JP2010263063A - Laser irradiation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein, when laser beams having polarization planes orthogonal to each other are combined with each other using a polarization beam splitter, it is difficult to apply a structure for cutting off return light. <P>SOLUTION: Each of a plurality of laser diode arrays emits a laser beam having a beam cross-section long in the long-axis direction. A rearrangement optical system rearranges the laser beams so that each of the laser beams emitted from the laser diode arrays are transmitted in a first direction; the long-axis directions of the beam cross-section are set parallel to one another and arranged in the short-axis direction orthogonal to the long axis; and the polarization planes of the respective laser beams are aligned with one another. A stage holds an object. The rearranged laser beams overlaps one another on a surface of the object held to the stage. A polarization beam splitter is arranged in the path of the rearranged laser beams in a posture for transmitting or reflecting the laser beams. A 1/4 wavelength plate is arranged on a rear side relative to the polarization beam splitter when viewed from the rearrangement optical system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a laser irradiation apparatus that uses a plurality of laser diode arrays to irradiate a common region on the surface of an object with a laser beam.

  A technique is known in which annealing is performed using a semiconductor laser in order to activate impurities implanted into the back surface of an insulated gate bipolar transistor (IGBT) (Patent Document 1). In order to increase the power of the laser beam for annealing, it is effective to superimpose laser beams emitted from a plurality of semiconductor lasers.

  Two laser beams whose polarization planes are orthogonal to each other can be synthesized using a polarization beam splitter (Patent Document 2). In addition, a plurality of laser beams having slightly different wavelengths can be synthesized using a dichroic mirror (Patent Document 3).

JP 2006-351659 A Japanese Examined Patent Publication No. 7-94171 JP 2006-32937 A

  When the laser beam reflected by the surface of the irradiation object returns to the semiconductor laser element, the oscillation of the semiconductor laser element becomes unstable and the element may be damaged. In order to prevent the return light from reaching the semiconductor laser element, a polarization beam splitter and a quarter wavelength plate may be used. Incident light passes through the polarization beam splitter, is circularly polarized by the quarter-wave plate, and enters the object. The return light is converted into linearly polarized light having a polarization plane orthogonal to the polarization plane of the incident light by the quarter wavelength plate. Since this return light is reflected by the polarization beam splitter, it does not enter the semiconductor laser element.

  When laser beams whose polarization planes are orthogonal to each other are combined using a polarization beam splitter, the above-described configuration for blocking the return light cannot be applied.

  Since a laser beam synthesized using a dichroic mirror includes a plurality of wavelengths, it is necessary to remove chromatic aberration of a lens that collects the synthesized laser beam. This complicates the design of the optical system and makes it difficult to reduce the cost of the apparatus.

According to one aspect of the invention,
A plurality of laser diode arrays each including a plurality of semiconductor lasers arranged in a major axis direction and emitting a laser beam having a long beam cross section in the major axis direction;
Each of the laser beams emitted from the laser diode array propagates in the first direction, and the major axis directions of the beam cross-sections are parallel to each other and arranged in the minor axis direction orthogonal to the major axis. A rearrangement optical system for rearranging the laser beams so that the polarization planes of the laser beams are aligned,
A stage for holding the object;
A propagation optical system for propagating the laser beams so that the plurality of laser beams rearranged by the rearrangement optical system overlap on the surface of the object held on the stage;
A polarization beam splitter disposed in a position for transmitting or reflecting the laser beam in a path of the laser beam between the rearrangement optical system and the stage;
There is provided a laser irradiation apparatus having a quarter wave plate disposed behind the polarizing beam splitter as viewed from the rearrangement optical system.

  Due to the polarizing beam splitter and the quarter-wave plate, the return light deviates from the beam path of the incident laser beam. For this reason, it is possible to prevent the return light from entering the laser diode array. In addition, since no dichroic mirror is used, a plurality of laser diode arrays that emit laser beams having the same wavelength can be used.

1 is a schematic view of a laser irradiation apparatus according to Example 1. FIG. (2A)-(2C) is a figure which shows the beam cross section in the dashed-dotted lines 2A-2A, 2B-2B, and 2C-2C of FIG. 1, respectively. 6 is a schematic view of a laser irradiation apparatus according to Example 2. FIG. It is the schematic which shows the example of arrangement | positioning of the laser diode array of the laser irradiation apparatus by Example 2, a converging lens, and a knife edge mirror.

  FIG. 1A shows a schematic diagram of a laser irradiation apparatus according to the first embodiment. This laser irradiation apparatus includes first to fourth laser diode arrays 10A to 10D.

  FIG. 1B shows a perspective view of the first laser diode array 10A. The configurations of the second to fourth laser diode arrays 10B to 10D are also the same as the configuration of the first laser diode array 10A shown in FIG. 1B. The first laser diode array 10 </ b> A includes a plurality of semiconductor laser elements 30. The semiconductor laser elements 30 are arranged in a line on the emission surface of the first laser diode array 10A. An xyz orthogonal coordinate system in which the normal direction of the emission surface is the z axis and the arrangement direction of the semiconductor laser elements 30 is the y axis is defined. The x-axis corresponds to the thickness direction of each semiconductor laser element 30. The laser beam emitted from the first laser diode array 10A has a long beam cross section in the y-axis direction. The wavelength is, for example, 800 nm.

  Returning to FIG. 1A, the description will be continued. In FIG. 1A, an xyz orthogonal coordinate system is defined in which the traveling direction of the laser beam is the z axis and the major axis direction of the beam cross section is the y axis. Convergent lenses 11A to 11D are arranged in front of the first to fourth laser diode arrays 10A to 10D, respectively. The converging lens 11A is composed of, for example, a convex cylindrical lens, and emits the first laser beam L1 emitted from the first laser diode array 10A in the zx plane, that is, in a virtual plane orthogonal to the long axis direction of the beam cross section. Collimate.

  A knife edge mirror 12B is arranged on the side of the path of the collimated first laser beam L1 emitted from the first laser diode array 10A. The second laser beam L2 emitted from the second laser diode array 10B and collimated by the converging lens 11B is reflected by the knife edge mirror 12B. Due to the reflection, the traveling direction of the second laser beam L2 becomes parallel to the traveling direction of the first laser beam L1, and the major axis direction of the beam cross section of the first laser beam L1 and the second laser beam L2 The first and second laser beams L1 and L2 are rearranged so that the major axis direction of the beam cross section is parallel to each other.

  A knife edge mirror 12C is disposed on the side of the path of the rearranged first and second laser beams L1 and L2. The third laser beam L3 emitted from the third laser diode array 10C and collimated by the converging lens 11C is reflected by the knife edge mirror 12C and rearranged. A knife edge mirror 12D is arranged on the side of the path of the rearranged first to third laser beams L1 to L3. The fourth laser beam L4 emitted from the fourth laser diode array 10D and collimated by the converging lens 11D is rearranged by being reflected by the knife edge mirror 12D.

  FIG. 2A shows a cross-sectional view taken along the alternate long and short dash line 2A-2A of the first to fourth laser beams L1 to L4 after the rearrangement shown in FIG. 1A. Each of the first to fourth laser beams L1 to L4 has a long cross section in the y-axis direction and is arranged at a minute interval in the x-axis direction (short axis direction). The first to fourth laser beams L1 to L4 are linearly polarized light, and their polarization planes are aligned. For example, the first to fourth laser beams L1 to L4 have a polarization plane parallel to the zx plane.

  As shown in FIG. 1A, the rearranged first to fourth laser beams L <b> 1 to L <b> 4 pass through the polarization beam splitter 15 and are converted into circularly polarized light by the quarter wavelength plate 16. The first to fourth laser beams L1 to L4 converted to circularly polarized light are reflected by the mirror 17 and enter the anamorphic prism pair 18. The anamorphic prism pair 18 expands the beam cross sections of the first to fourth laser beams L1 to L4 in the minor axis direction (x-axis direction).

  FIG. 2B shows a beam cross section taken along the alternate long and short dash line 2B-2B of the first to fourth laser beams L1 to L4 after passing through the anamorphic prism pair 18. Each beam cross section of the first to fourth laser beams L1 to L4 is enlarged in the x-axis direction as compared with the beam cross section shown in FIG. 2A. As the beam cross section expands, the distance between the beam cross sections increases.

  As shown in FIG. 1A, after passing through the anamorphic prism pair 18, the first to fourth laser beams L <b> 1 to L <b> 4 enter the array lens telescope 19. The array lens telescope 19 makes the light intensity distribution of the first to fourth laser beams L1 to L4 uniform with respect to the y-axis direction (major axis direction).

  The uniformized first to fourth laser beams L <b> 1 to L <b> 4 are collected by the condenser lens 20.

  An object 26 is held on the XY stage 25. The object 26 is, for example, an IGBT substrate. The condenser lens 20 condenses the laser beams so that the first to fourth laser beams L1 to L4 overlap on the surface of the object 26.

  FIG. 2C shows a beam cross section on the surface of the object 26 (a chain line 2C-2C in FIG. 1A). The beam sections of the first to fourth laser beams L1 to L4 are overlapped to form one elongated beam incident region. On the surface of the object 26, the light intensity distribution in the y-axis direction in the beam cross section is substantially uniform. The light intensity distribution in the x-axis direction is, for example, a Gaussian distribution.

  The return light reflected from the surface of the object 26 is converted into linearly polarized light by the quarter-wave plate 16. The polarization plane of the return light is parallel to the yz plane and is orthogonal to the polarization plane of the incident light. For this reason, the return light is reflected by the polarization beam splitter 15. The reflected return light is absorbed by the beam damper 22.

  Since the return light does not reach the first to fourth laser diode arrays 10A to 10D, the oscillation of the semiconductor laser element due to the return light can be prevented from being disturbed. In addition, by superimposing the first to fourth laser beams L1 to L4 emitted from the first to fourth laser diode arrays 10A to 10D, the power is four times that when using one laser diode array. Can be obtained. The number of laser diode arrays is not limited to four. It is also possible to superimpose laser beams emitted from two to three or five or more laser diode arrays.

  Further, since no dichroic mirror is used, elements that emit laser beams having the same wavelength can be used for the first to fourth laser diode arrays 10A to 10D. For this reason, it is not necessary to correct the chromatic aberration of the optical element.

  The polarizing beam splitter 15 and the quarter wavelength plate 16 are disposed in the path after the first to fourth laser beams L1 to L4 are rearranged. For this reason, a pair of polarizing beam splitter 15 and quarter wavelength plate 16 may be prepared for a plurality of laser beams. Since a large (large diameter) optical element is generally expensive, a polarizing beam splitter and a quarter wavelength plate may be disposed for each of the laser beams L1 to L4. In this case, each of the polarization beam splitter and the quarter-wave plate can be downsized as compared with the case where the first to fourth laser beams L1 to L4 are arranged in the path after being rearranged. it can.

  FIG. 3 shows a schematic diagram of a laser irradiation apparatus according to the second embodiment. In the following description, attention is focused on differences from the laser irradiation apparatus according to the first embodiment shown in FIG. 1A.

  In the first embodiment, the traveling directions of the rearranged first to fourth laser beams L1 to L4 are parallel to each other, but in the second embodiment, the first to fourth laser beams travel in the traveling direction of the laser beam. The intervals between the laser beams L1 to L4 are gradually reduced.

  The converging lens 11A converts the laser beam emitted from the first laser diode array 10A into a converging light beam, not a parallel light beam. The first lens 11A and the condenser lens 20 form an image of the emission part on the emission surface of the first laser diode array 10A on the surface of the object 26 in the zx plane. Similarly, the emission portions P <b> 2 to P <b> 4 on the emission surfaces of the second to fourth laser diode arrays 10 </ b> B to 10 </ b> D form an image on the surface of the object 26 in the zx plane.

  FIG. 4 shows an example of the configuration of the first to fourth laser diode arrays 10A to 10D, the first to fourth converging lenses 11A to 11D, and the knife edge mirrors 12B to 12D.

  The first laser beam L1 emitted from the first laser diode array 10A is converged by the first converging lens 11A. The second laser beam L2 emitted from the second laser diode array 10B is converged by the second converging lens 11B and reflected by the knife edge mirror 12B.

  In the zx plane, the light emitting portion P1 on the emitting surface of the first laser diode array 10A and the light emitting portion P2 on the emitting surface of the second laser diode array 10B include a virtual surface including the reflecting surface of the knife edge mirror 12B. The plane 13B has a plane-symmetric positional relationship. The first converging lens 11A and the second converging lens 11B have a shape obtained by partially cutting off a general converging lens in order to avoid interference with other beam paths. In FIG. 4, a general convergent lens before being cut off is indicated by a broken line. The virtual converging lens having the first converging lens 11A as a part and the virtual converging lens having the second converging lens 11B as a part have a plane-symmetrical positional relationship with respect to the virtual plane 13B. For this reason, the second laser beam L2 reflected by the knife edge mirror 12B is emitted from the same position as the light emitting portion P1 of the first laser diode array 10A, and includes a first converging lens 11A as a part. This is the same as the laser beam converged by a converging lens.

  Similarly, the light emitting part P3 of the third laser diode array 11C is arranged at a position symmetrical to the light emitting part P1 of the first laser diode array 10A with respect to the virtual plane 13C including the reflecting surface of the knife edge mirror 12C. Yes. The virtual converging lens partially including the third converging lens 11C is in a plane-symmetric positional relationship with the virtual converging lens partially including the first converging lens 11A with respect to the virtual plane 13C.

  The light emitting part P4 of the fourth laser diode array 11D is disposed at a position symmetrical to the light emitting part P1 of the first laser diode array 10A with respect to the virtual plane 13D including the reflecting surface of the knife edge mirror 12D. The virtual converging lens partially including the fourth converging lens 11D is in a plane-symmetric positional relationship with the virtual converging lens including part of the first converging lens 11A with respect to the virtual plane 13D.

  Therefore, the first to fourth laser beams L1 to L4 reflected and rearranged by the knife edge mirrors 12B to 12D are all assumed to be equivalent to those emitted from the light emitting part P1 of the first laser diode array 10A. Can be handled. In the case where the first converging lens 11A and the condenser lens 20 are configured to form an image of the light emitting part P1 of the first laser diode array 10A on the surface of the object 26, the second to fourth laser diode arrays 10B to 10D. The light emitting portions P2 to P4 are also imaged on the surface of the object 26.

  In the second embodiment, as in the first embodiment, the oscillation of the semiconductor laser element due to the return light can be prevented from being disturbed.

  In place of the knife edge mirror used in the above embodiment, a dielectric multilayer reflective film in which a reflective region is provided in a part of the transparent region can be used. In this case, the reflective region functions as a reflective surface of the knife edge mirror.

  Further, instead of the anamorphic prism pair 18, another optical element that expands the beam cross-sectional shape only in one direction may be used. Further, instead of the array lens telescope 19, another uniformizing optical element may be used.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

10A to 10D First to fourth laser diode arrays 11A to 11D First to fourth converging lenses 12B to 12D Knife edge mirror 15 Polarizing beam splitter 16 1/4 wavelength plate 17 Mirror 18 Anamorphic prism pair 19 Array lens Telescope 20 Condenser lens 22 Damper 25 XY stage 26 Target 30 Semiconductor laser element

Claims (3)

A plurality of laser diode arrays each including a plurality of semiconductor lasers arranged in a major axis direction and emitting a laser beam having a long beam cross section in the major axis direction;
Each of the laser beams emitted from the laser diode array propagates in the first direction, and the major axis directions of the beam cross-sections are parallel to each other and arranged in the minor axis direction orthogonal to the major axis. A rearrangement optical system for rearranging the laser beams so that the polarization planes of the laser beams are aligned,
A stage for holding the object;
A propagation optical system for propagating the laser beams so that the plurality of laser beams rearranged by the rearrangement optical system overlap on the surface of the object held on the stage;
A polarization beam splitter disposed in a position for transmitting or reflecting the laser beam in a path of the laser beam between the rearrangement optical system and the stage;
A laser irradiation apparatus comprising: a quarter-wave plate disposed behind the polarizing beam splitter as viewed from the rearrangement optical system. further,
A converging lens arranged corresponding to each of the plurality of laser diode arrays and collimating a laser beam emitted from the laser diode array in a virtual plane orthogonal to the major axis direction;
The laser irradiation apparatus according to claim 1, wherein the rearrangement optical system rearranges the laser beams so that traveling directions of the rearranged laser beams are parallel to each other. further,
A converging lens that is arranged corresponding to each of the plurality of laser diode arrays and converges a laser beam emitted from the laser diode array in a virtual plane perpendicular to the major axis direction;
The converging lens, the rearrangement optical system, and the propagation optical system are configured so that an emission surface of a laser beam of the laser diode array is an object held on the stage with respect to a virtual plane orthogonal to the major axis direction. The laser irradiation apparatus according to claim 1, wherein an image is formed at the same location on the surface.

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