Laser processing equipment

Abstract

To provide a laser beam machining apparatus which does not need to irradiate a work with laser beams again to remove debris after irradiating the work with laser beams to form a groove.SOLUTION: A laser oscillation mechanism 38 of laser beam irradiation means has a first mode to break growing debris, a second mode to suppress generation of molten debris, and a third mode to break the growing debris and suppress generation of the molten debris. The laser oscillation mechanism includes selecting means that selects any of the first mode, the second mode, and the third mode. A repetition frequency is set with a first group as one unit in a first mode, a repetition frequency is set with a second group as one unit in a second mode, and a repetition frequency is set with a third group as one unit in a third mode.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a laser processing apparatus including holding means for holding a workpiece, laser beam irradiation means for irradiating a laser beam onto the workpiece held by the holding means, and feeding means for relatively feeding the holding means and the laser beam irradiation means.

Background Art

[0002] A wafer on which a plurality of devices such as ICs and LSIs are partitioned by a division planned line and formed on the surface is divided into individual device chips by a laser processing apparatus, and each of the divided device chips is used in electric devices such as mobile phones and personal computers.

[0003] A laser processing apparatus includes holding means for holding a workpiece, laser beam irradiation means for irradiating a laser beam having a wavelength that is absorbable to the workpiece held by the holding means, and feeding means for relatively feeding the holding means and the laser beam irradiation means, and can divide a wafer into individual device chips with high precision.

[0004] However, there is a problem that molten debris generated by irradiation of a laser beam adheres to the device and deteriorates the quality of the device chip. In particular, in a wafer in which a copper wiring is laminated on a silicon substrate, there is a problem that debris in which copper and silicon are melted and mixed adheres to the device due to irradiation of a laser beam and deteriorates the quality of the device chip. This debris is debris that is likely to occur in a workpiece containing a semiconductor material and a metal material, and is sometimes called growth debris because it grows over time after irradiation of a laser beam.

[0005] Therefore, the applicant of the present application has developed a technique of irradiating a laser beam again to remove molten debris and growth debris generated on the outer periphery of a device chip (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-133437 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in the technology disclosed in Patent Document 1 mentioned above, it is necessary to irradiate the workpiece with a laser beam to remove molten debris and growing debris after irradiating it with a laser beam to form grooves, so there is room for improvement in productivity.

[0008] The object of the present invention is to provide a laser processing apparatus that eliminates the need to irradiate a workpiece with a laser beam again to remove debris after forming grooves by irradiating the workpiece with a laser beam. [Means for solving the problem]

[0009] According to the present invention, the following laser processing apparatus is provided that solves the above problems. That is, A laser processing apparatus comprising: a holding means for holding a workpiece; a laser beam irradiation means for irradiating a laser beam onto the workpiece held by the holding means; and a feeding means for relatively feeding the holding means and the laser beam irradiation means for processing, The laser beam irradiation means includes an oscillation mechanism that emits a pulsed laser beam, and a concentrator that focuses the pulsed laser beam emitted by the oscillation mechanism and irradiates the workpiece held by the holding means. The oscillation mechanism is, A first mode comprising: a first group setting unit that sets the number of pulsed laser beams to form a first group, which are pulsed laser beams that are irradiated onto a workpiece by pulsed laser beams, and the next pulsed laser beam is irradiated within the time until the plasma generated from the workpiece by the irradiation of the workpiece disappears, thereby continuing the plasma without interruption and destroying the growing debris; and a first time interval setting unit that sets the time until the heat generated by the irradiation of the pulsed laser beams of the first group dissipates as the time interval between the first group and adjacent first groups, and sets the time interval of the pulsed laser beams that constitute the first group; A second mode comprising: a second group setting unit that sets the number of pulsed laser beams to be irradiated until the time it takes for the molten debris to solidify, under the condition that the pulsed laser beams are irradiated onto the workpiece for a time shorter than the time it takes for molten debris to be generated by the irradiation of the workpiece with pulsed laser beams, and a second time interval setting unit that sets the time interval between the second group and adjacent second groups, and the time interval between the pulsed laser beams constituting the second group, The third mode includes: a third group setting unit that sets the number of pulsed laser beams to be irradiated until the time it takes for the molten debris to solidify, under the condition that the next pulsed laser beam is irradiated within a time shorter than the time it takes for molten debris to be generated by irradiating the workpiece with a pulsed laser beam, and within the time it takes for the plasma generated from the workpiece by the irradiation of the pulsed laser beam to disappear, thereby continuing the plasma without interruption and destroying the growing debris; and a third time interval setting unit that sets the time interval between the third group and adjacent third groups, and the time interval between the pulsed laser beams constituting the third group, which is the time it takes for the heat generated by the irradiation of the pulsed laser beams of the third group to dissipate. The system includes a selection means for selecting one of the first mode, the second mode, and the third mode, In the first mode, the repetition frequency is set with the first group as one unit. In the second mode, the repetition frequency is set with the second group as one unit. A laser processing apparatus is provided in which the repetition frequency is set with the third group as a unit in the third mode.

[0010] Preferably, the oscillation mechanism comprises a plurality of laser diodes that oscillate pulsed laser beams. In the first group setting unit, the first group is set by the pulsed laser beams oscillated by the plurality of laser diodes. In the second group setting unit, the second group is set by the pulsed laser beam oscillated by the plurality of laser diodes. In the third group setting unit, the third group is set by the pulsed laser beam oscillated by the plurality of laser diodes. In the first time interval setting unit, a pulse delay generator inputs signals to the plurality of laser diodes at desired time intervals, and also inputs signals so that the time it takes for the heat generated by the irradiation of the pulsed laser beam of the first group to dissipate becomes the time interval between the first group and adjacent first groups. In the second time interval setting unit, a pulse delay generator inputs signals to the plurality of laser diodes at desired time intervals, and also inputs signals so that the time it takes for the heat generated by the irradiation of the pulsed laser beam of the second group to dissipate becomes the time interval between the second group and adjacent second groups. In the third time interval setting unit, a pulse delay generator inputs signals to the plurality of laser diodes at desired time intervals, and also inputs signals so that the time it takes for the heat generated by the irradiation of the pulsed laser beams of the third group to dissipate becomes the time interval between the third group and adjacent third groups.

[0011] The oscillation mechanism comprises multiple oscillators that emit pulsed laser beams, In the first group setting unit, the first group is set by pulsed laser beams emitted by the plurality of oscillators. In the second group setting unit, the second group is set by the pulsed laser beams emitted by the plurality of oscillators. In the third group setting unit, the third group is set by the pulsed laser beams emitted by the plurality of oscillators. In the first time interval setting unit, a delay voltage converter is used to apply voltage to the plurality of oscillators at desired time intervals, and a voltage is applied such that the time required for the heat generated by the irradiation of the pulsed laser beam of the first group to dissipate is equal to the time interval between the first group and adjacent first groups. In the second time interval setting unit, a delay voltage is applied to the plurality of oscillators at desired time intervals using a delay voltage converter, and a voltage is applied so that the time it takes for the heat generated by the irradiation of the pulsed laser beam of the second group to dissipate becomes the time interval between the second group and adjacent second groups. In the third time interval setting unit, a delay voltage converter may be used to apply voltage to the plurality of oscillators at desired time intervals, and a voltage may also be applied such that the time required for the heat generated by the irradiation of the pulsed laser beam of the third group to dissipate is the time interval between the third group and adjacent third groups.

[0012] In the first mode, the repetition frequency is set by thinning out a predetermined number of the first groups from a plurality of the first groups that oscillate per second. In the second mode, the repetition frequency is set by thinning out a predetermined number of the second groups from a plurality of the second groups that oscillate per second. In this third mode, it is desirable to set the repetition frequency by thinning out a predetermined number of the third groups from a plurality of third groups that oscillate per second. [Effects of the Invention]

[0013] According to the present invention, by selecting the first mode, it is possible to simultaneously irradiate the workpiece with a laser beam for forming a groove and irradiate the workpiece with a laser beam for destroying growth debris. Further, by selecting the second mode, it is possible to simultaneously irradiate the workpiece with a laser beam for forming a groove and irradiate the workpiece with a laser beam for suppressing the generation of molten debris. Furthermore, by selecting the third mode, it is possible to simultaneously irradiate the workpiece with a laser beam for forming a groove and irradiate the workpiece with a laser beam for destroying growth debris and suppressing the generation of molten debris. Therefore, after irradiating the workpiece with a laser beam to form a groove, there is no need to irradiate the workpiece with a laser beam again to remove debris, so that productivity can be improved.

Brief Description of the Drawings

[0014] [Figure 1] Perspective view of a laser processing apparatus configured according to the present invention. [Figure 2] Block diagram of the laser processing apparatus shown in FIG. 1. [Figure 3] Schematic diagram of the oscillation mechanism shown in FIG. 2. [Figure 4] Schematic diagram of an oscillation mechanism of another form. <0​​​​​​​​​​​​​​​​​​​​​Hereinafter, preferred embodiments of the laser processing apparatus according to the present invention will be described with reference to the drawings.

[0016] (Laser processing device 2) The laser processing apparatus, shown as a whole in Figure 1 by reference numeral 2, includes a holding means 4 for holding a workpiece such as a wafer, a laser beam irradiation means 6 for irradiating the workpiece held by the holding means 4 with a laser beam, and a feeding means 8 for relative feeding of the holding means 4 and the laser beam irradiation means 6 for processing.

[0017] (Holding means 4) As shown in Figure 1, the holding means 4 includes an X-axis movable plate 12 supported on the upper surface of the base 10 so as to be movable in the X-axis direction, a Y-axis movable plate 14 supported on the upper surface of the X-axis movable plate 12 so as to be movable in the Y-axis direction, a support column 16 fixed to the upper surface of the Y-axis movable plate 14, and a cover plate 18 attached to the upper end of the support column 16. An elongated hole 18a extending in the Y-axis direction is formed in the cover plate 18, and a chuck table 20 extending upward through the elongated hole 18a is rotatably mounted on the upper end of the support column 16. Multiple clamps 22 are arranged around the periphery of the chuck table 20 at intervals in the circumferential direction.

[0018] The upper end of the chuck table 20 is provided with a porous, circular suction chuck 24 connected to a suction means (not shown). In the holding means 4, the suction means generates suction force on the upper surface of the suction chuck 24 to hold the workpiece in place. The chuck table 20 is also rotated vertically around its axis by a motor (not shown) built into the support column 16.

[0019] The X-axis direction is indicated by arrow X in Figure 1, and the Y-axis direction is indicated by arrow Y in Figure 1, both being perpendicular to the X-axis direction. The XY plane defined by the X-axis and Y-axis directions is essentially horizontal.

[0020] (Feeding means 8) The feeding means 8 in the illustrated embodiment includes an X-axis feeding means 26 for machining feeding of the chuck table 20 in the X-axis direction and a Y-axis feeding means 28 for indexing feeding of the chuck table 20 in the Y-axis direction.

[0021] The X-axis feed mechanism 26 includes a ball screw 30 connected to the X-axis movable plate 12 and extending in the X-axis direction, and a motor 32 that rotates the ball screw 30. The X-axis feed mechanism 26 converts the rotational motion of the motor 32 into linear motion using the ball screw 30 and transmits it to the X-axis movable plate 12, moving the X-axis movable plate 12 in the X-axis direction along the guide rail 10a on the base 10. As a result, the chuck table 20 is fed for machining in the X-axis direction.

[0022] The Y-axis feed mechanism 28 includes a ball screw 34 connected to the Y-axis movable plate 14 and extending in the Y-axis direction, and a motor 36 that rotates the ball screw 34. The Y-axis feed mechanism 28 converts the rotational motion of the motor 36 into linear motion using the ball screw 34 and transmits it to the Y-axis movable plate 14, moving the Y-axis movable plate 14 in the Y-axis direction along the guide rail 12a on the X-axis movable plate 12. As a result, the chuck table 20 is indexed and fed in the Y-axis direction.

[0023] (Laser beam irradiation means 6) Referring to Figures 1 and 2, the laser beam irradiation means 6 includes an oscillation mechanism 38 (see Figure 2) that emits a pulsed laser beam, and a concentrator 40 that focuses the pulsed laser beam emitted by the oscillation mechanism 38 and irradiates the workpiece held by the holding means 4.

[0024] As shown in Figure 1, the laser beam irradiation means 6 has a housing 42 that extends upward from the upper surface of the base 10 and then substantially horizontally. The oscillation mechanism 38 is housed inside the housing 42, and the light concentrator 40 is mounted on the lower front surface of the housing 42. An imaging means 44 for imaging a workpiece held by the holding means 4 is attached to the lower front surface of the housing 42, and a display means 45 for displaying the image captured by the imaging means 44 is provided on the upper surface of the housing 42.

[0025] (Oscillation mechanism 38) As shown in Figure 2, the oscillation mechanism 38 includes an oscillator 46 that emits a pulsed laser beam with a wavelength absorbed by the workpiece, a group setting unit 48, a time interval setting unit 50, and an attenuator 54 that adjusts the output of the pulsed laser beam emitted by the oscillator 46.

[0026] (Oscillator 46) Figure 2 shows a single box representing an oscillator 46, but the number of oscillators 46 provided in the oscillation mechanism 38 may be one or more. If only one oscillator 46 is provided, for example, as shown in Figure 3, that single oscillator 46 may be equipped with multiple laser diodes LD. Also, as shown in Figure 4, the oscillation mechanism 38 may be equipped with multiple oscillators 46. The laser medium is not limited to semiconductors, and other known mediums (for example, gases) may be used.

[0027] (Group setting section 48) As shown in Figure 2, the group setting unit 48 of the illustrated embodiment includes a first group setting unit 48a, a second group setting unit 48b, and a third group setting unit 48c.

[0028] (First group setting section 48a) The first group setting unit 48a sets the number of pulsed laser beams that irradiate the workpiece with a pulsed laser beam within the time it takes for the plasma generated from the workpiece by the irradiation of the workpiece to disappear, thereby continuing the plasma without interruption and destroying the growing debris, and defines this as the first group.

[0029] Plasma generated when a workpiece is irradiated with a pulsed laser beam generally appears about 10 ns after irradiation and disappears about 30 ns after irradiation. Therefore, an example of the "time until the plasma generated from the workpiece disappears due to irradiation with a pulsed laser beam" is the time from irradiation with the pulsed laser beam to about 30 ns.

[0030] Next, referring to Figure 5, we will explain how to maintain the plasma without interruption. Following the example above, with the time of irradiation of the workpiece with the first pulsed laser beam LB1 (1st pulse) as the reference (0 s), plasma P1 related to the 1st pulse is generated after 10 ns, and plasma P1 disappears after 30 ns.

[0031] In this case, for example, if the second pulsed laser beam LB2 (second pulse) is irradiated 15 ns after the first pulse (within the time it takes for plasma P1 from the first pulse to disappear, which is 30 ns), then plasma P2 from the second pulse will be generated 25 ns after the first pulse and will disappear 45 ns later. In other words, plasma P2 will be generated before plasma P1 disappears. Similarly, if the time interval between the second and third pulses is also 15 ns, then plasma P3 from the third pulsed laser beam LB3 (third pulse) will be generated before plasma P2 disappears.

[0032] In this way, by irradiating the workpiece with a pulsed laser beam and then irradiating it with the next pulsed laser beam within the time it takes for the plasma generated from the workpiece by the pulsed laser beam to disappear (in the above example, the time interval between pulsed laser beams is set to 15 ns), the plasma generated from the workpiece can be continuously supplied without interruption. This allows the growth debris generated by the pulsed laser beam irradiation to be destroyed by the plasma. Furthermore, for example, six pulses of pulsed laser beams are sufficient to destroy the growth debris.

[0033] Furthermore, the phrase "within the time until the plasma generated from the workpiece disappears due to irradiation with a pulsed laser beam" is not limited to 15 ns after irradiation with the pulsed laser beam.

[0034] In the example shown in Figure 3, the first group setting unit 48a can set the first group using pulsed laser beams oscillated by multiple (for example, six) laser diodes LD. Alternatively, the first group setting unit 48a may set the first group using pulsed laser beams oscillated by some of the laser diodes LD (for example, six out of ten) provided in the oscillator 46.

[0035] Furthermore, in the example shown in Figure 4, the first group setting unit 48a can also set the first group using pulsed laser beams emitted by multiple oscillators 46. Alternatively, the first group setting unit 48a may set the first group using pulsed laser beams emitted by some of the oscillators 46 provided in the oscillation mechanism 38.

[0036] In this specification, among the debris generated on a workpiece by irradiation with pulsed laser light, debris that grows over time (gradually becomes larger after generation) is referred to as growing debris, and debris that does not grow over time is referred to as molten debris.

[0037] (Second group setting section 48b) The second group setting unit 48b sets the number of pulsed laser beams to be irradiated until the molten debris solidifies, on the condition that the pulsed laser beam is irradiated onto the workpiece for a time shorter than the time it takes for molten debris to be generated by the irradiation of the pulsed laser beam, and sets this number as the second group.

[0038] The applicant has confirmed that the molten debris generated when a workpiece is irradiated with a pulsed laser beam occurs approximately 100 ns after irradiation and solidifies approximately 500 ns after irradiation.

[0039] Therefore, the second group setting unit 48b sets the number of pulsed laser beams to be irradiated within 500 ns after the first pulsed laser beam (1st pulse) is irradiated, under the condition that pulsed laser beams are irradiated at time intervals (pulse intervals) shorter than 100 ns, and sets this as the second group. By setting the number of pulsed laser beams in the second group in this way, the generation of molten debris can be suppressed when pulsed laser beams are irradiated onto the workpiece.

[0040] In the second group setting unit 48b, similar to the first group setting unit 48a, the second group can be set by pulsed laser beams oscillated by multiple laser diodes LD or multiple oscillators 46.

[0041] (Third group setting section 48c) The third group setting unit 48c sets the number of pulsed laser beams to be irradiated until the molten debris solidifies, under the condition that the number of pulsed laser beams to be irradiated until the time it takes for molten debris to be generated by the irradiation of the workpiece with pulsed laser beams is shorter than the time it takes for molten debris to be generated by the irradiation of the workpiece with pulsed laser beams, and that the next pulsed laser beam is irradiated within the time it takes for the plasma generated from the workpiece by the irradiation of pulsed laser beams to disappear, thereby continuing the plasma without interruption and destroying the growing debris, and sets this number as the third group.

[0042] As mentioned above, it is known that molten debris generated when a workpiece is irradiated with a pulsed laser beam occurs approximately 100 ns after irradiation, and plasma generated when a workpiece is irradiated with a pulsed laser beam disappears approximately 30 ns after irradiation.

[0043] Therefore, the phrase "a time shorter than the time it takes for molten debris to be generated by the irradiation of the workpiece with a pulsed laser beam, and within the time until the plasma generated from the workpiece by the irradiation of the pulsed laser beam disappears" can be defined as a time shorter than 100 ns from the irradiation of the pulsed laser beam, and within the time until approximately 30 ns has elapsed from the irradiation of the pulsed laser beam (for example, 15 ns).

[0044] Furthermore, as described above, the molten debris solidifies approximately 500 ns after the workpiece is irradiated with a pulsed laser beam. For this reason, the third group setting unit 48c sets the number of pulsed laser beams to be irradiated within 500 ns after the first pulsed laser beam (1st pulse) is irradiated, under the condition that the plasma generated by the irradiation of the workpiece with a pulsed laser beam is continuously supplied without interruption to destroy the growing debris, and sets this to the third group. Incidentally, in the case where the pulse interval is 15 ns as in the example above, the number of pulsed laser beams in the third group can be set to 34 (34 pulses).

[0045] In this way, by setting the number of pulsed laser beams in the third group, when pulsed laser beams are irradiated onto a workpiece, the growth debris generated by the irradiation of the pulsed laser beams can be destroyed by plasma, and the generation of molten debris can be suppressed.

[0046] In the third group setting unit 48c, similar to the first and second group setting units 48a and 48b, the third group can be set by pulsed laser beams oscillated by multiple laser diodes LD or multiple oscillators 46.

[0047] (Time interval setting unit 50) As shown in Figure 2, the time interval setting unit 50 of the illustrated embodiment includes a first time interval setting unit 50a, a second time interval setting unit 50b, and a third time interval setting unit 50c.

[0048] (First time interval setting unit 50a) The first time interval setting unit 50a sets the time required for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the first group to dissipate as the time interval between the first group and adjacent first groups, and also sets the time interval between the pulsed laser beams that constitute the first group.

[0049] It is known that in workpieces formed from semiconductor materials such as silicon, the heat generated in the workpiece by the pulsed laser beam dissipates approximately 5 μs after irradiation, and the temperature of the workpiece drops to almost the same level as before irradiation. For this reason, as shown in Figure 6, the first time interval setting unit 50a sets the time interval between the first group and the adjacent first group to 5 μs or more.

[0050] This allows the heat generated in the workpiece to dissipate between the irradiation of the first group of pulsed laser beams and the irradiation of the next group of pulsed laser beams, thus preventing a deterioration in device quality due to heat.

[0051] Furthermore, the first time interval setting unit 50a sets the time interval (pulse interval) of the pulsed laser beams constituting the first group. In the case shown in Figure 3, the first time interval setting unit 50a inputs signals to multiple laser diodes LD at desired time intervals (15 ns in the illustrated example) using the pulse delay generator 56, and also inputs signals such that the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the first group to dissipate is the time interval between the first group and the adjacent first group (5 μs in the above example). The pulse width of the signal input from the pulse delay generator 56 to each laser diode LD can be any value (for example, 10 ps).

[0052] On the other hand, in the case shown in Figure 4, the first time interval setting unit 50a applies voltage to a plurality of oscillators 46 at desired time intervals using a delay voltage converter 58, and applies voltage so that the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beam of the first group to cool down is equal to the time interval between the first group and the adjacent first group. The pulse width of the pulsed laser beam oscillated by each oscillator 46 by applying voltage from the delay voltage converter 58 can be any value.

[0053] As described above, when signals are input to multiple laser diodes LD by the pulse delay generator 56, or when a voltage is applied to multiple oscillators 46 by the delay voltage generator 58, pulsed laser beams are generated, as shown in Figure 6, with a predetermined time interval (5 μs in the illustrated example) between the first groups (for example, 6 pulses). In other words, the repetition frequency of the pulsed laser beams is set with the first group (6 pulses) as one unit. When the time interval between the first groups is 5 μs as in the illustrated example, the repetition frequency is 200 kHz.

[0054] The pulsed laser beams of the first group, each having a predetermined time interval, are then adjusted in output by the attenuator 54, focused by the light concentrator 40, and irradiated onto the workpiece. A light guide means, such as an optical fiber, is provided between the oscillator 46 and the attenuator 54, so that the pulsed laser beams of the first group are guided from the oscillator 46 to the attenuator 54.

[0055] The time interval between the first groups (5 μs in the illustrated example) may be set by the first time interval setting unit 50a as described above, or it may be set by a decimation unit 52 (see Figure 2) that decimates a predetermined number of first groups from the multiple first groups that the oscillator 46 oscillates in one second. The decimation unit 52 may be composed of an acoustic-optic element or an electro-optic element.

[0056] In other words, in the example shown in Figure 3, the first group is formed by pulsed laser beams emitted from multiple laser diodes LD, and in the example shown in Figure 4, it is formed by pulsed laser beams emitted from multiple oscillators 46. Then, in both the example shown in Figure 3 and Figure 4, with the first group as one unit, the decimation unit 52 decimates a predetermined number of first groups from the multiple first groups emitted per second by the multiple laser diodes LD or the multiple oscillators 46, thereby generating pulsed laser beams with a predetermined time interval between the first groups.

[0057] (Second time interval setting unit 50b) The second time interval setting unit 50b, similar to the first time interval setting unit 50a, sets the time required for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the second group to dissipate as the time interval between the second group and the adjacent second group (for example, 5 μs), and also sets the time interval between the pulsed laser beams constituting the second group (for example, 50 ns).

[0058] The second time interval setting unit 50b then inputs signals to multiple laser diodes LD at desired time intervals (50 ns in the above example) using the pulse delay generator 56, and also inputs a signal to the second group so that the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beam of the second group to dissipate is the time interval between the second group and the adjacent second group (5 μs in the above example). The pulse width of the signal input from the pulse delay generator 56 to each laser diode LD can be any value (for example, 10 ps).

[0059] Alternatively, the second time interval setting unit 50b applies a voltage to the multiple oscillators 46 at a desired time interval (50 ns in the above example) using the delay voltage unit 58, and applies a voltage such that the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beam of the second group to cool down is equal to the time interval between the second group and the adjacent second group. The pulse width of the pulsed laser beam oscillated by each oscillator 46 by applying a voltage from the delay voltage unit 58 can be any value.

[0060] When signals are input to multiple laser diodes LD by the pulse delay generator 56, or when voltages are applied to multiple oscillators 46 by the delay voltage generator 58, pulsed laser beams are generated, as shown in Figure 7, with a predetermined time interval (5 μs in the illustrated example) between second groups (for example, 11 pulses). In other words, the repetition frequency of the pulsed laser beams is set with the second group (11 pulses) as one unit. Note that the time interval between the second groups may be set by the decimation unit 52, similar to the time interval between the first groups.

[0061] Then, the pulsed laser beams from the second group, which have a predetermined time interval between them, have their output adjusted by the attenuator 54, and are then focused by the concentrator 40 and irradiated onto the workpiece.

[0062] (Third time interval setting section 50c) The third time interval setting unit 50c, similar to the first and second time interval setting units 50a and 50b, sets the time required for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the third group to dissipate as the time interval between the third group and adjacent third groups (for example, 5 μs), and also sets the time interval between the pulsed laser beams constituting the third group (for example, 15 ns).

[0063] The third time interval setting unit 50c then inputs signals to multiple laser diodes LD at desired time intervals (15 ns in the above example) using the pulse delay generator 56, and also inputs a signal to the third group so that the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the third group to dissipate is the time interval between the third group and the adjacent third group (5 μs in the above example). The pulse width of the signal input from the pulse delay generator 56 to each laser diode LD can be any value (for example, 10 ps).

[0064] Alternatively, the third time interval setting unit 50c applies a voltage to the multiple oscillators 46 at a desired time interval (15 ns in the above example) using the delay voltage unit 58, and applies a voltage such that the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the third group to cool down is equal to the time interval between the third group and the adjacent third group. The pulse width of the pulsed laser beams oscillated by each oscillator 46 can be any value as a result of the voltage applied from the delay voltage unit 58 to each oscillator 46.

[0065] When signals are input to multiple laser diodes LD by the pulse delay generator 56, or when voltages are applied to multiple oscillators 46 by the delay voltage generator 58, a pulsed laser beam is generated, as shown in Figure 8, in which a third group (for example, 34 pulses) has a predetermined time interval (5 μs in the illustrated example). In other words, the repetition frequency of the pulsed laser beam is set with the third group (34 pulses) as one unit. Note that the time interval between the third group may be set by the decimation unit 52, similar to the time interval between the first and second groups.

[0066] Then, the pulsed laser beams from the third group, which have a predetermined time interval between them, have their output adjusted by the attenuator 54, and are then focused by the concentrator 40 and irradiated onto the workpiece.

[0067] Referring to Figure 2, the oscillation mechanism 38 has three operating modes: a first mode for removing growing debris, a second mode for removing molten debris, and a third mode for removing both growing debris and molten debris. As shown by the dotted lines in Figure 2, the first mode is a mode comprising a first group setting unit 48a and a first time interval setting unit 50a. The second mode is a mode comprising a second group setting unit 48b and a second time interval setting unit 50b, and the third mode is a mode comprising a third group setting unit 48c and a third time interval setting unit 50c.

[0068] Furthermore, the oscillation mechanism 38 is equipped with a selection means (not shown) for selecting one of the first to third modes. The selection means, for example, displays a screen as shown in Figure 9 on the display means 45, allowing the operator to select one of the first to third modes, and then operates the oscillation mechanism 38 in the mode selected by the operator.

[0069] Furthermore, the oscillation mechanism 38 sets the repetition frequency in the first mode with the first group as one unit, in the second mode with the second group as one unit, and in the third mode with the third group as one unit.

[0070] (Workpiece) Figure 2 also shows a wafer W as a workpiece that can be processed by the laser processing apparatus 2. The disc-shaped wafer W can be formed from a suitable semiconductor material such as silicon. The surface Wa of the wafer W is divided into multiple rectangular regions by grid-like division lines L, and a device D such as an IC or LSI is formed in each of the multiple rectangular regions. Although not shown, the surface Wa of the wafer W is coated with a metal film such as copper.

[0071] In the illustrated embodiment, the back surface Wb of the wafer W is attached to an adhesive tape T fixed to an annular frame F, but the front surface Wa of the wafer W may also be attached to the adhesive tape T.

[0072] (Laser processing method) Next, we will explain a method for forming grooves in a wafer W, which is the workpiece, using the laser processing apparatus described above.

[0073] In the illustrated embodiment, first, the wafer W is held in place by suction on the upper surface of the chuck table 20 with its surface Wa facing upwards. The annular frame F is then fixed with a clamp 22. Next, the wafer W is imaged by the imaging means 44, and the planned division line L is aligned in the X-axis direction based on the image of the wafer W captured by the imaging means 44. The pulsed laser beam is then aimed at the planned division line L aligned in the X-axis direction, and the height of the focal point of the pulsed laser beam is adjusted to the surface Wa of the wafer W.

[0074] Next, while the chuck table 20 is fed in the X-axis direction, a pulsed laser beam LB with a wavelength absorbed by the wafer W is irradiated onto the wafer W from the focuser 40, and ablation is performed along the planned division line L. This forms a groove G (see Figure 2) that cuts along the planned division line L.

[0075] Next, the chuck table 20 is indexed and moved in the Y-axis direction relative to the light concentrator 40 by the amount of the spacing in the Y-axis direction of the division line L. Then, by alternately repeating the irradiation of the pulsed laser beam and indexing and moving the table, grooves G are formed on all of the division line L that are aligned in the X-axis direction.

[0076] Furthermore, by rotating the chuck table 20 by 90 degrees and repeatedly alternating between pulse laser beam irradiation and indexing feed, grooves G are formed on all of the division lines L that are perpendicular to the division lines L where grooves G were previously formed. By performing the groove formation process in this manner, grooves G are formed in a grid pattern along the grid-like division lines L. This makes it possible to divide the wafer W into individual device chips.

[0077] As described above, when forming grooves G in a workpiece such as a wafer W, the processing conditions are appropriately set according to the workpiece so that it is not necessary to irradiate it again with a laser beam to remove debris.

[0078] (First mode) In workpieces that generate a relatively large amount of growth debris when irradiated with a laser beam (for example, workpieces containing semiconductor and metallic materials), the first mode is selected to form grooves G while destroying the growth debris.

[0079] When the first mode is selected, the first group setting unit 48a sets the number of pulsed laser beams in the first group that will irradiate the workpiece with the next pulsed laser beam within the time it takes for the plasma generated from the workpiece by the irradiation of the workpiece with a pulsed laser beam to disappear, thereby continuing the plasma without interruption and destroying the growing debris. The first time interval setting unit 50a sets the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the first group to dissipate as the time interval between the first group and adjacent first groups, and also sets the time interval between the pulsed laser beams that make up the first group.

[0080] As mentioned above, the plasma generated when a workpiece is irradiated with a pulsed laser beam generally appears about 10 ns after the workpiece is irradiated with the pulsed laser beam and disappears about 30 ns after that time.

[0081] Therefore, the first time interval setting unit 50a sets the time interval between the first and second pulses to, for example, 15 ns. In this case, as shown in Figure 5, the plasma P2 related to the irradiation of the second pulse is generated 25 ns after the irradiation of the first pulse and disappears 45 ns later. In other words, plasma P2 is generated before plasma P1 disappears. Similarly, if the time interval between the second and third pulses is also set to 15 ns, plasma P3 related to the third pulsed laser beam LB3 (third pulse) is generated before plasma P2 disappears.

[0082] As a result, the plasma continues uninterrupted while the first group of pulsed laser beams is irradiating the workpiece. Therefore, the growth debris generated by the pulsed laser beam irradiation can be reliably destroyed by the plasma.

[0083] (Time interval between the first groups) In the first time interval setting unit 50a, in addition to setting the time interval of the pulsed laser beams constituting the first group (15 ns in the above example), the time required for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the first group to dissipate is set as the time interval between the first group and the adjacent first group. This is because if pulsed laser beams are continuously irradiated onto the workpiece, heat will accumulate in the workpiece, raising concerns about adverse effects on the device due to heat (deterioration of device quality).

[0084] As described above, in the case of workpieces formed from semiconductor materials such as silicon, it is known that after about 5 μs of time has elapsed since irradiation with a pulsed laser beam, the heat generated in the workpiece by the irradiation with the pulsed laser beam dissipates, and the temperature of the workpiece drops to almost the same level as before irradiation with the pulsed laser beam. For this reason, as shown in Figure 6, the first time interval setting unit 50a sets the time interval between the first group and the adjacent first group to 5 μs or more.

[0085] This allows the heat generated in the workpiece to dissipate between the irradiation of the first group of pulsed laser beams and the irradiation of the next group of pulsed laser beams, thus preventing adverse effects on the device caused by heat.

[0086] Furthermore, it is preferable that the number of pulsed laser beams constituting the first group is set by the first group setting unit 48a so that the heat generated by the irradiation of the pulsed laser beams of the first group is below a temperature that does not adversely affect the device.

[0087] As described above, once the number of pulsed laser beams in the first group (6 pulses), the time interval between the first groups (5 μs), and the time interval between the pulsed laser beams constituting the first group (15 ns) are set, the first time interval setting unit 50a uses the pulse delay generator 56 to input signals to multiple laser diodes LD at 15 ns intervals, and also inputs signals so that the time interval between the first groups becomes 5 μs (see Figure 3).

[0088] Alternatively, the first time interval setting unit 50a may apply voltage to the multiple oscillators 46 at 15 ns intervals using a delay voltage converter 58, and apply voltage so that the time interval between the first groups becomes 5 μs (see Figure 4).

[0089] Furthermore, the time interval between the first groups may be set to 5 μs by thinning out a predetermined number of groups from the multiple groups that oscillate per second using the thinning unit 52.

[0090] In other words, signals may be input to multiple laser diodes LD at 15 ns intervals via a pulse delay generator 56, or voltages may be applied to multiple oscillators 46 at 15 ns intervals via a delay voltage converter 58, while a predetermined number of groups are thinned out by a thinning unit 52 from multiple groups that oscillate per second, so that the time interval between the first groups becomes 5 μs. When the time interval between the first groups is 5 μs, the repetition frequency becomes 200 kHz.

[0091] In this way, by selecting the first mode and activating the oscillation mechanism 38, a pulsed laser beam is generated as shown in Figure 6, with a pulse count of 6 in the first group, a pulse interval of 15 ns, and a time interval of 5 μs between the first groups. After the output of this pulsed laser beam is appropriately adjusted by the attenuator 54, it is focused by the concentrator 40 and irradiated along the planned division line L of the workpiece. This makes it possible to form grooves G while destroying the growth debris generated by the irradiation of the pulsed laser beam with plasma.

[0092] The first mode can be carried out, for example, under the following processing conditions: Wavelength of pulsed laser beam: 355nm Average output: 30W Repetition frequency of the first group: 200kHz Configuration of the first group: 6 pulsed lasers Power density of the first group: 30 J / cm² 2 Pulse width of the first group: 75 ns (see Figure 6) Spot size for the first group: 10 μm in the X-axis direction, 50 μm in the Y-axis direction. Overlap rate between the first groups: 50% Feed rate: 1 m / s Plasma generation time: Generated 10 ns after laser irradiation (see Figure 5). Plasma annihilation time: Annihilation occurs 30 ns after laser irradiation (see Figure 5). Power density of one pulse: 5 J / cm² 2 Pulse width per pulse: 10 ps Pulse overlap rate: 99.8% Time interval between pulses: 15 ns (see Figure 6)

[0093] (Second mode) For workpieces that generate a relatively large amount of molten debris when irradiated with a laser beam, the second mode is selected to form grooves G while suppressing the generation of molten debris.

[0094] When the second mode is selected, the second group setting unit 48b sets the number of pulses of the second group of pulsed laser beams to be irradiated until the time when the molten debris solidifies, on condition that the pulsed laser beams are irradiated in a time shorter than the time when molten debris is generated by irradiating the workpiece with the pulsed laser beams. Further, the second time interval setting unit 50b sets the time until the heat generated in the workpiece by the irradiation of the pulsed laser beams of the second group cools down as the time interval between the second group and the second group adjacent to the second group, and also sets the time interval of the pulsed laser beams constituting the second group.

[0095] (Pulse interval and number of pulses) The time interval (pulse interval) of the pulsed laser beams constituting the second group and the number of pulses (number of pulses) of the pulsed laser beams of the second group will be described. When molten debris is generated at time t1 and the molten debris solidifies at time t2 after irradiating the workpiece with the pulsed laser beams, the second time interval setting unit 50b sets the time interval (pulse interval) t3 of the pulsed laser beams of the second group to t3 < t1, and the second group setting unit 48b sets the number of pulses (number of pulses) n of the pulsed laser beams of the second group to n = the integer part of (t2 / t3)+1.

[0096] As described above, it has been confirmed that the molten debris generated when irradiating the workpiece with the pulsed laser beams occurs after about 100 ns have elapsed since irradiating the workpiece with the pulsed laser beams, and solidifies after about 500 ns have elapsed.

[0097] Therefore, taking the time when the first pulsed laser beam (the first pulse) is irradiated to the workpiece as a reference (0 s), the time t1 when the molten debris is generated is set to 100 ns, and the time t2 when the molten debris solidifies is set to 500 ns. In this case, the second time interval setting unit 50b sets the time interval (pulse interval) t3 of the pulsed laser beams of the second group to, for example, 50 ns. However, t3 is not limited to 50 ns, and may be any time shorter than the time t1 = 100 ns when the molten debris is generated.

[0098] When the second time interval setting unit 50b sets the pulse interval t3 to 50ns, the second group setting unit 48b sets the number of pulsed laser beams (number of pulses) n for the second group, n = (t2 / t3) integer part + 1 = (500ns / 50ns) integer part + 1 = 10 + 1 =11 Set to this.

[0099] In the above case, (t2 / t3) is a combination of numbers that divide evenly, but for example, if the second time interval setting unit 50b is set to t3 = 60ns, the second group setting unit 48b will set the number of pulses n as follows: n = (t2 / t3) integer part + 1 = (500ns / 60ns) integer part + 1 = (8.333···)'s integer part + 1 =8+1 =9 Set to this.

[0100] Thus, the second group setting unit 48b sets the number of pulsed laser beams (n=11) of the second group to be irradiated from the time of the first pulsed laser beam (1st pulse) until the time of solidification of the molten debris (t2=500ns), under the condition that pulsed laser beams are irradiated at time intervals (t3=50ns) shorter than the time (t1=100ns) during which molten debris is generated by the irradiation of the workpiece with pulsed laser beams. This makes it possible to suppress the generation of molten debris when pulsed laser beams are irradiated onto the workpiece.

[0101] (Time interval between the second group) In the second time interval setting unit 50b, similar to the first time interval setting unit 50a, not only is the time interval of the pulsed laser beams constituting the second group set, but the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the second group to dissipate is set to the time interval between the second group and the adjacent second group (for example, 5 μs).

[0102] As described above, once the number of pulsed laser beams in the second group (n=11), the time interval between the second groups (5μs), and the time interval between the pulsed laser beams constituting the second group (t3=50ns) are set, the second time interval setting unit 50b uses the pulse delay generator 56 to input signals to multiple laser diodes LD at 50ns intervals, and also inputs signals so that the time interval between the second groups becomes 5μs.

[0103] Alternatively, the second time interval setting unit 50b may apply voltage to the multiple oscillators 46 at 50 ns intervals using a delay voltage converter 58, and apply voltage so that the time interval between the second groups becomes 5 μs.

[0104] Regarding the time interval between the second groups, similar to the time interval between the first groups in the first mode, a predetermined number of groups may be thinned out by the thinning unit 52 from the multiple groups oscillating per second, so that the time interval between the second groups becomes 5 μs. When the time interval between the second groups is 5 μs, the repetition frequency becomes 200 kHz.

[0105] In this way, by selecting the second mode and activating the oscillation mechanism 38, a pulsed laser beam is generated as shown in Figure 7, with the second group having n=11 pulses, a pulse interval t3=50ns, and a time interval of 5μs between the second groups. After the output of this pulsed laser beam is appropriately adjusted by the attenuator 54, it is focused by the concentrator 40 and irradiated along the planned division line L of the workpiece. This makes it possible to form grooves G while suppressing the generation of molten debris.

[0106] The second mode can be implemented, for example, under the following processing conditions: Wavelength of pulsed laser beam: 355nm Average output: 30W Repeat frequency of the second group: 200kHz Configuration of the second group: 11 pulsed lasers Power density of the second group: 30 J / cm² 2 Pulse width for the second group: 500 ns (see Figure 7) Spot size for the second group: 10 μm in the X-axis direction, 50 μm in the Y-axis direction. Overlap rate between the second group: 50% Feed rate: 1 m / s Time t1 for the generation of molten debris: Occurs 100 ns after laser irradiation. Solidification time t2 of molten debris: Solidification occurs 500 ns after laser irradiation. Time interval t3 between pulses: 50 ns (see Figure 7) Power density per pulse: 2.7 J / cm² 2 Pulse width per pulse: 10 ps Pulse overlap rate: 99.5%

[0107] (Third mode) In workpieces where both growth debris and molten debris are generated in large quantities when irradiated with a laser beam, a third mode is selected to destroy the growth debris and suppress the generation of molten debris while forming grooves G.

[0108] When the third mode is selected, the third group setting unit 48c sets the number of pulses of the third group of pulsed laser beams to be irradiated within the time until the molten debris solidifies, on condition that the time is shorter than the time during which molten debris is generated by irradiating the workpiece with the pulsed laser beam, and that the next pulsed laser beam is irradiated within the time until the plasma generated from the workpiece by the irradiation of the pulsed laser beam disappears, so as to continuously grow the plasma without interruption to break up the growth debris. Also, the third time interval setting unit 50c sets the time until the heat generated in the workpiece by the irradiation of the pulsed laser beams of the third group cools down as the time interval between the third group and the third group adjacent thereto, and sets the time interval of the pulsed laser beams constituting the third group.

[0109] (Pulse interval and number of pulses) The time interval (pulse interval) of the pulsed laser beams constituting the third group and the number of pulses (number of pulses) of the pulsed laser beams of the third group will be described. When molten debris is generated at time t1 after irradiating the workpiece with the pulsed laser beam and the molten debris solidifies at time t2, the third time interval setting unit 50c sets the time interval (pulse interval) T3 of the pulsed laser beams of the third group such that T3 < t1, and also sets it such that t4 < T3 < t5, where t4 is the time when plasma is generated from the workpiece and t5 is the time when the plasma disappears. Also, the third group setting unit 48c sets the number of pulses (number of pulses) N of the pulsed laser beams of the third group to N = integer part of (t2 / T3) + 1.

[0110] As described above, it has been confirmed that the molten debris generated when irradiating the workpiece with the pulsed laser beam occurs after about 100 ns have elapsed since irradiating the workpiece with the pulsed laser beam, and solidifies after about 500 ns have elapsed. Also, the plasma generated when irradiating the workpiece with the pulsed laser beam generally occurs after about 10 ns have elapsed and disappears after about 30 ns have elapsed.

[0111] Therefore, the time it takes for the first pulsed laser beam (1st pulse) to be irradiated onto the workpiece is taken as the reference (0 s). Time t1 = 100 ns for molten debris to form The time t2 for molten debris to solidify is 500 ns. Plasma generation time t4 = 10ns The time it takes for the plasma to disappear is t5 = 30ns. In this case, the third time interval setting unit 50c sets the time interval (pulse interval) T3 of the third group of pulsed laser beams to, for example, 15 ns. If T3 = 15 ns, T3 <t1(100ns) t4(10ns) <T3<t5(30ns) This will satisfy both conditions.

[0112] When the third time interval setting unit 50c sets the pulse interval T3 to 15ns, the third group setting unit 48c sets the number of pulsed laser beams (number of pulses) N for the third group, N = (t² / T³) integer part + 1 = (500ns / 15ns) integer part + 1 = (33.333...) integer part + 1 =33+1 =34 Set to this.

[0113] Thus, in the third group setting unit 48c, the number of pulsed laser beams (N=34) of the third group to be irradiated from the first pulsed laser beam (1st pulse) until the time when the molten debris solidifies (t2=500ns) is set, under the condition that the next pulsed laser beam is irradiated within a time shorter than the time when molten debris is generated by the irradiation of the workpiece with a pulsed laser beam (t1=100ns), and within the time until the plasma generated from the workpiece by the irradiation of the pulsed laser beam disappears (t5=30ns), thereby continuing the plasma without interruption and destroying the growing debris. This allows for the destruction of the growing debris generated by the irradiation of the pulsed laser beam by the plasma when the workpiece is irradiated with a pulsed laser beam, while suppressing the generation of molten debris.

[0114] (Time interval between the third group) In the third time interval setting unit 50c, similar to the first and second time interval setting units 50a and 50b, not only is the time interval of the pulsed laser beams constituting the third group set, but the time it takes for the heat generated in the workpiece by the irradiation of the pulsed laser beams of the third group to dissipate is set to the time interval between the third group and the adjacent third group (for example, 5 μs).

[0115] As described above, once the number of pulsed laser beams in the third group (N=34), the time interval between the third groups (5μs), and the time interval between the pulsed laser beams constituting the third group (T3=15ns) are set, the third time interval setting unit 50c uses the pulse delay generator 56 to input signals to multiple laser diodes LD at 15ns intervals, and also inputs signals so that the time interval between the third groups becomes 5μs.

[0116] Alternatively, the third time interval setting unit 50c may apply voltage to the multiple oscillators 46 at 15 ns intervals using a delay voltage converter 58, and apply voltage so that the time interval between the third groups becomes 5 μs.

[0117] Furthermore, the time interval between the third groups may be set to 5 μs by thinning out a predetermined number of groups from the multiple groups oscillating per second using the thinning unit 52, similar to the time interval between the first groups in the first mode. When the time interval between the third groups is 5 μs, the repetition frequency becomes 200 kHz.

[0118] In this way, by selecting the third mode and activating the oscillation mechanism 38, a pulsed laser beam is generated as shown in Figure 8, with a third group of pulses N=34, a pulse interval T3=15ns, and a time interval of 5μs between the third groups. After the output of this pulsed laser beam is appropriately adjusted by the attenuator 54, it is focused by the concentrator 40 and irradiated along the planned division line L of the workpiece. This makes it possible to destroy the growth debris generated by the irradiation of the pulsed laser beam with plasma, while suppressing the generation of molten debris and forming grooves G.

[0119] The third mode can be implemented, for example, under the following processing conditions: Wavelength of pulsed laser beam: 355nm Average output: 60W The repetition frequency of the third group is 200 kHz. Third group configuration: 34 pulsed lasers Power density of the third group: 60 J / cm² 2 Pulse width of the third group: 495 ns = T3 × (34 - 1) Third group spot size: 10 μm in the X-axis direction, 50 μm in the Y-axis direction Overlap rate between the third group: 50% Feed rate: 1 m / s Time t1 for the generation of molten debris: Occurs 100 ns after laser irradiation. Solidification time t2 of molten debris: Solidification occurs 500 ns after laser irradiation. Time interval T3 between pulses: 15 ns (see Figure 8) Plasma generation time t4: Generated 10 ns after laser irradiation (see Figure 5). Plasma annihilation time t5: Annihilation 30 ns after laser irradiation (see Figure 5). Power density per pulse: 1.7 J / cm² 2 Pulse width per pulse: 10 ps Pulse overlap rate: 99.8%

[0120] As described above, in the illustrated embodiment of the laser processing apparatus 2, by selecting the first mode, grooves G can be formed while destroying growth debris generated by pulsed laser irradiation with plasma. Furthermore, by selecting the second mode, grooves G can be formed while suppressing the generation of molten debris. Moreover, by selecting the third mode, grooves G can be formed while destroying growth debris with plasma and suppressing the generation of molten debris. Therefore, since it is not necessary to irradiate the workpiece with a laser beam again to remove debris after forming grooves by irradiating it with a laser beam, productivity can be improved. [Explanation of symbols]

[0121] 2: Laser processing equipment 4: Holding means 6: Laser beam irradiation means 8: Feeding method 38: Oscillation mechanism 40: Light concentrator 46: Oscillator 48: Group Setting Section 48a: First group setting section 48b: Second group setting section 48c: Third group setting section 50: Time interval setting section 50a: First time interval setting unit 50b: Second time interval setting section 50c: Third time interval setting section 56: Pulse delay generator 58: Delay voltage converter LD: Laser Diode

Claims

1. A laser processing apparatus comprising: a holding means for holding a workpiece; a laser beam irradiation means for irradiating a laser beam onto the workpiece held by the holding means; and a feeding means for relative feeding of the holding means and the laser beam irradiation means, The laser beam irradiation means includes an oscillation mechanism that emits a pulsed laser beam, and a concentrator that focuses the pulsed laser beam emitted by the oscillation mechanism and irradiates the workpiece held by the holding means. The oscillation mechanism is, A first mode comprising: a first group setting unit that sets the number of pulsed laser beams to form a first group, which are pulsed laser beams that are irradiated onto a workpiece by pulsed laser beams, and the next pulsed laser beam is irradiated within the time until the plasma generated from the workpiece by the irradiation of the workpiece disappears, thereby continuing the plasma without interruption and destroying the growing debris; and a first time interval setting unit that sets the time until the heat generated by the irradiation of the pulsed laser beams of the first group dissipates as the time interval between the first group and adjacent first groups, and sets the time interval of the pulsed laser beams that constitute the first group; A second mode comprising: a second group setting unit that sets the number of pulsed laser beams to be irradiated until the time it takes for the molten debris to solidify, under the condition that the pulsed laser beams are irradiated onto the workpiece for a time shorter than the time it takes for molten debris to be generated by the irradiation of the workpiece with pulsed laser beams, and a second time interval setting unit that sets the time interval between the second group and adjacent second groups, and the time interval between the pulsed laser beams constituting the second group, The third mode includes: a third group setting unit that sets the number of pulsed laser beams to be irradiated until the time it takes for the molten debris to solidify, under the condition that the next pulsed laser beam is irradiated within a time shorter than the time it takes for molten debris to be generated by irradiating the workpiece with a pulsed laser beam, and within the time it takes for the plasma generated from the workpiece by the irradiation of the pulsed laser beam to disappear, thereby continuing the plasma without interruption and destroying the growing debris; and a third time interval setting unit that sets the time interval between the third group and adjacent third groups, and the time interval between the pulsed laser beams constituting the third group, which is the time it takes for the heat generated by the irradiation of the pulsed laser beams of the third group to dissipate. The system includes a selection means for selecting one of the first mode, the second mode, and the third mode, In the first mode, the repetition frequency is set with the first group as one unit. In the second mode, the repetition frequency is set with the second group as one unit. A laser processing apparatus in which the repetition frequency is set with the third group as a single unit in the third mode.

2. The oscillation mechanism comprises multiple laser diodes that emit pulsed laser beams, In the first group setting unit, the first group is set by the pulsed laser beams oscillated by the plurality of laser diodes. In the second group setting unit, the second group is set by the pulsed laser beam oscillated by the plurality of laser diodes. In the third group setting unit, the third group is set by the pulsed laser beam oscillated by the plurality of laser diodes. In the first time interval setting unit, a pulse delay generator inputs signals to the plurality of laser diodes at desired time intervals, and also inputs signals so that the time it takes for the heat generated by the irradiation of the pulsed laser beam of the first group to dissipate becomes the time interval between the first group and adjacent first groups. In the second time interval setting unit, a pulse delay generator inputs signals to the plurality of laser diodes at desired time intervals, and also inputs signals so that the time it takes for the heat generated by the irradiation of the pulsed laser beam of the second group to dissipate becomes the time interval between the second group and adjacent second groups. The laser processing apparatus according to claim 1, wherein the third time interval setting unit inputs signals to the plurality of laser diodes at desired time intervals using a pulse delay generator, and inputs signals such that the time until the heat generated by the irradiation of the pulse laser beam of the third group dissipates becomes the time interval between the third group and adjacent third groups.

3. The oscillation mechanism comprises multiple oscillators that emit pulsed laser beams, In the first group setting unit, the first group is set by pulsed laser beams emitted by the plurality of oscillators. In the second group setting unit, the second group is set by the pulsed laser beams emitted by the plurality of oscillators. In the third group setting unit, the third group is set by the pulsed laser beams emitted by the plurality of oscillators. In the first time interval setting unit, a delay voltage converter is used to apply voltage to the plurality of oscillators at desired time intervals, and a voltage is applied such that the time required for the heat generated by the irradiation of the pulsed laser beam of the first group to dissipate is equal to the time interval between the first group and adjacent first groups. In the second time interval setting unit, a delay voltage is applied to the plurality of oscillators at desired time intervals using a delay voltage converter, and a voltage is applied so that the time it takes for the heat generated by the irradiation of the pulsed laser beam of the second group to dissipate becomes the time interval between the second group and adjacent second groups. The laser processing apparatus according to claim 1, wherein the third time interval setting unit applies a voltage to the plurality of oscillators at a desired time interval using a delay voltage converter, and applies a voltage such that the time it takes for the heat generated by the irradiation of the pulsed laser beam of the third group to dissipate is the time interval between the third group and the adjacent third group.

4. In the first mode, the repetition frequency is set by thinning out a predetermined number of the first groups from a plurality of the first groups that oscillate per second. In the second mode, the repetition frequency is set by thinning out a predetermined number of the second groups from a plurality of the second groups that oscillate per second. The laser processing apparatus according to claim 1, wherein in the third mode, the repetition frequency is set by thinning out a predetermined number of the third groups from a plurality of the third groups that oscillate per second.

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