Laser processing equipment

Abstract

[Problem] This invention provides a laser processing apparatus that, after forming a groove by irradiating a workpiece with a laser beam, eliminates the need for re-irradiation of the laser beam to remove debris. [Solution] The laser oscillation mechanism of the laser beam irradiation unit has: a first mode that destroys growing debris; a second mode that suppresses the generation of molten debris; and a third mode that destroys growing debris and suppresses the generation of molten debris. The laser oscillation mechanism includes a selection unit for selecting any one of the first, second, and third modes. In the first mode, a repetition frequency is set using a first group as a unit; in the second mode, a repetition frequency is set using a second group as a unit; and in the third mode, a repetition frequency is set using a third group as a unit.

Description

Technical Field

[0001] The present invention relates to a laser processing device. Prior Art

[0002] A wafer with multiple components such as ICs and LSIs divided by multiple intersecting dividing lines on the front is divided into individual component chips by a laser processing device. The divided component chips are used in electronic devices such as mobile phones and personal computers.

[0003] A laser processing device includes: a chuck table that holds a workpiece; a laser beam irradiation unit that irradiates a laser beam having a wavelength that is absorptive to the workpiece held on the chuck table; and a feed mechanism that feeds the chuck table and the laser beam irradiation unit relative to each other for processing. The laser processing device can divide a wafer into individual component chips with high precision.

[0004] However, there is a problem with molten debris generated by laser beam irradiation, which can adhere to components and degrade the quality of the wafer. Furthermore, in wafers with copper wiring layered on a silicon substrate, there is a problem with debris resulting from the melting and mixing of copper and silicon during laser irradiation, which can adhere to components and degrade the quality of the wafer. This debris is easily generated in workpieces composed of semiconductor and metal materials, and because it grows over time after laser beam irradiation, it is sometimes called growth debris.

[0005] Therefore, the applicant of this case has developed a technology for re-irradiating a laser beam to remove molten debris and grown debris generated on the periphery of a device wafer (for example, see Patent Document 1). [Conventional technical literature] [Patent Document]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-133437 Summary of the Invention

[0007] [Problems to be Solved by the Invention] However, in the technology disclosed in Patent Document 1, after irradiating the workpiece with a laser beam for forming a groove, it is necessary to irradiate the workpiece with a laser beam for removing molten chips and growing chips, so there is room for improvement in productivity.

[0008] Therefore, an object of the present invention is to provide a laser processing device that, after irradiating a laser beam onto a workpiece to form a groove, does not require re-irradiation of the laser beam to remove debris.

[0009] [Technical means to solve the problem] According to the present invention, a laser processing device is provided, which comprises: a chuck table that holds a workpiece; a laser beam irradiation unit that irradiates a pulsed laser beam to the workpiece held on the chuck table; and a feeding mechanism that performs processing feeding on the chuck table and the laser beam irradiation unit relative to each other, and the laser beam irradiation unit includes: a laser oscillating mechanism that emits a pulsed laser beam; and a condenser that condenses the pulsed laser beam emitted by the laser oscillating mechanism and irradiates the workpiece held on the chuck table, and the laser oscillating mechanism includes a first mode, a second mode and a third mode, the first mode having: a first group setting portion that is set in the state where the workpiece is irradiated with a pulsed laser beam. The first mode comprises: irradiating a pulse laser beam and irradiating a next pulse laser beam within a time period from when the plasma generated by the workpiece disappears so that the plasma continues uninterruptedly to destroy the number of pulse laser beams that grow debris, and setting the number of pulse laser beams to be a first group; and a first time interval setting unit, which sets the time period until the heat generated by the irradiation of the pulse laser beam of the first group cools down as the time interval between the first group and the adjacent first group, and sets the time interval of the pulse laser beams constituting the first group. The second mode comprises: a second group setting unit, which sets the time period until the molten debris is solidified by irradiating the pulse laser beam for a time period shorter than the time period when the molten debris is generated by irradiating the pulse laser beam to the workpiece as a condition. The number of pulse laser beams irradiated until the time is set as the second group; and a second time interval setting unit, which sets the time until the heat generated by the irradiation of the pulse laser beam of the second group is cooled as the time interval between the second group and the adjacent second group, and sets the time interval of the pulse laser beams constituting the second group. The third mode has: a third group setting unit, which irradiates the next pulse laser beam within a time shorter than the time when the molten debris is generated by irradiating the pulse laser beam to the workpiece and within a time until the plasma generated from the workpiece by irradiating the pulse laser beam disappears, so that the plasma continues to destroy the growing debris without interruption, and sets it as a condition until the molten debris solidifies The laser oscillator mechanism further includes a selection unit that selects any one of the first mode, the second mode, and the third mode, wherein a repetition frequency is set using the first group as a unit in the first mode, the second group as a unit in the second mode, and the third group as a unit in the third mode.

[0010] Preferably, the laser oscillator mechanism includes a plurality of laser diodes that emit pulsed laser beams. In the first group setting section, the first group is set by the pulsed laser beams emitted by the plurality of laser diodes. In the second group setting section, the second group is set by the pulsed laser beams emitted by the plurality of laser diodes. In the third group setting section, the third group is set by the pulsed laser beams emitted by the plurality of laser diodes. In the first time interval setting section, a pulse delay generator is used to input signals to the plurality of laser diodes at desired time intervals, and the time until heat generated by irradiation with the pulsed laser beam of the first group is cooled becomes the time interval between the first group and the corresponding group. The first group of adjacent laser diodes is input with a signal at a desired time interval. The second time interval setting unit uses the pulse delay generator to input a signal to the plurality of laser diodes at a desired time interval, and the signal is input so that the time required for heat generated by irradiation with the pulse laser beam of the second group to cool down becomes the time interval between the second group and the adjacent second group. The third time interval setting unit uses the pulse delay generator to input a signal to the plurality of laser diodes at a desired time interval, and the signal is input so that the time required for heat generated by irradiation with the pulse laser beam of the third group to cool down becomes the time interval between the third group and the adjacent third group.

[0011] Preferably, the laser oscillator mechanism includes a plurality of laser oscillators that emit pulsed laser beams. In the first group setting section, the first group is set by the pulsed laser beams emitted by the plurality of laser oscillators. In the second group setting section, the second group is set by the pulsed laser beams emitted by the plurality of laser oscillators. In the third group setting section, the third group is set by the pulsed laser beams emitted by the plurality of laser oscillators. In the first time interval setting section, a voltage is applied to the plurality of laser oscillators at a desired time interval by a delay voltage device, and the time until heat generated by irradiation with the pulsed laser beams of the first group is cooled becomes the time interval of the first group. The voltage is applied to the plurality of laser oscillators at a desired time interval with the adjacent first group by a delay voltage device in the second time interval setting unit, and the voltage is applied so that the time required for heat generated by irradiation of the pulsed laser beam of the second group to cool down becomes the time interval between the second group and the adjacent second group. The voltage is applied to the plurality of laser oscillators at a desired time interval with the delay voltage device in the third time interval setting unit, and the voltage is applied so that the time required for heat generated by irradiation of the pulsed laser beam of the third group to cool down becomes the time interval between the third group and the adjacent third group.

[0012] Preferably, in the first mode, the repetition frequency is set by eliminating a predetermined number of the first groups from the plurality of the first groups emitted during one second, in the second mode, the repetition frequency is set by eliminating a predetermined number of the second groups from the plurality of the second groups emitted during one second, and in the third mode, the repetition frequency is set by eliminating a predetermined number of the third groups from the plurality of the third groups emitted during one second.

[0013] [Effects of the invention] 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 a laser beam for destroying growing debris. Furthermore, by selecting the second mode, it is possible to simultaneously irradiate the workpiece with a laser beam for forming a groove and 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 a laser beam for destroying growing 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 re-irradiate the workpiece with a laser beam to remove debris, thereby improving productivity. Simple diagram description

[0014] FIG1 is a perspective view of a laser processing device according to an embodiment of the present invention. FIG2 is a block diagram of the laser processing device shown in FIG1 . FIG3 is a schematic diagram of the laser oscillation mechanism shown in FIG2. FIG4 is a schematic diagram of another form of a laser oscillation mechanism. FIG. 5 is a schematic diagram showing the generation time and disappearance time of plasma generated by irradiation with a pulsed laser beam. FIG6 is a schematic diagram of a pulsed laser beam irradiated onto a workpiece in the first mode. FIG. 7 is a schematic diagram of a pulsed laser beam irradiated onto a workpiece in the second mode. FIG8 is a schematic diagram of a pulse laser beam irradiated onto a workpiece in the third mode. FIG. 9 is a schematic diagram of a display unit displaying a screen prompting selection of any one of the first, second, and third modes. Implementation Method

[0015] Hereinafter, a laser processing device according to an embodiment of the present invention will be described with reference to the drawings.

[0016] The laser processing device represented by symbol 2 in Figure 1 includes: a holding unit 4, which holds a workpiece such as a wafer; a laser beam irradiation unit 6, which irradiates the laser beam to the workpiece held in the holding unit 4; and a feeding mechanism 8, which feeds the holding unit 4 and the laser beam irradiation unit 6 relative to each other for processing.

[0017] As shown in Figure 1, the holding unit 4 includes an X-axis movable plate 12, which is supported on the upper surface of a base 10 for free movement in the X-axis direction; a Y-axis movable plate 14, which is supported on the upper surface of the X-axis movable plate 12 for free movement 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 mounted on the upper end of the support column 16. The cover plate 18 has an elongated hole 18a extending in the Y-axis direction. A chuck table 20, which extends upward through the elongated hole 18a, is rotatably mounted on the upper end of the support column 16. A plurality of clamps 22 are arranged circumferentially around the periphery of the chuck table 20 at intervals.

[0018] A porous, circular suction chuck 24 connected to a suction mechanism (not shown) is mounted on the top of the chuck table 20. In the holding unit 4, the suction mechanism generates a suction force on the top surface of the suction chuck 24, thereby holding the workpiece. Furthermore, the chuck table 20 is rotated about its vertical axis by a motor (not shown) built into the support column 16.

[0019] In addition, the X-axis direction is the direction indicated by arrow X in Figure 1, and the Y-axis direction is the direction indicated by arrow Y in Figure 1 and is a direction perpendicular to the X-axis direction. The XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

[0020] The feed mechanism 8 of this embodiment includes: an X-axis feed mechanism 26 that feeds the chuck table 20 for processing in the X-axis direction; and a Y-axis feed mechanism 28 that feeds the chuck table 20 for indexing 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 via the ball screw 30 and transmits it to the X-axis movable plate 12, causing the X-axis movable plate 12 to move in the X-axis direction along the guide rail 10a on the base 10. This allows the chuck table 20 to be fed in the X-axis direction during machining.

[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 via the ball screw 34 and transmits it to the Y-axis movable plate 14, causing the Y-axis movable plate 14 to move in the Y-axis direction along the guide rail 12a on the X-axis movable plate 12. This indexes and feeds the chuck table 20 in the Y-axis direction.

[0023] 1 and 2 , the laser beam irradiation unit 6 includes: a laser oscillator mechanism 38 (refer to FIG. 2 ), which emits a pulsed laser beam; and a condenser 40, which focuses the pulsed laser beam emitted by the laser oscillator mechanism 38 and irradiates the workpiece held in the holding unit 4.

[0024] As shown in Figure 1, the laser beam irradiation unit 6 includes a housing 42 that extends upward from the upper surface of the base 10 and then extends substantially horizontally. The laser oscillator 38 is housed within the housing 42, and the condenser 40 is mounted on the front lower surface of the housing 42. Furthermore, a camera unit 44 is attached to the front lower surface of the housing 42 for capturing images of the workpiece held by the holding unit 4. A display unit 45 is provided on the upper surface of the housing 42 for displaying images captured by the camera unit 44.

[0025] As shown in FIG. 2 , the laser oscillator mechanism 38 includes: a laser oscillator 46 that emits a pulsed laser beam having a wavelength that is absorbent to 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 laser oscillator 46.

[0026] Figure 2 shows a single block representing a laser oscillator 46. However, the number of laser oscillators 46 provided in the laser oscillator mechanism 38 may be one or more. In the case of a single laser oscillator 46, for example, as shown in Figure 3, a single laser oscillator 46 may include multiple laser diodes LD. Furthermore, as shown in Figure 4, multiple laser oscillators 46 may also be provided in the laser oscillator mechanism 38. The laser medium is not limited to semiconductors; other conventional media (such as gases) may also be used.

[0027] As shown in FIG. 2 , the group setting unit 48 of this embodiment includes a first group setting unit 48 a , a second group setting unit 48 b , and a third group setting unit 48 c .

[0028] The first group setting unit 48a sets the number of pulse laser beams that are used to irradiate the workpiece with the next pulse laser beam within the time until the plasma generated from the workpiece disappears due to the irradiation of the pulse laser beam so that the plasma continues uninterruptedly and destroys the growing debris, and sets it as the first group.

[0029] The plasma generated when a pulsed laser beam is irradiated on a workpiece generally occurs approximately 10 nanoseconds after the pulsed laser beam is irradiated, and disappears approximately 30 nanoseconds after the pulsed laser beam is irradiated. Therefore, an example of the time period from the time the plasma generated in the workpiece due to irradiation with the pulsed laser beam disappears is the time period of approximately 30 nanoseconds from the time the pulsed laser beam is irradiated.

[0030] Next, the method of maintaining plasma without interruption will be described with reference to Figure 5. In the above example, taking the time when the initial pulsed laser beam LB1 (the first pulse) irradiates the workpiece as the reference (0s), plasma P1 associated with the first pulse is generated 10ns later and disappears 30ns later.

[0031] In this case, for example, if the second pulse laser beam LB2 (second pulse) is applied 15 ns after the disappearance of plasma P1 associated with the first pulse (30 ns), plasma P2 associated with the second pulse will be generated 25 ns after the first pulse and disappear 45 ns after the first pulse. 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 set to 15 ns, plasma P3 associated with the third pulse laser beam LB3 (third pulse) will be generated before plasma P2 disappears.

[0032] In this way, by irradiating the workpiece with the next pulsed laser beam (in the above example, the interval between pulsed laser beams is set to 15ns) within the time it takes for the plasma generated from the workpiece to disappear, the plasma generated from the workpiece can be continuously generated. This allows the plasma to destroy the growing debris generated by the pulsed laser beam. Furthermore, the number of pulsed laser beams used to destroy the growing debris can be, for example, six (six pulses).

[0033] In addition, the time from the time when the plasma generated from the workpiece disappears by irradiating the workpiece with a pulsed laser beam is not limited to 15 ns after irradiation with the pulsed laser beam.

[0034] In the example shown in FIG3 , the first group setting unit 48 a can set the first group using pulsed laser beams emitted by a plurality (e.g., six) of the laser diodes LD. Alternatively, the first group setting unit 48 a can set the first group using pulsed laser beams emitted by a portion (e.g., six out of ten) of the laser diodes LD included in the laser oscillator 46.

[0035] Furthermore, in the example shown in FIG4 , the first group setting unit 48 a may also set the first group using the pulsed laser beams emitted by the plurality of laser oscillators 46. Furthermore, the first group setting unit 48 a may also set the first group using the pulsed laser beams emitted by the laser oscillator 46 provided as part of the laser oscillator mechanism 38.

[0036] In this specification, among the chips generated in the workpiece by irradiation with a pulsed laser beam, chips that grow over time (gradually become larger after generation) are referred to as growing chips, while chips that do not grow over time are referred to as molten chips.

[0037] The second group setting unit 48b sets the number of pulse laser beams to be irradiated until the molten chips are solidified under the condition that the pulse laser beam is irradiated for a time shorter than the time when molten chips are generated by irradiating the workpiece with the pulse laser beam, and sets it as the second group.

[0038] The applicant has confirmed that the molten chips generated when the pulsed laser beam is irradiated onto the workpiece are produced approximately 100 ns after the pulsed laser beam is irradiated onto the workpiece, and solidify approximately 500 ns after the pulsed laser beam is irradiated onto the workpiece.

[0039] Therefore, in the second group setting section 48b, the number of pulsed laser beams to be irradiated from the initial pulsed laser beam (first pulse) until 500 ns has passed is set, using the pulsed laser beam irradiation time interval (pulse interval) shorter than 100 ns as a condition. This is used to create the second group. By setting the number of pulsed laser beams in the second group, the generation of molten chips can be suppressed when the workpiece is irradiated with the pulsed laser beam.

[0040] In the second group setting unit 48b, similarly to the first group setting unit 48a, the second group can be set by using the pulsed laser beams emitted from the plurality of laser diodes LD or the plurality of laser oscillators 46.

[0041] The third group setting unit 48c sets the number of pulse laser beams to be irradiated until the molten debris is solidified, under the condition that the next pulse laser beam is irradiated within a time shorter than the time when molten debris is generated by irradiating the workpiece with the pulse laser beam and within the time when the plasma generated from the workpiece due to irradiating the pulse laser beam disappears so that the plasma continues uninterruptedly to destroy the growing debris, and sets it as the third group.

[0042] As mentioned above, it is known that the molten debris generated when the pulsed laser beam is irradiated onto the workpiece is produced about 100ns from the irradiation of the pulsed laser beam, and the plasma generated when the pulsed laser beam is irradiated onto the workpiece disappears about 30ns from the irradiation of the pulsed laser beam.

[0043] Therefore, the above-mentioned "within a time shorter than the time when molten debris is generated by irradiating the workpiece with the pulse laser beam and within a time until plasma generated from the workpiece due to irradiation with the pulse laser beam disappears" can refer to a time shorter than 100ns from irradiation with the pulse laser beam and a time until approximately 30ns has passed from irradiation with the pulse laser beam (for example, 15ns).

[0044] As mentioned above, the molten chips solidify approximately 500 ns after the pulsed laser beam is irradiated onto the workpiece. Therefore, in the third group setting section 48c, the number of pulsed laser beams irradiated from the initial pulsed laser beam (first pulse) until 500 ns has passed is set, with the condition that the plasma generated by irradiating the workpiece with the pulsed laser beam continues uninterrupted, thus destroying the workpiece into growing chips. This is then defined as the third group. Incidentally, if 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 pulse laser beams in the third group, when the pulse laser beam is irradiated to the workpiece, the growing debris generated by the irradiation of the pulse laser beam can be destroyed by plasma, and the generation of molten debris can be suppressed.

[0046] Even in the third group setting unit 48c, similarly to the first and second group setting units 48a and 48b, the third group can be set by the pulse laser beams emitted by the plurality of laser diodes LD or the plurality of laser oscillators 46.

[0047] As shown in FIG. 2 , the time interval setting unit 50 of this embodiment includes a first time interval setting unit 50 a , a second time interval setting unit 50 b , and a third time interval setting unit 50 c .

[0048] The first time interval setting unit 50a sets the time interval between the first group and the adjacent first group, and sets the time interval of the pulse laser beams constituting the first group.

[0049] It is known that in workpieces made of semiconductor materials such as silicon, the heat generated by the pulsed laser beam cools down after approximately 5 μs has passed since irradiation, and the workpiece temperature drops to approximately the same level as before irradiation. Therefore, as shown in FIG6 , the first time interval setting unit 50a sets the time interval between the first group and the adjacent first group to be at least 5 μs.

[0050] Thus, after the first group of pulse laser beams is irradiated onto the workpiece, the heat generated in the workpiece will cool down before the next first group of pulse laser beams is irradiated, thereby preventing the quality of the component from being degraded 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 scenario shown in FIG3 , the first time interval setting unit 50a then inputs a signal to the plurality of laser diodes LD at a desired time interval (15 ns in the illustrated example) via the pulse delay generator 56. The signal is input so that the time required for the workpiece to cool down after the heat generated by the first group of pulsed laser beams is equal to 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 (e.g., 10 ps).

[0052] On the other hand, in the case shown in FIG4 , the first time interval setting unit 50a applies voltage to the plurality of laser oscillators 46 at desired time intervals via a delay voltage device 58. The voltage is applied so that the time required for the workpiece to cool from the heat generated by irradiation with the first group of pulsed laser beams becomes the time interval between the first group and the adjacent first group. By applying voltage from the delay voltage device 58 to each laser oscillator 46, the pulse width of the pulsed laser beam emitted by each laser oscillator 46 can be set to any value.

[0053] As described above, when a signal is input to multiple laser diodes LD via pulse delay generator 56, or when a voltage is applied to multiple laser oscillators 46 via delay voltage generator 58, a first group (e.g., six pulses) of pulsed laser beams is generated, as shown in FIG6 , with a predetermined time interval (5 μs in the illustrated example) between each pulse. In other words, the repetition frequency of the pulsed laser beam is set using the first group (six pulses) as a unit. When the time interval between the first group pulses is 5 μs, as in the illustrated example, the repetition frequency is 200 kHz.

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

[0055] The time interval between the first groups (5 μs in the illustrated example) can be set by the first time interval setting unit 50a as described above, but can also be set by a rejection unit 52 (see FIG. 2 ) that rejects a predetermined number of first groups from the plurality of first groups emitted by the laser oscillator 46 within one second. The rejection unit 52 can be formed by an acousto-optic element or a photoelectric element.

[0056] That is, in the example shown in FIG3 , the first group is set by pulsed laser beams emitted from multiple laser diodes LD, and in the example shown in FIG4 , the first group is set by pulsed laser beams emitted from multiple laser oscillators 46. Then, in both the examples shown in FIG3 and FIG4 , the first group is treated as a unit, and the culling unit 52 culls a predetermined number of first groups from the plurality of first groups emitted by the plurality of laser diodes LD or the plurality of laser oscillators 46 during one second, thereby generating pulsed laser beams having predetermined time intervals between the first groups.

[0057] Similar to the first time interval setting unit 50a, the second time interval setting unit 50b sets the time from the heat generated in the workpiece due to the irradiation of the second group's pulse laser beam to the cooling time as the time interval between the second group and the adjacent second group (for example, 5μs), and sets the time interval of the pulse laser beams constituting the second group (for example, 50ns).

[0058] The second time interval setting unit 50b then inputs a signal to the plurality of laser diodes LD at a desired time interval (50 ns in the above example) via the pulse delay generator 56. The signal is input so that the time required for the workpiece to cool down after the heat generated by the second group of pulsed laser beams is equal to the time interval between the adjacent second groups (5 μs in the above example). The pulse width of the signal input to each laser diode LD from the pulse delay generator 56 can be any value (e.g., 10 ps).

[0059] Alternatively, the second time interval setting unit 50b applies voltage to the plurality of laser oscillators 46 at a desired time interval (50 ns in the above example) via the delay voltage device 58. The voltage is applied so that the time required for the workpiece to cool from the heat generated by the second group of pulsed laser beams is the time interval between the second group and the adjacent second group. By applying voltage from the delay voltage device 58 to each laser oscillator 46, the pulse width of the pulsed laser beam emitted by each laser oscillator 46 can be set to any value.

[0060] When a signal is input to multiple laser diodes LD via pulse delay generator 56, or a voltage is applied to multiple laser oscillators 46 via delay voltage generator 58, a second group (e.g., 11 pulses) of pulsed laser beams is generated, as shown in Figure 7, with a predetermined time interval (5 μs in the illustrated example). In other words, the repetition frequency of the pulsed laser beam is set using the second group (11 pulses) as a unit. Furthermore, the time intervals between the second groups can be set by the elimination unit 52, similar to the time intervals between the first groups.

[0061] Then, the second group of pulse laser beams having a predetermined time interval therebetween are adjusted in output by the attenuator 54, focused by the condenser 40, and irradiated onto the workpiece.

[0062] Similar to the first and second time interval setting units 50a and 50b, the third time interval setting unit 50c sets the time from the heat generated in the workpiece due to the irradiation of the third group of pulse laser beams to the cooling of the heat as the time interval between the third group and the adjacent third group (for example, 5μs), and sets the time interval of the pulse laser beams constituting the third group (for example, 15ns).

[0063] The third time interval setting unit 50c then inputs a signal to the plurality of laser diodes LD at a desired time interval (15 ns in the above example) via the pulse delay generator 56. The signal is input so that the time required for the workpiece to cool down after the heat generated by the third group of pulsed laser beams is equal to 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 to each laser diode LD from the pulse delay generator 56 can be any value (e.g., 10 ps).

[0064] Alternatively, the third time interval setting unit 50c applies voltage to the plurality of laser oscillators 46 at a desired time interval (15 ns in the above example) via the delay voltage device 58. The voltage is applied so that the time required for the workpiece to cool from the heat generated by the third group of pulsed laser beams is the time interval between the third group and the adjacent third group. By applying voltage from the delay voltage device 58 to each laser oscillator 46, the pulse width of the pulsed laser beam emitted by each laser oscillator 46 can be set to any value.

[0065] When a signal is input to multiple laser diodes LD via pulse delay generator 56, or a voltage is applied to multiple laser oscillators 46 via delay voltage generator 58, a third group (e.g., 34 pulses) of pulsed laser beams is generated, as shown in Figure 8, with a predetermined time interval (5 μs in the illustrated example). In other words, the repetition frequency of the pulsed laser beam is set using the third group (34 pulses) as a unit. Furthermore, the time intervals between the third group can be set by the elimination unit 52, similar to the time intervals between the first and second groups.

[0066] Then, the third group of pulse laser beams having a predetermined time interval therebetween are adjusted in output by the attenuator 54, focused by the condenser 40, and irradiated onto the workpiece.

[0067] Referring to FIG. 2 , the laser oscillator 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 dashed lines in FIG. 2 , the first mode comprises a first group setting unit 48 a and a first time interval setting unit 50 a. Furthermore, the second mode comprises a second group setting unit 48 b and a second time interval setting unit 50 b. The third mode comprises a third group setting unit 48 c and a third time interval setting unit 50 c.

[0068] Furthermore, the laser oscillator mechanism 38 includes a selection means (not shown) for selecting one of the first through third modes. The selection means, for example, displays a screen such as that shown in FIG. 9 on the display unit 45, allowing the operator to select one of the first through third modes, and the laser oscillator mechanism 38 operates in the mode selected by the operator.

[0069] Then, the laser oscillator mechanism 38 sets the repetition frequency using the first group as a unit in the first mode, sets the repetition frequency using the second group as a unit in the second mode, and sets the repetition frequency using the third group as a unit in the third mode.

[0070] FIG2 also shows a wafer W, a workpiece that can be processed by the laser processing apparatus 2. The circular wafer W can be formed from a suitable semiconductor material, such as silicon. The front surface Wa of the wafer W is divided into a plurality of rectangular regions by grid-like dividing lines L, each of which contains a component D, such as an IC or LSI. Although not shown, the front surface Wa of the wafer W is coated with a metal film, such as copper.

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

[0072] Next, a method of forming grooves in a wafer W as a workpiece using the laser processing apparatus described above will be described.

[0073] In this embodiment, the wafer W is first positioned with its front surface Wa facing upward, and the upper surface of the chuck table 20 suction-holds the wafer W. Furthermore, the annular frame F is secured by the clamp 22. Next, the wafer W is imaged by the imaging unit 44. Based on the image of the wafer W captured by the imaging unit 44, the planned dividing line L, which extends in the first direction, is aligned with the X-axis. Furthermore, a pulsed laser beam is directed toward the planned dividing line L aligned with the X-axis, and the height of the pulsed laser beam's focal point is adjusted to the front surface Wa of the wafer W.

[0074] Next, while the chuck table 20 is being fed in the X-axis direction, a pulsed laser beam LB having a wavelength that is absorptive to the wafer W is irradiated from the condenser 40 onto the wafer W, performing ablation processing along the planned dividing line L. This forms a groove G that cuts along the planned dividing line L (see FIG. 2 ).

[0075] Next, the chuck stage 20 is indexed and fed relative to the condenser 40 in the Y-axis direction by the interval in the Y-axis direction of the intended dividing line L. Then, by alternately repeating irradiation with a pulsed laser beam and indexing, grooves G are formed along all the intended dividing lines L aligned with the X-axis direction.

[0076] Next, the chuck table 20 is rotated 90 degrees, and pulse laser beam irradiation and indexing are alternately repeated, thereby forming grooves G along all the predetermined dividing lines L extending in the second direction and perpendicular to the predetermined dividing lines L on which the grooves G were previously formed. By performing the groove forming step in this manner, the grooves G are formed in a grid pattern along the predetermined dividing lines L. This allows the wafer W to be divided into individual device wafers.

[0077] As described above, when the groove G is formed in the workpiece such as the wafer W, the processing conditions are appropriately set according to the workpiece so that the laser beam for removing debris does not need to be re-irradiated.

[0078] (First Mode) When irradiating the laser beam, in a workpiece that generates a large amount of growth debris (for example, a workpiece containing semiconductor materials and metal materials), the first mode is selected to form the groove G while destroying the growth debris.

[0079] When the first mode is selected, the first group setting unit 48a sets the number of pulse laser beams in the first group to be irradiated with the next pulse laser beam within the time period until the plasma generated in the workpiece by irradiating the pulse laser beam disappears, so that the plasma continues uninterrupted and the growth debris is destroyed. Furthermore, the first time interval setting unit 50a sets the time interval between the first group and the adjacent first group, setting the time interval between the pulse laser beams constituting the first group.

[0080] As mentioned above, the plasma generated when the pulsed laser beam is irradiated onto the workpiece generally occurs about 10ns after the pulsed laser beam is irradiated onto the workpiece and disappears about 30ns after the pulsed laser beam is irradiated onto the workpiece.

[0081] Therefore, the first time interval setting unit 50a sets the time interval between the first and second pulses to, for example, 15 ns. Consequently, as shown in FIG5 , plasma P2 associated with the second pulse is generated 25 ns after 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 associated with the third pulsed laser beam LB3 (the third pulse) is generated before plasma P2 disappears.

[0082] As a result, the plasma continues to flow continuously while the first group of pulsed laser beams is irradiating the workpiece. Therefore, the plasma can reliably destroy the growth debris generated by the pulsed laser beams.

[0083] As described above, the first time interval setting unit 50a not only sets the time interval of the pulsed laser beams constituting the first group (15 ns in the above example), but also sets the time interval between the first group and the adjacent first group, which is the time it takes for the heat generated in the workpiece by irradiation with the pulsed laser beams of the first group to cool down. This is because if the pulsed laser beam is continuously irradiated onto the workpiece, heat will accumulate in the workpiece, which may adversely affect the components (such as reducing component quality).

[0084] As previously mentioned, it is known that in a workpiece made of semiconductor materials such as silicon, the heat generated by the pulsed laser beam cools down after approximately 5 μs has passed since irradiation, and the workpiece temperature drops to approximately the same level as before irradiation. Therefore, as shown in FIG6 , the first time interval setting unit 50a sets the time interval between the first group and the adjacent first group to be at least 5 μs.

[0085] Thus, from the time when the first group of pulse laser beams is irradiated on the workpiece to the time when the next first group of pulse laser beams is irradiated, the heat generated in the workpiece is cooled, thereby preventing the adverse effects of heat on the components.

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

[0087] As described above, if 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 inputs signals to the multiple laser diodes LD at 15 ns intervals via the pulse delay generator 56, and inputs the signals in such a manner 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 plurality of laser oscillators 46 at 15 ns intervals via the delay voltage device 58, and apply voltage so that the time interval between the first groups becomes 5 μs (see FIG. 4 ).

[0089] Furthermore, regarding the time interval between the first groups, the culling unit 52 may be used to remove a predetermined number of groups from the plurality of groups emitted during one second, thereby reducing the time interval between the first groups to 5 μs.

[0090] In other words, while inputting signals to the plurality of laser diodes LD at 15 ns intervals via the pulse delay generator 56, or applying voltages to the plurality of laser oscillators 46 at 15 ns intervals via the delay voltage generator 58, the time intervals between the first groups can be reduced to 5 μs by culling a predetermined number of groups from the plurality of groups emitted during a one-second period using the culling unit 52. Furthermore, when the time intervals between the first groups are 5 μs, the repetition frequency becomes 200 kHz.

[0091] Thus, by selecting the first mode and operating the laser oscillator 38, a pulsed laser beam is generated, as shown in FIG6 , with a first group pulse count of 6, 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 condenser 40 and irradiated along the intended dividing line L of the workpiece. This allows the formation of grooves G while the plasma destroys the growing debris generated by the irradiation of the pulsed laser beam.

[0092] The first mode can be implemented, for example, using the following processing conditions. Wavelength of pulsed laser beam: 355nm Average output: 30W Repetition frequency of the first group: 200kHz The first group consists of 6 pulse lasers Power density of the first group: 30J / cm2 Pulse width of the first group: 75ns (see Figure 6) The spot size of the first group: 10μm in the X-axis direction, 50μm in the Y-axis direction Overlap rate of the first group: 50% Feed speed: 1m / s Plasma generation time: 10ns after laser irradiation (see Figure 5) Plasma disappearance time: disappears 30ns after laser irradiation (see Figure 5) Power density of one pulse: 5J / cm2 Pulse width of a pulse: 10ps Pulse overlap rate: 99.8% Time interval between pulses: 15 ns (refer to Fig. 6)

[0093] (Second mode) When irradiating the laser beam, in the workpiece that generates more molten debris, select the second mode, and form the groove G while suppressing the generation of molten debris.

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

[0095] Regarding the time interval (pulse interval) of the pulsed laser beam constituting the second group and the number of pulsed laser beams (pulse number) in the second group, in the case where molten debris is generated at time t1 and the molten debris solidifies at time t2 after irradiating the pulsed laser beam to the workpiece, the second time interval setting unit 50b sets the time interval (pulse interval) t3 of the pulsed laser beam in the second group such that t3 < t1, and the second group setting unit 48b sets the number of pulsed laser beams (pulse number) n in the second group as the integer part of n = (t2 / t3) + 1.

[0096] As described above, it has been confirmed that the molten debris generated when irradiating the pulsed laser beam to the workpiece is generated about 100 ns after irradiating the pulsed laser beam to the workpiece, and solidifies after about 500 ns.

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

[0098] If the second time interval setting unit 50b sets the pulse interval t3 to 50ns, then in the second group setting unit 48b, the number (pulse number) n of the pulse laser beams as the second group is set to: n=the integer part of (t2 / t3) + 1 =Integer part of (500ns / 50ns) + 1 =10+1 =11.

[0099] In the above case, (t2 / t3) is a combination of divisible values. However, for example, when the second time interval setting unit 50b is set to t3 = 60ns, the second group setting unit 48b sets the pulse number n to: n=the integer part of (t2 / t3) + 1 =Integer part of (500ns / 60ns) + 1 = the integer part of (8.333…) + 1 =8+1 =9.

[0100] Thus, in the second group setting section 48b, the number of pulsed laser beams (n = 11) in the second group to be irradiated from the initial pulsed laser beam (first pulse) to the time (t2 = 500 ns) when the molten chips solidify is set, using the condition that the pulsed laser beam is irradiated at a shorter time interval (t3 = 50 ns) than the time (t1 = 100 ns) when molten chips are generated by irradiating the workpiece with the pulsed laser beam. This prevents the generation of molten chips when the workpiece is irradiated with the pulsed laser beam.

[0101] In the second time interval setting section 50b, similarly to the first time interval setting section 50a, not only the time interval of the pulse laser beams constituting the second group is set, but also the time required for the heat generated in the workpiece due to the irradiation of the pulse laser beam of the second group to cool down is set as the time interval between the second group and the adjacent second group (for example, 5 μs).

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

[0103] Alternatively, the second time interval setting unit 50b may apply voltage to the plurality of laser oscillators 46 at intervals of 50 ns via the delay voltage device 58, and apply voltage so that the time intervals between the second groups become 5 μs.

[0104] Furthermore, similar to the time interval between the first groups in the first mode, the time interval between the second groups can be reduced to 5 μs by using the culling unit 52 to reduce a predetermined number of groups from the plurality of groups emitted during one second. Furthermore, when the time interval between the second groups is 5 μs, the repetition frequency is 200 kHz.

[0105] Thus, by selecting the second mode and operating the laser oscillator 38, a pulsed laser beam is generated, as shown in Figure 7, with a second group of pulses n = 11, a pulse interval t3 = 50 ns, and a time interval of 5 μs between the second groups. After the output of this pulsed laser beam is appropriately adjusted by the attenuator 54, it is focused by the condenser 40 and irradiated along the intended dividing line L of the workpiece. This allows the groove G to be formed while suppressing the generation of molten debris.

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

[0107] (Third mode) When irradiating the laser beam, in the workpiece that generates both a large amount of growth debris and molten debris, select the third mode, and while destroying the growth debris and suppressing the generation of molten debris, form the groove G.

[0108] If the third mode is selected, the third group setting unit 48c will irradiate the next pulsed laser beam within a time shorter than the time when molten debris is generated due to irradiating the pulsed laser beam to the workpiece and within the time until the plasma generated from the workpiece due to the irradiation of the pulsed laser beam disappears, so that the plasma continuously persists to destroy the growth debris as a condition, and set the number of pulsed laser beams in the third group irradiated until the time when the molten debris solidifies. Also, the third time interval setting unit 50c sets the time until the heat generated in the workpiece due to the irradiation of the pulsed laser beam in the third group cools down as the time interval between the third group and the adjacent third group, and sets the time interval of the pulsed laser beam constituting the third group.

[0109] Regarding the time interval (pulse interval) of the pulsed laser beam constituting the third group and the number of pulsed laser beams (pulse number) in the third group. In the case where molten debris is generated at time t1 and the molten debris solidifies at time t2 after irradiating the pulsed laser beam to the workpiece, the third time interval setting unit 50c sets the time interval (pulse interval) T3 of the pulsed laser beam in the third group to satisfy T3 < t1, and satisfies t4 < T3 < t5 between the time t4 when plasma is generated from the workpiece and the time t5 when the plasma disappears. Also, the third group setting unit 48c sets the number of pulsed laser beams (pulse number) N in the third group to N = the integer part of (t2 / T3) + 1.

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

[0111] Therefore, taking the time when the first pulse laser beam (first pulse) irradiates the workpiece as the reference (0s), we define: The time of molten debris generation t1=100ns The time for the molten debris to solidify is t2 = 500ns Plasma generation time t4 = 10ns Plasma disappearance time t5 = 30ns In this case, the third time interval setting unit 50c sets the time interval (pulse interval) T3 of the third group of pulse laser beams to, for example, 15 ns. If T3 = 15 ns, the following two conditions are satisfied: T3 <t1(100ns) t4 (10ns) <T3<t5(30ns)。

[0112] If the third time interval setting unit 50c sets the pulse interval T3 to 15 ns, then in the third group setting unit 48c, the number (pulse number) N of the pulse laser beams of the third group is set to: N = integer part of (t2 / T3) + 1 =Integer part of (500ns / 15ns) + 1 = the integer part of (33.333…) + 1 =33+1 =34.

[0113] Thus, in the third group setting section 48c, the number of pulsed laser beams (N = 34) in the third group to be irradiated from the initial pulsed laser beam (first pulse) to the solidification of the molten chips (t2 = 500 ns) is set, with the condition that the next pulsed laser beam is irradiated within a time shorter than the time (t1 = 100 ns) at which molten chips are generated by irradiating the workpiece with the pulsed laser beam and within the time (t5 = 30 ns) at which the plasma generated from the workpiece by irradiating the pulsed laser beam disappears, thereby allowing the plasma to continue uninterruptedly and destroy the growing chips. This allows the plasma to destroy the growing chips generated by irradiating the pulsed laser beam when the workpiece is irradiated with the pulsed laser beam, and the generation of molten chips to be suppressed.

[0114] In the third time interval setting unit 50c, similarly to the first and second time interval setting units 50a and 50b, not only the time interval of the pulse laser beams constituting the third group is set, but also the time required for the heat generated in the workpiece due to irradiation with the pulse laser beam of the third group to cool down is set as the time interval between the third group and the adjacent third group (for example, 5 μs).

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

[0116] Alternatively, the third time interval setting unit 50c may apply voltage to the plurality of laser oscillators 46 at intervals of 15 ns via the delay voltage device 58, and apply voltage so that the time intervals between the third groups are 5 μs.

[0117] Furthermore, similar to the time interval between the first groups in the first mode, the time interval between the third groups can be reduced to 5 μs by using the culling unit 52 to reduce a predetermined number of groups from the plurality of groups emitted in one second. Furthermore, when the time interval between the third groups is 5 μs, the repetition frequency is 200 kHz.

[0118] Thus, by selecting the third mode and operating the laser oscillator 38, a pulsed laser beam is generated, as shown in Figure 8, with a third group of pulses N = 34, a pulse interval T3 = 15 ns, and a time interval of 5 μs between the third groups. After the output of this pulsed laser beam is appropriately adjusted by the attenuator 54, it is focused by the condenser 40 and irradiated along the intended dividing line L of the workpiece. This allows the formation of the groove G while destroying the growing debris generated by the irradiation of the pulsed laser beam with plasma and suppressing the generation of molten debris.

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

[0120] As described above, in the laser processing apparatus 2 of this embodiment, by selecting the first mode, the groove G can be formed while plasma destroys the growing debris generated by irradiation with the pulsed laser beam. Furthermore, by selecting the second mode, the groove G can be formed while suppressing the generation of molten debris. Furthermore, by selecting the third mode, the groove G can be formed while plasma destroying the growing 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 re-irradiate the workpiece with the laser beam to remove the debris, thereby improving productivity.

[0121] 2: Laser processing equipment 4: Holding unit 6: Laser beam irradiation unit 8: Feeding mechanism 38: Laser oscillation mechanism 40: Concentrator 46: Laser Oscillator 48: Group Setting Section 48a: First group setting unit 48b: Second group setting unit 48c: Third group setting unit 50: Time interval setting unit 50a: First time interval setting unit 50b: Second time interval setting unit 50c: Third time interval setting unit 56: Pulse Delay Generator 58: Delay Voltage Device LD: Laser Diode

Claims

1. A laser processing apparatus comprising: a chuck stage for holding a workpiece; a laser beam irradiation unit for irradiating the workpiece held on the chuck stage with a pulsed laser beam; and a feed mechanism for feeding the chuck stage relative to the laser beam irradiation unit, the laser beam irradiation unit comprising: a laser oscillation mechanism for emitting the pulsed laser beam; and a concentrator for concentrating the pulsed laser beam emitted by the laser oscillation mechanism and irradiating the workpiece held on the chuck stage, the laser oscillation mechanism comprising a first mode, a second mode, and a third mode. The first mode includes: a first group setting unit that sets the number of pulsed laser beams that irradiate the workpiece with the next pulsed laser beam within the time until the plasma generated from the workpiece disappears after irradiation by the pulsed laser beam, so that the plasma continues uninterruptedly and destroys the growing debris, and sets this as a first group; and a first time interval setting unit that sets the time until the heat cooling caused by the irradiation of the pulsed laser beams of the first group is achieved as the time interval between the first group and the adjacent first group, and sets the time interval of the pulsed laser beams constituting the first group. The second mode includes: a second group setting unit, which sets the number of pulsed laser beams irradiated until the molten debris solidifies, based on the condition that the pulsed laser beam is irradiated for a shorter time than the time it takes for molten debris to be generated due to irradiation of the workpiece by the pulsed laser beam, and sets this as a second group; and a second time interval setting unit, which sets the time interval between the second group and adjacent second groups as the time until thermal cooling occurs due to irradiation by the pulsed laser beams of the second group, and sets the time interval between the pulsed laser beams constituting the second group. The third mode includes: a third group setting unit, which sets the number of pulsed laser beams irradiated up to the time until the molten debris solidifies, and sets this as a third group, based on the condition that the next pulsed laser beam is irradiated for a shorter time than the time it takes for the molten debris to be generated by irradiating the workpiece with the pulsed laser beam, and the time until the plasma generated from the workpiece disappears after irradiation with the pulsed laser beam, so that the plasma continues to destroy the growing debris without interruption; and a third time interval setting unit, which sets the time interval between the third group and the adjacent third group as the time until the heat cooling caused by the irradiation of the pulsed laser beam of the third group, and sets the time interval between the pulsed laser beams constituting the third group. The laser oscillation mechanism further includes: a selection unit, which selects any one of the first mode, the second mode, and the third mode, in which the first group is used as a unit and the repetition frequency is set; in the second mode, the second group is used as a unit and the repetition frequency is set; and in the third mode, the third group is used as a unit and the repetition frequency is set.

2. The laser processing apparatus as described in claim 1, wherein, The laser oscillation mechanism includes multiple laser diodes that emit pulsed laser beams. In the first group setting unit, the first group is set using the pulsed laser beams emitted by the multiple laser diodes. In the second group setting unit, the second group is set using the pulsed laser beams emitted by the multiple laser diodes. In the third group setting unit, the third group is set using the pulsed laser beams emitted by the multiple laser diodes. In the first time interval setting unit, a pulse delay generator inputs signals to the multiple laser diodes at desired time intervals, and the time interval between the first group and adjacent groups is defined as the time until the heat generated by the pulsed laser beams of the first group cools down. In the second time interval setting unit, the signal is input to the plurality of laser diodes at a desired time interval by means of the pulse delay generator, and the signal is input in such a way that the time until the heat cooling caused by the irradiation of the pulse laser beam of the second group is used as the time interval between the second group and the adjacent second group. In the third time interval setting unit, the signal is input to the plurality of laser diodes at a desired time interval by means of the pulse delay generator, and the signal is input in such a way that the time until the heat cooling caused by the irradiation of the pulse laser beam of the third group is used as the time interval between the third group and the adjacent third group.

3. The laser processing apparatus as described in claim 1, wherein, The laser oscillator mechanism includes multiple laser oscillators that emit pulsed laser beams. In the first group setting section, the first group is set using the pulsed laser beams emitted by the multiple laser oscillators. In the second group setting section, the second group is set using the pulsed laser beams emitted by the multiple laser oscillators. In the third group setting section, the third group is set using the pulsed laser beams emitted by the multiple laser oscillators. In the first time interval setting section, a voltage is applied to the multiple laser oscillators at desired time intervals using a delay voltage generator. The voltage is applied such that the time until the heat generated by the pulsed laser beams of the first group cools down is defined as the time interval between the first group and adjacent groups. In the second time interval setting unit, the voltage is applied to the plurality of laser oscillators at a desired time interval by means of the delay voltage, and the voltage is applied in such a way that the time until the heat generated by the irradiation of the pulsed laser beam of the second group is used as the time interval between the second group and the adjacent second group. In the third time interval setting unit, the voltage is applied to the plurality of laser oscillators at a desired time interval by means of the delay voltage, and the voltage is applied in such a way that the time until the heat generated by the irradiation of the pulsed laser beam of the third group is used as the time interval between the third group and the adjacent third group.

4. The laser processing apparatus as described in claim 1, wherein, In the first mode, the repetition frequency is set by removing a predetermined number of the first groups from the plurality of first groups fired in one second. In the second mode, the repetition frequency is set by removing a predetermined number of the second groups from the plurality of second groups fired in one second. In the third mode, the repetition frequency is set by removing a predetermined number of the third groups from the plurality of third groups fired in one second.

Images