Laser beam machining apparatus and laser beam machining method

Abstract

The present invention provides a laser beam machining apparatus for irradiating an object with a laser beam to form a modified area along a virtual plane inside the object along the plane of incidence of the laser beam on the object, the laser beam machining apparatus comprising: a support part that supports the object; an irradiation part that irradiates, with the laser beam, the object supported by the support part; a movement part that moves the support part and / or the irradiation part so that the focused spot of the laser beam moves along the virtual plane; and a control part that controls the support part, the irradiation part, and the movement part, wherein the irradiation part includes a spatial light modulator for modulating the laser beam and a focusing unit for focusing the laser beam that has passed through the spatial light modulator toward the object.

Description

Laser processing device and laser processing method

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

[0002] Patent Document 1 describes a substrate processing system. In this substrate processing system, a laser beam is first applied to the boundary between the peripheral portion and the central portion of the wafer to be processed, forming a ring-shaped modified layer. Next, a modified surface is formed by applying a laser beam to the peripheral portion of the wafer along the non-processed surface of the wafer, which is the surface of the wafer to be bonded to the support wafer and on which the device layer is to be formed. Next, the peripheral portion of the wafer is peeled and removed, starting from the modified layer and cracks extending from the modified layer in the thickness direction. Since the modified surface is formed at the interface between the wafer and the support wafer, the bonding strength between the wafer and the support wafer is reduced, allowing the peripheral portion to be properly removed. Then, the processed surface of the wafer is subjected to finish grinding.

[0003] Japanese Patent Application Laid-Open No. 2022-002312

[0004] In the substrate processing system described in Patent Document 1, a modified surface is formed by irradiating the interior of the wafer with laser light while rotating a chuck on which the wafer is placed and moving a laser head radially outward. In this case, multiple modified regions are formed in a YZ plane, which includes a Z direction intersecting the laser light incident surface of the object to be processed, such as the wafer, and a Y direction, which is the radial direction. In particular, in this case, multiple modified regions are formed sequentially in the YZ plane from one side of the Y direction to the other (from the inside to the outside in the radial direction).

[0005] When multiple modified regions aligned in the Y direction are sequentially formed in a first Y direction, from one side of the Y direction to the other, cracks extending from the modified regions toward the first Y direction may propagate at an angle relative to the first Y direction. In particular, a crack extending toward the first Y direction from the last modified region formed among the multiple modified regions may propagate further due to, for example, the crystalline structure of the object. If the crack propagates and reaches the bottom surface of the object opposite the incident surface, it may damage structures such as a device layer formed on the bottom surface or another wafer bonded to the bottom surface. Therefore, there is a need to suppress the propagation of cracks extending from the modified regions so that they do not reach the bottom surface.

[0006] Therefore, an object of the present disclosure is to provide a laser processing apparatus and a laser processing method that can suppress the growth of cracks extending from modified regions.

[0007] A laser processing apparatus according to the present disclosure is [1] "a laser processing apparatus for irradiating a target with laser light to form a modified region along a virtual surface inside the target that is aligned with an incident surface of the laser light of the target, the laser processing apparatus comprising: a support unit that supports the target; an irradiation unit that irradiates the target supported by the support unit with the laser light; a movement unit that moves at least one of the support unit and the irradiation unit so that a focused spot of the laser light moves along the virtual surface; and a control unit that controls the support unit, the irradiation unit, and the movement unit, the irradiation unit including a spatial light modulator that modulates the laser light, and a focusing unit that focuses the laser light that has passed through the spatial light modulator toward the target, the control unit moving the focused spot in the virtual surface in an X direction along the virtual surface. and performing a first processing process to form a first modified region as the modified region along the X direction by irradiating the laser light onto the object while changing the position of the focused spot in a Y direction that is along the imaginary plane and intersects the X direction, in a first Y direction from one side of the Y direction to the other, thereby forming a plurality of first modified regions lined up along the Y direction in a Y-Z plane that includes a Z direction intersecting the X and Y directions and the Y direction, and the Y direction, wherein in the first processing process, the control unit modulates the laser light by the spatial light modulator so that the beam shape at the focused spot of the laser light in the Y-Z plane is inclined in the first Y direction with respect to the Z direction, at least on the incident surface side of the center of the focused spot.

[0008] The laser processing method according to the present disclosure is

[10] "a laser processing method for forming a modified region along an imaginary surface inside an object that is along an incident surface of the laser light of the object by irradiating the object with laser light, the method comprising a processing step of irradiating the object with the laser light while moving a focused spot of the laser light along the imaginary surface to form the modified region, wherein in the processing step, a first modified region is formed along the X direction by irradiating the object with the laser light while moving the focused spot in the imaginary surface in an X direction along the imaginary surface. and performing X-direction processing while changing the position of the focused spot in a Y direction that is along the virtual plane and intersects the X direction in a first Y direction from one side of the Y direction to the other, thereby performing a first processing to form a plurality of first modified regions that are aligned along the Y direction in a YZ plane that includes a Z direction that intersects the X direction and the Y direction, and the Y direction, and in the first processing, the beam shape of the focused spot of the laser light in the YZ plane is tilted in the first Y direction at least on the incident surface side with respect to the center of the focused spot.

[0009] In this apparatus and method, a laser beam is irradiated onto an object within a virtual plane along the laser beam incidence surface while moving a focused spot in the X direction along the virtual plane, thereby forming a first modified region along the X direction. This X-direction processing is performed while changing the position of the focused spot in the Y direction, which is along the virtual plane and intersects the X direction, from one side of the Y direction to the other, in a first Y direction, thereby forming a plurality of first modified regions aligned along the Y direction in the YZ plane. In this case, as described above, there is a risk that cracks extending from the plurality of first modified regions toward the first Y direction may propagate at an angle relative to the first Y direction. In particular, a crack extending toward the first Y direction from the last-formed first modified region among the plurality of first modified regions may propagate further due to, for example, the crystalline structure of the object.

[0010] In contrast, with this device and method, when forming the first modified region, the beam shape of the focused spot of the laser light in the YZ plane is tilted in the first Y direction at least on the incident surface side from the center of the focused spot. By using a focused spot having such a beam shape when forming the first modified region, cracks extending from the first modified region in the first Y direction are prevented from propagating obliquely toward the side opposite the incident surface of the object (i.e., the bottom surface side). In other words, with this device and method, it is possible to suppress the propagation of cracks extending from the modified region.

[0011] The laser processing apparatus according to the present disclosure may be the laser processing apparatus described in [1] above, [2] "wherein a plurality of lines arranged concentrically when viewed from the Z direction are set on the target object, and the control unit irradiates the target with the laser light while moving the focused spot along one of the lines, thereby forming the first modified region along the X direction as a circumferential direction of the one line, and performing the X-direction processing across the plurality of lines while changing the one line in the first Y direction, thereby forming a plurality of first modified regions arranged along the Y direction as a radial direction of the line in the YZ plane." In this way, when processing is performed along a plurality of lines arranged concentrically (concentric processing), unlike when processing is performed along, for example, a spiral line (spiral processing), the spacing between modified regions in the Y direction in the YZ plane can be constant, thereby enabling stable processing.

[0012] The laser processing apparatus according to the present disclosure may be the laser processing apparatus described in [1] above, [3] "wherein a spiral line is set on the object when viewed from the Z direction, and the control unit irradiates the object with the laser light while moving the focused spot along the line, thereby performing the X-direction processing to form the first modified region along the X direction, which is the tangent direction of the line, from the start end of the line to the end end of the line, thereby forming a plurality of first modified regions aligned along the Y direction, which is the direction intersecting the tangent direction of the line, in the YZ plane." In this way, when performing spiral processing, continuous processing can be performed along a single line. This improves takt time, and stable processing is possible because the rise in the laser when turned on is affected only at the processing start point.

[0013] The laser processing apparatus according to the present disclosure may be [4] "the laser processing apparatus according to any one of [1] to [3] above, wherein the object has, as viewed from the Z direction, a first region including the center of the object and a second region outside the first region including the peripheral portion of the object, and the control unit performs the first processing process on the first region." In this case, it is possible to perform peeling using a first modified region formed along a virtual surface while suppressing crack propagation in the first region including the center of the object. Here, when peeling of the object is performed using a modified region formed along a virtual surface and a crack extending from the modified region, the longer the crack extending from the modified region toward the portion remaining after peeling, the rougher the peeled surface becomes. In contrast, here, the propagation of cracks extending from the first modified region formed along the virtual surface is suppressed, thereby suppressing roughness of the peeled surface and improving the quality of the peeled surface.

[0014] The laser processing apparatus according to the present disclosure may be the laser processing apparatus described in any one of [1] to [3] above, wherein [5] "the object has, as viewed from the Z direction, a first region including the center of the object and a second region outside the first region including the peripheral portion of the object, and the control unit performs the first processing process on the second region." In this case, it is possible to perform peeling using a first modified region formed along a virtual surface while suppressing crack propagation in the second region including the peripheral portion of the object. In this case, for the same reason as in [4] above, when peeling the object using the first modified region formed along the virtual surface and cracks extending from the first modified region, roughening of the peeled surface is suppressed, and the quality of the peeled surface is improved.

[0015] The laser processing device according to the present disclosure is, [6] "the second region has a boundary with the first region, and the control unit performs a second processing process after the first processing process to form, as the modified region, a plurality of second modified regions at the boundary that are positioned so as to intersect with a plurality of the first modified regions aligned along the Y direction, and in the second processing process, the control unit controls the spatial light modulator so that a third modified region, which is the second modified region closest to the first modified region among the plurality of second modified regions, becomes elongated in the Z direction. The laser processing apparatus may be the one described in [5] above, in which the laser light is modulated to impart a first aberration to the laser light, the third modified region is the second modified region among the plurality of second modified regions that is farthest from the incident surface, and the first aberration is an aberration for forming a focused spot that is longer in the Z direction than the focused spot of the laser light to which the reference aberration has been imparted, when the aberration that occurs in the optical axis direction of the laser light at the focusing position due to the focusing unit focusing the laser light on the object is taken as a reference aberration.

[0016] The long third modified region formed in this manner has the property that cracks extending from the third modified region are less likely to propagate in the Z direction (i.e., the cracks are shorter). Therefore, since cracks are less likely to propagate from the third modified region, the propagation of cracks from the third modified region to the bottom surface (the surface opposite the incident surface) of the object is suppressed.

[0017] On the other hand, if another modified region is formed close to the first modified region, cracks extending from the multiple first modified regions aligned in the Y direction may connect with the cracks extending from the other modified region and continue to grow. In contrast, here, the second modified region closest to the first modified region is the third modified region, which is less susceptible to crack growth. In such a case, the formation of the third modified region makes it less likely that the cracks extending from the first modified region will continue to grow. In other words, the growth of cracks from the first modified region to the bottom surface of the object is suppressed. As described above, in this case, it is possible to reliably suppress the growth of cracks extending from the modified region.

[0018] The laser processing apparatus according to the present disclosure may be the laser processing apparatus described in [7] above, wherein "the boundary includes an inclined portion inclined with respect to the Z direction in a YZ plane including the Z direction and the Y direction, and the control unit, when forming the modified region on the inclined portion, controls the spatial light modulator to modulate the laser light so that the beam shape at the focused spot of the laser light in the YZ plane is inclined in the inclination direction of the inclined portion at least on the incident surface side of the center of the focused spot." In this case, it is possible to form a crack extending obliquely with respect to the Z direction from the modified region along the inclined boundary. This makes it possible to reduce the impact on bottom-side structures, such as a device layer or other wafers, compared to when a crack extending from the modified region propagates along the Z direction and reaches the bottom surface.

[0019] The laser processing apparatus according to the present disclosure may be [8] "the laser processing apparatus according to any one of [1] to [7] above, wherein in the first processing step, the control unit branches the laser beam so that a plurality of focused spots are formed in the imaginary plane, the focused spots being at least at different positions in the Y direction." In this way, by branching the laser beam to form a plurality of focused spots at different positions in the Y direction, cracks extending from each of the first modified regions formed corresponding to the plurality of focused spots are more likely to connect with each other in the XY plane. As a result, cracks extending from the first modified region are prevented from propagating obliquely toward the bottom surface.

[0020] The laser processing apparatus according to the present disclosure may be [9] "the laser processing apparatus described in [8] above, wherein in the first processing step, the control unit branches the laser light so as to form a plurality of focused spots whose positions in the X direction are further different within the virtual plane." In this case, cracks extending from each of the first modified regions formed corresponding to the plurality of focused spots are more likely to connect with each other within the XY plane. As a result, cracks extending from the first modified region are more reliably prevented from propagating obliquely toward the bottom surface.

[0021] According to the present disclosure, it is possible to provide a laser processing apparatus and a laser processing method that can suppress the growth of cracks extending from modified regions.

[0022] FIG. 1 is a schematic diagram showing the configuration of a laser processing apparatus according to one embodiment. FIG. 2 is a schematic diagram showing the configuration of the irradiation unit shown in FIG. 1. FIG. 3 is a diagram showing an object to be laser processed according to the first embodiment. FIG. 4 is a diagram for explaining the laser processing method according to the first embodiment. FIG. 4(a) is a schematic side view showing the formation of a modified region, and FIG. 4(b) is a schematic side view showing the state after the modified region has been formed. FIG. 5 is a diagram for explaining the laser processing method according to the first embodiment. FIG. 5(a) is a plan view, and FIG. 5(b) is a schematic side view. FIG. 6 is a diagram for explaining the laser processing method according to the first embodiment. FIG. 6(a) is a schematic side view showing the state in which laser light is being irradiated, and FIGS. 6(b) and 6(c) are schematic plan and side views, respectively, showing the state after the modified region has been formed. FIG. 7 is a diagram showing an example of the object shown in FIGS. 5 and 6. FIG. 7A is a perspective view with a portion cut away, and FIG. 7B is a schematic cross-sectional view. FIG. 8 is a cross-sectional view showing an example of modified regions and crack formation in the object shown in FIG. 7. FIGS. 8A and 8B are schematic cross-sectional views showing how a crack propagates. FIG. 9 is a diagram for explaining the relationship between the first Y direction, which is the movement direction of the focused spot in the YZ plane, and the propagation of a crack. FIG. 9A is a schematic side view showing how the focused spot moves, and FIG. 9B is a schematic cross-sectional view showing how a crack extends from a modified region in the YZ plane. FIG. 10 is a diagram for explaining the relationship between the first Y direction, which is the movement direction of the focused spot in the YZ plane, and the propagation of a crack. FIG. 10A is a schematic side view showing how the focused spot moves, and FIG. 10B is a schematic cross-sectional view showing how a crack extends from a modified region in the YZ plane. Fig. 11 is a diagram for explaining the relationship between the beam shape at the focused spot and the propagation direction of the crack. Fig. 11(a) is a diagram showing the beam shape at the focused spot, and Fig. 11(b) is a cross-sectional photograph showing a modified region and a crack extending from the modified region. Fig. 12 is a diagram showing the relationship between each beam shape and the processing result when the first Y direction ND is the Y positive direction. Fig. 13 is a diagram showing an example of the beam shape at the focused spot.FIG. 13(a) shows the beam shape in the YZ plane, and FIG. 13(b) shows the beam shape (intensity distribution) in each cross section F1 to F7 in FIG. 13(a) (i.e., the XY plane). FIG. 14 is a diagram for explaining the post-processing of the laser processing method according to the first embodiment. FIGS. 14(a) and 14(b) are schematic side views. FIG. 15 is a diagram for explaining the laser processing method according to the second embodiment. FIG. 15(a) is a plan view, and FIG. 15(b) is a schematic side view. FIG. 16 is a diagram for explaining the laser processing method according to the second embodiment. FIG. 16(a) is a schematic cross-sectional view showing a state in which a focused spot is positioned on an imaginary plane, and FIG. 16(b) is a schematic cross-sectional view showing a state in which modified regions have been formed on the imaginary plane. FIG. 16 is a diagram for explaining the laser processing method according to the second embodiment. Specifically, it is a schematic cross-sectional view showing a state in which multiple modified regions have been formed along the imaginary plane. FIG. 18 is a diagram for explaining a laser processing method according to a second embodiment. FIG. 18(a) is a plan view, and FIG. 18(b) is a schematic side view. FIG. 19 is a diagram for explaining a laser processing method according to a second embodiment. FIG. 19(a) is a schematic cross-sectional view showing a state in which a focused spot is positioned at a boundary. FIG. 19(b) is a schematic cross-sectional view showing a state in which a modified region is formed at a boundary. FIG. 20 is a diagram for explaining aberrations occurring at the focused position of laser light. FIG. 21 is a diagram showing the intensity of laser light and the focused spot when multiple aberrations are applied based on a reference aberration. FIG. 22 is a diagram for explaining a laser processing method according to a second embodiment. FIG. 22(a) is a schematic cross-sectional view showing a state in which a focused spot is positioned at a boundary. FIG. 22(b) is a schematic cross-sectional view showing a state in which multiple modified regions aligned in the Z direction are formed at the boundary. FIG. 23 is a diagram for explaining a laser processing method according to a modified example. Specifically, (a) and (b) of Fig. 23 are schematic cross-sectional views showing the boundary between the effective area and the removal area in the target object. Fig. 24 is a diagram for explaining a laser processing method according to a modified example. Specifically, (a) and (b) of Fig. 24 are schematic cross-sectional views showing a state in which a modified area and a crack extending obliquely from the modified area have been formed.FIG. 25 is a schematic cross-sectional view (XY plane) for explaining a laser processing method according to another modified example. (a) of FIG. 25 is a schematic cross-sectional view showing a state in which a focused spot has been formed. (b) and (c) of FIG. 25 are schematic cross-sectional views showing a state in which a modified region has been formed. FIG. 26 is a schematic cross-sectional view (XY plane) for explaining a laser processing method according to another modified example. (a) of FIG. 26 is a schematic cross-sectional view showing a state in which a focused spot has been formed. (b) and (c) of FIG. 26 are schematic cross-sectional views showing a state in which a modified region has been formed. FIG. 27 is a schematic cross-sectional view (XY plane) for explaining a laser processing method according to another modified example. (a) of FIG. 27 is a schematic cross-sectional view showing a state in which a focused spot has been formed. (b) of FIG. 27 is a schematic cross-sectional view showing a state in which a modified region has been formed.

[0023] An embodiment will be described below with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations may be omitted. Each drawing may also show a Cartesian coordinate system defined by an X-axis, a Y-axis, and a Z-axis.

[0024] Fig. 1 is a schematic diagram showing the configuration of a laser processing apparatus according to one embodiment. As shown in Fig. 1, the laser processing apparatus 1 includes a stage (support unit) 2, an irradiation unit 3, movement units 4 and 5, and a control unit (processing control unit) 6. The laser processing apparatus 1 is an apparatus for forming a modified region 12 in an object 11 by irradiating the object 11 with laser light L.

[0025] The stage 2 supports the object 11, for example, by holding a film attached to the object 11. The stage 2 is rotatable about an axis parallel to the Z direction. The stage 2 may be movable along both the X direction and the Y direction. The X direction and the Y direction are first and second horizontal directions that intersect (are perpendicular to) each other, and the Z direction is a vertical direction.

[0026] The irradiation unit 3 is for irradiating the object 11 supported on the stage 2 with laser light L. The irradiation unit 3 focuses the laser light L, which is transparent to the object 11, and irradiates the object 11. When the laser light L is focused inside the object 11 supported on the stage 2, the laser light L is particularly absorbed in a portion corresponding to a focused spot C of the laser light L (for example, the center Ca shown in FIG. 18 ), and a modified region 12 is formed inside the object 11. The focused spot C is a position where the beam intensity of the laser light L is highest or a region within a predetermined range from the center Ca, which is the center of gravity of the beam intensity.

[0027] The modified region 12 is a region whose density, refractive index, mechanical strength, and other physical properties differ from those of the surrounding unmodified region. Examples of the modified region 12 include a melt-treated region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 12 can be formed so that a crack extends from the modified region 12 to the incident side of the laser light L and to the opposite side. Such modified region 12 and cracks are used, for example, to cut the object 11.

[0028] As an example, when the stage 2 is moved along the X direction and the focused spot C is moved along the X direction relative to the object 11, multiple modified spots 12s are formed lined up in a row along the X direction. 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 separated from each other depending on the relative moving speed of the focused spot C with respect to the object 11 and the repetition frequency of the laser light L.

[0029] The moving unit 4 includes a first moving unit 41 that moves the stage 2 in one direction within a plane intersecting (perpendicular to) the Z direction, and a second moving unit 42 that moves the stage 2 in another direction within the plane intersecting (perpendicular to) the Z direction. As an example, the first moving unit 41 moves the stage 2 along the X direction, and the second moving unit 42 moves the stage 2 along the Y direction. The moving unit 4 also rotates the stage 2 around an axis parallel to the Z direction. The moving unit 5 supports the irradiation unit 3. The moving unit 5 moves the irradiation unit 3 along the X direction, Y direction, and Z direction. By moving the stage 2 and / or the irradiation unit 3 while the focused spot C of the laser light L is formed, the focused spot C is moved relative to the object 11. That is, the moving units 4 and 5 move at least one of the stage 2 and the irradiation unit 3 to move the focused spot C of the laser light L relative to the object 11.

[0030] The control unit 6 controls the operations of the stage 2, the irradiation unit 3, and the movement 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 a GUI (Graphical User Interface).

[0031] FIG. 2 is a schematic diagram showing the configuration of the irradiation unit shown in FIG. 2. A virtual line A indicating the planned laser processing area is shown in FIG. 2. As shown in FIG. 2, the irradiation unit 3 includes a light source 31, a spatial light modulator 7, and a condensing lens (condensing unit) 33. The light source 31 outputs laser light L, for example, by a pulse oscillation method. Note that the irradiation unit 3 may not include the light source 31 and may instead be configured to introduce the laser light L from outside the irradiation unit 3. The spatial light modulator 7 modulates the laser light L output from the light source 31. The condensing lens 33 condenses the laser light L modulated by the spatial light modulator 7 and output from the spatial light modulator 7 (i.e., the laser light that has passed through the spatial light modulator 7) toward the object 11.

[0032] When a signal indicating a modulation pattern is input from the control unit 6 to the spatial light modulator 7, the modulation pattern is displayed in accordance with the signal. The modulation pattern is for modulating the laser light L. When the laser light L is incident from the outside, reflected, and emitted to the outside while the modulation pattern is displayed on the spatial light modulator 7, the laser light L is modulated in accordance with the displayed modulation pattern. In this way, the spatial light modulator 7 makes it possible to modulate the laser light L (for example, modulate the intensity, amplitude, phase, polarization, etc. of the laser light L) by appropriately setting the modulation pattern to be displayed.

[0033] As described above, the laser light L output from the light source 31 is incident on the condenser lens 33 via the spatial light modulator 7 and is focused by the condenser lens 33 within the object 11, thereby forming a modified region 12 and a crack extending from the modified region 12 in the object 11 at the focused spot C. Furthermore, the control unit 6 controls the moving units 4 and 5 to move the focused spot C relative to the object 11, thereby forming a modified region 12 and a crack along the movement direction of the focused spot C. [First Embodiment]

[0034] FIG. 3 is a diagram showing an object to be laser processed according to the first embodiment. FIG. 3A is a plan view, and FIG. 3B is a side view. As shown in FIG. 3, the object 11 is, for example, a silicon wafer. The object 11 includes a first surface 11a and a second surface 11b opposite the first surface 11a. A device layer including a plurality of functional elements is formed on the second surface 11b of the object 11. The object 11 is supported by the stage 2 so that the first surface 11a faces the irradiation unit 3 (i.e., so that the second surface 11b faces the stage 2).

[0035] The object 11 includes an effective area (first area) R and a removal area (second area) E. The effective area R is a portion corresponding to the semiconductor device to be acquired. The effective area R here is a disk-shaped portion including the center of the object 11 when viewed from the Z direction, which is the thickness direction of the object 11. The removal area E is a region located outside the effective area R in the object 11. In this embodiment, the removal area E is the outer edge portion of the object 11 other than the effective area R. The removal area E here is an annular portion surrounding the effective area R. The removal area E includes the peripheral portion (bevel portion of the outer edge) of the object 11 when viewed from the Z direction.

[0036] A virtual surface M1 is set on the object 11 as a surface to be removed. The virtual surface M1 is a surface on which the modified region 12 is planned to be formed. The virtual surface M1 is a surface along the first surface 11a, which is the laser light incident surface of the object 100. The virtual surface M1 is a surface parallel to the first surface 11a and has, for example, a circular shape. The virtual surface M1 is a virtual area and is not limited to a plane, but may also be a curved or three-dimensional surface. The effective area R, removal area E, and virtual surface M1 can be set in the control unit 6. The effective area R, removal area E, and virtual surface M1 may be specified by coordinates.

[0037] A line M3 is set on the object 11 as a planned trimming line. The line M3 is a line on which the formation of a modified region is planned. The line M3 extends in an annular shape inside the outer edge of the object 11. Here, the line M3 extends in an annular shape. The line M3 is set at the boundary between the effective region R and the removal region E in a portion inside the object 11 on the opposite side of the laser light incident surface from the imaginary plane M1 (i.e., the line M3 is also part of the boundary between the effective region R and the removal region E). The setting of the line M3 can be performed by the control unit 6. The line M3 is an imaginary line, but may also be an actually drawn line. The line M3 may also be specified by coordinates.

[0038] Next, a laser processing method for processing the above-described object 11 will be described. The laser processing method according to this embodiment is performed by the above-described laser processing apparatus 1. Therefore, the laser processing method described below is also an example of processing performed by the laser processing apparatus 1. That is, here, the control unit 6 controls the moving units 4 and 5 to move at least one of the stage 2 and the irradiation unit 3, thereby performing laser processing to form a modified region 12 in the object 11 by irradiating the object 11 with the laser light L while moving the focused spot C of the laser light L relative to the object 11.

[0039] In the laser processing method according to this embodiment, first, a trimming process is performed. That is, as shown in Fig. 4, a laser beam L is irradiated along a line M3 to a portion of the interior of the target object 11 on the opposite side of the laser beam incident surface (first surface 11a) from the imaginary plane M1 to form a modified region 12 (step S101).

[0040] More specifically, in step S101, the control unit 6 controls the moving units 4 and 5 to move the irradiation unit 3 and / or the stage 2 so that the focused spot C of the laser light L is positioned on line M3 and at a predetermined depth (position in the Z direction) from the first surface 11a of the object 11. In this state, the control unit 6 controls the moving unit 4 to rotate the stage 2 about an axis parallel to the Z direction as the rotation axis, and controls the light source 31 to start irradiating the laser light L and move the focused spot C of the laser light L relative to the object 11. As a result, an annular modified region 12 is formed along the circular line M3 in a portion of the object 11 on the opposite side of the virtual plane M1 from the laser light incident surface (the second surface 11b side). Step S101 is performed multiple times while sequentially changing the position of the focused spot C in the Z direction, for example, from the second surface 11b side to the first surface 11a side.

[0041] Next, peeling processing is performed. That is, as shown in FIG. 5, laser light L is irradiated onto the object 11 along the imaginary plane M1 to form a modified region 12 along the imaginary plane M1 (step S102: first processing treatment, processing step). Step S102 will be described in more detail. As shown in FIG. 5(a), a line A is set on the object 11 along the imaginary plane M1 when viewed from the Z direction. When viewed from the Z direction, line A extends in a spiral shape (involute curve) from the periphery to the center of the object 11, with the position of the rotation axis of the stage 2 as its center.

[0042] 6 , in step S102, the control unit 6 controls the moving units 4 and 5 to move the irradiation unit 3 and / or the stage 2 so that the focused spot C of the laser light L is located on the line A and at a depth (position in the Z direction) of the imaginary plane M1, which is the intended peeling surface, from the first surface 11a of the object 11. At this time, the control unit 6 positions the focused spot C of the laser light L at the starting end (e.g., the end on the peripheral side) or the ending end (e.g., the end on the central side) of the line A as viewed from the Z direction. In this state, the control unit 6 controls the moving unit 4 to rotate the stage 2 about an axis parallel to the Z direction as the rotation axis, and controls the moving unit 5 to move the irradiation unit 3 along the Y direction intersecting the Z direction, while controlling the light source 31 to start irradiating the laser light L and move the focused spot C of the laser light L relative to the object 11.

[0043] At this time, the control unit 6 can adjust the rotation speed of the stage 2 and the movement speed of the irradiation unit 3 in the Y direction so that the focused spot C moves relatively along the spiral line A as viewed from the Z direction. As a result, the focused spot C of the laser light L is moved relatively in the tangential direction of the line A intersecting the Z direction, and also in a first Y direction (e.g., the positive Y direction) ND from one side of the Y direction intersecting the tangential direction to the line A. As a result, a first modified region 121 is formed as the modified region 12 along the line A and the imaginary plane M1. Here, the tangential direction of the line A is the X direction, which is the processing progression direction PD (see FIG. 5A ) along the imaginary plane M1. In this case, a plurality of first modified regions 121 are formed lined up in the Y direction in the YZ plane including the Z direction and the Y direction intersecting the X direction and the Y direction.

[0044] That is, in step S102, the control unit 6 performs X-direction processing to form a first modified region 121 along the X direction as a modified region 12 by irradiating the object 11 with laser light L while moving the focused spot C in the X direction along the virtual plane M1 within the virtual plane M1, and by changing the position of the focused spot C in the Y direction which is along the virtual plane M1 and intersects the X direction to a first Y direction ND which runs from one side of the Y direction to the other, thereby performing a first processing process to form a plurality of first modified regions 121 lined up along the Y direction in the YZ plane which includes the Z direction and Y direction which intersect the X direction and the Y direction.

[0045] In particular, in step S102, the control unit 6 irradiates the object 11 with laser light L while moving the focused spot C along the spiral line A, thereby performing X-direction processing to form first modified regions 121 along the X direction, which is the tangent direction of the line A, from the start to the end of the line A, thereby forming multiple first modified regions 121 lined up along the Y direction, which is the direction intersecting the tangent direction of the line A in the YZ plane.

[0046] FIG. 7 is a diagram showing an example of the object shown in FIGS. 5 and 6 . FIG. 7A is a perspective view showing a portion cut away, and FIG. 7B is a schematic cross-sectional view. As shown in FIG. 7 , the object 11 is, for example, a wafer (e.g., a silicon wafer) with a <100> crystal orientation. That is, in the object 11, the first surface 11a (main surface) is a (100) surface. The object 11 is supported on the stage 2 so that the first surface 11a is the incident surface of the laser light L. The object 11 includes a (110) surface orthogonal to the first surface 11a, which is a (100) surface, and a (111) surface intersecting the (110) surface at an angle of 125.25°. The angle between the (111) surfaces extending in intersecting directions is 70.5°.

[0047] 8 is a cross-sectional view showing an example of the formation of modified regions and cracks in the object shown in FIG. 8A. When laser light L is irradiated onto the object 11 using the first surface 11a, which is the (100) plane, as the incident surface of the laser light L to form multiple modified regions 12 aligned along the Y direction (i.e., the (100) plane) in the YZ plane, as shown in FIG. 8A, it is desirable that the cracks 13 extending from the modified regions 12 also propagate along the Y direction (i.e., the (100) plane). This is because if the cracks 13 extending from the modified regions 12 propagate obliquely with respect to the (100) plane and reach, for example, the second surface 11b, they may adversely affect the device layer formed on the second surface 11b or another object that may be bonded to the second surface 11b via the device layer.

[0048] However, the target object 11 includes a (111) plane, which is easier to cleave than the (100) plane. Therefore, as shown in FIG. 8B, when laser light L is irradiated onto the target object 11 using the first surface 11a, which is the (100) plane, as the incident surface of the laser light L to form multiple modified regions 12 aligned along the Y direction (i.e., the (100) plane) in the YZ plane, cracks 13 extending from the modified regions 12 tend to propagate along the (111) plane. In this case, the cracks 13 may reach the second surface 11b. Therefore, there is a need to prevent the cracks 13 extending from the modified regions 12 from propagating to the second surface 11b.

[0049] 9 and 10 , among the cracks 13 extending along the (111) plane, the crack 13p extending from the last-formed modified region 12p among the multiple modified regions 12 formed in a line along the Y direction in the YZ plane tends to grow longer. In the example shown in Fig. 9 , the focused spot C of the laser light L is moved in the Y-positive direction from the center of the object 11 in the Y direction toward the periphery. That is, in the example of Fig. 9 , the first Y-direction ND is the Y-positive direction, and the crack 13p extending from the modified region 12p at the end of the first Y-direction ND (the end closest to the periphery of the object 11) tends to grow longer along the (111) plane.

[0050] 10 , the focused spot C of the laser light L is moved in the negative Y direction from the periphery in the Y direction toward the center of the object 11. That is, in the example of Fig. 10 , the first Y direction ND is the negative Y direction, and the crack 13p extending from the modified region 12p at the end of the first Y direction ND (the centermost side of the object 11) tends to propagate further along the (111) plane.

[0051] As described above, the (111) planes that affect the propagation of the crack 13 are present inside the object 11 so as to intersect with each other at an angle of 70.5°. Therefore, the crack 13p that propagates further in the first Y direction ND with respect to the Z direction includes one that extends along one of the intersecting (111) planes toward the first surface 11a (hereinafter, for convenience, referred to as the "incident surface side") and one that extends along the other of the intersecting (111) planes toward the second surface 11b (hereinafter, for convenience, referred to as the "bottom surface side"). Furthermore, as described above, if the crack 13 reaches the second surface 11b, it may adversely affect the device layer, etc., so it is important to suppress the propagation of the crack 13p that extends along the (111) plane toward the bottom surface.

[0052] In response to this, the propagation direction of the crack 13 extending from the modified region 12 can be controlled by adjusting the beam shape at the focused spot C of the laser light L. In the example shown in Fig. 11A, the beam shape at the focused spot C of the laser light L in the YZ plane is inclined in the negative Y direction with respect to the Z direction on the incident surface side of the center Ca of the focused spot C (here, the beam shape is an arc shape that is convex in the positive Y direction overall). When the beam shape at the focused spot C of the laser light L is adjusted to this shape, as shown in Fig. 11B, the crack 13 extending from the modified region 12a, 12b formed by irradiation with such laser light L becomes a crack 13a that extends obliquely in the same direction as the inclination direction of the beam shape on the incident surface side of the center Ca of the focused spot C (here, the negative Y direction).

[0053] The beam shape shown in (a) of FIG. 11 can be formed, for example, by controlling the spatial light modulator 7 to offset the center of the spherical aberration correction pattern in the spatial light modulator 7 in the tilt direction with respect to the center of the entrance pupil plane of the condenser lens 33, or by controlling the magnitude of coma aberration in a coma aberration pattern for imparting coma aberration to the laser light L.

[0054] Therefore, when forming multiple modified regions 12 arranged in the Y direction including modified region 12p, the progression of crack 13p can be suppressed by adjusting the beam shape of the focused spot C of laser light L so that the inclination direction of crack 13a relative to the Z direction is opposite to the inclination direction of crack 13p relative to the Z direction.

[0055] More specifically, when forming the modified region 12p, the inclination direction of the part of the beam shape of the focused spot C of the laser light L that is closer to the incident surface than the center Ca of the beam shape can be adjusted so that the inclination direction of the crack 13a that may be formed by irradiating the laser light L with respect to the Z direction is opposite to the inclination direction of the crack 13p extending toward the bottom surface, thereby suppressing the progression of the crack 13p.

[0056] 9, the inclination direction of the crack 13a that can be formed by irradiation of the laser light L with respect to the Z direction is the first Y direction ND, which is the Y positive direction, and the inclination direction of the portion of the focused spot C of the laser light L that is closer to the incident surface than the center Ca of the beam shape is also adjusted to the first Y direction ND, which is the Y positive direction, thereby suppressing the growth of the crack 13p that extends obliquely from the modified region 12p toward the bottom surface. Also, in the example of FIG. 10, the inclination direction of the crack 13a that can be formed by irradiation of the laser light L with respect to the Z direction is the first Y direction ND, which is the Y negative direction, and the inclination direction of the portion of the focused spot C of the laser light L that is closer to the incident surface than the center Ca of the beam shape is also adjusted to the first Y direction ND, which is the Y negative direction, thereby suppressing the growth of the crack 13p that extends obliquely from the modified region 12p toward the bottom surface.

[0057] In other words, by modulating the laser light L using the spatial light modulator 7 so that the beam shape at the focal spot C of the laser light L is inclined in the first Y direction ND with respect to the Z direction at least on the incident surface side of the center Ca of the focal spot C, the progression of the crack 13p extending diagonally from the modified region 12p toward the bottom surface can be suppressed.

[0058] 12 is a diagram showing the relationship between each beam shape and the processing result when the first Y direction ND is the Y-positive direction. The example shown in Fig. 12 shows the processing result when the offset amount of the spherical aberration correction pattern in the spatial light modulator 7 is changed from -15 to +5. When the offset amount is negative, the portion of the focused spot C of the laser light L that is closer to the incident surface than the center Ca of the beam shape is tilted in the first Y direction ND, which is the Y-positive direction with respect to the Z direction. When the offset amount is positive, the portion is tilted in the direction opposite to the first Y direction ND (i.e., the tilt direction of the crack 13p extending toward the bottom surface).

[0059] 12 , when the inclination direction of the portion of the laser beam L at the focal spot C closer to the incident surface than the center Ca of the beam shape with respect to the Z direction is the first Y direction ND (i.e., when the offset amount is negative), it can be seen that the propagation of the crack 13p extending toward the bottom surface is suppressed, as described above. On the other hand, when the offset amount is 0 or a positive offset amount, the propagation of the crack 13p extending toward the bottom surface is not suppressed.

[0060] From the above viewpoints, in step S102 (i.e., in the first processing step), the control unit 6 modulates the laser light L using the spatial light modulator 7 so that the beam shape at the focal spot C of the laser light L in the YZ plane is inclined in the first Y direction ND with respect to the Z direction at least on the incident surface side of the center Ca of the focal spot C.

[0061] In order to suppress the propagation of the crack 13p extending toward the bottom surface, the laser light L may be modulated by the spatial light modulator 7 so that the entire beam shape of the focused spot C of the laser light L in the YZ plane is tilted in the first Y direction ND, as shown in FIG. 13 . (a) of FIG. 13 shows the beam shape in the YZ plane, and (b) of FIG. 13 shows the beam shape (intensity distribution) in each cross section (i.e., the XY plane) at F1 to F7 in (a) of FIG. 13 . Each diagram in (b) of FIG. 13 is an actual observation result obtained by a camera. From FIG. 13 , it can be seen that as the position in the Z direction changes from F1 to F7, the focused spot C gradually shifts toward one side in the Y direction (here, the first Y direction ND, which is the Y positive direction).

[0062] In the case of the arc-shaped beam shape shown in Figure 11, it can be observed that, within the XY plane, the focused spot C gradually shifts to one side in the Y direction until the Z-direction position reaches the center Ca from the incident surface side, and at a position in the Z direction closer to the bottom surface than the center Ca, the focused spot C gradually shifts to the other side in the Y direction.

[0063] As described above, in the laser processing method according to this embodiment, trimming is performed in step S101, and peeling is performed in step S102. As a result, as shown in FIG. 14A, a portion of the object 11 can be peeled off, with the modified region 12 formed across the imaginary plane M1 and the crack 13 extending from the modified region 12 as boundaries. At the same time, a removal region E can be removed, with the modified region 12 formed along the line M3 and the crack 13 extending from the modified region 12 as boundaries. After this, for example, as shown in FIG. 13B, the peeled surface 11h of the object 11 can be subjected to finish polishing or polishing with an abrasive such as a grindstone. As a result of the above, a semiconductor device 11k is obtained from the object 11.

[0064] As described above, in the laser processing apparatus 1 and laser processing method according to this embodiment, within a virtual plane M1 along the incident surface (first surface 11a) of the laser light L of the object 11, the laser light L is irradiated while moving the focused spot C in the X direction along the virtual plane M1, thereby forming a first modified region 121 along the X direction. This X-direction processing is performed while changing the position of the focused spot C in the Y direction, which is along the virtual plane M1 and intersects the X direction, to a first Y direction ND that runs from one side of the Y direction to the other, thereby forming a plurality of first modified regions 121 lined up along the Y direction in the YZ plane.

[0065] In particular, in the laser processing apparatus 1 and laser processing method according to this embodiment, when forming the first modified region 121, the beam shape of the focused spot C of the laser light L in the YZ plane is tilted in the first Y direction ND at least on the incident surface side of the center Ca of the focused spot C. By using the focused spot C having such a beam shape when forming the first modified region 121, the crack 13 extending from the first modified region 121 in the first Y direction ND is prevented from growing obliquely toward the bottom surface side of the object 11. In other words, it is possible to suppress the growth of the crack 13 extending from the first modified region 121.

[0066] In the laser processing apparatus 1 and laser processing method according to this embodiment, in step S102, the control unit 6 irradiates the object 11 with laser light L while moving the focused spot C along a spiral line A. This performs X-direction processing, forming first modified regions 121 along the X direction, which is the tangent direction of the line A, from the start to the end of the line A, thereby forming multiple first modified regions 121 aligned along the Y direction, which is the direction intersecting the tangent direction of the line A in the YZ plane. In this way, the first processing may be performed along the line A set in a spiral shape on the object 11 (i.e., spiral processing may be performed). When spiral processing is performed, processing can be performed continuously along a single line A. This improves takt time and enables stable processing because the impact of the laser-on start-up is limited to a single point, the processing start point.

[0067] Furthermore, in the laser processing apparatus 1 and laser processing method according to this embodiment, the object 11 has, when viewed in the Z direction, an effective region R (first region) including the center of the object, and a removal region E (second region) outside the effective region R and including the peripheral portion of the object 11. The control unit 6 then executes a first processing process on the effective region R. This makes it possible to perform peeling processing using the first modified region 121 formed along the imaginary plane M1 while suppressing the growth of the crack 13 in the effective region R including the center of the object 11. In particular, because the growth of the crack extending from the first modified region 121 formed along the imaginary plane M1 is suppressed, the peeled surface is prevented from becoming rough, and the quality of the peeled surface is improved. [Second Embodiment]

[0068] Next, a laser processing method according to the second embodiment will be described. As shown in FIG. 15 , the object 100 to be laser processed according to this embodiment includes the object 11 described above and an object 11R that is a separate member from the object 11. The object 11R is, for example, a silicon wafer. The object 11 includes a device layer 110 that includes a plurality of functional elements and is formed on the second surface 11b. The object 11R includes a device layer 110R that includes a plurality of functional elements and is formed on the first surface 11Ra of the object 11R. The object 11 and the object 11R are bonded together by arranging the device layer 110 and the device layer 110R so that they face each other and joining them together, thereby constituting the object 100.

[0069] The effective area R (first area) and the removal area E (second area) of the object 11 have a boundary B. In this embodiment, the boundary B also serves as a planned trimming line. Furthermore, a virtual surface M2 is set in the removal area E of the object 11 as a planned peeling surface. The virtual surface M2 is a surface on which the modified area 12 is planned to be formed. The virtual surface M2 is a surface along the first surface 11a, which is the laser light incident surface of the object 11. The virtual surface M2 is a surface parallel to the first surface 11a and has, for example, a circular ring shape. The virtual surface M2 is a virtual area and is not limited to a plane, but may also be a curved or three-dimensional surface. The virtual surface M2 can be set by the control unit 6. The virtual surface M2 may be specified by coordinates.

[0070] The laser processing method according to this embodiment is carried out by the above-described laser processing apparatus 1. Therefore, the laser processing method described below is also an example of processing performed by the laser processing apparatus 1. That is, here, the control unit 6 controls the moving units 4 and 5 to move at least one of the stage 2 and the irradiation unit 3, thereby irradiating the object 11 with the laser light L while moving the focused spot C of the laser light L relative to the object 11, thereby performing laser processing to form a modified region 12 in the object 11.

[0071] In the laser processing method according to this embodiment, first, peeling processing is performed. That is, as shown in FIG. 15 , laser light L is irradiated onto the object 11 along an imaginary plane M2 to form a modified region 12 along the imaginary plane M2 (step S201: first processing treatment, processing step). Step S201 will be described in more detail. As shown in FIG. 15 (a), multiple circular lines A are set on the object 11 along the imaginary plane M2 when viewed from the Z direction. When viewed from the Z direction, the multiple lines A are arranged in concentric circles that share a center with the object 11.

[0072] In step S201, as shown in FIGS. 15 and 16A, the control unit 6 controls the moving units 4 and 5 to move the irradiation unit 3 and / or the stage 2 so that the focused spot C of the laser light L is positioned on one of the lines A and at a depth (position in the Z direction) of the imaginary surface M2, which is the intended peeling surface, from the first surface 11a of the object 11. In this state, the control unit 6 controls the moving unit 4 to rotate the stage 2 about an axis parallel to the Z direction as the rotation axis, and controls the light source 31 to start irradiating the laser light L and move the focused spot C (focused spot C0) of the laser light L relative to the object 11. As a result, as shown in FIG. 16B, first modified regions 121 arranged in a circular shape are formed as the modified region 12 on the circular line A when viewed from the Z direction. In this example, the one line A and the boundary B coincide with each other.

[0073] 17 , the control unit 6 repeatedly forms the first modified regions 121 while sequentially changing the position in the Y direction. That is, the control unit 6 performs X-direction processing, in which the control unit 6 irradiates the object 11 with the laser light L while moving the focused spot C0 in the X direction along the imaginary plane M2 within the imaginary plane M2 to form the first modified regions 121 as modified regions 12 along the X direction, while changing the position of the focused spot C0 in the Y direction along the imaginary plane M2 and intersecting the X direction in a first Y direction ND (here, the positive Y direction from the center to the periphery of the object 11) extending from one side of the Y direction to the other, thereby performing a first processing process to form a plurality of first modified regions 121 aligned along the Y direction in a YZ plane including the Z direction and the Y direction intersecting the X and Y directions.

[0074] In particular, in step S201, the control unit 6 irradiates the object 11 with laser light L while moving the focused spot C along one line A, thereby performing X-direction processing to form a first modified region 121 along the X direction, which is the circumferential direction of the one line A, across multiple lines A while changing the one line A to a first Y direction ND, thereby forming multiple first modified regions 121 aligned in the Y direction, which is the radial direction of the line A, in the YZ plane. This forms multiple first modified regions 121 arranged two-dimensionally within the imaginary plane M2.

[0075] Thus, in step S201, as in the first embodiment, multiple modified regions 12 aligned in the Y direction are formed in the YZ plane. Therefore, in this embodiment, as in the first embodiment, it is necessary to suppress the cracks 13 extending from the modified regions 12 from propagating along the (111) plane toward the bottom surface. Therefore, in step S201, as in step S102 in the first embodiment, the control unit 6 modulates the laser light L using the spatial light modulator 7 so that the beam shape at the focal spot C of the laser light L in the YZ plane is inclined in the first Y direction ND with respect to the Z direction, at least on the incident surface side of the center Ca of the focal spot C. This completes the peeling process.

[0076] In the next step, trimming is performed. As described above, the effective area R and the removal area E have a boundary B, which is also the planned trimming line. That is, in the next step, as shown in FIG. 18 , laser light L is irradiated at the boundary B to form the modified area 12 (step S202, second processing). More specifically, in step S202, the control unit 6 first controls the moving units 4 and 5 to move the irradiation unit 3 and / or the stage 2 so that the focused spot C of the laser light L is located at the boundary B and at a predetermined depth (position in the Z direction) from the first surface 11a of the object 11.

[0077] In this state, the control unit 6 controls the moving unit 4 to rotate the stage 2 about an axis parallel to the Z direction as the rotation axis, and also controls the light source 31 to start irradiating the laser light L and move the focused spot C of the laser light L relative to the object 11. As a result, modified regions 12 arranged in a circular shape are formed at the boundary B which is circular when viewed from the Z direction.

[0078] 19(a), the control unit 6 controls the spatial light modulator 7 to modulate the laser light L so that a focused spot C1 that is elongated in the Z direction is formed as the focused spot C compared to the focused spot C0 when the first modified region 121 is formed in step S201, thereby imparting a first aberration to the laser light L. As a result, as shown in FIG. 19(b), a third modified region 123 that is elongated in the Z direction can be formed at the boundary B as the modified region 12 (and the second modified region 122 described later). That is, in step S202, the control unit 6 executes a process of irradiating the object 11 with the laser light L so as to form a third modified region 123 that is elongated in the Z direction as the modified region 12 at the boundary B between the effective region R and the removal region E.

[0079] The first aberration imparted to the laser beam in step S202 will be described. FIG. 20 is a diagram for explaining aberrations occurring at the focusing position of the laser beam. When the laser beam L is a plane wave (flat wavefront (phase)), it geometrically focuses to one point. However, the wavefront of the plane wave laser beam L usually changes due to various influences, and the laser beam L focused on the object 11 may not focus to one point, i.e., aberrations may occur naturally. The aberrations include, for example, Seidel aberrations (astigmatism, coma, spherical aberration, field curvature, and distortion), as well as longitudinal aberration, which is an aberration in the vertical direction (along the optical axis direction), and transverse aberration, which is an aberration in a direction intersecting the vertical direction.

[0080] 20 , when laser light L is focused on the object 11 by a focusing lens 33 or the like, if the laser light L is incident on the object 11 during the focusing process, spherical aberration occurs naturally, in which light rays at different angles of incidence are focused at different positions due to refraction (Snell's law). In other words, as shown in the figure, due to the laser light L being focused on the object 11, aberration occurs naturally at the focusing position without depending on the spatial light modulator 7, and a range of aberration along the optical axis direction (a range in which the intensity of the laser light L is equal to or greater than the processing threshold value α) exists as a reference aberration H.

[0081] By modulating the laser light L including such a reference aberration H using the spatial light modulator 7, it is possible to impart an aberration different from the reference aberration H to the laser light L. Fig. 21 is a diagram showing the intensity and focused spots of the laser light when multiple aberrations are imparted based on the reference aberration. The intensity distributions D10, D11, D12, and D13 shown in Fig. 21 respectively represent a case where a reference aberration H10 corresponding to the reference aberration H is imparted, a case where a first aberration H11 having a longer range (more negative) than the reference aberration H10 is imparted, a case where a first aberration H12 having an even longer range (more negative) than the reference aberration H10 is imparted, and a case where a second aberration H13 having a shorter range (more positive) than the reference aberration H10 is imparted. Furthermore, the focused spots C10, C11, C12, and C13 are, for example, regions in the intensity distributions D10, D11, D12, and D13 that are equal to or greater than the processing threshold α.

[0082] 21 , the control unit 6 controls the spatial light modulator 7 to modulate the laser beam L, thereby imparting first aberrations H11 and H12 to the laser beam L such that focused spots C11 and C12 that are longer in the Z direction than the focused spot C10 of the laser beam L to which the reference aberration H10 has been imparted are formed. Examples of such modulation include phase modulation that realizes the function of an axicon lens, phase modulation that realizes the function of a diffraction grating, and phase modulation that generates a predetermined spherical aberration. Each of the examples of phase modulation can be implemented by, for example, causing the spatial light modulator 7 to display an axicon lens pattern, a diffraction grating pattern, or a predetermined spherical aberration pattern, respectively, as a modulation pattern.

[0083] As described above, in step S202, when the aberration occurring in the optical axis direction of the laser light L at the focusing position due to focusing the laser light L on the object 11 by the focusing lens 33 is defined as the reference aberration H10, the control unit 6 controls the spatial light modulator 7 to modulate the laser light L so that focused spots C11 and C12 that are elongated in the Z direction are formed relative to the focused spot C10 of the laser light L to which the reference aberration H10 has been added, thereby imparting the first aberrations H11 and H12 to the laser light L. As a result, as shown in FIG. 19(b), a third modified region 123 that is elongated in the Z direction is formed at the boundary B as the second modified region 122.

[0084] It has been confirmed that the elongated third modified region 123 formed in this manner has the property that cracks extending from the third modified region 123 are less likely to propagate in the Z direction (i.e., the cracks are shorter) compared to modified regions 12 formed by laser light L to which, for example, the reference aberration H10 or the second aberration H13 is imparted. As a result, when the third modified region 123 is formed near another modified region 12, it has the effect of suppressing a crack extending from the third modified region 123 from connecting with a crack extending from the other modified region 12 and inducing further propagation. In other words, by using such a third modified region 123 as the second modified region 122 formed near the first modified region 121 where the propagation of the crack 13 extending along the (111) plane is predicted as described above, it is possible to suppress the propagation of the crack 13 extending from the first modified region 121 so that it does not reach the second surface 11b.

[0085] 22 , laser processing is then performed in the YZ plane to form a plurality of second modified regions 122 aligned in the Z direction along the boundary B as modified regions 12 (step S202: second processing). More specifically, the control unit 6 first controls the movement units 4 and 5 to move the irradiation unit 3 and / or the stage 2 so that the focused spot C2 of the laser light L is positioned at the boundary B and at a predetermined depth (position in the Z direction) from the first surface 11a of the object 11. At this time, as shown in FIG. 22 (a), the position of the focused spot C2 in the Z direction is set closer to the incident surface of the laser light L than the position of the focused spot C1 in the Z direction when the third modified region 123 was formed.

[0086] In this state, the control unit 6 controls the moving unit 4 to rotate the stage 2 about an axis parallel to the Z direction as the rotation axis, and controls the light source 31 to start irradiating the laser light L and move the focused spot C2 of the laser light L relative to the target 11. At this time, the focused spot C2 is made shorter in the Z direction than the focused spot C1 when the third modified region 123 was formed. As a result, as shown in Figure 22 (b), second modified regions 122 arranged in a circular shape are formed as the modified region 12 at the boundary B that is circular when viewed from the Z direction.

[0087] The formation of this second modified region 122 is performed multiple times while sequentially changing the Z-direction position of the focused spot C2 from the bottom surface side toward the incident surface side. As a result, multiple second modified regions 122 aligned along the Z direction at the boundary B in the YZ plane are formed as modified regions 12. In this way, in step S202, after the first processing process, the control unit 6 performs the second processing process to form multiple second modified regions 122 (including the third modified region 123) as modified regions 12, which are positioned at the boundary B so as to intersect with the multiple first modified regions 121 aligned along the Y direction.

[0088] Note that an intersecting positional relationship is a positional relationship in which a virtual line (surface) connecting multiple first modified regions and a virtual line (surface) connecting multiple second modified regions 122 intersect with each other, and the multiple first modified regions 121 and the multiple second modified regions 122 may actually intersect, or they may not intersect (for example, a gap is formed in the Z direction).

[0089] Of the multiple second modified regions 122, the above-mentioned elongated third modified region 123 is the second modified region 122 that is closest to the first modified region 121 and located closest to the bottom surface. In this embodiment, the third modified region 123 is closest to the first modified region 121 that is located at the end of the first Y direction ND (i.e., the first modified region 121 that was formed last in step S201). As described above, in step S202, the control unit 6 controls the spatial light modulator 7 to modulate the laser light L and impart the first aberrations H11 and H12 to the laser light L so that the third modified region 123, which is the second modified region 122 that is closest to the first modified region 121 among the multiple second modified regions 122, becomes elongated in the Z direction.

[0090] As a result of step S202, a crack 13 is formed at the boundary B, extending across the plurality of second modified regions 122 including the third modified region 123. The crack 13 may reach the first surface 11a.

[0091] As described above, in the laser processing method according to this embodiment, peeling is performed in step S201, and trimming is performed in step S202. As a result, a part of the object 11 (removal area E) can be peeled off along the boundary between the modified area 12 formed across the imaginary plane M2 and the crack 13 extending from the modified area 12, and the modified area formed along the boundary B and the crack 13 extending from the modified area 12.

[0092] As described above, in the laser processing apparatus 1 and laser processing method according to this embodiment, within a virtual plane M2 along the incident surface (first surface 11a) of the laser light L of the object 11, the laser light L is irradiated while moving the focused spot C (focused spot C0) in the X direction along the virtual plane M2, thereby forming a first modified region 121 along the X direction. This X-direction processing is performed while changing the position of the focused spot C in the Y direction, which is along the virtual plane M2 and intersects with the X direction, to a first Y direction ND that runs from one side of the Y direction to the other, thereby forming a plurality of first modified regions 121 lined up along the Y direction in the YZ plane.

[0093] In particular, in the laser processing apparatus 1 and laser processing method according to this embodiment, when forming the first modified region 121, the beam shape of the focused spot C of the laser light L in the YZ plane is tilted in the first Y direction ND at least on the incident surface side of the center Ca of the focused spot C. By using the focused spot C having such a beam shape when forming the first modified region 121, the crack 13 extending from the first modified region 121 in the first Y direction ND is prevented from growing obliquely toward the bottom surface side of the object 11. In other words, it is possible to suppress the growth of the crack 13 extending from the first modified region 121.

[0094] In the laser processing apparatus 1 and laser processing method according to this embodiment, multiple lines A are set on the object 11 in a concentric pattern as viewed in the Z direction. In step S201, the control unit 6 irradiates the object 11 with laser light L while moving the focused spot C along one line A to form a first modified region 121 along the X direction, which is the circumferential direction of the line A. This X-direction processing is then performed across the multiple lines A while changing the direction of the line A to the first Y direction ND, thereby forming multiple first modified regions 121 aligned along the Y direction, which is the radial direction of the line A, in the YZ plane (virtual plane M2). In this way, the first processing may be performed along multiple lines A set concentrically on the object 11 (i.e., concentric processing may be performed). Unlike spiral processing, concentric processing allows the spacing of the first modified regions 121 in the YZ plane to be constant in the Y direction, enabling stable processing.

[0095] Furthermore, in the laser processing apparatus 1 and laser processing method according to this embodiment, the object 11 has, when viewed from the Z direction, an effective region R (first region) including the center of the object 11, and a removal region E (second region) that is an area outside the effective region R and includes the peripheral portion of the object 11. The control unit 6 then executes a first processing process on the removal region E. This makes it possible to perform peeling processing using the first modified region 121 formed along the imaginary plane M2 in the removal region E, including the peripheral portion of the object 11, while suppressing the growth of the crack 13. In particular, because the growth of the crack extending from the first modified region 121 formed along the imaginary plane M2 is suppressed, the peeled surface is prevented from becoming rough, and the quality of the peeled surface is improved.

[0096] Furthermore, in the laser processing apparatus 1 and laser processing method according to this embodiment, the control unit 6 performs a second processing process after the first processing process, in which a plurality of second modified regions 122 are formed as modified regions 12 at the boundary B so as to intersect with a plurality of first modified regions 121 lined up along the Y direction. In the second processing process (step S202), the control unit 6 modulates the laser light L by controlling the spatial light modulator 7 to impart first aberrations H11 and H12 to the laser light L so that a third modified region 123, which is the second modified region 122 closest to the first modified region 121 among the plurality of second modified regions 122, becomes elongated in the Z direction. The third modified region 123 is the second modified region 122 among the multiple second modified regions 122 that is farthest from the incident surface, and the first aberrations H11 and H12 are aberrations for forming focused spots C11 and C12 that are longer in the Z direction than the focused spot C10 of the laser light L to which the reference aberration H10 has been added, when the aberration that occurs in the optical axis direction of the laser light L at the focusing position due to focusing the laser light L on the object 11 is defined as the reference aberration H10.

[0097] The elongated third modified region 123 thus formed has the property that cracks extending from the third modified region 123 are less likely to propagate in the Z direction (i.e., the cracks become shorter). Therefore, since cracks are less likely to propagate from the third modified region 123, the propagation of the crack 13 from the third modified region 123 to the bottom surface (second surface 11b) of the object 11 is suppressed. Furthermore, in this case, the second modified region 122 closest to the first modified region 121 is the third modified region 123 in which cracks are less likely to propagate. In such a case, the formation of the third modified region 123 makes it less likely that the crack 13 extending from the first modified region 121 will further propagate. In other words, the propagation of the crack 13 from the first modified region 121 to the bottom surface of the object 11 is suppressed. As described above, in this case, it is possible to reliably suppress the propagation of the crack 13 extending from the modified region 12. [Modification]

[0098] The above embodiment has described one aspect of the laser processing apparatus and laser processing method according to the present disclosure. Therefore, the laser processing apparatus and laser processing method according to the present disclosure are not limited to the above embodiment and can be modified as desired. Next, modified examples will be described.

[0099] 23 is a diagram illustrating a laser processing method according to a modified example. As shown in FIG. 23 , the boundary B between the effective region R and the removal region E may include an inclined portion B1 inclined with respect to the Z direction in the YZ plane. In the example of FIG. 23 (a), a portion of the boundary B on the second surface 11b side is the inclined portion B1. In the example of FIG. 23 (b), the entire boundary B is the inclined portion B1. In this case, when the boundary B includes the inclined portion B1, when forming the modified region 12 in the inclined portion B1, it is required to form a crack 13 extending obliquely (with respect to the Z direction) from the modified region 12 along the inclined portion B1.

[0100] Therefore, as shown in Figure 11, when forming the modified region 12 in the inclined portion B1 (in the illustrated example, step S202, second processing process), the control unit 6 can control the spatial light modulator 7 to modulate the laser light L so that the beam shape at the focused spot C of the laser light L in the YZ plane is inclined in the inclination direction of the inclined portion B1 (here, the negative Y direction) at least on the incident surface (first surface 11a) side of the center Ca of the focused spot C.

[0101] As a method for modulating such laser light L, various methods can be considered, and any method can be selected. Examples include the above-mentioned method of offsetting the center of the spherical aberration correction pattern in the tilt direction with respect to the center of the entrance pupil plane of the condenser lens 33, the method of controlling the magnitude of coma aberration in the coma aberration pattern for imparting coma aberration to the laser light L, and the method of modulating the laser light L with a modulation pattern that is asymmetric with respect to an axis along the X direction, which is the processing progression direction.

[0102] By controlling the shape of the focused spot C as described above, as shown in (a) of Figure 24, it is possible to form the third modified region 123 in step S202 and to form a crack 13a extending obliquely along the inclined portion B1 between the third modified region 123 and the second modified region 122 closest to the third modified region 123. In the example of (a) of Figure 24, in step S202, the second modified regions 122 aligned in the Z direction are formed without tilting the focused spot C, thereby forming a crack 13b extending in the Z direction from the second modified region 122.

[0103] 24(b), the focused spot C is also tilted in step S202, and a plurality of second modified regions 122 and third modified regions 123 are formed at an angle with respect to the Z direction across the entire boundary B that is tilted with respect to the Z direction, thereby forming a crack 13a extending in an angle with respect to the Z direction across the entire boundary B. By forming the crack 13a extending obliquely with respect to the Z direction from the modified region 12 along the tilted boundary B in this manner, it is possible to reduce the impact on bottom-side structures such as the device layer 110, 110R and other objects 11R, compared to when the crack 13 extending from the modified region 12 progresses along the Z direction and reaches the bottom surface (second surface 11b).

[0104] 25A and 25B are schematic cross-sectional views (XY plane) illustrating a laser processing method according to another modification. As shown in (a) of Fig. 25A, the laser beam L can be branched so that multiple (here, two) focused spots C are formed at different positions in the Y direction, which intersects with the X direction, the processing direction, within imaginary planes M1 and M2. The laser beam L can be branched, for example, by displaying a branching pattern, such as a diffraction grating pattern, on the spatial light modulator 7 and modulating the laser beam L using the pattern.

[0105] In the first embodiment, in step S102, which is the first processing step, and in the second embodiment, in step S201, which is also the first processing step, such branching of the laser light L can be performed. That is, in the first processing step, the control unit 6 can branch the laser light L so that a plurality of focused spots C, which are positioned at least in the Y direction and differ from each other, are formed within the imaginary planes M1 and M2.

[0106] By forming multiple focused spots C at different positions in the Y direction in this manner, as shown in (b) and (c) of Figures 25, multiple (here, two) first modified regions 121a, 121b at different positions in the Y direction can be formed as modified regions 12 at positions corresponding to each focused spot C. The first modified region 121b is formed next to the first modified region 121a. By branching the laser light L to form multiple focused spots C at different positions in the Y direction in this manner, the cracks 13 extending from each of the first modified regions 121a, 121b formed corresponding to the multiple focused spots C are more likely to connect with each other in the XY plane (virtual planes M1, M2). As a result, the cracks 13 extending from the first modified regions 121a, 121b are prevented from propagating obliquely toward the bottom surface.

[0107] 26(a), the laser light L may be branched so that a plurality of (here, two) focused spots C are formed in the Y direction intersecting with the X direction, which is the processing progress direction, and at different positions in the X direction within the imaginary surfaces M1 and M2. That is, in the first processing process, the control unit 6 may branch the laser light L so that a plurality of focused spots C are formed at further different positions in the X direction within the imaginary surfaces M1 and M2.

[0108] In the illustrated example, as shown in (b) and (c) of Figure 26, one of the first modified regions 121a is aligned in the Y direction with the first modified region 121b formed next to the first modified region 121a when viewed from the Z direction. This makes it easier for cracks 13 to connect in the Y direction between the first modified region 121a and the first modified region 121b. As a result, the cracks 13 extending from each of the first modified regions 121a, 121b formed corresponding to the multiple focused spots C are more likely to connect with each other in the XY plane. This more reliably prevents the cracks 13 extending from the first modified regions 121a, 121b from propagating obliquely toward the bottom surface.

[0109] 27A, when forming the focused spots C at different positions in the X and Y directions within the imaginary planes M1 and M2, the shift amount in the X direction between one focused spot C and another focused spot C may be made larger. In the illustrated example, as shown in FIG. 27B, the shift amount in the X direction of the focused spots C may be made larger than the distance between the first modified region 121a and the first modified region 121b formed next to the first modified region 121a.

[0110] In this example, the shift amount of the focused spot C in the X direction is set so that when the first modified regions 121a, 121b, 121c, and 121d are formed in sequence, one first modified region 121a is aligned with the first modified region 121d in the Y direction. By doing so, internal stress in the Y direction can be accumulated when the first modified regions 121a to 121d are formed, making it easier for the crack 13 to propagate along the Y direction.

[0111] As described above, in the first processing step, when the laser light L is branched to form multiple focused spots C, the control unit 6 can modulate the laser light L using the spatial light modulator 7 so that the beam shape of the laser light L in each of the multiple focused spots C is inclined in the first Y direction ND with respect to the Z direction at least on the incident surface side of the center Ca of the focused spot C.

[0112] Although the main modifications have been described above, any other modifications are possible. For example, in the above embodiment, during the first processing, while the focused spot C orbits along the circular line A as viewed from the Z direction, the beam shape is adjusted so that at least the portion on the incident surface side is tilted toward the first Y direction ND along the entire circumference of the line A. However, such beam shape adjustment may be performed only on a portion of the line A.

[0113] For example, when the object 11 is a wafer with a crystal orientation <100> and is supported on the stage 2 so that the first surface 11a, which is the (100) plane, faces the irradiation unit 3, and when viewed from the Z direction, the intersections of the (110) plane of the object 11 and the line A are set to processing angles of 0° and 180°, and the intersections of the (100) plane of the object 11 and the line A are set to processing angles of 90° and 270°, the modulation pattern displayed on the spatial light modulator 7 may be controlled to adjust the above-mentioned beam shape only in a partial region that includes at least the processing angles of 0°, 90°, 180°, and 270° of the line A.

[0114] 1...laser processing device, 2...stage (support part), 3...irradiation part, 4, 5...movement part, 6...control part, 7...spatial light modulator, 11...object, 11a...first surface (incident surface), 11b...second surface (bottom surface), 12...modified region, 13, 13a, 13b, 13p...crack, 31...light source, 33...condensing lens (condensing part), 121...first modified region, 122...second modified region, 123...third modified region, L...laser light, H, H10...reference aberration, H11, H12...first aberration.

Claims

1. A laser processing device for irradiating a target with laser light to form a modified region along a virtual surface inside the target that is aligned with the incident surface of the laser light of the target, comprising: a support unit that supports the target; an irradiation unit that irradiates the target supported by the support unit with the laser light; a movement unit that moves at least one of the support unit and the irradiation unit so that a focused spot of the laser light moves along the virtual surface; and a control unit that controls the support unit, the irradiation unit, and the movement unit, wherein the irradiation unit includes: a spatial light modulator that modulates the laser light; and a focusing unit that focuses the laser light that has passed through the spatial light modulator toward the target, the control unit performs a first processing step in which an X-direction processing is performed to form a first modified region along the X direction by irradiating the object with the laser light while moving the focused spot in an X direction along the imaginary plane, and a Y direction in which a position of the focused spot in a Y direction along the imaginary plane and intersecting the X direction is changed in a first Y direction from one side of the Y direction to the other, thereby forming a plurality of first modified regions aligned along the Y direction in a Y-Z plane that includes a Z direction intersecting the X direction and the Y direction, and the Y direction; and in the first processing step, the control unit modulates the laser light by the spatial light modulator so that a beam shape of the focused spot of the laser light in the Y-Z plane is inclined in the first Y direction with respect to the Z direction at least on the incident surface side of the center of the focused spot.

2. The laser processing device according to claim 1, wherein a plurality of lines are set on the object, the lines being arranged concentrically when viewed from the Z direction, and the control unit irradiates the object with the laser light while moving the focused spot along one of the lines, thereby forming the first modified region along the X direction as a circumferential direction of the one line, and performs the X-direction processing across the plurality of lines while changing the one line in the first Y direction, thereby forming a plurality of the first modified regions arranged along the Y direction as a radial direction of the line in the YZ plane.

3. The laser processing device according to claim 1, wherein a spiral line is set on the object when viewed from the Z direction, and the control unit irradiates the object with the laser light while moving the focused spot along the line, thereby performing the X-direction processing to form the first modified region along the X direction as a tangent direction of the line from the start end to the end end of the line, thereby forming a plurality of the first modified regions lined up along the Y direction as a direction intersecting the tangent direction of the line in the YZ plane.

4. A laser processing device as described in any one of claims 1 to 3, wherein the object has, when viewed from the Z direction, a first region including the center of the object and a second region that is an area outside the first region and includes the peripheral edge of the object, and the control unit performs the first processing process on the first region.

5. A laser processing device according to any one of claims 1 to 3, wherein the object has, when viewed from the Z direction, a first region including the center of the object and a second region that is an area outside the first region and includes the peripheral edge of the object, and the control unit performs the first processing process on the second region.

6. The second region has a boundary with the first region, and the control unit performs a second processing process after the first processing process to form, as the modified region, a plurality of second modified regions at the boundary that are positioned so as to intersect with a plurality of first modified regions lined up along the Y direction, and in the second processing process, the control unit modulates the laser light by controlling the spatial light modulator to impart a first aberration to the laser light so that a third modified region, which is the second modified region closest to the first modified region among the plurality of second modified regions, is elongated in the Z direction, and the third modified region is the second modified region among the plurality of second modified regions that is furthest from the incident surface, and the first aberration is an aberration for forming a focused spot that is elongated in the Z direction than the focused spot of the laser light to which the reference aberration has been imparted, when aberration occurring in the optical axis direction of the laser light at a focusing position due to focusing the laser light on the object by the focusing unit is defined as a reference aberration. The laser processing device according to claim 5.

7. The laser processing apparatus according to claim 6, wherein the boundary includes an inclined portion inclined with respect to the Z direction in a YZ plane including the Z direction and the Y direction, and the control unit, when forming the modified region in the inclined portion, controls the spatial light modulator to modulate the laser light so that the beam shape at the focused spot of the laser light in the YZ plane is inclined in the inclination direction of the inclined portion at least on the incident surface side of the center of the focused spot.

8. A laser processing device according to any one of claims 1 to 7, wherein in the first processing step, the control unit branches the laser light so that a plurality of focused spots are formed in the virtual plane, the focused spots being at mutually different positions at least in the Y direction.

9. The laser processing device according to claim 8, wherein in the first processing step, the control unit branches the laser light so as to form a plurality of focused spots whose positions in the X direction are further different within the virtual plane.

10. A laser processing method for forming a modified region along a virtual surface inside an object that is aligned with the laser light incident surface of the object by irradiating the object with laser light, comprising a processing step of irradiating the object with the laser light while moving a focused spot of the laser light along the virtual surface to form the modified region, wherein the processing step includes: an X-direction processing step in which, within the virtual surface, the object is irradiated with the laser light while moving the focused spot in an X direction along the virtual surface to form a first modified region along the X direction as the modified region, and a first processing step in which the position of the focused spot in a Y direction that is along the virtual surface and intersects the X direction is changed in a first Y direction from one side of the Y direction to the other side of the Y direction to form a plurality of first modified regions aligned along the Y direction in a YZ plane that includes a Z direction intersecting the X direction and the Y direction, and the Y direction; In the first processing, a beam shape of the focused spot of the laser light in the YZ plane is tilted in the first Y direction at least on the incident surface side of the center of the focused spot.

Images