Laser processing device and laser processing method

Abstract

To improve laser processing precision in a laser processing device that forms multiple rows of modification regions for division in a semiconductor substrate.SOLUTION: A laser processing device comprises a laser irradiation unit 3 and a control part 8. The control part 8 is configured to execute: first control for controlling the laser irradiation unit 3 so that modification regions for division are formed along each line extending in an X direction, and a crack 14 extends in a direction of a surface 21a from the modification regions 12a, b; second control for controlling the laser irradiation unit 3 so that after the first control, the modification regions for division are formed along each of a plurality of lines in a Y direction, and the crack 14 extends in the direction of the surface 21a from the modification regions; and third control for controlling the laser irradiation unit 3 so that before the second control, the crack 14 extending from a plurality of modification regions for warpage suppression reaches a rear face 21b and is formed discontinuously to the crack 14 extending from the modification regions for division.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] One aspect of the present invention relates to a laser processing apparatus and a laser processing method. [Background technology]

[0002] A laser processing device is known that cuts a wafer, which includes a semiconductor substrate and a functional element layer formed on one surface of the semiconductor substrate, along each of a plurality of lines by irradiating the wafer from the other surface side of the semiconductor substrate with laser light to form a plurality of rows of modified regions for dividing (cutting) inside the semiconductor substrate along each of the plurality of lines (see, for example, Patent Document 1). With such a laser processing device, after processing to form the modified regions, the modified regions are ground, thereby making it possible to produce semiconductor chips with high flexural strength. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 376209 Summary of the Invention [Problem to be solved by the invention]

[0004] In laser processing using the above-mentioned laser processing device, modified regions for division may be formed sequentially along a plurality of lines intersecting each other. In this case, the formation of modified regions along the line (first line) to which the laser light is first irradiated may cause warping of the wafer, and the accuracy of processing the intersecting line (second line) to which the laser light is later irradiated may decrease due to the influence of the warping of the wafer. In other words, if processing of the line (second line) to which the laser light is later irradiated is performed in a warped state, it becomes difficult to ensure the accuracy of autofocusing for adjusting the focal spot of the laser light when processing the second line, and there is a risk that the modified regions may not be formed appropriately.

[0005] One aspect of the present invention has been made in consideration of the above-mentioned circumstances, and has an object to appropriately form modified regions for dividing an object and improve laser processing accuracy. [Means for solving the problem]

[0006] A laser processing apparatus according to one aspect of the present invention includes a laser irradiation unit that irradiates a laser beam onto an object using a first surface of the object, the first surface including a first surface and a second surface opposite to the first surface, as an incident surface, and a control unit, wherein the control unit performs a first control to control the laser irradiation unit while relatively moving a focused spot of the laser beam along each of a plurality of first lines extending in a first direction along the incident surface, so that a first modified region for division is formed inside the object by the irradiation of the laser beam and a crack extends from the first modified region in a second surface direction; and a second control to control a second modified region for division extending in a second direction intersecting the first direction and along the incident surface after the first control. The laser irradiation unit is configured to execute a second control in which the laser irradiation unit is controlled so that a second modified region for division is formed inside the object by irradiation with laser light and cracks extend from the second modified region in a direction toward the second surface while relatively moving the focused spot of the laser light along each of a plurality of second lines formed by the laser light irradiation, and a third control in which the laser irradiation unit is controlled before the second control in which a plurality of third modified regions for warp suppression are formed inside the object by irradiation with laser light and cracks extending from the third modified regions reach the first surface and are not continuous with the cracks extending from the first modified regions.

[0007] In the laser processing device according to one aspect of the present invention, a first modified region for division is formed along each of a plurality of first lines extending in a first direction along the incident surface by irradiation with laser light, and a crack extending from the first modified region to the second surface direction is formed. Then, a second modified region for division is formed along each of a plurality of second lines intersecting with the first direction and extending in a second direction along the incident surface by irradiation with laser light, and a crack extending from the second modified region to the second surface direction is formed. In this way, when modified regions are formed sequentially along a plurality of lines intersecting with each other, the formation of the first modified region along the line (first line) to which the laser light is first irradiated may cause warping of the object, and the effect of the warping of the object may decrease the processing accuracy of the line (second line) to which the laser light is later irradiated. Specifically, the warping of the object is caused by stress concentration on one side of the object (here, the second side, which is the direction in which the crack mainly extends) due to the formation of the first modified region and the formation of the crack extending from the first modified region to the second surface direction. Such warping of the object is particularly noticeable when the object is a microchip or when a relatively large crack is formed. If the line (second line) to be irradiated with laser light is processed later in a warped state, it becomes difficult to ensure the accuracy of autofocusing for adjusting the focal spot of the laser light when processing the second line, and there is a risk that the second modified region cannot be formed appropriately.

[0008] In this regard, in the laser processing apparatus according to one aspect of the present invention, prior to the control (second control) regarding the processing of the second line, a plurality of third modified regions for suppressing warping are formed inside the object by irradiation with laser light, and cracks extending from the third modified regions are formed so as to reach the first surface and not to be continuous with the cracks extending from the first modified region. In this manner, the third modified region is formed so that the cracks reach the first surface opposite to the second surface on which stress is concentrated by the formation of the first modified region for division, thereby alleviating the localization of stress and reducing the warping of the object. This makes it possible to appropriately form the second modified region in the processing of the second line performed after the formation of the third modified region for suppressing warping. Furthermore, the cracks extending from the third modified region are formed so as not to be continuous with the cracks extending from the first modified region, thereby appropriately suppressing the occurrence of unintended cracks in the object due to the formation of the third modified region for suppressing warping. As described above, according to the laser processing apparatus of one aspect of the present invention, it is possible to appropriately form a modified region for dividing an object while suppressing unintended cracking of the object, thereby improving the laser processing accuracy.

[0009] The control unit may control the laser irradiation unit in the third control so that the third modified region is formed at a position different from the position where the first modified region is formed in the second direction. This makes it possible to appropriately prevent cracks from the first modified region and the third modified region from continuing together, and more suitably suppresses unintended cracks in the object.

[0010] In the third control, the control unit may control the laser irradiation unit so that the third modified region is formed in a position midway in the second direction between the formation positions of two first lines adjacent in the second direction. By forming the third modified region exactly in the middle between the two first lines, the distance between the modified regions of both first lines and the third modified region can be increased, and it is possible to appropriately prevent cracks in the first modified region and cracks in the third modified region from continuing together. This makes it possible to appropriately prevent unintended cracks from occurring in the object.

[0011] The laser irradiation unit has a spatial light modulator that modulates the laser light according to a set modulation pattern, and the control unit may set the modulation pattern in the third control so that the third modified region is formed at a position different from the position at which the first modified region is formed in the second direction. In this way, the position at which the third modified region is formed is adjusted by setting the modulation pattern of the spatial light modulator, and thus the processing time can be shortened compared to the case where the position at which the modified region is formed is changed by stage movement.

[0012] The laser irradiation unit has a spatial light modulator that modulates the laser light according to a set modulation pattern, and the control unit may set the modulation pattern in at least one of the first control and the third control so that the position of the end of the crack extending from the first modified region on the first surface side is different from the position of the end of the crack extending from the third modified region on the second surface side. In this way, the position of the end of the crack extending from the modified region is adjusted by setting the modulation pattern of the spatial light modulator, so that the position of the crack end can be appropriately adjusted and unintended cracks in the target object caused by the cracks being continuous with each other can be more suitably suppressed.

[0013] In the third control, the control unit may control the laser irradiation unit so that cracks extending from the third modified region are shorter than cracks extending from the first modified region. Since the cracks extending from the third modified region for warping suppression are not cracks that are desired to contribute to division, unlike the cracks extending from the first modified region for division, shortening the cracks can more suitably prevent unintended cracks in the object from occurring due to the cracks continuing together.

[0014] In the third control, the control unit may control the laser irradiation unit so that a greater number of third modified regions than the number of first modified regions are formed in the second direction. As described above, in order to perform appropriate division, it is desirable to shorten the cracks extending from the third modified region for suppressing warping. However, if the cracks extending from the third modified region are shortened, there is a risk that the effect of suppressing warping will not be fully achieved. In this regard, by increasing the number of third modified regions in the second direction (more than the first modified regions), it is possible to suppress the occurrence of unintended cracks in the target object due to cracks extending from a large number of third modified regions while fully achieving the effect of suppressing warping.

[0015] The control unit may control the laser irradiation unit in the third control so that the third modified region is formed so that, when comparing the third modified region in the center of the object in the second direction with the third modified region in both ends, at least one of the following is satisfied: the number of the third modified regions in the second direction is greater at both ends, and the length of the cracks extending from the third modified regions is longer at both ends. Warping of the object caused by the formation of the first modified region is more pronounced at both ends in the second direction. In this regard, by making the number of the third modified regions greater or making the length of the cracks extending from the third modified regions longer at both ends of the object than at the center in the second direction, warping of the object at both ends in the second direction where warping is more pronounced can be effectively suppressed.

[0016] The control unit may control the laser irradiation unit so as to alternately perform the formation of the first modified region related to any one of the first lines in the first control and the formation of the third modified region in the third control. The warping of the object due to the formation of the first modified region gradually progresses as the formation of the first modified regions related to the multiple first lines progresses. Therefore, the influence of the processing of the first line that is processed first will affect the processing of the first line that is processed later. That is, in the processing of the first line that is processed relatively later among the multiple first lines, the first modified region will be formed in a warped state of the object, so that, for example, cracks may extend obliquely to the second surface of the object, the processing position accuracy may deteriorate, and poor adsorption may occur during processing. In this regard, the formation of the first modified region for division and the formation of the third modified region for warping suppression are alternately performed, so that the influence of the processing of the first line that was performed earlier on the processing of the first line that is performed later can be suppressed, and the first modified region for division can be appropriately formed on the object.

[0017] The control unit is further configured to execute a fourth control for controlling the laser irradiation unit so that a plurality of fourth modified regions for suppressing warping are formed inside the object by irradiation with the laser light, and cracks extending from the fourth modified regions reach the first surface and are not continuous with cracks extending from the second modified regions, and may control the laser irradiation unit so that the formation of the second modified regions relating to any of the second lines in the second control and the formation of the fourth modified regions in the fourth control are alternately performed. In this way, the formation of the second modified regions relating to the second lines and the formation of the fourth modified regions for suppressing warping are alternately performed, thereby suppressing the influence of the processing of the second lines performed earlier on the processing of the second lines performed later, and the second modified regions for dividing the object can be appropriately formed.

[0018] A laser processing method according to one aspect of the present invention is a laser processing method for irradiating a laser beam onto an object using a first surface of the object, the first surface of the object including a first surface and a second surface opposite to the first surface, as an incident surface, to perform laser processing of the object, the method including: a first step of forming a first modified region for division inside the object by irradiating the laser beam while relatively moving a focused spot of the laser beam along each of a plurality of first lines extending in a first direction along the incident surface, and forming a crack extending from the first modified region in a second surface direction; and a second step of forming a crack intersecting the first direction after the first step. and a second step of forming a second modified region for division inside the object by irradiating the laser light while relatively moving the focused spot of the laser light along each of a plurality of second lines extending in a second direction along the incident surface, and forming cracks extending from the second modified region in the second surface direction; and a third step of forming a plurality of third modified regions for suppressing warping inside the object by irradiating the laser light before the second step, and forming cracks that reach the first surface from the third modified region and are not continuous with the cracks extending from the first modified region.

[0019] In the third step, the third modified region may be formed at a position in the second direction different from the position at which the first modified region is formed.

[0020] In the third step, a third modified region may be formed in a middle position in the second direction between the positions where two first lines adjacent to each other in the second direction are formed.

[0021] In the third step, a third modified region may be formed at a position in the second direction different from the position at which the first modified region is formed, by setting a modulation pattern of a spatial light modulator that modulates the laser light.

[0022] In at least one of the first and third steps, the position of the end of the crack extending from the first modified region on the first surface side may be made different from the position of the end of the crack extending from the third modified region on the second surface side by setting a modulation pattern of a spatial light modulator that modulates laser light.

[0023] In the third step, the third modified region may be formed so that a crack extending from the third modified region is shorter than a crack extending from the first modified region.

[0024] In the third step, the number of third modified regions formed in the second direction may be greater than the number of the first modified regions.

[0025] In the third step, the third modified region may be formed so that, when comparing the third modified region in the center of the object in the second direction with the third modified regions at both ends, at least one of the following is satisfied: the number of third modified regions in the second direction is greater at the ends, and / or the length of cracks extending from the third modified region is longer at the ends.

[0026] The formation of the first modified region on any one of the first lines in the first step and the formation of the third modified region in the third step may be carried out alternately.

[0027] The above-mentioned laser processing method further includes a fourth step of forming a plurality of fourth modified regions for suppressing warping inside the object by irradiating laser light, and forming cracks from the fourth modified regions that reach the first surface and are not continuous with the cracks extending from the second modified regions, and the formation of the second modified regions related to any of the second lines in the second step and the formation of the fourth modified regions in the fourth step may be performed alternately. Effect of the Invention

[0028] According to one aspect of the present invention, it is possible to appropriately form modified regions for dividing an object, thereby improving the laser processing accuracy. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a configuration diagram of an inspection device according to an embodiment. [Diagram 2] FIG. 2 is a plan view of a wafer according to an embodiment. [Diagram 3] 3 is a cross-sectional view of a portion of the wafer shown in FIG. 2. [Figure 4]FIG. 2 is a configuration diagram of a laser irradiation unit shown in FIG. [Diagram 5] FIG. 5 is a diagram showing the 4f lens unit shown in FIG. 4. [Figure 6] FIG. 5 is a diagram illustrating the spatial light modulator shown in FIG. [Figure 7] FIG. 2 is a configuration diagram of an inspection imaging unit shown in FIG. [Figure 8] FIG. 2 is a configuration diagram of an alignment correction imaging unit shown in FIG. [Figure 9] 1A to 1C are diagrams for explaining the principle of wafer warpage. [Figure 10] FIG. 13 is a diagram showing warpage in the CH2 processing direction after CH1 processing. [Figure 11] FIG. 13 is a diagram for explaining AF (autofocus) tracking failure during CH2 processing. [Figure 12] 11A to 11C are diagrams illustrating the formation of modified regions for suppressing warpage. [Figure 13] 11A to 11C are diagrams illustrating the formation of a modified region for suppressing warpage near the center position of the chip. [Figure 14] 11A to 11C are diagrams illustrating the formation of modified regions for suppressing warpage by multi-point branching processing. [Figure 15] 1A to 1C are diagrams illustrating a processing method for selectively suppressing warpage in the outer peripheral portion of a wafer. [Figure 16] FIG. 13 is a diagram showing warpage in the CH2 processing direction after CH1 processing, depending on the form of the modified region for suppressing warpage. [Figure 17] 11A and 11B are diagrams for explaining a shift in processing position due to the modulation pattern setting of a spatial light modulator. [Figure 18] 1A to 1C are diagrams illustrating the formation of oblique cracks by setting a modulation pattern of a spatial light modulator. [Figure 19] FIG. 13 is a diagram illustrating deterioration of machining stability during the latter half of machining in CH1. [Figure 20] 11A to 11C are diagrams illustrating a processing method for alternately forming modified regions for division and modified regions for suppressing warpage. [Figure 21]FIG. 13 is a diagram for explaining the function and effect of the present embodiment, showing warpage in the CH2 processing direction after CH1 processing. [Figure 22] 11A and 11B are diagrams for explaining the effects of the present embodiment and are diagrams showing warpage of a wafer after CH2 processing. [Figure 23] FIG. 13 is a diagram showing warpage in the CH1 processing direction after CH1 processing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0031] [Inspection equipment configuration] 1, the laser processing apparatus 1 includes a stage 2, a laser irradiation unit 3, a plurality of imaging units 4, 5, and 6, a drive unit 9, a control unit 8, and a display 150 (display unit). The laser processing apparatus 1 is an apparatus that forms a modified region 12 in an object 11 by irradiating the object 11 with laser light L.

[0032] The stage 2 supports the object 11, for example, by adsorbing a film attached to the object 11. The stage 2 is movable along both the X direction and the Y direction, and is rotatable about an axis parallel to the Z direction. The X direction and the Y direction are a first horizontal direction and a second horizontal direction that are perpendicular to each other, and the Z direction is a vertical direction.

[0033] The laser irradiation unit 3 focuses 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 by the stage 2, the laser light L is particularly absorbed in a portion corresponding to the focused spot C of the laser light L, and a modified region 12 is formed inside the object 11.

[0034] The modified region 12 is a region that differs from the surrounding non-modified region in terms of density, refractive index, mechanical strength, and other physical properties. Examples of the modified region 12 include a melting treatment region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 12 has a property that cracks tend to extend from the modified region 12 to the incident side of the laser light L and to the opposite side. Such a property of the modified region 12 is utilized for cutting the target object 11.

[0035] 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 in a row along the X direction. One modified spot 12s is formed by irradiating one pulse of laser light L. One 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.

[0036] The imaging unit 4 is configured to be able to capture images of the modified region 12 formed in the target object 11 and the tip of a crack extending from the modified region 12. Although the imaging unit 4 is not an essential component, the present embodiment will be described assuming that the laser processing apparatus 1 includes the imaging unit 4.

[0037] Under the control of the control unit 8, the imaging units 5 and 6 capture an image of the object 11 supported on the stage 2 by light passing through the object 11. The images captured by the imaging units 5 and 6 are used, for example, to align the irradiation position of the laser light L. Note that the imaging units 5 and 6 are not essential components, but the present embodiment will be described assuming that the laser processing apparatus 1 includes the imaging units 5 and 6.

[0038] The drive unit 9 supports the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6. The drive unit 9 moves the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6 along the Z direction.

[0039] The control unit 8 controls the operations of the stage 2, the laser irradiation unit 3, the multiple imaging units 4, 5, and 6, and the drive unit 9. The control unit 8 is configured as a computer device including a processor, a memory, a storage, a communication device, etc. In the control unit 8, the processor executes software (programs) loaded into the memory, etc., and controls the reading and writing of data in the memory and storage, as well as communication by the communication device.

[0040] The display 150 functions as an input unit that accepts information input from the user, and as a display unit that displays information to the user.

[0041] [Object composition] The object 11 of this embodiment is a wafer 20, as shown in FIG. 2 and FIG. 3. The wafer 20 includes a semiconductor substrate 21 and a functional element layer 22. In this embodiment, the wafer 20 is described as having the functional element layer 22, but the wafer 20 may or may not have the functional element layer 22, and may be a bare wafer. The semiconductor substrate 21 has a front surface 21a and a back surface 21b. The semiconductor substrate 21 is, for example, a silicon substrate. The functional element layer 22 is formed on the front surface 21a of the semiconductor substrate 21. The functional element layer 22 includes a plurality of functional elements 22a arranged two-dimensionally along the front surface 21a. The functional elements 22a are, for example, light receiving elements such as photodiodes, light emitting elements such as laser diodes, circuit elements such as memories, etc. The functional elements 22a may be three-dimensionally configured by stacking a plurality of layers. The semiconductor substrate 21 is provided with a notch 21c indicating a crystal orientation, but an orientation flat may be provided instead of the notch 21c.

[0042] The wafer 20 is cut into functional elements 22a along each of the lines 15. The lines 15 pass between the functional elements 22a when viewed from the thickness direction of the wafer 20. More specifically, the lines 15 pass through the center (the center in the width direction) of the street region 23 when viewed from the thickness direction of the wafer 20. The street region 23 extends in the functional element layer 22 so as to pass between the adjacent functional elements 22a. In this embodiment, the functional elements 22a are arranged in a matrix shape along the surface 21a, and the lines 15 are set in a lattice shape. That is, the wafer 20 has a plurality of lines 15 (first lines) extending in the X direction and a plurality of lines 15 (second lines) extending in the Y direction. The lines 15 are virtual lines, but may be lines that are actually drawn.

[0043] [Laser irradiation unit configuration] As shown in Fig. 4, the laser irradiation unit 3 includes a light source 31 (laser irradiation section), a spatial light modulator 7, a condenser lens 33, and a 4f lens unit 34. The light source 31 outputs laser light L, for example, by a pulse oscillation method. The spatial light modulator 7 modulates the laser light L output from the light source 31. The spatial light modulator 7 is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator). The condenser lens 33 condenses the laser light L modulated by the spatial light modulator 7. The condenser lens 33 may be a correction ring lens.

[0044] In this embodiment, the laser irradiation unit 3 irradiates the wafer 20 with laser light L from the back surface 21b side of the semiconductor substrate 21 along each of the multiple lines 15, thereby forming modified regions 12 (e.g., two rows of modified regions 12a, 12b) inside the semiconductor substrate 21 along each of the multiple lines 15. The modified region 12a is the modified region closest to the front surface 21a among the two rows of modified regions 12a, 12b. The modified region 12b is the modified region closest to the modified region 12a among the two rows of modified regions 12a, 12b, and is the modified region closest to the back surface 21b.

[0045] The two rows of modified regions 12a, 12b are adjacent to each other in the thickness direction (Z direction) of the wafer 20. The two rows of modified regions 12a, 12b are formed by moving the two focused spots C1, C2 along the line 15 relative to the semiconductor substrate 21. The laser light L is modulated by the spatial light modulator 7 so that the focused spot C2 is located on the rear side of the focused spot C1 in the traveling direction and on the incident side of the laser light L. The modified regions may be formed by a single focus or multiple focuses, and one row of modified regions may be formed (one pass) or multiple rows of modified regions may be formed (multiple passes) on one planned cutting line.

[0046] The formation of the two rows of modified regions 12a, 12b and the cracks 14 is performed in the following case: That is, in a later process, for example, by grinding the back surface 21b of the semiconductor substrate 21 to thin the semiconductor substrate 21 and expose the cracks 14 on the back surface 21b, and then cutting the wafer 20 into a plurality of semiconductor devices along each of the plurality of lines 15.

[0047] 5, the 4f lens unit 34 has a pair of lenses 34A, 34B arranged on the optical path of the laser light L traveling from the spatial light modulator 7 to the condenser lens 33. The pair of lenses 34A, 34B configure a double-telecentric optical system in which the modulation surface 7a of the spatial light modulator 7 and the entrance pupil surface (pupil surface) 33a of the condenser lens 33 are in an imaging relationship. As a result, an image of the laser light L on the modulation surface 7a of the spatial light modulator 7 (an image of the laser light L modulated in the spatial light modulator 7) is transferred (imaged) on the entrance pupil surface 33a of the condenser lens 33. Note that Fs in the figure indicates a Fourier plane.

[0048] 6, the spatial light modulator 7 is a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator). The spatial light modulator 7 is configured by laminating a drive circuit layer 72, a pixel electrode layer 73, a reflective film 74, an alignment film 75, a liquid crystal layer 76, an alignment film 77, a transparent conductive film 78, and a transparent substrate 79 in this order on a semiconductor substrate 71.

[0049] The semiconductor substrate 71 is, for example, a silicon substrate. The drive circuit layer 72 configures an active matrix circuit on the semiconductor substrate 71. The pixel electrode layer 73 includes a plurality of pixel electrodes 73a arranged in a matrix along the surface of the semiconductor substrate 71. Each pixel electrode 73a is formed of, for example, a metal material such as aluminum. A voltage is applied to each pixel electrode 73a by the drive circuit layer 72.

[0050] The reflective film 74 is, for example, a dielectric multilayer film. The alignment film 75 is provided on the surface of the liquid crystal layer 76 on the reflective film 74 side, and the alignment film 77 is provided on the surface of the liquid crystal layer 76 opposite the reflective film 74. Each alignment film 75, 77 is formed of, for example, a polymer material such as polyimide, and the contact surface of each alignment film 75, 77 with the liquid crystal layer 76 is subjected to, for example, rubbing treatment. The alignment films 75, 77 align the liquid crystal molecules 76a contained in the liquid crystal layer 76 in a fixed direction.

[0051] The transparent conductive film 78 is provided on the surface of the transparent substrate 79 on the alignment film 77 side, and faces the pixel electrode layer 73 with the liquid crystal layer 76 and the like sandwiched therebetween. The transparent substrate 79 is, for example, a glass substrate. The transparent conductive film 78 is formed of, for example, a light-transmitting and conductive material such as ITO. The transparent substrate 79 and the transparent conductive film 78 transmit the laser light L.

[0052] In the spatial light modulator 7 configured as above, when a signal indicating a modulation pattern is input from the control unit 8 to the drive circuit layer 72, a voltage corresponding to the signal is applied to each pixel electrode 73a, and an electric field is formed between each pixel electrode 73a and the transparent conductive film 78. When the electric field is formed, the arrangement direction of the liquid crystal molecules 76a in the liquid crystal layer 76 changes for each region corresponding to each pixel electrode 73a, and the refractive index changes for each region corresponding to each pixel electrode 73a. This state is a state in which the modulation pattern is displayed on the liquid crystal layer 76. The modulation pattern is for modulating the laser light L.

[0053] That is, when a laser light L enters the liquid crystal layer 76 from the outside through the transparent substrate 79 and the transparent conductive film 78 while a modulation pattern is displayed on the liquid crystal layer 76, is reflected by the reflective film 74, and is emitted from the liquid crystal layer 76 to the outside through the transparent conductive film 78 and the transparent substrate 79, the laser light L is modulated according to the modulation pattern displayed on the liquid crystal layer 76. In this way, the spatial light modulator 7 allows modulation of the laser light L (e.g., modulation of the intensity, amplitude, phase, polarization, etc. of the laser light L) by appropriately setting the modulation pattern to be displayed on the liquid crystal layer 76. The modulation surface 7a shown in FIG. 5 is, for example, the liquid crystal layer 76.

[0054] 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 the 4f lens unit 34, and is focused by the condenser lens 33 inside the object 11, thereby forming the 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 8 controls the stage 2 to move the focused spot C relative to the wafer 20, thereby forming the modified region 12 and the crack along the moving direction of the focused spot C.

[0055] As shown in Fig. 4, the laser irradiation unit 3 further includes an AF (autofocus) unit 91 (measurement section, measurement unit). The AF unit 91 is configured to precisely align the focused spot of the laser light L at a position at a predetermined distance from the back surface 21b even when the back surface 21b, which is the incident surface of the wafer 20, has a displacement (waviness) in the thickness direction (Z direction). The AF unit 91 measures the displacement on the back surface 21b (surface to be measured) in order to adjust the focused spot of the laser light L irradiated onto the wafer 20 by the light source 31. Specifically, the AF unit 91 irradiates the back surface 21b with AF laser light LA ​​(measurement light) and receives and detects the reflected light of the AF laser light LA ​​on the back surface 21b to obtain displacement data of the back surface 21b (measures the displacement).

[0056] The AF unit 91 has an AF light source 91a that outputs AF laser light LA, and a displacement detection section 91b that receives and detects the reflected light of the AF laser light LA. The AF laser light LA ​​emitted from the AF light source 91a is reflected by the AF dichroic mirror 92 and is irradiated onto the rear surface 21b via the condenser lens 33. In this way, the AF laser light LA ​​and the laser light L are irradiated onto the wafer 20 from the same condenser lens 33 (they are coaxial). Then, the reflected light of the AF laser light LA ​​on the rear surface 21b is reflected by the AF dichroic mirror 92 and detected by the displacement detection section 91b. The displacement detection section 91b is configured to include, for example, a four-segment photodiode. The four-segment photodiode is configured to receive the condensed image of the reflected light of the AF laser light LA ​​by dividing it, and output a voltage value according to the respective light amounts. Since astigmatism is added to the reflected light of the AF laser light LA, the shape of the focused image (vertical, circular, horizontal) changes depending on the position of the back surface 21b of the wafer 20 relative to the focused spot of the AF laser light LA. That is, the focused image changes according to the position of the back surface 21b of the wafer 20 relative to the focused spot. Therefore, the voltage value output from the four-segment photodiode changes according to the position of the back surface 21b of the wafer 20 relative to the focused spot of the AF laser light LA.

[0057] The voltage value output from the four-segment photodiode of the displacement detection unit 91b is input to the control unit 8. Based on the voltage value output from the four-segment photodiode of the displacement detection unit 91b, the control unit 8 calculates a calculation value as position information regarding the position of the back surface 21b of the wafer 20 relative to the focused spot of the AF laser light LA. Based on the calculation value, the control unit 8 controls the drive unit 9 (actuator) to finely adjust the position of the focusing lens 33 in the vertical direction so that the position of the focused spot of the laser light L irradiated from the light source 31 is at a certain depth from the back surface 21b. In this way, by performing control based on the distance measurement result by the AF unit 91 together with the laser processing using the laser light L (prior to the laser processing), the focused spot of the laser light L can be accurately aligned at a position at a predetermined distance from the back surface 21b even if there is waviness on the back surface 21b, which is the incident surface.

[0058] [Configuration of the inspection imaging unit] As shown in FIG. 7, the imaging unit 4 (imaging section) has a light source 41, a mirror 42, an objective lens 43, and a light detection section 44. The imaging unit 4 captures an image of the wafer 20. The light source 41 outputs light I1 that is transparent to the semiconductor substrate 21. The light source 41 is composed of, for example, a halogen lamp and a filter, and outputs light I1 in the near-infrared region. The light I1 output from the light source 41 is reflected by the mirror 42, passes through the objective lens 43, and is irradiated onto the wafer 20 from the back surface 21b side of the semiconductor substrate 21. At this time, the stage 2 supports the wafer 20 on which the two rows of modified regions 12a and 12b are formed as described above.

[0059] The objective lens 43 passes the light I1 reflected by the surface 21a of the semiconductor substrate 21. That is, the objective lens 43 passes the light I1 propagated through the semiconductor substrate 21. The numerical aperture (NA) of the objective lens 43 is, for example, 0.45 or more. The objective lens 43 has a correction collar 43a. The correction collar 43a corrects aberrations occurring in the light I1 in the semiconductor substrate 21, for example, by adjusting the distances between the multiple lenses constituting the objective lens 43. Note that the means for correcting the aberrations is not limited to the correction collar 43a, and may be other correction means such as a spatial light modulator. The light detection unit 44 detects the light I1 transmitted through the objective lens 43 and the mirror 42. The light detection unit 44 is, for example, configured by an InGaAs camera, and detects the light I1 in the near-infrared region. The means for detecting (capturing) the light I1 in the near-infrared region is not limited to an InGaAs camera, and may be any other imaging means that captures images in a transmission type, such as a transmission confocal microscope.

[0060] The imaging unit 4 can capture images of each of the two rows of modified regions 12a, 12b and the tips of each of the multiple cracks 14a, 14b, 14c, and 14d. The crack 14a is a crack that extends from the modified region 12a to the front surface 21a. The crack 14b is a crack that extends from the modified region 12a to the back surface 21b. The crack 14c is a crack that extends from the modified region 12b to the front surface 21a. The crack 14d is a crack that extends from the modified region 12b to the back surface 21b.

[0061] [Configuration of the imaging unit for alignment correction] 8, the imaging unit 5 has a light source 51, a mirror 52, a lens 53, and a light detection unit 54. The light source 51 outputs light I2 that is transparent to the semiconductor substrate 21. The light source 51 is composed of, for example, a halogen lamp and a filter, and outputs light I2 in the near-infrared region. The light source 51 may be shared with the light source 41 of the imaging unit 4. The light I2 output from the light source 51 is reflected by the mirror 52 and passes through the lens 53, and is irradiated onto the wafer 20 from the back surface 21b side of the semiconductor substrate 21.

[0062] The lens 53 passes the light I2 reflected by the surface 21a of the semiconductor substrate 21. That is, the lens 53 passes the light I2 propagating through the semiconductor substrate 21. The numerical aperture of the lens 53 is 0.3 or less. That is, the numerical aperture of the objective lens 43 of the imaging unit 4 is larger than the numerical aperture of the lens 53. The light detection unit 54 detects the light I2 that passes through the lens 53 and the mirror 52. The light detection unit 54 is configured, for example, by an InGaAs camera, and detects the light I2 in the near-infrared region. The light detection unit 54 may be an SD camera, or may be one that detects non-transparent light.

[0063] The imaging unit 5, under the control of the control unit 8, irradiates the wafer 20 with light I2 from the back surface 21b side and detects the light I2 returning from the front surface 21a (functional element layer 22), thereby capturing an image of the functional element layer 22. Similarly, under the control of the control unit 8, the imaging unit 5, under the control of the control unit 8, irradiates the wafer 20 with light I2 from the back surface 21b side and detects the light I2 returning from the positions where the modified regions 12a and 12b are formed in the semiconductor substrate 21, thereby acquiring an image of the region including the modified regions 12a and 12b. These images are used for alignment of the irradiation position of the laser light L. The imaging unit 6 has a similar configuration to the imaging unit 5, except that the lens 53 has a lower magnification (for example, 6x in the imaging unit 5 and 1.5x in the imaging unit 6), and is used for alignment in the same manner as the imaging unit 5.

[0064] [Laser processing method details] The laser processing method performed by the laser processing device 1 will be described in detail below. The laser processing method according to this embodiment is a laser processing method in which the wafer 20 (object) including the back surface 21b (first surface) and the front surface 21a (second surface) opposite to the back surface 21b is irradiated with laser light L using the back surface 21b of the wafer 20 as an incident surface, thereby performing laser processing of the wafer 20. This laser processing method includes a first step and a second step performed after the first step. As described above, the wafer 20 is cut into functional elements 22a along each of the multiple lines 15. In the first step, laser irradiation is performed along each of the multiple lines 15 (first lines, see FIG. 2) extending in the X direction (first direction) along the back surface 21b. In the second step, laser irradiation is performed along each of the multiple lines 15 (second lines, see FIG. 2) extending in the Y direction (second direction) along the back surface 21b. In the following, the first process may be referred to as CH1 process, and the second process may be referred to as CH2 process.

[0065] In detail, in the first process (CH1 process), the laser light L is irradiated to form a modified region 12 for division (first modified region) inside the wafer 20 while relatively moving the focused spot of the laser light L along each of a plurality of lines 15 extending in the X direction, and a crack 14 extending from the modified region 12 toward the surface 21a is formed. The control unit 8 controls the laser irradiation unit 3 so as to form such a crack 14 (first control). Here, in the first process, the modified region 12 is formed so as to be in a so-called BHC (Bottom side half-cut) state in which the crack 14 reaches the surface 21a. Note that in the first process, the modified region 12 may be formed so as to be in a so-called ST (Stealth) state in which the crack 14 does not reach the surface 21a. In the second process (CH2 process), the laser light L is irradiated to form a modified region 12 for division (second modified region) inside the wafer 20 while relatively moving the focused spot of the laser light L along each of a plurality of lines 15 extending in the Y direction, and a crack 14 extending from the modified region 12 toward the surface 21a is formed. The control unit 8 controls the laser irradiation unit 3 so as to form such a crack 14 (second control). Here, it is assumed that the modified region 12 is formed in the second process so as to be in a so-called BHC state in which the crack 14 has reached the surface 21a. Note that the modified region 12 may be formed in the second process so as to be in a so-called ST state in which the crack 14 has not reached the surface 21a.

[0066] Here, when the modified regions 12 are formed sequentially along a plurality of lines 15 intersecting each other as in the above-mentioned CH1 processing and CH2 processing, the formation of the modified regions 12 along the lines 15 (first lines) extending in the X direction to which the laser light L is first irradiated may cause warping of the wafer 20. FIG. 9 is a diagram for explaining the principle of occurrence of warping of the wafer 20. Specifically, as shown in FIG. 9, the warping of the wafer 20 occurs due to stress concentration on one side of the wafer 20 (the surface 21a to which the cracks 14 reach) caused by the formation of the modified regions 12 and the formation of the cracks 14 extending from the modified regions 12 toward the surface 21a. In the example shown in FIG. 9, the modified regions 12 are formed sequentially along a plurality of lines 15 (first lines) extending in the X direction and adjacent to each other in the Y direction in the CH1 processing, and the cracks 14 extend toward the surface 21a, so that the amount of warping is particularly large on both end sides in the Y direction of the wafer 20. That is, the CH1 processing causes warping in the Y direction, which is the processing progress direction in the CH2 processing. Such warping of the wafer 20 becomes particularly noticeable when the wafer 20 is a microchip or when a relatively large crack 14 is formed in the wafer 20.

[0067] FIG. 10 is a diagram showing warpage in the CH2 processing direction after CH1 processing and before CH2 processing. In FIG. 10, the horizontal axis indicates the processing direction of CH2 (width direction of the wafer 20), and the vertical axis indicates the amount of displacement indicated by the voltage value. A voltage value of 1V on the vertical axis corresponds to a displacement amount of about 8 μm, for example. FIG. 10 shows an example of the results when CH1 processing is performed under the following conditions: work size: 775 μm (65 mm×36 mm small piece), chip size: 1 mm, finishing thickness after grinding: 80 μm, modified region for division: 3 passes (total cracks: about 300 μm, BHC cracks: about 80 μm), measurement point: 1.5 mm from the end of the small piece. As is clear from FIG. 10, after CH1 processing, the amount of warpage is large at both ends (wafer edge parts) in the CH2 processing direction.

[0068] 11 is a diagram for explaining AF (autofocus) tracking failure during CH2 processing after CH1 processing. As described above, in the laser irradiation unit 3, the AF unit 91 detects reflected light from the back surface 21b to obtain displacement data of the back surface 21b. However, as described above, the amount of warping at the wafer edge portion increases after CH1 processing, which may cause AF tracking failure and prevent accurate displacement data of the back surface 21b from being obtained even by the AF unit 91. This may result in a deterioration in the accuracy of formation of the modified region 12 (second modified region) during CH2 processing.

[0069] Therefore, in the laser processing method according to the present embodiment, a third step for suppressing warpage is performed before the second step. In the third step, before the second step, a modified region 12 for suppressing warpage (third modified region) is formed inside the wafer 20 by irradiation with laser light L, and a crack 114 (see FIG. 12) is formed that reaches the rear surface 21b, which is the incident surface, from the modified region 12 and is not continuous with the crack 14 extending from the modified region 12 for division. In this case, the control unit 8 controls the laser irradiation unit 3 (third control) so that a plurality of modified regions 12 for suppressing warpage are formed by irradiation with laser light L, and the crack 114 extending from the modified region 12 reaches the rear surface 21b and is not continuous with the crack 14 extending from the modified region 12 for division.

[0070] FIG. 12 is a diagram for explaining the formation of the warp suppression modified region 12. As shown in FIG. 12, it is assumed that the division modified region 12 is formed in the CH1 processing, and the crack 14 is formed from the modified region 12 in the direction of the surface 21a. The division modified region 12 in the CH1 processing and the crack 14 extending from the modified region 12 are formed, for example, in the center of the street region 23 where the line 15 (first line) extending in the X direction is formed. In this case, as shown in FIG. 12, in the third step, the warp suppression modified region 12 (modified region 12 related to the crack 114) is formed in a position in the Y direction different from the division modified region 12 (modified region 12 related to the crack 14) (position shifted from the division modified region 12). That is, in the third control, the control unit 8 controls the laser irradiation unit 3 so that the warp suppression modified region 12 is formed in a position different from the formation position of the division modified region 12 in the Y direction. In the third step, the warp suppression modified region 12 is formed so that the crack 114 reaches the rear surface 21b in a so-called HC (Half-cut) state. By achieving the HC state in this way, warp originating from the warp suppression modified region 12 is generated, and warp originating from the division modified region 12 can be further reduced (details will be described later). There are no limitations on the way to shift the position of the division modified region 12 and the position of the warp suppression modified region 12 (and the position of the crack 14 and the position of the crack 114), but this is performed, for example, by the operation of the stage 2 or the Y-shift pattern of the spatial light modulator 7 (details will be described later).

[0071] In the third step, the warp suppression modified region 12 may be formed in the middle position in the Y direction between the formation positions of two adjacent lines 15 (first lines) in the Y direction. In this case, the control unit 8 controls the laser irradiation unit 3 in the third control so that the warp suppression modified region 12 is formed in the middle position in the Y direction between the formation positions of two adjacent lines 15 (first lines) in the Y direction. As described above, in the lines 15 (first lines) adjacent to each other in the Y direction and extending in the X direction, the division modified region 12 and the cracks 14 extending from the modified region 12 are formed in the CH1 processing. Therefore, the middle position in the Y direction between the formation positions of two adjacent lines 15 in the Y direction is the center position of the chip after cutting (division). FIG. 13 is a diagram for explaining the formation of the warp suppression modified region 12 near the center position of the chip. In the third step, the warp suppression modified region 12 is formed in such a chip center position, so that the distance between the cracks 14 extending from the division modified region 12 and the cracks 14 extending from the warp suppression modified region 12 can be maximized, and the risk of the wafer cracking due to the continuation of these cracks can be reduced. As shown in FIG. 13(a), the vicinity of the chip center position where the warp suppression modified region 12 is formed is on the functional element 22a, so that the warp suppression modified region 12 is formed on the active area. However, since the distance from the focused spot in the third step to the functional element 22a can be made sufficiently far, the functional element 22a is not damaged by the escape light associated with the laser irradiation in the third step. As shown in FIG. 13(b), the warp suppression modified region 12 is removed in the subsequent grinding, so even if the warp suppression modified region 12 is formed on the active area in the third step, it does not affect the chipped semiconductor device.

[0072] In the third step, the cracks 114 may be formed so that the cracks 114 extending from the warp-suppressing modified regions 12 are shorter than the cracks 14 extending from the modified regions 12 for division. Furthermore, in the third step, the number of warp-suppressing modified regions 12 may be greater than the number of warp-suppressing modified regions 12 for division, while shortening the length of the cracks 114 as described above. FIG. 14 is a diagram for explaining the formation of the warp-suppressing modified regions by multi-point branching. As a processing method for increasing the number of warp-suppressing modified regions 12 while shortening the length of the cracks 114 extending from the warp-suppressing modified regions 12, for example, multi-point branching processing using a modulation pattern (multi-point branching pattern) set in the spatial light modulator 7 may be performed. In this case, the control unit 8 sets the modulation pattern (multi-point branching pattern) in the spatial light modulator 7 so that the cracks 114 are shorter than the cracks 14 and a greater number of warp-suppressing modified regions 12 are formed than the modified regions 12 for division. As shown in FIG. 14, a large number of warp suppression modified regions 12 are formed at once by the multi-point branching process of the spatial light modulator 7. In addition, the number of focused spots is increased to disperse energy, thereby shortening the vertical cracks 114 (reducing the risk of wafer cracking). Such multi-point branching process using a modulation pattern (multi-point branching pattern) set in the spatial light modulator 7 enables warp suppression processing with reduced risk of wafer cracking without reducing takt time. Note that the method of shortening the cracks 114 compared to the cracks 14 and forming more warp suppression modified regions 12 than the division modified regions 12 is not limited to the multi-point branching process by the spatial light modulator 7, and may be performed, for example, by feeding the table and processing one line at a time.

[0073] In the third step, the warp-suppressing modified region 12 may be formed so as to focus on suppressing warpage in the outer peripheral portion of the wafer 20 (wafer edge portions at both ends in the CH2 processing advancement direction) where the amount of warpage is large. FIG. 15 is a diagram for explaining a processing method for focusing on suppressing warpage in the outer peripheral portion of the wafer 20. As shown in FIG. 15(a), in the third step, the warp-suppressing modified region 12 may be formed by changing the processing index depending on the location so that the number of warp-suppressing modified regions 12 in the second direction is greater at both ends when comparing the warp-suppressing modified region 12 at the center in the Y direction of the wafer 20 with the warp-suppressing modified region 12 at both ends. In this case, the control unit 8 controls the laser irradiation unit 3 in the third control so that the number of warp-suppressing modified regions 12 at both ends in the Y direction is greater. 15(b), in the third step, the warp-suppressing modified region 12 may be formed such that, when comparing the warp-suppressing modified region 12 at the center in the Y direction of the wafer 20 with the warp-suppressing modified region 12 at both ends, the length of the crack 114L, which is the crack 114 at both ends, is longer than the crack 114S, which is the crack 114 at the center. In this case, in the third control, the control unit 8 controls the laser irradiation unit 3 such that the length of the crack 114 extending from the warp-suppressing modified region 12 at both ends in the Y direction is longer.

[0074] FIG. 16 is a diagram showing warpage in the CH2 processing direction after CH1 processing for each form of the warpage suppression modified region. In FIG. 16, the horizontal axis indicates the CH2 processing direction (width direction of the wafer 20), and the vertical axis indicates the amount of displacement indicated by the voltage value. A voltage value of 1V on the vertical axis corresponds to a displacement amount of about 8 μm, for example. FIG. 16 shows an example of the results when CH1 processing is performed under the following conditions: work size: 775 μm (65 mm×36 mm small piece), chip size: 1 mm, finishing thickness after grinding: 80 μm, modified region for division: 3 passes (total cracks about 300 μm, BHC cracks about 80 μm), measurement point: 1.5 mm from the end of the small piece. 16 shows the amount of warpage (amount of displacement) for each of the following cases: when only the modified regions 12 for division are formed (Pattern 1); when the modified regions 12 for division are formed and the same number of modified regions 12 for warpage suppression are formed (Pattern 2); and when, in addition to Pattern 2, two lines of modified regions 12 for warpage suppression are formed in the edge 10 mm portion that is the outer periphery of the wafer 20 (Pattern 3). As shown in FIG. 16, when Pattern 3 is adopted, the amount of warpage can be suppressed even in the outer periphery of the wafer 20 where the amount of warpage is likely to be large.

[0075] 15(c), in the third step, each warp-suppressing modified region 12 may be formed such that the warp-suppressing modified region 12 in the center of the wafer 20 is thinned out. For example, in a case where the amount of warp is extremely small in the center of the wafer 20 and the amount of warp is large only at both ends, warp of the wafer 20 can be appropriately suppressed even if the warp-suppressing modified region 12 in the center of the wafer 20 is thinned out in this manner.

[0076] In the third step, the modified region 12 for warping suppression may be formed at a position different from the modified region 12 for division in the Y direction by setting a modulation pattern (a modulation pattern for shifting the focused spot) of the spatial light modulator 7 that modulates the laser light L. That is, the control unit 8 may set a modulation pattern in the third control so that the modified region 12 for warping suppression is formed at a position different from the position where the modified region 12 for division is formed in the Y direction. FIG. 17 is a diagram for explaining the shift of the processing position by setting the modulation pattern of the spatial light modulator 7. In the example shown in FIG. 17, the focused spot of the modified region 12 for division is shifted in the −Y direction from the reference focused position in the first step, and the focused spot of the modified region 12 for warping suppression is shifted in the +Y direction from the reference focused position in the third step. This allows the modified region 12 for division and the modified region 12 for warping suppression to be shifted in opposite directions in the Y direction, and the positions of these modified regions 12 and the cracks 14, 114 extending from these modified regions 12 can be sufficiently separated from each other. Furthermore, in the first and third steps, the processing position can be shifted simply by switching the modulation pattern, so the processing time required for processing can be shortened compared to the case where the stage 2 is operated.

[0077] In at least one of the first step and the third step, the modulation pattern of the spatial light modulator 7 may be set to make the position of the end of the crack 14 on the back surface 21b side extending from the modified region 12 for division different from the position of the end of the crack 114 on the front surface 21a side extending from the modified region 12 for warpage suppression. That is, in at least one of the first control and the third control, the control unit 8 may set the modulation pattern so that the position of the end of the crack 14 on the back surface 21b side extending from the modified region 12 for division is different from the position of the end of the crack 114 on the front surface 21a side extending from the modified region 12 for warpage suppression. Here, it is described that the position of the end of the crack 14 on the back surface 21b side is made different from the position of the end of the crack 114 on the front surface 21a side by setting the modulation pattern of the spatial light modulator 7 in the first step. Specifically, in the first step, a crack 14 is formed that is inclined with respect to the Z direction and the Y direction, so that the position of the end of the crack 14 on the back surface 21b side is made different from the position of the end of the crack 14 on the front surface 21a side (see Figure 18(a)).

[0078] FIG. 18 is a diagram for explaining the formation of oblique cracks by setting the modulation pattern of the spatial light modulator. In the example shown in FIG. 18(a), in the first step, two rows of modified regions 12 for division are formed, and the cracks 14A extending from the modified region 12 on the front surface 21a side are formed to extend along the line 15, and the cracks 14B extending from the modified region 12 on the back surface 21b side are formed as oblique cracks that are continuous with the cracks 14A and are inclined with respect to the Z direction and the Y direction. As a result, even when the modified region 12 for warpage suppression is formed so that the cracks 114 are formed at the same positions in the Y direction as the cracks 14A as shown in FIG. 18(a) in the third step, the position of the end of the cracks 14 (more specifically, the cracks 14B) on the back surface 21b side extending from the modified region 12 for division can be made different from the position of the end of the cracks 114 on the front surface 21a side. Since the crack 14A connected to the crack 14B extends along the line 15, the crack 14 (specifically, the crack 14A) can be appropriately extended in the position and direction required for the splitting crack 14.

[0079] In the example shown in FIG. 18(b), three rows of modified regions 12 for division are formed, and the modified region 12 closest to the front surface 21a (SD1 in FIG. 18(b)) is formed so that the crack 14A extends along the line 15. In addition, by setting the modulation pattern of the spatial light modulator 7 (setting the Y shift and coma aberration), the modified region 12 in the middle (SD2 in FIG. 18(b)) shifts from SD1 in the Y direction and a diagonal crack 14B extends from there, and the modified region 12 closest to the back surface 21b (SD3 in FIG. 18(b)) further softens in the Y direction from SD2 and a diagonal crack 14C extends from there. The diagonal crack 14B is continuous with the crack 14A and the diagonal crack 14C, and the diagonal crack 14B and the diagonal crack 14C extend in the same direction (diagonal direction).

[0080] Up to this point, it has been explained that in order to prevent the first process (CH1 process) from causing warpage in the wafer 20 and adversely affecting the second process (CH2 process), the modified region 12 for warpage suppression (third modified region) is formed inside the wafer 20 in the third process before the second process. Here, the warpage of the wafer 20 caused by the formation of the modified region 12 in the CH1 process gradually progresses as the formation of the modified region 12 for division related to the multiple lines 15 progresses. Therefore, in the CH1 process, the processing of the line 15 that is processed first affects the processing of the line 15 that is processed later. That is, in the CH1 process, in the processing of the line 15 that is processed relatively later among the multiple lines 15, the modified region 12 for division may be formed in a warped state of the wafer 20, and in this case, the processing stability may be deteriorated.

[0081] FIG. 19 is a diagram for explaining the deterioration of processing stability during the latter half processing of CH1. As shown in FIG. 19, when the modified regions 12 have already been formed for a plurality of lines and the cracks 14 extend from the modified regions 12, the wafer 20 is warped. In this state, when the laser light L is irradiated to form the modified regions 12 for further division in the CH1 processing, problems occur such as the cracks 14 extending obliquely to the device surface of the wafer 20 and the processing position accuracy being deteriorated. In addition, when the wafer 20 is warped, the wafer 20 may not be adsorbed properly on the stage 2. Thus, in the latter half processing of CH1, it may be difficult to perform processing stably and with high accuracy.

[0082] In view of such circumstances, in the laser processing method according to the present embodiment, the formation of the modified region 12 for division related to any of the lines 15 in the first step and the formation of the modified region 12 for warp suppression in the third step may be performed alternately. That is, the control unit 8 controls the laser irradiation unit 3 so as to alternately perform the formation of the modified region 12 for division related to any of the lines 15 in the first control and the formation of the modified region 12 for warp suppression in the third control. The term "alternately performed" as used herein does not only mean a completely one-to-one alternation, but also includes the alternation of the formation of multiple modified regions 12 for division and the formation of multiple modified regions 12 for warp suppression.

[0083] FIG. 20 is a diagram for explaining a processing method for alternately forming modified regions 12 for division and modified regions 12 for warpage suppression. In FIG. 20(a) to FIG. 20(c), the numbers 1 to 9 indicate processing orders. In the example shown in FIG. 20(a), the modified regions 12 for warpage suppression and the cracks 114 extending from the modified regions 12 are formed in the third step (processing order 1), followed by the modified regions 12 for division and the cracks 14 extending from the modified regions 12 in the first step (processing order 2), after which the third step and the first step are performed one by one in sequence. In this case, the processing locations in each process are arranged in the Y direction in the processing order. In the example shown in FIG. 20(b), first, the modified region 12 for suppressing warpage and the crack 114 extending from the modified region 12 are formed in the third step (processing order 1, 2), then, the modified region 12 for division and the crack 14 extending from the modified region 12 are formed in the first step (processing order 3, 4), and then, such two-processing processes are repeatedly performed. In this case, when each of the first step and the third step is viewed individually, the processing locations in each process are arranged in the Y direction in the processing order. In the example shown in FIG. 20(c), first, the modified region 12 for suppressing warpage and the crack 114 extending from the modified region 12 are formed in the third step (processing order 1, 2, 3), then, the modified region 12 for division and the crack 14 extending from the modified region 12 are formed in the first step (processing order 4, 5, 6). In this case, when the first and third processes are viewed individually, the machining locations in each process are lined up in the Y direction in the order of the machining sequence.

[0084] In addition, the influence of a previous process on a subsequent process in the same process (CH1 process in the above example) also occurs in CH2 process. For this reason, the following fourth process may be further performed in order to suppress deterioration of processing stability during the latter half of CH2 processing. That is, the laser processing method according to this embodiment may further include a fourth process of forming a plurality of modified regions 12 (fourth modified regions) for warpage suppression inside the wafer 20 by irradiating laser light, and forming a crack 114 that reaches the rear surface 21b from the modified region 12 and is not continuous with the crack 14 extending from the modified region 12 for division formed by CH2 processing. In this case, the formation of the modified region 12 for division related to any of the lines 15 in the second process and the formation of the modified region 12 for warpage suppression in the fourth process may be performed alternately.

[0085] Next, the effects of the laser processing device 1 according to this embodiment will be described.

[0086] The laser processing apparatus 1 according to the present embodiment includes a laser irradiation unit 3 and a control unit 8. The control unit 8 performs a first control to control the laser irradiation unit 3 so that a modified region 12 for division is formed inside the wafer 20 by irradiation with the laser light L and a crack 14 extends from the modified region 12 in the direction of the front surface 21a while relatively moving the focused spot of the laser light L along each of a plurality of lines 15 extending in the X direction along the back surface 21b, and a second control to control the laser irradiation unit 3 so that a modified region 12 for division is formed inside the wafer 20 by irradiation with the laser light L and a crack 14 extends from the modified region 12 in the direction of the front surface 21a after the first control. The control unit 3 is configured to execute a second control in which the laser irradiation unit 3 is controlled so that a modified region 12 for division is formed inside the wafer 20 by irradiation with laser light L and a crack 14 extends from the modified region 12 in the direction of the front surface 21a while moving the wafer relative to the rear surface 21a, and a third control in which the laser irradiation unit 3 is controlled before the second control in which a plurality of modified regions 12 for warp suppression are formed inside the wafer 20 by irradiation with laser light L and a crack 114 extending from the modified region 12 reaches the rear surface 21b and is not continuous with the crack 14 extending from the modified region 12 for division.

[0087] In the laser processing device 1 according to the present embodiment, the modified regions 12 for division are formed along each of the multiple lines 15 extending in the X direction along the back surface 21b by irradiation with the laser light L, and the cracks 14 extending from the modified regions 12 toward the front surface 21a are formed, and then the modified regions 12 for division are formed along each of the multiple lines 15 extending in the Y direction by irradiation with the laser light L, and the cracks 14 extending from the modified regions 12 toward the front surface 21a are formed. In this manner, when the modified regions 12 are formed sequentially along the multiple lines 15 intersecting each other, the formation of the modified regions 12 (CH1 processing) along the lines 15 (first lines) to which the laser light L is first irradiated may cause the wafer 20 to warp, and the accuracy of processing the lines 15 (second lines) to which the laser light L is subsequently irradiated may decrease due to the influence of the warping of the wafer 20. Specifically, the warping of the wafer 20 occurs due to the concentration of stress on one side of the wafer 20 (here, the surface 21a, which is the direction in which the crack 14 mainly extends) caused by the formation of the modified region 12 and the formation of the crack 14 extending from the modified region 12 toward the surface 21a. Such warping of the wafer 20 is particularly noticeable when the wafer 20 is a microchip or when a relatively large crack is formed. If processing (CH2 processing) of the line 15 (second line) to which the laser light L is irradiated later is performed in a warped state, it becomes difficult to ensure the accuracy of autofocus and the like for adjusting the focal spot of the laser light L when processing the line 15, and there is a risk that the modified region 12 cannot be appropriately formed in the CH2 processing.

[0088] In this regard, in the laser processing apparatus 1 according to the present embodiment, prior to the control (second control) related to the CH2 processing, a plurality of modified regions 12 for warpage suppression are formed inside the wafer 20 by irradiation with the laser light L, and the cracks 114 extending from the modified regions 12 reach the rear surface 21b and are formed so as not to be continuous with the cracks 14 extending from the modified regions 12 for division. In this manner, the modified regions 12 for warpage suppression are formed so that the cracks 141 reach the rear surface 21b opposite to the front surface 21a on which stress is concentrated by the formation of the modified regions 12 for division, thereby mitigating the localization of stress and reducing the warpage of the wafer 20. This makes it possible to appropriately form the modified regions 12 in the CH2 processing performed after the formation of the modified regions 12 for warpage suppression. Furthermore, the cracks 141 extending from the warp-suppressing modified regions 12 are formed so as not to continue to the cracks 14 extending from the dividing modified regions 12, thereby making it possible to appropriately prevent unintended cracks in the wafer 20 from occurring due to the formation of the warp-suppressing modified regions 12. As described above, the laser processing apparatus 1 according to this embodiment can appropriately form the dividing modified regions 12 in the wafer 20 while preventing unintended cracks in the wafer 20, thereby improving the laser processing accuracy.

[0089] FIG. 21 is a diagram for explaining the action and effect of the laser processing apparatus 1 according to this embodiment, and is a diagram showing warpage in the CH2 processing progress direction after CH1 processing. In FIG. 21, the horizontal axis indicates the processing progress direction of CH2 (width direction of the wafer 20), and the vertical axis indicates the amount of displacement indicated by the voltage value. A voltage value of 1V on the vertical axis corresponds to a displacement amount of, for example, about 8 μm. FIG. 21 shows the amount of warpage after CH1 processing and before CH2 processing, and shows the results of the amount of warpage for each of the cases where the warpage-suppressing modified region 12 is not formed (shown as "BHC only" in FIG. 21), where the crack 114 extending from the warpage-suppressing modified region 12 is in the ST state (shown as "BHC+warpage-suppressing SD(ST)" in FIG. 21), and where the crack 114 extending from the warpage-suppressing modified region 12 reaches the back surface 21b and is in the HC state (shown as "BHC+warpage-suppressing SD(HC)" in FIG. 21). 21 shows an example of the results when processing was performed under the following conditions: work size: 775 μm (65 mm × 36 mm small piece), chip size: 1 mm, finish thickness after grinding: 80 μm, modified region for division: 3 passes (total cracks: about 300 μm, BHC cracks: about 80 μm), modified region for warpage suppression: 1 pass (total cracks: about 60 μm). As is clear from FIG. 21, the modified region for warpage suppression 12 is formed, and the cracks 114 extending from the modified region for warpage suppression 12 reach the back surface 21b, resulting in a HC state, and thus warpage of the wafer 20 caused by the BHC associated with the formation of the modified region for division 12 can be significantly reduced.

[0090] FIG. 22 is a diagram for explaining the action and effect of the laser processing apparatus 1 according to this embodiment, and is a diagram showing the warpage of the wafer 20 after CH1 processing and CH2 processing. In FIG. 22, the horizontal axis indicates the position in the width direction of the wafer 20, and the vertical axis indicates the surface displacement. The surface displacement here is measured by a microscope. FIG. 22 shows the surface displacement indicating the amount of warpage of the wafer 20 after CH1 processing and CH2 processing, and shows the surface displacement indicating the amount of warpage for each of the cases where the modified region 12 for suppressing warpage is not formed (indicated as "only SD for division" in FIG. 22) and where the modified region 12 for suppressing warpage is formed in the center of the chip (indicated as "SD for division + SD for suppressing warpage (processed in the center of the chip)" in FIG. 22). FIG. 22 shows an example of the results of processing under the following conditions: work size: 775 μm (12 inches), chip size: 1 mm, finish thickness after grinding: 80 μm, modified region for division: 3 passes (total cracks of about 300 μm, BHC cracks of about 80 μm), modified region for warpage suppression: 3 passes (total cracks of about 150 μm). As shown in FIG. 22, when the modified region for warpage suppression 12 is formed in the center of the chip, the amount of warpage (displacement) at both ends of the wafer 20 can be reduced to half or less compared to the case where the modified region for warpage suppression 12 is not formed. If the amount of warpage at both ends of the wafer 20 is large, the wafer 20 cannot be properly adsorbed to the transport arm after processing, and there is a risk of transport failure such as the wafer 20 dropping. In this regard, the wafer 20 in which the amount of warpage is reduced to half or less by the modified region for warpage suppression 12 as described above can be properly transported. In addition, no cracks were generated in the wafer 20 after transport.

[0091] In the third control, the control unit 8 may control the laser irradiation unit 3 so that the warp-suppressing modified region 12 is formed at a position different from the position in the Y direction where the division-use modified region 12 is formed. This makes it possible to appropriately prevent the crack 14 from the division-use modified region 12 and the crack 114 from the warp-suppressing modified region 12 from continuing together, and more suitably prevents the wafer 20 from cracking unintentionally.

[0092] In the third control, the control unit 8 may control the laser irradiation unit 3 so that the warp-suppressing modified region 12 is formed in the middle in the Y direction between the formation positions of two adjacent lines 15 in the Y direction. By forming the warp-suppressing modified region 12 exactly in the middle between the two lines 15, the distance between each of the division modified regions 12 and the warp-suppressing modified region 12 can be increased, and the cracks 14 and 114 can be appropriately prevented from continuing together. This makes it possible to appropriately prevent unintended cracks from occurring in the wafer 20.

[0093] In the third control, the control unit 8 may set the modulation pattern so that the warp suppression modified region 12 is formed at a position different from the formation position of the division modified region 12 in the Y direction. In this way, the formation position of the warp suppression modified region 12 is adjusted by setting the modulation pattern of the spatial light modulator 7, so that the processing time can be shortened compared to the case where the formation position of the modified region 12 is changed by the operation of the stage 2.

[0094] The control unit 8 may set the modulation pattern in at least one of the first control and the third control such that the position of the end of the crack 14 on the back surface 21b side is different from the position of the end of the crack 114 on the front surface 21a side. In this manner, the positions of the ends of the cracks 14, 114 extending from the modified region 12 are adjusted by setting the modulation pattern of the spatial light modulator 7, so that the positions of the ends of the cracks 14, 114 can be appropriately adjusted, and unintended cracks in the wafer 20 caused by the cracks 14, 114 being continuous with each other can be more suitably prevented.

[0095] In the third control, the control unit 8 may control the laser irradiation unit 3 so that the crack 114 extending from the warp-suppressing modified region 12 is shorter than the crack 14 extending from the division modified region 12. Unlike the crack 14 extending from the division modified region 12, the crack 114 extending from the warp-suppressing modified region 12 is not a crack that is desired to contribute to division, and therefore, by shortening the crack 114, it is possible to more suitably suppress unintended cracks in the wafer 20 caused by the cracks 14, 114 being continuous with each other.

[0096] In the third control, the control unit 8 may control the laser irradiation unit 3 so that a greater number of warp-suppressing modified regions 12 are formed in the Y direction than the number of division-use modified regions 12. As described above, in order to perform appropriate division, it is desirable to shorten the cracks 114 extending from the warp-suppressing modified regions 12. However, if the cracks 114 extending from the warp-suppressing modified regions 12 are shortened, there is a risk that the effect of warp suppression will not be fully achieved. In this regard, by increasing the number of warp-suppressing modified regions 12 (more than the division-use modified regions 12), the cracks 114 extending from the many warp-suppressing modified regions 12 can be used to fully achieve the warp suppression effect while suppressing unintended cracks in the wafer 20.

[0097] In the third control, the control unit 8 may control the laser irradiation unit 3 to form the warp-suppressing modified regions 12 so that, when comparing the warp-suppressing modified regions 12 at the center of the wafer 20 in the Y direction with the warp-suppressing modified regions 12 at both ends, at least one of the following is satisfied: the number of warp-suppressing modified regions 12 in the Y direction is greater at both ends, and the length of the cracks 114 extending from the warp-suppressing modified regions 12 is longer at both ends. The warp of the wafer 20 caused by the formation of the modified regions 12 for division is more prominent at both ends in the Y direction. In this regard, by making the number of warp-suppressing modified regions 12 greater or making the length of the cracks 114 extending from the warp-suppressing modified regions 12 longer at both ends of the wafer 20 in the Y direction than at the center of the wafer 20 in the Y direction, the warp of the wafer 20 at both ends in the Y direction where the warp is prominent can be effectively suppressed.

[0098] The control unit 8 may control the laser irradiation unit 3 so as to alternately perform the formation of the modified region 12 for division related to any one of the lines 15 in the first control and the formation of the modified region 12 for warping suppression. The warping of the wafer 20 caused by the formation of the modified region 12 for division gradually progresses as the formation of the modified region 12 for division related to the multiple lines 15 progresses. Therefore, the influence of the processing of the line 15 that is processed first is exerted on the processing of the line 15 that is processed later. That is, in the processing of the line 15 that is processed relatively later among the multiple lines 15, the modified region 12 is formed in a state in which the wafer 20 is warped, so that, for example, the crack 14 may extend obliquely with respect to the surface 21a of the wafer 20, the processing position accuracy may deteriorate, or poor adsorption may occur during processing. In this regard, by alternately forming the modified regions 12 for dividing and the modified regions 12 for suppressing warping, the influence of the processing of the lines 15 performed earlier on the processing of the lines 15 performed later is suppressed, and the modified regions 12 for dividing can be more appropriately formed on the wafer 20.

[0099] In addition, the formation of the modified region 12 for suppressing warpage in the CH1 processing (processing in which the modified region 12 for division and the modified region 12 for suppressing warpage are alternately performed) does not necessarily have to be performed, and may be performed only when, for example, unevenness occurs in the wafer 20 in the CH1 processing direction after the CH1 processing. FIG. 23 is a diagram showing the warpage in the CH1 processing progress direction after the CH1 processing. In FIG. 23, the horizontal axis indicates the CH1 processing progress direction, and the vertical axis indicates the amount of displacement indicated by the voltage value. FIG. 23 shows an example of the result when the CH1 processing is performed under the following conditions: work size: 775 μm (65 mm×36 mm small piece), chip size: 1 mm, finishing thickness after grinding: 80 μm, modified region for division: 3 passes (total cracks about 300 μm, BHC cracks about 80 μm), and measurement point: 1.5 mm from the end of the small piece. 23, although the amount of warpage changes before and after processing, no irregularities are observed in the processing direction of CH1 even after processing. In such a case, it is not necessary to form the warpage-suppressing modified region 12 during CH1 processing, and it is sufficient to form the warpage-suppressing modified region 12 before CH2 processing.

[0100] The control unit 8 is configured to further execute a fourth control for controlling the laser irradiation unit 3 so that a plurality of modified regions 12 for warpage suppression are formed inside the wafer 20 by irradiation with the laser light L, and the cracks 114 extending from the modified regions 12 reach the rear surface 21b and are not continuous with the cracks extending from the modified regions 12 for division in the CH2 processing (second modified regions), and the control unit 8 may control the laser irradiation unit 3 so that the formation of the modified regions 12 relating to any of the lines 15 in the second control and the formation of the modified regions 12 in the fourth control are alternately performed. In this way, the formation of the modified regions 12 in the CH2 processing and the formation of the modified regions 12 for warpage suppression are alternately performed, so that the influence of the processing of the lines 15 performed earlier on the processing of the lines 15 performed later is suppressed in the CH2 processing, and the modified regions 12 for division can be appropriately formed on the wafer 20. [Explanation of symbols]

[0101] 1...laser processing apparatus, 3...laser irradiation unit (laser irradiation section), 7...spatial light modulator, 8...control section, 12...modified area (first modified area, second modified area, third modified area), 14, 114...cracks, 15...lines (first line, second line), 20...wafer (object).

Claims

1. a laser irradiation unit that irradiates a laser beam onto an object including a first surface and a second surface opposite to the first surface, the first surface being used as an incident surface of the object; A control unit, The control unit is a first control for controlling the laser irradiation unit so that a first modified region for division is formed inside the object by irradiation with the laser light and a crack extends from the first modified region in the second surface direction while relatively moving a focused spot of the laser light along each of a plurality of first lines extending in a first direction along the incident surface; a second control for controlling the laser irradiation unit after the first control, while relatively moving a focused spot of the laser light along each of a plurality of second lines that intersect with the first direction and extend in a second direction along the incident surface, so that a second modified region for division is formed inside the object by irradiation with the laser light, and a crack extends from the second modified region in the second surface direction; The laser processing apparatus is configured to execute a third control that controls the laser irradiation unit before the second control, so that a plurality of third modified regions for suppressing warping are formed inside the object by irradiating the laser light, and cracks extending from the third modified regions reach the first surface and are formed so as not to be continuous with the cracks extending from the first modified regions.

2. The laser processing apparatus according to claim 1 , wherein the control unit, in the third control, controls the laser irradiation unit so that the third modified region is formed at a position different from a position in the second direction where the first modified region is formed.

3. The laser processing apparatus of claim 2, wherein the control unit controls the laser irradiation unit in the third control so that the third modified region is formed at a midpoint in the second direction between the formation positions of two adjacent first lines in the second direction.

4. the laser irradiation unit has a spatial light modulator that modulates the laser light in accordance with a set modulation pattern; 4. The laser processing apparatus according to claim 2 or 3, wherein the control unit, in the third control, sets the modulation pattern so that the third modified region is formed at a position different from a position at which the first modified region is formed in the second direction.

5. the laser irradiation unit has a spatial light modulator that modulates the laser light in accordance with a set modulation pattern; A laser processing apparatus as described in any one of claims 1 to 4, wherein the control unit, in at least one of the first control and the third control, sets the modulation pattern so that the position of an end of a crack extending from the first modified region on the first surface side is different from the position of an end of a crack extending from the third modified region on the second surface side.

6. A laser processing apparatus as described in any one of claims 1 to 5, wherein, in the third control, the control unit controls the laser irradiation unit so that a crack extending from the third modified area is shorter than a crack extending from the first modified area.

7. 7. The laser processing apparatus according to claim 6, wherein in the third control, the control unit controls the laser irradiation unit so that a greater number of the third modified regions are formed in the second direction than the number of the first modified regions.

8. The laser processing apparatus of any one of claims 1 to 7, wherein, in the third control, the control unit controls the laser irradiation unit so that, when comparing the third modified region in the center of the object in the second direction with the third modified region at both ends, at least one of the following is satisfied: the number of the third modified regions in the second direction is greater at the both ends, and the length of the crack extending from the third modified region is longer at the both ends.

9. A laser processing apparatus as described in any one of claims 1 to 8, wherein the control unit controls the laser irradiation unit to alternately perform formation of the first modified area on any of the first lines in the first control and formation of the third modified area in the third control.

10. The control unit is a fourth control is further executed to control the laser irradiation unit so that a plurality of fourth modified regions for suppressing warpage are formed inside the object by the irradiation of the laser light, and cracks extending from the fourth modified regions reach the first surface and are not continuous with cracks extending from the second modified region; The laser processing apparatus according to claim 9, wherein the laser irradiation unit is controlled so as to alternately perform formation of the second modified region relating to any of the second lines in the second control and formation of the fourth modified region in the fourth control.

11. A laser processing method for performing laser processing on an object, the method comprising: irradiating a laser beam onto the object, the laser beam being incident on the first surface of the object, the second surface being opposite to the first surface; a first step of forming a first modified region for division inside the object by irradiating the laser light while relatively moving a focused spot of the laser light along each of a plurality of first lines extending in a first direction along the incident surface, and forming a crack extending from the first modified region in the second surface direction; a second step of forming a second modified region for dividing the object by irradiating the laser light while relatively moving a focused spot of the laser light along each of a plurality of second lines that intersect with the first direction and extend in a second direction along the incident surface, and forming a crack extending from the second modified region in the second surface direction; a third step, prior to the second step, of forming a plurality of third modified regions for suppressing warping inside the object by irradiating the laser light, and forming cracks that reach the first surface from the third modified regions and are not continuous with the cracks extending from the first modified regions.

12. The laser processing method according to claim 11 , wherein in the third step, the third modified region is formed at a position different from a position in the second direction where the first modified region is formed.

13. The laser processing method according to claim 12 , wherein in the third step, the third modified region is formed at a midpoint in the second direction between respective formation positions of two of the first lines adjacent to each other in the second direction.

14. 14. The laser processing method according to claim 12 or 13, wherein in the third step, the third modified region is formed at a position different from the formation position of the first modified region in the second direction by setting a modulation pattern of a spatial light modulator that modulates the laser light.

15. A laser processing method according to any one of claims 11 to 14, wherein in at least one of the first step and the third step, a modulation pattern of a spatial light modulator that modulates the laser light is set to make the position of an end of a crack extending from the first modified region on the first surface side different from the position of an end of a crack extending from the third modified region on the second surface side.

16. The laser processing method according to any one of claims 11 to 15, wherein in the third step, the third modified region is formed so that a crack extending from the third modified region is shorter than a crack extending from the first modified region.

17. The laser processing method according to claim 16 , wherein in the third step, a greater number of the third modified regions are formed in the second direction than a number of the first modified regions.

18. A laser processing method according to any one of claims 11 to 17, wherein in the third step, when comparing the third modified region in the center of the object with the third modified region at both ends in the second direction, the number of the third modified regions in the second direction is greater at the both ends, and the length of cracks extending from the third modified regions is longer at the both ends.

19. The laser processing method according to any one of claims 11 to 18, wherein the formation of the first modified area relating to any one of the first lines in the first step and the formation of the third modified area in the third step are alternately carried out.

20. A fourth step of forming a plurality of fourth modified regions for suppressing warpage inside the object by irradiating the laser light, and forming cracks that reach the first surface from the fourth modified regions and are not continuous with the cracks extending from the second modified regions, 20. The laser processing method according to claim 19, wherein formation of the second modified region relating to any one of the second lines in the second step and formation of the fourth modified region in the fourth step are alternately performed.

Images