Laser processing device

Abstract

Laser processing device (1) comprising: a clamping table (36) holding a workpiece (10); a laser beam irradiation device (6) which irradiates the workpiece (10) held by the clamping table (36) with a laser beam (LB1, LB2); and a machining feed means (37) which performs a relative machining feed of the clamping table (36) and the laser beam irradiation device (6), wherein the laser beam irradiation device (6) includes: a pulse laser beam oscillating means (62) which oscillates a pulsed laser beam (LB1), a condenser (67) which condenses the pulsed laser beam (LB1, LB2) oscillated by the pulsed laser beam oscillation means (62) and irradiates the workpiece (10) held by the clamping table (36) with the laser beam (LB1, LB2) and a beam splitter means (65) arranged between the pulse laser beam oscillation means (62) and the condenser (67) and splitting the pulsed laser beam (LB) oscillated by the pulse laser beam oscillation means (62), and the beam splitter means (65) includes: a λ / 2 plate (651) which rotates a polarization plane of the pulsed laser beam (LB) oscillated by the pulsed laser beam oscillation means (62), a birefringent lens (652) which splits the pulsed laser beam (LB) which has passed through the λ / 2 plate (651) into ordinary light and extraordinary light, the birefringent lens (652) being formed by connecting two kinds of bodies to each other via a curved plane of a concave surface of a crystalline body (652a) and a convex surface of a glass body (652b), and a splitting angle adjusting means (653) that moves the birefringent lens (652) in a direction perpendicular to the pulsed laser beam (LB) that has passed through the λ / 2 plate (651) so that the lens (652) is moved in the machining feed direction and / or in a direction orthogonal thereto to change an incident angle of the pulsed laser beam (LB) with respect to the curved plane and to adjust a beam splitting angle.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a laser processing apparatus for performing laser processing for a workpiece such as an optical device wafer or a semiconductor wafer. Description of the state of the art

[0002] In an optical device manufacturing method, an optical device wafer is formed by forming optical devices, such as light-emitting diodes or laser diodes, in multiple regions obtained by depositing a light-emitting layer composed of an n-type semiconductor layer and a p-type semiconductor layer on a surface of a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, etc., having a substantially circular disk shape, and dividing the light-emitting layer by a plurality of streets formed in a grid array. Subsequently, the optical device wafer is divided along the streets to fabricate individual optical devices.

[0003] Cutting the optical device wafer along the streets described above is typically performed by a cutting device called a dicing saw. This cutting device includes a chuck table that holds a workpiece, a cutting unit for cutting the workpiece held by this chuck table, and a cutting feed unit that causes the chuck table and the cutting unit to move relatively. The cutting unit includes a rotary spindle, a cutting blade attached to this spindle, and a drive mechanism that rotates the rotary spindle. The cutting blade consists of a base having a circular disk shape and an annular cutting edge attached to the side surface peripheral part of this base.For example, the cutting blade is formed with a thickness of approximately 20 μm by electroforming diamond abrasive grains with a grain size of approximately 3 μm onto the base. However, since the sapphire substrate, silicon carbide substrate, gallium nitride substrate, etc., used to form the optical device wafer have high Mohs hardness, there is a problem that cutting with the cutting blade described above is not necessarily easy, and productivity is low.

[0004] To solve the above-described problem, a laser machining method is attempted as a method for dividing an optical device wafer along streets, in which a pulsed laser beam having a wavelength such that it is transmitted through the wafer is used and the wafer is irradiated with the pulsed laser beam with the light focus located within the region along which cutting is to be performed. The dividing method using this laser machining method is the following method. Specifically, a modified layer is formed continuously within the wafer along streets by irradiating the wafer with the pulsed laser beam having a wavelength such that it is transmitted through the wafer from one surface side of the wafer along the streets with the light focus located within the wafer.Subsequently, the wafer is divided by applying an external force along the streets, the strength of which is reduced due to the formation of the modified layer (see, for example, Japanese Patent Laid-Open JP 2011 - 114 018 A).

[0005] Furthermore, the following method has been proposed as a method for dividing an optical device wafer along streets. Specifically, a laser processing groove is formed along the streets by irradiating the wafer with a pulsed laser beam having a wavelength such that it is absorbed by the wafer. Subsequently, the wafer is divided by applying an external force along the streets along which the laser processing groove is formed (see, for example, Japanese Patent Laid-Open No. 2008-311404 A).

[0006] US 7,402,773 B2 relates to a laser processing device. US 5,867,315 A relates to a bifocal crystalline optical lens.

[0007] WO 2011 / 001 765 A1 relates to a laser irradiation device.

[0008] US 8 450 638 B2 relates to a method and apparatus for forming a linear, scribed groove. SUMMARY OF THE INVENTION

[0009] However, when a modified layer or a laser processing groove for an optical device wafer is formed along streets and then the optical device wafer is divided along the streets along which the modified layer or the laser processing groove is formed, there is a problem that the division surface becomes a flat surface and a part of the light from the light-emitting layer is confined in the substrate, thereby causing the reduction of the luminance of the optical device.

[0010] Therefore, it is an object of the present invention to provide a laser processing apparatus capable of performing laser processing for dividing an optical device wafer along streets in such a manner as to increase the luminance of an optical device.

[0011] According to one aspect of the present invention, there is provided a laser processing apparatus comprising: a chuck table holding a workpiece; a laser beam irradiation device that irradiates the workpiece held by the chuck table with a laser beam; and processing feed means that performs relative processing feed of the chuck table and the laser beam irradiation device, wherein the laser beam irradiation device includes pulse laser beam oscillation means that oscillates a pulsed laser beam, a condenser that condenses the pulsed laser beam oscillated by the pulse laser beam oscillation means and irradiates the workpiece held by the chuck table with the laser beam, and beam splitter means that is disposed between the pulse laser beam oscillation means and the condenser and splits the pulsed laser beam oscillated by the pulse laser beam oscillation means.and the beam splitter means includes a λ / 2 plate that rotates a polarization plane of the pulsed laser beam oscillated by the pulsed laser beam oscillation means, a birefringent lens that splits the pulsed laser beam that has passed through the λ / 2 plate into ordinary light and extraordinary light, the birefringent lens being formed by connecting two types of bodies together via a curved plane of a concave surface of a crystalline body and a convex surface of a glass body, and a splitting angle adjusting means that moves the birefringent lens in a direction perpendicular to the pulsed laser beam that has passed through the λ / 2 plate so that the lens is moved in the processing feed direction and / or in a direction orthogonal thereto to change an incident angle of the pulsed laser beam with respect to the curved plane and adjust a beam splitting angle.

[0012] Preferably, the beam splitter means further includes an λ / 4 plate disposed between the birefringent lens and the condenser, which converts a linearly polarized pulsed laser beam oscillated by the pulse laser beam oscillating means into a circularly polarized pulsed laser beam.

[0013] In the laser processing apparatus of the present invention, the beam splitter means includes the λ / 2 plate that rotates the polarization plane of the pulsed laser beam, the birefringent lens that splits the pulsed laser beam that has passed through the λ / 2 plate into ordinary light and extraordinary light, the birefringent lens being formed by connecting two kinds of bodies together across the curved plane of the concave surface and the convex surface, and the beam splitting angle adjusting means that moves the birefringent lens in a direction perpendicular to the pulsed laser beam that has passed through the λ / 2 plate to change the incident angle with respect to the curved plane and adjust the beam splitting angle. Therefore, the pulsed laser beam can be split into the ordinary light and the extraordinary light.In addition, a light focus of the ordinary light and a light focus of the extraordinary light may be arranged to be offset from each other in the X-axis direction and the Y-axis direction.

[0014] For example, modified layers serving as a starting point for cutting can be formed along streets on an optical device wafer. Therefore, when the optical device wafer is divided into individual optical devices along the streets along which the modified layers are formed, the cut surface is formed in a zigzag shape. This can increase the luminance of the optical device.

[0015] The above and other objects, features and advantages of the present invention and the manner of carrying them out will become more apparent and the invention itself will be best understood by studying the following description and the appended claims with reference to the accompanying drawings which show a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a laser processing apparatus constructed in accordance with the present invention; Fig. 2 is a block diagram of a laser beam irradiation device used in the Fig. 1 shown laser processing device; Fig. 3 is a perspective view of a pitch angle adjusting unit constituting a pitch unit which generates a pulse laser beam oscillation unit of the type shown in Fig. 2 shown laser beam irradiation device divides the oscillated pulsed laser beam; Fig. 4A and Fig. 4B are explanatory diagrams showing the incident position of the pulsed laser beam in a birefringent lens constituting the splitting unit which divides the beam oscillated by the pulsed laser beam oscillation unit of the Fig. 2 shown laser beam irradiation device divides the oscillated pulsed laser beam; Fig. 5 is an explanatory diagram showing light focuses of ordinary light and extraordinary light formed by a focusing lens of the type shown in Fig. 2 shown laser beam irradiation device; Fig. 6 is a block diagram of a device used in Fig. Control unit mounted on the laser processing device shown in Figure 1; Fig. 7A is a perspective view of an optical device wafer as a workpiece; Fig. 7B is an enlarged sectional view of the main part of the optical device wafer; Fig. 8A and Fig. 8B are explanatory diagrams showing a protective member attaching step for attaching a protective tape to a front surface of the Fig. 7A; Fig. 9A to 9D are explanatory diagrams showing a Fig. 1 shown laser processing apparatus performed modification layer formation step; and Fig. 10 is a perspective view of an optical device obtained by dividing the optical device wafer in which the Fig. 9 shown modification layer formation step was carried out. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] A preferred embodiment of a laser processing apparatus constructed according to the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 is a perspective view of a laser processing apparatus 1 constructed according to the present invention. Fig. 1 includes a stationary base 2, a chucking table mechanism 3 movably disposed on this stationary base 2 in a machining feed direction indicated by an arrow X and holding a workpiece, a laser beam irradiation unit holding mechanism 4 movably disposed on the stationary base 2 in a pitch direction indicated by an arrow Y perpendicular to the direction indicated by the arrow X, and a laser beam irradiation unit 5 movably disposed on this laser beam irradiation unit holding mechanism 4 in a focus position adjusting direction indicated by an arrow Z.

[0017] The chuck table mechanism 3 includes a pair of guide rails 31 arranged on the stationary base 2 in parallel along the direction indicated by arrow X, a first slide block 32 movably mounted on these guide rails 31 in the direction indicated by arrow X, and a second slide block 33 movably mounted on this first slide block 32 in the direction indicated by arrow Y. The chuck table mechanism 3 further includes a holding table 35 supported by a cylindrical member 34 above the second slide block 33, and a chuck table 36 as a workpiece holder. This chuck table 36 has a workpiece holding surface 361 formed of a porous material, and a wafer as a workpiece is held on the chuck table 36 by a suction means (not shown).The chuck table 36 is rotated by a pulsed motor (not shown) disposed in the cylindrical member 34.

[0018] For the first slide block 32, a pair of guided grooves 321 attached to the pair of guide rails 31 are formed on its lower surface, and a pair of guide rails 322 formed in parallel along the direction indicated by arrow Y are provided on its upper surface. The first slide block 32 thus formed is configured to be movable in the direction indicated by arrow X along the pair of guide rails 31 by attaching the guided grooves 321 to the pair of guide rails 31. The chuck table mechanism 3 includes a machining feed unit 37 for moving the first slide block 32 in the direction indicated by arrow X along the pair of guide rails 31.The machining feed unit 37 includes a male threaded rod 371 arranged in parallel between the pair of guide rails 31, and a drive source, such as a pulsed motor 372, for rotating this male threaded rod 371. One end of the male threaded rod 371 is rotatably supported by a bearing block 373 fixed to the stationary base 2, and the other end is transferably connected to the output shaft of the pulsed motor 372. The male threaded rod 371 is screwed into an internally threaded through hole formed in an internally threaded block (not shown) protrudingly provided on the lower surface of the middle part of the first slide block 32.Therefore, the first slide block 32 is moved along the guide rails 31 in the machining feed direction indicated by the arrow X by driving the externally threaded rod 371 by the pulsed motor 372 to cause the forward rotation and reverse rotation thereof.

[0019] A pair of guided grooves 331 are formed on the lower surface of the second slide block 33, which are attached to the pair of guide rails 322 provided on the upper surface of the first slide block 32. The second slide block 33 is configured to be movable in the direction indicated by arrow Y by attaching these guided grooves 331 to the pair of guide rails 322. The chuck table mechanism 3 includes a first indexing feed unit 38 for moving the second slide block 33 in the direction indicated by arrow Y along the pair of guide rails 322 provided on the first slide block 32. The first indexing feed unit 38 includes an externally threaded rod 381 arranged in parallel between the pair of guide rails 322, and a drive source, such as a pulsed motor 382, for rotationally driving this externally threaded rod 381.One end of the male threaded rod 381 is rotatably supported by a bearing block 383 fixed to the upper surface of the first slide block 32, and the other end is transferably connected to the output shaft of the pulsed motor 382. The male threaded rod 381 is screwed into a female threaded through hole formed in a female threaded block (not shown) protrudingly provided on the lower surface of the central part of the second slide block 33. Therefore, the second slide block 33 is moved in the indexing feed direction indicated by arrow Y along the guide rails 322 by driving the male threaded rod 381 by the pulsed motor 382 to cause the forward and reverse rotation thereof.

[0020] The laser beam irradiation unit holding mechanism 4 includes a pair of guide rails 41 arranged on the stationary base 2 in parallel along the direction indicated by arrow Y, and a movable holding base 42 movably mounted on these guide rails 41 in the direction indicated by arrow Y. This movable holding base 42 consists of a movable holding part 421 movably mounted on the guide rails 41 and a mounting part 422 mounted on this movable holding part 421. On a side surface of the mounting part 422, a pair of guide rails 423 extending along a direction indicated by arrow Z are provided in parallel. The laser beam irradiation unit holding mechanism 4 includes a second indexing feed unit 43 for moving the movable holding base 42 in the direction indicated by arrow Y along the pair of guide rails 41.The second indexing feed unit 43 includes a male threaded rod 431 arranged in parallel between the pair of guide rails 41, and a drive source such as a pulsed motor 432 for rotating this male threaded rod 431. One end of the male threaded rod 431 is rotatably supported by a bearing block (not shown) fixed to the stationary base 2, and the other end is transferably connected to the output shaft of the pulsed motor 432. The male threaded rod 431 is screwed into an internally threaded hole formed in an internally threaded block (not shown) protrudingly provided on the lower surface of the central portion of the movable support member 421 constituting the movable support base 42.Therefore, the movable support base 42 is moved in the indexing feed direction indicated by the arrow Y along the guide rails 41 by driving the externally threaded rod 431 by the pulsed motor 432 to cause the forward rotation and reverse rotation thereof.

[0021] The laser beam irradiation unit 5 includes a unit holder 51 and a laser beam irradiation device 6 mounted on this unit holder 51. A pair of guided grooves 511 are provided on the unit holder 51, which are slidably mounted on the pair of guide rails 423 provided on the mounting part 422. The unit holder 51 is movably supported in the direction indicated by arrow Z by mounting these guided grooves 511 on the guide rails 423.

[0022] The laser beam irradiation unit 5 includes a light focus position adjuster 53 for moving the unit holder 51 in the direction indicated by the arrow Z along the pair of guide rails 423. The light focus position adjuster 53 includes an externally threaded rod (not shown) arranged between the pair of guide rails 423 and a drive source, such as a pulse motor 532, for rotating this externally threaded rod. By driving the externally threaded rod (not shown) by the pulse motor 532 to cause the forward rotation or reverse rotation thereof, the unit holder 51 and the laser beam irradiation device 6 are moved in the direction indicated by the arrow Z along the pair of guide rails 423.In the embodiment shown in the diagram, the laser beam irradiation device 6 is moved upward by driving by the pulsed motor 532 for forward rotation, and the laser beam irradiation device 6 is moved downward by driving by the pulsed motor 532 for reverse rotation.

[0023] The laser beam irradiation device 6 includes a cylindrical housing 61 which is fixed to the unit holder 51 and extends substantially horizontally. This laser beam irradiation device 6 will be described with reference to Fig. 2. The Fig. The laser beam irradiation device 6 shown in Fig. 2 includes a pulse laser beam oscillation unit 62 arranged in the casing 61, an output power adjusting device 63 which adjusts the output power of a pulsed laser beam oscillated by this pulse laser beam oscillation unit 62, and a beam expander 64 which reduces the beam diameter of the pulsed laser beam whose output power has been adjusted by this output power adjusting device 63 (for example, it reduces the beam diameter from φ 4 mm to φ 1 mm).The laser beam irradiation device 6 further includes a splitting unit (beam splitter unit) 65 that splits the pulsed laser beam whose beam diameter has been reduced by the beam expander 64, a λ / 4 plate 66 that converts the linearly polarized pulsed laser beams obtained by splitting by this splitting unit 65 into circularly polarized beams, and a condenser 67 that condenses the pulsed laser beams converted into the circularly polarized beams by this λ / 4 plate 66 and irradiates a workpiece W held by the chuck table 36 with the pulsed laser beams. The pulse laser beam oscillation unit 62 is composed of a pulse laser oscillator 621 formed of a YAG laser oscillator or a YVO4 laser oscillator, and a repetition frequency adjuster 622 attached thereto.The pulse laser beam oscillation unit 62 constructed in this manner oscillates a linearly polarized pulsed laser beam LB.

[0024] In the present embodiment, the splitting unit 65 included in the laser beam irradiation device 6 includes a λ / 2 plate 651, a birefringent lens 652, and a splitting angle adjusting unit 653. The λ / 2 plate 651 rotates the polarization plane of the pulsed laser beam LB oscillated by the pulsed laser beam oscillation unit 62 and whose beam diameter has been reduced by the beam expander 64, so that the polarization plane can be at 45 degrees with respect to the birefringent lens 652. The birefringent lens 652 is composed of a YVO4 crystalline body 652a having a concave surface and a LASF35 glass body 652b having a convex surface in such a manner that they are connected to each other via the curved plane of the concave surface and the convex surface.The birefringent lens 652 splits the pulsed laser beam LB, whose beam diameter has been reduced by the beam expander 64, into ordinary light LB1 and extraordinary light LB2.

[0025] The splitting angle adjusting unit 653 included in the splitting unit 65 has a function of moving the birefringent lens 652 in a direction perpendicular to the pulsed laser beam LB that has passed through the λ / 2 plate 651 to change the angle of incidence with respect to the curved plane of the concave surface and the convex surface and adjust the splitting angle. This splitting angle adjusting unit 653 is described with reference to Fig. 3. The pitch angle adjustment unit 653 in the Fig. 3 includes a lens holding case 654 that holds the birefringent lens 652, a movable table 655 that supports this lens holding case 654 movable in a processing feed direction indicated by an arrow X, and a pair of guide rails 656 that support this movable table 655 movable in a grading direction indicated by an arrow Y. The grading angle adjusting unit 653 further includes a first moving unit 657 that moves the lens holding case 654 in the processing feed direction indicated by the arrow X, and a second moving unit 658 that moves the movable table 655 in the grading direction indicated by the arrow Y.

[0026] The first movement unit 657 is formed of a first pulsed motor 657a, a male threaded rod 657b connected to this first pulsed motor 657a, and a female threaded block 657c connected to the lens holding case 654 and into which the male threaded rod 657b is screwed. By driving the male threaded rod 657b by the first pulsed motor 657a to cause the same to rotate forward and backward, the lens holding case 654 is moved in the processing feed direction indicated by arrow X. The second movement unit 658 is formed of a second pulsed motor 658a, a male threaded rod 658b connected to this second pulsed motor 658a, and a female threaded block 658c connected to the movable table 655 and into which the male threaded rod 658b is screwed.By driving the externally threaded rod 658b by the second pulsed motor 658a to cause the forward rotation and reverse rotation thereof, the movable table 655 is moved in the indexing direction indicated by the arrow Y.

[0027] The thus constructed pitch angle adjusting unit 653 operates the first pulsed motor 657a to move the lens holding case 654 in the processing feed direction indicated by arrow X, and operates the second pulsed motor 658a to move the movable table 655 in the pitch direction indicated by arrow Y. Thereby, the pitch angle adjusting unit 653 adjusts the incident position of the pulsed laser beam LB in the birefringent lens 652, for example, at coordinates (xa, yb) with respect to the center point (O) of the birefringent lens 652, as shown in Fig. 4A. By changing the incident position of the pulsed laser beam LB in this birefringent lens 652, the incident angle can be changed with respect to the curved plane, wherein the curved plane is formed by connecting the concave surface and the convex surface of the YVO4 crystalline body 652a with the concave surface and the LASF35 glass body 652b with the convex surface, which form the birefringent lens 652, and the splitting angle of the ordinary light LB1 and the extraordinary light LB2 changes depending on the incident position of the pulsed laser beam LB, as shown in Fig. 4B. Specifically, the pulsed laser beam LB is not split when the incident position of the pulsed laser beam LB is the center (O) of the birefringent lens 652. When the incident position of the pulsed laser beam LB is (a), the pulsed laser beam LB is split into the ordinary light LB1 and the extraordinary light LB2 with a splitting angle of (α). When the incident position of the pulsed laser beam LB is (b), the pulsed laser beam LB is split into the ordinary light LB1 and the extraordinary light LB2 with a splitting angle of (β). In this way, the splitting angle of the ordinary light LB1 and the extraordinary light LB2 becomes larger when the incident position of the pulsed laser beam LB is located on the side closer to the circumference relative to the center (O) of the birefringent lens 652.

[0028] The λ / 4 plate 66 converts the linearly polarized ordinary light LB1 and the linearly polarized extraordinary light LB2 obtained by splitting by the birefringent lens 652 into circularly polarized light. The purpose of converting the linearly polarized ordinary light LB1 and the linearly polarized extraordinary light LB2 into circularly polarized light by using the λ / 4 plate 66 in this way is to make the processing accuracy with the ordinary light LB1 identical to that with the extraordinary light LB2.

[0029] As in Fig. 2, the condenser 67 included in the laser beam irradiation device 6 consists of a direction conversion mirror 671 and a focusing lens 672. The direction conversion mirror 671 converts the directions of the ordinary light LB1 and the extraordinary light LB2, which were obtained by splitting by the birefringent lens 652 and converted into circularly polarized light by the λ / 4 plate 66, into the downward direction in Fig. 2, that is, the direction toward the chuck table 36. The focusing lens 672 focuses both the ordinary light LB1 and the extraordinary light LB2, whose directions have been converted by the direction conversion mirror 671, and irradiates the workpiece W held by the chuck table 36 with the focused light. The distance between the ordinary light LB1 and the extraordinary light LB2 focused by this focusing lens 672 is adjusted by the splitting angle adjusting unit 653. In addition, the line coupling the ordinary light LB1 and the extraordinary light LB2 is adjusted to have a predetermined angle from the X-axis or the Y-axis. In the present embodiment, as shown in Fig. 5, the adjustment is made so that the ordinary light LB1 and the extraordinary light LB2 are focused at distances of Xa and Yb from each other in the X-axis direction and the Y-axis direction, respectively, so that the line coupling them may be at 60° from the X-axis and the distance d1 therebetween may be 3 µm.

[0030] With further reference to Fig. 1, at the front end part of the casing 61 constituting the laser beam irradiation device 6, an imaging device 7 is arranged, which detects a processing area where laser processing is to be performed by the laser beam irradiation device 6. In the present embodiment, this imaging device 7 is composed of, in addition to a normal imaging element (CCD) that performs imaging by a visible ray, an infrared illuminator that irradiates a workpiece with infrared light, an optical system that captures the infrared light irradiated by this infrared illuminator, an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared light captured by this optical system, and so on. The imaging device 7 sends an image signal obtained by imaging to a control unit (not shown).

[0031] The laser processing device 1 includes a Fig. 6. The control unit 8 is formed of a computer. It includes a processor (CPU) 81 that performs arithmetic processing according to a control program, a read-only memory (ROM) 82 for storing the control program, etc., a read / write random access memory (RAM) 83 for storing an arithmetic result, etc., an input interface 84, and an output interface 85. Detection signals from the imaging device 7, an input unit 80, etc. are input to the input interface 84 of the control unit 8.From the output interface 85 of the control unit 8, control signals are output to the pulsed motor 372, the pulsed motor 382, the pulsed motor 432, the pulsed motor 532, the pulse laser oscillator 621 and the repetition frequency adjuster 622 constituting the pulse laser beam oscillation unit 62, the output power adjuster 63, the first pulsed motor 657a and the second pulsed motor 658a constituting the pitch angle adjuster 653, and so on.

[0032] The laser processing device 1 is constructed as described above. Its operation is described below. Fig. 7A and Fig. 7B, a perspective view of an optical device wafer 10 as a wafer that is a workpiece to be processed by the laser processing apparatus 1 and an enlarged sectional view showing the main part of the optical device wafer 10 are shown. Fig. 7A and Fig. In the optical device wafer 10 shown in FIG. 7B, a light-emitting layer 110 consisting of an n-type nitride semiconductor layer 111 and a p-type nitride semiconductor layer 112 with a thickness of, for example, 10 µm is deposited over a front surface 100a of a sapphire substrate 100 having a thickness of, for example, 150 µm. Furthermore, optical devices 130, such as light-emitting diodes or laser diodes, are formed in a plurality of regions obtained by dividing the light-emitting layer 110 by a plurality of streets 120 formed in a grid array. A method for forming modified layers within this optical device wafer 10 along the streets 120 will be described below.

[0033] First, a protective element attachment step is performed for attaching a protective element to a surface 110a of the light-emitting layer 110 of the optical device wafer 10 in order to protect the optical components 130 formed on the front surface 100a of the sapphire substrate 100 constituting the optical device wafer 10. Specifically, as shown in Fig. 8A and Fig. 8B, a protective tape T as the protective member is attached to the surface 110a of the light-emitting layer 110 of the optical device wafer 10. The protective tape T is formed by applying, for example, acrylic resin-based paste having a thickness of approximately 5 µm to a surface of a film base made of polyvinyl chloride (PVC) having a thickness of 100 µm.

[0034] After the protective element attaching step described above has been performed, the protective tape T side of the optical device wafer 10 is clamped to the chuck table 36 of the Fig. 1, and the optical device wafer 10 is held by suction on this chuck table 36 (wafer holding step). Therefore, with the optical device wafer 10 held on the chuck table 36, a rear surface 100b of the sapphire substrate 100 faces upward.

[0035] The chuck table 36, which holds the optical device wafer 10 by suction as described above, is arranged immediately below the imaging device 7 by the processing feed unit 37. After the chuck table 36 is arranged immediately below the imaging device 7, an alignment process for detecting a processing area where laser processing is to be performed on the optical device wafer 10 is performed by the imaging device 7 and the control unit (not shown). Specifically, the imaging device 7 and the control unit (not shown) perform image processing such as pattern matching to perform positional adjustment between the streets 120 formed along a first direction of the optical device wafer 10 and the condenser 67 of the laser beam irradiation device 6, which irradiates a laser beam along the streets 120, to perform alignment of the laser beam irradiation position.Furthermore, alignment of the laser beam irradiation position is similarly performed for the streets 120 formed on the optical device wafer 10 and extending along a second direction perpendicular to the first direction. At this time, the front surface 110a on which the streets 120 of the optical device wafer 10 are formed is located on the lower side. However, since the imaging device 7 includes an imaging unit composed of the infrared illuminator, the optical system that captures infrared light, the imaging element (infrared CCD) that outputs an electrical signal corresponding to infrared light, etc., as described above, the streets 120 can be imaged transparently from the rear surface 100b of the sapphire substrate 100 constituting the optical device wafer 10.Since the sapphire substrate 100 constituting the optical device wafer 10 is transparent to visible light, the infrared CCD does not necessarily have to be used.

[0036] After the streets 120 formed on the optical component wafer 10 held on the chuck table 36 have been detected in the manner described above and the alignment of the laser beam irradiation position has been performed, the chuck table 36 is moved to the laser beam irradiation area over which the condenser 67 of the laser beam irradiation device 6 is arranged, as shown in Fig. 9A, and the predetermined road 120 is arranged immediately below the condenser 67. Then, as shown in Fig. 9A, a light focus Pa of the ordinary light LB1 and a light focus Pb of the extraordinary light LB2 of the pulsed laser beam emitted from the condenser 67 are arranged within the sapphire substrate 100 constituting the optical device wafer 10. The light focus Pa of the ordinary light LB and the light focus Pb of the extraordinary light LB2 of the pulsed laser beam emitted from the condenser 67 are arranged at distances Xa and Yb from each other in the X-axis direction and the Y-axis direction, respectively, as shown in Fig. 9B is shown.

[0037] Subsequently, the control unit 8 operates the pulse laser beam oscillation unit 62 to radiate the ordinary light LB1 and the extraordinary light LB2 of the pulsed laser beam LB, which has a wavelength such that it is transmitted through the optical device wafer, from the condenser 67. In addition, the control unit 8 operates the processing feed unit 37 to rotate the chuck table 36 in a Fig. 9A at a predetermined processing feed speed (modification layer forming step). Then, when the irradiation position of the condenser 67 reaches the other end of the road 120 (the right end in Fig. 9C) as in Fig. 9C, the emission of the pulsed laser beam is stopped and the movement of the chuck table 36 is stopped. As a result, as shown in Fig. 9D, a plurality of modified layers S1 by the ordinary light LB1 and a plurality of modified layers S2 by the extraordinary light LB2 are formed along the predetermined road 120 so as to be offset from each other by Xa and Yb in the X-axis direction and the Y-axis direction, respectively.

[0038] The processing condition of the modification layer formation step described above is set, for example, as follows. Wavelength: 1064 nm Repetition frequency: 100 kHz Average output power: 1 W Focused light spot diameter: φ 1 µm Machining feed speed: 300 mm / second

[0039] Under this processing condition, Fig. 9D the distance d1 between the modified layer S1 and the modified layer S2 is 3 µm and the distance d2 between the modified layers S1 and between the modified layers S2 in the X-axis direction is 3 µm (300 mm / 100 kHz = 3 µm).

[0040] After the modification layer formation step has been performed along all the streets 120 formed along the first direction of the optical device wafer 10 as described above, the chuck table 36 holding the optical device wafer 10 is moved to a position resulting from a 90-degree rotation. Then, the modification layer formation step is performed along all the streets 120 formed along the second direction perpendicular to the first direction of the optical device wafer 10. The optical device wafer 10 for which the modification layer formation step has been performed along all the streets 120 is conveyed to a wafer dividing step, in which the optical device wafer 10 is cut along the streets 120 along which the modified layers S1 and S2 are formed.Then, in the wafer dividing step, the optical device wafer 10 is divided into the individual optical devices 130 along the modified layers S1 and S2 by applying an external force along the streets 120 along which the modified layers S1 and S2 are formed. In the optical device 130 obtained by the division in this manner, a cut surface 130a is formed in a zigzag shape, as shown in FIG. Fig. 10, which increases the luminosity.

[0041] Next, another laser processing method using the laser processing apparatus described above will be described.

[0042] In this laser processing method, the processing condition is set as follows. Wavelength: 355 nm Repetition frequency: 100 kHz Average output power: 4 W Focused light spot diameter: φ 1 µm Machining feed speed: 300 mm / second

[0043] Under this specified processing condition, in a semiconductor wafer having a configuration in which semiconductor devices are formed with a functional layer obtained by depositing a low dielectric constant insulating film (low-k film) made of an inorganic substance-based film of SiOF, BSG (SiOB), or the like, or an organic substance-based film that is a polymer film made of a polyimide-based or a parylene-based film, or the like, over a surface of a silicon substrate or the like, laser processing is performed so that an ordinary light focus and an extraordinary light focus are arranged at intervals from each other in the X-axis direction and the Y-axis direction.

[0044] This allows the functional layer along roads to be removed.

Claims

[1] Laser processing device (1) comprising: a clamping table (36) holding a workpiece (10); a laser beam irradiation device (6) which irradiates the workpiece (10) held by the clamping table (36) with a laser beam (LB1, LB2); and a machining feed means (37) which performs a relative machining feed of the clamping table (36) and the laser beam irradiation device (6), wherein the laser beam irradiation device (6) includes: a pulse laser beam oscillating means (62) which oscillates a pulsed laser beam (LB1), a condenser (67) which condenses the pulsed laser beam (LB1, LB2) oscillated by the pulsed laser beam oscillation means (62) and irradiates the workpiece (10) held by the clamping table (36) with the laser beam (LB1, LB2) and a beam splitter means (65) arranged between the pulse laser beam oscillation means (62) and the condenser (67) and splitting the pulsed laser beam (LB) oscillated by the pulse laser beam oscillation means (62), and the beam splitter means (65) includes: a λ / 2 plate (651) which rotates a polarization plane of the pulsed laser beam (LB) oscillated by the pulsed laser beam oscillation means (62), a birefringent lens (652) which splits the pulsed laser beam (LB) which has passed through the λ / 2 plate (651) into ordinary light and extraordinary light, the birefringent lens (652) being formed by connecting two kinds of bodies to each other via a curved plane of a concave surface of a crystalline body (652a) and a convex surface of a glass body (652b), and a splitting angle adjusting means (653) that moves the birefringent lens (652) in a direction perpendicular to the pulsed laser beam (LB) that has passed through the λ / 2 plate (651) so that the lens (652) is moved in the machining feed direction and / or in a direction orthogonal thereto to change an incident angle of the pulsed laser beam (LB) with respect to the curved plane and adjust a beam splitting angle. [2] The laser processing apparatus (1) according to claim 1, wherein the beam splitter means further includes a λ / 4 plate (66) disposed between the birefringent lens (652) and the condenser (67) and converting a linearly polarized pulsed laser beam (LB1, LB2) oscillated by the pulse laser beam oscillation means (62) into a circularly polarized pulsed laser beam (LB1, LB2).

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