Manufacturing method for substrate

Abstract

To provide a manufacturing method for a substrate capable of improving the productivity of substrates when manufacturing, from a work piece made of gallium oxide, a thinner substrate than the work piece.SOLUTION: A manufacturing method for a substrate includes: a peeling layer forming step of forming a plurality of lines of peeling layers inside a work piece; and, after the peeling layer forming step, a separating step of manufacturing a substrate by separating the work piece using the lines of peeling layers as a separation start point. The peeling layer forming step includes a first processing step of forming a plurality of lines of first peeling layers separated from each other, each including a modified part, which is a part where a crystal structure of gallium oxide is disordered, and after the first processing step, a second processing step of forming a plurality of lines of second peeling layers each including the modified part and a crack extending from the modified part and existing between a pair of first peeling layers that are adjacent to each other among the plurality of lines of the first peeling layers.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a substrate from a workpiece made of gallium oxide to produce a substrate thinner than the workpiece. [Background technology]

[0002] The most stable phase of crystalline polymorphic gallium oxide (Ga2O3) is the monoclinic β-phase (β-Ga2O3). β-phase gallium oxide (hereinafter referred to as "gallium oxide") is a wide-gap semiconductor with a band gap of approximately 4.8 eV. Therefore, gallium oxide is expected to be a material for semiconductor devices such as power devices.

[0003] Semiconductor devices are generally formed using disk-shaped substrates, which are manufactured by cutting a workpiece, such as a cylindrical block called an ingot, with a wire saw to separate a portion having a predetermined thickness from the workpiece (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-13929 Summary of the Invention [Problem to be solved by the invention]

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

[0006] In view of this, an object of the present invention is to provide a substrate manufacturing method capable of improving substrate productivity when manufacturing a substrate thinner than a workpiece made of gallium oxide. [Means for solving the problem]

[0007] According to the present invention, there is provided a method for manufacturing a substrate from a workpiece made of gallium oxide to produce a substrate thinner than the workpiece, the method comprising: a separation layer forming step of forming a plurality of rows of peeling layers inside the workpiece; and a separation step of, after the separation layer forming step, separating the workpiece using the plurality of rows of peeling layers as separation starting points to manufacture the substrate. The separation layer forming step comprises a first processing step of forming a plurality of rows of first peeling layers that are spaced apart from one another, each of which includes a modified portion; and a second processing step of forming a plurality of rows of second peeling layers that, after the first processing step, includes the modified portion and cracks extending from the modified portion, and each of which is located between a pair of adjacent first peeling layers of the plurality of rows of first peeling layers. In the first processing step, The method for manufacturing a substrate includes alternately repeating a first laser beam irradiation step in which a focal point at which a laser beam having a wavelength that transmits gallium is focused is positioned inside the workpiece, and the workpiece and the focal point are moved relatively along a first direction, and a first index feed step in which the workpiece and the position where the focal point is formed are moved relatively along a second direction perpendicular to the first direction, and in the second processing step, a second laser beam irradiation step in which the focal point is positioned between the pair of adjacent first release layers, and the workpiece and the position where the focal point is formed are moved relatively along the first direction, and a second index feed step in which the workpiece and the position where the focal point is formed are moved relatively along the second direction.

[0008] Furthermore, the output of the laser beam in the first laser beam irradiation step may be set to be smaller than the output of the laser beam in the second laser beam irradiation step, and in the first processing step, the plurality of rows of first peeling layers each including the crack may be formed, and the crack included in each of the plurality of rows of first peeling layers may be smaller than the crack included in each of the plurality of rows of second peeling layers. In this case, it is preferable that the peeling layer formation step further includes, after the second processing step, a third laser beam irradiation step of irradiating the laser beam onto at least one of the plurality of rows of first peeling layers so as to further extend the crack.

[0009] Alternatively, the output of the laser beam in the first laser beam irradiation step may be set smaller than the output of the laser beam in the second laser beam irradiation step, and the first processing step may form the plurality of rows of first peeling layers, each of which does not include the crack. In this case, it is preferable that the peeling layer forming step further includes, after the second processing step, a third laser beam irradiation step of irradiating the laser beam onto at least one of the plurality of rows of first peeling layers so that the crack propagates from the modified portion.

[0010] Alternatively, the output of the laser beam in the first laser beam irradiation step may be set to be the same as the output of the laser beam in the second laser beam irradiation step, and the first processing step may form the plurality of rows of first peeling layers, each of which includes the crack. In this case, it is preferable that the peeling layer forming step further includes, after the second processing step, a third laser beam irradiation step of irradiating the laser beam onto at least one of the plurality of rows of first peeling layers and / or at least one of the plurality of rows of second peeling layers so as to further extend the crack.

[0011] In addition, it is preferable that the depth of the focal point from the surface of the workpiece in the first laser beam irradiation step is set to be the same as the depth of the focal point from the surface in the second laser beam irradiation step. [Effects of the Invention]

[0012] In the present invention, a substrate is manufactured by forming a plurality of rows of first release layers and a plurality of rows of second release layers inside a workpiece, and then separating the workpiece using these release layers as separation starting points, thereby improving productivity of the substrate compared to manufacturing the substrate from the workpiece using a wire saw. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1(A) is a perspective view schematically showing an example of an ingot made of gallium oxide, and FIG. 1(B) is a side view schematically showing the ingot shown in FIG. 1(A). [Figure 2] FIG. 2 is a flowchart schematically illustrating an example of a method for manufacturing a substrate. [Figure 3] FIG. 3 is a flow chart schematically illustrating an example of the release layer forming step shown in FIG. [Figure 4] FIG. 4 is a perspective view schematically showing the release layer forming step. [Figure 5] FIG. 5 is a flowchart schematically illustrating an example of the first processing step shown in FIG. [Figure 6] FIG. 6(A) is a plan view that schematically shows the state of the first processing step, and FIG. 6(B) is a partially enlarged vertical cross-sectional view that schematically shows the ingot after the first processing step. [Figure 7] FIG. 7 is a flowchart schematically illustrating an example of the second processing step shown in FIG. [Figure 8] FIG. 8(A) is a plan view that schematically shows the state of the second processing step, and FIG. 8(B) is a partially enlarged vertical cross-sectional view that schematically shows the ingot after the second processing step. [Figure 9] 9(A) and 9(B) are side views each showing a schematic view of the separation step shown in FIG. [Figure 10] FIG. 10 is a flow chart schematically illustrating another example of the release layer forming step shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described with reference to the accompanying drawings, which are provided to facilitate understanding of the present invention and do not necessarily accurately reflect the objects and / or methods in which the present invention is embodied.

[0015] Fig. 1(A) is a perspective view showing an example of an ingot made of gallium oxide, and Fig. 1(B) is a side view showing the ingot shown in Fig. 1(A). Fig. 1(A) and Fig. 1(B) also show the crystal planes of the gallium oxide contained in the ingot. Fig. 1(B) also shows the crystal orientation of the gallium oxide.

[0016] The crystal structure of gallium oxide is a monoclinic crystal, in which the angle between the crystal orientation <0100> (a-axis) and the crystal orientation <0001> (c-axis) is 103.7°, and the angle between the crystal orientation <0010> (b-axis) and each of the crystal orientations <0100> (a-axis) and <0001> (c-axis) is 90°. 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 the crystal plane {001} is exposed on each of the front surface 11a and the back surface 11b (for convenience, the plane exposed on the front surface 11a is referred to as the crystal plane (001)).

[0017] 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, due to processing errors during manufacturing, a plane slightly tilted from the crystal plane {001} may be exposed on each of the front surface 11a and the back surface 11b. 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.

[0018] Furthermore, two flat portions indicating the crystal orientation of gallium oxide, namely, a primary orientation flat 13 and a secondary orientation flat 15, are formed on the 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.

[0019] Furthermore, 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 that exposes the crystal plane (010). 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.

[0020] It is noted 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. 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 the gallium oxide.

[0021] 2 is a flow chart schematically illustrating an example of a substrate manufacturing method for manufacturing a substrate thinner than the ingot 11 from the ingot 11 that serves as the workpiece. In this method, first, a plurality of rows of peeling layers are formed inside the ingot 11 (peeling layer forming step S1). Each peeling layer includes a modified portion, which is a portion where the crystal structure of gallium oxide is disrupted. Each peeling layer may also include cracks extending from the modified portion.

[0022] In this separation layer formation step S1, multiple rows of separation layers are formed in order inside the ingot 11. However, if the multiple rows of separation layers are formed in order from the end, that is, if the ones located at the ends in the direction perpendicular to the direction in which each separation layer extends are formed first, and the remaining separation layers are formed adjacent to the separation layer formed immediately before, very long cracks may extend from the modified parts included in the separation layers along the way.

[0023] Specifically, when the peeling layers are formed in this order, internal stress generated in the ingot 11 due to the formation of the modified portion contained in the peeling layer acts on the modified portion contained in the newly formed peeling layer, and cracks may extend excessively from the newly formed modified portion. In other words, if the internal stress accumulated due to the formation of the modified portion becomes too large, a very long crack may form from the newly formed modified portion in order to release the internal stress all at once.

[0024] In this case, the crack may extend to a region of ingot 11 where no peeling layer is intended to be formed, making it difficult to subsequently form a desired peeling layer in that region. In addition, in this case, the crack component along the thickness direction of ingot 11 may become large, which may reduce the productivity of substrates when manufacturing substrates from ingot 11.

[0025] Therefore, in the peeling layer forming step S1, multiple rows of peeling layers are formed inside the ingot 11 in an order that prevents cracks from excessively extending from the modified portion. Fig. 3 is a flowchart that schematically shows an example of the peeling layer forming step S1 in which multiple rows of peeling layers are formed in this manner.

[0026] In this peeling layer forming step S1, first, a plurality of rows of first peeling layers each including a modified portion and spaced apart from one another are formed (first processing step S11). Then, after the first processing step S11, a plurality of rows of second peeling layers each including a modified portion and a crack and each located between a pair of adjacent first peeling layers among the plurality of rows of first peeling layers are formed (second processing step S12).

[0027] That is, in the peeling layer formation step S1, multiple rows of first peeling layers are formed so as to leave the areas between adjacent pairs of first peeling layers in the ingot 11 unprocessed (first processing step S11), and then multiple rows of second peeling layers are formed in each of the remaining multiple rows of unprocessed areas (second processing step S12).

[0028] In this case, in the first processing step S11, internal stress generated in the ingot 11 due to the formation of the modified portion contained in the first separation layer is less likely to act on the newly formed modified portion contained in the first separation layer. Also, in the second processing step S12, the range in which a crack extending from the modified portion contained in the second separation layer can extend can be limited to between a pair of adjacent first separation layers.

[0029] Each first release layer may contain, for example, cracks smaller than those extending from the modified portions included in each second release layer, or may contain no cracks. Alternatively, each first release layer may contain cracks of approximately the same size as those extending from the modified portions included in each second release layer.

[0030] 4 is a perspective view schematically illustrating the release layer forming step S1. In FIG. 4, the direction indicated by arrow X (X direction) and the direction indicated by arrow Y (Y direction) are directions perpendicular to each other on a horizontal plane, and the direction indicated by arrow Z (Z direction) is a direction perpendicular to the X direction and the Y direction (vertical direction).

[0031] The peeling layer forming step S1 is performed in 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 that can hold an ingot 11 on this holding surface.

[0032] The chuck table 4 is connected to a suction mechanism (not shown). This suction mechanism includes, 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.

[0033] 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 around a rotation axis that passes through the center of the holding surface and is a straight line along the Z 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 direction.

[0034] 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 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.

[0035] The base end of the housing 10 is connected to a movement mechanism. This movement mechanism includes, for example, a ball screw and a motor. When the movement mechanism operates, the housing 10 moves along the X direction, Y direction, and / or Z direction. The laser beam irradiation unit 6 also includes, for example, a laser oscillator (not shown) including Nd:YAG or the like as a laser medium.

[0036] This laser oscillator generates a laser beam (for example, a pulsed laser beam with a frequency of 30 kHz and a pulse width of 4 ns) with a wavelength (for example, 1064 nm) that is transparent to gallium oxide. Then, this laser beam is adjusted by an attenuator so that its output (power) becomes a predetermined value (for example, 0.1 W to 2.0 W), and then emitted directly downward from head 8 via the optical system contained in housing 10 and head 8.

[0037] Furthermore, an imaging unit 12 capable of capturing an image of the area directly below is provided on a side of the housing 10. This 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 through 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.

[0038] When performing the peeling 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.

[0039] Next, with reference to this image, the rotation mechanism rotates the chuck table 4 so that the secondary orientation flat 15 is parallel to the X direction. That is, the rotation mechanism rotates the chuck table 4 so that the crystal orientation

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

[0010] is parallel to the Y direction.

[0040] Next, the movement mechanism moves the housing 10 along the X direction and / or the Y direction so that a region of the ingot 11 near one end in the Y direction (for example, a region near the secondary orientation flat 15) is positioned in the X direction when viewed from the head 8. Next, the movement mechanism moves the housing 10 along the Z direction so that a focal point P 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 (for example, a depth of 300 μm from the surface 11a).

[0041] Next, a first processing step S11 is performed. Fig. 5 is a flow chart showing an example of the first processing step S11. Fig. 6(A) is a plan view showing the first processing step S11, and Fig. 6(B) is a partially enlarged vertical cross-sectional view showing the ingot 11 after the first processing step S11.

[0042] In this first processing step S11, first, a focal point P where the laser beam is focused is positioned inside the ingot 11, and then the ingot 11 and the focal point P are moved relatively along the X direction (first laser beam irradiation step S111).

[0043] Specifically, in the first laser beam irradiation step S111, while a laser beam is emitted from the head 8, the movement mechanism moves the housing 10 along the X direction so that the focal point P at which the laser beam is focused passes from one end to the other end in the X direction of the ingot 11 at a predetermined speed (e.g., 390 mm / s). In other words, the laser beam is irradiated onto the ingot 11 with the scanning direction of the laser beam being parallel to the crystal orientation

[0100] of gallium oxide.

[0044] As a result, a modified portion 17, which is a portion where the crystal structure of gallium oxide is disrupted, is formed inside the ingot 11, centered around the focal point P where the laser beam is focused. 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.

[0045] This internal stress increases in proportion to the size of the modified region 17, i.e., the output of the laser beam. As the internal stress increases, cracks propagate from the modified region 17 to release the internal stress. Therefore, by appropriately setting the output of the laser beam, it is possible to control to some extent whether or not cracks propagate from the modified region 17 and the size of the cracks.

[0046] For example, when the modified region 17 is formed in the first processing step S11 but cracks are not allowed to extend from the modified region 17, the output of the laser beam is set to, for example, 0.3 W. When a crack of approximately the same size as a crack extending from the modified region 17 formed in the second processing step S12 is allowed to extend from the modified region 17 in the first processing step S11, the output of the laser beam is set to, for example, 0.8 W. When a crack smaller than a crack extending from the modified region 17 formed in the second processing step S12 is allowed to extend from the modified region 17 in the first processing step S11, the output of the laser beam is set to, for example, 0.4 W to 0.7 W.

[0047] In gallium oxide, the crystal plane (100) is most likely to cleave, followed by the crystal plane (001). Here, in the first laser beam irradiation step S111, the scanning direction of the laser beam is set to a direction that forms a large angle with respect to the crystal plane (100) (specifically, a direction parallel to the crystal orientation

[0100] ). In this case, the ingot 11 is less likely to cleave at the crystal plane (100) of gallium oxide. That is, in the first laser beam irradiation step S111, the occurrence of cracks with a large component along the thickness direction of the ingot 11 is suppressed.

[0048] When the focal point P at which the laser beam emitted from the head 8 is focused passes the other end of the ingot 11 in the X direction, the first laser beam irradiation step S111 is completed. By carrying out the first laser beam irradiation step S111 in this manner, a linear peeling layer (first peeling layer) 19 including the modified portion 17 and cracks, or including the modified portion 17 but no cracks, is formed inside the ingot 11. Note that, for convenience, a first peeling layer 19 including no cracks is illustrated in FIG. 5 and FIGS. 6(A) and 6(B).

[0049] Then, if the first peeling layer 19 is not formed in the regions of the ingot 11 near both ends in the Y direction (step S112: NO), the ingot 11 and the position where the focal point P is formed are moved relatively along the Y direction (first index feed step S113). In this first index feed step S113, the moving mechanism moves the housing 10 along the Y direction by a predetermined index amount (for example, 0.1 mm to 0.2 mm) so that the head 8 is positioned in the X direction when viewed in a plan view from a region slightly farther from the secondary orientation flat 15 than the region previously irradiated with the laser beam.

[0050] Next, a first laser beam irradiation step S111 is performed with the laser beam scanning direction set to the opposite direction to the X direction. Furthermore, the first indexing step S113 and the first laser beam irradiation step S111 are alternately repeated until irradiation of the laser beam is completed on the region of the ingot 11 near the other end in the Y direction (e.g., the region farthest from the secondary orientation flat 15).

[0051] That is, the relative movement of the ingot 11 along the Y direction and the position where the laser beam is focused to form the focal point P, and the irradiation of the ingot 11 with the laser beam scanning in the X direction or the opposite direction are alternately repeated. Then, when the first peeling layer 19 is formed in each of the regions near both ends of the ingot 11 in the Y direction (step S112: YES), the first processing step S11 is completed.

[0052] After the first processing step S11, a second processing step S12 is performed. Fig. 7 is a flow chart showing an example of the second processing step S12. Fig. 8(A) is a plan view showing the second processing step S12, and Fig. 8(B) is a partially enlarged vertical cross-sectional view showing the ingot 11 after the second processing step S12.

[0053] In this second processing step S12, first, the focal point P where the laser beam is focused is positioned between a pair of adjacent first peeling layers 19, and the ingot 11 and the focal point P are moved relatively along the X direction (second laser beam irradiation step S121).

[0054] Specifically, in the second laser beam irradiation step S121, while a laser beam is emitted from the head 8, the movement mechanism moves the housing 10 along the X direction so that the focal point P at which the laser beam is focused passes from one end to the other end of the ingot 11 in the X direction at a predetermined speed (e.g., 390 mm / s). In other words, the laser beam is irradiated onto the ingot 11 with the scanning direction of the laser beam being parallel to the crystal orientation

[0100] of gallium oxide.

[0055] In the second laser beam irradiation step S121, the output of the laser beam is set to a value (for example, 0.8 W) that allows the crack 21 to extend from the modified portion 17. As a result, the modified portion 17 and the crack 21 are formed between a pair of adjacent first peeling layers 19.

[0056] The second laser beam irradiation step S121 is completed when the focal point P at which the laser beam emitted from the head 8 is focused passes the other end in the X direction of the ingot 11. By carrying out the second laser beam irradiation step S121 in this manner, a linear peeling layer (second peeling layer) 23 including the modified portion 17 and the crack 21 is formed between a pair of adjacent first peeling layers 19.

[0057] Then, if the second peeling layer 23 has not been formed in all of the regions between the rows of first peeling layers 19 (i.e., the rows of unprocessed regions) (step S122: NO), the ingot 11 and the position where the focal point P is formed are moved relatively along the Y direction (second index feed step S123). In this second index feed step S123, the movement mechanism moves the housing 10 along the Y direction by a predetermined index amount (e.g., 0.1 mm to 0.2 mm) so that the head 8 is positioned in the X direction when viewed in plan from the unprocessed region adjacent to the region between a pair of adjacent first peeling layers 19 that was previously irradiated with the laser beam.

[0058] Next, a second laser beam irradiation step S121 is performed with the laser beam scanning direction set to the opposite direction to the X direction. Furthermore, the second indexing step S123 and the second laser beam irradiation step S121 are alternately repeated until irradiation of all of the regions between the rows of first release layers 19 with the laser beam is completed.

[0059] That is, the relative movement of the ingot 11 along the Y direction and the position where the focal point P where the laser beam is focused is formed, and the irradiation of the ingot 11 with the laser beam scanning in the X direction or the opposite direction are alternately repeated. Then, when the second peeling layers 23 are formed in all the regions between the multiple rows of first peeling layers 19 (step S122: YES), the second processing step S12 is completed, that is, the peeling layer forming step S1 is completed.

[0060] In the above-mentioned peeling layer formation step S1 (specifically, the first processing step S11 and the second processing step S12), the direction parallel to the crystal orientation

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

[0061] However, if the scanning direction of the laser beam becomes parallel to the crystal orientation

[0010] of gallium oxide, there is a risk that the proportion of cracks 21 extending along the crystal plane (100) parallel to the crystal orientation

[0010] will increase. If the proportion of cracks 21 extending along the crystal plane (100) increases, the thickness of each of the peeling layers 19, 23 (particularly each of the second peeling layers 23) formed inside the ingot 11 will increase, and the productivity of manufacturing substrates from the ingot 11 will decrease.

[0062] In this case, the proportion of cracks 21 extending along the crystal plane (001), i.e., cracks 21 extending parallel to the surface 11a of the ingot 11, decreases, so the width (length in the direction perpendicular to the thickness direction of the ingot 11 and the scanning direction of the laser beam) of each peeling layer 19, 23 (particularly each second peeling layer 23) formed inside the ingot 11 decreases. Therefore, in this case, the index amount must be reduced, and the throughput of the laser processing device 2 decreases.

[0063] 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 the angle it makes with a line parallel to the crystal orientation

[0010] of gallium oxide is large, that is, so that the angle it makes with a line parallel to the crystal orientation

[0100] is small.

[0064] Furthermore, in the above-described peeling layer forming step S1, the depth from the surface 11a of the ingot 11 of the focal point P where the laser beam is focused is maintained constant, but this depth may be changed during the process. For example, in the peeling layer forming step S1, the depth from the surface 11a of the focal point in the first laser beam applying step S111 may be different from the depth from the surface 11a of the focal point in the second laser beam applying step S121.

[0065] However, cracks 21 contained in second peeling layer 23 formed in second laser beam irradiation step S121 tend to extend toward first peeling layer 19. Therefore, if the two depths are different, the thickness of each second peeling layer 23 formed inside ingot 11 increases, reducing productivity when manufacturing substrates from ingot 11. In light of this, it is preferable to set the two depths to be the same in order to improve productivity when manufacturing substrates from ingot 11.

[0066] Furthermore, in the above-described peeling layer forming step S1, the laser beam may be irradiated onto the ingot 11 only along one direction (for example, the X direction). That is, in the peeling 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 scanning direction of the laser beam being the opposite direction to the one direction (for example, the opposite direction to the X direction).

[0067] After the separation layer formation step S1, the ingot 11 is separated using the multiple rows of separation layers 19, 23 as separation starting points to manufacture a substrate (separation step S2). Each of FIGS. 9(A) and 9(B) is a side view schematically illustrating 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.

[0068] The chuck table 16 is connected to a table-side suction mechanism (not shown). This table-side suction mechanism includes, 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.

[0069] A separation unit 18 is provided above the chuck table 16. This separation unit 18 has a suction plate 20 with a plurality of suction ports formed on its underside. 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 underside of the suction plate 20.

[0070] A vertical movement mechanism 22 is connected to the upper surface of the suction plate 20. The vertical movement mechanism 22 includes, for example, a ball screw and a motor. When the vertical movement mechanism 22 operates, the suction plate 20 moves in the vertical direction.

[0071] When performing the separation step S2 in the separation device 14, first, the ingot 11, inside which multiple rows of peeled layers 19, 23 have been formed, 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 sufficiently spaced apart. Next, the table-side suction mechanism is operated so that the ingot 11 is held on the chuck table 16.

[0072] Next, the vertical movement mechanism 22 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. 9(A)). Next, the separation unit side suction mechanism is operated so that the front surface 11a of the ingot 11 is sucked upward. Next, the vertical movement mechanism 22 raises the suction plate 20 so that the suction plate 20 is separated from the chuck table 16 (see FIG. 9(B)).

[0073] This applies an external force to ingot 11 that separates front surface 11a and back surface 11b of ingot 11, further extending cracks 21 contained in multiple rows of peeling layers 19, 23. As a result, ingot 11 is separated from multiple rows of peeling layers 19, 23 as separation starting points, producing substrate 25. This completes separation step S2, i.e., the method for producing the substrate shown in FIG.

[0074] 2, multiple rows of first peeling layers 19 and multiple rows of second peeling layers 23 are formed inside ingot 11, and then ingot 11 is separated using these peeling layers 19, 23 as separation starting points to produce substrate 25. This allows for improved productivity of substrate 25 compared to when substrate 25 is produced from ingot 11 using a wire saw.

[0075] The above-described content is one embodiment of the present invention, and the present invention is not limited to the above-described content. For example, in the peeling layer formation step S1 of the present invention, it is sufficient that the ingot 11 and the focal point P at which the laser beam is focused can be moved relatively, and there is no limitation on the structure for this purpose.

[0076] Specifically, this peeling layer forming step S1 may be performed in a laser processing device provided with a movement mechanism for moving the chuck table 4 along each of the X direction, Y direction and / or Z direction.

[0077] Alternatively, the peeling 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. The scanning optical system may include, for example, a galvanometer scanner, an acousto-optical device (AOD), and / or a polygon mirror.

[0078] Furthermore, the release layer forming step S1 of the present invention may include a step of reinforcing the rows of release layers 19, 23 as separation starting points after the second processing step S12. Fig. 10 is a flow chart schematically showing an example of the release layer forming step S1 including such a step.

[0079] In this release layer forming step S1, after the second processing step S12, a laser beam is irradiated onto at least one of the rows of first release layers 19 (third laser beam irradiating step S13).

[0080] This third laser beam irradiation step S13 is performed, for example, in the same manner as the above-described first laser beam irradiation step S111. Alternatively, the third laser beam irradiation step S13 may be performed in the same manner as the above-described first processing step S11. That is, in the third laser beam irradiation step S13, the laser beam may be irradiated onto only one of the multiple rows of first peeling layers 19, or onto all of them.

[0081] Furthermore, in the third laser beam irradiation step S13, the laser beam may be selectively irradiated onto the first peeling layers 19 in multiple rows. For example, in the third laser beam irradiation step S13, the laser beam may be irradiated onto the first peeling layers 19 in odd-numbered or even-numbered positions when counting up from those at one end of the multiple rows of first peeling layers to those at the other end. Alternatively, in the third laser beam irradiation step S13, the laser beam may be irradiated onto those in positions that are multiples of k (k is a natural number greater than or equal to 3) when counting up in the same manner.

[0082] When the first processing step S11 is performed to form a first peeling layer 19 that includes cracks 21, the third laser beam irradiation step S13 can be performed to further extend the cracks 21 included in the first peeling layer 19. When the first processing step S11 is performed to form a first peeling layer 19 that does not include cracks 21, the third laser beam irradiation step S13 can be performed to extend the cracks 21 from the modified portions 17 included in the first peeling layer 19.

[0083] The peeling layer forming step S1 shown in Fig. 10 is preferable to the peeling layer forming step S1 shown in Fig. 3 in that it makes it easier to separate the ingot 11 in the separation step S2. On the other hand, the peeling layer forming step S1 shown in Fig. 3 is preferable to the peeling layer forming step S1 shown in Fig. 10 in that it can improve the throughput of the laser processing apparatus 2.

[0084] In addition, when the first processing step S11 is carried out to form a first peeling layer 19 containing cracks 21 of approximately the same size as the cracks 21 contained in the second peeling layer 23, in the third laser beam irradiation step S13, a laser beam may be irradiated onto at least one of the multiple rows of second peeling layers 23 instead of or in addition to at least one of the multiple rows of first peeling layers 19.

[0085] Furthermore, in the separation step S2 of the present invention, ultrasonic vibrations may be applied to the ingot 11 as an external force for producing the substrate 25. That is, in this separation step S2, ultrasonic vibrations 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.

[0086] Furthermore, the workpiece used in the substrate manufacturing method of the present invention may be an ingot manufactured so that a crystal face other than the {001} crystal face of gallium oxide (for example, the (100) crystal face) is exposed on the surface.

[0087] Furthermore, the workpiece used in the substrate manufacturing method of the present invention may be, for example, a bare wafer having a thickness between two and five times that of the substrate to be manufactured. Note that this bare wafer is manufactured, for example, by separating ingot 11 using a method similar to the method described above. In this case, it can also be said that substrate 25 is manufactured by repeating the above method twice.

[0088] The workpiece used in the substrate manufacturing method of the present invention 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.

[0089] 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]

[0090] 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: Release layer (first release layer) 20: Suction plate 21: Crack 22: Vertical movement mechanism 23: Release layer (second release layer) 25: Circuit board

Claims

1. A substrate manufacturing method for manufacturing a substrate thinner than a workpiece made of gallium oxide, a release layer forming step of forming a plurality of rows of release layers inside the workpiece; a separation step of manufacturing the substrate by separating the workpiece using the rows of release layers as separation starting points after the release layer forming step, The release layer forming step includes: a first processing step of forming a plurality of rows of first release layers, each row including a modified portion and spaced apart from one another; a second processing step, after the first processing step, of forming a plurality of rows of second peeling layers, each of which includes the modified portion and a crack extending from the modified portion, and each of which is located between a pair of adjacent first peeling layers among the plurality of rows of first peeling layers; In the first processing step, a first laser beam irradiation step in which a focal point at which a laser beam having a wavelength that transmits through the gallium oxide is focused is positioned inside the workpiece, and the workpiece and the focal point are moved relatively along a first direction; a first index feed step of relatively moving the workpiece and the position where the focal point is formed along a second direction perpendicular to the first direction, and In the second processing step, a second laser beam irradiation step of relatively moving the workpiece and the focal point along the first direction with the focal point positioned between the pair of adjacent first peeling layers; a second index feed step of relatively moving the workpiece and the position where the focal point is formed along the second direction, the steps being alternately repeated.

2. an output of the laser beam in the first laser beam irradiation step is set to be smaller than an output of the laser beam in the second laser beam irradiation step; In the first processing step, the plurality of rows of first peeling layers each including the crack are formed; The method for manufacturing a substrate according to claim 1 , wherein the cracks contained in each of the rows of first release layers are smaller than the cracks contained in each of the rows of second release layers.

3. The method for manufacturing a substrate according to claim 2, wherein the peeling layer forming step further comprises a third laser beam irradiation step, after the second processing step, of irradiating the laser beam to at least one of the rows of first peeling layers so as to further extend the cracks.

4. an output of the laser beam in the first laser beam irradiation step is set to be smaller than an output of the laser beam in the second laser beam irradiation step; The method for manufacturing a substrate according to claim 1 , wherein the first processing step forms the plurality of rows of first peeled layers each of which does not include the crack.

5. The method for manufacturing a substrate described in claim 4, wherein the peeling layer formation step further includes a third laser beam irradiation step, after the second processing step, of irradiating the laser beam to at least one of the multiple rows of first peeling layers so that the crack extends from the modified portion.

6. an output of the laser beam in the first laser beam irradiation step is set to be the same as an output of the laser beam in the second laser beam irradiation step; The method for manufacturing a substrate according to claim 1 , wherein the first processing step forms the plurality of rows of first peeled layers, each of which includes the crack.

7. The method for manufacturing a substrate described in claim 6, wherein the peeling layer formation step further includes a third laser beam irradiation step, after the second processing step, of irradiating the laser beam to at least one of the rows of first peeling layers and / or at least one of the rows of second peeling layers so as to further extend the crack.

8. 8. The method for manufacturing a substrate according to claim 1, wherein a depth of the focal point from the surface of the workpiece in the first laser beam irradiation step is set to be the same as a depth of the focal point from the surface in the second laser beam irradiation step.

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