Laser processing device and laser processing method

Abstract

This laser processing device comprises: a light source that emits a laser beam; a spatial light modulator for modulating the laser beam emitted from the light source; a light condensing unit that condenses the laser beam, which has passed through the spatial light modulator, toward an object; and a processing control unit that performs laser processing for forming a modified region in the object by irradiating the object with the laser beam while causing the condensed spot of the laser beam to move relative to the object. The object, as viewed from a Z direction intersecting the surface of the object on which the laser beam is incident, includes a first region and a second region that has a boundary with the first region and is located to the outside of 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] The laser processing apparatus according to the present disclosure includes: [1] "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 a focused spot of the laser light relative to the object, wherein the object includes, when viewed from a Z direction intersecting an incident plane 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 so as to form a first modified region that is elongated in the Z direction at the boundary between the first region and the second region as the modified region; and and after the first processing, a second processing process is performed in which the laser light is irradiated onto the object so as to form, as the modified regions, a plurality of second modified regions aligned in a Y direction intersecting the Z direction between the boundary and an end of the second region opposite the boundary. In the first 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, when the aberration occurring 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 defined as a reference aberration, 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 is formed. In the second processing process, the processing control unit controls the Z direction position of the second modified region to be included in the Z direction range in which the first modified region exists.

[0007] The laser processing method according to the present disclosure [7] includes a processing step of forming a modified region in an 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 a first modified region elongated in the Z direction at the boundary between the first region and the second region as the modified region; and a second processing step of irradiating the object with the laser light after the first processing step, the second region opposite 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 aligned in a Y direction intersecting the Z direction between the end of the object on the side and the boundary, wherein, in the first processing step, a first aberration is imparted to the laser light so that, when an aberration occurring 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, 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 is formed, and in the second processing step, the position of the second modified region in the Z direction is set to be included in the range in the Z direction in which the first modified region exists.

[0008] This apparatus and method laser-machines 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 the laser light incident surface. Specifically, laser light is first applied to the boundary between the first and second regions to form a first modified region elongated in the Z direction. Laser light is then applied to the second region between the boundary and an end of the second region opposite the boundary to form a plurality of second modified regions aligned in the Y direction intersecting the Z direction.

[0009] When forming the first modified region, if the aberration occurring 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 the reference aberration, the laser light is modulated to impart the first aberration to the laser light so that a focused spot longer in the Z direction than the focused spot of the laser light to which the reference aberration is imparted is formed. This makes it possible to elongate the first modified region in the optical axis direction (Z direction) of the laser light. The elongated first modified region formed in this manner has the property that cracks extending from the first 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 first modified region, propagation of cracks from the first modified region to the bottom surface (the surface opposite the incident surface) of the object is suppressed.

[0010] Furthermore, the second modified region is formed so that its position in the Z direction is within the range in which the first modified region exists. Therefore, even if a crack extending from the second modified region propagates in a direction intersecting the Z direction, once the crack reaches the first modified region, the first modified region prevents further propagation. In other words, the crack is prevented from propagating from the second modified region to the bottom surface of the object. As described above, this device and method make it possible to suppress the propagation of a crack extending from the modified region.

[0011] The laser processing apparatus according to the present disclosure may be [2] "the laser processing apparatus described in [1] above, wherein the processing control unit performs a third processing process of irradiating the object with the laser light after the first processing process and before the second processing process so as to form a third modified region as the modified region at the boundary closer to the incident surface than the first modified region." In this case, before forming the second modified regions aligned in the Y direction, the third modified region is formed closer to the incident surface than the first modified region. Therefore, stress within the object when the second modified region is formed can reliably generate a crack that extends from the third modified region to the incident surface.

[0012] The laser processing apparatus according to the present disclosure may be [3] "the laser processing apparatus described in [1] above, wherein the processing control unit, after the first processing process and the second processing process, performs a third processing process of irradiating the object with the laser light so as to form a third modified region as the modified region at the boundary closer to the incident surface than the first modified region." In this case, second modified regions aligned in the Y direction are formed before the third modified region is formed closer to the incident surface than the first modified region. This makes it possible to form the second modified region without being affected by the third modified region located closer to the incident surface.

[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 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 in the inclination direction of the inclined portion at least on the incident surface side from 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.

[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 object has a bonding surface opposite to the incident surface to be bonded to another structure, and in the first processing step, the processing control unit irradiates the object with the laser light so that the first modified region is in contact with the bonding surface." In this case, a crack extending from the second modified region is suppressed from progressing between the first modified region and the bonding surface (bottom surface).

[0015] The laser processing apparatus according to the present disclosure may be [6] "the laser processing apparatus described in [5] above, wherein in the second processing step, the processing control unit irradiates the object with the laser light so that the plurality of second modified regions contact the bonding surface." In this case, the second modified regions contacting the bonding surface and cracks extending from the second modified regions can be used to preferably remove the second regions closer to the bonding surface.

[0016] 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.

[0017] 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, FIG. 8 is a diagram for explaining aberrations that occur at the focused position of laser light. FIG. 9 is a diagram for explaining a laser processing method according to this embodiment. Specifically, FIG. 9 is a diagram showing the intensity of laser light and the focused spot when multiple aberrations are applied based on a reference aberration. FIG. 10 is a diagram for explaining the laser processing method according to the present 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. FIG. 12 is a diagram for explaining the laser processing method according to the present embodiment. FIG. 12(a) is a cross-sectional view showing a state in which laser light is focused, and FIG. 12(b) is a cross-sectional view showing a state in which a modified region has been formed. FIG. 13 is a diagram for explaining the laser processing method according to the present embodiment. FIG. 14 is a diagram for explaining a laser processing method according to a modified example. FIG. 14(a) is a schematic cross-sectional view showing a state in which a first modified region has been formed, and FIG. 14(b) is a schematic cross-sectional view showing a state in which a second modified region has also been formed. FIG. 15 is a diagram for explaining the laser processing method according to the modified example. Specifically, FIG. 15 shows a state in which a third modified region has also been formed. FIG. 16 is a diagram for explaining the laser processing method according to another modified example. Specifically, (a) and (b) of FIG. 16 are schematic cross-sectional views showing the boundary between the effective area and the removal area in the target object.Fig. 17 is a diagram for explaining a laser processing method according to another modified example. Specifically, Fig. 17 is a diagram showing a focused spot of laser light in the YZ plane. Fig. 18 is a diagram for explaining a laser processing method according to another modified example. Specifically, (a) and (b) of Fig. 18 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. 19 is a diagram for explaining a laser processing method according to yet another modified example. Specifically, Fig. 19 is a schematic cross-sectional view showing a state in which a first modified region, a second modified region, and a third modified region have been formed.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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).

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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°.

[0033] 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.

[0034] 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.

[0035] 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 object 11 with the laser light L while moving the focused spot C of the laser light L relative to the object 11 (processing step). That is, as shown in FIG. 6, first, laser processing is performed at the boundary B (step S101: first processing step, first processing process).

[0036] More specifically, in step S101, first, 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 at the boundary B 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 irradiation of 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.

[0037] 7A, the control unit 6 controls the spatial light modulator 7 to modulate the laser light L so that a focused spot C1 elongated in the Z direction is formed as the focused spot C, thereby imparting a first aberration to the laser light L. As a result, as shown in FIG. 7B, a first modified region 121 elongated in the Z direction can be formed at the boundary B as the modified region 12. That is, in step S101, the control unit 6 executes a process (first processing process) of irradiating the object 11 with the laser light L so as to form a first modified region 121 elongated in the Z direction as the modified region 12 at the boundary B between the effective region R and the removal region E.

[0038] The first aberration imparted to the laser beam in step S101 will be described. FIG. 8 is a diagram for explaining the aberration 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., aberration may occur naturally. The aberration may 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.

[0039] 8, 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.

[0040] 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. 9 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. 9 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.

[0041] 9 , 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.

[0042] As described above, in step S101, 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. 7B , a first modified region 121 that is elongated in the Z direction is formed at the boundary B as the modified region 12.

[0043] It has been confirmed that the elongated first modified region 121 formed in this manner has the property that cracks extending from the first modified region 121 are less likely to propagate in the Z direction (i.e., the cracks become shorter) compared to modified regions 12 formed by laser light L to which, for example, the reference aberration H10 or the second aberration H13 has been imparted. As a result, the first modified region 121 can prevent the propagation of a crack 13 that has extended from another modified region 12 and reached the first modified region 121 from passing through the first modified region 121. In other words, by forming the first modified region 121 in advance in a region where the propagation of a crack 13 extending along the (111) plane is predicted as described above, it is possible to suppress the propagation of the crack 13 so that it does not reach the second surface 11b.

[0044] 10 , laser processing is continued at boundary B (step S102: third processing). More specifically, first, 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 at 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. 10 (a), 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 of the focused spot C1 in the Z direction when the first modified region 121 was formed in step S101.

[0045] 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 is set to a focused spot C0 that is shorter in the Z direction than the focused spot C1 used when the first modified region 121 was formed in step S101. As a result, third modified regions 123 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.

[0046] This step S102 is performed multiple times while sequentially changing the position of the focused spot C0 in the Z direction from the second surface 11b side toward the first surface 11a side. As a result, multiple third modified regions 123 aligned along the Z direction in the YZ plane are formed as modified regions 12. The first modified region 121 is formed closer to the second surface 11b than the third modified region 123 closest to the second surface 11b.

[0047] As a result, the first modified region 121, the third modified region 123, and a crack 13 extending across the first modified region 121 and the plurality of third modified regions 123 are formed at the boundary B. The crack 13 may reach the first surface 11a. As described above, in step S102, the control unit 6 performs a process (third processing process) of irradiating the object 11 with laser light L so as to form the third modified region 123 as the modified region 12 at the boundary B closer to the first surface 11a than the first modified region 121.

[0048] 11 to 13, horizontal processing is performed between the boundary B and the end of the removal region E on the opposite side from the boundary B (step S103: second processing step, second processing treatment). More specifically, in step S103, as shown in FIG. 11, 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 a line A extending in a circular shape concentric with the boundary B outside the boundary B and at a predetermined depth (Z-direction position) from the first surface 11a of the object 11. At this time, as shown in FIG. 12(a), the Z-direction position of the focused spot C is set to be included in the Z-direction range in which the first modified region 121 formed in step S101 exists.

[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 object 11. At this time, the focused spot C is set to a focused spot C2 that is shorter in the Z direction than the focused spot C1 used when the first modified region 121 was formed in step S101. As a result, second modified regions 122 arranged in a circle are formed as the modified region 12 on the circular line A when viewed from the Z direction.

[0050] This step S103 is performed multiple times while sequentially changing the Y-direction position of the focused spot C2, 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 on each of the multiple lines A. As a result, as shown in FIG. 13 , multiple second modified areas 122 aligned in the Y direction in the YZ plane are formed as modified areas 12. That is, here, multiple second modified areas 122 are formed two-dimensionally in a virtual plane (planned slicing surface) along the first surface 11a (XY plane). As a result, it is possible to remove the removal area E from the effective area R along the first modified area 121, multiple third modified areas 123, and cracks 13 extending therefrom aligned along the boundary B, and the multiple second modified areas 122 and cracks 13 extending therefrom extending in the horizontal direction.

[0051] 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.

[0052] As described above, in step S103, 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 aligned in the Y direction intersecting the Z direction between the boundary B and the end of the removal region E on the opposite side from the boundary B. The control unit 6 also adjusts the Z-direction position of the second modified region 122 to be included in the Z-direction range in which the first modified region 121 exists.

[0053] In this way, in step S103, a plurality of second modified regions 122 aligned along the Y direction (i.e., the (100) plane) are formed in the object 11, which is a <100> wafer. Therefore, there is a risk that the cracks 13 extending from the second modified regions 122 will propagate along the (111) plane. In contrast, in this embodiment, as described above, in step S101, the first modified regions 121 are formed in advance in the regions where the propagation of the cracks 13 extending along the (111) plane is predicted. Therefore, it is possible to inhibit the propagation of the cracks 13 extending from the second modified regions 122 in the first modified regions 121 and prevent them from reaching the second surface 11b.

[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 first processing process for forming the first modified region 121, the second processing process for forming the second modified region 122, and the third processing process for forming the third modified region 123.

[0055] First processing: Laser light L wavelength 1099 nm, frequency 60 kHz, pulse width 45 nsec, output 1.5 W, relative movement speed of focused spot C 300 mm / sec, aberration correction to remove spherical aberration of Si. Aberration is given so that a focused area longer than the focused area with the reference aberration is formed.

[0056] Second processing: wavelength of laser light L is 1099 nm, frequency is 60 kHz, pulse width is 45 nsec, output is 0.14 W, speed of relative movement of focused spot C is 300 mm / sec, spacing of line A in the Y direction is 5 μm, aberration correction is performed to remove spherical aberration of Si.

[0057] Third processing: wavelength of laser light L is 1099 nm, frequency is 120 kHz, pulse width is 700 nsec, output is 3 W, speed of relative movement of focused spot C is 800 mm / sec, aberration correction is performed to remove spherical aberration of Si.

[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 includes, when viewed from the Z direction intersecting the first surface 11a, which is the laser light incident surface, 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 at the boundary B between the effective region R and the removal region E to form a first modified region 121 that is elongated in the Z direction. Next, laser light L is irradiated between the end of the removal region E opposite to the boundary B and the boundary B to form a plurality of second modified regions 122 lined up in the Y direction intersecting the Z direction.

[0059] When forming the first modified region 121, if the aberrations occurring in the optical axis direction (Z direction) of the laser light L at the focusing position due to focusing the laser light L on the object 11 are defined as reference aberrations H and H10, the laser light L is modulated to impart the first aberrations H11 and H12 to the laser light L so that focused spots C11 and C12 that are elongated in the Z direction are formed relative to the focused spots C and C10 of the laser light L to which the reference aberrations H and H10 have been imparted. This makes it possible to elongate the first modified region 121 in the optical axis direction (Z direction) of the laser light L. The elongated first modified region 121 formed in this manner has the property that cracks extending from the first modified region 121 are less likely to propagate in the Z direction (i.e., the cracks are shorter). As a result, cracks are less likely to extend from the first modified region 121, and the cracks are prevented from progressing from the first modified region 121 to the bottom surface of the object 11 (the second surface 11b opposite the incident surface).

[0060] Furthermore, the second modified region 122 is formed so that its position in the Z direction is within the range in which the first modified region 121 exists. Therefore, even if a crack 13 extending from the second modified region 122 propagates along a direction intersecting the Z direction (for example, along the (111) plane), once the crack reaches the first modified region 121, further propagation is prevented by the first modified region 121. In other words, the propagation of the crack 13 from the second modified region 122 to the bottom surface of the object 11 is suppressed. As described above, the propagation of the crack 13 extending from the modified region 122 is suppressed.

[0061] Furthermore, in the laser processing apparatus 1 and laser processing method according to this embodiment, the control unit 6 performs a third processing process (step S102) after the first processing process (step S101) and before the second processing process (step S103), in which the control unit 6 irradiates the object 11 with laser light L so as to form a third modified region 123 as a modified region 12 at the boundary B closer to the first surface 11a than the first modified region 121. In this way, before forming the second modified regions 122 aligned in the Y direction, the third modified region 123 is formed closer to the first surface 11a than the first modified region 121. Therefore, stress within the object 11 when the second modified region 122 is formed can reliably generate a crack 13 that extends from the third modified region 123 to the first surface 11a.

[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] For example, in the above embodiment, an example has been described in which, after forming the first modified region 121 in step S101, a plurality of third modified regions 123 aligned in the Z direction are formed in the first modified region 121 in step S102, and then a plurality of second modified regions 122 aligned in the Y direction are formed in step S103. However, after forming the first modified region 121 in step S101 as shown in Figure 14(a), step S103 may be performed to form a plurality of second modified regions 122 aligned in the Y direction as shown in Figure 14(b), and then a plurality of third modified regions 123 aligned in the Z direction may be formed in the first modified region 121 in step S102 as shown in Figure 15.

[0064] That is, after the first processing process (step S101) and the second processing process (step S103), the control unit 6 may perform a third processing process (step S102) in which the object 11 is irradiated with laser light L so as to form a third modified region 123 as a modified region 12 at the boundary B closer to the first surface 11a than the first modified region 121. In this case, the second modified regions 122 aligned in the Y direction are formed before the third modified region 123 is formed closer to the incident surface (first surface 11a) than the first modified region 121. This makes it possible to form the second modified region 122 without being affected by the third modified region 123 located closer to the incident surface.

[0065] 16 is a diagram illustrating a laser processing method according to another modification. As shown in FIG. 16, 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. 16(a), a portion of the boundary B on the second surface 11b side is the inclined portion B1. In the example of FIG. 16(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 necessary to form a crack 13 extending obliquely (with respect to the Z direction) from the modified region 12 along the inclined portion B1.

[0066] Therefore, as shown in Figure 17, when forming a modified region 12 in the inclined portion B1 in the first formation process (step S101) and the third formation process (S103), 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.

[0067] 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.

[0068] 18(a), by controlling the shape of the focused spot C as described above, it is possible to form the first modified region 121 in step S101 and to form a crack 13a extending obliquely along the inclined portion B1 between the first modified region 121 and the third modified region 123 closest to the first modified region 121. In the example of FIG. 18(a), in step S103, the third modified region 123 aligned in the Z direction is formed without tilting the focused spot C, thereby forming a crack 13b extending from the third modified region 123 in the Z direction.

[0069] 18(b), in step S103, the focused spot C is tilted in the same manner as in step S101, and a first modified region 121 and a plurality of third modified regions 123 are formed along the entire boundary B tilted with respect to the Z direction, thereby forming a crack 13a extending in a direction tilted with respect to the Z direction along the entire boundary B. In this way, by forming the crack 13a extending obliquely with respect to the Z direction from the modified region 12 along the tilted boundary B, it is possible to reduce the impact on the 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).

[0070] 19 , the first modified region 121 may be in contact with the second surface 11b. More specifically, as described above, the object 11 has a second surface 11b, which is a bonding surface to which another object 11R (structure) is bonded via a device layer 110, 110R, on the opposite side of the first surface 11a, which is the incident surface of the laser light L. Then, in the first processing treatment (step S101), the control unit 6 may irradiate the object 11 with the laser light L so that the first modified region 121 is in contact with the second surface 11b. In this case, since the first modified region 121, which has the function of preventing crack propagation, is in contact with the second surface 11b of the object 11, when second modified regions 122 aligned in the Y direction are formed, the crack 13 extending from the second modified region 122 is prevented from propagating between the first modified region 121 and the second surface 11b.

[0071] Furthermore, when the first modified region 121 is formed so as to contact the second surface 11b, the second modified region 122 may also be formed so as to contact the second surface 11b. More specifically, in the second processing treatment (step S102), the control unit 6 may irradiate the object 11 with the laser light L so that the multiple second modified regions 122 contact the second surface 11b. In this case, by utilizing the second modified regions 122 contacting the second surface 11b and the cracks 13 extending from the second modified regions 122, it is possible to preferably remove the removal region E closer to the second surface 11b.

[0072] Although various modifications have been described above, these modifications and embodiments may be applied in any combination. For example, in the example in which the crack 13a extending obliquely with respect to the Z direction is formed, the first modified region 121 and the second modified region 122 may be formed so as to be in contact with the second surface 11b, or the order of the second processing step (step S102) and the third processing step (step S103) may be reversed.

[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 (bonding 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 plane 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 that irradiates the object with the laser light so as to form a first modified region that is elongated in the Z direction at the boundary between the first region and the second region as the modified region; a second processing process is performed after the first processing process, in which the laser light is irradiated onto the object so as to form, as the modified regions, a plurality of second modified regions lined up in a Y direction intersecting the Z direction between the boundary and an end of the second region opposite the boundary; wherein, in the first 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, when aberration occurring 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 defined as a reference aberration, a focused spot is formed that is longer in the Z direction than the focused spot of the laser light to which the reference aberration has been imparted; and, in the second processing process, the processing control unit adjusts the Z direction position of the second modified region to be included in the Z direction range in which the first modified region exists.

2. The laser processing device of claim 1, wherein the processing control unit performs a third processing process, after the first processing process and before the second processing process, in which the laser light is irradiated onto the object so as to form a third modified region at the boundary closer to the incident surface than the first modified region as the modified region.

3. The laser processing device of claim 1, wherein the processing control unit performs a third processing process in which, after the first processing process and the second processing process, the laser light is irradiated onto the object so as to form a third modified region at the boundary closer to the incident surface than the first modified region.

4. A laser processing device according to any one of claims 1 to 3, 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 in the inclination direction of the inclined portion at least on the incident surface side of the center of the focused spot.

5. A laser processing device according to any one of claims 1 to 4, wherein the object has a bonding surface on the opposite side to the incident surface to be bonded to another structure, and in the first processing step, the processing control unit irradiates the object with the laser light so that the first modified region is in contact with the bonding surface.

6. The laser processing device according to claim 5, wherein in the second processing step, the processing control unit irradiates the object with the laser light so that the second modified regions contact the bonding surface.

7. 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 a first modified region elongated in the Z direction at the boundary between the first region and the second region as the modified region; and a second processing step of irradiating the object with the laser light after the first processing step so as to form a plurality of second modified regions lined up in a Y direction intersecting the Z direction as the modified region between the boundary and an end of the second region opposite the boundary. a first processing step of imparting a first aberration to the laser light so that, when the aberration occurring in the optical axis direction of the laser light at the focusing position due to focusing the laser light on the object is taken as a reference aberration, a focusing spot that is longer in the Z direction than the focusing spot of the laser light to which the reference aberration has been imparted is formed; and a second processing step of making the Z direction position of the second modified region fall within the Z direction range in which the first modified region exists.

Images