JP6184798B2 - Gas laser device, pulse laser beam output method, and laser processing apparatus - Google Patents

Description

  The present invention relates to a gas laser device that outputs a pulse laser beam, a pulse laser beam output method, and a laser processing apparatus that performs processing using a pulse laser beam.

  When a pulse laser beam is output from a laser device, a phenomenon in which a laser pulse is not output when the laser pulse is to be output (mispulse), a weak pulse whose peak intensity is smaller than a set value, and a peak intensity that is greater than a set value A defective pulse such as a strong pulse may occur. Patent Document 1 below discloses a technique for preventing the occurrence of these defective pulses.

  In the method disclosed in Patent Document 1, the light intensity at the rising portion of the laser pulse is detected by a sensor. If the detection result is normal, the laser pulse is incident on the object to be processed, and if the detection result is abnormal, the laser pulse is incident on the beam damper or the like without being incident on the object to be processed. The beam path toward the workpiece and the beam path toward the beam damper are switched by an optical path deflector such as an acoustooptic device. Thereby, it is possible to prevent the defective pulse from entering the workpiece.

JP 2004-25292 A

  In the conventional method, an optical path deflector such as an acousto-optic element is required to avoid incidence of an abnormal pulse on a workpiece. Providing the acousto-optic element leads to an increase in the manufacturing cost of the laser processing apparatus. An object of the present invention is to provide a gas laser apparatus and a laser processing apparatus that can suppress an increase in manufacturing cost and can avoid a defective pulse from entering a workpiece. Another object of the present invention is to provide a pulse laser beam output method capable of avoiding the generation of defective pulses.

According to one aspect of the invention,
Silent discharge excitation gas laser,
A power source for applying a high frequency voltage for excitation to the gas laser;
A current sensor for measuring a current flowing through the gas laser;
A control device that controls application of a high-frequency voltage from the power source to the gas laser;
The controller is
Applying a preceding pulse of a high-frequency voltage only for a short period when laser oscillation does not occur to the gas laser, and obtaining a current measurement value measured by the current sensor during the period in which the preceding pulse is applied,
Determine if the acquired current measurements are within acceptable limits,
If the obtained current measured value is within the allowable range, the fall time of the preceding pulse, before the upper laser level lifetime of the gas laser has elapsed, the main high-frequency voltage to the gas laser Apply a pulse to cause laser oscillation,
If the obtained current measured value is less than the lower limit of the allowable range, the fall time of the leading pulse, the time until the upper laser level lifetime of the gas laser has passed, the high-frequency voltage to the gas laser A gas laser device without application is provided.

According to another aspect of the invention,
Applying a preceding pulse of a high frequency voltage to a silent discharge excitation type gas laser only for a short period in which laser oscillation does not occur;
Measuring a current flowing through the gas laser during a period in which the preceding pulse is applied to obtain a current measurement value;
Determining whether the current measurement is within an acceptable range;
When the measured value of the current is within the allowable range, the main frequency of the high-frequency voltage is applied to the gas laser before the lifetime of the upper laser level of the gas laser elapses from the time when the preceding pulse falls. Applying a pulse to cause laser oscillation;
When the measured value of the current is less than the lower limit value of the allowable range, a high-frequency voltage is applied to the gas laser for the time from when the preceding pulse falls until the lifetime of the upper laser level of the gas laser elapses. A non-applied pulsed laser beam output method is provided.

According to yet another aspect of the invention,
Silent discharge excitation gas laser,
A power supply for applying a high frequency voltage for excitation to the gas laser;
A control device that sends to the power source a start command to start application of a high-frequency voltage to the gas laser and a stop command to stop application of the high-frequency voltage;
A stage for holding the workpiece,
A condensing optical system for condensing the laser beam output from the gas laser onto the surface of the workpiece held by the stage;
Applying a preceding pulse of a high-frequency voltage only for a short period in which laser oscillation does not occur to the gas laser, and measuring a current flowing through the gas laser during a period in which the preceding pulse is applied to obtain a current measurement value,
Determine if the acquired current measurements are within acceptable limits,
If the obtained current measured value is within the allowable range, the fall time of the preceding pulse, before the upper laser level lifetime of the gas laser has elapsed, the main high-frequency voltage to the gas laser Apply a pulse to cause laser oscillation,
If the obtained current measured value is less than the lower limit of the allowable range, the fall time of the leading pulse, the time until the upper laser level lifetime of the gas laser has passed, the high-frequency voltage to the gas laser A laser processing apparatus that does not apply is provided.

  By applying no high-frequency voltage to the gas laser for the time from when the preceding pulse falls until the lifetime of the upper laser level of the gas laser elapses when the discharge current at the time of applying the preceding pulse is not within the allowable range The generation of defective laser pulses can be avoided. Since no defective laser pulse is generated, it is not necessary to prepare an optical path deflector such as an acousto-optic device.

FIG. 1 is a schematic diagram of a laser processing apparatus according to an embodiment. FIG. 2 is an energy level diagram of the laser medium gas accommodated in the gas laser. FIG. 3 is a flowchart of a pulse laser beam output method according to the embodiment. FIG. 4 is a graph showing an example of the trigger signal, the high-frequency voltage, the discharge current, the inversion distribution density, and the time change of the pulse laser beam. 5A to 5C are cross-sectional views of a workpiece to be processed by the laser processing apparatus according to the embodiment.

  FIG. 1 shows a schematic diagram of a laser processing apparatus according to an embodiment. A gas laser device is used as a laser light source of a laser processing apparatus. The gas laser device includes a silent discharge excitation type gas laser 10, a power supply 15, a current sensor 18, and a control device 20. For the gas laser 10, for example, a carbon dioxide laser is used. The gas laser 10 includes a partial reflection mirror 12 and a total reflection mirror 13 that constitute an optical resonator, and a pair of discharge electrodes 11. A laser medium gas is accommodated between the pair of discharge electrodes 11.

  The power supply 15 is controlled by the control device 20 to apply the excitation high frequency voltage Vrf to the gas laser 10. The power supply 15 includes an inverter 16 and a timing generator 17. The timing generator 17 sends a timing signal for controlling on / off of the switching element of the inverter 16 to the inverter 16. The inverter 16 applies the high frequency voltage Vrf to the discharge electrode 11 based on the timing signal from the timing generator 17. When the high-frequency voltage Vrf is applied to the discharge electrode 11, a discharge occurs between the discharge electrodes 11, and a discharge current Irf flows.

  The control device 20 sends a trigger signal Trg to the timing generator 17. The trigger signal Trg includes a start command for starting application of the high-frequency voltage Vrf to the gas laser 10 and a stop command for stopping application of the high-frequency voltage Vrf. As an example, the rise and fall of the trigger signal Trg correspond to a start command and a stop command, respectively.

  The current sensor 18 measures the discharge current Irf flowing through the gas laser 10. The measurement result of the current sensor 18 is input to the control device 20.

  When a high frequency voltage is applied to the gas laser 10, the pulse laser beam LB is output from the gas laser 10 when the laser oscillation condition is satisfied. The pulse laser beam LB is incident on the workpiece 40 via the folding mirror 31, the galvano scanner 32, and the condensing optical system 33. The galvano scanner 32 scans the pulse laser beam LB in a two-dimensional direction. The condensing optical system 33 condenses the pulse laser beam LB on the surface of the workpiece 40. For the condensing optical system 33, for example, an fθ lens is used. The workpiece 40 is held on the stage 34. The stage 34 moves the workpiece 40 in a two-dimensional direction parallel to the surface.

  FIG. 2 shows an energy level diagram of the laser medium gas accommodated in the gas laser 10. In the carbon dioxide laser, the transition from the (001) level to the (100) level or the (020) level of carbon dioxide molecules contributes to laser oscillation. The (001) level corresponds to the upper laser level E2, and the (100) level and the (020) level correspond to the lower laser level E1. Here, the first, second, and third numbers in parentheses mean the quantum numbers of the symmetric stretching mode, the bending mode, and the asymmetric stretching mode, respectively. The laser medium gas contains nitrogen molecules. When the excited nitrogen molecule (v = 1) collides with the carbon dioxide molecule, vibration energy is transferred from the nitrogen molecule to the carbon dioxide molecule. Thereby, carbon dioxide molecules are excited to the (001) state.

The densities of the molecules of the lower laser level E1 and the upper laser level E2 are represented by N1 and N2, respectively. In the thermal equilibrium state, N1> N2 is established. When the laser medium gas is excited, an inversion distribution state, that is, a state of N1 <N2 is obtained. Inversion distribution density, ie, N2-N1
When exceeds the critical value, laser oscillation occurs. Here, the lifetime of the upper laser level E2 including energy transfer from the nitrogen molecule to the carbon dioxide molecule is represented by τ2. Here, the lifetime τ2 means the time during which the density of the molecules of the upper laser level E2 decreases to 1 / e due to spontaneous emission.

  FIG. 3 shows a flowchart of the pulse laser beam output method according to the embodiment. FIG. 4 shows the trigger signal Trg, the high-frequency voltage Vrf, the effective value of the discharge current Irf, the inversion distribution density N2-N1, and the time of the pulse laser beam LB. An example of the change is shown. The rising edge and the falling edge of the trigger signal Trg correspond to a start command and a stop command for applying a high-frequency voltage to the gas laser 10, respectively. Hereinafter, a method for outputting the pulse laser beam LB will be described with reference to FIGS. 1, 3, and 4.

  In step S1 (FIG. 3), a preceding pulse Vp1 of a high frequency voltage is applied to the gas laser 10. As shown in FIG. 4, the preceding pulse Vp1 is applied to the gas laser 10 during the period from time t1 to t2.

  Hereinafter, the operation of step S1 will be described. The trigger signal Trg rises at time t1, and the trigger signal Trg falls at time t2. Prior to time t1, the laser medium gas of the gas laser 10 is in a thermal equilibrium state. At this time, no inversion distribution occurs and the inversion distribution density N2-N1 is 0 or negative.

  By sending the trigger signal Trg from the control device 20 to the power source 15, the preceding pulse Vp1 of the high-frequency voltage Vrf is applied from the power source 15 to the gas laser 10 from time t1 to time t2. When a discharge occurs in the gas laser 10 after the application of the preceding pulse Vp1 is started, the discharge current Irf starts to flow. When discharge occurs in the gas laser 10, the laser medium gas is excited, and the density N2 of molecules at the upper laser level E2 (FIG. 2) and the inversion distribution density N2-N1 increase.

  At time t2, the application of the preceding pulse Vp1 is stopped, so that the discharge current Irf becomes zero. When the energy level of the molecules of the laser medium gas transitions from the upper laser level E2 to the lower laser level E1, the inversion distribution density N2-N1 decreases.

  The preceding pulse Vp1 is applied to the gas laser 10 for a short time that does not cause laser oscillation. Specifically, at the time t2 when the application of the preceding pulse Vp1 is stopped, the inversion distribution density N2-N1 does not exceed the critical value Th that leads to laser oscillation.

  In step S2 (FIG. 3), the control device 20 acquires a measured value of the discharge current Irf from the current sensor 18 during a period from time t1 to t2. In step S3 (FIG. 3), the control device 20 determines the normality of the discharge state based on the acquired measured value of the discharge current Irf. For example, when the discharge current Irf from time t1 to time t2 is within the allowable range, it is determined that the discharge state is normal, and when the discharge current Irf is not within the allowable range, the discharge state is abnormal. It is determined that Whether or not the discharge current Irf is within the allowable range is determined based on the peak value of the discharge current Irf. When the absolute value of the peak value of the discharge current Irf is greater than or equal to the determination threshold value It, it is determined that the discharge state is normal.

  When it is determined that the discharge state is normal, the main pulse Vp2 of the high frequency voltage is applied to the gas laser 10 in step S4 (FIG. 3).

Hereinafter, the operation of step S4 will be described. As shown in FIG. 4, the trigger signal Trg rises at time t3, and the trigger signal Trg falls at time t5. From time t3 to t5, the main pulse Vp2 of the high frequency voltage Vrf is applied to the gas laser 10. When the main pulse Vp2 is applied, discharge occurs and the discharge current Irf begins to flow. When the gas laser 10 generates a discharge, the density N2 of molecules at the upper laser level E2 increases, and the inversion distribution density N2-N1 increases.

  When the inverted distribution density N2-N1 exceeds the critical value Th at time t4, laser oscillation is started and the laser pulse of the pulse laser beam LB rises. The waveform of the laser pulse depends on the characteristics of the gas laser 10. FIG. 4 shows an example in which the light intensity has a peak at the rising edge of the laser pulse, and thereafter a substantially constant light intensity is maintained.

  When the trigger signal Trg falls at time t5, the application of the main pulse Vp2 to the gas laser 10 is stopped. As a result, the discharge current Irf becomes 0, the inversion distribution density N2-N1 starts to decrease, and the laser pulse of the pulse laser beam LB falls.

  The elapsed time from the application stop time t2 of the preceding pulse Vp1 to the application start time t3 of the main pulse Vp2 is shorter than the lifetime τ2 of the upper laser level E2 of the gas laser 10. For this reason, at time t3, a sufficiently large number of molecules remain in the upper laser level E2. Thereby, the inversion distribution density N2-N1 can reach the critical value Th in an extremely short time from the application start time t3 of the main pulse Vp2. Moreover, the excitation energy supplied to the gas laser 10 when the preceding pulse Vp1 is applied can be used effectively.

  Since the normality of the discharge state is confirmed when the preceding pulse Vp1 is applied, the normality of the discharge state is ensured with a high probability even when the main pulse Vp2 is applied.

  If it is determined in step S3 (FIG. 3) that the discharge state is abnormal, in step S5 (FIG. 3), the high frequency voltage Vrf is applied for a time longer than the lifetime τ2 of the upper laser level E2. Wait without.

  Hereinafter, the operation of step S5 (FIG. 3) will be described. The trigger signal Trg rises at time t10 shown in FIG. 4, and the trigger signal Trg falls at time t11. From time t10 to t11, the preceding pulse Vp1 of the high frequency voltage Vrf is applied to the gas laser 10, and the discharge current Irf flows. The measured value of the discharge current Irf from time t10 to t11 in FIG. 4 is not within the allowable range. FIG. 4 shows an example in which the measured value of the discharge current Irf is smaller than the lower limit value of the allowable range. For this reason, at time t11, the inversion distribution density N2-N1 does not reach the target value. When it is determined that the discharge state is abnormal, the control device 20 waits for a longer time than the lifetime τ2 of the upper laser level E2 without applying the main pulse Vp2 of the high-frequency voltage. Then, it returns to step S1 (FIG. 3).

  When the measured value of the discharge current Irf flowing by applying the preceding pulse Vp1 is smaller than the lower limit value of the allowable range, if the main pulse Vp2 is applied thereafter, abnormal laser oscillation occurs and a weak pulse with a small peak power is output. Probability is high. On the contrary, when the measured value of the discharge current Irf flowing by applying the preceding pulse Vp1 is larger than the upper limit value of the allowable range, if the main pulse Vp2 is applied thereafter, abnormal laser oscillation occurs, and a strong pulse with a large peak power is generated. There is a high possibility of output. In the embodiment, the output of the defective laser pulse can be prevented by detecting the abnormal discharge by applying the preceding pulse Vp1 of the high frequency voltage Vrf.

With reference to FIG. 5A-FIG. 5C, the processing method using the laser processing apparatus by an Example is demonstrated. FIG. 5A shows a cross-sectional view of the workpiece before processing. For example, a build-up substrate is used as the processing object. A first metal film 42 is formed on the lower resin layer 41. An upper resin layer 43 is formed on the first metal film 42 and the lower resin layer 41. A second metal film 44 is formed on the resin layer 43. For the resin layers 41 and 43, for example, polyimide containing glass fiber is used. For the first metal film 42 and the second metal film 44, for example, copper is used. A metal other than copper may be used.

  As shown in FIG. 5B, an opening 45 is formed in the second metal film 44 by causing the first laser pulse Lp1 to enter the resin layer 43 and the second metal film 44 on the first metal film. The recess 46 is formed in the resin layer 43. The side surface of the recess 46 is inclined so that the flat cross section becomes smaller as it becomes deeper. FIG. 5B shows an example in which the recess 46 does not reach the first metal film 42, but a part of the first metal film 42 may be exposed on the bottom surface of the recess 46. Also in this case, the side surface of the recess 46 is inclined. For this reason, the area of the portion where the first metal film 42 is exposed is smaller than the area of the opening 45. The depth of the recess 46 depends on the pulse energy density of the first laser pulse Lp1.

  As shown in FIG. 5C, a plurality of second laser pulses Lp <b> 2 are incident on the recess 46. Each pulse width of the second laser pulse Lp2 is shorter than the pulse width of the first laser pulse Lp1. By the incidence of the second laser pulse Lp 2, the resin layer 43 on the side surface and the bottom surface of the recess 46 is removed, and the first metal film 42 is exposed on the bottom surface of the recess 46. If the first metal film 42 is exposed on the bottom surface of the recess 46 at the stage shown in FIG. 5B, the region where the first metal film 42 is exposed is increased by the incidence of the second laser pulse Lp2. Become.

  The first laser pulse Lp1 and the second laser pulse Lp2 are generated by the output method of the pulse laser beam LB according to the embodiment shown in FIGS. For this reason, generation | occurrence | production of a defective laser pulse can be avoided beforehand and the fall of processing quality can be prevented.

  Furthermore, the laser processing apparatus according to the embodiment does not need to prepare an optical deflector such as an acousto-optic element for preventing the pulse laser beam LB output from the gas laser 10 from entering the workpiece 40. For this reason, it becomes possible to reduce the manufacturing cost of the laser processing apparatus.

  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 Gas laser 11 Discharge electrode 12 Partial reflection mirror 13 Total reflection mirror 15 Power supply 16 Inverter 17 Timing generator 18 Current sensor 20 Control apparatus 31 Folding mirror 32 Galvano scanner 33 Condensing optical system 34 Stage 40 Work target 41 Resin layer 42 1st Metal film 43 Resin layer 44 Second metal film 45 Opening 46 Recess

Claims (5)

Silent discharge excitation gas laser,
A power source for applying a high frequency voltage for excitation to the gas laser;
A current sensor for measuring a current flowing through the gas laser;
A control device that controls application of a high-frequency voltage from the power source to the gas laser;
The controller is
Applying a preceding pulse of a high-frequency voltage only for a short period when laser oscillation does not occur to the gas laser, and obtaining a current measurement value measured by the current sensor during the period in which the preceding pulse is applied,
Determine if the acquired current measurements are within acceptable limits,
If the obtained current measured value is within the allowable range, the fall time of the preceding pulse, before the upper laser level lifetime of the gas laser has elapsed, the main high-frequency voltage to the gas laser Apply a pulse to cause laser oscillation,
If the obtained current measured value is less than the lower limit of the allowable range, the fall time of the leading pulse, the time until the upper laser level lifetime of the gas laser has passed, the high-frequency voltage to the gas laser Gas laser device that does not apply. The controller is
When the acquired current measurement value is less than the lower limit value , the procedure after the application of the preceding pulse is executed after the lifetime of the upper laser level of the gas laser has elapsed from the time of the falling of the preceding pulse. The gas laser device according to claim 1. Applying a preceding pulse of a high frequency voltage to a silent discharge excitation type gas laser only for a short period in which laser oscillation does not occur;
Measuring a current flowing through the gas laser during a period in which the preceding pulse is applied to obtain a current measurement value;
Determining whether the current measurement is within an acceptable range;
When the measured value of the current is within the allowable range, the main frequency of the high-frequency voltage is applied to the gas laser before the lifetime of the upper laser level of the gas laser elapses from the time when the preceding pulse falls. Applying a pulse to cause laser oscillation;
When the measured value of the current is less than the lower limit value of the allowable range, a high-frequency voltage is applied to the gas laser for the time from when the preceding pulse falls until the lifetime of the upper laser level of the gas laser elapses. Pulse laser beam output method without applying. 4. When the measured value of the current is less than the lower limit value , the process returns to the step of applying the preceding pulse after the lifetime of the upper laser level of the gas laser has elapsed from the falling point of the preceding pulse. The pulse laser beam output method described in 1. Silent discharge excitation gas laser,
A power supply for applying a high frequency voltage for excitation to the gas laser;
A control device that sends to the power source a start command to start application of a high-frequency voltage to the gas laser and a stop command to stop application of the high-frequency voltage;
A stage for holding the workpiece,
A condensing optical system for condensing the laser beam output from the gas laser onto the surface of the workpiece held by the stage;
Applying a preceding pulse of a high-frequency voltage only for a short period in which laser oscillation does not occur to the gas laser, and measuring a current flowing through the gas laser during a period in which the preceding pulse is applied to obtain a current measurement value,
Determine if the acquired current measurements are within acceptable limits,
If the obtained current measured value is within the allowable range, the fall time of the preceding pulse, before the upper laser level lifetime of the gas laser has elapsed, the main high-frequency voltage to the gas laser Apply a pulse to cause laser oscillation,
If the obtained current measured value is less than the lower limit of the allowable range, the fall time of the leading pulse, the time until the upper laser level lifetime of the gas laser has passed, the high-frequency voltage to the gas laser Laser processing equipment that does not apply.

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