TW201815506A - Laser processing method - Google Patents

Abstract

The present invention is a laser processing method that forms a thermally denatured region inside a transparent member by concentration and irradiation with ultrashort pulse laser light. The ultrashort pulse laser light is constituted of a pulse train P2 wherein peak intensity changes periodically. The pulse train P2 includes, within a single period Ts wherein the peak intensity changes, a maximum pulse Pb1 where the peak intensity is a maximum, a minimum pulse Pb2 where the peak intensity is a minimum, and an intermediate pulse group Pb3 that is formed from a plurality of pulses between the maximum pulse Pb1 and the minimum pulse Pb2 and wherein the peak intensity gradually decreases moving from the maximum pulse Pb1 side to the minimum pulse Pb2 side.

Description

Laser processing method

The present invention relates to a laser processing method.

In recent years, as one of laser processing methods, the following methods have been researched and developed: by irradiating ultra-short pulse laser light with a very small pulse width to generate non-linear light absorption (multiphoton absorption) phenomenon, such as glass A thermally modified region is formed inside the transparent member (for example, refer to Patent Document 1).

The laser processing method using non-linear light absorption has the advantage of forming a thermally modified region only by locally melting a light-condensing region of an ultra-short pulse laser light, for example, it is used when two transparent members are joined. [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2015-98042

[Problems to be Solved by the Invention] In a laser processing method using non-linear light absorption, ultra-short pulse laser light having a fixed peak intensity is condensed and irradiated onto a transparent member with high repetition.

However, if the ultra-short pulse laser light is condensed and irradiated in this state, the structure of the thermally modified region is likely to be periodically disordered. Periodic structural disturbances in the thermally modified region may cause strain or cracks in or around the thermally modified region.

Here, it is considered that the periodic structural disorder of the thermally modified region is caused by the following reason. First, by the condensing irradiation of the ultra-short pulse laser light, the temperature in the condensing region increases, and the light absorption rate in the condensing region also increases. At this time, since the ultra-short pulse laser light with a constant peak intensity is repeatedly irradiated, the temperature in the light-concentrating region tends to rise excessively. When the temperature in the light-concentrating region is excessively increased, the light absorption rate in the light-concentrating region is drastically reduced due to the thermal modification of the transparent member. If the light absorptivity decreases sharply, an excessive temperature rise in the light-concentrating region is temporarily alleviated. In this way, the temperature in the light-concentrating region starts to rise again, and at the same time, the light absorption rate in the light-concentrating region also starts to rise again. After that, in the same state, the light absorptivity in the light-condensing region periodically repeated fluctuations. Further, due to such a large periodic variation in the light absorption rate in the light-condensing region, a periodic structural disorder occurs in the thermally modified region.

A technical object of the present invention is to provide a laser processing method capable of suppressing periodic structural disturbances in a thermally modified region due to strain or cracks generated in or around a thermally modified region of a transparent member. [Means for solving problems]

The present invention completed to solve the problem is a laser processing method that irradiates an ultra-short pulse laser light by condensing and condensing a light-condensing region inside a transparent member to form a thermally modified region. It is characterized in that the peak intensity of ultra-short pulse laser light changes periodically, and the pulse sequence that exists within one week of the peak intensity change includes: the maximum pulse with the highest peak intensity; the minimum pulse with the smallest peak intensity; and the intermediate pulse The intermediate pulse group includes a plurality of pulses whose peak intensity gradually decreases from the maximum pulse side to the minimum pulse side between the maximum pulse and the minimum pulse. According to this configuration, the ultra-short pulse laser light is focused and irradiated to the transparent member while periodically increasing or decreasing its peak intensity. By the periodic increase and decrease of the peak intensity, the peak intensity itself decreases before the temperature in the light-concentrating region excessively rises, so that excessive temperature rise in the light-concentrating region or a decrease in the light absorption rate accompanying it can be prevented. Therefore, it is possible to suppress the periodic structural disorder of the thermally modified region formed in the light-condensing region, and it is not easy to cause strain or cracks in the thermally modified region or the periphery thereof.

In the above configuration, the peak intensity of the minimum pulse is preferably 25% or more of the peak intensity of the maximum pulse. Accordingly, it is possible to prevent the temperature in the light-condensing region from falling excessively, and to improve the processing efficiency.

In the above-mentioned configuration, it is preferable that the intensity of the ultra-short pulse laser light is adjusted at a frequency of 1 kHz to 50 kHz. Accordingly, there are cases where the period of the change in the peak intensity of the ultrashort pulse laser light is the same as the period of the change in the light absorption rate that can be generated in the transparent member when the peak intensity of the ultrashort pulse laser light is irradiated in a fixed manner. degree. In this case, it is possible to more reliably suppress the periodic fluctuation of the light absorption rate.

In the above configuration, the overlapping frequency of the ultra-short pulse laser light is preferably 100 kHz to 1 MHz. With such a high repetition frequency, the interval between adjacent pulses is narrowed, so that the peak intensity can be changed smoothly and continuously. Therefore, the temperature of the light-concentrating region can be controlled more precisely.

In the above-mentioned configuration, the thermally modified region may be formed in a line shape along a planned cutting line of the transparent member, and a tensile stress may be applied to the thermally modified region to cut the transparent member.

In the above configuration, the transparent member may be a laminated body including a first member and a second member, and a thermally modified region is formed at an interface between the first member and the second member, and the first member and the second member are joined .

In the above configuration, the transparent member is preferably glass. [Effect of the invention]

According to the present invention as described above, it is possible to suppress periodic structural disturbances in the thermally modified region due to strain or cracks occurring in or around the thermally modified region of the transparent member.

Hereinafter, one embodiment of the laser processing method of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the laser processing method of this embodiment uses the laser processing apparatus 1. The laser processing device 1 includes a laser light source 2 that outputs the ultrashort pulse laser light L1 with high repeatability as an intensity modulator that performs intensity modulation on the ultrashort pulse laser light L1 output from the laser light source 2. An acoustic optical element 3 and a lens 4 for condensing the intensity-modulated ultra-short pulse laser light L2.

The laser light source 2 repeatedly outputs ultra-short pulse laser light L1 having a fixed peak intensity. The ultrashort-pulse laser light L1 is composed of a pulse sequence P1 including a plurality of pulses Pa having a constant peak intensity. In this embodiment, the ultra-short-pulse laser light L1 is one having a pulse width of 1 × 10 ⁻⁹ seconds or less. The pulse width of the ultra-short pulse laser light L1 is preferably from femtosecond ( ^10-15 seconds) to picosecond ( ^10-12 seconds) (for example, 10 picoseconds). The repeating frequency of the ultra-short pulse laser light L1 is preferably 100 kHz to 1 MHz, and more preferably 500 kHz to 1 MHz.

The acoustic optical element 3 adjusts the intensity of the ultra-short pulse laser light L1 based on a signal output from the oscillator 5 and outputs the ultra-short pulse laser light L2. The intensity-modulated ultra-short pulse laser light L2 is composed of a pulse sequence P2 including a plurality of pulses Pb whose peak intensity is periodically changed. In this embodiment, the modulation signal output from the oscillator 5 is a sine wave signal having a predetermined frequency. In this case, the intensity of the ultra-short pulse laser light L1 is adjusted at the frequency of a sine wave signal. The frequency (modulation frequency) of the modulation signal for modulating the intensity of the ultra-short pulse laser light L1 is preferably 1 kHz to 50 kHz. The overlapping frequency of the ultra-short pulse laser light L2 is the same as that of the ultra-short pulse laser light L1 before the intensity modulation. The intensity modulator is not limited to the acoustic optical element 3. For example, the intensity of the ultra-short pulse laser light output from the laser light source 2 can also be adjusted by using the electro-optical effect, magneto-optical effect, thermo-optical effect, and non-linear optical effect, or the modulation signal can be directly input to The laser light source 2 outputs an ultra-short pulse laser light whose intensity is modulated from the laser light source 2.

The lens 4 focuses the intensity-modulated ultra-short pulse laser light L2 and forms a light-concentrating area CA inside the glass plate G as a transparent member. Here, the transparent member refers to a member that transmits the ultra-short pulse laser light L2 used. In this embodiment, the ultra-short pulse laser light L2 is incident from the first main surface Ga side to the first main surface Ga and the second main surface Gb which are opposite to each other in the thickness direction of the glass plate G. The incident surface of the ultra-short pulse laser light L2 is not particularly limited.

When the laser processing method is implemented using the laser processing apparatus 1 having the above-mentioned configuration, a nonlinear light absorption phenomenon occurs in the light-concentrating area CA inside the glass plate G, and the light-concentrating area CA is locally melted. Therefore, if the light-concentrating area CA is scanned in the X direction, the heat-modified area HA is formed in a linear shape inside the glass plate G at a position corresponding to the light-concentrating area CA. In this embodiment, the heat-modified region HA is formed along a predetermined cutting line of the glass plate G. Thereafter, in order to apply tensile stress to the thermally modified region HA, the thermally modified region HA is heated and cooled to generate thermal stress, or the thermally modified region HA is used as a center to generate bending stress, and the like along the thermally modified region. The glass region G is cut off in the quality region HA.

The diameter of the light spot in the light-concentrating area CA is preferably 0.5 μm to 2 μm. The depth D from the first main surface Ga of the thermally modified region HA (or the light-condensing region CA) is preferably 20 μm or more.

When the thermally modified region is formed as described above, as shown in FIG. 2, if the ultra-short pulse laser light with a fixed peak intensity is converged and irradiated onto the glass plate repeatedly, the excessive temperature rise in the condensed region becomes One of the reasons is that, as shown in FIG. 3, there is a problem that the temporal change of the light absorption rate in the light-concentrating region of the glass plate becomes very large. In detail, the light absorptance periodically fluctuates sharply, and the light absorptivity decreases sharply to zero over a predetermined period of time. As a result, as shown in, for example, FIG. 4A, when the glass plate is a soda-lime glass, it has been confirmed that a crack is generated around the heat-modified region HAx. In addition, for example, as shown in FIG. 4B, when the glass plate is an alkali-free glass, it is confirmed that in the heat-modified region HAx periodically generates a point-like structural disorder with a diameter of about 10 μm, and the heat-modified region HAx cannot be formed as Dense linear problems.

Therefore, as shown in FIG. 5, in the present embodiment, the ultra-short pulse laser light L2 whose intensity is adjusted is concentrated and irradiated onto the glass plate G repeatedly. In detail, the pulse sequence P2 constituting the ultra-short pulsed laser light L2 includes, in the period (period of the modulation signal) Ts of the peak intensity change: the maximum pulse Pb1 with the highest peak intensity; the minimum pulse Pb2 with the smallest peak intensity; The intermediate pulse group Pb3 includes a plurality of pulses whose peak intensity gradually decreases from the maximum pulse Pb1 side to the minimum pulse Pb2 side between the maximum pulse Pb1 and the minimum pulse Pb2.

In this embodiment, the maximum pulse Pb1 exists at the beginning and end of one period Ts, and the minimum pulse Pb2 exists at the center (equivalent to a half period) between the beginning and end of the maximum pulse Pb1. The intermediate pulse group Pb3 exists between the maximum pulse Pb1 and the minimum pulse Pb2 at the beginning, and between the minimum pulse Pb2 and the maximum pulse Pb1 at the end.

The period Ts of the change in the peak intensity can be appropriately adjusted according to the thermal diffusivity of the glass sheet G. For example, the period Ts is reduced when the thermal diffusivity of the glass sheet G is large, and the period Ts is increased when the thermal diffusivity of the glass sheet G is small. In the case of the adjustment period Ts, the frequency of the modulation signal (modulation frequency) is changed. When the frequency of the modulation signal is changed in the range of 1 kHz to 50 kHz, the period Ts is adjusted in the range of 0.02 ms to 1 ms.

The peak intensity of the minimum pulse Pb2 is preferably 25% or more of the peak intensity of the maximum pulse Pb1, and more preferably 50% or more. The peak intensity of the minimum pulse Pb2 is preferably 80% or less of the peak intensity of the maximum pulse Pb1, and more preferably 60% or less.

According to the laser processing method described above, the ultra-short pulse laser light L2 whose peak intensity is periodically increased or decreased is condensed onto the glass plate G. By the periodic increase and decrease of the peak intensity, the peak intensity itself decreases before the temperature of the light-concentrating region CA increases excessively, so that excessive temperature rise of the light-concentrating region CA can be prevented. As a result, as shown in FIG. 6, the temporal change of the light absorption rate in the light-concentrating area CA becomes very small, and the light absorption rate can be kept substantially constant. Therefore, for example, when the glass plate G is a soda-lime glass as shown in FIG. 7A, or when the glass plate G is an alkali-free glass as shown in FIG. 7B, the generation of periodic Structural disorder. As a result, the heat-modified region HA becomes dense and linear, and it is also difficult to cause strain or cracks in the heat-modified region HA or its surroundings.

In addition, although it is a secondary effect, by focusing the light while periodically increasing or decreasing the peak intensity of the ultra-short pulse laser light L2, compared with the case where the light intensity is maintained while maintaining the peak intensity constant. The total output power of the laser light source 2 can be increased. This can increase the amount of fusion in the light-condensing region CA of the glass plate G, and therefore also has the advantage that the width of the heat-modified region HA can be increased. In addition, in the case of condensing irradiation while maintaining the peak intensity constant, if the total output power of the laser light source is increased to the same level, cracks occur in the glass plate.

Here, as a comparative example, the laser processing conditions of the soda-lime glass of FIG. 4A are (1) a light source: a laser diode (LD) excited Nd: YAG (neodymium-doped yttrium-doped aluminum garnet) yttrium aluminium garnet)) picosecond pulse laser; (2) wavelength: 1064 nm; (3) repeated frequency: 500 kHz; (4) average output: 6 W; (5) pulse width: 0.028 ns; (6) Light spot diameter: 1 μm; (7) Scanning speed: 10 mm / s. In addition, as a comparative example, the laser processing conditions of the alkali-free glass of FIG. 4B are (1) light source: LD excitation Nd: YAG picosecond pulse laser; (2) wavelength: 1064 nm; (3) repeat frequency: 500 kHz; (4) average output: 8 W; (5) pulse width: 0.028 ns; (6) light spot diameter: 1 μm; (7) scanning speed: 10 mm / s.

On the other hand, the laser processing conditions of the soda-lime glass of FIG. 7A as an example are (1) light source: LD excitation Nd: YAG picosecond pulse laser; (2) wavelength: 1064 nm; (3) repeated frequency : 500 kHz; (4) modulation frequency: 2 kHz; (5) average output (maximum output, minimum output): 6 W (8 W, 4 W); (6) pulse width: 0.028 ns; (7) light Point diameter: 1 μm; (8) Scanning speed: 10 mm / s. In addition, as an example, the laser processing conditions of the alkali-free glass of FIG. 7B are (1) light source: LD excitation Nd: YAG picosecond pulse laser; (2) wavelength: 1064 nm; (3) repeat frequency: 500 kHz; (4) modulation frequency: 1 kHz; (5) average output (maximum output, minimum output): 12 W (16 W, 8 W); (6) pulse width: 0.028 ns; (7) light spot diameter : 1 μm; (8) scanning speed: 10 mm / s.

In addition, the present invention is not limited to the configuration of the embodiment, and is not limited to the above-mentioned effects. The present invention can be modified in various ways without departing from the gist of the present invention.

In the embodiment, as shown in FIG. 5, the case where the sine wave signal is used as the modulation signal to obtain the ultra-short pulse laser light L2 with intensity modulation has been described, but the modulation signal is not limited to this. For example, as shown in FIG. 8, the sawtooth wave signal can also be used as the modulation signal to obtain the intensity-modulated ultra-short pulse laser light L2. In this case, for example, the pulse sequence P2 constituting the ultra-short pulse laser light L2 has the maximum pulse Pb1 at the beginning and end of one period Ts of the modulation signal, and has the minimum pulse at or near the position immediately before the maximum pulse Pb1 at the end. Pb2. The intermediate pulse group Pb3 is set only between the first maximum pulse Pb1 and the minimum pulse Pb2.

Moreover, in the said embodiment, although the case where the thermal modification area | region HA which is a starting point of a cutting | disconnection was formed as the laser processing was demonstrated as laser processing, laser processing is not limited to this. For example, laser processing includes bonding, forming, transfer, and the like. If the case of joining is described as an example, as shown in FIG. 9, first, it is prepared that the first glass plate G1 and the second glass plate G2 are laminated as a transparent member. Next, the light-concentrating region CA of the ultra-short pulsed laser light L2 whose intensity is adjusted is set as the interface Gs of the first glass plate G1 and the second glass plate G2. Thereby, a thermally modified region HA is formed in a portion including the interface Gs, and the first glass plate G1 and the second glass plate G2 are bonded to each other.

Furthermore, although glass was illustrated as a transparent member in the said embodiment, it is not limited to this. The transparent member may be, for example, a single crystal such as sapphire or crystal, a transparent ceramic, or a resin such as acrylic.

1‧‧‧laser processing device

2‧‧‧laser light source

3‧‧‧ Acoustic Optics

4‧‧‧ lens

5‧‧‧ Oscillator

CA‧‧‧ Concentrated area

D‧‧‧ Depth

G‧‧‧ glass plate

G1‧‧‧The first glass plate

G2‧‧‧Second glass plate

Ga‧‧‧ First main face

Gb‧‧‧ Second main face

Gs‧‧‧ interface

HA, HAx‧‧‧Heat Modified Area

L1‧‧‧ ultra-short pulse laser light (before intensity modulation)

L2‧‧‧ ultra-short pulse laser light (after intensity modulation)

P1‧‧‧pulse sequence (before intensity modulation)

P2‧‧‧pulse sequence (after intensity modulation)

Pa‧‧‧pulse (fixed peak intensity)

Pb‧‧‧pulse (periodically changing peak intensity)

Pb1‧‧‧Maximum pulse

Pb2‧‧‧minimum pulse

Pb3‧‧‧Intermediate burst

Ts‧‧‧ cycle

X‧‧‧ direction

FIG. 1 is a schematic configuration diagram of a laser processing apparatus used in a laser processing method according to an embodiment of the present invention. FIG. 2 is a conceptual diagram showing a temporal change of an ultrashort pulse laser light according to a comparative example of the present embodiment. FIG. 3 is a conceptual diagram illustrating a temporal change in a light absorption rate in a light-condensing region according to a comparative example of the present embodiment. FIG. 4A is a photograph showing an example of a laser processing result of a soda-lime glass in a comparative example of the present embodiment. FIG. 4B is a photograph showing an example of a laser processing result of the alkali-free glass in the comparative example of the present embodiment. FIG. 5 is a conceptual diagram showing a temporal change of the ultra-short pulse laser light in the present embodiment. FIG. 6 is a conceptual diagram showing a temporal change of a light absorption rate in a light-concentrating region according to the present embodiment. FIG. 7A is a photograph showing an example of a laser processing result of a soda lime glass in an example of the present embodiment. FIG. 7B is a photograph showing an example of a laser processing result of the alkali-free glass in the example of the embodiment. FIG. 8 is a conceptual diagram showing a modification example of the ultra-short pulse laser light of this embodiment. FIG. 9 is a schematic configuration diagram of a laser processing apparatus used in a modified example of the laser processing method of the present embodiment.

Claims (7)

A laser processing method which focuses and irradiates an ultra-short pulse laser light to form a thermally modified region in a light-condensing area inside a transparent member. The laser processing method is characterized in that: The peak intensity changes periodically, and the pulse sequence that exists within one week of the peak intensity change includes: the largest pulse with the highest peak intensity; the smallest pulse with the smallest peak intensity; and an intermediate pulse group, where the intermediate pulse group is Between the maximum pulse and the minimum pulse, a plurality of pulses having a peak intensity gradually decreasing from the maximum pulse side to the minimum pulse side are included. The laser processing method according to item 1 of the scope of patent application, wherein the peak intensity of the minimum pulse is more than 25% of the peak intensity of the maximum pulse. The laser processing method according to item 1 or item 2 of the patent application scope, wherein the ultra-short pulse laser light is intensity modulated at a frequency of 1 kHz to 50 kHz. The laser processing method according to any one of claims 1 to 3, wherein a repeating frequency of the ultra-short pulse laser light is 100 kHz to 1 MHz. The laser processing method according to any one of claims 1 to 4, wherein the thermally modified region is formed into a line shape along a predetermined cutting line of the transparent member, so that tensile stress acts The transparent member is cut at the thermally modified region. The laser processing method according to any one of claims 1 to 5, wherein the transparent member is a laminated body including a first member and a second member, and the thermally modified region is formed on An interface between the first member and the second member, and joining the first member and the second member. The laser processing method according to any one of claims 1 to 6, wherein the transparent member is glass.