Laser processing method and laser processing system

Abstract

This laser processing method comprises: a first step for concentrating a laser beam on the surface of a to-be-processed object so as to form a recess therein; and a second step for concentrating a laser beam on the bottom surface of the recess. In the second step, when the fluence of the laser beam at the upper end of the recess is defined as Fin, the upper limit fluence at which a film is generated from a chemical reaction between the to-be-processed object and the atmosphere by the irradiation of the laser beam is defined as Ffth, and the lower limit fluence at which processing can be performed is defined as Fmth, the fluence Fin satisfied the relation: Ffth<Fin<Fmth.

Description

Technical Field

[0001] The present disclosure relates to a laser processing method and a laser processing system.

Background Art

[0002] In recent years, in semiconductor exposure apparatuses, with the miniaturization and high integration of semiconductor integrated circuits, improvement in resolution has been demanded. For this reason, the shortening of the wavelength of light emitted from an exposure light source has been promoted. For example, as a gas laser device for exposure, a KrF excimer laser device that outputs laser light with a wavelength of about 246.0 nm and an ArF excimer laser device that outputs laser light with a wavelength of about 193.4 nm are used.

[0003] The spectral linewidth of the spontaneous emission light of a KrF excimer laser device and an ArF excimer laser device is as wide as 350 pm to 400 pm. Therefore, when a projection lens is configured with a material that transmits ultraviolet rays such as KrF and ArF laser light, chromatic aberration may occur. As a result, the resolution may decrease. Therefore, it is necessary to narrow the spectral linewidth of the laser light output from the gas laser device to such an extent that chromatic aberration can be ignored. For this reason, a narrowbanding module (Line Narrowing Module: LNM) including a narrowbanding element (etalon, grating, etc.) may be provided in the laser resonator of the gas laser device in order to narrow the spectral linewidth. Hereinafter, a gas laser device whose spectral linewidth is narrowed is referred to as a narrowbanded gas laser device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] According to one aspect of the present disclosure, a laser processing method includes a first step of condensing laser light on the surface of a workpiece to form a recess, and a second step of condensing laser light on the bottom surface of the recess. In the second step, when the fluence of the laser light at the upper end of the recess is Fin, the upper limit fluence Ffth at which a film is formed by the chemical reaction between the workpiece and the atmosphere, and the lower limit fluence Fmth at which the workpiece can be processed by the laser light, the fluence Fin may satisfy the formula Ffth < Fin < Fmth.

[0006] According to one aspect of the present disclosure, a laser processing system includes an optical system that irradiates laser light, and an fθ lens that condenses the laser light from the optical system on the surface of a workpiece. When the fluence of the laser light at the upper end of the recess formed by condensing the laser light on the surface is Fin, the upper limit fluence Ffth at which a film is formed by the chemical reaction between the workpiece and the atmosphere, and the lower limit fluence Fmth at which the workpiece can be processed by the laser light, the optical system may irradiate laser light having a fluence Fin that satisfies the formula Ffth < Fin < Fmth.

Brief Description of the Drawings

[0007] Some embodiments of the present disclosure will be described below by way of example with reference to the accompanying drawings.

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[0008] 1. Description of the Laser Processing System and Laser Processing Method of the Comparative Example 1.1 Configuration 1.2 Operation 1.3 Problems 2. Description of the Effective Machining Depth of the Workpiece and the Cross - sectional Area of the Laser Light 3. Description of the Laser Processing System and Laser Processing Method of Embodiment 1 3.1 Configuration 3.2 Operation 3.3 Function and Effect 4. Description of the Laser Processing System and Laser Processing Method of Embodiment 2 4.1 Configuration 4.2 Operation 4.3 Function and Effect 5. Description of the Laser Processing System and Laser Processing Method of Embodiment 3 5.1 Configuration 5.2 Operation 5.3 Function and Effect 6. Description of Modification Examples of Gas Laser Devices

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below show some examples of the present disclosure and do not limit the content of the present disclosure. In addition, not all of the configurations and operations described in each embodiment are essential as the configurations and operations of the present disclosure. Note that the same reference numerals are assigned to the same components, and duplicate descriptions are omitted.

[0010] 1. Description of the Laser Processing System and Laser Processing Method of the Comparative Example 1.1 Configuration The laser processing system and laser processing method of the comparative example will be described. Note that the comparative example of the present disclosure is a form recognized by the applicant as being known only to the applicant and is not a known example recognized by the applicant.

[0011] FIG. 1 is a schematic diagram showing an overall schematic configuration example of a laser processing system 10. The laser processing system 10 mainly includes a gas laser device 100, a laser processing device 300, and an optical path tube 500 that connects the gas laser device 100 and the laser processing device 300. Hereinafter, the direction parallel to the optical axis direction of the laser light incident on the workpiece 20 will be described as the Z direction, the direction orthogonal to the Z direction will be described as the X direction, and the direction orthogonal to the X direction and the Z direction will be described as the Y direction.

[0012] The gas laser device 100 is, for example, an ArF excimer laser device that uses a mixed gas containing argon (Ar), fluorine (F2), and neon (Ne). This gas laser device 100 outputs laser light with a central wavelength of approximately 193.4 nm. Note that the gas laser device 100 may be a gas laser device other than an ArF excimer laser device, for example, a KrF excimer laser device that uses a mixed gas containing krypton (Kr), F2, and Ne. In this case, the gas laser device 100 emits laser light with a central wavelength of approximately 246.0 nm. The mixed gas containing Ar, F2, and Ne as the laser medium or the mixed gas containing Kr, F2, and Ne as the laser medium may be called a laser gas.

[0013] The gas laser device 100 mainly includes a housing 110, a laser oscillator 130, a monitor module 150, a shutter 170, and a laser processor 190 disposed in the internal space of the housing 110.

[0014] The laser oscillator 130 includes a laser chamber 131, a charger 141, a pulse power module 143, a rear mirror 145, and an output coupling mirror 147. FIG. 1 shows the internal configuration of the laser chamber 131 viewed from a direction substantially perpendicular to the traveling direction of the laser light.

[0015] The laser chamber 131 includes an internal space where light is generated by excitation of the laser medium in the above laser gas. The light travels to windows 139a and 139b, which will be described later. The laser gas is supplied from a laser gas supply source (not shown) to the internal space of the laser chamber 131 through a pipe (not shown). Further, the laser gas in the laser chamber 131 is subjected to a process such as removing F2 gas by a halogen filter and is exhausted to the housing 110 through a pipe (not shown) by an exhaust pump (not shown).

[0016] Inside the internal space of the laser chamber 131, a pair of electrodes 133a and 133b face each other, and their respective longitudinal directions are arranged along the traveling direction of light. The electrodes 133a and 133b are discharge electrodes for exciting the laser medium by glow discharge. In this example, the electrode 133a is the cathode and the electrode 133b is the anode.

[0017] The electrode 133a is supported by an electrical insulating part 135. The electrical insulating part 135 closes an opening formed in the laser chamber 131. A conductive part (not shown) is embedded in the electrical insulating part 135, and the conductive part applies a high voltage supplied from the pulse power module 143 to the electrode 133a. The electrode 133b is supported by a return plate 137, and the return plate 137 is connected to the inner surface of the laser chamber 131 by wiring (not shown).

[0018] The charger 141 is a DC power supply device that charges a charging capacitor (not shown) in the pulse power module 143 with a predetermined voltage. The pulse power module 143 includes a switch 143a controlled by the laser processor 190. When the switch 143a changes from OFF to ON, the pulse power module 143 generates a pulsed high voltage from the electrical energy held in the charger 141 and applies this high voltage between the electrode 133a and the electrode 133b.

[0019] When a high voltage is applied between the electrode 133a and the electrode 133b, a discharge occurs between the electrode 133a and the electrode 133b. The energy of this discharge excites the laser medium in the laser chamber 131, and the excited laser medium emits light when transitioning to the ground state.

[0020] The laser chamber 131 is provided with windows 139a and 139b. Window 139a is located on one end side in the traveling direction of the laser beam in the laser chamber 131, window 139b is located on the other end side in the traveling direction, and windows 139a and 139b sandwich the space between the electrodes 133a and 133b. Windows 139a and 139b are inclined at a Brewster angle with respect to the traveling direction of the laser beam so that the reflection of the P-polarized light of the laser beam is suppressed. The laser beam oscillated as described later is emitted to the outside of the laser chamber 131 through windows 139a and 139b. Since a pulsed high voltage is applied between the electrodes 133a and 133b by the pulse power module 143 as described above, this laser beam is a pulsed laser beam.

[0021] The rear mirror 145 is disposed in the internal space of a housing 145a connected to one end side of the laser chamber 131, reflects the laser beam emitted from the window 139a, and returns it to the laser chamber 131. The output coupling mirror 147 is disposed in the internal space of an optical path tube 147a connected to the other end side of the laser chamber 131, transmits a part of the laser beam emitted from the window 139b, and reflects the other part of the laser beam back to the internal space of the laser chamber 131. In this way, the rear mirror 145 and the output coupling mirror 147 constitute a Fabry - Perot type laser resonator, and the laser chamber 131 is disposed on the optical path of the laser resonator.

[0022] The monitor module 150 is disposed on the optical path of the laser beam emitted from the output coupling mirror 147. The monitor module 150 includes, for example, a housing 151, a beam splitter 153 disposed in the internal space of the housing 151, and an optical sensor 155. An opening is formed in the housing 151, and through this opening, the internal space of the housing 151 communicates with the internal space of the optical path tube 147a.

[0023] The beam splitter 153 transmits a part of the laser light emitted from the output coupling mirror 147 toward the shutter 170, and reflects the other part of the laser light toward the light receiving surface of the photosensor 155. The photosensor 155 measures the energy E of the laser light incident on the light receiving surface. The photosensor 155 outputs a signal indicating the measured energy E to the laser processor 190.

[0024] The laser processor 190 of the present disclosure is a processing device including a storage device 190a storing a control program and a CPU (Central Processing Unit) 190b executing the control program. The laser processor 190 is specially configured or programmed to execute various processes included in the present disclosure. Further, the laser processor 190 controls the entire gas laser device 100.

[0025] The laser processor 190 transmits and receives various signals to and from the laser processing processor 310 of the laser processing apparatus 300. For example, the laser processor 190 receives from the laser processing processor 310 a signal indicating a light emission trigger Tr and a target energy Et, which will be described later. The laser processor 190 controls the charging voltage of the charger 141 based on the energy E and the target energy Et received from the photosensor 155 and the laser processing processor 310. By controlling this charging voltage, the energy of the laser light is controlled. Further, the laser processor 190 transmits an ON or OFF command signal for the switch 143a to the pulse power module 143. Further, the laser processor 190 is electrically connected to the shutter 170 and controls the opening and closing of the shutter 170.

[0026] The laser processor 190 closes the shutter 170 until the difference ΔE between the energy E received from the monitor module 150 and the target energy Et received from the laser processing processor 310 is within the allowable range. When the difference ΔE is within the allowable range, the laser processor 190 transmits a reception preparation completion signal to the laser processing processor 310, indicating that the reception preparation for the emission trigger Tr is complete. When the laser processing processor 310 receives the reception preparation completion signal, it transmits a signal indicating the emission trigger Tr to the laser processor 190, and the laser processor 190 opens the shutter 170 upon receiving the signal indicating the emission trigger Tr. The emission trigger Tr is defined by a predetermined repetition frequency f and a predetermined number of pulses P of the laser light, and is a timing signal for the laser processing processor 310 to cause the laser oscillator 130 to oscillate, and is an external trigger. The repetition frequency f of the laser light is, for example, 1 kHz or more and 10 kHz or less.

[0027] The shutter 170 is disposed in the optical path of the laser light that has passed through an opening formed on the side opposite to the side where the optical path tube 147a in the housing 151 is connected, after passing through the beam splitter 153 of the monitor module 150. Further, the shutter 170 is disposed in the internal space of the optical path tube 171, and the optical path tube 171 is connected to the housing 151 so as to surround the opening and communicates with the housing 151. Further, the optical path tube 171 communicates with the laser processing apparatus 300 through the opening of the housing 110 and the optical path tube 500.

[0028] The internal spaces of the optical path tube 171 and the optical path tube 147a, and the internal spaces of the housing 151 and the housing 145a are filled with a purge gas. The purge gas includes an inert gas such as nitrogen (N2). The purge gas is supplied from a purge gas supply source (not shown) through a pipe (not shown) to the internal spaces of the optical path tube 171 and the optical path tube 147a, and the internal spaces of the housing 151 and the housing 145a.

[0029] The laser processing apparatus 300 mainly includes a laser processing processor 310, a housing 355, a frame 357, an optical system 330, an fθ lens 375, and a stage 350 disposed in the internal space of the housing 355. The housing 355 is fixed to the frame 357. An optical path tube 500 is connected to the housing 355. Through the opening of the housing 355, the internal space of the housing 355 communicates with the internal space of the optical path tube 500, and the laser light that has passed through the shutter 170 enters the housing 355.

[0030] The laser processing processor 310 is a processing device including a storage device 310a in which a control program is stored and a CPU 310b that executes the control program. The laser processing processor 310 is specially configured or programmed to execute various processes included in the present disclosure. Further, the laser processing processor 310 controls the entire laser processing apparatus 300.

[0031] The optical system 330 includes high reflection mirrors 331a, 331b, an attenuator 333, and an irradiation optical system 370. The high reflection mirrors 331a, 331b, the attenuator 333, and the irradiation optical system 370 are each fixed to a holder (not shown) and disposed at predetermined positions within the housing 355.

[0032] The high reflection mirrors 331a, 331b are formed by coating a reflective film that highly reflects laser light on the surfaces of transparent substrates made of, for example, synthetic quartz or calcium fluoride. The high reflection mirror 331a reflects the laser light incident from the gas laser device 100 toward the attenuator 333. The high reflection mirror 331b reflects the laser light from the attenuator 333 toward the irradiation optical system 370.

[0033] The attenuator 333 is disposed on the optical path between the high-reflection mirror 331a and the high-reflection mirror 331b. The attenuator 333 includes, for example, rotary stages 333a, 333b and partial reflection mirrors 333c, 333d fixed to the rotary stages 333a, 333b. Each of the rotary stages 333a, 333b is electrically connected to the laser processing processor 310 and rotates around the Y-axis by a control signal from the laser processing processor 310. When the rotary stages 333a, 333b rotate respectively, the partial reflection mirrors 333c, 333d also rotate respectively. The partial reflection mirrors 333c, 333d are optical elements whose transmittance changes depending on the incident angle of the laser light to the partial reflection mirrors 333c, 333d. The rotation angles of the partial reflection mirrors 333c, 333d around the Y-axis are adjusted by the rotation of the rotary stages 333a, 333b so that the incident angles of the laser light coincide with each other and the transmittance of the partial reflection mirrors 333c, 333d becomes the desired transmittance. Thereby, the laser light from the high-reflection mirror 331a is attenuated to the desired energy and passes through the attenuator 333.

[0034] The irradiation optical system 370 guides the laser light emitted from the gas laser device 100 to the workpiece 20, and moves the irradiation spot of the guided laser light in the in-plane direction of the projection plane of the workpiece 20 to irradiate the laser light. The projection plane is a plane located in the XY plane when viewing the workpiece 20 from the direction opposite to the traveling direction of the laser light to the workpiece 20. In the irradiation of the laser light in the present embodiment, the laser light moves in the XY plane. The irradiation optical system 370 includes galvano scanners 371, 373.

[0035] The galvano scanner 371 includes a drive unit 371a and a mirror 371b attached to the swing axis of the drive unit 371a and swingable around the swing axis. The configuration of the galvano scanner 373 is the same as that of the galvano scanner 371, and the galvano scanner 373 includes a drive unit 373a and a mirror 373b attached to the swing axis of the drive unit 373a and swingable around the swing axis.

[0036] The drive units 371a and 373a are motors or the like and are electrically connected to the laser processing processor 310. The swing speed and swing angle of the swing axes of the drive units 371a and 373a are controlled by control signals from the laser processing processor 310. The swing axis of the drive unit 371a is orthogonal to the swing axis of the drive unit 373a.

[0037] The mirror 371b reflects the laser light from the high-reflection mirror 331b toward the mirror 373b, and the mirror 373b reflects the laser light from the mirror 371b toward the fθ lens 375. The respective orientations of the mirrors 371b and 373b are adjusted by the swing angles of the respective swing axes of the drive units 371a and 373a. The adjustment of the respective orientations of the mirrors 371b and 373b may be synchronized. The speeds of the mirrors 371b and 373b during swinging are adjusted by the swing speeds when the swing axes of the drive units 371a and 373a swing.

[0038] The galvanoscanners 371 and 373 as described above irradiate the surface of the workpiece 20 with the laser light while moving it in the X direction and the Y direction by the mirrors 371b and 373b, and process the workpiece 20 by the movement and irradiation. In the movement and irradiation, the interval and movement speed of the irradiation lines of the laser light irradiating the workpiece 20 are controlled by the orientations and speeds of the mirrors 371b and 373b. The irradiation line is a line along which the irradiation spot of the laser light moves on the workpiece 20.

[0039] The fθ lens 375 is fixed to a holder (not shown) on the optical path between the mirror 373b and the workpiece 20 and is arranged at a predetermined position in the housing 355. The optical axis of the fθ lens 375 is along the Z direction. The fθ lens 375 condenses the laser light irradiated from the galvanoscanner 373 of the optical system 330 onto the surface of the workpiece 20 along the optical axis of the fθ lens 375. Further, the fθ lens 375 condenses the laser light onto the workpiece 20 so that the diameter of the irradiation spot of the laser light on the workpiece 20 is smaller than the diameter of the processed portion formed on the workpiece 20.

[0040] The stage 350 is disposed on the bottom surface of the housing 355 and includes a table 351. Further, the stage 350 can move the table 351 in the X direction, Y direction, and Z direction according to a control signal from the laser processing processor 310, and the position of the table 351 can be adjusted by this movement.

[0041] The table 351 supports the workpiece 20. The front and back surfaces, which are the main surfaces of the table 351, are inclined with respect to the XY plane. Accordingly, the front and back surfaces of the workpiece 20 are inclined with respect to the optical axis direction of the laser beam, and obliquely drilled holes are formed. In FIG. 1, the inclination angle of the back surface of the workpiece 20 with respect to the XY plane is denoted as the inclination angle θ1. With the above configuration, the stage 350 can move the workpiece 20 by the table 351 so that the laser beam emitted from the optical system 330 irradiates a desired position of the workpiece 20, and adjust the position of the workpiece 20.

[0042] The workpiece 20 is an object to be laser processed by irradiation with a laser beam. Examples of the workpiece 20 include, for example, quartz glass. Further, examples of the workpiece 20 include, for example, a material containing carbon atoms, an organic material such as polyimide or a fluororesin, a composite material of carbon fiber and resin (Carbon Fiber Reinforced Plastics: CFRP), or diamond. Furthermore, examples of the workpiece 20 include, for example, wide bandgap materials such as sapphire and SiC (silicon carbide), transparent materials such as CaF2 crystal, MgF2 crystal, and glass materials.

[0043] During the operation of the laser processing system 10, an inert gas constantly flows through the internal space of the housing 355. This inert gas is, for example, nitrogen gas. The housing 355 is provided with an intake port (not shown) for inhaling the inert gas into the housing 355 and an exhaust port (not shown) for discharging the inert gas from the housing 355 to the outside. An intake pipe and an exhaust pipe (not shown) are connected to the intake port and the exhaust port, respectively. A gas supply source (not shown) for supplying the inert gas is connected to the intake port through the intake pipe. The inert gas supplied from the intake port also flows into the optical path pipe 500 communicating with the housing 355.

[0044] 1.2 Operation Next, the operation of the laser processing system 10 of the comparative example will be described.

[0045] In the gas laser device 100, before the gas laser device 100 emits laser light, the internal spaces of the optical path pipes 147a, 171, 500 and the internal spaces of the housings 145a, 151 are filled with a purge gas from a purge gas supply source (not shown). Also, a laser gas is supplied from a laser gas supply source (not shown) to the internal space of the laser chamber 131. In the laser processing device 300, an inert gas such as nitrogen gas flows through the internal space of the housing 355.

[0046] In the laser processing device 300, the workpiece 20 is supported on the table 351. The laser processing processor 310 sets the coordinates X, Y, and Z of the initial irradiation position for irradiating the laser light to form the processed part on the stage 350. Thereby, the stage 350 moves the table 351 together with the workpiece 20 to the set initial irradiation position.

[0047] After the table 351 moves, the laser processing processor 310 controls the orientations of the mirrors 371b and 373b by the driving units 371a and 373a of the galvanoscanners 371 and 373 so that the laser beam irradiates the initial irradiation position. Further, the laser processing processor 310 controls the transmittance of the attenuator 332 of the gas laser device 100 and the optical system 330 so that the laser beam irradiated on the workpiece 20 has a desired fluence F required for laser processing. The fluence F is defined as a value obtained by dividing the energy of the laser beam by the cross-sectional area of the laser beam perpendicular to the optical axis of the laser beam.

[0048] The laser processor 190 closes the shutter 170 and drives the charger 141. Further, the laser processor 190 turns on the switch 143a of the pulse power module 143. As a result, the pulse power module 143 applies a pulsed high voltage between the electrode 133a and the electrode 133b from the electrical energy held in the charger 141. Due to this high voltage, a discharge occurs between the electrode 133a and the electrode 133b, and the laser medium contained in the laser gas between the electrode 133a and the electrode 133b is excited, and light is emitted when the laser medium returns to the ground state. Due to this light, light resonates between the rear mirror 145 and the output coupling mirror 147, and the light is amplified every time it passes through the discharge space in the internal space of the laser chamber 131, and laser oscillation occurs. Then, a part of the laser beam passes through the output coupling mirror 147 as pulsed laser light and travels to the beam splitter 153.

[0049] A part of the laser beam that has traveled to the beam splitter 153 is reflected by the beam splitter 153 and received by the optical sensor 155. The optical sensor 155 measures the energy E of the received laser beam and outputs a signal indicating the energy E to the laser processor 190. The laser processor 190 controls the charging voltage so that the difference ΔE between the energy E and the target energy Et is within an allowable range, and after the difference ΔE is within the allowable range, the laser processor 190 transmits a reception preparation completion signal indicating that the reception preparation for the emission trigger Tr has been completed to the laser processing processor 310.

[0050] When the laser processing processor 310 receives the reception ready signal, it transmits the emission trigger Tr to the laser processor 190. When the laser processor 190 opens the shutter 170 in synchronization with the reception of the emission trigger Tr, the laser light that has passed through the shutter 170 enters the laser processing apparatus 300. This laser light is, for example, pulsed laser light with a central wavelength of 193.4 nm.

[0051] The laser light that has entered the laser processing apparatus 300 travels through the high reflection mirror 331a, the attenuator 333, the high reflection mirror 331b, and the irradiation optical system 370 and proceeds to the fθ lens 375, and is focused on the surface of the workpiece 20 by the fθ lens 375.

[0052] The laser light irradiates the workpiece 20 according to the emission trigger Tr defined by the repetition frequency f and the number of pulses P required for laser processing. When the irradiation of the laser light is continued, ablation occurs near the surface of the workpiece 20, resulting in defects. As a result, as shown in FIG. 2, a recess 20a is formed on the surface of the workpiece 20. Further, when the laser light is focused on the bottom surface of the recess 20a, a processed portion 20c such as a through hole is formed. In FIG. 2, in order to distinguish the recess 20a and the processed portion 20c, the processed portion 20c is indicated by a one-dot chain line.

[0053] After the processed portion 20c is formed, when another processed portion 20c is formed in another part of the workpiece 20, the laser processing processor 310 sets the coordinates X, Y, and Z of the initial irradiation position for irradiating the laser light to form another processed portion 20c on the stage 350. Thereby, the stage 350 moves to the initial irradiation position set together with the workpiece 20. Thereafter, at the coordinates, laser processing is performed on the workpiece 20. If another processed portion 20c is not formed, the laser processing ends. Such a procedure is repeated until the laser processing for all the processed portions 20c is completed. In this example, the workpiece 20 is processed until a plurality of processed portions 20c are formed.

[0054] 1.3 Problems At the end of the processing by the laser processing apparatus 300 of the comparative example, the processing depth of the concave portion 20a becomes deeper, and at the upper end side of the concave portion 20a, the cross-sectional area of the laser beam perpendicular to the optical axis is larger than the condensing position of the laser beam on the bottom surface side of the concave portion 20a. When the cross-sectional area becomes larger, the fluence of the laser beam decreases compared to the condensing position. Then, as shown in FIG. 3, when the laser beam with reduced fluence irradiates the wall surface 20e on the upper end side of the concave portion 20a, the wall surface 20e chemically reacts with the atmosphere in which the workpiece 20 is disposed, and a film (not shown) may be generated on the wall surface 20e due to the chemical reaction. Further, the film may be generated at the irradiated portion of the laser beam due to the above chemical reaction even when the laser beam with reduced fluence irradiates the workpiece 20 other than the wall surface. By the way, the workpiece 20 including the through hole may be covered with a protective film (not shown). In this case, the protective film also covers the film generated by the chemical reaction. If the film generated by the chemical reaction peels off from the wall surface 20e or the workpiece 20, the protective film may also peel off from the workpiece 20 due to the peeling of the film, and the workpiece 20 may not be protected by the protective film. Therefore, suppression of the generation of such a film is required. In order to suppress the generation of such a film, the fluence of the laser beam on the upper end side may be increased. However, if the energy of the laser beam is increased to increase the fluence, the workpiece 20 may be unnecessarily processed, such as the upper end of the concave portion 20a being cut off.

[0055] Therefore, in the following embodiments, a laser processing system 10 and a laser processing method capable of suppressing the generation of a film and unnecessary processing of the workpiece 20 are exemplified.

[0056] In the embodiment, the workpiece 20 is described as including a plurality of fibers and a matrix material. Examples of such a workpiece 20 include ceramic matrix composites (CMCs). In this case, examples of the fibers include any one of silicon carbide fibers, carbon fibers, silicon nitride fibers, alumina fibers, and boron nitride fibers. Note that the fibers may be made of other appropriate ceramics. Examples of the matrix material include silicon carbide. The workpiece 20 as described above is used as a component of an engine in fields such as aviation, space, automobiles, and power generation, where lightweight, high strength, and heat resistance are required. Specifically, the workpiece 20 is used, for example, as at least a part of at least one of a shroud, a combustion liner, a fuel nozzle, a swirler, a compressor blade, and a turbine blade.

[0057] In the embodiment, the workpiece 20 is, for example, plate-shaped, but the shape is not particularly limited. Further, the processed portion 20c formed in the workpiece 20 is described as a through-hole formed by oblique hole machining. The through-hole communicates with a pipe (not shown) on the back surface of the workpiece 20, and the pipe communicates with a cooling source (not shown). The cooling source sends a cooling fluid into the through-hole through the pipe. The fluid flows from the through-hole to the surface of the workpiece 20 and cools the surface of the workpiece 20.

[0058] 2. Explanation of the effective processing depth of the workpiece and the cross-sectional area of the laser beam FIG. 4 is a diagram for explaining the effective machining depth teff of the workpiece 20 to be obliquely drilled and the cross-sectional area of the laser beam. The effective machining depth teff is the length in the optical axis direction of the machined portion 20c formed by oblique hole machining in the workpiece 20 whose main surface is inclined with respect to the optical axis. Specifically, it is the length from the front surface to the back surface of the workpiece 20 in the optical axis direction of the laser beam. The effective machining depth teff is t / sinθ2, where θ2 is the inclination angle of the front surface of the workpiece 20 with respect to the optical axis of the laser beam, and t is the thickness of the workpiece 20, which is the length in the direction perpendicular to the front surface, which is the main surface of the workpiece 20. The inclination angle θ2 is the angle obtained by subtracting the inclination angle θ1 of the back surface of the workpiece 20 with respect to the XY plane from 90°. Note that when the main surface of the workpiece 20 is along the XY plane and perpendicular to the optical axis of the laser beam instead of oblique hole machining, the effective machining depth teff is the thickness t of the workpiece 20.

[0059] Also, in FIG. 4, in the laser beam traveling from the fθ lens 375 to the workpiece 20, the cross-sectional area of the laser beam at the beam waist of the laser beam is shown as the cross-sectional area Smin. The cross-sectional area Smin is the minimum cross-sectional area among the cross-sectional areas of the laser beam. Also, in FIG. 4, the cross-sectional area of the laser beam at a position Rayleigh length away from the beam waist in the direction opposite to the traveling direction of the laser beam is shown as the cross-sectional area 2×Smin. Also, in FIG. 4, the cross-sectional area of the laser beam at the upper end of the concave portion 20a formed by focusing the laser beam on the workpiece 20 is shown as the cross-sectional area Sin. The cross-sectional area of the laser beam increases in the order of the cross-sectional area Smin, the cross-sectional area 2×Smin, and the cross-sectional area Sin. In FIG. 4, the above-described effective machining depth teff is a value that satisfies 2×Smin < Sin when the beam waist is located on the back surface of the workpiece 20 and is larger than the Rayleigh length. Note that the effective machining depth teff does not have to be a value that satisfies 2×Smin < Sin and may be less than or equal to the Rayleigh length.

[0060] 3. Explanation of the Laser Processing System and Laser Processing Method of Embodiment 1 Next, the laser processing system 10 and the laser processing method of Embodiment 1 will be described. Regarding the configurations similar to those described above, the same reference numerals will be given, and redundant descriptions will be omitted unless otherwise specified.

[0061] 3.1 Configuration In the laser processing system 10 of this embodiment, the laser processing processor 310 calculates the effective processing depth teff in advance, and the storage device 310a stores parameters.

[0062] These parameters include data indicating the relationship between the cross-sectional areas Sin,2×Smin,Smin and their respective coordinates Z of these cross-sections. In the above relationship, the cross-sectional area is used for explanation, but it may be the beam diameter of the laser beam in the cross-section instead of the cross-sectional area. Also, in the parameters of this embodiment, the coordinate Z of the table 351 when the beam waist of the laser beam is located on the surface of the workpiece 20 is stored as Z0.

[0063] The parameters also include the fluence Fin shown in FIG. 4, the fluence Ffth, and the fluence Fmth. The fluence Fin is the fluence at the cross-sectional area Sin, that is, the fluence at the upper end of the concave portion 20a. The fluence Fin is calculated by the laser processing processor 310 from the cross-sectional area Sin and the energy of the laser beam. The fluence Ffth is the upper limit fluence at which a film (not shown) is formed on the workpiece 20 due to the chemical reaction between the workpiece 20 and the atmosphere by the irradiation of the laser beam. When the workpiece 20 is CMC, the fluence Ffth is 2 or more and 2 or less, and is preferably set to 2 1.5 [J / cm

[0064] In the parameters as described above, the cross-sectional areas Sin, 2×Smin, Smin and the coordinates Z of each of these cross-sections may be measured in advance by sample machining of the workpiece 20, and the fluences Ffth, Fmth may also be calculated in advance from the sample machining. These sample machinings are oblique hole machinings.

[0065] Alternatively, the cross-sectional areas Sin, 2×Smin, Smin and the coordinates Z of each of these cross-sections may be calculated from sample machining in which the main surface of the workpiece 20 is irradiated with laser light in a state perpendicular to the optical axis of the laser light. In this sample machining, a plurality of workpieces 20 are prepared, the coordinates Z of the beam waist of the laser light are positioned at different positions for each of the workpieces 20, and a machined portion 20c is formed on each of the workpieces 20. When the machined portion 20c is formed, the cross-sectional area on the surface of the workpiece 20 among each of the machined portions 20c is measured. An approximate curve is calculated from the relationship between each coordinate Z and the cross-sectional area corresponding to the coordinate Z, and the cross-sectional areas Sin, 2×Smin, Smin and the coordinate Z are calculated from the approximate curve. Note that if the approximate curve cannot be calculated, the storage device 310a stores the relationship between each of the above-described coordinates Z and the cross-sectional area corresponding to the coordinate Z, and the laser processing processor 310 may calculate the cross-sectional areas Sin, 2×Smin, Smin by a complementary method from the relationship.

[0066] In the above sample machining in which the main surface of the workpiece 20 is irradiated with laser light in a state perpendicular to the optical axis, the cross-sectional areas Sin, 2×Smin, Smin may be calculated from the beam diameter of the laser light. The beam diameter can be calculated from the M square obtained from the relationship between the position of the beam waist of the laser light and the diameter of the machined portion 20c on the surface of the workpiece 20. When the cross-section of the laser light is elliptical, the M square in each of the major axis direction and the minor axis direction of the cross-section may be obtained. In this case, the beam diameters in the major axis direction, the minor axis direction, and the coordinate Z at the coordinate Z are calculated based on the M squares in the major axis direction and the minor axis direction of the cross-section and the coordinate Z, respectively, and the cross-sectional area Sin, 2×Smin, Smin of the laser light may be calculated as the product of the beam diameter in the major axis direction and the beam diameter in the minor axis direction.

[0067] Next, the wavelength of the laser light will be described. FIG. 5 shows the spectral waveform FR of the free running of an ArF excimer laser light in nitrogen gas that does not contain oxygen. N2 The center wavelength of the spectral waveform FR N2 is approximately 193.4 nm, and the spectral linewidth is about 450.0 pm at full width at half maximum (FWHM). By the way, it is known that oxygen has a plurality of absorption lines which are absorption bands that absorb laser light. If a part of the spectral waveform FR N2 overlaps with the absorption lines of oxygen in a gas containing oxygen, for example, in air, in the overlapping part, a part of the laser light is absorbed by oxygen. As a result, ozone is generated from oxygen, and the ozone absorbs another part of the laser light. When absorption of the laser light occurs, the spectral waveform FR air has a drop in the light intensity I at a plurality of absorption lines as compared with the spectral waveform FR N2 . Here, the relative intensity on the vertical axis in FIG. 5 is a value obtained by normalizing the light intensity I.

[0068] For example, as described in Japanese Patent Laid-Open No. 3-157917, the absorption lines in the wavelength range from 175.0 nm to 250.0 nm are due to absorption transitions in the Schumann-Runge band. This absorption line corresponds to absorption bands represented by branches R(17), P(15), R(19), P(17), R(21), P(19), R(23), P(21). As shown in FIG. 5, in the spectral waveform FR air of the ArF excimer laser light, the light intensity I drops at the absorption lines corresponding to these branches.

[0069] As described above, if the wavelength of the laser light overlaps with the absorption line of oxygen in the atmosphere, the intensity of the laser light decreases, raising concerns that the workpiece 20 may not be properly processed. However, in the present embodiment, an inert gas flows through the internal space of the housing 355, oxygen is discharged from the housing 355, and the overlap between the wavelength of the laser light and the absorption line of oxygen is suppressed. As a result, the generation of ozone and the absorption of the laser light by the ozone are suppressed, and the light that suppresses the decrease in the intensity of the laser light due to absorption irradiates the workpiece 20.

[0070] 3.2 Operation Next, the operation of the laser processing processor 310 in the present embodiment will be described.

[0071] FIG. 6 is a diagram showing a control flowchart of the laser processing processor 310 of the present embodiment. The control flowchart of the present embodiment includes steps SP11 to SP15 and shows a laser processing method for forming a processed portion 20c on the workpiece 20.

[0072] In the initial state shown in FIG. 6, the laser processing processor 310 has received a reception ready signal from the laser processor 190, but has not transmitted a light emission trigger Tr to the laser processor 190. Therefore, although the laser light is emitted from the laser oscillator 130, since the shutter 170 is closed, the laser light does not enter the laser processing apparatus 300 from the gas laser apparatus 100. Also, in the initial state, the workpiece 20 is already supported by the table 351, and the fluences Ffth and Fmth have been calculated in advance.

[0073] (Step SP11) In this step, the laser processing processor 310 sets the coordinates X and Y of the irradiation position of the laser beam on the stage 350 so that the processed part 20c is formed at the desired position on the workpiece 20. Also, the laser processing processor 310 sets the coordinate Z of the table 351 to Z0 so that the beam waist of the laser beam is located on the surface of the workpiece 20 as shown in FIG. 7. When this setting is made, the stage 350 moves the table 351 on which the workpiece 20 is placed so that the laser beam is irradiated at the set position. When the movement of the table 351 is completed, the stage 350 transmits a signal indicating that fact to the laser processing processor 310. When the laser processing processor 310 receives the signal, it advances the control flow to step SP12.

[0074] (Step SP12) In this step, when the current Z coordinate of the table 351 is Z0, that is, when the beam waist of the laser beam is located on the surface of the workpiece 20 as shown in FIG. 7, the laser processing processor 310 sets the energy of the laser beam so that the fluence Fmax satisfies the formula Fmax≧Fmth. The fluence Fmax is the fluence at the beam waist when the beam waist is located on the surface of the workpiece 20, and is equal to the value obtained by dividing the energy of the laser beam by the cross-sectional area Smin. Further, when the current Z coordinate of the table 351 is Z0+teff, that is, when the beam waist is located at the bottom surface of the deepest recess 20a, the laser processing processor 310 sets the energy of the laser beam so that the fluence Fin satisfies the formula Ffth<Fin=F(Z0+teff)<Fmth. The fluence F(Z0+teff) indicates the fluence Fin when the current Z coordinate of the table 351 is Z0+teff. Further, when the beam waist is located at the bottom surface of the recess 20a, the laser processing processor 310 sets the energy of the laser beam so that the fluence Fb satisfies the formula Fb≧Fmth. The fluence Fb is the fluence at the beam waist, and is equal to the value obtained by dividing the energy of the laser beam by the cross-sectional area Smin, similar to the fluence Fmax. The laser processor 190 sets the energy of the laser beam for the fluences Fin, Fmax, Fb from the fluences Ffth, Fmth calculated by the above-described sample processing. For setting the energy of the laser beam, in this embodiment, the laser processing processor 310 adjusts the transmittance of the attenuator 333 through which the laser beam passes. Therefore, this step can be understood as a transmittance adjustment step of adjusting the transmittance of the attenuator 333 through which the laser beam passes so that the fluence Fmax satisfies the formula Fmax≧Fmth, the fluence Fin satisfies the formula Ffth<Fin<Fmth, and the fluence Fb satisfies the formula Fb≧Fmth. When the laser processing processor 310 adjusts the transmittance of the attenuator 333, the control flow proceeds to step SP13.

[0075] (Step SP13) The laser processing processor 310 transmits the emission trigger Tr to the laser processor 190, causing the shutter 170 to open in the laser processor 190. As a result, the laser light is incident from the gas laser device 100 into the laser processing device 300. The incident laser light travels in the order of the high reflection mirror 331a, the attenuator 333, the high reflection mirror 331b, the mirror 371b, the mirror 373b, and the fθ lens 375, and irradiates the workpiece 20. The laser processing processor 310 performs helical processing.

[0076] Figure 8 is a diagram for explaining helical processing. In Figure 8, the area on the surface of the workpiece 20 where the laser light irradiates to form the processed part 20c is shown as the processing area 23, and Figure 8 is a view of the processing area 23 from the fθ lens 375 side. The dashed lines shown in Figure 8 indicate a plurality of circular irradiation lines that are generally concentric and located at regular intervals in the processing area 23, and in helical processing, the laser light irradiates each irradiation line. In Figure 8, in order to clearly show the outermost circular irradiation line, the irradiation line is shifted inside the processing area 23 for illustration. The inside of the irradiation line is the processing area 23. Each arrow shown in Figure 8 indicates the traveling direction of the laser light irradiating each irradiation line. In helical processing, when the laser light moves and irradiates at least one full circle of the outermost irradiation line, it then moves and irradiates at least one full circle of the irradiation line that is the first one inside the said irradiation line. The laser light gradually shifts the irradiation line it irradiates inward, and finally moves and irradiates the innermost irradiation line. The above movement of the laser light is controlled by the orientation of the mirrors 371b and 373b via the swing angle of the swing axes of the drive units 371a and 373a. Therefore, the irradiation spot of the laser light moves in the in-plane direction of the projection plane of the processing area 23 at a certain height position and irradiates the entire area of the processing area 23. In this irradiation, at least a part of each irradiation spot of the laser light overlaps with another irradiation spot adjacent to the said irradiation spot. Adjacent means indicating the circumferential direction and the radial direction of the irradiation line. When the shutter 170 opens, the laser light irradiates the workpiece 20, and helical processing is performed, the laser processing processor 310 advances the control flow to step SP14.

[0077] (Step SP14) The laser processing processor 310 sets the stage 350 so that the beam waist of the laser beam is displaced by a predetermined amount in the Z direction from the surface of the workpiece 20 toward the back side of the workpiece 20. When this setting is made, the stage 350 moves the table 351 on which the workpiece 20 is placed in the Z direction so that the laser beam is focused at a position displaced by the predetermined amount. When the movement of the table 351 is completed, the stage 350 transmits a signal indicating that fact to the laser processing processor 310. When the laser processing processor 310 receives the signal, it advances the control flow to step SP15.

[0078] (Step SP15) The laser processing processor 310 determines whether or not the current coordinate Z of the table 351 is Z≧Z0 + teff. If the current coordinate Z is not Z≧Z0 + teff, the laser processing processor 310 returns the control flow to step SP13 to continue the processing, and if the current coordinate Z is Z≧Z0 + teff, the laser processing processor 310 ends the control flow.

[0079] In the above control flowchart, when the control flow first proceeds to step SP13, step SP13 becomes the first step of condensing laser light on the surface of the workpiece 20 to form a recess 20a as shown in FIGS. 7 and 9. Further, when the control flow proceeds in the order of steps SP13, SP14, and SP15, and the current coordinate Z is not Z≧Z0+teff and returns from step SP15 to step SP13, the second and subsequent steps SP13 become the second step of condensing laser light on the bottom surface of the recess 20a as shown in FIG. 10. In the second step, by satisfying the formula Fb≧Fmth for the fluence Fb, ablation occurs and defects are generated when the laser light is condensed on the bottom surface of the recess 20a regardless of the height position of the beam waist of the laser light. As a result, the depth of the recess 20a increases. The last step SP13 among the second and subsequent steps becomes the second step performed at the position where the machining depth in the optical axis direction of the workpiece 20 is the deepest. In this last step SP13, the current coordinate Z of the table 351 is Z0+teff, and the fluence Fin satisfies the formula Ffth<Fin<Fmth. Since the fluence Fin is larger than the fluence Ffth, even when the laser light irradiates the wall surface 20e on the upper end side of the recess 20a as shown in FIG. 3, the chemical reaction between the workpiece 20 and the atmosphere is suppressed, and the generation of a film (not shown) on the wall surface 20e due to the chemical reaction is suppressed. Further, since the fluence Fin is smaller than the fluence Fmth, unnecessary machining of the workpiece 20 is suppressed as compared with the case where the fluence Fmth is not set as the upper limit value. When the last step SP13 ends, a through hole, which is the machined part 20c, is formed in the workpiece 20 as shown in FIG. 11. In the first and second steps, since the in-plane direction of the surface of the workpiece 20 is inclined with respect to the optical axis of the laser light, the through hole is formed inclined with respect to the in-plane direction. Further, step SP14 becomes the third step of moving the table 351 on which the workpiece 20 is disposed in the direction opposite to the traveling direction of the laser light between the first step and the second step.

[0080] 3.3 Operation and Effect In the steps SP13 after the second time, which is the second step of the laser processing method of the present embodiment, the fluence Fin satisfies the formula Ffth < Fin < Fmth. Further, in the laser processing system 10 of the present embodiment, the optical system 330 irradiates the workpiece 20 with laser light having a fluence Fin that satisfies the formula Ffth < Fin < Fmth.

[0081] When the fluence Fin is less than or equal to the fluence Ffth, when the workpiece 20 is irradiated with the laser light, the workpiece 20 may chemically react with the atmosphere, and a film may be formed on the workpiece 20 by the chemical reaction. However, in the above configuration, since the fluence Fin is greater than the fluence Ffth, the chemical reaction can be suppressed, and the formation of the film can be suppressed. Further, as the fluence Fin is increased, the formation of the film is suppressed, but the workpiece 20 may be unnecessarily processed, such as the upper end of the concave portion 20a being cut off. However, in the above configuration, since the fluence Fin is less than the fluence Fmth, unnecessary processing of the workpiece 20 can be suppressed as compared with the case where the fluence Fmth is not set as the upper limit value.

[0082] Further, in the laser processing method of the present embodiment, in the first step and the second step, which are the steps SP13 where the control flow first advances, the in-plane direction of the surface of the workpiece 20 is inclined with respect to the optical axis.

[0083] According to the above configuration, the processed portion 20c can be formed in a state inclined with respect to the in-plane direction of the surface.

[0084] Further, in the laser processing method of the present embodiment, in the first step and the second step, the laser light irradiates at least one round of a part of the plurality of concentric irradiation lines, and then irradiates at least one round of another part of the plurality of irradiation lines. That is, in the first step and the second step, helical machining is performed.

[0085] For the processing of forming, for example, a circular through-hole as the processed part 20c in the workpiece 20, in addition to helical drilling, raster scan processing can also be mentioned. Raster scan processing is a process in which, when viewing the through-hole from the front, the laser beam is linearly moved and irradiated left and right from the lower end to the upper end of the through-hole. In this case, the laser beam gradually shifts the irradiation line to be moved and irradiated upward. When forming a circular hole, helical drilling is easier to form the through-hole than raster scan processing.

[0086] Also, in the laser processing method of the present embodiment, the fluence Ffth and the fluence Fmth are calculated in advance by sample processing of the workpiece 20.

[0087] According to the above configuration, the processing time can be shortened compared to the case where the fluence Ffth and the fluence Fmth are calculated during the processing of the workpiece 20.

[0088] Also, in the laser processing method of the present embodiment, the laser beam for irradiating the workpiece 20 is emitted from the gas laser device 100 which is an excimer laser device.

[0089] According to the above configuration, compared to the case where the laser beam is emitted from a device other than the excimer laser device, it is easier to shorten the wavelength of the laser beam, increase the energy of the laser beam, and suppress the divergence angle of the laser beam. When the divergence angle is suppressed, the depth of focus in the workpiece 20 becomes deeper, and for the workpiece 20 with a deep recess 20a on the surface of the workpiece 20, the workpiece 20 with a high convex part on the surface of the workpiece 20, and the thick workpiece 20, the laser processing method is easy to perform processing.

[0090] Also, the wavelength of the laser beam for irradiating the workpiece 20 is a wavelength that is narrowed down so as not to include the absorption line of oxygen.

[0091] According to the above configuration, when the workpiece 20 is disposed in the internal space of the housing 355, it is not necessary for an inert gas such as nitrogen gas to constantly flow through the internal space during processing. Further, when the workpiece 20 is CMC, the laser beam can process the CMC even if no inert gas is flowing.

[0092] In the laser processing method of the present embodiment, each of the fluences Fin and Fmax is adjusted by the transmittance of the attenuator 333, but is not limited thereto. Each of the fluences Fin and Fmax may be adjusted, for example, by the voltage in the charger 141. In this case, the attenuator 333 may be omitted.

[0093] In the laser processing method of the present embodiment, helical machining is used, but the laser beam may be focused on a single point to process the processed portion 20c without moving the laser beam in the in-plane direction. Further, in the laser processing method of the present embodiment, the in-plane direction of the surface of the processed portion 20c is inclined with respect to the optical axis, but may be perpendicular to the optical axis.

[0094] 4. Description of the Laser Processing System and Laser Processing Method of Embodiment 2 Next, the laser processing system 10 and the laser processing method of Embodiment 2 will be described. Note that the same components as those described above are denoted by the same reference numerals, and redundant descriptions are omitted unless otherwise specified.

[0095] 4.1 Configuration FIG. 12 is a schematic diagram showing an overall schematic configuration example of the laser processing system 10 of the present embodiment. In the laser processing system 10 of the present embodiment, the configuration of the optical system 330 of the laser processing apparatus 300 is different from the configuration of the optical system 330 of Embodiment 1. The optical system 330 of the present embodiment further includes a variable beam expander 380 disposed between the high reflection mirror 331b and the mirror 371b in the internal space of the housing 355 and electrically connected to the laser processing processor 310. In FIG. 12, the variable beam expander 380 is simply illustrated.

[0096] FIG. 13 is a schematic diagram showing a schematic configuration example of the variable beam expander 380. The variable beam expander 380 includes a base member 381, lenses 383a, 383b, 383c, stages 385, 387, and holders 389a, 389b, 389c that hold the lenses 383a, 383b, 383c, respectively.

[0097] The base member 381 is provided with the holder 389a and the stage 385. The holder 389b and the stage 387 are arranged on the table 385b of the stage 385. The holder 389c is arranged on the table 387c of the stage 387. The lenses 383a, 383b, 383c are arranged in this order from the high reflection mirror 331b toward the mirror 371b, and the collimated light from the high reflection mirror 331b is incident on the lens 383a. The lenses 383a, 383b, 383c are composed of a combination of a convex lens and a concave lens.

[0098] Each of the stages 385, 387 moves the tables 385b, 387c in the X direction by a control signal from the laser processing processor 310, and adjusts the positions of the lenses 383b, 383c by this movement. By this adjustment, the distance L1 between the lens 383a and the lens 383b and the distance L2 between the lens 383b and the lens 383c are adjusted, and the laser light whose magnification of the laser light and the cross-sectional area of the laser light at the beam waist are adjusted is emitted from the lens 383c as collimated light.

[0099] 4.2 Operation Next, the operation of the laser processing processor 310 in the present embodiment will be described.

[0100] FIG. 14 is a diagram showing a control flowchart of the laser processing processor 310 of the present embodiment. The control flowchart of the present embodiment is different from the control flowchart of the first embodiment in that it includes step SP21 instead of step SP12.

[0101] (Step SP21) In this step, similar to Embodiment 1, when the current coordinate Z of the table 351 is Z0, the laser processing processor 310 sets the energy of the laser beam so that the formula Fmth ≤ Fmax is satisfied, and when the current coordinate Z is Z0 + teff, the formula Ffth < Fin = F(Z0 + teff) < Fmth is satisfied. For the setting of the energy, in the laser processing method of this embodiment, unlike Embodiment 1, the laser processing processor 310 adjusts the distances L1 and L2 of the respective lenses 383a, 383b, 383c by the stages 385 and 387. Therefore, this step can be understood as a distance adjustment step of adjusting the distances L1 and L2 of the plurality of lenses 383a, 383b, 383c through which the laser beam passes in the variable beam expander 380 so that the fluence Fin satisfies the formula Ffth < Fin < Fmth. Thereby, the fluences Fin and Fmax are roughly adjusted. Also, for the setting of the energy of the laser beam, in the laser processing method of this embodiment, similar to Embodiment 1, the laser processing processor 310 adjusts the transmittance of the attenuator 333 through which the laser beam passes. Thereby, the fluences Fin and Fmax are finely adjusted. Further, when the current coordinate Z of the table 351 is Z0 + teff, the variable beam expander 380 adjusts the cross-sectional area Sin and the cross-sectional area Smin so that the cross-sectional area Sin and the cross-sectional area Smin satisfy the following formula. 2 × Smin < Sin

[0102] When the laser processing processor 310 adjusts the distances L1 and L2 and the transmittance, it advances the control flow to step SP13.

[0103] 4.3 Actions and Effects The laser processing method of this embodiment further includes a distance adjustment step of adjusting the distances L1 and L2 of the lenses 383a, 383b, 383c so that the fluence Fin satisfies the formula Ffth < Fin < Fmth.

[0104] According to the above configuration, the magnification of the laser light transmitted through the lenses 383a, 383b, and 383c and the cross-sectional area of the laser light in the beam waist of the laser light are adjusted, and the fluence Fin can satisfy the formula Ffth < Fin < Fmth.

[0105] When the energy of the laser light is sufficiently high, instead of the variable beam expander 380, a variable aperture may be arranged, and the variable aperture may adjust the diameter of the laser light incident on the fθ lens 375. Alternatively, instead of the variable beam expander 380, a beam expander having a plurality of types of fixed magnification lenses may be arranged. Further, the variable beam expander 380 may be omitted, and a zoom lens capable of varying the focal length may be arranged instead of the fθ lens 375. Further, instead of the zoom lens, a plurality of types of condenser lenses with fixed focal lengths may be arranged.

[0106] 5. Description of the laser processing system and laser processing method of Embodiment 3 Next, the laser processing system 10 and the laser processing method of Embodiment 3 will be described. Regarding the configurations similar to those described above, the same reference numerals are given, and redundant descriptions are omitted unless otherwise particularly described.

[0107] 5.1 Configuration Since the configuration of the laser processing system 10 of the present embodiment is the same as that of the laser processing system 10 of Embodiment 2, the description thereof is omitted.

[0108] 5.2 Operation Next, the operation of the laser processing processor 310 in the present embodiment will be described.

[0109] FIG. 15 is a diagram showing a control flowchart of the laser processing processor 310 of the present embodiment. The control flowchart of the present embodiment includes steps SP31 to SP37.

[0110] (Step SP31) In this step, the laser processing processor 310 calculates the beam size of the laser beam that satisfies the respective equations of 2×Smin < Sin = S(Z0 + teff), Fmth ≤ Fmax, and Ffth < Fin = F(Z0 + teff) within the adjustment ranges of the distances L1 and L2 of the lenses 383a, 383b, and 383c. The cross-sectional area S(Z0 + teff) represents the cross-sectional area Sin when the coordinate Z of the table 351 is Z0 + teff. The fluence F(Z0 + teff) represents the fluence Fin when the coordinate Z of the table 351 is Z0 + teff. Also, the laser processing processor 310 sets the magnification of the laser beam in the case of 2×Smin < Sin = S(Z0 + teff) as the magnification Mmin. That is, the laser processing processor 310 pre-sets the magnification in the case where the effective processing depth is the deepest as the magnification Mmin. When the laser processing processor 310 sets the magnification Mmin, it advances the control flow to step SP32.

[0111] (Step SP32) In this step, the laser processing processor 310 sets the magnification M of the laser beam when it is focused on the workpiece 20 to a value larger than the magnification Mmin. For this purpose, the laser processing processor 310 adjusts the positions of the lenses 383b and 383c by the stages 385 and 387, and the cross-sectional area of the laser beam at the beam waist becomes smaller due to this adjustment. When the laser processing processor 310 sets the magnification M, it advances the control flow to step SP33.

[0112] (Step SP33) In this step, similar to step SP11, the laser processing processor 310 sets the coordinates X and Y of the irradiation position for irradiating the laser beam on the stage 350 so that the processed part 20c is formed at a desired position on the workpiece 20. Also, the laser processing processor 310 sets the coordinate Z of the table 351 to Z0 so that the beam waist of the laser beam is located on the surface of the workpiece 20. When this setting is made, the stage 350 moves the table 351 on which the workpiece 20 is placed so that the laser beam is irradiated at the set position. When the movement of the table 351 is completed, the stage 350 transmits a signal indicating that fact to the laser processing processor 310. When receiving the signal, the laser processing processor 310 transmits the emission trigger Tr to the laser processor 190 and causes the laser processor 190 to open the shutter 170, similar to step SP13. As a result, as shown in FIG. 16, the laser beam irradiates the workpiece 20, and the laser processing processor 310 performs helical machining. In FIG. 16, for ease of understanding, the main surface of the workpiece 20 is shown along the XY plane. By focusing the laser beam on the surface of the workpiece 20, a recess 20a (not shown in FIG. 16) is formed on the surface of the workpiece 20. When the helical machining is performed, the laser processing processor 310 advances the control flow to step SP34.

[0113] (Step SP34) In this step, when the laser processing processor 310 receives a signal indicating that the movement of the table 351 from the stage 350 is completed, it determines whether the current coordinate Z of the table 351 is Z≧Z0 + teff. If Z≧Z0 + teff, the laser processing processor 310 ends the processing and ends the control flow. If Z≧Z0 + teff is not satisfied, since the processing is in progress, the laser processing processor 310 advances the control flow to step SP35.

[0114] (Step SP35) In this step, the laser processing processor 310 determines whether the fluence Fin satisfies the formula Fin = F(Z) > Ffth. The fluence F(Z) indicates the fluence Fin at the current coordinate Z of the table 351. If Fin = F(Z) > Ffth, the generation of the film in the recess 20a is suppressed, and thus the laser processing processor 310 advances the control flow to step SP36. If Fin = F(Z) > Ffth does not hold, when the laser beam with reduced fluence irradiates the wall surface 20e on the upper end side of the recess 20a as shown in FIG. 17, a film (not shown) may be generated on the wall surface 20e by the chemical reaction as described above. In FIG. 17, for ease of understanding, the main surface of the workpiece 20 is shown along the XY plane as in FIG. 16. Therefore, the laser processing processor 310 advances the control flow to step SP37.

[0115] (Step SP36) In this step, the laser processing processor 310 moves the table 351 by a predetermined amount ΔZ, updates the coordinate Z of the table 351 to Z + ΔZ, and continues the processing. When the movement of the table 351 is completed, the stage 350 transmits a signal indicating that fact to the laser processing processor 310. In this step, when the coordinate Z of the table 351 is Z + ΔZ, the helical machining is performed.

[0116] When the helical machining at the said coordinate is finished, the laser processing processor 310 returns the control flow to step SP34. If the current coordinate Z of the table 351 at step SP34 is not Z ≧ Z0 + teff, the control flow advances to step SP35. In step SP35, the laser processing processor 310 determines whether the fluence Fin at the current coordinate Z of the table 351 moved in step SP36 satisfies the formula Fin = F(Z) > Ffth. Depending on the determination result in step SP35, the control flow advances to step SP36 or step SP37.

[0117] (Step SP37) In this step, the laser processing processor 310 decreases the magnification M by ΔM within the range where the magnification M satisfies M ≥ Mmin. The magnification M is adjusted by adjusting the distances L1 and L2 of the plurality of lenses 383a, 383b, and 383c through which the laser light passes in the variable beam expander 380. As the processing depth increases, the laser processing processor 310 gradually decreases the magnification, thereby increasing the cross-sectional area Smin of the laser light at the beam waist and decreasing the cross-sectional area Sin of the laser light at the upper end of the recess 20a, as shown in FIG. 18. In FIG. 18, the laser light shown in FIG. 17 is indicated by a dashed line, and for ease of understanding, the main surface of the workpiece 20 is shown along the XY plane, similar to FIGS. 16 and 17. As a result, the fluence Fin at the upper end of the recess 20a increases. When the fluence Fin becomes greater than the fluence Ffth, the formation of the film is suppressed. When the laser processing processor 310 decreases the magnification M, it returns the control flow to step SP35.

[0118] In this embodiment, step SP33 is the first step of focusing the laser light on the surface of the workpiece 20 to form the recess 20a. Further, steps SP34 to SP37 are the second step of focusing the laser light on the bottom surface of the recess 20a.

[0119] 5.3 Operation and Effect In the second step of this embodiment, as the processing depth in the optical axis direction of the workpiece 20 increases, the cross-sectional area of the laser light at the beam waist of the laser light increases. When the cross-sectional area of the laser light at the beam waist increases, the fluence at the processing point becomes higher, and the processing time can be shortened.

[0120] 6. Description of a Modified Example of the Gas Laser Device Next, a modified example of the gas laser device 100 of the above embodiment will be described. Note that the same components as those described above are denoted by the same reference numerals, and redundant descriptions are omitted unless otherwise specifically described.

[0121] FIG. 19 is a schematic diagram showing an overall schematic configuration example of a gas laser device 100 according to a modified example.

[0122] In the gas laser device 100 of this modified example, the laser oscillator 130 is a master oscillator. In the laser oscillator 130, the gas laser device 100 of this modified example includes a narrowbanding module 210 instead of the rear mirror 145. The narrowbanding module 210 includes a housing 210d, a prism 210a, a grating 210b, and a rotary stage 210c disposed in the internal space of the housing 210d. Note that the number of prisms is one in this example, but is not particularly limited as long as at least one prism rotated by the rotary stage 210c is included.

[0123] The prism 210a expands the beam diameter of the light emitted from the window 139a of the laser chamber 131 and makes the light incident on the grating 210b. Further, the prism 210a reduces the beam diameter of the reflected light from the grating 210b and returns the light to the internal space of the laser chamber 131 via the window 139a.

[0124] The surface of the grating 210b is made of a material with high reflectivity, and a large number of grooves are formed on the surface at predetermined intervals. The cross-sectional shape of each groove is, for example, a right triangle. The light incident from the prism 210a to the grating 210b is reflected by these grooves and diffracted in a direction according to the wavelength of the light. The grating 210b is retrofitted so that the incident angle of the light incident from the prism 210a to the grating 210b coincides with the diffraction angle of the diffracted light of the desired wavelength. Thereby, the light near the desired wavelength is returned to the laser chamber 131 via the prism 210a. Note that the incident angle of the light with respect to the grating 210b is changed by the orientation of the prism 210a around the Z axis by the rotary stage 210c. Therefore, by rotating the prism 210a, the wavelength of the light returning from the grating 210b to the laser chamber 131 via the prism 210a can be selected. In this way, the gas laser device 100 corresponds to a wavelength-variable laser device capable of changing the wavelength of the output laser light.

[0125] In the laser oscillator 130, a laser resonator is configured by the output coupling mirror 147 provided with the laser chamber 131 interposed therebetween and the grating 210b, and the laser chamber 131 is disposed on the optical path of this laser resonator. Therefore, the light from the internal space of the laser chamber 131 reciprocates between the grating 210b of the narrowbanding module 210 and the output coupling mirror 147 via the windows 139a and 139b and the prism 210a.

[0126] In the laser oscillator 130, the laser processor 190 controls the charger 141 and the switch 143a in the pulse power module 143 to apply a high voltage between the electrodes 133a and 133b, in the same manner as in the first embodiment. When a high voltage is applied between the electrodes 133a and 133b, a discharge occurs between the electrodes 133a and 133b. The energy of this discharge excites the laser medium in the laser chamber 131, and the excited laser medium emits light when transitioning to the ground state. A part of this light is ultraviolet light and passes through the window 139a. The transmitted light is expanded in the traveling direction of the light when passing through the prism 210a. Also, the light is wavelength-dispersed when passing through the prism 210a and is guided to the grating 210b. The light is incident on the grating 210b at a predetermined angle and diffracted, and the light of a predetermined wavelength is reflected by the grating 210b at the same reflection angle as the incident angle. The light reflected by the grating 210b propagates from the window 139a again into the internal space of the laser chamber 131 via the prism 210a. The wavelength of the light propagating into the internal space of the laser chamber 131 is narrowed so as not to include the absorption line of oxygen. Due to this narrowed light, the excited laser medium causes stimulated emission and the light is amplified. The light passes through the window 139b and travels toward the output coupling mirror 147. A part of the light passes through the output coupling mirror 147, and the remaining part of the light is reflected by the output coupling mirror 147 and passes through the window 139b and propagates into the internal space of the laser chamber 131. The light propagating into the internal space of the laser chamber 131 travels to the grating 210b as described above. Thus, the light of a predetermined wavelength reciprocates between the grating 210b and the output coupling mirror 147. Each time the light passes through the discharge space in the internal space of the laser chamber 131, it is amplified and laser oscillation occurs. And a part of the laser light passes through the output coupling mirror 147.

[0127] The gas laser device 100 further includes an amplifier 430 disposed on the optical path of the laser beam between the output coupling mirror 147 of the laser oscillator 130 and the beam splitter 153 of the monitor module 150. The amplifier 430 is a power oscillator that amplifies the energy of the laser beam output from the laser oscillator 130.

[0128] The amplifier 430 has substantially the same configuration as the laser oscillator 130. To distinguish the components of the amplifier 430 from those of the laser oscillator 130, each component of the amplifier 430 will be described as a laser chamber 431, a pair of electrodes 433a, 433b, an electrical insulation part 435, a return plate 437, a pair of windows 439a, 439b, a charger 441, a pulse power module 443, a switch 443a, an output coupling mirror 447, and an optical path tube 447a. The electrodes 433a, 433b generate a discharge for amplifying the laser beam from the laser oscillator 130. The pulse power module 443 is a voltage application circuit similar to the pulse power module 143. The output coupling mirror 447 is disposed between the window 439b and the beam splitter 153 in the internal space of the optical path tube 447a. The optical path tube 447a has the same configuration as the optical path tube 147a.

[0129] The amplifier 430 further includes a rear mirror 445 disposed between the window 439a and the output coupling mirror 147, and the output coupling mirror 447 and the rear mirror 445 constitute a Fabry - Perot type laser resonator. The output coupling mirror 447 and the rear mirror 445 reflect a part of the laser beam and transmit the remaining part. The rear mirror 445 is disposed in the internal space of the optical path tube 147a together with the output coupling mirror 147.

[0130] In the monitor module 150 of this modification example, a beam splitter 157 and a wavelength monitor 159 are added.

[0131] The beam splitter 157 is disposed between the beam splitter 153 and the optical sensor 155, reflects a part of the reflected light reflected by the beam splitter 153, and transmits the rest. The transmitted light that has passed through the beam splitter 157 is incident on the optical sensor 155, and the reflected light reflected by the beam splitter 157 is incident on the wavelength monitor 159.

[0132] The wavelength monitor 159 is a well-known etalon spectrometer. The etalon spectrometer is composed of, for example, a diffuser plate, an air-gap etalon, a condenser lens, and a line sensor. The etalon spectrometer generates interference fringes of the incident laser light by the diffuser plate and the air-gap etalon, and images the generated interference fringes on the light-receiving surface of the line sensor with the condenser lens. Then, the wavelength λ of the laser light is measured by measuring the interference fringes imaged on the line sensor. The wavelength monitor 159 is electrically connected to the laser processor 190, and outputs a signal indicating data related to the measured wavelength λ of the laser light to the laser processor 190.

[0133] When the laser processor 190 receives signals indicating the target energy Et, the target wavelength λt, etc. from the laser processing processor 310, it controls the charging voltage of the chargers 141, 441 and the rotation of the rotary stage 210c so as to perform laser oscillation with these target values. The target wavelength λt may be, for example, a wavelength that avoids the oxygen absorption line within the amplification region of the ArF excimer laser light. Such a wavelength may be, for example, a wavelength of 193.4 nm.

[0134] When the laser processor 190 receives the emission trigger Tr from the laser processing processor 310, it causes the laser oscillator 130 to perform laser oscillation as described above, and drives the amplifier 430 in synchronization with the laser oscillator 130. At that time, the laser processor 190 turns on the switch 443a of the pulse power module 443 of the amplifier 430 so that discharge occurs when the laser light output from the laser oscillator 130 is incident on the discharge space in the laser chamber 431 of the amplifier 430. As a result, the laser light incident on the amplifier 430 is amplified and oscillated in the amplifier 430.

[0135] The laser light amplified and output by the amplifier 430 travels to the monitor module 150, and the energy and wavelength of the light are measured in the monitor module 150. The laser processor 190 controls the charging voltages of the chargers 141 and 441 and the narrowband module 210 so that the measured actual values of the energy and wavelength approach the target energy Et and the target wavelength λt, respectively.

[0136] When the laser processor 190 opens the shutter 170, the laser light transmitted through the beam splitter 153 of the monitor module 150 enters the laser processing apparatus 300.

[0137] The wavelength of the laser light is narrowed so as not to include the absorption line of oxygen. Therefore, in the laser processing apparatus 300, it is not necessary for an inert gas, which is nitrogen gas, to constantly flow in the internal space of the housing 355 where the workpiece 20 is disposed during the operation of the laser processing system 10. Further, even when the inert gas is not flowing, the laser light can process CMC.

[0138] Incidentally, since high energy is often required for laser processing, as in the gas laser device 100 of this example, by providing the amplifier 430, the energy of the laser light can be increased. Further, when using the narrowed laser light for laser processing as in this example, the energy decreases compared to the case of using the laser light of spontaneous oscillation. In the gas laser device 100 of this example, the decrease in energy can be suppressed by the amplifier 430.

[0139] In this example, a Fabry - Perot type resonator is used as the amplifier 430, but a ring type resonator may also be used. Further, the amplifier 430 may include a convex mirror and a concave mirror instead of the output coupling mirror 447 and the rear mirror 445.

[0140] The laser oscillator 130 may include a semiconductor laser that outputs seed light, a titanium sapphire amplifier that amplifies the seed light, and a wavelength conversion system.

[0141] The semiconductor laser is a distributed feedback type semiconductor laser that outputs CW (Continuous Wave) laser light, which is laser light with a wavelength of 773.6 nm and continuous oscillation, as seed light. By changing the temperature setting of the semiconductor laser, the oscillation wavelength can be changed.

[0142] The titanium sapphire amplifier includes a titanium sapphire crystal and a pumping pulsed laser device. The titanium sapphire crystal is disposed on the optical path of the seed light. The pumping pulsed laser device is a laser device that outputs the second harmonic light of a YLF laser.

[0143] The wavelength conversion system is a wavelength conversion system that generates fourth harmonic light with a central wavelength near 193.4 nm, and includes an LBO (LiB3O5) crystal and a KBBF (KBe2BO3F2) crystal that converts the wavelength from the fundamental wave to the fourth harmonic light. Each crystal is disposed on a rotation stage (not shown) and is configured to be able to change the incident angle of the seed light with respect to each crystal.

[0144] The laser oscillator 130 may include a solid-state laser device that emits ultraviolet laser light with a central wavelength near 193.4 nm and a wavelength conversion system including a nonlinear crystal. In this case, the laser oscillator 130 corresponds to a wavelength-variable laser device, and it is not necessary to oscillate the laser light in the amplification region of an ArF laser, and it is sufficient to oscillate the laser light within the wavelength range of 175.0 nm to 250.0 nm.

[0145] The above description is intended to be illustrative rather than restrictive. Therefore, it is obvious to those skilled in the art that changes can be made to the embodiments of the present disclosure without departing from the scope of the claims. It is also obvious to those skilled in the art that the embodiments of the present disclosure can be used in combination. The terms used throughout this specification and the claims should be construed as "non-limiting" terms unless otherwise specified. For example, terms such as "comprising", "having", "including", and "containing" should be construed as not excluding the presence of elements other than those described. Also, the modifier "one" should be construed to mean "at least one" or "one or more". Further, the term "at least one of A, B, and C" should be construed as "A", "B", "C", "A + B", "A + C", "B + C", or "A + B + C", and should further be construed to include combinations with things other than "A", "B", and "C".

Claims

1. A first step of condensing a laser beam on the surface of a workpiece to form a recess, A second step of condensing the laser beam on the bottom surface of the recess, comprising: In the second step, the fluence of the laser beam at the upper end of the recess is Fin, the upper limit fluence Ffth at which a film is formed by a chemical reaction between the workpiece and the atmosphere due to irradiation of the laser beam, and the lower limit fluence Fmth at which the workpiece can be processed by the laser beam. Then, the fluence Fin satisfies the following formula Ffth < Fin < Fmth Laser processing method.

2. The laser processing method according to claim 1, further comprising a transmittance adjustment step of adjusting the transmittance of an attenuator through which the laser beam passes so that the fluence Fin satisfies the formula.

3. The laser processing method according to claim 1, further comprising a distance adjustment step of adjusting the distance between a plurality of lenses through which the laser beam passes in a variable beam expander so that the fluence Fin satisfies the formula.

4. The laser processing method according to claim 3, The cross-sectional area of the laser beam at the upper end of the recess is Sin, and the cross-sectional area of the laser beam at the beam waist of the laser beam is Smin. The variable beam expander adjusts the cross-sectional area Sin and the cross-sectional area Smin so that the cross-sectional area Sin and the cross-sectional area Smin satisfy the following formula by adjusting the distance. 2 × Smin < Sin

5. The laser processing method according to claim 1, In the second step, a through hole is formed.

6. The laser processing method according to claim 1, In the first step and the second step, the in-plane direction of the surface is inclined with respect to the optical axis of the laser beam.

7. A laser processing method according to claim 1, further comprising a third step of moving a table on which the workpiece is placed in a direction opposite to the traveling direction of the laser beam traveling to the workpiece between the first step and the second step.

8. A laser processing method according to claim 1, In the first step and the second step, the laser beam irradiates at least one round of a part of the irradiation lines among a plurality of concentric irradiation lines, and then irradiates at least one round of another part of the irradiation lines among the plurality of irradiation lines.

9. A laser processing method according to claim 1, The second step is performed at a position where the processing depth in the optical axis direction of the workpiece is the deepest.

10. A laser processing method according to claim 1, In the second step, as the processing depth in the optical axis direction of the workpiece increases, the cross-sectional area of the laser beam in the beam waist of the laser beam is increased.

11. A laser processing method according to claim 10, The size of the cross-sectional area of the laser beam in the beam waist is adjusted by adjusting the distance between a plurality of lenses through which the laser beam passes in a variable beam expander.

12. A laser processing method according to claim 1, The fluence Ffth and the fluence Fmth are calculated in advance by sample processing of the workpiece.

13. A laser processing method according to claim 1, The processing depth in the optical axis direction of the workpiece is larger than the Rayleigh length of the laser beam.

14. The laser processing method according to claim 1, wherein the laser beam is emitted from an excimer laser device.

15. The laser processing method according to claim 1, wherein the fluence Ffth is 1 [J / cm 2 ] or more and 2 [J / cm 2 ] or less.

16. The laser processing method according to claim 1, wherein the wavelength of the laser beam is a narrowband wavelength that does not include the absorption line of oxygen.

17. The laser processing method according to claim 1, wherein the workpiece is made of a ceramic-based composite material.

18. An optical system for irradiating a laser beam, an fθ lens that condenses the laser beam from the optical system onto the surface of the workpiece, and When the fluence of the laser beam at the upper end of the concave portion formed by condensing the laser beam onto the surface is Fin, the upper limit fluence at which a film is formed by the chemical reaction between the workpiece and the atmosphere due to the irradiation of the laser beam is Ffth, and the lower limit fluence at which the workpiece can be processed by the laser beam is Fmth, the optical system irradiates the laser beam with the fluence Fin that satisfies the following formula Ffth < Fin < Fmth Laser processing system.

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