JP5988903B2 - Laser processing apparatus and laser processing method - Google Patents

Description

  The present invention relates to a laser processing apparatus that performs laser processing by emitting a pulse laser, and a laser processing method.

  In a gas laser such as a carbon dioxide laser, impurities in the laser medium gas affect the discharge. For this reason, variation occurs in pulse energy for each emitted laser pulse. When laser pulses are used for drilling, if the pulse energy varies, the processing quality varies.

  Patent Document 1 below discloses a laser oscillation method that reduces variations in pulse energy. In the method disclosed in Patent Document 1, the energy value of the laser beam emitted from the laser oscillator is measured a plurality of times during one pulse excitation. A plurality of measured energy values are added, and a predicted total energy value of the laser light oscillated by the pulse excitation is predicted. The excitation time is controlled based on this expected total energy value. Thereby, the total energy value (pulse energy) can be stabilized.

Japanese Patent Laid-Open No. 2002-299736

  When the pulse width is relatively long, for example, about several hundred μs, it is possible to adjust the pulse energy by the method disclosed in Patent Document 1. However, when the pulse width is short, for example, several tens of μs, it is difficult to control the excitation time in consideration of energy detection sensitivity and calculation time.

  An object of the present invention is to provide a laser processing apparatus and a laser processing method capable of stabilizing pulse energy for each pulse even when the pulse width is short.

According to one aspect of the invention,
A discharge electrode for exciting the laser medium gas;
A drive circuit that starts supplying power to the discharge electrode by receiving a discharge start trigger and stops supplying power to the discharge electrode by receiving a discharge stop trigger;
A measuring instrument for measuring a physical quantity of at least one of a voltage and a current applied to the discharge electrode;
After giving the discharge start trigger to the drive circuit, based on the measured value of the physical quantity measured by the measuring instrument , the electric power to the discharge electrode after the discharge start trigger is given to the drive circuit There is provided a laser processing apparatus having a control device that gives the discharge stop trigger to the drive circuit during a period in which the supply continues .

According to another aspect of the invention,
Providing a gas laser oscillator with a command to start power supply to the discharge electrode;
A step of measuring a physical quantity of at least one of a voltage or a current applied to the discharge electrode from a time when the gas laser oscillator is instructed to start power supply;
Based on the measured value of the physical quantity, calculating a time width for supplying power to the discharge electrode;
And a step of instructing the gas laser oscillator to stop power supply to the discharge electrode when the calculated time width has elapsed from the time of the power supply start command. .

  The pulse energy can be stabilized by giving a discharge stop trigger to the drive circuit according to the physical quantity supplied to the discharge electrode. The voltage or current applied to the discharge electrode can be measured easily and in a short time compared to the light intensity of the emitted laser pulse. For this reason, even if the pulse width is shortened, it is possible to stabilize the pulse width.

FIG. 1 is a schematic diagram of a laser processing apparatus according to an embodiment. FIG. 2 is a sectional view of a laser oscillator used in the laser processing apparatus according to the embodiment and a block diagram of a control system. FIG. 3 is a timing chart of the trigger signal, the high frequency voltage, the discharge current, and the light output. 4A is a graph showing the relationship between the peak value of the discharge current and the pulse energy, and FIG. 4B is a graph showing the relationship between the high frequency voltage application time and the pulse energy. FIG. 5 is a graph showing the relationship between the peak value of the discharge current and the high frequency voltage application time under the condition that the pulse energy is constant. FIG. 6 is a flowchart of processing executed by the control device of the laser processing apparatus according to the embodiment. FIG. 7 is a timing chart of the trigger signal, the high frequency voltage, the discharge current, and the light output.

  FIG. 1 shows a schematic diagram of a laser processing apparatus according to an embodiment. The laser oscillator 10 receives power from the drive circuit 11 and emits a pulsed laser beam. As the laser oscillator 10, a gas laser oscillator such as a carbon dioxide laser oscillator is used. The drive circuit 11 supplies and stops power to the laser oscillator 10 in synchronization with the trigger signal from the control device 20.

  The laser beam emitted from the laser oscillator 10 passes through the spot position stabilizing optical system 12 and enters the aspherical lens 13. The spot position stabilizing optical system 12 includes a plurality of convex lenses, and stabilizes the position of the beam spot at the position where the aspherical lens 13 is disposed even if the traveling direction of the laser beam emitted from the laser oscillator 10 is deviated. The aspheric lens 13 changes the profile of the laser beam. For example, a Gaussian beam profile is changed to a top flat beam profile.

  The laser beam transmitted through the aspherical lens 13 is collimated by the collimating lens 14 and then enters the mask 15. The mask 15 includes a transmission window and a light shielding portion, and shapes the beam cross section of the laser beam. The laser beam transmitted through the transmission window of the mask 15 enters the beam scanner 18 via the field lens 16 and the folding mirror 17. The beam scanner 18 scans the laser beam in a two-dimensional direction. For example, a galvano scanner is used as the beam scanner 18.

  The laser beam scanned by the beam scanner 18 is condensed by the fθ lens 19 and enters the workpiece 30. The workpiece 30 is held on the stage 25. The field lens 16 and the fθ lens 19 image the transmission window of the mask 15 on the surface of the workpiece 30. The stage 25 moves the workpiece 30 in a direction parallel to the surface.

  Next, the configuration of the control device 20 will be briefly described. Detailed processing performed by the control device 20 will be described later with reference to FIGS. 6 and 7. The control device 20 includes a functional block 20 </ b> A that receives a measurement value of a physical quantity of at least one of current and voltage supplied to the laser oscillator 10. The control device 20 stores condition data 20B that makes the pulse energy constant. The function block 20C that adjusts the time at which the discharge stop trigger is sent out of the control device 20 adjusts the time at which the discharge stop trigger is sent based on the measured value of the physical quantity and the condition data 20B that makes the pulse energy constant.

  The trigger generation function block 20D of the control device 20 sends the discharge stop trigger to the drive circuit 11 at the time adjusted by the function block 20C for adjusting the time for sending the discharge stop trigger. By adjusting the time at which the discharge stop trigger is sent, variation in pulse energy is suppressed and the pulse energy is made uniform.

  FIG. 2 shows a sectional view of the laser oscillator 10 according to the embodiment and a block diagram of a control system. A blower 40, a pair of discharge electrodes 41, a heat exchanger 46, and a laser medium gas are accommodated in the chamber 50. A discharge space 42 is defined between the pair of discharge electrodes 41. The discharge of the discharge space 42 excites the laser medium gas. In FIG. 2, a cross section orthogonal to the length direction of the discharge electrode 41 is shown. For the blower 40, for example, a turbo blower is used. Instead of a turbo blower, a cross flow fan, an axial flow fan or the like may be used. Each of the discharge electrodes 41 includes a conductive member 43 and a ceramic member 44. The ceramic member 44 isolates the conductive member 43 and the discharge space 42.

  A circulation path from the blower 40 to the blower 40 via the discharge space 42 between the discharge electrodes 41 and the heat exchanger 46 is formed in the chamber 50. The heat exchanger 46 cools the laser medium gas that has become hot due to the discharge.

  A pair of terminals 51 are attached to the wall surface of the chamber 50. The conductive member 43 of the discharge electrode 41 is connected to the terminal 51 by an in-chamber current path 52, respectively. The terminal 51 is connected to the drive circuit 11 by a chamber outside current path 55. The measuring instrument 56 measures the current flowing through the chamber outside current path 55. A measured value of the current measured by the measuring instrument 56 is input to the control device 20. The control device 20 controls the drive circuit 11 based on the current measured value by the measuring instrument 56.

  3 shows a trigger signal given from the control device 20 (FIG. 1) to the drive circuit 11 (FIG. 1), a high-frequency voltage applied to the discharge electrode 41 (FIG. 2), a discharge current flowing through the discharge electrode 41, and a laser oscillator. 10 shows a timing chart of the light output emitted from 10 (FIG. 1).

  At time t1, the trigger signal rises. The rising edge of the trigger signal corresponds to a discharge start trigger. When the drive circuit 11 receives a discharge start trigger at time t <b> 1, the drive circuit 11 applies a high frequency voltage to the discharge electrode 41. The frequency of the high frequency voltage is 2 MHz, for example. When the discharge starts at time t2 after the high frequency voltage is applied, the discharge current starts to flow.

  After the discharge starts, the optical output (laser pulse) rises at time t3 when the gain in the optical resonator of the laser oscillator 10 exceeds the loss. The light output shows a sharp peak instantaneously at the rise, and then stabilizes.

In the transient state immediately after the start of discharge, the amplitude of the discharge current is smaller than the amplitude in the steady state and gradually increases with time. After the light output rises at time t3, the discharge current is in a steady state with a substantially constant amplitude.

  At time t4, the trigger signal falls. The falling edge of the trigger signal corresponds to a discharge stop trigger. When the drive circuit 11 receives the discharge stop trigger from the control device 20, the drive circuit 11 stops applying the high-frequency voltage. When the high frequency voltage is no longer applied to the discharge electrode 41, the discharge stops, the discharge current stops flowing, and the light output becomes 0 (the laser pulse falls). The time width from time t3 to time t4 corresponds to the pulse width of the laser pulse.

  The excitation intensity of the laser medium gas is proportional to the input power. The pulse energy of the pulse laser beam emitted from the laser oscillator is proportional to the excitation intensity under the condition that the pulse width is constant. Therefore, the pulse energy can be predicted from the input power, that is, the high frequency voltage and the discharge current.

  FIG. 4A shows the relationship between the peak value Ipp of the discharge current and the pulse energy under the condition that the high-frequency voltage application time (time from time t1 to time t4) is constant. Here, the peak value Ipp of the discharge current corresponds to twice the amplitude of the discharge current. The horizontal axis of FIG. 4A represents the peak value Ipp in the steady state, and the vertical axis represents the pulse energy. As the peak value Ipp of the discharge current increases, the pulse energy increases, and the relationship between them is almost linear.

  After the discharge current is in a steady state, the peak value Ipp of the discharge current is substantially constant. Therefore, by measuring the peak value Ipp of the discharge current from the start of discharge to a certain time before the stop of discharge, The pulse energy of the laser pulse can be predicted.

  FIG. 4B shows the relationship between the high frequency voltage application time (time from time t1 to time t4 in FIG. 3) and pulse energy under the condition that the peak value Ipp of the discharge current is constant. The horizontal axis represents the high frequency voltage application time, and the vertical axis represents the pulse energy. The pulse energy increases as the high-frequency voltage application time increases, and the relationship between them is almost linear.

  From the graphs shown in FIGS. 4A and 4B, the following can be derived. As the discharge current peak value Ipp decreases, the pulse energy also decreases. Increasing the high-frequency voltage application time so as to compensate for the decrease in pulse energy makes it possible to maintain the pulse energy constant. From the graphs shown in FIGS. 4A and 4B, it is possible to obtain the correspondence between the peak value Ipp of the discharge current for maintaining the pulse energy constant and the high-frequency voltage application time.

  FIG. 5 shows the correspondence between the peak value Ipp of the discharge current for maintaining the pulse energy constant and the high frequency voltage application time. The horizontal axis represents the peak value Ipp of the discharge current, and the vertical axis represents the high frequency voltage application time. As the peak value Ipp of the discharge current increases, the high frequency voltage application time is shortened. The correspondence shown in FIG. 5 is stored in advance in the control device 20 (FIG. 1). This correspondence corresponds to the condition data 20B for making the pulse energy constant shown in FIG.

  Next, with reference to FIG.6 and FIG.7, the laser processing method using the laser processing apparatus by an Example is demonstrated. Prior to laser processing, the workpiece 30 is first held on the stage 25 (FIG. 1), and the stage 25 is moved to position the workpiece 30. A plurality of processing points are defined in the processing object 30 within a range that can be scanned by the beam scanner 18. During laser processing, the control device 20 controls the beam scanner 18 so that the laser pulses are incident on the processing points on the processing object 30 in order to perform drilling processing.

FIG. 6 shows a flowchart of processing executed by the control device 20 (FIG. 1) of the laser processing apparatus according to the embodiment. FIG. 7 shows a timing chart of the trigger signal, the high frequency voltage, the discharge current, and the light output. When the workpiece 30 is held on the stage 25 and the positioning of the workpiece 30 is completed, the beam scanner 18 is controlled so that a laser pulse is incident on a workpiece to be processed first. In step S1, the process waits until the positioning of the beam scanner 18 is completed. When the positioning of the beam scanner 18 is completed, a discharge start trigger (power supply start command) is given to the drive circuit 11 in step S2. Step S2 corresponds to the times t11, t21, and t31 shown in FIG.

  Laser pulses Lp1, Lp2, and Lp3 rise after high-frequency voltage application start times t11, t21, and t31, respectively.

  In step S3, the peak value Ipp of the discharge current is measured until a predetermined determination time Tj (FIG. 7) elapses. This measurement is performed by the measuring instrument 56 (FIG. 2). The determination time Tj is shorter than the rated pulse width of the laser pulse to be emitted. As an example, the rated pulse width is 50 μs, and the determination time Tj is 5 μs. When the frequency of the high-frequency voltage is 2 MHz, the determination time Tj of 5 μs corresponds to 10 periods of the high-frequency voltage.

  Measurement of the peak value Ipp of the discharge current is started after the discharge current is in a steady state. When the discharge current becomes a steady state in about three cycles, the peak value Ipp from the fourth cycle to the tenth cycle is measured.

  The peak values of the discharge current due to the discharge start trigger at times t11, t21, and t31 shown in FIG. 7 are represented by Ipp1, Ipp2, and Ipp3, respectively. In the example shown in FIG. 7, the magnitude relationship between the three peak values is Ipp2 <Ipp1 <Ipp3.

  In step S4 (FIG. 6), it is determined whether or not the peak value Ipp of the discharge current is within the standard. If the measured peak value Ipp is out of specification, the supply of power to the discharge electrode 41 (FIG. 1) is stopped in step S8. Abnormal oscillation can be prevented by stopping the supply of power.

  When the measured peak value Ipp is within the standard, in step S5, a time width from the discharge start trigger to the discharge stop trigger is calculated based on the peak value Ipp. Hereinafter, an example of the process of step S5 will be described. For example, an average of a plurality of peak values Ipp measured during the determination time Tj (FIG. 7) is obtained. The high frequency voltage application time is obtained from the average value of the peak values Ipp and the correspondence shown in FIG.

  From the correspondence shown in FIG. 5, time widths Pd1, Pd2, and Pd3 are obtained for the peak values Ipp1, Ipp2, and Ipp3, respectively. The magnitude relationship of these time widths is Pd3 <Pd1 <Pd2.

  In step S6 (FIG. 6), a discharge stop trigger (power supply stop command) is sent out when the time width obtained in step S5 has elapsed from the discharge start trigger. In FIG. 7, the discharge stop trigger is sent out at times t12, t22, and t32. The time width from time t11 to t12 is equal to Pd1, the time width from time t21 to t22 is equal to Pd2, and the time width from time t31 to t32 is equal to Pd3. Discharge stops at times t12, t22, and t32, and laser pulses Lp1, Lp2, and Lp3 fall, respectively.

In step S7 (FIG. 6), it is determined whether or not the processing is finished. When an unprocessed processing point remains, the beam scanner 18 is controlled so that the laser pulse is incident on the processing point to be processed next, and the process returns to step S1. When the processing of all the processing points is completed, the laser processing is finished.

  The light output of the laser pulse Lp2 in the steady state is lower than the light output of the laser pulse Lp1. By making the pulse width of the laser pulse Lp2 longer than the pulse width of the laser pulse Lp1, the decrease in light output is compensated. Further, the light output of the laser pulse Lp3 in the steady state is higher than the light output of the laser pulse Lp1. By making the pulse width of the laser pulse Lp3 shorter than the pulse width of the laser pulse Lp1, the increase in the optical output is compensated. Since the time width from the discharge start trigger to the discharge stop trigger is determined based on the correspondence shown in FIG. 5, the pulse energy of the laser pulses Lp1, Lp2, and Lp3 can be made uniform.

  By increasing the peak value Ipp of the discharge current, the time width from the discharge start trigger to the discharge stop trigger is shortened, whereby the pulse energy of the laser pulse can be made closer to the uniform.

  The peak value Ipp of the discharge current can be measured easily and in a short time compared to the light output. For this reason, the method according to the embodiment can shorten the determination time Tj (FIG. 7) as compared with the case where the light output is measured and the pulse width is adjusted. For this reason, even if the pulse width of the laser pulse to be emitted is 100 μs or less, the method according to the above embodiment can be applied.

  In the above embodiment, the peak value Ipp of the discharge current is measured during the determination time Tj, but other physical quantities depending on the power supplied to the discharge electrode 41 (FIG. 2) may be measured. For example, the effective value of the discharge current may be measured.

  When the discharge state changes, the voltage applied between the pair of discharge electrodes 41 also changes. This change in voltage follows the change in power supplied to the discharge electrode 41. For this reason, the peak value or effective value of the voltage applied between the discharge electrodes 41 may be employed as another physical quantity that depends on the power supplied to the discharge electrodes 41 (FIG. 2). In this way, it is only necessary to measure at least one physical quantity of voltage or current applied to the discharge electrode 41.

  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.

DESCRIPTION OF SYMBOLS 10 Laser oscillator 11 Drive circuit 12 Spot position stabilization optical system 13 Aspherical lens 14 Collimating lens 15 Mask 16 Field lens 17 Folding mirror 18 Beam scanner 19 f (theta) lens 20 Control apparatus 20A Functional block 20B which receives the measured value of physical quantity Pulse Condition data 20C for making the energy constant Function block 20D for adjusting the time for sending out the discharge stop trigger Trigger generation function block 25 Stage 30 Work object 40 Blower 41 Discharge electrode 42 Discharge space 43 Conductive member 44 Ceramic member 46 Heat exchanger 50 Chamber 51 Terminal 52 Chamber current path 55 Chamber outside current path 56 Measuring instrument

Claims (6)

A discharge electrode for exciting the laser medium gas;
A drive circuit that starts supplying power to the discharge electrode by receiving a discharge start trigger and stops supplying power to the discharge electrode by receiving a discharge stop trigger;
A measuring instrument for measuring a physical quantity of at least one of a voltage and a current applied to the discharge electrode;
After giving the discharge start trigger to the drive circuit, based on the measured value of the physical quantity measured by the measuring instrument , the electric power to the discharge electrode after the discharge start trigger is given to the drive circuit A laser processing apparatus comprising: a control device that applies the discharge stop trigger to the drive circuit during a period in which the supply continues .   The control device provides the discharge start trigger after giving the discharge start trigger to the drive circuit, based on a measurement result by the measuring instrument until a predetermined determination time elapses. The laser processing apparatus according to claim 1, wherein a time width until a stop trigger is given is calculated.   The laser processing apparatus according to claim 1, wherein the control device shortens a time width from the discharge start trigger to the discharge stop trigger as the physical quantity measured by the measuring instrument is larger. The control device stores the correspondence between the physical quantity measured by the measuring instrument and the time from the discharge start trigger to the discharge stop trigger,
The laser according to any one of claims 1 to 3, wherein a time width from the discharge start trigger to the discharge stop trigger is obtained based on the measured value of the physical quantity measured by the measuring instrument and the correspondence relationship. Processing equipment. Providing a gas laser oscillator with a command to start power supply to the discharge electrode;
A step of measuring a physical quantity of at least one of a voltage or a current applied to the discharge electrode from a time when the gas laser oscillator is instructed to start power supply;
Based on the measured value of the physical quantity, calculating a time width for supplying power to the discharge electrode;
A step of instructing the gas laser oscillator to stop power supply to the discharge electrode when the calculated time width has elapsed from the time point of the power supply start command. 6. The time width is calculated based on a measured value of the voltage or current until a predetermined determination time elapses from the time point of the power supply start command in the step of calculating the time width. The laser processing method as described in.

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