Laser beam machining apparatus and laser beam machining method

Abstract

The present invention provides a laser beam machining apparatus comprising: a light source that emits a laser beam; a spatial light modulator for modulating the laser beam emitted from the light source; a focusing unit that focuses the laser beam that has passed through the spatial light modulator toward an object; and a machining control unit that performs laser beam machining for forming a modified area in the object by irradiating the object with the laser beam while causing the focused spot of the laser beam to move relative to the object, wherein, when viewed from the Z direction that intersects the plane of incidence of the laser beam in the object, the object includes a first region and a second region which borders the first region and which is located more to the outside than the first region.

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] However, when forming a modified region in an object such as the wafer to be processed, if a crack extending from the modified region reaches the bottom surface of the object such as the non-processed 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 the crack so that the crack extending from the modified region does not reach the bottom surface.

[0005] 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.

[0006] a processing control unit that performs laser processing to form a modified region in the object by irradiating the object with the laser light while moving a focused spot of the laser light relative to the object, the object including, when viewed from a Z direction intersecting a plane of incidence of the laser light on the object, a first region and a second region having a boundary with the first region and positioned outside the first region, the processing control unit performing a first processing process of irradiating the object with the laser light so as to form, as the modified region, a plurality of first modified regions aligned in a Y direction intersecting the Z direction from an end of the second region opposite the boundary across the boundary; and performing a second processing process of irradiating the object with the laser light so as to form, as the modified regions, a plurality of second modified regions that are positioned so as to intersect with a plurality of the first modified regions lined up in the Y direction, wherein in the second processing process, the processing control unit imparts a first aberration to the laser light by controlling the spatial light modulator to modulate 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, becomes elongated in the Z direction, the third modified region being 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 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 the focusing position due to focusing the laser light on the object by the focusing unit is defined as a reference aberration.

[0007] The laser processing method according to the present disclosure [6] includes a processing step of forming a modified region in the object by irradiating the object with the laser light while moving a focused spot of the laser light relative to the object, wherein the object includes a first region and a second region having a boundary with the first region and positioned outside the first region when viewed from a Z direction intersecting a plane of incidence of the laser light on the object, the processing step including a first processing step of irradiating the object with the laser light so as to form, as the modified region, a plurality of first modified regions aligned in a Y direction intersecting the Z direction from an end of the second region opposite to the boundary across the boundary; and a second processing step of irradiating the object with the laser light so as to form, as the modified regions, a plurality of second modified regions having a positional relationship such that the modified regions are formed as the first modified region and the second modified region are formed as the second modified region and the third modified region is the second modified region among the plurality of second modified regions that is closest to the first modified region, and 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 aberration that occurs in the optical axis direction of the laser light at a focusing position due to focusing the laser light on the object is defined as a reference aberration.

[0008] This apparatus and method perform laser processing on an object including a first region and a second region having a boundary with the first region and positioned outside the first region, as viewed from a Z direction intersecting a laser beam incident surface. Specifically, laser light is first applied from an end of the second region opposite the boundary to the boundary, forming a plurality of first modified regions aligned in a Y direction intersecting the Z direction. Laser light is then applied at the boundary between the first and second regions to form a plurality of second modified regions that intersect with the first modified regions aligned in the Y direction. In particular, when forming the second modified regions, a spatial light modulator is controlled to modulate the laser light so that a third modified region, which is the second modified region closest to the first modified region, is elongated in the Z direction, thereby imparting a first aberration to the laser light.

[0009] This allows the third modified region to be elongated in the direction of the optical axis of the laser light (Z direction). The elongated 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, because 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.

[0010] 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, this device and method make it possible to suppress the growth of cracks extending from modified regions.

[0011] The laser processing apparatus according to the present disclosure may be [2] "the laser processing apparatus described in the above [1], wherein in the second processing step, the processing control unit irradiates the object with the laser light so that the third modified region intersects with a plurality of the first modified regions." In this case, it is possible to reliably suppress the growth of a crack extending from the first modified region located on the innermost side (first region side) of the object.

[0012] The laser processing apparatus according to the present disclosure may be [3] "the laser processing apparatus described in [2] above, wherein in the second processing step, the processing control unit irradiates the object with the laser light so that the third modified region intersects with the plurality of first modified regions on the side opposite the incident surface from the center of the third modified region in the Z direction." In this case, most of the area on the incident surface side of the third modified region is located closer to the incident surface than the first modified region. This makes it possible to reliably suppress the growth of cracks extending from the first modified region.

[0013] The laser processing device according to the present disclosure may be [4] "the laser processing device described in the above [2] or [3], wherein in the second processing step, the processing control unit irradiates the object with the laser light such that no cracks are included in a region of the third modified region on the opposite side of the incident surface from the intersection position with the first modified region in the Z direction." In this case, it is possible to more reliably suppress the growth of cracks extending from the first modified region.

[0014] The laser processing apparatus according to the present disclosure may be [5] "the laser processing apparatus according to any one of [1] to [4] 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 processing 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 along 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.

[0015] 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.

[0016] 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 this embodiment. FIG. 4 is a diagram showing an example of the object shown in FIG. 3. FIG. 5 is a cross-sectional view showing an example of modified regions and cracks formed in the object shown in FIG. 4. FIG. 6 is a diagram for explaining a laser processing method according to this embodiment. FIG. 6(a) is a plan view, and FIG. 6(b) is a side view. FIG. 7 is a diagram for explaining a laser processing method according to this embodiment. FIG. 7(a) is a cross-sectional view showing a state in which laser light is focused, and FIG. 7(b) is a cross-sectional view showing a state in which a modified region has been formed. FIG. 8 is a diagram for explaining a laser processing method according to this embodiment. Specifically, it is a schematic cross-sectional view showing a state in which a modified region has been formed. FIG. 9 is a diagram for explaining a laser processing method according to this embodiment. FIG. 9(a) is a plan view, and FIG. 9(b) is a side view. FIG. 10 is a diagram for explaining a laser processing method according to this embodiment. FIG. 10(a) is a cross-sectional view showing a state in which laser light is focused, and FIG. 10(b) is a cross-sectional view showing a state in which a modified region has been formed. FIG. 11 is a diagram for explaining the laser processing method according to the present embodiment. Specifically, FIG. 11 is a diagram for explaining aberrations that occur at the focusing position of laser light. FIG. 12 is a diagram for explaining the laser processing method according to the present embodiment. Specifically, FIG. 12 is a diagram showing the intensity of laser light and the focused spot when multiple aberrations are applied based on a reference aberration. FIG. 13 is a diagram for explaining the laser processing method according to the present embodiment. FIG. 13(a) is a cross-sectional view showing a state in which laser light is focused, and FIG. 13(b) is a cross-sectional view showing a state in which a modified region has been formed. FIG. 14 is a diagram for explaining a laser processing method according to a modified example. Specifically, FIGS. 14(a) and 14(b) are schematic cross-sectional views showing the boundary between an effective region and a removal region in a target object. FIG. 15 is a diagram for explaining the laser processing method according to a modified example. Specifically, Fig. 15 is a diagram showing a focused spot of laser light in the YZ plane, and Fig. 16 is a diagram for explaining a laser processing method according to a modified example.Specifically, (a) and (b) of Fig. 16 are schematic cross-sectional views showing a state in which a modified region and a crack extending obliquely from the modified region have been formed. Fig. 17 is a diagram for explaining a laser processing method according to another modified example. (a) of Fig. 17 is a schematic cross-sectional view showing one example. (b) of Fig. 17 is a schematic cross-sectional view showing another example. Fig. 18 is a diagram for explaining a laser processing method according to yet another modified example.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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 of gravity of the beam intensity.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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).

[0025] 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.

[0026] 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.

[0027] 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.

[0028] FIG. 3 is a diagram illustrating an object to be laser processed according to this embodiment. FIG. 3A is a plan view, and FIG. 3B is a side view. As shown in FIG. 3, the object 100 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 first surface 11a and a second surface 11b opposite the first surface 11a. The object 11 includes a device layer 110 that includes multiple functional elements and is formed on the second surface 11b. The object 11R includes a device layer 110R that includes multiple 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 bonding them together, thereby constituting the object 100.

[0029] The object 11 includes an effective region (first region) R and a removal region (second region) E. The effective region R is a portion corresponding to the semiconductor device to be acquired. The effective region R here is a disk-shaped portion including the central portion of the object 11 when viewed from the Z direction, which is the thickness direction of the object 11. The removal region E has a boundary B with the effective region R and is a region located outside the effective region R in the object 11. In this embodiment, the removal region E is the outer edge portion of the object 11 other than the effective region R. The removal region E here is an annular portion surrounding the effective region R.

[0030] In this embodiment, modified regions 12 and cracks extending from the modified regions 12 are formed in the boundary B between the effective region R and the removal region E, and in the horizontal region extending from the outer edge of the removal region E (the end opposite the boundary B) to the boundary B, and trimming is performed to remove the removal region E of the object 11 using these modified regions 12 and cracks. Therefore, the boundary B is also one of the above-mentioned lines A along which the laser light L is to be irradiated.

[0031] FIG. 4 is a diagram showing an example of the object shown in FIG. 3 . FIG. 4A is a perspective view showing a portion cut away, and FIG. 4B is a schematic cross-sectional view. As shown in FIG. 4 , 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) plane. 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) plane perpendicular to the first surface 11a, which is the (100) plane, and a (111) plane intersecting the (110) plane at an angle of 125.25°. The angle between the (111) planes extending in directions that intersect each other is 70.5°.

[0032] 5 is a cross-sectional view showing an example of the formation of modified regions and cracks in the object shown in FIG. 5A. 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. 5A, 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 110 formed on the second surface 11b or another object 11R bonded to the second surface 11b via the device layer 110.

[0033] However, the target object 11 includes a (111) plane, which is easier to cleave than the (100) plane. Therefore, as shown in FIG. 5B, 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. Laser processing for suppressing the propagation of the cracks 13 will now be described.

[0034] 6 to 13 are diagrams illustrating the laser processing method according to this embodiment. The laser processing method according to this embodiment is performed by the laser processing apparatus 1 described above. Therefore, the laser processing method described below is an example of processing performed by the laser processing apparatus 1. In this embodiment, the control unit 6 irradiates the target object 11 with the laser light L while moving the focused spot C of the laser light L relative to the target object 11 (processing step). That is, as shown in FIGS. 6 to 8, first, horizontal processing is performed from the end of the removal area E opposite the boundary B to the vicinity of the boundary B (step S101: first processing step, first processing).

[0035] 6 and 7, in step S101, 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 positioned on one of a plurality of lines A extending in a circular shape concentric with the boundary B from the end of the removal area E opposite the boundary B to the vicinity of the boundary B, and at a predetermined depth (position in the Z direction) from the first surface 11a of the object 11. Note that an example is shown in which the line A coincides with the boundary B.

[0036] 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 along the line A. As a result, first modified regions 121 arranged in a circle are formed as modified regions 12 on the circular line A when viewed from the Z direction.

[0037] This step S101 is performed multiple times while sequentially changing the Y-direction position of the focused spot C0, for example, from the end of the removal area E opposite the boundary B toward the boundary B (or from the boundary B toward the end of the removal area E opposite the boundary B). That is, the laser light L is irradiated onto each of the multiple lines A. As a result, as shown in FIG. 8 , multiple first modified regions 121 aligned in the Y-direction within the YZ plane are formed as the modified regions 12. That is, here, multiple first modified regions 121 are formed that are two-dimensionally arranged within a virtual plane (planned slicing plane) along the first surface 11a (XY plane).

[0038] As described above, in step S101, the control unit 6 performs a process (first processing process) of irradiating the object 11 with laser light L so as to form multiple first modified regions 121 arranged in the Y direction intersecting the Z direction from the end opposite the boundary B in the removal area E to the boundary B, as modified regions 12.

[0039] 9 and 13, after the first processing process, laser processing is performed to form, as modified regions 12, a plurality of second modified regions 122 aligned in the Z direction along the boundary B in the YZ plane (step S102: second processing step, second processing process). More specifically, in step S102, as shown in FIG. 9, 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.

[0040] 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.

[0041] 10(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 S101, thereby imparting a first aberration to the laser light L. As a result, as shown in FIG. 10(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). That is, in step S102, 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.

[0042] The first aberration imparted to the laser beam in step S102 will be described. FIG. 11 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.

[0043] 11 , 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 relying 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.

[0044] 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. 12 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. 12 respectively represent the cases where a reference aberration H10 corresponding to the reference aberration H is imparted, a first aberration H11 having a longer range (more negative) than the reference aberration H10 is imparted, a first aberration H12 having an even longer range (more negative) than the reference aberration H10 is imparted, and 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.

[0045] 12 , 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 so 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.

[0046] As described above, in step S102, 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. 10(b), a third modified region 123 that is elongated in the Z direction is formed as the second modified region 122 at the boundary B as the modified region 12.

[0047] 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.

[0048] In the next step, laser processing is performed to form multiple second modified regions 122 aligned in the Z direction along the boundary B in the YZ plane as modified regions 12 (step S102: second processing step, second processing process). More specifically, first, the control unit 6 controls the movement 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. At this time, as shown in (a) of Figure 13, the position of the focused spot C in the Z direction is set closer to the first surface 11a, which is the incident surface of the laser light L, than the position in the Z direction of the focused spot C1 when the third modified region 123 was formed.

[0049] 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 target 11. At this time, the focused spot C becomes a focused spot C2 that is shorter in the Z direction than the focused spot C1 when the third modified region 123 is formed. As a result, the 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.

[0050] 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 second surface 11b side toward the first surface 11a 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. The second modified region 122 including the third modified region 123 is positioned so as to intersect with the multiple first modified regions 121 aligned in the Y direction. The intersecting positional relationship refers to a positional relationship in which an imaginary line (plane) connecting the multiple first modified regions and an imaginary line (plane) connecting the multiple second modified regions 122 intersect with each other. The multiple first modified regions 121 and the multiple second modified regions 122 may actually intersect or may not intersect (e.g., gaps may be formed in the Z direction). The third modified region 123 is the second modified region 122 located closest to the second surface 11b among the multiple second modified regions 122.

[0051] As a result of this step S102, 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. As described above, in step S102, the control unit 6 performs a process (second processing process) of irradiating the object 11 with laser light L so as to form, as modified regions 12, a plurality of second modified regions 122 that are positioned so as to intersect with the plurality of first modified regions 121 aligned in the Y direction at the boundary B. In particular, the control unit 6 imparts first aberrations H11 and H12 to the laser light L by controlling the spatial light modulator 7 to modulate the laser light L so that the third modified region 133, 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.

[0052] In addition, when laser processing is performed by moving the focused spot C relatively in a circular manner, as in the laser processing method according to this embodiment, the processing progress direction PD (i.e., the circumferential direction of the circle), which is the direction in which the focused spot C moves, can be defined as the X direction, and the direction perpendicular to the processing progress direction PD (i.e., the radial direction of the circle) can be defined as the Y direction.

[0053] As described above, in the laser processing method according to this embodiment, in step S101, a plurality of first modified regions 121 are formed in the object 11, which is a <100> wafer, along the Y direction (i.e., the (100) plane). Therefore, if another modified region 12 is formed adjacent to the first modified region 121, there is a risk that the crack 13 extending from the first modified region 121 will further propagate along the (111) plane. In contrast, in this embodiment, as described above, in step S102, the third modified region 123, which is the second modified region 122 closest to the first modified region 121 and closest to the second surface 11b, is made elongated in the Z direction. In this embodiment, the third modified region 123 is adjacent to the innermost first modified region 121 (on the effective region R side) among the plurality of first modified regions 121 aligned in the Y direction. Therefore, when the third modified region 123 is formed, the crack extending from the third modified region 123 is prevented from connecting with the crack 13 extending from the first modified region 121 and inducing further propagation of the crack 13 along the (111) plane.

[0054] In addition, in the laser processing apparatus 1 according to this embodiment, the processing conditions can be set as follows for each of the formation of the first modified region 121, the formation of the second modified region 122, and the formation of the third modified region 123.

[0055] Formation of first modified region 121: wavelength of laser light L 1099 nm, frequency 60 kHz, pulse width 45 nsec, output 0.14 W, speed of relative movement of focused spot C 300 mm / sec, spacing of line A in Y direction 5 μm, aberration correction performed to remove spherical aberration of Si.

[0056] Formation of second modified region 122: laser light L wavelength 1099 nm, frequency 120 kHz, pulse width 700 nsec, output 3 W, relative movement speed of focused spot C 800 mm / sec, aberration correction to remove spherical aberration of Si.

[0057] Formation of the third modified region 123: Laser light L wavelength 1099 nm, frequency 60 kHz, pulse width 45 nsec, output 1.5 W, relative movement speed of the focused spot C 300 mm / sec, aberration correction to remove the spherical aberration of Si. Aberration is imparted so that a focused region longer than the focused region with the reference aberration is formed.

[0058] As described above, the laser processing apparatus 1 and laser processing method according to this embodiment perform laser processing on an object 11 that, when viewed from the Z direction intersecting the first surface 11a, which is the laser light incident surface, includes an effective region R and a removal region E that has a boundary B with the effective region R and is located outside the effective region R. That is, first, laser light L is irradiated from the end of the removal region E opposite to the boundary B to the boundary B, so as to form a plurality of first modified regions 121 lined up in the Y direction intersecting the Z direction.

[0059] Next, laser light L is irradiated at the boundary B between the effective region R and the removal region E so as to form a plurality of second modified regions 122 that are positioned so as to intersect with the first modified regions 121 aligned in the Y direction. In particular, when forming the second modified regions 122, the spatial light modulator 7 is controlled to modulate the laser light L so that the third modified region 123, which is the second modified region 122 closest to the first modified region 121, becomes elongated in the Z direction, thereby imparting first aberrations H11 and H12 to the laser light L.

[0060] This makes it possible to elongate the third modified region 123 in the optical axis direction (Z direction) of the laser light L. 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). Therefore, because cracks are less likely to propagate from the third modified region 123, the propagation of cracks from the third modified region 123 to the bottom surface of the object (the second surface 11b opposite the incident surface) is suppressed.

[0061] On the other hand, if another modified region 12 is formed close to the first modified region 121, the crack 13 extending from the multiple first modified regions 121 arranged in the Y direction may connect with the crack extending from the other modified region 12 and continue to grow. In contrast, here, the second modified region 122 closest to the first modified region 121 is the third modified region 123, which is less susceptible to crack growth. 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 continue to grow as described above. In other words, the crack 13 is prevented from growing from the first modified region 121 to the bottom surface of the object 11. As described above, the growth of the crack 13 extending from the modified region 12 is suppressed.

[0062] The above embodiment describes one aspect of the laser processing apparatus and laser processing method according to the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiment and may be modified as desired. Next, modified examples will be described.

[0063] 14 is a diagram illustrating a laser processing method according to a modified example. As shown in FIG. 14, 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. 14(a), a portion of the boundary B on the second surface 11b side is the inclined portion B1. In the example of FIG. 14(b), the entire boundary B is the inclined portion B1. In this way, 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.

[0064] Therefore, as shown in Figure 15, when forming a modified region 12 in the inclined portion B1 in the second formation process (step S102), 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.

[0065] As a method for modulating such laser light L, various methods can be considered, and any method can be selected. Examples include a 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, a method of controlling the magnitude of coma aberration in a coma aberration pattern for imparting coma aberration to the laser light L, and a method of modulating the laser light L using a modulation pattern that is asymmetric with respect to an axis along the X direction, which is the processing progression direction.

[0066] 16(a), by controlling the shape of the focused spot C as described above, it is possible to form the third modified region 123 in step S102 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 FIG. 16(a), in step S102, the second modified regions 122 aligned in the Z direction are formed without tilting the focused spot C, thereby forming a crack 13b extending from the second modified region 122 in the Z direction.

[0067] 16(b), the focused spot C is also tilted in step S102, 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 way, 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).

[0068] 17 and 18 are diagrams illustrating a laser processing method according to another modification. As shown in (a) of FIG. 17 , in the YZ plane, the first modified regions 121 aligned in the Y direction may be formed, for example, within 1 mm inward (toward the effective region R) of the second modified regions 122 aligned in the Z direction along the boundary B. In this case, the line A used to form the innermost first modified region 121 is located inside the boundary B. Also, as shown in (b) of FIG. 17 , in the YZ plane, the first modified regions 121 aligned in the Y direction and the second modified regions 122 aligned in the Z direction along the boundary B may be separated in the Z direction by an unmodified region of, for example, 50 μm or less.

[0069] 18 , in the YZ plane, first modified regions 121 aligned in the Y direction and multiple second modified regions 122 aligned in the Z direction may actually intersect. In the illustrated example, the first modified regions 121 aligned in the Y direction intersect with the third modified region 123. That is, the first modified region 121 and the third modified region 123 overlap along the Y direction. In this way, in step S101, the control unit 6 may irradiate the object 11 with the laser light L so that the third modified region 123 intersects with the multiple first modified regions 121. In this case, it is possible to reliably suppress the growth of the crack 13 extending from the first modified region 121 located at the innermost side (the effective region R side) of the object 11.

[0070] Furthermore, at this time, the control unit 6 may irradiate the object 11 with the laser light L so that the third modified region 123 intersects with the first modified region 121 on the side opposite the incident surface (first surface 11a) from the center of the third modified region 123 in the Z direction. In this case, most of the area on the incident surface side of the third modified region 123 is located closer to the incident surface side than the first modified region 121. This makes it possible to reliably suppress the growth of the crack 13 extending from the first modified region 121.

[0071] Furthermore, at this time, the control unit 6 may irradiate the object 11 with the laser light L so that no cracks are included in the region of the third modified region 123 on the opposite side of the incident surface (first surface 11a) from the intersection position with the first modified region 121 in the Z direction. In this case, it is possible to more reliably suppress the progression of the crack 13 extending from the first modified region 121. Note that, for example, the innermost first modified region 121 (closer to the effective region R) among the multiple first modified regions 121 may be in contact (overlap) with the third modified region 123.

[0072] Although various modifications have been described above, these modifications and embodiments may be applied in any combination. For example, in an example in which a crack 13 a extending obliquely with respect to the Z direction is formed, the first modified region 121 and the third modified region 123 may be formed so as to intersect.

[0073] In addition, any other modifications may be applied. For example, in the above embodiment and modification, an example of processing based on the boundary B between the effective area R and the removal area E in trimming processing has been described. However, the laser processing apparatus 1 and laser processing method according to the above embodiment and modification may be applied to processing based on the boundary between an arbitrary first area in the object and a second area outside the first area. Furthermore, the object 11 to be laser processed is not limited to being bonded to another object 11R.

[0074] 1...laser processing device, 6...control unit, 7...spatial light modulator, 11...object, 11a...first surface (incident surface), 11b...second surface (bottom surface), 12...modified region, 13, 13a, 13b...crack, 31...light source, 33...condensing lens (condensing portion), 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 apparatus comprising: a light source that emits laser light; a spatial light modulator that modulates the laser light emitted from the light source; a focusing unit that focuses the laser light that has passed through the spatial light modulator toward an object; and a processing control unit that performs laser processing to form a modified region in the object by irradiating the object with the laser light while moving the focused spot of the laser light relative to the object, wherein the object includes, when viewed from a Z direction that intersects with the incident surface of the laser light on the object, a first region and a second region that has a boundary with the first region and is located outside the first region, and the processing control unit performs a first processing process of irradiating the object with the laser light from an end of the second region opposite to the boundary across the boundary, so as to form, as the modified region, a plurality of first modified regions lined up in a Y direction that intersects with the Z direction; a second processing process is performed after the first processing process, in which the object is irradiated with the laser light so as to form, as the modified regions, a plurality of second modified regions that are positioned so as to intersect with the plurality of first modified regions lined up in the Y direction at the boundary; wherein in the second processing process, the processing control unit imparts a first aberration to the laser light by controlling the spatial light modulator to modulate 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, becomes elongated in the Z direction; 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 elongated in the Z direction than the focused spot of the laser light to which the reference aberration has been imparted, when aberration generated 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.

2. The laser processing device according to claim 1, wherein in the second processing step, the processing control unit irradiates the object with the laser light so that the third modified region intersects with a plurality of the first modified regions.

3. The laser processing device described in claim 2, wherein in the second processing step, the processing control unit irradiates the object with the laser light so that the third modified region intersects with multiple first modified regions on the side opposite the incident surface from the center of the third modified region in the Z direction.

4. A laser processing device as described in claim 2 or 3, wherein in the second processing step, the processing control unit irradiates the laser light onto the object so that no cracks are included in the area opposite the incident surface from the intersection position of the third modified area with the first modified area in the Z direction.

5. A laser processing device as described in any one of claims 1 to 4, 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 processing 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 along the inclination direction of the inclined portion at least on the incident surface side of the center of the focused spot.

6. A processing step of forming a modified region in an object by irradiating the object with laser light while moving a focused spot of the laser light relative to the object, wherein the object includes a first region and a second region having a boundary with the first region and positioned outside the first region when viewed from a Z direction intersecting a plane of incidence of the laser light on the object, the processing step including: a first processing step of irradiating the object with the laser light so as to form, as the modified region, a plurality of first modified regions aligned in a Y direction intersecting the Z direction from an end of the second region opposite the boundary across the boundary; and a second processing step of irradiating the object with the laser light after the first processing step so as to form, at the boundary, a plurality of second modified regions positioned so as to intersect with the plurality of first modified regions aligned in the Y direction. a laser processing method in which, in the second processing step, a first aberration is imparted 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, becomes elongated in the Z direction, the third modified region being 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 elongated 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 focusing the laser light on the object is defined as a reference aberration.

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