Method of manufacturing substrate

Abstract

To provide a method of manufacturing substrates, capable of improving the productivity of substrates at the time of manufacturing, from a workpiece, a substrate thinner than the workpiece.SOLUTION: A method of manufacturing substrates includes: a peel-off layer formation step of irradiating a workpiece with a laser beam of a wavelength transmittable through a material of the workpiece, thereby forming a peel-off layer inside the workpiece; and separation step of, after the peel-off layer formation step, separating the workpiece with the peel-off layer as a starting point of separation, thereby manufacturing a substrate. In the peel-off layer formation step, by alternately repeating a laser beam irradiation step of moving the workpiece and a focusing point at which the laser beam is focused relative to each other along a first direction, in a state where the focusing point is positioned inside the workpiece, and a moving step of moving the workpiece and a position at which the focusing point is formed relative to each other along a second direction perpendicular to the first direction, the peel-off layer including first modified portions and second modified portions which are alternately lined up in the second direction is formed.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a substrate from a workpiece, the method comprising the steps of: (a) forming a substrate having a thickness smaller than that of the workpiece; [Background technology]

[0002] 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]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-13929 Summary of the Invention [Problem to be solved by the invention]

[0004] 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.

[0005] In view of this, an object of the present invention is to provide a method for manufacturing a substrate that can improve productivity when manufacturing a substrate thinner than a workpiece from the workpiece. [Means for solving the problem]

[0006] According to the present invention, a method for manufacturing a substrate from a workpiece, in which a substrate thinner than the workpiece is manufactured, includes a peeling layer forming step of forming a peeling layer inside the workpiece by irradiating the workpiece with a laser beam having a wavelength that transmits through the material of the workpiece, and a separation step of manufacturing the substrate by separating the workpiece using the peeling layer as a separation starting point after the peeling layer forming step, in which the workpiece and the focal point at which the laser beam is focused are moved relatively along a first direction with the focal point positioned inside the workpiece. and a moving step of relatively moving the workpiece and the position where the focal point is formed along a second direction perpendicular to the first direction, thereby forming the peeling layer including first modified portions and second modified portions arranged alternately in the second direction, the first modified portions being formed at the first focal point where a first laser beam having a first output is focused, and the second modified portions being formed at the second focal point where a second laser beam having a second output greater than the first output is focused.

[0007] Preferably, in the laser beam application step, an original laser beam having a wavelength that transmits through the material of the workpiece is split into the first laser beam and the second laser beam, and the first and second focal points, which are spaced apart in the second direction, are positioned inside the workpiece, and the workpiece and the first and second focal points are moved relatively along the first direction.More preferably, in the laser beam application step, the first focal point moves through the workpiece ahead of the second focal point in the first direction.

[0008] Furthermore, the cracks extending from the first modified region may be smaller than the cracks extending from the second modified region, or alternatively, no cracks may extend from the first modified region, but cracks may extend from the second modified region.

[0009] Furthermore, the substrate manufacturing method of the present invention may further include a final laser beam irradiation step, after the peeling layer formation step is performed so that the modified portion closest to one end of the workpiece in the second direction becomes the second modified portion and the modified portion closest to the other end becomes the first modified portion, and before the separation step, of relatively moving the workpiece and the second focal point along the first direction while positioning the second focal point so that it overlaps the first modified portion closest to the other end. Alternatively, in the substrate manufacturing method of the present invention, the peeling layer formation step may be performed so that the modified portions closest to each of the ends of the workpiece in the second direction become the second modified portions. [Effects of the Invention]

[0010] In the present invention, a substrate is manufactured by forming a release layer inside a workpiece and then separating the workpiece from the release layer as a separation starting point, thereby improving productivity of the substrate compared to manufacturing substrates from workpieces using a wire saw. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1(A) is a perspective view that schematically shows an example of an ingot, and FIG. 1(B) is a side view that schematically shows 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 diagram schematically illustrating an example of a laser processing device for forming a peeling layer inside an ingot. [Figure 4] FIG. 4 is a flow chart that schematically shows the procedure for forming the release layer. [Figure 5] FIG. 5(A) is a plan view showing a schematic diagram of how a separation layer is formed inside an ingot, and FIG. 5(B) is a partially enlarged vertical cross-sectional view showing a schematic diagram of the ingot on which the separation layer has been formed. [Figure 6]6(A) and 6(B) are side views each showing a schematic view of the separation step. [Figure 7] FIG. 7 is a flowchart schematically showing another example of a method for manufacturing a substrate. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] Fig. 1(A) is a perspective view showing an example of an ingot, 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 material of the ingot. Fig. 1(B) also shows the crystal orientation of the material.

[0014] The material of the ingot 11 shown in Figures 1(A) and 1(B) is, for example, β-phase gallium oxide (β-Ga2O3) (hereinafter simply referred to as "gallium oxide"). 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.

[0015] 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)).

[0016] 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.

[0017] In addition, two flat portions, namely, a primary orientation flat 13 and a secondary orientation flat 15, are formed on the side surface 11c of the ingot 11 to indicate the crystal orientation of the material 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.

[0018] 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.

[0019] It is not necessary for one or both of the primary orientation flat 13 and the secondary orientation flat 15 to 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 material of the ingot 11.

[0020] 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 laser beam having a wavelength that is transmitted through the material of the ingot 11 is irradiated onto the ingot 11 to form a peeling layer inside the ingot 11 (peeling layer forming step S1). The peeling layer is a layer that includes a modified portion, which is a portion where the crystalline structure of the material of the ingot 11 is disrupted, and cracks extending from this modified portion.

[0021] In the peeling layer formation step S1, multiple rows of modified regions are formed sequentially inside the ingot 11. However, if multiple rows of modified regions are formed sequentially from the end using a laser beam whose output is maintained constant, that is, if the modified regions located at the end in a direction perpendicular to the direction in which each modified region extends are formed first, and the remaining modified regions are formed adjacent to the modified region formed immediately before, very long cracks may extend from the modified regions during the process.

[0022] Specifically, if modified regions are formed in this order using a laser beam whose output is maintained constant, the internal stress generated in the ingot 11 as the modified regions are formed acts on the newly formed modified regions, and cracks may extend excessively from the newly formed modified regions. In other words, if the internal stress accumulated as the modified regions are formed becomes too large, very long cracks may form from the newly formed modified regions as if to release the internal stress all at once.

[0023] In this case, the crack may extend to a region of the ingot 11 where the crack is not intended to be formed, making it difficult to subsequently form a desired modified portion in that region. In addition, in this case, the crack component along the thickness direction of the ingot 11 may become large, which may reduce the productivity of substrates when manufacturing substrates from the ingot 11.

[0024] Therefore, in the peeling layer forming step S1, the output of the laser beam is adjusted so that cracks do not extend excessively from the modified portions, and multiple rows of modified portions are formed inside the ingot 11. Specifically, in this peeling layer forming step S1, a peeling layer is formed that includes first modified portions and second modified portions that are alternately arranged in a direction perpendicular to the direction in which each modified portion extends.

[0025] Here, the first modified portion is formed at a focal point (first focal point) where a laser beam (first laser beam) having a relatively small output (first output) is focused, and the second modified portion is formed at a focal point (second focal point) where a laser beam (second laser beam) having a relatively large output, i.e., an output (second output) greater than the first output, is focused.

[0026] The first output may be set to a value that causes a crack to propagate from the first modified portion, or may be set to a value that causes a crack not to propagate from the first modified portion. Even if the first output is set to a value that causes a crack to propagate from the first modified portion, the first output is smaller than the second output, and therefore the crack propagating from the first modified portion will be smaller than the crack propagating from the second modified portion.

[0027] When the release layer is formed in this manner, the range within which a crack can extend from the second modified portion can be limited to between a pair of adjacent first modified portions, thereby preventing a very long crack from extending from the second modified portion during the release layer formation step S1.

[0028] Fig. 3 is a diagram schematically illustrating an example of a laser processing apparatus for forming a peeling layer inside an ingot 11. In Fig. 3, 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 (vertical direction) perpendicular to both the X direction and the Y direction. In Fig. 3, some of the components of the laser processing apparatus are shown as blocks.

[0029] 3 includes a chuck table 4 having a circular holding surface that is approximately parallel to a horizontal plane. The chuck table 4 is connected to a suction mechanism (not shown) having, for example, an ejector, and a rotation mechanism (not shown) having, for example, a pulley, a motor, and the like.

[0030] 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.

[0031] Furthermore, 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 aligned in 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.

[0032] A laser beam irradiation unit 6 is provided above the chuck table 4. The laser beam irradiation unit 6 has a laser oscillator 8 having, for example, Nd:YAG or the like as a laser medium.

[0033] The laser oscillator 8 emits 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 or 1342 nm) that is transparent to the material (for example, gallium oxide) of the ingot 11. The output (power) of this laser beam is adjusted by the attenuator 10, and then supplied to the branching unit 12.

[0034] The branching unit 12 has a spatial light modulator including a liquid crystal phase control element called LCoS (Liquid Crystal on Silicon) and / or a diffractive optical element (DOE), etc. The branching unit 12 branches the laser beam (original laser beam) whose output has been adjusted in the attenuator 10, for example, into a first laser beam LB1 having a first output and a second laser beam LB2 having a second output greater than the first output.

[0035] Each of the laser beams LB1 and LB2 is reflected by a mirror 14 and directed to a head 16. This head 16 contains a condenser lens (not shown) that condenses each of the laser beams LB1 and LB2. Each of the laser beams LB1 and LB2 condensed by the condenser lens is emitted toward the holding surface of the chuck table 4, or more simply, directly downward, with the central region of the lower surface of the head 16 as the emission region.

[0036] The first focusing point P1 where the first laser beam LB1 is focused and the second focusing point P2 where the second laser beam LB2 is focused may, for example, be at the same position (height) in the Z direction but at different positions in the Y direction. The positions of the two focusing points P1 and P2 in the X direction may be the same or different.

[0037] Furthermore, the head 16 of the laser beam irradiation unit 6 and an optical system (e.g., mirror 14) for directing the laser beams LB1 and LB2 to the head 16 are connected to a movement mechanism (not shown) including, for example, a ball screw, etc. When this movement mechanism operates, the emission areas of the laser beams LB1 and LB2 move along the X direction, Y direction, and / or Z direction.

[0038] In the laser processing device 2, by operating this movement mechanism, it is possible to adjust the positions (coordinates) in the X direction, Y direction and / or Z direction of the first focal point P1 where the first laser beam LB1 emitted from the head 16 onto the holding surface side of the chuck table 4 is focused and the second focal point P2 where the second laser beam LB2 is focused.

[0039] When performing the peeling layer forming step S1 in the laser processing device 2, first, the ingot 11 is placed with the surface 11a facing up on the holding surface of the chuck table 4. Next, the suction mechanism is operated so that the ingot 11 is held on the chuck table 4.

[0040] Next, for example, 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 the gallium oxide is parallel to the X direction and the crystal orientation

[0010] is parallel to the Y direction.

[0041] Next, the moving mechanism moves the head 16 etc. along the X direction and / or the Y direction so that a linear region along the X direction located near one end of the ingot 11 in the Y direction (for example, a linear region along the X direction located near the secondary orientation flat 15) is positioned in the X direction when viewed from the head 16 in a plan view.

[0042] Next, a peeling layer is formed inside the ingot 11, the peeling layer including first modified areas formed by irradiating a first laser beam LB1 having a first output and second modified areas formed by irradiating a second laser beam LB2 having a second output, which are arranged alternately in the Y direction.

[0043] Fig. 4 is a flow chart showing a procedure for forming such a separation layer. Fig. 5(A) is a plan view showing a process for forming the separation layer inside the ingot 11, and Fig. 5(B) is a partially enlarged vertical cross-sectional view showing the ingot 11 on which the separation layer has been formed.

[0044] When forming the peeling layer 17 shown in FIG. 5(B), first, a first focal point P1 where the first laser beam LB1 is focused and a second focal point P2 where the second laser beam LB2 is focused are positioned inside the ingot 11, and then the ingot 11 and the two focal points P1 and P2 are moved relatively along the X direction (laser beam irradiation step S11).

[0045] Specifically, in the laser beam irradiation step S11, while both laser beams LB1 and LB2 are emitted from the head 16, the movement mechanism moves the head 16 etc. along the X direction so that both focal points P1 and P2 pass from one end to the other end of the ingot 11 in the X direction at a predetermined speed (e.g., 390 mm / s). That is, both laser beams LB1 and LB2 are irradiated onto the ingot 11 with the scanning direction being parallel to the crystal orientation

[0100] of gallium oxide.

[0046] At this time, both laser beams LB1 and LB2 are obtained by branching the original laser beam so that the positions of both focal points P1 and P2 in the X, Y and Z directions satisfy the following conditions:

[0047] First, in the X direction, the first focal point P1 and the second focal point P2 are positioned so that they move ahead of each other inside the ingot 11. That is, when the moving mechanism moves the head 16 and the like along the X direction in the laser beam irradiation step S11, the focal point P1 is positioned on the X direction side as viewed from the focal point P2.

[0048] In addition, in the Y direction, both focal points P1 and P2 are positioned so that they are spaced apart and the second focal point P2 is closer to one end of the ingot 11 in the Y direction (specifically, the secondary orientation flat 15) than the first focal point P1. In addition, in the Z direction, both focal points P1 and P2 are positioned at the same position (height).

[0049] In the laser beam irradiation step S11, a first modified region 19a and a second modified region 19b are formed inside the ingot 11 (specifically, in two linear rows each extending along the X direction). The first modified region 19a is formed at a first focal point P1 where the first laser beam LB1 is focused, and the second modified region 19b is formed at a second focal point P2 where the second laser beam LB2 is focused.

[0050] Furthermore, when the first modified region 19a and the second modified region 19b are formed inside the ingot 11, the volume of the ingot 11 expands, causing internal stress in the ingot 11. This internal stress increases in proportion to the respective sizes of the first modified region 19a and the second modified region 19b, i.e., the output of each of the laser beams LB1 and LB2.

[0051] When the internal stress increases, cracks propagate from each of the first modified region 19 a and the second modified region 19 b so as to release the internal stress. Therefore, by appropriately setting the output of each of the laser beams LB1 and LB2, it is possible to control to some extent whether or not cracks 21 propagate from each of the first modified region 19 a and the second modified region 19 b, and the size of the cracks 21.

[0052] For example, in the laser beam irradiation step S11, the output of each laser beam LB1, LB2 is set so that cracks smaller than the cracks 21 extending from the second modified region 19b extend from the first modified region 19a. Alternatively, in the laser beam irradiation step S11, the output of each laser beam LB1, LB2 may be set so that cracks 21 extend from the second modified region 19b but do not extend from the first modified region 19a. For convenience, Figures 4, 5(A), and 5(B) show the release layer 17 that does not include cracks extending from the first modified region 19a.

[0053] Furthermore, in gallium oxide, the crystal plane (100) is most likely to cleave, followed by the crystal plane (001). Here, in the laser beam irradiation step S11, the scanning directions of the two laser beams LB1 and LB2 are 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 laser beam irradiation step S11, the occurrence of cracks with a large component along the thickness direction of the ingot 11 is suppressed.

[0054] When the first focal point P1 where the first laser beam LB1 emitted from the head 16 is focused and the second focal point P2 where the second laser beam LB2 is focused pass the other end of the ingot 11 in the X direction, the laser beam irradiation step S11 is completed.

[0055] By carrying out the laser beam irradiation step S11 in this manner, a second modified portion 19b and a crack 21 extending from the second modified portion 19b are formed in a linear region along the X direction located near one end of the ingot 11 in the Y direction (specifically, the secondary orientation flat 15), and a first modified portion 19a is formed in a linear region along the X direction located slightly farther from the secondary orientation flat 15 than this region.

[0056] Then, if no modified region (specifically, the first modified region 19a or the second modified region 19b) is formed in each of the regions near both ends of the ingot 11 in the Y direction (step S12: NO), the ingot 11 and the positions where the two focal points P1 and P2 are formed are moved relatively along the Y direction (movement step S13).

[0057] In this movement step S13, the movement mechanism moves the head 16 etc. by a predetermined distance (e.g., 0.1 mm to 0.2 mm) along the Y direction so that the head 16 is positioned in the X direction when viewed in a plan view from a linear region that is slightly farther from the secondary orientation flat 15 than the region previously irradiated with the laser beam. Note that this distance is set to, for example, twice the center-to-center distance in the Y direction between both focal points P1 and P2 in the laser beam irradiation step S11.

[0058] Next, a laser beam irradiation step S11 is performed with the scanning directions of the two laser beams LB1 and LB2 set to the opposite X direction. At this time, the two laser beams LB1 and LB2 are obtained, for example, by branching the original laser beam so that the positions of the two focal points P1 and P2 in the X, Y, and Z directions satisfy the above-mentioned conditions. Note that in this laser beam irradiation step S11, since the scanning directions of the two laser beams LB1 and LB2 are set to the opposite X direction, the focal point P1 is positioned on the opposite side in the X direction from the focal point P2.

[0059] Furthermore, the movement step S13 and the laser beam irradiation step S11 are alternately repeated until irradiation of the region of the ingot 11 near the other end in the Y direction (for example, the region farthest from the secondary orientation flat 15) with the first laser beam LB1 or the second laser beam LB2 is completed. That is, the relative movement of the ingot 11 along the Y direction and the positions where the two focal points P1 and P2 are formed and the irradiation of the ingot 11 with the two laser beams LB1 and LB2 in the X direction or the opposite direction as the scanning direction are alternately repeated.

[0060] Then, when modified regions (specifically, the first modified region 19a or the second modified region 19b) are formed in each of the regions near both ends of the ingot 11 in the Y direction (step S12: YES), the peeling layer forming step S1 is completed.

[0061] In the above-mentioned separation layer forming step S1, it is preferable that the separation layer 17 is formed so that the modified portion closest to not only one end but also the other end in the Y direction of the ingot 11 becomes the second modified portion 19b. In this case, the crack 21 is extended to both ends in the Y direction of the ingot 11, making it easier to separate the ingot 11 in the separation step S2 described below.

[0062] In order to form such a peeling layer 17, for example, after grasping the distance L from one end to the other end of the ingot 11 in the Y direction, the distance D0 in the Y direction from one end of the ingot 11 in the Y direction to the focal point P2 in the laser beam irradiation step S11 that is performed first, the distance I in the Y direction between the focal points P1 and P2 in each laser beam irradiation step S11, and the distance D by which the head 16 and the like move in the movement step S13 are calculated. Y and the number of times n that the laser beam irradiation step S11 is performed may be set so as to satisfy the following formula (1).

number

[0063] More specifically, the distance D0, the interval I, and the distance D Y When the ratio is set to 1:2:4, the distance D Y and the number of executions n may be set so as to satisfy the following formula (2).

number

[0064] Also, distance D0, interval I, and distance D Y When the ratio is set to 1:1:2, the distance D Y and the number of executions n may be set so as to satisfy the following formula (3).

number

[0065] Also, distance D0, interval I, and distance D Y When the ratio is set to 2:1:2, the distance D Y and the number of executions n may be set so as to satisfy the following formula (4).

number

[0066] Furthermore, in the above-mentioned peeling layer formation step S1, irradiation of the ingot 11 with the first laser beam LB1 and irradiation of the ingot 11 with the second laser beam LB2 are carried out in a common laser beam irradiation step S11, but these may also be carried out in separate laser beam irradiation steps S11.

[0067] For example, in the peeling layer formation step S1, multiple laser beam irradiation steps S11 may be performed to form all of the multiple rows of first modified portions 19a, and then multiple laser beam irradiation steps S11 may be performed to form all of the multiple rows of second modified portions 19b.

[0068] Alternatively, the first modified portions 19a and the second modified portions 19b may be formed alternately in the peeling layer forming step S1. For example, in the peeling layer forming step S1, the laser beam applying step S11 in which the X direction is set as the scanning direction of the second laser beam LB2, the above-mentioned moving step S13, the laser beam applying step S11 in which the direction opposite to the X direction is set as the scanning direction of the first laser beam LB1, and the above-mentioned moving step S13 may be repeated in order.

[0069] However, in these cases, the number of times that the laser beam irradiation step S11 and the movement step S13 are performed in the peeling layer formation step S1 will roughly double, which will result in a decrease in the throughput of the laser processing device 2.

[0070] In consideration of this, it is preferable that the irradiation of the ingot 11 with the first laser beam LB1 and the irradiation of the ingot 11 with the second laser beam LB2 are carried out in a common laser beam irradiation step S11.

[0071] Furthermore, in the above-described peeling layer forming step S1, the laser beam applying step S11 is performed so that the first focal point P1 at which the first laser beam LB is focused precedes the second focal point P2 at which the second laser beam LB2 is focused in the X direction inside the ingot 11, but the laser beam applying step S11 may also be performed so that both focal points P1 and P2 run side by side. That is, in the peeling layer forming step S1, the laser beam applying step S11 may be performed with the positions of both focal points P1 and P2 aligned in the X direction.

[0072] However, in this case, there is a risk that cracks 21 extending at a large angle in a plan view will extend from second modified region 19b. That is, in this case, there is a risk that cracks 21 will extend so as to cross a region of ingot 11 where first modified region 19a is to be formed but where first modified region 19a has not yet been formed. Therefore, in this case, first modified region 19a will not be formed as intended, and the thickness of peeling layer 17 formed inside ingot 11 will increase, which may reduce productivity when manufacturing substrates from ingot 11.

[0073] In consideration of this, it is preferable that the laser beam irradiation step S11 is performed so that the first focal point P1 precedes the second focal point P2 inside the ingot 11 in the X direction.

[0074] Furthermore, in the above-mentioned peeling layer formation step S1, 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 both laser beams LB1 and LB2, but a direction non-parallel to this may also be set as the scanning direction of both laser beams LB1 and LB2.

[0075] However, if the scanning directions of the laser beams LB1 and LB2 become 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 the peeled layer 17 formed inside the ingot 11 will increase, reducing productivity when manufacturing substrates from the ingot 11.

[0076] 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, and therefore the width (length in the direction perpendicular to the thickness direction of the ingot 11 and the scanning directions of both laser beams LB1 and LB2) of the peeling layer 17 formed inside the ingot 11 decreases. Therefore, in this case, the distance traveled by the head 16 and the like in the movement step S13 must be reduced, and the throughput of the laser processing apparatus 2 decreases.

[0077] 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 directions of both laser beams LB1 and LB2 so that the angle they form with respect to a line parallel to the crystal orientation

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

[0100] is small.

[0078] Furthermore, in the above-described peeling layer forming step S1, the irradiation of both laser beams LB1 and LB2 onto the ingot 11 may be performed only along one direction (for example, the X direction). That is, in the peeling layer forming step S1, the irradiation of both laser beams LB1 and LB2 onto the ingot 11 with the one direction as the scanning direction may be repeated, without the opposite direction (for example, the opposite direction to the X direction) being the scanning direction of both laser beams LB1 and LB2.

[0079] After the separation layer forming step S1, the ingot 11 is separated using the separation layer 17 as a separation starting point to manufacture a substrate (separation step S2). FIGS. 6(A) and 6(B) are side views each showing a schematic view of the separation step S2. This separation step S2 is performed in a separation apparatus 18. The separation apparatus 18 includes a chuck table 20 having a structure similar to that of the chuck table 4 shown in FIG. 3.

[0080] The chuck table 20 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 20. 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 20.

[0081] A separation unit 22 is provided above the chuck table 20. The separation unit 22 has a suction plate 24 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 24. When the separation unit-side suction mechanism operates, a suction force acts on the space near the underside of the suction plate 24.

[0082] A vertical movement mechanism 26 is connected to the upper surface of the suction plate 24. The vertical movement mechanism 26 includes, for example, a ball screw and a motor. When the vertical movement mechanism 26 operates, the suction plate 24 moves in the vertical direction.

[0083] When performing separation step S2 in separation device 18, first, with chuck table 20 and suction plate 24 sufficiently spaced apart, ingot 11 having peeled layer 17 formed therein is placed on the holding surface of chuck table 20 with surface 11a facing up. Next, the table-side suction mechanism is operated so that ingot 11 is held on chuck table 20.

[0084] Next, the vertical movement mechanism lowers the suction plate 24 so that the lower surface of the suction plate 24 contacts the front surface 11a of the ingot 11 (see FIG. 6(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 26 raises the suction plate 24 so that the suction plate 24 is separated from the chuck table 20 (see FIG. 6(B)).

[0085] 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 peeling layer 17. As a result, ingot 11 is separated from peeling layer 17 as a separation starting point, producing substrate 23. This completes separation step S2, i.e., the method for producing the substrate shown in FIG. 2.

[0086] 2, a peeling layer 17 is formed inside an ingot 11, and then the ingot 11 is separated using this peeling layer 17 as a separation starting point to produce a substrate 23. This improves the productivity of the substrate 25 compared to when the substrate 25 is produced from the ingot 11 using a wire saw.

[0087] Note that 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 only necessary to relatively move the ingot 11 and the first focal point P1 where the first laser beam LB1 is focused and / or the second focal point P2 where the second laser beam LB2 is focused, and there is no limitation on the structure for this.

[0088] 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.

[0089] 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 first laser beam LB1 and / or the second laser beam LB2 emitted from the head 16 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.

[0090] 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 23. 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.

[0091] Furthermore, when the peeling layer formation step S1 is performed so that the modified portion closest to one end of the ingot 11 in the Y direction (specifically, the secondary orientation flat 15) becomes the second modified portion 19b, and the modified portion closest to the other end becomes the first modified portion 19a, the substrate manufacturing method of the present invention may include a step of reinforcing the vicinity of the other end as the separation starting point after the peeling layer formation step S1 and before the separation step S2.

[0092] That is, the method for manufacturing a substrate of the present invention may include, for example, a step for facilitating separation of the ingot 11 in the separation step S2 by extending the crack 21 to the other end in the Y direction of the ingot 11. Figure 7 is a flowchart schematically showing an example of a method for manufacturing a substrate including such a step.

[0093] In this method, after the peeling layer formation step S1 and before the separation step S2, the second focal point P2 is positioned so as to overlap the first modified portion 19a that is closest to the other end of the ingot 11 in the Y direction, and the ingot 11 and the second focal point P2 are moved relatively along the X direction (final laser beam irradiation step S3).

[0094] The final laser beam irradiation step S3 is performed in the same manner as the above-described laser beam irradiation step S11, except that, for example, the first laser beam LB1 is not emitted from the head 16 and only the second laser beam LB2 is emitted.

[0095] Specifically, first, the movement mechanism moves the head 16 and the like along the X direction and / or Y direction so that the first modifying section 19a closest to the other end of the ingot 11 is positioned in the X direction when viewed from the head 16 in a plan view. Then, while emitting the second laser beam LB2 from the head 16, the movement mechanism moves the head 16 and the like along the X direction so that the focal point P2 passes from one end to the other end of the ingot 11 in the X direction at a predetermined speed.

[0096] Alternatively, the final laser beam irradiation step S3 may be performed in the same manner as the above-described laser beam irradiation step S11, including the point that both the first laser beam LB1 and the second laser beam LB2 are emitted from the head 16. In other words, the final laser beam irradiation step S3 may be performed in the same manner as the above-described laser beam irradiation step S11, except that the final laser beam irradiation step S3 is performed so that the focal point P1 does not pass through the inside of the ingot 11.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] Furthermore, the material of the workpiece used in the substrate manufacturing method of the present invention is not limited to gallium oxide, and may be, for example, a single crystal of silicon (Si), silicon carbide (SiC), gallium nitride (GaN), lithium tantalate (LiTaO3:LT), lithium niobate (LiNbO3:LN), or the like.

[0101] 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]

[0102] 2: Laser processing equipment 4: Chuck table 6: Laser beam irradiation unit 8: Laser oscillator 10: Attenuator 11: Ingot (11a: front surface, 11b: back surface, 11c: side surface) 12: Branch unit 13: Primary Orientation Flat 14: Mirror 15: Secondary Orientation Flat 16: Head 17: Peeling layer 18: Separation device 19a: First reforming section 19b: Second reforming section 20: Chuck table 21: Crack 22: Separation unit 23: Substrate 24: Suction plate 26: Vertical movement mechanism

Claims

1. A method for manufacturing a substrate by manufacturing a substrate thinner than a workpiece from the workpiece, comprising: a peeling layer forming step of forming a peeling layer inside the workpiece by irradiating the workpiece with a laser beam having a wavelength that transmits through the material of the workpiece; a separation step of manufacturing the substrate by separating the workpiece using the release layer as a separation starting point after the release layer formation step, In the release layer forming step, a laser beam irradiation step of relatively moving the workpiece and the focal point along a first direction while positioning the focal point at which the laser beam is focused inside the workpiece; a moving step of relatively moving the workpiece and the position where the focal point is formed along a second direction perpendicular to the first direction; by alternately repeating the steps above, the release layer is formed to include first modified portions and second modified portions that are alternately arranged in the second direction, the first modified portion is formed at a first focal point where a first laser beam having a first output is focused; A method for manufacturing a substrate, wherein the second modified portion is formed at a second focal point where a second laser beam having a second output greater than the first output is focused.

2. 2. The method for manufacturing a substrate according to claim 1, wherein in the laser beam irradiation step, an original laser beam having a wavelength that transmits through a material of the workpiece is split into the first laser beam and the second laser beam, and the first focal point and the second focal point, which are spaced apart in the second direction, are positioned inside the workpiece, and the workpiece and the first focal point and the second focal point are moved relatively along the first direction.

3. 3. The method for manufacturing a substrate according to claim 2, wherein in the laser beam irradiation step, the first focal point moves within the workpiece ahead of the second focal point in the first direction.

4. The method for manufacturing a substrate according to claim 1 , wherein the crack extending from the first modified portion is smaller than the crack extending from the second modified portion.

5. The method for manufacturing a substrate according to claim 1 , wherein cracks do not propagate from the first modified portion, but do propagate from the second modified portion.

6. A method for manufacturing a substrate as described in any one of claims 1 to 5, further comprising a final laser beam irradiation step, after the peeling layer formation step is performed so that the modified portion closest to one end of the workpiece in the second direction becomes the second modified portion and the modified portion closest to the other end becomes the first modified portion, and before the separation step, in which the workpiece and the second focal point are positioned so that they overlap the first modified portion closest to the other end, and the method further comprises a final laser beam irradiation step in which the workpiece and the second focal point are moved relatively along the first direction.

7. The method for manufacturing a substrate according to any one of claims 1 to 5, wherein the peeling layer forming step is carried out so that the modified portion closest to each of both ends of the workpiece in the second direction becomes the second modified portion.

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