Laser processing device

Abstract

Laser processing device (2) comprising: a holding unit (30) having a holding table (34) holding a plate-shaped workpiece; a laser beam application unit (6) which applies a laser beam (LB) to the workpiece held on the holding table (34) in order to machine the workpiece; and a liquid supply mechanism (40) arranged at an upper portion of the holding unit (30), wherein the liquid supply mechanism (40) comprises: a liquid chamber (41) having a transparent plate (42) positioned to form a gap between it and an upper surface of the workpiece held on the holding table (34), a roller (52) formed of a transparent member, which is arranged in a non-contact state at a position near the upper surface of the workpiece held on the holding table (34) inside the liquid chamber (41) and which generates a liquid flow on the workpiece, a roller rotation mechanism that rotates the roller (52), a liquid supply nozzle (43) which supplies the liquid into the gap from one side of the liquid chamber (41), and a liquid discharge nozzle (44) which discharges the liquid from the other side of the liquid chamber (41), and wherein the laser beam application unit (6) comprises a laser oscillator (82) which emits the laser beam (LB), and a condenser (86) which condenses the laser beam (LB) emitted from the laser oscillator (82) to apply the laser beam (LB) to the workpiece held on the holding table (34) through the transparent plate (42), the roller (52) and the liquid supplied to the gap.

Description

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

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

[0002] A wafer having a plurality of devices such as integrated circuits (ICs) and large-scale integrations (LSIs) formed on a front surface of the wafer by separating lines (streets) is divided into individual device chips by a laser processing apparatus, and the divided device chips are used for electronic equipment such as a mobile phone, a personal computer, and lighting equipment.

[0003] Examples of laser processing apparatuses include the following types: a laser processing apparatus employing ablation processing by which a laser beam having a wavelength absorbed by a workpiece is applied to the workpiece with a focal point of the laser beam positioned on a front surface of the workpiece to thereby form grooves serving as cutting start points (see, for example, Japanese Unexamined Patent Publication No. H10-305420A); a laser processing apparatus in which a laser beam having a wavelength transmissible through a workpiece is applied to the workpiece with a focal point of the laser beam positioned inside the workpiece to thereby form modified layers serving as cutting start points inside the workpiece (see, for example, Japanese Unexamined Patent Publication No. 3408805B2);and a laser processing apparatus in which a laser beam having a wavelength transmissible through a workpiece is applied to the workpiece, with a focal point of the laser beam positioned inside the workpiece, to thereby form a plurality of shielding tunnels, each including a fine hole extending from a front surface to a back surface of the workpiece and serving as a separation starting point, and an amorphous region surrounding the fine hole (see, for example, Japanese Patent Application Laid-Open No. 2014-221483). One of these types of laser processing apparatuses is appropriately selected in accordance with a workpiece type, required processing accuracy, and similar factors.

[0004] Of the above-mentioned laser processing apparatuses, the one performing ablation processing in particular has a problem that residues (laser processing chips) generated when the laser beam is applied to the front surface of the wafer may scatter and adhere to the front surfaces of the devices formed on the wafer, thereby reducing the quality of the devices. To solve this problem, a technique has been proposed in which a liquid resin through which the laser beam used for processing can be transmitted is applied to the front surface of the wafer before performing laser processing to thereby prevent residue adhesion, and the liquid resin is removed after performing laser processing (see, for example, Japanese Patent Application Laid-Open No. 2004-188475).

[0005] Furthermore, published patent application DE 10 2010 015 739 A1 discloses a laser beam processing device that irradiates a predetermined area of a workpiece with a laser beam for a predetermined processing step. Published patent application US 2005 / 0 003 737 A1 also deals with various techniques that can be used individually or in combination to improve the contact between a processed substrate and applied ultrasonic energy. SUMMARY OF THE INVENTION

[0006] According to the technique described in Japanese Patent Application Laid-Open No. 2004-188475, coating with liquid resin prevents residues from adhering to the front surfaces of components, thereby ensuring machining quality. However, this technique requires the step of applying the liquid resin and the step of removing the liquid resin after machining, which poses a problem in productivity. Furthermore, since the liquid resin cannot be reused, the use of the liquid resin is uneconomical.

[0007] A technique has also been proposed in which laser beam application is performed with a wafer immersed in water to cause residues to float in the water, thereby preventing the residues from adhering to the front surface of the wafer. However, in a case where the laser beam is applied to the wafer with the wafer immersed in water, small bubbles are generated at the part of the wafer where the laser beam is applied, resulting in the problem that the propagation of the laser beam is disrupted by the bubbles, and desired processing cannot be achieved.

[0008] It is therefore an object of the present invention to provide a laser processing apparatus by which a laser beam can be applied to a plate-shaped workpiece to process the workpiece while preventing obstruction of the application of the laser beam to the workpiece.

[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 applying unit that applies a laser beam to the workpiece held on the holding table to machine the workpiece, and a liquid supply mechanism arranged at an upper portion of the holding unit.The liquid supply mechanism includes a liquid chamber having a transparent plate positioned to form a gap between it and an upper surface of the workpiece held on the holding table, a roller formed of a transparent member, which is arranged in a non-contact state at a position near the upper surface of the workpiece held on the holding table inside the liquid chamber and which generates a liquid flow on the workpiece, a roller rotating mechanism that rotates the roller, a liquid supply nozzle that supplies the liquid into the gap from one side of the liquid chamber, and a liquid discharge nozzle that discharges the liquid from the other side of the liquid chamber.The laser beam application unit includes a laser oscillator that emits a laser beam and a condenser that condenses the laser beam emitted from the laser oscillator to apply the laser beam to the workpiece held on the holding table through the transparent plate, the roller, and the liquid supplied into the gap.

[0010] Preferably, the laser beam application 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 in which application of a laser beam to a workpiece is not hindered. Furthermore, in a case where the present invention is applied to a laser processing apparatus performing ablation processing, adhesion of residues generated at the time of laser processing to components can be restrained, and a decrease in the processing quality of the components can be prevented without coating the front surface of the wafer with a liquid resin.

[0012] The above and other objects, features and advantages of the present invention and the manner of carrying them into effect 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 perspective view showing a liquid supply mechanism and a holding unit of the Fig. 1 in a disassembled state; Fig. 3 is a perspective view showing the Fig. 2 illustrates the liquid supply mechanism and the holding unit in a partially disassembled state; Fig. 4 is a perspective view of a laser beam application unit of the Fig. 1 illustrated laser processing device; Fig. 5 is an exploded perspective view of the Fig. 4 illustrated laser beam application unit in a partially disassembled state; Fig. 6 is a block diagram showing an optical system of the Fig. 4 illustrated laser beam application unit; Fig. 7A is a perspective view illustrating a state in which laser processing is performed by the Fig. 5 illustrated laser beam application unit; Fig. 7B is a side view of the Fig. 7A; and Fig. Fig. 8 is a side view of the laser beam application unit for explaining a state in which laser processing is carried out with a laser beam scattered by a scattering means of the type shown in Fig. 7A illustrated laser beam application unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] A laser processing apparatus in accordance with an embodiment of the present invention will be described in more detail below with reference to the attached drawings. Fig. 1 illustrates a perspective view of a laser processing apparatus 2 in 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, a frame body 22 including a vertical wall portion 221 erected on the base 21 on a lateral side of the holding unit 30 in a Z direction indicated by an arrow Z, and a horizontal wall portion 222 extending from an upper end portion of the vertical wall portion 221 in a horizontal direction, a liquid supply mechanism 40 disposed at an upper portion of the holding unit 30, and a laser beam application unit 6 disposed on a lower surface of the horizontal wall portion 222.

[0014] Fig. Fig. 2 is a perspective view illustrating the liquid supply mechanism 40 and the holding unit 30 of the laser processing apparatus 2 in a disassembled state. Fig. 3 is a perspective view illustrating each of the components of the holding unit 30, as well as a liquid chamber 41, a liquid supply nozzle 43, and a liquid discharge nozzle 44, which form the liquid supply mechanism 40, in a disassembled state. Each of the components will be described below.

[0015] As in Fig. 3, the holding unit 30 includes a holding base 31 having a rectangular parallelepiped shape, a rectangular base table 32 disposed on an upper surface of the holding base 31, a central table 33 disposed substantially at the center of the base table 32 and configured to have substantially one half in a region of the base table 32, and a circular holding table 34 disposed on the central table 33. The holding table 34 is configured to be rotatable by an unillustrated rotation mechanism. A central region of the holding table 34 is configured with a circular suction chuck 34a formed of a gas-permeable material such as a porous ceramic. The suction chuck 34a is connected to an unillustrated suction source and holds a plate-shaped workpiece placed on the suction chuck 34a under suction.

[0016] The liquid supply mechanism 40 is arranged at the upper portion of the holding unit 30. On the base table 32 arranged on the holding base 31 of the holding unit 30, a liquid chamber 41 is placed so as to be displaceable in a Y-axis direction. The liquid chamber 41 includes a frame 41a extending in an X-axis direction and the Y-axis direction, a transparent plate 42 closing a space 41b defined by the frame 41a from above, and a roller 52 generating a flow when liquid is supplied into the space 41b. This structure ensures that the space 41b can be a closed space enclosed by the base table 32, the transparent plate 42, and the frame 41a. The frame 41a has end portions positioned to face each other in the Y-axis direction.One end portion of the frame 41a is provided with a liquid supply port 41c that provides communication between the space 41b and the outside, and the other end portion of the frame 41a is provided with a liquid discharge port 41d that provides communication between the space 41b and the outside. The liquid supply port 41c and the liquid discharge port 41d extend in a horizontal direction at the above-mentioned end portions of the frame 41a and are formed with a size larger than a diameter of the suction chuck 34a. The transparent plate 42 is configured to be detachable to open an upper side of the liquid chamber 41 at the time of placing the workpiece on the holding table 34 or removing the workpiece from the holding table 34. The transparent plate is constructed of, for example, a glass plate.

[0017] A liquid supply nozzle 43 is connected to a position of the frame 41a where the liquid supply port 41c is located. Furthermore, a liquid discharge nozzle 44 for discharging the liquid is connected to a position of the frame 41a where the liquid discharge port 41d is located. With this configuration, the liquid is supplied through the liquid supply nozzle 43 from one side of the liquid chamber 41, and the liquid is discharged through the liquid discharge nozzle 44 from the other side of the liquid chamber 41. This will be described in more detail below.

[0018] The liquid supply nozzle 43 is provided with a supply port 43a for supplying liquid, a passage 43b for passing the liquid supplied from the supply port 43a, and a discharge port 43c for discharging the liquid passing through the passage 43b. As indicated by dotted lines in the figure, the supply port 43a is located in a lower surface of the liquid supply nozzle 43, the passage 43b is formed inside the liquid supply nozzle 43, and the discharge port 43c is formed in the same shape as the liquid supply port 41c at a position facing the liquid supply port 41c of the liquid chamber 41.With the liquid supply nozzle 43 connected to the liquid chamber 41, the discharge port 43c of the liquid supply nozzle 43 and the liquid supply port 41c of the liquid chamber 41 are connected to each other, and the supply port 43a of the liquid supply nozzle 43 and the space 41b inside the liquid chamber 41 communicate with each other.

[0019] The liquid discharge nozzle 44 is configured with the same shape as the liquid supply nozzle 43. The liquid discharge nozzle 44 is provided with a supply opening 44c supplied with the liquid, a passage 44b through which the liquid supplied from the supply opening 44c passes, and a discharge opening 44a through which the liquid passing through the passage 44b is discharged. As shown in Fig. As illustrated in Fig. 3, the supply port 44c of the liquid discharge nozzle 44 is formed with the same shape as that of the liquid discharge port 41d of the liquid chamber 41 at a position facing the liquid discharge port 41d of the liquid chamber 41. The passage 44b is formed inside the liquid discharge nozzle 44, and the discharge port 44a is arranged in a lower surface of the liquid discharge nozzle 44. With the liquid supply nozzle 43 and the liquid discharge nozzle 44 connected to the liquid chamber 41, the supply port 43a of the liquid supply nozzle 43 and the discharge port 44a of the liquid discharge nozzle 44 communicate with each other through the space 41b inside the liquid chamber 41.

[0020] As in Fig. As illustrated in Fig. 3, the roller 52 is a rod-shaped member with a diameter of 5.0 mm, which traverses the space 41b inside the liquid chamber 41 in the X-axis direction and is formed of a transparent member such as glass through which the laser beam is transmitted. One end portion of the roller 52 is rotatably supported substantially at the center of a portion of the frame 41a arranged along the Y-axis direction, and the other end portion of the roller 52 is rotatably supported substantially at a central portion of a portion of the frame 41a facing the above-mentioned portion of the frame 41a that supports the one end portion of the roller 52. A motor 54 as a roller rotation mechanism that rotates the roller 52 in a direction indicated by an arrow R1 is connected to the other end portion of the roller 52.The motor 54 is fixed to the frame 41a, and when the motor 54 rotates, the roller 52 is rotated in the direction of the arrow R1.

[0021] As in Fig. As illustrated in Fig. 2, a pair of guide rails 23 and 23 extending in the Y-axis direction and a holding table moving means 24 that moves the holding base 31 in the Y-axis direction along the guide rails 23 and 23 are arranged on an upper surface of the base 21. A lower surface of the holding base 31 is provided with a pair of guide grooves 31a and 31a that fit the guide rails 23 and 23, respectively. With the guide grooves 31a and 31a fitting the guide rails 23 and 23, respectively, the holding base 31 can be moved along the guide rails 23 and 23 in the Y-axis direction.

[0022] The holding table moving means 24 includes a male threaded rod 241 arranged parallel to and between the pair of guide rails 23 and 23, and a stepping motor 242 fixed to the base 21 for driving the male threaded rod 241 in the rotational direction. The male threaded rod 241 is rotatably supported at one end by a bearing block 25 fixed to the base 21 and is connected at the other end to an output shaft of the stepping motor 242. In addition, the male threaded rod 241 is screwed into a female threaded through hole 31b formed in a lower central portion of the holding base 31 along the Y-axis direction (see also Fig. 3). With the male screw rod 241 driven by the stepping motor 242 to rotate forward and backward, the support base 31 is moved along the guide rails 23 and 23 in the Y-axis direction. Although its illustration is omitted, it should be noted that the support table moving means 24 is provided with position detecting means, whereby a position of the support base 31 in the Y-axis direction is precisely detected. Based on the position information, a drive signal for the stepping motor 242 is generated in a control means, which is omitted in the illustration, of the laser processing apparatus 2, and the drive signal is output to the stepping motor 242, whereby the support table 34 arranged on the upper surface of the support base 31 can be precisely positioned at a desired position.

[0023] Although an illustration of a specific fixing method is omitted for ease of explanation, the liquid supply mechanism 40 is fixed relative to the base 21. Specifically, when the support base 31 is moved in the Y-axis direction as mentioned above, the liquid supply mechanism 40 disposed at an upper portion of the support base 31 is not moved. With the support base 31 in motion, the workpiece held on the support table 34 on the base 21 is therefore moved in the Y-axis direction and is also moved with respect to the liquid supply mechanism 40 in the Y-axis direction. Note that the liquid supply mechanism 40 only needs to be arranged so as not to be moved relative to the base 21 and may be fixed to the horizontal wall portion 222 by clamps or the like.

[0024] The base table 32 arranged on the support base 31 is formed to be longer in size in the Y-axis direction than the frame 41a forming the liquid chamber 41. As a result, a state in which the lower side of the space 41b of the liquid chamber 41 is closed is maintained by the base table 32 even when the support base 31 is moved below the liquid chamber 41 in the Y-axis direction. Note that a lower surface of the liquid chamber 41 and / or an upper surface of the base table 32 is coated with a fluorine coating, thereby ensuring maintenance of a hermetically sealed state of the space 41b inside the liquid chamber 41 and smooth movement of the support base 31.

[0025] Embodiments of the liquid supply mechanism 40 and its surroundings are described below. As in Fig. As illustrated in FIG. 2, the laser processing apparatus 2 according to the present embodiment includes a liquid supply pump 45, a filter 46, and a liquid reserve tank 47 in such a manner that the liquid is continuously supplied to the inside of the liquid supply mechanism 40. The liquid reserve tank 47 is arranged at the filter 46. The liquid supply pump 45 and the liquid supply nozzle 43 are connected to each other by a first hose 48a, the liquid discharge nozzle 44 and the filter 46 are connected to each other by a second hose 48b, and the filter 46 and the liquid supply pump 45 are connected to each other by a third hose 48c. The hoses 48a to 48c are constructed with flexible hoses made of plastic.

[0026] In accordance with the above-mentioned structure and as described in Fig. 1, the liquid W discharged from the liquid supply pump 45 is supplied to the liquid chamber 41 through the first hose 48a and the liquid supply nozzle 43, and the liquid W supplied to the liquid chamber 41 is discharged through the liquid discharge nozzle 44. Then, the liquid W discharged from the liquid discharge nozzle 44 is supplied to the filter 46 to be filtered and then returned to the liquid supply pump 45. In the liquid supply mechanism 40 of the present embodiment, the liquid W is allowed to gradually leak through a gap between the liquid chamber 41 and the base table 32, a gap between the frame 41a and the transparent plate 42, and the like, and the leaked liquid W can be collected at the base 21 and returned to the filter 46.In a case where an amount of the liquid W decreases due to the leakage, the liquid W can be appropriately replenished from the liquid reserve tank 47. Note that the liquid reserve tank 47 is directly connected to the filter 46 and also serves to discharge air bubbles contained in the liquid W supplied to the filter 46.

[0027] According to the above configuration, the liquid W is circulated in the liquid supply mechanism 40, the liquid supply pump 45, the filter 46, and the liquid reserve tank 47. A flow rate of the liquid W flowing into the liquid chamber 41 can be controlled by adjusting a pressure supply efficiency of the liquid supply pump 45, changing an internal volume of the liquid chamber 41, or adjusting opening areas of the liquid supply port 41c and the liquid discharge port 41d.

[0028] Now referring to Fig. 1, Fig. 4 and Fig. 5, the laser beam application unit 6 is described. It should be noted that Fig. 5 is an exploded perspective view of the laser beam application unit 6 shown in Fig. 4 is illustrated.

[0029] The laser beam application unit 6 includes a guide plate 60 fixed to the lower surface of the horizontal wall portion 222 of the frame body 22 by an unillustrated fastening means, a Y-axis movable member 62 supported by the guide plate 60 so as to be movable in the Y-axis direction, 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 in the Y-axis direction is formed at a lower portion of one of the ends of the guide plate 60 in the X-axis direction. As shown in FIGS. Fig. 4 and Fig. As illustrated in Fig. 5, the Y-axis movable member 62 includes a pair of guide portions 66 spaced apart from each other in the X-axis direction, and a mounting portion 68 disposed between lower ends of the guide portions 66 and extending in the X-axis direction. A guide rail 66a extending in the Y-axis direction is formed at an upper portion of each of the guide portions 66. The guide rails 66a of the guide portions 66 and the guide rails 60a of the guide plate 60 are engaged with each other, whereby the Y-axis movable member 62 is supported by the guide plate 60 so as to be movable in the Y-axis direction. In addition, a pair of guide rails 68a extending in the X-axis direction is formed at a lower portion of one of the ends of the mounting portion 68 in the Y-axis direction.The Y-axis direction moving mechanism 64 includes a ball screw 70 extending below the guide plate 60 in the Y-axis direction, and a motor 72 connected to one end portion of the ball screw 70. A gate-shaped nut portion 70a of the ball screw 70 is fixed to an upper surface of the mounting portion 68. The other end portion of the ball screw 70, to which the motor 72 is not connected, is screwed into the nut portion 70a before being rotatably supported by a support member portion 60b formed at a front edge portion of the guide plate 60.The Y-axis direction moving mechanism 64 converts a rotary motion of the motor 72 into a rectilinear motion and transmits the rectilinear motion to the Y-axis direction movable member 62 through the ball screw 70, whereby the Y-axis direction movable member 62 is movable along the guide rails 60a of the guide plate 60 in the Y-axis direction.

[0030] With reference to Fig. 5, the description of the laser beam application unit 6 continues. The laser beam application unit 6 further includes an X-axis movable plate 74 mounted on the mounting portion 68 of the Y-axis movable member 62 so as to be movable in the X-axis direction, and the X-axis moving mechanism 76 that moves the X-axis movable plate 74 in the X-axis direction. Both end portions of the X-axis movable plate 74 in the Y-axis direction and the guide rails 68a of the mounting portion 68 are engaged with each other, whereby the X-axis movable plate 74 is mounted on the mounting portion 68 so as to be movable in the X-axis direction.The X-axis direction moving mechanism 76 includes a ball screw 78 extending in the X-axis direction on the upper side of the mounting portion 68, and a motor 80 connected to one end portion of the ball screw 78 and supported by one of the guide portions 66. A nut portion 78a of the ball screw 78 is passed through an opening 68b of the mounting portion 68 and fixed to an upper surface of the X-axis direction movable plate 74. The other end portion of the ball screw 78, to which the motor 80 is not connected, is rotatably supported by the other of the guide portions 66 to which the motor 80 is not attached.The X-axis direction moving mechanism 76 converts a rotary motion of the motor 80 into a rectilinear motion through the ball screw 78 and transmits the rectilinear motion to the X-axis direction movable plate 74, thereby moving the X-axis direction movable plate 74 along the guide rails 68a of the mounting portion 68 in the X-axis direction.

[0031] Further, with reference to the Fig. 5 to 8, a structure of an optical system of the laser beam application unit 6 is described. As in Fig. 5, the laser beam application unit 6 includes a laser oscillator 82 that emits a pulsed laser beam LB, an attenuator (omitted in the illustration) that controls an output of the laser beam LB emitted from the laser oscillator 82, a right-angle prism mirror 84 mounted on a lower surface of the mounting portion 68 of the Y-axis movable member 62 so as to be spaced apart from the laser oscillator 82 in the Y-axis direction, a condenser 86 mounted on a lower surface of the X-axis movable plate 74 so as to be movable in the Z-axis direction, and a focal point position control means (omitted in the illustration) configured to move the condenser 86 in the Z-axis direction to control the position of the focal point of the condenser 86 in the Z-axis direction. steer.The laser oscillator 82 oscillates, for example, a laser at a wavelength (e.g., 355 nm) that is absorbed in the workpiece. As shown in . Fig. 6, the propagation direction of the laser beam LB output from the laser oscillator 82 in the Y-axis direction is changed by 90° by the right-angle prism mirror 84 so that it is guided to the condenser 86.

[0032] As in Fig. 7a, inside an upper casing 86a of the condenser 86, there are provided a polygon mirror 91 as a scattering means that scatters the laser beam LB oscillated by 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 apply the laser beam LB to the workpiece. As shown in Fig. As illustrated in Figure 8, the polygon mirror 91 includes a plurality of mirrors M arranged concentrically with respect to a rotation axis of the polygon mirror 91. The fθ lens 86b is arranged below the polygon mirror 91 and focuses the laser beam LB to apply the laser beam LB to the workpiece on the holding table 34. The laser beam LB guided by the right-angle prism mirror 84 is guided to the fθ lens 86b in such a manner that the radiation direction of the laser beam LB is diffused in the X-axis direction by the rotating mirrors M, and the laser beam LB is applied to the workpiece while being diffused in a predetermined range in the X-axis direction. It should be noted that the transparent plate 42 in Fig. 7A has been omitted for ease of explanation.

[0033] To continue the description of the Fig. Returning to Fig. 5, on the lower surface of the X-axis movable plate 74, an alignment means 88, which is mounted spaced apart in the X-axis direction from the condenser 86, is arranged together with the condenser 86. The alignment means 88 is configured to image the workpiece held on the holding table 34 to detect a region to be laser-machined. Further, the laser beam application unit 6 includes unillustrated focal position control means. Although a specific configuration of the focal position control means is omitted in the illustration, the structure may include, for example, a ball screw having a nut portion fixed to the condenser 86 and extending in the Z-axis direction, and a motor connected to an end portion of the ball screw.By such a structure, a rotational motion of the motor is converted into a rectilinear motion, and the condenser 86 is moved along guide rails arranged in the Z-axis direction (omitted in the illustration), thereby controlling the position of the focal point of the laser beam LB condensed by the condenser 86 in the Z-axis direction.

[0034] The laser processing apparatus 2 of the present invention is generally configured as mentioned above, and its operation will be described below. When performing laser processing by the laser processing apparatus 2 of the present embodiment, first, a plate-shaped workpiece is prepared, such as a wafer 10 formed of silicon (Si) and having components formed on its front surface. After the wafer 10 has been prepared, the Fig. 1 is temporarily removed to open the upper side of the liquid chamber 41, and the wafer 10 is placed on the holding table 34 in a state where the front surface formed with components is facing upward. After the wafer 10 is placed on the holding table 34, an unillustrated suction source is actuated to generate suction force on the suction chuck 34a of the holding table 34, thereby holding the wafer 10 under suction. After the wafer 10 is held on the suction chuck 34a, the transparent plate 42 is fixed to the liquid chamber 41 by an appropriate fixing means, resulting in a state where the upper side of the liquid chamber 41 is closed.

[0035] After the wafer 10 is held on the holding table 34 and the upper side of the liquid chamber 41 is closed with the transparent plate 42, a sufficient amount of liquid W is supplied to the liquid reserve tank 47, and the liquid supply pump 45 is actuated. As the liquid W supplied to the liquid supply mechanism 40, pure water, for example, can be used.

[0036] After the lapse of a predetermined period of time after the start of operation of the liquid supply pump 45, the space 41b inside the liquid chamber 41 is filled with the liquid W, and the liquid W is continuously circulated in the liquid supply mechanism 40, the filter 46 and the liquid supply pump 45.

[0037] In the state where the liquid W is continuously circulated in the liquid supply mechanism 40, the holding table moving means 24 is actuated, and the alignment means 88 is positioned above the wafer 10 by the X-axis direction moving mechanism 76 and the Y-axis direction moving mechanism 64 of the laser beam application unit 6. Since the transparent plate 42 is arranged to completely cover the holding table 34 from above, the alignment means 88 is capable of imaging the entire area including the components on the wafer 10. After the alignment means 88 is positioned above the wafer 10, the wafer 10 is imaged by the alignment means 88. At this time, the wafer 10 is imaged through the transparent plate 42 and the liquid W. Next, based on the image of the wafer 10 imaged by the alignment means 88, alignment is performed between the wafer 10 and the condenser 86.After the alignment, the holding table 34 is rotated, the X-axis movable plate 74 is moved by the X-axis moving mechanism 76, and the Y-axis movable member 72 is moved by the Y-axis moving mechanism 64, whereby a predetermined one of the dividing lines formed as a lattice structure on the wafer 10 is positioned along the X-axis direction and the condenser 86 is positioned at an end portion of the predetermined dividing line, that is, a start position for irradiation of the laser beam.

[0038] Fig. Fig. 7A is a perspective view illustrating a state in which laser processing is performed by the laser beam application unit 6, and Fig. 7B is a side view of the state of a Fig. 7A. In the laser processing apparatus 2 of the present embodiment, the roller 52 is disposed in a gap formed between the transparent plate 42, which closes the upper side of the liquid chamber 41, and the wafer 10. The roller 52 is positioned in a non-contact state at a position close to an upper surface of the wafer 10 serving as a workpiece, such as at a position such that a distance from the front surface of the wafer 10 to a lower surface of the roller 52 is 0.5 to 2.0 mm. Furthermore, the condenser 86, as shown in Fig. 7B, the condenser 86 is set in such a state that the laser beam LB applied from the condenser 86 is always transmitted through the center of the roller 52, that is, the position in the Y-axis direction to which the laser beam LB is applied coincides with the position at which the roller 52 is arranged. Next, the condenser 86 is moved in the Z-axis direction by the unillustrated focal point position control means to position the focal point at the level of a front surface of one end portion of the dividing line on the wafer 10. After the focal point position of the laser beam LB to be applied from the condenser 86 is positioned on the wafer 10, the motor 54 is actuated to rotate the roller 52 in a direction indicated by the arrow R1.As a result, a flow of the liquid W is accelerated in a direction from the liquid supply nozzle 43 toward the liquid discharge nozzle 44 in the Y-axis direction between the roller 52 and the front surface of the wafer 10, so that a faster flow is generated.

[0039] After the focal point position is positioned at the level of the front surface of the wafer 10 while rotating the roller 52 as mentioned above, the condenser 86 is moved at a predetermined moving speed in the X-axis direction while operating the laser beam application unit 6 to apply the laser beam LB. When performing laser processing by applying the laser beam LB to the wafer 10, the polygon mirror 91 is positioned as based on the Fig. 7A to 8, rotated by the motor 92 at an appropriate rotation speed. With the positions of the mirrors M forming the polygon mirror 91 changed during the rotation of the polygon mirror 91, the laser beam LB is applied while being scattered in the X-axis direction of the wafer 10. As shown in the Fig. 7A and Fig. As shown in Fig. 7B, the direction in which the laser beam LB is scattered is the X-axis direction, and therefore, the laser beam LB is scattered along the roller 52. After the laser beam LB is applied to a predetermined mirror M, the laser beam LB is applied to the downstream side mirror M with respect to the rotation direction R2 of the polygon mirror 91, thereby applying the laser beam LB continuously and scatteredly to the wafer 10. While the laser beam LB is emitted from the laser oscillator 82 and the polygon mirror 91 is rotated, laser processing is thus repeated. Note that the number of faces of the mirrors M constituting the polygon mirror 91, the rotation speed of the polygon mirror 91, and the like are appropriately determined in accordance with the workpiece.

[0040] The laser processing by the laser processing device 2 described above can be carried out, 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 100 mm / s

[0041] In the present embodiment, the liquid chamber 41 of the liquid supply mechanism 40 is positioned at an upper portion of the holding table 34, and as shown in Fig. As illustrated in Figure 7B, the operation of the rotating roller 52 generates a flow of the liquid W in the Y-axis direction perpendicular to the processing feed direction (X-axis direction). In this state, the laser beam LB is applied to the parting line on the wafer 10 through the transparent plate 42, the roller 52, and the liquid W, thereby performing ablation. When ablation is applied to the front surface of the wafer W, air bubbles B are generated in the liquid W at the position where the laser beam LB is applied. In the present embodiment, as shown in Fig. 7B illustrates, a flow velocity is generated by rotation of the roller 52 in the liquid W supplied to the wafer 10, and the air bubbles B generated in the vicinity of the application position of the laser beam LB are quickly transported to the downstream side of the liquid chamber 41 to be removed. In the case of applying the laser beam LB to the wafer 10 in a scattered manner by using the polygon mirror 91, the laser beam LB can be applied to the wafer 10 while avoiding air bubbles B generated due to ablation, so that favorable ablation can be consistently performed.Furthermore, according to the present embodiment, even if residues are generated due to ablation, the residues discharged into the liquid W are quickly removed from the liquid chamber 41 because the flow velocity is generated in the liquid W on the upper surface of the wafer 10. Since the residues discharged into the liquid W are trapped by the filter 46, the residues are prevented from being circulated back to the liquid chamber 41.

[0042] After the ablation for the predetermined separation line described above has been carried out, the holding table 34 is moved to the holding base 31 by the holding table moving means 24 in the Y-axis direction or the direction indicated by an arrow D in Fig.1, the X-axis direction moving mechanism 76 of the laser beam application unit 6 is operated to position the condenser 86 at an end portion of an unprocessed dicing line adjacent to the currently processed dicing line, and the same laser processing as the above-mentioned ablation is performed. After ablation is performed for all the adjacent dicing lines, the holding table 34 is rotated by 90°, and the same ablation is also performed for the unprocessed dicing lines perpendicular to the previously processed dicing lines. In this way, ablation can be performed for all the dicing lines on the wafer 10.

[0043] As mentioned above, the closed space 41b is formed by the liquid chamber 41 on the holding table 34, and at least the upper side of the holding table 34 is covered by the transparent plate 42. The liquid W is introduced into the space 41b, and the laser beam is applied through the transparent plate 42, the rotating roller 52, and the liquid W to perform laser processing. As a result, the air bubbles B generated in the liquid W around the front surface of the wafer 10, the residues generated and discharged from the liquid W due to laser processing, and the like are quickly removed, thus preventing them from interfering with the laser processing. In addition, adhesion of the residues to components after processing and similar troubles are prevented, thereby preventing a deterioration in processing quality.

[0044] In the above embodiment, the wafer 10 as a workpiece is placed on the holding table 34 configured to be movable in the Y-axis direction on the base 21, the condenser 86 of the laser beam application unit 6 disposed on the lower surface of the horizontal wall portion 222 is moved in the X-axis direction to thereby perform desired laser processing, and the application position of the laser beam LB to the wafer 10 is moved by moving the holding base 31 disposed on the holding table 34 along the guide rails 23 and 23 in a pitch feed direction or the Y-axis direction. However, the present invention is not limited to this.For example, a method may be adopted in which the support base 31 is fixedly mounted on the base 21, and the liquid supply mechanism 40 and the condenser 86 are moved together in the Y-axis direction in such a manner that the liquid supply mechanism 40 and the condenser 86 are moved in the indexing feed direction relative to the wafer 10, thereby performing laser processing. In this case, a structure may be adopted in which a pair of guide rails extending in the Y-axis direction is arranged on the base table 32 arranged on the support base 31, guide grooves are formed in the bottom surface or side surfaces of the liquid chamber 41 of the liquid supply mechanism 40, and a moving means (a stepping motor, a male screw rod, and the like) that moves the liquid supply mechanism 40 is arranged to thereby move the liquid supply mechanism 40.

[0045] Although the transparent plate 42 and the roller 52 are formed of glass in the above embodiment, this is not limitative. Any transparent plate through which the laser beam LB can be transmitted can be used. For example, these components can be formed of a plastic member such as an acrylic resin member.

[0046] Although an example was illustrated in the above embodiment in which the laser beam LB applied from the laser oscillator 82 is guided to the condenser lens 86b while being diffused by the polygon mirror 91, this configuration is not limitative. Instead, a reflection mirror arranged in a fixed position may be used instead of the polygon mirror 91. Furthermore, although an example was illustrated in the above embodiment in which the laser processing applied to the wafer 10 is ablation, the laser processing may be processing involving the formation of modified layers inside a workpiece (for example, the laser processing described in Japanese Patent JP 3 408 805 B2) or processing involving the formation of so-called shielding tunnels (for example, the processing described in Japanese Patent Laid-Open No. 2014-221 483 A).

[0047] 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 by the invention.

Claims

[1] Laser processing device (2) comprising: a holding unit (30) having a holding table (34) holding a plate-shaped workpiece; a laser beam application unit (6) which applies a laser beam (LB) to the workpiece held on the holding table (34) in order to machine the workpiece; and a liquid supply mechanism (40) arranged at an upper portion of the holding unit (30), wherein the liquid supply mechanism (40) comprises: a liquid chamber (41) having a transparent plate (42) positioned to form a gap between it and an upper surface of the workpiece held on the holding table (34), a roller (52) formed of a transparent member, which is arranged in a non-contact state at a position near the upper surface of the workpiece held on the holding table (34) inside the liquid chamber (41) and which generates a liquid flow on the workpiece, a roller rotation mechanism that rotates the roller (52), a liquid supply nozzle (43) which supplies the liquid into the gap from one side of the liquid chamber (41), and a liquid discharge nozzle (44) which discharges the liquid from the other side of the liquid chamber (41), and wherein the laser beam application unit (6) comprises a laser oscillator (82) which emits the laser beam (LB), and a condenser (86) which condenses the laser beam (LB) emitted from the laser oscillator (82) to apply the laser beam (LB) to the workpiece held on the holding table (34) through the transparent plate (42), the roller (52) and the liquid supplied to the gap. [2] The laser processing apparatus (2) according to claim 1, wherein the laser beam application unit (6) further comprises a scattering means that scatters the laser beam (LB) emitted from the laser oscillator (82).

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