JP2008093706A - Laser beam machining method and laser beam machining apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining method and laser beam machining apparatus that can prevent expansion of a heat-affected layer caused by excessive heat input and generation of micro crack due to supercooling, by optimizing a light intensity distribution profile in the irradiation face. <P>SOLUTION: The laser beam machining apparatus is composed of a laser oscillator 10 for outputting a nearly parallel laser beams LB, a converging optical system 30 having a converging power in the X direction, a converging optical system 40 having a converging power in the Y direction, and the like. The laser beams LB passed through the converging optical system 40 is provided with an elliptical beam shape PB having a major axis in the relative moving direction (Y direction), in the irradiation position B of a workpiece 50, wherein the light intensity distribution YB along the major axis is asymmetric. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser processing method and a laser processing apparatus that perform processing while moving a laser beam relative to a workpiece.

  In recent years, in order to process a semiconductor material or the like with high accuracy, processing using a laser has been performed. When processing a semiconductor material such as silicon, a normal circular spot condensing causes a temperature rise and cooling instantaneously, so that microcracks occur in the processed cross section of the workpiece and the strength decreases. There was a problem.

  As a countermeasure, an attempt has been proposed to moderate the temperature profile change by making the laser beam profile linear (Patent Document 1 below). In Patent Document 1, a linear light beam is obtained by condensing a substantially parallel laser beam with a condensing lens and further expanding in one direction using a transparent cylindrical rod.

JP 2000-141071 (FIGS. 1 and 2) JP 2001-212683 A

  When laser processing is performed on the substrate, the light intensity distribution on the irradiated surface must have a peak intensity that exceeds a certain level, and the light intensity distribution during heating or cooling is optimized to reduce steep temperature changes. It is necessary to suppress the occurrence of microcracks.

  In the laser processing method according to Patent Document 1, only a condensing lens and a cylindrical rod are disposed between the laser oscillator and the workpiece. When a condensing lens and a cylindrical rod are used, the only things that can be adjusted are the beam diameter and peak intensity on the irradiated surface, and the light intensity distribution has a profile that is symmetrical with respect to the peak. Therefore, it is difficult to control the light intensity distribution for obtaining the optimum heat input temperature profile and the cooling temperature profile at the same time. If an appropriate light intensity distribution cannot be obtained, the heat-affected layer may expand due to excessive heat input, or microcracks may occur due to overcooling, resulting in a decrease in strength of the resulting cut piece.

  An object of the present invention is to provide a laser processing method and a laser processing apparatus capable of preventing the expansion of a heat-affected layer due to excessive heat input and the generation of microcracks due to overcooling by optimizing the light intensity distribution shape on the irradiated surface. It is to be.

In order to achieve the above object, a laser processing method according to the present invention is a laser processing method for performing processing while moving a laser beam relative to a workpiece,
The laser beam has an elliptical beam shape having a long axis in the relative movement direction on the irradiation surface of the work piece, and the light intensity distribution along the long axis direction is asymmetric.

A laser processing apparatus according to the present invention is a laser processing apparatus that performs processing while moving a laser beam relative to a workpiece,
A condensing optical system for condensing a substantially parallel laser beam and forming an elliptical beam shape having a long axis in the relative movement direction on the irradiation surface of the workpiece,
The light intensity distribution along the long axis direction is asymmetric.

  According to the present invention, when the laser beam is moved relative to the workpiece by asymmetricing the light intensity distribution along the long axis direction on the irradiation surface of the workpiece, the peak intensity required for processing It is possible to independently control the light intensity change (temporal beam profile) along the relative movement direction. Therefore, the optimum heating profile and cooling profile can be arbitrarily set according to the shape, type, and characteristics of the workpiece. As a result, for example, expansion of the heat-affected layer due to excessive heat input and generation of microcracks due to overcooling can be prevented.

Embodiment 1 FIG.
Fig.1 (a) is a block diagram which shows 1st Embodiment of this invention. For easy understanding, the direction perpendicular to the paper surface is taken as the X axis, the upward direction parallel to the paper surface and perpendicular to the X axis is taken as the Y axis, and the right direction perpendicular to the X axis and Y axis is taken as the Z axis.

  The laser processing apparatus includes a laser oscillator 10 that outputs a substantially parallel laser beam LB, a condensing optical system 30 having condensing power in the X direction, a condensing optical system 40 having condensing power in the Y direction, and the like. Is done. The workpiece 50 is mounted on the moving stage 60. During the processing, the moving stage 60 moves in the Y direction, so that the laser beam LB moves relative to the workpiece 50.

  A laser beam LB from a general laser oscillator has a light intensity distribution having a Gaussian distribution (normal distribution) centered on the optical axis LA. As shown in FIG. 1B, a circular beam shape PA is shown in the XY plane at a position A before the condensing optical system 30, and the light intensity distribution XA along the X direction is the peak of the laser beam LB. A symmetrical Gaussian shape centered on the intensity is shown, and the light intensity distribution YA along the Y direction also shows a symmetrical Gaussian shape centered on the peak intensity of the laser beam LB.

  When a normal rod type YAG (yttrium, aluminum, garnet) laser excited by using a halogen lamp or the like is used as the laser oscillator 10, multi-beam light in which a plurality of Gaussian beams are overlapped at the exit of the oscillator. Usually, a laser beam having a shape close to a Gaussian distribution is obtained on the condensing surface, and further, for example, by installing a pinhole of an appropriate size at the center of the optical axis, a single mode having a single Gaussian distribution is obtained. A laser beam is easily obtained.

  The condensing optical system 30 may be composed of an optical element having a condensing power in the X direction and no condensing power in the Y direction, for example, a cylindrical lens (cylindrical lens) having a generatrix parallel to the Y direction. As shown in FIG. 1C, the light intensity distribution XB in the X direction at the irradiation position B of the workpiece 50 is determined.

  The condensing optical system 40 can be configured by an optical element having no condensing power in the X direction and having condensing power in the Y direction, for example, a cylindrical lens (cylindrical lens) having a generatrix parallel to the X direction. As shown in FIG. 1C, it has a role of determining the light intensity distribution YB in the Y direction at the irradiation position B of the workpiece 50.

  In the present embodiment, the example in which the condensing optical system 40 having the condensing power in the Y direction is arranged after the condensing optical system 30 having the condensing power in the X direction is shown. The condensing optical system 40 having the condensing optical system 30 having the condensing power in the X direction may be disposed later. Further, as the condensing optical system 30, a spherical lens not only having condensing power in the X direction but also having condensing power in the Y direction may be used. In this case, the same effect can be obtained by using a condensing optical system 40 in which the condensing power in the Y direction is reduced by the condensing power in the Y direction applied to the condensing optical system 30.

  In this embodiment, the laser beam LB that has passed through the condensing optical system 40 has a long axis in the relative movement direction (here, the Y direction) at the irradiation position B of the workpiece 50 as shown in FIG. The condensing optical system 40 is configured such that the light intensity distribution YB along the major axis direction is asymmetric.

  Such a condensing optical system 40 can be composed of, for example, a cylindrical lens having an asymmetric surface shape around the optical axis LA (hereinafter also referred to as an asymmetric cylindrical lens).

  FIG. 2A is a configuration diagram illustrating an example in which an asymmetric cylindrical lens 41 is used as the condensing optical system 40. The optical axis LA of the laser beam LB coincides with the optical axis center of the asymmetric cylindrical lens 41, and the laser beam LB has a Gaussian light intensity distribution in both the X direction and the Y direction immediately before the asymmetric cylindrical lens 41.

  Since the asymmetric cylindrical lens 41 has an asymmetric cylindrical shape in which the upper portion has a small radius of curvature and the lower portion has a large radius of curvature around the optical axis LA, the laser beam LB that has passed through the asymmetric cylindrical lens 41 is provided. As shown in FIG. 2B, the surface of the workpiece 50 exhibits an asymmetric light intensity distribution along the Y direction. This asymmetric light intensity distribution corresponds to the light intensity distribution YB in the Y direction shown in FIG.

  FIG. 3 is a graph showing the surface temperature distribution of the workpiece when a laser beam having an asymmetric light intensity distribution in the Y direction is used. The laser beam has an elliptical elongated beam shape having a long axis in the Y direction on the surface of the workpiece 50, and the workpiece 50 relatively moves along the Y direction as described above.

  The light intensity distribution in the Y direction has a peak shifted from the optical axis LA in the pre-processing direction as shown in FIG. 2B, and the region Ra in the pre-processing direction from this peak position has a relatively steep distribution. The region Rb in the post-processing direction from the peak position shows a comparatively gentle distribution shape. When the workpiece 50 is irradiated with a laser beam having such an asymmetric light intensity distribution, the workpiece 50 has an asymmetric surface temperature distribution approximately approximate to the light intensity distribution in the Y direction, as shown in FIG. As shown. That is, the surface temperature distribution has a peak temperature shifted from the center in the pre-processing direction, and the region Ra from the peak position to the pre-processing direction shows a relatively steep distribution shape, and the region from the peak position to the post-processing direction. Rb indicates a comparatively gentle distribution shape.

  During laser processing, it is considered that the workpiece 50 is melted or evaporated in a region of a certain temperature Tw or higher.

  When the laser beam having such an asymmetric light intensity distribution moves relative to the workpiece 50, the region Ra is first irradiated onto the workpiece 50, the temperature rises due to energy absorption, and then the region Rb The workpiece 50 is irradiated and melts and evaporates due to energy absorption, and the processing proceeds. Subsequently, as the light intensity decreases, the temperature decreases, and the melted portion is recrystallized and solidified. The process is stopped. Therefore, when a laser beam having an asymmetric light intensity distribution is used, the temperature change rate in the region Ra is larger than that in a laser beam having a symmetric light intensity distribution, and the temperature change rate in the region Rb is Smaller.

  In the case of high-quality processing of a workpiece, the reason why the temperature profile of the workpiece, that is, the light intensity distribution of the irradiated laser beam is related is as follows. When the workpiece is irradiated with linear laser light, the workpiece absorbs the laser light and is heated and melted. In order to remove the melted part by ablation, the temperature of the processing point needs to reach the boiling point or higher. At this time, the spread of the heat-affected layer can be narrowed by giving a larger temperature change in the region Ra according to the heating rate. In addition, when the melted portion solidifies, recrystallization occurs as the temperature decreases. However, if the cooling rate is rapid, recrystallization nuclei occur in the entire melted portion, and recrystallization proceeds in each part, and between the crystal grains. The hot water is not supplied to the generated gap or the like, and the whole solidifies. If cooling is performed with the gap remaining, the gap expands as the workpiece contracts, and remains as a microcrack. If the cooling rate is sufficiently slow, melted hot water is supplied to the gap, so that processing with few microcracks can be achieved.

  Thus, when the light intensity distribution in the Y direction has a peak shifted from the optical axis LA in the pre-processing direction, the region Rb showing a gentle light intensity distribution shape is irradiated last, so that the peak necessary for laser processing is obtained. Since the cooling time can be increased while maintaining the strength, the solidification time of the workpiece 50 can be secured long, and the occurrence of microcracks can be reduced. In particular, since microcracks in brittle materials such as glass and silicon can be reduced, there is an effect in maintaining the strength after processing.

  In the above description, the example in which the workpiece 50 moves relative to the laser beam has been described. However, the laser beam may move relative to the workpiece 50 in a stationary state, or the workpiece 50 may be moved. Similar results are obtained when both the object 50 and the laser beam are moved relative to each other.

  When the workpiece 50 is silicon or the like, a laser oscillator having an oscillation wavelength of 330 nm to 800 nm is preferable from the viewpoint of light absorption characteristics. That is, when silicon is irradiated with laser light having a wavelength of about 330 nm to 800 nm, the energy of the laser light is absorbed stably and efficiently, and is heated almost uniformly in the film thickness direction. Is easy and suitable.

  A typical laser having an oscillation wavelength between 330 nm and 800 nm is, for example, a solid-state laser harmonic generation source. That is, the second harmonic (532 nm) and third harmonic (355 nm) of the Nd: YAG laser (wavelength 1.06 μm), the second harmonic (524 nm) and third of the Nd: YLF laser (wavelength 1.05 μm). A harmonic (349 nm), a second harmonic (515 nm), a third harmonic (344 nm), or the like of a Yb: YAG laser (wavelength 1.03 μm) can be used. In addition, a fundamental wave (792 nm) or a second harmonic (396 nm) of a Ti: sapphire laser may be used. By using a solid-state laser harmonic generation source as the laser light source, the laser processing apparatus can be made compact and stable operation can be performed for a long time.

  As described above, the light intensity distribution of the laser beam in the long axis direction of the elliptical shape in the cross section perpendicular to the optical axis of the laser beam irradiated to the workpiece is set asymmetrically, and suitable for advancing the processing. By adjusting the shape so as to have a shape portion and a shape portion suitable for reducing the occurrence of microcracks during solidification, laser processing with a small heat-affected layer and few microcracks becomes possible.

  Further, by using the asymmetric cylindrical lens 41 having a surface shape asymmetric with respect to the laser beam optical axis, an asymmetric light intensity distribution along one direction can be easily realized.

Embodiment 2. FIG.
FIG. 4A is a configuration diagram showing a second embodiment of the present invention. For easy understanding, the direction perpendicular to the paper surface is taken as the X axis, the upward direction parallel to the paper surface and perpendicular to the X axis is taken as the Y axis, and the right direction perpendicular to the X axis and Y axis is taken as the Z axis.

  The laser processing apparatus according to the present embodiment has a laser oscillator 10 that outputs a substantially parallel laser beam LB and a condensing optical system 30 having a condensing power in the X direction, as in the configuration shown in FIG. In FIG. 4A, another configuration example of the condensing optical system 40 is shown. The workpiece 50 is mounted on the moving stage 60. During the processing, the moving stage 60 moves in the Y direction, so that the laser beam LB moves relative to the workpiece 50.

  In the present embodiment, a cylindrical lens 42 that is inclined with respect to the optical axis LA of the laser beam LB is used as the condensing optical system 40.

  The cylindrical lens 42 has a symmetric lens surface shape having a generatrix parallel to the X direction, and realizes asymmetrical condensing characteristics by angularly displacing the entire lens around the X axis. The laser beam LB that has passed through the cylindrical lens 42 exhibits an asymmetric light intensity distribution along the Y direction on the surface of the workpiece 50, as shown in FIG. 4B. This asymmetric light intensity distribution corresponds to the light intensity distribution YB in the Y direction shown in FIG.

  When a laser beam having such a light intensity distribution moves relative to the workpiece 50 in the Y direction, if the light intensity distribution in the Y direction has a peak shifted from the optical axis LA in the pre-processing direction, the light intensity distribution is gentle. Since the region showing the shape is irradiated last, the temperature change rate during cooling becomes smaller, and the influence of rapid cooling can be mitigated.

  Thus, by arranging the cylindrical lens 42 so as to be inclined with respect to the optical axis LA of the laser beam LB, an asymmetric light intensity distribution along one direction can be easily realized by utilizing the coma aberration of the cylindrical lens 42. be able to.

Embodiment 3 FIG.
Fig.5 (a) is a block diagram which shows 3rd Embodiment of this invention. For easy understanding, the direction perpendicular to the paper surface is taken as the X axis, the upward direction parallel to the paper surface and perpendicular to the X axis is taken as the Y axis, and the right direction perpendicular to the X axis and Y axis is taken as the Z axis.

  The laser processing apparatus according to the present embodiment has a laser oscillator 10 that outputs a substantially parallel laser beam LB and a condensing optical system 30 having a condensing power in the X direction, as in the configuration shown in FIG. And a condensing optical system 40 having a condensing power in the Y direction, and FIG. The workpiece 50 is mounted on the moving stage 60. During the processing, the moving stage 60 moves in the Y direction, so that the laser beam LB moves relative to the workpiece 50.

  In the present embodiment, a cylindrical lens 43 inclined with respect to the optical axis LA of the laser beam LB is used as the condensing optical system 40, and the laser beam LB is further directed with respect to the normal direction of the cylindrical lens 43 and the workpiece 50. Is incident obliquely.

  The cylindrical lens 43 has a symmetric lens surface shape having a generatrix parallel to the X direction, and realizes asymmetrical focusing characteristics by angularly displacing the incident direction of the laser beam LB around the X axis. The laser beam LB that has passed through the cylindrical lens 43 shows an asymmetric light intensity distribution along the Y direction on the surface of the workpiece 50 as shown in FIG. This asymmetric light intensity distribution corresponds to the light intensity distribution YB in the Y direction shown in FIG.

  When a laser beam having such a light intensity distribution moves relative to the workpiece 50 in the Y direction, if the light intensity distribution in the Y direction has a peak shifted from the optical axis LA in the pre-processing direction, the light intensity distribution is gentle. Since the region showing the shape is irradiated last, the temperature change rate during cooling becomes smaller, and the influence of rapid cooling can be mitigated.

  By making the laser beam LB obliquely incident on the normal direction of the cylindrical lens 43 and the workpiece 50 in this manner, the optical path length change due to the coma aberration of the cylindrical lens 43 and the inclination of the processing surface is utilized. An asymmetric light intensity distribution along one direction can be easily realized.

Embodiment 4 FIG.
FIG. 6A is a configuration diagram showing a fourth embodiment of the present invention. For easy understanding, the direction perpendicular to the paper surface is taken as the X axis, the upward direction parallel to the paper surface and perpendicular to the X axis is taken as the Y axis, and the right direction perpendicular to the X axis and Y axis is taken as the Z axis.

  The laser processing apparatus according to the present embodiment has a laser oscillator 10 that outputs a substantially parallel laser beam LB and a condensing optical system 30 having a condensing power in the X direction, as in the configuration shown in FIG. And a condensing optical system 40 having condensing power in the Y direction, and FIG. The workpiece 50 is mounted on the moving stage 60. During the processing, the moving stage 60 moves in the Y direction, so that the laser beam LB moves relative to the workpiece 50.

  In this embodiment, a combination of a cylindrical lens 44 and a wedge plate 45 is used as the condensing optical system 40.

  The cylindrical lens 44 has a symmetrical lens surface shape having a generatrix parallel to the X direction, and is arranged so that the optical axis of the lens coincides with the optical axis LA of the laser beam LB.

  The wedge plate 45 is an optical element in which the optical path length linearly changes along the Y direction. By arranging the wedge plate 45 behind the cylindrical lens 44, the wedge plate 45 realizes a condensing characteristic asymmetric in the Y direction. The laser beam LB that has passed through the cylindrical lens 42 and the wedge plate 45 exhibits an asymmetric light intensity distribution along the Y direction on the surface of the workpiece 50 as shown in FIG. 6B. This asymmetric light intensity distribution corresponds to the light intensity distribution YB in the Y direction shown in FIG.

  When a laser beam having such a light intensity distribution moves relative to the workpiece 50 in the Y direction, if the light intensity distribution in the Y direction has a peak shifted from the optical axis LA in the pre-processing direction, the light intensity distribution is gentle. Since the region showing the shape is irradiated last, the temperature change rate during cooling becomes smaller, and the influence of rapid cooling can be mitigated.

  By combining the cylindrical lens 42 and the wedge plate 45 in this way, an asymmetric light intensity distribution along one direction can be easily realized.

Embodiment 5. FIG.
Fig.7 (a) is a block diagram which shows 5th Embodiment of this invention. For easy understanding, the direction perpendicular to the paper surface is taken as the X axis, the upward direction parallel to the paper surface and perpendicular to the X axis is taken as the Y axis, and the right direction perpendicular to the X axis and Y axis is taken as the Z axis.

  The laser processing apparatus according to the present embodiment has a laser oscillator 10 that outputs a substantially parallel laser beam LB and a condensing optical system 30 having a condensing power in the X direction, as in the configuration shown in FIG. And a condensing optical system 40 having condensing power in the Y direction. FIG. 7A shows still another configuration example of the condensing optical system 40. The workpiece 50 is mounted on the moving stage 60. During the processing, the moving stage 60 moves in the Y direction, so that the laser beam LB moves relative to the workpiece 50.

  In the present embodiment, as the condensing optical system 40, an asymmetric cylindrical lens 46 having a shape inverted with respect to the Y direction is used so as to obtain a light intensity distribution opposite to that in FIG.

  Since the asymmetric cylindrical lens 46 has an asymmetric cylindrical shape in which the upper portion has a large radius of curvature and the lower portion has a small radius of curvature around the optical axis LA, the laser beam LB that has passed through the asymmetric cylindrical lens 46. As shown in FIG. 7B, the surface of the workpiece 50 exhibits an asymmetric light intensity distribution along the Y direction. This asymmetric light intensity distribution corresponds to the light intensity distribution YB in the Y direction shown in FIG.

  FIG. 8 is a graph showing the surface temperature distribution of the workpiece when the laser beam having the light intensity distribution shown in FIG. 7B is used. The laser beam has an elliptical elongated beam shape having a long axis in the Y direction on the surface of the workpiece 50, and the workpiece 50 relatively moves along the Y direction as described above.

  As shown in FIG. 7B, the light intensity distribution in the Y direction has a peak shifted from the optical axis LA in the post-processing direction, and the region Rc in the pre-processing direction from this peak position has a relatively gentle distribution. A region Rd from the peak position to the post-processing direction shows a relatively steep distribution shape. When the workpiece 50 is irradiated with the laser beam having such an asymmetric light intensity distribution, the workpiece 50 has an asymmetric surface temperature distribution approximately approximate to the light intensity distribution in the Y direction, as shown in FIG. As shown. That is, the surface temperature distribution has a peak temperature shifted from the center in the post-processing direction, and the region Rc from the peak position to the pre-processing direction shows a relatively gentle distribution shape, and the region from the peak position to the post-processing direction. Rd shows a relatively steep distribution shape.

  During laser processing, it is considered that the workpiece 50 is melted or evaporated in a region of a certain temperature Tw or higher.

  In each of the embodiments described above, the temperature distribution shown in FIG. 3, that is, the light intensity distribution in the Y direction is shifted from the optical axis LA to the pre-processing direction with respect to a brittle material such as silicon that easily generates microcracks. The example in which the region showing a gentle light intensity distribution shape is set from the peak to the post-processing direction so that the cooling time after the peak elapses can be taken long has been described.

  On the other hand, for alloys mixed with materials with different melting points, processing with a light intensity distribution with a steep shape during initial heating causes ablation of only low melting point components, resulting in high quality processing. May not be obtained.

  As a countermeasure, in this embodiment, the temperature distribution shown in FIG. 8, that is, the light intensity distribution in the Y direction has a peak shifted from the optical axis LA in the post-processing direction, and the temperature change rate during heating is smaller. As described above, it is preferable to set the region Rc showing a gentle light intensity distribution shape from the peak to the pre-processing direction.

  The light intensity distribution in the Y direction in this embodiment can also be realized by arranging the condensing optical system 40 shown in Embodiments 2 to 4 in the reverse direction with respect to the Y direction, and the temperature change rate during overheating is The same effect of being smaller can be obtained.

FIG. 1A is a configuration diagram showing a first embodiment of the present invention, FIG. 1B shows a beam shape PA and light intensity distributions XA and YA at a position A, and FIG. The beam shape PB and the light intensity distributions XB and YB at the irradiation position B are shown. FIG. 2A is a configuration diagram showing an example of the condensing optical system 40, and FIG. 2B shows a light intensity distribution in the Y direction at the irradiation position. It is a graph which shows surface temperature distribution of a workpiece. FIG. 4A is a configuration diagram showing the second embodiment of the present invention, and FIG. 4B shows the light intensity distribution in the Y direction at the irradiation position. FIG. 5A is a block diagram showing a third embodiment of the present invention, and FIG. 5B shows the light intensity distribution in the Y direction at the irradiation position. FIG. 6A is a block diagram showing a fourth embodiment of the present invention, and FIG. 6B shows the light intensity distribution in the Y direction at the irradiation position. FIG. 7A is a block diagram showing a fifth embodiment of the present invention, and FIG. 7B shows the light intensity distribution in the Y direction at the irradiation position. It is a graph which shows surface temperature distribution of a workpiece.

Explanation of symbols

10 laser oscillator, 30, 40 condensing optical system, 41, 46 asymmetric cylindrical lens 42, 43, 44 cylindrical lens, 45 wedge plate, 50 workpiece,
60 Moving stage, LA optical axis, LB laser beam.

Claims (11)

A laser processing method for performing processing while moving a laser beam relative to a workpiece,
The laser beam has an elliptical beam shape having a major axis in the relative movement direction on the irradiation surface of the workpiece, and the light intensity distribution along the major axis direction is asymmetric. Method.   2. The laser processing method according to claim 1, wherein the light intensity distribution along the major axis direction has a peak shifted from the laser beam optical axis in the pre-processing direction.   2. The laser processing method according to claim 1, wherein the light intensity distribution along the major axis direction has a peak shifted in the post-processing direction from the laser beam optical axis.   The laser processing method according to claim 1, wherein a substantially parallel laser beam is condensed in a relative movement direction using a cylindrical lens having a surface shape asymmetric with respect to the optical axis of the laser beam.   The laser processing method according to claim 1, wherein a substantially parallel laser beam is condensed in a relative movement direction using a cylindrical lens inclined with respect to the laser beam optical axis.   4. The laser processing method according to claim 1, wherein the laser beam is incident obliquely on the cylindrical lens, and the substantially parallel laser beam is condensed in the relative movement direction.   2. The laser beam is incident on a cylindrical lens, and further incident on a wedge plate whose optical path length varies along the relative movement direction, thereby condensing a substantially parallel laser beam in the relative movement direction. The laser processing method in any one of -3. A laser processing apparatus that performs processing while moving a laser beam relative to a workpiece,
A condensing optical system for condensing a substantially parallel laser beam and forming an elliptical beam shape having a long axis in the relative movement direction on the irradiation surface of the workpiece,
A laser processing apparatus, wherein the light intensity distribution along the long axis direction is asymmetric.   The laser processing apparatus according to claim 8, wherein the condensing optical system includes a cylindrical lens having a surface shape asymmetric with respect to an optical axis of the laser beam.   The laser processing apparatus according to claim 8, wherein the condensing optical system includes a cylindrical lens inclined with respect to an optical axis of the laser beam.   9. The laser processing apparatus according to claim 8, wherein the condensing optical system includes a wedge plate whose optical path length changes along a relative movement direction.

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