JPH0750442A - Laser equipment for processing - Google Patents

Abstract

PURPOSE:To provide a laser equipment for processing, which makes it possible to obtain a laser beam, which is used in a laser processing for obtaining a uniformly processed surface with a comparatively short-wavelength laser beam, by converting a fundamental wave laser beam into a short-wavelength laser beam. CONSTITUTION:Crystals having a large phase matching allowable incident angle are used as nonlinear optical crystals 8 and 10 and the beam divergence angle of a fundamental wave laser beam, which is emitted from an output mirror 2 of a fundamental wave laser equipment within the extent of the phase matching allowable incident angle of these nonlinear optical crystals, is set large, whereby a multi-mode laser beam for processing is obtained while the wavelength conversion efficiency of the laser is maintained comparatively high.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention makes it possible to obtain a laser beam used in laser processing for obtaining a uniform processed surface with a laser beam having a relatively short wavelength, by converting a fundamental wave laser beam into a short wavelength. The present invention relates to a processing laser device.

[0002]

2. Description of the Related Art For example, as a method for accurately removing only a predetermined region of a resin thin film formed on the surface of an IC circuit without damaging the IC circuit or the like, laser light having a relatively short wavelength in the ultraviolet region or in the vicinity thereof is used. There has been proposed a method of performing laser processing by using. In this way, laser processing using a short-wavelength laser beam is performed by irradiating a resin or the like to be processed with a short-wavelength laser beam such as ultraviolet light so that a chemical bond state (bond) only in the irradiated region is obtained. After instant destruction by photochemical reaction, a small amount of heat energy quickly removes the part where the bond is destroyed. Therefore, the risk of thermal damage to the object to be processed is extremely small. Therefore, only the irradiated portion can be removed accurately, and since the wavelength is short, it is limited to a part in the thickness direction of the thin film. Since it has various characteristics such that it can be irradiated with light and precise processing of a thin film is possible, its application has been studied in various fields in recent years.

Incidentally, as a laser oscillator capable of generating a laser beam of a short wavelength having a high output which can be used for laser processing, there is, for example, an excimer laser, but its application is still limited because the device is large and expensive. ing.

As a method of relatively easily obtaining a laser beam of a short wavelength, for example, an Nd: YAG laser (wavelength of about 106) is used.
4 nm) as the fundamental wave and the first nonlinear optical crystal for wavelength conversion generates the second harmonic (wavelength approximately 532 nm) from the fundamental wave (wavelength approximately 1064 nm), and the second harmonic for second wavelength conversion There is a method of generating a fourth harmonic (wavelength of about 266 nm) with a nonlinear optical crystal.

In addition, for example, the first non-linear optical crystal for wavelength conversion changes the fundamental wave (wavelength of about 1064 nm) to the second wave.
A harmonic (wavelength of about 532 nm) is generated, and then a second harmonic conversion optical crystal is used to generate a sum frequency of a third harmonic (wavelength of about 355 nm) from the second harmonic and the fundamental wave. By the non-linear optical crystal for wavelength conversion of 3,
From the third harmonic and the fundamental wave to the fourth harmonic (wavelength approx. 266n
m) is a method of generating a sum frequency (Japanese Patent Laid-Open No. 4-111).
484).

In any of the above-mentioned conventional methods, in order to obtain higher wavelength conversion efficiency, the laser device for generating the fundamental wave has a beam divergence angle as small as possible, that is, laser oscillation close to the fundamental mode (single mode). Was considered to be obtained. Laser light close to the fundamental mode has high coherency, and wavelength-converted harmonics also have high coherence. Normally, laser light with high coherence such as the fourth harmonic of an Nd: YAG laser is focused at one point on the surface of the workpiece to form a hole, and the focused point is scanned. Used for wire or surface processing.

[0007]

However, the normal N
When laser light with high coherence such as the 4th harmonic of a d: YAG laser and an image forming optical system are combined for processing, the interference effect is high, and thus uneven processing marks remain on the surface of the workpiece. There is a problem that it will end up. Laser light with low coherence, that is, laser light with a large number of transverse modes is required in order to avoid the generation of uneven processing marks on the surface of the workpiece.

However, for example, the above-mentioned Nd: YA
In a laser such as a G laser that requires wavelength conversion to generate ultraviolet light, it is difficult to perform wavelength conversion if the transverse mode of the laser is simply increased to reduce coherence. There was a problem.

The present invention has been made under the above-mentioned background, and in particular, a laser beam used for laser processing for obtaining a uniform processed surface with a laser beam having a relatively short wavelength is converted into a fundamental wavelength laser beam having a short wavelength. It is an object of the present invention to provide a processing laser device which can be obtained relatively easily by conversion.

[0010]

In order to solve the above-mentioned problems, a processing laser device according to the present invention comprises: (Structure 1) a fundamental wave laser device for generating a fundamental wave laser beam; Having a nonlinear optical crystal that converts the wavelength to a short wavelength and emits, using a large allowable incident angle of phase matching as the nonlinear optical crystal, within the range of the phase matching allowable incident angle of the nonlinear optical crystal,
The configuration is characterized in that multi-mode processing laser light is obtained by setting a large beam divergence angle of the fundamental wave laser light emitted from the fundamental wave laser device. ) In the processing laser device of configuration 1, the beam divergence angle of the fundamental wave laser light emitted from the fundamental wave laser device has a product of the beam diameter and the divergence angle (half angle) of the fundamental wave laser light in the vertical or horizontal direction. At 20 mm mrad
An oscillation condition of the fundamental laser device is set as described above, and as a mode of the configuration 1 or 2, (configuration 3) in the processing laser device of configuration 1 or 2, As the fundamental wave laser device, by providing a cylindrical lens or an anamorphic prism as a primary magnifying optical system in the resonator and selecting these optical conditions, the fundamental wave laser light emitted from the fundamental wave laser device is selected. A configuration characterized by using a laser oscillator or a laser amplifier in which a beam divergence angle is set to a predetermined angle, and (Configuration 4) In the processing laser device of Configuration 1 or 2, the fundamental wave laser device As a configuration, a laser oscillator or a laser amplifier using a laser medium having an aspect ratio of the emission opening of 1: 2 or more is used. Further, as a mode of Configuration 4, (Configuration 5) In the processing laser device of Configuration 4, a slab type laser medium is used as the laser medium. As a mode, (Structure 6) In the processing laser device according to any one of Structures 1 to 5, as the nonlinear optical crystal, an angular phase matching nonlinear optical crystal that generates a second harmonic light of the fundamental laser light, A configuration characterized by using a temperature-phase-matched nonlinear optical crystal that generates fourth harmonic light is provided. As an aspect of this configuration 6, (configuration 7), in the processing laser device of configuration 6, the fundamental laser light is used. Using the LBO crystal or the KTP crystal as the non-linear optical crystal of the angular phase matching for generating the second harmonic light, the non-linear optical crystal of the temperature phase matching for generating the fourth harmonic light And a DKDP crystal is used, and as an aspect of any one of configurations 1 to 5, (configuration 8) in the processing laser device of any one of configurations 1 to 5, the nonlinear optical crystal As the configuration, a non-linear optical crystal of angular phase matching that generates second harmonic light of the fundamental laser light and a non-linear optical crystal of angular phase matching that generates third harmonic light are used. As a mode of Configuration 8, (Configuration 9) In the processing laser device of Configuration 8, as the angle phase matching nonlinear optical crystal that generates the second harmonic light and the angle phase matching nonlinear optical crystal that generates the third harmonic light, And LBO crystals are used together, and as an aspect of any one of configurations 1 to 9, (10) processing of any one of configurations 1 to 9 In the laser device, as the laser device is obtained by a configuration characterized by using a laser oscillator or laser amplifier using a Nd · YAG laser medium.

[0011]

According to the above configuration 1, a nonlinear optical crystal having a large allowable incident angle of phase matching is used, and within the range of the allowable incident angle of phase matching of the nonlinear optical crystal, the fundamental laser device is used. By setting a large beam divergence angle of the emitted fundamental wave laser light, it becomes possible to obtain a multi-mode processing laser light while maintaining the wavelength conversion efficiency relatively high. This makes it possible to obtain a laser beam used for laser processing for obtaining a uniform processed surface with a laser beam having a relatively short wavelength by converting a fundamental laser beam into a short wavelength very easily.

In this case, by setting the beam divergence angle to the degree of the configuration 2, it becomes possible to use a nonlinear optical crystal that is easily available.

Further, according to the constitutions 3 to 5, the beam divergence angle of the fundamental wave laser light can be easily set to a desired angle.

According to the configurations 6 to 9, it is possible to obtain the second to fourth harmonic light of the fundamental laser light.

According to the structure 10, a fundamental wave laser device having a necessary and sufficient output can be easily obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a schematic structure of a processing laser device according to an embodiment of the present invention, FIG. 2 is an explanatory view of a vertical beam divergence angle, and FIG. 3 is an explanatory view of a horizontal beam divergence angle. is there.

In FIG. 1, reference numeral 1 is an Nd: YAG slab laser medium, reference numeral 2 is an output mirror, reference numeral 3 is a total reflection mirror, reference numeral 4 is a Pockels cell necessary for Q switch operation, and reference numeral 5 is also Q. Polarizers necessary for switching operation, reference numerals 6a and 6b are two cylindrical lenses, reference numeral 7 for adjusting the beam diameter (only in the vertical direction) to the size of the wavelength conversion crystals LBO and DKDP.
Is a 1/2 wavelength plate for adjusting the polarization direction of the fundamental wave, reference numeral 8 is an LBO crystal for second harmonic generation (SHG), and reference numeral 9 is 1 / for adjusting the polarization direction of the second harmonic. Two-wave plate, reference numeral 10 is DKDP for fourth harmonic generation (FHG)
Crystal, reference numeral 11 indicates the generated fourth harmonic light (ultraviolet light; 26
6 nm) and the fundamental wave light (1064 nm) and the second harmonic light (532 nm).

These optical elements are arranged so that their optical axes are common, and an output mirror 2 and a total reflection mirror 3 which form a resonator by sandwiching the Nd: YAG slab laser medium 1 are arranged.
Further, a polarizer 5 and a Pockels cell 4 are arranged between the Nd: YAG slab laser medium 1 and the output mirror 2 in order from the Nd: YAG slab laser medium 1 side.
Further, on the outside of the output mirror 2, the cylindrical lenses 6a and 6b, the half-wave plate 7, and the LB are arranged in this order from the output mirror 2 side.
An O crystal 8, a half-wave plate 9, a DKDP crystal 10 and a prism 11 are arranged.

Here, a flash lamp for exciting the Nd: YAG slab laser medium 1, Nd: YA.
G slab laser medium 1, a lamp house for housing a flash lamp, a power supply device for supplying power to the flash lamp, a Nd: YAG slab laser medium 1, a cooler for cooling the flash lamp, Nd: YAG
Slab laser medium 1, resonator composed of output mirror 2 and total reflection mirror 3, cylindrical lenses 6a, 6b, 1/2
Illustration of a housing for accommodating the wave plate 7, the LBO crystal 8, the half wave plate 9, the DKDP crystal 10, the prism 11 and the like is omitted.

The Nd: YAG slab laser medium 1 is
The length is 180 mm, the width is 20 mm, the thickness is 5 mm, and the end face is cut at 30 degrees. As is well known, the excitation light is introduced from a pair of parallel surfaces facing each other in the thickness direction, and a pair of surfaces facing each other in the length direction. Laser light is generated by entering and emitting laser light through the sloping end faces, and by alternately repeating zigzag reflection with a pair of parallel surfaces facing each other in the thickness direction as total reflection surfaces inside. A total reflection mirror 3 is a concave mirror having a radius of curvature of 3 m, and an output mirror 2 is a partial transmission mirror having a reflectance of 30%. These are Nd: Y.
The AG slab laser medium 1, the polariser 5, and the Pockels cell 4 are sandwiched in between and are arranged facing each other with an interval of about 55 cm to form a laser resonator.

An apparatus constructed by sandwiching an Nd: YAG slab laser medium 1, a polarizer 5 and a Pockels cell 4 with a total reflection mirror 3 and an output mirror 2 constitutes a Q-switch pulse laser oscillator which is a fundamental wave laser apparatus. Is what
For example, by inputting excitation energy of about 40 J to a flash lamp (not shown) to excite the Nd: YAG slab laser medium 1 and driving the Pockels cell 4, the output mirror 2 outputs a pulse width of about 15 nanoseconds and an output energy of about Four
A fundamental wave laser light (wavelength: 1064 nm) having a repetition frequency of 50 mJ and laser oscillation of 100 Hz can be taken out.

The LBO crystal 8 has a rectangular parallelepiped shape with a length and width of 8 mm and a length of 12 m, and the DKDP crystal 10 has a length and width of 10 mm and a length of 30 mm with a rectangular parallelepiped shape. It can be adjusted by attaching it to a stage with a tilt adjustment function.

In this case, the LBO crystal 8 for second harmonic generation (SHG) has an allowable angle of ΔΦ = 6.5 mrad · cm ⁻¹ and Δθ = 7 in TYPEI angle phase matching.
It is 5 mrad · cm ⁻¹ . Also, the fourth harmonic generation (F
DKDP crystal 10 (Noncritical) for HG) is TYP
In EI temperature phase matching, there is no ΔΦ direction dependency, Δθ
= 23 mrad · cm ⁻¹ , very wide.

In the apparatus having the above-mentioned structure, when the fundamental wave laser light (wavelength of about 1064 nm) is emitted from the output mirror 2, the fundamental wave laser light is incident on the LBO crystal 8 and the second
A harmonic (wavelength of about 532 nm) is generated, and then the generated second harmonic enters the DKDP crystal 10 to generate a fourth harmonic (wavelength of about 266 nm). Then, these are separated and taken out by the prism 11.

Here, it is known that the beam quality of the laser oscillator is generally proportional to the length of the resonator in the case of a stable resonator and inversely proportional to the square of the size of the opening of the support in the resonator. Has been. In the present embodiment, this is utilized to make use of the wavelength conversion nonlinear optical crystal (LBO crystal 8, DKD).
As long as the allowable incident angle of the P crystal 10) allows, that is, the range in which the wavelength conversion efficiency does not significantly decrease (here, the wavelength conversion efficiency (theoretical value) of an ideal single-mode laser having the same intensity).
In the range of not less than 1/2 of
The beam quality was set as low as possible, that is, the beam divergence angle was made large, in other words, the multimode oscillation resonator was configured.

That is, as shown in FIG. 2, the beam quality of the fundamental laser light immediately after leaving the output mirror 2 of the laser oscillator, that is, the beam divergence angle, is in the vertical direction (the direction in which the size of the slab opening is large; Width direction: Opening width about 15m
m) is about 15 mrad, which is about ² if expressed in terms of M ² factor.
It was set to 00. Approximately 4 in the lateral direction (direction in which the size of the slab opening is small; thickness direction; opening width is about 5 mm).
When expressed in mrad and M ² factors, it was set to about 20. In this state, the size of the laser beam in the vertical direction is the wavelength conversion crystal (LBO crystal 8, DKDP crystal 1).
0), so two cylindrical lenses 6
The beam diameter in the vertical direction is reduced to about 5 mm by a and 6b. The beam divergence angle at this time is about 45 mr in the vertical direction.
It becomes ad, and the lateral direction remains about 4 mrad.

The LBO crystal 8 is held so that the direction in which the allowable incident angle of the LBO crystal 8 is large coincides with the direction in which the divergence angle of the fundamental wave laser beam emitted from the output mirror 2 is large (longitudinal direction), and 1/2 The polarization direction is adjusted by the wave plate 7 so that the wavelength conversion efficiency of the LBO crystal 8 is maximized. LBO at this time
In the crystal 8, about 40% of the fundamental wave is converted into the second harmonic wave. This conversion efficiency is as high as about 80% as compared with the experiment using the single mode laser, which is a practically sufficient value.

The wavelength-converted second harmonic enters the DKDP crystal 10. Therefore, the crystal 10 is held so that the direction in which the allowable incident angle of the DKDP crystal 10 is large matches the direction in which the divergence angle of the second harmonic is large (longitudinal direction), and the ½ wavelength plate 9 is used to hold the crystal 10. The polarization direction is adjusted so that the wavelength conversion efficiency is maximized. At this time, DKDP
The crystal 10 has about 30 second harmonics (wavelength about 532 nm).
% Was wavelength converted to the 4th harmonic. This conversion efficiency is about 70% higher than that in the experiment using a single mode laser, which is a practically sufficient value.

As the fourth harmonic light separated and output by the prism 11, the output mirror 2 is finally used in this embodiment.
45 which is about 10% of the fundamental laser light emitted from
Ultraviolet light with low coherence having energy of mJ / pulse was repeatedly obtained stably at 100 Hz.

This ultraviolet light was shaped by a rectangular mask, and this was reduced and imaged on a polyimide resin by an imaging lens.
It was possible to easily perform processing with almost no uneven processing unevenness due to the interference effect that has occurred in the past.

Here, LBO and DK are used as wavelength conversion elements.
Although DP is used, other than this, a nonlinear optical crystal having a large phase matching allowable angle even in one direction, such as KTP, may be used. Also, here, the fundamental wave 1 of the Nd: YAG laser is used.
Although the case where the second harmonic and the fourth harmonic are generated from 064 nm is described as an example, it is of course possible to generate the second harmonic and the third harmonic in the same manner. In addition to Nd: YAG, for example, laser glass, alexandrite, or the like can be used as the laser medium that generates the fundamental wave.

[0032]

As described above in detail, according to the present invention, a nonlinear optical crystal having a large allowable incident angle of phase matching is used. By setting a large beam divergence angle of the fundamental wave laser light emitted from the wave laser device, it is possible to obtain a multi-mode processing laser light while maintaining a relatively high wavelength conversion efficiency.
Obtaining a processing laser device that makes it possible to obtain a laser beam used for laser processing with a laser beam of a relatively short wavelength, which is used for laser processing, by converting a fundamental laser beam into a short wavelength very easily. There is something.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a processing laser device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a vertical beam divergence angle.

FIG. 3 is an explanatory diagram of a lateral beam divergence angle.

[Explanation of symbols]

1 ... Nd: YAG slab laser medium, 2 ... Output mirror, 3 ...
Total reflection mirror, 4 ... Pockels cell, 5 ... Polarizer,
6a, 6b ... Cylindrical lens, 7, 9 ... 1/2 wave plate, 8 ... LBO crystal, 10 ... DKDP crystal, 11 ... Prism.

Claims (10)

[Claims] 1. A fundamental wave laser device for generating a fundamental wave laser light, and a nonlinear optical crystal for converting the wavelength of the fundamental laser light into a short wavelength and emitting the short wavelength laser light. Using a large allowable incident angle, within the range of the phase matching allowable incident angle of the nonlinear optical crystal, by setting a large beam divergence angle of the fundamental laser light emitted from the fundamental laser device A processing laser device characterized by obtaining a processing laser beam. 2. The processing laser device according to claim 1, wherein a beam divergence angle of the fundamental wave laser light emitted from the fundamental wave laser device is equal to a beam diameter and a divergence angle (half angle) of the fundamental wave laser light. Product of 20mm · mr in vertical or horizontal direction
A laser device for processing, wherein an oscillation condition of the fundamental wave laser device is set to be equal to or more than ad. 3. The processing laser device according to claim 1, wherein as the fundamental wave laser device, a cylindrical lens or an anamorphic prism is provided as a primary expansion optical system in a resonator to meet these optical conditions. A laser device for processing, characterized in that a laser oscillator or a laser amplifier is used in which the beam divergence angle of the fundamental laser light emitted from the fundamental laser device is set to a predetermined angle by selection. 4. The processing laser device according to claim 1, wherein the fundamental wave laser device is a laser oscillator or a laser amplifier using a laser medium having an aspect ratio of the emission opening of 1: 2 or more. A laser device for processing characterized in that 5. The processing laser device according to claim 4, wherein a slab type laser medium is used as the laser medium. 6. The processing laser device according to claim 1, wherein the non-linear optical crystal is a second laser beam of the fundamental wave laser beam.
A processing laser device using an angle-phase-matched nonlinear optical crystal that generates harmonic light and a temperature-phase-matched nonlinear optical crystal that generates fourth harmonic light. 7. The processing laser device according to claim 6, wherein an LBO crystal or a KTP crystal is used as the angle-phase-matched nonlinear optical crystal that generates the second harmonic light of the fundamental laser light, and the fourth harmonic light is used. A laser device for processing, characterized in that a DKDP crystal is used as a temperature-matched nonlinear optical crystal for generating a laser beam. 8. The processing laser device according to claim 1, wherein the nonlinear optical crystal is the second fundamental laser light beam.
A processing laser device comprising an angle-phase-matched nonlinear optical crystal that generates harmonic light and an angle-phase-matched nonlinear optical crystal that generates third harmonic light. 9. The processing laser device according to claim 8, wherein both the angle-phase-matched nonlinear optical crystal that generates the second harmonic light and the angle-phase-matched nonlinear optical crystal that generates the third harmonic light are used together. A processing laser device using an LBO crystal. 10. The processing laser device according to claim 1, wherein the laser device is:
A processing laser device comprising a laser oscillator or a laser amplifier using an Nd.YAG laser medium.