JP2016002569A - Laser machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a modified layer of a good quality, while suppressing the generation of damage or ablation.SOLUTION: A beam splitter 421 divides an incident laser beam into a first laser beam 493 in a first direction, and a second laser beam 492 in a second direction. A circulation circuit 424 is equipped with mirrors 441a-441d, and the second laser beam 492 divided by the beam splitter 421 is circulated and made incident to the beam splitter 421 again. A laser beam 491 radiated by a laser emitting portion 141 is incident to the beam splitter 421, and the first laser beam 493 divided by the beam splitter 421 is incident to a condenser 143.

Description

  The present invention relates to a laser processing apparatus for processing a workpiece by condensing a laser beam having a wavelength that is transmissive to the workpiece within the workpiece.

  A modified layer is continuously formed along the street by condensing a laser beam having a wavelength that is transmissive to a plate-like workpiece such as a semiconductor wafer inside the workpiece. There is a technique of dividing an object to be processed by applying an external force along a street whose strength has been reduced by forming (see Patent Documents 1 and 2). In addition, a laser beam having a wavelength that is absorptive with respect to the workpiece is condensed on the front or back surface of the workpiece and ablated to form a groove along the street, and an external force is applied along the groove. There is also a technique for dividing the workpiece by this (see Patent Document 3).

Japanese Patent No. 3408805 JP 2008-170366 A JP 2014082421 A

  However, to form a modified layer or groove with a predetermined depth, it is not sufficient to irradiate with a single laser beam. The laser beam can be applied many times while changing the depth of the focal point along the same street. Since it is necessary to irradiate, there is a problem in terms of processing efficiency. For example, when a groove is formed by ablation, it is necessary to defocus the bottom of the groove formed by the first laser light irradiation, change the focal point, and then irradiate the laser light. There is.

  In addition, when a modified layer is formed inside the workpiece, if the laser beam is incident from the back side of the workpiece, the laser beam used for laser processing passes through the condensing point, and the workpiece The device formed on the surface may be damaged. Moreover, the back surface may be vaporized due to ablation. If the pulse width of the laser beam is shortened to reduce the output, the occurrence of such damage and ablation problems can be avoided, but the processing efficiency is lowered and a good quality modified layer can be formed. The problem of not being able to occur. On the other hand, if the output is increased instead of shortening the pulse width, the processing efficiency can be improved and a high-quality modified layer can be formed, but ablation tends to occur on the back surface.

  The present invention has been considered in view of such problems, and an object thereof is to form a high-quality modified layer without reducing the processing efficiency.

  A laser processing apparatus according to the present invention includes a holding unit that holds a workpiece, a laser emitting unit that emits laser light to the workpiece held by the holding unit, and a laser emitting unit that emits the laser beam. Burst generating means for converting the laser light into a plurality of burst laser lights, and the plurality of burst laser lights generated by the burst generating means are condensed inside the workpiece to be processed. A laser processing apparatus, wherein the burst generation means converts the laser light emitted from the laser emitting section into a first laser light directed in a first direction, A beam splitter that divides the laser beam into a second laser beam directed in the direction of 2 and a mirror having a reflecting surface, and reflects the beam on the reflecting surface and circulates the second laser beam, thereby splitting the beam splitter. A recirculation circuit that re-enters the laser beam, the laser beam emitted by the laser emitting unit is incident on the beam splitter, and the first laser beam split by the beam splitter is incident on the condenser To do.

  The beam splitter is a polarization beam splitter that divides the incident laser beam by a polarization plane, and the circulation circuit rotates the polarization plane of the second laser beam divided by the beam splitter. It is preferable that the second laser beam, which includes a plate and whose polarization plane is rotated by the half-wave plate, is incident on the beam splitter again. In this case, a second half-wave plate for rotating the polarization plane of the laser light emitted by the laser emitting unit is provided, and the polarization plane is rotated by the second half-wave plate. It is preferable that the laser light is incident on the beam splitter.

  The circulation circuit includes a convex lens that condenses the second laser light divided by the beam splitter, and the more the number of times the burst laser light generated by the burst generation unit circulates through the circulation circuit, It is preferable that the burst laser beam is configured so that a condensing point where the concentrator condenses the laser beam is close to the concentrator.

  The circulation circuit includes a concave lens that diverges the second laser light divided by the beam splitter, and the more the number of times the burst laser light generated by the burst generation unit circulates through the circulation circuit, the more It is preferable that the condensing point where the concentrator collects the burst laser light is far from the concentrator.

  The circulation circuit includes a beam expander that expands a beam diameter of the second laser light divided by the beam splitter, and the burst laser light generated by the burst generation unit circulates through the circulation circuit. It is preferable that the beam diameter of the burst laser light be increased as the number of times increases.

  Preferably, the burst generation means includes optical path length adjustment means for adjusting the optical path length of the circulation circuit, and the time intervals of the plurality of burst laser lights can be changed.

  According to the laser processing apparatus according to the present invention, the laser beam is converted into a plurality of burst laser beams and irradiated onto the workpiece, so that a high-quality modified layer or ablation groove can be formed without reducing the processing efficiency. Can do. In addition, the second laser beam split by the beam splitter is caused to circulate in the circulation circuit, thereby causing a time delay and re-entering the beam splitter to generate a plurality of burst laser beams. Gradually decreases. Thereby, it can prevent that a workpiece is damaged.

  If the beam splitter is a polarizing beam splitter, the split ratio can be changed depending on the direction of the polarization plane of the laser light incident on the beam splitter, so the burst can be changed by changing the angle of rotation of the polarization plane with a half-wave plate. The reduction rate of the energy of the laser beam can be adjusted, and a burst laser beam most suitable for processing can be generated. In addition, the energy ratio of the first burst laser light can be adjusted by changing the angle at which the polarization plane of the laser light emitted from the laser emitting part is rotated by the second half-wave plate. Suitable burst laser light can be generated.

  If the converging point of the burst laser beam moves in the thickness direction of the workpiece, it is possible to form a modified layer or ablation groove that is long in the thickness direction of the workpiece and to form a modified layer. Generation of ablation at the time can be prevented.

  If a convex lens that condenses the second laser beam divided by the beam splitter is provided and the condensing point of the burst laser light approaches the concentrator, for example, damage to the far side from the concentrator is possible. By disposing the surface of the workpiece on which the easily received device is formed, the condensing point moves away from the device, so that the device can be prevented from being damaged. Therefore, it is suitable for forming a modified layer.

  If a concave lens that condenses the second laser beam divided by the beam splitter is provided, and the condensing point of the burst laser beam moves away from the concentrator, for example, damage to the far side of the concentrator will occur. By arranging the surface of the workpiece on which the device that is easy to receive is placed, the energy of the burst laser light becomes smaller as the focal point gets closer to the device, so that the device can be prevented from being damaged. . Further, in the ablation processing in which a groove is formed on the incident surface of the workpiece, it is suitable for forming a groove having a depth that is not sufficient by one laser light irradiation.

  If the configuration is such that the beam diameter of the burst laser beam increases as the number of cycles in the circulation circuit increases, the focal point can be reduced even if the energy of the burst laser beam is reduced. The energy density can be maintained, and a high-quality modified layer extending in the depth direction can be formed.

  If the configuration is such that the optical path length of the circulation circuit can be adjusted, the time interval of the burst laser light can be adjusted, so that the burst laser light most suitable for processing can be generated.

The perspective view which shows a laser processing apparatus. The block diagram which shows a laser irradiation means. The graph which shows the output of a burst laser beam. The block diagram which shows another laser irradiation means. The block diagram which shows another laser irradiation means.

  A laser processing apparatus 10 shown in FIG. 1 is held by a holding unit 11 that holds a plate-shaped workpiece 20 such as a semiconductor wafer, two feeding units 12 and 13 that move the holding unit 11, and a holding unit 11. And laser irradiation means 14 for irradiating the workpiece W with laser light.

  A plurality of devices are formed on the surface 20 a of the workpiece 20. In the workpiece 20, for example, a state in which a protective tape 21 for protecting a device is attached to the front surface 20a, a side on which the protective tape T is attached is down (−Z side), and a back surface 20b is exposed. Is placed on the holding surface of the holding means 11. The holding means 11 sucks and holds the placed workpiece.

  The feed unit 12 is configured such that when the motor 121 rotates the screw shaft 122 parallel to the ± X direction, the moving portion 123 engaged with the screw shaft 122 is guided by the guide 124 and moved in the ± X direction. Yes. The holding means 11 is fixed to the moving unit 123 and moves in the ± X direction as the moving unit 123 moves.

  The feeding means 13 is configured such that when the motor 131 rotates the screw shaft 132 parallel to the ± Y direction, the moving portion 133 engaged with the screw shaft 132 is guided by the guide 134 and moves in the ± Y direction. Yes. The feeding unit 12 is fixed to the moving unit 133, and moves in the ± Y direction as the moving unit 133 moves, and accordingly, the holding unit 11 also moves in the ± Y direction.

  As shown in FIG. 2, the laser irradiation unit 14 includes a laser emitting unit 141 that emits a laser beam 491, and a burst generation unit 142 that converts the laser beam 491 emitted by the laser emitting unit 141 into a plurality of burst laser beams 493. And a condenser 143 for condensing a plurality of burst laser beams 493 generated by the burst generation means 142 inside the workpiece 20. In FIG. 2, illustration of the protective tape 21 shown in FIG. 1 is omitted.

  Laser light 491 emitted from the laser emitting unit 141 is linearly polarized parallel light, and has the same pulse width (for example, 1 ns to 10 ns) as the burst laser light 493 generated by the burst generation unit 142.

The burst generation unit 142 divides the incident laser beam into two laser beams 492 and 493, and a circulation circuit 424 that circulates the laser beam 492 divided by the beam splitter 421 and re-enters the beam splitter 421. And a plurality of burst laser beams 493 are generated by delaying the divided laser beams by the circulation circuit 424.
The condenser 143 includes a convex lens, for example, and condenses the burst laser light 493 at the condensing point 481.

  The beam splitter 421 is, for example, a polarization beam splitter, and branches incident laser light into two by the polarization plane. That is, the beam splitter 421 reflects the s-polarized component of the incident laser light and transmits the p-polarized component. Therefore, the division ratio of the laser light by the beam splitter 421 is determined by the direction of the polarization plane of the laser light incident on the beam splitter 421. For example, when the angle formed by the polarization plane and the incident plane is 45 degrees, the beam splitter 421 divides the incident laser light into 1: 1. The larger the angle formed between the polarization plane and the incident plane, the higher the ratio of reflected laser light. Conversely, the smaller the angle formed between the polarization plane and the incident plane, the higher the ratio of transmitted laser light.

  Laser light 491 emitted from the laser emitting unit 141 enters the beam splitter 421 from a direction having an angle of 45 degrees with respect to the reflection surface of the beam splitter 421, passes through the beam splitter 421, and is the same as the laser light 491. The first laser beam 493 traveling in the first direction and the second laser beam 492 traveling in the second direction reflected by the beam splitter 421 and making an angle of 90 degrees with respect to the traveling direction of the laser beam 491 are split. Is done. Since the laser beam 491 is linearly polarized light and the beam splitter 421 is a polarizing beam splitter, the division ratio of the laser beam 491 can be changed by changing the angle formed by the polarization plane and the incident plane.

  The second laser light 492 divided by the beam splitter 421 circulates in the circulation circuit 424 and enters the beam splitter 421 again. The laser beam 495 that re-enters the beam splitter 421 has the same traveling direction as the laser beam 492, enters the beam splitter 421 from the opposite side of the laser beam 492, and is split into two laser beams 492 and 493. The Contrary to the laser light 491, the first laser light 493 is laser light reflected by the beam splitter 421 (that is, the s-polarized component), and the second laser light 492 is laser light transmitted through the beam splitter 421. (That is, the p-polarized component).

  The circulation circuit 424 circulates the second laser beam 492 divided by the beam splitter 421 and re-enters the beam splitter 421, and an optical path through which the mirrors 441a to 441d circulate the laser beam 492. Are provided with a half-wave plate 442 and a convex lens 443. Each of the four mirrors 441a to 441d has a reflecting surface that reflects the laser light.

  The half-wave plate 442 rotates the polarization plane of the incident laser light. The angle at which the half-wave plate 442 rotates the polarization plane of the laser light is determined by the angle between the slow axis of the half-wave plate 442 and the polarization plane. The half-wave plate 442 is arranged so that the direction of the slow axis can be adjusted. When the direction of the slow axis is changed, the direction of the polarization plane of the laser beam 495 that reenters the beam splitter 421 is changed, so that the division ratio of the laser beam 495 in the beam splitter 421 can be changed. For example, it is assumed that the division ratio of the laser beam 491 in the beam splitter 421 is 1: 1 and the division ratio of the laser beam 495 is also 1: 1.

  The convex lens 443 collects the incident laser light. The focal length of the convex lens 443 is longer than the optical path length L of the circulation circuit 424, and is, for example, about several tens to several hundred times the optical path length L. That is, the convex lens 443 is a lens having a very small numerical aperture (NA) and a very low magnification.

  In the laser processing apparatus 10 shown in FIG. 1, when the modified layer is formed by condensing the laser light inside the workpiece 20 held by the holding means 11, the laser irradiation means 14 is placed on the holding means 11. From the upper side (+ Z side) toward the back surface 20b of the workpiece 20 held, the pulse width is extremely high at a wavelength that passes through the workpiece (for example, 1064 nm when the workpiece is formed of silicon). Are irradiated with a short (for example, 1 ns to 10 ns) burst laser light to be condensed inside the workpiece.

  As shown in FIG. 3, when the laser emitting unit 141 emits the laser light 491a, half of the light is transmitted through the beam splitter 421 and becomes the first burst laser light 493a.

  The other half of the laser light 491a is reflected by the beam splitter 421 to become laser light 492 (see FIG. 2), goes around the circulation circuit 424, and enters the beam splitter 421 again. Half of them are reflected by the beam splitter 421 to become the second burst laser beam 493b. Assuming that the optical path length of the circulation circuit 424 is L, it takes only the time L / c obtained by dividing the optical path length L of the circulation circuit 424 by the speed of light c to go around the circulation circuit 424. Therefore, the first burst laser beam 493a and the second The time difference 482 from the burst laser beam 493b is L / c.

  The remaining half of the laser light re-entered on the beam splitter 421 passes through the beam splitter 421 to become laser light 492, makes a further round of the circulation circuit 424, and enters the beam splitter 421 again. Half of the light is reflected by the beam splitter 421 to become the third laser light 493c, and the other half is transmitted through the beam splitter 421 to become the laser light 492. By repeating this, a plurality of burst laser beams 493 are generated. The burst laser beam 493 is repeatedly emitted at a predetermined time difference 482, and the output thereof is attenuated in a geometric series.

  When the output becomes almost zero due to attenuation, the laser emitting unit 141 emits a new laser beam 491a. In the same manner as described above, burst laser beams 493a, 493b, 493c,... Are generated by the beam splitter 421 and condensed inside the workpiece 20 to form a modified layer. Since the energy per burst laser beam is small, the occurrence of damage due to ablation or light leakage can be suppressed. Moreover, even if the energy per burst laser beam is small, the total energy of a plurality of burst laser beams repeatedly irradiated increases, so that a high-quality modified layer is formed inside the workpiece. And the processing efficiency is not lowered.

  The burst laser beam 493 that has not contributed to the formation of the modified layer at the condensing point 481 passes through the condensing point 481 and reaches the device formed on the surface of the workpiece 20. However, since the energy per one burst laser beam is small, no ablation occurs on the back surface 20b, and the device alone is not damaged. By repeatedly irradiating multiple burst laser beams, energy is accumulated and the device is easily damaged. However, the multiple burst laser beams irradiated repeatedly are gradually attenuated, so the energy of the burst laser beam is reduced. It can be smaller and prevent the device from being damaged.

  The ratio between the intensity of the first burst laser beam 493a and the total intensity of the second and subsequent burst laser beams is determined by the division ratio of the laser beam 491. If the angle between the plane of polarization of the laser light 491 and the incident surface is reduced to increase the ratio of transmitted light, the first burst laser light 493a becomes stronger. Conversely, if the angle between the polarization plane and the incident plane of the laser beam 491 is increased to increase the ratio of the reflected light, the first burst laser beam 493a becomes weaker. If the angle between the plane of polarization of the laser beam 491 and the incident surface is 90 degrees, the intensity of the first burst laser beam 493a becomes zero.

  The ratio (attenuation rate) between the intensity of the second and subsequent burst laser lights and the intensity of the next burst laser light is determined by the division ratio of the laser light 495. If the angle between the plane of polarization of the laser light 491 and the incident surface is reduced to increase the ratio of transmitted light, the attenuation factor is reduced. Conversely, if the angle formed by the plane of polarization of the laser beam 491 and the incident surface is increased to increase the ratio of reflected light, the attenuation rate increases.

  In this way, the intensity ratio of multiple burst laser beams can be changed relatively freely, so the quality pattern of multiple burst laser beams can be formed while suppressing the generation of ablation and damage. The pattern can be optimized.

Next, the effect of the convex lens 443 will be described.
Since the laser light 491 emitted from the laser emitting unit 141 is parallel light, the first burst laser light 493a divided from the laser light 491 is also parallel light, and thus the condenser 143 collects the laser light 493a. A condensing point 481 (see FIG. 2) is a focal point of the condenser 143.

  On the other hand, the laser light 492 split from the laser light 491 is also parallel light, but the laser light 495 that has made a round of the circulation circuit 424 passes through the convex lens 443 having a very long focal length, and is almost parallel light. However, the light tends to be slightly collected. The condensing point 481 where the concentrator 143 condenses the second burst laser beam 493 divided from there is slightly closer to the concentrator 143 than the focal point of the concentrator 143. When the laser beam 492 divided from the laser beam 495 further goes around the circulation circuit 424, the laser beam 492 passes through the convex lens 443 once again, so that the tendency to condense becomes stronger. Therefore, the condensing point 481 is further closer to the condenser 143.

  In this way, every time the laser light goes around the circulation circuit, it passes through the convex lens 443 and the condensing tendency becomes stronger, so that the condensing point of the burst laser light 493 gradually approaches the condenser 143. Since the condensing point 481 moves little by little, a long modified layer in the thickness direction of the workpiece can be formed, and the workpiece can be easily divided. Moreover, compared with the case where the condensing points of the plurality of burst laser beams 493 do not move and are condensed at the same position, the occurrence of ablation on the back surface 20b can be suppressed.

  Also, as the energy of the burst laser beam is accumulated and the device is more susceptible to damage, the focal point gradually moves away from the device, so the burst laser beam that reaches the device through the focal point diverges and the energy density increases. Get smaller. Not only does the energy of the burst laser light itself decrease, but the energy density of the burst laser light that reaches the device is reduced, so the energy that the burst laser light gives to the device is further reduced, preventing the device from being damaged. Can do.

  The laser irradiation means 14A shown in FIG. 4 can be used in the laser processing apparatus 10 in place of the laser irradiation means 14, and compared with the laser irradiation means 14, the circulation circuit 424 has an incidence instead of the convex lens 443. The difference is that a lens 443A for diverging the laser beam is provided.

  The lens 443A is, for example, a concave lens, and has a focal length longer than the optical path length L of the circulation circuit 424, for example, about several tens to several hundred times the optical path length L, like the convex lens 443. That is, the lens 443A is a lens having a very small numerical aperture (NA) and a very low magnification.

  Since the laser light 491 emitted from the laser emitting unit 141 is parallel light, the first burst laser light 493a divided from the laser light 491 is also parallel light, and thus the condenser 143 collects the laser light 493a. A condensing point 481 is a focal point of the condenser 143.

  The laser beam 492 split from the laser beam 491 is also a parallel beam, but the laser beam 495 that has made a round of the circulation circuit 424 is almost a parallel beam by passing through the lens 443A having a very long focal length. The light tends to diverge slightly. A condensing point 481 at which the concentrator 143 condenses the second burst laser light 493 divided therefrom is slightly farther from the concentrator 143 than the focal point of the concentrator 143. When the laser beam 492 split from the laser beam 495 further goes around the circulation circuit 424, the laser beam 492 passes through the lens 443A once again, and the tendency to diverge is increased. Therefore, the condensing point 481 is further away from the condenser 143.

  In this way, every time the laser beam goes around the circulation circuit, the laser beam passes through the lens 443A, and the tendency of divergence becomes stronger. Therefore, the condensing point 481 of the burst laser beam 493 gradually moves away from the condenser 143. Since the condensing point 481 moves little by little, a long modified layer in the thickness direction of the workpiece can be formed, and the workpiece can be easily divided. Moreover, compared with the case where the condensing points of the plurality of burst laser beams 493 do not move and are condensed at the same position, generation of ablation on the back surface 20b can be suppressed.

As the condensing point gradually approaches the device, the energy density of the burst laser light that passes through the condensing point and reaches the device increases, but the energy of the burst laser light decreases, so that the burst laser light enters the device. The amount of energy applied is reduced, and the device can be prevented from being damaged. Thereby, the modified layer can be formed to a position relatively close to the device.
In addition, when the incident surface such as the back surface 20b is ablated, the light can be condensed at a position deeper than the bottom of the groove formed by the first irradiation, and a deep ablation groove is formed in the thickness direction. be able to.

  The laser irradiation means 14B shown in FIG. 5 can be used in the laser processing apparatus 10 in place of the laser irradiation means 14. Compared with the laser irradiation means 14, the laser irradiation means 14 B is provided between the laser emitting unit 141 and the burst generation means 142. A second half-wave plate 145 disposed on the optical path length, a burst generation unit 142 includes an optical path length adjustment unit 425 that adjusts an optical path length of the circulation circuit 424, and a circulation circuit 424 includes a convex lens. The difference is that a beam expander 444 that expands the beam diameter of the incident laser light is provided instead of 443.

  The half-wave plate 145 rotates the polarization plane of the incident laser light. The half-wave plate 442 is arranged so that the direction of the slow axis can be adjusted. When the direction of the slow axis is changed, the direction of the polarization plane of the laser light 496 incident on the beam splitter 421 changes. The division ratio of the laser light 496 in the beam splitter 421 can be changed. As a result, the intensity of the first burst laser beam can be easily changed, and the intensity pattern of multiple burst laser beams can be changed to an optimum pattern for forming a high quality modified layer while suppressing the occurrence of ablation and damage. can do.

  The optical path length adjusting means 425 includes, for example, a ball screw mechanism, and changes the optical path length L of the circulation circuit 424 by moving the two mirrors 441b and 44c. As the optical path length L increases, the time interval between the plurality of burst laser beams 493 increases. Conversely, when the optical path length L is shortened, the time interval between the plurality of burst laser beams 493 is narrowed. Since the time intervals of the plurality of burst laser beams 493 can be changed relatively freely, it is possible to set the time interval optimal for forming a high-quality modified layer while suppressing generation of ablation and damage.

  The beam expander 444 expands the light flux without changing the parallelism of the laser light. Since the laser light 491 emitted by the laser emitting unit 141 is parallel light, the burst laser light 493 remains parallel light no matter how many times it passes through the beam expander 444. The position of the condensing point 481 where the laser beam 493 condenses the laser beam 493 does not change from the focal point of the condensing point 481, but the size of the condensing point 481 decreases as the beam expander 444 increases the beam diameter. To go. As a result, the energy density at the condensing point 481 is increased, and the decrease in energy density due to the decrease in the energy of the burst laser beam is offset, so that a high-quality modified layer can be formed.

Since the half-wave plate 145, the optical path length adjusting means 425, and the beam expander 444 have independent effects, the laser irradiation means 14B includes the second half-wave plate 145. A configuration without the optical path length adjusting unit 425 or a configuration without the beam expander 444 may be used.
Further, the laser irradiation means 14 and the laser irradiation means 14A described above may be configured to include the second half-wave plate 145, or may be configured to include the optical path length adjusting means 425, or the beam. The structure provided with the expander 444 may be sufficient.
Instead of providing the half-wave plate 145, for example, a polarization plane adjustment unit that can relatively rotate the laser emitting unit 141 and the beam splitter 421 around the optical axis of the laser light 491 is provided. The configuration may be such that the orientation of the polarization plane of the laser light incident on the beam splitter 421 can be adjusted by the configuration.
Instead of providing the convex lens 443 and the lens 443A in the circulation circuit 424, a lens may be provided in front of the beam splitter 421 to collect or diverge the laser light emitted from the laser emitting unit 141. In this case, the number of times that the laser beam passes through the lens is one regardless of the number of circulations. However, as the number of circulations increases, the optical path length between the lens and the condenser 143 becomes longer. 481 moves.
The beam splitter is not limited to the polarization beam splitter, and may be a non-polarization beam splitter having a predetermined division ratio such as a half mirror.
The number of mirrors in the circulation circuit 424 is not limited to four, and may be other numbers. In order to make the second laser beam 492 reenter the beam splitter 421 from the opposite side without passing through the beam splitter 421, three or more mirrors are necessary. Further, the circulation circuit 424 is not limited to a mirror, and may be configured using, for example, an optical fiber.

10 laser processing apparatus, 11 holding means,
12, 13 Feed means, 121, 131 Motor, 122, 132 Screw shaft,
123, 133 moving part, 124, 134 guide,
14, 14A, 14B Laser irradiation means, 141 laser emitting part,
142 burst generation means, 421 beam splitter, 424 circulation circuit,
425 optical path length adjusting means, 441a to 441d mirror,
145,442 half-wave plate,
443 convex lens, 443A lens, 444 beam expander,
143 concentrator, 481 condensing point, 482 time difference,
491 to 496, 491a, 491b, 493a to 493c laser light,
20 Workpiece

Claims (7)

Holding means for holding the workpiece;
A laser emitting unit that emits laser light to the workpiece held by the holding means;
Burst generating means for converting the laser light emitted by the laser emitting unit into a plurality of burst laser lights;
A concentrator for processing the workpiece by condensing the plurality of burst laser beams generated by the burst generating means inside the workpiece;
A laser processing apparatus comprising:
The burst generation means includes:
A beam splitter that divides the laser light emitted from the laser emitting unit into a first laser light traveling in a first direction and a second laser light traveling in a second direction;
A circulation circuit comprising a mirror having a reflection surface, circulating the second laser light reflected by the reflection surface and re-entering the beam splitter;
With
The laser processing apparatus, wherein the laser light emitted by the laser emitting unit is incident on the beam splitter, and the first laser light divided by the beam splitter is incident on the condenser. The beam splitter is a polarization beam splitter that divides the incident laser light by a polarization plane;
The circulation circuit is
A half-wave plate for rotating the polarization plane of the second laser beam divided by the beam splitter;
The laser processing apparatus according to claim 1, wherein the second laser light whose polarization plane is rotated by the half-wave plate is incident on the beam splitter again. A second half-wave plate that rotates the plane of polarization of the laser light emitted by the laser emitting unit;
3. The laser processing apparatus according to claim 2, wherein the laser light having the polarization plane rotated by the second half-wave plate is incident on the beam splitter. The circulation circuit is
A convex lens for condensing the second laser beam divided by the beam splitter;
The more the number of times the burst laser light generated by the burst generation means circulates in the circulation circuit, the closer the condensing point at which the light collector collects the burst laser light is closer to the light collector. Item 4. The laser processing apparatus according to any one of Items 1 to 3. The circulation circuit is
A concave lens for diverging the second laser beam divided by the beam splitter,
The more the number of times that the burst laser light generated by the burst generation means circulates in the circulation circuit, the farther the condensing point at which the condenser condenses the burst laser light is farther from the condenser. Item 4. The laser processing apparatus according to any one of Items 1 to 3. The circulation circuit includes
A beam expander that expands a beam diameter of the second laser beam divided by the beam splitter;
4. The laser processing apparatus according to claim 1, wherein the beam diameter of the burst laser beam increases as the number of times the burst laser beam generated by the burst generation unit circulates in the circulation circuit increases. 5. . The burst generation means includes
An optical path length adjusting means for adjusting the optical path length of the circulation circuit;
The laser processing apparatus according to claim 1, wherein a time interval between the plurality of burst laser beams is changeable.

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