Optical modulation device and method, and laser processing device and method

Abstract

To provide an optical modulator, a method for optical modulation, a laser processor, and a method for laser processing that can precisely cut off a workpiece along a cut-scheduled line.SOLUTION: An optical modulator (10) includes: a spatial optical modulator (28); and control means (50) for setting a hologram pattern to present in the spatial optical modulator, to be a striped Fresnel pattern including a first rectangular region and a second rectangular region, the first rectangular region including an optical axis of an incident light and at least two second rectangular regions located with the first rectangular region in between and having different curvatures from each other, and collectively emitting light modulated by the first rectangular region and the second rectangular region, to different light collection positions.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical modulation device and method for irradiating a laser beam to a plurality of focal points inside a workpiece, and more particularly to a laser processing device and method for forming a laser processed area by irradiating a laser beam inside a workpiece using this optical modulation device and method. [Background technology]

[0002] BACKGROUND ART Conventionally, laser processing devices have been known that irradiate a laser beam from a focal point on the inside of a workpiece, thereby forming a laser processing area inside the workpiece along a line to cut the workpiece (see, for example, Patent Document 1).

[0003] In the laser processing device described in Patent Document 1, when a workpiece is irradiated with laser light and moved relatively along the line to cut, the laser light is simultaneously focused at two positions in the workpiece that are different from each other in the thickness direction and separated along the direction of relative movement of the laser light, thereby simultaneously forming a pair of laser processing areas. This makes it possible to form two rows of laser processing areas within the workpiece for one line to cut in one scan. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-051011 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the laser processing device described in Patent Document 1, as described above, when simultaneously forming a pair of laser processing areas, the laser light is simultaneously focused at two positions in the workpiece that are different from each other in the thickness direction and separated along the relative movement direction of the laser light, so the two laser processing areas lined up in the thickness direction in the workpiece are formed at different times. As a result, cracks generated in the two laser processing areas lined up in the thickness direction are difficult to connect, resulting in problems such as poor cutting accuracy of the workpiece.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide an optical modulation device and method, and a laser processing device and method, which can cut a workpiece accurately along a planned cutting line. [Means for solving the problem]

[0007] In order to achieve the above object, the light modulation device according to the first aspect of the present invention comprises a spatial light modulator, and a control means for setting a hologram pattern to be presented by the spatial light modulator as a striped Fresnel pattern consisting of a first rectangular area including the optical axis of the incident light and at least two second rectangular areas arranged on either side of the first rectangular area, the Fresnel pattern having different curvatures, and for focusing and irradiating the light modulated by the first rectangular area and the second rectangular area at different focusing positions.

[0008] In the optical modulation device according to the second aspect of the present invention, in the first aspect, the control means changes the area ratio of the first rectangular area and the second rectangular area depending on the positional relationship of the focusing positions of the light modulated by the first rectangular area and the second rectangular area.

[0009] The optical modulation device according to the third aspect of the present invention is the first or second aspect, wherein the control means sets the Fresnel pattern set in at least one of the first rectangular area and the second rectangular area to an elliptical or oblong shape whose major axis direction is parallel to the longitudinal direction of the first rectangular area and the second rectangular area.

[0010] The optical modulation device according to a fourth aspect of the present invention is the optical modulation device according to any one of the first to third aspects, wherein the control means sets a random pattern in at least one of the first rectangular area and the second rectangular area.

[0011] A laser processing apparatus according to a fifth aspect of the present invention includes a laser light source that outputs laser light, an optical modulation device according to any one of the first to fourth aspects, and a focusing lens that focuses and irradiates the laser light modulated by the optical modulation device inside a workpiece.

[0012] A laser processing apparatus according to a sixth aspect of the present invention is the fifth aspect, wherein the longitudinal direction of the first rectangular area and the second rectangular area is perpendicular to the processing direction of the laser processing apparatus.

[0013] The laser processing apparatus according to a seventh aspect of the present invention is the fifth or sixth aspect, and further comprises a correction collar for correcting aberration of the laser light occurring inside the workpiece.

[0014] The laser processing apparatus according to an eighth aspect of the present invention is any of the fifth to seventh aspects, in which the control means superimposes an aberration correcting hologram pattern on the hologram pattern to correct aberrations of the laser light generated inside the workpiece.

[0015] A laser processing apparatus according to a ninth aspect of the present invention is any of the fifth to eighth aspects, wherein the control means superimposes a wavefront distortion correcting hologram pattern on the hologram pattern to correct wavefront distortion of the laser light.

[0016] An optical modulation method according to a tenth aspect of the present invention sets a hologram pattern to be presented by a spatial light modulator as a striped Fresnel pattern consisting of a first rectangular area including the optical axis of the incident light and at least two second rectangular areas arranged on either side of the first rectangular area, the Fresnel patterns having different curvatures, and focuses and irradiates the light modulated by the first rectangular area and the second rectangular area at different focusing positions.

[0017] A laser processing method according to an eleventh aspect of the present invention modulates laser light from a laser light source by the light modulation method according to the tenth aspect, and focuses and irradiates the modulated laser light inside a workpiece. [Effects of the Invention]

[0018] According to the present invention, it is possible to cut the workpiece along the line to cut with high precision. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a laser processing device equipped with an optical modulation device according to one embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of a hologram pattern. [Figure 3] FIG. 3 is a simplified diagram showing laser light modulated by a hologram pattern according to this embodiment. [Figure 4] FIG. 4 is a diagram for explaining a laser processing method according to one embodiment of the present invention. [Figure 5] FIG. 5 is a diagram for explaining a laser processing method according to one embodiment of the present invention. [Figure 6] FIG. 6 is a diagram for explaining a laser processing method according to one embodiment of the present invention. [Figure 7] FIG. 7 is a perspective view schematically showing the shape of the modulated laser light. [Figure 8] FIG. 8 is a plan view showing an example of a pattern presented in a rectangular region of a hologram pattern. [Figure 9] FIG. 9 is a plan view showing a hologram pattern according to the first modification. [Figure 10] FIG. 10 is a plan view showing a hologram pattern according to the second modification. [Figure 11] FIG. 11 is a diagram showing a focal point of a laser beam modulated by a hologram pattern according to the second modification. [Figure 12]FIG. 12 is a plan view showing another example of a hologram pattern according to the second modification. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an optical modulation device and method, and a laser processing device and method according to the present invention will be described with reference to the accompanying drawings.

[0021] [Laser processing equipment] Fig. 1 is a schematic diagram showing the configuration of a laser processing apparatus equipped with an optical modulation device according to one embodiment of the present invention. As shown in Fig. 1, the laser processing apparatus 1 according to this embodiment includes a stage 11, a laser engine (optical system unit) 20, and a control unit 50. Note that, although this embodiment illustrates a case in which the laser engine 20 and the control unit 50 are configured separately, this configuration is not limiting, and the laser engine 20 may include part or all of the control unit 50.

[0022] The stage 11 is used to hold a workpiece by suction. The stage 11 includes a stage movement mechanism (not shown) and is configured to be movable in the X, Y, Z, and θ directions by the stage movement mechanism. The stage movement mechanism can be configured using various mechanisms, such as a ball screw mechanism or a linear motor mechanism. In FIG. 1, the three directions X, Y, and Z are mutually orthogonal, and of these, the X and Y directions are horizontal directions, and the Z direction is vertical. The θ direction is a rotation direction around the vertical axis (Z axis). The stage 11 is an example of a relative movement means of the present invention.

[0023] In this embodiment, a semiconductor wafer (hereinafter referred to as "wafer") W such as a silicon wafer is used as the workpiece. The wafer W is partitioned into a plurality of regions by lines to cut arranged in a grid pattern, and various devices constituting semiconductor chips are formed in each of these partitioned regions. Note that, although this embodiment describes a case where a wafer W is used as the workpiece, the present invention is not limited to this, and for example, a glass substrate, a piezoelectric ceramic substrate, a glass substrate, etc. can also be used.

[0024] The wafer W has a backgrind tape (hereinafter referred to as BG tape) having an adhesive attached to the surface on which devices are formed (device surface), and is placed with the back surface facing upward on the stage 11. The thickness of the wafer W is not particularly limited, but is, for example, 700 μm or more or 700 μm to 800 μm.

[0025] The wafer W may be mounted on the stage 11 with a dicing tape having an adhesive attached to one surface thereof and integrated with the frame via the dicing tape.

[0026] The laser engine 20 includes a laser light source 22, a spatial light modulator 28, a condenser lens 38, etc. The light modulation device 10 according to this embodiment includes the spatial light modulator 28 and a control unit 50.

[0027] The laser light source (IR (Infrared) laser light source) 22 outputs laser light L for processing to form a laser processing region inside the wafer W under the control of the control unit 50. The laser light L is irradiated with, for example, a semiconductor laser pumped Nd:YAG (Neodym: Yttrium Aluminum Garnet) laser as the light source, a wavelength of 1.1 μm, and a laser light spot cross-sectional area of 3.14×10 -8 cm 2 The oscillation form is Q-switched pulse, the repetition frequency is 80kHz to 200kHz, the pulse width is 180ns to 370ns, and the output is 8W.

[0028] The spatial light modulator 28 is of a phase modulation type, and receives the laser light L (incident light) 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. As a result, as will be described in detail later, when the laser light L is irradiated and moved relatively along the planned cutting line, the laser light L is simultaneously focused at two positions inside the wafer W that are different from each other in the thickness direction and are equal to each other in the direction of relative movement of the laser light L.

[0029] For example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator) 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 a control unit 50. Here, the control unit 50 is an example of the control means of the present invention.

[0030] The condenser lens 38 is an objective lens (infrared objective lens) that condenses the laser light L inside the wafer W. The numerical aperture (NA) of the condenser lens 38 is, for example, 0.65.

[0031] The condenser lens 38 is provided with a correction collar 40 to correct aberration of the laser light L occurring inside the wafer W. This correction collar 40 is configured to be rotatable manually, and by rotating the correction collar 40 in a predetermined direction, the spacing between the lens groups that make up the condenser lens 38 is changed, and the aberration of the laser light L at a position at a predetermined depth from the laser light irradiation surface (back surface) of the wafer W can be corrected to be equal to or less than a predetermined aberration.

[0032] The correction collar 40 may be configured to be rotated electrically by a correction collar drive unit (not shown). In this case, the control unit 50 controls the operation of the correction collar drive unit to rotate the correction collar 40, thereby correcting the aberration of the laser light L to a desired state.

[0033] The laser engine 20 includes a beam expander 24, a λ / 2 wave plate 26, a reduction optical system 36, and the like.

[0034] 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.

[0035] Although not shown in the figure, the laser engine 20 is also 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.

[0036] The control unit 50 is a control device that controls the operation of each part of the laser processing apparatus 1, and includes a CPU (Central Processing Unit) that functions as a controller that executes various processes, a RAM (Random Access Memory) and a ROM (Read Only Memory) that function as memories that store various information, etc. The control unit 50 controls the operation of each part (stage 11, laser engine 20, etc.) of the laser processing apparatus 1 based on processing information (processing conditions, etc.) specified by an operator, thereby controlling the operation for forming a laser processing area inside the wafer W.

[0037] 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.

[0038] The laser processing device 1 is composed of a wafer transport means, an operation panel, a television monitor, an indicator light, and the like, all of which are not shown.

[0039] The operation panel is equipped with switches and a display device for controlling the operation of each part of the laser processing device 1. The television monitor displays images of the wafer W captured by a CCD (Charge Coupled Device) camera (not shown), as well as program contents and various messages. The indicator light displays the operating status of the laser processing device 1, such as when processing is in progress, processing is complete, and when there is an emergency stop.

[0040] Next, a laser processing method according to one embodiment of the present invention will be described. This laser processing method is carried out using the laser processing apparatus 1 of this embodiment described above.

[0041] First, the correction collar 40 provided on the condenser lens 38 is rotated manually (or electrically) to adjust the aberration correction amount so that the aberration of the laser light L is equal to or less than a predetermined value at the position inside the wafer W where the laser light L is condensed (the processing depth of the laser processing area). In this specification, the "aberration correction amount" is a value converted into a depth from the laser light irradiated surface (back surface) of the wafer W. That is, for example, if the aberration correction amount is 500 μm, this means that the aberration of the laser light is minimized at a position approximately 500 μm deep from the laser light irradiated surface of the wafer W. For example, if the thickness (initial thickness) of the wafer W is 775 μm, the aberration correction amount by the correction collar 40 is preferably set to 500 μm.

[0042] In this way, by using the correction collar 40 of the focusing lens 38 to correct the aberration at the position where the focusing point of the laser light L is aligned so that it is equal to or less than a predetermined aberration, it becomes possible to efficiently focus the laser light L at a deep position in the thickness direction of the wafer W, even if the wafer W is thick. Note that the reason why using the correction collar 40 to perform aberration correction is effective and other aberration correction means are described in detail in Japanese Patent Application Laid-Open No. 2016-011315 filed by the applicant of the present application, and therefore a description thereof will be omitted here.

[0043] In this embodiment, aberration correction is performed using the correction collar 40, but this is not necessarily limited to this. For example, aberration correction does not necessarily have to be performed using the correction collar 40. In this case, aberration correction may be performed using the spatial light modulator 28. Furthermore, aberration correction may be performed using both the spatial light modulator 28 and the correction collar 40.

[0044] Next, after the wafer W to be processed is placed on the stage 11, the wafer W is aligned using an alignment optical system (not shown).

[0045] Next, the wafer W is moved relatively along the line to cut while being irradiated with a laser beam L. The relative movement of the laser beam L is performed by feeding the stage 11, which holds the wafer W by suction, in the X direction.

[0046] At this time, the laser light L output from the laser light source 22 has its beam diameter expanded by the beam expander 24, is reflected by the first mirror 30, has its polarization direction changed by the λ / 2 wave plate 26, and is incident on the spatial light modulator 28.

[0047] The beam of laser light L incident on spatial light modulator 28 is modulated by the hologram pattern presented on spatial light modulator 28. As will be described later, hologram pattern PA1 (see FIG. 2) according to this embodiment modulates laser light L so that the beam of laser light L is focused and irradiated onto two focusing points inside wafer W.

[0048] The laser light L emitted from the spatial light modulator 28 in this manner is reflected successively by the second mirror 31 and the third mirror 32, passes through the first lens 36a, is further reflected by the fourth mirror 33 and the fifth mirror 34, passes through the second lens 36b, and is incident on the condenser lens 38. As a result, the laser light L emitted from the spatial light modulator 28 is reduced and projected onto the condenser lens 38 by the reduction optical system 36 consisting of the first lens 36a and the second lens 36b. Then, the laser light L incident on the condenser lens 38 is focused by the condenser lens 38 at two different focusing positions inside the wafer W.

[0049] [Example of hologram pattern] FIG. 2 is a diagram showing an example of a hologram pattern.

[0050] As shown in Fig. 2, the hologram pattern PA1 according to this embodiment is a combination of two types of Fresnel patterns FL1 and FL2. The Fresnel patterns FL1 and FL2 have different curvatures, and the hologram pattern PA1 is created by alternately arranging patterns (regions K1 to Kn and regions L1 to Ln, where n is an integer of 2 or more, and n=5 in the example shown in Fig. 2) obtained by dividing the Fresnel patterns FL1 and FL2 into rectangular (oblong) regions.

[0051] As shown in FIG. 2, in the hologram pattern PA, the central region K1 (first rectangular region) of the Fresnel pattern FL1 is located at the center, i.e., at the position of the optical axis AX of the laser light L, and regions L2, K3, L4, and K5 (second rectangular regions) are arranged in stripes on both sides of the X direction (processing direction) of the central region K1.

[0052] 2, n=5, but the present invention is not limited to this. That is, the hologram pattern PA1 according to this embodiment can be realized by combining at least three striped patterns, each consisting of a central region K1 and regions L2 arranged on both sides of the central region K1.

[0053] FIG. 3 is a simplified diagram showing laser light L modulated by the hologram pattern PA1 according to this embodiment.

[0054] In the example shown in Figure 3, the components of the laser light L modulated by pattern FL1 (areas K1, K3 and K5) are focused at a focusing point FP1, and the components modulated by pattern FL2 (areas L2 and L4) are focused at a focusing point FP2.

[0055] As described above, when the laser light L is modulated by the hologram pattern PA1, which is a combination of two types of Fresnel patterns FL1 and FL2 with different curvatures, the laser light L can be simultaneously focused and irradiated onto two focusing points FP1 and FP2 inside the wafer W, as shown in FIG. 3.

[0056] 3, the focal point FP1 is closer to the front surface of the wafer W than the focal point FP2 (lower in FIG. 3), but the present invention is not limited to this. By adjusting the curvatures of the Fresnel patterns FL1 and FL2, the focal point FP2 can also be located closer to the front surface of the wafer W than the focal point FP1.

[0057] 2, the regions K1, L2, K3, L4, and K5 are arranged adjacent to each other with no gaps between them, but the present invention is not limited to this. For example, there may be gaps between the regions K1, L2, K3, L4, and K5.

[0058] Furthermore, in this embodiment, a random pattern can be arranged between any of the regions K1, L2, K3, L4, and K5 to control (attenuate) the power of the laser light L at the focusing points FP1 and FP2. In this case, the power of the laser light L at the focusing points FP1 and FP2 can be controlled (attenuated) while maintaining the Gaussian distribution specific to the laser light L.

[0059] [Laser processing method] Figures 4 to 6 are diagrams for explaining a laser processing method according to one embodiment of the present invention. Fig. 4 is a diagram showing a state in which laser light L is focused inside a wafer W. Fig. 5 is a diagram showing a state in which a laser processing region is formed at the focusing position of the laser light L shown in Fig. 4. Fig. 6 is a diagram showing a state in which two rows of laser processing regions are formed inside the wafer W along the line to cut.

[0060] As shown in FIG. 4, the laser light L modulated by the spatial light modulator 28 is simultaneously focused by the focusing lens 38 at two positions (first focusing position FP1 and second focusing position FP2) inside the wafer W that are different from each other in the thickness direction and are equal to each other in the relative movement direction M of the laser light L. As a result, as shown in FIG. 5, a pair of laser processing areas P1 and P2 are formed near the two focusing positions FP1 and FP2. Furthermore, when the pair of laser processing areas P1 and P2 are formed, cracks Ki1 and Ki2 are formed starting from the respective laser processing areas P1 and P2 and extending in the thickness direction of the wafer W. Therefore, when a single scan is performed along the planned cutting line, two rows of laser processing areas P1 and P2 can be formed inside the wafer W, as shown in FIG. 6. Note that, as an example, the distance between the two focusing positions FP1 and FP2 in the thickness direction inside the wafer W is set to 50 μm to 80 μm.

[0061] In this way, two rows of laser processing areas P1 and P2 are formed inside the wafer W with one scan along the planned cutting line, and then the stage 11 is indexed and fed one pitch in the Y direction, and the next planned cutting line is similarly formed with laser processing areas P1 and P2.

[0062] Once the laser processing areas P1 and P2 have been formed along all of the lines to be cut that are parallel to the X direction, the stage 11 is rotated 90°, and the laser processing areas P1 and P2 are similarly formed on all of the lines that are perpendicular to the previous lines. As a result, the laser processing areas P1 and P2 are formed along all of the lines to be cut.

[0063] After the laser processing areas P1 and P2 have been formed along the intended cutting line in the manner described above, a backside grinding process is performed in which the backside of the wafer W is ground using a grinding device (not shown) to process the thickness (initial thickness) T1 of the wafer W to a predetermined thickness (final thickness) T2 (e.g., 30 μm to 50 μm).

[0064] After the back grinding process, an expandable tape (dicing tape) is attached to the back surface of the wafer W, and after the BG tape attached to the front surface of the wafer W is peeled off, an expandable process is performed in which tension is applied to the expandable tape attached to the back surface of the wafer W to stretch it.

[0065] As a result, the wafer W is cut from the cracks that have extended to the device surface (front surface) of the wafer W. That is, the wafer W is cut along the cutting lines and divided into a plurality of chips.

[0066] As described above, in this embodiment, when the wafer W is irradiated with the laser light L and moved relatively along the line to cut, the laser light L is simultaneously focused by the focusing lens 38 at two focusing positions FP1 and FP2 that are different from each other in the thickness direction within the wafer W and are equal to each other in the relative movement direction M of the laser light L, thereby simultaneously forming laser processing areas P1 and P2. Therefore, the two laser processing areas P1 and P2 aligned in the thickness direction within the wafer W are formed at approximately the same time. As a result, when two rows of laser processing areas P1 and P2 are formed within the wafer W by a single scan along the line to cut, cracks generated from the laser processing areas P1 and P2 formed at approximately the same time are formed continuously in the thickness direction of the wafer W. Therefore, compared to when the laser processing areas P1 and P2 aligned in the thickness direction are formed at different times, the linearity of the cracks generated from the laser processing areas P1 and P2 is better, and it is possible to extend cracks generated within the wafer W efficiently and with high precision.

[0067] [Convergence of laser light L] FIG. 7 is a perspective view schematically showing the shape of the modulated laser light L.

[0068] As shown in FIG. 7, the hologram pattern PA1 of this embodiment is a combination of multiple rectangular patterns, and the laser light L modulated by each region K1, L2, K3, L4, and K5 of the hologram pattern PA1 is shaped into a rectangle whose longitudinal direction is perpendicular to the processing direction (X direction).

[0069] When the rectangular laser beam L is focused by the focusing lens 38, it becomes a rectangle with the processing direction as its longitudinal direction. Therefore, in this embodiment, by shaping the laser beam L into a rectangle, astigmatism is generated, and it is possible to give directionality to the extension of the cracks Ki1 and Ki2. In this way, the cracks can be extended along the processing direction starting from the laser processing regions P1 and P2, which makes it possible to improve the continuity of the cracks in the processing direction along the line to cut.

[0070] FIG. 8 is a plan view showing an example of a pattern presented in a rectangular region of the hologram pattern PA1.

[0071] Area K1-1 shown in FIG. 8 shows an example of a circular Fresnel pattern, and area K1-2 shows an example of an elliptical Fresnel pattern whose major axis direction is perpendicular to the processing direction.

[0072] As shown in region K1-2, by forming the Fresnel pattern into an elliptical shape with the direction perpendicular to the processing direction as the major axis direction, it is possible to further improve the crack propagation performance and continuity. Note that the Fresnel pattern is not limited to an elliptical shape and may be, for example, an oval shape.

[0073] In this embodiment, a two-stage process is performed in which the laser beam L is simultaneously focused by the focusing lens 38 at two different focusing points FP1 and FP2 in the thickness direction within the wafer W to simultaneously form the laser processing regions P1 and P2. The backside of the wafer W is then ground to separate the wafer W into individual chips. However, this process is not limited to this. For example, laser processing may be performed multiple times while changing the position at which the laser beam L is focused (the processing depth of the laser processing region) within the wafer W as needed. In this case, a correction pattern (an aberration-correcting hologram pattern; in this case, a pattern in a direction that cancels the correction by the correction collar 40) for correcting aberrations within the wafer W may be superimposed by the laser engine 20 on the hologram pattern presented by the spatial light modulator 28 according to the processing depth of the laser processing region. This enables appropriate aberration correction even for portions of the wafer W that are relatively shallow from the laser beam irradiation surface.

[0074] Furthermore, a wavefront distortion correcting hologram pattern for correcting wavefront distortion of laser light may be superimposed on the hologram pattern.

[0075] [Variation 1] FIG. 9 is a plan view showing a hologram pattern according to the first modification.

[0076] 9, in the hologram pattern PA1 according to the above embodiment, the width Δ in the processing direction of each of the regions K1, L2, K3, L4, and K5 is equal (Δ=500 pixels in one example), whereas in the hologram pattern PA2 according to Modification 1, the width Δ1 of the regions K1, K3, and K5 is longer than the width Δ2 of the regions L2 and L4. Here, Δ1=560 pixels, Δ2=440 pixels, or Δ1=600 pixels, Δ2=400 pixels. This makes it possible to increase the intensity and concentration of the laser light L at the focal point FP1 compared to the focal point FP2.

[0077] For example, the intensity and concentration of the laser light L at the focal points FP1 and FP2 can be adjusted by adjusting the sizes (area ratios) of the regions K1, K3, and K5 and the regions L2 and L4 according to the relative positions (distances) between the surface of the wafer W and the focal points FP1 and FP2. For example, when the distance between the surface of the wafer W and the focal point FP1 is long, the width Δ1 of the regions K1, K3, and K5 can be increased to increase the intensity and concentration at the focal point FP1. This allows the crack Ki1 extending from the focal point FP1 to be elongated so that it reaches the surface of the wafer W. Furthermore, when the distance between the surface of the wafer W and the focal point FP1 is short and the distance between the focal points FP1 and FP2 is long, the continuity of the crack between the focal points FP1 and FP2 can be improved by making Δ1 < Δ2.

[0078] [Variation 2] FIG. 10 is a plan view showing a hologram pattern according to the second modification, and FIG. 11 is a diagram showing the focal point of the laser light modulated by the hologram pattern according to the second modification.

[0079] 10, the Fresnel patterns of the regions K1, L2, M3, N4, and O5 have different curvatures. This configuration makes it possible to focus the laser light L modulated by each region at different focusing points FP1 to FP5.

[0080] Furthermore, as shown in Figure 12, by changing the widths (area ratios) of regions K1, L2, M3, N4 and O5, it is possible to adjust the intensity and concentration of the laser light L at the focal points FP1 to FP5 according to the positional relationship (distance) between the surface of the wafer W and the focal points FP1 to FP5.

[0081] [Variation 3] In the above embodiment, the longitudinal direction of the regions of the hologram patterns PA1 to PA3 (regions K1, L2, K3, L4 and K5, or regions K1, L2, M3, N4 and O5) is set to a direction perpendicular to the processing direction (X direction) of the laser processing apparatus 1, but the present invention is not limited to this. For example, the longitudinal direction of the regions of the hologram patterns PA1 to PA3 (regions K1, L2, K3, L4 and K5, or regions K1, L2, M3, N4 and O5) may also be set to a direction parallel to the processing direction of the laser processing apparatus 1.

[0082] In this case, the pattern presented in the rectangular region of the hologram pattern may be an elliptical or oblong Fresnel pattern with the long axis direction of each region being the same as in the example shown in FIG.

[0083] [Variation 4] In the above-described embodiments, examples have been described in which the laser light L is focused and irradiated at focusing positions that are different within the wafer W in the thickness direction and are the same along the processing direction (X direction) of the laser processing apparatus 1, but the present invention is not limited to this. For example, the present invention can also be applied to a case in which the laser light L is focused and irradiated at focusing positions that are the same within the wafer W in the thickness direction and are different along the processing direction of the laser processing apparatus 1, or a case in which the laser light L is focused and irradiated at focusing positions that are different within the wafer W in the thickness direction and are different along the processing direction of the laser processing apparatus 1.

[0084] In this embodiment, a reflective spatial light modulator (LCOS-SLM) is used as the spatial light modulator 28, but the present invention is not limited to this and may be a MEMS-SLM (Micro Electro Mechanical System-SLM) or a DMD (Deformable Mirror Device), etc. Furthermore, the spatial light modulator 28 is not limited to a reflective type and may be a transmissive type. Furthermore, examples of the spatial light modulator 28 include a liquid crystal cell type and an LCD (Liquid Crystal Display) type. [Explanation of symbols]

[0085] 1...laser processing device, 10...light modulation device, 11...stage, 20...laser engine, 22...laser light source, 24...beam expander, 26...λ / 2 wave plate, 28...spatial light modulator, 36...reduction optical system, 38...condenser lens, 40...correction collar, 50...control unit

Claims

1. a spatial light modulator; a control means for setting the hologram pattern to be presented by the spatial light modulator as a striped Fresnel pattern consisting of a first rectangular area including an optical axis of incident light and at least two second rectangular areas arranged so as to sandwich the first rectangular area, the Fresnel pattern having different curvatures, and for condensing and irradiating the light modulated by the first rectangular area and the second rectangular area at different condensing positions; An optical modulation device comprising:

2. 2. The optical modulation device according to claim 1, wherein the control means sets the areas of the first rectangular region and the second rectangular region to be different from each other.

3. 3. The optical modulation device according to claim 1, wherein the control means sets a Fresnel pattern to at least one of the first rectangular region and the second rectangular region in an elliptical or oval shape whose major axis direction is parallel to the longitudinal direction of the first rectangular region and the second rectangular region.

4. The optical modulation device according to claim 1 , wherein the control means sets a random pattern between the first rectangular area and the second rectangular area.

5. a laser light source that outputs laser light; The optical modulation device according to any one of claims 1 to 4; a condenser lens that condenses and irradiates the laser light modulated by the optical modulator onto the inside of a workpiece; A laser processing device comprising:

6. The laser processing device according to claim 5 , wherein the longitudinal direction of the first rectangular area and the second rectangular area is perpendicular to the processing direction of the laser processing device.

7. 7. The laser processing device according to claim 5, further comprising a correction collar for correcting aberration of the laser light occurring inside the workpiece.

8. 8. The laser processing device according to claim 5, wherein the control means superimposes an aberration-correcting hologram pattern on the hologram pattern to correct aberration of the laser light generated inside the workpiece.

9. 9. The laser processing device according to claim 5, wherein the control means superimposes a wavefront distortion correcting hologram pattern on the hologram pattern to correct wavefront distortion of the laser light.

10. a hologram pattern to be presented by the spatial light modulator is set to a striped Fresnel pattern consisting of a first rectangular area including an optical axis of the incident light and at least two second rectangular areas arranged so as to sandwich the first rectangular area, the Fresnel patterns having mutually different curvatures; a light modulation method for irradiating the light modulated by the first rectangular area and the light modulated by the second rectangular area at different focusing positions;

11. modulating laser light from a laser light source by the optical modulation method according to claim 10; A laser processing method in which modulated laser light is focused and irradiated onto the inside of a workpiece.

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