Laser processing device and laser processing method

Abstract

Laser processing device (300) for converging laser light (L) on an object (1) to be processed in order to form a modified area (7) within the object (1) along a line (5) to be cut, the laser processing device (300) comprising: a laser light source (202) designed to emit the laser light (L); an optical convergence system (204) configured to focus the laser light (L) emitted by the laser light source (202) at the object (1); and a spatial light modulator (203) configured to modulate the laser light (L) emitted by the laser light source (202) in such a way that the laser light (L) is caused to branch into at least a first processing light and a second processing light, and wherein the first processing light is focused at a first convergence point (P1) and the second processing light is focused at a second convergence point (P2) by the optical convergence system (204); an optical focusing system (241) comprising a first optical element (241a) and a second optical element (241b), each serving as a lens; wherein the first convergence point and the second convergence point have a positional relationship in which, in the object (1), the first convergence point is located on a first surface side as the opposite side to the laser light entry side of the object (1) with respect to the second convergence point (P2), and the first convergence point is located on a front side in a relative direction of movement of the laser light (L) along the line (5) with respect to the second convergence point (P2), the first optical element (241a) and the second optical element (241b) are arranged such that a distance of an optical path between the spatial light modulator (203) and the first optical element (241a) equals a first focal length of the first optical element (241a), a distance of an optical path between the optical convergence system (204) and the second optical element (241b) equals a second focal length of the second optical element (241b), a distance of an optical path between the first optical element (241a) and the second optical element (241b) equals the sum of the first focal length and the second focal length, and the first optical element (241a) and the second optical element (241b) form a double-telecentric optical system. the spatial light modulator (203) has a plurality of pixels (216) for displaying a modulation pattern, and in a case where D is a distance between the first convergence point (P1) and the second convergence point (P2) when viewed from a direction perpendicular to the first surface (3), d is a distance between adjacent pixels, m is a magnification of the optical focusing system (241), f is a focal length of the optical convergence system (204), and λ is a wavelength of the laser light (L), W1 is a radius of the first processing light on the first surface (3), and W2 is a radius of the second processing light on the first surface (3), the spatial light modulator (203) modulates the laser light (L) such that the expression D <2 × f × tan [asin {λ / (d × 4 × m)}] and the expression D > W1 + W2 are satisfied.

Description

Technical field

[0001] The present invention relates to a laser processing device and a laser processing method which are capable of focusing laser light on an object to be processed in order to create a modified area within the object along a cutting line. State of the art

[0002] A laser processing method is known from the prior art which modulates laser light in such a way that the laser light is caused to branch into a plurality of processing light beams, and each of the processing light beams is bundled at each of a plurality of convergence points and forms a modified area in each of a plurality of areas corresponding to each of the convergence points in an object to be processed (see, for example, patent literature 1).

[0003] JP 2011 - 51 011 A describes a laser processing method and a method for manufacturing a semiconductor device.

[0004] JP 2013 - 128 088 A describes a laser processing method and a laser processing device for cutting an object to be processed. Citation list of patent literature

[0005] [Patent Literature 1] Japanese Unexamined Patent Publication JP 2011 - 51 011 A Summary of the invention: Technical problem

[0006] For an object to be processed that has multiple functional devices on one surface, a situation may arise where a cutting line is defined such that the line passes through an area between adjacent functional devices, and the laser light is directed to enter the object from a rear surface, creating a modified area along the line. However, it has been found that in such a case, when a laser processing procedure is carried out as described above, damage may occur in an area along the line on the front surface, which is the side opposite the laser light entry surface of the object (that is, the area between the adjacent functional devices).

[0007] It is therefore an object of the present invention to provide a laser processing device and a laser processing method which are able to prevent damage to the front surface as the side opposite the laser light entry surface of the object when the laser light is caused to branch into a plurality of processing light beams in order to form a modified area by each of the processing light beams. Solution to the problem

[0008] The laser processing device according to one aspect of the present invention relates to a laser processing device for converging laser light at an object to be processed in order to form a modified area within the object along a line to be cut, the laser processing device comprising: a laser light source that emits the laser light, an optical convergence system that focuses the laser light emitted by the laser light source at the object, and a spatial light modulator that modulates the laser light emitted by the laser light source such that the laser light is caused to branch into at least a first processing light and a second processing light, wherein the optical convergence system focuses the first processing light at a first convergence point and the second processing light at a second convergence point.wherein the first convergence point and the second convergence point have a positional relationship in which, in the object, the first convergence point is located on a first surface face opposite the laser light entry face of the object with respect to the second convergence point, and the first convergence point is located on a front face in a relative direction of motion of the laser light along the line with respect to the second convergence point, and in a case where W1 is a radius of the first processing light on the first surface, W2 is a radius of the second processing light on the first surface, and D is a distance between the first convergence point and the second convergence point when viewed from a direction perpendicular to the first surface, the spatial light modulator modulates the laser light such thatthat the expression D > W1 + W2 is satisfied; and furthermore, an optical focusing system with a first optical element and a second optical element, each serving as a lens, wherein the first optical element and the second optical element are arranged such that a distance of an optical path between the spatial light modulator and the first optical element equals a first focal length of the first optical element, a distance of an optical path between the optical convergence system and the second optical element equals a second focal length of the second optical element, a distance of an optical path between the first optical element and the second optical element equals the sum of the first focal length and the second focal length, and the first optical element and the second optical element form a double-telecentric optical system.the spatial light modulator has a plurality of pixels for representing a modulation pattern, and in a case where d is a distance between the adjacent pixels, m is a magnification of the optical focusing system, f is a focal length of the optical convergence system, and λ is a wavelength of the laser light, the spatial light modulator modulates the laser light such that the expression D < 2 × f × tan [asin {λ / (d × 4 × m)}] is satisfied.

[0009] The laser processing device modulates the laser light such that the expression D > W1 + W2 is satisfied, thus preventing leakage light from the first processing light and leakage light from the second processing light reaching the first surface of the object from interfering with and reinforcing each other. Therefore, the laser processing device can prevent damage to the front surface, which is the side opposite the laser light entry point of the object (i.e., the first surface), when the laser light branches into a multitude of processing light beams to form a modified area through each of the processing light beams. The processing light is light with an energy capable of forming the modified area in a region corresponding to the point of convergence (the same applies to the subsequent area).

[0010] To increase the previously mentioned distance D between the first and second convergence points when viewed from the direction perpendicular to the first surface, it is necessary to decrease the number of grating pixels in the modulation pattern of the reflecting spatial light modulator. However, if the number of grating pixels is reduced too much, there is a risk that the leakage light will increase due to the increase in components where wavefront control cannot be performed in the laser light L. By modulating the laser light such that it satisfies the expression D < 2 × f × tan[asin{λ / (d × 4 × m)}], the increase in leakage light due to the increase in components where wavefront control cannot be performed in the laser light L is prevented, and damage is prevented at the front surface, which is the opposite side of the object from the laser light entrance side.

[0011] In the laser processing device according to one aspect of the present invention, the first surface can be formed with a plurality of two-dimensionally arranged functional devices and a metal structure located in a region between the adjacent functional devices. The line can be defined such that it passes through the region between the adjacent functional devices when viewed from a direction orthogonal to the first surface. If the metal structure is located between the adjacent functional devices opposite the laser light entrance side of the object, the metal structure absorbs the leakage light, thus easily causing damage to the front surface. However, even in such a case, damage to the front surface opposite the laser light entrance side of the object can be prevented.

[0012] The laser processing method relates to a laser processing method for forming a modified area within an object to be processed along a line to be cut by using an optical convergence system configured to focus the laser light, a spatial light modulator configured to modulate the laser light, and an optical focusing system with a first optical element and a second optical element, each serving as a lens, wherein the laser processing method comprises: modulating the laser light by using the spatial light modulator such that the laser light is caused to branch into at least a first processing light and a second processing light,wherein the first processing light at a first convergence point and the second processing light at a second convergence point are focused by the optical convergence system; and forming the modified region in each of the plurality of regions corresponding to the first and second convergence points in the object, wherein the first and second convergence points have a positional relationship, wherein in the object the first convergence point is located on a first surface face opposite the laser light entry face of the object with respect to the second convergence point, and the first convergence point is located on a front face in a relative direction of motion of the laser light along the line with respect to the second convergence point, the first optical element and the second optical element are arranged such thatthat a distance of an optical path between the spatial light modulator and the first optical element is equal to a first focal length of the first optical element, a distance of an optical path between the optical convergence system and the second optical element is equal to a second focal length of the second optical element, a distance of an optical path between the first optical element and the second optical element is equal to the sum of the first focal length and the second focal length, and the first optical element and the second optical element form a double-telecentric optical system, the spatial light modulator has a plurality of pixels for representing a modulation pattern, and in a case where D is a distance between the first convergence point and the second convergence point when viewed from a direction perpendicular to the first surface, d is a distance between the adjacent pixels,m is a magnification of the optical focusing system, f is a focal length of the optical convergence system, and λ is a wavelength of the laser light, W1 is a radius of the first processing light on the first surface, W2 is a radius of the second processing light on the first surface, and the spatial light modulator modulates the laser light (L) such that the expression, D<2×f×tan[asin{λ / (d×4×m)}] and the expression D>W1+W2 are fulfilled.

[0013] For the same reason as the previously mentioned laser processing device, the laser processing method can prevent the occurrence of damage on the front surface as the side opposite the laser light entry surface of the object (that is, the first surface) when the laser light branches into a multitude of processing light beams in order to form a modified area by each of the processing light beams. Advantageous effects of the invention

[0014] According to the present invention, the laser processing device and the laser processing method can be provided which are able to prevent the occurrence of damage on the front surface as the side opposite to the laser light entry side of the object when the laser light is made to branch into a plurality of processing light beams to form a modified area with each of the processing light beams. Brief description of the drawings Fig. Figure 1 shows a schematic structure diagram of the laser processing device used to create a modified area. Fig. Figure 2 shows a top view of an object to be processed, for which the modified area is created. Fig. Figure 3 shows a cross-sectional view of the object along line III-III of the Fig. 2. Fig. Figure 4 shows a top view of the object after laser processing. Fig. Figure 5 shows a cross-sectional view of the object along line VV of Fig. 4. Fig. Figure 6 shows a cross-sectional view of the object along line VI-VI. Fig. 4. Fig. Figure 7 shows a schematic structure diagram of the laser processing device according to an embodiment of the present invention. Fig. Figure 8 shows a partial cross-sectional view of a reflective spatial light modulator of the laser processing device of the Fig. 7. Fig. Figure 9 shows (a) a top view and (b) a partially enlarged sectional view of an object that is subjected to a laser processing method according to an embodiment of the present invention. Fig.Figure 10 shows a cross-sectional view to illustrate the laser processing method according to an embodiment of the present invention. Fig. Figure 11 shows a cross-sectional view to illustrate the laser processing method according to an embodiment of the present invention. Fig. Figure 12 shows a diagram to explain the number of grid pixels in the reflecting spatial light modulator of the Fig. 8. Fig. Figure 13 shows a diagram to illustrate experimental results according to the present invention. Fig. Figure 14 shows a diagram to illustrate a light-blocking part used for the laser processing device of the Fig. 7 is used. Fig. Figure 15 shows a diagram to explain the light blocking part used for the laser processing device of the Fig. 7 is used. Fig.Figure 16 shows a diagram to explain the light blocking part used for the laser processing device of the Fig. 7 is used. Fig. Figure 17 shows a diagram to illustrate an experiment according to the present invention. Fig. Figure 18 shows a diagram to illustrate a comparative example according to the present invention. Fig. Figure 19 shows a diagram to illustrate a result of a case from the comparative example of the Fig. 18. Fig. Figure 20 shows a diagram to illustrate an example according to the present invention. Fig. Figure 21 shows a diagram to illustrate a result of a case of the example of Fig. 20. Fig. Figure 22 shows a diagram to illustrate an example according to the present invention. Fig. Figure 23 shows a diagram to illustrate a result of a case of the example of Fig. 22. Fig. Figure 24 shows a diagram to illustrate experimental results according to the present invention. Description of embodiments

[0015] In the following, embodiments of the present invention are explained in detail with reference to the drawings. In the drawings, identical or equivalent parts are designated with the same reference numerals without repeating the description.

[0016] A laser processing device and a laser processing method of an embodiment of the present invention focus laser light on an object to be processed such that a modified area is created in the object along a line to be cut. Therefore, first, with reference to Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. 6 explains the generation of the modified area.

[0017] As in Fig.As shown in Figure 1, a laser processing device 100 comprises a laser light source 101 that causes the laser light L to oscillate in a pulsed manner, a dichroic mirror 103 arranged to change the direction of the optical axis (optical path) of the laser light L by 90°, and a converging lens 105 for focusing the laser light L. The laser processing device 100 further comprises a holding table 107 for holding an object 1 to be processed, which is irradiated with the laser light L focused by the converging lens 105, a support 111 for moving the holding table 107, a laser light source controller 102 for controlling the laser light source 101 to adjust the output, pulse width, pulse waveform, and the like of the laser light L, and a support controller 115 for controlling the movement of the support 111.

[0018] In the laser processing device 100, the laser light L emitted by the laser light source 101 changes the direction of its optical axis by 90° due to the dichroic mirror 103, and the light is then focused by the converging lens 105 onto the object 1, which is mounted on the holding table 107. Simultaneously, the support 111 is moved so that the object 1 moves relative to the laser light L along a line 5 to be cut. This creates a modified area in the object 1 along the line 5. Although the support 111 is moved here to generate the relative movement of the laser light L, the converging lens 105 can be moved instead or simultaneously.

[0019] Object 1 is defined as a planar element (for example, a substrate or a disk), including semiconductor substrates made of semiconductor materials and piezoelectric substrates made of piezoelectric materials. As in Fig. As shown in Figure 2, line 5 is defined in object 1 for cutting object 1. Line 5 is a virtual line that extends in a straight line. When a modified area is created in object 1, the laser light L is directed relatively along line 5 (i.e., in the direction of arrow A in Figure 2). Fig. 2) moves while a convergence point (convergence position) P is positioned in object 1, as in Fig. Figure 3 shows that this creates a modified area in object 1 along line 5, as shown in Figure 3. Fig. 4, Fig. 5 and Fig.6 is shown, whereby the modified area 7, which is generated along line 5, becomes a cutting start area 8.

[0020] The convergence point P is a position where the laser light L is focused or converges. Line 5 can be curved instead of straight, can be three-dimensional if these two types are combined, or can be specified by coordinates. Line 5 can actually be drawn on a front surface 3 of object 1 without being restricted to the virtual line. The modified region 7 can be generated continuously or in a discontinuous manner. The modified region 7 can be generated either in rows or points, and it is only required that it be generated at least within object 1. There are cases in which fractures or break lines or break points are generated starting from the modified region 7, which serves as a starting point, and the fractures and the modified region 7 can appear on outer surfaces (the front surface 3, the rear surface 21, and an outer circumferential surface) of object 1.The laser light entry area for forming the modified region 7 is not limited to the front surface 3 of the object 1, but it can be the rear surface 21 of the object 1.

[0021] In this process, the laser light L is absorbed, particularly near the convergence point P, within object 1 as it passes through the object, thereby creating the modified area 7 within object 1 (i.e., laser processing of the internal absorption type). Therefore, the front surface 3 of object 1 hardly absorbs the laser light L and does not melt. In the case of creating a cut-out part, such as a hole or groove, by melting away from the front surface 3 (laser processing of the surface absorption type), the processed area gradually progresses from the front surface 3 towards the rear surface.

[0022] The modified region 7 produced in this embodiment refers to regions whose physical properties, such as density, refractive index, and mechanical strength, exhibit assumed states that differ from those of their surroundings. Examples of modified region 7 include molten machined regions (i.e., at least one region that has resolidified after being molten, those in the molten state, and those in the process of resolidification from the molten state), crack regions, regions with dielectric breakdown, regions with a modified refractive index, and similarly mixed regions.Other examples of the modified region 7 include areas where the density of the modified region 7 has changed relative to an unmodified region, and areas created with a lattice defect in a material of object 1 (which can also be collectively referred to as high-density transition regions).

[0023] The molten machined areas, the areas with a modified refractive index, the areas where the modified area 7 has a different density than the unmodified area, or areas formed with a lattice defect, may furthermore contain a fracture or fracture line or fracture point (cut or microcrack) within it or at an interface between the modified area 7 and the unmodified area. The fracture may be present over the entire surface of the modified area 7 or only in a part or several parts thereof. Examples of object 1 include those made of or containing: silicon (Si), glass, silicon carbide (SiC), LiTaO3, and sapphire (Al2O3).

[0024] This embodiment generates multiple modified spots (processing areas) along line 5, thereby creating the modified area 7. The modified spots, each of which is a modified part created by a single pulse of pulsed laser light (i.e., a pulse of laser irradiation; laser shot), collectively constitute the modified area 7. Examples of the modified spots include spots in the form of cracks, molten processed spots, spots with a modified refractive index, and spots containing a mixture with at least one of these spots. The size of the modified spots and the lengths of any fractures originating from them can be controlled, if necessary, with regard to the required cutting accuracy, the required flatness of cut surfaces, the thickness, type, and crystal orientation of object 1, and the like.

[0025] Next, a laser processing device and a laser processing method of the embodiment of the present invention will be described. As in Fig. As shown in Figure 7, a laser processing device 300 comprises a laser light source 202, a reflective spatial light modulator 203, a 4f optical system 241, a light blocking element 220, and an optical convergence system 204, all within a housing 231. The laser processing device 300 focuses the laser light L on the object 1 such that the modified area 7 is created within the object 1 along line 5.

[0026] The laser light source 202 emits the laser light L, which has a wavelength of, for example, 1000 nm to 1500 nm, and is, for example, a fiber laser. The laser light source 202 is attached to an upper plate 236 of the housing 231 with a screw or similar fastener to emit the laser light L horizontally.

[0027] The reflective spatial light modulator 203 modulates the laser light L emitted by the laser light source 202 and is a reflective liquid crystal (liquid crystal on silicon (LCOS)) in the form of a spatial light modulator (SLM), to give an example. The reflective spatial light modulator 203 modulates the laser light L incident horizontally upon it, reflecting it obliquely upwards with respect to the horizontal direction.

[0028] As in Fig.As shown in Figure 8, the reflective spatial light modulator 203 is composed of a silicon substrate 213, a control layer 914, several pixel electrodes 214, a reflective layer 215, such as a dielectric multilayer mirror, an alignment layer 999a, a liquid crystal layer 216, an alignment layer 999b, a transparent conductive layer 217 and a transparent substrate 218, such as a glass substrate, which are stacked in this order.

[0029] The transparent substrate 218 has a front surface 218a extending along an XY plane, and the front surface 218a forms a front surface of the reflecting spatial light modulator 203. The transparent substrate 218 is made of a translucent material, for example, glass, and allows the laser light L to pass through, which, at a predetermined wavelength, originates from the front surface 218a of the reflecting spatial light modulator 203 and penetrates into the interior of the reflecting spatial light modulator 203. The transparent conductive layer 217 is formed on a rear surface of the transparent substrate 218 and comprises a conductive material (for example, ITO) that transmits the laser light L.

[0030] The multiple pixel electrodes 214 are arranged in a matrix on the silicon substrate 213 along the transparent conductive layer 217. Each pixel electrode 214 is made of a metallic material, for example, aluminum, with its front surface 214a being flat and smooth. The multiple pixel electrodes 214 are controlled by an active matrix circuit provided in the control layer 914.

[0031] The circuit for an active matrix is ​​arranged between the multiple pixel electrodes 214 and the silicon substrate 213 and controls a voltage applied to the pixel electrodes 214 according to a light image to be emitted by the reflective spatial light modulator 203. Such an active matrix circuit has a first driver circuit for controlling the applied voltage for the pixel rows aligned in the X-axis direction, and a second driver circuit for controlling the applied voltage for pixel rows aligned, for example, in the Y-axis direction, which are not shown. It is designed such that the control circuit 250 (see Fig. 7) a predetermined voltage is applied to the pixel electrodes 214 of a pixel selected by the driver circuits.

[0032] The alignment layers 999a, 999b are arranged on both end faces of the liquid crystal layer 216 such that they align or adjust a group of liquid crystal molecules in a defined direction. The alignment layers 999a, 999b are made of a polymer material, such as polyimide, the surfaces of which, coming into contact with the liquid crystal layer 216, are subject to abrasion and the like.

[0033] The liquid crystal layer 216 is arranged between the multiple pixel electrodes 214 and the transparent conductive layer 217 and modulates the laser light L according to an electric field that is formed between each pixel electrode 214 and the transparent conductive layer 217. That is, when a voltage is applied to the pixel electrodes 214 by the circuit for an active matrix of the drive layer 914, an electric field forms between the transparent conductive layer 217 and the pixel electrodes 214, and the orientation of liquid crystal molecules 216a changes according to the magnitude of the electric field formed in the liquid crystal layer 216.When the laser light L enters the liquid crystal layer 216 through the transparent substrate 218 and the transparent conductive layer 217, the laser light L is modulated by the liquid crystal molecules 216a as it passes through the liquid crystal layer 216, and it is reflected by the reflective layer 215 and subsequently modulated again by the liquid crystal layer 216 and then emitted.

[0034] The voltage applied to the pixel electrodes 215 is controlled by the controller 250 (see Fig.7) controlled, and according to the voltage, a refractive index changes in a part enclosed between the transparent conductive layer 217 and the pixel electrodes 214 in the liquid crystal layer 216 (the refractive index of the liquid crystal layer 216 changes at positions corresponding to the pixels). The change in the refractive index can change the phase of the laser light L for each pixel of the liquid crystal layer 216 according to the applied voltage. That is, a phase modulation corresponding to a hologram pattern can be achieved by the liquid crystal layer 216 for each pixel (i.e., the liquid crystal layer 216 of the reflecting spatial light modulator 203 can be caused to display a modulation pattern as a hologram pattern that provides modulation).Consequently, the wavefront of the laser light L passing through the modulation pattern is adjusted such that individual beams comprising the laser light L vary component-wise in their phase in a predetermined direction perpendicular to their propagation direction. Therefore, the laser light L can be modulated (for example, its intensity, amplitude, phase, and polarization can be modulated) by setting the modulation pattern as required, which is to be displayed in the reflecting spatial light modulator 203.

[0035] With renewed reference to Fig.7, the 4f optical system 241 sets a wavefront shape of the laser light L, which is modulated by the reflecting spatial light modulator 203, and has a first lens (first optical element) 241a and a second lens (second optical element) 241b.The first lens 241a and the second lens 241b are arranged on an optical path between the reflecting spatial light modulator 203 and the optical convergence system 204 such that the distance of the optical path between the reflecting spatial light modulator 203 and the first lens 241a is equal to a first focal length f1 of the first lens 241a, the distance of the optical path between the optical convergence system 204 and the lens 241b is equal to a second focal length f2 of the second lens 241b, the distance of the optical path between the first lens 241a and the second lens 241b is equal to a sum of the first focal length f1 and the second focal length f2 (that is, f1+f2), and the first lens 241a and the second lens 241b form a double telecentric optical system.This 4f optical system 241 can prevent the laser light L modulated by the reflecting spatial light modulator 203 from changing its wavefront through spatial propagation and thus increasing aberration.

[0036] The light-blocking element 220 is an aperture element with an aperture 220a through which a first processing light L1 and a second processing light L2, which will be described later, can move. The light-blocking element 220 is located on a Fourier plane between the first lens 241a and the second lens 241b (that is, a plane with a confocal point O).

[0037] The optical convergence system 204 focuses the laser light L, which is emitted by the laser light source 202 and modulated by the reflecting spatial light modulator 203, into the object 1. The optical convergence system 204, which has several lenses, is arranged on a base plate 233 of the housing 231, with a drive unit 232 with a piezoelectric device and the like arranged between them.

[0038] In the laser processing device 300, which is constructed as described above, the laser light L emitted by the laser light source 202 travels horizontally within the housing 231 and is then reflected downwards by a screen 205a, whereupon its light intensity is adjusted by an attenuator 207. Subsequently, the laser light L is reflected horizontally by a mirror 205b and enters the reflecting spatial light modulator 203 with an intensity distribution that has been balanced by a steel homogenizing unit 260.

[0039] The laser light L entering the reflecting spatial light modulator 203 passes through the modulation pattern shown in the liquid crystal layer 216, so that the light is modulated according to the modulation pattern and is subsequently reflected upwards by a mirror 206a, changes its polarization direction due to a half-wave plate 228 and is reflected horizontally by a mirror 206b, so that it enters the 4f optical system 241.

[0040] The laser light L entering the 4f optical system 241 has a wavefront shaped such that it enters the optical convergence system 204 as parallel light. Specifically, the laser light L is focused by passing through the first lens 241a, is reflected downwards by a mirror 219, is made divergent at a confocal point O, and passes through the second lens 241b, where it is recombined to become parallel light again. The laser light L then passes through dichroic mirrors 210 and 238 in succession to enter the optical convergence system 204, where it is focused onto the object 1 mounted on the bracket 111.

[0041] The laser processing device 300 further comprises a surface observation unit 211 for observing the laser light entry surface of the object 1, and an autofocus (AF) unit 212 for fine-tuning the distance between the optical convergence system 204 and the object 1 inside the housing 231.

[0042] The surface observation unit 211 has an observation light source 211a for emitting visible light VL1 and a detector 211b for receiving and detecting reflected light VL2 of the visible light VL1 reflected from the laser light entry surface of the object. In the surface observation unit 211, the visible light VL1 emitted from the observation light source 211a is reflected by or transmitted through a mirror 208 and dichroic mirrors 209, 210, 238, so that it is focused onto the object 1 by the optical convergence system 204. The light VL2 reflected from the laser light entry surface of object 1 is focused by the optical convergence system 204 so that it passes through or is reflected by the dichroic mirrors 238, 210, and then passes through the dichroic mirror 209 to be received by the detector 211b.

[0043] The AF unit 212 emits AF laser light LB1 and receives and detects reflected light LB2 of the AF laser light LB1, which is reflected from the laser light entrance surface, thereby obtaining displacement data of the laser light entrance surface along line 5. Subsequently, when generating the modified area 7, the AF unit 212 controls the drive unit 232 according to the displacement data obtained in this way, in order to move the optical convergence system 204 back and forth in the direction of its optical axis along vibrations of the laser light entrance surface of the object 1.

[0044] The laser processing device 300 further comprises the controller 250, which is formed by a CPU, ROM, RAM, and the like, for controlling the laser processing device 300. The controller 250 controls the laser light source 202 such that it adjusts the output power, pulse width, and the like of the laser light L emitted by the laser light source 202. During the generation of the modified area 7, the controller 250 controls the position of the housing 231 and / or the support 111 and / or the control of the drive unit 232 such that the convergence point P of the laser light L moves relatively along the line 5, while the convergence point P of the laser light L is positioned at a predetermined distance with respect to the rear surface 21 or the front surface 3 of the object 1.

[0045] During the formation of the modified region 7, the controller 250 applies a predetermined voltage to the pixel electrodes 214 in the reflective spatial light modulator 203 to cause the liquid crystal layer 216 to display a predetermined modulation pattern, thereby enabling the reflective spatial light modulator 203 to modulate the laser light L as required. The modulation pattern displayed in the liquid crystal layer 216 is derived in advance from the position to be formed in the modified region 7, the wavelength of the emitted laser light L, the material of the object 1, the refractive indices of the optical convergence system 204 and the object 1, and similar parameters stored in the controller 250.This modulation pattern includes an individual difference correction pattern to correct individual differences that occur in the laser processing device 300 (for example, distortions that occur in the liquid crystal layer 216 of the reflecting spatial light modulator 203), a spherical aberration correction pattern to correct spherical aberration, and the like.

[0046] The object 1, which is to be subjected to the laser processing method carried out in the laser processing device 300, which is constructed as described above, comprises, as shown in Fig.Figure 9 shows a substrate 11 made of, for example, a semiconductor material such as silicon, and a functional device layer 15 formed on a front surface 11a of the substrate 11. The functional device layer 15 comprises a plurality of functional devices 15a arranged in a matrix along the front surface 11a of the substrate 11 (for example, light-receiving devices such as photodiodes, light-emitting devices such as laser diodes, or switching devices configured as circuits), and a metal structure 16 (for example, TEG (a test element group)) formed in an intersection area (region) 17 between the adjacent functional devices 15a.In this way, the front surface (first surface) 3 of the object 1 is formed with the plurality of two-dimensionally arranged functional devices 15a and the metal structure 16 arranged in the cutting area 17 between the adjacent functional devices 15a. The functional device layer 15 comprises an intermediate insulating layer (for example, a layer with low k) that is formed over the entire front surface 11a of the substrate 11.

[0047] The laser processing method to be carried out in the laser processing device 300 is used as a chip manufacturing method for producing a plurality of chips by cutting the object 1 for each of the functional devices 15a. For this reason, in the laser processing method, the plurality of lines 5 are arranged in a grid such that they traverse the cutting area 17 between the adjacent functional devices 15a when viewed from a direction perpendicular to the front surface 3 (for example, passing through the midpoint of the width of the cutting area 17 when viewed from the thickness direction of the object 1). The laser light L entering from the back surface (second surface) 21 of the object 1, where the back surface 21 is a back surface 11b of the substrate 11, is focused at the object 1, and the modified area 7 is formed within the object 1 along each of the lines 5.Incidentally, in the substrate 11 made of semiconductor material, such as silicon, a case can occur in which a microcavity 7a is formed at a position of the convergence point P of the laser light L and the molten processing area 7b is formed at an entrance side of the laser light L with reference to the convergence point P as the modified area 7.

[0048] The laser processing method carried out in the laser processing device 300 is described below. First, the liquid crystal layer 216 of the reflecting spatial light modulator 203 is made to display the modulation pattern, which has a diffraction function that splits the laser light L into zero-order light and ±n-order light (n being a natural number) in a direction along line 5. In this way, the liquid crystal layer 216 in the reflecting spatial light modulator 203 serves as the plurality of pixels for displaying the modulation pattern. As in Fig.As shown in Figure 10, the convergence points of zeroth-order light and ±nth-order light have a positional relationship in which the points are arranged on the side of the front surface 3 as the opposite side to the entrance side of the laser light L of object 1 and are positioned on the front in a relative direction of motion of the laser light L along line 5 when a value indicating the order (which includes zero and ±n, where a “+” value indicates that the value is larger as its absolute value increases, and a “-” value means that the value is smaller as its absolute value increases) increases in object 1.

[0049] In the Fig.In the laser processing method shown in Figure 10(a), +1st order light and -1st order light are used as the first processing light L1 and the second processing light L2, respectively (processing light: light with an energy capable of forming the modified area in a region corresponding to the convergence point). Thus, the first convergence point P1 and the second convergence point P2 have a positional relationship, with the first convergence point P1 being located on the side of the front surface 3 opposite the entrance side of the laser light L of the object 1 with respect to the second convergence point P2, and the first convergence point P1 being located on the front surface in the relative direction of motion of the laser light L along line 5 with respect to the second convergence point P2 in the object 1.

[0050] As in Fig.As shown in Figure 10(b), the +1-th order light, the +0-th order light, and the -1-th order light are used as the first processing light L1, the second processing light L2, and the third processing light L3, respectively. That is, the first processing light L1 and the second processing light L2 are selected from the zeroth order light, the ±1-th order light, and the nth order light focused at object 1.

[0051] As previously described, the reflecting spatial light modulator 203 modulates the laser light L emitted from the laser light source 202, so that the laser light L is forced to branch into zeroth order light and ±nth order light, which contains at least the first processing light L1 and the second processing light L2, and wherein the optical convergence system 204 focuses the first processing light L1 at the first convergence point P1, and focuses the second processing light L2 at the second convergence point P2.

[0052] Here, the distance is defined as D between the first convergence point P1 and the second convergence point P2 when viewed from a direction perpendicular to the front surface 3 of object 1 (a distance between the adjacent processing light convergence points in the direction along line 5 viewed from the direction perpendicular to the front surface 3 of object 1). In a case where the radius of the first processing light L1 at the front surface 3 is W1 and the radius of the second processing light L2 at the front surface 3 is W2, the following is subsequently modulated as in Fig.As shown in Figure 11, the reflective spatial light modulator 203 modulates the laser light L such that the relationship D > W1 + W2 is satisfied. This prevents leakage light from the first processing light L1 (light that is not absorbed by the object in the region corresponding to the convergence point) and leakage light from the second processing light L2, which reaches the front surface 3 of the object 1, from interfering with and reinforcing each other at the front surface 3.

[0053] For example, if a silicon wafer with a thickness of 300 µm, a crystal orientation of (100) and a resistivity of 1 Ω·cm UP is prepared as object 1 and the laser light L is directed under the in Fig.Under the conditions shown in Table 1 below, the distance D (= W1 + W2) between the first convergence point P1 and the second convergence point P2 is 31.32641 µm when the leakage light of the first processing light L1 and the leakage light of the second processing light L2 touch each other at the front surface 3, which is the side opposite the entrance side of the laser light L of the object 1. A scanning speed of the laser light L is a relative motion speed of the first convergence point P1 and the second convergence point P2 along line 5. [Table 1] Value formula Wavelength of laser light L (nm) 1080 Repetition frequency of the laser light L (kHz) 80 Pulse width of laser light L (ns) 500 Laser light scanning speed L (mm / s) 300 Laser light output L (W) 3,2 Number of laser light branches L 2 Branching ratio of the laser light L 50:50 Distance H1 between front surface 3 and the first convergence point P1 (µm) 46 Distance H2 between front surface 3 and the second convergence point P2 (µm) 96 Numerical aperture Na of the first processing light L1 and of the second processing light L2 0,754 Refractive index n1 of the surrounding atmosphere 1 Refractive index n2 of object 1 3,5 Radius W1 of the first processing light L1 at the front surface 3 (µm) 10,14799 W1=H1×tanθ2θ2=asin(n1×sinθ1 / n2)θ1=asin(NA / n1) Radius W1 of the first processing light L1 at the front surface 3 (µm) 21,17842 W2=H2×tanθ2θ2=asin(n1×sinθ1 / n2)θ1=asin(NA / n1)

[0054] Table 2 shows the result of an experiment in which damage to the front surface 3 occurs when the distance D between the first convergence point P1 and the second convergence point P2 is 30 µm or less (the distance D is less than 31.32641 µm), and no damage to the front surface 3 occurs when the distance D between the first convergence point P1 and the second convergence point P2 is 40 µm or more (the distance D is greater than 31.32641 µm). From this result, it was found that modulating the laser light L such that D > W1 + W2 satisfies prevents the leakage light of the first processing light L1 and the leakage light of the second processing light L2, which reach the front surface 3 of object 1, from interfering with and reinforcing each other at the front surface 3, and thus prevents damage to the front surface 3. [Table 2] Distance D (µm) 20 30 40 50 60 Damage to the front surface 3 occurs occurs does not occur does not occur does not occur

[0055] In the liquid crystal layer 216, which serves as the multitude of pixels for displaying the modulation pattern, the reflecting spatial light modulator 203 modulates the laser light in a case where the distance between neighboring pixels is D, the magnification of the 4f optical system is 241 m, the focal length of the optical convergence system is 204 f, and the wavelength of the laser light is L λ, such that the relationship D < 2 × f × tan[asin{λ / (d × 4 × m)}] is satisfied. In the formula described above, “4” denotes the number of grid pixels in the modulation pattern of the reflecting spatial light modulator 203, and the number of grid pixels: 4 corresponds to the one in Fig. Case 12(a) shown. For comparison, the number of grid pixels corresponds to 2 in Fig. 12(b) case shown.

[0056] To increase the previously mentioned distance D between the first convergence point P1 and the second convergence point P2, it is necessary to decrease the number of grating pixels in the modulation pattern of the reflecting spatial light modulator 203. However, if the number of grating pixels is reduced too much, there is a risk that the leakage light will increase due to the increase in components where wavefront control in the laser light L cannot be performed. Thus, a silicon wafer with a thickness of 300 µm, a crystal orientation of (100), and a resistivity of 1 Ω·cm UP is prepared as object 1 and irradiated with the laser light L under the conditions specified in Fig.The conditions shown in Figure 11 and Table 3 below were used to investigate a relationship between the number of grid pixels and the occurrence of damage on the front surface 3. The distance D between the first convergence point P1 and the second convergence point P2 can be calculated using the expression D = 2 × f × tan[asin{λ / (d × number of grid pixels × m)}]. [Table 3] Value Wavelength λ of laser light L (nm) 1080 Repetition frequency of the laser light L (kHz) 80 Pulse width of laser light L (ns) 500 Laser light scanning speed L (mm / s) 300 Output Laser Light L (W) 3,2 Number of laser light branches L 2 Branching ratio of the laser light L 50:50 Distance H1 between front surface 3 and the first convergence point P1 (µm) 46 Distance H2 between front surface 3 and the second convergence point P2 (µm) 96 Numerical aperture Na of the first processing light L1 and the second processing light L2 0,754 Refractive index n1 of the surrounding atmosphere 1 Refractive index n2 of object 1 3,5 Distance d between adjacent pixels (µm) 20 Magnification m of the 4f optical system 241 0,485437 Focal length f of the optical convergence system 204 (mm) 1,83

[0057] Table 4 shows the result of an experiment in which damage to the front surface 3 occurs when the number of grid pixels is 4 or less (in other words, when the distance D between the first convergence point P1 and the second convergence point P2 is 102 µm or more), and no damage to the front surface 3 occurs when the number of grid pixels is 5 or more (in other words, when the distance D between the first convergence point P1 and the second convergence point P2 is 80 µm or less). Based on this result, it was found that modulating the laser light L such that the relationship D < 2 × f × tan[asin{λ / (d × 4 × m)}] satisfies prevents the leakage light from increasing due to the increase in components where wavefront control cannot be performed in the laser light L, and thus prevents damage to the front surface 3 from occurring. [Table 4] Number of grid pixels 2 3 4 5 6 Distance D (µm) 204 136 102 80 66 Damage to the front surface 3 occurs occurs occurs does not occur does not occur

[0058] Furthermore, based on the results in Table 2 and Table 4, it was found that modulating the laser light L such that the distance between the first convergence point P1 and the second convergence point P2 is between 40 µm and 80 µm can prevent damage to the front surface 3. This is as shown in Fig.As shown in Figure 13, where the distance D between the first convergence point P1 and the second convergence point P2 is 20 µm, it is evident that the leakage light from the first processing light L1 and the leakage light from the second processing light L2, which reach the front surface 3 of object 1, interfere with and reinforce each other at the front surface 3 (upper part), resulting in damage to the front surface 3 (lower part). If the distance D between the first convergence point P1 and the second convergence point P2 is 102 µm, it is shown that the leakage light in the -1st order (upper part) is increased, and damage occurs on the front surface 3 (lower part).If, in contrast, the distance D between the first convergence point P1 and the second convergence point P2 is 40 µm, it is not apparent that the leakage light of the first processing light L1 and the leakage light of the second processing light L2, which reach the front surface 3 of object 1, interfere with and reinforce each other at the front surface 3, with the leakage light in the -1st order light (upper part) increasing and no damage occurring at the front surface 3 (lower part). The diagrams in the upper part of the . Fig. Figure 13 are photographs of zero-order and ±n-order light states at front surface 3, viewed from the side of front surface 3 when the modified region was not formed. The diagrams in the lower part of the Fig. 13 are photographs of cut surfaces of object 1 cut along line 5.

[0059] The light-blocking element 220 blocks the ±2nd order light and the higher order light of the ±nth order light that is to be focused at object 1 (here, the ±2nd order light and the ±3rd order light). It can therefore be seen that the light-blocking element 220 blocks the light to be focused on the outside with respect to the first processing light L1 and the second processing light L2 of the zeroth order light and the ±nth order light that is focused at object 1.Alternatively, it can be seen that the light-blocking part 220 blocks the light to be focused on the side of the front surface 3, which is the side opposite the entrance side of the laser light L of the object with respect to the first processing light L1 and the second processing light L2 of the zeroth-order light and the ±nth-order light focused at the object 1, and the light to be focused on the side of the rear surface 21, which is the entrance side of the laser light L of the object with respect to the first processing light L1 and the second processing light L2. The reflective spatial light modulator 203 can modulate the laser light L such that at least a portion of the light to be blocked passes through the outside of the opening 220a of the light-blocking part 220.

[0060] In a case where X is a radius of the aperture 220a of the light-blocking part 220, which is on a Fourier plane of the 4f optical system 241, as in Fig.14(a) shown, arranged, and D is the distance between the first convergence point P1 and the second convergence point P2 viewed from the direction perpendicular to the front surface 3 of the object 1, f2 is the second focal length of the second lens 241b and f is the focal length of the optical convergence system 204 as previously described, the expression D × f2 / f < 2X < 20 × f2 / f must be satisfied in order to block the ±2nd order light and the higher order light (outer part off-center for the ±2nd order light) using the light-blocking part 220. That is, if the reflective spatial light modulator 203 modulates the laser light L such that the expression (X × f) / (2 × f2) < D / 2 < (X × f) / f2 is satisfied, the light blocking part 220 can block the ±2nd order light and the higher order light (outer part off-center for the ±2nd order light).

[0061] As in Fig.As shown in Figure 14(b), it is necessary that the expression D × f² / f < 2X < 3D × f² / f be satisfied in order to block the ±3rd order light and the higher order light (outer part, outside the center, for the ±3rd order light) using the light-blocking part 220. That is, if the reflecting spatial light modulator 203 modulates the laser light L such that the expression (X × f) / (3 × f²) < D / 2 < (X × f) / f² is satisfied, the light-blocking part 220 can block the ±3rd order light and the higher order light (outer part, outside the center, for the ±3rd order light).

[0062] For example, in a case where D = 50 µm, f2 = 150 mm and f = 1.8 mm, if the radius X of the aperture 220a of the light-blocking part 220 is set such that the expression 4166.7 µm < 2X < 8.333 µm is satisfied, the light-blocking part 220 can block the ±2nd order light and the higher order light (outer part off-center for the ±2nd order light). In other words, in a case where 2X = 10000 µm, f2 = 150 mm and f = 1.8 mm, if the distance D between the first convergence point P1 and the second convergence point P2 is set such that the expression 30 µm < D / 2 < 60µm is satisfied, the light blocking part 220 can block the ±2nd order light and the higher order light (outer part off-center for the ±2nd order light).

[0063] In a case where D = 50 µm, f2 = 150 mm and f = 1.8 mm, if the radius X of the aperture 220a of the light-blocking part 220 is set such that it satisfies the expression 4166.7 µm < 2X < 12,500 µm, the light-blocking part 220 can block the ±3rd order light and the higher order light (outer part off-center for the ±3rd order light). In other words, in a case where 2X = 10,000 µm, f2 = 150 mm and f = 1.8 mm, if the distance D between the first convergence point P1 and the second convergence point P2 is set such that it satisfies the expression 20 µm < D / 2 <60 µm, the light blocking part 220 can block the ±3rd order light and the higher order light (outer part off-center for the ±3rd order light).

[0064] Furthermore, to prevent damage to the front surface 3, which is the side opposite the entrance side of the laser light L of the object 1, the light-blocking element 220 can be an element that blocks ±n-th order light. In this case, as in Fig.As shown in Figure 15(a), it is required that in a case where the distance X from the focal point O to the light-blocking part 220 (an edge of a side of the focal point O of the light-blocking part 220) on the Fourier plane of the 4f optical system 241 is denoted, the expression D × f² / f < 2X < 20 × f² / f is satisfied in order to block the +2nd order light and the higher order light (outer part off-center for the +2nd order light) using the light-blocking part 220. That is, if the reflecting spatial light modulator 203 modulates the laser light L such that the expression (X × f) / (2 × f²) < D / 2 < (X × f) / f² is satisfied, the light-blocking part 220 can block the +2nd order light. Order and higher order light (outer part outside the center for the +2nd order light) are blocked.

[0065] As in Fig.As shown in Figure 15(b), the expression D × f² / f < 2X < 3D × f² / f must be satisfied to block the +3rd order light and the higher order light (outer part, outside the center, for the +3rd order light) using the light-blocking part 220. That is, if the reflecting spatial light modulator 203 modulates the laser light L such that the expression (X × f) / (3 × f²) < D / 2 < (X × f) / f² is satisfied, the light-blocking part 220 can block the +3rd order light and the higher order light (outer part, outside the center, for the +3rd order light).

[0066] Furthermore, the light-blocking part 220 can be provided on a light-entry part of the optical convergence system 204 to limit a lens field of view of the optical convergence system 204. In a case where X is a radius of the aperture 220a of the light-blocking part 220, which is located on the light-entry part of the optical convergence system 204, as in Fig.16(a) shown, is arranged, and the distance between the first convergence point P1 and the second convergence point P2, from the perspective of the direction perpendicular to the front surface 3 of the object 1, as previously described, is designated as D, and if the reflecting spatial light modulator 203 modulates the laser light L such that the expression X / 2 < D / 2 < X is satisfied, the light-blocking part 220 can block the ±2nd order light and the higher order light (outer part from the center of the ±2nd order light). If, as in Fig. As shown in Figure 16(b), the reflecting spatial light modulator 203 modulates the laser light L such that the expression X / 3 < D / 2 < X is satisfied, the light blocking part 220 can block the ±3rd order light and the higher order light (outer part off-center for the ±3rd order light).

[0067] For example, in a case where 2X = 150 µm, if the distance D between the first convergence point P1 and the second convergence point P2 is set such that it satisfies the expression 37.5 µm < D / 2 < 75 µm, the light-blocking part 220 can block ±2nd order light and higher order light (outer part, off-center, for ±2nd order light). In a case where 2X = 150, if the distance D between the first convergence point P1 and the second convergence point P2 is set such that it satisfies the expression 25 µm < D / 2 < 75 µm, the light-blocking part 220 can block ±3rd order light and higher order light (outer part, off-center, for ±3rd order light).

[0068] Here, a silicon wafer with a thickness of 300 µm, a crystal orientation of (100), and a resistance value of 1 Ω·cm UP is prepared as object 1 and exposed to the laser light L under the in Fig.The surface 3 was irradiated under the conditions shown in Figure 11 and Table 3 above to investigate a relationship between third-order light and the occurrence of damage on the front surface 3. To simplify the determination of the occurrence of damage on the front surface 3, a heat-sensitive film was formed on the front surface 3 for conducting an experiment.

[0069] One result of the experiment showed that the damage to the front surface 3, the side opposite the entrance side of the laser light L of object 1, was due to at least the influence of the 3rd order light, as in Fig. 17(d) shown, occur. Fig. Figure 17(a) shows a diagram representing a positional relationship of the convergence points of zeroth order light and ±nth order light in the cross-sectional area of ​​object 1 cut along line 5. Fig.Figure 17(b) shows a photograph of the states of zeroth order light and ±nth order light at the front surface 3 from the view of the side of the front surface 3 when the modified region was not formed. Fig. Figure 17(c) shows a photograph of the states of zeroth order light and ±nth order light at the front surface 3 from the view of the side of the front surface 3 when the modified region was formed. Fig. Figure 17(d) shows a photograph of the heat-sensitive film from the view of the side of the front surface 3 when the modified area was formed.

[0070] Fig.Figure 18 shows a diagram illustrating a comparative example of the present invention; (a) is a simulation diagram representing a state of the laser light L near the Fourier plane, and (b) is a simulation diagram representing a state of the laser light L near the convergence point. It has been found that the most severe damage to the front surface 3 is the side opposite the entrance side of the laser light L of the object 1 due to the influence of the +3rd order light, as shown in Figure 1. Fig. As shown in 19, this occurs when the +3rd order light is not blocked. The upper part of the Fig. Figure 19 is a photograph of the heat-sensitive film viewed from the side of the front surface 3 when the laser light L is moved relatively in a direction parallel to a direction in which the convergence points of the zeroth-order light and the ±nth-order light branch off, and the lower part of the Fig.Figure 19 is a photograph of the heat-sensitive film viewed from the side of the front surface 3 when the laser light L is moved relatively in a direction perpendicular to the direction in which the convergence points of the zeroth order light and the ±nth order light branch off.

[0071] Fig. Figure 20 shows a diagram illustrating an example of the present invention; (a) is a simulation diagram representing a state of the laser light L near the Fourier plane, and (b) is a simulation diagram representing a state of the laser light L near the convergence point. It was found that the damage to the front surface 3 of object 1 due to the influence of the +3rd order light, as shown in Figure 20, is reduced by the influence of the laser light L near the convergence point. Fig. 21 shows that the light decreases when part of the +3rd order light is blocked using the light-blocking part 220. The upper part of the Fig.Figure 21 shows a photograph of the heat-sensitive film from the perspective of the side of the front surface 3 when the laser light L is moved relatively in the direction parallel to the direction in which the convergence points of the zeroth-order light and the ±nth-order light branch off, and the lower part of the Fig. 21 is a photograph of the heat-sensitive film from the viewpoint of the side of the front surface 3 when the laser light L is moved relatively in the direction perpendicular to the direction in which the convergence points of the zeroth order light and the ±nth order light branch off.

[0072] Fig.Figure 22 shows a diagram illustrating an example of the present invention; (a) is a simulation diagram representing a state of the laser light L near the Fourier plane, and (b) is a simulation diagram representing a state of the laser light L near the convergence point. It was found that the damage to the front surface 3 of object 1 due to the influence of the +3rd order light, as in Fig. 23 shows that they essentially disappear when the +3rd order light is completely blocked using the light-blocking part 220. The upper part of the Fig. Figure 23 is a photograph of the heat-sensitive film from the perspective of the side of the front surface 3 when the laser light L is moved relatively in the direction parallel to the direction in which the convergence points of the zeroth-order light and the ±nth-order light branch off, and the lower part of the Fig.23 is a photograph of the heat-sensitive film from the viewpoint of the side of the front surface 3 when the laser light L is moved relatively in the direction perpendicular to the direction in which the convergence points of the zeroth order light and the ±nth order light branch off.

[0073] Fig. Figure 24 shows a diagram illustrating the experimental results of the present invention. In this case, the light-blocking element 220 is provided at the light-entry element of the optical convergence system 204 to limit the lens field of view of the optical convergence system 204, wherein the lens field of view can block the +3rd order light when the distance D between the first convergence point P1 and the second convergence point P2 is 50 µm or more. From the experimental results in Fig.24. It was found that the damage to the front surface 3 of object 1, caused by the influence of +3rd order light, essentially disappears when the +3rd order light is blocked by the light-blocking part 220. The upper part of the Fig. Figure 24 is a photograph of the heat-sensitive film from the perspective of the side of the front surface 3 when the laser light L is moved relatively in the direction parallel to the direction in which the convergence points of the zeroth-order light and the ±nth-order light diverge, and the lower part of the Fig. Figure 24 is a photograph of the heat-sensitive film from the viewpoint of the side of the front surface 3 when the laser light L is moved relatively in the direction perpendicular to the direction in which the convergence points of the zeroth order light and the ±nth order light branch off.

[0074] It is evident from the foregoing that the laser processing method carried out in the laser processing device 300 causes the laser light L to split into zeroth order light and ±nth order light comprising the first processing light L1 and the second processing light L2, modulates the laser light L such that the first processing light L1 is focused at the first convergence point P1 and the second processing light L2 is focused at the second convergence point P2, and forms the modified region 7 in each of the regions corresponding to the first convergence point P1 and the convergence point P2 in the object 1.

[0075] At this point, in a case where the radius of the first processing light L1 at the front surface 3 is denoted as W1, the radius of the second processing light L2 at the front surface 3 is denoted as W2, and the distance between the first convergence point P1 and the second convergence point P2 is denoted as D when observed from the direction perpendicular to the front surface 3, the laser light L is modulated such that it satisfies the expression D > W1 + W2. Alternatively, the laser light L is modulated such that the distance between the first convergence point P1 and the second convergence point P2, viewed from the direction perpendicular to the front surface 3, is between 40 µm and 80 mm.

[0076] The light focused on the outer surface with respect to the first processing light L1 and the second processing light L2 of the zeroth-order and ±nth-order light focused on object 1 is blocked. Alternatively, of the zeroth-order and ±nth-order light focused on object 1, the light focused on the side of the front surface 3 opposite the entrance side of the laser light L of object 1 with respect to the first processing light L1 and the second processing light L2, and the light focused on the side of the rear surface 21 with respect to the entrance side of the laser light L of object 1 with respect to the first processing light L1 and the second processing light L2, are blocked.

[0077] After the formation of the modified area 7 within the object 1, a strain relief band is glued and stretched on the back surface 21 of the object 1. This causes the fractures extending in the thickness direction of the object 1 from the modified area 7 formed along line 5 to reach the front surface 3 and the back surface 21 of the object 1, and the laser processing method cuts the object 1 along line 5 for each of the functional devices 15a to obtain a multitude of chips.

[0078] As previously described, in a case where W1 is the radius of the first processing light L1 at the front surface 3, W2 is the radius of the second processing light L2 at the front surface 3, and D is the distance between the first convergence point P1 and the second convergence point P2 when viewed from the direction orthogonal to the front surface 3, the laser processing device modulates the laser light L such that D > W1 + W2. This prevents the leakage light of the first processing light L1 and the leakage light of the second processing light L2, which reach the front surface 3 of the object 1, from interfering with each other and reinforcing each other at the front surface 3.If the laser light L is made to branch into a multitude of processing light beams in order to form the modified area 7 with each of the processing light beams, damage to the front surface 3 as the opposite side of the entry side of the laser light L of the object 1 can be prevented.

[0079] In a case where d is the distance between adjacent pixels in the reflecting spatial light modulator 203, m is the magnification of the 4f optical system 241, f is the focal length of the optical convergence system 204, and λ is the wavelength of the laser light L, the reflecting spatial light modulator 203 modulates the laser light L such that the expression D < 2 × f × tan[asin{A / (d × 4 × m)}] is satisfied. To increase the distance D between the first convergence point P1 and the second convergence point P2 when viewed from the direction perpendicular to the front surface 3, it is necessary to decrease the number of grating pixels in the modulation pattern of the reflecting spatial light modulator 203. However, if the number of grid pixels is excessively reduced, there is a possibility that the leakage light will increase due to the increase in components where wavefront control in the laser light L cannot be performed.By modulating the laser light L such that the expression D < 2 × f × tan[asin{λ / (d × 4 × m)}] is satisfied, the leakage light is prevented from increasing due to the increase in components where wavefront control cannot be performed in the laser light L, and damage is prevented from occurring on the front surface 3 as the opposite side of the entrance side of the laser light L of the object 1.

[0080] The front surface 3, as the side opposite the entrance side of the laser light L of the object 1, comprises the plurality of functional devices 15a, which are arranged two-dimensionally, and the metal structure 16, which is arranged in the cutting area 17 between the adjacent functional devices 15a, wherein the line 5 is defined such that it passes through the cutting area 17 between the adjacent functional devices 15a perpendicular to the front surface 3. If the metal structure 16 is arranged at the cutting area 17 between the adjacent functional devices 15a from the front surface 3 as the side opposite the entrance side of the laser light L of the object 1, the metal structure 16 absorbs the leakage light, thereby easily causing damage to the front surface 3.However, even in such a case, damage to the front surface 3, which is the side opposite the entrance side of the laser light L of the object 1, can be prevented. In particular, if the intermediate insulating layer (for example, a film with low k) is formed over the entire front surface 11a of the substrate 11, the detachment of the intermediate insulating film and the like is effectively prevented.

[0081] The light to be focused on the outside is blocked with respect to the first processing light L1 and the second processing light L2 of the zeroth-order and ±nth-order light focused on object 1. Alternatively, the zeroth-order and ±nth-order light focused on object 1 block the light focused on the side of the front surface 3 opposite the entrance side of the laser light L of the object, with respect to the first processing light L1 and the second processing light L2, and the light focused on the side of the rear surface 21, with respect to the entrance side of the laser light L of the object, with respect to the first processing light L1 and the second processing light L2. This prevents the light from focusing near the rear surface 21 and near the front surface 3 of object 1.If the laser light L is thus made to branch into a multitude of processing light beams in order to form the modified area 7 by each of the processing light beams, damage to the front surface 3 as the side opposite to the entry side of the laser light L of the object 1 and to the rear surface 21 as the entry side of the laser light L of the object can be prevented.

[0082] The first processing light L1 and the second processing light L2 are selected from the zeroth-order and ±1st-order light and the ±nth-order light focused on object 1, and the light-blocking element 220 blocks the ±2nd-order and ±3rd-order light focused on object 1. This more reliably prevents damage to the front surface 3 (the side opposite the entrance side of the laser light L from object 1) and to the rear surface 21 (the entrance side of the laser light L from object 1), while allowing the zeroth-order and ±1st-order light to be used efficiently with relatively high energy as the first processing light L1 and the second processing light L2. In particular, blocking the ±3rd-order light...Order with relatively high energy is important to prevent damage to the front surface 3 as the side opposite the entrance side of the laser light L of the object 1.

[0083] The light-blocking element 220 has an opening 220a that allows the first processing light L1 and the second processing light L2 to pass through. This makes it possible to design the light-blocking element 220 with a simple structure such that at least the first processing light L1 and the second processing light L2 can pass through it, and that it can block other predetermined light besides the first processing light L1 and the second processing light L2.

[0084] The light-blocking element 220 is located on the Fourier plane between the first lens 241a and the second lens 241b. This makes it possible to reliably block any predefined light other than the first processing light L1 and the second processing light L2. Even if the light-blocking element 220 is located at the light-entry point of the optical convergence system 204, it is still possible to reliably block any predefined light other than the first processing light L1 and the second processing light L2. The reflective spatial light modulator 203 can modulate the laser light such that at least a portion of the light to be blocked passes through the outer surface of the aperture 220a. This makes it possible to block any predefined light other than the first processing light L1 and the second processing light L2 more reliably.

[0085] The embodiment of the present invention is described above; however, the present invention is not limited to the embodiment mentioned above. For example, the structure and material of object 1 are not limited to those mentioned above. For example, the substrate 11 may comprise a semiconductor substrate other than the silicon substrate, sapphire substrate, SiC substrate, glass substrate (tempered glass substrate), transparent insulating substrate, or the like.

[0086] The convergence points of zeroth-order light and ±nth-order light have a positional relationship in which the points on the front surface 3 are located opposite the entrance side of the laser light L of object 1, and on the front surface, they are located in the relative direction of motion of the laser light L along line 5 as the order-indicating value in object 1 decreases. The laser light L can penetrate from the front surface 3 of object 1. In this case, the rear surface 21 is the first surface opposite the entrance side of the laser light L of object 1, and the front surface 3 is the second surface opposite the entrance side of the laser light L of object 1.

[0087] The light-blocking element 220 can be a part comprising an element that blocks +nth order light and an element that blocks -nth order light, allowing the first processing light L1 and the second processing light L2 to pass through in a region between the facing elements. The light-blocking element 220 can selectively block ±2nd order light and higher-order light, for example, ±nth order light focused at object 1; only the light on the side of the front surface 3 opposite the entrance side of the laser light L of object 1 with respect to the first processing light L1 and the second processing light L2; or only the +3rd order light. Industrial applicability

[0088] According to the present invention, the laser processing device and the laser processing method can be provided which are able to prevent the occurrence of damage on the front surface as the side opposite to the laser light entry side of the object when the laser light is made to split into a plurality of processing light beams to form a modified area with each of the processing light beams. List of reference symbols 1 object to be edited 3 Front surface (first surface) 5 lines to be cut 7 Modified Area 15a Functional device 16 Metal structure 17 Cutting area (area) 21 Back surface (second surface) 202 Laser light source 203 Reflective spatial light modulator (spatial light modulator) 204 Optical Convergence System 216 Liquid crystal layer (multiple pixels) 241 4f optical system (optical adjustment system) 241a first lens (first optical element) 241b second lens (second optical element) 300 laser processing device L laser light L1 first processing light L2 second processing light P1 first convergence point P2 second point of convergence

Claims

[1] Laser processing device (300) for converging laser light (L) on an object (1) to be processed in order to form a modified area (7) within the object (1) along a line (5) to be cut, the laser processing device (300) comprising: a laser light source (202) designed to emit the laser light (L); an optical convergence system (204) configured to focus the laser light (L) emitted by the laser light source (202) at the object (1); and a spatial light modulator (203) configured to modulate the laser light (L) emitted by the laser light source (202) in such a way that the laser light (L) is caused to branch into at least a first processing light and a second processing light, and wherein the first processing light is focused at a first convergence point (P1) and the second processing light is focused at a second convergence point (P2) by the optical convergence system (204); an optical focusing system (241) comprising a first optical element (241a) and a second optical element (241b), each serving as a lens; wherein the first convergence point and the second convergence point have a positional relationship in which, in the object (1), the first convergence point is located on a first surface side as the opposite side to the laser light entry side of the object (1) with respect to the second convergence point (P2), and the first convergence point is located on a front side in a relative direction of movement of the laser light (L) along the line (5) with respect to the second convergence point (P2), the first optical element (241a) and the second optical element (241b) are arranged such that a distance of an optical path between the spatial light modulator (203) and the first optical element (241a) equals a first focal length of the first optical element (241a), a distance of an optical path between the optical convergence system (204) and the second optical element (241b) equals a second focal length of the second optical element (241b), a distance of an optical path between the first optical element (241a) and the second optical element (241b) equals the sum of the first focal length and the second focal length, and the first optical element (241a) and the second optical element (241b) form a double-telecentric optical system. the spatial light modulator (203) has a plurality of pixels (216) for displaying a modulation pattern, and in a case where D is a distance between the first convergence point (P1) and the second convergence point (P2) when viewed from a direction perpendicular to the first surface (3), d is a distance between adjacent pixels, m is a magnification of the optical focusing system (241), f is a focal length of the optical convergence system (204), and λ is a wavelength of the laser light (L), W1 is a radius of the first processing light on the first surface (3), and W2 is a radius of the second processing light on the first surface (3), the spatial light modulator (203) modulates the laser light (L) such that the expression D <2 × f × tan [asin {λ / (d × 4 × m)}] and the expression D > W1 + W2 are satisfied. [2] Laser processing device (300) according to claim 1, wherein the first surface (3) is formed with a plurality of two-dimensionally arranged functional devices (15a) and a metal structure (16) which is arranged in an area between the adjacent functional devices (15a), and the line (5) is defined such that it passes through the area between the adjacent functional devices (15a) when viewed from a direction orthogonal to the first surface (3). [3] Laser processing method for forming a modified area (7) within an object to be processed (1) along a line to be cut (5) by using an optical convergence system (204) configured to focus the laser light (L), a spatial light modulator (203) configured to modulate the laser light (L), and an optical focusing system (241) with a first optical element (241a) and a second optical element (241b), each serving as a lens, wherein the laser processing method comprises: Modulating the laser light (L) by using the spatial light modulator (203) such that the laser light (L) is caused to branch into at least one first processing light and one second processing light, wherein the first processing light is focused at a first convergence point (P1) and the second processing light at a second convergence point (P2) by the optical convergence system (204); and forming the modified region (7) in each of the plurality of regions corresponding to the first convergence point (P1) and the second convergence point (P2) in the object (1), wherein the first convergence point and the second convergence point have a positional relationship in which, in the object (1), the first convergence point is located on a first surface side as the opposite side to the laser light entry side of the object (1) with respect to the second convergence point (P2), and the first convergence point is located on a front side in a relative direction of movement of the laser light (L) along the line (5) with respect to the second convergence point (P2), the first optical element (241a) and the second optical element (241b) are arranged such that a distance of an optical path between the spatial light modulator (203) and the first optical element (241a) equals a first focal length of the first optical element (241a), a distance of an optical path between the optical convergence system (204) and the second optical element (241b) equals a second focal length of the second optical element (241b), a distance of an optical path between the first optical element (241a) and the second optical element (241b) equals the sum of the first focal length and the second focal length, and the first optical element (241a) and the second optical element (241b) form a double-telecentric optical system. the spatial light modulator (203) has a plurality of pixels (216) for displaying a modulation pattern, and in a case where D is a distance between the first convergence point (P1) and the second convergence point (P2) when viewed from a direction perpendicular to the first surface (3), d is a distance between adjacent pixels, m is a magnification of the optical focusing system (241), f is a focal length of the optical convergence system (204), and λ is a wavelength of the laser light (L), W1 is a radius of the first processing light on the first surface (3), and W2 is a radius of the second processing light on the first surface (3), the spatial light modulator (203) modulates the laser light (L) such that the expression D <2 × f × tan [asin {λ / (d × 4 × m)}] and the expression D > W1 + W2 are satisfied.

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