JP2007054853A - Laser beam machining device and machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining device where the machining quality of an object to be machined in a plane can be made almost uniform. <P>SOLUTION: A laser emitting means emits pulse laser beams in which pulse energy is changed for each laser pulse while being controlled from the outside. A stage holds the object to be machined. A beam scanner scans the pulse laser beams emitted from the laser emitting means. A lens condenses the pulse laser beams scanned by the beam scanner on the object to be machined held to the surface of the stage. A controller controls the laser emitting means and the beam scanner in such a manner that the pulse energy of the laser pulses emitted from the laser emitting means is changed on the basis of the positions of the incident points of the pulse laser beams scanned by the beam scanner. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser processing apparatus and a processing method, and more particularly, to a laser processing apparatus and a processing method for performing processing while moving an incident position by scanning a pulse laser beam.

  The laser processing apparatus described in Patent Document 1 below will be described. Two laser pulses having a short pulse width are cut out from one laser pulse emitted from the laser oscillator. One of the cut laser pulses is made incident on a beam scanner, and the scanned beam is condensed on the object to be processed by the fθ lens. Similarly, the other laser pulse is also incident on the object to be processed via the beam scanner and the fθ lens. Thereby, a hole can be formed in the processing object at a position where the laser beam is incident.

JP 2005-34859 A

  In the laser processing apparatus disclosed in Patent Document 1, the size of the beam spot on the surface of the processing object changes depending on the position due to the field curvature characteristic of the fθ lens. In general, the beam spot becomes larger as the passing position of the pulse laser beam moves away from the center of the fθ lens. For this reason, if processing is performed with a constant pulse energy, the pulse energy density varies depending on the position.

  Further, the transmittance of the fθ lens decreases as the distance from the center increases. For this reason, the light intensity of the laser beam transmitted near the outer periphery of the fθ lens is lower than the light intensity of the laser beam transmitted through the center. Variation in the transmittance of the fθ lens also causes the pulse energy density to vary depending on the position.

When the processing quality is sensitively influenced by the pulse energy density, it is difficult to obtain a uniform processing quality within the surface of the processing object.
An object of the present invention is to provide a laser processing apparatus and a processing method capable of bringing the processing quality close to uniform within the surface of the processing object.

  According to one aspect of the present invention, a laser emitting unit that emits a pulsed laser beam that is controlled from the outside and changes pulse energy for each laser pulse, a stage that holds a workpiece, and the laser emitting unit. A beam scanner that scans the emitted pulsed laser beam, a lens that focuses the pulsed laser beam scanned by the beam scanner onto a workpiece to be held on the stage, the laser emitting means and the beam A control device for controlling a scanner, wherein the pulse energy of a laser pulse emitted from the laser emitting means is changed based on a position of an incident point of a pulse laser beam scanned by the beam scanner. Is provided.

  According to another aspect of the present invention, (a) a step of emitting a pulsed laser beam, and (b) incident the emitted pulsed laser beam on a processing point located within a scannable range on the surface of the workpiece. And performing laser processing of a plurality of processing points while moving the incident position by scanning the pulsed laser beam, and in step b, the laser pulse is moved to the incident position within the scannable range. Based on this, a laser processing method for changing the pulse energy of a laser pulse is provided.

  By changing the pulse energy based on the position of the incident point, fluctuations in the pulse energy density due to the position of the incident point can be corrected, and the pulse energy density can be made to be uniform regardless of the position of the incident point.

  FIG. 1 shows a schematic diagram of a laser processing apparatus according to an embodiment of the present invention. The laser oscillator 1 emits a pulsed laser beam LB1. The laser pulse emission timing is instructed by a control signal sig2 from the control device 10. As the laser oscillator 1, for example, a carbon dioxide laser can be used. Other laser oscillators such as Nd: YAG laser and excimer laser can also be used.

  A pulsed laser beam LB1 emitted from the laser oscillator 1 enters the beam cutting device 2. The beam cutting device 2 is composed of, for example, an acousto-optic element (AOM). The beam cutting device 2 takes one of two states: a transmission state in which the laser beam is incident on the subsequent beam expander 3 and a non-transmission state in which the laser beam is incident on the beam damper 15. When the beam cutting device 2 is in the transmission state, the incident pulse laser beam LB1 is transmitted and the pulse laser beam LB2 is emitted. The transmission state and the non-transmission state are switched by a signal sig3 from the control device 2.

  The laser beam whose beam diameter has been expanded by the beam expander 3 is folded by the folding mirror 4 and enters the mask 5. The mask 5 has a through hole through which the laser beam is transmitted. The laser beam transmitted through the through hole of the mask 5 enters the beam scanner 6.

  The beam scanner 6 is composed of, for example, a galvano scanner including two sets of oscillating mirrors, and scans an incident laser beam in a two-dimensional direction by a control signal sig1 from the control device 10. The laser beam scanned by the beam scanner 6 is converged by the fθ lens 7 and enters the workpiece 20 held on the XY stage 8. The fθ lens 7 images the through hole of the mask 5 on the surface of the processing target 20.

  FIG. 2A is a plan view of a scannable range in which a laser beam can be incident by the beam scanner 6 and the fθ lens 7. The relative position of the scannable range 30 with respect to the fθ lens 7 is fixed. On the surface of the workpiece 20, the scanable range 30 is a square having a side length of 50 mm, for example. An XY orthogonal coordinate system with the center of this square as the origin (reference point) O is defined. The X axis and the Y axis are parallel to one side of the scannable range 30. The laser beam that has passed through the center of the fθ lens 7 enters the origin O. Let r be the distance between the laser beam incident position P and the origin O within the scannable range 30.

  FIG. 2B shows the relationship between the distance r from the origin O to the beam incident position P and the pulse energy density at the beam incident position P. The horizontal axis represents distance r, and the vertical axis represents pulse energy density and pulse energy. A solid line D1 indicates the pulse energy density when the pulse energy of the pulse laser beam before entering the fθ lens 7 is constant for each laser pulse. When the beam incident position P moves away from the origin O, the pulse energy density decreases due to a decrease in the transmittance of the fθ lens 7 and an increase in the beam spot size.

  The pulse energy before entering the fθ lens 7 when performing laser processing using the laser processing apparatus according to the embodiment is indicated by a broken line E. As the distance r increases, the pulse energy increases. The pulse energy density when the pulse energy is changed as indicated by a broken line E is indicated by a solid line D2. The pulse energy increases so as to compensate for the decrease in the transmittance of the fθ lens 7 due to the increase in the distance r and the decrease in the pulse energy density due to the increase in the beam spot size. For this reason, the pulse energy density is substantially constant even if the distance r changes.

The operation of the laser processing apparatus shown in FIG. 1 will be described with reference to FIG. Between time t ₁₁ and t ₁₂ , the control device 10 transmits a control signal sig 1 for instructing the beam incident position to the beam scanner 6. The control signal sig1 includes position information indicating the incident position of the laser beam. When receiving the control signal sig1, the beam scanner 6 changes the posture of the swinging mirror so that the laser beam is incident on the position designated by the control signal sig1. When the posture change is completed, a completion signal is transmitted to the control device 10.

Controller 10 from the time _{t 13} after receiving a completion signal from the beam scanner 6 _{t 17,} and transmits the oscillation command signal sig2 to the laser oscillator 1. The laser oscillator 1 emits a pulsed laser beam LB1 while receiving the oscillation command signal sig2. The light intensity of the pulsed laser beam LB1 is started to increase from the time _{t 13,} reaches a substantially steady state at time _{t 14.} Further, begins to decrease the light intensity at time _{t 17,} at time _{t 18} becomes zero.

During the period from the time t ₁₅ where the light intensity of the pulsed laser beam LB1 is included in the period from the time t ₁₄ which is a steady state until the time t ₁₇ to time t _16, control signal control device 10 to the beam cut device 2 Send sig3. The beam cutting device 2 is in a transmission state during the period when the control signal sig3 is transmitted. Therefore, only during the period from time _{t 15} to _{t 16,} the pulse laser beam LB2 is output.

  By changing the length of the period during which the beam cutting device 2 is in the transmission state, the pulse width of the pulse laser beam LB2 can be changed. The peak power of the pulse laser beam LB1 emitted from the laser oscillator 1 is constant. For this reason, the peak power of the pulse laser beam LB2 is also constant. By changing the pulse width, the pulse energy of the pulse laser beam LB2 can be changed.

When the light intensity of the pulsed laser beam LB1 is 0 at time _{t 18,} the control unit 10, the period from time _{t 21} of _{t 22,} a signal sig1 to command next position to be incident laser beam beam scanner 6 Send to. The basic operation of the subsequent time _{t 23} to _{t 28} is the same as the operation from the time _{t 13} to the time _{t 18.} Note that the length from the time t ₂₅ to t ₂₆ corresponding to the pulse width of the pulse laser beam LB2 is controlled to a desired value according to the incident position of the laser beam.

  Returning to FIG. 2A and FIG. 2B, the description will be continued. As the distance r from the origin O to the incident position P of the laser beam becomes longer, the pulse width of the pulse laser beam LB2 is increased, and as shown by the broken line E in FIG. The pulse energy can be increased.

  For example, when the beam scanner 6 is controlled so that the incident position of the laser beam becomes the origin O, the control device 10 causes the beam cutting device 2 so that the pulse width of the pulse laser beam LB2 becomes a certain reference value. To control. When the incident position of the laser beam is different from the origin O, the pulse width is increased depending on the distance r from the origin O to the incident position P of the laser beam. Thereby, the pulse energy density on the surface of the workpiece 20 can be brought close to the pulse energy density when entering the origin O.

  In the said Example, the case where the light intensity and beam spot size in the surface of the workpiece 20 depend on the distance r from the origin O was shown. More generally, even when the light intensity and the beam spot size depend on the incident position of the laser beam, the pulse energy density is changed to the incident position by changing the pulse width of the pulse laser beam LB2 based on the incident position. Regardless, it can be approached uniformly.

With reference to FIG. 4 (A) and FIG. 4 (B), an example which performs laser processing using the laser processing apparatus by the said Example is demonstrated.
FIG. 4A shows a partial cross-sectional view of the workpiece 20. The processing target 20 is a vinyl chloride film having a thickness of 0.2 mm. A through hole 21 having a substantially circular opening is formed at a position where the laser beam is incident. The diameter of the through hole 21 in the surface on which the laser beam is incident (the top diameter) and D _T, the diameter at the surface of the opposite side (bottom diameter) and D _B. Usually, top diameter _{D T} is greater than the bottom diameter _{D B.}

FIG. 4B shows the relationship between the pulse energy density and the diameter of the opening of the through hole 21. The horizontal axis represents the pulse energy density, and the vertical axis represents the diameter of the opening. A solid line R _L and a broken line R _S in the figure indicate the diameters of the through-hole openings when the beam spot size on the surface of the workpiece 20 is relatively large and relatively small, respectively. Further, a thick solid line R _L and a thick broken line R _S indicate the top diameter D _T, and a thin solid line R _L and a thin broken line R _S indicate the bottom diameter D _B.

As the pulse energy density increases, both the top diameter D _T and the bottom diameter D _B increase. The top diameter D _T greatly depends on the beam spot size, but the bottom diameter D _B does not change much even when the beam spot size changes. That is, the pulse energy density, by controlling so as to be uniform irrespective of the position of incidence of the laser beam can be made closer to uniform bottom diameter D _B of the through-hole 21.

If you want align bottom diameter D _B of the through hole 21, the laser processing apparatus according to the embodiment it is useful.
In the above embodiment, the pulse energy is changed by adjusting the pulse width of the pulse laser beam, but the pulse energy can be changed by other methods. For example, the pulse energy can be changed by changing the peak power. By using the variable optical attenuator, the peak power can be changed.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

It is the schematic of the laser processing apparatus by an Example. (A) is a plan view showing a coordinate system within the operable range, and (B) shows the relationship between the distance from the origin within the scanable range to the laser beam incident position and the pulse energy and pulse energy density. It is a graph to show. It is a timing chart for demonstrating operation | movement of the laser processing apparatus shown in FIG. (A) is a partial cross-sectional view of the workpiece, and (B) is a graph showing the relationship between the pulse energy density and the diameter of the opening.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Beam cutting device 3 Beam expander 4 Folding mirror 5 Mask 6 Beam scanner 7 f (theta) lens 8 XY stage 10 Control apparatus 15 Beam damper 20 Work target 21 Through hole 30 Scanable range

Claims (8)

Laser emitting means for emitting a pulsed laser beam that is controlled from the outside and changes the pulse energy for each laser pulse;
A stage for holding the workpiece,
A beam scanner that scans the pulse laser beam emitted from the laser emitting means;
A lens for condensing the pulse laser beam scanned by the beam scanner onto the workpiece held on the stage;
A control device for controlling the laser emitting means and the beam scanner, the pulse of the laser pulse emitted from the laser emitting means based on the position of the incident point of the pulse laser beam scanned by the beam scanner A laser processing apparatus having a control device for changing energy. The laser emitting means is
A laser oscillator that emits a pulsed laser beam;
Beam cutting means for switching between a transmission state in which the pulse laser beam emitted from the laser oscillator is transmitted and a non-transmission state in which the pulse laser beam is not transmitted are controlled by control from the control device;
2. The laser processing apparatus according to claim 1, wherein the control device controls the beam cutting unit so that the laser pulse is transmitted only during a part of a pulse width of each laser pulse emitted from the laser oscillator.   The control device includes the laser emitting means so that the pulse width of the laser pulse becomes a reference value when the pulse laser beam is incident on a reference point within a scannable range whose relative position is fixed with respect to the lens. When the incident position of the pulse laser beam is different from the reference point, the pulse energy density at the surface of the workpiece is set to approach the pulse energy density when incident on the reference point. The laser processing apparatus according to claim 1, wherein the width is changed.   The lens is an fθ lens, and the reference point is an incident position when the pulse laser beam passes through the center of the fθ lens, and the controller is configured to provide a distance from the reference point to the incident position of the pulse laser beam. The laser processing apparatus according to claim 3, wherein the pulse width is changed based on the above. (A) emitting a pulsed laser beam;
(B) The emitted pulsed laser beam is incident on a workpiece point located within a scannable range on the surface of the workpiece, and a plurality of workpieces are scanned while moving the incident position by scanning the pulsed laser beam. A laser processing method for changing the pulse energy of the laser pulse based on the incident position of the laser pulse within the scannable range in the step b.   The laser processing method according to claim 5, wherein in step b, the pulse energy is changed by changing a pulse width of the laser pulse.   The laser processing method according to claim 5 or 6, wherein in the step b, the pulse energy of the laser pulse is changed so that the variation in the pulse energy density of the laser pulse incident on the processing point depends on the incident position.   In the step b, a pulse laser beam is scanned by a beam scanner, the scanned pulse laser beam is condensed on a workpiece by an fθ lens, and a pulse laser beam that has passed through the center of the fθ lens is incident. The laser processing method according to claim 5 or 6, wherein a pulse width of a laser pulse incident on the processing point is changed based on a distance from the point to the processing point.

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