Laser processing device, method for manufacturing semiconductor product, and laser processing method

Abstract

A laser processing device 1A comprises a light generation unit 3A, a condensing optical system 5, and a control unit 6A. The light generation unit 3A generates a laser beam L that is radially polarized light or azimuthally polarized light and has a spiral phase distribution. The condensing optical system 5 condenses the laser beam L at a condensing position in a workpiece 11, which is a uniaxial birefringent crystal. The control unit 6A shifts the condensing position in the workpiece 11 and forms a modified region 12 for cutting the workpiece 11.

Description

Laser processing device, semiconductor product manufacturing method, and laser processing method

[0001] This application claims priority to Japanese Patent Application No. 2024-146336 filed on August 28, 2024, and Japanese Patent Application No. 2025-007069 filed on January 17, 2025, and incorporates all of the contents of the aforementioned Japanese applications by reference.

[0002] Patent Document 1 discloses a laser processing apparatus that irradiates a semiconductor object made of a birefringent material with laser light to perform laser processing of the semiconductor object. The laser processing apparatus includes a laser output unit that outputs laser light, a spatial light modulator that modulates the laser light output from the laser output unit, a focusing lens that focuses the laser light toward the semiconductor object, and a polarization component control unit that controls the polarization component of the laser light so that the laser light is focused at a single point in the optical axis direction on the semiconductor object.

[0003] Japanese Patent Application Laid-Open No. 2021-086902

[0004] There are devices and methods that focus laser light inside a workpiece to form a modified region through multiphoton absorption, single-photon absorption, or a combination of these, and then cut the workpiece starting from the modified region. Cutting here includes slicing, dicing including stealth dicing, laser ablation, and edge trimming. In such devices and methods, when laser light is focused on a uniaxial birefringent crystal, such as gallium nitride (GaN) or silicon nitride (SiN), the refractive indexes of the P-polarized and S-polarized components of the incident light are different. Incident light is divided into an ordinary ray and an extraordinary ray, of which the extraordinary ray does not follow Snell's law and propagates within the crystal at a different refraction angle than the ordinary ray. As a result, the P-polarized and S-polarized components are focused at different positions in the depth direction of the crystal.

[0005] To prevent the focused spot from separating in the depth direction, methods such as converting the polarization state of the laser light from linear polarization to radial polarization or azimuth polarization, or blocking either the P-polarized or S-polarized component using a slit or the like, are conceivable. However, when radially polarized or azimuthally polarized light is focused, the focused spot becomes annular with a hole, dispersing the energy of the laser light. In addition, blocking either the P-polarized or S-polarized component eliminates part of the energy of the laser light. Therefore, these methods reduce the utilization efficiency of the laser light energy.

[0006] The present disclosure aims to provide a laser processing apparatus, a semiconductor product manufacturing method, and a laser processing method that can improve the efficiency of laser light energy utilization while suppressing separation of the focused spot in the depth direction when processing a uniaxial birefringent crystal with laser light.

[0007] [1] A laser processing apparatus according to one aspect of the present disclosure includes a light generating unit, a focusing optical system, and a focusing position control unit. The light generating unit generates radially polarized or azimuthal polarized laser light having a helical phase distribution. The focusing optical system focuses the laser light at a focusing position within a uniaxial birefringent crystal. The focusing position control unit moves the focusing position within the birefringent crystal to form a modified region for cutting the birefringent crystal.

[0008] As described above, when radially polarized light and azimuthally polarized light are focused, the focused spot has a ring shape with a hole. In contrast, the present inventors discovered that when a spiral phase distribution is imparted to radially polarized light or azimuthally polarized light, the hole in the focused spot closes, enabling the energy of the laser light to be concentrated. In other words, the laser processing device described in [1] above can form a modified region without separating the focused spot of the laser light, while improving the utilization efficiency of the energy of the laser light.

[0009] [2] The laser processing device of [1] may further include a cutting unit that cuts the birefringent crystal along the modified region. In this case, the formation of the modified region and the cutting of the birefringent crystal can be performed by a single device, thereby improving the efficiency of the processing work.

[0010] [3] In the laser processing apparatus of [1] or [2] above, the focusing optical system may include an objective lens, and the numerical aperture of the objective lens may be 0.04 or more and 3.0 or less. Typically, the peak intensity of laser light obtained by imparting a spiral phase distribution to radially polarized or azimuthally polarized light is smaller than that of circularly polarized laser light. However, because circularly polarized light is affected by birefringence in birefringent crystals, the peak intensity at the focused spot decreases as the focused position becomes deeper. On the other hand, the peak intensity at the focused spot of laser light obtained by imparting a spiral phase distribution to radially polarized or azimuthally polarized light does not depend on the depth of the focused position. Therefore, when the depth of the focused position exceeds a certain depth, the peak intensity at the focused spot becomes greater than the peak intensity at the focused spot of circularly polarized light. The "certain depth" depends on the numerical aperture of the objective lens, and the greater the numerical aperture of the objective lens, the shallower the depth becomes. By using an objective lens with a numerical aperture of 0.04 or more, the effects of the laser processing apparatus of [1] or [2] above can be obtained even when the focused position is relatively shallow.

[0011] [4] In the laser processing apparatus of any one of [1] to [3] above, the light generation unit may have a phase control unit and a polarization control unit. The phase control unit imparts a helical phase distribution to the laser light. The polarization control unit converts the laser light after the helical phase distribution has been imparted or before the helical phase distribution has been imparted to the laser light into radially polarized or azimuthally polarized light. For example, with this configuration, it is possible to suitably generate radially polarized or azimuthally polarized laser light having a helical phase distribution.

[0012] [5] In the laser processing apparatus of [4] above, the phase control unit may include a phase plate, and the polarization control unit may include a vector polarizer. Alternatively, [6] In the laser processing apparatus of [4] above, the phase control unit may include a first spatial light modulator, and the polarization control unit may include a vector polarizer. Alternatively, [7] In the laser processing apparatus of [4] above, the phase control unit may include a phase plate, and the polarization control unit may include a second spatial light modulator. Alternatively, [8] In any one of the laser processing apparatuses of [1] to [3] above, the light generation unit may include a quarter-wave plate, a half-wave plate, and a spatial light modulator arranged on the optical path between the quarter-wave plate and the half-wave plate. The quarter-wave plate, the half-wave plate, and the spatial light modulator may cooperate to generate radially polarized or azimuthally polarized laser light having a helical phase distribution. For example, any one of the configurations of [5] to [8] above can suitably generate radially polarized or azimuthally polarized laser light having a helical phase distribution.

[0013] [9] In any one of the laser processing devices [1] to [8] above, the light generating unit may alternately generate radially polarized laser light having a spiral phase distribution and azimuthally polarized laser light having a spiral phase distribution. The modified regions formed by radially polarized light and the modified regions formed by azimuthally polarized light have different shape characteristics due to differences in polarization direction. By alternately irradiating the birefringent crystal with radially polarized laser light and azimuthally polarized laser light, a modified region having the characteristics of both (e.g., one that complements the shortcomings of the other) can be formed.

[0014]

[10] In the laser processing apparatus of [9] above, the focusing position control unit may overlap at least a portion of the range of the focused spot of the radially polarized laser light having a spiral phase distribution with at least a portion of the range of the focused spot of the azimuthally polarized laser light having a spiral phase distribution. When the same focusing optical system is used for the radially polarized light and the azimuthally polarized light, the depths of the focused spots are different. By at least partially overlapping the ranges of the focused spots of both the radially polarized light and the azimuthally polarized light using the focusing position control unit, both the radially polarized light and the azimuthally polarized light can be applied to a single point.

[0015]

[11] A method for manufacturing a semiconductor product according to one aspect of the present disclosure is a method for manufacturing a semiconductor product having a uniaxial birefringent crystal, and includes a light generating step, a light focusing step, a forming step, and a cutting step. In the light generating step, radially or azimuthally polarized laser light having a helical phase distribution is generated. In the focusing step, the laser light is focused at a focusing position within the birefringent crystal. In the forming step, the focusing position is moved within the birefringent crystal to form a modified region. In the cutting step, the birefringent crystal is cut along the modified region. A laser processing method according to one aspect of the present disclosure includes a light generating step, a light focusing step, and a forming step. In the light generating step, radially or azimuthally polarized laser light having a helical phase distribution is generated. In the focusing step, the laser light is focused at a focusing position within the uniaxial birefringent crystal. In the forming step, the focusing position is moved within the birefringent crystal to form a modified region for cutting the birefringent crystal.

[0016] According to the semiconductor product manufacturing method and laser processing method described in

[11] above, it is possible to form a modified region without separating the focused spot of the laser light, while improving the efficiency of use of the energy of the laser light.

[0017]

[12] In the focusing step of the semiconductor product manufacturing method and laser processing method of

[11] above, the laser light may be focused using an objective lens, and the numerical aperture of the objective lens may be 0.04 or more and 3.0 or less. As described above, by having the numerical aperture of the objective lens be 0.04 or more, the effects of the semiconductor product manufacturing method and laser processing method of

[11] above can be obtained even if the depth of the focusing position is relatively shallow.

[0018]

[13] In the semiconductor product manufacturing method and laser processing method according to

[11] or

[12] , the light generating step may include a step of imparting a helical phase distribution to the laser light, and a step of radially or azimuthally polarizing the laser light after the helical phase distribution has been imparted or before the helical phase distribution has been imparted. For example, by such a method, it is possible to suitably generate radially or azimuthally polarized laser light having a helical phase distribution.

[0019]

[14] In the light generation step of any one of the semiconductor product manufacturing methods and laser processing methods described above in

[11] to

[13] , radially polarized laser light having a spiral phase distribution and azimuthally polarized laser light having a spiral phase distribution may be alternately generated. The modified regions formed by radially polarized light and the modified regions formed by azimuthally polarized light have different shape characteristics due to differences in polarization direction. By alternately irradiating the birefringent crystal with radially polarized laser light and azimuthally polarized laser light, a modified region having the characteristics of both (e.g., one that complements the shortcomings of both) can be formed.

[0020]

[15] In the forming step of the semiconductor product manufacturing method and laser processing method described above in

[14] , at least a portion of the range of the focused spot of radially polarized laser light having a spiral phase distribution may overlap with at least a portion of the range of the focused spot of azimuthally polarized laser light having a spiral phase distribution. When the same focusing optical system is used for radially polarized light and azimuthally polarized light, the depths of the focused spots are different. By at least partially overlapping the ranges of the focused spots of both radially polarized light and azimuthally polarized light, it is possible to apply both radially polarized light and azimuthally polarized light to a single point.

[0021]

[16] In the light generation step of the semiconductor product manufacturing method and the laser processing method according to any one of

[11] to

[15] above, the birefringent crystal is SiC, GaN, LiNbO ３ , LiTaO ３ , β-BBO, sapphire, polyimide, Nd:YVO ４ , Nd:GdVO ４ , α-Quartz, AlN, ZnO, 4H—SiC, 6H—SiC, and Nd:YCOB.

[0022] According to the present disclosure, it is possible to provide a laser processing apparatus, a semiconductor product manufacturing method, and a laser processing method that can improve the utilization efficiency of the energy of laser light while suppressing separation of the focused spot in the depth direction when processing a uniaxial birefringent crystal with laser light.

[0023] FIG. 1 is a diagram schematically showing the configuration of a laser processing apparatus according to an embodiment. FIG. 2 is a side view showing an ingot as a processing object. FIG. 3 is a plan view showing the ingot. FIG. 4 is a diagram schematically showing a longitudinal section of a portion of the ingot. FIG. 5 is a diagram schematically showing a transverse section of a portion of the ingot. FIG. 6 is a diagram showing a process of cutting the processing object along a modified region. FIG. 7 is a diagram showing a process of obtaining multiple wafers from an ingot. FIG. 8 is a block diagram showing the configuration of a light generating unit according to an embodiment. FIG. 9 is a diagram showing a spiral phase distribution imparted to laser light by a phase plate. FIG. 10 is a flowchart showing a semiconductor product manufacturing method and a laser processing method according to an embodiment. FIG. 11 is a schematic diagram showing how laser light is irradiated onto a crystal. FIG. 12 is a graph showing the phase distribution and polarization direction distribution of an ordinary light component. Part (a) of FIG. 13 is a graph showing the phase distribution and polarization direction distribution of an extraordinary light component. FIG. 14 is a diagram showing the results of a simulation of the focused spot shape when laser light is focused within a birefringent crystal. Fig. 15 is a diagram showing the results of a simulation of the shape of the focused spot when laser light is focused within a birefringent crystal. Fig. 16 is a diagram showing the results of a simulation of the shape of the focused spot. Fig. 17 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot for each numerical aperture of the objective lens. Fig. 18 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot for each numerical aperture of the objective lens. Fig. 19 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot. Fig. 20 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot. Fig. 21 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot for each numerical aperture of the objective lens. Fig. 22 is a diagram showing the change in the focused spot depending on the processing depth when the laser light is circularly polarized and when the laser light is azimuthally polarized or radially polarized and has a spiral phase distribution.FIG. 23 is a diagram showing changes in the focused spot depending on the processing depth when the laser light is circularly polarized and when the laser light is azimuthally polarized or radially polarized and has a spiral phase distribution. FIG. 24 is a diagram showing a schematic configuration of a laser processing apparatus according to a first modified example. FIG. 25 is a diagram showing a schematic configuration of a laser processing apparatus according to a second modified example. FIG. 26 is an example of a phase distribution displayed on a spatial light modulator. FIG. 27 is a diagram showing a modulation pattern. FIG. 28 is a diagram showing a schematic configuration of a laser processing apparatus according to a third modified example. FIG. 29 is a diagram showing simulation results when multiple focused spots are formed simultaneously. FIG. 30 is a diagram showing simulation results when multiple focused spots are formed simultaneously. FIG. 31 is a diagram showing simulation results. FIG. 32 is a diagram showing a schematic configuration of a laser processing apparatus according to a sixth modified example. FIG. 33 is a diagram showing results of verification using Stokes parameters.

[0024] Specific examples of the present disclosure will be described below with reference to the drawings. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the following description, the same elements in the description of the drawings will be given the same reference numerals, and duplicate explanations will be omitted.

[0025] FIG. 1 is a diagram schematically illustrating the configuration of a laser processing apparatus 1A according to an embodiment. As shown in FIG. 1, the laser processing apparatus 1A includes a stage 2, a light generating unit 3A, a focusing optical system 5, and a control unit 6A (focusing position control unit). The laser processing apparatus 1A is an apparatus that irradiates a workpiece 11, which is a uniaxial birefringent crystal, with laser light L to perform laser processing of the workpiece 11. The birefringent crystal is an anisotropic uniaxial crystalline material with a (001) plane orientation. The birefringent crystal may be a tetragonal or hexagonal crystal. Examples of birefringent crystals include gallium nitride (GaN), silicon carbide (SiC), and LiNbO. ３ , LiTaO ３ , β-BBO, sapphire, polyimide, Nd:YVO ４ , Nd:GdVO ４The object includes at least one material selected from the group consisting of α-Quartz, aluminum nitride (AlN), zinc oxide (ZnO), 4H-SiC, 6H-SiC, and Nd:YCOB. The laser processing apparatus 1A forms a modified region 12 in the object 11 by irradiating it with laser light L. The laser processing apparatus 1A may be a laser slicing apparatus or a laser dicing apparatus. Hereinafter, the first horizontal direction will be referred to as the X-direction, and the second horizontal direction perpendicular to the first horizontal direction will be referred to as the Y-direction. The vertical direction will be referred to as the Z-direction.

[0026] The stage 2 supports the workpiece 11 by adsorbing the film attached to the workpiece 11 so that the Z direction is perpendicular to the main surface of the workpiece 11. In this embodiment, the stage 2 is movable along both the X direction and the Y direction. The stage 2 is rotatable about an axis parallel to the Z direction.

[0027] The light generating unit 3A generates ultrashort pulsed laser light L that is radially polarized or azimuthally polarized and has a helical phase distribution. A detailed configuration of the light generating unit 3A will be described later. The focusing optical system 5 irradiates the main surface of the workpiece 11 with the laser light L output from the light generating unit 3A and focuses the laser light L at a focusing position within the workpiece 11. The focusing optical system 5 of this embodiment is movable along the Z direction. The focusing optical system 5 includes an objective lens 51 that faces the workpiece 11 and focuses the laser light L. The objective lens 51 is, for example, a dry objective lens or an immersion objective lens (such as an oil immersion objective lens, a silicone immersion objective lens, or a water immersion objective lens).

[0028] As described above, the stage 2 is movable along each of the X direction and the Y direction, and the focusing optical system 5 is movable along the Z direction, so that the focusing optical system 5 is movable relative to the workpiece 11. This is not limiting, and the position of the workpiece 11 may be fixed and only the focusing optical system 5 may be movable, or the position of the focusing optical system 5 may be fixed and only the workpiece 11 may be movable.

[0029] The control unit 6A controls the stage 2, the light generating unit 3A, and the focusing optical system 5. The control unit 6A is configured as a computer device including a processor, memory, storage, communication devices, etc. In the control unit 6A, software (programs) loaded into the memory, etc. are executed by the processor, and the processor controls the reading and writing of data in the memory and storage, as well as communication by the communication devices. In this way, the control unit 6A realizes various functions.

[0030] The control unit 6A is a focusing position control unit in this embodiment, and moves the focusing position within the workpiece 11 by controlling the stage 2 and the focusing optical system 5. If the focusing optical system 5 is movable, the control unit 6A drives an actuator attached to the focusing optical system 5. If the workpiece 11 is movable, the control unit 6A drives the stage 2 on which the workpiece 11 is mounted. By moving the focusing position within the workpiece 11, a modified region 12 is formed.

[0031] That is, when the laser light L is focused inside the workpiece 11 supported by the stage 2, the laser light L is particularly absorbed at the focusing point C of the laser light L, and a modified region 12 is formed inside the workpiece 11. The modified region 12 is a region in which the density, refractive index, mechanical strength, and other physical properties differ from those of the surrounding unmodified region, and is formed in order to cut (slicing or dicing) the workpiece 11. Examples of the modified region 12 include a melting treatment region, a crack region, a dielectric breakdown region, a refractive index change region, etc.

[0032] The control unit 6A moves the stage 2 along a certain direction in the XY plane, and moves the focal point C relative to the workpiece 11 along a certain direction in the XY plane. At this time, multiple modified spots 13 are formed so as to be lined up in a row along a certain direction in the XY plane. One modified spot 13 is formed by irradiating one pulse of laser light L. A row of modified regions 12 is a collection of multiple modified spots 13 lined up in a row. Adjacent modified spots 13 may be connected to each other or separated from each other depending on the relative movement speed of the focal point C with respect to the workpiece 11 and the repetition frequency of the laser light L.

[0033] FIG. 2 is a side view showing an ingot 20 as the workpiece 11. FIG. 3 is a plan view showing the ingot 20. As an example of a method for manufacturing a semiconductor product using the laser processing apparatus 1A, a process of slicing the ingot 20 to obtain a plurality of wafers 30 will be described with reference to FIGS. 2 and 3. The wafers 30 are an example of a semiconductor product in this embodiment. In this embodiment, the workpiece 11 is an ingot 20 formed, for example, in a disk shape from gallium nitride (GaN) or silicon carbide (SiC). As an example, the diameter of the ingot 20 is 2 inches (50.8 mm), and the thickness of the ingot 20 is 2 mm. As an example, the diameter of the wafer 30 is 2 inches, and the thickness of the wafer 30 is 100 μm.

[0034] First, the laser processing apparatus 1A described above forms a modified region 12 including a plurality of modified spots 13 along each of a plurality of imaginary surfaces 15. Each of the imaginary surfaces 15 is a surface parallel to the main surface 20a of the ingot 20 within the ingot 20 and is set to be aligned in the normal direction of the main surface 20a. Each of the imaginary surfaces 15 is set to overlap each other when viewed from the main surface 20a side. A plurality of peripheral regions 16 are set in the ingot 20 to surround each of the imaginary surfaces 15. In other words, each of the imaginary surfaces 15 does not reach the side surface 20b of the ingot 20. As an example, the distance between adjacent imaginary surfaces 15 is 100 μm, and the width of the peripheral region 16, i.e., the distance between the outer edge of the imaginary surface 15 and the side surface 20b, is 30 μm or more.

[0035] The formation of the multiple modified spots 13 is performed sequentially for each imaginary surface 15, starting from the surface opposite the main surface 20a, by irradiating laser light L having a wavelength of, for example, 532 nm. Since the formation of the multiple modified spots 13 is the same for each of the multiple imaginary surfaces 15, the formation of the multiple modified spots 13 along the imaginary surface 15 closest to the main surface 20a will be described below with reference to Figures 4 and 5. Figure 4 is a diagram schematically showing a vertical cross section of a portion of the ingot 20. Figure 5 is a diagram schematically showing a horizontal cross section of a portion of the ingot 20. In Figure 5, the arrow indicates the trajectory of the focal point C of the laser light L.

[0036] First, the laser processing apparatus 1A forms multiple modified spots 13 along an imaginary plane 15 by irradiating laser light L into the interior of the ingot 20 from the main surface 20a. At this time, the laser processing apparatus 1A may form the multiple modified spots 13 so that the multiple cracks 14 extending from the multiple modified spots 13 do not connect to each other, or may form the multiple modified spots 13 so that the multiple cracks 14 connect to each other. The laser processing apparatus 1A forms multiple rows of modified spots 13 by moving the focal point C of the laser light L along the imaginary plane 15. In Figures 4 and 5, the modified spots 13 are shown in white (without hatching), and the ranges to which the cracks 14 extend are shown by dashed lines.

[0037] The pulse pitch of the laser light L, i.e., the value obtained by dividing the relative moving speed of the plurality of focal points C by the repetition frequency of the laser light L, is, for example, 10 μm. The pulse energy of the laser light L per focal point C is, for example, 0.33 μJ.

[0038] Next, as shown in FIG. 6 , the cutting unit 4 cuts the object 11 along the modified region. The cutting unit 4 is, for example, a heating device equipped with a heater or the like. In this case, the heating device heats the ingot 20, and connects the multiple cracks 14 extending from the multiple modified spots 13 on each of the multiple imaginary surfaces 15, thereby forming a crack 17 (hereinafter simply referred to as a "crack 17") across the multiple imaginary surfaces 15 on each of the multiple imaginary surfaces 15. In FIG. 6 , the multiple modified spots 13 and the multiple cracks 14, as well as the range in which the crack 17 is formed, are indicated by dashed lines. The cutting unit 4 may also apply some kind of force to the ingot 20 by a method other than heating, thereby connecting the multiple cracks 14 to form the crack 17. The multiple modified spots 13 may be formed along the imaginary surfaces 15, thereby connecting the multiple cracks 14 to form the crack 17.

[0039] Here, particularly in the ingot 20, which is a gallium nitride (GaN) ingot, nitrogen gas is generated in the multiple cracks 14 extending from the multiple modified spots 13. Therefore, by heating the ingot 20 to expand the nitrogen gas, cracks 17 can be formed using the pressure (internal pressure) of the nitrogen gas. Moreover, the peripheral region 16 prevents the multiple cracks 14 from propagating outside the imaginary surface 15 surrounded by the peripheral region 16 (e.g., the side surface 20b of the ingot 20), thereby preventing the nitrogen gas generated in the multiple cracks 14 from escaping outside the imaginary surface 15. In other words, the peripheral region 16 is a non-modified region that does not include the modified spots 13, and when cracks 17 are formed in the imaginary surface 15 surrounded by the peripheral region 16, it prevents the multiple cracks 14 from propagating outside the imaginary surface 15 surrounded by the peripheral region 16. For this reason, it is preferable that the width of the peripheral region 16 be 30 μm or more.

[0040] Next, a grinding device grinds (polishes) portions of the ingot 20 corresponding to each of the peripheral regions 16 and each of the imaginary surfaces 15, thereby obtaining a plurality of wafers 30 from the ingot 20 using each of the cracks 17 as a boundary, as shown in Fig. 7. In this manner, the ingot 20 is cut along each of the imaginary surfaces 15. In this step, the portions of the ingot 20 corresponding to each of the peripheral regions 16 may be removed by mechanical processing, laser processing, or the like other than grinding.

[0041] The configuration of the light generation unit 3A will be described in detail. Fig. 8 is a block diagram showing the configuration of the light generation unit 3A according to this embodiment. The light generation unit 3A generates laser light L. The laser light L is radially polarized or azimuthally polarized and has a spiral phase distribution. The light generation unit 3A according to this embodiment is configured to be able to generate both radially polarized laser light L having a spiral phase distribution and azimuthally polarized laser light L having a spiral phase distribution.

[0042] Specifically, the light generating unit 3A includes a laser light source 21, a phase plate 22, a double-telecentric relay lens system 23, a vector polarizer 24, and a double-telecentric relay lens system 25. The laser light source 21 outputs linearly polarized laser light L1 that is transparent to the workpiece 11, for example, by a pulse oscillation method. The laser light L1 has a uniform phase distribution in a cross section perpendicular to the optical axis. The laser light source 21 includes, for example, a semiconductor laser element. The wavelength of the laser light L1 is, for example, 350 nanometers or more and 2000 nanometers or less. The laser light L1 is pulsed light, and the pulse width is, for example, 15 femtoseconds or more and 1 microsecond or less.

[0043] The phase plate 22 is optically coupled to the laser light source 21. The phase plate 22 is a phase control unit in this embodiment, and generates laser light L2 by imparting a helical phase distribution to the laser light L1. That is, the laser light L2 is linearly polarized light including a helical phase distribution. FIG. 9 is a diagram showing the helical phase distribution imparted to the laser light L1 by the phase plate 22. In FIG. 9, the magnitude of the phase is indicated by a shade of color, which changes from white to black as the phase approaches 0 (rad) to 2π (rad). As shown in FIG. 9, the helical phase distribution is a phase distribution in which the phase changes from 0 (rad) to 2π (rad) in the azimuthal direction around the optical axis. The phase plate 22 may impart to the laser light L1 a phase distribution obtained by superimposing the helical phase distribution on a phase distribution different from the helical phase distribution.

[0044] The double telecentric relay lens system 23 is optically coupled to the phase plate 22. The double telecentric relay lens system 23 has a focal length (f １ +f ２ ) and a set of lenses 231 (focal length f １ ) and lens 232 (focal length f ２ ) and optically couples the phase plate 22 and the vector polarizer 24. If the distance between the phase plate 22 and the vector polarizer 24 is short, the double-telecentric relay lens system 23 may be omitted. An aperture may be disposed on the optical path between the lens 231 and the lens 232 to modulate the intensity of the laser light L2.

[0045] The vector polarizer 24 is a polarization control unit in this embodiment. The vector polarizer 24 converts the polarization of the laser light L2 after the helical phase distribution has been imparted from linear polarization to radial polarization or azimuth polarization, thereby generating the laser light L. That is, the laser light L is radially polarized or azimuthally polarized light containing a helical phase distribution. When the vector polarizer 24 forms a predetermined first angle around the optical axis with respect to the polarization direction of the laser light L2, the laser light L becomes radially polarized. When the vector polarizer 24 forms a predetermined second angle around the optical axis with respect to the polarization direction of the laser light L2, the laser light L becomes azimuthally polarized. The difference between the first angle and the second angle is 90°.

[0046] In the illustrated example, the vector polarizer 24 is provided after the phase plate 22, and the vector polarizer 24 controls the polarization of the laser light L2 after it has been given a spiral phase distribution. This configuration is not limiting, and the vector polarizer 24 may be provided before the phase plate 22. In this case, the vector polarizer 24 controls the polarization of the laser light L1 before it has been given a spiral phase distribution. The phase plate 22 then gives a spiral phase distribution to the laser light that is radially polarized or azimuthally polarized.

[0047] The double telecentric relay lens system 25 is optically coupled to the vector polarizer 24. The double telecentric relay lens system 25 has a distance from each other equal to a focal length (f ３ +f ４ ) and a set of lenses 251 (focal length f ３ ) and lens 252 (focal length f ４ ) and optically couples the vector polarizer 24 and the focusing optical system 5. If the distance between the vector polarizer 24 and the focusing optical system 5 is short, the double-telecentric relay lens system 23 may be omitted. An aperture may be disposed on the optical path between the lens 251 and the lens 252 to modulate the intensity of the laser light L.

[0048] The control unit 6A controls the angle around the optical axis of the vector polarizer 24. In other words, the angle around the optical axis of the vector polarizer 24 is switchable. The control unit 6A controls the angle around the optical axis of the vector polarizer 24 to a first angle at which the laser light L becomes radially polarized, or to a second angle at which the laser light L becomes azimuthal polarized.

[0049] The control unit 6A may control the angle of the vector polarizer 24 around the optical axis so that the first angle and the second angle alternate. In this case, the light generation unit 3A alternately generates radially polarized laser light L having a spiral phase distribution and azimuthally polarized laser light L having a spiral phase distribution. In this case, the control unit 6A controls the relative positional relationship between the focusing optical system 5 and the workpiece 11 so that at least a portion of the range of the focused spot of the radially polarized laser light L having a spiral phase distribution overlaps with at least a portion of the range of the focused spot of the azimuthally polarized laser light L having a spiral phase distribution.

[0050] Next, a method for manufacturing a semiconductor product and a laser processing method according to this embodiment will be described. The method for manufacturing a semiconductor product and a laser processing method can be performed, for example, by the laser processing apparatus 1A described above. Figure 10 is a flowchart showing the method for manufacturing a semiconductor product and a laser processing method according to this embodiment.

[0051] First, in the light generation step ST1, a radially or azimuthally polarized laser light L having a helical phase distribution is generated. The light generation step ST1 includes a step ST11 of imparting a helical phase distribution to the laser light L1 and a step ST12 of converting the laser light L2 after the helical phase distribution has been imparted to the laser light L1 into a radially or azimuthally polarized laser light L2. However, in the light generation step ST1, the order of steps ST11 and ST12 may be reversed, and the laser light L1 before the helical phase distribution is imparted may be radially or azimuthally polarized. Then, in the focusing step ST2, the laser light L is focused at a focusing position within the workpiece 11. Then, in the forming step ST3, the focusing position is moved within the workpiece 11. Thereafter, the above-described focusing step ST2 and forming step ST3 are repeated to form the modified region 12. After the formation of the modified regions 12 is completed (step ST4: YES), the object 11 is cut along the modified regions 12 to form semiconductor products (cutting step ST5).

[0052] In the light generating step ST1, radially polarized laser light L having a spiral phase distribution and azimuthally polarized laser light L having a spiral phase distribution may be alternately generated. In this case, in the forming step ST3, at least a part of the range of the focused spot of the radially polarized laser light L having a spiral phase distribution is overlapped with at least a part of the range of the focused spot of the azimuthally polarized laser light L having a spiral phase distribution.

[0053] The effects obtained by the laser processing apparatus 1A, semiconductor product manufacturing method, and laser processing method according to the present embodiment described above will now be described. In uniaxial birefringent crystals such as lithium niobate, the refractive index of one axis (here, the z-axis) differs from the refractive index of the other two axes (the x-axis and the y-axis). A birefringent crystal having a principal surface perpendicular to the z-axis is called a z-cut crystal, and a birefringent crystal having a principal surface perpendicular to the x-axis or y-axis is called an x-cut crystal or a y-cut crystal, respectively. In some birefringent crystals, such as sapphire, the axis whose refractive index differs from the other two axes is sometimes called the c-axis instead of the z-axis, and the principal surface perpendicular to the c-axis is sometimes called the c-plane.

[0054] Part (a) of Figure 11 is a schematic diagram showing how laser light L is irradiated onto a z-cut crystal 18 (or a c-plane crystal). Part (b) of Figure 11 is a schematic diagram showing how laser light L is irradiated onto a y-cut crystal 19. Conventionally, when light is focused using a lens or an objective lens at a deep position in a z-cut crystal 18 to form a modified region 12, the focused spot of the laser light L splits into two along the optical axis direction due to the influence of birefringence. Specifically, when the numerical aperture of the lens is low or the focusing position is shallow, the focused spot does not split. However, as the numerical aperture of the lens increases or the focusing position becomes deeper, the ideal elliptical focused shape in the x-z plane (or y-z plane) gradually changes and eventually splits into two. Therefore, conventionally, it has been difficult to form a modified region 12 at a deep position in a z-cut crystal 18, and it has been common to form the modified region 12 at a shallow position in the z-cut crystal 18 or to focus the light using a lens with a small numerical aperture.

[0055] The reason why the focused spot splits into two along the optical axis direction is that the laser light L contains an ordinary light component and an extraordinary light component. Part (a) of FIG. 12 is a graph showing the phase distribution of the ordinary light component. Part (a) of FIG. 13 is a graph showing the phase distribution of the extraordinary light component. In Part (a) of FIG. 12 and Part (a) of FIG. 13, axes A1 and A2 represent coordinates in a plane perpendicular to the optical axis, and axis A3 represents phase values ​​(both normalized values). Part (b) of FIG. 12 is a diagram showing the distribution of the polarization direction of the ordinary light component in a plane perpendicular to the optical axis. Part (b) of FIG. 13 is a diagram showing the distribution of the polarization direction of the extraordinary light component in a plane perpendicular to the optical axis. As shown in these figures, the ordinary light component and the extraordinary light component have significantly different characteristics in their phase distribution and polarization distribution. That is, in the phase distribution, the ordinary light component and the extraordinary light component are defocused in opposite directions, and in the polarization distribution, the ordinary light component is azimuthally polarized light, whereas the extraordinary light component is radially polarized light.

[0056] Therefore, the inventors considered focusing radially polarized or azimuthally polarized laser light within the Z-cut crystal 18. In this case, it was confirmed that a single focused spot could be formed without separation even at a deep position within the Z-cut crystal 18. However, it became clear that in this case, the focused spot would be annular with a hole, and there was a risk that the energy required for processing would not be sufficiently focused on the processing area.

[0057] Parts (a) to (e) of Fig. 14 and parts (a) and (b) of Fig. 15 are diagrams showing the results of a simulation of the shape of the focused spot when the laser beam L is focused in a birefringent crystal. In this simulation, the z-cut crystal 18 is made of lithium niobate (LiNbO ３ ), the wavelength of the laser light L was 1030 nm, the numerical aperture (NA) of the objective lens was 0.9, the depth of the light-focusing position was 335 μm, and only the influence due to birefringence was taken into consideration.

[0058] Part (a) of Figure 14 shows the case where the laser light L is linearly polarized and the polarization direction is parallel to the x-axis of the z-cut crystal 18. Part (b) of Figure 14 shows the case where the laser light L is linearly polarized and the polarization direction is parallel to the y-axis of the z-cut crystal 18. Part (c) of Figure 14 shows the case where the laser light L is circularly polarized. Referring to parts (a) to (c) of Figure 14, it can be seen that when the laser light L is linearly polarized or circularly polarized, the focused spot is separated into two along the optical axis direction (depth direction). In contrast, part (d) of Figure 14 shows the case where the laser light L is radially polarized. Part (e) of Figure 14 shows the case where the laser light L is azimuthally polarized. Referring to parts (d) and (e) of Figure 14, it can be seen that the focused spot is formed as a single spot without separation. However, as is clear from part (f) of FIG. 14, which is a cross section taken along line BB of part (e) of FIG. 14, the focused spot is annular with a hole.

[0059] In contrast, part (a) of Figure 15 shows the case where the laser light L is radially polarized and has a helical phase distribution. Part (b) of Figure 15 shows the case where the laser light L is azimuthally polarized and has a helical phase distribution. Referring to parts (a) and (b) of Figure 15, it can be seen that the hole in the focused spot is closed. This allows energy to be sufficiently concentrated in the processing area. It is presumed that the hole in the light spot is closed because the polarization direction rotates over time due to the helical phase, causing opposing polarized light to have the same direction. In other words, according to the laser processing apparatus 1A, semiconductor product manufacturing method, and laser processing method of this embodiment, a modified region 12 can be efficiently formed without separating the focused spot of the laser light L, even deep in the processing object 11, which is a Z-cut crystal. This improves the energy utilization efficiency of the laser light L. In addition, by not separating the focused spot of the laser light L, kerf loss (material loss that occurs during cutting) can be reduced.

[0060] FIG. 16 shows a z-cut crystal 18 made of LiNbO ３ 16 is a diagram showing a simulation result of the focused spot shape when the wavelength of the laser light L is 400 nm, the numerical aperture (NA) of the objective lens is 0.1, and the depth of the focused position is 2230 μm. As shown in FIG. 16, even when the numerical aperture of the objective lens is small, the laser processing apparatus 1A, the semiconductor product manufacturing method, and the laser processing method of the present embodiment can efficiently form the modified region 12 at a deep position in the workpiece 11 without separating the focused spot of the laser light L.

[0061] As in the present embodiment, the laser processing apparatus 1A may include a cutting unit 4 that cuts the object 11 along the modified region 12. In this case, the formation of the modified region 12 and the cutting of the object 11 can be performed by a single apparatus, thereby improving the efficiency of the processing work.

[0062] As in the present embodiment, the light generation unit 3A may have a phase control unit (phase plate 22) and a polarization control unit (vector polarizer 24). The phase control unit imparts a helical phase distribution to the laser light L. The polarization control unit radially polarizes or azimuthally polarizes the laser light L after the helical phase distribution has been imparted to the laser light L or before the helical phase distribution has been imparted to the laser light L. Similarly, the light generation step ST1 may include a step ST11 of imparting a helical phase distribution to the laser light L and a step ST12 of radially polarizing or azimuthally polarizing the laser light L after the helical phase distribution has been imparted to the laser light L or before the helical phase distribution has been imparted to the laser light L. For example, these configurations or methods can suitably generate laser light L that is radially polarized or azimuthally polarized and has a helical phase distribution.

[0063] As in the present embodiment, the phase control section may include a phase plate 22, and the polarization control section may include a vector polarizer 24. For example, with such a configuration, it is possible to suitably generate laser light L that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0064] As in this embodiment, the light generating unit 3A may be configured to generate both radially polarized laser light L having a spiral phase distribution and azimuthally polarized laser light L having a spiral phase distribution, and these laser lights L may be generated alternately. Similarly, in the light generating step ST1, radially polarized laser light L having a spiral phase distribution and azimuthally polarized laser light L having a spiral phase distribution may be generated alternately. The modified regions 12 formed by radial polarization and the modified regions 12 formed by azimuth polarization have different shape characteristics due to differences in polarization direction. By alternately irradiating the workpiece 11 with radially polarized laser light L and azimuthally polarized laser light L, it is possible to form modified regions 12 having both characteristics (e.g., mutually compensating for the shortcomings of both), or modified regions 12 in which both characteristics are reduced or eliminated (e.g., nanostructures due to the polarization state are reduced or eliminated).

[0065] In this case, the control unit 6A may cause at least a portion of the range of the focused spot of the radially polarized laser light L having a spiral phase distribution to overlap with at least a portion of the range of the focused spot of the azimuthally polarized laser light L having a spiral phase distribution. Similarly, in the forming step ST3, at least a portion of the range of the focused spot of the radially polarized laser light L having a spiral phase distribution may overlap with at least a portion of the range of the focused spot of the azimuthally polarized laser light L having a spiral phase distribution. When the same focusing optical system 5 is used for the radially polarized light and the azimuthally polarized light, the depths of the focused spots are different, as is clear from a comparison between parts (a) and (b) of FIG. 15 . The control unit 6A may move the focusing position so that the ranges of the two focused spots at least partially overlap, thereby allowing both radially polarized light and azimuthally polarized light to act on a single point.

[0066] Here, we consider the numerical aperture (NA) of the objective lens 51 of the focusing optical system 5. FIGS. 17 to 21 are graphs showing the relationship between the position of the focused spot in the optical axis direction (depth direction) (hereinafter referred to as the processing position) and the peak intensity (normalized intensity) of the focused spot for each numerical aperture of the objective lens 51. In FIGS. 17 to 21, the dashed line Q indicates the peak intensity of the focused spot when the laser light L is azimuthally polarized or radially polarized and has a spiral phase distribution, i.e., in this embodiment. The peak intensity of the focused spot in this embodiment is constant regardless of the processing position. In FIGS. 17 to 21, plots P1 to P11 indicate the peak intensity of the focused spot when the laser light is circularly polarized.

[0067] FIG. 17 shows a z-cut LiNbO ３ 17 shows the relationship when the objective lens 51 is a dry objective lens, the wavelength of the laser light L is 800 nm, and the numerical aperture of the objective lens 51 is 0.1, 0.3, 0.5, and 0.9, respectively. ３18 shows the relationship when the wavelength of the laser light L is 800 nm and the objective lens 51 is a water immersion objective lens. Plots P5 to P7 shown in FIG. 18 show the cases when the numerical aperture of the objective lens 51 is 0.8, 1.0, and 1.2, respectively. FIG. 19 shows the relationship when the workpiece 11 is a z-cut LiNbO ３ 19 shows the relationship when the objective lens 51 is a silicone immersion objective lens, the wavelength of the laser light L is 800 nm, and the numerical aperture of the objective lens 51 is 1.3. ３ The graph shows the relationship when the numerical aperture of the objective lens 51 is 1.5, the wavelength of the laser light L is 800 nm, and the objective lens 51 is an oil-immersion objective lens. Plot P9 shown in Fig. 20 shows the relationship when the numerical aperture of the objective lens 51 is 1.5. Fig. 21 shows the relationship when the workpiece 11 is z-cut 4H—SiC, the wavelength of the laser light L is 515 nm, and the objective lens 51 is a dry objective lens. Plots P10 and P11 shown in Fig. 21 show the relationships when the numerical aperture of the objective lens 51 is 0.2 and 0.6, respectively.

[0068] In this embodiment, when the laser light L is azimuthally polarized or radially polarized, the light intensity of the laser light L irradiated onto the workpiece 11 is lower than when the laser light is circularly polarized. Therefore, when the processing position is shallow, the peak intensity of the focused spot in this embodiment is lower than the peak intensity of the focused spot when the laser light is circularly polarized. However, when the laser light is circularly polarized, the influence of birefringence is significant, so the peak intensity of the focused spot decreases as the processing depth increases. In contrast, the peak intensity of the focused spot in this embodiment is constant regardless of the processing depth, and therefore, at a certain depth, the peak intensity of the focused spot in this embodiment becomes greater than the peak intensity of the focused spot when the laser light is circularly polarized.

[0069] The "certain depth" depends on the numerical aperture of the objective lens 51. As shown in Figures 17, 18, and 21, the processing position where the peak intensity of the focused spot begins to decrease when the laser light is circularly polarized becomes shallower as the numerical aperture of the objective lens 51 increases. Therefore, the "certain depth" also becomes shallower as the numerical aperture of the objective lens 51 increases. Therefore, the effect of this embodiment becomes more pronounced as the numerical aperture of the objective lens 51 increases.

[0070] As described above, the numerical aperture of the objective lens 51 may be 0.1 or more and 3.0 or less. By making the numerical aperture of the objective lens 51 0.1 or more, the effect of the laser processing apparatus 1A of this embodiment can be obtained even if the depth of the focused spot is relatively shallow.

[0071] The numerical aperture of the objective lens 51 may be 0.04 or more and 3.0 or less. Even if the depth of the focused spot is relatively shallow, the effect of the laser processing apparatus 1A of this embodiment can be obtained by making the numerical aperture of the objective lens 51 to be 0.04 or more.

[0072] When the laser beam is linearly or circularly polarized, the focused spot splits into two along the optical axis (depth direction), as shown in parts (a) to (c) of Figure 14. However, when the processing depth is shallow, the focused spot does not split. Figures 22 and 23 are diagrams showing the change in the focused spot depending on the processing depth when the laser beam is circularly polarized and when the laser beam is azimuthally or radially polarized and has a helical phase distribution, respectively. Parts (a) and (c) of Figure 22 and parts (a) and (c) of Figure 23 show the case when the laser beam is circularly polarized. Parts (b) and (d) of Figure 22 and parts (b) and (d) of Figure 23 show the case when the laser beam is azimuthally or radially polarized and has a helical phase distribution. Parts (a) and (b) of Figure 22 show the case when the processing depth is 0 μm. Parts (c) and (d) of Figure 22 show the case when the processing depth is 240 μm. Parts (a) and (b) of Fig. 23 show the case where the processing depth is 1372 μm. Parts (c) and (d) of Fig. 23 show the case where the processing depth is 2471 μm. In Fig. 22 and Fig. 23, the workpiece 11 is z-cut 4H—SiC, the wavelength of the laser light L is 515 nm, and the objective lens 51 is a dry objective lens with a numerical aperture of 0.6.

[0073] As shown in parts (a) and (c) of Figure 22, when the processing depth is relatively shallow, the focused spots do not separate even if the laser light is circularly polarized. In contrast, as shown in parts (a) and (c) of Figure 23, when the laser light is circularly polarized, the focused spots separate in the optical axis direction as the processing depth increases, and the greater the processing depth, the greater the distance between the two separated focused spots. In other words, the greater the processing depth, the greater the kerf loss during slicing. Therefore, circularly polarized laser light and azimuthally or radially polarized laser light L having a spiral phase distribution may be used depending on the processing depth. That is, when the processing depth is shallower than a certain threshold, the laser light may be circularly polarized, and when the processing depth is deeper than that threshold, the laser light may be azimuthally or radially polarized and having a spiral phase distribution. This increases the peak intensity of the focused spots while preventing them from separating.

[0074] 24 is a diagram schematically illustrating the configuration of a laser processing apparatus 1B according to a first modification of the present disclosure. The laser processing apparatus 1B includes a light generation unit 3B and a control unit 6B instead of the light generation unit 3A and the control unit 6A of the above embodiment. The light generation unit 3B includes a spatial light modulator (SLM) 26 and a mirror 271 as a phase control unit instead of the phase plate 22 of the above embodiment. The SLM 26 includes, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon).

[0075] In addition to the functions of the controller 6A in the above embodiment, the controller 6B also has the function of controlling the phase distribution displayed on the SLM 26. The controller 6B causes the SLM 26 to display a spiral phase distribution. The SLM 26 is a first spatial light modulator in this disclosure. The spiral phase distribution displayed on the SLM 26 is the same as the spiral phase distribution possessed by the phase plate 22 in the above embodiment (see FIG. 9 ). The controller 6B may also cause the SLM 26 to display a phase distribution obtained by superimposing the spiral phase distribution on a phase distribution different from the spiral phase distribution. The SLM 26 receives the laser light L1 output from the laser light source 21 and reflected by the mirror 271, and generates the laser light L2 by phase-modulating the laser light L1. The SLM 26 is optically coupled to the vector polarizer 24 via the double-telecentric relay lens system 23 (or directly), and provides the laser light L2 having a spiral phase distribution to the vector polarizer 24.

[0076] According to the configuration of this modified example, it is possible to obtain the same effects as in the above embodiment. In addition, as in this modified example, the phase control unit may include an SLM 26, and the polarization control unit may include a vector polarizer 24. Even with this configuration, it is possible to preferably generate laser light L that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0077] When radially polarized laser light L and azimuthally polarized laser light L are alternately irradiated, the depth of the focused spot differs between the radially polarized light and the azimuthally polarized light, as described above. In this modification, in order to overlap the range of the focused spot of the radially polarized light with the range of the focused spot of the azimuthally polarized light, the control unit 6B may adjust the defocus component in the SLM 26 instead of, or in addition to, controlling the relative positional relationship between the focusing optical system 5 and the workpiece 11.

[0078] If the SLM 26 is a polarization-dependent SLM, such as a liquid crystal type, the laser light must be converted into radially polarized light or azimuthally polarized light after being given a helical phase by the SLM 26. Therefore, in this case, in this modified example, the SLM 26 is placed before the vector polarizer 24. However, if the SLM 26 is a polarization-independent SLM, such as a MEMS (Micro Electro Mechanical Systems) type, the SLM 26 may be placed either before or after the vector polarizer 24.

[0079] [Second Modification] Figure 25 is a diagram schematically illustrating the configuration of a laser processing apparatus 1C according to a second modification of the present disclosure. The laser processing apparatus 1C includes a light generation unit 3C and a control unit 6C instead of the light generation unit 3A and the control unit 6A of the above embodiment. The light generation unit 3C includes a spatial light modulator (SLM) 26 and a mirror 271 as a phase control unit instead of the phase plate 22 of the above embodiment. Furthermore, the light generation unit 3C includes a spatial light modulator (SLM) 28, a mirror 272, a half-wave plate 291, and a quarter-wave plate 292 as a polarization control unit instead of the vector polarizer 24 of the above embodiment. The SLM 28 is the second spatial light modulator of the present disclosure. The configurations of the SLM 26 and the mirror 271 are the same as those of the first modification described above.

[0080] In addition to the functions of the control unit 6A in the above embodiment, the control unit 6C has a function of controlling the phase distribution displayed on the SLM 26 and the phase distribution displayed on the SLM 28. The control unit 6C causes the SLM 28 to display a phase distribution for converting the laser light L2 into radially polarized or azimuthally polarized light having a spiral phase to generate the laser light L. Part (a) of Figure 26 is an example of a phase distribution displayed on the SLM 28 for converting the laser light L2 into radially polarized light having a spiral phase. Part (b) of Figure 26 is an example of a phase distribution displayed on the SLM 28 for converting the laser light L2 into azimuthally polarized light having a spiral phase. In these figures, the magnitude of the phase is indicated by a shade of color, which changes from white to black as the phase approaches 0 (rad) to 2π (rad). 26(a) and 26(b), the control unit 6C causes the SLM 28 to display a phase distribution in which a phase change from 0 (rad) to 2π (rad) around the optical axis is repeated twice (in other words, the phase changes from 0 (rad) to 4π (rad) around the optical axis). The circumferential position at which the phase becomes 0 (rad) differs by 90° between the phase distribution for converting the laser light L2 into radially polarized light (part (a) of FIG. 26) and the phase distribution for converting the laser light L2 into azimuthal polarization (part (b) of FIG. 26).

[0081] The control unit 6C controls the SLM 26 to display a phase correction pattern such as that shown in part (a) of FIG. 27 or an unmodulated pattern such as that shown in part (b) of FIG. 27. The control unit 6C may also control the SLM 26 to display a phase correction pattern for an axicon lens pattern to form a focused spot that is long in the optical axis direction. The control unit 6C may also control the SLM 26 to display a phase correction pattern for splitting the laser light L into multiple beams to simultaneously form multiple focused spots. That is, the multiple modified spots 13 shown in FIG. 4 may be simultaneously formed. In this case, the multiple focused spots may be aligned along the XY plane or aligned in a direction inclined relative to the XY plane. The laser light L2 modulated by the SLM 26 is guided to the SLM 28 by the double-telecentric relay lens system 23 and the mirror 27 via the half-wave plate 291.

[0082] The half-wave plate 291 is disposed on the optical path of the laser light L2 between the SLM 26 and the SLM 28. The quarter-wave plate 292 is disposed on the optical path of the laser light between the SLM 28 and the focusing optical system 5. The half-wave plate 291 and the quarter-wave plate 292 cooperate with the SLM 28 to convert the laser light L2 into radially polarized or azimuthally polarized light having a helical phase, thereby generating the laser light L.

[0083] The configuration of this modification can achieve the same effects as the above embodiment. In addition, as in this modification, the SLM 28 functions as a phase control unit and a polarization control unit. Even with this configuration, it is possible to preferably generate radially polarized or azimuthally polarized laser light L having a spiral phase distribution.

[0084] When radially polarized laser light L and azimuthally polarized laser light L are alternately irradiated, it is preferable to overlap the range of the focused spot of the radially polarized light with the range of the focused spot of the azimuthally polarized light. To achieve this, instead of or in addition to controlling the relative positional relationship between the focusing optical system 5 and the workpiece 11, the control unit 6C may adjust the defocus component in one or both of the SLMs 26 and 28.

[0085] A circularly polarized laser beam and an azimuthally polarized or radially polarized laser beam L having a spiral phase distribution may be selectively used depending on the processing depth. In this case, the phase patterns of one or both of the SLMs 26 and 28 may be switched to make the laser beam L circularly polarized.

[0086] [Third Modification] Figure 28 is a diagram schematically illustrating the configuration of a laser processing apparatus 1D according to a third modification of the present disclosure. The laser processing apparatus 1D includes a light generation unit 3D and a control unit 6D instead of the light generation unit 3A and the control unit 6A of the above embodiment. The light generation unit 3D includes an SLM 28, a mirror 272, a half-wave plate 291, and a quarter-wave plate 292 as a polarization control unit instead of the vector polarizer 24 of the above embodiment. The SLM 28 is the second spatial light modulator of the present disclosure. The configurations of the SLM 28, the mirror 272, the half-wave plate 291, and the quarter-wave plate 292 are the same as those of the second modification described above.

[0087] The configuration of this modification can achieve the same effects as the above embodiment. In addition, as in this modification, the phase control section may include a phase plate 22, and the polarization control section may include an SLM 28. Even with this configuration, it is possible to suitably generate radially polarized or azimuthally polarized laser light L having a spiral phase distribution.

[0088] When radially polarized laser light L and azimuthally polarized laser light L are alternately irradiated, it is preferable to overlap the range of the focused spot of the radially polarized light with the range of the focused spot of the azimuthally polarized light. To achieve this, the control unit 6D may adjust the defocus component of the SLM 28 instead of or in addition to controlling the relative positional relationship between the focusing optical system 5 and the workpiece 11.

[0089] [Fourth Modification] As described above, the phase plate 22 and the SLM 26 may provide the laser light L1 with a phase distribution obtained by superimposing a phase distribution different from the spiral phase distribution on the spiral phase distribution. Fig. 29 shows the results of a simulation in which a plurality of (e.g., two) focused spots aligned in a direction intersecting with the optical axis direction are simultaneously formed by superimposing a phase distribution representing a grating on the spiral phase distribution. In this example, the z-cut crystal 18 is made of LiNbO ３The wavelength of the laser light L is 1030 nm, the numerical aperture (NA) of the objective lens is 0.4, and the depth of the focusing position is 669 μm. Part (a) of Figure 29 shows a case where a phase distribution representing a certain grating is superimposed on a spiral phase distribution. Part (b) of Figure 29 shows a case where a phase distribution representing a different grating from that shown in Part (a) of Figure 29 is superimposed on a spiral phase distribution.

[0090] The multiple focused spots aligned in a direction intersecting the optical axis direction form multiple modified regions 12 along multiple imaginary surfaces 15. According to the laser processing apparatus, semiconductor product manufacturing method, and laser processing method of the above-described embodiment and each modification, multiple focused spots can be formed simultaneously, thereby allowing the multiple modified regions 12 along multiple imaginary surfaces 15 to be formed more quickly. In addition, the distance between the two focused spots shown in part (b) of FIG. 29 is shorter than the distance between the two focused spots shown in part (a) of FIG. 29 . In this way, by changing the overlapping phase distribution, the distance between the focused spots (in other words, the spacing between the multiple modified regions 12 along each of the multiple imaginary surfaces 15) can be freely changed. The multiple focused spots aligned in a direction intersecting the optical axis direction may form multiple modified regions 12 along different imaginary surfaces 15. In this case, the multiple focused spots aligned in a direction intersecting the optical axis direction are formed at different positions relative to the optical axis direction, allowing the modified regions 12 to be formed as the stage 2 moves. The modified region 12 may be formed by forming a plurality of focused spots at different positions in a direction intersecting the optical axis direction and in the optical axis direction on a certain imaginary surface 15. In this case, since the plurality of focused spots are formed at different positions in a direction intersecting the optical axis direction and in the optical axis direction, the modified region 12 can be formed on the certain imaginary surface 15 as the stage 2 moves.

[0091] 30 shows the results of a simulation in which a phase distribution representing a Fresnel lens is superimposed on a spiral phase distribution to simultaneously form multiple (for example, two) focused spots aligned in the optical axis direction. In this example, the z-cut crystal 18 is also made of LiNbO ３The wavelength of the laser light L is 1030 nm, the numerical aperture (NA) of the objective lens is 0.4, and the depth of the focal position is 669 μm. Part (a) of FIG. 30 shows a case where a phase distribution representing a certain Fresnel lens is superimposed on a spiral phase distribution. Part (b) of FIG. 30 shows a case where a phase distribution representing a different Fresnel lens from that shown in Part (a) of FIG. 30 is superimposed on a spiral phase distribution. According to the laser processing apparatus, optical device manufacturing method, and laser processing method of the above embodiment and each modification, it is also possible to simultaneously form multiple focal spots aligned in the optical axis direction. In addition, the distance between the two focal spots shown in Part (b) of FIG. 30 is shorter than the distance between the two focal spots shown in Part (a) of FIG. 30. While the distance between the upper and lower separated focal spots (see Part (c) of FIG. 14) formed when the laser light L is circularly polarized cannot be changed, according to the above embodiment and each modification, the distance between the focal spots can be freely changed by changing the superimposed phase distribution.

[0092] [Fifth Modification] As described above, the phase plate 22 and the SLM 26 may impart to the laser light L1 a phase distribution obtained by superimposing a phase distribution different from the helical phase distribution on the helical phase distribution. Part (c) of Figure 31 shows the simulation results when a phase distribution for correcting spherical aberration is superimposed on the helical phase distribution when the numerical aperture (NA) of the objective lens is large. For comparison, part (a) of Figure 31 shows the case where the laser light L is circularly polarized, no helical phase is imparted, and no spherical aberration is corrected. Part (b) of Figure 31 shows the case where the laser light L is circularly polarized, no helical phase is imparted, and spherical aberration is corrected. Part (d) of Figure 31 shows the case where the laser light L is azimuthally polarized, no helical phase is imparted, and no spherical aberration is corrected. In this example, the z-cut crystal 18 is made of LiNbO ３ The wavelength of the laser light L is 1030 nm, the numerical aperture (NA) of the objective lens is 0.9, and the depth of the light-condensing position is 335 μm.

[0093] 31(a) and (b), when the laser light L is circularly polarized, even if the spherical aberration is corrected, the focused spot will still be separated into upper and lower parts. As shown in FIG. 31(c), according to the above embodiment and each modified example, by superimposing a phase distribution for correcting spherical aberration on a spiral phase distribution, it is possible to form a single focused spot without separation, and to reduce the spherical aberration, thereby further shortening the dimension of the focused spot in the optical axis direction and further concentrating energy on the processed area.

[0094] [Sixth Modification] FIG. 32 is a diagram schematically illustrating the configuration of a laser processing apparatus 1E according to a sixth modification of the present disclosure. The laser processing apparatus 1E includes a light generation unit 3E and a controller 6E instead of the light generation unit 3A and the controller 6A of the above embodiment. The light generation unit 3E includes an SLM 28, a half-wave plate 291, and a quarter-wave plate 292 as phase and polarization controllers instead of the phase plate 22 and the vector polarizer 24 of the above embodiment. The laser light L1 output from the laser light source 21 is reflected by mirrors 271 and 273 and reaches the half-wave plate 291. The controller 6E has the function of controlling the phase distribution displayed on the SLM 28 in addition to the function of the controller 6A of the above embodiment. The controller 6E converts the laser light L1 into radially polarized or azimuthally polarized light having a helical phase to generate the laser light L, and causes the SLM 28 to display a phase distribution.

[0095] The SLM 28 is disposed on the optical path between the half-wave plate 291 and the quarter-wave plate 292. The half-wave plate 291 is disposed so that its fast axis forms an angle of π / 8 (rad) with respect to the polarization direction of the incident light, and the quarter-wave plate 292 is disposed so that its fast axis forms an angle of π / 4 (rad) with respect to the polarization direction of the incident light. Thus, the half-wave plate 291 and the quarter-wave plate 292, in cooperation with the SLM 28, generate laser light L that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0096] 33 is a diagram showing the results of verifying, using Stokes parameters, whether or not a laser beam L that is radially polarized or azimuthally polarized and has a spiral phase distribution can be generated even when the light generation unit 3E includes an SLM 28, a half-wave plate 291, and a quarter-wave plate 292 as phase and polarization control units. Parts (a) to (c) of FIG. 33 show Stokes parameters when the laser beam is radially polarized and does not have a spiral phase distribution. Parts (d) to (f) of FIG. 33 show Stokes parameters when a laser beam L that is radially polarized and has a spiral phase distribution is generated using a vector polarizer and a phase plate (i.e., in the above embodiment). Parts (g) to (i) of FIG. 33 show Stokes parameters when laser beam L is generated using the light generation unit 3E according to this modification. In Fig. 33, parts (a), (d), and (g) show the Stokes parameter S0, parts (b), (e), and (h) show the Stokes parameter S1, and parts (c), (f), and (i) show the Stokes parameter S2. Since the Stokes parameters S0 to S2 shown in parts (g) to (i), respectively, of Fig. 33 are the same as the Stokes parameters S0 to S2 shown in parts (d) to (f), respectively, it can be seen that even when the light generation unit 3E of this modified example is used, it is possible to generate laser light L that is radially polarized or azimuthally polarized and has a spiral phase distribution, as in the above embodiment.

[0097] According to the configuration of this modification, the SLM 28, the half-wave plate 291, and the quarter-wave plate 292 function as a phase control unit and a polarization control unit. Therefore, the same effects as those of the above embodiment can be obtained. That is, even with the configuration of this modification, it is possible to preferably generate laser light L that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0098] When radially polarized laser light L and azimuthally polarized laser light L are alternately irradiated, it is preferable to overlap the range of the focused spot of the radially polarized light with the range of the focused spot of the azimuthally polarized light. To achieve this, the control unit 6E may adjust the defocus component in the SLM 28 instead of or in addition to controlling the relative positional relationship between the focusing optical system 5 and the workpiece 11.

[0099] The laser processing apparatus, optical device manufacturing method, and laser processing method according to the present disclosure are not limited to the above-described embodiments and may be modified in various ways. For example, in the above-described embodiments, the light generation unit includes a phase control unit that imparts a helical phase distribution to the laser light and a polarization control unit that radially or azimuthally polarizes the laser light. This configuration is not limited to this, and the phase control unit may be omitted from the light generation unit. That is, the laser processing apparatus may include a light generation unit that generates radially or azimuthally polarized laser light, a focusing optical system that focuses the laser light at a focusing position within a uniaxial birefringent crystal, and a focusing position control unit that moves the focusing position within the birefringent crystal to form an optical structure. In this case, the light generation unit may include a polarization control unit that radially or azimuthally polarizes the laser light. The configuration example of the polarization control unit is the same as that of the above-described embodiments or each modified example. However, in the second modified example shown in Figure 25, the phase distribution displayed on the SLM 26 is different from that shown in Figure 26, and is a phase distribution (see Figure 9) in which the phase changes from 0 (rad) to 2π (rad) in the azimuthal direction centered on the optical axis.

[0100] The laser processing apparatus, semiconductor product manufacturing method, and laser processing method according to the present disclosure are not limited to the above-described embodiments, and various other modifications are possible. For example, although a semiconductor wafer is exemplified as the semiconductor product in the above-described embodiments, the semiconductor product may be a semiconductor chip formed by dicing.

[0101] While the principles of the present invention have been illustrated and described in preferred embodiments, it will be recognized by those skilled in the art that the present invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the particular constructions disclosed herein. We therefore claim all modifications and variations that come within the scope and spirit of the following claims.

[0102] 1A to 1E...Laser processing apparatus, 2...Stage, 3A to 3E...Light generating section, 4...Cutting section, 5...Converging optical system, 6A to 6E...Control section, 11...Processing object, 12...Modified region, 13...Modified spot, 14...Crack, 15...Imaginary surface, 16...Peripheral region, 17...Crack, 18...Z-cut crystal, 19...Y-cut crystal, 20...Ingot, 20a...Main surface, 20b...Side surface, 21...Laser Light source, 22...phase plate, 23, 25...double telecentric relay lens system, 24...vector polarizer, 26, 28...spatial light modulator (SLM), 27...mirror, 30...wafer, 51...objective lens, 231, 232, 251, 252...lenses, 271 to 273...mirrors, 291...half wave plate, 292...quarter wave plate, C...focus point, L, L1, L2...laser light.

Claims

1. A laser processing device comprising: a light generating unit that generates radially polarized or azimuthally polarized laser light having a helical phase distribution; a focusing optical system that focuses the laser light at a focusing position within a uniaxial birefringent crystal; and a focusing position control unit that moves the focusing position within the birefringent crystal to form a modified region for cutting the birefringent crystal.

2. The laser processing device according to claim 1, further comprising a cutting section for cutting the birefringent crystal along the modified region.

3. The laser processing device according to claim 1 or 2, wherein the focusing optical system includes an objective lens, and the numerical aperture of the objective lens is 0.04 or more and 3.0 or less.

4. A laser processing device according to any one of claims 1 to 3, wherein the light generating unit comprises: a phase control unit that imparts the helical phase distribution to the laser light; and a polarization control unit that converts the laser light after being given the helical phase distribution or before being given the helical phase distribution into the radially polarized or azimuthally polarized light.

5. The laser processing device according to claim 4, wherein the phase control section includes a phase plate and the polarization control section includes a vector polarizer.

6. The laser processing device according to claim 4, wherein the phase control section includes a first spatial light modulator, and the polarization control section includes a vector polarizer.

7. The laser processing device according to claim 4, wherein the phase control section includes a phase plate, and the polarization control section includes a second spatial light modulator.

8. The laser processing device according to any one of claims 1 to 3, wherein the light generating unit has a quarter wave plate, a half wave plate, and a spatial light modulator arranged on an optical path between the quarter wave plate and the half wave plate, and the quarter wave plate, the half wave plate, and the spatial light modulator work together to generate the laser light that is radially polarized or azimuthally polarized and has a spiral phase distribution.

9. A laser processing device according to any one of claims 1 to 8, wherein the light generating unit alternately generates the laser light that is radially polarized and has the spiral phase distribution and the laser light that is azimuthally polarized and has the spiral phase distribution.

10. The laser processing device described in claim 9, wherein the focusing position control unit overlaps at least a portion of the range of the focusing spot of the radially polarized laser light having the spiral phase distribution with at least a portion of the range of the focusing spot of the azimuthally polarized laser light having the spiral phase distribution.

11. A method for manufacturing a semiconductor product having a uniaxial birefringent crystal, comprising: a light generating step of generating radially polarized or azimuthally polarized laser light having a helical phase distribution; a focusing step of focusing the laser light at a focusing position within the birefringent crystal; a forming step of moving the focusing position within the birefringent crystal to form a modified region; and a cutting step of cutting the birefringent crystal along the modified region.

12. The method for manufacturing a semiconductor product according to claim 11, wherein in the focusing step, the laser light is focused using an objective lens, and the numerical aperture of the objective lens is 0.04 or more and 3.0 or less.

13. A method for manufacturing a semiconductor product as described in claim 11 or 12, wherein the light generation step includes: a step of imparting the spiral phase distribution to laser light; and a step of converting the laser light after being imparted with the spiral phase distribution or before being imparted with the spiral phase distribution into the radially polarized or azimuthally polarized light.

14. A method for manufacturing a semiconductor product according to any one of claims 11 to 13, wherein the laser light that is radially polarized and has the spiral phase distribution and the laser light that is azimuthally polarized and has the spiral phase distribution are alternately generated in the light generation step.

15. A method for manufacturing a semiconductor product as described in claim 14, wherein in the forming step, at least a portion of the range of the focused spot of the radially polarized laser light having the spiral phase distribution is overlapped with at least a portion of the range of the focused spot of the azimuthal polarized laser light having the spiral phase distribution.

16. The birefringent crystal is SiC, GaN, or LiNbO ３ , LiTaO ３ , β-BBO, sapphire, polyimide, Nd:YVO ４ , Nd:GdVO ４ 16. The method of claim 11, wherein the semiconductor product comprises at least one material selected from the group consisting of α-Quartz, AlN, ZnO, 4H—SiC, 6H—SiC, and Nd:YCOB.

17. A laser processing method comprising: a light generating step of generating radially polarized or azimuthally polarized laser light having a helical phase distribution; a focusing step of focusing the laser light at a focusing position within a uniaxial birefringent crystal; and a forming step of moving the focusing position within the birefringent crystal to form a modified region for cutting the birefringent crystal.

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