JPWO2007138884A1 - Laser pulse generating apparatus and method, and laser processing apparatus and method - Google Patents

Abstract

Provided is a stabilized laser processing apparatus that stabilizes a pulse output of a solid-state laser and irradiates a workpiece with fine processing. The Q switch element 6 and the laser medium 5 installed in the laser resonator, the excitation laser oscillator 46 that is optically excited in advance, and the upper level excitation density in the laser medium are irradiated for a predetermined period at a laser wavelength other than the oscillation target wavelength. A laser oscillator 41 that performs de-excitation for reduction is provided, and after de-excitation in the laser resonator, the Q-switch element 6 is cut off (closed) in the laser oscillation state to perform upper-level photo-excitation to accumulate energy in the laser medium for a predetermined period Next, the Q switch 6 is switched to the laser oscillation enabled (open) state and the Q switch pulse is oscillated and output, so that an equal Q switch pulse output for each pulse is guided to the workpiece regardless of the Q switch pulse oscillation interval, and precision machining is performed. Laser processing equipment.

Description

  The present invention relates to a processing apparatus using a laser oscillation apparatus suitable for processing circuit components of semiconductor devices on a semiconductor wafer, and an apparatus and method for obtaining a stable high output Q switch pulse even when the pulse repetition frequency is changed. obtain. Furthermore, a fine processing apparatus and method capable of always obtaining a stable output at any irradiation timing are realized.

  As is well known to those skilled in the art, such as adjustment, correction, and processing of miniaturized circuit components in the electronics industry, it is irradiated with a Q-switch pulse output obtained from a solid-state laser and used in manufacturing processes such as removal, marking, trimming, and scribing. Yes. In this laser processing method, it is desirable that a predetermined output is always obtained even when the output energy and waveform of each laser pulse are repeated and the frequency is changed. For example, circuit fuse cutting for defect relief for switching a redundant circuit of a semiconductor memory is performed by irradiating a focused laser beam to a circuit fuse while scanning unequally spaced cutting points at high speed. . This requires high-precision processing of highly integrated memory cells by irradiation with a stable pulse waveform and energy according to a high-speed oscillation command toward the cutting point. In many cases, the time interval of laser pulse irradiation to these workpieces is not uniform, and contrivances have been made to equalize the pulse energy, pulse width, and peak output emitted from the laser oscillator. In the related art, a pulse stabilization method using a combination of a pulse laser oscillation device and an acousto-optic element (AOM) as shown in FIG. 1 has been proposed.

FIG. 1 shows a pulse stabilization method in which the AOM is operated for each pulse, and uses a method in which the low output pulse generated after the oscillation of the Q switch pulse is removed by the AOM. This has the disadvantage of using expensive AOM equipment. This will be described below. Laser light emitted from the excitation light source 1 such as a semiconductor laser is emitted toward the laser oscillation excitation condensing unit 10 of the solid-state laser medium 5. A high-reflecting mirror 4 is interposed between the condensing optical system 3 such as a lens and the laser wavelength constituting the solid-state laser resonator, which is highly reflective and transparent to the excitation light wavelength. The other output mirror 7 of the laser resonator is installed on the opposite side of the laser medium 5 from the high reflection mirror 4. Between the laser medium 5 and the output mirror 7, there is a Q switch element 6 made of an acousto-optic switch element. Installed. An operation control signal is sent from the control unit 11 of the laser device to the excitation light source drive unit 8, the Q switch drive unit 9, and the AOM drive unit 12 that controls the AOM 29 installed outside the laser resonator. The AOM applies RF power to an ultrasonic transducer to generate a Bragg diffraction cell and diffracts the passing beam. Accordingly, when RF is applied to the cell from the driving unit 12, a part of the beam is separated by diffraction at the time of RF application. The laser pulse that propagates the RF power sound wave to the AOM diffraction cell and passes through the diffraction grating is collimated by the beam expander 15, proceeds to the reflecting mirror 16, is reflected and directed to the workpiece 20, and is collected by the lens 18. Then, the surface of the processing object 20 is focused and irradiated to perform processing. The workpiece 20 is precisely positioned and driven by the drive table 23. The drive is performed by the drive unit 21 via the control signal line 26 from the control unit 11 by a known technique.

With such a configuration, laser oscillation is performed according to the procedure shown in FIG. The excitation laser beam 2 from the semiconductor laser is emitted in advance, and the laser medium is placed in an excitation state in advance. Here, when a pulse trigger is generated at time t1, t3, t5,... In (a), the power of RF1 is applied to the Q switch element 6 from the drive unit 9, and between the high reflection mirror 4 and the output mirror 7 of the laser oscillator. This increases the loss of the reciprocating optical path of the laser oscillation and forms a state in which oscillation is suppressed. This state lasts for the time t1-t2, t3-t4, t5-t6,..., And during this time, the excitation energy is accumulated in the laser medium 5, and this accumulation amount depends on the intensity of the excitation light and t1-t2, t3-t4. , T5 to t6,... At time t2, t4, t6, the RF power supply to the Q switch 6 is cut off by the drive unit 9. As a result, a Q switch pulse is suddenly generated in the laser resonator and transmitted through the output mirror 7 to obtain the output beam 30MIR of (c). Subsequently, since the laser medium is in an excited state, the laser oscillation gain is restored to the laser medium, and no RF power is applied to the Q switch element 6, so that a continuous low output oscillation portion is shown in FIG. c) Sustained oscillation as shown by 13SIR. Accordingly, the laser output beam 30IR includes a Q switch pulse portion 30MIR and a continuous output portion 13SIR.

Since the AOM 29 is installed in the beam optical path outside the laser resonator, the RF power RFD is applied to the AOM 29 from the drive unit 12 at the timing of continuous oscillation after the end of the Q switch pulse 30MIR as shown in FIG. The oscillation of the partial 13SIR and the timing are inserted. Since the continuous oscillation portion 13SIR is diffracted by the AOM 29, it is separated from the Q switch pulse 30MIR to obtain a beam 13SIR in another direction as shown in FIG. The continuous lasing portion 14 shows this. The continuous laser portion 13SIR separated from the Q switch pulse portion 30MIR is prevented from being directed to the workpiece 20. Therefore, only the Q switch pulse 30MIR is irradiated to the processing object 20, which contributes to the processing.

In such a conventional configuration, it is necessary to install the AOM 29 outside the oscillator and control the operation timing in synchronization with pulse oscillation. There is a loss due to the AOM 29, there is a loss of power, the use of the AOM 29 has the disadvantages of increasing the cost of the apparatus and requiring an installation location. Furthermore, when the laser beam wavelength changes, the AOM 29 needs to optimize the installation conditions such as the installation angle and the necessity of changing the antireflection film on the optical end face again.

Further, in order to avoid the phenomenon that the first pulse differs from the subsequent pulse output in the repetitive pulse oscillation output, there is a technique for reducing the excitation intensity of the light source for exciting the Nd: YAG laser medium immediately before the Q switch pulse oscillation. This is disclosed in U.S. Pat. No. 4,337,442. In order to make the pulse output constant, continuous excitation is continued in this way, and the oscillation is interrupted by the Q switch to stop the oscillation operation for a predetermined period before the Q switch pulse oscillation, and energy for the Q switch pulse is accumulated. A method of adjusting the number of distributions of the upper level of laser oscillation, such as a method of oscillating a Q switch pulse after the lapse of time and a method of reducing the excitation intensity from the excitation light source before the Q switch pulse oscillation is disclosed.

U.S. Pat. No. 4,337,442 US Pat. No. 5,018,152 US Pat. No. 5,291,505 US Pat. No. 5,339,323 US Pat. No. 5,821,569 US Pat. No. 5,982,790 US Pat. No. 6,038,241 US Pat. No. 6,418,154 US Pat. No. 6,0091,910 US Pat. No. 6,683,893 US6931035 specification US Pat. No. 6,172,325 US Pat. No. 5,719,372 U.S. Pat. No. 4,412,330 Special table 2002-518834 gazette

The problem to be solved by the present invention is equalization of the output of repeated Q switch pulses. That is, it is to provide a laser pulse generating apparatus and method capable of obtaining a stabilized Q-switch pulse laser oscillation output that does not depend on the pulse repetition time interval, and a laser processing apparatus using the same. And providing a method.

In order to solve the above problems, the present invention provides a laser medium, a laser resonator, a Q switch element that suppresses laser oscillation by controlling a Q value of the laser resonator, a deexcitation source of the laser medium, A predetermined energy is stored in the laser medium by operating a deexcitation source for a first predetermined time to release stored energy from the laser medium and applying a laser oscillation suppression signal to the Q switch element for a second predetermined time. And a means for stopping a laser oscillation suppression signal to the Q switch element in order to obtain a Q switch laser pulse oscillation output.

The laser medium excitation source may further include means for reducing the excitation intensity of the excitation source or stopping or blocking excitation. The means for accumulating energy further comprises means for setting the level of the laser oscillation suppression signal to a level that does not have sufficient oscillation suppression capability. Further, the means for releasing the stored energy further comprises means for setting the first predetermined time to zero or more.

Next, a laser medium, a laser resonator, a Q switch element that suppresses laser oscillation by controlling the Q value of the laser resonator,
Means for applying a laser oscillation suppression signal at a level that does not have sufficient oscillation suppression capability to the Q switch element for a predetermined time to accumulate predetermined energy in the laser medium;
And means for stopping a laser oscillation suppression signal to the Q switch element in order to obtain a Q switch laser pulse oscillation output.

Next, a laser medium, a laser resonator, a Q switch element that suppresses laser oscillation by controlling a Q value of the laser resonator, and means for providing a modulated excitation signal to the laser medium;
Means for storing a predetermined energy in the laser medium by applying a laser oscillation suppression signal and applying the laser oscillation suppression signal to the Q switch element for a predetermined time; and suppressing laser oscillation to the Q switch element to obtain a Q switch laser pulse oscillation output And a means for stopping the signal.

Next, a laser medium, a laser resonator, a Q switch element that suppresses laser oscillation by controlling a Q value of the laser resonator, a laser oscillation suppression signal is applied to the Q switch element, and energy is applied to the laser medium. Means for accumulating, means for modulating a laser oscillation suppression signal depending on the generation interval from the previous pulse in order to obtain a Q-switched laser pulse oscillation output in a state where there is a loss corresponding to the generation interval from the previous pulse It is characterized by.

Furthermore, the present invention is characterized in that a nonlinear optical element is further provided in the optical path of the Q-switched laser pulse. Further, the laser processing apparatus irradiates the processing target with the pulse output from these laser pulse generators, and the processing target is an electronic device such as a link wiring, a capacitor, a resistor, and an inductor on the semiconductor substrate. Or a display device such as a liquid crystal display device, an electroluminescence display device, or a plasma display device.

On the other hand, the present invention provides a step of providing a laser medium, a laser resonator, a Q switch element for suppressing laser oscillation by controlling a Q value of the laser resonator, and a deexcitation source of the laser medium, Operating for a predetermined period of time to release stored energy from the laser medium; applying a laser oscillation suppression signal to the Q switch element for a second predetermined period of time; and storing the predetermined energy in the laser medium; And a step of obtaining a Q-switched laser pulse oscillation output by stopping the laser oscillation suppression signal.

Further, in the step of releasing the stored energy, the excitation intensity to the laser medium is further reduced, or excitation is stopped or cut off. In the step of storing predetermined energy in the laser medium, the level of the laser oscillation suppression signal is set to a level that does not have sufficient oscillation suppression capability. In the step of releasing the stored energy, the first predetermined time is zero or more.

Next, a step of providing a laser medium, a laser resonator, and a Q switch element that suppresses laser oscillation by controlling the Q value of the laser resonator, and a signal that does not have sufficient oscillation suppression capability for a predetermined time Storing a predetermined energy in the laser medium by applying a laser oscillation suppression signal at a level, and obtaining a Q-switched laser pulse oscillation output by stopping the laser oscillation suppression signal to the Q switch element It is characterized by.

Next, a step of providing a laser medium, a laser resonator, and a Q switch element for suppressing laser oscillation by controlling the Q value of the laser resonator, a step of providing a modulated excitation signal to the laser medium, and a Q switch element Storing a predetermined energy in the laser medium by applying a laser oscillation suppression signal to the laser switch for a predetermined time, and obtaining a Q-switched laser pulse oscillation output by stopping the laser oscillation suppression signal to the Q switch element It is characterized by that.

Next, a step of providing a Q switching element that suppresses laser oscillation by controlling the Q value of the laser medium, the laser resonator, and the laser resonator, and applying a laser oscillation suppression signal to the Q switch element to apply energy to the laser medium. Q-switched laser pulse oscillation output in the state where the laser resonator has a loss corresponding to the generation interval from the previous pulse by modulating the laser oscillation suppression signal depending on the accumulation step and the generation interval from the previous pulse And obtaining a step.

Furthermore, the present invention is characterized by further comprising the step of converting the Q-switched laser pulse into a harmonic and outputting it. Further, the laser processing method includes a step of irradiating a processing target with a laser pulse generated by these laser pulse generation methods. Further, the processing target is a link wiring, a capacitor, a resistor, an inductor, or the like on a semiconductor substrate. It is an electronic device or a display device such as a liquid crystal display device, an electroluminescence display device, or a plasma display device.

According to the laser pulse generating apparatus and method of the present invention, it is possible to obtain a stable Q switch pulse that does not depend on a change in the time interval of pulse repetition. Moreover, according to the laser pulse processing apparatus and method of the present invention, it is possible to irradiate a processed object with a uniform laser pulse at an arbitrary timing. In object processing using laser pulses, processing positions may be distributed on the substrate at unequal intervals when irradiating a beam. Even in such a case, according to the present invention, the processing positions are unevenly distributed according to the processing positions. Although it is an arbitrary timing, it is possible to irradiate a uniform laser pulse.

In addition, according to the present invention, stable processing with a Q-switched laser pulse can be realized without the need for a continuous oscillation output of an external beam such as an AOM and a branching element for selection of a Q-switched pulse oscillation output unit. When obtaining a harmonic component from the fundamental wave from the laser oscillation medium, it is possible to prevent light having a wavelength other than the de-excitation light component or the wavelength converted by the harmonic element from being mixed into the Q switch pulse or the harmonic component. By using a holey fiber with a waveguide around the core that employs a waveguide as the laser medium, the effect of refractive index fluctuations due to temperature changes in the laser medium due to the temperature distribution formed in the laser medium is reduced and the laser is reduced. The stability of the oscillation mode can also be improved.

Explanatory drawing of the apparatus which performs the processing method by the laser beam irradiation of the prior art example regarding this invention. Operational explanatory diagram of the conventional apparatus configuration of FIG. FIG. 3 is an apparatus configuration diagram of Examples 1 and 2. FIG. 3 is an operation explanatory diagram of the apparatus according to the first embodiment. It is an ion energy level figure of the laser medium for explaining the principle of the present invention, and shows the Nd ion energy level in the Nd: YAG crystal. Operation explanatory diagram of Embodiment 2 Device configuration diagram of Examples 3 and 4 Operation explanatory diagram of Embodiment 3 Operation explanatory diagram of Embodiment 4 Different examples of the configuration of the second harmonic resonator

Explanation of symbols

1: Excitation semiconductor laser light source 2: Excitation laser beam 3: Condensing optical system 4: High-reflection mirror for laser resonator 4 ′: End mirror 5: Laser medium for solid-state laser 6: Q switch element 7: Output for laser resonator Mirror 7 ': Output mirror
8: excitation light source drive unit 9: Q switch drive unit 10: condensing unit for laser oscillation excitation 11: laser device control unit 12: AOM drive unit 14: continuous laser oscillation unit 15: beam expander 16: reflector 18: Condensing lens 19 for processing: Q switch pulse laser oscillation part 20: Processing object 21: Drive table drive units 26, 27, 40: Control signal line 23: Drive table 29: Acousto-optic element (AOM)
31: Nonlinear optical element 32: Wavelength filter 34: Beam absorber 41: Deexcitation laser oscillator 42, 43: Collimating lens 44: Polarized beam superimposing device 45: Composite beam 46: Excitation semiconductor laser oscillator 50: Laser device controller

Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS.

Hereinafter, the first embodiment of the present invention will be described in detail with reference to FIGS. Parts having the same functions as the numbers used in FIG. 1 of the description of the prior art are used for the explanation numbers in the figure. Here, the output mirror 7 ′ is an output mirror having high reflectivity for the fundamental wave and high transmittance for the second harmonic. An excitation laser beam from a semiconductor laser oscillator 46 that is a laser excitation light source is converted into a parallel beam via a collimator lens 43 and guided to a polarization beam superimposing device 44. On the other hand, the de-excitation laser oscillator 41 for reducing the laser upper level excitation density is a de-excitation source for irradiating the laser medium with a laser wavelength outside the laser oscillation target wavelength. A laser beam from the deexcitation laser oscillator 41 is converted into a parallel beam by a collimator lens 42 and guided to a polarization beam superimposing unit 44. A synthesized beam 45 in which these two beams are superimposed or shifted on the same axis is coaxially arranged. Then, the laser beam is focused on the laser medium 5 through the high reflection mirror 4 for the fundamental wavelength of the laser resonator. A nonlinear optical element 31 is installed between the output mirror 7 ′ of the laser resonator and the Q switch element 6. With this configuration, the on / off timing of the RF power is controlled in the Q switch element 6 between the laser resonator mirror 4 and the output mirror 7 'as shown in FIG.

In the example of FIG. 3, the light of the pumping semiconductor laser oscillator 46 is transmitted in space, but the light of the pumping oscillator can also be transmitted by a fiber. In this case, a deexcitation light source beam is transmitted to the fiber. Combine and transmit coaxially.

The oscillation wavelengths of the deexcitation laser oscillator 41 and the excitation semiconductor laser oscillator 46 are shown in FIG. 5 as excitation wavelengths when the laser medium is Nd: YAG, Nd: YVO4, Nd: YLF, etc., with Nd ⁺³ ions added. From the well-known energy level diagram of Nd, a wavelength near 808 nm is used, and laser light having a wavelength near 0.9 μm, 1.1 μm, and 1.3 μm is effective for deexcitation. This is because there are 946 nm, 1123 nm, and 1319 nm as other transition wavelengths starting from ⁴ F _3/2 at the upper level of the laser transition of the commonly used wavelength of the Nd: YAG crystal used in the laser medium. is there. In these configurations, an example of operation timing of each element and the control unit will be described.

The drive table 23 is driven by the drive unit 21 with a signal from the control unit 50 in order to set the processing position of the workpiece 20. The control position of the drive table may be a closed loop position control system (not shown) with an encoder. At this stage, prior to time t1 in FIG. 4, in order to drive the Q switch element 6 and the excitation semiconductor laser oscillator 46 for applying ultrasonic waves, the application of RF by controlling the application timing of RF1 in FIG. c) Start the excitation power (PL). The Q switch element 6 applies RF power from the Q switch drive unit 9 to the ultrasonic transducer of the Q switch element 6 to keep the laser resonator in a laser oscillation cutoff state with a large loss. On the other hand, an excitation laser output is applied to the laser medium 5, and the control signal line 27 is supplied from the control unit 50 so that the thermal temperature distribution in the laser medium is formed in an equilibrium state before laser oscillation. An oscillation command is sent to the pumping semiconductor laser oscillator 46 via.

A time t3 when the processing position of the processing object 20 reaches the condensing point of the corresponding condensing lens 18 is predicted, and a command signal for starting the laser oscillation operation process is issued from the control unit 50. First, in order to apply laser light in the vicinity of the deexcitation wavelength for reducing the inversion distribution density of the upper level that has been excited so far, an oscillation command is sent from the control unit 50 to the deexcitation laser oscillator 41 as a control signal line 40. Send via. The oscillation command is issued by the trigger signal shown in FIG. 4A, and de-excitation laser oscillation is started at times t1, t5, and t9 by the falling edge of the trigger signal as shown in FIG. The deexcitation laser light is collimated by the collimator lens 42 to be parallel, enters the polarization beam superimposing unit 44, passes through, and is irradiated to the laser medium 5 by the condenser lens 3. The laser medium 5 is preliminarily collimated by the collimating lens 43 from the pumping semiconductor laser oscillator 46 and pumped by the pumping laser beam coaxially formed by the polarization beam superimposing unit 44, and the temperature of the crystal is increased. Excitation energy is accumulated to the position as shown by the broken line level in FIG. Since the laser beam for deexcitation is irradiated to the same crystal space there, it transits from the upper level to the lower level at a wavelength different from the fundamental wavelength of laser oscillation, and light is emitted. Since this light has such a large loss that it does not satisfy the conditions for satisfying the laser resonator and sufficient oscillation conditions, laser light does not oscillate. The density of the upper energy level accumulated so far can be reduced as shown in FIG. 4 (e) UL-1.

De-excitation is performed during a predetermined time period t1-t2, and then the laser medium is excited between t2-t3 with only the excitation laser, and excitation for generating an inversion distribution at the upper level is performed (UL-2). Thereafter, as shown in FIG. 4 (b), the driving RF power to the Q switch element 6 is cut off between t3 and t4 to be in a transmission (open) state, and the Q switch pulse 33G is oscillated. Here, the excitation density of the upper level decreases with laser oscillation (UL-3). At this time, the Q switch pulse output 33G releases 33G of pulse energy (f) Q0 corresponding to the energy accumulated in the laser medium 5 during the time t2-t3. After oscillating the Q switch pulse, RF power is applied to the Q switch element 6 in order to turn the Q switch off (closed) again from time t4. The first machining target point is machined by a Q switch pulse that oscillates and is emitted between times t3 and t4 in this process. Next, similarly, the timing of the Q switch pulse oscillation obtained from the position and the scanning speed is obtained for the second workpiece point, and the de-excitation DPL1 is continued for the time t5-t6 in a time relationship based on the timing. Laser excitation is performed between time t6 and t7, and then RF is cut off between time t7 and t8 to oscillate the Q switch pulse 33G. In this case, even if the times of the time t3-t7 and t7-t11 that are the intervals of the Q switch pulses change, that is, even if the time between the times t4-t5 and t8-t9 is different, the de-excitation process (d) Since DPL1 is introduced between the pulse oscillation cycles of the Q-switch repetitive operation, the upper level energy accumulated before t1, t5, and t9 is decreased by the deexcitation laser. (F) Since the output energy of the Q switch pulse output 33G indicated by Q0 is set by the excitation energy after deexcitation, output equalization irrespective of the pulse repetition frequency can be achieved. Therefore, by using these equalized pulse outputs, it has become possible to precisely process a workpiece regardless of the laser irradiation timing. The third and subsequent Q switch pulse operations are similar processes.

In the embodiment of the above figure, an example is shown in which the laser output PL for excitation is operated at a constant intensity as shown in FIG. 4 (c). Thus, the excitation laser output PL may be modulated to accelerate the deexcitation rate.

In the above description, the nonlinear optical element 31 is not necessary when the fundamental wavelength is used as the processing wavelength. However, when the second harmonic is used, a known nonlinear optical element is used for the fundamental beam. Installed to satisfy the phase matching condition. As a result, the Q switch pulse is converted into the second harmonic and emitted from the output mirror 7 '. In this case, the ASE component (ASE = Amplified Spontaneous Emission, amplified spontaneous emission) stimulated and released by the fundamental wave component or deexcitation wavelength component of the Q switch pulse mixed into the second harmonic output as necessary. (Meaning of light) is removed by the wavelength filter 32, the mixed component 33IR is guided to the beam absorber 34, and only the second harmonic component 33G is collimated by the beam expander 15 and reflected by the reflecting mirror 16, and then the condenser lens 18 Then, it can be formed into a fine spot and irradiated to the object to be processed to be processed.

In order for the nonlinear optical element 31 to have a nonlinear action, the input light needs to be polarized. When there is an element with polarization in the resonator, for example, when a laser medium and Nd: YVO or Nd: YLF are used, polarization oscillation is possible without using any polarization means. You can enter. However, when the laser medium does not have an element accompanied by polarization, it is necessary to separately insert a polarizing means such as a polarizer in the optical path. The necessity of the polarizing means shown here is common to all cases where a nonlinear optical element is inserted in the present invention.

When the second harmonic component of the fundamental wavelength is converted into a wavelength by a nonlinear optical element and used for processing, a continuous oscillation component may be mixed into the fundamental wave. Most of the second harmonic component to be wavelength converted is This is because only the component of the Q switch element that provides high conversion efficiency is output as the second harmonic component. Even if the continuous wave component is emitted on the same axis as the harmonic without being wavelength-converted, the wavelength filter 32 can delete other than the harmonic. Therefore, the continuous component can be completely removed.

By passing through the nonlinear optical element 31, the burden of the oscillation suppression capability in the resonator with respect to the fundamental wave component of the Q switch element 6 can be relieved significantly. Conventionally, when a fundamental wave is used, the driving power of the Q switch element is increased so that a continuous output component is not output, and the RF power of the Q switch element drive is increased to suppress continuous oscillation in order to increase the suppression capability of the Q switch element. Or, after outputting the continuous component, it must be deleted by AOM as described in the prior art. In the former case, in order to increase the maximum power of the RF circuit of the Q switch driving unit 9, the reliability decreases due to heat generation, the limit to the maximum repetition rate accompanying the increase in the load on the high repetition RF modulation element, the Q switch transducer There are disadvantages in that a number of disadvantageous phenomena such as peeling of the joint of the transducer with the diffraction medium due to increased power consumption and cracking of the transducer for ultrasonic vibration occur. In the latter case, in order to install an AOM having a high diffraction efficiency that separates the Q-switch pulse component and the continuous oscillation component, a high RF power drive is required for the AOM transducer, and design restrictions on the RF driver in the Q-switch element 6 Arises as a drawback.

The second embodiment is an example in which the continuous output component is alternately generated with the Q switch pulse in the fundamental wave oscillation. The configuration of FIG. 3 is used. FIG. 6 illustrates the operation according to this embodiment. The output of the semiconductor laser oscillator 46 for excitation is generated in advance and the laser medium 5 is excited. During this time, the diffraction power is low enough to suppress the RF power of the Q switch element 6 to the required energy accumulation level at the repetition pulse rate. RF1 in (b) is set to a relatively low level so as to reduce the RF power until it has. Therefore, as the accumulation of excitation energy proceeds, the laser overcomes the suppression of the Q switch element 6 and starts continuous oscillation, and outputs a continuous low output LP as indicated by (f) Q0. Next, de-excitation DPL1 is generated during (d) t1-t2 of DPL and de-excited, and the accumulated energy is released as ASE, and the upper level energy is (e) UL-1 of UL-N. Consume as shown (UL-1). In the meantime, the semiconductor laser for excitation is stopped or cut off as in (c) t1-t2 of PL. Note that the de-excitation laser oscillation command is issued by the trigger signal shown in FIG.

During the period from t2 to t3, the excitation medium is again irradiated with excitation light to excite the laser medium 5, and necessary excitation level energy is accumulated (UL-2). After that, at t3, RF application of the Q switch element 6 is stopped, Q switch pulse oscillation is caused, and the Q switch pulse 33G is emitted (UL-3). Next, RF1 power is applied to the Q switch element 6 to optically excite the laser medium 5 from the pumping semiconductor laser oscillator 46, and the continuous oscillation component LP oscillates. Thereafter, de-excitation laser irradiation is performed at a necessary timing t5-t6, excitation is performed with a semiconductor laser for excitation for a predetermined time (t6-t7), and then a Q switch pulse is oscillated repeatedly. Even if a continuous output is generated in this cycle, the conversion efficiency in the nonlinear optical element 31 is proportional to the square of the power, so the conversion efficiency of the continuous output is overwhelming compared to that of the Q switch pulse. Since it is low, it passes through the nonlinear optical element 31 as the fundamental wave, is separated by the wavelength filter 32, becomes heat by the beam absorber 34, and can be eliminated. Accordingly, the object to be processed is irradiated with only the converted component from the Q switch pulse of the harmonic component and processed.

The deexcitation periods t1-t2, t5-t6, and t9-t10 can be zero. When zero, the deexcitation laser can be omitted, and therefore, from FIG. 3, the deexcitation laser transmitter 41, the control signal line 40, the collimator lens 42, the polarization beam superimposing unit 44, and the laser device controller The function relating to the control of the de-excitation laser oscillator at 50 may be omitted.

When the state diagram 6 (g) UL′-N is used in which the number of inversion distributions in the upper level is suppressed by setting the level at which oscillation cannot be completely suppressed when RF power is applied to the Q switch element 6, 6 (g) (h) (i) shows the operation when the deexcitation times t1-t2, t5-t6, and t9-t10 are set to zero. In this case, the low peak Q switch can be stably obtained at any interval from low repetition to high repetition operation. At this time, the upper level energy is shown in FIG. The time lapse of the oscillation output corresponding to FIG. 6 (f) is as shown in FIG. 6 (h). The continuous leakage component LP ′ oscillates overcoming the loss due to the suppression capability of the Q switch and continues until just before the Q switch pulse oscillation command timing t3, t7, t11, and when the RF power is turned off, it is suppressed by applying the RF power. Due to the remaining gain, 33G of low peak Q switch pulse (h) Q′0 is obtained. By converting the wavelength of this into a harmonic with a non-linear optical element, the second harmonic Q switch output (i) QSHG 33G 'is obtained. According to this method, the Q switch pulse 33G and the second harmonic output 33G ′ can be obtained at a constant output up to such a high repetition rate that the leakage oscillation component LP ′ cannot be generated. A stable harmonic Q-switch pulse unrelated to

Example 3 is an example in which a nonlinear optical element is used without using a deexcitation laser oscillator. FIG. 7 shows the configuration. Although not described because it is the same as FIG. 1, a nonlinear optical element 31 is added in FIG. 7, and it has a high reflectance for the fundamental wave and a high transmittance for the second harmonic. An output mirror 7 ′ having characteristics is used. The operation in this case is shown in FIG. (A) shows the excitation laser power. Here, it is assumed that the signal is not continuous wave but modulated. (B) is a trigger signal. Trigger signal intervals t1-t2, t2-t3, and t3-t4 may not be constant. When a trigger signal (in this case, a rising edge) is input, an oscillation suppression signal RF1 is applied to the Q switch element 6 as shown in (c). As a result, when energy is accumulated in the laser medium, since the RF1 application time is constant, the energy accumulated in the laser medium is constant even if the interval between trigger signals is not constant. When the RF1 application is completed, a Q switch pulse 33G is generated as shown in (d), but since the stored energy is constant, a Q switch pulse with constant energy can be obtained. This pulse is converted into a harmonic wave by the non-linear optical element 31 as it is or becomes a Q switch pulse 33G ′ as shown in (e), and is irradiated to the processed object 20, but the energy of each pulse irradiated is constant. Kept. As described above, in this embodiment, since RF is applied to the Q switch element 6 for a certain period of time in response to the trigger signal, the energy accumulation time in the laser medium 5 is constant, so that a uniform Q switch pulse is generated. There is an effect that can be obtained. In addition, since the amount of heat generated in the laser crystal is constant, the beam characteristics can be kept constant.

In this embodiment, a continuous wave may be generated between the Q switch pulses 33G depending on the modulation method of the excitation laser power. As described above, due to the non-linearity of the non-linear optical element, the continuous wave with low power originally has a very low conversion efficiency to the harmonic, so that only the fundamental wave component exits from the non-linear optical element 31. Since the fundamental wave is separated by the wavelength filter 32, the processed object 20 is not irradiated.

In the fourth embodiment, the energy is made constant by generating a Q switch pulse in a state where the resonator has a loss. The configuration is the same as in FIG. 7, and the operation at this time is shown in FIG. As shown in FIG. 9A, the pump laser power is operated continuously. Further, as shown in FIG. 9C, an RF signal for suppressing oscillation is applied to the Q switch element 6 in order to accumulate energy in the laser medium. As shown in FIG. 9B, the trigger intervals t1-t2, t2-t3, t3-t4, and t4-t5 are arbitrary. With respect to the trigger generated at such an arbitrary timing, the intensity of the oscillation suppression RF signal is multiplied by a fixed time modulation DRF1, DRF2, DRF3, etc. by the input of a trigger pulse (a falling edge in the case of FIG. 9). To do. At this time, the modulation amount depends on the interval from the previous trigger (for example, 3-t4 and t4-t5 for DRF4 and DRF5, respectively), and the decrease in the RF signal intensity is reduced as the trigger interval is longer. Modulate to When the intensity of the RF signal input to the Q switch element 6 decreases, the Q value of the resonator increases as shown in (d). As a result, the energy accumulated in the laser medium 5 is released, and a Q switch pulse 30G is generated as shown in FIG. However, unlike other embodiments in which the RF signal is always zero when a pulse is generated, the Q value does not rise sufficiently when the RF signal is weak but not zero. For this reason, when the RF signal is weak but not zero, it oscillates in a state with some loss in the laser resonator. At this time, the energy of the generated Q switch pulse is determined by the stored energy in the laser medium and the Q value in the resonator. Therefore, if the former is large, the energy of the generated pulse can be reduced by controlling the latter small. Can be constant. That is, when the interval from the previous trigger is long, the accumulated energy in the laser medium 5 is large. Therefore, the modulation factor of the RF signal is decreased, the Q value in the resonator is decreased, the loss is increased, and the pulse is increased. When Q is generated, it becomes possible to generate a Q switch pulse having a constant energy.

A table indicating the modulation amount of the RF signal corresponding to the trigger time interval is generated in order to generate a Q-switch pulse with a constant energy, and the above method is implemented by providing the table in the laser controller 50 in FIG. It is possible. A necessary modulation amount may be read from the trigger pulse interval by referring to a table, and a predetermined RF modulation amount may be given to the Q switch element 6 under the control of the laser controller 50.

In addition, by changing the set value of the RF modulation amount applied to the Q switch element corresponding to the trigger time interval, an arbitrary energy is given for each pulse instead of a constant energy as shown in this embodiment. It is also possible to do so.

In this embodiment, the energy of the Q switch pulse can be made constant, and the Q value is increased only when the laser is output, so that the pump power can be used to the maximum and the energy utilization efficiency is high.

FIG. 10 shows an example of the configuration of the second harmonic (SHG) resonator that is different from those shown in FIGS. 3 and 7. In this figure, there is no deexcitation laser oscillator 41 as in the configuration of FIG. 7, but the deexcitation laser oscillator 41 is as shown in FIG. 3 for the configuration of the second harmonic resonator in FIG. Needless to say, this is applicable to certain configurations. The use of the nonlinear optical element 31 is common to FIG. 3 or FIG. Further, an end mirror 4 'having total reflection characteristics with respect to the fundamental wave and the second harmonic is provided. This configuration has an advantage that the conversion efficiency is increased by the fundamental wave reciprocating the nonlinear optical element 31.

In the above embodiment, a wavelength conversion technique that is known to set the wavelength converted from the fundamental wave by the nonlinear optical element to the third harmonic, the fourth harmonic, or the fifth harmonic in addition to the second harmonic is used. This is clearly possible.

Unlike the laser oscillation method in which continuous oscillation output at the fundamental wavelength output and Q switch pulse oscillation are mixed, the present invention oscillates only the Q switch pulse with the fundamental or harmonic converted output. Each Q switch pulse output can be equalized regardless of the pulse repetition period. Accordingly, there is an advantage that a configuration that does not require a continuous oscillation output removing device can be realized. Moreover, even if continuous components are mixed in the fundamental wave by converting to harmonics, only the Q switch pulse can be used due to the difference in conversion efficiency and the wavelength filter action. In either case of using the fundamental wave output or the case of using the harmonic output, since only a short pulse by the Q switch is irradiated by the relative high-speed scanning when scanning the workpiece, it is continuous. Irradiation by the components does not occur, so no thermal effects occur. It is possible to simplify the circuit by reducing the RF circuit output power of the Q switch driving unit operating in a high repetition operating range.

Further, the configuration in which the laser medium is pumped coaxially through the high-reflection mirror has been shown, but the laser medium can be pumped by other known side surface pumps such as laser diode stag pumping and lamp pumping.

Although the laser medium has been described as an Nd-doped crystal, a laser is used by using an optical waveguide (holi-fiber) having a kind of laser active material in which a large number of holes are provided around the core in the axial direction and the central portion is a waveguide. By using the medium, the influence of the refractive index variation due to the temperature change in the laser medium due to the temperature distribution formed in the laser medium can be reduced, and the stability of the laser oscillation mode can be further improved.

A number of embodiments of the present invention have been described above. Obviously, modifications may be made to the invention without departing from the scope of the invention as set forth in the appended claims.

Examples of applications of the present invention include cutting circuit elements of silicon wafers of semiconductor memories, trimming capacitors, resistors, inductances, LCD display panel correction processing, PDP display device correction processing, circuit board function trimming, and other semiconductor substrate lasers. When applied to precision machining, it is possible to reduce the manufacturing cost of electronic components by improving the product yield by reducing the machining width and reducing the amount of processed removal.

Claims (33)

A laser medium, a laser resonator, a Q switch element that suppresses laser oscillation by controlling a Q value of the laser resonator, and a deexcitation source of the laser medium;
A predetermined energy is stored in the laser medium by operating the deexcitation source for a first predetermined time to release the stored energy from the laser medium and applying a laser oscillation suppression signal to the Q switch element for a second predetermined time. Means to
A laser pulse generator comprising: a laser oscillation suppression signal stop means for the Q switch element to obtain a Q switch laser pulse oscillation output. The laser pulse generator according to claim 1, further comprising a nonlinear optical element in an optical path of the Q-switched laser pulse. An excitation source for the laser medium,
2. The laser pulse generator according to claim 1, wherein said means for releasing stored energy further comprises means for reducing excitation intensity of said excitation source or stopping or blocking excitation. 2. The laser pulse generator according to claim 1, wherein said means for accumulating energy further comprises means for setting the level of said laser oscillation suppression signal to a level that does not have sufficient oscillation suppression capability. 5. The laser pulse generator according to claim 4, wherein said means for releasing stored energy further comprises means for setting a first predetermined time to zero or more. 6. The laser pulse generator according to claim 3, further comprising a nonlinear optical element in the optical path of the Q-switched laser pulse. A laser medium, a laser resonator, and a Q switch element for suppressing laser oscillation by controlling a Q value of the laser resonator;
Means for applying a laser oscillation suppression signal at a level that does not have sufficient oscillation suppression capability to the Q switch element for a predetermined time to accumulate predetermined energy in the laser medium;
A laser pulse generator comprising: means for stopping a laser oscillation suppression signal to the Q switch element to obtain a Q switch laser pulse oscillation output. 8. The laser pulse generator according to claim 7, further comprising a nonlinear optical element in the optical path of the Q-switched laser pulse. A laser medium, a laser resonator, and a Q switch element for suppressing laser oscillation by controlling a Q value of the laser resonator;
Means for providing a modulated excitation signal to the laser medium;
Means for storing a predetermined energy in the laser medium by applying a laser oscillation suppression signal to the Q switch element for a predetermined time;
A laser pulse generator comprising: means for stopping a laser oscillation suppression signal to the Q switch element to obtain a Q switch laser pulse oscillation output. The laser pulse generator according to claim 9, further comprising a nonlinear optical element in an optical path of the Q-switched laser pulse. A laser medium, a laser resonator, and a Q switch element for suppressing laser oscillation by controlling a Q value of the laser resonator;
Means for applying a laser oscillation suppression signal to the Q switch element to accumulate energy in the laser medium;
A laser pulse generator comprising means for modulating a laser oscillation suppression signal depending on a generation interval from a previous pulse in order to obtain a Q-switch laser pulse oscillation output in a state where there is a loss corresponding to the generation interval from the previous pulse. The laser pulse generator according to claim 11, further comprising a nonlinear optical element in an optical path of the Q-switched laser pulse. The de-excitation source is a laser, and the wavelength of the de-excitation light is light having a wavelength in the vicinity of 0.9 μm, 1.1 μm, and 1.3 μm that makes a transition other than the fundamental oscillation wavelength of Nd ⁺³ ions. Item 13. A laser pulse generator according to items 1 to 12. 13. The laser according to claim 1, wherein an excitation source of the laser medium is a semiconductor laser, the laser medium is Nd: YAG, Nd: YVO4, Nd: YLF, and the deexcitation source is a semiconductor laser. Pulse generator. 13. The laser pulse generator according to claim 1, wherein the laser medium is a holey fiber doped with laser active ions having a large number of holes around a core forming an optical waveguide. A fundamental wave of laser oscillation is a stimulated emission wavelength from Nd ⁺³ ions, and a harmonic wave generated by the nonlinear optical element is a second harmonic wave, a third harmonic wave, a fourth harmonic wave, or a fifth harmonic wave. The laser pulse generator according to claim 2, 6, 8, 10, or 12. A laser processing apparatus for irradiating a workpiece with a pulse output from the laser pulse apparatus according to claim 1. The laser processing apparatus according to claim 17, wherein the laser processing object is an electronic device such as a link wiring, a capacitor, a resistor, or an inductor on a semiconductor substrate. 18. The laser processing apparatus according to claim 17, wherein the object to be processed is a display device such as a liquid crystal display device, an electroluminescence display device, or a plasma display device. Providing a laser medium, a laser resonator, a Q switch element that suppresses laser oscillation by controlling a Q value of the laser resonator, and a laser medium deexcitation source;
Operating the deexcitation source for a first predetermined time to release stored energy from the laser medium; and applying a laser oscillation suppression signal to the Q switch element for a second predetermined time to store the predetermined energy in the laser medium; ,
And a step of obtaining a Q-switched laser pulse oscillation output by stopping a laser oscillation suppression signal to the Q-switch element. 21. The laser pulse generation method according to claim 20, further comprising the step of converting the Q-switched laser pulse into a harmonic and outputting the harmonic. The laser pulse generation method according to claim 20 or 21, wherein in the step of releasing the stored energy, the excitation intensity to the laser medium is further reduced, or excitation is stopped or cut off. The laser pulse generation method according to claim 20 or 21, wherein in the step of storing predetermined energy in the laser medium, the level of the laser oscillation suppression signal is set to a level that does not have sufficient oscillation suppression capability. The laser pulse generation method according to claim 23, wherein the first predetermined time is zero or more in the step of releasing the stored energy. Providing a laser medium, a laser resonator, and a Q switch element for suppressing laser oscillation by controlling the Q value of the laser resonator;
Storing predetermined energy in the laser medium by applying a laser oscillation suppression signal having a signal level that does not have sufficient oscillation suppression capability to the Q switch element for a predetermined time;
And a step of obtaining a Q-switched laser pulse oscillation output by stopping a laser oscillation suppression signal to the Q-switch element. 26. The laser pulse generation method according to claim 25, further comprising the step of converting the Q-switched laser pulse into a harmonic and outputting the harmonic. Providing a laser medium, a laser resonator, and a Q switch element for suppressing laser oscillation by controlling the Q value of the laser resonator;
Applying a modulated excitation signal to the laser medium, and storing a predetermined energy in the laser medium by applying a laser oscillation suppression signal to the Q switch element for a predetermined time;
And a step of obtaining a Q-switched laser pulse oscillation output by stopping a laser oscillation suppression signal to the Q-switch element. 28. The laser pulse generation method according to claim 27, further comprising the step of converting the Q-switched laser pulse into a harmonic and outputting the harmonic. Providing a Q switching element that suppresses laser oscillation by controlling the Q value of the laser medium, the laser resonator, and the laser resonator;
Applying a laser oscillation suppression signal to the Q switch element to store energy in the laser medium;
Obtaining a Q-switched laser pulse oscillation output in a state where the laser resonator has a loss corresponding to the generation interval from the previous pulse by modulating the laser oscillation suppression signal depending on the generation interval from the previous pulse. Laser pulse generation method. 30. The laser pulse generation method according to claim 29, further comprising the step of converting the Q-switched laser pulse into a harmonic and outputting the harmonic. 31. A laser processing method comprising a step of irradiating a processing object with a laser pulse generated by the laser pulse generating method according to claim 20. 32. The laser processing method according to claim 31, wherein the laser processing object is an electronic device such as a link wiring, a capacitor, a resistor, or an inductor on a semiconductor substrate. 32. The laser processing method according to claim 31, wherein the laser processing object is a display device such as a liquid crystal display device, an electroluminescence display device, or a plasma display device.

Images