JP2004160478A - Laser processing method and laser processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deposit of debris without adding special processes and without using a special apparatus. <P>SOLUTION: A workpiece 5 mounted on a table 6 is irradiated with a laser beam 3, which has been radiated from a continuous oscillation laser source 1 and the enlargement of the beam diameter and the reforming of energy distribution within the beam has been carried out in a shaping optical system 2, if necessary. Ablation is carried out by continuously moving the spot 4 of the laser beam 3 by continuously moving the table 6 or by carrying out the beam deflection using an optical path adjustable deflecting means (not shown) arranged in the optical path of the laser beam 3. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ablation processing method and apparatus using laser light, and more particularly to a laser processing method and a laser processing apparatus for preventing adhesion of debris generated accompanying ablation processing.
[0002]
[Prior art]
Laser light can be used as a beam with high energy density and power density. Although depending on the material to be processed, when absorption of several hundred MW / cm ² at the peak power density occurs on the material surface by laser irradiation, a phenomenon called ablation occurs, and the material surface can be removed. This ablation processing using a laser beam is a useful processing technique applicable to a wide range of materials such as metals, semiconductors, ceramics, and glass.
However, because of the ablation processing, scattered matter called debris adheres to the processing region and the peripheral surface thereof, so that a desired processing accuracy may not be obtained or an appearance defect may occur. Conventionally, debris has been removed by adding a special step before or during ablation processing using a laser or during processing.
[0003]
For example, Patent Document 1 discloses a processing method in which a cleaning process is performed using a second laser beam lower than the energy density used for ablation after ablation. In Patent Document 2, an organic thin film is formed in advance on the surface of the processed material. In Patent Document 3, a liquid layer is formed on the surface of the processed material, and ablation processing is performed over the organic thin film or the liquid layer. A method for preventing debris adhesion by removing an organic thin film or liquid after being performed is disclosed.
[0004]
Further, in Patent Document 4, after the ablation processing of the material surface is performed by sequentially changing the relative position between the laser beam and the material, the relative position between the laser beam and the material is first determined using a beam having the same energy density as the previous one. A method of cleaning debris adhering to the processing area and its periphery by changing the speed earlier is disclosed. In Patent Document 5, ablation processing is performed using a laser beam having an energy distribution such that the central portion has an energy density that causes ablation and the peripheral portion has an energy density suitable for the debris cleaning process. And a processing method for performing the cleaning process simultaneously.
[0005]
Furthermore, Patent Document 6 discloses a processing method in which generated debris is reacted with a reactive gas to be gasified and extinguished by performing ablation processing in a reactive gas atmosphere in a vacuum vessel. Patent Document 7 discloses a method in which a nozzle of a vacuum suction device is installed at a position facing the ablation process, and debris generated by ablation is sucked and removed.
[0006]
[Patent Document 1]
JP-A-6-339784 (page 3, FIG. 1)
[Patent Document 2]
JP-A-8-187588 (page 3, FIG. 1)
[Patent Document 3]
JP-A-9-141480 (second and third pages, FIG. 1)
[Patent Document 4]
JP 2002-248589 A (page 3, FIG. 2)
[Patent Document 5]
JP-A-8-1357 (page 3, FIGS. 1 to 3)
[Patent Document 6]
Japanese Patent Laid-Open No. 7-9182 (second and third pages, FIG. 1)
[Patent Document 7]
JP-A-8-318390 (page 4, FIG. 1)
[0007]
[Problems to be solved by the invention]
All of the methods disclosed in Patent Documents 1 to 4 require a separate process in addition to the ablation process, and the process requires a long time as a whole, and it is also necessary to add a special function to the apparatus. In some cases, the cost is high.
[0008]
On the other hand, in the method disclosed in Patent Document 5, a special beam shaping optical system is used to obtain a desired energy distribution. In the method disclosed in Patent Document 6, introduction and discharge of a vacuum apparatus and reactive gas are performed. -Since a processing apparatus and the method currently disclosed by patent document 7 require a vacuum suction apparatus, an apparatus becomes complicated.
An object of the present invention is to solve the above-mentioned problems of the prior art, and the object thereof is a laser that does not require a special process and does not require a complicated device, and prevents adhesion of debris. An ablation processing method using light and an apparatus therefor are provided.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in a laser processing method for performing ablation processing on a workpiece using a laser beam emitted from a laser light source, the laser light source continuously oscillates and emits continuous light. There is provided a laser processing method characterized by being emitted and having a power density (luminance) of 10 kW / cm ² or more at the exit of the laser light source.
[0010]
In order to achieve the above object, according to the present invention, in a laser processing method for performing ablation processing on a workpiece using a laser beam emitted from a laser light source, the laser light source continuously oscillates. There is provided a laser processing method which emits light and has a laser beam spot power density of 100 MW / cm ² or more on a workpiece.
[0011]
In order to achieve the above object, according to the present invention, a laser light source, an optical system for shaping a laser beam emitted from the laser light source to form a spot on the workpiece, and the workpiece are held. In a laser processing apparatus comprising a table and performing ablation processing on a workpiece with a laser beam, the laser light source continuously oscillates and emits continuous light, and the power density (luminance at the exit of the laser light source) ) Is 10 kW / cm ² or more.
[0012]
[Action]
Usually, in the ablation processing, a pulse laser having a pulse width of about several to several hundred ns is used in order to realize several hundred MW / cm ² which is a peak power density of absorption necessary for causing ablation. The energy density per pulse necessary to cause ablation when using a pulsed laser is 0. It is several to tens of J / cm ² . Due to such high energy density or high power density absorption, the material surface instantaneously reaches a high temperature, the material on the material surface scatters, and a high temperature plasma plume is generated. The hot plasma plume grows away from the ambient gas for the duration of the pulse and increases its volume.
[0013]
In the case of ablation using a pulsed laser, after the pulse duration is over, the energy supply to the material surface and the plasma plume is stopped, the plume is cooled and the plume volume contracts. In order to fill the density cavity generated by the volume shrinkage of the plume, atmospheric gas flows from the surroundings, and the debris collides with and adheres to the material surface at a high speed by the flow of the atmospheric gas.
The present inventors diligently studied the debris adhesion mechanism in the ablation processing using the laser described above, and found that the debris adhesion due to the generation of density cavities can be prevented by continuing and maintaining the high temperature plasma plume. The present invention has been reached. According to the present invention, since ablation processing is performed using a continuous wave as a laser light source, the high-temperature plasma plume generated along with the ablation processing is continued and maintained without interruption, and no density cavity is generated, Accordingly, it is possible to prevent debris from adhering due to the generation of the density cavity.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view showing an embodiment of the present invention of a laser processing apparatus used for laser ablation processing. A laser beam 3 emitted from a continuously oscillating laser light source 1 such as a fiber laser is used to expand the beam diameter, shape the energy distribution in the beam, or cause ablation on the surface of the workpiece 5 as necessary. After appropriate focusing is performed by the shaping optical system 2 so that a necessary power density is obtained in the spot 4 having a diameter smaller than 100 μm on the workpiece 5, the workpiece 5 on the table 6 is irradiated. The
[0015]
When the workpiece 5 is an inorganic material such as a metal, a semiconductor, ceramics, or glass, the power density of the beam spot on the workpiece surface necessary for causing ablation on the surface is 100 MW / cm ² or more. In general, a high-power laser has low coherence, and it is difficult to narrow it down even if a condensing element is used. Assuming that various optical elements are combined and condensed, the diameter of the focused beam spot of the high-power laser is about 1/100 of the exit diameter of the laser light source, and about 1 of the exit area of the laser light source in the focused beam spot area. / 10000 is considered to be an industrially usable range. Therefore, in order to realize the power density that causes ablation in the spot 4, the laser light source needs to have a power density of at least 10 kW / cm ² at the exit.
The diameter of the spot 4 may have a diameter of up to 100 μm if the desired power density is obtained within the spot 4. When the diameter of the spot 12 exceeds 100 μm, the thermal diffusion becomes slow, so that the temperature rise near the processing point becomes remarkable and the thermal influence becomes serious, which is not preferable.
[0016]
If the exit has a power density exceeding 10 kW / cm ² , a continuous wave laser such as a gas laser such as Ar ions, a solid-state laser such as Nd: YAG, and a light source that generates harmonics thereof is used as the laser light source. May be.
The table 6 is movable in the X, Y, and Z-axis directions so that the laser beam spot 4 irradiated on the workpiece 5 on the table 6 can continuously move on the workpiece 5. , A Z stage and a θ, φ stage rotatable about an axis parallel and perpendicular to the Z axis, or some of these stages.
[0017]
The means for continuously changing the relative positions of the laser beam spot 4 and the workpiece 5 is not limited to the movable table 6. If the same action can be obtained, the laser light source 1 may have a means capable of continuously moving in the space, or the galvano is in the optical path of the laser beam 3 from the laser light source 1 to the workpiece 5. An optical path variable deflection element such as a mirror may be provided.
When the power density in the spot 4 on the workpiece 5 exceeds a certain threshold, ablation occurs on the surface of the workpiece 5 and the surface of the workpiece 5 is scraped.
[0018]
【Example】
The workpiece 5 processed in the example is carbon steel (SPCC). When a pulsed Nd: YAG laser (oscillation wavelength 1064 nm, pulse width 9 ns) is used, when the energy density in the spot 4 is 5 J / cm ² (peak power density is about 0.56 GW / cm ² ), about 1 pulse It is known to be cut down to a depth of 0.01 μm. Moreover, the threshold value at which ablation of carbon steel (SPCC) occurs is approximately 1 J / cm ² (peak power density of about 0.11 GW / cm ² ) in terms of energy density.
[0019]
When the light is focused on a small spot with a diameter of less than 100 μm, the intensity distribution in the spot is generally concentric, approximated by a normal distribution with r as the distance from the center of the concentric circle and r as a variable. Can be expressed.
The radius r ₀ [cm] of the spot 4 is represented by the maximum value between points that is 1 / e ² of the peak of the normal distribution. When the output of the laser light source 1 is p [W], the power density distribution P (r) [W / cm ² ] in the spot 4 is approximately expressed by the following equation.
P (r) = {2p / (πr ₀ ² )} exp (−2r ² / r ₀ ² )
A radius r [cm] at which a certain power density P [W / cm ² ] is obtained is approximately expressed by the following equation.
^{_{r = (r 0/2 1/2}} ) {ln [2p / (πr 0 2 P)]} 1/2
[0020]
Next, with reference to FIG. 2, the processing method by the Example of this invention is demonstrated. As a laser light source, a continuous wave fiber laser having an oscillation wavelength of 1064 nm, a maximum output of 150 W, and a maximum energy density of 7.6 MW / cm ² at the exit was used. The output from the light source is adjusted by the shaping optical system 2 so that the diameter of the spot 4 on the workpiece 5 is 5 μm and the average power density in the spot 4 is 0.28 GW / cm ² .
At this time, the power density exceeds 0.56 GW / cm ² within a radius of about 35 nm (diameter of about 70 nm) from the spot center, and within a radius of about 2.3 μm (diameter of about 4.6 μm) from the spot center, The power density exceeds 0.11 GW / cm ² .
[0021]
A galvano mirror (not shown) is installed in the optical path of the laser beam 3 between the laser light source 1 and the table 6, and the spot 4 moves on the workpiece 5 at a linear velocity of about 1 m / s. Adjusted to do. The galvanometer mirror is controlled by a computer (not shown), and the spot 4 on the workpiece 5 performs surface scanning by raster scanning as shown.
The moving speed of the spot 4 on the workpiece 5 is not limited to 1 m / s, and may be appropriately selected in consideration of the power density distribution in the spot 4 so as to obtain a desired ablation process. In addition, the spot can be moved along an arbitrary curve, and an arbitrary pattern can be drawn.
[0022]
The ablation process is performed when the spot 4 moves on the surface of the carbon steel (SPCC) that is the workpiece 5. During processing, the high temperature plasma plume is continuously maintained, and moves on the surface of the carbon steel (SPCC) that is the workpiece 5 following the movement of the spot 4. Accordingly, no density cavity is generated, and debris adhesion due to this is prevented. The ablation depth can be adjusted by a combination of the spot 4 diameter, power density distribution, and moving speed, or by repeating the ablation process by tracing the movement of the spot 4 a plurality of times. .
[0023]
Although preferred embodiments and examples have been described above, the present invention is not limited to these embodiments, and appropriate modifications can be made without departing from the scope of the present invention. For example, a movable / rotatable table and a galvanometer mirror that scans a laser beam may be used in combination.
[0024]
【The invention's effect】
As described above, the present invention is ablation processed using a continuous wave laser light source having a power density of 10 kW / cm ² or more at the exit or a spot power density of 100 MW / cm ² or more on the workpiece. Therefore, the high-temperature plasma plume generated during the ablation process is continued and maintained without interruption, and the generation of density cavities can be prevented. Therefore, according to the present invention, it is possible to prevent adhesion of debris due to the generation of density cavities without using a separate process or a special device such as a vacuum device or a suction device. Furthermore, according to the present invention, since a continuous wave is used as the laser, the ablation processing speed is improved as compared with the case where a conventional pulse laser is used.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a laser processing apparatus used in an embodiment and examples of the present invention.
FIG. 2 is a view showing a state of movement of a beam spot when processing is performed by a laser processing method according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser light source 2 Shaping optical system 3 Laser beam 4 Laser beam spot 5 Work piece 6 Table

Claims (10)

In a laser processing method for performing ablation processing on a workpiece using a laser beam emitted from a laser light source, the laser light source emits continuous light by oscillating continuously and power at the exit of the laser light source A laser processing method characterized by having a density (luminance) of 10 kW / cm ² or more. In a laser processing method for performing ablation processing on a workpiece using a laser beam emitted from a laser light source, the laser light source continuously oscillates and emits continuous light, and the laser beam on the workpiece The laser beam processing method is characterized in that the power density of the spot is 100 MW / cm ² or more. 3. The laser processing method according to claim 1, wherein a diameter of a spot formed on the workpiece is 100 μm or less. 4. The laser processing method according to claim 1, wherein ablation processing is performed while moving a spot formed on the workpiece on the workpiece. The laser processing method according to claim 1, wherein the workpiece is an inorganic material. A laser light source, an optical system that shapes a laser beam emitted from the laser light source and forms a spot on the workpiece, and a table that holds the workpiece, and ablation processing the workpiece with the laser beam. In the laser processing apparatus for performing laser processing, the laser light source emits continuous light by continuous oscillation, and the power density (luminance) at the exit of the laser light source is 10 kW / cm ² or more. apparatus. 7. The table according to claim 6, wherein the table is capable of moving in three directions orthogonal to each other and capable of realizing all or part of being rotatable about two orthogonal axes. Laser processing equipment. 8. The laser processing apparatus according to claim 6, wherein optical path variable deflecting means for deflecting the laser beam is disposed in the optical path of the laser beam. The laser processing apparatus according to claim 6, wherein the laser light source is a solid-state laser. The laser processing apparatus according to claim 6, wherein the laser light source is a fiber laser.

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