JP2002096187A - Laser beam machine and machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machine capable of flexibly changing characteristics of a pulse laser beam according to the quality of a material and structure of a machining object and a shape of a hold to be machined. SOLUTION: A pulse laser beam which is emitted from a laser beam source 1 is branched off to the first beam propagating along the first optical axis 25 and the second beam propagating along the second optical axis 26 by the first optical element 10. The second optical element 11 which changes optical characteristics of the second beam is arranged inside of an optical path of the second beam. The second beam 26 and the first beam 25 which are changed their optical characteristics by the second optical element 11 is propagated by the third optical element 12 along the same optical axis. A machining object 20 is held on a stage 8. The first and the second beams are condensed on the machining object 20 along the same optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing apparatus and a processing method, and more particularly to a processing apparatus and a processing method for piercing a workpiece by irradiating a pulsed laser beam.

[0002]

2. Description of the Related Art In conventional laser processing, processing is performed by focusing a pulse laser beam emitted from a laser light source on one processing point. The pulse waveform of the pulse laser beam is almost determined by the laser light source. For this reason, it has been difficult to flexibly change the pulse waveform depending on the material of the processing object and the shape of the hole to be processed. Further, it has been difficult to flexibly change a wavelength, a pulse interval, a power density distribution in a beam cross section, and the like depending on an object to be processed.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser processing apparatus capable of flexibly changing the characteristics of a pulse laser beam according to the material and structure of a workpiece and the shape of a hole to be processed. To provide.

Another object of the present invention is to provide a laser processing method capable of preventing the shape of a hole from being disturbed due to melting of an object to be processed.

[0005]

According to one aspect of the present invention, there is provided a laser light source for emitting a pulsed laser beam, and a first light source for transmitting the pulsed laser beam emitted from the laser light source at least along a first optical axis. A first optical element for splitting into a second beam propagating along the second optical axis and a second beam propagating along the second optical axis; A second optical element to be changed, a second beam whose optical characteristics have been changed by the second optical element, and the first beam so that the first beam propagates along the same optical axis. A third optical element for changing the traveling direction of the first or second beam, a stage for holding the object to be processed, and the first and second beams propagating along the same optical axis to the stage. Focus on the held workpiece The laser processing apparatus is provided with a fourth optical element.

Since the first beam and the second beam having different optical characteristics from the first beam are converged on the object to be processed along the same optical axis, the first beam has a pulse waveform or the like suitable for processing. Processing can be performed with a beam.

According to another aspect of the present invention, a pulse laser beam having a pulse shape in which the time from the rise of the pulse to the peak power is longer than the time from the peak power to the completion of the fall is generated. A laser processing method is provided, which includes a step of irradiating the pulsed laser beam onto a surface of a processing target to perform a boring process.

According to still another aspect of the present invention, a pulse having a pulse shape in which the absolute value of the slope of the rising portion at the time when the power becomes の of the peak power is smaller than the absolute value of the slope of the falling portion. There is provided a laser processing method including a step of generating a laser beam, and a step of performing a boring process by irradiating the surface of a processing target with the pulsed laser beam.

[0009] The sharp fall of the pulse waveform prevents the material around the hole from melting after the hole is opened. Thereby, a hole having a desired shape can be formed.

[0010]

FIG. 1 is a schematic view of a laser processing apparatus according to an embodiment of the present invention. The laser light source 1 emits a pulse laser beam. The laser light source 1 is, for example, CO 2
It is composed of a _two- gas laser, a YAG laser, a YLF laser, a YVO ₄ laser, an excimer laser, a Ti: sapphire laser, a semiconductor laser, an argon ion laser, or the like. The pulse laser beam emitted from the laser light source 1 is
The light is incident on the first surface of the polarizing plate 3 at an incident angle of 45 °. An S component (a component polarized in a direction perpendicular to the plane of incidence) of the pulsed laser beam is reflected by the polarizing plate 3 and becomes a first beam PL1 that propagates along the optical axis 25. The P component (the component polarized in a direction parallel to the incident surface) of the pulsed laser beam becomes the second beam PL2 that passes through the polarizing plate 3 and propagates along the optical axis 26. When the energies of the S component and the P component of the pulsed laser beam incident on the polarizing plate 3 are equal, the energies per pulse of the first beam PL1 and the second beam PL2 are equal.

In the optical path of the pulse laser beam between the laser light source 1 and the polarizing plate 3, an optical element 10 is arranged as required. When the energies of the S component and the P component of the pulsed laser beam are not equal, the energy of both components can be equalized by disposing the Faraday rotator at the position of the optical element 10. Note that an optical element capable of changing the polarization direction, such as a half-wave plate or a quarter-wave plate, may be used outside the Faraday rotator. In the embodiment described below, it is assumed that the energies of the S component and the P component are equal.

A second beam P propagating along the optical axis 26
L2 is reflected by the reflection mirrors 4, 5, and 6, and re-enters the second surface of the polarizing plate 3 at an incident angle of 45 °. Since the second beam PL2 includes only the P component with respect to the polarizing plate 3,
The same optical axis 25 as that of the first beam PL1 is transmitted through the polarizing plate 3.
Propagate along. If necessary, an optical element 11 is arranged in an optical path between the polarizing plate 3 and the reflection mirror 4, and an optical element 12 is arranged in an optical path between the reflection mirrors 5 and 6. In addition, another optical element may be arranged in the optical path between the reflection mirrors 4 and 5 or between the reflection mirror 6 and the polarizing plate 3.

A stage 8 holds a workpiece 20 on its upper surface. A condensing optical element 7, for example, a convex lens, includes a first beam PL1 and a second beam PL1 propagating along the first optical axis 25.
Is focused on the surface of the workpiece 20.

The optical elements 11 and 12 provide a second beam P
Changes the optical properties of L2. For example, it performs wavelength conversion, changes a pulse waveform, changes a power density distribution in a beam cross section, or causes a delay. A first beam PL1 and a second beam having changed optical characteristics.
Is irradiated onto the surface of the processing object 20, so that the characteristics of the pulsed laser beam are more flexibly changed than in the case where the optical properties of one pulsed laser beam are changed. It becomes possible.

Further, when a Faraday rotator or the like is arranged in the optical path of the second beam PL2 to shift the polarization direction, the second
Part of the beam PL2 is reflected by the polarizing plate 3 and re-enters the optical element 11. As a result, the beam is gradually introduced into the processing object 20 while circulating in the circulating optical path defined by the polarizing plate 3 and the reflection mirrors 4, 5, and 6.

Next, referring to FIG. 2, the first embodiment of the above embodiment will be described.
A specific example will be described. In the first specific example, a delay element, for example, an optical fiber is used as the optical element 11, and an axicon telescope is used as the optical element 12.

FIG. 2A shows a power density distribution in the beam cross section of the first beam PL1. Generally, the power density distribution can be approximated by a Gaussian distribution. FIG. 2B shows a power density distribution of the second beam PL <b> 2 after passing through the optical element 11. By passing through an axicon telescope, it is possible to obtain a distribution with a concave center.
That is, the gradient of the power density distribution in the radial direction of the second beam PL2 is opposite to that of the first beam PL1. Since the optical element 12 delays the second beam PL2, the first beam PL1 reaches the workpiece 20 first, and then the second beam PL2.

FIG. 2C shows a cross-sectional shape of a hole formed by the irradiation of the first beam PL1. First beam P
Since the power density distribution of L1 is approximated to a Gaussian distribution,
A U-shaped hole with a deep center is formed. FIG. 2 (D)
7 shows a cross-sectional shape of the hole after the irradiation with the second beam PL2. The side surface of the hole is shaved by the second beam PL2, and a hole having a steep side sectional shape is obtained.

In the first specific example, the optical element 1
The case where the axicon telescope is used as 1 has been described, but instead of the axicon telescope, another optical element that can reduce the power density at the center of the beam and increase the power density at the periphery is used. You may. An example of such an optical element is an aspheric lens.

Next, referring to FIG. 3, the second embodiment of the above embodiment will be described.
A specific example will be described. In the second specific example, an element for generating frequency chirp is arranged at the position of the optical element 10, an element for performing chirp compensation is arranged at the position of the optical element 11, and a delay element is arranged at the position of the optical element 12. For example, an optical fiber having a self-phase modulation effect can be used as an element for generating a frequency chirp. As an element for performing chirp compensation, for example, a grating pair can be used.

FIG. 3A shows the pulse waveforms of the first beam PL1 and the second beam PL2 when they do not overlap on the time axis on the optical axis 25. First beam P
L1 has a relatively long pulse width because it has undergone frequency chirp. The second beam PL2 has a relatively short pulse width because of chirp compensation.

By irradiating the first object PL1 with the first beam PL1, the beam irradiation point of the object 20 is heated. Since the peak power is low, no holes are formed or shallow holes are formed. First beam PL
Before the first irradiation point is cooled, the second beam PL2
Is irradiated. Due to the irradiation of the second beam PL2, a deep hole is formed at the irradiation point.

It is considered that the hole is formed by laser irradiation in the infrared region due to the thermal effect of the laser. That is, when laser irradiation is performed, the vicinity of the irradiation point of the object to be processed melts and evaporates. Since the second beam PL2 is irradiated before the position to be drilled is cooled, the hole is drilled relatively easily. Even after the hole is formed, if a laser beam having sufficient power to melt the workpiece is irradiated, a molten layer is formed on the side wall of the hole and solidifies without being removed. Therefore, it leads to a decrease in processing quality. For this reason, it is difficult to form a hole having a desired shape.
The second beam PL2 shown in FIG. 3A has a shorter pulse, and its pulse waveform has a sharp fall. Therefore, after the hole is formed, the material around the hole is prevented from being melted, and a hole having a desired shape can be formed.

FIG. 3B shows that the second beam PL2 is the first beam PL2.
Shows a pulse waveform when the pulse overlaps the falling portion of the pulse PL1. The overlapped pulse has a pulse waveform such that the time from the rise to the peak power is longer than the time from the peak power to the fall. Alternatively, it has a pulse waveform in which the absolute value of the slope of the rising portion at the time when the power becomes １ ／ of the peak power is smaller than the absolute value of the slope of the falling portion. In the pulse waveform shown in FIG. 3B as well, the falling edge is steep, so that a hole having a desired shape can be formed.

In the above example, a chirp element is arranged at the position of the optical element 10, a chirp compensating element is arranged at the position of the optical element 11, and a delay element is arranged at the position of the optical element 12. Other combinations of these arrangements are also conceivable. For example, a chirp element may be arranged at the position of the optical element 11 and a delay element may be arranged at the position of the optical element 12.
In this case, the second beam PL2 is changed to the first beam PL1.
And the pulse width of the second beam PL2 becomes shorter than the pulse width of the first beam PL1.
If a chirp compensating element is further arranged after the chirp element arranged at the position of the optical element 11, the second beam PL2 can be made shorter in pulse than the first beam PL1. When an optical fiber is used as the chirp element, the chirp element can also serve as a delay element.

Next, another specific example will be described. When a delay element such as an optical fiber is disposed at the position of the optical element 11, the first beam PL1 and the second beam PL2 overlap with a slight shift. Thereby, the pulse width can be increased. By changing the delay time of the second beam PL2, the width of the pulse on which the first beam PL1 and the second beam PL2 are superimposed can be changed. Also,
If the delay time is increased to such an extent that the second beam PL2 does not overlap the first beam PL1, a pulse train in which two pulses are arranged on the time axis can be formed.

When the zoom lens is arranged at the position of the optical element 11, the spot size of the second beam PL2 on the surface of the processing object 20 can be changed. When the first beam PL1 and the second beam PL2 are irradiated in a superimposed manner, the tail of the power density distribution of the beam spot becomes gentle. If the second beam PL2 is delayed, laser irradiation can be performed first on a small area with a high power density and subsequently on a wider area with a low power density. Conversely, it is also possible to first irradiate a large area with a low power density with a laser and then to irradiate a small area with a high power density.

When the wavelength conversion element is arranged at the position of the optical element 11, the wavelength of the second beam PL2 and the first beam PL
One wavelength can be different. For example, an optical parametric oscillator can be used as the wavelength conversion element. This makes it possible to simultaneously irradiate a pulsed laser beam containing two wavelength components. The wavelength suitable for processing differs depending on the material. By performing the drilling process by simultaneously irradiating a pulsed laser beam containing components of two wavelengths, the shape of the hole may be able to be approximated to a desired shape.

When a laser amplifier is arranged at the position of the optical element 11 and a delay element is arranged at the position of the optical element 12, the processing object 20 is irradiated with the first beam PL1, and subsequently, the high-power second The beam PL2 can be irradiated.

When a combination of an electro-optical element such as a Pockels element and a polarizing plate or an acousto-optical element is arranged at the position of the optical element 11, only a specific part can be cut out from the time waveform of the second beam PL2.

When an image relay optical system including a mask and a beam expander are arranged at the position of the optical element 11,
The beam diameter can be increased, and the tail of the power density distribution (beam profile) in the beam cross section can be cut off. This combination is suitable for, for example, drilling a resin substrate coated with a metal film. For example, it is possible to make a hole in the metal film with a first beam PL1 of a short pulse, and make a hole in a resin substrate with a broad second beam. Since the beam profile of the broad second pulse is shaped, high processing quality can be obtained.

In the above embodiment, the first beam PL1 and the second beam PL2 have the same energy per pulse, but they may have different energies per pulse. When a Faraday rotator, a half-wave plate, a quarter-wave plate, or the like is arranged at the position of the optical element 10 to control the polarization direction, the energy distribution rate of the polarizing plate 3 can be controlled. Furthermore, if a delay element is arranged at the position of the optical element 11, two pulses having different energies per pulse can be applied to the object 20 at predetermined time intervals.

When an electro-optical element is disposed at the position of the optical element 10 and the polarization direction is changed with time, the polarization plate 3
Can be changed over time. For example, when the P component is set to 0 in the first period and the S component is set to 0 in the other second periods, only the first beam PL1 is irradiated in the first period, and the irradiation is performed in the second period. Irradiation with only the second beam PL2 can be performed. That is, the pulse laser beam can be divided into the first beam PL1 and the second beam PL2 in units of pulses.
When the first period and the second period are switched at the same period as the pulse repetition period of the laser light source 1, the irradiation of the first beam PL1 and the irradiation of the second beam PL2 can be performed alternately. it can.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0035]

As described above, according to the present invention,
The pulsed laser beam can be split into two beams to change the optical properties of one beam. After changing the optical properties of one of the beams, the two beams are propagated along the same optical axis and illuminate the workpiece. With this, the characteristics of the beam irradiated on the workpiece
This makes it suitable for laser processing.

[Brief description of the drawings]

FIG. 1 is a schematic view of a laser processing apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing the power density distribution in the beam cross section of the first and second beams used in the method according to the first embodiment of the present invention; FIG. 4 is a cross-sectional view and a cross-sectional view of a hole after irradiation with a second beam.

FIG. 3 is a graph showing pulse waveforms of first and second beams used in a method according to a second example of the embodiment of the present invention;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 3 Polarizer 4, 5, 6 Reflection mirror 7 Condensing optical element 8 Stage 10, 11, 12 Optical element 20 Workpiece 25 First optical axis 26 Second optical axis

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 3/00 G02B 27/00 E

Claims (10)

[Claims] 1. A laser light source for emitting a pulsed laser beam, a first beam propagating the pulsed laser beam emitted from the laser light source at least along a first optical axis, and a second light source.
A first optical element for splitting into a second beam propagating along the optical axis of the second beam, and a second optical element arranged in an optical path of the second beam for changing an optical characteristic of the second beam. An optical element; a second beam whose optical characteristics have been changed by the second optical element; and the first or second beam so that the first beam propagates along the same optical axis. A third optical element that changes the traveling direction of the beam, a stage that holds the object to be processed, and the first and second beams that propagate along the same optical axis. A laser processing apparatus comprising: a fourth optical element that focuses light on an object. 2. The laser processing apparatus according to claim 1, wherein the second optical element delays the second beam. 3. The laser processing apparatus according to claim 1, wherein the second optical element reverses a gradient of a power density distribution in a radial direction in a beam cross section. 4. The second optical element further comprises a second optical element.
4. The laser processing apparatus according to claim 3, wherein the beam is delayed. 5. The laser processing apparatus according to claim 1, wherein the second optical element shortens and delays a pulse width of the second beam. 6. The second optical element according to claim 5, wherein the second optical element delays the second beam such that the shortened second beam overlaps a falling portion of the pulse of the first beam. The laser processing apparatus according to the above. 7. The laser according to claim 5, further comprising a chirp element for imparting a frequency chirp to the pulse laser beam emitted from the laser light source, wherein the second optical element includes a chirp compensating element. Processing equipment. 8. The laser processing apparatus according to claim 1, wherein the first optical system divides the pulse laser beam emitted from the laser light source into the first beam and the second beam in pulse units. 9. A step of generating a pulsed laser beam having a pulse shape in which the time from the rise of the pulse to the peak power is longer than the time from the peak power to the completion of the fall; Irradiating the surface of the object to be drilled to perform drilling. 10. A step of generating a pulsed laser beam having a pulse shape in which the absolute value of the slope of the rising portion at the time when the power becomes １ ／ of the peak power is smaller than the absolute value of the slope of the falling portion. Irradiating the pulsed laser beam on the surface of the object to be drilled to perform drilling.