Laser processing method and laser processing device

Abstract

To provide a laser processing method and a laser processing device capable of suppressing heat damage that may occur around intersections of streets on a wafer.SOLUTION: A laser processing method according to an embodiment of the present invention is a laser processing method for irradiating inside a wafer with a laser beam to form a modified region, and includes a first irradiation step of irradiating a first street of the wafer with laser beam, and a second irradiation step of irradiating a second street intersecting the first street with laser beam after the first irradiation step, and the total output of the laser beam at the intersection of the first street and the second street is changed in the second irradiation step.SELECTED DRAWING: Figure 14

Description

[Technical Field]

[0001] The present invention relates to a laser processing method and a laser processing apparatus. [Background technology]

[0002] Conventionally, a laser processing device is known that performs internal focusing processing to form a laser processing area that serves as a starting point for cutting inside a wafer along multiple streets (streets CH1, CH2) formed in a grid pattern (Patent Document 1).

[0003] When performing internal focusing processing of a wafer using the laser processing apparatus described in Patent Document 1, first, a laser beam is irradiated along street CH1 to form a laser processing region inside the wafer, and then a laser processing region is formed inside the wafer along street CH2 that intersects with street CH1.

[0004] When the laser beam along the street CH2 reaches the intersection with the street CH1, the laser beam is scattered by the laser processing area that was previously formed at the intersection, which may cause thermal damage around the street and adversely affect the device layer formed around the street.

[0005] Here, by switching the laser beam that performs the internal focusing processing at the intersection, it is possible to suppress scattering of the laser beam in the laser processing region that was previously formed at the intersection, and therefore it is possible to suppress the occurrence of the above-mentioned thermal damage. Conventionally, optical modulators capable of switching a single laser beam into multiple laser beams have been known (Patent Document 2). Patent Document 2 discloses a reflective crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM) (LCOS-SLM) as an example of an optical modulator. This reflective crystal spatial light modulator can switch a single laser beam into multiple laser beams. Furthermore, it is also possible to change the intensity ratio of each laser beam among the multiple laser beams. By switching the laser beams or changing the intensity ratio of the laser beams in this way at the intersection, the occurrence of the thermal damage can be suppressed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-006548 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-107334 Summary of the Invention [Problem to be solved by the invention]

[0007] Here, the switching of the laser beam by the LCOS-SLM is usually performed when the scanning direction of the laser beam is changed (when the laser beam returns from back-and-forth processing). In addition, for a wafer with a diameter of 300 mm, the time required to process one line of the wafer (for example, to form a crack inside) is approximately 270 ms to 500 ms. On the other hand, the switching of the laser beam by the LCOS-SLM takes approximately 50 ms to 150 ms. Therefore, because the time required for switching is long, it is not possible to switch the laser beam during processing.

[0008] Other known means for switching a single laser beam into multiple laser beams include the use of a diffractive optical element (DOE), a half mirror, or a polarizing beam splitter (PBS).However, even when using a DOE, a half mirror, or a polarizing beam splitter (PBS), the response speed is insufficient to switch the laser beam only around the intersection, as with the use of an LCOS-SLM, and it is difficult to suppress thermal damage around the intersection while maintaining processing quality.

[0009] The present invention has been made in view of the above circumstances, and has an object to provide a laser processing method and a laser processing apparatus that can suppress thermal damage that can occur around intersections in a wafer. [Means for solving the problem]

[0010] The present invention has been made to solve the above problems, and proposes the following means. <1> A laser processing method according to one embodiment of the present invention is a laser processing method for irradiating a laser beam into the interior of a wafer to form a modified region, and includes a first irradiation step of irradiating the laser beam onto a first street of the wafer, and a second irradiation step of irradiating a laser beam onto a second street that intersects with the first street after the first irradiation step, wherein in the second irradiation step, the total output of the laser beam at the intersection of the first street and the second street is changed. <2> the above <1> In the laser processing method described in the above, in the second irradiation step, the total output of the laser light irradiated onto the intersection may be changed by an acousto-optic element. <3> the above <1> or <2> In the laser processing method described in the above, in the second irradiation step, at least one of the intensity and the number of the laser beams irradiated onto the intersection may be changed. <4> the above <3> In the laser processing method described above, in the second irradiation step, a plurality of focal points are generated in the depth direction of the wafer by a plurality of the laser beams, and the total output of the laser beams may be changed so that the laser irradiation intensity of the focal point with the smallest intensity among the plurality of focal points is less than the modification limit.

[0011] <5> Furthermore, a laser processing apparatus according to one embodiment of the present invention is a laser processing apparatus that irradiates laser light into the interior of a wafer to form a modified region, and changes the total output of the laser light at the intersection of a first street of the wafer and a second street that intersects with the first street. [Effects of the Invention]

[0012] According to the present invention, it is possible to suppress thermal damage that may occur around the intersections of the wafer. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an outline of thermal damage evaluation using a wafer having a low-melting-point metal film. [Figure 2] 1 is an optical microscope image of the Sn film after being scanned with laser light L. [Figure 3] 10 is an optical microscope image of the Sn film after laser light L is scanned on a first street CH1 and a second street CH2 perpendicular to the first street CH1. [Figure 4] 1 is a schematic configuration diagram of a laser processing device according to a first embodiment of the present invention. [Figure 5] FIG. 2 is a conceptual diagram for explaining laser light L. [Figure 6] FIG. 1 is a conceptual diagram showing an example of the intensities of three laser beams. [Figure 7] FIG. 10 is a graph showing an example of reforming limit energy. [Figure 8] FIG. 8 is an enlarged view of region VII in FIG. 7. [Figure 9]10 is an optical microscope image of a cross section of a wafer W after being irradiated with laser light L of different energies. [Figure 10] FIG. 10 is a schematic diagram of a cross section near an intersection on a second street where a modified region is formed by a single laser beam. [Figure 11] FIG. 10 is a schematic diagram of a cross section near a crossing point CR on a second street that has been processed by a laser beam. [Figure 12] FIG. 10 is a schematic diagram of a cross section near a crossing point CR on a second street that has been processed using a plurality of laser beams. [Figure 13] 1 is a flowchart illustrating a flow of a laser processing method according to an embodiment of the present invention. [Figure 14] 10 is a flowchart illustrating the flow of a second irradiation step in the same embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Before describing the embodiments of the present invention, thermal damage that occurs in a wafer will be described. Figure 1 is a schematic diagram illustrating an overview of thermal damage evaluation using a wafer with a low-melting-point metal film. Figure 1 is a cross-sectional view of a wafer W along the scanning direction of a laser beam L, and illustrates the formation of modified regions R on the wafer W along the scanning direction of the laser beam L. The wafer W with a low-melting-point metal film is a wafer used to evaluate thermal damage to product wafers in advance. A Sn film is formed on the underside of the substrate. The low-melting-point metal film is, for example, a Sn film made of tin (Sn). The melting point of Sn is 232°C. As shown in Figure 1, laser beam L is irradiated into the interior of the wafer W from the side opposite the Sn film. This forms modified regions R, and thermal damage occurs in the Sn film located directly below each modified region R in the Z direction. The thermal damage of the wafer W after the modified regions R (modified layers) are formed is evaluated using the Sn film. If the irradiation of the laser light L is inappropriate, thermal damage may occur not only directly below the modified region R but also in the surrounding area. Evaluation of thermal damage using a wafer W having an Sn film is performed to determine in advance the locations where thermal damage may occur.

[0015] Figure 2 is an optical microscope image of the Sn film after scanning with laser light L. As shown in Figure 2, thermal damage has been caused to the Sn film by the laser light L. In this way, thermal damage can be evaluated by observing the Sn film. In Figure 2, a crack can be seen extending in the direction of the thermal damage. This crack was caused when a crack that had occurred in the Si (base material) above the Sn film reached the Sn film.

[0016] Figure 3 shows an optical microscope image of a Sn film after laser light L is scanned on a first street CH1 and a second street CH2 perpendicular to the first street CH1. When a modified region is formed on the first street CH1 and the second street CH2 by irradiating laser light using a conventional method, the laser light L may be reflected and scattered by the modified region R formed on the first street CH1 at the intersection between the first street CH1 and the second street, and may reach the periphery of the intersection. As a result, as shown in Figure 3, thermal damage may occur around the streets, especially around the intersection. If such thermal damage occurs to a wafer carrying devices, it may result in product defects. Therefore, it is important to prevent thermal damage from occurring around the streets.

[0017] (First embodiment) Hereinafter, a laser processing apparatus 1 according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 4 is a schematic diagram of the processing apparatus according to the first embodiment of the present invention. In the XYZθ directions shown in each figure, the direction indicated as the + direction is the positive direction, and the direction indicated as the - direction is the negative direction. As shown in Fig. 4, the θ direction is the direction of rotation parallel to the XY plane with the Z axis as the central axis.

[0018] As shown in FIG. 1, the laser processing apparatus 1 according to this embodiment includes a wafer moving unit 11, a laser head 20, and a control unit 50.

[0019] The wafer moving unit 11 is composed of a suction stage 13 that suction-holds the wafer W, and an XYZθ table 12 that is provided on the main body base 16 of the laser processing device 1 and that precisely moves the suction stage 13 in the XYZθ directions. The wafer moving unit 11 precisely moves the wafer W in the XYZθ directions in the figure.

[0020] The wafer W has a backgrinding tape (hereinafter referred to as BG tape) having an adhesive attached to the surface on which devices are formed, and is placed with the back surface facing upward on the suction stage 13. Alternatively, the wafer W may have a dicing sheet having an adhesive attached to one surface, and be placed on the suction stage 13 in a state where it is integrated with a frame via this dicing sheet.

[0021] The laser head 20 mainly includes a laser light source 22, a spatial light modulator 28, a condenser lens 38, and the like.

[0022] The laser light source 22 outputs processing laser light L for forming a modified region inside the wafer W under the control of the control unit 50. The conditions of the laser light L are, for example, a semiconductor laser pumped Nd:YAG laser as the light source, a wavelength of 1.1 μm, a repetition frequency of 80 to 200 kHz, a pulse width of 180 to 400 ns, and an output of 10 to 40 W. The wavelength of the laser light L is preferably 1.0 μm or more and 1.5 μm or less. When forming a modified region R inside a wafer with the laser light L, wider cracks can be formed by using a laser light L with a longer wavelength. Furthermore, under the wavelength conditions of the laser light L as described above, the pulse pitch of the laser light L can be increased. Therefore, the pulse pitch of the laser light L is preferably 4 μm or more and 12 μm or less. Based on the above wavelength and pulse pitch conditions, the processing speed of the modified region R by the laser light L can be improved. Furthermore, the relative speed at which the laser light L travels with respect to the wafer W is, for example, 800 to 1600 mm / s.

[0023] The laser light source 22 includes an intensity modulation element (not shown). The intensity modulation element modulates the intensity of the laser light. As the intensity modulation element, an acousto-optic element, an electro-optic modulator, or a Mach-Zehnder interferometer may be used. As an acousto-optic element, for example, an AOM (acousto-optic modulator) may be used. Since high-speed intensity modulation is possible, an acousto-optic element is preferable as the intensity modulation element.

[0024] The spatial light modulator 28 is a phase modulation type that inputs the laser light L output from the laser light source 22, presents a predetermined hologram pattern that modulates the phase of the laser light L in each of a plurality of two-dimensionally arranged pixels, and outputs the phase-modulated laser light L. This hologram pattern is a combination of a plurality of Fresnel lens patterns with different focusing positions. This allows a plurality of laser lights to be focused at an arbitrary intensity ratio at positions within the wafer W that are at different depths from the laser light irradiation surface (the back surface of the wafer W).

[0025] The spatial light modulator 28 can modulate the laser light L, for example, so that the laser light L comprises any number of laser beams. FIG. 5 is a conceptual diagram for explaining the laser light L. FIG. 5(a) shows a single laser beam L (L10). The spatial light modulator 28 may, for example, modulate the laser light L (FIG. 5(a)) comprising only the single laser beam L10 so that the laser light L comprises a first laser beam L11 and a second laser beam L12, as shown in FIG. 5(b), or may modulate the laser light L so that the laser light L comprises a third laser beam L13, a fourth laser beam L14, and a fifth laser beam L15, as shown in FIG. 5(c).

[0026] FIG. 6 is a conceptual diagram showing an example of the intensities of three laser beams. In FIG. 6(a), the relationship among the intensity P3 of the three branched laser beams L13, the intensity P4 of the laser beam L14, and the intensity P5 of the laser beam L15 is P3 < P4 < P5. In FIG. 6(b), the relationship among the intensities of the three branched laser beams is P3 = P4 = P5. In FIG. 6(c), the relationship among the intensities of the three branched laser beams is P3 > P4 > P5. As described above, the spatial light modulator 28 can change the intensity ratio of a plurality of laser beams.

[0027] For example, an LCOS-SLM is used as the spatial light modulator 28. The operation of the spatial light modulator 28 and the hologram pattern presented by the spatial light modulator 28 are controlled by the control unit 50. Since the specific configuration of the spatial light modulator 28 and the hologram pattern presented by the spatial light modulator 28 are already known, detailed description thereof is omitted here. The hologram pattern is derived in advance based on the formation position of the modification region, the wavelength of the irradiated laser beam L, the refractive index of the condenser lens 38, the wafer W, etc., and is stored in the control unit 50.

[0028] The intensity modulation element modulates the intensity (total output) of the laser beam L. By reducing the intensity of the laser beam L before branching, the intensity of at least one or more of the plurality of laser beams after branching can be made less than the modification limit at which the modification region R is formed.

[0029] FIG. 7 is a graph showing an example of the modification energy limit. The modification energy limit refers to the minimum energy of laser light capable of forming a modified region on a wafer. The modification limit varies depending on the depth at which the modified region is formed, the pulse width, pulse shape, frequency, and beam condition of the laser light, etc. FIG. 7 is a graph plotting the width of the modified region R formed by irradiation with a single laser beam in the thickness direction of the wafer W as a function of the energy (μJ) of the single laser beam per pulse. FIG. 8 is an enlarged view of region VII in FIG. 7. As shown in FIGS. 7 and 8, when the laser beam energy was 3.5 μJ or less, the width of the modified region R in the thickness direction of the wafer W was 0.0 μm. On the other hand, when the laser beam energy was 3.6 μJ or more, the width of the modified region R in the thickness direction of the wafer W was approximately 10.0 μm or more. FIG. 9 is an optical microscope image of a cross section of a wafer W along the scanning direction of the laser beam after irradiation with laser beam L of different energies. As shown in Figure 9, when the laser beam energy was 3.6 μJ or more, modified regions were formed along the scanning direction. On the other hand, when the laser beam energy was 3.4 μJ or less, modified regions were hardly formed, or not formed at all. In this way, the formation of modified regions can be controlled by modulating the energy, i.e., intensity, of the laser beam. Therefore, in the case of multiple branched laser beams, by reducing the total output of the laser beam before branching, the intensity of one or more of the multiple branched laser beams can be made below the modification limit at which no modified region is formed.

[0030] FIG. 10 is a schematic diagram of a cross section near an intersection on a second street where a modified region is formed by a single laser beam. FIG. 10(a) shows a cross section of a wafer W in which a modified region R is formed along a second street CH2 by a laser beam of excessive intensity. FIG. 10(b) shows a cross section of a wafer W when the intensity of the laser beam is reduced near the intersection CR to form a modified region R along the second street CH2. FIGS. 10(a) and 10(b) are schematic diagrams of a cross section of a wafer W along a second street CH2. Note that the ratio of the intensity of the laser beam before the reduction in intensity to the intensity of the laser beam after the reduction in intensity in FIG. 10(b) is, for example, 8:7, and the intensity of the laser beam near the intersection CR in FIG. 10(b) is below the modification limit.

[0031] 10(a), the modified region R near the intersection CR is smaller than the modified region R formed at a position other than the intersection CR due to reflection and scattering of the laser light in the modified region R formed on the first street CH1. Furthermore, thermal damage may occur around the street.

[0032] On the other hand, in FIG. 10(b), the intensity of the laser light is reduced near the intersection CR, which makes it possible to prevent thermal damage caused by reflection and scattering by the modified region R formed on the first street CH1. 10(b), the degree of propagation of the crack formed near the intersection CR is slightly reduced compared to the case of FIG. 10(a). However, the crack continues uninterrupted in the Y direction. Therefore, after a crack is formed in the wafer W, when the wafer W is divided along the formed crack, the straightness of the division can be maintained.

[0033] Fig. 11 is a schematic diagram of a cross section near an intersection on a second street processed by a laser beam. Fig. 11(a) is a schematic diagram showing a modified region R and a crack formed along the second street CH2 by a single laser beam, and Fig. 11(b) is a schematic diagram showing a modified region R and a crack formed along the second street CH2 near the intersection CR by a laser beam split into two by a spatial light modulator after the total output of the laser beam is increased by an intensity modulation element. Note that, for example, the total output of the laser beam before splitting is set to 80%, and the total output of the split laser beam is set to 100%.

[0034] As shown in Figure 11(a), when a single laser beam is used to form a modified region R and a crack, the laser beam is reflected and scattered by the modified region R formed on the first street CH1, causing the modified region R formed near the intersection CR to be smaller than the modified region R formed outside the intersection CR. Furthermore, the quality of the modified region R may also deteriorate. As a result, the degree of extension of the crack formed near the intersection CR may be reduced compared to the crack formed outside the intersection CR.

[0035] On the other hand, in Figure 11(b), near the intersection CR, modified regions are formed near the surface and at a deeper position by the two laser beams. As a result, the crack formed near the intersection CR has the same degree of extension as cracks formed outside the intersection CR. As a result, after a crack is formed in the wafer W, when the wafer W is divided along the formed crack, the straightness of the division can be maintained.

[0036] FIG. 12 is a schematic diagram of a cross section near an intersection on the second street processed by multiple laser beams. In FIG. 12, the laser beam L is branched into a first laser beam, a second laser beam, and a third laser beam. The first laser beam is irradiated at a depth D1, the second laser beam at a depth D2, and the third laser beam at a depth D3. If the intensity of the first laser beam is P1, the intensity of the second laser beam is P2, and the intensity of the third laser beam is P3, the intensities of the three laser beams are modulated so that P1 > P2 > P3. FIG. 12(a) shows a cross section of a wafer W in which a modified region R is formed along the second street CH2 by laser beams with excessive total power. FIG. 12(b) shows a cross section of a wafer W in which the total power of the laser beam L at the intersection CR is reduced by an intensity modulation element (20% reduction compared to when the power is not reduced). 12(a) and 12(b) are schematic diagrams of a cross section of the wafer W taken along the second street CH2.

[0037] When a modified region R is formed at a deeper position in the Z direction (thickness direction) of the second street CH2, the laser beam irradiated at the deeper position, for example, the second laser beam irradiated at position D2 and the third laser beam irradiated at position D3, is easily affected by the modified region R previously formed on the first street CH1. Specifically, cracks in the first street CH1 may cause a portion of the second laser beam and the third laser beam to be reflected and scattered, resulting in the formation of an incompletely modified region at each depth. Furthermore, the reflection and scattering may cause thermal damage around the street. For example, in FIG. 12(a), homogeneous modified regions R are formed at regular intervals in the scanning direction of the laser beam at depth D1. Meanwhile, incompletely modified regions R are formed near the intersections CR at depths D2 and D3. When an incompletely modified region R is formed, the cracks caused by the incompletely modified region R may prevent the wafer W from being divided in a straight line. Furthermore, thermal damage may occur around the street.

[0038] In FIG. 12(b), the intensity modulation element reduces the total output of the laser beam L near the intersection CR, thereby reducing the intensities of the first, second, and third laser beams. As a result, the intensities of each laser beam are below the modification limit at depths D2 and D3. Compared to FIG. 12(a), no modified region is formed even in areas farther from the first street CH1. However, because the modified region R is continuously formed at depth D1, cracks form along the second street CH2 near the surface of the wafer W. This maintains the dividing force, allowing the wafer W to be divided. Furthermore, because the formation of an incompletely modified region is suppressed, linearity can be maintained during division. Furthermore, because reflection and scattering of the second and third laser beams are suppressed, thermal damage can also be prevented.

[0039] In the present embodiment, the laser light L is described as having a single laser light L10 in the portion of the second street CH2 other than the intersection CR, but this is not limiting. For example, the laser light L may have a plurality of laser lights in the portion of the second street CH2 other than the intersection CR.

[0040] Returning to Fig. 4, the configuration of the laser processing apparatus 1 will be described. The condenser lens 38 is an objective lens (infrared objective lens) that condenses the laser light L inside the wafer W. The condenser lens 38 has a numerical aperture (NA) of 0.65 to 0.85 (for example, 0.85).

[0041] In addition to the above configuration, the laser head 20 also includes a beam expander 24, a λ / 2 wave plate 26, a reduction optical system 36, and the like.

[0042] The beam expander 24 expands the laser light L output from the laser light source 22 to a beam diameter appropriate for the spatial light modulator 28. The λ / 2 wave plate 26 adjusts the polarization plane of the laser light incident on the spatial light modulator 28. The reduction optical system 36 is an afocal optical system (a double-telecentric optical system) consisting of a first lens 36a and a second lens 36b, and reduces and projects the laser light L modulated by the spatial light modulator 28 onto a condenser lens 38.

[0043] Although not shown in the figure, the laser head 20 is equipped with an alignment optical system for aligning with the wafer W, an autofocus unit for maintaining a constant distance (working distance) between the wafer W and the focusing lens 38, and the like.

[0044] The control unit 50 is configured by an arithmetic device such as a personal computer, and includes an arithmetic circuit configured by various processors, memories, etc. The various processors include a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), and a programmable logic device (e.g., simple programmable logic device (SPLD), complex programmable logic device (CPLD), and field programmable gate array (FPGA)). The various functions of the control unit 50 may be realized by a single processor, or by multiple processors of the same or different types.

[0045] Furthermore, the control unit 50 controls the operation of the spatial light modulator 28, causing the spatial light modulator 28 to present a predetermined hologram pattern.

[0046] The control unit 50 also receives operation input from an operator via an operation unit (not shown), and transmits control signals corresponding to the operation input to each part of the laser processing apparatus 1 to control the operation of each part. The operation unit (not shown) is a means for receiving operation input from the operator. The operation unit (not shown) includes, for example, a keyboard, a mouse, or a touch panel.

[0047] The laser processing device 1 may also be configured with a wafer transport means, an operation panel, a monitor, an indicator light, and the like, all of which are not shown.

[0048] The operation panel is fitted with switches and display devices for controlling the operation of each part of the laser processing device 1. The monitor displays wafer images captured by a CCD camera (not shown), as well as program contents and various messages. The indicator lights display the operating status of the laser processing device 1, such as when processing is in progress, when processing is complete, and when there is an emergency stop.

[0049] Next, a laser processing method according to an embodiment of the present invention will be described with reference to Figures 13 and 14. Figure 13 is a flowchart illustrating the flow of the laser processing method according to an embodiment of the present invention. Figure 14 is a flowchart illustrating the flow of the second irradiation step in the same embodiment.

[0050] The laser processing method according to this embodiment is a laser processing method for forming a modified region by irradiating a laser into the interior of a wafer. As shown in Fig. 13, the laser processing method according to this embodiment includes a first irradiation step (step S1) of irradiating a first street with a laser, and a second irradiation step (step S2) of irradiating a second street intersecting the first street with the laser after the first irradiation step. In the second irradiation step, the total output of the laser at the intersection of the first street and the second street is changed.

[0051] In the second irradiation step, when the laser light L reaches the vicinity of the intersection CR, at least one of the total output of the laser light L and the number of laser beams (number of focal points) is changed (step S21). At the intersection CR, the wafer W is processed by the changed laser light L (step S22). After passing through the intersection CR, at least one of the total output of the laser light L and the number of laser beams is changed. In other words, the conditions changed in step S21 are restored (step S23), and the portion after the second street is processed. The second irradiation step (steps S21 to S23) is performed for one second street as many times as the number of intersections. The second irradiation step is performed, for example, several hundred times for one second street. Furthermore, a wafer W has multiple second streets. For example, a wafer W with a diameter of 300 mm has several hundred second streets. The second irradiation step is performed for the multiple second streets arranged on the wafer W, and processing of one wafer W is completed.

[0052] Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0053] The condenser lens 38 may simultaneously condense the laser light L at two positions spaced apart from each other in the wafer movement direction.

[0054] In addition, in the above embodiment, the control unit 50 comprehensively controls the laser processing apparatus 1, but multiple control units may control the laser processing apparatus 1. Furthermore, the control units may be provided integrally with the processing apparatus or separately.

[0055] In the above embodiment, in step S23, the conditions changed in step S21 are returned to the original conditions, but they may be changed to other conditions, or the conditions at the intersection CR may be maintained.

[0056] Furthermore, within the scope of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modifications may be combined as appropriate. [Explanation of symbols]

[0057] 1. Laser processing equipment 11 Wafer transfer unit 12 tables 13. Adsorption stage 20 laser head 22 Laser light source 24 Beam Expander 26 λ / 2 wave plate 28 Spatial Light Modulator 36 Reduction optical system 38 Condenser Lens 50 control section

Claims

1. A laser processing method for forming a modified region by irradiating a laser beam inside a wafer, comprising: a first irradiation step of irradiating a first street of the wafer with the laser light; a second irradiation step of irradiating a laser onto a second street intersecting the first street after the first irradiation step, a laser processing method in which, in the second irradiation step, a total output of the laser light at an intersection of the first street and the second street is changed;

2. 2. The laser processing method according to claim 1, wherein in the second irradiation step, a total output of the laser light irradiated onto the intersection is changed by an acousto-optical element.

3. The laser processing method according to claim 1 or 2, wherein at least one of an intensity and a number of the laser beams irradiated onto the intersection is changed in the second irradiation step.

4. In the second irradiation step, a plurality of focal points are generated in a depth direction of the wafer by the plurality of laser beams; 4. The laser processing method according to claim 3, wherein the total output of the laser beam is changed so that the laser irradiation intensity at the focal point with the lowest intensity among the plurality of focal points is less than a modification limit.

5. A laser processing device that irradiates a laser beam inside a wafer to form a modified region, a laser processing device that changes the total output of the laser light at an intersection of a first street on the wafer and a second street that intersects with the first street;

Images