reference length in the moving direction of the preliminary modification portion after the preliminary modification portion forming step and before the separation layer forming step, and it is preferable that irradiation conditions of the laser beam in the separation layer forming step are set so that the center distance is 1.63 times or more and 2.73 times or less the reference length.

Advantages of the Invention

[0009] In the present invention, after forming a separation layer including a plurality of modified portions and cracks extending from each of the plurality of modified portions inside a workpiece, the substrate is manufactured by splitting the workpiece at the separation layer. In this case, the productivity of the substrate can be improved as compared with the case where the substrate is manufactured from the workpiece by cutting the workpiece using a wire saw.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0011] Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1(A) is a perspective view schematically showing an example of an ingot made of gallium oxide (here, β-phase gallium oxide), and FIG. 1(B) is a side view schematically showing the ingot shown in FIG. 1(A). In FIGS. 1(A) and 1(B), the crystal planes of gallium oxide contained in this ingot are also shown. Further, in FIG. 1(B), the crystal orientation of this gallium oxide is also shown.

[0012] The crystal structure of β-phase gallium oxide is a monoclinic crystal in which the angle formed by the crystal orientation

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

[0001] (c-axis) is 103.7°, and the angles formed by the crystal orientation

[0010] (b-axis) with the crystal orientations

[0100] (a-axis) and

[0001] (c-axis) are each 90°. And the ingot 11 shown in FIGS. 1(A) and 1(B) has parallel front surface 11a and back surface 11b, and the crystal plane {001} is exposed on each of the front surface 11a and the back surface 11b (here, for convenience, the surface exposed on the front surface 11a is taken as the crystal plane (001).).

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

[0014] Also, on the side surface 11c of the ingot 11, two flat portions for indicating the crystal orientation of gallium oxide are formed, that is, a primary orientation flat 13 and a secondary orientation flat 15. And 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] Further, 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 obtuse angle formed between the crystal plane (100) and the front surface 11a or the back surface 11b is 103.7°, and the secondary orientation flat 15 is orthogonal to the secondary orientation flat 15.

[0016] Note that 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. Further, instead of the primary orientation flat 13 and the secondary orientation flat 15, a notch for indicating the crystal orientation of gallium oxide may be formed on the side surface 11c of the ingot 11.

[0017] FIG. 2 is a flowchart schematically showing an example of a method for manufacturing a substrate thinner than the ingot 11 from the ingot 11 to be a workpiece. In this method, first, a separation layer is formed inside the ingot 11 (separation layer forming step S1).

[0018] FIG. 3 is a perspective view schematically showing the state of the separation layer forming step S1. The X-axis direction and the Y-axis direction shown in FIG. 3 are directions orthogonal to each other on a horizontal plane, and the Z-axis direction is a direction (vertical direction) orthogonal to each of the X-axis direction and the Y-axis direction.

[0019] This separation layer forming step S1 is carried out 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 this holding surface.

[0020] The chuck table 4 is connected to a suction mechanism (not shown). This suction mechanism has, for example, an ejector or the like. 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] Also, the chuck table 4 is connected to a rotation mechanism (not shown). This rotation mechanism has, for example, a pulley and a motor or the like. When the rotation mechanism operates, the chuck table 4 rotates about a straight line passing through the center of the holding surface and along the Z-axis direction as the rotation axis. 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] Above the chuck table 4, a head 8 of the laser beam irradiation unit 6 is provided. 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. This moving mechanism has, for example, a ball screw and a motor or the like. When the moving mechanism operates, the housing 10 moves along the X-axis direction, the Y-axis direction, and / or the Z-axis direction. Also, the laser beam irradiation unit 6 has, for example, a laser oscillator (not shown) containing Nd:YAG or the like as a laser medium.

[0024] This laser oscillator has a wavelength (e.g., 1064 nm) that penetrates β-phase gallium oxide and generates a laser beam (e.g., a laser beam with a frequency of 30 kHz and a pulse width of 4 ns) that repeats a pulsed output (power). Then, after the output of this laser beam is adjusted by an attenuator, it is emitted downward directly from the head 8 through an optical system housed in the housing 10 and 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. This imaging unit 12 has, for example, a light source such as an LED (Light Emitting Diode) that emits light with a wavelength that penetrates β-phase gallium oxide (e.g., visible light), 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 so that the surface 11a faces upward. Next, the suction mechanism is operated so that the ingot 11 is held on the holding surface of the chuck table 4. Next, the imaging unit 12 is operated to image the surface 11a of the ingot 11 and form an image.

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

[0100] of β-phase 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 direction and / or the Y-axis direction so that a region slightly inside from the secondary orientation flat 15 of the ingot 11 is positioned in the X-axis direction as viewed in a plan view from the head 8. Next, the moving mechanism moves the housing 10 along the Z-axis direction so that the condensing point of the laser beam emitted from the head 8 is positioned inside the ingot 11.

[0029] Next, while emitting a laser beam from the head 8, the moving mechanism moves the housing 10 along the X-axis direction at a predetermined speed (processing feed speed) so that the condensing point of the laser beam passes from one end to the other end of the ingot 11 in the X-axis direction. That is, the laser beam is irradiated onto the ingot 11 with the crystal orientation

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

[0030] As a result, pulse energy of the laser beam is applied to each of a plurality of points included in the ingot 11 (specifically, a plurality of points arranged along the X-axis direction and each overlapping with the condensing point of the laser beam that repeats a pulsed output). As a result, a plurality of portions (a plurality of modified portions) 17 in which the crystal structure of the β-phase gallium oxide is disturbed are formed around each of the plurality of points. That is, a plurality of modified portions 17 arranged along the moving direction (specifically, the X-axis direction) in which the condensing point of the laser beam moves with respect to the ingot 11 are formed inside the ingot 11.

[0031] FIG. 4 is a plan view schematically showing the plurality of modified portions 17 formed inside the ingot 11 in this way. In FIG. 4, for the sake of convenience, circular modified portions 17a, 17b, 17c, 17d are shown in a plan view, but the modified portions 17a, 17b, 17c, 17d may be non-circular (for example, elliptical) in a plan view.

[0032] When a plurality of modified portions 17 are formed inside the ingot 11, the volume of the ingot 11 expands and internal stress is generated in the ingot 11. This internal stress is relaxed by cracks extending from each of the plurality of modified portions 17. As a result, a plurality of modified portions 17 arranged along the X-axis direction, that is, the crystal orientation

[0100] of β-phase gallium oxide, and cracks extending from each of the plurality of modified portions 17 are formed inside the ingot 11.

[0033] Here, when the center-to-center distance I between a pair of adjacent modified portions (for example, modified portion 17b and modified portion 17c) in the X-axis direction among the plurality of modified portions 17 is too short or too long, the cracks formed inside the ingot 11 tend to be short. That is, in these cases, the component along the Y-axis direction of the cracks extending from each of the plurality of modified portions 17 also tends to be small.

[0034] Specifically, when the center-to-center distance I is too short, most of the internal stress is released by cracks extending so as to connect the modified portion 17b and the modified portion 17c, so the cracks formed inside the ingot 11 tend to be short. Also, when the center-to-center distance I is too long, only the internal stress generated with the formation of the modified portion 17b contributes to the formation of the cracks extending from each modified portion (for example, modified portion 17b). That is, since the influence of the internal stress generated with the formation of the modified portions 17a and 17c adjacent to the modified portion 17b does not affect the cracks, the cracks extending from the modified portion 17b tend to be short.

[0035] Further, if the pulse energy of the laser beam increases, the sizes of the modified portion 17b and the modified portion 17c, for example, the length L along the X-axis direction thereof, increase, and the internal stress generated around each of the modified portion 17b and the modified portion 17c also increases. And when the internal stress generated around these increases, the cracks are less likely to be short even when the center-to-center distance I is long. On the other hand, when the center-to-center distance I is short, the cracks tend to be short based on the length L along the X-axis direction of each of the modified portion 17b and the modified portion 17c.

[0036] Therefore, in order to increase the component along the Y-axis direction of the cracks extending from each of the modification parts 17b and 17c, it is important to set the ratio of the center distance I to the length L along the X-axis direction of each of the modification parts 17b and 17c to an appropriate ratio, that is, to set the value I / L obtained by dividing the center distance I by the length L to an appropriate value.

[0037] FIG. 5 is a graph showing the relationship between the crack length and the value I / L obtained by dividing the center distance I by the length L. Specifically, FIG. 5 is a graph based on data obtained by evaluating a plurality of modification parts formed inside the ingot 11 and the cracks extending from each of the plurality of modification parts under a plurality of conditions in which each of the output of the laser beam and the machining feed rate when irradiating the ingot 11 with the laser beam is different.

[0038] Note that this data is data obtained when the output of the laser beam is 0.75W, 1W, 1.25W, or 1.5W. Further, in FIG. 5, the value obtained by normalizing the length of the crack formed inside the ingot 11 under each condition (specifically, the value obtained by dividing the length of the crack under each condition by the length of the largest crack (maximum crack length) among a plurality of conditions with the same output of the laser beam) is shown.

[0039] As shown in FIG. 5, the length of the crack formed inside the ingot 11 becomes the largest when the value I / L is about 2.22, becomes 90% or more of the maximum crack length when it is 2.11 or more and 2.33 or less, becomes 70% or more of the maximum crack length when it is 1.94 or more and 2.43 or less, and becomes 50% or more of the maximum crack length when it is 1.63 or more and 2.73 or less.

[0040] Based on this point, the irradiation of the laser beam on the ingot 11 described above is performed such that the component along the Y-axis direction of the crack extending from each of the plurality of modified portions 17 becomes large. Specifically, the irradiation of this laser beam is such that the value obtained by dividing the center distance between a pair of adjacent modified portions in the X-axis direction among the plurality of modified portions 17 by the length of each of the pair of modified portions in the X-axis direction is 1.63 or more and 2.73 or less, preferably 1.94 or more and 2.43 or less, more preferably 2.11 or more and 2.33 or less, and most preferably about 2.22.

[0041] Next, in a plan view, the moving mechanism moves the housing 10 along the Y-axis direction by a predetermined distance (index amount) so that the head 8 is positioned in the X-axis direction when viewed from a region slightly farther from the secondary orientation flat 15 than the region where the laser beam has already been irradiated.

[0042] Next, with the direction opposite to the X-axis direction as the scanning direction of the laser beam, the laser beam is irradiated on the ingot 11 as described above. Further, the above-described operation is repeated until the irradiation of the laser beam on the region of the ingot 11 farthest from the secondary orientation flat 15 is completed.

[0043] That is, the relative movement between the ingot 11 along the Y-axis direction and the position where the condensing point of the laser beam is formed (specifically, the movement of the housing 10) and the irradiation of the laser beam on the ingot 11 with the X-axis direction or the opposite direction thereof as the scanning direction of the laser beam are alternately repeated. As a result, a separation layer having a plurality of regions each extending along the X-axis direction and each including a plurality of modified portions 17 and cracks extending from each of the plurality of modified portions 17 is formed inside the ingot 11, and the separation layer forming step S1 is completed.

[0044] In the above-described separation layer forming step S1, the direction parallel to the crystal orientation <0100> of β-phase gallium oxide (the X-axis direction or the opposite direction) is set as the scanning direction of the laser beam. However, a direction non-parallel to this may also be set as the scanning direction of the laser beam.

[0045] Further, in the separation layer forming step S1, the irradiation of the laser beam on the ingot 11 may be performed only along one direction (for example, the X-axis direction). That is, in the separation layer forming step S1, the irradiation of the laser beam on the ingot 11 with the one direction as the scanning direction of the laser beam may be repeated without setting 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.

[0046] Further, in the separation layer forming step S1, the irradiation of the laser beam on the ingot 11 may be performed such that the locus drawn by the condensing point of the laser beam in the ingot 11 is spiral. That is, this irradiation of the laser beam may be performed, for example, while linearly moving the head 8 so as to bring the condensing point closer to the center from the outer periphery of the ingot 11 and rotating the chuck table 4 that holds the ingot 11.

[0047] After the separation layer forming step S1, a substrate is manufactured by splitting the ingot 11 at the separation layer (splitting step S2). Each of FIGS. 6(A) and 6(B) is a side view schematically showing the state of the splitting step S2. This splitting step S2 is performed in the suction force applying device 14. The suction force applying device 14 includes a chuck table 16 having the same structure as the chuck table 4 shown in FIG. 3.

[0048] 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 or the like. 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.

[0049] Above the chuck table 16, a separation unit 18 is provided. This separation unit 18 has a suction plate 20 with a plurality of suction ports formed on its lower surface. The plurality of suction ports communicate with a separation-unit-side suction mechanism such as a vacuum pump via a suction passage 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.

[0050] Also, a vertical movement mechanism 22 is connected to the upper surface of the suction plate 20. This vertical movement mechanism 22 has, for example, a ball screw and a motor or the like. When the vertical movement mechanism 22 operates, the suction plate 20 moves along the vertical direction.

[0051] When performing the splitting process S2 in the suction force applying device 14, first, with the chuck table 16 and the suction plate 20 sufficiently separated, the ingot 11 having a separation layer 19 formed therein is placed on the holding surface of the chuck table 16 with its surface 11a facing upward. Next, the table-side suction mechanism is operated so that the ingot 11 is held on the holding surface of the chuck table 16.

[0052] Next, the vertical movement mechanism lowers the suction plate 20 so that the lower surface of the suction plate 20 contacts the surface 11a of the ingot 11 (see Fig. 6(A)). Next, the separation-unit-side suction mechanism is operated so that the 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. 6(B)).

[0053] As a result, an external force that separates the front surface 11a side and the back surface 11b side of the ingot 11 is applied to the ingot 11, and the cracks included in the separation layer 19 further extend. As a result, the ingot 11 splits at the separation layer 19, and a substrate 21 thinner than the ingot 11 is manufactured. Thus, the splitting step S2, that is, the method for manufacturing the substrate shown in FIG. 2, is completed.

[0054] In the method for manufacturing a substrate shown in FIG. 2, after forming a separation layer 19 including a plurality of modified portions 17 and cracks extending from each of the plurality of modified portions 17 inside the ingot 11, the substrate 21 is manufactured by splitting the ingot 11 at the separation layer 19. In this case, the productivity of the substrate 21 can be improved as compared with the case where the substrate 21 is manufactured from the ingot 11 by cutting the ingot 11 using a wire saw.

[0055] Further, in this method, the separation layer 19 is formed inside the ingot 11 such that a value obtained by dividing the center distance between a pair of adjacent modified portions in the moving direction (for example, the X-axis direction) in which the condensing point of the laser beam moves with respect to the ingot 11 among the plurality of modified portions 17 by the length of each of the pair of modified portions in the moving direction is 1.63 or more and 2.73 or less. In this case, the index amount in the separation layer forming step S1 can be increased. Therefore, in this method, the time required for manufacturing the substrate 21 from the ingot 11 can be shortened.

[0056] Note that the above-described content is one aspect of the present invention, and the present invention is not limited to the above-described content. For example, in the separation layer forming step S1, it is only necessary that the ingot 11 and the condensing point of the laser beam can be relatively moved, and there is no limitation on the structure therefor.

[0057] Specifically, the separation layer forming step S1 may be performed in a laser processing apparatus provided with a moving mechanism that moves the chuck table 4 along each of the X-axis direction, the Y-axis direction, and / or the Z-axis direction.

[0058] Alternatively, the separation layer formation step S1 may be carried out 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 galvanometer scanner, an acousto-optic element (AOD), and / or a polygon mirror.

[0059] Further, in the cleavage step S2, ultrasonic vibration may be applied to the ingot 11 as an external force for manufacturing the substrate 21. That is, in this cleavage step S2, ultrasonic vibration may be applied to the surface 11a side of the ingot 11 in place of or prior to the application of an external force (suction force) that separates the front surface 11a side and the back surface 11b side of the ingot 11.

[0060] Further, the workpiece used for manufacturing the substrate 21 may be an ingot manufactured such that a crystal plane other than the crystal plane {001} of β-phase gallium oxide (for example, the crystal plane (100)) is exposed on the surface.

[0061] Further, the workpiece used for manufacturing the substrate 21 may be, for example, a bare wafer having a thickness that is 2 times or more and 5 times or less the thickness of the substrate 21 to be manufactured. Note that this bare wafer is manufactured, for example, by cleaving the ingot 11 at the separation layer 19 by the same method as described above. In this case, it can also be expressed that the substrate 21 is manufactured by repeating the above-described method twice.

[0062] Further, the workpiece used for manufacturing the substrate 21 may be a device wafer manufactured by forming a semiconductor device on one surface of this bare wafer. In this case, the laser beam is preferably irradiated to the device wafer from the side where the semiconductor device of the device wafer is not formed in order to prevent adverse effects on the semiconductor device.

[0063] Further, the present invention may also be a method for manufacturing a substrate that is thinner than the ingot 11 from the ingot 11 after grasping the irradiation conditions of the laser beam (for example, the output of the laser beam, the machining feed rate, etc.) for setting the above value I / L within a suitable range.

[0064] FIG. 7 is a flowchart schematically showing an example of such a method for manufacturing a substrate. In this method, first, a preliminary modification part is formed inside the ingot 11 (preliminary modification part formation step S3). This preliminary modification part formation step S3 is carried out, for example, in the above-described laser processing apparatus 2.

[0065] When carrying out the preliminary modification part formation step S3 in the laser processing apparatus 2, first, the ingot 11 is placed on the holding surface of the chuck table 4 so that the surface 11a faces upward. Next, the suction mechanism is operated so that the ingot 11 is held by the chuck table 4. Next, the moving mechanism moves the housing 10 along the X-axis direction and / or the Y-axis direction so that the head 8 is positioned directly above the ingot 11.

[0066] Next, the moving mechanism moves the housing 10 along the Z-axis direction so that the focus point of the laser beam emitted from the head 8 is positioned at the same height as the focus point in the separation layer formation step S1. Next, a laser beam is emitted from the head 8 toward the ingot 11 so that the pulse energy is equal to that of the laser beam irradiated to the ingot 11 in the separation layer formation step S1. Thereby, a preliminary modification part is formed inside the ingot 11 and the preliminary modification part formation step S3 is completed.

[0067] Note that the number of pre-modification portions formed inside the ingot 11 may be one or plural. When forming one pre-modification portion inside the ingot 11, for example, the ingot 11 may be irradiated with a single-pulse laser beam without operating the moving mechanism. Further, when forming a plurality of pre-modification portions inside the ingot 11, for example, the ingot may be irradiated with a laser beam that repeats a pulsed output while operating the moving mechanism so that the plurality of formed pre-modification portions do not overlap.

[0068] Before the separation layer forming step S1 and after the pre-modification portion forming step S3, the reference length in the moving direction (for example, the X-axis direction) in which the condensing point of the laser beam moves with respect to the ingot 11 in the separation layer forming step S1 of the pre-modification portion is measured (measurement step S4).

[0069] In this measurement 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 one or a plurality of pre-modification portions. Next, the imaging unit 12 is operated to image one or a plurality of pre-modification portions to form an image. Next, with reference to this image, the above reference length is measured. Thereby, the measurement step S4 is completed.

[0070] After the measurement step S4, the above-described separation layer forming step S1 and cleavage step S2 are sequentially performed. However, in this separation layer forming step S1, the center distance (for example, the center distance I shown in FIG. 4) between a pair of adjacent modification portions in the moving direction (for example, the X-axis direction) in which the condensing point of the laser beam moves with respect to the ingot 11 among the plurality of modification portions 17 is 1.63 times or more and 2.73 times or less, preferably 1.94 times or more and 2.43 times or less, more preferably 2.11 times or more and 2.33 times or less, and most preferably about 2.22 times the above reference length. The irradiation conditions of the laser beam (for example, the machining feed rate) are set.

[0071] As a result, it is possible to increase the component along the direction (for example, the Y-axis direction) orthogonal to each of the thickness direction of the ingot 11 and the moving direction in which the condensing point of the laser beam moves with respect to the ingot 11, of the cracks extending from each of the plurality of modified portions 17 included in the separation layer 19 formed inside the ingot 11 in the separation layer forming step S1. In this case, the index amount in the separation layer forming step S1 can be increased. Therefore, in the method for manufacturing a substrate shown in FIG. 7, the time required for manufacturing the substrate 21 from the ingot 11 can be shortened.

[0072] In addition, the structures, methods, etc. according to the above-described embodiments can be appropriately modified and implemented without departing from the scope of the object of the present invention.

Explanation of Reference Numerals

[0073] 2: Laser processing apparatus 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: Cleaving device 15: Secondary orientation flat 16: Chuck table 17: Plurality of modified portions (17a, 17b, 17c, 17d: modified portions) 18: Separation unit 19: Separation layer 20: Suction plate 21: Substrate 22: Vertical movement mechanism

Claims

1. A substrate manufacturing method for manufacturing a substrate thinner than a workpiece made of gallium oxide, comprising the steps of: a separation layer forming step of forming a separation layer inside the workpiece, the separation layer including a plurality of modified portions arranged along a moving direction of the focus point relative to the workpiece and cracks extending from each of the plurality of modified portions, by positioning a focus point of a laser beam having a wavelength that transmits the gallium oxide and that repeats a pulsed output inside the workpiece and relatively moving the workpiece and the focus point perpendicular to a thickness direction of the workpiece; a cleaving step of manufacturing the substrate by cleaving the workpiece at the separation layer after the separation layer forming step, A method for manufacturing a substrate, in which the value obtained by dividing the center-to-center distance between a pair of adjacent modified areas among the plurality of modified areas in the movement direction by the length in the movement direction of each of the pair of modified areas is 1.63 or greater and 2.73 or less.

2. The method for manufacturing a substrate according to claim 1 , wherein the value is 1.94 or more and 2.43 or less.

3. The method for manufacturing a substrate according to claim 1 , wherein the value is 2.11 or more and 2.33 or less.

4. a preliminary modified portion forming step of forming a preliminary modified portion inside the workpiece by irradiating the workpiece with the laser beam while positioning the focusing point inside the workpiece so that the pulse energy of the laser beam irradiated to the workpiece in the separation layer forming step is equal to that of the laser beam; A measuring step of measuring a reference length of the preliminary reforming section in the moving direction after the preliminary reforming section forming step and before the separation layer forming step, 2. The method for manufacturing a substrate according to claim 1, wherein the irradiation conditions of the laser beam in the separation layer forming step are set so that the center-to-center distance is 1.63 to 2.73 times the reference length.

Images