LASER PROCESSING DEVICE

Abstract

Laser processing device (2) comprising: a holding unit (30) with a holding table (32) for holding a plate-shaped workpiece; a laser beam irradiation unit (6) which irradiates the workpiece held by the holding table (32) with a laser (LB) and carries out processing; and a liquid supply mechanism (40) arranged above the holding unit (30), wherein the liquid supply mechanism (40) comprises a liquid chamber (41) having a circular disc-shaped transparent plate (42) positioned to form a gap (S) between the circular disc-shaped transparent plate (42) and an upper surface of the workpiece held by the holding table, a liquid supply nozzle (43) that supplies a liquid (W) to the gap (S) from one side of the liquid chamber (41), a liquid discharge nozzle (44) that discharges the liquid (W) from another side of the liquid chamber (41), and a rotation mechanism that rotates the circular disc-shaped transparent plate (42) and generates a flow velocity in the liquid (W) supplied to the gap (S) toward the liquid discharge nozzle (44), and the laser beam irradiation unit (6) comprises a laser oscillator (82) which emits the laser beam (LB), and a condenser (86) which concentrates the laser beam (LB) emitted by the laser oscillator (82) and irradiates the workpiece held by the holding table (32) with the laser beam (LB) transmitted through the transparent plate (42) and the liquid (W) supplied to the gap (S).

Description

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0001] The present invention relates to a laser processing apparatus that irradiates a plate-shaped workpiece with a laser beam to process the workpiece. DESCRIPTION OF THE RELATED PRIOR ART

[0002] A wafer on which a plurality of components such as integrated circuits (ICs) and large-scale integrations (LSIs) are formed on one surface in such a manner as to be marked by planned division lines is divided into individual component chips by a laser processing apparatus, and the component chips obtained by the division are used for parts of electronic equipment such as mobile phones, personal computers, and lighting equipment.

[0003] As a laser processing device, there are the following types of devices: a device that forms grooves serving as separation starting points by ablation processing, in which the focal point of a laser beam having a wavelength absorbed by a workpiece is positioned at the surface of the workpiece (see, for example, Japanese Unexamined Patent Application Laid-Open No. H10-305420); a device that performs irradiation in such a manner that the focal point of a laser beam having a wavelength transmitted through a workpiece is positioned inside the workpiece and forms modified layers serving as separation starting points inside the workpiece (see, for example, Japanese Unexamined Patent Application Laid-Open No. H10-305420);and a type of device that performs irradiation in such a way that the focal point of a laser beam having a wavelength that transmits through a workpiece is positioned inside the workpiece, forming a plurality of shielding tunnels that reach the back surface of the workpiece from the front surface, each constructed with a fine pore serving as a separation starting point and an amorphous region surrounding this fine pore (see, for example, Japanese Patent Application Laid-Open No. 2014-221483). The laser processing device is appropriately selected in accordance with the type of workpiece, processing accuracy, etc.

[0004] Particularly in the type that performs ablation processing among the laser processing apparatuses described above, it is possible that residues (laser processing dust) generated when a wafer surface is irradiated with a laser beam may be scattered and adhered to the surfaces of components formed on the wafer, degrading the quality of the components. For this reason, it has been proposed that the wafer surface be covered with a liquid resin through which a laser beam used for processing is transmitted to prevent residue adhesion before laser processing is performed, and this liquid resin be removed after the laser processing is performed (see, for example, Japanese Patent Application Laid-Open No. 2004-188475 A).

[0005] Furthermore, DE 10 2010 015 739 A1 discloses a laser beam processing unit for directing a laser beam onto a workpiece held by a clamping table under a water-containing cover. JP H09-167 747 A, on the other hand, relates to a device for treating a substrate, in which a treatment disk is rotated at a short distance from the surface of the substrate in order to convey a treatment liquid from its center to its periphery via this rotation. DE 101 59 369 A1 also discloses a laser marking method, and DE 10 2016 107 593 A1 discloses a laser processing device for processing a workpiece held on a clamping table. SUMMARY OF THE INVENTION

[0006] According to the technique disclosed in Japanese Patent Application Laid-Open No. 2004-188475, adhesion of residues to the surface of components can be prevented by covering them with liquid resin, ensuring machining quality. However, a step of applying the liquid resin and a step of removing the liquid resin after machining are required, so productivity requires a process. Furthermore, the liquid resin cannot be reused, so this technique also poses the problem of being uneconomical.

[0007] Furthermore, a technique has also been proposed in which adhesion of residues to the surface of a wafer is prevented by irradiating the wafer with a laser beam while the wafer is immersed in water and causing the residues to float on the water. However, if the wafer is irradiated with the laser beam while the wafer is immersed in water, small bubbles are generated at the location on the wafer where the laser beam is irradiated. Consequently, there is a problem that the movement of the laser beam is obstructed by these bubbles, and desired processing cannot be performed.

[0008] Accordingly, it is an object of the present invention to provide a laser machining apparatus with which irradiation of a plate-shaped workpiece with a laser beam is not hindered when machining is carried out by irradiating the workpiece with the laser beam.

[0009] In accordance with one aspect of the present invention, there is provided a laser machining apparatus including a holding unit having a holding table that holds a plate-shaped workpiece, a laser beam irradiation unit that irradiates the workpiece held by the holding table with a laser beam and performs machining, and a liquid supply mechanism arranged above the holding unit.The liquid supply mechanism includes a liquid chamber having a circular disc-shaped transparent plate positioned to form a gap between the circular disc-shaped transparent plate and an upper surface of the workpiece held by the holding table, a liquid supply nozzle that supplies a liquid to the gap from one side of the liquid chamber, a liquid discharge nozzle that discharges the liquid from the other side of the liquid chamber, and a rotation mechanism that rotates the circular disc-shaped transparent plate and generates a flow velocity in the liquid supplied to the gap toward the liquid discharge nozzle.The laser beam irradiation unit includes a laser oscillator that emits the laser beam and a condenser that condenses the laser beam emitted from the laser oscillator and irradiates the workpiece held by the holding table with the laser beam transmitted through the transparent plate and the liquid supplied to the gap.

[0010] Preferably, the laser beam irradiation unit further includes a scattering means that scatters the laser beam emitted from the laser oscillator.

[0011] According to the present invention, a laser processing apparatus is provided that does not interfere with irradiation of a workpiece with a laser beam. Furthermore, when the present invention is applied to a laser processing apparatus that performs ablation processing, residues generated at the time of laser processing can be avoided on the components without covering the surface of a wafer with liquid resin, and a reduction in the processing quality of the components is prevented.

[0012] The above and other objects, features and advantages of the present invention and the mode for carrying them out will become more apparent and the invention itself will be best understood by studying the following description and 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 in accordance with an embodiment of the present invention; Fig. 2 is a partially exploded perspective view of a liquid chamber forming a liquid supply mechanism and a holding unit in the laser processing apparatus shown in Fig. 1 is shown; Fig. 3 is a perspective view of the liquid supply mechanism and the holding unit of the Fig. 1 shown laser processing device; Fig. 4 is a perspective view of a laser beam irradiation unit of the Fig. 1 shown laser processing device; Fig. 5 is an exploded perspective view of the Fig. 4 shown laser beam irradiation unit; Fig. 6 is a block diagram showing the outline of an optical system of the Fig. 4; Fig. 7 is a perspective view showing the state in which laser processing is carried out by the Fig. 5 shown laser beam irradiation unit is executed; and Fig. Fig. 8 is a side view of the laser beam irradiation unit, explaining the state in which the Fig. 7 shown laser processing is carried out. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] A laser processing apparatus in accordance with an embodiment based on the present invention will now be described in detail with reference to the accompanying drawings. Fig. 1 is a perspective view of a laser processing apparatus 2 of the present embodiment. The laser processing apparatus 2 includes a base 21, a holding unit 30 disposed on the base 21 and holding a workpiece, and a frame body 22 constructed with a vertical wall portion 221 erected along a Z-axis direction indicated by an arrow Z on a lateral side of the holding unit 30 on the base 21, and a horizontal wall portion 222 extending from the upper end portion of the vertical wall portion 221 in the horizontal direction. The laser processing apparatus 2 further includes a liquid supply mechanism 40 disposed on the holding unit 30 and a laser beam irradiation unit 6 disposed on the lower surface of the horizontal wall portion 222.

[0014] Fig. Fig. 2 is an exploded view showing the respective structures of the holding unit 30 and a liquid chamber 41, a liquid supply nozzle 43, and a liquid discharge nozzle 44, which constitute the liquid supply mechanism 40, in a disassembled manner. Each structure will be described below.

[0015] As in Fig. As shown in Figure 2, the holding unit 30 includes a holding base 31 fixed to the base 21 and having a rectangular parallelepiped shape, and a holding table 32 disposed on an upper surface 31a of the holding base 31 and having a circular shape. The holding table 32 is configured to be capable of being rotated by a rotating mechanism not shown in the diagram. The central portion of the holding table 32 is formed with a holding jig 32a constructed of an air-permeable material such as a porous ceramic and having a circular shape. The holding jig 32a is connected to a suction source not shown in the diagram and sucks and holds a plate-shaped workpiece placed on the holding jig 32a.

[0016] The liquid supply mechanism 40 shown in the diagram is arranged at the upper part of the holding unit 30. Specifically, the liquid chamber 41 is placed on and fixed to the upper surface 31a of the holding base 31. The liquid chamber 41 is constructed with a frame base part 41a, a U-shaped frame 41b connected to the frame base part 41a, and a transparent plate 42 having a circular disk shape. The frame base part 41a is formed to have a thickness dimension larger than the frame 41b by the thickness of the transparent plate 42. An inner side surface 411 of the frame base part 41a has a shape along the circular arc of the transparent plate 42 in plan view. By positioning the transparent plate 42 on the inner side surface 411, the upper side of a space 41e formed by the frame base part 41a and the frame 41b is closed.In the frame 41b, a liquid supply port 41c is arranged on one of two side surfaces positioned in a Y-axis direction indicated by an arrow Y and opposite each other, which makes the space 41e communicate with the outside. A liquid discharge port 41d is arranged on the other side surface, which makes the space 41e communicate with the outside. The liquid supply port 41c and the liquid discharge port 41d extend in the horizontal direction and are formed in the respective side surfaces in which they are arranged with a dimension larger than the diameter of the holding jig 32a.

[0017] The liquid supply nozzle 43 is connected to the side surface where the liquid supply opening 41c is located in the frame 41b. Furthermore, the liquid discharge nozzle 44 for discharging a liquid is connected to the side surface where the liquid discharge opening 41d is located in the frame 41b. The thicknesses of the liquid supply nozzle 43 and the liquid discharge nozzle 44 are set to be substantially the same as the thickness of the frame 41b described above.

[0018] The liquid supply nozzle 43 includes a supply port 43a from which a liquid is supplied, a passage 43b through which the liquid supplied from the supply port 43a passes, and a discharge port 43c from which the liquid that has passed through the passage 43b is discharged. As shown by the dotted lines in the diagram, the supply port 43a is located in the lower surface of the liquid supply nozzle 43, and the passage 43b is formed inside the liquid supply nozzle 43. The discharge port 43c is formed in the same shape as the liquid supply port 41c at a position opposite to the liquid supply port 41c of the liquid chamber 41.By connecting the liquid supply nozzle 43 to the liquid chamber 41, the discharge port 43c of the liquid supply nozzle 43 is made to coincide with the liquid supply port 41c of the liquid chamber 41, providing the state that the supply port 43a of the liquid supply nozzle 43 communicates with the space 41e of the liquid chamber 41.

[0019] The liquid discharge nozzle 44 is formed with the same shape as the liquid supply nozzle 43. The liquid discharge nozzle 44 includes a supply opening 44c from which the liquid is supplied, a passage 44b through which the liquid supplied from the supply opening 44c passes, and a discharge opening 44a from which the liquid that has passed through the passage 44b is discharged. As shown in Fig. 2, the supply port 44c of the liquid discharge nozzle 44 is formed at a position opposite to the liquid discharge port 41d of the liquid chamber 41, having the same shape as the liquid discharge port 41d of the liquid chamber 41. The passage 44b is formed inside the liquid chamber 41, and the discharge port 44a is located in the lower surface of the liquid chamber 41. Connection of the liquid supply nozzle 43 and the liquid discharge nozzle 44 to the liquid chamber 41 provides the state where the supply port 43a of the liquid supply nozzle 43 communicates with the discharge port 44a of the liquid discharge nozzle 44 via the space 41e of the liquid chamber 41.

[0020] A gasket is arranged at the edge portion of the lower surface of the liquid chamber 41 over the entire circumference, the diagrammatic representation of which is omitted. By placing the liquid chamber 41 on the upper surface 31a of the support base 31 and establishing the state in which the liquid chamber 41 is closed by the transparent plate 42, a substantially sealed gap is formed on the support table 32.

[0021] The transparent plate 42 has, as described above, a circular disk shape, and a shaft of a rotation mechanism (motor M) that rotates the transparent plate 42 is fixed to the center of the transparent plate 42. The motor M is fixed to the horizontal wall part 222 of the Fig. 1. The motor M rotates, whereby the transparent plate 42 is rotated in a direction shown by an arrow R1 in the state in which the transparent plate 42 closes the liquid chamber 41 from the upper side. The transparent plate 42 is arranged in such a way that the transparent plate 42, together with the motor M, extends outward (in a direction shown by an arrow A in Fig. 1), and the upper side of the liquid chamber 41 can be opened when a workpiece is placed on and removed from the holding table 32. The transparent plate 42 is formed, for example, with a glass plate.

[0022] In addition, the liquid supply mechanism 40 and the peripheral structure of the liquid supply mechanism 40 will be described with reference to Fig. 3 described. In Fig. 3 shows the state in which a wafer 10, on which components are formed on one surface, is held as a plate-shaped workpiece by suction force on the holding table 32. As shown on the upper side of the Fig. 3 is shown as a schematic sectional view in which a part of the wafer 10 and the transparent plate 42 is enlarged, a gap S of approximately 0.5 to 2.0 mm is formed between the wafer 10 and the transparent plate 42. As shown in Fig. As shown in Fig. 3, the laser processing apparatus 2 according to the present embodiment includes a liquid supply pump 45, a filtration filter 46, and a liquid reservoir tank 47 so that liquid can be constantly supplied into the liquid supply mechanism 40. The liquid reservoir tank 47 is disposed on the filtration filter 46. The liquid supply pump 45 and the liquid supply nozzle 43 are connected by a first hose 48a. The liquid discharge nozzle 44 and the filtration filter 46 are connected by a second hose 48b. The filtration filter 46 and the liquid supply pump 45 are connected by a third hose 48c. The respective hoses 48a to 48c are formed of flexible hoses made of a resin.

[0023] Based on the structure described above, a liquid W discharged from the liquid supply pump 45 is supplied to the liquid chamber 41 via the first hose 48a and the liquid supply nozzle 43, and the liquid W supplied to the liquid chamber 41 passes through the liquid discharge nozzle 44 to be discharged. At this time, the transparent plate 42 is rotated by the motor M in the direction shown by arrow R1. The motor M constitutes the rotation mechanism that rotates the transparent plate 42 relative to the liquid W passing through the liquid chamber 41 and generates a flow velocity. Furthermore, the liquid W discharged from the liquid discharge nozzle 44 is supplied to the filtration filter 46 to be filtered and returned to the liquid supply pump 45.In the liquid supply mechanism 40 of the present embodiment, liquid W is allowed to gradually leak from the gap between the frame base part 41a and the frame 41b of the liquid chamber 41 and the upper surface 31a of the support base 31, the gap between the frame base part 41a and the frame 41b and the transparent plate 42, etc. The leaked liquid W can be recovered at the base 21 and made to flow back to the filtration filter 46. Furthermore, when the liquid W is reduced due to the above-described leakage, the liquid W can be appropriately replenished from the liquid reservoir tank 47. The liquid reservoir tank 47 is directly attached to the filtration filter 46 and also has the function of discharging air bubbles contained in the liquid W supplied to the filtration filter 46.

[0024] Based on the above structure, the liquid W is circulated in the liquid supply mechanism 40, the liquid supply pump 45, the filtration filter 46, and the liquid reservoir tank 47. The flow rate of the liquid W flowing into the liquid chamber 41 can be adjusted by adjusting the rotation speed of the transparent plate 42 or the pumping efficiency of the liquid supply pump 45, or changing the volume of the liquid chamber 41, or adjusting the opening area of the liquid supply port 41c and the liquid discharge port 41d, and is adjusted to become a predetermined flow rate.

[0025] Next, the laser beam irradiation unit 6 will be described with reference to Fig. 1, Fig. 4 and Fig. 5 described. Fig. Fig. 5 is an exploded perspective view of the laser beam irradiation unit 6 shown in Fig. 4 is shown.

[0026] The laser beam irradiation unit 6 includes a guide plate 60 fixed to the lower surface of the horizontal wall part 222 of the frame body 22 by a fixing means not shown in the diagram, a Y-axis movable member 62 supported by the Y-axis movable guide plate 60, and a Y-axis moving mechanism 64 that moves the Y-axis movable member 62 in the Y-axis direction. A pair of guide rails 60a extending along the Y-axis direction are formed at the lower parts of both ends of the guide plate 60 in an X-axis direction. As shown in FIGS. Fig. 4 and Fig. As shown in Figure 5, the Y-axis movable member 62 includes a pair of guide pieces 66 spaced apart in the X-axis direction, and a mounting piece 68 configured to bridge the space between the lower ends of the guide pieces 66 and extending along the X-axis direction. Guide rails 66a extending along the Y-axis direction are formed at the upper portions of the respective guide pieces 66. The guide rails 66a of the guide pieces 66 engage with the guide rails 60a of the guide plate 60, thereby supporting the Y-axis movable member 62 movably in the Y-axis direction by the guide plate 60. Furthermore, a pair of guide rails 68a extending along the X-axis direction are formed at the lower portions of both ends of the mounting piece 68 in the Y-axis direction.The Y-axis direction movement mechanism 64 includes a ball screw 70 extending along the Y-axis direction under the guide plate 60, and a motor 72 connected to a single end portion of the ball screw 70. A gate-shaped nut portion 70a of the ball screw 70 is fixed to the upper surface of the mounting portion 68. The other single end portion of the ball screw 70, to which the motor 72 is not connected, is threadably engaged with the nut portion 70a and is then rotatably supported by a support piece portion 60b formed at the edge portion of the front side of the guide plate 60.In addition, the Y-axis direction moving mechanism 64 converts a rotary motion of the motor 72 into a linear motion through the ball screw 70 and transmits the linear motion to the Y-axis direction movable member 62 to move the Y-axis direction movable member 62 along the guide rails 60a of the guide plate 60 in the Y-axis direction.

[0027] The description of the laser beam irradiation unit 6 will be made with reference to Fig. 5. The laser beam irradiation unit 6 further includes an X-axis movable plate 74 mounted on the mounting portion 68 of the Y-axis movable member 62 for movement in the X-axis direction, and an X-axis moving mechanism 76 for movement of the X-axis movable plate 74 in the X-axis direction. Both end portions of the X-axis movable plate 74 engage with the guide rails 68a of the mounting portion 68, thereby mounting the X-axis movable plate 74 on the mounting portion 68 for movement in the X-axis direction. The X-axis direction moving mechanism 76 includes, above the mounting part 68, a ball screw 78 extending along the X-axis direction, and a motor 80 connected to a single end part of the ball screw 78 and supported by a guide part 66.A nut part 78a of the ball screw 78 passes through an opening 68b of the mounting part 68 and is fixed to the upper surface of the X-axis movable plate 74. The other single end part on the ball screw 78, to which the motor 80 is not connected, is rotatably supported by the other guide part 66, to which the motor 80 is not attached. Furthermore, the X-axis moving mechanism 76 converts a rotational movement of the motor 80 into a linear movement through the ball screw 78 and transmits the linear movement to the X-axis movable plate 74 to move the X-axis movable plate 74 along the guide rails 68a of the mounting part 68 in the X-axis direction.

[0028] Furthermore, the structure of an optical system of the laser beam irradiation unit 6 will be described with reference to Fig. 5 to 8. As described in Fig. 5, the laser beam irradiation unit 6 includes a laser oscillator 82 that is installed in the horizontal wall part 222 of the frame body 22 and oscillates a pulsed laser, an attenuator (a diagram of which is omitted) that adjusts the output power of a laser beam LB emitted from the laser oscillator 82, and a rectangular prism mirror 84 that is mounted at a distance from the laser oscillator 82 in the Y-axis direction on the lower surface of the mounting part 68 of the Y-axis movable member 62.The laser beam irradiation unit 6 further includes a condenser 86 mounted on the lower surface of the X-axis movable plate 74 for movement in the Z-axis direction, and a focal point position adjustment means (a diagram of which is omitted) that moves the condenser 86 in the Z-axis direction and adjusts the position of the focal point of the condenser 86 in the Z-axis direction. The laser oscillator 82 oscillates a laser at a wavelength (e.g., 355 nm) that is absorbed by the workpiece, for example. As shown in FIG. Fig. 6, the moving direction of the laser beam LB emitted from the laser oscillator 82 in the Y-axis direction is changed by 90° by the right-angle prism mirror 84, and the laser beam LB is guided to the condenser 86.

[0029] As in Fig. 7, inside an upper casing 86a of the condenser 86, there are arranged a polygon mirror 91 as a scattering means that scatters the laser beam LB emitted from the laser oscillator 82, a motor 92 that rotates the polygon mirror 91 at a high speed in a direction indicated by an arrow R2, and a condenser lens (fθ lens) 86b that condenses the laser beam LB to irradiate the workpiece with the laser beam LB. As shown in Fig. 8, in the polygon mirror 91, a plurality of mirrors M are arranged concentrically around the rotation axis of the polygon mirror 91. The fθ lens 86b is arranged below the above-described polygon mirror 91 and converges the laser beam LB to irradiate the workpiece on the holding table 32 with the laser beam LB. The laser beam LB guided by the rectangular prism mirror 84 is guided to the fθ lens so that its radiation direction is scattered in the X-axis direction by the rotating mirrors M, so that irradiation is performed on the workpiece with scattering in a predetermined range in the X-axis direction.

[0030] Again referring to Fig. 5, on the lower surface of the X-axis movable plate 74, an alignment unit 88 is mounted at a distance from the condenser 86 in the X-axis direction, together with the condenser 86. The alignment unit 88 images the workpiece held by the holding table 32 and detects a region to be subjected to laser processing. Furthermore, the laser beam irradiation unit 6 includes the focal position adjusting means, which is not shown in the diagram. Although a diagrammatic representation of the specific configuration of the focal position adjusting means is omitted, a structure including a ball screw having a nut portion fixed to the condenser 86 and extending along the Z-axis direction, and a motor connected to a single end portion of this ball screw, may be employed.Based on such a structure, the rotary motion of the motor is converted into a linear motion, and the condenser 86 is moved along guide rails (illustrated here is omitted) arranged along the Z-axis direction. This adjusts the position of the focal point of the laser beam LB converged by the condenser 86 in the Z-axis direction.

[0031] The laser processing apparatus 2 of the present invention essentially has the structure described above. Its operation will be described below. First, the wafer 10 is prepared, which in the present embodiment is the plate-shaped workpiece, is made of silicon (Si), and has components formed on one surface. After the wafer 10 is prepared, the Fig. 1 is temporarily moved outward (in the direction indicated by arrow A in the diagram) to open the upper side of the liquid chamber 41, and the wafer 10 is placed on the holding chuck 32a of the holding table 32 in such a manner that the surface on which the components are formed faces upward. After the wafer 10 is placed on the holding chuck 32a, the suction source, which is not shown in the diagram, is actuated, and suction force is generated on the holding chuck 32a to cause the wafer 10 to adhere and be held on the holding chuck 32a by suction. After the wafer 10 is held on the holding chuck 32a, the transparent plate 42 is moved onto the liquid chamber 41 to bring about the state in which the liquid chamber 41 is closed.

[0032] After the wafer 10 is held on the holding chuck 32a and the upper side of the liquid chamber 41 is closed by the transparent plate 42, the liquid reservoir tank 47 is refilled with sufficient liquid W, and the liquid supply pump 45 and the motor M are actuated. As the liquid W supplied to the liquid supply mechanism 40, for example, purified water is used.

[0033] After the operation of the liquid supply pump 45 and the motor M starts, the space 41e of the liquid chamber 41 is filled with the liquid W over a predetermined period of time. In addition, the liquid W is accelerated by coming into contact with the lower surface of the transparent plate 42 rotating in the direction shown by the arrow R1, so that the flow velocity of the liquid W is generated. In this way, the state in which the liquid W is circulated continuously and at a high speed inside the liquid supply mechanism 40 is achieved.

[0034] In the state where the liquid W is circulated continuously and at high speed by the liquid supply mechanism 40, the X-axis movable plate 74 is moved by the X-axis moving mechanism 76 of the laser beam irradiation unit 6, and the Y-axis movable member 62 is moved in the Y-axis direction by the Y-axis moving mechanism 64 (see Fig. 4 and Fig. 5) to position the alignment unit 88 over the wafer 10. Since the transparent plate 42 is arranged to cover the entire holding table 32 from the upper side as described above, the alignment unit 88 can accommodate the entire area including the components on the wafer 10. After the alignment unit 88 is positioned over the wafer 10, the wafer 10 is imaged by the alignment unit 88. At this time, the wafer 10 is imaged through the transparent plate 42 and the liquid W. Subsequently, position adjustment is performed between the wafer 10 and the condenser 86 based on an image of the wafer 10 acquired by the alignment unit 88. After this position adjustment, the holding table 32 is rotated, and the X-axis movable plate 74 is moved by the X-axis moving mechanism 76.Furthermore, the Y-axis movable member 62 is moved by the Y-axis moving mechanism 64. This positions the planned dividing lines formed in a grid-like manner on the wafer 10 along the X-axis direction, and the condenser 86 is positioned at a single end portion of the planned dividing line, that is, the irradiation start position of the laser beam. Subsequently, the condenser 86 is moved in the Z-axis direction by the focal point position adjusting means (not shown in the diagram), and the focal point is positioned at the planned dividing line of the wafer 10 at the surface height of the single end portion.

[0035] After the condenser 86 is moved in the Z-axis direction and the focal position is adjusted to the surface height of the wafer 10, the X-axis movable plate 74 is moved at a predetermined movement speed by the X-axis direction moving mechanism 76 while the laser beam irradiation unit 6 is actuated. When the wafer 10 is irradiated with the laser beam LB to perform laser processing, the polygon mirror 91 is arranged as based on Fig. 7 and Fig. 8, rotated by the motor 92 at an appropriate rotation speed. The positions of the mirrors M constituting the polygon mirror 91 change with the rotation of the polygon mirror 91, thereby irradiating the wafer 10 with the laser beam LB in a scattered manner. After the predetermined mirror M is irradiated with the laser beam LB, the mirror M on the downstream side in the rotation direction R2 of the polygon mirror 91 is irradiated with the laser beam LB, so that the wafer 10 is irradiated with the laser beam LB in a scattered manner. Such laser processing is repeated while the laser beam LB is emitted from the laser oscillator 82 and the polygon mirror 91 rotates. The number of mirrors M constituting the polygon mirror 91, the rotation speed of the polygon mirror 91, etc., are appropriately determined in accordance with the workpiece.

[0036] The laser processing can be carried out in the laser processing device 2 described above, for example, under the following processing conditions: Laser beam wavelength: 226 nm, 355 nm, 532 nm, 1064 nm Average output power: 10 to 100 watts Repetition frequency: 0 to 300 MHz Pulse width: 50 fs to 1 ns Machining feed speed: 10 to 1000 mm / s

[0037] In the present embodiment, the liquid chamber 41 of the liquid supply mechanism 40 is placed on the holding table 32. Due to the operation of the rotating transparent plate 42, the liquid W flows as shown in Fig. 7, along the rotation direction R1 of the transparent plate 42, which is substantially equal to the Y-axis direction perpendicular to the X-axis direction, which is the direction in which the processing is performed. In this state, the laser beam LB is transmitted through the transparent plate 42 and the liquid W and is applied to the intended separation line on the wafer 10, so that ablation processing is performed. When the ablation processing is performed on the surface of the wafer 10, air bubbles are generated in the liquid W, which are present at the position irradiated with the laser beam LB. In the present embodiment, by rotating the transparent plate 42, a flow velocity is generated for the liquid W supplied to the wafer 10, and the liquid W is caused to flow rapidly toward the liquid discharge nozzle 44 (see Fig. 1). Consequently, the air bubbles generated near the irradiation position of the laser beam LB are caused to quickly flow to the downstream side of the liquid chamber 41 and are removed. Therefore, when the wafer 10 is irradiated with the laser beam LB in a scattered manner by using the polygon mirror 91, the wafer 10 can be irradiated with the laser beam LB while avoiding the air bubbles generated due to the ablation processing, and favorable ablation processing can be continuously performed. Moreover, according to the present embodiment, even if residues are generated due to the ablation processing, the residues discharged into the liquid W are quickly removed from the liquid chamber 41 because the liquid W continuously flows in the liquid chamber 41.These residues released into the liquid W are quickly captured by the filtration filter 46 and therefore prevented from being recirculated in the liquid chamber 41.

[0038] After the above-described ablation processing has been performed for the predetermined planned parting line extending along a first direction, the Y-axis movable member 62 is moved in the Y-axis direction by the Y-axis direction moving mechanism 64, and the condenser 86 is positioned at a single end portion of a planned parting line that is adjacent and has not yet been processed, and the same laser processing as the above-described ablation processing is performed. After the ablation processing has been performed for all the planned parting lines extending along the first direction, the holding table 32 is rotated 90°, and thereby the same ablation processing is then also performed for the planned parting lines perpendicular to the planned parting lines extending along the first direction and that have not yet been processed.In this way, the ablation processing can be carried out for all planned separation lines on the wafer 10.

[0039] As described above, the space 41e closed by the liquid chamber 41 is formed on the holding table 32, and at least the upper side of the holding table 32 is covered by the rotating transparent plate 42. Moreover, the liquid W is caused to flow in the space 41e at a predetermined flow rate, and irradiation with the laser beam is carried out through the rotating transparent plate 42 and through the liquid W to perform laser processing. Due to this, air bubbles generated on the surface of the wafer 10, residues generated due to laser processing, etc., are quickly removed and do not hinder the laser processing. Furthermore, adhesion of residues to components after processing, etc., is prevented, and quality is not degraded.

[0040] In the above-described embodiment, the desired laser processing is performed by placing the wafer 10 as a workpiece on the holding unit 30 fixed to the base 21 and moving the condenser 86 of the laser beam irradiation unit 6 arranged on the lower surface of the horizontal wall part 222. However, the present invention is not limited to this. The condenser 86 may be arranged at the top of the lower surface of the horizontal wall part 222 in such a way that it is fixed with respect to the X-axis and Y-axis directions, and laser processing may be performed in such a way that the side of the holding unit 30 is moved relative to the condenser 86 in the X-axis and Y-axis directions. In this case, the motor M constituting the rotation mechanism may be installed on the holding unit 30, and the transparent plate 42 may be moved together with the holding unit 30.

[0041] Furthermore, in the above-described embodiment, the liquid supply mechanism 40 is arranged on the upper surface 31a of the holding base 31 of the holding unit 30. However, the present invention is not limited to this, and the liquid supply mechanism 40 may be arranged above the holding unit 30 by being arranged on the condenser 86. In this case, the condenser 86 is fixed to the lower surface of the horizontal wall part 222. In addition, the rotating transparent plate 42 is arranged in a circular disk shape that is smaller than that shown in Fig. 2 and Fig. 3. Furthermore, it is preferable for the support base 31 to be configured to move on the base 21 in the X-axis direction (machining feed direction) and the Y-axis direction (graduating feed direction).

[0042] In the above-described embodiment, the transparent plate 42 is formed with a glass plate. However, the transparent plate 42 is not limited to this. It is sufficient for the transparent plate 42 to be a transparent plate through which the laser beam LB is transmitted, and the transparent plate 42 may be a plate made of a resin, such as an acrylic plate.

[0043] In the above-described embodiment, the example in which the laser beam LB emitted from the laser oscillator 82 is diffused by the polygon mirror 91 to be guided to the condenser lens 86b is presented. However, the structure is not limited to this, and a fixed reflecting mirror may be used instead of the polygon mirror 91. Furthermore, in the above-described embodiment, the example in which the laser processing performed on the wafer 10 is ablation processing is presented. However, this does not prevent the laser processing from being applied to processing for forming modified layers inside the workpiece (for example, the laser processing described in Japanese Patent Application Laid-Open No. 3408805) and processing involving the formation of so-called shielding tunnels (for example, the laser processing described in Japanese Patent Application Laid-Open No. 2014-221483).

[0044] The present invention is not limited to the details of the preferred embodiment described above. The scope of the invention is defined by the appended claims, and all changes and modifications that fall within the equivalent scope of the claims are therefore included in the invention.

Claims

[1] Laser processing device (2) comprising: a holding unit (30) with a holding table (32) for holding a plate-shaped workpiece; a laser beam irradiation unit (6) which irradiates the workpiece held by the holding table (32) with a laser (LB) and carries out processing; and a liquid supply mechanism (40) arranged above the holding unit (30), wherein the liquid supply mechanism (40) comprises a liquid chamber (41) having a circular disc-shaped transparent plate (42) positioned to form a gap (S) between the circular disc-shaped transparent plate (42) and an upper surface of the workpiece held by the holding table, a liquid supply nozzle (43) that supplies a liquid (W) to the gap (S) from one side of the liquid chamber (41), a liquid discharge nozzle (44) that discharges the liquid (W) from another side of the liquid chamber (41), and a rotation mechanism that rotates the circular disc-shaped transparent plate (42) and generates a flow velocity in the liquid (W) supplied to the gap (S) toward the liquid discharge nozzle (44), and the laser beam irradiation unit (6) comprises a laser oscillator (82) which emits the laser beam (LB), and a condenser (86) which focuses the laser beam (LB) emitted by the laser oscillator (82) and irradiates the workpiece held by the holding table (32) with the laser beam (LB) transmitted through the transparent plate (42) and the liquid (W) supplied to the gap (S). [2] The laser processing apparatus (2) according to claim 1, wherein the laser beam irradiation unit (6) further comprises a scattering means that scatters the laser beam (LB) emitted from the laser oscillator (82). [3] Laser processing apparatus (2) according to claim 2, wherein the scattering means of the laser beam irradiation unit (6) is a polygon mirror (91) by the rotation of which the workpiece is irradiated in a scattered manner.

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