WO2019156183A1

WO2019156183A1 - Processing device, processing method, and transparent substrate

Info

Publication number: WO2019156183A1
Application number: PCT/JP2019/004479
Authority: WO
Inventors: 直彦杉田; 佑介伊藤; れいな吉▲崎▼; 直之宮本
Original assignee: 国立大学法人東京大学
Priority date: 2018-02-09
Filing date: 2019-02-07
Publication date: 2019-08-15

Abstract

[Problem] A technique is provided allowing fine processing at high efficiency without requiring reforming of a material. [Solution] A first laser 10 irradiates a processing object 100 with a first laser light 11 having a wavelength that passes through the processing object 100, via a light-focusing unit 31. A second laser 20 irradiates the processing object 100 with a second laser light having a wavelength that passes through the processing object 100. By focusing the first laser light 11, the light-focusing unit 31 generates a high-electron-density region in which free electrons are excited within the processing object 100. Irradiation of the processing object 100 with the light of the second laser 20 is performed so as to pass through the position of the high-electron-density region during the period from before the disappearance of the high-electron-density region generated by the radiation of the first laser light 11, until immediately after the disappearance.

Description

Processing apparatus, processing method, and transparent substrate

The present invention relates to a technique for processing a workpiece using a laser.

Conventionally, a technique for removing a workpiece using a high-power continuous wave laser having a wavelength absorbed by the workpiece is known. According to this technique, a workpiece can be processed with high efficiency. However, this technique has a problem that microfabrication is difficult.

On the other hand, a technique for removing a workpiece by irradiating the workpiece with an ultrashort pulse laser is also known. According to this technique, fine processing can be performed. However, there is a problem that the processing efficiency is low.

Further, in Patent Document 1, in order to cleave a workpiece, the workpiece is modified with a first laser beam, the second laser beam is irradiated to the modified portion, and thermal stress is applied to the workpiece. A technique for cleaving a workpiece by generating it is described.

However, in this technique, in order to modify the workpiece to a depth necessary for cleaving, it is necessary to irradiate the workpiece with a high-power first laser beam, which increases the cost of the laser apparatus. Further, in the case of a material that is difficult to modify, for example, pure SiO ₂ glass, there is a problem that processing efficiency is poor. Further, in this technique, laser light is irradiated for the purpose of modifying a non-workpiece for cutting using thermal stress, but laser light is not irradiated for the purpose of partially removing the work piece.

Further, Patent Document 2 describes a technique for processing a workpiece using a first laser and a second laser.

However, with this technique, the amount of processing removal per irradiation of the first laser and the second laser is small, and it is necessary to irradiate 100 to 5000 times of the first laser in order to form a deep hole. Described in the examples. For this reason, processing time is long and processing efficiency is low. In addition, plasma is generated at each irradiation, and the holes on the surface of the workpiece are gradually enlarged by a plurality of irradiations. For this reason, the ratio of the depth of the hole to the diameter of the hole is small, and microfabrication is difficult. For this reason, highly efficient fine processing is difficult.

JP 2006-35710 A US Patent Publication No. 2015/0246412

The present invention has been made in view of the above problems. One of the main objects of the present invention is to provide a technology capable of highly efficient microfabrication without assuming material modification.

The means for solving the above problems can be described as follows.

(Item 1)
A first laser, a second laser, and a condensing unit;
The first laser has a configuration of irradiating the workpiece with a first laser beam having a wavelength that transmits the workpiece through the condensing unit,
The second laser has a configuration that irradiates the workpiece with a second laser beam having a wavelength that transmits the workpiece,
The condensing unit has a configuration in which a high electron density region in which free electrons are excited is generated in the workpiece by condensing the first laser beam,
Irradiation of the workpiece with the second laser light is performed at a timing from before the disappearance of the high electron density region generated by the irradiation of the first laser light to immediately after the disappearance of the high electron density region. A processing device characterized in that the processing device is passed through a position.

(Item 2)
The processing apparatus according to item 1, wherein the wavelength of the second laser light is set to a wavelength that is absorbed in at least one of the high electron density region and a region heated by relaxation of the free electrons.

(Item 3)
Item 3. The processing apparatus according to Item 1 or 2, wherein irradiation of the workpiece with the second laser light is performed so as to pass through an irradiation region of the first laser light.

(Item 4)
Any one of Items 1 to 3, wherein the first laser is a short pulse laser, and the second laser is a CW laser or a long pulse laser having a longer pulse width than the first laser. The processing apparatus according to claim 1.

(Item 5)
The light intensity of the first laser beam emitted from the first laser has a critical value for evaporating the workpiece and a critical value for modifying the workpiece in at least a part of the machining portion of the workpiece. The processing apparatus according to any one of items 1 to 4, wherein the processing apparatus is set to a value lower than both of the values.

(Item 6)
The processing apparatus according to claim 1, wherein the second laser has a higher output than the first laser.

(Item 7)
The processing apparatus according to any one of items 1 to 6, wherein the workpiece is a glass substrate or a semiconductor substrate.

(Item 8)
The processing apparatus according to any one of items 1 to 7, wherein the second laser light is incident on the workpiece from a side opposite to the first laser light with respect to the workpiece.

(Item 9)
Item 9. The processing apparatus according to any one of Items 1 to 8, wherein transparency of the first laser beam and the second laser beam with respect to the workpiece is 50% or more.

(Item 10)
A processing method,
(1) Condensing a first laser beam having a wavelength that passes through the workpiece and irradiating the workpiece, thereby generating a high electron density region in which free electrons are excited in the workpiece. A step to do;
(2) The high electron density at a timing from before the disappearance of the high electron density region generated by irradiation of the first laser light to the second laser light having a wavelength that transmits the workpiece, immediately after the disappearance. And a step of performing a process of removing a part of the workpiece by irradiating the workpiece so as to pass through a position of a region.

(Item 11)
In the step (2) of performing a process of removing a part of the workpiece, a processing depth in the workpiece is controlled by controlling an irradiation time of the second laser beam. 10. The processing method according to 10.

(Item 12)
A transparent substrate after drilling with a laser,
Without going through the annealing process and etching process,
A value obtained by dividing the depth of the hole by the laser by the maximum diameter on the incident side of the laser beam is 3.4 or more,
The maximum diameter of the laser light incident side of the hole is 25 μm or less,
There is a trace of melting by the laser on the surface of the hole.

According to the present invention, by irradiating the second laser beam at a predetermined timing with respect to the position of the high electron density region generated by the irradiation of the first laser beam, without assuming the modification of the material, Fine processing can be performed with high efficiency.

FIG. 1 is an explanatory diagram showing a schematic configuration of a processing apparatus according to the first embodiment of the present invention. FIG. 2 is an explanatory diagram for explaining a processing method using the apparatus of FIG. The figure (a) shows the state in the middle of processing, and the figure (b) shows the state of the workpiece after processing. FIG. 3 is a photograph showing a processing result in Experimental Example 1 of the first embodiment. FIG. 4 is a graph for explaining the irradiation timing of the laser light in Experimental Example 1. The horizontal axis represents time, and the vertical axis represents light intensity. FIG. 5 is a photograph showing a processing result in Comparative Example 1 of the first embodiment. FIG. 6 is a graph for explaining the irradiation timing of laser light in Experimental Example 2. The horizontal axis represents time, and the vertical axis represents light intensity. FIG. 7 is a photograph showing an observation result of the high electron density region in Experimental Example 3. FIG. 8 is a photograph showing the processing results in Experimental Example 4. FIG. 9 is a photograph showing the processing results in Comparative Example 3. FIG. 9A shows the result of Comparative Example 3, and FIG. 9B shows the result of Experimental Example 4 for control. FIG. 10 is an explanatory diagram showing a schematic configuration of a processing apparatus according to the second embodiment of the present invention.

Hereinafter, a processing apparatus according to a first embodiment of the present invention will be described with reference to the accompanying drawings.

(Configuration of the first embodiment)
The processing apparatus according to this embodiment includes a first laser 10, a second laser 20, and an optical system 30 (see FIG. 1). The processing apparatus according to the present embodiment performs removal processing of the workpiece 100. Here, although the glass substrate is assumed as the workpiece 100, the present invention is not limited to this.

(First laser)
The first laser 10 is configured to irradiate the workpiece 100 with the first laser light 11 having a wavelength that passes through the workpiece 100 via the optical system 30.

A so-called short pulse laser is used as the first laser beam 11 of the present embodiment. In this specification, a short pulse laser means a laser having a pulse width of less than 1 microsecond. The short pulse laser in this specification may be a laser with a pulse width on the order of picoseconds (10 ⁻¹² s) or femtoseconds (10 ⁻¹⁵ s).

The light intensity of the laser beam from the first laser 10 (the light intensity at the processing location of the workpiece 100) is a critical value for evaporating the workpiece and the workpiece at least at a part of the processing location of the workpiece 100. Is set to a value lower than both of the critical values for reforming. The significance of this critical value will be described later.

The transparency of the first laser beam 11 with respect to the workpiece is 50% or more, more preferably 80% or more. This transparency is determined by the wavelength of the laser beam and the material of the workpiece. In addition, transparency is synonymous with the transmittance | permeability with respect to the laser beam made into object, and it is the same below.

(Second laser)
The second laser 20 has a configuration in which a workpiece is irradiated with a second laser beam 21 having a wavelength that passes through the workpiece 100.

Irradiation of the workpiece 100 with the second laser beam 21 is performed at a timing from before the disappearance of the high electron density region generated by the irradiation of the first laser beam 11 to immediately after the disappearance of the second electron beam region. This is performed so that the laser beam 21 passes. This irradiation timing will be described later.

The wavelength of the second laser light 21 is set to the wavelength of the laser light absorbed in at least one of the high electron density region generated by the irradiation of the first laser and the region heated by the relaxation of free electrons. ing.

The irradiation of the workpiece 100 with the second laser light 21 is performed so as to be coaxial with the first laser light 11 via the optical system 30 (more specifically, a dichroic mirror 32 described later). Thereby, in this embodiment, irradiation with the second laser light 21 is performed so as to pass through the irradiation region of the workpiece 100 with the first laser light 11.

The second laser light 21 is a CW laser or a long pulse laser having a pulse width longer than that of the first laser light 11. In addition, the second laser 20 of the present embodiment has a higher output than the first laser 10.

The transparency of the second laser light 21 with respect to the workpiece 100 is 50% or more, more preferably 80% or more.

(Optical system)
The optical system 30 includes a condensing unit 31 and a dichroic mirror 32.

The first laser beam 11 from the first laser 10 is incident on the condenser 31 via the dichroic mirror 32.

The condensing unit 31 condenses the first laser light 11 to generate a high electron density region in which free electrons are excited inside the workpiece 100 (that is, a region to be processed). Moreover, as the condensing part 31 of this example, the lens which can condense a laser beam is used.

The second laser light 21 from the second laser 20 enters the dichroic mirror 32 and then enters the condensing unit 31 coaxially with the first laser light 11. Note that the first laser beam 11 and the second laser beam 21 do not have to be completely coaxial, and the irradiation regions of these laser beams need only overlap.

Note that the dichroic mirror 32 in the above example is used when the wavelengths of the first laser beam 11 and the second laser beam 21 are different. When the wavelengths of the first laser beam 11 and the second laser beam 21 are the same, a polarization beam splitter can be used instead of the dichroic mirror 32.

In FIG. 1, the first laser beam 11 passes through the dichroic mirror 32 and the second laser beam 21 is reflected by the dichroic mirror 32. However, the first laser beam 11 is reflected by the dichroic mirror 32 and the second laser beam is reflected. You may comprise so that 21 may permeate | transmit a dichroic mirror.

(Processing method of the first embodiment)
Next, a method for processing the workpiece 100 using the processing apparatus according to the present embodiment will be described with further reference to FIG.

(Irradiation of the first laser beam)
The workpiece 100 is irradiated with the first laser beam 11 from the first laser 10. The irradiated first laser beam 11 is condensed by the condensing unit 31 and enters the workpiece 100. In the present embodiment, by irradiating the workpiece 100 with the first laser beam 11, a high electron density region 110 in which free electrons are excited can be generated in the workpiece 100 (FIG. 2A). )reference). When light is collected by the lens, the light intensity increases in the Rayleigh length region, and free electrons are excited. In particular, when the first laser 10 is a short pulse laser, the region with high light intensity can be extended beyond the Rayleigh length. This phenomenon is known as filamentation. That is, in the present embodiment, by using the first laser 10 as a short pulse laser, filamentation can be easily generated, and the length of the high electron density region can be increased (that is, deepened). The generated high electron density region usually disappears in a very short time (eg, nanosecond order or less). The pulse width of the short pulse laser that generates filamentation is preferably 1 fs to 1 μs, more preferably 1 fs to 100 ps, and even more preferably 10 fs to 10 ps.

From the viewpoint of further improving the processing efficiency, it is preferable to form a high electron density region in which free electrons are excited deeper than the region of the workpiece 100 to be processed.

Here, in the present embodiment, the light intensity of the laser light from the first laser 10 (light intensity when passing through the processing portion in the workpiece 100) is expressed as “at least a part of the processing portion of the workpiece 100”. In this case, the threshold value is set to a value lower than both the critical value for evaporating the workpiece and the critical value for modifying the workpiece. More specifically, in the present embodiment, the pulse energy, pulse width, and the like of the first laser 10 are set so that the work piece is not evaporated or modified in the whole or most part of the work piece 100. The beam area (spot area) at the material position is set. For this reason, in this embodiment, a low-power laser can be used as the first laser 10, and there is an advantage that the cost of the apparatus can be kept low. Here, the majority of the processing points refer to 60% or more of the depth of the hole by processing. The light intensity of the first laser 10 is preferably a value at which the depth of the high electron density region formed by irradiation is 70% or more of the depth of the hole by processing, more preferably 80% or more. % Or more is more preferable. The judgment as to whether the workpiece is not evaporated or modified in the whole or most of the processing portion of the workpiece 100 is not less than 1 second after the first laser beam irradiation and the second laser beam irradiation. This is possible by observing the machining location of the previous workpiece.

(Irradiation of second laser beam)
On the other hand, in the present embodiment, the second laser light 21 is irradiated from the second laser 20 toward the workpiece 100. The irradiated second laser beam 21 is incident on the workpiece 100 coaxially with the first laser beam 11 via the condensing unit 31 (see FIG. 2A).

Here, irradiation of the workpiece 100 with the second laser light 21 is performed at a timing from before the disappearance of the high electron density region 110 generated by the irradiation of the first laser light to immediately after the disappearance. This is performed so that the light 21 passes through the position of the high electron density region 110.
In the present embodiment, as the irradiation timing of the first laser beam 11 and the second laser beam 21, for example, the following may be considered, but the present invention is not limited to these.
The second laser beam 21 is irradiated first, and the first laser beam is irradiated so as to overlap the irradiation time.
The irradiation of the first laser beam and the second laser beam is started simultaneously.
First irradiation with the first laser light is performed, and irradiation with the second laser light is started until the high electron density region disappears or immediately after the disappearance.

From the above example, when the timing immediately after the disappearance of the high electron density region by the first laser light 11 is not included, that is, before the disappearance of the high electron density region, the irradiation timing of the second laser light 21 is high. A certain period or point in time during which the electron density region 110 exists is included. That is, the “timing” of the timing from before the disappearance of the high electron density region 110 to immediately after the disappearance is at least a certain period or time point from the generation of the high electron density region 110 to immediately after the disappearance. A period before and after the period from generation of the electron density region 110 to immediately after disappearance may be included.

Irradiation of the workpiece 100 with the second laser light 21 is not limited to the period from before the disappearance of the high electron density region 110 generated by the irradiation of the first laser light to immediately after the disappearance. The second laser beam 21 may be performed so as to pass through the position of the high electron density region 110 at a timing including a part from before the disappearance of the high electron density region 110 generated by the above.

In the present embodiment, when a long pulse laser or a CW laser is used as the second laser 20, it is possible to turn on / off only the first laser beam 11 during the irradiation timing of the second laser beam 21. In the present embodiment, it is only necessary that the second laser beam 21 starts to be irradiated on the processing portion of the workpiece 100 at a timing until immediately after the disappearance of the high electron density region 110 generated by the irradiation of the first laser beam.

Here, in this specification, “immediately after the disappearance of the high electron density region” is after the disappearance of the high electron density region, and until the thermal effect caused by the relaxation of free electrons generated in the high electron density region disappears. A period. Here, the thermal influence means a state in which the work piece 100 has a high absorption rate for the first laser light. Although it depends on the material of the workpiece 100, “immediately after the disappearance of the high electron density region” means, for example, within 10 ms, more preferably within 1 ms, further preferably within 100 μs, and even more preferably 10 μs after the disappearance of the high electron density region. The period within. Although it depends on the material of the workpiece 100, “immediately after the disappearance of the high electron density region” is a period in which the temperature of the workpiece 100 is about 2000 ° C. or more after the disappearance of the high electron density region, for example, in the case of glass. is there. When the irradiation of the second laser beam 21 is started after the irradiation of the first laser beam 11 is finished, the closer the irradiation timing of the both, and the shorter the rise time of the second laser beam, the more the relaxation occurs due to free electrons. It is considered that the processing using the thermal effect can be performed reliably. The specific irradiation timing of the laser light pulse can be experimentally determined according to the characteristics of the pulse waveform, the restrictions of the apparatus, and the like.

By irradiating the second laser light 21 to the high electron density region 110, the second laser light 21 that is originally transparent to the workpiece 100 (that is, has a low absorption rate) is emitted from the high electron density region 110. Absorbed and the workpiece 100 partially evaporates. Therefore, in this embodiment, removal processing in the high electron density region 110 can be performed. A state in which a hole (removal portion) 120 is formed in the workpiece 100 is shown in FIG.

Here, in the present embodiment, the high electron density region 110 formed in a fine shape using the first laser 10 which is a short pulse laser can be processed with the high power second laser 20. There is an advantage that fine processing can be performed with high efficiency.

Further, in this embodiment, since a long pulse laser or a CW laser can be used as the second laser 20, it is easy to achieve high power, and in this respect as well, the apparatus cost can be kept low.

Here, in the high electron density region 110, since free electrons are excited, it is considered that absorption occurs regardless of the wavelength of the second laser light 21. If the absorption efficiency is low at a specific wavelength, it is preferable not to use that wavelength. In addition, a wavelength with poor absorption efficiency can be determined by experiment.

Note that, at the position where the high electron density region 110 is generated, even when the excited free electrons are relaxed, the absorptance of the workpiece 100 changes due to thermal effects due to the relaxation. Therefore, by setting the wavelength of the second laser beam 21 to a wavelength at which the absorption rate to the workpiece 100 increases, only the portion that has been thermally affected (that is, the portion where the high electron density region existed) is provided. Absorption can occur, and that part can be removed.

Further, the first laser 10 used in the present embodiment may be one that locally removes or modifies the workpiece 100, for example. Even in this case, according to the present embodiment, since the high electron density region 110 including the non-modified portion can be processed by the second laser 20, the processing efficiency can be improved.

Further, when the workpiece is processed by the second laser on the premise that the workpiece is modified by the first laser as in the prior art, the modified portion that has not been removed by the second laser remains as a defect. There's a problem. In particular, when a large (or deep) modified portion is formed by the first laser in order to improve the processing efficiency, this problem is expected to become apparent. On the other hand, in the present embodiment, since it is not premised on the modification of the workpiece, there is an advantage that a portion remaining on the workpiece as a defect can be reduced or ideally eliminated.

In the present embodiment, a value obtained by dividing the depth of the processed hole by the maximum diameter on the incident side of the second laser light (hereinafter referred to as an aspect ratio) can be made larger than that of the prior art. The reason will be explained. In the present embodiment, the beam energy (spot area) of the first laser pulse energy, the pulse width, and the material position is set so that the work piece is not evaporated or modified in the whole or most part of the work piece. ) And the length of the high electron density region can be lengthened (that is, deepened), so that the removal processing in the high electron density region can be performed at least once by irradiation with the second laser. On the other hand, in the prior art, since the processing efficiency of laser irradiation for removal processing corresponding to the second laser of the present embodiment is lower than the processing efficiency of the present embodiment, multiple irradiations are necessary. For this reason, in the prior art, plasma is generated each time irradiation is performed, and the holes on the surface of the workpiece are gradually enlarged, and the aspect ratio is reduced. For the above reason, in this embodiment, for example, the maximum diameter of the hole is 25 μm or less, 20 μm or less, or 15 μm or less, and an aspect ratio of 3.4 or more is possible. According to this embodiment, the aspect ratio can be 5 or more, 10 or more, or 15 or more.

Specifically, in conventional processing by laser irradiation, since the depth to be removed per shot is small, laser irradiation is performed several hundred to several thousand times. For example, when a non-alkali glass is irradiated with a plurality of shots as low as 5000 shots (50 ms at 100 kHz), a hole having a depth of 300 μm can be processed. However, since plasma is generated around the opening at every shot, the opening is exposed to 5000 times of plasma generation. For this reason, due to the fact that the material around the opening is repeatedly removed by the plasma, the opening diameter is in principle 30 μm or more or 50 μm or more, and fine processing cannot be performed. In addition, the plasma causes damage around the hole.

On the other hand, in this embodiment, a high density electron region is formed in the whole or most of the depth to be removed in one shot, and the high density electron region is removed by the second laser. The depth removed at the perimeter is orders of magnitude greater. As described above, in the present embodiment, the number of shots can be significantly reduced, and the phenomenon that the maximum diameter of the opening is widened by plasma can be significantly suppressed.

(Glass substrate)
Next, an embodiment of the transparent substrate of the present invention will be described. The transparent substrate after the hole processing by the laser according to the present embodiment has a hole aspect ratio of 3.4 or more without being subjected to the annealing process and the etching process, and is the maximum of the laser light incident side of the hole. The diameter is 25 μm or less, and the surface of the hole has a trace of melting by the laser.

The material of the transparent substrate is, for example, transparent glass, plastic, or ceramics. The thickness of the transparent substrate is, for example, in the range of 0.05 to 20 mm. The transparency of the transparent substrate with respect to the wavelength of the laser beam is preferably 60% or more, more preferably 70% or more, and still more preferably 80% or more.

The state where the annealing process and the etching process have not been performed are an annealing process for removing distortion remaining in the workpiece, a trace of melting of the hole surface by the laser, This refers to a state where the etching process for removing traces of sublimation is not performed.

The melting trace is a trace of melting due to the heat of the laser remaining on the processed surface of the workpiece, and is different from a trace of sublimation due to the heat of the laser. The trace of melting has a high surface smoothness, which is a so-called fire-making surface. On the other hand, traces due to sublimation have low smoothness.

In the case of conventional laser processing and low processing efficiency, there is a possibility that after annealing and etching, the aspect ratio is relatively large and the trace of melting around the hole by the laser can be eliminated.

For this reason, a transparent substrate as an intermediate workpiece is used as an embodiment in order to distinguish it from conventional laser processing.

The residual stress around the hole in the transparent substrate of the present embodiment does not need to be irradiated with a plurality of laser beams from the laser corresponding to the second laser. The residual stress is about half that of the conventional laser processing method. When the transparent substrate is a brittle material such as glass, the residual stress on the tension side around the hole should be low in order not to damage the substrate.

The aspect ratio of the hole of this embodiment is 3.4 or more, preferably 5 or more, more preferably 10 or more, and further preferably 15 or more. Further, the maximum diameter of the laser light incident side of the hole of this embodiment is 25 μm or less, preferably 20 μm, and more preferably 15 μm or less.

(Experimental example and comparative example)
(Experimental example 1)
The workpiece was processed using the above-described apparatus under the following conditions. Here, glass (AGC Co., Ltd., non-alkali glass AN100) was used as the workpiece.

(Experimental conditions)
First laser wavelength: 780 nm
Pulse width: 210 fs
Pulse energy: 64μJ
Spot diameter (beam diameter after focusing): 7.2 μm
Number of pulses: 1
Second laser wavelength: 1070 nm
Pulse width: Continuous output: 80W
Spot diameter: 12 μm
Irradiation time: 0.2ms
A photograph showing the processing result of Experimental Example 1 is shown in FIG. In Experimental Example 1, the time (processing time) required to form a hole having a depth of 136 μm was about 0.2 ms. Further, the maximum diameter of the hole workpiece surface was 13.6 μm, the hole diameter at the center in the depth direction of the hole was 9.4 μm, and the aspect ratio was 10. FIG. 4 shows the irradiation timing of the first laser beam 11 and the second laser beam 21 in this example. In the explanatory diagram of the irradiation timing, reference numeral 11 indicates the pulse waveform of the first laser beam, and reference numeral 21 indicates the pulse waveform of the second laser beam. Here, the processing time is the sum of the second laser light irradiation time t ₁ before the first laser light irradiation and the second laser light irradiation time t ₂ after the first laser light irradiation. In this example, t ₁ = 0.1 ms and t ₂ = 0.1 ms.

(Comparative Example 1)
For comparison, the workpiece was processed under the following conditions using only a short pulse laser for the workpiece similar to Experimental Example 1.

(Experimental conditions)
Wavelength: 780nm
Pulse width: 210 fs
Pulse energy: 64μJ
Spot diameter (beam diameter after focusing): 7.2 μm
Repeat frequency: 1kHz
Number of pulses: 200
A photograph showing the processing result of Comparative Example 1 is shown in FIG. In Comparative Example 1, the time required to form the 117 μm deep hole was about 200 ms. The maximum diameter of the hole workpiece surface was 32.2 μm, the diameter at the center in the depth direction of the hole was 8.8 μm, and the aspect ratio was 3.6.

Therefore, it can be seen that the processing efficiency of 1000 times or more can be realized by the apparatus of Experimental Example 1. Furthermore, according to the apparatus of Experimental Example 1, it can be seen that precise machining can be realized while suppressing cracks near the hole (see FIG. 3).

(Experimental example 2)
The workpiece was processed using the above-described apparatus under the following conditions. Here, synthetic quartz (pure SiO ₂ ) was used as the workpiece.

(Experimental conditions)
First laser wavelength: 780 nm
Pulse width: 210 fs
Pulse energy: 52μJ
Spot diameter (beam diameter after focusing): 3.6 μm
Repeat frequency: 1kHz
Number of pulses: 20
Second laser wavelength: 1070 nm
Pulse width: Continuous output: 100W
Spot diameter: 6 μm
Irradiation time: 20 ms
In Experimental Example 2, the time required to form the hole having a depth of 65 μm was about 20 ms. Moreover, the maximum diameter of the surface of the workpiece in the hole was 19 μm, the diameter at the center in the depth direction of the hole was 11 μm, and the aspect ratio was 3.4. The irradiation timing of the first laser beam and the second laser beam is shown in FIG. In the example of FIG. 6, t ₁ = 0.1 ms and t ₂ = 19.9 ms.

(Comparative Example 2)
For comparison, the workpiece was processed under the following conditions using only a short pulse laser for the workpiece similar to Experimental Example 2.

(Experimental conditions)
Wavelength: 780nm
Pulse width: 210 fs
Pulse energy: 52μJ
Spot diameter (beam diameter after focusing): 3.6 μm
Repeat frequency: 1kHz
Number of pulses: 50
In Comparative Example 2, the time required to form the hole having a depth of 65 μm was about 50 ms.

Therefore, it can be seen that the processing efficiency of about 2.5 times can be realized by the apparatus of Experimental Example 2.

(Experimental example 3)
Next, as Experimental Example 3, the observation results of the high density electron region are shown in FIGS. The experimental conditions in Experimental Example 3 are the same as in Experimental Example 1. 7A to 7C schematically show the boundary between the lower workpiece region (glass) and the upper air region.

After 400 ps after irradiation with the first laser beam (FIG. 7A), an elongated filamentation (high electron density region) F can be observed inside the workpiece 100. Moreover, in this figure, the code | symbol S has shown the shock wave produced by laser beam irradiation.

Even after 2.5 ns after irradiation with the first laser beam (FIG. 7B), the filamentation F inside the workpiece 100 can be observed.

The filamentation F has already disappeared 1 ms after the irradiation with the first laser beam (FIG. 7C). Then, the hole formed by the second laser light being absorbed by the filamentation F can be observed.

(Experimental example 4)
Next, as Experimental Example 4, FIGS. 8A to 8D show the relationship between the irradiation time of the second laser beam and the processing result of the workpiece. The experimental conditions in Experimental Example 4 are the same as in Experimental Example 1. The irradiation time of the second laser light in this experimental example 4 is set as follows.
FIG. 8A: t ₁ = 0.1 ms, t ₂ = 0.1 ms, total 0.2 ms
FIG. 8B: t ₁ = 0.1 ms, t ₂ = 0.2 ms, total 0.3 ms
FIG. 8C: t ₁ = 0.1 ms, t ₂ = 0.3 ms, total 0.4 ms
FIG. 8D: t ₁ = 0.1 ms, t ₂ = 0.4 ms, total 0.5 ms
Therefore, according to the processing method of this embodiment, the processing depth can be controlled by controlling the irradiation time of the second laser light. Here, the number of pulses of the first laser light is 1 (see FIG. 4). That is, in this embodiment, the processing depth can be increased by extending the irradiation time of the second laser light even after the disappearance of the high electron density region (filamentation) caused by the irradiation of the first laser light. it can. The reason for this is considered that when the second laser beam is absorbed in the high electron density region, the absorption wavelength of the workpiece changes due to the thermal effect thereof, and the absorption of the second laser beam is sustained. .

8A, the maximum diameter of the surface hole was 19.0 μm, the depth of the hole was 128.8 μm, and the aspect ratio was 6.8.

In FIG. 8B, the maximum diameter of the surface hole was 19.2 μm, the depth of the hole was 164.8 μm, and the aspect ratio was 8.6.

8 (c), the maximum diameter of the surface hole was 19.6 μm, the depth of the hole was 207.4 μm, and the aspect ratio was 10.6.

In FIG. 8 (d), the maximum diameter of the hole on the surface was 18.8 μm, the depth of the hole was 322.4 μm, and the aspect ratio was 17.1.

(Comparative Example 3)
For comparison with Experimental Example 4, the workpiece was processed under the same conditions as Comparative Example 1 using only a short pulse laser. However, the processing time is extended by increasing the number of pulses.

The result of Comparative Example 3 is shown in FIG. As can be seen from the results of 500 ms and 1000 ms, the processing depth is saturated. This saturation is assumed to have occurred between 200 ms and 500 ms. One possible cause of such saturation is that the workpiece is transparent to the laser beam, so that the laser beam leaks to the side. 9A, the maximum diameter of the surface hole was 32.8 μm, the hole depth was 181.6 μm, and the aspect ratio was 5.5.

9 (b) is attached for reference and is the same photo as FIG. 8 (d).

As can be seen from these, in the processing using only the short-pulse laser, saturation occurs relatively early, whereas according to the processing method of the present embodiment, the irradiation time of the second laser light is considerably controlled. It is possible to process deep regions. Moreover, according to the present embodiment, there is an advantage that fine and deep processing can be performed in a short time (in the example of FIG. 9B, in 0.5 ms).

(Second Embodiment)
Next, with reference further to FIG. 10, the processing apparatus which concerns on 2nd Embodiment of this invention is demonstrated. In the description of the second embodiment, the same reference numerals are used for elements that are basically the same as those of the apparatus of the first embodiment described above, thereby avoiding complicated description.

In the second embodiment, a spatial phase modulator (hereinafter abbreviated as “SLM”) 33 is disposed on the optical path of the first laser light 11, and an SLM 34 is disposed on the optical path of the second laser light 21. . The mirror 35 a is configured to send the first laser light 11 to the SLM 33, and the mirror 35 b is configured to send the first laser light 11 phase-modulated by the SLM 33 toward the workpiece 100. Similarly, the mirror 36 a is configured to send the second laser light 21 to the SLM 34, and the mirror 36 b is configured to send the second laser light 21 phase-modulated by the SLM 34 toward the workpiece 100. Yes.

In the present embodiment, when the first laser beam 11 and the second laser beam 21 are reflected by the SLMs 33 and 34 respectively and then passed through the light collecting unit 31, the beam shape is changed to a desired shape (that is, an arbitrary shape). Can be made. That is, by changing the beam shape, it is possible to simultaneously irradiate a plurality of different positions with the beam. For example, it is possible to simultaneously irradiate 100 different positions with a laser (the number of positions is not particularly limited, and 10 or 1000 is theoretically possible).

In the first embodiment described above, if it takes about 1 ms to form one hole (that is, a waiting time of about 1 ms exists), the maximum is 1000 holes / second. On the other hand, with existing technology, it is generally necessary to irradiate a short pulse laser about 100 times to form one hole. Since some commercially available lasers oscillate at 100 kHz, 1000 holes / second can be achieved even with existing technology.

On the other hand, in the second embodiment using the SLM, 100 holes can be formed in 1 ms, so that 100,000 holes / second can be achieved. This is a level that is difficult to reach with the prior art.

Note that the content of the present invention is not limited to the above embodiment. In the present invention, various modifications can be made to the specific configuration within the scope of the claims.

For example, in the above-described embodiment, the first laser beam 11 and the second laser beam 21 are irradiated from the same surface of the workpiece 100. However, the second laser beam 21 can also be incident on the workpiece 100 from the side opposite to the first laser beam 11 (for example, from the lower surface side of the workpiece in FIG. 1). In this way, the risk of the laser light 21 being absorbed by the vaporized gas or the workpiece in the plasma state is reduced, so an improvement in machining efficiency can be expected.

Furthermore, a semiconductor element such as a silicon semiconductor or a semiconductor substrate can be used as the workpiece. In this case, as the first laser beam and the second laser beam, it is preferable to use a wavelength that is not easily absorbed (that is, easily transmitted) by the semiconductor in order to improve processing efficiency.

In the above-described embodiment, the hole whose upper surface is opened is formed, but a hole (cavity) whose periphery is closed can also be formed. The processing location can be selected by controlling the position where the high electron density region is formed. By using a laser with a wavelength that is transparent to the workpiece, it is possible to process any location within the workpiece. When forming the cavity, it is considered that the evaporated workpiece adheres to the inner surface of the cavity.

Furthermore, groove processing can also be performed by appropriately shifting (that is, scanning) the irradiation position of the first laser.

Further, the means for changing the laser irradiation position is not limited to moving the workpiece side, and may be a means for changing the optical axis of the laser beam. For example, a mechanism for scanning laser light using an fθ lens can be used.
(Modification 1)
As a modification in the first embodiment, the first laser beam is preferably a burst shot. The burst shot is an irradiation form in which a plurality of pulses are irradiated within a short time. The number of pulses constituting the burst shot is preferably about 2 to 10, but may be 10 or more. Further, the pulse energies of the plurality of pulses may be the same or different. Furthermore, the time from the first pulse to the last pulse constituting the burst shot is preferably within 1 ns.

The reason why the burst shot is performed within 1 ns is that it is necessary to finish the pulse irradiation during the time until the plasma is generated. Non-Patent Document 1 describes that plasma is generated after several ns to several tens of ns by pulse laser irradiation and takes several thousand ns until it disappears. When the subsequent pulse laser is irradiated during the generation of the plasma, most of the energy is absorbed by the plasma, so that the intended effect cannot be exhibited. Therefore, when the first laser irradiation is a burst shot in this embodiment, the plurality of pulse groups are preferably performed within a time of 1 ns.
(Modification 2)
In the first embodiment and the second embodiment, irradiation of the workpiece with the first laser and the second laser is performed from one side. However, the present invention is not limited to this example. You may irradiate 1 laser and 2nd laser, and process a through-hole. As another modification, the hole may be processed by irradiating the first laser beam from the surface of the workpiece and irradiating the second laser beam from the back surface facing the surface.

This international patent application is Japanese Patent Application No. 2018-021548 filed on Feb. 9, 2018, Japanese Patent Application No. 2018-053992 filed on Mar. 22, 2018, August 2, 2018 The priority is claimed based on Japanese Patent Application No. 2018-145613 filed in Japan, and the entire contents of Japanese Patent Application Nos. 2018-021548, 2018-053992, and 2018-145613 are referred to here. Incorporated into.

DESCRIPTION OF SYMBOLS 10 1st laser 11 1st laser beam 20 2nd laser 21 2nd laser beam 30 Optical system 31 Condensing part 32 Dichroic mirror 100 Work piece 110 High electron density area | region 120 Hole

Claims

A first laser, a second laser, and a condensing unit;
The first laser has a configuration of irradiating the workpiece with a first laser beam having a wavelength that transmits the workpiece through the condensing unit,
The second laser has a configuration that irradiates the workpiece with a second laser beam having a wavelength that transmits the workpiece,
The condensing unit has a configuration in which a high electron density region in which free electrons are excited is generated in the workpiece by condensing the first laser beam,
Irradiation of the workpiece with the second laser light is performed at a timing from before the disappearance of the high electron density region generated by the irradiation of the first laser light to immediately after the disappearance of the high electron density region. A processing device characterized in that the processing device is passed through a position.
The processing apparatus according to claim 1, wherein the wavelength of the second laser light is set to a wavelength that is absorbed in at least one of the high electron density region and a region heated by relaxation of the free electrons. .
The processing apparatus according to claim 1, wherein the workpiece is irradiated with the second laser light so as to pass through an irradiation region of the first laser light.
The first laser is a short pulse laser, and the second laser is a CW laser or a long pulse laser having a longer pulse width than the first laser. The processing apparatus of any one of Claims.
The light intensity of the first laser beam emitted from the first laser has a critical value for evaporating the workpiece and a critical value for modifying the workpiece in at least a part of the machining portion of the workpiece. The processing apparatus according to claim 1, wherein the processing apparatus is set to a value lower than both of the values.
The processing apparatus according to claim 1, wherein the second laser has a higher output than the first laser.
The processing apparatus according to claim 1, wherein the workpiece is a glass substrate or a semiconductor substrate.
The processing apparatus according to claim 1, wherein the second laser light is incident on the workpiece from a side opposite to the first laser light with respect to the workpiece. .
9. The processing apparatus according to claim 1, wherein transparency of the first laser beam and the second laser beam with respect to the workpiece is 50% or more, respectively.
A processing method,
(1) Condensing a first laser beam having a wavelength that passes through the workpiece and irradiating the workpiece, thereby generating a high electron density region in which free electrons are excited in the workpiece. A step to do;
(2) The high electron density at a timing from before the disappearance of the high electron density region generated by irradiation of the first laser light to the second laser light having a wavelength that transmits the workpiece, immediately after the disappearance. And a step of performing a process of removing a part of the workpiece by irradiating the workpiece so as to pass through a position of a region.
In the step (2) of performing a process for removing a part of the workpiece, a processing depth in the workpiece is controlled by controlling an irradiation time of the second laser light. Item 11. The processing method according to Item 10.
In the step (2) of performing a process of removing a part of the workpiece, the second laser beam is at least one of the period from generation of the high electron density region by irradiation of the first laser beam to immediately after disappearance. Irradiating the workpiece so as to pass through the position of the high electron density region at a timing including a certain period or time of the part,
The processing method according to claim 10 or 11.
In the step (1) of generating the high electron density region in which the free electrons are excited, the high electron density region is formed to a depth equal to or greater than a depth at which processing is to be performed on the workpiece. Item 13. The processing method according to any one of Items 10 to 12.
The intensity of the first laser beam is higher than both of a critical value for evaporating the workpiece and a critical value for modifying the workpiece at 60% or more in the depth direction of the processing portion of the workpiece. The processing method according to claim 10, wherein the processing method is set to a low value.
The processing method according to claim 10, wherein the first laser light generates filamentation.
The said 1st laser beam is a burst shot, Comprising: The time from the 1st pulse which comprises this burst shot to the last pulse is less than 1 ns, The any one of Claims 10 thru | or 15 characterized by the above-mentioned. Processing method.
17. The wavelength of the second laser light is set to a wavelength that is absorbed in at least one of the high electron density region and a region heated by relaxation of the free electrons. The processing method according to item 1.
The first laser light is a short pulse laser, and the second laser light is a CW laser or a long pulse laser having a pulse width longer than that of the first laser light. The processing method according to item 1.
A transparent substrate after drilling with a laser,
Without going through the annealing process and etching process,
The value obtained by dividing the depth of the hole by the laser by the maximum diameter on the incident side of the laser beam is 3.4 or more,
The maximum diameter of the laser light incident side of the hole is 25 μm or less,
There is a trace of melting by the laser on the surface of the hole.