Laser processing device and laser processing method

Abstract

According to the present invention, a control unit causes a drive unit to drive at least one of a support unit and a light condensing unit such that a light condensing spot of a laser light relatively moves along a line intersecting a pair of first cleavage planes on a wafer. The control unit causes a spatial light modulator to display a modulation pattern including a trefoil aberration pattern such that a beam shape of the laser light at the light condensing spot includes a center part, and a first extension part, a second extension part, and a third extension part that extend radially from the center part, the beam shape having the highest intensity at the center part, and such that, on the front side in a direction in which the light condensing spot relatively moves along the line, the second extension part is positioned on one side with respect to the line, the third extension part is positioned on the other side with respect to the line, and on the rear side in said direction, the first extension part is positioned on the line.

Description

Laser processing device and laser processing method

[0001] The present disclosure relates to a laser processing apparatus and a laser processing method.

[0002] A laser processing apparatus is known that includes a support section that supports a wafer, a light source that emits laser light, a spatial light modulator that modulates the laser light emitted from the light source, a focusing section that focuses the laser light modulated by the spatial light modulator onto the wafer, and an image transfer section that transfers an image of the laser light in the spatial light modulator onto an entrance pupil plane of the focusing section (see, for example, Patent Document 1).

[0003] JP 2011-51011 A

[0004] The laser processing device described above can form modified regions and cracks in a wafer. The formation of such modified regions and cracks can be applied to various processes, such as a dicing process for dividing a wafer into multiple chips and a trimming process for removing unnecessary portions from a wafer.

[0005] The present disclosure aims to provide a laser processing apparatus and a laser processing method that can sufficiently ensure the extension of a crack in the thickness direction of a wafer when forming a modified region and a crack along a line that intersects with a pair of cleavage planes in a wafer having a pair of cleavage planes that intersect with each other.

[0006] A laser processing apparatus according to one aspect of the present disclosure includes: [1] "a support unit that supports a wafer having a pair of first cleavage planes that intersect with each other; a light source that emits laser light; a spatial light modulator that modulates the laser light emitted from the light source by displaying a modulation pattern; a focusing unit that focuses the laser light modulated by the spatial light modulator on the wafer; a drive unit that drives at least one of the support unit and the focusing unit; and a control unit that controls at least the spatial light modulator and the drive unit, wherein the control unit controls at least one of the support unit and the focusing unit so that a focused spot of the laser light moves relatively along a line that intersects with the pair of first cleavage planes on the wafer." the driving unit, and the control unit controls the spatial light modulator to display the modulation pattern including a trefoil aberration pattern so that the beam shape of the laser light at the focused spot includes a center and a first extension portion, a second extension portion, and a third extension portion extending radially from the center and has the highest intensity at the center, and so that the second extension portion is located on one side of the line and the third extension portion is located on the other side of the line in front of a direction in which the focused spot moves relatively along the line, and the first extension portion is located on the line in rear of the direction.

[0007] In the laser processing apparatus, the focused spot is moved relatively along a line intersecting a pair of first cleavage planes on the wafer in a state in which the beam shape of the laser light at the focused spot includes a center and first, second, and third extensions extending radially from the center, with the beam intensity at the center being highest, and the second extension is located on one side of the line in front of the direction in which the focused spot moves relative to the line, the third extension is located on the other side of the line, and the first extension is located on the line in rear of the direction in which the focused spot moves relative to the line. This makes it easier for cracks to extend from the modified region formed along the line in the thickness direction of the wafer. Therefore, with the laser processing apparatus, when a modified region and a crack are formed along the line intersecting the pair of cleavage planes (i.e., the first cleavage planes) in a wafer having a pair of intersecting cleavage planes (i.e., the first cleavage planes), a sufficient amount of extension of the crack in the thickness direction of the wafer can be ensured.

[0008] The laser processing apparatus according to one aspect of the present disclosure may be [2] "the laser processing apparatus according to the above [1], wherein the wafer further has a second cleavage plane intersecting the pair of first cleavage planes, the cleavage characteristic of each of the pair of first cleavage planes being higher than the cleavage characteristic of the second cleavage plane, and the line is set to extend along the second cleavage plane." With this laser processing apparatus, even when the cleavage characteristic of each of the pair of first cleavage planes is higher than the cleavage characteristic of the second cleavage plane, it is possible to ensure a sufficient amount of extension of the crack in the thickness direction of the wafer.

[0009] The laser processing apparatus according to one aspect of the present disclosure may be [3] "the laser processing apparatus according to the above [2], wherein each of the pair of first cleavage planes is a (110) plane and the second cleavage plane is a (100) plane." With this laser processing apparatus, even when each of the pair of first cleavage planes is a (110) plane and the second cleavage plane is a (100) plane, it is possible to ensure a sufficient amount of extension of the crack in the thickness direction of the wafer.

[0010] The laser processing device according to one aspect of the present disclosure may be [4] "the laser processing device according to any one of [1] to [3] above, wherein the lines are each a plurality of lines extending in a grid pattern when viewed in the thickness direction of the wafer." With this laser processing device, the wafer can be efficiently divided into a plurality of chips.

[0011] The laser processing device according to one aspect of the present disclosure may be [5] "the laser processing device according to any one of [1] to [3] above, in which the line is part of a line extending along the outer edge of the wafer when viewed in the thickness direction of the wafer." With this laser processing device, the outer edge portion of the wafer can be efficiently removed from the wafer.

[0012] The laser processing device according to one aspect of the present disclosure may be [6] "the laser processing device according to any one of [1] to [5] above, wherein, when a predetermined portion of the wafer is to be removed from the surface on which the laser light is incident, the control unit controls at least the spatial light modulator and the drive unit so as to form a modified region within the portion." With this laser processing device, even when the thickness of the portion remaining after removing the predetermined portion is large, it is possible to extend a crack to the surface of the wafer opposite to the side on which the laser light is incident.

[0013] A laser processing method according to one aspect of the present disclosure is [7] "a laser processing method carried out by a laser processing apparatus including: a support portion for supporting a wafer having a pair of first cleavage planes intersecting with each other; a light source for emitting laser light; a spatial light modulator for modulating the laser light emitted from the light source by displaying a modulation pattern; a focusing portion for focusing the laser light modulated by the spatial light modulator on the wafer; and a drive portion for driving at least one of the support portion and the focusing portion, wherein the drive portion drives at least one of the support portion and the focusing portion so that a focused spot of the laser light moves relatively along a line on the wafer that intersects with the pair of first cleavage planes. and causing the spatial light modulator to display the modulation pattern including a trefoil aberration pattern so that the beam shape of the laser light at the focused spot includes a center and a first extension portion, a second extension portion, and a third extension portion extending radially from the center and has the highest intensity at the center, and so that the second extension portion is located on one side of the line and the third extension portion is located on the other side of the line at the front side in a direction in which the focused spot moves relatively along the line, and the first extension portion is located on the line at the rear side in the direction.

[0014] According to the above laser processing method, for the same reasons as those of the above laser processing apparatus, when a modified region and a crack are formed along a line intersecting the pair of cleavage planes in a wafer having a pair of cleavage planes that intersect with each other, it is possible to ensure a sufficient amount of extension of the crack in the thickness direction of the wafer.

[0015] According to the present disclosure, it is possible to provide a laser processing apparatus and a laser processing method that can sufficiently ensure the extension of the crack in the thickness direction of the wafer when forming a modified region and a crack along a line that intersects with the pair of cleavage planes in a wafer having a pair of cleavage planes that intersect with each other.

[0016] FIG. 1 is a configuration diagram of a laser processing apparatus according to an embodiment. FIG. 2 is a configuration diagram of an irradiation unit shown in FIG. 1. FIG. 3 is a configuration diagram of a 4f lens unit shown in FIG. 2. FIG. 4 is a cross-sectional view of a portion of a spatial light modulator shown in FIG. 2. FIG. 5 is a configuration diagram of an imaging unit shown in FIG. 1. FIG. 6 is a diagram showing an example of a trefoil aberration pattern. FIG. 7 is a diagram showing an example of a focusing state of laser light and an example of a beam shape of laser light at a focused spot. FIG. 8 is a diagram showing an example of a beam shape of laser light for each trefoil aberration intensity. FIG. 9 is a diagram showing an example of a beam shape of laser light modulated by a trefoil aberration pattern. FIG. 10 is a diagram showing an example of a beam shape of laser light modulated by a trefoil aberration pattern and an astigmatism pattern. FIG. 11 is a diagram showing an example of a beam shape of laser light modulated by a trefoil aberration pattern, an astigmatism pattern, and a spherical aberration pattern. FIG. 12 is a diagram showing an example of a beam shape of laser light modulated by a trefoil aberration pattern. FIG. 13 is a diagram showing an example of a focused state of laser light and an example of damage caused by laser light leakage. FIG. 14 is a plan view of a wafer to be processed by the laser processing apparatus shown in FIG. 1. FIG. 15 is a plan view of a wafer to be processed by the laser processing apparatus shown in FIG. 1. FIG. 16 is a diagram showing the processing surface, beam shape, energy, and internal state. FIG. 17 is a diagram showing the processing surface, beam shape, energy, and internal state. FIG. 18 is a diagram showing the processing surface, beam shape, energy, and internal state. FIG. 19 is a diagram showing the processing surface, beam shape, crack length, and cut surface state. FIG. 20 is a diagram showing an example of a preparatory step of a laser processing method performed by the laser processing apparatus shown in FIG. 1. FIG. 21 is a diagram showing an example of a processing step of a laser processing method performed by the laser processing apparatus shown in FIG. 1. FIG. 22 is a diagram showing a modified example of the preparatory step of a laser processing method performed by the laser processing apparatus shown in FIG. 1. FIG. 23 is a diagram showing a modified example of a processing step of a laser processing method performed by the laser processing apparatus shown in FIG. 1.

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted. [Configuration of laser processing device]

[0018] The configuration of a laser processing apparatus according to one embodiment will be described with reference to Figures 1 to 5. As shown in Figure 1, the laser processing apparatus 1 includes a support unit 2, an irradiation unit 3, an imaging unit 8, drive units 4 and 5, and a control unit 6. The laser processing apparatus 1 irradiates a wafer 11 with laser light L to form a modified region 12 in the wafer 11.

[0019] The support unit 2 supports the wafer 11, for example, by holding a film attached to the wafer 11. In this embodiment, the support unit 2 is movable in both the X and Y directions and is rotatable about an axis parallel to the Z direction. As an example, the X and Y directions are a first horizontal direction and a second horizontal direction that are perpendicular to each other, and the Z direction is a vertical direction.

[0020] The irradiation unit 3 focuses laser light L, which is transparent to the wafer 11, and irradiates the wafer 11 with the focused laser light. In this embodiment, the irradiation unit 3 is movable in the Z direction. When the laser light L is focused inside the wafer 11 supported by the support unit 2, the laser light L is particularly absorbed in a portion corresponding to a focused spot C of the laser light L, and a modified region 12 is formed inside the wafer 11. The focused spot C is also referred to as a focused region or a focused point.

[0021] The modified region 12 is a region whose density, refractive index, mechanical strength, and other physical properties are different from those of the surrounding unmodified region. Examples of the modified region 12 include a melt-processed region, a crack region, a dielectric breakdown region, and a refractive index change region. Cracks 13 are formed in the modified region 12 on both the incident side of the laser light L and the opposite side. Such modified regions 12 and cracks 13 are used to cut the wafer 11.

[0022] As an example, when the focused spot C is moved relatively along a line A set on the wafer 11 that is parallel to the X direction, multiple modified spots 12s are formed in a row along the line A. One modified spot 12s is formed by irradiating one pulse of laser light L. A row of modified regions 12 is a collection of multiple modified spots 12s lined up in a row. Adjacent modified spots 12s may be connected to each other or may be separated from each other depending on the relative moving speed of the focused spot C with respect to the wafer 11 and the repetition frequency of the laser light L.

[0023] The imaging unit 8 images the modified regions 12 and cracks 13 formed on the wafer 11 by irradiation with the laser light L. The imaging unit 8 can image the cracks 13 that have occurred in a direction intersecting the line A (a direction intersecting the line A when viewed from the Z direction) from each of the multiple modified spots 12s formed along the line A as the modified regions 12, or can image the cracks 13 that have occurred along the line A (along the line A when viewed from the Z direction) from each of the multiple modified spots 12s formed along the line A as the modified regions 12.

[0024] The driver 4 supports the support part 2 and drives the support part 2. In this embodiment, the driver 4 moves the support part 2 in each of the X and Y directions and rotates the support part 2 about an axis parallel to the Z direction. The driver 5 supports the irradiation part 3 and the imaging part 8 and drives the irradiation part 3 and the imaging part 8. In this embodiment, the driver 5 moves the irradiation part 3 and the imaging part 8 in the Z direction. As an example, in the laser processing apparatus 1, the driver 4 rotates the support part 2 so that the line A is parallel to the X direction, the driver 4 moves the support part 2 in the Y direction so that the focused spot C is located on the line A, the driver 5 moves the irradiation part 3 in the Z direction so that the focused spot C is located inside the wafer 11, and the driver 4 moves the support part 2 so that the focused spot C moves relatively along the line A.

[0025] The control unit 6 controls the support unit 2, the irradiation unit 3, the imaging unit 8, and the drive units 4 and 5. The control unit 6 has a processing unit, a memory unit, and an input reception unit (not shown). The processing unit is configured as a computer device including a processor, memory, storage, communication devices, etc. In the processing unit, the processor executes software (programs) loaded into the memory, etc., and controls reading and writing of data in the memory and storage, as well as communication by the communication devices. The memory unit is, for example, a hard disk, and stores various data. The input reception unit is an interface unit that displays various information and receives input of various information from the user. The input reception unit constitutes, for example, a GUI (Graphical User Interface).

[0026] As shown in FIG. 2 , the irradiation unit 3 includes a light source 31, a spatial light modulator 7, a focusing unit 33, and a 4f lens unit 34. The light source 31 emits laser light L, for example, by pulse oscillation. The spatial light modulator 7 modulates the laser light L emitted from the light source 31 by displaying a modulation pattern. The focusing unit 33 is composed of at least one lens and focuses the laser light L modulated by the spatial light modulator 7 onto the wafer 11. The 4f lens unit 34 transfers an image of the laser light L on the modulation surface of the spatial light modulator 7 onto the entrance pupil plane of the focusing unit 33. Note that the light source 31 may be provided outside the irradiation unit 3, and the laser light L emitted from the light source 31 may be guided to the irradiation unit 3. The irradiation unit 3 may also include other optical systems. For example, the irradiation unit 3 may include an optical system (e.g., an attenuator, a beam expander, etc.) arranged on the optical path between the light source 31 and the spatial light modulator 7.

[0027] As shown in FIG. 3 , the 4f lens unit 34 has a pair of lenses 34A and 34B. The pair of lenses 34A and 34B are arranged on the optical path of the laser light L traveling from the spatial light modulator 7 to the condenser 33. The pair of lenses 34A and 34B form a double-telecentric optical system in which the modulation surface 7a of the spatial light modulator 7 and the entrance pupil plane 33a of the condenser 33 are in an imaging relationship. As a result, the image of the laser light L on the modulation surface 7a of the spatial light modulator 7 (the image of the laser light L modulated by the spatial light modulator 7) is transferred (imaged) on the entrance pupil plane 33a of the condenser 33. Note that in FIG. 3 , f1 and f2 indicate the focal lengths of the lenses 34A and 34B, respectively, and Fs indicates the Fourier plane.

[0028] 4, the spatial light modulator 7 is a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM). The spatial light modulator 7 is configured by laminating a drive circuit layer 72, a pixel electrode layer 73, a reflective film 74, an alignment film 75, a liquid crystal layer 76, an alignment film 77, a transparent conductive film 78, and a transparent substrate 79 in this order on a semiconductor substrate 71.

[0029] The semiconductor substrate 71 is, for example, a silicon substrate. The drive circuit layer 72 forms an active matrix circuit on the semiconductor substrate 71. The pixel electrode layer 73 includes a plurality of pixel electrodes 73a arranged in a matrix along the surface of the semiconductor substrate 71. Each pixel electrode 73a is made of, for example, a metal material such as aluminum. A voltage is applied to each pixel electrode 73a by the drive circuit layer 72.

[0030] The reflective film 74 is, for example, a dielectric multilayer film. The alignment film 75 is provided on the surface of the liquid crystal layer 76 facing the reflective film 74, and the alignment film 77 is provided on the surface of the liquid crystal layer 76 opposite the reflective film 74. Each alignment film 75, 77 is formed from, for example, a polymer material such as polyimide, and the contact surfaces of each alignment film 75, 77 with the liquid crystal layer 76 are subjected to, for example, rubbing treatment. The alignment films 75, 77 align the liquid crystal molecules 76a contained in the liquid crystal layer 76 in a fixed direction.

[0031] The transparent conductive film 78 is provided on the surface of the transparent substrate 79 on the alignment film 77 side, and faces the pixel electrode layer 73 with the liquid crystal layer 76 and the like sandwiched therebetween. The transparent substrate 79 is, for example, a glass substrate. The transparent conductive film 78 is formed of a light-transmitting and conductive material such as ITO. The transparent substrate 79 and the transparent conductive film 78 transmit the laser light L.

[0032] In the spatial light modulator 7 configured as described above, when a signal indicating a modulation pattern is input from the control unit 6 to the drive circuit layer 72, a voltage corresponding to the signal is applied to each pixel electrode 73a, and an electric field is formed between each pixel electrode 73a and the transparent conductive film 78. When this electric field is formed, the alignment direction of the liquid crystal molecules 76a in the liquid crystal layer 76 changes for each region corresponding to each pixel electrode 73a, and the refractive index changes for each region corresponding to each pixel electrode 73a. This state is when the spatial light modulator 7 displays a modulation pattern.

[0033] With the spatial light modulator 7 displaying a modulation pattern, laser light L enters the liquid crystal layer 76 from the outside through the transparent substrate 79 and the transparent conductive film 78, is reflected by the reflective film 74, and is emitted from the liquid crystal layer 76 to the outside through the transparent conductive film 78 and the transparent substrate 79. The intensity, amplitude, phase, polarization, etc. of the laser light L are modulated according to the modulation pattern displayed on the liquid crystal layer 76. The modulation surface 7a shown in FIG. 3 corresponds to the liquid crystal layer 76.

[0034] 5, the imaging unit 8 includes a light source 81, a mirror 82, an objective lens 83, and an imaging element 84. The light source 81 emits light L1 that is transparent to the wafer 11. The light source 81 is configured, for example, by a halogen lamp and a filter, and emits light L1 in the near-infrared region. The light L1 emitted from the light source 81 is reflected by the mirror 82, passes through the objective lens 83, and is irradiated onto the wafer 11 on which the modified regions 12 and cracks 13 have been formed. The light L1 reflected by the wafer 11 passes through the objective lens 83 and the mirror 82, and is incident on the imaging element 84. The imaging element 84 detects the light L1 that has passed through the objective lens 83 and the mirror 82. The imaging element 84 is configured, for example, by an InGaAs sensor, and detects the light L1 in the near-infrared region. [Modulation Pattern Including Trefoil Aberration Pattern]

[0035] Modulation patterns including trefoil aberration patterns will be described with reference to Figs. 6 to 13. In the laser processing apparatus 1, the control unit 6 can cause the spatial light modulator 7 to display modulation patterns including trefoil aberration patterns. Fig. 6 is a diagram showing an example of a trefoil aberration pattern. Trefoil aberration is one of the third-order Zernike aberrations. Note that spherical aberration and astigmatism are included in the second-order Zernike aberrations, and coma aberration and trefoil aberration are included in the third-order Zernike aberrations.

[0036] When the laser light L modulated by the spatial light modulator 7 displaying the trefoil aberration pattern is focused by the focusing portion 33, the laser light L is most focused at the focused spot C, as shown in Fig. 7A. At this time, the beam shape 9 of the laser light L at the focused spot C (i.e., the intensity distribution of the laser light L in the "plane perpendicular to the optical axis of the laser light L (the dashed dotted line shown in Fig. 7A) and including the focused spot C") becomes a beam shape that includes a center portion 90 and first, second, and third extension portions 91, 92, and 93 extending radially from the center portion 90, and has the highest intensity at the center portion 90, as shown in Fig. 7B. As an example, the width of each of the first extension portion 91, the second extension portion 92, and the third extension portion 93 decreases with increasing distance from the center 90, and the intensity of each of the first extension portion 91, the second extension portion 92, and the third extension portion 93 decreases with increasing distance from the center 90. As an example, the beam shape 9 of the laser light L is a triangle with each side curved inward.

[0037] It should be noted that the modulation pattern including the trefoil aberration pattern includes not only a modulation pattern including only the trefoil aberration pattern, but also a modulation pattern including both the trefoil aberration pattern and other patterns. Even when the modulation pattern includes a pattern other than the trefoil aberration pattern, when the laser light L modulated by the spatial light modulator 7 displaying the modulation pattern including the trefoil aberration pattern is focused by the focusing portion 33, the beam shape 9 of the laser light L at the focused spot C becomes a beam shape that includes a center portion 90 and first, second, and third extension portions 91, 92, and 93 extending radially from the center portion 90, and has the highest intensity at the center portion 90. As an example, when the laser light L modulated by the spatial light modulator 7 displaying a modulation pattern including a trefoil aberration pattern and an astigmatism pattern is focused by the focusing unit 33, multiple focused spots C may appear. Even in such a case, the beam shape 9 of the laser light L at each focused spot C (in this case, the intensity distribution of the laser light L within "a plane perpendicular to the optical axis of the laser light L focused at the focused spot C and including the focused spot C") becomes a beam shape that includes a center 90 and a first extension 91, a second extension 92, and a third extension 93 extending radially from the center 90, and has the highest intensity at the center 90.

[0038] 8 is a diagram showing an example of the beam shape of the laser light L for each trefoil aberration intensity. The absolute value of the trefoil aberration intensity indicates the strength of the trefoil aberration, and the larger the absolute value of the trefoil aberration intensity, the stronger the trefoil aberration (hence, "strong trefoil aberration intensity" means that the absolute value of the trefoil aberration intensity is large). The positive or negative sign of the trefoil aberration intensity indicates the direction of the trefoil aberration, and the direction of the trefoil aberration with a positive sign differs by 180 degrees from that with a negative sign. FIG. 8 shows a camera image captured by a camera as the beam shape of the laser light L.

[0039] As shown in Figure 8, when the laser light L is modulated by a trefoil aberration pattern having any of the trefoil aberration intensities, the beam shape 9 of the laser light L at the focused spot C is a beam shape that includes a center portion 90 and a first extension portion 91, a second extension portion 92, and a third extension portion 93, and has the highest intensity at the center portion 90 (see (b) of Figure 7). At this time, the beam shape of the laser light L at the position of -20 μm and the beam shape of the laser light L at the position of +20 μm are also beam shapes having the same shape and direction as the beam shape 9 of the laser light L at the focused spot C. At first glance in the camera image, the beam shape 9 of the laser light L at the focused spot C may appear to be pointing in the opposite direction to the beam shapes of the laser light L at the position of -20 μm and the beam shapes of the laser light L at the position of +20 μm. However, even in such cases, when not only the high-intensity portions but also the low-intensity portions are included, it can be seen that the beam shape 9 of the laser light L is pointing in the same direction as those beam shapes. The "-20 μm position" is a position 20 μm away from the focusing spot C on the side of the focusing section 33, and the "+20 μm position" is a position 20 μm away from the focusing spot C on the side opposite the focusing section 33.

[0040] Fig. 9 is a diagram showing an example of the beam shape of laser light L modulated by a trefoil aberration pattern. Fig. 10 is a diagram showing an example of the beam shape of laser light L modulated by a trefoil aberration pattern and an astigmatism pattern (i.e., a modulation pattern in which they are superimposed). Fig. 11 is a diagram showing an example of the beam shape of laser light L modulated by a trefoil aberration pattern, an astigmatism pattern, and a spherical aberration pattern (i.e., a modulation pattern in which they are superimposed). Figs. 9 to 11 show a simulation image obtained by simulation and a camera image captured by a camera as the beam shape of laser light L. In each of Figs. 9 to 11, the trefoil aberration intensity of the trefoil aberration pattern is -0.6.

[0041] As shown in Figures 9 to 11, when the laser light L is modulated by a modulation pattern including a trefoil aberration pattern, the beam shape 9 of the laser light L at the focused spot C becomes a beam shape that includes a center 90 and a first extension 91, a second extension 92, and a third extension 93, and has the highest intensity at the center 90 (see (b) of Figure 7). At this time, the beam shape of the laser light L at the position of -20 μm and the beam shape of the laser light L at the position of +20 μm also become beam shapes having the same shape and direction as the beam shape 9 of the laser light L at the focused spot C. At first glance in the camera image, the beam shape 9 of the laser light L at the focused spot C may appear to be pointing in the opposite direction to the beam shapes of the laser light L at the position of -20 μm and the beam shapes of the laser light L at the position of +20 μm. However, even in such cases, when not only the high-intensity portions but also the low-intensity portions are included, it can be seen that the beam shape 9 of the laser light L is pointing in the same direction as those beam shapes.

[0042] 12 is a diagram showing an example of the beam shape of laser light L modulated by the trefoil aberration pattern. In this case, the trefoil aberration intensity of the trefoil aberration pattern is −0.5. As shown in FIG. 12, the beam shapes of laser light L at the −100 μm position and the +100 μm position are beam shapes facing in the opposite direction to the beam shape 9 of laser light L at the focused spot C. Note that the “−100 μm position” is a position 100 μm away from the focused spot C toward the focusing unit 33, and the “+100 μm position” is a position 100 μm away from the focused spot C on the opposite side from the focusing unit 33.

[0043] In contrast, as described above, the beam shape of the laser light L at the position of −20 μm and the beam shape of the laser light L at the position of +20 μm are beam shapes having the same shape and direction as the beam shape 9 of the laser light L at the focused spot C (see FIGS. 8 to 11 ). In particular, the beam shape of the laser light L at the position of −20 μm more clearly shows the beam shape 9 of the laser light L at the focused spot C than the beam shape of the laser light L at the position of +20 μm. Therefore, in order to estimate the beam shape 9 of the laser light L at the focused spot C when the laser light L modulated by a modulation pattern including a trefoil aberration pattern is focused, the beam shape of the laser light L at the position of −20 μm may be captured by a camera and the camera image may be observed.

[0044] 13A, a metal film 110 is formed on the second main surface 11b of a silicon wafer 11. The first main surface 11a of the wafer 11 is used as the incident surface of the laser light L, and a focusing spot C is aligned with a position inside the wafer 11 that is 20 to 30 μm from the second main surface 11b. When the laser light L is irradiated onto the wafer 11, if the laser light L is modulated by a modulation pattern including a trefoil aberration pattern and focused, damage having a shape and orientation similar to the beam shape 9 of the laser light L at the focusing spot C is formed in the metal film 110, as shown in FIG. 13B. Therefore, in order to estimate the beam shape 9 of the laser light L at the focusing spot C when the laser light L modulated by a modulation pattern including a trefoil aberration pattern is focused, damage can be formed in the metal film 110 as described above and the damage observed. [Relationship between Beam Shape Orientation and Crack Extension Amount]

[0045] The relationship between the direction of the beam shape 9 and the extension amount of the crack 13 will be described with reference to Figures 14 to 19. Figures 14 and 15 are plan views of two types of wafers 11A, 11B to be processed by the laser processing device 1. Each wafer 11A, 11B has a first main surface 11a and a second main surface 11b opposite the first main surface 11a. A plurality of lines A are set on each wafer 11A, 11B. The multiple lines A extend in a lattice pattern when viewed from the thickness direction of each wafer 11A, 11B.

[0046] As an example, each wafer 11A, 11B includes a semiconductor wafer and multiple functional elements formed on the first main surface 11a of the semiconductor wafer. The multiple functional elements are arranged in a matrix along the first main surface 11a, based on a notch 11c formed in each wafer 11A, 11B. When viewed from the thickness direction of each wafer 11A, 11B, multiple lines A extend in a grid pattern so as to pass between adjacent functional elements. The semiconductor wafer constituting each wafer 11A, 11B is, for example, a single-crystal silicon wafer. Each functional element may be, for example, a light-receiving element such as a photodiode, a light-emitting element such as a laser diode, or a circuit element such as a memory. Each functional element may be three-dimensionally configured by stacking multiple layers. Note that each wafer 11A, 11B may have an orientation flat formed thereon instead of the notch 11c.

[0047] Each wafer 11A, 11B has a pair of first cleavage planes F1 that intersect with each other and a pair of second cleavage planes F2 that intersect with each other. Each of the first cleavage planes F1 and each of the second cleavage planes F2 is a cleavage plane that intersects with the first main surface 11a and the second main surface 11b. In this embodiment, the pair of first cleavage planes F1 is a pair of (110) planes that are perpendicular to each other at an arbitrary point, and the pair of second cleavage planes F2 is a pair of (100) planes that are perpendicular to each other at an arbitrary point. At an arbitrary point, the pair of (110) planes and the pair of (100) planes are positioned such that when the pair of (110) planes are rotated 45 degrees around the point, they coincide with the pair of (100) planes. In other words, each of the second cleavage planes F2 intersects with the pair of first cleavage planes F1 at an arbitrary point. The cleavage tendency of the (110) plane is higher than that of the (100) plane. In other words, the cleavage tendency of the first cleavage plane F1 is higher than that of the second cleavage plane F2. Note that cleavage tendency refers to the ease of cracking along a crystal plane. Therefore, each of the wafers 11A and 11B is more likely to crack along the first cleavage plane F1 than along the second cleavage plane F2.

[0048] In wafer 11A, each line A intersects with a pair of second cleavage planes F2 and extends along one of the first cleavage planes F1. That is, in wafer 11A, the processed surface extending along line A is the (110) plane. In wafer 11B, each line A intersects with a pair of first cleavage planes F1 and extends along one of the second cleavage planes F2. That is, in wafer 11B, the processed surface extending along line A is the (100) plane.

[0049] 16 to 18 are diagrams showing the processed surface extending along the line A, the beam shape 9 of the laser light L at the focused spot C, the energy of the laser light L, and the internal state of the wafer 11. The wafer 11 shown in Fig. 16 is the wafer 11A described above, and the wafer 11 shown in Figs. 17 and 18 is the wafer 11B described above.

[0050] As shown in Figure 16, when the processing surface extending along line A is a (110) plane, when irradiation with laser light L is performed under "condition A of circular beam shape 9 and 2 μJ energy," multiple modified spots 12s are formed inside the wafer 11 along line A, but hardly any cracks 13 are generated from each modified spot 12s. When the processing surface extending along line A is a (110) plane, when irradiation with laser light L is performed under "condition B of circular beam shape 9 and 6.5 μJ energy," which differs from condition A only in that the energy is increased, multiple modified spots 12s are formed inside the wafer 11 along line A, and cracks 13 are generated along directions parallel to line A and perpendicular to line A (i.e., the directions in which each of the pair of (110) planes extends). When the processing surface extending along line A is a (110) plane, when laser light L is irradiated under "condition C of an elliptical beam shape 9 with a longitudinal direction parallel to line A and an energy of 6.5 μJ," which differs from condition B only in that an astigmatism pattern is further added to the modulation pattern of the laser light L, multiple modified spots 12s are formed inside the wafer 11 along line A, cracks 13 occur along directions parallel to line A and perpendicular to line A, and the cracks 13 are connected along line A. Thus, when the processing surface extending along line A is a (110) plane, cracks 13 are likely to occur along directions parallel to line A and perpendicular to line A, and the cracks 13 are likely to be connected along line A.

[0051] As shown in Figure 17, when the processing surface extending along line A is a (100) plane, when irradiation with laser light L is performed under the above-mentioned condition A, multiple modified spots 12s are formed inside the wafer 11 along line A, but cracks 13 hardly occur from each modified spot 12s. When the processing surface extending along line A is a (100) plane, when irradiation with laser light L is performed under the above-mentioned condition B, multiple modified spots 12s are formed inside the wafer 11 along line A, and cracks 13 occur along a direction inclined at an angle of 45 degrees to line A (i.e., the direction in which each of the pair of (110) planes extends). When the processing surface extending along line A is a (100) plane, when irradiation with laser light L is performed under the above-mentioned condition C, multiple modified spots 12s are formed inside the wafer 11 along line A, and cracks 13 occur along a direction inclined at an angle of 45 degrees to line A, and the cracks 13 do not connect along line A. In this way, when the processed surface extending along line A is the (100) plane, cracks 13 are likely to occur along a direction inclined at an angle of 45 degrees to line A, and cracks 13 are unlikely to connect along line A.

[0052] As shown in Figure 18, when the processing surface extending along line A is a (100) plane, when laser light L is irradiated under "condition D: a backward beam shape 9 with a trefoil aberration pattern and energy of 6.5 μJ," which differs from condition C only in that a trefoil aberration pattern is further added to the modulation pattern of the laser light L, multiple modified spots 12s are formed inside the wafer 11 along line A, cracks 13 are generated along a direction inclined at an angle of 45 degrees to line A, and the cracks 13 are connected along line A. Here, the backward beam shape 9 due to the trefoil aberration pattern is a beam shape that includes a center 90 and first extensions 91, second extensions 92, and third extensions 93 extending radially from the center 90, and has the highest intensity at the center 90, in which the second extension 92 is located on one side of the line A in front of the direction in which the focused spot C moves relatively along the line A, and the third extension 93 is located on the other side of the line A, and the first extension 91 is located on the line A behind the direction in which the focused spot C moves relatively along the line A. Thus, even when the processing surface extending along the line A is a (100) plane, when the backward beam shape 9 due to the trefoil aberration pattern is used, cracks 13 are generated along a direction inclined at an angle of 45 degrees to the line A, but the cracks 13 are connected along the line A.

[0053] 19 is a diagram showing the processed surface extending along line A, the beam shape 9 of the laser light L at the focused spot C, the extension amount of the crack 13 extending from the modified region 12 to the side opposite the incident side of the laser light L, and the state of the cut surface of the wafer 11. In the case shown in FIG. 19, the wafer 11 whose processed surface is the (110) plane is the wafer 11A described above, and the wafer 11 whose processed surface is the (100) plane is the wafer 11B described above. The extension amount of the crack 13 extending from the modified region 12 to the side opposite the incident side of the laser light L was obtained by changing the distance between two rows of modified regions 12 arranged at the same interval in the thickness direction of the wafer 11 and the main surface of the wafer 11 opposite the incident side of the laser light L, and determining the maximum value of the distance when the crack 13 reaches the main surface from the two rows of modified regions 12. The state of the cut surface of the wafer 11 is an image of the cut surface of the wafer 11 when the wafer 11 is cut along line A by expanding.

[0054] 19 , when the processing surface extending along line A is a (110) plane, and laser light L is irradiated under "condition E of an elliptical beam shape 9 with a longitudinal direction parallel to line A" in which an astigmatism pattern is added to the modulation pattern of the laser light L, the extension amount of the crack 13 extending from the modified region 12 to the opposite side to the incident side of the laser light L is 63 μm. When the processing surface extending along line A is a (100) plane, and laser light L is irradiated under the above-mentioned condition E, the extension amount of the crack 13 extending from the modified region 12 to the opposite side to the incident side of the laser light L is 55 μm. When the processing surface extending along the line A is a (100) plane, when the laser light L is irradiated under "condition F of a forward beam shape 9 due to a trefoil aberration pattern," which differs from condition E only in that a trefoil aberration pattern is further added to the modulation pattern of the laser light L, the extension amount of the crack 13 extending from the modified region 12 to the opposite side of the incident side of the laser light L was 55 μm. Here, the forward beam shape 9 due to the trefoil aberration pattern is a beam shape including a center 90 and a first extension portion 91, a second extension portion 92, and a third extension portion 93 extending radially from the center 90 and having the highest intensity at the center 90, and the first extension portion 91 is located on the line A in front of the direction in which the focused spot C moves relatively along the line A, and the second extension portion 92 is located on one side of the line A on the rear side of the direction, and the third extension portion 93 is located on the other side of the line A. This is a beam shape. When the processed surface extending along line A is a (100) plane, and laser light L is irradiated under "condition G of backward beam shape 9 with trefoil aberration pattern," which differs from condition E only in that a trefoil aberration pattern is further added to the modulation pattern of the laser light L, the extension amount of the crack 13 extending from the modified region 12 to the opposite side to the incident side of the laser light L is 63 μm.

[0055] In this way, when the processed surface extending along line A is a (100) plane, cracks 13 are less likely to extend from modified region 12 to the opposite side of the incident side of laser light L compared to when the processed surface extending along line A is a (110) plane. Also, even when the processed surface extending along line A is a (100) plane, if a backward beam shape 9 due to a trefoil aberration pattern is used, cracks 13 will extend from modified region 12 to the opposite side of the incident side of laser light L to the same extent as when the processed surface extending along line A is a (110) plane. [Laser processing method performed in laser processing device]

[0056] The laser processing method performed by the laser processing apparatus 1 will be described with reference to Figures 20 and 21. In this embodiment, it is assumed that it is not known in advance whether the wafer 11 to be processed is a "wafer 11A having a (110) surface" or a "wafer 11B having a (100) surface." Furthermore, it is assumed that after the processing step described below is performed, a predetermined portion 11d is to be removed from the second main surface (front surface) 11b of the wafer 11 onto which the laser light L is incident, as shown in Figure 21(b).

[0057] 20 , laser light L having a circular beam shape 9 is irradiated along line A, and multiple modified spots 12s are formed inside wafer 11 along line A. Next, control unit 6 causes imaging unit 8 to capture images of modified regions 12 and cracks 13 formed in wafer 11 by irradiation with laser light L, and determines beam shape 9 of laser light L to be used in the processing step based on the image capture results.

[0058] Specifically, if the imaging result shows that a crack 13 has occurred along a direction parallel to line A and a direction perpendicular to line A, the directions in which each of the pair of (110) planes (i.e., each of the pair of first cleavage planes F1) extends are parallel to line A and perpendicular to line A. Therefore, the control unit 6 determines that the wafer 11 to be processed is "a wafer 11A whose processing surface is a (110) plane," and selects a forward beam shape 9 with a trefoil aberration pattern as the beam shape 9 of the laser light L used in the processing step. Note that the occurrence of a crack 13 along a direction perpendicular to line A means that the crack 13 has occurred in a direction intersecting line A at an angle of 85 to 95 degrees when viewed from the thickness direction of the wafer 11.

[0059] On the other hand, if the imaging result shows that the crack 13 has occurred along a direction inclined with respect to the line A, the direction in which each of the pair of (110) planes (i.e., each of the pair of first cleavage planes F1) extends is a direction inclined at an angle of 45 degrees with respect to the line A. Therefore, the control unit 6 determines that the wafer 11 to be processed is "a wafer 11B whose processing surface is a (100) plane," and selects a backward beam shape 9 due to a trefoil aberration pattern as the beam shape 9 of the laser light L used in the processing step. Note that the occurrence of the crack 13 along a direction inclined with respect to the line A means that the crack 13 has occurred in a direction intersecting the line A at an angle of 40 to 50 degrees when viewed from the thickness direction of the wafer 11.

[0060] In this way, the control unit 6 determines the orientation of the beam shape 9 with respect to the line A based on the state (in this embodiment, the orientation) of the cracks 13 generated in the direction intersecting the line A from each of the multiple modified spots 12s formed along the line A as the modified regions 12. In other words, when the control unit 6 causes the spatial light modulator 7 to display a modulation pattern including a trefoil aberration pattern, it determines the orientation of the beam shape 9 with respect to the line A based on the state of the cracks 13 imaged in advance by the imaging unit 8 (preparation step).

[0061] When the wafer 11 to be processed is a wafer 11B whose processing surface is the (100) plane (i.e., when each line A intersects with a pair of first cleavage planes F1 and extends along the second cleavage plane F2), as shown in (a) and (b) of Figure 21, the control unit 6 controls the spatial light modulator 7 to display a modulation pattern including a trefoil aberration pattern so that the beam shape 9 of the laser light L at the focused spot C includes a center 90 and a first extension portion 91, a second extension portion 92, and a third extension portion 93 extending radially from the center 90, and has the highest intensity at the center 90, and so that the second extension portion 92 is located on one side of the line A and the third extension portion 93 is located on the other side of the line A in front of the direction in which the focused spot C moves relatively along the line A, and the first extension portion 91 is located on the line A in the rear of the direction. At this time, the wafer 11B is supported by the support unit 2 with the protective tape 14 attached to the first main surface 11a. In this state, the control unit 6 controls the drive unit 4 to drive the support unit 2 so that the focused spot C of the laser light L moves relatively along each line A within the portion 11d of the wafer 11B, with the second main surface 11b of the wafer 11B serving as the incident surface of the laser light L (processing step).

[0062] As a result, modified regions 12 (e.g., two rows of modified regions 12 aligned in the thickness direction of the wafer 11B) are formed along each line A in the portion 11d of the wafer 11B, and cracks 13 reach the first main surface 11a of the wafer 11B from the modified regions 12 along each line A. Then, after the processing step is performed, for example, the second main surface 11b of the wafer 11B is polished, thereby removing the portion 11d together with the modified regions 12 from the wafer 11B, and dividing the wafer 11B into multiple chips. In this way, when it is planned to remove a predetermined portion 11d from the second main surface 11b of the wafer 11, on which the laser light L is incident, the control unit 6 controls at least the spatial light modulator 7 and the driving units 4 and 5 so that modified regions 12 are formed in the portion 11d.

[0063] When the wafer 11 to be processed is a wafer 11A having a (110) surface, the control unit 6 causes the spatial light modulator 7 to display a modulation pattern including a trefoil aberration pattern so that the first extension 91 is located on the line A at the front side in the direction in which the focused spot C moves relatively along the line A, and the second extension 92 is located on one side of the line A at the rear side in the direction in which the focused spot C moves relatively along the line A, and the third extension 93 is located on the other side of the line A. Then, in this state, the control unit 6 causes the drive unit 4 to drive the support unit 2 so that the focused spot C of the laser light L moves relatively along each line A. [Action and Effect]

[0064] In the laser processing apparatus 1, the beam shape 9 of the laser light L at the focused spot C includes a center 90 and first, second, and third extensions 91, 92, and 93 extending radially from the center 90, with the beam intensity at the center 90 being the highest, and the focused spot C is moved relatively along a line A intersecting with a pair of first cleavage planes F1 on the wafer 11B in a state in which the second extension 92 is located on one side of the line A in front of the direction in which the focused spot C moves relative to the line A and the third extension 93 is located on the other side of the line A, and the first extension 91 is located on the line A in the rear of the direction in which the focused spot C moves relative to the line A. This makes it easier for cracks 13 to extend from the modified region 12 formed along the line A in the thickness direction of the wafer 11B. Therefore, in a wafer 11B having a pair of intersecting first cleavage planes F1, when the modified region 12 and the crack 13 are formed along the line A intersecting the pair of first cleavage planes F1, the laser processing apparatus 1 can ensure a sufficient extension of the crack 13 in the thickness direction of the wafer 11B. In the present embodiment, when a plurality of functional elements are formed on the first main surface 11a side of the wafer 11B opposite to the side onto which the laser light L is incident, even if the modified region 12 is located away from the first main surface 11a, the crack 13 can extend from the modified region 12 toward the first main surface 11a, thereby preventing damage to the functional elements due to leakage of the laser light L.

[0065] In the laser processing apparatus 1, the cleavage characteristic of each of the pair of first cleavage planes F1 in the wafer 11B is set higher than the cleavage characteristic of the second cleavage plane F2, and the line A is set to extend along the second cleavage plane F2. This ensures a sufficient extension of the crack 13 in the thickness direction of the wafer 11B, even when the cleavage characteristic of each of the pair of first cleavage planes F1 is higher than the cleavage characteristic of the second cleavage plane F2.

[0066] In the laser processing apparatus 1, each of the pair of first cleavage planes F1 is a (110) plane, and the second cleavage plane F2 is a (100) plane. In this case, too, the extension of the crack 13 in the thickness direction of the wafer 11B can be sufficiently ensured.

[0067] In the laser processing device 1, the focused spot C of the laser light L having a backward beam shape 9 due to the trefoil aberration pattern is moved relatively along each of a plurality of lines A extending in a lattice pattern when viewed in the thickness direction of the wafer 11B, thereby enabling the wafer 11B to be efficiently divided into a plurality of chips.

[0068] In the laser processing apparatus 1, when a predetermined portion 11d is to be removed from the second main surface 11b of the wafer 11B onto which the laser light L is incident, the control unit 6 controls at least the spatial light modulator 7 and the driving units 4 and 5 so as to form a modified region 12 within the portion 11d. This allows the crack 13 to extend to the first main surface 11a of the wafer 11B opposite to the side onto which the laser light L is incident, even if the thickness of the remaining portion after removing the portion 11d is large.

[0069] In the laser processing apparatus 1, the focused spot C is moved relatively along a line A set on the wafer 11B while the beam shape 9 of the laser light L at the focused spot C includes a center 90 and first, second, and third extensions 91, 92, and 93 extending radially from the center 90, with the beam shape 9 having the highest intensity at the center 90. The direction of the beam shape 9 at this time is determined based on the state of the crack 13 imaged in advance by the imaging unit 8. This allows the state of the crack 13 to be adjusted in the wafer 11B having a pair of intersecting first cleavage planes F1. Therefore, the laser processing apparatus 1 allows the formation of appropriate modified regions 12 and cracks 13 according to the processing in the wafer 11B having a pair of intersecting first cleavage planes F1.

[0070] In the laser processing apparatus 1, the control unit 6 causes the spatial light modulator 7 to display a modulation pattern including a trefoil aberration pattern such that, when the line A intersects with the pair of first cleavage planes F1, the second extension portion 92 is located on one side of the line A and the third extension portion 93 is located on the other side of the line A on the front side of the direction in which the focused spot C moves relatively along the line A, and the first extension portion 91 is located on the rear side of the direction in which the focused spot C moves relatively along the line A. This makes it easier for the crack 13 to extend in the thickness direction of the wafer 11B from the modified region 12 formed along the line A, so that when the modified region 12 and the crack 13 are formed along the line A that intersects with the pair of first cleavage planes F1 in the wafer 11B having the pair of first cleavage planes F1 that intersect with each other, a sufficient amount of extension of the crack 13 in the thickness direction of the wafer 11B can be ensured.

[0071] In the laser processing apparatus 1, each of the pair of first cleavage planes F1 is a (110) plane, and the second cleavage plane F2 is a (100) plane. In this case, too, the extension of the crack 13 in the thickness direction of the wafer 11B can be sufficiently ensured.

[0072] In the laser processing apparatus 1, the control unit 6 determines the orientation of the beam shape 9 with respect to the line A based on the state of the cracks 13 generated in the direction intersecting the line A from each of the multiple modified spots 12s formed along the line A as the modified regions 12. This makes it possible to reliably determine the orientation of the beam shape 9 suitable for forming the modified regions 12 and the cracks 13 along the line A intersecting the pair of first cleavage planes F1. Specifically, when the state of the crack 13 is such that the crack 13 has occurred along a direction perpendicular to the line A, the control unit 6 causes the spatial light modulator 7 to display a modulation pattern including a trefoil aberration pattern so that the first extension portion 91 is located on the line A in front of the direction in which the focused spot C moves relatively along the line A, and the second extension portion 92 is located on one side of the line A and the third extension portion 93 is located on the other side of the line A in the rear of that direction; and when the state of the crack 13 is such that the crack 13 has occurred along a direction inclined with respect to the line A, the control unit 6 causes the spatial light modulator 7 to display a modulation pattern including a trefoil aberration pattern so that the second extension portion 92 is located on one side of the line A in front of the direction in which the focused spot C moves relatively along the line A, and the third extension portion 93 is located on the other side of the line A in the rear of that direction. This allows appropriate modified regions 12 and cracks 13 to be formed depending on the relationship between the pair of intersecting cleavage planes F1 and the line A. As described above, when the crack 13 occurs along a direction perpendicular to the line A, each of the pair of (110) planes (i.e., each of the pair of first cleavage planes F1) extends in a direction parallel to the line A and a direction perpendicular to the line A. In this case, the crack 13 can be prevented from meandering relative to the line A while ensuring a sufficient extension amount of the crack 13 in the thickness direction of the wafer 11A. On the other hand, when the crack 13 occurs along a direction inclined relative to the line A, each of the pair of (110) planes (i.e., each of the pair of first cleavage planes F1) extends in a direction inclined at an angle of 45 degrees relative to the line A. In this case, the crack 13 can be sufficiently extended in the thickness direction of the wafer 11B. [Modification]

[0073] The present disclosure is not limited to the above embodiment. For example, when the control unit 6 causes the spatial light modulator 7 to display a modulation pattern including a trefoil aberration pattern in the preparation step, the control unit 6 may determine the orientation of the beam shape 9 relative to the line A as shown in FIG. 22 based on the state of the crack 13 captured in advance by the imaging unit 8.

[0074] First, laser light L having an elliptical beam shape 9 with its longitudinal direction parallel to the line A is irradiated along the line A, and multiple modified spots 12s are formed inside the wafer 11 along the line A. Next, the control unit 6 causes the imaging unit 8 to capture images of the modified regions 12 and cracks 13 formed in the wafer 11 by the irradiation of the laser light L, and determines the beam shape 9 of the laser light L to be used in the processing step based on the image results.

[0075] Specifically, in the imaging results, regardless of whether the cracks 13 generated along the line A from each of the multiple modified spots 12s are connected (here, they are connected), if the cracks 13 are generated along a direction perpendicular to the line A, the directions in which each of the pair of (110) planes (i.e., each of the pair of first cleavage planes F1) extends are parallel to the line A and perpendicular to the line A. Therefore, the control unit 6 determines that the wafer 11 to be processed is "a wafer 11A whose processing surface is a (110) plane," and selects a forward beam shape 9 due to a trefoil aberration pattern as the beam shape 9 of the laser light L used in the processing step.

[0076] On the other hand, in the imaging results, regardless of whether the cracks 13 generated along the line A from each of the multiple modified spots 12s are connected (here, they are not connected), if the cracks 13 are generated along a direction inclined with respect to the line A, the direction in which each of the pair of (110) planes (i.e., each of the pair of first cleavage planes F1) extends is a direction inclined at an angle of 45 degrees with respect to the line A. Therefore, the control unit 6 determines that the wafer 11 to be processed is "a wafer 11B whose processing surface is a (100) plane," and selects a backward beam shape 9 due to a trefoil aberration pattern as the beam shape 9 of the laser light L to be used in the processing step.

[0077] In either case shown in Figures 20 and 22, if the imaging results show that a crack 13 has occurred along a direction perpendicular to line A, an elliptical beam shape 9 with its longitudinal direction parallel to line A may be selected.

[0078] 23 , the focused spot C of the laser beam L having the backward beam shape 9 due to the trefoil aberration pattern may be relatively moved along a portion A1 of a line A extending along the outer edge 11e of the wafer 11 when viewed in the thickness direction of the wafer 11B. As an example, the portion A1 is a portion of the circular line A where the angle between a tangent to the circular line A and one of the second cleavage planes F2 is 20 degrees or less. This allows the outer edge portion of the wafer 11B to be efficiently removed from the wafer 11B.

[0079] Furthermore, the pair of first cleavage planes F1 are not limited to a pair of (110) planes orthogonal to each other at any point, and the pair of second cleavage planes F2 are not limited to a pair of (100) planes orthogonal to each other at any point. The pair of first cleavage planes F1 and the pair of second cleavage planes F2 may be any planes as long as the cleavage characteristic of the first cleavage plane F1 is higher than the cleavage characteristic of the second cleavage plane F2. As an example, the pair of first cleavage planes F1 may be a pair of cleavage planes of different types, or the pair of first cleavage planes F1 may be a pair of cleavage planes that intersect with line A at different angles. Furthermore, the wafer 11 does not necessarily have to have a second cleavage plane F2 extending along line A.

[0080] Furthermore, the spatial light modulator 7 is not limited to a reflective type and may be a transmissive type. Furthermore, the optical system that transfers the image of the laser light L on the modulation surface 7a of the spatial light modulator 7 onto the entrance pupil plane 33a of the light collecting unit 33 is not limited to the 4f lens unit 34 having a pair of lenses 34A and 34B, but may be one that includes a first lens system (e.g., a cemented lens, three or more lenses, etc.) on the spatial light modulator 7 side and a second lens system (e.g., a cemented lens, three or more lenses, etc.) on the light collecting unit 33 side.

[0081] Furthermore, in the above embodiment, the driver 4 drives the support unit 2, and the driver 5 drives the irradiation unit 3 to drive the condenser 33. However, the driver of the present disclosure is not limited to this. As an example, the driver 4 may move the support unit 2 in each of the Z direction, X direction, and Y direction, and rotate the support unit 2 around an axis parallel to the Z direction as the rotation axis. Alternatively, the driver 5 may move the condenser 33 in each of the Z direction, X direction, and Y direction, and move the condenser 33 around an axis parallel to the Z direction as the center line. In other words, the driver of the present disclosure may be configured to drive at least one of the support unit and the condenser.

[0082] 1...laser processing apparatus, 2...support part, 4, 5...drive part, 6...control part, 7...spatial light modulator, 9...beam shape, 11, 11A, 11B...wafer, 11b...second main surface (surface), 11d...portion, 11e...outer edge, 12...modified region, 13...crack, 31...light source, 33...focusing part, 90...center part, 91...first extension part, 92...second extension part, 93...third extension part, A...line, A1...part, C...focusing spot, F1...first cleavage plane, F2...second cleavage plane, L...laser light.

Claims

1. A laser beam emitting device comprising: a support for supporting a wafer having a pair of first cleavage planes that intersect with each other; a light source for emitting laser light; a spatial light modulator for modulating the laser light emitted from the light source by displaying a modulation pattern; a focusing unit for focusing the laser light modulated by the spatial light modulator onto the wafer; a drive unit for driving at least one of the support and the focusing unit; and a control unit for controlling at least the spatial light modulator and the drive unit, wherein the control unit controls the drive unit to drive at least one of the support and the focusing unit so that a focused spot of the laser light moves relatively along a line on the wafer that intersects with the pair of first cleavage planes, the control unit controls the spatial light modulator to display the modulation pattern including a trefoil aberration pattern so that the beam shape of the laser light at the focused spot includes a center and first, second, and third extensions extending radially from the center and has the highest intensity at the center, and so that the second extension is located on one side of the line and the third extension is located on the other side of the line in front of a direction in which the focused spot moves relatively along the line, and the first extension is located on the line in rear of the direction.

2. The laser processing device according to claim 1, wherein the wafer further has a second cleavage plane intersecting the pair of first cleavage planes, the cleavage characteristic of each of the pair of first cleavage planes is higher than the cleavage characteristic of the second cleavage plane, and the line is set to extend along the second cleavage plane.

3. The laser processing device according to claim 2, wherein each of the pair of first cleavage planes is a (110) plane, and the second cleavage plane is a (100) plane.

4. A laser processing device according to any one of claims 1 to 3, wherein the lines are each a plurality of lines extending in a grid pattern when viewed in the thickness direction of the wafer.

5. A laser processing device according to any one of claims 1 to 3, wherein the line is part of a line extending along the outer edge of the wafer when viewed in the thickness direction of the wafer.

6. A laser processing device as described in any one of claims 1 to 5, wherein the control unit controls at least the spatial light modulator and the drive unit so that, when a predetermined portion of the wafer is scheduled to be removed from the surface onto which the laser light is incident, a modified region is formed within the portion.

7. A laser processing method carried out in a laser processing apparatus comprising: a support part for supporting a wafer having a pair of first cleavage planes that intersect with each other; a light source for emitting laser light; a spatial light modulator for modulating the laser light emitted from the light source by displaying a modulation pattern; a focusing part for focusing the laser light modulated by the spatial light modulator onto the wafer; and a drive part for driving at least one of the support part and the focusing part, driving at least one of the support unit and the focusing unit with the driving unit so that a focused spot of the laser light moves relatively along a line on the wafer that intersects with the pair of first cleavage planes, and displaying the modulation pattern including a trefoil aberration pattern on the spatial light modulator so that a beam shape of the laser light at the focused spot includes a center and first, second, and third extensions extending radially from the center and has the highest intensity at the center, and so that the second extension is located on one side of the line and the third extension is located on the other side of the line in front of a direction in which the focused spot moves relatively along the line, and so that the first extension is located on the line in rear of the direction.

Images