Substrate manufacturing method

Abstract

To improve a throughput of a manufacturing method of a substrate using a laser beam.SOLUTION: In a state for conversing a laser beam so that a length along an allocation transfer direction becomes larger than a length along a processing transfer direction, a peeling layer is formed in an inner part of a processed material. In this case, a cracking contained in the peeling layer is easily extended along the allocation transfer direction. Thus, a relative movement distance (index) between, a location where the laser beam in an allocation transfer step is conversed and the processed material can be increased. As a result, a throughput of a manufacturing method of a substrate using the laser beam can be improved.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a substrate from a workpiece having a first surface and a second surface opposite to the first surface.

Background Art

[0002] Chips of semiconductor devices are generally manufactured from cylindrical substrates made of semiconductor materials such as silicon (Si) or silicon carbide (SiC). This substrate is cut out from an ingot made of a cylindrical semiconductor material using, for example, a wire saw (see, for example, Patent Document 1).

[0003] However, the cutting width when cutting out a substrate from an ingot using a wire saw is around 300 μm, which is relatively large. In addition, fine irregularities are formed on the surface of the substrate cut out in this way, and this substrate is curved as a whole (the wafer warps). Therefore, in this substrate, it is necessary to perform lapping, etching, and / or polishing on its surface to flatten the surface.

[0004] In this case, the amount of material finally used as a substrate is about 2 / 3 of the amount of material of the entire ingot. That is, about 1 / 3 of the amount of material of the entire ingot is discarded when cutting out the substrate from the ingot and flattening the substrate. Therefore, when manufacturing a substrate using a wire saw in this way, the productivity is low.

[0005] In view of this point, it has been proposed to manufacture a substrate from an ingot using a laser beam having a wavelength that penetrates the material constituting the ingot (see, for example, Patent Document 2). In this method, first, relative movement along the processing feed direction between the ingot and the focal point is repeated while positioning the focal point of the laser beam inside the ingot.

[0006] As a result, a delamination layer, including a modified area formed around the focal point of the laser beam and cracks extending from the modified area, is formed in each of several regions along the processing feed direction of the ingot. Then, by applying an external force to this ingot, the substrate is separated from the ingot starting from the delamination layer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-262826 [Patent Document 2] Japanese Patent Publication No. 2016-111143 [Overview of the project] [Problems that the invention aims to solve]

[0008] When manufacturing circuit boards using a laser beam, the amount of waste material can be reduced compared to when manufacturing circuit boards using a wire saw. In other words, the former method can improve the productivity of circuit board production compared to the latter.

[0009] On the other hand, in the former case, it is impossible or difficult to manufacture multiple substrates simultaneously from an ingot, whereas in the latter case, multiple wire saws can be used to cut the ingot simultaneously, allowing for the simultaneous manufacture of multiple substrates. Therefore, in the former case, the throughput is often lower compared to the latter case.

[0010] In view of this, an object of the present invention is to improve the throughput of a substrate manufacturing method using a laser beam. [Means for solving the problem]

[0012] Honpatsu ClearlyAccording to the present invention, a method for manufacturing a substrate from a workpiece having a first surface and a second surface opposite to the first surface, comprising: a release layer forming step in which a laser beam of a wavelength that penetrates the material constituting the workpiece is focused inside the workpiece, and the workpiece is moved relative to the location where the laser beam is focused along a processing feed direction parallel to the first surface; an indexing feed step in which the workpiece is moved relative to the location where the laser beam is focused along an indexing feed direction perpendicular to the processing feed direction and parallel to the first surface; and after repeatedly performing the release layer forming step and the indexing feed step alternately, the substrate is manufactured from the workpiece starting from the release layer. A method for manufacturing a substrate is provided, comprising a separation step, wherein in the delamination layer formation step, the laser beam is focused such that the length along the indexing feed direction is greater than the length along the processing feed direction, and in the delamination layer formation step, the laser beam, whose wavefront is controlled by a spatial light modulator, is irradiated onto the workpiece, and the light constituting the laser beam incident on the spatial light modulator that is located towards the center in the direction corresponding to the indexing feed direction is focused to both ends of the location in the indexing feed direction, and the light constituting the laser beam incident on the spatial light modulator that is located towards both ends in the direction corresponding to the indexing feed direction is focused to the center of the location in the indexing feed direction.

[0013] Preferably, the laser beam is branched so as to be focused at each of a plurality of locations that are spaced apart from each other in the indexing feed direction. [Effects of the Invention]

[0014] In this invention, a delamination layer is formed inside the workpiece when the laser beam is focused such that the length of the delamination layer along the indexing feed direction is greater than the length along the machining feed direction. In this case, cracks contained in the delamination layer are more likely to propagate along the indexing feed direction.

[0015] This allows for a larger relative movement distance (index) between the point where the laser beam is focused and the workpiece during the indexing feed step. As a result, it becomes possible to improve the throughput of the substrate manufacturing method using a laser beam. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a schematic perspective view showing an example of an ingot. [Figure 2] Figure 2 is a schematic top view showing an example of an ingot. [Figure 3] Figure 3 is a flowchart schematically showing an example of a substrate manufacturing method. [Figure 4] Figure 4 is a schematic diagram showing an example of a laser processing apparatus. [Figure 5] Figure 5(A) schematically shows the wavefront of an uncontrolled laser beam and the location where the laser beam is focused in a spatial light modulator, while Figures 5(B) and 5(C) schematically show the wavefront of a controlled laser beam and the location where the laser beam is focused in a spatial light modulator. [Figure 6] Figure 6 is a schematic top view showing a holding table for holding ingots. [Figure 7] Figure 7(A) is a schematic top view showing an example of the delamination layer formation step, and Figure 7(B) is a schematic partial cross-sectional side view showing an example of the delamination layer formation step. [Figure 8] Figure 8 is a schematic cross-sectional view showing an example of a delamination layer formed inside the ingot during the delamination layer formation step. [Figure 9] Figures 9(A) and 9(B) are schematic cross-sectional side views illustrating an example of the separation step. [Figure 10] Figures 10(A) and 10(B) are schematic partial cross-sectional side views illustrating another example of the separation step. [Modes for carrying out the invention]

[0017] Referring to the accompanying drawings, embodiments of the present invention will be described. FIG. 1 is a perspective view schematically showing an example of a columnar ingot made of single crystal silicon, and FIG. 2 is a top view schematically showing an example of this ingot. In FIG. 1, the crystal planes of the single crystal silicon exposed on the plane included in this ingot are also shown. In FIG. 2, the crystal orientation of the single crystal silicon constituting this ingot is also shown.

[0018] In the ingot 11 shown in FIGS. 1 and 2, a specific crystal plane included in the crystal plane {100} (here, for convenience, the crystal plane (100)) is exposed on each of the circular front surface (first surface) 11a and the circular back surface (second surface) 11b. That is, in this ingot 11, the perpendiculars (crystal axes) of the front surface 11a and the back surface 11b respectively are along the crystal orientation <0100>.

[0019] Although the ingot 11 is manufactured such that the crystal plane (100) is exposed on each of the front surface 11a and the back surface 11b, due to processing errors during manufacturing or the like, a plane slightly inclined from the crystal plane (100) may be exposed on each of the front surface 11a and the back surface 11b. Specifically, on each of the front surface 11a and the back surface 11b of the ingot 11, a plane having an angle of 1° or less with respect to the crystal plane (100) may be exposed. That is, the crystal axis of the ingot 11 may be along a direction having an angle of 1° or less with respect to the crystal orientation <0100>.

[0020] In addition, an orientation flat 13 is formed on the side surface 11c of the ingot 11, and the center C of the ingot 11 is located in a specific crystal orientation included in the crystal orientation <110> (here, for convenience, the crystal orientation <0011>) as seen from this orientation flat 13. That is, in this orientation flat 13, the crystal plane (011) of the single crystal silicon is exposed.

[0021] Figure 3 is a schematic flowchart illustrating an example of a substrate manufacturing method for producing a substrate from an ingot 11, which is the workpiece. In short, in this method, a delamination layer is formed inside the ingot 11 using a laser processing device, and then the substrate is separated from the ingot 11 starting from this delamination layer.

[0022] Figure 4 is a schematic diagram showing an example of a laser processing apparatus used to form a delamination layer inside an ingot 11. The X-axis direction (processing feed direction) and Y-axis direction (indexing feed direction) shown in Figure 4 are mutually orthogonal directions on the horizontal plane, while the Z-axis direction is perpendicular to both the X-axis and Y-axis directions (vertical direction). Furthermore, in Figure 4, some of the components of the laser processing apparatus are shown as functional blocks.

[0023] The laser processing apparatus 2 shown in Figure 4 has a cylindrical holding table 4. This holding table 4 has a circular upper surface (holding surface) that is wider than the front surface 11a and back surface 11b of the ingot 11, and holds the ingot 11 on this holding surface. A cylindrical porous plate (not shown) is exposed on this holding surface.

[0024] Furthermore, this porous plate is in communication with a suction source (not shown), such as an ejector, via a flow path or the like provided inside the holding table 4. When this suction source operates, a negative pressure is generated in the space near the holding surface of the holding table 4. This allows, for example, the holding table 4 to hold the ingot 11 placed on the holding surface.

[0025] Furthermore, a laser beam irradiation unit 6 is provided above the holding table 4. This laser beam irradiation unit 6 has a laser oscillator 8. This laser oscillator 8 has, for example, Nd:YAG as the laser medium and irradiates the ingot 11 with a pulsed laser beam LB with a wavelength (for example, 1064 nm) that penetrates the material (single crystal silicon) constituting the ingot 11.

[0026] This laser beam LB is incident on a spatial light modulator 10 which includes a liquid crystal phase control element commonly called LCoS (Liquid Crystal on Silicon). Then, in the spatial light modulator 10, the laser beam LB incident on the spatial light modulator 10 is branched to form multiple laser beams LB that are separated from each other in the Y-axis direction.

[0027] Furthermore, in the spatial light modulator 10, the wavefront of the laser beam LB is controlled such that the length along the Y-axis of the location where each branched laser beam LB is focused is greater than the length along the X-axis.

[0028] Figure 5(A) schematically shows the wavefront of the uncontrolled laser beam LB in the spatial light modulator 10 and the location where the laser beam LB is focused. Figures 5(B) and 5(C) schematically show the wavefront of the controlled laser beam LB in the spatial light modulator 10 and the location where the laser beam LB is focused.

[0029] For example, the spatial light modulator 10 controls the wavefront of the laser beam LB so that it becomes the wavefront WF2 shown in Figure 5(B) or the wavefront WF3 shown in Figure 5(C), which has a longer length along the Y-axis direction than the wavefront WF1 shown in Figure 5(A). In this case, irradiating the ingot 11 with the laser beam LB makes it easier for cracks in the delamination layer formed inside the ingot 11 to propagate along the Y-axis direction. This makes it possible to increase the relative movement distance (index) between the location where the laser beam LB is focused and the ingot 11 in the indexing feed step (S2) described later.

[0030] Furthermore, when the wavefront of the laser beam LB becomes the wavefront WF3 shown in Figure 5(C), the light constituting the laser beam LB that is located towards the center in the Y-axis direction is focused to both ends, and the light located at those ends is focused towards the center. In this case, the probability of the laser beam LB focusing at multiple locations separated in the Z-axis direction due to astigmatism is reduced. As a result, by irradiating the ingot 11 with the laser beam LB, the increase in the thickness of the delamination layer (length along the Z-axis direction) formed inside the ingot 11 can be suppressed, thereby improving the productivity of the substrate.

[0031] Furthermore, the laser beam LB, whose wavefront is controlled in the spatial light modulator 10, may be reflected by a mirror 12 or the like (described later) and then focused before being irradiated onto the ingot 11. In such cases, the wavefront of the laser beam LB may be controlled in the spatial light modulator 10 so that after the laser beam LB is reflected, it becomes the wavefront WF3 shown in Figure 5(C).

[0032] In other words, the spatial light modulator 10 may control the wavefront of the laser beam LB such that light located towards the center in the direction corresponding to the Y-axis direction (the direction parallel to the Y-axis direction after the laser beam LB is reflected) is focused towards both ends in the Y-axis direction, and light located towards both ends is focused towards the center in the Y-axis direction.

[0033] The laser beam LB, whose wavefront is controlled in the spatial light modulator 10, is reflected by the mirror 12 and guided to the irradiation head 14. The irradiation head 14 houses a focusing lens (not shown) for focusing the laser beam LB. The laser beam LB, focused by this focusing lens, is then irradiated onto the holding surface side of the holding table 4.

[0034] Furthermore, the irradiation head 14 of the laser beam irradiation unit 6 is connected to a moving mechanism (not shown). This moving mechanism, for example, includes a ball screw and moves the irradiation head 14 along the X-axis, Y-axis, and / or Z-axis directions. In the laser processing apparatus 2, by operating this moving mechanism, the position (coordinates) in the X-axis, Y-axis, and Z-axis directions of the location where the laser beam LB emitted from the irradiation head 14 is focused is adjusted.

[0035] Then, when forming a delamination layer over the entire interior of the ingot 11 in the laser processing apparatus 2, the holding table 4 first holds the ingot 11 with its surface 11a facing upwards. Figure 6 is a schematic top view showing the holding table 4 that holds the ingot 11.

[0036] The ingot 11 is held on the holding table 4 in a state where, for example, the direction from the orientation flat 13 toward the center C of the ingot 11 (crystal orientation

[0011] ) makes an angle of 45° with respect to both the X-axis and Y-axis directions. That is, the ingot 11 is held on the holding table 4 in a state where, for example, the crystal orientation

[0010] is parallel to the X-axis direction and the crystal orientation

[0001] is parallel to the Y-axis direction.

[0037] Next, a delamination layer is formed in the region at one end of the ingot 11 in the Y-axis direction. Specifically, first, the irradiation head 14 of the laser beam irradiation unit 6 is positioned so that, in a plan view, the region is positioned in the X-axis direction from the irradiation head 14. Then, the irradiation head 14 is raised and lowered so that the location where the laser beam LB irradiated from the irradiation head 14 is focused is positioned at a height corresponding to the interior of the ingot 11.

[0038] Furthermore, the irradiation head 14 emits multiple laser beams LB that are branched to be separated from each other in the Y-axis direction. The laser beams LB emitted from the irradiation head 14 are then focused at multiple locations (for example, 8 locations) that are separated from each other in the Y-axis direction. In addition, the length along the Y-axis direction of the location where each branched laser beam LB is focused is greater than the length along the X-axis direction.

[0039] Next, a delamination layer is formed by relatively moving the ingot 11 to the point where the laser beam LB is focused along the X-axis (delamination layer formation step: S1). Figure 7(A) is a schematic top view showing an example of the delamination layer formation step (S1), and Figure 7(B) is a schematic partial cross-sectional side view showing an example of the delamination layer formation step (S1). Figure 8 is a schematic cross-sectional view showing the delamination layer formed inside the ingot 11 in the delamination layer formation step (S1).

[0040] In this delamination layer formation step (S1), the irradiation head 14 is moved so that, in a plan view, it passes from one end to the other of the ingot 11 in the X-axis direction, while each branched laser beam LB is irradiated from the irradiation head 14 toward the holding table 4 (see Figures 7(A) and 7(B)).

[0041] In other words, with the point where the laser beam LB is focused located inside the ingot 11, the point where the laser beam LB is focused and the ingot 11 are moved relative to each other along the X-axis. As a result, a modified region 15a with a disordered crystal structure of single-crystal silicon is formed, centered around the point where each branched laser beam LB is focused, and where the length along the Y-axis is greater than the length along the X-axis.

[0042] Then, when the modified portion 15a is formed inside the ingot 11, the volume of the ingot 11 expands, and internal stress is generated in the ingot 11. This internal stress is relieved by the extension of cracks 15b from the modified portion 15a. As a result, a delamination layer 15 is formed inside the ingot 11, which includes multiple modified portions 15a and cracks 15b propagating from each of the multiple modified portions 15a.

[0043] Next, the ingot 11 and the location where each branched laser beam LB is focused are moved relative to each other along the Y-axis (indexing step: S2). Specifically, the irradiation head 14 is moved along the Y-axis so that the movement distance (index) of the irradiation head 14 is longer than the width of the peeling layer 15 along the Y-axis. Then, the peeling layer formation step (S1) described above is performed again.

[0044] As a result, two peel layers 15 that are separated in the Y-axis direction and parallel to each other are formed inside the ingot 11. Furthermore, the indexing feed step (S2) and the peel layer formation step (S1) are repeatedly performed until a peel layer 15 is formed in the region on the other end side in the Y-axis direction inside the ingot 11.

[0045] Specifically, the delamination layer formation step (S1) and the indexing and feeding step (S2) are repeatedly performed alternately so that the delamination layer 15 is formed throughout the entire interior of the ingot 11, from one end to the other in the Y-axis direction. Once the delamination layer 15 is formed throughout the entire interior of the ingot 11 (step (S3): YES), the substrate is separated from the ingot 11 starting from the delamination layer 15 (separation step: S4).

[0046] Figures 9(A) and 9(B) are schematic partial cross-sectional side views illustrating an example of the separation step (S4). This separation step (S4) is carried out, for example, in the separation apparatus 18 shown in Figures 9(A) and 9(B). This separation apparatus 18 has a holding table 20 that holds the ingot 11 on which the peeled layer 15 has been formed.

[0047] The holding table 20 has a circular top surface (holding surface), on which a porous plate (not shown) is exposed. Furthermore, this porous plate is in communication with a suction source (not shown), such as a vacuum pump, via a flow path or the like provided inside the holding table 20. When this suction source operates, negative pressure is generated in the space near the holding surface of the holding table 20.

[0048] Furthermore, a separation unit 22 is provided above the holding table 20. This separation unit 22 has a cylindrical support member 24. A rotational drive source, such as a ball screw type lifting mechanism (not shown) and a motor, is connected to the upper part of this support member 24. The separation unit 22 moves up and down by operating this lifting mechanism. Also, by operating this rotational drive source, the support member 24 rotates with a rotation axis that passes through the center of the support member 24 and is aligned perpendicular to the holding surface of the holding table 20.

[0049] Furthermore, the lower end of the support member 24 is fixed to the center of the upper part of the disc-shaped base 26. On the lower side of the outer peripheral region of the base 26, a plurality of movable members 28 are provided at roughly equal intervals along the circumferential direction of the base 26. Each of these movable members 28 has a plate-shaped upright portion 28a that extends downward from the lower surface of the base 26.

[0050] The upper end of this upright portion 28a is connected to an actuator such as an air cylinder built into the base 26, and by operating this actuator, the movable member 28 moves along the radial direction of the base 26. In addition, a plate-shaped wedge portion 28b is provided on the inner surface of the lower end of this upright portion 28a, extending toward the center of the base 26 and becoming thinner as it approaches the tip.

[0051] In the separation device 18, for example, the separation step (S4) is carried out in the following order. Specifically, first, the ingot 11 is placed on the holding table 20 so that the center of the back surface 11b of the ingot 11 on which the peeled layer 15 is formed coincides with the center of the holding surface of the holding table 20.

[0052] Next, a suction source communicating with a porous plate exposed on the holding surface is activated so that the ingot 11 is held by the holding table 20. Then, actuators are activated to position each of the multiple movable members 28 radially outward from the base 26.

[0053] Next, the lifting mechanism is operated to position the tips of the wedge portions 28b of each of the multiple movable members 28 at a height corresponding to the peeling layer 15 formed inside the ingot 11. Next, the actuator is operated so that the wedge portions 28b are driven into the side surface 11c of the ingot 11 (see Figure 9(A)). Next, the rotation drive source is operated so that the wedge portions 28b driven into the side surface 11c of the ingot 11 rotate.

[0054] Next, the lifting mechanism is operated to raise the wedge portion 28b (see Figure 9(B)). After driving the wedge portion 28b into the side surface 11c of the ingot 11 and rotating it as described above, raising the wedge portion 28b causes the cracks 15b contained in the delamination layer 15 to extend further. As a result, the front surface 11a and the back surface 11b of the ingot 11 are separated. In other words, the substrate 17 is manufactured from the ingot 11, starting from the delamination layer 15.

[0055] Furthermore, if the front surface 11a and back surface 11b of the ingot 11 are separated when the wedge portion 28b is driven into the side surface 11c of the ingot 11, it is not necessary to rotate the wedge portion 28b. Alternatively, the actuator and the rotation drive source may be operated simultaneously to drive the rotating wedge portion 28b into the side surface 11c of the ingot 11.

[0056] In the substrate manufacturing method described above, a delamination layer 15 is formed inside the ingot 11 with the laser beam LB focused such that the length along the Y-axis is greater than the length along the X-axis. In this case, cracks 15b contained in the delamination layer 15 are more likely to propagate along the Y-axis.

[0057] This allows for a larger relative movement distance (index) between the point where the laser beam LB is focused and the ingot 11 during the indexing feed step (S2). As a result, it becomes possible to improve the throughput of the manufacturing method of the substrate 17 using the laser beam LB.

[0058] Furthermore, in the substrate manufacturing method described above, the delamination layer 15 is formed by relatively moving the ingot 11 and the location where each of the multiple laser beams LB, which are separated from each other in the Y-axis direction (crystal orientation

[0001] ), are focused, along the X-axis direction (crystal orientation

[0010] ). In this case, the amount of material discarded when manufacturing the substrate 17 from the ingot 11 can be further reduced, and the productivity of the substrate 17 can be improved.

[0059] The following explains this point in detail. First, single-crystal silicon is generally most easily cleaved at a specific crystal plane within crystal plane {111}, and second most easily cleaved at a specific crystal plane within crystal plane {110}. Therefore, for example, the crystal orientation of the single-crystal silicon constituting ingot 11 <110> When a modified portion is formed along a specific crystal orientation (for example, crystal orientation

[0011] ) contained within the material, many cracks are generated from this modified portion that extend along the specific crystal plane contained within the crystal plane {111}.

[0060] On the other hand, the crystal orientation of single-crystal silicon <100> When multiple modified regions are formed in a region along a specific crystal orientation within the material, such that they are aligned in a direction perpendicular to the direction in which the region extends when viewed from a plan perspective, many cracks are generated from each of these modified regions along the crystal plane {N10} (where N is an integer with an absolute value of 10 or less, excluding 0) that is parallel to the direction in which the region extends.

[0061] For example, as in the substrate manufacturing method described above, if multiple modified portions 15a are formed in a region along the crystal orientation

[0010] so as to be aligned along the crystal orientation

[0001] , then many cracks will extend from each of these multiple modified portions 15a along the crystal plane {N10} (where N is a natural number less than or equal to 10) that is parallel to the crystal orientation

[0010] .

[0062] Specifically, when multiple modified regions 15a are formed in this manner, cracks are more likely to propagate in the following crystal planes.

number

number

[0063] Furthermore, the angle that the crystal planes (100) exposed on the surface 11a and back surface 11b of the ingot 11 make with the crystal planes parallel to the crystal orientation

[0010] within the crystal plane {N10} is 45° or less. On the other hand, the angle that the crystal plane (100) makes with a specific crystal plane included in the crystal plane {111} is approximately 54.7°.

[0064] Therefore, in the above-described substrate manufacturing method, the peel layer 15 tends to be wider and thinner compared to the case where multiple modified parts are formed in a region along the crystal orientation

[0011] of the single-crystal silicon, such that they are aligned in a direction perpendicular to the direction in which the region extends when viewed in plan. As a result, in the above-described substrate manufacturing method, the amount of material discarded when manufacturing the substrate 17 from the ingot 11 can be reduced, and the productivity of the substrate 17 can be improved.

[0065] The above-described method for manufacturing the substrate is one aspect of the present invention, and the present invention is not limited to the method described above. For example, the ingot used to manufacture the substrate in the present invention is not limited to the ingot 11 shown in Figures 1 and 2, etc. Specifically, in the present invention, the substrate may be manufactured from an ingot made of single-crystal silicon in which crystal planes not included in the crystal plane {100} are exposed on the front and back surfaces, respectively.

[0066] Furthermore, in the present invention, the substrate may be manufactured from a cylindrical ingot having a notch formed on its side surface. Alternatively, in the present invention, the substrate may be manufactured from a cylindrical ingot having neither an orientation flat nor a notch formed on its side surface. Furthermore, in the present invention, the substrate may be manufactured from a cylindrical ingot made of a semiconductor material other than silicon, such as silicon carbide.

[0067] Furthermore, the structure of the laser processing apparatus used in the present invention is not limited to the structure of the laser processing apparatus 2 described above. For example, the present invention may be carried out using a laser processing apparatus provided with a moving mechanism that moves the holding table 4 along the X-axis, Y-axis, and / or Z-axis directions, respectively.

[0068] In other words, in the present invention, it is sufficient that the holding table 4 that holds the ingot 11 and the irradiation head 14 of the laser beam irradiation unit 6 that irradiates the laser beam LB can move relative to each other along the X-axis, Y-axis, and Z-axis directions, and there are no limitations on the structure for this purpose.

[0069] Furthermore, in the present invention, after the delamination layer 15 has been formed in the entire ingot 11 from one end to the other end in the Y-axis direction (step S3: YES), the delamination layer formation step (S1) and the indexing and feeding step (S2) may be repeated. That is, the laser beam LB may be irradiated again to form the delamination layer 15 in the ingot 11 from one end to the other end in the Y-axis direction, where the delamination layer 15 has already been formed.

[0070] Furthermore, in the present invention, the peel layer formation step (S1) may be performed again after the peel layer formation step (S1) and before the indexing feed step (S2). That is, the laser beam LB may be irradiated again to form the peel layer 15 on a linear region inside the ingot 11 where the peel layer 15 has already been formed.

[0071] When the delamination layer formation step (S1) is performed again on a region where the delamination layer 15 has already been formed, the density of the modified portion 15a and the crack 15b contained in the already formed delamination layer 15 increases. This facilitates the separation of the substrate 17 from the ingot 11 in the separation step (S4).

[0072] Furthermore, in this case, the cracks 15b contained in the delamination layer 15 extend further, increasing the length (width) of the delamination layer 15 along the Y-axis. Therefore, in this case, the travel distance (index) of the irradiation head 14 of the laser beam irradiation unit 6 in the indexing feed step (S2) can be increased.

[0073] Furthermore, in the present invention, if it is possible to extend the cracks 15b contained in the delamination layer 15 in the separation step (S4), the delamination layer 15 does not need to be formed over the entire interior of the ingot 11 in the delamination layer formation step (S2). For example, if it is possible to extend the cracks 15b to the region near the side surface 11c of the ingot 11 by performing the separation step (S4) using the separation device 18, the delamination layer 15 does not need to be formed over part or all of the region near the side surface 11c of the ingot 11 in the delamination layer formation step (S2).

[0074] Furthermore, the separation step (S4) of the present invention may be carried out using an apparatus other than the separation apparatus 18 shown in Figures 9(A) and 9(B). Figures 10(A) and 10(B) are schematic partial cross-sectional side views showing an example of the separation step (S4) carried out using an apparatus other than the separation apparatus 18.

[0075] The separation device 30 shown in Figures 10(A) and 10(B) has a holding table 32 for holding ingots 11 on which a peeled layer 15 has been formed. This holding table 32 has a circular upper surface (holding surface), on which a porous plate (not shown) is exposed.

[0076] Furthermore, this porous plate is in communication with a suction source (not shown), such as a vacuum pump, via a flow path or the like provided inside the holding table 32. Therefore, when this suction source operates, negative pressure is generated in the space near the holding surface of the holding table 32.

[0077] Furthermore, a separation unit 34 is provided above the holding table 32. This separation unit 34 has a cylindrical support member 36. A ball screw type lifting mechanism (not shown), for example, is connected to the upper part of this support member 36, and the separation unit 34 moves up and down by operating this lifting mechanism.

[0078] Furthermore, the lower end of the support member 36 is fixed to the center of the upper part of the disc-shaped suction plate 38. Multiple suction ports are formed on the lower surface of this suction plate 38, and each of these ports is connected to a suction source (not shown), such as a vacuum pump, via a flow path or the like provided inside the suction plate 38. Therefore, when this suction source operates, negative pressure is generated in the space near the lower surface of the suction plate 38.

[0079] In the separation device 30, for example, the separation step (S4) is carried out in the following order. Specifically, first, the ingot 11 is placed on the holding table 32 so that the center of the back surface 11b of the ingot 11 on which the peeled layer 15 is formed coincides with the center of the holding surface of the holding table 32.

[0080] Next, a suction source communicating with a porous plate exposed on the holding surface is activated so that the ingot 11 is held by the holding table 32. Then, the lifting mechanism is activated to lower the separation unit 34 so that the lower surface of the suction plate 38 comes into contact with the surface 11a of the ingot 11.

[0081] Next, a suction source communicating with multiple suction ports is activated so that the surface 11a side of the ingot 11 is sucked through the multiple suction ports formed in the suction plate 38 (see Figure 10(A)). Then, the lifting mechanism is activated to raise the separation unit 34 so that the suction plate 38 is separated from the holding table 32 (see Figure 10(B)).

[0082] At this time, an upward force acts on the surface 11a side of the ingot 11, which is being sucked in through multiple suction ports formed in the suction plate 38. As a result, the cracks 15b contained in the delamination layer 15 extend further, separating the surface 11a side and the back surface 11b side of the ingot 11. In other words, the substrate 17 is manufactured from the ingot 11, starting from the delamination layer 15.

[0083] Furthermore, in the separation step (S4) of the present invention, ultrasonic waves may be applied to the surface 11a side of the ingot 11 prior to the separation of the surface 11a side and the back surface 11b side of the ingot 11. In this case, the cracks 15b contained in the delamination layer 15 will extend further, making it easier to separate the surface 11a side and the back surface 11b side of the ingot 11.

[0084] Furthermore, in the present invention, prior to the delamination layer formation step (S1), the surface 11a of the ingot 11 may be flattened by grinding or polishing (flattening step). For example, this flattening may be performed when manufacturing multiple substrates from the ingot 11. Specifically, when the ingot 11 is separated in the delamination layer 15 and a substrate 17 is manufactured, the newly exposed surface of the ingot 11 forms irregularities that reflect the distribution of modified parts 15a and cracks 15b contained in the delamination layer 15.

[0085] Therefore, when manufacturing a new substrate from this ingot 11, it is preferable to planarize the surface of the ingot 11 prior to the delamination layer formation step (S1). This suppresses diffuse reflection of the laser beam LB irradiated onto the ingot 11 in the delamination layer formation step (S1) on the surface of the ingot 11. Similarly, in the present invention, the surface of the substrate 17 separated from the ingot 11 on the side of the delamination layer 15 may be planarized by grinding or polishing.

[0086] Furthermore, in the present invention, a substrate may be manufactured using a bare wafer made of a semiconductor material such as silicon or silicon carbide as the workpiece. This bare wafer has, for example, a thickness of 2 to 5 times that of the substrate to be manufactured. This bare wafer is manufactured, for example, by separating it from an ingot made of a semiconductor material such as silicon or silicon carbide by a method similar to the one described above. In this case, the substrate can also be described as being manufactured by repeating the above method twice.

[0087] Furthermore, in the present invention, a substrate may be manufactured using a device wafer, which is produced by forming a semiconductor device on one surface of the bare wafer, as the workpiece. In addition, the structures and methods described in the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Examples]

[0088] We investigated the maximum index at which a peel-off layer could be formed without gaps inside a workpiece made of 775 μm thick single-crystal silicon under multiple conditions with different shapes of the area where the laser beam LB is focused. In this investigation, the laser beam LB, adjusted to a power of 4.0 W, was split into eight beams spaced apart from each other in the indexing feed direction (Y-axis direction) and irradiated onto the workpiece.

[0089] Furthermore, the irradiation of this laser beam LB was performed with each of the branched laser beams LB focused inside the workpiece. In addition, the relative movement speed (machining feed rate) between this laser beam LB and the workpiece along the machining feed direction (X-axis direction) was set to 360 mm / s.

[0090] Table 1 shows the maximum index for which a peel layer can be formed without gaps inside the workpiece in the following cases: when each of the branched laser beams LB is focused to form a circle with a diameter of 1 μm on a plane parallel to the X-axis and Y-axis (XY plane) (Comparative Example); when each of the branched laser beams LB is focused to form a shape that is extended 1 μm along the Y-axis from the circle on the XY plane (Example 1); when each of the branched laser beams LB is focused to form a shape that is extended 2 μm along the Y-axis from the circle on the XY plane (Example 2); and when each of the branched laser beams LB is focused to form a shape that is extended 3 μm along the Y-axis from the circle on the XY plane (Example 3).

[0091] In the Comparative Example and Example 1, the distance between the points where the branched laser beam LB was focused was approximately 12 μm. In Example 2, the distance between the points where the branched laser beam LB was focused was 13 μm to 14 μm. In Example 3, the distance between the points where the branched laser beam LB was focused was approximately 13 μm.

[0092] [Table 1]

[0093] As shown in Table 1, it was found that in Examples 1 to 3, the index could be increased by about 10% compared to the comparative example. [Explanation of Symbols]

[0094] 2: Laser processing equipment 4: Holding Table 6: Laser beam irradiation unit 8: Laser Oscillator 10: Branch Unit 11: Ingot (11a: Front, 11b: Back, 11c: Side) 12: Mirror 13: Orientation Flat 14: Irradiation head 15: Delamination layer (15a: Modified area, 15b: Crack) 17: Circuit board 18: Separation device 20: Holding Table 22: Separation Unit 24: Support member 26: Base 28: Movable member (28a: Upright part, 28b: Wedge part) 30: Separation device 32: Holding Table 34: Separation Unit 36: Support member 38: Suction plate

Claims

1. A method for manufacturing a substrate from a workpiece having a first surface and a second surface opposite to the first surface, A peel layer forming step in which a laser beam of a wavelength that penetrates the material constituting the workpiece is focused inside the workpiece, and the workpiece is moved relative to the location where the laser beam is focused along a processing feed direction parallel to the first surface to form a peel layer, An indexing feed step that moves the workpiece relative to the location where the laser beam is focused, along an indexing feed direction that is perpendicular to the machining feed direction and parallel to the first surface, The process includes, after repeatedly performing the delamination layer formation step and the indexing feed step alternately, a separation step in which the substrate is separated from the workpiece starting from the delamination layer, In the peel layer formation step, the laser beam is focused such that the length along the indexing feed direction is greater than the length along the processing feed direction. In the peel layer formation step, the laser beam, whose wavefront is controlled by a spatial light modulator, is irradiated onto the workpiece. Of the light constituting the laser beam incident on the spatial light modulator, the light located towards the center in the direction corresponding to the indexing feed direction is focused to both ends of that location in the indexing feed direction. A method for manufacturing a substrate, wherein the light constituting the laser beam incident on the spatial light modulator, located at both ends in the direction corresponding to the indexing feed direction, is focused towards the center of that location in the indexing feed direction.

2. The method for manufacturing a substrate according to claim 1, wherein the laser beam is branched so as to be focused at each of a plurality of locations that are spaced apart from each other in the indexing feed direction.

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