Laser processing apparatus, laser processing method, and method for manufacturing electronic components

Abstract

The laser processing apparatus (100) comprises a pulsed laser oscillator (1) that emits pulsed laser light (L), a mask (3) that shapes the pulsed laser light (L), an optical deflector (6) that diffracts the pulsed laser light (L), a polygon mirror (7) that reflects the pulsed laser light (L), a third relay optical system (53) that generates a conjugate point on the optical path of the pulsed laser light (L) that is optically conjugate with the polygon mirror (7), an fθ lens (8) that is positioned at a front focal point where the conjugate point is located and has telecentric properties that focus the pulsed laser light (L) toward the workpiece (W), and a processing stage (9) on which the workpiece (W) is placed and which changes the position of the workpiece (W) by a moving mechanism.

Description

[Technical Field]

[0001] This disclosure relates to a laser processing apparatus, a laser processing method, and a method for manufacturing electronic components. [Background technology]

[0002] Conventionally, laser processing devices are known for forming vias for interlayer connections in workpieces such as electronic circuit boards. Laser processing devices are desired to be able to form holes at high speed and with high precision. For example, Patent Document 1 discloses a laser processing device comprising a laser light source, an acousto-optic deflector, a polygon mirror, and a focusing lens. In this laser processing device, the polygon mirror is positioned at the front focal point of the focusing lens. Generally, the focusing lens used to focus the beam onto the workpiece is a telecentric fθ lens, which minimizes changes in the workpiece's processing position even if the distance between the focusing lens and the workpiece fluctuates slightly. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0036301 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the technology disclosed in Patent Document 1 places a focusing lens after the polygon mirror. Generally, a telecentric fθ lens is used as the focusing lens in a scanning optical system. The scanning mirror is placed at the front focal position of the telecentric fθ lens. When a polygon mirror is used as the scanning mirror, a large polygon mirror must be placed close to the focusing lens to prevent the laser beam from being deflected. In this case, vibrations caused by the rotation of the polygon mirror may be transmitted to the focusing lens, potentially reducing the accuracy of the laser beam irradiated onto the workpiece.

[0005] The present disclosure has been made in view of the foregoing, and an object of the present disclosure is to obtain a laser processing apparatus capable of suppressing vibration of an fθ lens caused by rotation of a polygon mirror and improving irradiation accuracy of laser light irradiated onto a workpiece. Means for Solving the Problem

[0006] To solve the above-described problem and achieve the object, the laser processing apparatus according to the present disclosure includes: a pulse laser oscillator that emits pulse laser light; a mask that shapes the pulse laser light emitted from the pulse laser oscillator; an optical deflector that diffracts the pulse laser light that has passed through the mask; a polygon mirror that reflects the pulse laser light that has passed through the optical deflector; a third relay optical system through which the pulse laser light reflected by the polygon mirror passes, and which generates a conjugate point that is in an optically conjugate relationship with the polygon mirror on the optical path of the pulse laser light; an fθ lens having telecentricity that is disposed at a position where the conjugate point serves as a front focal position, and condenses the pulse laser light that has passed through the third relay optical system toward a workpiece; and a processing stage on which the workpiece is placed and whose position of the workpiece is changed by a moving mechanism; A first encoder measures the rotation angle of the polygon mirror, and a second encoder measures the position of the machining stage. comprising. The optical deflector predicts the rotation angle of the polygon mirror and the position of the processing stage at a time later than the measurement time, when the pulsed laser beam is irradiated onto the workpiece, based on the measurement information from the first encoder and the second encoder. Based on these predicted values, it corrects the command value of the deflection angle set on the processing stage so that the pulsed laser beam is irradiated onto the target irradiation position. Effects of the Invention

[0007] According to the laser processing apparatus of the present disclosure, there is obtained an effect that vibration of the fθ lens caused by rotation of the polygon mirror can be suppressed, and the irradiation accuracy of laser light irradiated onto a workpiece can be improved. Brief Description of the Drawings

[0008] [Figure 1] Overall view schematically showing the laser processing apparatus according to the first embodiment [Figure 2] Explanatory view schematically showing an example of a workpiece processed by the laser processing apparatus according to the first embodiment [Figure 3]Explanatory diagram showing pulsed laser light after passing through an fθ lens when the pulsed laser light is offset from the optical axis center of the fθ lens at the front focal position [Figure 4] Explanatory diagram showing pulsed laser light after passing through an fθ lens when the pulsed laser light passes through the optical axis center of the fθ lens at the front focal position [Figure 5] Explanatory diagram showing pulsed laser light deflected by an acousto-optic deflector when no second relay optical system is provided [Figure 6] Explanatory diagram showing pulsed laser light deflected by an acousto-optic deflector when a second relay optical system is provided [Figure 7] Explanatory diagram schematically showing the irradiation position of pulsed laser light irradiated onto a workpiece in the laser processing apparatus according to Embodiment 1 [Figure 8] Explanatory diagram schematically showing a state where pulsed laser light is irradiated onto a corner portion of a polygon mirror [Figure 9] Explanatory diagram schematically showing a case where the irradiation shape of pulsed laser light on a workpiece is an elongated hole shape [Figure 10] Graph showing the time waveform of pulses oscillated by a laser oscillator in the laser processing apparatus according to Embodiment 1 [Figure 11] Graph showing the time waveform of burst pulses oscillated by a laser oscillator in the laser processing apparatus according to Embodiment 1 [Figure 12] Explanatory diagram showing irradiation positions by respective pulses in burst pulses oscillated from a laser oscillator in the laser processing apparatus according to Embodiment 1 [Figure 13] Overall view schematically showing Modification 1 of the laser processing apparatus according to Embodiment 1 [Figure 14] Overall view schematically showing Modification 2 of the laser processing apparatus according to Embodiment 1 [Figure 15] Overall view schematically showing the laser processing apparatus according to Embodiment 2 [Figure 16] Explanatory diagram schematically showing a workpiece processed by the laser processing apparatus according to Embodiment 2 [Modes for carrying out the invention]

[0009] The laser processing apparatus, laser processing method, and method for manufacturing electronic components according to embodiments of this disclosure will be described in detail below with reference to the drawings.

[0010] Embodiment 1. Figure 1 is a schematic overall view of a laser processing apparatus according to Embodiment 1. As shown in Figure 1, the laser processing apparatus 100 according to Embodiment 1 is used to manufacture electronic components by drilling holes in a workpiece W, such as an electronic circuit board. The laser processing apparatus 100 includes a pulse laser oscillator 1, an optical system 2, a mask 3, a lens 4, a first relay optical system 51, an acousto-optic deflector 6, a second relay optical system 52, a polygon mirror 7, a third relay optical system 53, a telecentric fθ lens 8, and a processing stage 9.

[0011] The pulsed laser oscillator 1 emits pulsed laser light L. The pulse frequency is, for example, between 100 kHz and 10 MHz. The pulsed laser light L emitted from the pulsed laser oscillator 1 passes through the optical system 2 and irradiates the mask 3.

[0012] Optical system 2 adjusts the beam diameter of the pulsed laser light L emitted from the pulsed laser oscillator 1 according to the diameter of the circular aperture of the mask 3. Optical system 2 may also convert the beam into a top-hat beam, which has a flat intensity and a cylindrical beam intensity distribution.

[0013] Mask 3 has a circular aperture with a diameter d that allows a portion of the pulsed laser beam L to pass through, shaping the pulsed laser beam L emitted from the pulsed laser oscillator 1. Mask 3 is positioned on the optical path of the pulsed laser beam L. The pulsed laser beam L, whose beam diameter has been adjusted by the optical system 2, is incident on Mask 3. Normally, the pulsed laser beam L emitted from the pulsed laser oscillator 1 has a Gaussian profile, but it may not be a perfect Gaussian and its shape may be distorted. Mask 3 shapes the pulsed laser beam L into a perfect circle and cuts off the tail of the Gaussian beam, generating a beam with sharp edges. After passing through Mask 3, a portion of the pulsed laser beam L is diffracted and incident on Lens 4.

[0014] Lens 4 is positioned on the optical path of the pulsed laser beam L. Lens 4 has a focal length of f1 and is positioned at a distance f1 from the mask 3. The pulsed laser beam L passes through lens 4 after passing through mask 3, and generates the Fourier surface of mask 3 at position FT1 downstream of mask 3. As the pulsed laser beam L passes through mask 3, a portion of the beam is diffracted, and a Fourier transform image of mask 3 is generated at position FT1, a distance f1 from lens 4.

[0015] The first relay optical system 51 is positioned on the optical path of the pulsed laser light L between the lens 4 and the acousto-optic deflector 6. The first relay optical system 51 is an optical system for relaying the pulsed laser light L that has passed through the lens 4 to the acousto-optic deflector 6. The first relay optical system 51 includes at least one lens or a curved reflective mirror. The first relay optical system 51 transfers the image of the pulsed laser light L at position FT1 to transfer position FT2 with a transfer magnification M1. The acousto-optic deflector 6 is positioned at transfer position FT2. That is, the first relay optical system 51 makes the Fourier plane of the mask 3 at position FT1 and the position of the acousto-optic deflector 6 optically conjugate.

[0016] The Acousto-Optic Deflector 6 (AOD) uses the acousto-optic effect to deflect the pulsed laser light L that has passed through the mask 3. The pulsed laser light L that has passed through the lens 4 passes through the first relay optical system 51 and is incident on the Acousto-Optic Deflector 6. The Acousto-Optic Deflector 6 has two acousto-optic elements 60 and 61 whose deflection directions are substantially orthogonal to each other. Having two acousto-optic elements 60 and 61 with orthogonal deflection directions allows for free positioning of the processing point and facilitates setting the command value for the deflection angle of the Acousto-Optic Deflector 6. The acousto-optic elements 60 and 61 are arranged such that the transfer position FT2 of the Fourier plane position FT1 of the mask 3 by the first relay optical system 51 exists between the two acousto-optic elements 60 and 61. It is desirable that a half-wave plate be inserted between the two acousto-optic elements 60 and 61. Since the diffraction efficiency of the acousto-optic deflector 6 changes depending on the polarization direction, a half-wave plate makes it possible to obtain high diffraction efficiency for each acousto-optic element 60, 61. The diffraction angle of the acousto-optic elements 60, 61 is controlled by the corresponding AOD driver. The pulsed laser light L emitted from the acousto-optic deflector 6 passes through the second relay optical system 52 and is reflected by the polygon mirror 7. The acousto-optic deflector 6 preferably has the two acousto-optic elements 60, 61 shown in the figure, but it may also be composed of, for example, one acousto-optic element. In this case, the transfer position FT2 of the Fourier plane position FT1 of the mask 3 by the first relay optical system 51 will be inside the acousto-optic element. In the laser processing apparatus 100 according to Embodiment 1, other optical deflectors may be used instead of the acousto-optic deflector 6. Other optical deflectors include, for example, an electro-optic deflector (EOD) or a mirror optical deflector using a piezoelectric element (piezo element) capable of high-speed response.

[0017] The second relay optical system 52 is positioned on the optical path of the pulsed laser beam L between the acousto-optic deflector 6 and the polygon mirror 7. The second relay optical system 52 is an optical system for relaying the pulsed laser beam L that has passed through the acousto-optic deflector 6 to the polygon mirror 7. The second relay optical system 52 includes at least one lens or a curved reflective mirror. The second relay optical system 52 transfers the image of the pulsed laser beam L that has passed through the acousto-optic deflector 6 at the transfer position FT2 to the transfer position FT3 with a transfer magnification M2. The polygon mirror 7 is positioned so that the beam irradiation position of the pulsed laser beam L and the transfer position FT3 coincide. That is, the second relay optical system 52 makes the position of the acousto-optic deflector 6 and the beam irradiation position of the polygon mirror 7 optically conjugate.

[0018] The polygon mirror 7 reflects the pulsed laser light L that has passed through the acousto-optic deflector 6. The polygon mirror 7 is constructed in a polygonal prism shape. For example, the polygon mirror 7 can be constructed in a 12-sided to 36-sided prism shape. The outer surface of the polygon mirror 7 consists of multiple flat reflective surfaces 70 that reflect the pulsed laser light L. For example, if the polygon mirror 7 is constructed in a 12-sided prism shape, there will be 12 reflective surfaces 70. The shape of the polygon mirror 7 and the number of reflective surfaces 70 are appropriately selected according to the content of the laser processing. Each reflective surface 70 is connected to an adjacent reflective surface 70, and the connection points between the reflective surfaces 70 constitute the corners 71 of the polygon mirror 7.

[0019] A rotational drive source (not shown), such as a motor, is connected to the polygon mirror 7 to rotate it. The polygon mirror 7 rotates around a rotation axis (not shown) driven by the rotational drive source. The polygon mirror 7 rotates at a substantially constant speed during processing. The rotational speed of the polygon mirror 7 is set to, for example, 100 to 20,000 rpm. As the polygon mirror 7 rotates, the reflective surface 70 sequentially becomes the surface to be irradiated by the pulsed laser light L. The pulsed laser light L reflected by the polygon mirror 7 passes through the third relay optical system 53 and the fθ lens 8, and is irradiated onto the workpiece W placed on the processing stage 9. The polygon mirror 7 is also provided with a first encoder 72 for measuring the rotation angle of the polygon mirror 7.

[0020] The third relay optical system 53 is positioned on the optical path of the pulsed laser beam L between the polygon mirror 7 and the fθ lens 8. The third relay optical system 53 includes at least one lens or a curved reflective mirror. The third relay optical system 53 generates a conjugate point on the optical path of the pulsed laser beam L, through which the pulsed laser beam L reflected by the polygon mirror 7 passes, and which is optically conjugate to the polygon mirror 7. The third relay optical system 53 transfers the image of the pulsed laser beam L reflected by the polygon mirror 7 at the transfer position FT3 to the transfer position FT4 with a transfer magnification M3. The fθ lens 8 is positioned so that its front focal position and the transfer position FT4 coincide. That is, the third relay optical system 53 transfers the image of the beam irradiation position on the polygon mirror 7 to the front focal position of the fθ lens 8, which is the conjugate point. In the illustrated example, a reflective mirror 54 is provided between the two lenses constituting the third relay optical system 53 as an example.

[0021] The fθ lens 8 has telecentric properties and focuses the pulsed laser light L that has passed through the third relay optical system 53 toward the workpiece W, which is the object to be processed, placed on the processing stage 9.

[0022] A workpiece W, which is the object to be processed, is placed on the processing stage 9. The processing stage 9 is configured to change the processing position of the workpiece W by a moving mechanism (not shown). The moving mechanism has a moving axis that moves the processing stage 9 in a direction perpendicular to the direction in which the pulsed laser beam L is deflected by the polygon mirror 7 at the position of the workpiece W, and a moving axis that moves the processing stage 9 in the same direction as the direction in which the pulsed laser beam L is deflected by the polygon mirror 7. Alternatively, the moving mechanism may consist only of a moving axis that moves the processing stage 9 in a direction perpendicular to the direction in which the pulsed laser beam L is deflected by the polygon mirror 7 at the position of the workpiece W. During processing of the workpiece W, the processing stage 9 moves at a substantially constant speed in a direction perpendicular to the deflection direction of the polygon mirror 7. The processing stage 9 is also provided with a second encoder 90 for measuring its position.

[0023] Figure 2 is a schematic diagram illustrating an example of a workpiece processed by the laser processing apparatus according to Embodiment 1. As shown in Figure 2, the laser processing apparatus 100 forms a processing hole 202 that exposes the copper foil 200 in a workpiece W having, for example, a copper foil 200 and an insulator 201 provided on the upper surface of the copper foil 200. The insulator 201 is, for example, a resin such as ABF or polyimide.

[0024] In the laser processing apparatus 100 with the above configuration, the circular aperture image of the mask 3 is transferred onto the workpiece W by the lens 4, the first relay optical system 51, the second relay optical system 52, the third relay optical system 53, and the fθ lens 8. That is, the position of the transfer point on the mask 3 and the position of the workpiece W are optically conjugate. Because the transfer point on the mask 3 is located on the workpiece W, the pulsed laser light L shaped by the mask 3 is irradiated onto the workpiece W, making it possible to form a circular processing hole. As already mentioned, FT2 is the transfer position of the Fourier plane position FT1 of the mask 3 by the first relay optical system 51. The position of the first relay optical system 51 and the position of the acousto-optic deflector 6 are designed so that the transfer position FT2 is located between the two acousto-optic elements 60 and 61. FT3 is the transfer position of FT2 by the second relay optical system 52. The position of the second relay optical system 52 and the position of the polygon mirror 7 are designed so that the beam irradiation position of the polygon mirror 7 is substantially the transfer position FT3. FT4 is the transfer position of FT3 by the third relay optical system 53. The positions of the third relay optical system 53 and the fθ lens 8 are designed so that the front focal position of the fθ lens 8 is substantially the transfer position FT4. In other words, in the laser processing apparatus 100 according to Embodiment 1, the position FT1 of the Fourier plane of the mask 3, the position FT2 of the acousto-optic deflector 6, the transfer position FT3 which is the beam irradiation position of the polygon mirror 7, and the transfer position FT4 which is the front focal position of the fθ lens 8 are conjugate to each other.

[0025] Figure 3 is an explanatory diagram showing the pulsed laser beam after passing through the fθ lens when the pulsed laser beam is offset from the optical axis center of the fθ lens at the front focal position. As shown in Figure 3, when the point where the pulsed laser beam L and the optical axis 80 of the fθ lens 8 intersect is offset from the front focal position 81 of the fθ lens 8, the pulsed laser beam L after passing through the fθ lens 8 is not parallel to the optical axis 80 of the fθ lens 8. In this case, if the distance between the fθ lens 8 and the workpiece W changes slightly, the irradiation position of the pulsed laser beam L irradiated onto the workpiece W changes. That is, a positional shift occurs in the processing position of the workpiece W.

[0026] Figure 4 is an explanatory diagram showing the pulsed laser beam after passing through the fθ lens when the pulsed laser beam passes through the optical axis center of the fθ lens at the front focal position. As shown in Figure 4, when the point where the pulsed laser beam L and the optical axis 80 of the fθ lens 8 intersect is the front focal position 81 of the fθ lens 8, the pulsed laser beam L after passing through the fθ lens 8 is parallel to the optical axis 80 of the fθ lens 8. The workpiece W is positioned perpendicular to the optical axis 80 of the fθ lens 8. Therefore, the pulsed laser beam L is irradiated perpendicularly to the workpiece W. In this case, even if the distance between the fθ lens 8 and the workpiece W changes slightly, the irradiation position of the pulsed laser beam L irradiated onto the workpiece W does not change because the workpiece W and the optical axis 80 of the fθ lens 8 are perpendicular.

[0027] In the laser processing apparatus 100 according to Embodiment 1, the position FT2 of the acousto-optic deflector 6, the transfer position FT3 which is the beam irradiation position of the polygon mirror 7, and the transfer position FT4 which is the front focal position 81 of the fθ lens 8 are conjugate to each other. Therefore, the pulsed laser light L deflected by the acousto-optic deflector 6 and the polygon mirror 7 is optically equivalent to being deflected on the optical axis 80 of the fθ lens 8 and at the front focal position 81 of the fθ lens 8. As a result, as shown in Figure 4, the pulsed laser light L is irradiated perpendicularly to the workpiece W.

[0028] Next, the effects of having a second relay optical system 52 in the laser processing apparatus 100 according to Embodiment 1 will be explained. Figure 5 is an explanatory diagram showing pulsed laser light deflected by an acousto-optic deflector when there is no second relay optical system. As shown in Figure 5, when there is no second relay optical system 52, the pulsed laser light L deflected by the acousto-optic deflector 6 changes the beam irradiation position on the polygon mirror 7 depending on the deflection angles γ1 and γ2 of the acousto-optic deflector 6. This is because even if the angle of the polygon mirror 7 at the timing of beam irradiation is known, depending on the deflection angles γ1 and γ2 of the acousto-optic deflector 6, there is a possibility that the pulsed laser light L may be irradiated onto the corners 71 of the polygon mirror 7 or an unintended reflective surface 70. This may cause problems such as a change in the shape of the pulsed laser light L at the processing point or a large shift in the processing position of the workpiece W.

[0029] Figure 6 is an explanatory diagram showing pulsed laser light deflected by an acousto-optic deflector in the case of having a second relay optical system. As shown in Figure 6, in the laser processing apparatus 100 according to Embodiment 1, the position FT2 of the acousto-optic deflector 6 and the transfer position FT3, which is the beam irradiation position of the polygon mirror 7, are conjugate by the second relay optical system 52. Therefore, regardless of the deflection angles γ1 and γ2 of the acousto-optic deflector 6, the irradiation position of the pulsed laser light L on the polygon mirror 7 is the same. Note that the irradiation position of the pulsed laser light L on the polygon mirror 7 being the same means that the transfer position FT3, which is the beam irradiation position of the polygon mirror 7, is the same position on the optical axis, and does not mean that it is the same position on the reflective surface of the rotating polygon mirror 7.

[0030] Next, the effects of having a third relay optical system 53 in the laser processing apparatus 100 according to Embodiment 1 will be explained. In conventional laser processing apparatuses, the fθ lens 8 is placed near the polygon mirror 7. The rotation speed of the polygon mirror 7 is set to, for example, 100 to 20,000 rpm. Therefore, as the polygon mirror 7 rotates at high speed, vibrations of the polygon mirror 7 are transmitted to the surroundings, and there is a risk that the surrounding optical elements will vibrate. For example, if vibrations due to the rotation of the polygon mirror 7 are transmitted to the fθ lens 8 and the fθ lens 8 vibrates, the irradiation position of the pulsed laser light L at the processing point will shift. This will worsen the accuracy of the processing position of the workpiece W. Also, when processing with multiple pulses, effects such as the processed shape not being a perfect circle may occur. In particular, when processing small diameter holes, the focal length fθ lens 8 fθ Since the distance between the fθ lens 8 and the polygon mirror 7 becomes shorter, it is necessary to bring them closer together, which makes a practical arrangement difficult. Also, if the distance between the polygon mirror 7 and the fθ lens 8 is close, dust generated from the rapidly rotating polygon mirror 7 may adhere to the fθ lens 8, potentially degrading the performance of the fθ lens 8, or the pulsed laser beam L may damage the fθ lens 8.

[0031] In the laser processing apparatus 100 according to Embodiment 1, a third relay optical system 53 is arranged between the polygon mirror 7 and the fθ lens 8, so that the distance between the polygon mirror 7 and the fθ lens 8 can be increased. This allows the focal length f fθ Even when using a short fθ lens 8, vibrations of the fθ lens 8 caused by the rotation of the polygon mirror 7 can be suppressed, thereby improving the irradiation accuracy of the pulsed laser light L irradiated onto the workpiece W. Furthermore, since it is not necessary to bring the polygon mirror 7 and the fθ lens 8 close together, the focal length f fθEven when a short fθ lens 8 is used, interference between the polygon mirror 7 and the holder or the like of the fθ lens 8 does not occur, which facilitates the arrangement of the polygon mirror 7 and the fθ lens 8. In addition, it is possible to suppress problems such as adhesion of dust or the like caused by rotation of the polygon mirror 7 to the fθ lens 8, damage to the fθ lens 8 caused by such dust, and deterioration of the processed shape due to distortion of the profile of the pulsed laser beam L caused by dust. Furthermore, since the position of the polygon mirror 7 can be optically aligned with the front focal position of the fθ lens 8, telecentric processing can be achieved.

[0032] Next, the setting of deflection angles θ x,AOD , θ y,AOD of the acousto-optic deflector 6 in the laser processing apparatus 100 according to the first embodiment will be described. The deflection angle θ x,AOD is the deflection angle of the acousto-optic element 60. The deflection angle θ y,AOD is the deflection angle of the acousto-optic element 61. FIG. 7 is an explanatory diagram schematically showing the irradiation position of pulsed laser light irradiated onto a workpiece in the laser processing apparatus according to the first embodiment. In FIG. 7, on the processing surface, the deflection direction by the acousto-optic element 60 is parallel to the deflection direction by the polygon mirror 7, and the deflection direction by the acousto-optic element 61 is shown as being orthogonal to the deflection direction by the polygon mirror 7. However, the relationship between the deflection directions of the acousto-optic elements 60 and 61 and the deflection direction by the polygon mirror 7 is not limited to the illustrated example. The circular marks in the figure indicate the irradiation positions of the pulsed laser beam L. Δ in the figure AOD indicates the scanning range by the acousto-optic deflector 6 on the workpiece W. δ pg indicates the irradiation interval of the pulsed laser beam L in the polygon scanning direction on the workpiece W. δ tb indicates the irradiation interval of the pulsed laser beam L in the processing stage scanning direction on the workpiece W.

[0033] The pulsed laser beam L is output at constant pulses from the pulsed laser oscillator 1 during processing of the workpiece W. The polygon mirror 7 rotates at a constant speed V pgIt rotates at a constant speed V. Therefore, when the diffraction direction of the acousto-optic deflector 6 is fixed, pulsed laser light L is irradiated onto the workpiece W at constant distance intervals. As a result, as shown in Figure 7, rows L1 are formed on the workpiece W by the irradiation marks of the pulsed laser light L. In addition, the processing stage, which operates in a direction perpendicular to the deflection direction of the polygon mirror 7, also moves at a constant speed V. tb Because it operates in this manner, when the reflective surface 70 of the polygon mirror 7 that is irradiated with the laser changes, another row L2 is formed. As a result, a grid of irradiation positions of the pulsed laser light L is formed on the processing point. The acousto-optic deflector 6 uses the deflection angles θ of the acousto-optic elements 60,61 to shift each point of the grid formed by the rotation of the polygon mirror 7 and the movement of the processing stage 9 to the point to be laser processed. x,AOD ,θ y,AOD The settings are configured as follows. For example, point P1 in Figure 7 is the center of the scan range of the acousto-optic deflector 6 at a certain time t1 when pulsed laser light L is output. Point P2 is the center of the scan range of the acousto-optic deflector 6 at time t1+Δt when the next pulsed laser light L is output. Δt is the time interval between pulses of pulsed laser light L output from pulsed laser oscillator 1. Point P0 is the point to be processed. Vector Γ1 represents the vector from point P1 to point P0. Vector Γ2 represents the vector from point P2 to point P0. At time t1, the deflection angle θ is set so that the displacement at the processing point is equal to vector Γ1. x,AOD ,θ y,AOD Set the deflection angle θ such that at time t1+Δt, the displacement at the machining point is vector Γ2. x,AOD ,θ y,AOD By setting this, it becomes possible to irradiate the same processing location on the workpiece W with multiple pulsed laser beams L for processing.

[0034] Next, we will explain the polygon scanning direction on the workpiece W and the irradiation position of the pulsed laser light L in a direction orthogonal to the polygon scanning. The ABCD ray matrix is ​​used to calculate the beam position and beam angle of the pulsed laser light L with respect to the optical axis. That is, if the position of the main beam ray of the pulsed laser light L with respect to the optical axis at a certain point 1 is r1 and the angle is r1', then the position of the main beam ray of the pulsed laser light L with respect to the optical axis at point 2 after passing through an optical system with an ABCD ray matrix, r2 and the angle r2' can be expressed by the following equation (1).

[0035]

number

[0036] When points 1 and 2 are optically conjugate, B in the ABCD ray matrix is ​​0. In this case, the ABCD ray matrix of the second relay optical system 52 is given by equation (2) below. Note that M2 is the transfer magnification of the second relay optical system 52.

[0037]

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[0038] Furthermore, the ABCD ray matrix of the third relay optical system 53 is given by equation (3) below. Note that M3 is the transfer magnification of the third relay optical system 53.

[0039]

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[0040] The deflection angle of the pulsed laser beam L by the acousto-optic deflector 6 in the polygon scanning direction is θ. x,AOD The deflection angle of the pulsed laser light L by the acousto-optic deflector 6 in a direction orthogonal to the polygon scanning direction is θ. y,AOD The polarization angle of the pulsed laser light L by the polygon mirror 7 is θ pgThe deflection angles are the differences from the reference deflection angles. Since the main beam ray at the position of the acousto-optic deflector 6 is on the optical axis of the pulsed laser light L, the position of the main beam ray at the front focal position of the fθ lens 8 is r fθ This becomes 0. Also, the angle r of the principal ray of the beam at the front focal position of lens fθ 8. fθ ' is given by the following equation (4).

[0041]

number

[0042] Then, the irradiation position Δ of the pulsed laser light L in the polygon scanning direction on the workpiece W. x This is given by the following equation (5). Note that f fθ This is the focal length of lens 8 at fθ.

[0043]

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[0044] Furthermore, the irradiation position Δ of the pulsed laser light L is perpendicular to the polygon scanning on the workpiece W. y This is given by equation (6) below. Note that the direction orthogonal to the polygon scanning on the workpiece W is the scanning direction of the machining stage 9.

[0045]

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[0046] The second relay optical system 52 and the third relay optical system 53 are conjugate. Therefore, the irradiation position of the pulsed laser light L on the workpiece W can be separated into the deflection component by the acousto-optic deflector 6 and the deflection component by the polygon mirror 7. This makes it easier to calculate the irradiation position of the pulsed laser light L on the workpiece W, and also makes it easier to calculate the command amount for the acousto-optic deflector 6 when correcting the angular displacement of the polygon mirror 7 with the acousto-optic deflector 6.

[0047] Furthermore, the polygon mirror 7 and the processing stage 9 are operated at a constant speed, but in reality, they deviate slightly from that constant speed. The polygon mirror 7 is equipped with a first encoder 72 for measuring the rotation angle. The processing stage 9 is equipped with a second encoder 90 for measuring its position. From the information of the first encoder 72 and the second encoder 90, the irradiation position of the pulsed laser beam L after a certain period of time is predicted, and this is reflected in the setting angle of the acousto-optic deflector 6 so that the pulsed laser beam L is irradiated to the target processing position. At time t0, the rotation angle of the polygon mirror 7 can be measured from the first encoder 72. Also, by combining the information from the first encoder 72 at time t0 with the information from the first encoder 72 at a time before time t0, the rotation speed of the polygon mirror 7 at time t0 can be calculated. From this information, the rotation angle of the polygon mirror 7 at time t1, which is after time t0 and when the pulsed laser beam L is irradiated onto the workpiece W, can be predicted. The difference between the predicted rotation angle of the polygon mirror 7 at time t1, calculated from the information of the first encoder 72, and the set value of the rotation angle of the polygon mirror 7 at time t1 is Δθ. pg,t1 Let's assume the following: The difference Δθ between the predicted rotation angle of polygon mirror 7 at time t1 and the set value of the rotation angle of polygon mirror 7 at time t1. pg,t1 The amount of displacement Δ of the irradiation position of the pulsed laser light L on the workpiece W. x,t1 This is given by equation (7) below.

[0048]

number

[0049] Command value Δθ of the deflection angle of the acousto-optic deflector 6 in the polygon scanning direction at time t1 x,AOD,t1 By changing the setting by only the amount shown in equation (8) below from the original setting value at time t1, it becomes possible to keep the irradiation position of the pulsed laser light L on the workpiece W constant even if the rotation angle of the polygon mirror 7 deviates from the set value.

[0050]

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[0051] Similarly, the position and velocity of the machining stage 9, which moves in a direction orthogonal to the polygon scanning direction, at time t0 can be measured from a second encoder 90 provided on the machining stage 9. The position of the machining stage 9 at time t1 can be predicted from the information from the second encoder 90. The difference between the predicted value and the set value of the position of the machining stage 9 at time t1 is Δ y,tb,t1 Therefore, the command value Δθ of the acousto-optic deflector 6, which deflects in a direction orthogonal to the polygon scanning direction at time t1. y,AOD,t1 By changing the setting by only the amount shown in equation (9) below from the original setting value at time t1, it becomes possible to keep the irradiation position of the pulsed laser light L on the workpiece W constant even if the position of the processing stage 9 deviates from the set value.

[0052]

number

[0053] Next, the effects of having a first relay optical system 51 in the laser processing apparatus 100 according to Embodiment 1 will be explained. Beam diameter φ at the position of the acousto-optic deflector 6 AOD This is given by the following equation (10).

[0054]

number

[0055] λ is the wavelength. K is the proportionality constant, determined by the definition of the beam diameter. If we consider the beam diameter to extend to the first dark ring of the diffracted light from mask 3, then K ≈ 1.22. The acousto-optic deflector 6 has an effective area where the pulsed laser light L deflected by the acousto-optic deflector 6 can be used without distortion. In this case, the pulsed laser light L must be incident within the effective area. Beam diameter φ at the position of the acousto-optic deflector 6. AODIf the beam diameter φ becomes large, the pulsed laser beam L may extend beyond the effective area, potentially distorting the beam profile at the processing point and leading to processing defects. On the other hand, if the pulse energy of the pulsed laser beam L is high, the beam diameter φ at the position of the acousto-optic deflector 6 may be large. AOD If the value becomes small, the acousto-optic deflector 6 may be damaged or its lifespan may be reduced. Also, if the beam diameter on the workpiece W is fixed, the beam diameter φ at the position of the acousto-optic deflector 6. AOD If it is small, for example, the transfer magnification M2 of the second relay optical system 52 and the transfer magnification M3 of the third relay optical system 53 need to be increased. The range of the deflection angle in the acousto-optic deflector 6 is Δθ AOD Therefore, the scan range Δ by the acousto-optic deflector 6 on the workpiece W is AOD This is given by the following equation (11).

[0056]

number

[0057] Therefore, as the transfer magnification M2 increases, the scan range Δ by the acousto-optic deflector 6 on the workpiece W increases. AOD The beam diameter becomes smaller, making it impossible to irradiate the pulsed laser light L to the desired position on the workpiece W. That is, the beam diameter φ at the position of the acousto-optic deflector 6. AOD There is an appropriate size for this. The first relay optical system 51, together with the lens 4, transfers the position FT1 of the Fourier plane of the mask 3 onto the acousto-optic deflector 6. The distance between the mask 3 and the lens 4 is equal to the focal length f1 of the lens 4. Also, the distance between the lens 4 and position FT1 is equal to the focal length f1 of the lens 4. If the diameter d of the circular aperture of the mask 3 is large, the divergence angle of the diffracted light becomes small. For example, if the first relay optical system 51 is not provided, the focal length f1 of the lens 4 must be increased in order to obtain an appropriate beam diameter for the illumination of the acousto-optic deflector 6 at position FT1 of the Fourier plane of the mask 3, and the entire optical system becomes large. When the first relay optical system 51 is present, the design of the first relay optical system 51, together with the lens 4, allows for an appropriate beam diameter φ at the position of the acousto-optic deflector 6. AODWith this setup, the position FT1 of the Fourier plane of mask 3 can be substantially created on the acousto-optic deflector 6 using a short optical system.

[0058] Generally, to change the machining diameter formed on the workpiece W, the diameter d of the circular opening of the mask 3 is changed by modifying the mask 3. The beam diameter at the machining point is given by the following equation (12).

[0059]

number

[0060] If the diameter d of the circular aperture of the mask 3 is changed to change the beam diameter at the processing point, the size of the diffracted light by the mask 3 changes, and therefore the beam diameter on the acousto-optic deflector 6 changes from the appropriate beam diameter. On the other hand, in the laser processing apparatus 100 according to Embodiment 1, the second relay optical system 52 maintains a conjugate relationship between the position FT2 of the acousto-optic deflector 6 and the transfer position FT3, which is the beam irradiation position of the polygon mirror 7, and sets the transfer magnification M2 according to the size of the processing hole to be formed in the workpiece W, which is the object to be processed. That is, the second relay optical system 52 is a variable zoom system, and instead of changing the diameter d of the circular aperture of the mask 3 when changing the beam diameter at the processing point, the transfer magnification M2 of the second relay optical system 52 is changed. Since the diameter d of the circular aperture of the mask 3 does not change, the beam diameter φ at the position of the acousto-optic deflector 6 AOD The beam diameter does not change. Therefore, regardless of the beam diameter at the processing point, the beam diameter φ at the position of the acousto-optic deflector 6 remains constant. AOD This makes it possible to make it the optimal size within the effective area of ​​the acousto-optic deflector 6 while suppressing damage to the acousto-optic deflector 6 and reducing its lifespan.

[0061] If the pulse energy of the pulsed laser light L required for processing is low, it is also possible to change the transfer magnification M1 of the first relay optical system 51. In this case, the first relay optical system 51 maintains a conjugate relationship between the position FT1 which is the Fourier plane of the mask 3 and the position FT2 of the acousto-optic deflector 6, and sets the transfer magnification M1 according to the size of the processing hole to be formed in the workpiece W, which is the object to be processed. When the transfer magnification M1 is reduced, the beam diameter on the acousto-optic deflector 6 becomes smaller. Because the pulse energy is low, damage to the acousto-optic deflector 6 and reduction of its lifespan do not occur.

[0062] The response time of the acousto-optic deflector 6 is proportional to the beam diameter on the acousto-optic deflector 6. That is, as the beam diameter on the acousto-optic deflector 6 decreases, the response time of the acousto-optic deflector 6 decreases. In Embodiment 1, the upper limit of the pulse frequency setting of the pulsed laser oscillator 1 is determined by the response time of the acousto-optic deflector 6. When the response time of the acousto-optic deflector 6 decreases, it becomes possible to increase the pulse frequency of the pulsed laser oscillator 1, making it possible to complete processing in a shorter time. Generally, increasing the pulse frequency of the pulsed laser oscillator 1 decreases the pulse energy, but this is not a problem when the pulse energy required for processing is low.

[0063] It is also effective to change both the transfer magnification M1 of the first relay optical system 51 and the transfer magnification M2 of the second relay optical system 52. In this case, the pulse frequency of the pulsed laser light L of the pulsed laser oscillator 1 is set according to the pulse energy required to process the workpiece W, which is the object to be processed. For example, if the processing hole is small in diameter, the pulse energy required to process the workpiece is low. That is, the pulse frequency of the pulsed laser oscillator 1 is increased. The transfer magnification M1 of the first relay optical system 51 is set so that the position FT1 which is the Fourier plane of the mask 3 and the position FT2 of the acousto-optic deflector 6 are in a conjugate relationship, and the response time of the acousto-optic deflector 6 corresponds to the pulse frequency of the pulsed laser light L. This adjusts the beam diameter on the acousto-optic deflector 6. The second relay optical system 52 maintains a conjugate relationship between the position FT2 of the acousto-optic deflector 6 and the transfer position FT3, which is the beam irradiation position of the polygon mirror 7. Furthermore, the transfer magnification M2 is set according to the size of the machining hole formed in the workpiece W, which is the object to be machined, and the transfer magnification M1 of the first relay optical system 51. This makes it possible to machine small-diameter holes at high speed.

[0064] The same effect can be obtained by changing the diameter d of the circular aperture of the mask 3 instead of changing the transfer magnification M1 of the first relay optical system 51. In this case as well, the pulse frequency of the pulsed laser light L of the pulsed laser oscillator 1 is set according to the pulse energy required to process the workpiece W, which is the object to be processed. For example, if the processing hole is small in diameter, the pulse energy required to process the workpiece is low. That is, the pulse frequency of the pulsed laser oscillator 1 is increased. The diameter d of the circular aperture of the mask 3 is set according to the pulse frequency of the pulsed laser light L. As a result, the beam diameter on the acousto-optic deflector 6 is adjusted so that the response time of the acousto-optic deflector 6 corresponds to the pulse frequency. The second relay optical system 52 maintains a conjugate relationship between the position FT2 of the acousto-optic deflector 6 and the transfer position FT3, which is the beam irradiation position of the polygon mirror 7, and sets the transfer magnification M2 according to the size of the processing hole formed in the workpiece W, which is the object to be processed, and the diameter d of the circular aperture of the mask 3.

[0065] Figure 8 is a schematic diagram illustrating how pulsed laser light is irradiated onto the corners of a polygon mirror. As shown in Figure 8, when the pulsed laser light L has a large beam diameter, it is more likely to irradiate the corners 71 of the polygon mirror 7 upon entry into the polygon mirror 7. The pulsed laser light L irradiated onto the corners 71 of the polygon mirror 7 cannot be used for processing because its profile is distorted. In this case, the number of laser shots effective for processing is reduced, and the processing speed slows down. When processing small diameter holes, the beam diameter of the pulsed laser light L needs to be large at the front focal position of the fθ lens 8. If the polygon mirror 7 is placed at the front focal position of the fθ lens 8, the beam diameter at the position of the polygon mirror 7 needs to be large, which increases the proportion of pulsed laser light L irradiated onto the corners 71 of the polygon mirror 7. By conjugating the irradiation position of the polygon mirror 7 and the front focal position of the fθ lens 8 in the third relay optical system 53, the distance between the polygon mirror 7 and the fθ lens 8 can be increased while maintaining the telecentricity of the pulsed laser beam L. By setting the transfer magnification M3 of the third relay optical system 53 to 1 or more, the beam diameter at the position of the polygon mirror 7 can be made smaller than the beam diameter at the front focal position of the fθ lens 8, thereby reducing the number of laser shots irradiated onto the corners 71 of the polygon mirror 7 and improving the processing speed. Alternatively, the size of the polygon mirror 7 can be reduced without changing the number of laser shots irradiated onto the corners 71 of the polygon mirror 7. Miniaturizing the polygon mirror 7 reduces its inertia, allowing for high-precision rotation control, and also reduces the current supplied to the rotation drive source that rotates the polygon mirror 7, leading to reduced power consumption. Furthermore, since the angular magnification of the third relay optical system 53 is 1 / M3, setting M3 to 1 or greater makes it possible to reduce the angular deviation at the front focal position of the fθ lens 8 in relation to the deviation from the set value of the rotation angle of the polygon mirror 7. This reduces the deviation of the irradiation position of the pulsed laser beam L at the processing point, improving positioning accuracy.

[0066] Figure 9 is a schematic diagram illustrating the case where the irradiation shape of the pulsed laser beam L on the workpiece is elongated. The polygon mirror 7 rotates during the machining of the workpiece W. Therefore, if the pulse width τ of the pulsed laser beam L is long, the irradiation shape of the pulsed laser beam L on the workpiece W may become elongated, as shown in Figure 9. In this case, the machining marks of the pulsed laser beam L will be larger than expected, and machining defects such as overlapping with adjacent machining holes may occur. Therefore, the upper limit of the pulse width τ of the pulsed laser beam L is determined by the acceptable roundness of the irradiation shape of the pulsed laser beam L. Here, the scan angle range of the polygon mirror 7 is 2 × 2π / N f N f is the number of reflective surfaces of the polygon mirror 7. The scan range of the polygon mirror 7 on the processed surface is given by the following equation (13).

[0067]

number

[0068] Furthermore, the scanning speed of the pulsed laser beam L at the processing point by the polygon mirror 7 is given by the following equation (14). However, f rot This is the rotation frequency of Polygon Mirror 7.

[0069]

number

[0070] Then, at the processing point, the amount of positional shift of the pulsed laser beam L due to the pulse width τ is given by the following equation (15).

[0071]

number

[0072] The condition for the displacement of the pulsed laser beam L due to the pulse width τ on the workpiece W to be smaller than the transfer beam diameter at the processing point is given by the following equation (16).

[0073]

number

[0074] In other words, since it becomes smaller than the transfer beam diameter at the processing point, the pulse width τ is given by equation (17) below. The condition for the laser pulse width (for example, the condition for an elongated hole with a ratio of 1:<2) is given by equation (17). Note that <2 represents a value smaller than 2. In other words, by satisfying the condition of equation (17), the irradiation shape of the pulsed laser beam L can be made to an acceptable degree of roundness.

[0075]

number

[0076] Figure 10 is a graph showing the time waveform of a pulse oscillated by a laser oscillator in a laser processing apparatus according to Embodiment 1. Figure 11 is a graph showing the time waveform of a burst pulse oscillated by a laser oscillator in a laser processing apparatus according to Embodiment 1. In Figures 10 and 11, the vertical axis represents laser intensity. In Figures 10 and 11, the horizontal axis represents time.

[0077] The pulse laser oscillator 1 of the laser processing apparatus 100 according to Embodiment 1 is not limited to the configuration that oscillates a general pulse as shown in Figure 10, but may also be configured to oscillate a burst pulse as shown in Figure 11. As shown in Figure 11, one burst pulse contains multiple pulses. The pulse laser oscillator 1 oscillates a burst pulse at a constant period. If the pulse interval within the burst pulse is Δt and the number of pulses within the burst pulse is Np, then the time interval from the first pulse to the last pulse within the burst pulse, i.e., the irradiation time of one burst pulse, is Δt × Np. The pulse interval Δt is, for example, 100 ps to 1 ns. The frequency of the burst pulse is, for example, 100 kHz to 10 MHz. The frequency of the burst pulse is approximately the same as the frequency of a general pulse shown in Figure 10. When the irradiation time of one burst pulse Δt × Np is sufficiently small, the amount of beam movement by the polygon mirror 7 on the workpiece W during the irradiation time of one burst pulse becomes sufficiently small relative to the beam diameter on the workpiece W. Therefore, the displacement of the workpiece W processing position due to pulses within a burst pulse is small relative to the target processing hole diameter. Figure 12 is an explanatory diagram showing the irradiation position of each pulse within a burst pulse emitted from a laser oscillator in a laser processing apparatus according to Embodiment 1. That is, as shown in Figure 12, when the irradiation time Δt × Np of one burst pulse is sufficiently small, it becomes possible to process a nearly perfect circle.

[0078] Generally, when performing via processing with a laser processing device, in order to suppress the effects of variations in laser pulses and maintain hole quality such as the shape of the processed hole, processing is done with multiple pulses of relatively low pulse energy rather than with a single pulse of high pulse energy. For example, when processing with 30 pulses in the laser processing device 100 according to Embodiment 1, the points of the grid formed by the polygon mirror 7 and the processing stage 9 are moved to the processing point by the acousto-optic deflector 6, and this must be done for 30 pulses. This means that the acousto-optic deflector 6 must be operated 30 times for each processing point, and the laser pulses must be superimposed on the same location.

[0079] On the other hand, when processing with burst pulses in the laser processing apparatus 100, since there are multiple pulses within a single burst pulse, processing can be completed with fewer burst pulses. Therefore, the time required to process a single processing point is reduced. Since one point on the grid formed by the polygon mirror 7 and the processing stage 9 corresponds to one burst pulse, processing with fewer burst pulses also reduces the number of operations required for the acousto-optic deflector 6, and the misalignment of the burst pulse irradiation position is reduced.

[0080] Figure 13 is a schematic overall diagram showing a modified example 1 of the laser processing apparatus according to Embodiment 1. The laser processing apparatus 100A shown in Figure 13 comprises a pulsed laser oscillator 1, an optical system 2, a mask 3, a lens 4, an acousto-optic deflector 6, a second relay optical system 52, a polygon mirror 7, a third relay optical system 53, an fθ lens 8, and a processing stage 9. In other words, the laser processing apparatus 100A is a configuration in which the first relay optical system 51 is omitted. In the laser processing apparatus 100A, pulsed laser light L emitted from the pulsed laser oscillator 1 passes through the optical system 2 and then irradiates the mask 3. The lens 4 has a focal length of f1 and is positioned at a distance f1 from the mask 3. The pulsed laser light L that has passed through the mask 3 passes through the lens 4, generating the Fourier surface of the mask 3 at a downstream position FT1. The pulsed laser light L that has passed through the lens 4 is incident on the acousto-optic deflector 6 and is partially deflected by diffraction by the acousto-optic deflector 6. The pulsed laser light L emitted from the acousto-optic deflector 6 passes through the second relay optical system 52 and is reflected by the polygon mirror 7. The pulsed laser light L reflected by the polygon mirror 7 passes through the third relay optical system 53 and the fθ lens 8 and is irradiated onto the workpiece W, which is the object to be processed, placed on the processing stage 9.

[0081] When the pulsed laser beam L passes through the mask 3, a portion of the beam is diffracted, and the lens 4 generates a Fourier transform image of the mask 3 at position FT1, which is at a focal length f1 from the lens 4. That is, position FT1 is the Fourier plane of the mask 3. The position of the lens 4, the focal length f1 of the lens 4, and the position of the acousto-optic deflector 6 are designed so that position FT1 is the position of the acousto-optic deflector 6. FT3 is the transfer position of FT1 by the second relay optical system 52. The position of the second relay optical system 52 and the position of the polygon mirror 7 are designed so that FT3 is substantially the beam irradiation position of the polygon mirror 7. FT4 is the transfer position of FT3 by the third relay optical system 53. The position of the third relay optical system 53 and the position of the fθ lens 8 are designed so that the front focal position of the fθ lens 8 is substantially the transfer position FT4. That is, in the laser processing apparatus 100A, the Fourier plane of the mask 3 and the position of the acousto-optic deflector 6 coincide. Therefore, the position FT1 of the Fourier plane of mask 3, the position FT1 of acousto-optic deflector 6, the transfer position FT3 which is the beam irradiation position of polygon mirror 7, and the transfer position FT4 which is the front focal position of fθ lens 8 are all conjugate to each other or located at the same position.

[0082] Figure 14 is a schematic overall view showing a modified example 2 of the laser processing apparatus according to Embodiment 1. The laser processing apparatus 100B shown in Figure 14 comprises a pulsed laser oscillator 1, an optical system 2, a mask 3, an acousto-optic deflector 6, a polygon mirror 7, a third relay optical system 53, an fθ lens 8, and a processing stage 9. In other words, the laser processing apparatus 100B omits the first relay optical system 51, the second relay optical system 52, and the lens 4. In the laser processing apparatus 100B, the pulsed laser light L emitted from the pulsed laser oscillator 1 passes through the optical system 2 and is then irradiated onto the mask 3. The pulsed laser light L that has passed through the mask 3 is then incident on the acousto-optic deflector 6 and is partially deflected by diffraction in the acousto-optic deflector 6. The pulsed laser light L emitted from the acousto-optic deflector 6 is reflected by the polygon mirror 7. The pulsed laser light L reflected by the polygon mirror 7 passes through the third relay optical system 53 and the fθ lens 8, and is irradiated onto the workpiece W, which is the object to be processed, placed on the processing stage 9.

[0083] The third relay optical system 53 transfers the image from the transfer position FT3, which is the beam irradiation position of the polygon mirror 7, to the transfer position FT4, which is the front focal position of the fθ lens 8. In other words, the transfer position FT3, which is the beam irradiation position by the polygon mirror 7, and the transfer position FT4, which is the front focal position of the fθ lens 8, are conjugate to each other. As shown in Figure 4, when the position where the pulsed laser light L and the optical axis 80 of the fθ lens 8 intersect is the front focal position of the fθ lens 8, the pulsed laser light L after passing through the fθ lens 8 becomes parallel to the optical axis 80 of the fθ lens 8.

[0084] On the other hand, as shown in Figure 3, if the point where the pulsed laser beam L and the optical axis 80 of the fθ lens 8 intersect is offset from the front focal position of the fθ lens 8, the pulsed laser beam L after passing through the fθ lens 8 will not be parallel to the optical axis 80 of the fθ lens 8. In this case, the amount of angular deviation of the pulsed laser beam L with respect to the optical axis 80 of the fθ lens 8 increases as the distance between the point where the pulsed laser beam L and the optical axis 80 of the fθ lens 8 intersect and the front focal position on the optical axis 80 of the fθ lens 8 increases. The acousto-optic deflector 6 and the polygon mirror 7 are located in close proximity. The position FT2 of the acousto-optic deflector 6 and the front focal position of the fθ lens 8 are not conjugate. Therefore, the pulsed laser beam L deflected by the acousto-optic deflector 6 does not pass through the front focal position on the optical axis 80 of the fθ lens 8, but after passing through the fθ lens 8, it deviates from being parallel to the optical axis 80 of the fθ lens 8. However, because the acousto-optic deflector 6 and the polygon mirror 7, which is conjugate to the front focal position of the fθ lens 8, are arranged in close proximity, the amount of deviation between the pulsed laser light L deflected by the acousto-optic deflector 6 and the front focal position on the optical axis 80 of the fθ lens 8 is small. Therefore, after passing through the fθ lens 8, the amount of angular deviation of the pulsed laser light L with respect to the optical axis 80 of the fθ lens 8 can be suppressed.

[0085] Embodiment 2. Next, a laser processing apparatus according to Embodiment 2 will be described. Note that components identical to those in Embodiment 1 are denoted by the same reference numerals, and their descriptions are omitted as appropriate. Figure 15 is a schematic overall view of the laser processing apparatus according to Embodiment 2.

[0086] As shown in Figure 15, the laser processing apparatus 101 according to Embodiment 2 has, in addition to the configuration of the laser processing apparatus 100 of Embodiment 1, a galvanometer scanner 10 positioned at the front focal point of the fθ lens 8. The other configurations are the same as in Embodiment 1. In the laser processing apparatus 101, the polygon mirror 7 and the processing stage 9 scan the entire surface of the electronic substrate, which is the workpiece W. However, since the polygon mirror 7 and the processing stage 9 operate at a constant speed during processing, if there is a non-processing area in addition to the processing area, the scanning speed of the non-processing area is also the same. The processing area is the area where processing holes exist. The processing area is, for example, the size of a semiconductor package. The non-processing area is the area where no processing holes exist.

[0087] In the laser processing apparatus 101 according to Embodiment 2, a galvanometer scanner 10 is positioned at the front focal point of the fθ lens 8. The galvanometer scanner 10 deflects the pulsed laser beam L in a direction perpendicular to the polygon scanning direction on the workpiece W, and also deflects the pulsed laser beam L in a direction parallel to the polygon scanning direction. The galvanometer scanner 10 may also be configured to only deflect the pulsed laser beam L in a direction perpendicular to the polygon scanning direction on the workpiece W.

[0088] Figure 16 is a schematic diagram illustrating an object to be processed by the laser processing apparatus according to Embodiment 2. As shown in Figure 16, if there is a non-processing area A2 on the substrate, the galvanometer scanner 10 can deflect the non-processing area A2, allowing the polygon mirror 7 and processing stage 9 to move at a constant speed without scanning the non-processing area A2. In this case, from the perspective of the processing stage 9, the polygon mirror 7 and processing stage 9 can scan the entire processing area A1 by moving only a short distance equivalent to the non-processing area A2 while maintaining a constant speed, thus enabling processing to be completed in a short time.

[0089] The configurations shown in the above embodiments are merely examples and can be combined with other known technologies, or the embodiments themselves can be combined. Furthermore, it is possible to omit or modify parts of the configuration without departing from the gist of the invention. [Explanation of symbols]

[0090] 1 Pulsed laser oscillator, 2 Optical system, 3 Mask, 4 Lens, 6 Acousto-optic deflector (optical deflector), 7 Polygon mirror, 8 fθ lens, 9 Processing stage, 10 Galvano scanner, 51 First relay optical system, 52 Second relay optical system, 53 Third relay optical system, 54 Reflecting mirror, 60, 61 Acousto-optic elements, 70 Reflecting surface, 71 Corner, 72 First encoder, 80 Optical axis, 81 Front focal position, 90 Second encoder, 100, 100A, 100B, 101 Laser processing device, 200 Copper foil, 201 Insulator, 202 Processing hole, L Pulsed laser light, W Workpiece (object to be processed).

Claims

1. A pulsed laser oscillator that emits pulsed laser light, A mask for shaping the pulsed laser light emitted from the pulsed laser oscillator, An optical deflector that diffracts the pulsed laser light that has passed through the mask, A polygon mirror that reflects the pulsed laser light that has passed through the optical deflector, A third relay optical system through which the pulsed laser light reflected by the polygon mirror passes, and which generates a conjugate point on the optical path of the pulsed laser light that is optically conjugate with the polygon mirror, An fθ lens having telecentric properties is positioned at a location where the conjugate point is the front focal point, and which focuses the pulsed laser light that has passed through the third relay optical system toward the workpiece. A processing stage on which the workpiece is placed and on which the position of the workpiece is changed by a moving mechanism, A first encoder for measuring the rotation angle of the polygon mirror, The system includes a second encoder for measuring the position of the processing stage, The optical deflector predicts the rotation angle of the polygon mirror and the position of the processing stage at a time later than the measurement time, when the pulsed laser light is irradiated onto the workpiece, based on the measurement information from the first encoder and the second encoder, and corrects the command value of the deflection angle set so that the pulsed laser light is irradiated onto the target irradiation position on the processing stage, based on the predicted values. A laser processing apparatus characterized by the following features.

2. The pulsed laser light that has passed through the mask passes through a lens that generates the Fourier surface of the mask downstream of the mask, The system further comprises a second relay optical system, which is positioned on the optical path of the pulsed laser light between the optical deflector and the polygon mirror, and which has an optically conjugate relationship between the position of the optical deflector and the beam irradiation position of the polygon mirror. The laser processing apparatus according to feature 1.

3. The second relay optical system maintains a conjugate relationship between the position of the optical deflector and the beam irradiation position of the polygon mirror, and the transfer magnification is set according to the size of the machining hole formed in the workpiece. The laser processing apparatus according to feature 2.

4. The pulse frequency of the pulsed laser light is set according to the pulse energy required for processing the workpiece in the pulsed laser oscillator. The diameter of the circular aperture of the mask is set according to the pulse frequency of the pulsed laser light. The second relay optical system maintains a conjugate relationship between the position of the optical deflector and the beam irradiation position of the polygon mirror, and the transfer magnification is set according to the size of the machining hole formed in the workpiece and the diameter of the circular aperture of the mask. The laser processing apparatus according to feature 2.

5. The system further comprises a first relay optical system, which is positioned on the optical path of the pulsed laser light between the lens and the optical deflector, and which has an optically conjugate relationship between the Fourier plane and the position of the optical deflector. The laser processing apparatus according to feature 2.

6. The first relay optical system maintains a conjugate relationship between the Fourier plane and the position of the optical deflector, and the transfer magnification is set according to the size of the machining hole formed in the workpiece. The laser processing apparatus according to feature 5.

7. The system further comprises a first relay optical system, which is positioned on the optical path of the pulsed laser light between the lens and the optical deflector, and which has an optically conjugate relationship between the Fourier plane and the position of the optical deflector. The pulse frequency of the pulsed laser light is set according to the pulse energy required for processing the workpiece in the pulsed laser oscillator. The first relay optical system maintains a conjugate relationship between the Fourier plane and the position of the optical deflector, and the transfer magnification is set according to the pulse frequency of the pulsed laser light. The second relay optical system maintains a conjugate relationship between the position of the optical deflector and the beam irradiation position of the polygon mirror, and the transfer magnification is set according to the size of the machining hole formed in the workpiece and the transfer magnification of the first relay optical system. The laser processing apparatus according to feature 2.

8. Let d be the diameter of the circular opening formed in the mask, and f be the focal length of the lens. １ The focal length of the fθ lens is f ｆθ The transfer magnification of the first relay optical system is set to M. １ The transfer magnification of the second relay optical system is set to M ２、 The transfer magnification of the third relay optical system is set to M. ３、 The rotation frequency of the polygon mirror is f ｒｏｔ Therefore, the pulse width τ of the pulsed laser light satisfies equation 1. The laser processing apparatus according to feature 5. [Math 1]

9. The optical deflector has two acousto-optic elements whose deflection directions are mutually orthogonal. The relationship between the two acousto-optic elements is optically conjugate to the beam irradiation position of the polygon mirror. The laser processing apparatus according to feature 1.

10. The third relay optical system has a transfer magnification greater than 1x. The laser processing apparatus according to feature 1.

11. The pulsed laser oscillator outputs burst pulses, which are clusters of multiple laser pulses, at regular intervals. The laser processing apparatus according to feature 1.

12. The lens further comprises a galvanometer mirror positioned at the front focal point of the fθ lens. The laser processing apparatus according to feature 1.

13. A laser processing method that performs hole drilling by irradiating a workpiece with pulsed laser light, The steps include: emitting pulsed laser light, A step of shaping the emitted pulsed laser light, The steps include diffracting the shaped pulsed laser light, The steps include: reflecting the diffracted pulsed laser light using a polygon mirror; The steps include: passing the pulsed laser light reflected by the polygon mirror through a conjugate point generated in the optical path of the pulsed laser light and having an optically conjugate relationship with the polygon mirror; The step includes focusing the pulsed laser light that has passed through the conjugate point toward the workpiece, which is placed on a processing stage that changes the position of the workpiece, The rotation angle of the polygon mirror is measured, and the position of the processing stage is measured. From this measurement information, the rotation angle of the polygon mirror and the position of the processing stage are predicted at a time later than the measurement time, when the pulsed laser light is irradiated onto the workpiece. Based on these predicted values, the command value of the deflection angle, which is set so that the pulsed laser light is irradiated onto the target irradiation position on the processing stage, is corrected, and the shaped pulsed laser light is diffracted. A laser processing method characterized by the following features.

14. A laser processing apparatus according to any one of claims 1 to 12 is used to drill holes in an electronic substrate, which is a workpiece, in order to manufacture an electronic component. A method for manufacturing electronic components, characterized by the following:

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