Laser processing method and laser processing apparatus

Abstract

The laser processing method is a laser processing method of irradiating a laser inside a wafer to form a modified region, including: a first irradiation step of irradiating a laser to a first track of the wafer; and a second irradiation step of irradiating a laser to a second track intersecting the first track after the first irradiation step, in which the total output of the laser at the intersection of the first track and the second track is changed in the second irradiation step.

Description

Technical Field

[0001] This invention relates to laser processing methods and laser processing apparatus. This application claims priority based on Japanese Patent Application No. 2024-055602, filed on March 29, 2024, the contents of which are incorporated herein by reference. Background Technology

[0002] Previously, a laser processing apparatus (Patent Document 1) was known to perform internal focusing processing along multiple traces (traces CH1, CH2) formed in a lattice pattern, wherein the internal focusing processing forms a laser processing area inside the wafer that serves as the starting point for cutting.

[0003] When performing internal laser processing on a wafer using the laser processing apparatus described in Patent Document 1, a laser is first irradiated along track CH1 to form a laser processing area inside the wafer. Then, a laser processing area is formed inside the wafer along track CH2, which intersects track CH1.

[0004] When the laser along track CH2 reaches the intersection with track CH1, the laser is scattered due to the laser processing area previously formed at the intersection. As a result, thermal damage occurs around the track, which may adversely affect the device layer formed around the track.

[0005] Here, by switching the laser used for internal focusing processing at the intersection, laser scattering in the laser processing area previously formed at the intersection can be suppressed. Therefore, the aforementioned thermal damage can be suppressed.

[0006] Previously, a type of optical modulator (Patent Document 2) was known, which could switch a single laser beam into multiple laser beams. As an example of an optical modulator, Patent Document 2 discloses a spatial light modulator (SLM) based on a reflective crystal (LCOS, Liquid Crystal on Silicon). This reflective crystal spatial light modulator can switch a single laser beam into multiple laser beams. Furthermore, it can vary the intensity ratio of each laser beam. By performing such laser switching or laser intensity ratio changes at the aforementioned intersections, the aforementioned thermal damage can be suppressed.

[0007] Patent Document 1: Japanese Patent Application Publication No. 2022-006548

[0008] Patent Document 2: Japanese Patent Application Publication No. 2016-107334

[0009] Here, laser switching performed by LCOS-SLM typically occurs when the laser scanning direction changes (during reciprocating machining). Furthermore, in the case of a 300mm diameter wafer, the time required to process a single line (e.g., forming internal cracks) on that wafer is approximately 270ms to 500ms. On the other hand, the aforementioned laser switching performed by LCOS-SLM requires approximately 50ms to 150ms. Therefore, due to the long switching time, it is impossible to switch the laser during the machining process.

[0010] Other methods for switching a single laser beam into multiple laser beams include the use of diffractive optical elements (DOEs), semi-transparent mirrors, or polarizing beam splitters (PBSs). However, even with DOEs and PBSs, the response speed is insufficient to switch the laser only around the intersection, similar to the case with LCOS-SLMs. This makes it difficult to maintain processing quality while suppressing thermal damage around the intersection. Summary of the Invention

[0011] The present invention was made in view of the above circumstances, and its object is to provide a laser processing method and laser processing apparatus that can suppress thermal damage that may occur around the intersection of parts in a wafer.

[0012] This invention was made to solve the above-mentioned problems and proposes the following solutions.

[0013] <1> One aspect of the present invention relates to a laser processing method that forms a modified region by irradiating a laser into the interior of a wafer, comprising: a first irradiation step, wherein the laser is irradiated into a first track of the wafer; and a second irradiation step, wherein, after the first irradiation step, the laser is irradiated into a second track that intersects with the first track, wherein, in the second irradiation step, the total laser output at the intersection of the first track and the second track is changed.

[0014] <2> In the laser processing method described in <1> above, in the second irradiation step, the total output of the laser irradiating the intersection can be changed by an acousto-optic element.

[0015] <3> In the laser processing method described in <1> or <2> above, in the second irradiation step, at least one of the intensity and quantity of the laser irradiating the intersection can be changed.

[0016] <4> In the laser processing method described in <3> above, in the second irradiation step, multiple laser beams can be used to generate multiple focal points in the depth direction of the wafer, thereby changing the total output of the laser beams so that the laser irradiation intensity of the focal point with the lowest intensity among the multiple focal points is lower than the quality modification limit.

[0017] <5> In addition, one aspect of the present invention relates to a laser processing apparatus that forms a modified region by irradiating a laser into the interior of a wafer, wherein the total output of the laser is changed at the intersection of the first track of the wafer and the second track that intersects with the first track.

[0018] According to the present invention, thermal damage that may occur around the intersections in a wafer can be suppressed. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the outline of thermal damage evaluation using a wafer with a low-melting-point metal film.

[0020] Figure 2 This is an optical microscope image of the Sn film after laser L-scanning.

[0021] Figure 3 This is an optical microscope image of the Sn film after laser L-scanning of the first trace CH1 and the second trace CH2, which is orthogonal to the first trace CH1.

[0022] Figure 4 This is a schematic structural diagram of the laser processing apparatus according to the first embodiment of the present invention.

[0023] Figure 5 This is a conceptual diagram used to illustrate the laser L.

[0024] Figure 6 This is a conceptual diagram illustrating an example of the intensity of three laser beams.

[0025] Figure 7 This is a graph illustrating an example of the remodeling limit energy.

[0026] Figure 8 yes Figure 7 An enlarged view of region VII in the image.

[0027] Figure 9 These are optical microscope images of the cross-section of a wafer W after being irradiated with lasers L of different energies.

[0028] Figure 10 This is a schematic diagram of a cross section near the intersection of the modified regions formed by a single laser in the second track.

[0029] Figure 11This is a schematic diagram of the cross section near the intersection CR in the second track after laser processing.

[0030] Figure 12 This is a schematic diagram of the cross section near the intersection CR in the second trace, after being processed by multiple lasers.

[0031] Figure 13 This is a flowchart illustrating the process of the laser processing method according to the embodiments of the present invention.

[0032] Figure 14 This is a flowchart illustrating the process of the second irradiation step in the same embodiment. Detailed Implementation

[0033] Before describing the embodiments of the present invention, thermal damage generated in the wafer will be explained.

[0034] Figure 1 This is a schematic diagram illustrating the outline of thermal damage evaluation using a wafer with a low-melting-point metal film. Figure 1 This is a cross-sectional view of wafer W along the scanning direction of laser L, schematically illustrating the formation of a modified region R in wafer W along the scanning direction of laser L. Wafer W, with a low-melting-point metal film, is used for preliminary evaluation of thermal damage to product wafers, and a Sn film is provided on the lower surface of the substrate. The low-melting-point metal film is, for example, a Sn film composed of Sn (tin). The melting point of Sn is 232°C. Figure 1 As shown, a laser L is irradiated into the interior of wafer W from the side opposite to the side with the Sn film. While forming modified regions R, thermal damage is generated at the Sn film located directly below each modified region R in the Z direction. The thermal damage of wafer W after the formation of the modified regions R (modified layer) is evaluated using the Sn film. If the laser L irradiation is inappropriate, thermal damage may occur not only directly below the modified region R but also around it. Thermal damage evaluation using a wafer W with a Sn film is performed to determine in advance the locations where thermal damage may occur.

[0035] Figure 2 These are optical microscope images of the Sn film after laser L-scanning. For example... Figure 2 As shown, thermal damage was induced in the Sn film by the laser L. Therefore, the thermal damage can be evaluated by observing the Sn film. Furthermore, Figure 2 Cracks extending in the direction of thermal damage are visible. These cracks originate in the Si (substrate) above the Sn film and extend to the Sn film.

[0036] Figure 3This is an optical microscope image of the Sn film after laser scanning (L) of the first channel CH1 and the second channel CH2, which is orthogonal to the first channel CH1. When a modified region is formed in the first channel CH1 and the second channel CH2 by laser irradiation using existing methods, the laser L sometimes reflects and scatters at the modified region R formed in the first channel CH1, reaching the periphery of the intersection. As a result, as... Figure 3 As shown, thermal damage can sometimes occur around traces, especially around intersections. If this thermal damage occurs on a wafer containing devices, it can sometimes lead to product defects. Therefore, it is important to prevent thermal damage around traces.

[0037] (First Implementation)

[0038] Hereinafter, the laser processing apparatus 1 according to the first embodiment of the present invention will be described with reference to the accompanying drawings. Figure 4 This is a schematic structural diagram of the processing apparatus according to the first embodiment of the present invention. Furthermore, in the XYZθ directions shown in each diagram, the direction indicated by the + direction is designated as the positive direction, and the direction indicated by the - direction is designated as the negative direction. For example... Figure 4 As shown, the θ direction is the direction of rotation that is centered on the Z-axis and parallel to the XY plane.

[0039] like Figure 1 As shown, the laser processing apparatus 1 according to this embodiment includes a wafer moving part 11, a laser head 20, and a control part 50.

[0040] The wafer moving section 11 consists of an adsorption stage 13 for holding the wafer W and an XYZθ stage 12 disposed on the main body base 16 of the laser processing apparatus 1 to precisely move the adsorption stage 13 in the XYZθ direction. Through this wafer moving section 11, the wafer W is precisely moved in the XYZθ direction shown in the figure.

[0041] Wafer W has a back-side grinding tape (hereinafter referred to as BG tape) with adhesive material attached to the surface on which the device is formed, and is placed on the adsorption stage 13 with the back side facing up. Alternatively, wafer W may have a dicing film with adhesive material attached to one side, and be placed on the adsorption stage 13 in a state where it is integrated with the frame via the dicing film.

[0042] The laser head 20 mainly includes a laser source 22, a spatial light modulator 28, and a focusing lens 38.

[0043] Laser source 22, under the control of control unit 50, outputs laser L for processing to form a modified region inside wafer W. As for the conditions of laser L, for example, the light source is a semiconductor laser-excited Nd:YAG laser with a wavelength of 1.1 μm, a repetition frequency of 80 kHz to 200 kHz, a pulse width of 180 ns to 400 ns, and an output of 10 W to 40 W.

[0044] The wavelength of laser L is preferably 1.0 μm or more and 1.5 μm or less. When forming a modified region R inside a wafer using laser L, a wider crack can be formed by using a longer wavelength for laser L. Furthermore, under the wavelength conditions of laser L described above, the pulse spacing of laser L can be increased. Therefore, the pulse spacing of laser L is preferably 4 μm or more and 12 μm or less. Based on the above wavelength and pulse spacing conditions, the processing speed of laser L on the modified region R can be increased. Additionally, the relative speed of laser L traveling relative to wafer W is, for example, 800 mm / s to 1600 mm / s.

[0045] The laser source 22 includes an intensity modulation element (not shown). The intensity modulation element modulates the intensity of the laser (laser irradiation intensity). As the intensity modulation element, an acousto-optic element, an electro-optic modulator, or a Mach-Zehnder interferometer, etc., are used. For example, an AOM (acousto-optic modulator) can be used as an acousto-optic element. Since high-speed intensity modulation is possible, an acousto-optic element is preferred as the intensity modulation element.

[0046] The spatial light modulator 28 is a phase-modulated type. It takes as input the laser L output from the laser source 22, and presents a predetermined holographic pattern that modulates the phase of the laser L in each of a plurality of pixels arranged in a two-dimensional array. It then outputs the phase-modulated laser L. This holographic pattern is formed by superimposing multiple Fresnel lens patterns at different focusing positions. Thus, within the wafer W, multiple laser beams are focused at arbitrary intensity ratios to positions at different depths from the laser irradiation surface (the back side of the wafer W). In other words, the spatial light modulator 28 generates multiple focusing points along the depth direction of the wafer W.

[0047] Spatial light modulator 28, for example, can modulate laser L to give laser L any number of laser beams. Figure 5 This is a conceptual diagram used to illustrate the laser L. Figure 5 (a) shows a single laser L (L10). For example, for a laser L (L10) that has only a single laser L10... Figure 5 (a)), the spatial light modulator 28 can modulate the laser L into such a shape as Figure 5 As shown in (b), it has a first laser L11 and a second laser L12, and can also be modulated as follows: Figure 5As shown in (c), it has a third laser L13, a fourth laser L14 and a fifth laser L15.

[0048] Figure 6 This is a conceptual diagram illustrating an example of the intensity of three laser beams. Figure 6 In (a), among the three branched lasers, the intensity P3 of laser L13, the intensity P4 of laser L14, and the intensity P5 of laser L15 are related as P3 < P4 < P5. Figure 6 In (b), the intensity relationship of the three laser beams after branching is P3 = P4 = P5. Figure 6 In (c), the intensity relationship of the three lasers after branching is P3 > P4 > P5. As mentioned above, the spatial light modulator 28 can vary the intensity ratio of more lasers.

[0049] As the spatial light modulator 28, for example, an LCOS-SLM is used. The operation of the spatial light modulator 28 and the holographic pattern presented by the spatial light modulator 28 are controlled by the control unit 50. Furthermore, since the specific structure of the spatial light modulator 28 and the holographic pattern presented by the spatial light modulator 28 are already known, detailed descriptions are omitted here. In addition, the holographic pattern is pre-derived and stored in the control unit 50 based on the formation position of the modified region, the wavelength of the irradiated laser L, and the refractive index of the focusing lens 38 and the wafer W.

[0050] An intensity modulation element modulates the intensity (total output) of laser L. By reducing the intensity of laser L before branching, the intensity modulation element can ensure that the intensity of at least one of the multiple lasers after branching is below the remodeling limit that forms the remodeling region R. For example, the total output of laser L can be altered by ensuring that the laser irradiation intensity of the focal point with the lowest intensity among multiple focal points is below the remodeling limit.

[0051] Figure 7 This is a graph illustrating an example of the modification limit energy. The modification limit energy refers to the minimum energy of a laser beam capable of forming a modified region in a wafer. The modification limit varies depending on the depth of the modified region, the laser pulse width, pulse shape, frequency, and beam state. Figure 7 The graph is obtained by plotting the width of the modified region R formed by irradiation by a single laser in the thickness direction of the wafer W, based on the energy (μJ) of each laser pulse. Figure 8 yes Figure 7 An enlarged view of region VII in the image. (See image for reference.) Figure 7 , Figure 8As shown, when the laser energy is 3.5 μJ or less, the width of the modified region R in the thickness direction of the wafer W is 0.0 μm. On the other hand, when the laser energy is 3.6 μJ or more, the width of the modified region R in the thickness direction of the wafer W is approximately 10.0 μm or more. Figure 9 These are optical microscope images of a cross-section of a wafer W along the laser scanning direction after it has been irradiated with lasers L of different energies. For example... Figure 9 As shown, when the laser energy is 3.6 μJ or higher, a modified region is formed along the scanning direction. On the other hand, when the laser energy is 3.4 μJ or lower, the modified region is hardly formed or not formed at all. Thus, by modulating the laser energy, i.e., the intensity, the formation of the modified region can be controlled. Therefore, in a laser after multiple branches, by reducing the total output of the laser before branching, the intensity of one or more of the lasers after multiple branches can be made lower than the modification limit at which a modified region is not formed.

[0052] Figure 10 This is a schematic diagram of a cross section near the intersection of the modified regions formed by a single laser in the second track. Figure 10 (a) shows a cross section of a wafer W in which a modified region R is formed along the second track CH2 by an excessive intensity laser. Figure 10 (b) shows a cross section of wafer W when the laser intensity is reduced near the intersection CR and a modified region R is formed along the second track CH2. Figure 10 of (a) Figure 10 (b) is a schematic diagram of a cross-section of wafer W along the second track CH2. Additionally, Figure 10 In (b), the ratio of the laser intensity before the intensity reduction to the laser intensity after the reduction is set to, for example, 8:7. Figure 10 In (b), the laser intensity near the cross section CR is set below the modification limit.

[0053] exist Figure 10 In (a), due to the reflection and scattering of laser light at the modified region R formed in the first track CH1, the modified region R near the cross CR is smaller than the modified region R formed at a location other than the cross CR. Consequently, thermal damage may sometimes occur around the track.

[0054] On the other hand, Figure 10 In (b), since the laser intensity is reduced near the intersection CR, thermal damage caused by reflection and scattering due to the modified region R formed in the first track CH1 can be prevented.

[0055] In addition, Figure 10 In (b), with Figure 10Compared to case (a), the extent of crack propagation near the intersection CR is slightly reduced. However, the crack is continuous and uninterrupted in the Y direction. Therefore, after a crack is formed in wafer W, the straightness of the dicing can be maintained when wafer W is diced according to the formed crack.

[0056] Figure 11 This is a schematic diagram of the cross section near the intersection after laser processing in the second track. Figure 11 (a) is a schematic diagram showing the modified region R and cracks formed by a single laser along the second trace CH2. Figure 11 (b) is a schematic diagram showing the increased total output of the laser near the intersection CR by an intensity modulation element, and the modified region R and cracks formed by the laser after it is branched into two lines by the spatial light modulator along the second track CH2. Additionally, for example, the total output of the laser before branching is set to 80%, and the total output of the laser after branching into two lines is set to 100%.

[0057] like Figure 11 As shown in (a), when the modified region R and cracks are formed by a single laser, the modified region R formed near the intersection CR is smaller than the modified region R formed outside the intersection CR due to reflection and scattering of the laser at the modified region R formed in the first track CH1. Consequently, the quality of the modified region R sometimes deteriorates. As a result, the extent of crack propagation near the intersection CR sometimes decreases compared to cracks formed outside the intersection CR.

[0058] On the other hand, Figure 11 In (b), near the intersection CR, two lasers are used to form a modified region at a location close to the surface and at a deeper location. As a result, the cracks formed near the intersection CR achieve the same degree of propagation as cracks formed outside the intersection CR. Consequently, after cracks are formed in wafer W, the straightness of the dicing can be maintained when wafer W is diced according to the formed cracks.

[0059] Figure 12 This is a schematic diagram of a cross-section near the intersection of multiple laser-processed sections in the second trace. Figure 12 In the diagram, laser L branches into a first laser, a second laser, and a third laser. The first laser illuminates a position at depth D1, the second laser illuminates a position at depth D2, and the third laser illuminates a position at depth D3. Let the intensity of the first laser be P1, the intensity of the second laser be P2, and the intensity of the third laser be P3. Then, the intensity of each laser is modulated to P1 > P2 > P3. Figure 12 (a) shows a cross section of a wafer W with a modified region R formed along the second track CH2 by a laser with excess total output. Figure 12(b) shows the cross section of the wafer W when the total output of the laser L is reduced (by 20% compared to the case where the intensity is not reduced) at the cross section CR by an intensity modulation element. Figure 12 of (a) Figure 12 (b) is a schematic diagram of the cross section of wafer W along the second track CH2.

[0060] When a modified region R is formed deeper in the Z-direction (thickness direction) of the second channel CH2, lasers irradiating deeper locations (e.g., the second laser irradiating location D2 and the third laser irradiating location D3) are easily affected by the modified region R previously formed in the first channel CH1. Specifically, due to cracks in the first channel CH1, a portion of the second and third lasers is reflected and scattered, sometimes forming incomplete modified regions at their respective depths. Furthermore, due to the aforementioned reflection and scattering, thermal damage may sometimes occur around the channel. For example, in... Figure 12 In (a), a uniform modified region R is formed at intervals along the laser scanning direction at depth D1. On the other hand, an incomplete modified region R is formed near the intersection CR at depths D2 and D3. With the incomplete modified region R present, cracks caused by this region cannot maintain straightness during wafer W dicing. Furthermore, thermal damage may sometimes occur around the trace.

[0061] exist Figure 12 In (b), the total output of laser L is reduced near the intersection CR by an intensity modulation element, thereby reducing the intensity of the first, second, and third lasers. As a result, at depths D2 and D3, the intensity of each laser is below the modification limit. Figure 12 Compared to (a), no modified region is formed even in areas farther from the first trace CH1. However, since the modified region R is continuously formed at depth D1, cracks occur along the second trace CH2 near the surface of wafer W. Therefore, the cutting force is maintained, thereby enabling the wafer W to be cut. Furthermore, since the formation of incompletely modified regions is suppressed, straight-line propagation can be maintained during dicing. Furthermore, since the reflection and scattering of the second and third lasers are suppressed, thermal damage can also be prevented.

[0062] Furthermore, in this embodiment, it is described that the laser L has a single laser L10 in the portion other than the intersection CR in the second track CH2, but it is not limited to this. For example, the laser L may also have multiple lasers in the portion other than the intersection CR in the second track CH2.

[0063] return Figure 4The structure of the laser processing apparatus 1 will be described below. The condenser lens 38 is an objective lens (infrared objective lens) that focuses the laser L onto the interior of the wafer W. The numerical aperture (NA) of the condenser lens 38 is 0.65 to 0.85 (e.g., 0.85).

[0064] In addition to the above-mentioned structure, the laser head 20 also includes a beam expander 24, a λ / 2 wavelength plate 26, and a reduction optical system 36.

[0065] The beam expander 24 expands the laser L output from the laser source 22 to a beam diameter suitable for use in the spatial light modulator 28. The λ / 2 wavelength plate 26 adjusts the incident polarization plane of the laser to the spatial light modulator 28. The reducing optical system 36 is an afocal optical system (telecentric optical system on both sides) consisting of a first lens 36a and a second lens 36b, which reduces and projects the laser L modulated by the spatial light modulator 28 onto the condenser lens 38.

[0066] In addition, although the illustration is omitted, the laser head 20 is equipped with an alignment optical system for aligning with the wafer W, an autofocus unit for maintaining a certain distance (working distance) between the wafer W and the condenser lens 38, etc.

[0067] The control unit 50 is, for example, a computing device such as a personal computer, and includes computing circuits composed of various processors and memory. These processors include a central processing unit (CPU), a graphics processing unit (GPU), an application-specific integrated circuit (ASIC), and programmable logic devices (SPLDs, CPLDs, and FPGAs). Furthermore, the various functions of the control unit 50 can be implemented using a single processor or multiple processors of the same or different types.

[0068] In addition, the control unit 50 controls the operation of the spatial light modulator 28 so that the spatial light modulator 28 presents a predetermined holographic pattern.

[0069] In addition, the control unit 50 receives operator input via an operation unit (not shown) and sends control signals corresponding to the operation input to various parts of the laser processing apparatus 1 to control the operation of each part. The operation unit (not shown) is a unit that receives operator input. The operation unit (not shown) may include, for example, a keyboard, mouse, or touch panel.

[0070] In addition, the laser processing apparatus 1 may also consist of a wafer transport unit (not shown), an operation panel, a monitor, and indicator lights.

[0071] The control panel is equipped with switches and displays for operating various parts of the laser processing apparatus 1. The monitor displays wafer images captured by a CCD camera (not shown), or displays program content and various messages. Indicator lights show the operating status of the laser processing apparatus 1, including processing in progress, processing completion, and emergency stop.

[0072] Next, refer to Figure 13 and Figure 14 The laser processing method involved in the embodiments of the present invention will be described. Figure 13 This is a flowchart illustrating the process of the laser processing method according to the embodiments of the present invention. Figure 14 This is a flowchart illustrating the process of the second irradiation step in the same embodiment.

[0073] The laser processing method described in this embodiment is a laser processing method that irradiates the interior of a wafer with a laser to form a modified region. For example... Figure 13 As shown, the laser processing method according to this embodiment includes: a first irradiation step (step S1), in which a laser is irradiated onto a first track; and a second irradiation step (step S2), in which, after the first irradiation step, a laser is irradiated onto a second track that intersects with the first track. In the second irradiation step, the total output of the laser at the intersection of the first track and the second track is changed.

[0074] In the second irradiation step, when the laser L reaches the vicinity of the intersection CR, at least one of the total output of the laser L and the number of lasers (number of focusing points) is changed (step S21). At the intersection CR, the wafer W is processed by the changed laser L (step S22). After passing through the intersection CR, at least one of the total output of the laser L and the number of lasers is changed. In other words, the conditions changed in step S21 are restored to their original state (step S23) to process the subsequent part of the second track. The second irradiation step (steps S21-23) is performed for one second track according to the number of intersections. The second irradiation step is performed hundreds of times for one second track, for example. In addition, the wafer W has multiple second tracks. For example, a wafer W with a diameter of 300 mm has hundreds of second tracks. The second irradiation step is performed for multiple second tracks arranged on the wafer W to complete the processing of one wafer W.

[0075] The embodiments of the present invention have now been described. However, the technical scope of the present invention is not limited to the foregoing embodiments, and various modifications can be made without departing from the spirit of the invention.

[0076] The focusing lens 38 can also simultaneously focus the laser L onto two positions that are separate from each other in the wafer movement direction.

[0077] Furthermore, in the above embodiment, the laser processing apparatus 1 is fully controlled by the control unit 50, but it is also possible to control the laser processing apparatus 1 through multiple control units. Additionally, the control unit can be integrated with the processing apparatus or it can be a separate unit.

[0078] In addition, in the above embodiment, in step S23, the conditions changed in step S21 are restored to the original conditions, but they can also be changed to other conditions, or the conditions at the intersection CR can be maintained.

[0079] Furthermore, without departing from the spirit of the invention, it is appropriate to replace the constituent elements in the foregoing embodiments with known constituent elements. In addition, the foregoing variations can be appropriately combined.

[0080] Symbol Explanation

[0081] 1. Laser processing equipment

[0082] 11 Wafer Moving Section

[0083] 12 workbenches

[0084] 13 Adsorption stage

[0085] 20 laser heads

[0086] 22 laser sources

[0087] 24 Beam expander

[0088] 26 λ / 2 wavelength plate

[0089] 28 Spatial Light Modulator

[0090] 36. Miniaturization of optical systems

[0091] 38 Condensing Lens

[0092] 50 Control Department

Claims

1. A laser processing method, wherein a modified region is formed by irradiating the interior of a wafer with a laser, the laser processing method comprising: The first irradiation step involves irradiating the first track of the wafer with the laser. The second irradiation step involves irradiating the second track, which intersects with the first track, with laser light after the first irradiation step. In the second irradiation step, the total output of the laser at the intersection of the first track and the second track is changed.

2. The laser processing method according to claim 1, wherein, In the second irradiation step, the total output of the laser irradiating the intersection is changed by an acousto-optic element.

3. The laser processing method according to claim 1 or 2, wherein, In the second irradiation step, at least one of the intensity and quantity of the laser irradiating the intersection is changed.

4. The laser processing method according to claim 3, wherein, In the second irradiation step, multiple laser beams generate multiple focusing points along the depth direction of the wafer. The total output of the laser is changed so that the laser irradiation intensity of the focal point with the lowest intensity among the multiple focal points is lower than the quality modification limit.

5. A laser processing apparatus for irradiating the interior of a wafer with a laser to form a modified region. At the intersection of the first track on the wafer and the second track that intersects with the first track, the total output of the laser is changed.

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