Laser processing method, semiconductor device manufacturing method, and laser processing apparatus

Abstract

To provide a laser processing method capable of shortening a processing time, improving flatness of a cut face and reducing an influence of laser irradiation on a workpiece, a method of manufacturing a semiconductor device and a laser processing device.SOLUTION: A laser processing method comprises a formation process of forming a plurality of modification spots along a virtual plane in the workpiece 10 by irradiating the inside of the workpiece 10 with laser light through its surface 10a. The workpiece 10 has a first region R1 and a second region R2 when viewed from a direction perpendicular to the surface 10a. In the formation process, a plurality of modification spot arrays 13 consisting of a plurality of modification spots arranged along a border B between the first region R1 and second region R2 are formed in the second region R2, and the plurality of modification spot arrays 13 are arranged side by side in the direction crossing the arrangement direction of the plurality of modification spots and are thus formed to form a crack extending from the second region R2 to the first region R1.SELECTED DRAWING: Figure 4

Description

[[Technical Field]]

[0001] The present invention relates to a laser processing method, a method for manufacturing a semiconductor device, and a laser processing apparatus. [[Background Art]]

[0002] A processing method is known in which a modified region is formed inside a workpiece such as a semiconductor wafer by irradiating the workpiece with laser light, and a semiconductor member such as a semiconductor substrate is cut out from the workpiece by separating the workpiece with the modified region as a boundary (see, for example, Patent Documents 1 and 2). [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2017-183600 [[Patent Document 2]] Japanese Unexamined Patent Application Publication No. 2017-057103 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] In the processing method as described above, it is preferable that the processing time is short, and that the cut surface is flat. It is also preferable that the influence of laser irradiation on the workpiece is small.

[0005] Accordingly, an object of the present invention is to provide a laser processing method, a method for manufacturing a semiconductor device, and a laser processing apparatus that can achieve shortening of processing time, improvement of flatness of a cut surface, and reduction of the influence of laser irradiation on a workpiece. [[Means for Solving the Problem]]

[0006] The laser processing method of the present invention is [1] "a laser processing method for cutting a workpiece along a virtual plane facing the surface of the workpiece inside the workpiece, comprising a forming step of irradiating laser light from the surface into the interior of the workpiece to form a plurality of modified spots along the virtual plane, wherein the workpiece has a first region and a second region when viewed from a direction perpendicular to the surface, and in the forming step, a plurality of modified spot rows consisting of the plurality of modified spots arranged along the boundary between the first region and the second region are formed in the second region, the plurality of modified spot rows are arranged along a direction intersecting the direction of arrangement of the plurality of modified spots, and the formation of the plurality of modified spot rows forms a crack extending from the second region to the first region."

[0007] In this laser processing method, cracks extending from the second region to the first region are formed by creating multiple rows of modified spots in the second region. By forming cracks that extend from the second region to the first region in this way, the processing time can be shortened and the flatness of the cut surface can be improved compared to, for example, a case where modified spots are formed in the first region to form cracks in the first region. Furthermore, in this laser processing method, cracks extending from the second region to the first region are formed by creating multiple rows of modified spots in the second region. This reduces the effect of laser irradiation on the first region. As a result, for example, when a device portion is formed in the first region, the effect of laser irradiation on the device portion can be reduced. Therefore, this laser processing method can shorten processing time, improve the flatness of the cut surface, and reduce the effect of laser irradiation on the workpiece. Furthermore, the inventors have discovered that by forming a row of modified spots in the second region, consisting of multiple modified spots aligned along the boundary between the first and second regions, in a direction intersecting the direction in which the multiple modified spots are aligned, it is possible to form a crack extending from the second region to the first region.

[0008] The laser processing method of the present invention may also be [2] "the laser processing method according to [1], wherein in the forming step, the plurality of modified spot rows are formed in the second region such that the crack is formed over the entire first region." In this case, the processing time can be further shortened and the flatness of the cut surface can be further improved.

[0009] The laser processing method of the present invention may also be [3] "the laser processing method according to [1] or [2], wherein the plurality of modified spot rows include a first modified spot row and a second modified spot row positioned closer to the first region than the first modified spot row, and in the forming step, the second modified spot row is formed after the first modified spot row is formed." In this case, cracks are more likely to propagate from the second region to the first region, the processing time can be further shortened, and the flatness of the cut surface can be further improved. It should be noted that the finding that cracks are more likely to propagate from the second region to the first region when a plurality of modified spot rows are formed in order of furthest from the first region is a finding discovered by the present inventors.

[0010] The laser processing method of the present invention may also be [4] "the laser processing method according to any one of [1] to [3], wherein the second region has a portion that surrounds the first region when viewed from a direction perpendicular to the surface." In this case, the crack can be suitably extended from the second region to the first region, the processing time can be further shortened, and the flatness of the cut surface can be further improved.

[0011] The laser processing method of the present invention may also be [5] "the laser processing method according to any one of [1] to [4], wherein in the forming step, at least two modified spot rows included in the plurality of modified spot rows are formed simultaneously by irradiating with a branched laser beam." In this case, cracks are more likely to propagate from the second region to the first region, the processing time can be further shortened, and the flatness of the cut surface can be further improved. It should be noted that the finding that cracks are more likely to propagate from the second region to the first region when at least two modified spot rows are formed simultaneously by irradiating with a branched laser beam is a finding discovered by the inventors.

[0012] The laser processing method of the present invention may also be [6] "the laser processing method according to any one of [1] to [5], wherein the second region has a grid-like portion including a plurality of linear portions, and the first region has a plurality of rectangular portions surrounded by the plurality of linear portions." In this case, cracks are more likely to propagate from the second region to the first region, the processing time can be further shortened, and the flatness of the cut surface can be further improved. Furthermore, for example, a grid-like cutting region for framing a semiconductor wafer can be used as the second region.

[0013] The laser processing method of the present invention may also be [7] "the laser processing method according to [6], wherein one linear portion included in the plurality of linear portions is defined as a reference linear portion, and of the reference linear portion, when viewed from a direction perpendicular to the surface, the region on one side of the center line of the reference linear portion extending along the extension direction of the reference linear portion is defined as a first portion, and the region on the other side of the center line is defined as a second portion, and in the forming step, at least one modified spot row included in the plurality of modified spot rows is formed in the first portion, and at least one modified spot row included in the plurality of modified spot rows is formed in the second portion." In this case, cracks are more likely to propagate from the second region to the first region, the processing time can be further shortened, and the flatness of the cut surface can be further improved.

[0014] The laser processing method of the present invention may also be [8] "the laser processing method according to [7], wherein the at least one modified spot row formed in the first portion includes a plurality of first modified spot rows, the at least one modified spot row formed in the second portion includes a plurality of second modified spot rows, and in the forming step, the plurality of first modified spot rows are formed in the first portion in order of proximity to the center line, and the plurality of second modified spot rows are formed in the second portion in order of proximity to the center line." In this case, cracks are more likely to propagate from the second region to the first region, the processing time can be further shortened, and the flatness of the cut surface can be further improved.

[0015] The laser processing method of the present invention may also be [9] "the laser processing method according to any one of [1] to [8], wherein the material of the workpiece comprises gallium nitride, silicon carbide, sapphire, silicon, gallium arsenide, magnesium oxide, magnesium fluoride, calcium fluoride, or mica." In this case as well, it is possible to shorten the processing time, improve the flatness of the cut surface, and reduce the influence of laser irradiation on the workpiece.

[0016] The laser processing method of the present invention may also be

[10] "the workpiece having a chip shape, wafer shape, or ingot shape, as described in any of [1] to [9]." In this case as well, it is possible to shorten the processing time, improve the flatness of the cut surface, and reduce the influence of laser irradiation on the workpiece.

[0017] The laser processing method of the present invention may also be

[11] "the laser processing method according to any one of [1] to

[10] wherein the workpiece is formed of a semiconductor material." In this case, a semiconductor workpiece formed of a semiconductor material can be suitably cut as a workpiece.

[0018] The laser processing method of the present invention may also be

[12] "the laser processing method according to any one of [1] to

[11] , wherein the first region is a region for forming a device portion, and the second region is a region in which no device portion is formed." In this case, the effect of laser irradiation on the device portion can be reduced.

[0019] The laser processing method of the present invention may also be

[13] "the laser processing method according to

[12] , wherein in the forming step, the plurality of modified spot rows are formed in the second region while the device portion is formed in the first region." In this case, the effect of laser irradiation on the device portion formed in the first region can be reduced.

[0020] The laser processing method of the present invention may also be

[14] "the laser processing method according to

[12] , wherein in the forming step, the plurality of modified spot rows are formed in the second region while the device portion is not formed in the first region." In this case, the effect of laser irradiation on the first region before the device portion is formed can be reduced, and as a result, the effect of laser irradiation on the device portion formed in the first region can be reduced.

[0021] The laser processing method of the present invention may also be

[15] "a laser processing method according to any one of [1] to

[14] , further comprising the step of separating the workpiece with the virtual surface as a boundary after the forming step." In this case, the workpiece can be suitably separated.

[0022] A method of manufacturing a semiconductor device according to the present invention is

[16] "A method of manufacturing a semiconductor device using the laser processing method according to any one of [1] to

[15] , wherein the object to be processed is formed of a semiconductor material, and the method of manufacturing a semiconductor device comprises the forming step, and a step of forming a device portion in the first region." According to this method of manufacturing a semiconductor device, for the reasons described above, it is possible to achieve a reduction in processing time, an improvement in the flatness of the cut surface, and a reduction in the influence of laser irradiation on the object to be processed.

[0023] A laser processing apparatus according to the present invention is

[17] "A laser processing apparatus for cutting an object to be processed along a virtual plane facing the surface of the object to be processed inside the object to be processed, comprising: a stage that supports the object to be processed; and a laser irradiation unit that forms a plurality of modified spots along the virtual plane by irradiating a laser beam from the surface into the interior of the object to be processed, wherein the object to be processed has a first region and a second region when viewed from a direction perpendicular to the surface, the laser irradiation unit forms a plurality of modified spot rows consisting of the plurality of modified spots arranged along a boundary between the first region and the second region in the second region, the plurality of modified spot rows are arranged along a direction intersecting the arrangement direction of the plurality of modified spots, and cracks extending from the second region to the first region are formed by forming the plurality of modified spot rows." According to this laser processing apparatus, for the reasons described above, it is possible to achieve a reduction in processing time, an improvement in the flatness of the cut surface, and a reduction in the influence of laser irradiation on the object to be processed. Effects of the Invention

[0024] According to the present invention, it is possible to provide a laser processing method and a laser processing apparatus that can achieve a reduction in processing time, an improvement in the flatness of a cut surface, and a reduction in the influence of laser irradiation on an object to be processed. Brief Description of the Drawings

[0025] [Figure 1]This is a diagram showing the configuration of a laser processing apparatus according to an embodiment. [Figure 2] This is a plan view of the workpiece in the laser processing method according to the embodiment. [Figure 3] This is a cross-sectional view of the workpiece. [Figure 4] (a) is a diagram illustrating an example of the modified spot formation process, and (b) is a diagram illustrating another example of the modified spot formation process. [Figure 5] This figure shows an example of the results obtained by actually processing an object. [Figure 6] This is a plan view of the workpiece of the laser processing method according to the first modified example. [Figure 7] (a) is a diagram illustrating an example of the modification spot formation process related to the first modified example, and (b) is a diagram illustrating another example of the modification spot formation process related to the first modified example. [Figure 8] This is a perspective view of the workpiece processed by the laser processing method according to the second modified example. [Figure 9] Figure 8 is a cross-sectional view of the workpiece. [Figure 10] Figure 8 is a bottom view of the workpiece. [Figure 11] (a) is a diagram illustrating the first example of the modification spot formation process related to the third modified example, and (b) is a diagram illustrating the second example of the modification spot formation process related to the third modified example. [Figure 12] This is a diagram illustrating the laser processing method according to the fourth modified example. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described in detail below with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant explanations will be omitted. [Configuration of the laser processing machine]

[0027] As shown in Figure 1, the laser processing apparatus 1 comprises a stage 2, a light source 3, a spatial light modulator 4, a focusing lens 5, and a control unit 6. The laser processing apparatus 1 is a device that forms a modified region 11 on a workpiece 10 by irradiating the workpiece 10 with laser light L. Hereinafter, the first horizontal direction will be referred to as the X direction, the second horizontal direction perpendicular to the first horizontal direction will be referred to as the Y direction, and the vertical direction will be referred to as the Z direction.

[0028] Stage 2 supports the workpiece 10, for example, by adsorbing a film attached to the workpiece 10. In this example, Stage 2 is movable along both the X and Y directions. Stage 2 is also rotatable about an axis parallel to the Z direction as its centerline.

[0029] The light source 3 outputs a laser beam L that is penetrating to the workpiece 10, for example, by a pulse oscillation method. The spatial light modulator 4 modulates the laser beam L output from the light source 3. The spatial light modulator 4 is, for example, a reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM). The focusing lens 5 focuses the laser beam L modulated by the spatial light modulator 4. In this example, the spatial light modulator 4 and the focusing lens 5 are movable along the Z direction as a laser irradiation unit.

[0030] When the laser beam L is focused into the workpiece 10 supported by stage 2, the laser beam L is particularly absorbed in the portion corresponding to the focal point C of the laser beam L, and a modified region 11 is formed inside the workpiece 10. The modified region 11 is a region whose density, refractive index, mechanical strength, and other physical properties differ from the surrounding unmodified region. Examples of modified regions 11 include melting regions, crack regions, dielectric breakdown regions, refractive index change regions, etc.

[0031] For example, by moving Stage 2 along the X direction and moving the focal point C relative to the workpiece 10 along the X direction, multiple modified spots 12 are formed in a line along the X direction. Each modified spot 12 is formed by irradiation with one pulse of laser light L. A row of modified regions 11 is a collection of multiple modified spots 12 arranged in a line. Adjacent modified spots 12 may be connected to each other or separated from each other, depending on the relative movement speed of the focal point C with respect to the workpiece 10 and the repetition frequency of the laser light L.

[0032] The control unit 6 controls the stage 2, light source 3, spatial light modulator 4, and focusing lens 5. The control unit 6 is configured as a computer device including a processor, memory, storage, and communication devices. In the control unit 6, software (programs) loaded into memory, etc., is executed by the processor, and the reading and writing of data in memory and storage, as well as communication by communication devices, are controlled by the processor. In this way, the control unit 6 realizes various functions. [Laser processing method and semiconductor device manufacturing method]

[0033] Figure 2 is a plan view of the workpiece 10 in the laser processing method and semiconductor device manufacturing method according to the embodiment, and Figure 3 is a cross-sectional view of the workpiece 10. In this laser processing method, the workpiece 10 is cut (slice / peeled) along a virtual plane S that faces the surface 10a of the workpiece 10 inside the workpiece 10. In this example, the workpiece 10 is a semiconductor workpiece formed from a semiconductor material. The workpiece 10 has a chip shape and constitutes one semiconductor device (semiconductor chip) after processing. In this example, the workpiece 10 is formed in the shape of a rectangular plate. Examples of semiconductor materials that constitute the workpiece 10 include gallium nitride (GaN), silicon carbide (SiC), sapphire, silicon (Si), gallium arsenide (GaAs), etc.

[0034] The laser processing method according to this embodiment includes a modification spot formation step in which a plurality of modification spots 12 are formed along a virtual surface S by irradiating the interior of the workpiece 10 from its surface 10a with laser light L. The modification spot formation step is performed by a laser processing apparatus 1. In this example, the virtual surface S is a rectangular surface in the interior of the workpiece 10 that faces the surface 10a and extends parallel to the surface 10a to the side surface 10c of the workpiece 10. The workpiece 10 has a surface 10a and a surface 10b opposite to the surface 10a. Surface 10a is the surface to which the laser light L output from the laser processing apparatus 1 is incident.

[0035] The workpiece 10 has a first region R1 and a second region R2 when viewed in plan (from a direction perpendicular to the surfaces 10a and 10b (the thickness direction of the workpiece 10)). In this example, the first region R1 is rectangular, and the second region R2 is a rectangular ring surrounding the first region R1. The second region R2 extends along the outer edge of the workpiece 10 and constitutes the peripheral edge of the workpiece 10.

[0036] The first region R1 is an effective region used to form the device portion 20. On the other hand, the second region R2 is an ineffective region where the device portion 20 is not formed. The device portion 20 is formed, for example, on the surface 10b of the workpiece 10 in the first region R1. The device portion 20 is, for example, an element that performs an arbitrary function, such as a light-emitting element, a light-receiving element, a circuit element, etc. Multiple device portions 20 may be formed in the first region R1. The device portion 20 may be formed before the modification spot formation step or after the modification spot formation step. That is, the device formation step of forming the device portion 20 in the first region R1 may be performed before the modification spot formation step or after the modification spot formation step. The former case will be explained below as an example. In this case, in the modification spot formation step, a modification spot 12 is formed on the workpiece 10 while the device portion 20 is formed in the first region R1.

[0037] As shown in Figure 4(a), in the modification spot formation process, multiple (three rows in this example) modification spot rows 13 are formed in the second region R2. Each modification spot row 13 consists of multiple modification spots 12 arranged along the boundary B between the first region R1 and the second region R2. In Figure 4(a), the arrangement and formation order of the multiple modification spots 12 constituting each modification spot row 13 are indicated by arrows. This is also true for Figures 4(b), 7, and 11, which will be described later. The multiple modification spot rows 13 are arranged along a direction that intersects the direction of arrangement of the multiple modification spots 12 (in this example, a direction perpendicular to that direction of arrangement). That is, in this example, the boundary B is rectangular and has a first side B1, a second side B2, a third side B3, and a fourth side B4. The first side B1 is parallel to the third side B3, and the second side B2 is parallel to the fourth side B4. Each modification spot row 13 is composed of multiple modification spots 12 arranged along each of the first to fourth sides B1. The multiple modification spots 12 that make up each modification spot row 13 are arranged in a rectangular shape in a plan view. In the portion along the first side B1, the multiple modification spot row 13 is arranged in a direction perpendicular to the direction in which the multiple modification spots 12 are arranged (parallel to the first side B1) and a direction perpendicular to the first side B1. The same applies to the portions along the second to fourth sides B2 and B4.

[0038] In the example shown in Figure 4(a), the multiple modified spot rows 13 include a first modified spot row 13A, a second modified spot row 13B, and a third modified spot row 13C. The third modified spot row 13C, the second modified spot row 13B, and the first modified spot row 13A are arranged in this order near the first region R1 (boundary B). In the modified spot formation process, the multiple modified spot rows 13 are formed in order from furthest from the first region R1. In this example, the multiple modified spot rows 13 are formed in the order of the first modified spot row 13A, the second modified spot row 13B, and the third modified spot row 13C.

[0039] In the modification spot formation process, multiple rows of modification spots 13 are formed in the second region R2, thereby forming cracks that extend from the second region R2 to the first region R1. More specifically, cracks extending from modification spots 12 formed in the second region R2 extend toward the first region R1 (towards the center of the workpiece 10), thereby forming cracks that extend from the second region R2 to the first region R1. In Figures 2 and 3, the direction of crack extension is indicated by arrows. This is also true for Figure 6, which will be described later. In this example, multiple rows of modification spots 13 are formed in the second region R2, resulting in the formation of cracks throughout the entire first region R1.

[0040] In the modification spot formation step, multiple modification spot rows 13 may be formed in the second region R2, as shown in Figure 4(b). In this example, multiple modification spots 12 are arranged in a continuous line in a substantially spiral (helical) shape in a plan view. Even in this case, it can be considered that multiple modification spot rows 13 are formed, arranged in a direction perpendicular to the direction in which the multiple modification spots 12 are arranged. That is, the multiple modification spot rows 13 can be considered to include a first modification spot row 13A, a second modification spot row 13B, and a third modification spot row 13C, similar to the example in Figure 4(a).

[0041] Figure 5 shows an example of the results of actually processing the workpiece 10. Figure 5 shows the workpiece 10 as viewed from the surface 10a side. In this example, a member formed in the shape of a rectangular plate from magnesium oxide (MgO) was used as the workpiece 10. The surface orientation of the surface 10a of the workpiece 10 is <100> The length of one side of surface 10a was 5 mm, and the thickness of the workpiece 10 was 500 μm. A region with a width of 1 mm was set as the second region R2. Therefore, the first region R1 is a square region with sides of 3 mm. Three rows of modification spot rows 13 were formed in the second region R2, similar to the example in Figure 4(a). The arrows in Figure 5 indicate the order in which multiple modification spot rows 13 are formed. In this example, similar to Figure 4(a), multiple modification spot rows 13 were formed in order from furthest from the first region R1. In the workpiece 10 after processing, cracks were formed extending from the second region R2 to the first region R1. These cracks were formed throughout the entire first region R1. Cracks extending from the modification spots 12 formed on the four sides of the second region R2 connected in the center of the first region R1, forming a closed region (closed space) inside the second region R2 where the cracks were connected.

[0042] The laser processing method according to the embodiment further includes a separation step after the modification spot formation step in which the workpiece 10 is separated with a virtual surface S as the boundary. In the separation step, for example, double-sided tape is attached to the surfaces 10a and 10b of the workpiece 10, and a force is applied to the workpiece 10 so that the surfaces 10a and 10b are separated from each other, thereby separating the workpiece 10 into two parts with the virtual surface S as the boundary. Of the two separated parts, the part including the surface 10b in which the device portion 20 is formed constitutes a semiconductor device. Through the above steps, a semiconductor device in which the device portion 20 is formed in the first region R1 is obtained. Note that the separation step is not limited to the above embodiment, and for example, the workpiece 10 may be separated by applying some force to the workpiece 10 without attaching double-sided tape to the surfaces 10a and 10b. [Mechanism of Action and Effects]

[0043] In the laser processing method according to the embodiment, a crack extending from the second region R2 to the first region R1 is formed by forming a plurality of modified spot rows 13 in the second region R2. By forming a crack by extending (propagating) from the second region R2 to the first region R1 in this way (i.e., by utilizing the cleavage of the workpiece 10 to propagate the crack), the processing time can be shortened and the flatness of the cut surface can be improved compared to, for example, the case where a crack is formed in the first region R1 by forming modified spots 12 in the first region R1. That is, when a crack is formed in the first region R1 by forming modified spots 12 in the first region R1, laser processing marks (modified spots 12) remain on the cut surface, which can cause irregularities on the cut surface. In contrast, in the laser processing method according to the embodiment, since the crack is formed by extending from the second region R2 to the first region R1, the occurrence of such irregularities can be suppressed and the flatness of the cut surface can be improved. Furthermore, in the laser processing method according to the embodiment, a plurality of modified spot rows 13 are formed in the second region R2, thereby forming a crack extending from the second region R2 to the first region R1. This reduces the effect of laser irradiation on the first region R1, and as a result, reduces the effect of laser irradiation on the device portion 20 formed in the first region R1. For example, if laser light L is irradiated onto the first region R1 to form modified spots 12 while the device portion 20 is already formed in the first region R1, the laser light L that has passed through the workpiece 10 may be incident on the device portion 20, potentially causing undesirable effects on the device portion 20. Alternatively, if laser light L is irradiated onto the first region R1 to form modified spots 12 before the device portion 20 is formed in the first region R1, and the device portion 20 is formed in the first region R1 after the formation of the modified spots 12, the device portion 20 will be formed in the first region R1 which has been damaged by laser irradiation, potentially causing undesirable effects on the device portion 20.In contrast, in the laser processing method according to the embodiment, by forming a plurality of modified spot rows 13 in the second region R2, a crack extending from the second region R2 to the first region R1 is formed, thereby suppressing the occurrence of the above-mentioned situation and reducing the effect of laser irradiation on the device portion 20 formed in the first region R1. Therefore, according to the laser processing method according to the embodiment, it is possible to shorten the processing time, improve the flatness of the cut surface, and reduce the effect of laser irradiation on the workpiece 10. It should be noted that the discovery that a crack extending from the second region R2 to the first region R1 can be formed by forming a plurality of modified spot rows 13, consisting of a plurality of modified spots 12 arranged along the boundary B between the first region R1 and the second region R2, in the second region R2 in a direction intersecting the direction in which the plurality of modified spots 12 are arranged, is a discovery made by the inventors.

[0044] In the modification spot formation process, multiple rows of modification spots 13 are formed in the second region R2 such that cracks are formed throughout the entire first region R1. This further reduces processing time and improves the flatness of the cut surface.

[0045] In the modification spot formation process, after forming the first modification spot row 13A, a second modification spot row 13B is formed, which is located closer to the first region R1 than the first modification spot row 13A. This makes it easier for cracks to propagate from the second region R2 to the first region R1, further shortening the processing time and further improving the flatness of the cut surface. It should be noted that the finding that cracks are more likely to propagate from the second region R2 to the first region R1 when multiple modification spot rows 13 are formed in order of their distance from the first region R1 is a finding discovered by the inventors.

[0046] The second region R2 surrounds the first region R1 in a plan view. This allows the crack to extend favorably from the second region R2 to the first region R1, further reducing processing time and improving the flatness of the cut surface.

[0047] The material of the workpiece 10 contains gallium nitride, silicon carbide, sapphire, silicon, or gallium arsenide. In the laser processing method according to this embodiment, even in such cases, it is possible to shorten the processing time, improve the flatness of the cut surface, and reduce the influence of laser irradiation on the workpiece 10.

[0048] The workpiece 10 has a chip shape. In the laser processing method according to this embodiment, even in such cases, it is possible to shorten the processing time, improve the flatness of the cut surface, and reduce the influence of laser irradiation on the workpiece 10.

[0049] The workpiece 10 is formed from a semiconductor material. In the laser processing method according to this embodiment, a semiconductor workpiece formed from a semiconductor material can be suitably cut as the workpiece 10.

[0050] The first region R1 is the region for forming the device portion 20, and the second region R2 is the region where the device portion 20 is not formed. In the laser processing method according to this embodiment, the effect of laser irradiation on the device portion 20 can be reduced.

[0051] In the modification spot formation process, while the device portion 20 is formed in the first region R1, multiple modification spot rows 13 are formed in the second region R2. In this case, the effect of laser irradiation on the device portion 20 formed in the first region R1 can be reduced.

[0052] Following the modification spot formation process, a separation process is performed to separate the workpiece 10 using the virtual surface S as a boundary. This allows for the efficient separation of the workpiece 10. [Differentiation]

[0053] As shown in the first modified example in Figures 6 and 7, the workpiece 10 may be formed in a circular shape in plan view. In this case, the virtual surface S is a circular surface inside the workpiece 10 that faces the surface 10a. In this example, the first region R1 is circular, and the second region R2 is a circular ring (annular) surrounding the first region R1. The boundary B between the first region R1 and the second region R2 is circular.

[0054] As shown in Figure 7(a), in the modification spot formation step, multiple (three rows in this example) modification spot rows 13 are formed in the second region R2. The multiple modification spot rows 13 are arranged in a direction intersecting the direction of arrangement of the multiple modification spots 12 (radial direction in this example), and are arranged concentrically. The multiple modification spot rows 13 include a first modification spot row 13A, a second modification spot row 13B, and a third modification spot row 13C. The third modification spot row 13C, the second modification spot row 13B, and the first modification spot row 13A are arranged in this order near the first region R1 (boundary B). In the modification spot formation step, the multiple modification spot rows 13 are formed in order from furthest from the first region R1. In this example, the multiple modification spot rows 13 are formed in the order of first modification spot row 13A, second modification spot row 13B, and third modification spot row 13C. In the modification spot formation step of the first modified example, multiple rows of modification spots 13 are formed in the second region R2, and cracks extending from the second region R2 to the first region R1 are formed throughout the entire first region R1.

[0055] In the modification spot formation step of the first modified example, a plurality of modification spot rows 13 may be formed in the second region R2, as shown in Figure 7(b). In this example, a plurality of modification spots 12 are arranged in a continuous spiral pattern in a plan view. Even in this case, it can be considered that a plurality of modification spot rows 13 are formed, arranged in a direction perpendicular to the direction in which the plurality of modification spots 12 are arranged. That is, the plurality of modification spot rows 13 can be considered to include a first modification spot row 13A, a second modification spot row 13B, and a third modification spot row 13C, similar to the example in Figure 7(a).

[0056] This first modification also makes it possible to shorten processing time, improve the flatness of the cut surface, and reduce the influence of laser irradiation on the workpiece 10, similar to the embodiment described above.

[0057] As shown in the second modified example in Figures 8, 9, and 10, the workpiece 10 may have a wafer shape. In the second modified example, the workpiece 10 is, for example, a semiconductor wafer formed in a disc shape from a semiconductor material. By cutting the workpiece 10 at the linear portion 33 described later and dividing it into individual pieces, multiple semiconductor devices (semiconductor chips) can be obtained.

[0058] The second region R2 of the second modification has a circular ring-shaped peripheral portion 31 that constitutes the periphery of the workpiece 10, and a grid-like grid portion 32. The grid portion 32 includes a plurality of linear portions 33. Some of the plurality of linear portions 33 are aligned along one direction, and the remaining plurality of linear portions 33 are aligned along a direction perpendicular to that direction. The grid portion 32 is a cutting region (dicing street) for cutting the workpiece 10. The first region R1 has a plurality of rectangular portions 41 surrounded by the plurality of linear portions 33. A device portion 20 is formed in each rectangular portion 41.

[0059] For each linear portion 33 (reference linear portion), in a plan view, the region on one side of the linear portion 33 with respect to the center line CL is designated as the first portion P1, and the region on the other side of the center line CL is designated as the second portion P2. The center line CL is a straight line that passes through the center of the linear portion 33 in the width direction in a plan view and extends along the direction of extension of the linear portion 33.

[0060] In the modification spot formation step, multiple rows of modification spots 13 are formed on the peripheral portion 31. The manner in which multiple rows of modification spots 13 are formed on the peripheral portion 31 is, for example, the same as the manner in which multiple rows of modification spots 13 are formed on the second region R2 in the first modified example. In addition, multiple (two rows in this example) first rows of modification spots 13D are formed on the first portion P1, and multiple (two rows in this example) second rows of modification spots 13E are formed on the second portion P2. More specifically, multiple rows of first modification spots 13D are formed in order of proximity to the center line CL (i.e., in order of furthest from the first region R1), and multiple rows of second modification spots 13E are formed in order of proximity to the center line CL. In the modification spot formation step of the second modified example, as multiple rows of modification spots 13 are formed on the second region R2, cracks extending from the second region R2 to the first region R1 are formed over the entire first region R1 (rectangular portion 41).

[0061] This second modification also makes it possible to shorten the processing time, improve the flatness of the cut surface, and reduce the influence of laser irradiation on the workpiece 10, similar to the embodiment described above.

[0062] Furthermore, in the second modified example, the second region R2 has a grid-like portion 32 that includes a plurality of linear portions 33, and the first region R1 has a plurality of rectangular portions 41 surrounded by the plurality of linear portions 33. In this case, cracks are more likely to propagate from the second region R2 to the first region R1, the processing time can be further reduced, and the flatness of the cut surface can be further improved. Also, for example, a grid-like cutting region for separating semiconductor wafers into individual pieces can be used as the second region R2.

[0063] In the modification spot formation process of the second modified example, a first row of modification spots 13D is formed in the first portion P1, and a second row of modification spots 13E is formed in the second portion P2. This facilitates crack propagation from the second region R2 to the first region R1, further shortening the processing time and improving the flatness of the cut surface.

[0064] In the modification spot formation process of the second modified example, multiple rows of first modification spots 13D are formed in the first portion P1 in order of proximity to the center line CL, and multiple rows of second modification spots 13E are formed in the second portion P2 in order of proximity to the center line CL. This makes it easier for cracks to propagate from the second region R2 to the first region R1, further shortening the processing time and further improving the flatness of the cut surface.

[0065] As shown in the third modified example in Figure 11, a first region R1 and a second region R2 may be set up. In the third modified example, the second region R2 is rectangular, and the first region R1 is a rectangular ring surrounding the second region R2. The first region R1 extends along the outer edge of the workpiece 10 and constitutes the peripheral edge of the workpiece 10. A device portion 20 may or may not be formed in the first region R1.

[0066] As shown in Figure 11(a), in the modification spot formation step, multiple (three rows in this example) modification spot rows 13 are formed in the second region R2. The multiple modification spot rows 13 include a first modification spot row 13A, a second modification spot row 13B, and a third modification spot row 13C. The third modification spot row 13C, the second modification spot row 13B, and the first modification spot row 13A are arranged in this order near the first region R1 (boundary B). In the modification spot formation step, multiple modification spot rows 13 are formed in order from furthest from the first region R1. In this example, the multiple modification spot rows 13 are formed in the order of first modification spot row 13A, second modification spot row 13B, and third modification spot row 13C. In the modification spot formation process of the third modified example, multiple rows of modification spots 13 are formed in the second region R2, so that cracks extending from the second region R2 to the first region R1 are formed throughout the first region R1. In the third modified example, cracks extending from the modification spots 12 formed in the second region R2 extend toward the first region R1 (towards the outer edge of the workpiece 10), so that cracks extending from the second region R2 to the first region R1 are formed.

[0067] In the modification spot formation step of the third modified example, a plurality of modification spot rows 13 may be formed in the second region R2, as shown in Figure 11(b). In this example, the plurality of modification spots 12 are arranged in a continuous, substantially spiral pattern in a plan view. Even in this case, it can be considered that a plurality of modification spot rows 13 are formed, arranged in a direction perpendicular to the direction in which the plurality of modification spots 12 are arranged. That is, the plurality of modification spot rows 13 can be considered to include a first modification spot row 13A, a second modification spot row 13B, and a third modification spot row 13C, similar to the example in Figure 11(a).

[0068] This third modification also makes it possible to shorten processing time, improve the flatness of the cut surface, and reduce the influence of laser irradiation on the workpiece 10, similar to the above embodiment.

[0069] As a fourth modification, in the modification spot formation step, multiple modification spot rows 13 may be formed simultaneously by branching and irradiating the laser beam L. In this case, for example, the laser beam L pulsed by the light source 3 is modulated by the spatial light modulator 4 so that it is focused on multiple (e.g., six) focal points C aligned in the Y direction. The multiple focal points C are then moved relative to each other on a virtual plane S along the X direction. As a result, multiple modification spot rows 13, each consisting of multiple modification spots 12 aligned in the X direction, are formed simultaneously so that they are aligned at equal intervals in the Y direction.

[0070] Figure 12 shows the result of simultaneously forming six rows of modified spots 13 by irradiating the material with a laser beam L split into six points. In this example, a material made of magnesium oxide (MgO) was used as the workpiece. Figure 12 shows the workpiece as seen from the surface. In Figure 12, the six rows of modified spots 13 are formed so that they are aligned vertically in the figure. In the workpiece after processing, cracks were formed extending from the region where the six rows of modified spots 13 were formed (second region R2) to each of the pair of adjacent regions A (first region R1). Furthermore, no cracks were formed on the surface of the workpiece; cracks were formed only inside the workpiece.

[0071] This fourth modification also achieves the same reduction in processing time, improvement in the flatness of the cut surface, and reduction in the effect of laser irradiation on the workpiece 10 as in the above embodiment. Furthermore, in the modification spot formation step of the fourth modification, multiple modification spot rows 13 are formed simultaneously by branching and irradiating the laser beam L. In this case, cracks tend to propagate from the second region R2 to the first region R1, further reducing processing time and further improving the flatness of the cut surface. It should be noted that the finding that cracks tend to propagate from the second region R2 to the first region R1 when multiple modification spot rows 13 are formed simultaneously by branching and irradiating the laser beam L is a finding discovered by the inventors. In the fourth modification, it is sufficient that at least two modification spot rows 13 are formed simultaneously by branching and irradiating the laser beam L; for example, two rows of modification spot rows 13 may be formed simultaneously by branching and irradiating the laser beam L at two points.

[0072] The present invention is not limited to the embodiments and modifications described above. For example, the materials and shapes of each component are not limited to those described above, but can be made from a variety of materials and shapes. The material of the workpiece 10 may be a non-semiconductor material such as magnesium oxide (MgO), magnesium fluoride (MgF), calcium fluoride (CaF2), or mica. The workpiece 10 may have an ingot shape. For example, the workpiece 10 may be a semiconductor ingot formed in a disc shape from a semiconductor material. A semiconductor wafer can be cut from a semiconductor ingot by cutting the semiconductor ingot along a virtual plane S facing the surface.

[0073] In the above embodiments and modifications, one virtual surface S is set inside the workpiece 10, and the workpiece 10 is separated into two parts. However, two or more virtual surfaces S arranged in the thickness direction are set inside the workpiece 10, and the workpiece 10 may be separated into three or more parts. In the above embodiments and modifications, the modification spot formation step is performed after the device formation step. However, the device formation step may be performed after the modification spot formation step. In this case, in the modification spot formation step, a plurality of modification spot rows 13 are formed on the workpiece 10 while the device portion 20 is not formed in the first region R1.

[0074] In the modified spot formation step of the above embodiment and modified example, a crack is formed throughout the entire first region R1 by the formation of multiple modified spot rows 13 in the second region R2. However, a crack may be formed partially in the first region R1 by the formation of multiple modified spot rows 13 in the second region R2. In this case as well, the workpiece 10 can be separated into two parts with the virtual surface S as the boundary by, for example, applying force to the workpiece 10 in the separation step.

[0075] In the above embodiments and modifications, the modified spot rows 13 were not formed in the portion of the workpiece 10 where the device portion 20 is formed in a plan view, but the modified spot rows 13 may be formed in a part of that portion. That is, the device portion 20 may be formed in the second region R2. In the above embodiments and modifications, the device portion 20 was formed on the surface 10b of the workpiece 10 in the first region R1, but instead of this, or in addition, the device portion 20 may be formed on the surface 10a of the workpiece 10 in the first region R1. [Explanation of Symbols]

[0076] 1... Laser processing device, 2... Stage, 10... Workpiece, 10a, 10b... Surface, 12... Modified spot, 13... Modified spot row, 13A, 13D... First modified spot row, 13B, 13E... Second modified spot row, 20... Device part, 32... Grid-like part, 33... Linear part, 41... Rectangular part, B... Boundary, CL... Centerline, L... Laser beam, P1... First part, P2... Second part, R1... First region, R2... Second region, S... Virtual plane.

Claims

1. A laser cutting method for cutting a workpiece along a virtual plane that faces the surface of the workpiece within the workpiece, The process includes a forming step of irradiating the interior of the workpiece from the surface with laser light to form a plurality of modified spots along the virtual surface, The workpiece has a first region and a second region when viewed from a direction perpendicular to the surface. In the formation step, a plurality of modified spot rows, each consisting of multiple modified spots arranged along the boundary between the first and second regions, are formed only in the second region without forming them in the first region, and the plurality of modified spot rows are arranged in a direction intersecting the direction in which the plurality of modified spots are arranged, and the formation of the plurality of modified spot rows creates a crack extending from the second region to the first region. The plurality of modification spot rows include a first modification spot row and a second modification spot row positioned closer to the first region than the first modification spot row, A laser processing method comprising forming the first modified spot row and then forming the second modified spot row in the formation step.

2. A laser cutting method for cutting a workpiece along a virtual plane that faces the surface of the workpiece within the workpiece, The process includes a forming step of irradiating the interior of the workpiece from the surface with laser light to form a plurality of modified spots along the virtual surface, The workpiece has a first region and a second region when viewed from a direction perpendicular to the surface. In the formation step, a plurality of modified spot rows, each consisting of multiple modified spots arranged along the boundary between the first and second regions, are formed only in the second region without forming them in the first region, and the plurality of modified spot rows are arranged in a direction intersecting the direction in which the plurality of modified spots are arranged, and the formation of the plurality of modified spot rows creates a crack extending from the second region to the first region. The second region has a grid-like portion that includes a plurality of linear portions, The first region has a plurality of rectangular portions enclosed by the plurality of linear portions, One of the linear portions included in the plurality of linear portions is designated as the reference linear portion. Of the aforementioned reference straight line portion, when viewed from a direction perpendicular to the surface, if the region on one side of the center line of the reference straight line portion extending along the extension direction of the reference straight line portion is defined as the first portion, and the region on the other side of the center line is defined as the second portion, In the formation step, at least one modified spot row included in the plurality of modified spot rows is formed in the first portion, and at least one modified spot row included in the plurality of modified spot rows is formed in the second portion. The at least one modified spot row formed in the first portion includes a plurality of first modified spot rows, and the at least one modified spot row formed in the second portion includes a plurality of second modified spot rows. A laser processing method comprising the formation step of forming a plurality of first modified spot rows in the first portion in order of proximity to the center line, and forming a plurality of second modified spot rows in the second portion in order of proximity to the center line.

3. A laser cutting method for cutting a workpiece along a virtual plane that faces the surface of the workpiece within the workpiece, The process includes a forming step of irradiating the interior of the workpiece from the surface with laser light to form a plurality of modified spots along the virtual surface, The workpiece has a first region and a second region when viewed from a direction perpendicular to the surface. In the formation step, a plurality of modified spot rows, each consisting of multiple modified spots arranged along the boundary between the first and second regions, are formed only in the second region without forming them in the first region, and the plurality of modified spot rows are arranged in a direction intersecting the direction in which the plurality of modified spots are arranged, and the formation of the plurality of modified spot rows creates a crack extending from the second region to the first region. The first region is a region for forming a device portion, and the second region is a region where no device portion is formed. A laser processing method comprising forming a plurality of modified spot rows in a second region while a device portion is formed in the first region during the formation step.

4. The laser processing method according to any one of claims 1 to 3, wherein in the forming step, the plurality of modified spot rows are formed in the second region such that the crack is formed over the entire first region.

5. The plurality of modification spot rows include a first modification spot row and a second modification spot row positioned closer to the first region than the first modification spot row, The laser processing method according to claim 2 or 3, wherein in the forming step, the second modified spot row is formed after the first modified spot row is formed.

6. The laser processing method according to any one of claims 1 to 3, wherein the second region has a portion that surrounds the first region when viewed from a direction perpendicular to the surface.

7. The laser processing method according to any one of claims 1 to 3, wherein in the forming step, at least two of the multiple modified spot rows are simultaneously formed by branching and irradiating the laser light.

8. The second region has a grid-like portion that includes a plurality of linear portions, The laser processing method according to claim 1 or 3, wherein the first region has a plurality of rectangular portions surrounded by the plurality of linear portions.

9. One of the linear portions included in the plurality of linear portions is designated as the reference linear portion. Of the aforementioned reference straight line portion, when viewed from a direction perpendicular to the surface, if the region on one side of the center line of the reference straight line portion extending along the extension direction of the reference straight line portion is defined as the first portion, and the region on the other side of the center line is defined as the second portion, The laser processing method according to claim 8, wherein in the forming step, at least one modified spot row included in the plurality of modified spot rows is formed in the first portion, and at least one modified spot row included in the plurality of modified spot rows is formed in the second portion.

10. The at least one modified spot row formed in the first portion includes a plurality of first modified spot rows, and the at least one modified spot row formed in the second portion includes a plurality of second modified spot rows. The laser processing method according to claim 9, wherein in the forming step, the plurality of first modified spot rows are formed in the first portion in order of proximity to the center line, and the plurality of second modified spot rows are formed in the second portion in order of proximity to the center line.

11. The laser processing method according to any one of claims 1 to 3, wherein the material of the object to be processed includes gallium nitride, silicon carbide, sapphire, silicon, gallium arsenide, magnesium oxide, magnesium fluoride, calcium fluoride, or mica.

12. The laser processing method according to any one of claims 1 to 3, wherein the object to be processed has a chip shape, a wafer shape, or an ingot shape.

13. The laser processing method according to any one of claims 1 to 3, wherein the object to be processed is formed of a semiconductor material.

14. The laser processing method according to claim 1 or 2, wherein the first region is a region for forming a device portion, and the second region is a region in which no device portion is formed.

15. The laser processing method according to claim 14, wherein in the forming step, the plurality of modified spot rows are formed in the second region while the device portion is formed in the first region.

16. The laser processing method according to claim 14, wherein in the forming step, the plurality of modified spot rows are formed in the second region while the device portion is not formed in the first region.

17. The laser processing method according to any one of claims 1 to 3, further comprising the step of separating the workpiece with the virtual surface as a boundary after the forming step.

18. A method for manufacturing a semiconductor device using the laser processing method described in any one of claims 1 to 3, The workpiece is formed from a semiconductor material. The method for manufacturing the aforementioned semiconductor device is: The forming step, A method for manufacturing a semiconductor device, comprising the step of forming a device portion in the first region.

19. A laser processing apparatus for cutting a workpiece along a virtual plane that faces the surface of the workpiece within the workpiece, A stage that supports the workpiece, The laser irradiation unit comprises a laser irradiation unit that irradiates laser light from the surface into the interior of the workpiece to form a plurality of modified spots along the virtual surface, The workpiece has a first region and a second region when viewed from a direction perpendicular to the surface. The laser irradiation unit forms multiple rows of modification spots, each consisting of multiple modification spots arranged along the boundary between the first and second regions, only in the second region without forming any in the first region, and the multiple rows of modification spots are arranged in a direction intersecting the direction in which the multiple modification spots are arranged, and the formation of the multiple rows of modification spots causes a crack to be formed extending from the second region to the first region. The plurality of modification spot rows include a first modification spot row and a second modification spot row positioned closer to the first region than the first modification spot row, The laser irradiation unit is a laser processing apparatus that forms the second modified spot row after forming the first modified spot row.

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