WO2012002155A1 - Laser lift-off method and laser lift-off apparatus - Google Patents

Laser lift-off method and laser lift-off apparatus Download PDF

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Publication number
WO2012002155A1
WO2012002155A1 PCT/JP2011/063777 JP2011063777W WO2012002155A1 WO 2012002155 A1 WO2012002155 A1 WO 2012002155A1 JP 2011063777 W JP2011063777 W JP 2011063777W WO 2012002155 A1 WO2012002155 A1 WO 2012002155A1
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Prior art keywords
laser
substrate
material layer
workpiece
laser beam
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PCT/JP2011/063777
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French (fr)
Japanese (ja)
Inventor
僚三 松田
恵司 鳴海
田中　一也
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ウシオ電機株式会社
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Publication of WO2012002155A1 publication Critical patent/WO2012002155A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/26—Bombardment with radiation
    • H01L21/263—Bombardment with radiation with high-energy radiation
    • H01L21/268—Bombardment with radiation with high-energy radiation using electromagnetic radiation, e.g. laser radiation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
    • B23K26/3568—Modifying rugosity
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/50—Working by transmitting the laser beam through or within the workpiece
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/50—Working by transmitting the laser beam through or within the workpiece
    • B23K26/57—Working by transmitting the laser beam through or within the workpiece the laser beam entering a face of the workpiece from which it is transmitted through the workpiece material to work on a different workpiece face, e.g. for effecting removal, fusion splicing, modifying or reforming
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
    • C30B33/06—Joining of crystals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
    • H01L21/0271—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers
    • H01L21/0272—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers for lift-off processes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/005—Processes
    • H01L33/0093—Wafer bonding; Removal of the growth substrate

Definitions

  • the present invention decomposes the material layer by irradiating the material layer formed on the substrate with a laser beam, and peels the material layer from the substrate (hereinafter referred to as the following).
  • the present invention relates to a laser lift-off method and a laser lift-off apparatus.
  • the material layer is formed by irradiating the laser beam so that each laser beam irradiated on the adjacent irradiation region on the workpiece is superimposed while changing the laser beam irradiation region on the workpiece.
  • the present invention relates to a laser lift-off method and a laser lift-off device for peeling from a substrate.
  • the GaN-based compound crystal layer may not have sufficient strength to withstand shear stress due to N 2 gas generation. Cracks are easily generated. Furthermore, cracks may propagate not only to the GaN-based compound crystal layer but also to the crystal layer formed thereon, and the device itself may be destroyed, which is a problem when forming a micro-sized device. Yes.
  • Patent Document 2 discloses that a street for separating a GaN layer formed on a sapphire substrate so as to correspond to a chip of a semiconductor light emitting device is formed, and a sapphire substrate and A technique for relieving residual stress generated at the interface with the GaN layer by the street is disclosed.
  • the GaN layer is divided into small areas, minimizing the effects of residual stress from the surroundings, and the small area itself has minimal residual stress, during laser lift-off. It is said that cracks in the GaN layer can be reduced.
  • each laser light irradiation region necessarily overlaps each end, but if each laser light irradiation region overlaps on the surface of the GaN layer (that is, the portion other than the street), This is because the energy of the laser light applied to the overlapped region becomes excessive, which may adversely affect the GaN layer.
  • the width of the streets must be increased to some extent in order to relieve the residual stress described above. By doing so, a semiconductor light emitting device collected from one sapphire substrate There is a problem that the number of chips decreases.
  • the laser light irradiation region and the GaN layer formed on the sapphire substrate are accurately aligned so that the edge of the laser light irradiation region coincides with the street. It becomes necessary to do. Therefore, when the street width is reduced, it becomes difficult to accurately align the edge portion of the laser light irradiation area on the street formed in the GaN layer, and the apparatus configuration for alignment becomes complicated. Or the operation and management becomes difficult. Furthermore, since it is necessary to perform the above-described alignment every time the chip size of the semiconductor light emitting element is different, there arises a problem that the laser lift-off process becomes extremely complicated.
  • Patent Document 3 discloses a sapphire substrate 121 and a GaN-based compound crystal as shown in FIG. 11 for the purpose of reducing cracks in the GaN layer without forming the street as described above in the GaN layer.
  • the laser beam 124 is shaped so that the irradiation region 123 to the interface of the layer 122 has a line shape, and the sapphire substrate 121 is moved in a direction perpendicular to the longitudinal direction of the laser beam 124.
  • a technique for irradiating from the back surface is disclosed.
  • the laser light 124 is shaped so as to have a line width less than or equal to the resolution of the optical system, so that the light intensity distribution in the line width direction of the laser light 124 is substantially at the center as shown in FIG. It has been described that it has a peak and becomes gentle toward the edge from the peak. According to this document, by shaping the laser beam 124 as described above, abrupt laser ablation is performed in the irradiation region that hits the edge in the line width direction of the laser beam 124 when the crystal layer 122 is irradiated with the laser beam 124. Is not done.
  • a first object of the present invention is to cause a crystal layer (hereinafter referred to as a material layer) formed on a substrate to not crack.
  • a second object of the present invention is to provide a sufficient laser energy to peel the material layer from the substrate so that the material layer formed on the substrate is not cracked and the material layer is formed on the substrate. It is an object to provide a laser lift-off method and a laser lift-off device that can peel the material layer from the substrate without causing problems such as re-adhesion.
  • a sapphire substrate (hereinafter referred to as a workpiece) on which a material layer is formed or a laser source is scanned, and the material layer is usually irradiated with laser light while changing the irradiation region of the laser beam on the workpiece.
  • the material layer is usually irradiated with laser light while changing the irradiation region of the laser beam on the workpiece.
  • the edge portions of the irradiation regions of the adjacent laser beams on the workpiece are necessarily overlapped.
  • how the laser beams are superimposed is extremely important. This will be described with reference to FIG.
  • a laser source that emits pulsed laser light is used, and the laser light is irradiated so that the irradiation region of the laser light changes every moment. That is, with reference to FIG. 2 described later, after irradiating the laser beam to the irradiation region S1 of the pulse laser beam, the workpiece or the laser source is conveyed and the next region S2 is irradiated with the laser beam. At this time, the respective edge portions of the irradiation regions S1 and S2 of the pulse laser beam are overlapped.
  • the irradiation amount of the pulse laser light irradiated to each of the irradiation regions S1 and S2 is not integrated for the following reason. This is because when the irradiation region is shifted from S1 to S2 after the irradiation region S1 is irradiated with the laser beam, the time required for the temperature of the GaN in the irradiation region S1 to fall to the room temperature level is reduced from S1 to S2. It is considered that this is because the temperature in the region S1 has already been lowered to the room temperature level because it is much shorter than the time required to shift to.
  • the time required for the temperature of the GaN in the irradiation region S1 to fall to the room temperature level is within 100 microseconds. Even if the irradiation region S2 is irradiated with the laser beam in a state where the temperature of the irradiation region S1 is lowered to the room temperature level, the region ST in which the irradiation regions S1 and S2 are superimposed is heated by the laser beam irradiated to the irradiation region S2. Only.
  • the irradiation amount of the pulse laser light irradiated to each of the irradiation regions S1 and S2 is not integrated, so the pulses irradiated to the regions S1 and S2 respectively. It is necessary to superimpose the laser light in an energy region exceeding the decomposition threshold of the material layer.
  • the intensity of the laser beam in the region where each laser beam is superimposed be VE ⁇ 1.15 or less with respect to the decomposition threshold VE necessary for peeling the material layer from the substrate.
  • the intensity of the laser beam in the region where the laser beams overlap is not too high.
  • [intensity of laser beam (maximum value) in region where laser beam is superimposed (maximum value)] / [decomposition threshold value VE] is defined as superposition degree T
  • the material layer formed on the substrate is cracked.
  • the superposition degree T is 1 ⁇ T, and in order to avoid re-adhesion between the substrate and the material layer, T ⁇ 1.15. It is desirable to do.
  • the above-described problem is solved as follows.
  • the pulse Laser light is irradiated so that each irradiation region adjacent to the workpiece overlaps while changing the irradiation region on the workpiece, and the size of each overlapping pulse laser beam peels the material layer from the substrate.
  • the amount of energy exceeds the decomposition threshold necessary for the reduction.
  • the decomposition necessary for peeling the material layer from the substrate is performed on the intensity of the laser beam in the region where the laser beams irradiated to the adjacent irradiation regions in the workpiece are superimposed.
  • VE ⁇ 1.15 or less with respect to the threshold value VE.
  • (3) In the above (1) and (2), a first transport operation for transporting the workpiece in the first transport direction and a second transport for transporting the workpiece in a direction orthogonal to the transport direction of the first transport operation. An operation and a third transport operation for transporting in a direction 180 ° different from the transport direction of the first transport operation are sequentially performed, and the pulse laser beam is sequentially irradiated to each irradiation region.
  • a laser optical system having a projection lens for shaping pulse laser light emitted from a laser source and irradiating the work is provided, and the light incident surface of the work is It arrange
  • each laser beam is irradiated so as to be superimposed. In this region, sufficient laser energy is applied to peel the material layer from the substrate, so that the material layer can be reliably peeled from the substrate without causing cracks in the material layer formed on the substrate.
  • the intensity of the laser beam in the region where the laser beams irradiated to the adjacent irradiation regions are overlapped is VE ⁇ 1 with respect to the decomposition threshold VE necessary for peeling the material layer from the substrate.
  • the beam profile of the pulsed laser light applied to the work has a gentle shape.
  • the illuminance distribution at the peripheral edge of the pulsed laser light to be irradiated has a shape that gradually decreases from the peak portion toward the edge portion).
  • FIG. 1 is a conceptual diagram illustrating an outline of laser lift-off processing according to an embodiment of the present invention.
  • the laser lift-off process is performed as follows.
  • a work 3 in which a material layer 2 is formed on a substrate 1 that transmits laser light is placed on a work stage 31.
  • the work stage 31 on which the work 3 is placed is placed on a transport mechanism 32 such as a conveyor, and is transported by the transport mechanism 32 at a predetermined speed.
  • the workpiece 3 is irradiated with a pulse laser beam L emitted from a pulse laser source (not shown) through the substrate 1 while being conveyed in the direction of arrow ABC in the figure together with the workpiece stage 31.
  • the workpiece 3 is formed by forming a material layer 2 of a GaN (gallium nitride) compound on the surface of a substrate 1 made of sapphire.
  • the substrate 1 may be any material as long as it can form a GaN-based compound material layer satisfactorily and transmits laser light having a wavelength necessary for decomposing the GaN-based compound material layer.
  • a GaN-based compound is used for the material layer 2 in order to efficiently output high-output blue light with low input energy.
  • the laser beam should be appropriately selected according to the substrate 1 and the substance constituting the material layer peeled from the substrate 1.
  • a KrF (krypton fluorine) excimer laser that emits a wavelength of 248 nm can be used.
  • the light energy at the laser wavelength of 248 nm is between the band gap of GaN (3.4 eV) and the band gap of sapphire (9.9 eV). Therefore, a laser beam having a wavelength of 248 nm is desirable for peeling the material layer of the GaN-based compound from the sapphire substrate.
  • FIG. 2 is a diagram illustrating a state in which the laser beam L is applied to the workpiece 3.
  • 2A shows a method of irradiating the workpiece 3 with the laser beam
  • FIG. 2B shows an enlarged view of a portion X in FIG. 2A
  • FIG. 2 shows an example of a cross-section of the light intensity distribution of laser light irradiated on each of the irradiation regions.
  • the solid line on the workpiece 3 shown in FIG. 2 is merely a virtual representation of the laser light irradiation area.
  • the workpiece 3 is repeatedly conveyed in the directions of arrows HA, HB, and HC shown in FIG.
  • the laser beam L is applied from the back surface of the sapphire substrate 1 and is applied to the interface between the substrate 1 and the material layer 2.
  • the shape of the laser beam L is formed into a substantially square shape.
  • the workpiece 3 corresponds to the size of the workpiece itself, and the first conveyance operation HA is conveyed in the direction of arrow A in FIG. 1 and the irradiation region S of one shot of laser light.
  • the third transport operation HC transported in the direction of arrow B is sequentially executed.
  • the transport directions of the first transport operation HA and the third transport operation HC differ by 180 °.
  • the optical system of the laser light remains fixed and is not transported. That is, when only the workpiece 3 is transported with the laser beam optical system fixed, the irradiation region of the laser beam L on the workpiece 3 is relatively relatively momentarily in the order of S1 to S12 as shown by the arrows in FIG. Will change.
  • the workpiece 3 has a circular outline, but the laser light irradiation area has a substantially rectangular shape, and a laser irradiation method for such a rectangular irradiation area will be described.
  • the laser beam is radiated once for each of the four irradiation areas S1, S2, S3, and S4 while transferring the workpiece 3 in the HA direction in FIG. . This is the first transport operation.
  • the workpiece 3 is transported in the HB direction in FIG. 2 in order to irradiate the next irradiation region S5 of the workpiece 3 with the laser light.
  • the distance by which the workpiece 3 is conveyed in the direction of the arrow HB is equal to the distance obtained by subtracting the overlapping area ST from the distance corresponding to the irradiation area for one shot (one pulse) of the pulse laser beam.
  • the laser beam is irradiated once for each of the six irradiation areas S5, S6, S7, S8, S9, and S10, a total of six times. to.
  • This is the third transport operation.
  • the laser beam is irradiated over the entire area of the workpiece 3 by conveying the workpiece 3 according to the above-described series of procedures.
  • the laser light irradiation area moves relatively in the order of S1, S2, and S3.
  • Each irradiation area is, for example, 0.5 mm ⁇ 0.5 mm, and the area is 0.25 mm. 2 .
  • the area of the work 3 is 4560 mm 2 . That is, the laser light irradiation areas S1, S2, and S3 are much smaller than the work area.
  • a laser beam in an irradiation area smaller than that of the workpiece 3 is irradiated to the workpiece 3 while scanning in the directions of arrows A and B shown in FIG.
  • the laser optical system may be transported in accordance with the transport operations HA or HC described above while the workpiece is fixed.
  • the laser beam may be irradiated to the workpiece so that the irradiation region of the laser beam on the workpiece changes with time.
  • the workpiece 3 is irradiated so that the end portions in the width direction overlap each other.
  • the laser beam L is a pulsed laser beam and is intermittently applied to the workpiece 3.
  • the width in which the laser light is superimposed is, for example, 0.1 mm.
  • the pulse interval of the laser light is appropriately set in consideration of the conveyance speed of the workpiece 3 and the width of the overlapping region ST of the laser beam irradiated on the adjacent irradiation regions S1, S2, S3,.
  • the pulse interval of the laser beam is determined so that the workpiece is not irradiated with the laser beam before the workpiece 3 moves to the next irradiation region. That is, the pulse interval of the laser beam is set longer than the time required for the work 3 to move a distance corresponding to the irradiation region for one shot of the laser beam.
  • the pulse interval of the laser light is 0.004 seconds (250 Hz).
  • FIG. 3 is a diagram showing the light intensity distribution of the laser beam irradiated on the workpiece so as to overlap the regions S1 and S2 adjacent to each other of the workpiece 3 shown in FIG. 2, and aa ′ in FIG. It is line sectional drawing.
  • the vertical axis indicates the intensity (energy value) of the laser beam irradiated to each irradiation area of the workpiece
  • the horizontal axis indicates the conveyance direction of the workpiece.
  • L1 and L2 indicate the profiles of the laser beams irradiated to the workpiece irradiation areas S1 and S2, respectively.
  • the laser beams L1 and L2 are not irradiated at the same time, but the laser beam L2 is irradiated after one pulse interval from the irradiation of the laser beam L1.
  • the cross sections of the laser beams L1 and L2 are formed in a substantially trapezoidal shape having a flat surface on the top (peak energy PE) following the edge portion LE that gently spreads in the circumferential direction.
  • the laser beams L1 and L2 are superimposed in an energy region exceeding a decomposition threshold VE necessary for decomposing and separating the material layer of the GaN-based compound from the sapphire substrate, as indicated by broken lines in FIG.
  • the intensity (energy value) CE of the laser beam at the intersection position C between the laser beams L1 and L2 is set to a value exceeding the decomposition threshold value VE. This is because, as described above, when the irradiation region is shifted from S1 to S2 after irradiating the irradiation region S1 of FIG. 2 with the laser beam, the temperature of the region S1 is already lowered to the room temperature level.
  • the irradiation amount of the pulse laser light irradiated to each of the irradiation regions S1 and S2 is not integrated.
  • the degree of superimposition T defined in the paragraph 0011 is preferably 1 ⁇ T.
  • the pulse interval of the laser beam is adjusted in advance so that the laser beam applied to the adjacent irradiation region of the workpiece 3 is superimposed as described above with respect to the relative movement amount of the workpiece 3 and the laser beam.
  • the decomposition threshold is 500 to 1500 J / cm 2 .
  • the decomposition threshold VE needs to be set for each substance constituting the material layer.
  • the laser beams L1 and L2 are superimposed in an energy region exceeding the decomposition threshold value VE. It is necessary to set the ratio of the size of each laser beam to the decomposition threshold VE to an appropriate value. Specifically, the ratio is set to be VE ⁇ 1.15 or less with respect to the decomposition threshold VE. Was found to be desirable.
  • the intensity (energy value) CE of the laser beam at the intersection position C of the laser beams L1 and L2 in the light intensity distribution of each laser beam is necessary for peeling the material layer from the substrate. It sets so that it may become VEx1.15 or less to decomposition threshold VE. That is, it is desirable that the degree of superimposition T is T ⁇ 1.15.
  • FIG. 4 is a conceptual diagram of a laser lift-off device according to an embodiment of the present invention.
  • a laser lift-off device 10 includes a laser source 20 that emits the above-described pulsed laser light, a laser optical system 40 for shaping the laser light into a predetermined shape, and a work stage 31 on which a work 3 is placed. And a transport mechanism 32 that transports the work stage 31, and a control unit 33 that controls the irradiation interval of the laser light generated by the laser source 20 and the operation of the transport mechanism 32.
  • the optical system 40 includes cylindrical lenses 41 and 42, a mirror 43 that reflects laser light in the direction of the workpiece, a mask 44 for shaping the laser light into a predetermined shape, and a laser beam L that has passed through the mask 44 as a workpiece. 3 is provided with a projection lens 45 for condensing the light.
  • a work 3 is disposed at the tip of the optical system 40. The work 3 is placed on the work stage 31. The work stage 31 is placed on the transport mechanism 32 and is transported by the transport mechanism 32. As a result, the workpiece 3 is sequentially conveyed in the directions of arrows A, B, and C shown in FIG. 1, and the irradiation region of the laser beam on the workpiece 3 changes every moment.
  • the control unit 33 controls the pulse interval of the pulsed laser light generated by the laser source 20 so that the degree of superimposition of each laser light irradiated on the irradiation region adjacent to the workpiece 3 becomes a desired value.
  • the laser light L generated from the laser source 20 is, for example, a KrF excimer laser that generates ultraviolet light having a wavelength of 248 nm.
  • An ArF laser or a YAG laser may be used as the laser source.
  • the light incident surface 3A of the work 3 is disposed farther in the optical axis direction of the laser light than the focal point F of the projection lens 45, or on the contrary, in the optical axis direction of the laser light, the work 3
  • the light incident surface 3 ⁇ / b> A may be disposed closer to the projection lens 45 than the focal point F of the projection lens 45.
  • the edge portions LE of the beam profiles of the laser beams L1 and L2 as shown in FIG. A laser beam having a light intensity distribution with a trapezoidal cross section is obtained.
  • the laser light L generated by the laser source 20 passes through the cylindrical lenses 41 and 42, the mirror 43, and the mask 44, and is then condensed on the work 3 by the projection lens 45.
  • Laser light incident on the light incident surface 3A of the workpiece 3 by the projection lens 45 is substantially trapezoidal light having a flat surface on the top following the edge portion LE that gently spreads in the circumferential direction in the cross section shown in FIG. Molded to have an intensity distribution.
  • FIG. 5 shows another embodiment of the light intensity distribution of the laser light applied to the workpiece.
  • the light intensity distribution of the laser light shown in FIG. 5A is formed in a substantially mountain shape having a peak at the center and an edge portion LE that gently spreads after the peak.
  • the light intensity distribution of the laser light can be changed as appropriate by adjusting the distance between the focal point F of the projection lens 45 and the light incident surface 3A of the workpiece 3 shown in FIG.
  • the light intensity distribution of the laser light becomes a sharp rectangular shape as the distance between the focal point F of the projection lens 45 and the light incident surface 3A of the workpiece 3 approaches, and the focal point F of the projection lens 45 and the light incident surface 3A of the workpiece 3 become smaller. As the distance increases, the edges are gently formed and formed in a mountain shape. Further, as shown in FIG. 5B, the light intensity distribution of the laser beams L1 and L2 may be rectangular. In this case, the intensity of the laser beam in the region where the laser beams L1 and L2 overlap (the intensity of the laser beam at the intersection of the laser beams L1 and L2, which corresponds to the peak value of the laser beam L1 in this case).
  • FIG. 3 shows the light intensity distribution of the laser light used in the laser lift-off method of this embodiment
  • FIG. 6 shows the light intensity distribution of the laser light for comparison with this.
  • L1 and L2 in FIGS. 3 and 6 indicate laser beams irradiated to the irradiation areas of S1 and S2 shown in FIG.
  • the influence of the degree of superimposition of the laser light applied to the irradiation area adjacent to the workpiece on the material layer after peeling from the substrate will be compared and examined with reference to FIGS.
  • the laser lift-off method of the embodiment of FIG. 3 when the surface of the material layer 2 on the interface side with the substrate 1 is irradiated with laser light and the GaN constituting the material layer 2 is decomposed, the N 2 gas rapidly It does not occur. Moreover, in the laser lift-off method of the embodiment of FIG. 3, the energy of the laser beam irradiated to the overlapping region ST where the laser beams L1 and L2 overlap in FIG.
  • the problem that the material layer 2 and the substrate 1 are re-adhered can be avoided, and the material layer 2 can be reliably peeled from the substrate 1.
  • the workpiece was actually irradiated with the laser beam of the embodiment shown in FIG. 3, the surface state of the material layer after peeling was very clean, and no material that adversely affects the light emission characteristics such as dirt and scratches was found.
  • the undecomposed region of GaN coincided with the overlapping region ST where the laser beams L1 and L2 overlap on the workpiece.
  • the workpiece is irradiated with the laser beam shown in the comparative example of FIG. 6B, since the degree of superimposition T of the laser beams L1 and L2 is too large, the laser beams L1 and L2 in the workpiece shown in FIG. There is a problem that a laser beam with excessive energy is irradiated onto the superposition region ST.
  • FIG. 7B-4 which will be described later, when the workpiece is actually irradiated with the laser light of the comparative example shown in FIG. A large number of such stains are formed.
  • the material layer once peeled off from the substrate is re-adhered by the second laser beam when the high-energy laser beam is irradiated twice at the same location, and the sapphire component constituting the substrate is It is thought that it adhered.
  • the black spot formed on the surface of the material layer has an adverse effect on the light emission characteristics.
  • FIG. 7 is a diagram showing the results.
  • FIG. 7 (a) is a diagram showing the light intensity distribution of the laser beam irradiated in an overlapping manner used in the experiment. In this experiment, as shown in the figure, the light intensity distribution has a rectangular shape.
  • Laser beams L1 and L2 pulse laser beams output from a KrF laser were irradiated to a work in which a GaN material layer was formed on a sapphire substrate.
  • the intensity of the laser beam in the region where the laser beams L1 and L2 overlap is changed to 105%, 110%, 115%, and 120% with respect to the decomposition threshold value VE (870 mJ / cm 2 ) of the GaN material layer.
  • the surface of the material layer after peeling was examined. 7 (b-1), (b-2), (b-3), and (b-4), the intensity of the laser beam in the overlapping region is 105%, 110%, and 115 with respect to the decomposition threshold VE, respectively.
  • % And 120% indicate the surface of the material layer after peeling. As shown in FIGS.
  • the laser beams L1 and L2 having a rectangular light intensity distribution are used.
  • the adjustment of the intensity of the laser beam in the overlapping region, which cannot be adjusted, must be performed by adjusting the intensity of the laser beams L1 and L2.
  • the light intensity distribution (beam profile) of the laser beams L1 and L2 has a shape having an edge LE that gently spreads in the circumferential direction as shown in FIG.
  • FIG. 8 (b-1) shows a case where the overlapping amount of the laser beams L1 and L2 is appropriate, and a case where the irradiation interval (or the moving speed of the workpiece) is appropriately adjusted, and is shown in FIG. 8 (b-2).
  • the surface state of the material layer after peeling was good, and no material that adversely affects the light emission characteristics such as dirt and scratches was found.
  • FIG. 8C-1 shows a case where the overlapping amount of the laser beams L1 and L2 is large, and the intensity of the laser beam in the overlapping region exceeds 115% with respect to the decomposition threshold VE.
  • the surface of the material layer after peeling had many stains such as black spots.
  • the laser optical system 40 shown in FIG. 4 causes the laser light 107 to have a substantially trapezoidal light intensity distribution having a flat surface on the top following the edge portion LE that gently spreads in the circumferential direction in the cross section shown in FIG.
  • the laser optical system 40 shown in FIG. 4 causes the laser light 107 to have a substantially trapezoidal light intensity distribution having a flat surface on the top following the edge portion LE that gently spreads in the circumferential direction in the cross section shown in FIG.
  • the laser beam is superimposed so that the laser beam irradiated to the adjacent irradiation region of the GaN layer 102 has an appropriate degree of superimposition.
  • the energy of the laser light applied to the edge portion of each irradiation region of the laser light of the GaN layer 102 is sufficient for peeling the GaN layer 102, and the GaN layer 102 is surely peeled from the sapphire substrate 101. be able to.
  • a method for manufacturing a semiconductor light emitting device to which the above-described laser lift-off process can be applied will be described.
  • the manufacturing method of the semiconductor light-emitting device formed of a GaN-based compound material layer will be described with reference to FIG.
  • a sapphire substrate capable of crystal growth of a gallium nitride (GaN) compound semiconductor that transmits laser light and forms a material layer is used.
  • GaN gallium nitride
  • FIG. 9A a GaN layer 102 made of a GaN-based compound semiconductor is rapidly formed on a sapphire substrate 101 by using, for example, a metal organic chemical vapor deposition method (MOCVD method). Subsequently, as illustrated in FIG.
  • MOCVD method metal organic chemical vapor deposition method
  • an n-type semiconductor layer 103 and a p-type semiconductor layer 104 that are light emitting layers are stacked on the surface of the GaN layer 102.
  • GaN doped with silicon is used as the n-type semiconductor
  • GaN doped with magnesium is used as the p-type semiconductor.
  • solder 105 is applied on the p-type semiconductor layer 104.
  • the support substrate 106 is attached on the solder 105.
  • the support substrate 106 is made of, for example, an alloy of copper and tungsten. Then, as shown in FIG.
  • the sapphire substrate 101 is decomposed by irradiating the laser beam 107 from the back surface side of the sapphire substrate 101 toward the interface between the sapphire substrate 101 and the GaN layer 102 to decompose the GaN layer 102. Peel off.
  • ITO 108 which is a transparent electrode is formed on the surface of the GaN layer 102 after peeling from the sapphire substrate 101 by vapor deposition, and the electrode 109 is attached to the surface of the ITO 108.

Abstract

Disclosed are a laser lift-off method and a laser lift-off apparatus, wherein a material layer formed on a substrate can be peeled from the substrate without generating cracks in the material layer formed on the substrate. In order to peel the material layer (2) from the substrate (1) at the interface between the substrate and the material layer, a pulsed laser beam is applied, through the substrate (1), to a work (3) wherein the material layer (2) is formed on the substrate (1), while constantly changing the irradiation region on the work (3), such that adjacent irradiation regions of the work (3) overlap each other. Respective laser beams in the overlapping irradiation region are set at levels having energy that exceeds a decomposition threshold value needed to peel the material layer (2) from the substrate (1), thereby having the material layer reliably peeled from the substrate without generating cracks in the material layer formed on the substrate.

Description

レーザリフトオフ方法及びレーザリフトオフ装置Laser lift-off method and laser lift-off apparatus
　本発明は、化合物半導体により形成される半導体発光素子の製造プロセスにおいて、基板上に形成された材料層にレーザ光を照射することによって、当該材料層を分解して当該基板から剥離する（以下、レーザリフトオフという）ためのレーザリフトオフ方法及びレーザリフトオフ装置に関する。
　特に、本発明は、ワーク上のレーザ光照射領域を刻々と変えながら、ワーク上の隣接する照射領域に照射される各レーザ光が重畳するようにしてレーザ光を照射することにより、材料層を基板から剥離するレーザリフトオフ方法及びレーザリフトオフ装置に関するものである。 In the manufacturing process of a semiconductor light emitting device formed of a compound semiconductor, the present invention decomposes the material layer by irradiating the material layer formed on the substrate with a laser beam, and peels the material layer from the substrate (hereinafter referred to as the following). The present invention relates to a laser lift-off method and a laser lift-off apparatus.
In particular, according to the present invention, the material layer is formed by irradiating the laser beam so that each laser beam irradiated on the adjacent irradiation region on the workpiece is superimposed while changing the laser beam irradiation region on the workpiece. The present invention relates to a laser lift-off method and a laser lift-off device for peeling from a substrate.
　ＧａＮ（窒化ガリウム）系化合物半導体により形成される半導体発光素子の製造プロセスにおいて、サファイア基板の上に形成されたＧａＮ系化合物結晶層を当該サファイア基板の裏面からレーザ光を照射することにより剥離するレーザリフトオフの技術が知られている。
　例えば、特許文献１においては、サファイア基板の上にＧａＮ層を形成し、当該サファイア基板の裏面からレーザ光を照射することにより、ＧａＮ層を形成するＧａＮが分解され、当該ＧａＮ層をサファイア基板から剥離する技術について記載されている。
　ところで、サファイア基板の上に形成されたＧａＮ系化合物結晶層を当該サファイア基板の裏面からレーザ光を照射することにより剥離するためには、ＧａＮ系化合物をＧａとＮ２とに分解するために必要な分解閾値以上の照射エネルギーを有するレーザ光を照射することが重要になる。
　ここで、レーザ光を照射した際には、ＧａＮが分解することによりＮ２ガスが発生することから、当該ＧａＮ層にせん断応力が加わり、当該レーザ光の照射領域の境界部においてクラックが生じる場合がある。例えば、図１０に示すように、レーザ光の１ショットの照射領域１１０が正方形状である場合、ＧａＮ層１１１のレーザ光の照射領域の境界１１２にクラックが発生してしまう問題がある。 Laser for peeling a GaN-based compound crystal layer formed on a sapphire substrate by irradiating laser light from the back surface of the sapphire substrate in a manufacturing process of a semiconductor light-emitting device formed of a GaN (gallium nitride) -based compound semiconductor Lift-off technology is known.
For example, in Patent Document 1, a GaN layer is formed on a sapphire substrate, and laser light is irradiated from the back surface of the sapphire substrate, whereby GaN forming the GaN layer is decomposed, and the GaN layer is separated from the sapphire substrate. A technique for peeling is described.
By the way, in order to peel off the GaN compound crystal layer formed on the sapphire substrate by irradiating laser light from the back surface of the sapphire substrate, it is necessary to decompose the GaN compound into Ga and N 2. It is important to irradiate a laser beam having an irradiation energy equal to or higher than a decomposition threshold.
Here, when laser light is irradiated, N 2 gas is generated by decomposition of GaN, so that a shear stress is applied to the GaN layer, and a crack occurs at the boundary of the laser light irradiation region. There is. For example, as shown in FIG. 10, when the irradiation region 110 of one shot of laser light is square, there is a problem that a crack occurs at the boundary 112 of the irradiation region of the GaN layer 111.
　特に、数μｍ以下の厚みのＧａＮ系化合物結晶層を用いて素子を形成する場合には、ＧａＮ系化合物結晶層がＮ２ガス発生によるせん断応力に耐えるための十分な強度を有しない場合もあり、容易にクラックが発生してしまう。更に、ＧａＮ系化合物結晶層のみならず、その上に形成された結晶層にクラックが伝播し、素子そのものが破壊されてしまう場合もあり、微小なサイズの素子を形成する際の問題となっている。
　かかる問題に対して特許文献２には、サファイア基板上に形成されたＧａＮ層を半導体発光素子のチップに対応するよう分離するためのストリートを形成し、レーザリフトオフの工程を実行中にサファイア基板とＧａＮ層との界面で発生する残留応力を、当該ストリートによって緩和する技術が開示されている。
　同文献によれば、ＧａＮ層を小領域に分断し、周囲からの残留応力による影響を最小にし、また、小領域自体は最小の残留応力しか有しないようにすることによって、レーザリフトオフの最中におけるＧａＮ層の割れを低減することができる、とされている。 In particular, when an element is formed using a GaN-based compound crystal layer having a thickness of several μm or less, the GaN-based compound crystal layer may not have sufficient strength to withstand shear stress due to N 2 gas generation. Cracks are easily generated. Furthermore, cracks may propagate not only to the GaN-based compound crystal layer but also to the crystal layer formed thereon, and the device itself may be destroyed, which is a problem when forming a micro-sized device. Yes.
With respect to such a problem, Patent Document 2 discloses that a street for separating a GaN layer formed on a sapphire substrate so as to correspond to a chip of a semiconductor light emitting device is formed, and a sapphire substrate and A technique for relieving residual stress generated at the interface with the GaN layer by the street is disclosed.
According to the document, the GaN layer is divided into small areas, minimizing the effects of residual stress from the surroundings, and the small area itself has minimal residual stress, during laser lift-off. It is said that cracks in the GaN layer can be reduced.
　このように、ＧａＮ層にストリート（チップ分離用境界線：スクライブライン）を形成してレーザリフトオフの工程を実行するときには、特許文献２のＦｉｇ．１３に示すように、レーザ光の照射領域のエッジ部が当該ストリートに一致するようにレーザ光を照射することが好ましい。これは、各レーザ光の照射領域は必然的にそれぞれの端部同士が重畳することになるが、各レーザ光の照射領域がＧａＮ層の表面（つまり、ストリート以外の部分）において重畳すると、当該重畳した領域に照射されるレーザ光のエネルギーが過大になるため、ＧａＮ層に悪影響を生じるおそれがあるからである。 As described above, when the street (chip separation boundary: scribe line) is formed in the GaN layer and the laser lift-off process is performed, the method described in FIG. As shown in FIG. 13, it is preferable to irradiate the laser beam so that the edge portion of the irradiation region of the laser beam coincides with the street. This is because each laser light irradiation region necessarily overlaps each end, but if each laser light irradiation region overlaps on the surface of the GaN layer (that is, the portion other than the street), This is because the energy of the laser light applied to the overlapped region becomes excessive, which may adversely affect the GaN layer.
　しかしながら、ＧａＮ層にストリートを形成した場合は、前記した残留応力を緩和するためにストリートの幅をある程度大きくしなければならないが、そうすることによって、１枚のサファイア基板から採取される半導体発光素子のチップの個数が減少するという問題がある。
　而して、ＧａＮ層にストリートを形成した場合は、レーザ光の照射領域のエッジ部がストリートに一致するように、レーザ光の照射領域とサファイア基板上に形成されたＧａＮ層とを精度良くアライメントすることが必要になる。したがって、ストリートの幅を小さくした場合は、レーザ光の照射領域のエッジ部をＧａＮ層に形成されたストリート上に精度良くアライメントすることが困難になり、アライメントのための装置構成が複雑になるばかりか、その操作・管理が難しくなる。
　さらには、半導体発光素子のチップサイズが相違する毎に、上記したアライメントを行うことが必要になるため、レーザリフトオフの工程が極めて複雑化するといった問題が生じる。 However, when streets are formed in the GaN layer, the width of the streets must be increased to some extent in order to relieve the residual stress described above. By doing so, a semiconductor light emitting device collected from one sapphire substrate There is a problem that the number of chips decreases.
Thus, when streets are formed in the GaN layer, the laser light irradiation region and the GaN layer formed on the sapphire substrate are accurately aligned so that the edge of the laser light irradiation region coincides with the street. It becomes necessary to do. Therefore, when the street width is reduced, it becomes difficult to accurately align the edge portion of the laser light irradiation area on the street formed in the GaN layer, and the apparatus configuration for alignment becomes complicated. Or the operation and management becomes difficult.
Furthermore, since it is necessary to perform the above-described alignment every time the chip size of the semiconductor light emitting element is different, there arises a problem that the laser lift-off process becomes extremely complicated.
　一方、特許文献３には、上記のようなストリートをＧａＮ層に形成することなく、ＧａＮ層の割れを低減することを目的として、図１１に示すように、サファイア基板１２１とＧａＮ系化合物の結晶層１２２の界面への照射領域１２３がライン状になるようにレーザ光１２４を成形し、サファイア基板１２１をレーザ光１２４の長手方向と垂直方向に移動させながら、当該レーザ光１２４をサファイア基板１２１の裏面から照射する技術が開示されている。同文献には、レーザ光１２４が光学系の解像度以下のライン幅になるように成形されていることにより、図１２に示すように、レーザ光１２４のライン幅方向の光強度分布が、略中央にピークを有し当該ピークからエッジ部に向けてなだらかになっていることが記載されている。
　同文献によれば、レーザ光１２４を上記のように成形することにより、レーザ光１２４を結晶層１２２に照射した際のレーザ光１２４のライン幅方向のエッジ部に当る照射領域で急激なレーザアブレーションが行われない。したがって、ＧａＮ層である結晶層１２２の分解時にＮ２が急激に発生することがないので、過剰な応力が結晶層１２２に加わらず、結晶層１２２及びその上に形成される素子へのクラック発生を低減することができる、とされている。
　しかしながら、本発明者らが上記特許文献３に開示されるレーザリフトオフ工程を検証したところ、ＧａＮ層である結晶層に発生する割れを低減する効果は、必ずしも十分でないことが確認された。 On the other hand, Patent Document 3 discloses a sapphire substrate 121 and a GaN-based compound crystal as shown in FIG. 11 for the purpose of reducing cracks in the GaN layer without forming the street as described above in the GaN layer. The laser beam 124 is shaped so that the irradiation region 123 to the interface of the layer 122 has a line shape, and the sapphire substrate 121 is moved in a direction perpendicular to the longitudinal direction of the laser beam 124. A technique for irradiating from the back surface is disclosed. In this document, the laser light 124 is shaped so as to have a line width less than or equal to the resolution of the optical system, so that the light intensity distribution in the line width direction of the laser light 124 is substantially at the center as shown in FIG. It has been described that it has a peak and becomes gentle toward the edge from the peak.
According to this document, by shaping the laser beam 124 as described above, abrupt laser ablation is performed in the irradiation region that hits the edge in the line width direction of the laser beam 124 when the crystal layer 122 is irradiated with the laser beam 124. Is not done. Therefore, since N 2 does not occur abruptly when the crystal layer 122 that is a GaN layer is decomposed, excessive stress is not applied to the crystal layer 122, and cracks are generated in the crystal layer 122 and elements formed thereon. It can be reduced.
However, when the present inventors verified the laser lift-off process disclosed in Patent Document 3 above, it was confirmed that the effect of reducing cracks generated in the crystal layer, which is a GaN layer, was not always sufficient.
特表２００１－５０１７７８号公報JP-T-2001-501778 特表２００７－５３４１６４号公報Special Table 2007-534164 特開２００３－１６８８２０号公報JP 2003-168820 A
　具体的に、本発明者らは、特許文献３に従って、サファイア基板上に形成された結晶層をライン状に成形されたレーザ光の長手方向と垂直な方向に移動させ、サファイア基板の移動速度及び間歇的に照射されるパルスレーザ光の照射間隔を適宜変更して、ライン状に成形したレーザ光を結晶層に照射したところ、結晶層であるＧａＮ層にクラックが生じることが確認された。
　本発明は、上記問題点を解決するためになされたものであって、本発明の第１の目的は、基板上に形成された結晶層（以下材料層と呼ぶ）に割れを生じさせることなく、当該基板から当該材料層を剥離することができるレーザリフトオフ方法およびレーザリフトオフ装置を提供することである。
　また、本発明の第２の目的は、材料層を基板から剥離させるために十分なレーザエネルギーを与えることで基板上に形成された材料層に割れを生じさせることなく、かつ、基板に材料層が再接着する等の不具合を生じさせることなく、当該基板から当該材料層を剥離することができるレーザリフトオフ方法およびレーザリフトオフ装置を提供することである。 Specifically, the inventors move the crystal layer formed on the sapphire substrate in a direction perpendicular to the longitudinal direction of the laser beam formed in a line according to Patent Document 3, and the movement speed of the sapphire substrate and It was confirmed that cracks were generated in the GaN layer as the crystal layer when the irradiation interval of the pulsed laser beam applied intermittently was appropriately changed and the crystal layer was irradiated with the laser beam formed in a line shape.
The present invention has been made to solve the above-described problems, and a first object of the present invention is to cause a crystal layer (hereinafter referred to as a material layer) formed on a substrate to not crack. It is another object of the present invention to provide a laser lift-off method and a laser lift-off device that can peel the material layer from the substrate.
In addition, a second object of the present invention is to provide a sufficient laser energy to peel the material layer from the substrate so that the material layer formed on the substrate is not cracked and the material layer is formed on the substrate. It is an object to provide a laser lift-off method and a laser lift-off device that can peel the material layer from the substrate without causing problems such as re-adhesion.
　レーザリフトオフでは、材料層が形成されたサファイア基板（以下、ワークという）或いはレーザ源をスキャンさせ、ワークに対するレーザ光の照射領域を刻々と変えながらレーザ光を材料層に照射することが通常行われる。それは、レーザ源から出射するレーザ光の照射領域をワークと同等の大きさにすることは困難だからである。このため、ワーク上の隣接する各レーザ光の照射領域のエッジ部は必然的に重畳することになるが、レーザリフトオフの工程では、いかにして各レーザ光を重畳させるかが極めて重要である。これについて図２を用いて説明する。
　レーザリフトオフ工程では、パルスレーザ光を出射するレーザ源を使用し、レーザ光の照射領域が刻々と変わるようにレーザ光を照射している。つまり、後述する図２を用いて説明すると、パルスレーザ光の照射領域Ｓ１にレーザ光を照射した後に、ワーク或いはレーザ源を搬送して次なる領域Ｓ２にレーザ光を照射する。このとき、パルスレーザ光の照射領域Ｓ１とＳ２のそれぞれのエッジ部が重畳する。 In laser lift-off, a sapphire substrate (hereinafter referred to as a workpiece) on which a material layer is formed or a laser source is scanned, and the material layer is usually irradiated with laser light while changing the irradiation region of the laser beam on the workpiece. . This is because it is difficult to make the irradiation area of the laser beam emitted from the laser source the same size as the workpiece. For this reason, the edge portions of the irradiation regions of the adjacent laser beams on the workpiece are necessarily overlapped. However, in the laser lift-off process, how the laser beams are superimposed is extremely important. This will be described with reference to FIG.
In the laser lift-off process, a laser source that emits pulsed laser light is used, and the laser light is irradiated so that the irradiation region of the laser light changes every moment. That is, with reference to FIG. 2 described later, after irradiating the laser beam to the irradiation region S1 of the pulse laser beam, the workpiece or the laser source is conveyed and the next region S2 is irradiated with the laser beam. At this time, the respective edge portions of the irradiation regions S1 and S2 of the pulse laser beam are overlapped.
　ここで、照射領域Ｓ１とＳ２のそれぞれのエッジ部が重畳する領域ＳＴにおいては、以下の理由により、照射領域Ｓ１およびＳ２のそれぞれに照射されるパルスレーザ光の照射量が積算されない。これは、照射領域Ｓ１にレーザ光を照射した後に照射領域をＳ１からＳ２に移行させたときには、照射領域Ｓ１のＧａＮの温度が室温レベルまで低下するのに要する時間が、照射領域をＳ１からＳ２に移行させるまでの時間に比べて格段に短いため、領域Ｓ１の温度は既に室温レベルまで低下した状態となるためであると考えられる。
　本発明者らがシミュレーションにより検討したところでは、照射領域Ｓ１のＧａＮの温度が室温レベルまで低下するのに要する時間は１００マイクロ秒以内であると推定される。照射領域Ｓ１の温度が室温レベルに低下した状態で照射領域Ｓ２にレーザ光を照射したとしても、照射領域Ｓ１とＳ２とが重畳した領域ＳＴは、照射領域Ｓ２に照射されたレーザ光によって加熱されるのみである。
　このように、照射領域Ｓ１、Ｓ２が重畳する領域ＳＴにおいては、それぞれの照射領域Ｓ１、Ｓ２に照射されるパルスレーザ光の照射量が積算されないので、領域Ｓ１、Ｓ２のそれぞれに照射されるパルスレーザ光を、材料層の分解閾値を超えるエネルギー領域で重畳させることが必要である。 Here, in the region ST where the respective edge portions of the irradiation regions S1 and S2 overlap, the irradiation amount of the pulse laser light irradiated to each of the irradiation regions S1 and S2 is not integrated for the following reason. This is because when the irradiation region is shifted from S1 to S2 after the irradiation region S1 is irradiated with the laser beam, the time required for the temperature of the GaN in the irradiation region S1 to fall to the room temperature level is reduced from S1 to S2. It is considered that this is because the temperature in the region S1 has already been lowered to the room temperature level because it is much shorter than the time required to shift to.
According to a study by the inventors, it is estimated that the time required for the temperature of the GaN in the irradiation region S1 to fall to the room temperature level is within 100 microseconds. Even if the irradiation region S2 is irradiated with the laser beam in a state where the temperature of the irradiation region S1 is lowered to the room temperature level, the region ST in which the irradiation regions S1 and S2 are superimposed is heated by the laser beam irradiated to the irradiation region S2. Only.
As described above, in the region ST where the irradiation regions S1 and S2 overlap, the irradiation amount of the pulse laser light irradiated to each of the irradiation regions S1 and S2 is not integrated, so the pulses irradiated to the regions S1 and S2 respectively. It is necessary to superimpose the laser light in an energy region exceeding the decomposition threshold of the material layer.
　一方、上記照射領域Ｓ１とＳ２のそれぞれのエッジ部が重畳する領域ＳＴにおける、それぞれのパルスレーザ光の強度が、前記材料層を前記基板から剥離させるに必要な分解閾値に対して大きすぎると、基板に材料層が再接着する等の不具合を生ずることが確認された。
　これは、同じ領域に、強度が大きなパルスレーザ光が２度照射されることにより、一度基板から剥離した材料層が、２度目に照射されるパルスレーザ光により再接着するものと考えられる。
　実験等により、各レーザ光が重畳している領域におけるレーザ光の強度は、前記材料層を前記基板から剥離させるに必要な分解閾値ＶＥに対して、ＶＥ×１．１５以下にするのが望ましいことが分かった。したがって、上記のような基板と材料層が再接着するという不具合を回避するためには、各レーザ光が重畳している領域におけるレーザ光の強度が大きすぎないようにすることが望ましい。
　ここで、［レーザ光が重畳している領域におけるレーザ光の強度（最大値）］／［分解閾値ＶＥ］を重畳度Ｔと定義すると、基板上に形成された材料層に割れを生じさせることなく、材料層を基板から確実に剥離させるためには、重畳度Ｔを１≦Ｔとするのが望ましく、また、基板と材料層の再接着を回避するためには、Ｔ≦１．１５とするのが望ましい。 On the other hand, if the intensity of each pulsed laser beam in the region ST where the respective edge portions of the irradiation regions S1 and S2 overlap is too large with respect to the decomposition threshold necessary for peeling the material layer from the substrate, It was confirmed that problems such as re-adhesion of the material layer to the substrate occurred.
This is thought to be because the material layer once peeled off the substrate is re-adhered by the pulsed laser light irradiated the second time when the same region is irradiated with the pulsed laser light having a high intensity twice.
By experiment etc., it is desirable that the intensity of the laser beam in the region where each laser beam is superimposed be VE × 1.15 or less with respect to the decomposition threshold VE necessary for peeling the material layer from the substrate. I understood that. Therefore, in order to avoid the problem that the substrate and the material layer are re-adhered as described above, it is desirable that the intensity of the laser beam in the region where the laser beams overlap is not too high.
Here, if [intensity of laser beam (maximum value) in region where laser beam is superimposed (maximum value)] / [decomposition threshold value VE] is defined as superposition degree T, the material layer formed on the substrate is cracked. In order to reliably peel the material layer from the substrate, it is desirable that the superposition degree T is 1 ≦ T, and in order to avoid re-adhesion between the substrate and the material layer, T ≦ 1.15. It is desirable to do.
　以上に基づき、本発明においては、以下のようにして前記課題を解決する。
（１）基板上に材料層が形成されてなる前記基板を通して、パルスレーザ光を照射し、前記基板と前記材料層との界面で前記材料層を前記基板から剥離するレーザリフトオフ方法において、前記パルスレーザ光を、ワークに対する照射領域を刻々と変えながら、前記ワークにおいて隣接する各照射領域が重畳するように照射し、重畳するそれぞれのパルスレーザ光の大きさが、前記材料層を前記基板から剥離させるに必要な分解閾値を超えるエネルギーの大きさになるようにする。
（２）上記（１）において、前記ワークにおいて隣接する各照射領域に照射される各レーザ光が重畳している領域におけるレーザ光の強度を、前記材料層を前記基板から剥離させるに必要な分解閾値ＶＥに対して、ＶＥ×１．１５以下とする。
（３）上記（１）（２）において、前記ワークを、第１の搬送方向に搬送する第１の搬送動作と、第１の搬送動作の搬送方向と直交する方向に搬送する第２の搬送動作と、前記第１の搬送動作の搬送方向と１８０°異なる方向に搬送する第３の搬送動作とを順次に実行し、順次、各照射領域に前記パルスレーザ光を照射する。
（４）上記レーザリフトオフを行うレーザリフトオフ装置において、レーザ源から発したパルスレーザ光を成形して、前記ワークに照射する投影レンズを有するレーザ光学系を設け、前記ワークの光入射面が、前記レーザ光の光軸方向において前記投影レンズの焦点位置に一致しないように配置する。 Based on the above, in the present invention, the above-described problem is solved as follows.
(1) In the laser lift-off method in which pulsed laser light is irradiated through the substrate having a material layer formed on the substrate, and the material layer is separated from the substrate at the interface between the substrate and the material layer, the pulse Laser light is irradiated so that each irradiation region adjacent to the workpiece overlaps while changing the irradiation region on the workpiece, and the size of each overlapping pulse laser beam peels the material layer from the substrate. The amount of energy exceeds the decomposition threshold necessary for the reduction.
(2) In the above (1), the decomposition necessary for peeling the material layer from the substrate is performed on the intensity of the laser beam in the region where the laser beams irradiated to the adjacent irradiation regions in the workpiece are superimposed. VE × 1.15 or less with respect to the threshold value VE.
(3) In the above (1) and (2), a first transport operation for transporting the workpiece in the first transport direction and a second transport for transporting the workpiece in a direction orthogonal to the transport direction of the first transport operation. An operation and a third transport operation for transporting in a direction 180 ° different from the transport direction of the first transport operation are sequentially performed, and the pulse laser beam is sequentially irradiated to each irradiation region.
(4) In the laser lift-off device for performing the laser lift-off, a laser optical system having a projection lens for shaping pulse laser light emitted from a laser source and irradiating the work is provided, and the light incident surface of the work is It arrange | positions so that it may not correspond with the focus position of the said projection lens in the optical axis direction of a laser beam.
　本発明のレーザリフトオフ方法によれば、次の効果を期待することができる。
（１）ワーク上の隣接する照射領域に照射されるレーザ光が、材料層を分解するために必要な分解閾値を超えるエネルギー領域で重畳しているので、各レーザ光が重畳するように照射された領域において、材料層を基板から剥離させるために十分なレーザエネルギーが与えられるので、基板上に形成された材料層に割れを生じさせることなく、材料層を基板から確実に剥離させることができる。
（２）隣接する各照射領域に照射される各レーザ光が重畳している領域におけるレーザ光の強度を、前記材料層を前記基板から剥離させるに必要な分解閾値ＶＥに対して、ＶＥ×１．１５以下とすることにより、基板と材料層が再接着するという不具合を回避することができる。
（３）ワークの光入射面が、前記レーザ光の光軸方向において前記投影レンズの焦点位置に一致しないように配置することにより、ワークに照射されるパルスレーザ光のビームプロファイルをなだらかな形状とする（照射されるパルスレーザ光の周縁部の光照度分布をピーク部からエッジ部に向けてなだらかに低下する形状とする）ことができる。これにより、パルスレーザ光の照射間隔を調整する（ワークを一定速度で搬送している場合）か、あるいは、ワークの搬送速度を調整する（パルスレーザ光の照射間隔が一定の場合）ことで、各レーザ光が重畳している領域における各レーザ光の強度を変えることができる。 According to the laser lift-off method of the present invention, the following effects can be expected.
(1) Since the laser beam irradiated to the adjacent irradiation region on the workpiece is superimposed in an energy region exceeding the decomposition threshold necessary for decomposing the material layer, each laser beam is irradiated so as to be superimposed. In this region, sufficient laser energy is applied to peel the material layer from the substrate, so that the material layer can be reliably peeled from the substrate without causing cracks in the material layer formed on the substrate. .
(2) The intensity of the laser beam in the region where the laser beams irradiated to the adjacent irradiation regions are overlapped is VE × 1 with respect to the decomposition threshold VE necessary for peeling the material layer from the substrate. By setting the ratio to 15 or less, it is possible to avoid the problem that the substrate and the material layer are reattached.
(3) By arranging the light incident surface of the work so as not to coincide with the focal position of the projection lens in the optical axis direction of the laser light, the beam profile of the pulsed laser light applied to the work has a gentle shape. (The illuminance distribution at the peripheral edge of the pulsed laser light to be irradiated has a shape that gradually decreases from the peak portion toward the edge portion). Thereby, by adjusting the irradiation interval of the pulse laser beam (when the workpiece is conveyed at a constant speed), or by adjusting the conveyance speed of the workpiece (when the irradiation interval of the pulse laser beam is constant), The intensity of each laser beam in the region where each laser beam is superimposed can be changed.
本発明の実施例のレーザリフトオフ処理の概要を説明する概念図である。It is a conceptual diagram explaining the outline | summary of the laser lift-off process of the Example of this invention. レーザ光がワークに照射される様子を示す図である。It is a figure which shows a mode that a laser beam is irradiated to a workpiece | work. 本発明の実施例において、ワークの互いに隣接する領域Ｓ１、Ｓ２に重畳して照射されるレーザ光の光強度分布を示す図である。In the Example of this invention, it is a figure which shows the light intensity distribution of the laser beam irradiated on the area | region S1, S2 which mutually adjoins a workpiece | work. 本発明の実施例のレーザリフトオフ装置の概念図である。It is a conceptual diagram of the laser lift-off apparatus of the Example of this invention. レーザ光の光強度分布のその他の実施例を示す図である。It is a figure which shows the other Example of the light intensity distribution of a laser beam. 本実施例のレーザ光の光強度分布と比較するための比較例を示す図である。It is a figure which shows the comparative example for comparing with the light intensity distribution of the laser beam of a present Example. レーザ光の重畳度が剥離後の材料層に与える影響を調べた実験結果を示す図である。It is a figure which shows the experimental result which investigated the influence which the superimposition degree of a laser beam has on the material layer after peeling. レーザ光の光強度分布をなだらかな形状とすることにより、重畳部分におけるレーザ光の強度を調整できることを説明する図である。It is a figure explaining that the intensity | strength of the laser beam in a superimposition part can be adjusted by making light intensity distribution of a laser beam into a gentle shape. レーザリフトオフ処理を適用することができる半導体発光素子の製造方法を説明する図である。It is a figure explaining the manufacturing method of the semiconductor light-emitting device which can apply a laser lift-off process. レーザ光の１ショットの照射領域が正方形状である場合を示す図である。It is a figure which shows the case where the irradiation area | region of 1 shot of a laser beam is square shape. ライン状のレーザ光を、レーザ光の長手方向と垂直方向に移動させながら、基板の裏面から照射する従来技術を説明する図である。It is a figure explaining the prior art which irradiates from the back surface of a board | substrate, moving a linear laser beam to the orthogonal | vertical direction with the longitudinal direction of a laser beam. 図１１に示す従来技術におけるレーザ光の光強度分布を示す図である。Is a graph showing the light intensity distribution of the laser beam in the prior art shown in FIG. 11.
　図１は、本発明の実施例のレーザリフトオフ処理の概要を説明する概念図である。
　同図に示すように、本実施例において、レーザリフトオフ処理は次のように行われる。
　レーザ光を透過する基板１上に材料層２が形成されたワーク３が、ワークステージ３１上に載置されている。ワーク３を載せたワークステージ３１は、コンベヤのような搬送機構３２に載置され、搬送機構３２によって所定の速度で搬送される。ワーク３は、ワークステージ３１と共に図中の矢印ＡＢＣ方向に搬送されながら、基板１を通じて、図示しないパルスレーザ源から出射するパルスレーザ光Ｌが照射される。
　ワーク３は、サファイアからなる基板１の表面に、ＧａＮ（窒化ガリウム）系化合物の材料層２が形成されてなるものである。基板１は、ＧａＮ系化合物の材料層を良好に形成することができ、尚且つ、ＧａＮ系化合物材料層を分解するために必要な波長のレーザ光を透過するものであれば良い。材料層２には、低い入力エネルギーによって高出力の青色光を効率良く出力するためにＧａＮ系化合物が用いられる。 FIG. 1 is a conceptual diagram illustrating an outline of laser lift-off processing according to an embodiment of the present invention.
As shown in the figure, in the present embodiment, the laser lift-off process is performed as follows.
A work 3 in which a material layer 2 is formed on a substrate 1 that transmits laser light is placed on a work stage 31. The work stage 31 on which the work 3 is placed is placed on a transport mechanism 32 such as a conveyor, and is transported by the transport mechanism 32 at a predetermined speed. The workpiece 3 is irradiated with a pulse laser beam L emitted from a pulse laser source (not shown) through the substrate 1 while being conveyed in the direction of arrow ABC in the figure together with the workpiece stage 31.
The workpiece 3 is formed by forming a material layer 2 of a GaN (gallium nitride) compound on the surface of a substrate 1 made of sapphire. The substrate 1 may be any material as long as it can form a GaN-based compound material layer satisfactorily and transmits laser light having a wavelength necessary for decomposing the GaN-based compound material layer. A GaN-based compound is used for the material layer 2 in order to efficiently output high-output blue light with low input energy.
　レーザ光は、基板１および基板１から剥離する材料層を構成する物質に対応して適宜選択すべきである。サファイアの基板１からＧａＮ系化合物の材料層２を剥離する場合には、例えば波長２４８ｎｍを放射するＫｒＦ（クリプトンフッ素）エキシマレーザを用いることができる。レーザ波長２４８ｎｍの光エネルギーは、ＧａＮのバンドギャップ（３．４ｅＶ）とサファイアのバンドギャップ（９．９ｅＶ）の間にある。したがって、波長２４８ｎｍのレーザ光はサファイアの基板からＧａＮ系化合物の材料層を剥離するために望ましい。 The laser beam should be appropriately selected according to the substrate 1 and the substance constituting the material layer peeled from the substrate 1. When the GaN-based compound material layer 2 is peeled from the sapphire substrate 1, for example, a KrF (krypton fluorine) excimer laser that emits a wavelength of 248 nm can be used. The light energy at the laser wavelength of 248 nm is between the band gap of GaN (3.4 eV) and the band gap of sapphire (9.9 eV). Therefore, a laser beam having a wavelength of 248 nm is desirable for peeling the material layer of the GaN-based compound from the sapphire substrate.
　続いて、本発明の実施例のレーザリフトオフ処理について、図１及び２を用いて説明する。図２は、レーザ光Ｌがワーク３に照射される様子を示す図である。
　図２（ａ）はワーク３に対するレーザ光の照射方法を示し、図２（ｂ）は図２（ａ）のＸ部を拡大して示したものであり、図２（ｂ）では、ワーク３の各照射領域の照射されるレーザ光の光強度分布の断面の一例を示している。なお、図２に示すワーク３上の実線は、レーザ光の照射領域を仮想的に示すものに過ぎない。
　ワーク３は、搬送機構３２によって図２に示す矢印ＨＡ、ＨＢ、ＨＣの方向に繰返し搬送される。レーザ光Ｌはサファイアの基板１の裏面から照射され、基板１と材料層２の界面に照射される。レーザ光Ｌの形状は略方形状に成形される。
　ワーク３は、図１、２に示すように、ワーク自体のサイズに対応して、図１の矢印Ａの方向に搬送される第１の搬送動作ＨＡと、レーザ光の１ショットの照射領域Ｓに相当する距離から重畳領域ＳＴを差し引いた距離だけ第１の搬送動作ＨＡの搬送方向と直交する方向（図１の矢印Ｃの方向）に搬送される第２の搬送動作ＨＢと、図１の矢印Ｂの方向に搬送される第３の搬送動作ＨＣとが順次に実行される。第１の搬送動作ＨＡおよび第３の搬送動作ＨＣのそれぞれの搬送方向は１８０°異なっている。
　ここで、レーザ光の光学系は固定されたままであり搬送されない。つまり、レーザ光の光学系を固定した状態でワーク３のみが搬送されることによって、ワーク３におけるレーザ光Ｌの照射領域が、図２の矢印に示すようにＳ１ないしＳ１２の順に相対的に刻々と変わることになる。 Next, laser lift-off processing according to an embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a diagram illustrating a state in which the laser beam L is applied to the workpiece 3.
2A shows a method of irradiating the workpiece 3 with the laser beam, FIG. 2B shows an enlarged view of a portion X in FIG. 2A, and FIG. 2 shows an example of a cross-section of the light intensity distribution of laser light irradiated on each of the irradiation regions. Note that the solid line on the workpiece 3 shown in FIG. 2 is merely a virtual representation of the laser light irradiation area.
The workpiece 3 is repeatedly conveyed in the directions of arrows HA, HB, and HC shown in FIG. The laser beam L is applied from the back surface of the sapphire substrate 1 and is applied to the interface between the substrate 1 and the material layer 2. The shape of the laser beam L is formed into a substantially square shape.
As shown in FIGS. 1 and 2, the workpiece 3 corresponds to the size of the workpiece itself, and the first conveyance operation HA is conveyed in the direction of arrow A in FIG. 1 and the irradiation region S of one shot of laser light. A second transport operation HB transported in a direction (in the direction of arrow C in FIG. 1) perpendicular to the transport direction of the first transport operation HA by a distance obtained by subtracting the overlapping region ST from the distance corresponding to The third transport operation HC transported in the direction of arrow B is sequentially executed. The transport directions of the first transport operation HA and the third transport operation HC differ by 180 °.
Here, the optical system of the laser light remains fixed and is not transported. That is, when only the workpiece 3 is transported with the laser beam optical system fixed, the irradiation region of the laser beam L on the workpiece 3 is relatively relatively momentarily in the order of S1 to S12 as shown by the arrows in FIG. Will change.
　次に、本発明の実施例のレーザリフトオフ処理についてより具体的に説明する。図２に示す実施例では、ワーク３は円形状の輪郭を持つものであるが、レーザ光の照射領域が略方形状となっており、このような方形状の照射領域に対するレーザ照射方法について説明する。
　図２に示すように、ワーク３を図２のＨＡ方向に搬送させながら、Ｓ１、Ｓ２、Ｓ３、Ｓ４の４つの照射領域に対して、それぞれ１回ずつ合計４回に亘りレーザ光を照射する。これが第１の搬送動作である。
　次に、レーザ光がワーク３の次なる照射領域Ｓ５に照射されるようにするため、ワーク３を図２のＨＢ方向に搬送する。これが第２の搬送動作である。ワーク３が矢印ＨＢ方向に搬送される距離は、パルスレーザ光の１ショット（１パルス）分の照射領域に相当する距離から重畳領域ＳＴを差し引いた距離に等しい。
　その次に、ワーク３を図２のＨＣ方向に搬送させながら、Ｓ５、Ｓ６、Ｓ７、Ｓ８、Ｓ９、Ｓ１０の６つの照射領域に対して、それぞれ１回ずつ合計６回に亘りレーザ光を照射する。これが第３の搬送動作である。ワーク３のその他の照射領域についても上記の一連の手順に従ってワーク３を搬送することにより、ワーク３の全域に亘りレーザ光が照射される。 Next, the laser lift-off process according to the embodiment of the present invention will be described more specifically. In the embodiment shown in FIG. 2, the workpiece 3 has a circular outline, but the laser light irradiation area has a substantially rectangular shape, and a laser irradiation method for such a rectangular irradiation area will be described. To do.
As shown in FIG. 2, the laser beam is radiated once for each of the four irradiation areas S1, S2, S3, and S4 while transferring the workpiece 3 in the HA direction in FIG. . This is the first transport operation.
Next, the workpiece 3 is transported in the HB direction in FIG. 2 in order to irradiate the next irradiation region S5 of the workpiece 3 with the laser light. This is the second transport operation. The distance by which the workpiece 3 is conveyed in the direction of the arrow HB is equal to the distance obtained by subtracting the overlapping area ST from the distance corresponding to the irradiation area for one shot (one pulse) of the pulse laser beam.
Next, while transporting the workpiece 3 in the HC direction in FIG. 2, the laser beam is irradiated once for each of the six irradiation areas S5, S6, S7, S8, S9, and S10, a total of six times. to. This is the third transport operation. Also in the other irradiation areas of the workpiece 3, the laser beam is irradiated over the entire area of the workpiece 3 by conveying the workpiece 3 according to the above-described series of procedures.
　レーザ光の照射領域は、図２に示すようにＳ１、Ｓ２、Ｓ３の順に相対的に移動することになるが、それぞれの照射領域は例えば０．５ｍｍ×０．５ｍｍであり面積は０．２５ｍｍ２とされる。これに対して、ワーク３の面積は４５６０ｍｍ２である。つまり、レーザ光の照射領域Ｓ１、Ｓ２、Ｓ３はワーク面積に比して遥かに小さいものである。
　本実施例のレーザリフトオフ処理では、ワーク３に比して小さい照射領域のレーザ光が図１に示す矢印ＡおよびＢの方向（つまりワークの左右方向）にスキャンしながらワーク３に対して照射される。なお、本発明の実施例とは逆に、ワークを固定したままで、上記した搬送動作ＨＡないしＨＣに従ってレーザの光学系を搬送しても良い。要は、ワーク上のレーザ光の照射領域が時間とともに刻々と移り変わるように、ワークに対してレーザ光が照射されれば良い。 As shown in FIG. 2, the laser light irradiation area moves relatively in the order of S1, S2, and S3. Each irradiation area is, for example, 0.5 mm × 0.5 mm, and the area is 0.25 mm. 2 . On the other hand, the area of the work 3 is 4560 mm 2 . That is, the laser light irradiation areas S1, S2, and S3 are much smaller than the work area.
In the laser lift-off process of the present embodiment, a laser beam in an irradiation area smaller than that of the workpiece 3 is irradiated to the workpiece 3 while scanning in the directions of arrows A and B shown in FIG. The In contrast to the embodiment of the present invention, the laser optical system may be transported in accordance with the transport operations HA or HC described above while the workpiece is fixed. In short, the laser beam may be irradiated to the workpiece so that the irradiation region of the laser beam on the workpiece changes with time.
　ここで、本発明のレーザリフトオフ処理においては、図２（ｂ）に示すように、レーザ光がワーク３の互いに隣接する照射領域Ｓ１、Ｓ２、Ｓ３において、間歇的に照射される各レーザ光の幅方向の端部が互いに重畳するようにワーク３に照射される。レーザ光Ｌは、パルスレーザ光であり、間歇的にワーク３に照射される。ワーク３の照射領域Ｓ１、Ｓ２、Ｓ３においてレーザ光が重畳する幅は、例えば０．１ｍｍである。
　レーザ光のパルス間隔は、ワーク３の搬送速度と、ワーク３上の隣接する照射領域Ｓ１、Ｓ２、Ｓ３、…に照射されるレーザ光の重畳領域ＳＴの幅を考慮して適宜設定される。
　基本的にはワーク３が次なる照射領域に移動する前にレーザ光がワークに照射されることのないように、レーザ光のパルス間隔が決められる。つまり、レーザ光のパルス間隔は、ワーク３がレーザ光の１ショット分の照射領域に相当する距離を移動するために要する時間よりも長く設定される。例えば、ワーク３の搬送速度が１００ｍｍ／秒、レーザ光の重畳領域ＳＴの幅が０．１ｍｍである場合、レーザ光のパルス間隔は０．００４秒（２５０Ｈｚ）である。 Here, in the laser lift-off process of the present invention, as shown in FIG. 2B, each laser beam irradiated intermittently in the irradiation regions S1, S2, and S3 of the workpiece 3 adjacent to each other as shown in FIG. The workpiece 3 is irradiated so that the end portions in the width direction overlap each other. The laser beam L is a pulsed laser beam and is intermittently applied to the workpiece 3. In the irradiation areas S1, S2, and S3 of the work 3, the width in which the laser light is superimposed is, for example, 0.1 mm.
The pulse interval of the laser light is appropriately set in consideration of the conveyance speed of the workpiece 3 and the width of the overlapping region ST of the laser beam irradiated on the adjacent irradiation regions S1, S2, S3,.
Basically, the pulse interval of the laser beam is determined so that the workpiece is not irradiated with the laser beam before the workpiece 3 moves to the next irradiation region. That is, the pulse interval of the laser beam is set longer than the time required for the work 3 to move a distance corresponding to the irradiation region for one shot of the laser beam. For example, when the conveying speed of the workpiece 3 is 100 mm / second and the width of the laser light overlapping region ST is 0.1 mm, the pulse interval of the laser light is 0.004 seconds (250 Hz).
　図３は、図２に示すワーク３の互いに隣接する領域Ｓ１、Ｓ２に重畳するようにワークに照射されるレーザ光の光強度分布を示す図であり、図２（ｂ）におけるａ－ａ´線断面図である。
　同図において縦軸はワークの各照射領域に照射されるレーザ光の強度（エネルギー値）を、横軸はワークの搬送方向を示す。また、Ｌ１、Ｌ２は、それぞれワークの照射領域Ｓ１、Ｓ２に照射されるレーザ光のプロファイルを示す。なお、レーザ光Ｌ１，Ｌ２は同時に照射されるわけではなく、レーザ光Ｌ１が照射されてから１パルス間隔後にレーザ光Ｌ２が照射される。
　この例では、図３に示すように、レーザ光Ｌ１、Ｌ２の断面は、周方向になだらかに広がるエッジ部ＬＥに続いて頂上（ピークエネルギーＰＥ）に平坦面を有する略台形状に形成されている。そして、レーザ光Ｌ１、Ｌ２は、図３に破線で示すように、ＧａＮ系化合物の材料層を分解してサファイアの基板から剥離させるために必要な分解閾値ＶＥを超えるエネルギー領域において重畳される。 FIG. 3 is a diagram showing the light intensity distribution of the laser beam irradiated on the workpiece so as to overlap the regions S1 and S2 adjacent to each other of the workpiece 3 shown in FIG. 2, and aa ′ in FIG. It is line sectional drawing.
In the figure, the vertical axis indicates the intensity (energy value) of the laser beam irradiated to each irradiation area of the workpiece, and the horizontal axis indicates the conveyance direction of the workpiece. L1 and L2 indicate the profiles of the laser beams irradiated to the workpiece irradiation areas S1 and S2, respectively. The laser beams L1 and L2 are not irradiated at the same time, but the laser beam L2 is irradiated after one pulse interval from the irradiation of the laser beam L1.
In this example, as shown in FIG. 3, the cross sections of the laser beams L1 and L2 are formed in a substantially trapezoidal shape having a flat surface on the top (peak energy PE) following the edge portion LE that gently spreads in the circumferential direction. Yes. The laser beams L1 and L2 are superimposed in an energy region exceeding a decomposition threshold VE necessary for decomposing and separating the material layer of the GaN-based compound from the sapphire substrate, as indicated by broken lines in FIG.
　すなわち、各レーザ光の光強度分布における、レーザ光Ｌ１とＬ２との交差位置Ｃでのレーザ光の強度（エネルギー値）ＣＥは、上記分解閾値ＶＥを越える値になるように設定される。
　これは、前述したように、図２の照射領域Ｓ１にレーザ光を照射した後に照射領域をＳ１からＳ２に移行させたとき、領域Ｓ１の温度は既に室温レベルまで低下した状態となるため、照射領域Ｓ１の温度が室温レベルに低下した状態で照射領域Ｓ２にレーザ光を照射したとしても、それぞれの照射領域Ｓ１、Ｓ２に照射されるパルスレーザ光の照射量が積算されないためである。
　レーザ光Ｌ１とＬ２との交差位置Ｃでのレーザ光の強度ＣＥ、すなわち、レーザ光が重畳して照射される領域におけるそれぞれのパルスレーザ光の強度を、上記分解閾値ＶＥを越える値になるように設定することで、材料層を基板から剥離させるために十分なレーザエネルギーが与えることができ、基板上に形成された材料層に割れを生じさせることなく、材料層を基板から確実に剥離させることができる。すなわち、前記段落００１１に定義される重畳度Ｔは、１≦Ｔとするのが望ましい。
　なお、ワーク３とレーザ光の相対的な移動量に対して、レーザ光のパルス間隔は、ワーク３の隣接する照射領域に照射されるレーザ光が前記のように重畳するように予め調整されている。同図に示す実施例では、材料層がＧａＮであるため、分解閾値は５００～１５００Ｊ／ｃｍ２である。分解閾値ＶＥは、材料層を構成する物質毎に設定することが必要とされる。 That is, in the light intensity distribution of each laser beam, the intensity (energy value) CE of the laser beam at the intersection position C between the laser beams L1 and L2 is set to a value exceeding the decomposition threshold value VE.
This is because, as described above, when the irradiation region is shifted from S1 to S2 after irradiating the irradiation region S1 of FIG. 2 with the laser beam, the temperature of the region S1 is already lowered to the room temperature level. This is because even if the irradiation region S2 is irradiated with the laser light in a state where the temperature of the region S1 is lowered to the room temperature level, the irradiation amount of the pulse laser light irradiated to each of the irradiation regions S1 and S2 is not integrated.
The intensity CE of the laser beam at the crossing position C between the laser beams L1 and L2, that is, the intensity of each pulsed laser beam in the region irradiated with the laser beam superimposed, becomes a value exceeding the decomposition threshold VE. By setting to, sufficient laser energy can be given to peel the material layer from the substrate, and the material layer is surely peeled from the substrate without causing cracks in the material layer formed on the substrate. be able to. That is, the degree of superimposition T defined in the paragraph 0011 is preferably 1 ≦ T.
Note that the pulse interval of the laser beam is adjusted in advance so that the laser beam applied to the adjacent irradiation region of the workpiece 3 is superimposed as described above with respect to the relative movement amount of the workpiece 3 and the laser beam. there. In the example shown in the figure, since the material layer is GaN, the decomposition threshold is 500 to 1500 J / cm 2 . The decomposition threshold VE needs to be set for each substance constituting the material layer.
　ここで、上記のようにレーザ光Ｌ１とＬ２とは分解閾値ＶＥを超えるエネルギー領域で重畳されるが、後述するように、基板と材料層が再接着するという不具合を回避するためには、重畳するそれぞれのレーザ光の分解閾値ＶＥに対する大きさの割合を適切な値に設定する必要があり、具体的に、上記分解閾値ＶＥに対して、ＶＥ×１．１５以下になるように設定するのが望ましいことが分かった。
　図３の実施例では、各レーザ光の光強度分布におけるレーザ光Ｌ１とＬ２との交差位置Ｃでのレーザ光の強度（エネルギー値）ＣＥは、前記材料層を前記基板から剥離させるに必要な分解閾値ＶＥに対して、ＶＥ×１．１５以下になるように設定する。
　すなわち、前記重畳度Ｔは、Ｔ≦１．１５とするのが望ましい。 Here, as described above, the laser beams L1 and L2 are superimposed in an energy region exceeding the decomposition threshold value VE. It is necessary to set the ratio of the size of each laser beam to the decomposition threshold VE to an appropriate value. Specifically, the ratio is set to be VE × 1.15 or less with respect to the decomposition threshold VE. Was found to be desirable.
In the embodiment of FIG. 3, the intensity (energy value) CE of the laser beam at the intersection position C of the laser beams L1 and L2 in the light intensity distribution of each laser beam is necessary for peeling the material layer from the substrate. It sets so that it may become VEx1.15 or less to decomposition threshold VE.
That is, it is desirable that the degree of superimposition T is T ≦ 1.15.
　図４は、本発明の実施例のレーザリフトオフ装置の概念図である。
同図において、レーザリフトオフ装置１０は、前記したパルスレーザ光を出射するレーザ源２０と、レーザ光を所定の形状に成形するためのレーザ光学系４０と、ワーク３が載置されるワークステージ３１と、ワークステージ３１を搬送する搬送機構３２と、レーザ源２０で発生するレーザ光の照射間隔および搬送機構３２の動作を制御する制御部３３とを備えている。
　光学系４０は、シリンドリカルレンズ４１、４２と、レーザ光をワークの方向へ反射するミラー４３と、レーザ光を所定の形状に成形するためのマスク４４と、マスク４４を通過したレーザ光Ｌをワーク３上に集光させる投影レンズ４５とを備えている。
　光学系４０の先にはワーク３が配置されている。ワーク３はワークステージ３１上に載置されている。ワークステージ３１は搬送機構３２に載置されており、搬送機構３２によって搬送される。これにより、ワーク３が、前記図１に示した矢印Ａ、Ｂ、Ｃの方向に順次に搬送され、ワーク３におけるレーザ光の照射領域が刻々と変わる。制御部３３は、ワーク３の隣接する照射領域に照射される各レーザ光の重畳度が所望の値になるように、レーザ源２０で発生するパルスレーザ光のパルス間隔を制御する。 FIG. 4 is a conceptual diagram of a laser lift-off device according to an embodiment of the present invention.
In the figure, a laser lift-off device 10 includes a laser source 20 that emits the above-described pulsed laser light, a laser optical system 40 for shaping the laser light into a predetermined shape, and a work stage 31 on which a work 3 is placed. And a transport mechanism 32 that transports the work stage 31, and a control unit 33 that controls the irradiation interval of the laser light generated by the laser source 20 and the operation of the transport mechanism 32.
The optical system 40 includes cylindrical lenses 41 and 42, a mirror 43 that reflects laser light in the direction of the workpiece, a mask 44 for shaping the laser light into a predetermined shape, and a laser beam L that has passed through the mask 44 as a workpiece. 3 is provided with a projection lens 45 for condensing the light.
A work 3 is disposed at the tip of the optical system 40. The work 3 is placed on the work stage 31. The work stage 31 is placed on the transport mechanism 32 and is transported by the transport mechanism 32. As a result, the workpiece 3 is sequentially conveyed in the directions of arrows A, B, and C shown in FIG. 1, and the irradiation region of the laser beam on the workpiece 3 changes every moment. The control unit 33 controls the pulse interval of the pulsed laser light generated by the laser source 20 so that the degree of superimposition of each laser light irradiated on the irradiation region adjacent to the workpiece 3 becomes a desired value.
　レーザ源２０から発生するレーザ光Ｌは波長２４８ｎｍの紫外線を発生する、例えばＫｒＦエキシマレーザである。レーザ源としてＡｒＦレーザやＹＡＧレーザを使用しても良い。
　ここで、ワーク３の光入射面３Ａは、投影レンズ４５の焦点Ｆよりもレーザ光の光軸方向において遠方側に配置するか、これとは反対に、レーザ光の光軸方向において、ワーク３の光入射面３Ａを投影レンズ４５の焦点Ｆよりも投影レンズ４５に近づけるように配置しても良い。このように、ワーク３の光入射面３Ａを投影レンズ４５の焦点Ｆに一致しないように配置することにより、図３に示すような、レーザ光Ｌ１，Ｌ２のビームプロファイルのエッジ部ＬＥがなだらかに低下する、断面が台形状の光強度分布を持つレーザ光が得られる。
　レーザ源２０で発生したレーザ光Ｌは、シリンドリカルレンズ４１、４２、ミラー４３、マスク４４を通過した後に、投影レンズ４５によってワーク３上に集光される。
　投影レンズ４５により、ワーク３の光入射面３Ａに入射されるレーザ光は、図３に示す断面において、周方向になだらかに広がるエッジ部ＬＥに続いて頂上に平坦面を有する略台形状の光強度分布を持つように成形される。 The laser light L generated from the laser source 20 is, for example, a KrF excimer laser that generates ultraviolet light having a wavelength of 248 nm. An ArF laser or a YAG laser may be used as the laser source.
Here, the light incident surface 3A of the work 3 is disposed farther in the optical axis direction of the laser light than the focal point F of the projection lens 45, or on the contrary, in the optical axis direction of the laser light, the work 3 The light incident surface 3 </ b> A may be disposed closer to the projection lens 45 than the focal point F of the projection lens 45. Thus, by arranging the light incident surface 3A of the workpiece 3 so as not to coincide with the focal point F of the projection lens 45, the edge portions LE of the beam profiles of the laser beams L1 and L2 as shown in FIG. A laser beam having a light intensity distribution with a trapezoidal cross section is obtained.
The laser light L generated by the laser source 20 passes through the cylindrical lenses 41 and 42, the mirror 43, and the mask 44, and is then condensed on the work 3 by the projection lens 45.
Laser light incident on the light incident surface 3A of the workpiece 3 by the projection lens 45 is substantially trapezoidal light having a flat surface on the top following the edge portion LE that gently spreads in the circumferential direction in the cross section shown in FIG. Molded to have an intensity distribution.
　ワークの隣接する照射領域に重畳するように照射される各々のレーザ光の光強度分布は、上記したように断面が略台形状であることが理想的であるが、必ずしも台形状でなくても良い。
　図５は、ワークに照射されるレーザ光の光強度分布のその他の実施例を示す。
　図５（ａ）に示すレーザ光の光強度分布は、中央にピークが位置すると共に、該ピークに続いてなだらかに広がるエッジ部ＬＥを有する略山状に形成されている。レーザ光の光強度分布は、図４に示す投影レンズ４５の焦点Ｆとワーク３の光入射面３Ａとの距離を調整することによって適宜変更することができる。
　レーザ光の光強度分布は、投影レンズ４５の焦点Ｆとワーク３の光入射面３Ａとの距離が近付くにつれてシャープな矩形状となり、投影レンズ４５の焦点Ｆとワーク３の光入射面３Ａとの距離が遠くなるにつれてエッジがなだらかに形成されると共に山状に形成される。
　また、図５（ｂ）に示すようにレーザ光Ｌ１，Ｌ２の光強度分布を矩形状にしても良い。この場合、レーザ光Ｌ１，Ｌ２が重なっている領域におけるレーザ光の強度（レーザ光Ｌ１とＬ２との交差位置でのレーザ光の強度であり、この場合はレーザ光Ｌ１のピーク値に対応）をＣＥとすると、前記重畳度Ｔは、Ｔ＝ＣＥ／［分解閾値ＶＥ］で計算される。
　この場合においても、上記レーザ光Ｌ１とＬ２との交差位置でのレーザ光の強度ＣＥは、前記材料層を前記基板から剥離させるに必要な分解閾値ＶＥより大きく、かつ、分解閾値ＶＥに対して、ＶＥ×１．１５以下とすることが望ましい。 As described above, it is ideal that the light intensity distribution of each laser beam irradiated so as to be superimposed on the adjacent irradiation region of the workpiece has a substantially trapezoidal cross section, but it does not necessarily have a trapezoidal shape. good.
FIG. 5 shows another embodiment of the light intensity distribution of the laser light applied to the workpiece.
The light intensity distribution of the laser light shown in FIG. 5A is formed in a substantially mountain shape having a peak at the center and an edge portion LE that gently spreads after the peak. The light intensity distribution of the laser light can be changed as appropriate by adjusting the distance between the focal point F of the projection lens 45 and the light incident surface 3A of the workpiece 3 shown in FIG.
The light intensity distribution of the laser light becomes a sharp rectangular shape as the distance between the focal point F of the projection lens 45 and the light incident surface 3A of the workpiece 3 approaches, and the focal point F of the projection lens 45 and the light incident surface 3A of the workpiece 3 become smaller. As the distance increases, the edges are gently formed and formed in a mountain shape.
Further, as shown in FIG. 5B, the light intensity distribution of the laser beams L1 and L2 may be rectangular. In this case, the intensity of the laser beam in the region where the laser beams L1 and L2 overlap (the intensity of the laser beam at the intersection of the laser beams L1 and L2, which corresponds to the peak value of the laser beam L1 in this case). Assuming CE, the degree of superimposition T is calculated by T = CE / [decomposition threshold VE].
Even in this case, the intensity CE of the laser beam at the crossing position of the laser beams L1 and L2 is larger than the decomposition threshold value VE necessary for peeling the material layer from the substrate, and with respect to the decomposition threshold value VE. VE × 1.15 or less is desirable.
　ここで、本実施例のレーザリフトオフ処理を実行することによって得られる効果について図３、図６を用いて説明する。
　図３は本実施例のレーザリフトオフ方法に使用されるレーザ光の光強度分布を示し、図６はこれと比較するためのレーザ光の光強度分布を示す。図３、図６のＬ１、Ｌ２は、図２に示すＳ１、Ｓ２の照射領域に照射されるレーザ光を示す。ワークの隣接する照射領域に照射されるレーザ光の重畳度が基板から剥離後の材料層に与える影響について、図３、６を用いて比較検討する。
　図３に示すレーザ光Ｌ１、Ｌ２は、周方向になだらかに広がるエッジ部ＬＥに続いて頂上に平坦面を有する略台形状の光強度分布を有し、尚且つ、分解閾値ＶＥを超えるエネルギー領域においてレーザ光Ｌ１、Ｌ２は重畳度Ｔが適切な値（１以上１．１５以内）になるように重畳している。
　従って、図３の実施例のレーザリフトオフ方法は、レーザ光が基板１との界面側の材料層２の表面に照射され材料層２を構成するＧａＮが分解する際に、Ｎ２ガスが急激に発生することがない。しかも、図３の実施例のレーザリフトオフ方法は、図２においてレーザ光Ｌ１とＬ２とが重畳する重畳領域ＳＴに対して照射されるレーザ光のエネルギーが、過不足なく最適なエネルギーになるため、材料層２と基板１が再接着する不具合を回避することができ、材料層２を基板１から確実に剥離させることができる。
　実際に図３に示す実施例のレーザ光をワークに照射した場合の、剥離後の材料層の表面状態はとても綺麗であり、汚れ、傷などといった発光特性に悪影響を与えるものは見あたらなかった。 Here, the effect obtained by executing the laser lift-off process of the present embodiment will be described with reference to FIGS.
FIG. 3 shows the light intensity distribution of the laser light used in the laser lift-off method of this embodiment, and FIG. 6 shows the light intensity distribution of the laser light for comparison with this. L1 and L2 in FIGS. 3 and 6 indicate laser beams irradiated to the irradiation areas of S1 and S2 shown in FIG. The influence of the degree of superimposition of the laser light applied to the irradiation area adjacent to the workpiece on the material layer after peeling from the substrate will be compared and examined with reference to FIGS.
The laser beams L1 and L2 shown in FIG. 3 have a substantially trapezoidal light intensity distribution having a flat surface on the top following an edge portion LE that gently spreads in the circumferential direction, and an energy region exceeding the decomposition threshold VE. The laser beams L1 and L2 are superposed so that the superposition degree T becomes an appropriate value (1 to 1.15).
Therefore, in the laser lift-off method of the embodiment of FIG. 3, when the surface of the material layer 2 on the interface side with the substrate 1 is irradiated with laser light and the GaN constituting the material layer 2 is decomposed, the N 2 gas rapidly It does not occur. Moreover, in the laser lift-off method of the embodiment of FIG. 3, the energy of the laser beam irradiated to the overlapping region ST where the laser beams L1 and L2 overlap in FIG. The problem that the material layer 2 and the substrate 1 are re-adhered can be avoided, and the material layer 2 can be reliably peeled from the substrate 1.
When the workpiece was actually irradiated with the laser beam of the embodiment shown in FIG. 3, the surface state of the material layer after peeling was very clean, and no material that adversely affects the light emission characteristics such as dirt and scratches was found.
　これに対し、図６（ａ）の比較例に示すレーザ光をワークに照射した場合は、レーザ光Ｌ１とＬ２のそれぞれの光強度分布が分解閾値ＶＥを下回るエネルギー領域で交差しているので、図２に示すワークにおいてレーザ光Ｌ１とＬ２との重畳領域ＳＴに照射されるレーザ光のエネルギーが不足するといった不具合がある。
　実際に図６（ａ）に示す比較例のレーザ光をワークに照射した場合、材料層を構成するＧａＮの未分解領域が形成され、材料層を基板から十分に剥離させることができなかった。ＧａＮの未分解領域は、ワークにおいてレーザ光Ｌ１とＬ２とが重畳する重畳領域ＳＴに一致していた。
　一方、図６（ｂ）の比較例に示すレーザ光をワークに照射した場合は、レーザ光Ｌ１とＬ２との重畳度Ｔが大きすぎるため、図２に示すワークにおいてレーザ光Ｌ１とＬ２との重畳領域ＳＴに過剰なエネルギーのレーザ光が照射されるといった不具合がある。
　後述する図７（ｂ－４）に示すように、実際に図６（ｂ）に示す比較例のレーザ光をワークに照射した場合の、剥離後の材料層の表面状態は、表面に黒いシミのような汚れが多数形成されている。
　これは、エネルギーが大きなレーザ光が同じ個所に２度照射されることにより、一度基板から剥離した材料層が、２度目に照射されるレーザ光により再接着し、基板を構成するサファイアの成分が付着したものと考えられる。このように材料層の表面に形成された黒いシミは発光特性に悪影響を及ぼす。 In contrast, when the workpiece is irradiated with the laser beam shown in the comparative example of FIG. 6A, the light intensity distributions of the laser beams L1 and L2 intersect each other in the energy region below the decomposition threshold VE. In the work shown in FIG. 2, there is a problem that the energy of the laser beam irradiated on the overlapping region ST of the laser beams L1 and L2 is insufficient.
When the workpiece was actually irradiated with the laser beam of the comparative example shown in FIG. 6A, an undecomposed region of GaN constituting the material layer was formed, and the material layer could not be sufficiently separated from the substrate. The undecomposed region of GaN coincided with the overlapping region ST where the laser beams L1 and L2 overlap on the workpiece.
On the other hand, when the workpiece is irradiated with the laser beam shown in the comparative example of FIG. 6B, since the degree of superimposition T of the laser beams L1 and L2 is too large, the laser beams L1 and L2 in the workpiece shown in FIG. There is a problem that a laser beam with excessive energy is irradiated onto the superposition region ST.
As shown in FIG. 7B-4, which will be described later, when the workpiece is actually irradiated with the laser light of the comparative example shown in FIG. A large number of such stains are formed.
This is because the material layer once peeled off from the substrate is re-adhered by the second laser beam when the high-energy laser beam is irradiated twice at the same location, and the sapphire component constituting the substrate is It is thought that it adhered. Thus, the black spot formed on the surface of the material layer has an adverse effect on the light emission characteristics.
　上記効果を確認するため、レーザ光が重畳する照射領域におけるレーザ光の重畳度が、剥離後の材料層に与える影響について実験を行った。
　図７はその結果を示す図である。図７（ａ）は実験に使用した隣接する領域に重畳させて照射したレーザ光の光強度分布を示す図であり、本実験では、同図に示すように、矩形状の光強度分布を有するレーザ光Ｌ１，Ｌ２（ＫｒＦレーザが出力するパルスレーザ光）を、サファイア基板上にＧａＮ材料層を形成したワークに照射して行った。
　レーザ光Ｌ１，Ｌ２が重畳する領域でのレーザ光の強度を、ＧａＮ材料層の分解閾値ＶＥ（８７０ｍＪ／ｃｍ２）に対して１０５％、１１０％、１１５％、１２０％と変えて照射し、剥離後の材料層の表面を調べた。
　図７（ｂ－１）、（ｂ－２）（ｂ－３）、（ｂ－４）に、重畳する領域におけるレーザ光の強度を分解閾値ＶＥに対して、それぞれ１０５％、１１０％、１１５％、１２０％と変えた場合の剥離後の材料層の表面を示す。
　図７（ｂ－１）、（ｂ－２）（ｂ－３）に示すように、分解閾値ＶＥに対して、重畳する領域でのレーザ光の強度が１０５％、１１０％、１１５％の場合には、剥離後の材料層の表面状態は良好であり、汚れ、傷などといった発光特性に悪影響を与えるものは見あたらなかった。これに対し、レーザ光の強度を分解閾値ＶＥに対して１２０％にすると、図７（ｂ－４）に示すように、剥離後の材料層の表面状態は、黒いシミのような汚れが多数形成された。
　なお、図７には示していないが、分解閾値ＶＥに対して、重畳する領域でのレーザ光の強度が１００％以下の場合も、レーザ光が重畳して照射される領域に、ＧａＮ材料層に未分解部分が発生することが確認された。 In order to confirm the above effect, an experiment was conducted on the influence of the degree of superimposition of the laser light on the irradiated region where the laser light is superimposed on the material layer after peeling.
FIG. 7 is a diagram showing the results. FIG. 7 (a) is a diagram showing the light intensity distribution of the laser beam irradiated in an overlapping manner used in the experiment. In this experiment, as shown in the figure, the light intensity distribution has a rectangular shape. Laser beams L1 and L2 (pulse laser beams output from a KrF laser) were irradiated to a work in which a GaN material layer was formed on a sapphire substrate.
The intensity of the laser beam in the region where the laser beams L1 and L2 overlap is changed to 105%, 110%, 115%, and 120% with respect to the decomposition threshold value VE (870 mJ / cm 2 ) of the GaN material layer. The surface of the material layer after peeling was examined.
7 (b-1), (b-2), (b-3), and (b-4), the intensity of the laser beam in the overlapping region is 105%, 110%, and 115 with respect to the decomposition threshold VE, respectively. % And 120% indicate the surface of the material layer after peeling.
As shown in FIGS. 7 (b-1), (b-2), and (b-3), when the intensity of the laser beam in the overlapping region is 105%, 110%, and 115% with respect to the decomposition threshold VE In this case, the surface condition of the material layer after peeling was good, and no material that adversely affects the luminescent properties such as dirt and scratches was found. On the other hand, when the intensity of the laser beam is set to 120% with respect to the decomposition threshold VE, as shown in FIG. 7B-4, the surface state of the material layer after peeling has many stains such as black spots. Been formed.
Although not shown in FIG. 7, even when the intensity of the laser beam in the overlapping region is 100% or less with respect to the decomposition threshold VE, the GaN material layer is applied to the region irradiated with the overlapping laser beam. It was confirmed that an undecomposed portion was generated.
　ところで、図７に示した例では、矩形状の光強度分布を有するレーザ光Ｌ１，Ｌ２を用いており、この場合、図８（ａ）に示すように重畳する領域でのレーザ光の強度を調整することができず、重畳する領域でのレーザ光の強度の調整は、各レーザ光Ｌ１，Ｌ２の強度を調整することにより行う必要がある。
　これに対し、レーザ光Ｌ１，Ｌ２の光強度分布（ビームプロファイル）を前記図３に示したように、周方向になだらかに広がるエッジ部ＬＥを有する形状とすることにより、レーザ光Ｌ１，Ｌ２の照射間隔（あるいはワークの移動速度）を調整し、上記エッジ部ＬＥの重なり程度を調整することで、重畳部分におけるレーザ光の強度を自在に調整することができる。
　図８（ｂ－１）はレーザ光Ｌ１，Ｌ２の重ね量が適正な場合であり、照射間隔（あるいはワークの移動速度）を適切に調整した場合であり、同図（ｂ－２）に示すように剥離後の材料層の表面状態は良好であり、汚れ、傷などといった発光特性に悪影響を与えるものは見あたらなかった。
　図８（Ｃ－１）はレーザ光Ｌ１，Ｌ２の重ね量が大きく、重畳する領域におけるレーザ光の強度が分解閾値ＶＥに対して１１５％を超える場合であり、同図（Ｃ－２）に示すように、剥離後の材料層の表面状態は、黒いシミのような汚れが多数形成された。 By the way, in the example shown in FIG. 7, the laser beams L1 and L2 having a rectangular light intensity distribution are used. In this case, the intensity of the laser beam in the overlapping region as shown in FIG. The adjustment of the intensity of the laser beam in the overlapping region, which cannot be adjusted, must be performed by adjusting the intensity of the laser beams L1 and L2.
On the other hand, the light intensity distribution (beam profile) of the laser beams L1 and L2 has a shape having an edge LE that gently spreads in the circumferential direction as shown in FIG. By adjusting the irradiation interval (or the moving speed of the workpiece) and adjusting the degree of overlap of the edge portions LE, the intensity of the laser beam at the overlapping portion can be freely adjusted.
FIG. 8 (b-1) shows a case where the overlapping amount of the laser beams L1 and L2 is appropriate, and a case where the irradiation interval (or the moving speed of the workpiece) is appropriately adjusted, and is shown in FIG. 8 (b-2). As described above, the surface state of the material layer after peeling was good, and no material that adversely affects the light emission characteristics such as dirt and scratches was found.
FIG. 8C-1 shows a case where the overlapping amount of the laser beams L1 and L2 is large, and the intensity of the laser beam in the overlapping region exceeds 115% with respect to the decomposition threshold VE. As shown in the figure, the surface of the material layer after peeling had many stains such as black spots.
　また、レーザ光１０７を図４に示すレーザ光学系４０によって、図３に示す断面において、周方向になだらかに広がるエッジ部ＬＥに続いて頂上に平坦面を有する略台形状の光強度分布を有するように成形することにより、図３に示すレーザ光をＧａＮ層１０２に照射した際に、レーザ光の照射領域のエッジ部において急激なレーザアブレーションが行わることを緩和することができる。
　よって、ＧａＮ層１０２の分解時にＮ２ガスが急激に発生することによる過剰な応力がＧａＮ層１０２に加わることを緩和し、剥離後のＧａＮ層１０２へのクラック発生を確実に低減することができる。
　さらに、本発明においては、レーザ光はＧａＮ層１０２の隣接する照射領域に照射されるレーザ光が適切な重畳度となるように重畳されている。それにより、ＧａＮ層１０２のレーザ光の各照射領域のエッジ部に照射されるレーザ光のエネルギーが、ＧａＮ層１０２を剥離させるために十分であり、ＧａＮ層１０２をサファイア基板１０１から確実に剥離させることができる。 Further, the laser optical system 40 shown in FIG. 4 causes the laser light 107 to have a substantially trapezoidal light intensity distribution having a flat surface on the top following the edge portion LE that gently spreads in the circumferential direction in the cross section shown in FIG. By shaping in this way, when laser light shown in FIG. 3 is irradiated onto the GaN layer 102, abrupt laser ablation at the edge of the laser light irradiation region can be mitigated.
Therefore, it is possible to alleviate the application of excessive stress to the GaN layer 102 due to the rapid generation of N 2 gas when the GaN layer 102 is decomposed, and to reliably reduce the occurrence of cracks in the GaN layer 102 after peeling. .
Furthermore, in the present invention, the laser beam is superimposed so that the laser beam irradiated to the adjacent irradiation region of the GaN layer 102 has an appropriate degree of superimposition. Thereby, the energy of the laser light applied to the edge portion of each irradiation region of the laser light of the GaN layer 102 is sufficient for peeling the GaN layer 102, and the GaN layer 102 is surely peeled from the sapphire substrate 101. be able to.
　次に、上記したレーザリフトオフ処理を適用することができる半導体発光素子の製造方法について説明する。以下ではＧａＮ系化合物材料層により形成される半導体発光素子の製造方法について図９を用いて説明する。
　結晶成長用の基板には、レーザ光を透過し材料層を構成する窒化ガリウム（ＧａＮ）系化合物半導体を結晶成長させることができるサファイア基板を使用する。
　図９（ａ）に示すように、サファイア基板１０１上には、例えば有機金属気相成長法（ＭＯＣＶＤ法）を用いて迅速にＧａＮ系化合物半導体よりなるＧａＮ層１０２が形成される。続いて、図９（ｂ）に示すように、ＧａＮ層１０２の表面には、発光層であるｎ型半導体層１０３とｐ型半導体層１０４とを積層させる。例えば、ｎ型半導体としてはシリコンがドープされたＧａＮが用いられ、ｐ型半導体としてはマグネシウムがドープされたＧａＮが用いられる。続いて、図９（ｃ）に示すように、ｐ型半導体層１０４上には、半田１０５が塗布される。続いて、図９（ｄ）に示すように、半田１０５上にサポート基板１０６が取付けられる。サポート基板１０６は例えば銅とタングステンの合金からなる。そして、図９（ｅ）に示すように、サファイア基板１０１の裏面側からサファイア基板１０１とＧａＮ層１０２との界面に向けてレーザ光１０７を照射し、ＧａＮ層１０２を分解することによってサファイア基板１０１を剥離する。サファイア基板１０１から剥離後のＧａＮ層１０２の表面に透明電極であるＩＴＯ１０８を蒸着により形成し、ＩＴＯ１０８の表面に電極１０９を取付ける。 Next, a method for manufacturing a semiconductor light emitting device to which the above-described laser lift-off process can be applied will be described. Below, the manufacturing method of the semiconductor light-emitting device formed of a GaN-based compound material layer will be described with reference to FIG.
As the substrate for crystal growth, a sapphire substrate capable of crystal growth of a gallium nitride (GaN) compound semiconductor that transmits laser light and forms a material layer is used.
As shown in FIG. 9A, a GaN layer 102 made of a GaN-based compound semiconductor is rapidly formed on a sapphire substrate 101 by using, for example, a metal organic chemical vapor deposition method (MOCVD method). Subsequently, as illustrated in FIG. 9B, an n-type semiconductor layer 103 and a p-type semiconductor layer 104 that are light emitting layers are stacked on the surface of the GaN layer 102. For example, GaN doped with silicon is used as the n-type semiconductor, and GaN doped with magnesium is used as the p-type semiconductor. Subsequently, as shown in FIG. 9C, solder 105 is applied on the p-type semiconductor layer 104. Subsequently, as shown in FIG. 9D, the support substrate 106 is attached on the solder 105. The support substrate 106 is made of, for example, an alloy of copper and tungsten. Then, as shown in FIG. 9E, the sapphire substrate 101 is decomposed by irradiating the laser beam 107 from the back surface side of the sapphire substrate 101 toward the interface between the sapphire substrate 101 and the GaN layer 102 to decompose the GaN layer 102. Peel off. ITO 108 which is a transparent electrode is formed on the surface of the GaN layer 102 after peeling from the sapphire substrate 101 by vapor deposition, and the electrode 109 is attached to the surface of the ITO 108.
１　　　　基板
２　　　　材料層
３　　　　ワーク
１０　　　レーザリフトオフ装置
２０　　　レーザ源
３１　　　ワークステージ
３２　　　搬送機構
３３　　　制御部
４０　　　レーザ光学系
４１、４２　　シリンドリカルレンズ
４３　　　ミラー
４４　　　マスク
４５　　　投影レンズ
１０１　　サファイア基板
１０２　　ＧａＮ層
１０３　　ｎ型半導体層
１０４　　ｐ型半導体層
１０５　　半田
１０６　　サポート基板
１０７　　レーザ光
１０８　　透明電極（ＩＴＯ）
１０９　　電極
Ｌ，Ｌ１，Ｌ２　　　　レーザ光
ＬＥ　　　エッジ部
ＶＥ　　　分解閾値 DESCRIPTION OF SYMBOLS 1 Substrate 2 Material layer 3 Work 10 Laser lift-off device 20 Laser source 31 Work stage 32 Transport mechanism 33 Control unit 40 Laser optical system 41, 42 Cylindrical lens 43 Mirror 44 Mask 45 Projection lens 101 Sapphire substrate 102 GaN layer 103 N-type semiconductor layer 104 p-type semiconductor layer 105 solder 106 support substrate 107 laser beam 108 transparent electrode (ITO)
109 Electrode L, L1, L2 Laser beam LE Edge portion VE Decomposition threshold

Claims (7)

  1. 　基板上に材料層が形成されてなる前記基板を通してパルスレーザ光を照射し、前記基板と前記材料層との界面で前記材料層を前記基板から剥離するレーザリフトオフ方法において、
    　前記パルスレーザ光は、ワークに対する照射領域を刻々と変えながら上記ワークに照射され、
    　前記ワークにおいて隣接する各照射領域に照射されるそれぞれのパルスレーザ光が、前記材料層を前記基板から剥離させるに必要な分解閾値を超えるエネルギー領域において重畳する
    ことを特徴とするレーザリフトオフ方法。     In a laser lift-off method of irradiating a pulse laser beam through the substrate in which a material layer is formed on the substrate and peeling the material layer from the substrate at an interface between the substrate and the material layer,
    The pulse laser light is irradiated to the workpiece while changing the irradiation area for the workpiece every moment,
    A laser lift-off method, wherein each pulsed laser beam irradiated to each irradiation region adjacent to the workpiece is superimposed in an energy region exceeding a decomposition threshold necessary for peeling the material layer from the substrate.
  2. 　前記ワークにおいて隣接する各照射領域に照射される各レーザ光が重畳している領域におけるレーザ光の強度が、前記材料層を前記基板から剥離させるに必要な分解閾値ＶＥに対して、ＶＥ×１．１５以下である
    ことを特徴とする請求項１記載のレーザリフトオフ方法。     The intensity of the laser beam in the region where each irradiation region irradiated on each irradiation region adjacent to the workpiece is overlapped is VE × 1 with respect to the decomposition threshold VE necessary for peeling the material layer from the substrate. The laser lift-off method according to claim 1, wherein the laser lift-off method is .15 or less.
  3. 　前記ワークを第１の搬送方向に搬送する第１の搬送動作と、前記ワークを第１の搬送動作の搬送方向と直交する方向に搬送する第２の搬送動作と、前記ワークを前記第１の搬送動作の搬送方向と１８０°異なる方向に搬送する第３の搬送動作とを順次に実行することを特徴とする請求項１または請求項２に記載のレーザリフトオフ方法。 A first transport operation for transporting the work in a first transport direction; a second transport operation for transporting the work in a direction perpendicular to the transport direction of the first transport operation; and the work in the first transport direction. 3. The laser lift-off method according to claim 1, wherein a third transport operation for transporting in a direction different from the transport direction of the transport operation by 180 ° is sequentially performed.
  4. 　基板上に材料層が形成されてなる前記基板を通してパルスレーザ光を照射し、前記基板と前記材料層との界面で前記材料層を前記基板から剥離するレーザリフトオフ装置において、
    　前記基板を透過すると共に前記材料層を分解するために必要な波長域のパルスレーザ光を発生するレーザ源と、
    　前記ワークと前記レーザ源とを相対的に搬送する搬送機構と、
    　前記レーザ源から発したパルスレーザ光を成形して、前記ワークに照射するレーザ光学系と、
    　前記レーザ光の照射間隔を制御するとともに、前記搬送機構を制御して、レーザ光の１ショット毎にワークに対する照射領域が刻々と変わるようにワークを移動させる制御部とを備え、
    　前記制御部は、前記ワークにおいて隣接する各照射領域に照射されるそれぞれのレーザ光を、前記材料層を前記基板から剥離させるに必要な分解閾値を超えるエネルギー領域において重畳させるように、レーザ光の照射間隔を制御することを特徴とするレーザリフトオフ装置。     In a laser lift-off device that irradiates a pulse laser beam through the substrate in which a material layer is formed on the substrate and peels the material layer from the substrate at an interface between the substrate and the material layer,
    A laser source that transmits pulsed laser light in a wavelength region that is necessary for transmitting the substrate and decomposing the material layer;
    A transport mechanism for relatively transporting the workpiece and the laser source;
    A laser optical system for shaping pulse laser light emitted from the laser source and irradiating the workpiece;
    A control unit for controlling the irradiation interval of the laser beam and controlling the transport mechanism to move the workpiece so that the irradiation region for the workpiece changes every moment of the laser beam;
    The control unit is configured to superimpose laser beams irradiated on each irradiation region adjacent to the workpiece in an energy region exceeding a decomposition threshold necessary for peeling the material layer from the substrate. A laser lift-off device that controls an irradiation interval.
  5. 　前記制御部は、前記ワークにおいて隣接する各照射領域に照射される各レーザ光の重畳度が、前記材料層を前記基板から剥離させるに必要な分解閾値ＶＥに対して、ＶＥ×１．１５以下となるように、前記レーザ光の照射間隔を制御することを特徴とする請求項４記載のレーザリフトオフ装置。 The controller is configured such that the degree of superimposition of each laser beam irradiated on each irradiation region adjacent to the workpiece is VE × 1.15 or less with respect to a decomposition threshold VE necessary for peeling the material layer from the substrate. The laser lift-off device according to claim 4, wherein an irradiation interval of the laser light is controlled so that
  6. 　前記レーザ光学系は、前記レーザ光を前記ワークに集光させる投影レンズを有し、
    　前記ワークの光入射面は、前記レーザ光の光軸方向において前記投影レンズの焦点位置に一致することなく配置されていることを特徴とする請求項４または請求項５記載のレーザリフトオフ装置。     The laser optical system has a projection lens that focuses the laser light on the workpiece,
    6. The laser lift-off device according to claim 4, wherein a light incident surface of the workpiece is arranged without being coincident with a focal position of the projection lens in an optical axis direction of the laser light.
  7. 　前記搬送機構は、前記ワークを第１の搬送方向に搬送する第１の搬送動作と、前記ワークを第１の搬送動作の搬送方向と直交する方向に搬送する第２の搬送動作と、前記ワークを前記第１の搬送動作の搬送方向と１８０°異なる方向に搬送する第３の搬送動作とを順次に実行することを特徴とする請求項４または請求項５記載のレーザリフトオフ装置。 The transport mechanism includes a first transport operation for transporting the work in a first transport direction, a second transport operation for transporting the work in a direction orthogonal to the transport direction of the first transport operation, and the work 6. The laser lift-off device according to claim 4, wherein a third transport operation for transporting the laser beam in a direction different from the transport direction of the first transport operation by 180 ° is sequentially performed.
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