Substrate manufacturing method

Abstract

To provide a method for manufacturing substrates with high productivity.SOLUTION: After forming a delamination layer inside the workpiece (e.g., ingot, bare wafer, or device wafer made of semiconductor material such as silicon (Si) or silicon carbide (SiC)) using a laser beam with a wavelength that penetrates the material constituting the workpiece, the substrate is separated from the workpiece using this delamination layer as a starting point. This process improves the productivity of substrates compared to the case where substrates are manufactured from the workpiece using a wire saw.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Semiconductor device chips are generally manufactured using disk-shaped substrates made of semiconductor materials such as silicon (Si) or silicon carbide (SiC), which are cut from cylindrical ingots of semiconductor material using, for example, a wire saw (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-262826 Summary of the Invention [Problem to be solved by the invention]

[0004] When cutting a substrate from an ingot using a wire saw, the cutting width is relatively large, about 300 μm. Furthermore, the surface of the substrate cut in this way has minute irregularities and is curved overall (causing warpage of the wafer). Therefore, the surface of the substrate needs to be flattened by lapping, etching, and / or polishing.

[0005] In this case, the amount of material ultimately used for the substrate is about two-thirds of the total ingot material. In other words, about one-third of the total ingot material is discarded during cutting and flattening of the substrate. Therefore, productivity is low when manufacturing substrates using a wire saw in this way.

[0006] In view of this, an object of the present invention is to provide a method for manufacturing a substrate with high productivity. [Means for solving the problem]

[0007] According to the present invention, there is provided a method for manufacturing a substrate from a workpiece having a first surface and a second surface opposite to the first surface, wherein a laser beam having a wavelength that is transmitted through a material constituting the workpiece is split and focused to form a plurality of focal points aligned along a first direction parallel to the first surface, and while the plurality of focal points are positioned inside the workpiece, the plurality of focal points and the workpiece are moved relatively along a second direction that is perpendicular to the first direction and parallel to the first surface, thereby forming a plurality of focal points each having a center. the separation layer forming step of forming a separation layer inside the workpiece, the separation layer including a plurality of modified regions formed by the formation of the plurality of light-focusing points and cracks extending from the plurality of modified regions; an indexing step of relatively moving the workpiece and the region where the plurality of light-focusing points are formed along the first direction; and a separation step of separating the substrate from the workpiece starting from the separation layer after alternately repeating the separation layer forming step and the indexing step. than the vicinity of the focal points formed on both ends In the vicinity of the central focal point Small The laser beam is diverged and focused so that the laser beam is small.

[0008] Preferably, in the peeling layer forming step, the laser beam is branched and focused so that the light intensity is relatively low at the focusing point formed on the central side.

[0009] Preferably, in the peeling layer forming step, the laser beam is branched and focused so that the intervals between the focusing points formed on the central side are relatively wide.

[0010] Preferably, the workpiece is an ingot made of single crystal silicon. [Effects of the Invention]

[0011] In the present invention, a release layer is formed inside the workpiece using a laser beam with a wavelength that is transparent to the material that makes up the workpiece, and then the substrate is separated from the workpiece using this release layer as a starting point. This improves productivity of the substrate compared to when substrates are manufactured from the workpiece using a wire saw. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view schematically showing an example of an ingot. [Figure 2] FIG. 2 is a top view schematically showing an example of an ingot. [Figure 3] FIG. 3 is a flow chart schematically showing an example of a method for manufacturing a substrate from an ingot that serves as a workpiece. [Figure 4] FIG. 4 is a diagram schematically illustrating an example of a laser processing device. [Figure 5] FIG. 5 is a top view schematically showing a holding table for holding an ingot. [Figure 6] FIG. 6(A) is a top view schematically showing an example of the release layer forming step, and FIG. 6(B) is a partially cross-sectional side view schematically showing an example of the release layer forming step. [Figure 7] FIG. 7 is a cross-sectional view schematically showing an example of a separation layer formed inside the ingot in the separation layer forming step. [Figure 8] 8(A) and 8(B) are each a partial cross-sectional side view that schematically shows an example of the separation step. [Figure 9] FIG. 9 is a cross-sectional view schematically showing a modified example of the separation layer formed inside the ingot in the separation layer forming step. [Figure 10] 10(A) and 10(B) are each a partial cross-sectional side view that schematically shows a modified example of the separation step. DETAILED DESCRIPTION OF THE INVENTION

[0013] Embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view schematically showing an example of an ingot made of single crystal silicon, and Fig. 2 is a top view schematically showing the example of this ingot. Fig. 1 also shows the crystal planes of the single crystal silicon exposed on the planes included in this ingot. Fig. 2 also shows the crystal orientation of the single crystal silicon constituting this ingot.

[0014] 1 and 2, a specific crystal plane included in the crystal plane {100} (here, for convenience, referred to as the crystal plane (100)) is exposed on each of the front surface (first surface) 11a and the back surface (second surface) 11b. That is, in this ingot 11, the perpendicular lines (crystal axes) of the front surface 11a and the back surface 11b are aligned along the crystal orientation

[0100] .

[0015] Although the ingot 11 is manufactured so 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, a plane slightly tilted from the crystal plane (100) 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 the crystal plane (100) may be exposed on each of the front surface 11a and the back surface 11b of the ingot 11. In other words, the crystal axis of the ingot 11 may be along a direction that forms an angle of 1° or less with the crystal orientation

[0100] .

[0016] An orientation flat 13 is formed on the side surface 11c of the ingot 11, and the crystal orientation as viewed from this orientation flat 13 is <110> The center C of the ingot 11 is located in a specific crystal orientation (here, for convenience, it is assumed to be the crystal orientation

[0011] ) included in the above. In other words, in this orientation flat 13, the crystal plane (011) of the single crystal silicon is exposed.

[0017] 3 is a flow chart showing a schematic example of a method for manufacturing a substrate from a workpiece, that is, an ingot 11. Briefly, in this method, a peeling layer is formed throughout the interior of the ingot 11 using a laser processing device, and then the substrate is separated from the ingot 11 using this peeling layer as a starting point.

[0018] Fig. 4 is a diagram schematically illustrating an example of a laser processing apparatus used when forming a peeling layer inside an ingot 11. Note that the X-axis direction (second direction) and the Y-axis direction (first direction) shown in Fig. 4 are directions perpendicular to each other on a horizontal plane, and the Z-axis direction is a direction (vertical direction) perpendicular to each of the X-axis direction and the Y-axis direction. Also, in Fig. 4, some of the components of the laser processing apparatus are shown in functional blocks.

[0019] The laser processing apparatus 2 shown in Fig. 4 has a disk-shaped holding table 4. This holding table 4 has, for example, a circular upper surface (holding surface) parallel to the X-axis direction and the Y-axis direction. The holding table 4 also has a disk-shaped porous plate (not shown) whose upper surface is exposed on this holding surface.

[0020] Furthermore, this porous plate is connected to a suction source (not shown) such as a vacuum pump via a flow path or the like provided inside the holding table 4. When this suction source is activated, 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 an ingot 11 placed on the holding surface.

[0021] 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 or the like as a laser medium, and irradiates a pulsed laser beam LB having a wavelength (for example, 1064 nm) that is transmitted through the material (single crystal silicon) that constitutes the ingot 11.

[0022] The output of this laser beam LB is adjusted by an attenuator 10, and then supplied to a branching unit 12. This branching unit 12 is configured to include a spatial light modulator including a liquid crystal phase control element generally called LCOS (Liquid Crystal On Silicon) and / or a diffractive optical element (DOE), etc. The branching unit 12 branches the laser beam LB so that the laser beam LB irradiated from an irradiation head 16 (described later) forms multiple focusing points aligned along the Y-axis direction.

[0023] For example, the branching unit 12 branches the laser beam LB so that the intervals between the central focusing points among the plurality of focusing points are relatively wide. That is, the branching unit 12 branches the laser beam LB so that the intervals between the central focusing points among the plurality of focusing points are wider than the intervals between the focusing points formed on both ends.

[0024] To form multiple focal points in this manner, for example, a laser beam LB whose output has been adjusted in an attenuator 10 may be split into two laser beams LB, and each of the two split laser beams LB may then be split into n beams (n is a natural number greater than or equal to 2).

[0025] The laser beam LB branched by the branching unit 12 is reflected by a mirror 14 and guided to an irradiation head 16. The irradiation head 16 contains a condenser lens (not shown) that condenses the laser beam LB. The laser beam LB condensed by the condenser lens is irradiated onto the holding surface side of the holding table 4.

[0026] Furthermore, the irradiation head 16 of the laser beam irradiation unit 6 is connected to a movement mechanism (not shown). This movement mechanism includes, for example, a ball screw or the like, and moves the irradiation head 16 along the X-axis, Y-axis, and / or Z-axis directions. In the laser processing apparatus 2, by operating this movement mechanism, the position (coordinates) of the focal point of the laser beam LB irradiated from the irradiation head 16 can be adjusted in the X-axis, Y-axis, and Z-axis directions.

[0027] When forming a peeling layer throughout the interior of the ingot 11 in the laser processing device 2, the ingot 11 is first held by the holding table 4 with the surface 11a facing upward. Figure 5 is a top view schematically showing the holding table 4 holding the ingot 11.

[0028] This 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] ) forms an angle of 45° with each of the X-axis direction and the Y-axis direction. 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.

[0029] Next, a peeling layer is formed in a region on one end side in the Y-axis direction inside the ingot 11. Specifically, first, the irradiation head 16 of the laser beam irradiation unit 6 is positioned so that the region is positioned in the X-axis direction when viewed from the irradiation head 16 in a plan view. Next, the irradiation head 16 is raised and lowered so that multiple focusing points formed by branching and focusing the laser beam LB are positioned at heights corresponding to the interior of the ingot 11.

[0030] Next, a separation layer is formed by relatively moving the multiple focal points and the ingot 11 along the X-axis direction (separation layer forming step: S1). Fig. 6(A) is a top view schematically showing an example of the separation layer forming step (S1), and Fig. 6(B) is a partially cross-sectional side view schematically showing an example of the separation layer forming step (S1). Fig. 7 is a cross-sectional view schematically showing the separation layer formed inside the ingot 11 in the separation layer forming step (S1).

[0031] In this peeling layer formation step (S1), the branched and focused laser beam LB is irradiated from the irradiation head 16 toward the holding table 4, while the irradiation head 16 is moved so as to pass from one end to the other end of the ingot 11 in the X-axis direction in a planar view (see Figures 6(A) and 6(B)).

[0032] As a result, the multiple focal points and the ingot 11 move relatively along the X-axis direction with the multiple focal points positioned inside the ingot 11. This laser beam LB forms, for example, eight focal points, and is branched and focused so that the distance between the two focal points formed in the center is relatively wide (see FIG. 7).

[0033] In other words, the distance between a pair of focusing points formed at the center of the eight focusing points of this laser beam LB is wider than the distance between a pair of adjacent focusing points of the four focusing points formed at one end and the distance between a pair of adjacent focusing points of the four focusing points formed at the other end.

[0034] Furthermore, modified regions 15a in which the crystal structure of the single crystal silicon is disturbed are formed around each of the multiple focal points inside the ingot 11. The formation of the modified regions 15a causes the volume of the ingot 11 to expand. Note that this volume expansion of the ingot 11 is relatively small near the two focal points formed in the center, which are spaced far apart.

[0035] Furthermore, the formation of the modified regions 15a generates internal stress in the ingot 11. Then, cracks 15b propagate from the modified regions 15a in the ingot 11, thereby relieving the internal stress. As a result, a peeling layer 15 is formed inside the ingot 11, the peeling layer 15 including a plurality of modified regions 15a formed around each of the plurality of focusing points and cracks 15b propagating from each of the plurality of modified regions 15a.

[0036] Next, the region where the multiple focal points are formed and the ingot 11 are moved relatively along the Y-axis direction (indexing step: S2). Specifically, the irradiation head 16 is moved along the Y-axis direction so that the movement distance (index) of the irradiation head 16 is longer than the width of the separation layer 15 along the Y-axis direction. Next, the above-mentioned separation layer forming step (S1) is performed again.

[0037] As a result, two peeling layers 15 that are spaced apart in the Y-axis direction and parallel to each other are formed inside the ingot 11. Furthermore, the indexing step (S2) and the peeling layer forming step (S1) are repeatedly performed until the peeling layer 15 is formed in the region on the other end side in the Y-axis direction inside the ingot 11.

[0038] That is, the peeling layer forming step (S1) and the indexing step (S2) are alternately repeated so that the peeling layer 15 is formed from one end region to the other end region in the Y-axis direction inside the ingot 11 (over the entire area). Then, when the peeling layer 15 is formed over the entire area inside the ingot 11 (step (S3): YES), the substrate is separated from the ingot 11 starting from the peeling layer 15 (separation step: S4).

[0039] 8(A) and 8(B) are partial cross-sectional side views each showing a schematic diagram of an example of the separation step (S4). This separation step (S4) is performed, for example, in a separation apparatus 18 shown in FIGS. 8(A) and 8(B). This separation apparatus 18 has a holding table 20 that holds the ingot 11 on which the peeled layer 15 is formed.

[0040] The holding table 20 has a circular upper surface (holding surface), and a porous plate (not shown) is exposed on this holding surface. 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 is activated, negative pressure is generated in the space near the holding surface of the holding table 20.

[0041] A separation unit 22 is provided above the holding table 20. The separation unit 22 has a cylindrical support member 24. A ball screw type lifting mechanism (not shown) and a rotary drive source such as a motor are connected to the upper part of the support member 24. The separation unit 22 moves up and down by operating the lifting mechanism. The support member 24 rotates around a rotation axis that passes through the center of the support member 24 and is perpendicular to the holding surface of the holding table 20 by operating the rotary drive source.

[0042] The lower end of the support member 24 is fixed to the center of the upper part of a disk-shaped base 26. A plurality of movable members 28 are provided below the outer periphery of the base 26 at approximately equal intervals along the circumferential direction of the base 26. Each movable member 28 has a plate-shaped erected portion 28a extending downward from the lower surface of the base 26.

[0043] The upper end of this standing 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, on the inner surface of the lower end of this standing portion 28a, a plate-shaped wedge portion 28b is provided which extends toward the center of the base 26 and becomes thinner as it approaches the tip.

[0044] In the separation device 18, the separation step (S4) is performed, for example, 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 peeling layer 15 is formed is aligned with the center of the holding surface of the holding table 20.

[0045] Next, a suction source communicating with the porous plate exposed on the holding surface is operated so that the ingot 11 is held by the holding table 20. Next, the actuator is operated so that each of the plurality of movable members 28 is positioned radially outward of the base 26.

[0046] Next, the lifting mechanism is operated to position the tip of each wedge portion 28b 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 to drive the wedge portion 28b into the side surface 11c of the ingot 11 (see FIG. 8(A)). Next, the rotation drive source is operated to rotate the wedge portion 28b driven into the side surface 11c of the ingot 11.

[0047] Next, the lifting mechanism is operated to lift the wedge portion 28b (see FIG. 8(B)). After the wedge portion 28b is driven into the side surface 11c of the ingot 11 and rotated as described above, the wedge portion 28b is lifted, whereby the crack 15b contained in the separation layer 15 is further extended. As a result, the front surface 11a side and the back surface 11b side of the ingot 11 are separated. That is, the substrate 17 is produced from the ingot 11, starting from the separation layer 15.

[0048] It should be noted that the wedge portion 28b does not need to be rotated if the front surface 11a and the 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. Alternatively, the actuator and the rotary drive source may be operated simultaneously to drive the rotating wedge portion 28b into the side surface 11c of the ingot 11.

[0049] In the above-described method for manufacturing a substrate, a laser beam LB having a wavelength that passes through the material (single crystal silicon) that constitutes ingot 11 is used to form a peeling layer 15 inside ingot 11, and then substrate 17 is separated from ingot 11 starting from this peeling layer 15. This reduces the amount of material wasted when manufacturing substrate 17 from ingot 11, and improves the productivity of substrate 17, compared to when substrate 17 is manufactured from ingot 11 using a wire saw.

[0050] Furthermore, when the laser beam LB is branched and focused so as to form multiple modified regions 15a, the volume of the ingot 11 expands with the formation of each of the multiple modified regions 15a. Here, cracks 15b tend to propagate from the central modified region 15a among the multiple modified regions 15a in a direction where no surrounding modified regions 15a exist.

[0051] For example, when multiple modified regions 15a are formed aligned along the X-axis and Y-axis directions, cracks with a large Z-axis component tend to propagate from the central modified region 15a among the multiple modified regions 15a. If cracks with a large Z-axis component propagate from the peeling layer 15, the amount of material discarded during planarization of the substrate 17 manufactured from the ingot 11 and during planarization of the ingot 11 for manufacturing a new substrate 17 from the ingot 11 increases. Therefore, in this case, the productivity of the substrate 17 may decrease.

[0052] In contrast, in the above-described substrate manufacturing method, the modified regions 15a formed at the center among the plurality of modified regions 15a are formed so that the intervals between the modified regions 15a are relatively wider (wider than the intervals between the modified regions 15a formed at both ends), so that the volume expansion of the ingot 11 caused by the formation of the plurality of modified regions 15a is relatively smaller in the vicinity of the central focal point among the plurality of focal points.

[0053] In this case, it is possible to suppress an increase in the Z-axis component of cracks 15b extending from the central modified region 15a among the multiple modified regions 15a. As a result, in the above-described substrate manufacturing method, the amount of material discarded when manufacturing substrates 17 from ingot 11 can be further reduced, and the productivity of substrates 17 can be further improved.

[0054] Furthermore, in the above-described method for manufacturing a substrate, the peeling layer 15 is formed by relatively moving the ingot 11 and a plurality of focusing points aligned along the Y-axis direction (crystal orientation

[0001] ) 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 further improved.

[0055] This point will be explained in detail below. First, single crystal silicon generally cleaves most easily along a specific crystal plane included in the crystal plane {111}, and second most easily along a specific crystal plane included in the crystal plane {110}. Therefore, for example, when the crystal orientation of the single crystal silicon constituting the ingot 11 is <110> When a modified region is formed along a specific crystal orientation (for example, crystal orientation

[0011] ) included in the crystal plane {111}, many cracks are generated from this modified region, extending along a specific crystal plane included in the crystal plane {111}.

[0056] 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 included in the above, so that they are lined up in a direction perpendicular to the direction in which this region extends in a planar view, many cracks will occur from each of these multiple modified regions, extending along one of the crystal planes {N10} (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.

[0057] For example, as in the substrate manufacturing method described above, when multiple modified regions 15a are formed in a region along the crystal orientation

[0010] so that they are aligned along the crystal orientation

[0001] , an increasing number of cracks will extend from each of these multiple modified regions 15a along the crystal planes {N10} (N is a natural number less than or equal to 10) that are parallel to the crystal orientation

[0010] .

[0058] Specifically, when a plurality of modified regions 15a are formed in this way, cracks tend to propagate in the following crystal planes.

number

number

[0059] The angle that the crystal plane (100) exposed on the front surface 11a and back surface 11b of the ingot 11 makes with the crystal plane {N10} parallel to the crystal orientation

[0010] 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 about 54.7°.

[0060] Therefore, in the above-described substrate manufacturing method, the peeling layer 15 is likely to be wider and thinner than when a plurality of modified regions are formed in a region along the crystal orientation

[0011] of the single crystal silicon so as to be aligned in a direction perpendicular to the direction in which this region extends in a plan view. As a result, in the above-described substrate manufacturing method, the amount of material wasted when manufacturing the substrate 17 from the ingot 11 can be further reduced, and the productivity of the substrate 17 can be further improved.

[0061] The above-described method for manufacturing a substrate is one embodiment of the present invention, and the present invention is not limited to the above-described method. For example, the ingot used to manufacture a substrate in the present invention is not limited to the ingot 11 shown in Figures 1 and 2. Specifically, in the present invention, a 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.

[0062] In the present invention, the substrate may be manufactured from an ingot having a notch formed on the side surface. Alternatively, in the present invention, the substrate may be manufactured from an ingot having neither an orientation flat nor a notch formed on the side surface. In the present invention, the substrate may be manufactured from an ingot made of a semiconductor material other than silicon, such as silicon carbide.

[0063] Furthermore, the structure of the laser processing device used in the present invention is not limited to the structure of the above-described laser processing device 2. For example, the present invention may be implemented using a laser processing device provided with a movement mechanism that moves the holding table 4 along each of the X-axis, Y-axis, and / or Z-axis directions.

[0064] That is, in the present invention, it is sufficient that the holding table 4 that holds the ingot 11 and the irradiation head 16 of the laser beam irradiation unit 6 that irradiates the laser beam LB can move relatively along each of the X-axis, Y-axis, and Z-axis directions, and there are no limitations on the structure for this purpose.

[0065] Furthermore, in the peeling layer forming step (S1) of the present invention, it is only necessary to suppress an increase in the Z-axis component of the cracks 15b extending from the modified region 15a formed on the central side of the multiple modified regions 15a, and there is no limitation on the method of branching the laser beam LB for this purpose. That is, in the peeling layer forming step (S1) of the present invention, it is only necessary to branch and focus the laser beam LB so that the volume expansion of the ingot 11 accompanying the formation of the multiple modified regions 15a is relatively small in the vicinity of the central focusing point among the multiple focusing points.

[0066] For example, in the separation layer forming step (S1) of the present invention, the laser beam LB may be branched and focused so that the light intensity is relatively low at the central focus point among the multiple focus points. Figure 9 is a cross-sectional view schematically showing an example of a separation layer formed inside the ingot 11 in the separation layer forming step using the branched and focused laser beam LB in this way.

[0067] 9 forms ten focusing points at equal intervals along the Y-axis direction, and is branched and focused so that the light intensity of the laser beam LB is relatively low at the four focusing points formed toward the center. That is, the light intensity of the laser beam LB at each of the four focusing points formed toward the center among the ten focusing points of the laser beam LB is lower than the light intensity of the laser beam LB at each of the six focusing points formed at both ends.

[0068] As a result, the volume expansion of the ingot 11 due to the formation of the multiple modified regions 15a is relatively small near the central focus points among the multiple focus points. In this case, the cracks 15b extending from the central modified regions 15a among the multiple modified regions 15a become shorter.

[0069] That is, it is possible to suppress an increase in the Z-axis component of cracks 15b extending from modified region 15a formed at the center of multiple modified regions 15a. As a result, even when laser beam LB shown in Fig. 9 is used in the peeling layer formation step (S1) of the present invention, the amount of material discarded when manufacturing substrate 17 from ingot 11 can be further reduced, and the productivity of substrate 17 can be further improved.

[0070] Furthermore, in the peeling layer formation step (S1) of the present invention, the laser beam may be branched and focused so that the light intensity is relatively low at the focal point formed toward the center among the multiple focal points, and the distance between the focal points is relatively wide.

[0071] Furthermore, in the present invention, after the separation layer 15 is formed (over the entire area) from one end region in the Y-axis direction to the other end region inside the ingot 11 (step S3: YES), the separation layer forming step (S1) and the indexing step (S2) may be repeated again. That is, the laser beam LB may be irradiated again from the one end region in the Y-axis direction inside the ingot 11 where the separation layer 15 has already been formed to the other end region so as to form the separation layer 15.

[0072] In the present invention, after the separation layer forming step (S1) and before the indexing step (S2), the separation layer forming step (S1) may be performed again. That is, the laser beam LB may be irradiated again to the linear region inside the ingot 11 where the separation layer 15 has already been formed, so as to form the separation layer 15.

[0073] When the separation layer forming step (S1) is performed again on the region where the separation layer 15 has already been formed, the density of the modified regions 15a and the cracks 15b included in the already formed separation layer 15 increases, which makes it easier to separate the substrate 17 from the ingot 11 in the separation step (S4).

[0074] Furthermore, in this case, the cracks 15b included in the release layer 15 extend further, widening the length (width) along the Y-axis direction of the release layer 15. Therefore, in this case, the movement distance (index) of the irradiation head 16 of the laser beam irradiation unit 6 in the indexing feed step (S2) can be increased.

[0075] Furthermore, in the present invention, if it is possible to extend the cracks 15b contained in the peeling layer 15 in the separation step (S4), the peeling layer 15 does not have to be formed throughout the entire interior of the ingot 11 in the peeling 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 peeling layer 15 does not have to be formed in part or all of the region near the side surface 11c of the ingot 11 in the peeling layer formation step (S2).

[0076] Furthermore, the separation step (S4) of the present invention may be performed using an apparatus other than the separation apparatus 18 shown in Figures 8(A) and 8(B). Figures 10(A) and 10(B) are partial cross-sectional side views schematically showing an example of the separation step (S4) performed using an apparatus other than the separation apparatus 18.

[0077] 10(A) and 10(B) has a holding table 32 that holds the ingot 11 on which the peeling layer 15 is formed. The holding table 32 has a circular upper surface (holding surface), and a porous plate (not shown) is exposed on this holding surface.

[0078] Furthermore, this porous plate is connected to 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 is operated, a negative pressure is generated in the space near the holding surface of the holding table 32.

[0079] A separation unit 34 is provided above the holding table 32. The separation unit 34 has a cylindrical support member 36. A ball screw type lifting mechanism (not shown), for example, is connected to the top of the support member 36, and the separation unit 34 moves up and down by operating this lifting mechanism.

[0080] The lower end of the support member 36 is fixed to the center of the upper part of a disk-shaped suction plate 38. A plurality of suction ports are formed in the lower surface of the suction plate 38, and each of the plurality of suction 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 the suction source is operated, a negative pressure is generated in the space near the lower surface of the suction plate 38.

[0081] In the separation device 30, the separation step (S4) is performed, for example, 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 peeling layer 15 is formed is aligned with the center of the holding surface of the holding table 32.

[0082] Next, a suction source communicating with the porous plate exposed on the holding surface is operated so that the ingot 11 is held by the holding table 32. Next, the lifting mechanism is operated to lower the separation unit 34 so that the lower surface of the suction plate 38 contacts the surface 11a of the ingot 11.

[0083] Next, a suction source communicating with the plurality of suction ports is operated so that the front surface 11a side of the ingot 11 is sucked through the plurality of suction ports formed in the suction plate 38 (see FIG. 10(A)). Next, the lifting mechanism is operated to lift the separation unit 34 so that the suction plate 38 is separated from the holding table 32 (see FIG. 10(B)).

[0084] At this time, an upward force acts on the front surface 11a side of the ingot 11, which is being sucked through the multiple suction ports formed in the suction plate 38. As a result, the crack 15b contained in the peeling layer 15 further extends, and the front surface 11a side and the back surface 11b side of the ingot 11 are separated. In other words, the substrate 17 is produced from the ingot 11, starting from the peeling layer 15.

[0085] Furthermore, in the separation step (S4) of the present invention, prior to separation of the front surface 11a side and the back surface 11b side of the ingot 11, ultrasonic waves may be applied to the front surface 11a side of the ingot 11. In this case, the cracks 15b contained in the peeling layer 15 are further extended, making it easier to separate the front surface 11a side and the back surface 11b side of the ingot 11.

[0086] Furthermore, in the present invention, prior to the separation layer forming 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 a plurality of substrates from the ingot 11. Specifically, when the ingot 11 is separated at the separation layer 15 to manufacture the substrates 17, the newly exposed surface of the ingot 11 has irregularities that reflect the distribution of the modified regions 15a and cracks 15b contained in the separation layer 15.

[0087] Therefore, when a new substrate is manufactured from this ingot 11, it is preferable to flatten the surface of ingot 11 prior to the peeling layer forming step (S1). This makes it possible to suppress diffuse reflection of the laser beam LB irradiated onto ingot 11 at the surface of ingot 11 in the peeling layer forming step (S1). Similarly, in the present invention, the surface of substrate 17 separated from ingot 11 on the peeling layer 15 side may be flattened by grinding or polishing.

[0088] 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. The bare wafer has a thickness, for example, two to five times that of the substrate to be manufactured. The bare wafer is manufactured by separating it from an ingot made of a semiconductor material such as silicon or silicon carbide by a method similar to the above-described method. In this case, the substrate can also be expressed as being manufactured by repeating the above-described method twice.

[0089] In the present invention, a substrate may be manufactured using a device wafer, which is manufactured by forming semiconductor devices on one surface of the bare wafer. In addition, the structures and methods according to the above-described embodiments can be appropriately modified and implemented without departing from the scope of the present invention. [Explanation of symbols]

[0090] 2: Laser processing equipment 4: Holding 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: Orientation Flat 14: Mirror 15: Peeling layer (15a: modified region, 15b: crack) 16: Irradiation head 17: Circuit board 18: Separation device 20: Holding table 22: Separation unit 24: Support member 26: Foundation 28: Movable member (28a: Standing portion, 28b: Wedge portion) 30: Separation device 32: Holding table 34: Separation unit 36: Support member 38: Suction plate

Claims

1. A method for manufacturing a substrate, comprising the steps of: manufacturing a substrate from a workpiece having a first surface and a second surface opposite to the first surface; a peeling layer forming step in which a laser beam having a wavelength that is transmitted through the material constituting the workpiece is branched and focused to form a plurality of focal points aligned along a first direction parallel to the first surface, and the plurality of focal points and the workpiece are moved relatively along a second direction that is perpendicular to the first direction and parallel to the first surface while the plurality of focal points are positioned inside the workpiece, thereby forming a peeling layer inside the workpiece, the peeling layer including a plurality of modified regions formed around each of the plurality of focal points and cracks extending from the plurality of modified regions; an indexing step of relatively moving the area where the plurality of focal points are formed and the workpiece along the first direction; a separation step of separating the substrate from the workpiece starting from the release layer after alternately repeating the release layer forming step and the indexing step; A method for manufacturing a substrate, characterized in that in the peeling layer formation step, the laser beam is branched and focused so that the volume expansion of the workpiece due to the formation of the multiple modified regions is smaller near the focal point formed toward the center than near the focal points formed at both ends of the multiple focal points.

2. 2. The method for manufacturing a substrate according to claim 1, wherein in the peeling layer forming step, the laser beam is branched and focused so that the light intensity at the focusing point formed on the central side is relatively low.

3. 3. The method for manufacturing a substrate according to claim 1, wherein in the peeling layer forming step, the laser beam is branched and focused so that the distance between the focusing points formed on the central side is relatively wide.

4. 4. The method for manufacturing a substrate according to claim 1, wherein the workpiece is an ingot made of single crystal silicon.

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