WO2022079962A1 - １３族元素窒化物結晶層の育成方法、窒化物半導体インゴットおよびスパッタリングターゲット - Google Patents

１３族元素窒化物結晶層の育成方法、窒化物半導体インゴットおよびスパッタリングターゲット Download PDF

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WO2022079962A1
WO2022079962A1 PCT/JP2021/026080 JP2021026080W WO2022079962A1 WO 2022079962 A1 WO2022079962 A1 WO 2022079962A1 JP 2021026080 W JP2021026080 W JP 2021026080W WO 2022079962 A1 WO2022079962 A1 WO 2022079962A1
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crystal layer
group
nitride
substrate
nitride semiconductor
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義孝 倉岡
健太朗 野中
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NGK Insulators Ltd
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    • 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
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/403—AIII-nitrides
    • C30B29/406—Gallium nitride
    • C—CHEMISTRY; METALLURGY
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    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/38—Nitrides
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    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/34—Sputtering
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    • 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
    • C30B19/00—Liquid-phase epitaxial-layer growth
    • C30B19/02—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux
    • 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
    • C30B19/00—Liquid-phase epitaxial-layer growth
    • C30B19/02—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux
    • C30B19/04—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux the solvent being a component of the crystal composition
    • 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
    • C30B19/00—Liquid-phase epitaxial-layer growth
    • C30B19/12—Liquid-phase epitaxial-layer growth characterised by the substrate
    • 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
    • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
    • C30B23/02—Epitaxial-layer growth
    • 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
    • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
    • C30B23/02—Epitaxial-layer growth
    • C30B23/025—Epitaxial-layer growth characterised by the substrate
    • 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
    • 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
    • C30B9/00—Single-crystal growth from melt solutions using molten solvents
    • C30B9/04—Single-crystal growth from melt solutions using molten solvents by cooling of the solution
    • C30B9/08—Single-crystal growth from melt solutions using molten solvents by cooling of the solution using other solvents
    • C30B9/12—Salt solvents, e.g. flux growth

Definitions

  • the present invention relates to a method for growing a group 13 element nitride crystal layer, a nitride semiconductor ingot and a sputtering target.
  • Nitride semiconductors have a wide bandgap of direct transition type, a high dielectric breakdown electric field, and a high saturated electron velocity. Therefore, they are used as semiconductor materials for light emitting devices such as LEDs and LDs and high frequency / high power electronic devices. Attention has been paid.
  • Patent Document 1 Japanese Patent Application Laid-Open No. 2005-206415.
  • elements such as Mn, Fe, Cr, Co, and Ni are added to the melt in order to promote the N-plane growth of gallium nitride crystals on the inner wall surface of the rutsubo, but in the example, the length is 1.5. Only the growth of columnar crystals of about mm is obtained.
  • Patent Document 2 Japanese Patent Laid-Open No. 2010-280562
  • a gallium nitride crystal is grown thickly by combining a flux method and a gas phase method, and the surface roughness Ra is 5 nm or less and the radius of curvature of the warp is 2 m or more.
  • a method of processing to produce an ingot is shown.
  • Patent Document 3 WO2016 / 158651.
  • Patent Document 4 JP-A-2019-003090 (0060) to (0061) to (0061).
  • Patent Document 5 JP-A-2000-101139. This method is hereinafter referred to as a laser lift-off method.
  • Patent Document 6 Japanese Patent Laid-Open No. 2005-263622
  • the upper limit of the growth rate of a GaN crystal by the flux method is about 100 ⁇ m / h.
  • Patent Document 3 when a gallium nitride powder is sintered and a gallium nitride thin film is formed by using a sputtering target obtained by sintering the gallium nitride powder, the oxygen concentration of the gallium nitride thin film is larger than 1 ⁇ 10 20 cm -3 . It is shown. Since the surface area of powdered gallium nitride is large, the surface is easily oxidized in the atmosphere, oxygen is released at the start of the sputtering process, a gallium nitride thin film is formed on the substrate, and oxygen is easily mixed inside. Therefore, it is considered difficult to form a homogeneous gallium nitride thin film having a low oxygen concentration.
  • GaN can be thickly grown on an oriented crystal by, for example, the HVPE method or the flux method instead of a sintered body of GaN powder to form a GaN bulk material, it can be used as a sputtering target with a low impurity concentration, especially oxygen concentration, and oxygen can be obtained by sputtering processing. It should be possible to form a low-concentration gallium nitride thin film. However, it is considered difficult to produce a sputtering target by the existing manufacturing method because it takes time to grow and the thickness is easily cracked due to warping in order to make the thickness suitable for the sputtering target.
  • An object of the present invention is to grow a group 13 elemental nitride crystal layer at a high growth rate so that a thick group 13 elemental nitride crystal layer can be obtained.
  • an object of the present invention is to obtain a homogeneous sputtering target having a low oxygen concentration.
  • the present invention is a method for growing a group 13 element nitride crystal layer on a base substrate including at least a seed crystal layer.
  • the base substrate is immersed in a melt containing flux, and a group 13 element nitride crystal layer is two-dimensionally grown on the nitrogen polar plane of the seed crystal layer by a flux method.
  • the present invention also relates to a nitride semiconductor ingot, which comprises a group 13 elemental nitride and has a diameter of 75 mm or more, 200 mm or less, a thickness of 5 mm or more, and a thickness of 50 mm or less. It is a method of manufacturing a base substrate for growing a group 13 element nitride crystal layer. The process of forming a seed crystal layer on the substrate, By joining the group 13 element polar plane of the seed crystal layer to the support substrate and peeling the substrate from the seed crystal layer, a base substrate containing the seed crystal layer and the support substrate is obtained.
  • a method for producing a base substrate which comprises a step of exposing the nitrogen polar surface of the seed crystal layer.
  • the present inventor puts a seed crystal into the melt when growing the group 13 elemental nitride crystal layer by the flux method, and two-dimensionally puts the group 13 elemental nitride crystal layer on the nitrogen polar plane of the seed crystal.
  • the group 13 element nitride crystal layer is grown on the group 13 element polar plane (for example, gallium polar plane)
  • the group 13 element nitride crystal layer can be grown at a higher growth rate than the case where the group 13 element nitride crystal layer is grown. I found it.
  • a thick film for example, a group 13 element nitride crystal layer having a thickness of 5 mm or more at a practical speed
  • a nitride semiconductor ingot has excellent properties as a sputtering target, for example, and can provide a homogeneous target having a particularly low oxygen concentration.
  • nitride semiconductor wafers can be produced by slicing from the nitride semiconductor ingot thus obtained, which is an extremely excellent mass production method.
  • the crystal lattice is appropriately curved inside, and the orientation of the crystal lattice (particularly the c-plane) between the nitrogen polar plane and the group 13 element polar plane is moderately curved. It turned out that it was changing.
  • the growth plane side becomes closer to a single crystal as the crystal growth progresses, so that the crystal strain in the plane of the nitride semiconductor wafer obtained by slicing the nitride semiconductor ingot becomes smaller. To go. As a result, a nitride semiconductor wafer having a small distribution of off-angles in the plane was obtained.
  • (A) shows a state in which the seed crystal layer 2 is formed on the substrate 1, and (b) irradiates the surface 2a of the seed crystal layer 2 and the surface 3a of the support substrate 3 with the activation beams A and B.
  • (C) shows a state in which the seed crystal layer 2 and the support substrate 3 are directly bonded.
  • (A) shows a state in which the substrate 1 is peeled off from the seed crystal layer 2, and (b) shows a state in which the group 13 element nitride crystal layer 4 is grown on the nitrogen polar surface 2b of the seed crystal layer 2.
  • (C) show a state in which the support substrate 3 is peeled off from the group 13 elemental nitride crystal layer 4, and (d) shows an ingot 5 made of the group 13 elemental nitride crystal layer. It is a top view which shows the measurement point in the nitride semiconductor wafer obtained by slicing a nitride semiconductor ingot 5 and a nitride semiconductor ingot.
  • the seed crystal layer 2 is formed on the surface 1a of the substrate 1.
  • 2b is a nitrogen polar surface
  • the growth surface 2a is a Group 13 element polar surface.
  • this seed crystal layer 2 is bonded to a separate support substrate.
  • the activation beam A is irradiated on the group 13 element polar surface 2a of the seed crystal layer 2 to activate the surface.
  • the surface 3a of the support substrate 3 is irradiated with an activation beam as shown by an arrow B to activate the surface.
  • a bonded body can be obtained by bringing the group 13 element polar surface 2a of the seed crystal layer 2 into contact with the activated surface 3a of the support substrate 3 and directly bonding them. ..
  • the substrate 1 is separated from the seed crystal layer 2 to obtain the underlying substrate 6.
  • the nitrogen polar surface 2b of the seed crystal layer 2 is exposed.
  • the Group 13 element nitride crystal layer 4 is grown on the nitrogen polar plane 2b of the seed crystal layer 2 by the flux method.
  • a group 13 element nitride crystal layer is grown on a base substrate containing at least a seed crystal layer.
  • the entire base substrate may be composed of a seed crystal layer, but preferably, a seed crystal layer is formed on the support substrate.
  • the Group 13 element nitride crystal layer is two-dimensionally grown on the nitrogen polar plane of the seed crystal layer by the flux method.
  • the two-dimensional growth of the Group 13 element nitride crystal layer means that the crystal grows so as to cover the nitrogen polar plane of the seed crystal layer to form a crystal layer.
  • the Group 13 element nitride crystal layer it is preferable to grow the Group 13 element nitride crystal layer to a thickness of 5 mm or more on the nitrogen polar plane of the seed crystal layer, and it is more preferable to grow it to a thickness of 10 mm or more. Further, although there is no particular upper limit to the thickness of the Group 13 element nitride crystal layer, it is often 50 mm or less in practice.
  • the seed crystal layer is formed on the substrate, the seed crystal layer is bonded to a separate support substrate, and then the original substrate is removed to support the seed crystal layer. The nitrogen polar surface of the seed crystal layer on the substrate is exposed.
  • the crystal is peeled off at the interface between the support substrate and the crystal before the crystal is cracked together with the support substrate, so that the crystal is cracked. It is possible to obtain thick crystals while preventing the above. This made it possible to obtain a sufficiently thick nitride semiconductor ingot.
  • a seed crystal layer on the substrate after providing the low temperature buffer layer.
  • a vapor phase growth method is preferable, and examples thereof include a metalorganic chemical vapor deposition (MOCVD) method, a hydride vapor phase growth (HVPE) method, and an MBE method.
  • MOCVD metalorganic chemical vapor deposition
  • HVPE hydride vapor phase growth
  • MBE MBE method
  • the vapor phase deposition method can be mentioned, and the metalorganic chemical vapor deposition (MOCVD) method, the hydride vapor phase deposition (HVPE) method, and the pulse-excited deposition (MOCVD: Metalorganic Chemical Vapor Deposition) method can be mentioned.
  • MOCVD metalorganic chemical vapor deposition
  • HVPE hydride vapor phase deposition
  • MOCVD Metalorganic Chemical Vapor Deposition
  • the PXD) method, the MBE method, and the sublimation method can be exemplified.
  • the metalorganic chemical vapor deposition method is particularly preferred.
  • the group 13 element is the group 13 element according to the periodic table formulated by IUPAC.
  • Specific examples of the Group 13 element are boron, gallium, aluminum, indium, thallium and the like.
  • the thickness of the seed crystal layer is preferably 0.5 ⁇ m or more, and more preferably 2 ⁇ m or more, from the viewpoint of preventing meltback and disappearance during crystal growth.
  • the thickness of the seed crystal layer is preferably 15 ⁇ m or less from the viewpoint of productivity.
  • the material of the substrate is not particularly limited, but it is necessary to enable crystal growth in the direction in which the group 13 element polar plane of the seed crystal layer is exposed. From this point of view, the material of the substrate can be exemplified by sapphire, crystal-oriented alumina, or a group 13 element nitride single crystal.
  • the material of the support substrate is not particularly limited, and examples thereof include sapphire, crystal-oriented alumina, and Group 13 element nitride single crystal.
  • the thickness of the support substrate is preferably 500 ⁇ m or more, more preferably 1000 ⁇ m or more, from the viewpoint of handling.
  • the joining method for joining the seed crystal layer on the substrate and the support substrate can be exemplified by direct joining or bonding with an adhesive.
  • the growth plane of the Group 13 element nitride crystal layer is the nitrogen polar plane.
  • the CBED convergent electron diffraction
  • it can be confirmed as a nitrogen polar surface by converging an electron beam on the sample, acquiring a circular diffraction spot from the sample, and comparing it with the diffraction image (CBED pattern) calculated by simulation. ..
  • the Group 13 element nitride crystal layer is grown by the flux method.
  • the Group 13 element is a Group 13 element according to the periodic table formulated by IUPAC.
  • the group 13 element nitride specifically, GaN, AlN, InN, AlGaN or a mixed crystal thereof is preferable.
  • the group 13 element nitride crystal layer is preferably a single crystal.
  • the definition of a single crystal will be described. It includes, but is not limited to, a textbook-like single crystal in which atoms are regularly arranged throughout the crystal, but means a single crystal that is generally distributed in the industrial world. That is, the crystal may contain some defects, may have internal strain, or may contain impurities, and these are referred to as single crystals to distinguish them from polycrystals (ceramics). Is synonymous with.
  • the type of flux is not particularly limited as long as gallium nitride crystals can be produced.
  • it is a flux containing at least one of an alkali metal and an alkaline earth metal, and a flux containing a sodium metal is particularly preferable.
  • a metal raw material is mixed with the flux and used.
  • the metal raw material elemental metals, alloys, and metal compounds can be applied, but elemental metals are also suitable in terms of handling.
  • the growth temperature of the Group 13 element nitride crystal layer in the flux method and the holding time at the time of growth are not particularly limited, and are appropriately changed according to the composition of the flux. In one example, when growing a gallium nitride crystal using a sodium or lithium-containing flux, the growth temperature is preferably 800 to 950 ° C, more preferably 850 to 900 ° C.
  • a group 13 element nitride crystal layer is grown in an atmosphere containing a gas containing nitrogen atoms.
  • This gas is preferably nitrogen gas, but may be ammonia.
  • the pressure of the atmosphere is not particularly limited, but from the viewpoint of preventing evaporation of the flux, 10 atm or more is preferable, and 30 atm or more is more preferable. However, since the device becomes large when the pressure is high, the total pressure of the atmosphere is preferably 2000 atm or less, and more preferably 500 atm or less.
  • the gas other than the gas containing nitrogen atoms in the atmosphere is not limited, but an inert gas is preferable, and argon, helium, and neon are particularly preferable.
  • the base substrate In order to grow the Group 13 element nitride crystal layer two-dimensionally on the nitrogen polar plane of the seed crystal layer by the flux method, it is preferable to arrange the base substrate horizontally in the rutsubo, whereby the seed of the base substrate is formed. It is preferable to promote the nitrogen supply over the entire surface of the crystal layer. Further, it is preferable to sufficiently increase the nitrogen concentration in the flux liquid. In order to increase the nitrogen concentration, it is necessary to raise the temperature of the flux liquid to a high temperature and then sufficiently stir the flux liquid to dissolve the nitrogen until the nitrogen concentration of the whole liquid becomes supersaturated.
  • the method of separating the substrate and the seed crystal layer and the method of separating the support substrate from the group 13 element nitride crystal layer are not particularly limited, and examples thereof include grinding, laser ablation, and chemical mechanical polishing, but laser lift-off.
  • the method is particularly preferred.
  • the laser light sources include the 3rd harmonic, 4th harmonic, 5th harmonic, F2 excima laser, ArF excima laser, KrF excima laser, XeCl excima laser, and XeF excima laser of the Nd: YAG laser.
  • the 3rd and 4th harmonics of the YVO4 laser, and the 3rd and 4th harmonics of the YLF laser can be exemplified.
  • Particularly preferred laser light sources include the 3rd harmonic of the Nd: YAG laser, the 4th harmonic of the Nd: YAG laser, the 3rd and 4th harmonics of the YVO4 laser, and the KrF excimer laser.
  • the irradiation type of the laser may be circular, elliptical, square, or linear.
  • the laser profile may be shaped through a beam profiler.
  • the laser profile may be Gaussian, Gaussian-like, donut, or top hat. Gaussian and top hats are preferred.
  • the substrate may be irradiated with the laser after passing through a lens, a slit, or an aperture.
  • a pulsed laser there is no particular limitation on the pulse width of the laser, but a laser of 100 fs to 200 ns can be used.
  • the pulse width of the laser is preferably 200 ns or less, more preferably 1 ns or less. You may irradiate the laser while heating the support substrate. Since the warp is reduced when heated, uniform processing can be performed on the substrate surface.
  • nitride semiconductor wafers having a nitrogen polar plane and a group 13 element polar plane can be manufactured. This significantly improves productivity as compared to producing wafers on a sheet-fed basis.
  • the material of the nitride semiconductor wafer is the same as that of the nitride semiconductor ingot, and examples thereof include a GaN wafer, an AlN wafer, and an AlGaN wafer.
  • Niride semiconductor ingot (Nitride semiconductor ingot) According to the present invention, it is possible to provide a nitride semiconductor ingot made of Group 13 elemental nitride having a diameter of 75 mm or more, a diameter of 200 mm or less, and a thickness of 5 mm or more. Such nitride semiconductor ingots are difficult to manufacture and have not been provided so far.
  • the nitride semiconductor ingot of the present invention has a low oxygen concentration as an impurity, and has a small oxygen concentration unevenness in the thickness direction and in the plane. That is, the oxygen concentration on the polar surface of the group 13 element is 0.8 ⁇ 10 17 cm -3 or more and 2 ⁇ 10 17 cm -3 or less, and the oxygen concentration on the nitrogen polar surface of the nitride semiconductor ingot is 0.5 ⁇ 10 17 It can be cm -3 or more and 1.5 ⁇ 10 17 cm -3 or less.
  • Nitride semiconductor ingots made of conventional sintered bodies have only high concentrations of impurities such as oxygen. However, in the present invention, a group 13 element nitride crystal layer having high purity can be used, and in particular, a sputtering target having a sufficiently low oxygen concentration can be provided.
  • a functional element structure can be formed on the group 13 element nitride crystal layer thus obtained.
  • this functional element structure can also be obtained by forming a film by a sputtering process using the obtained sputtering target.
  • This functional element structure can be used for high-brightness, high-color rendering white LEDs, blue-purple laser disks for high-speed high-density optical memory, power devices for inverters for hybrid vehicles, and the like.
  • Example 1 Film formation of seed crystal layer
  • the group 13 element nitride crystal layer and the nitride semiconductor ingot of the present invention were produced. Specifically, a 3-inch sapphire substrate (base 1) with an off-angle of 0.5 degrees is placed on a susceptor in a MOCVD furnace (metalorganic chemical vapor deposition furnace), and the substrate temperature is raised to 1200 ° C for cleaning in a hydrogen atmosphere. Processing was performed.
  • MOCVD furnace metalorganic chemical vapor deposition furnace
  • the temperature was lowered to 520 ° C., and a gallium nitride layer (buffer layer) was formed to a thickness of 20 nm using hydrogen as a carrier gas and TMG (trimethylgallium) and ammonia as raw materials.
  • the substrate temperature was raised to 1100 ° C. using nitrogen and hydrogen as carrier gases, and the GaN seed crystal layer 2 was grown to a thickness of 3 ⁇ m using TMG (trimethylgallium) and ammonia as raw materials.
  • the substrate on which the GaN crystal layer was grown was lowered to room temperature in a nitrogen atmosphere, and then taken out from the MOCVD furnace (see FIG. 1 (a)).
  • the substrate 1 on which the GaN seed crystal layer 2 was formed was taken out, and the surface of the GaN seed crystal layer 2 and the support substrate 3 made of polycrystalline alumina were directly bonded at room temperature (surface activation method).
  • the surface roughness RMS of the support substrate 3 made of polycrystalline alumina was set to 1 nm by polishing the surface.
  • Argon beams A and B were irradiated, and the polished surfaces were brought into contact with each other in a vacuum to apply a load to directly bond them.
  • the repetition frequency is 10 Hz
  • the pulse width is 10 ns
  • the focal length is 700 mm
  • the lens is focused
  • the distance between the lens and the substrate surface is 400 mm
  • the light energy density at the time of laser lift-off is 500 mJ / cm 2
  • the irradiation is performed by a pulse laser. The entire substrate was scanned so that the dots overlap.
  • the GaN crystal layer 4 was grown into a thick film by the flux method using the 3-inch polycrystalline alumina-supported substrate 3 to which the GaN seed crystal layer 2 was bonded (FIG. 2 (b)). Specifically, after preparing an alumina crucible and arranging a 3-inch polycrystalline alumina support substrate 3 to which the GaN seed crystal layer 2 is bonded in the alumina crucible, 400 g of metal Ga and 800 g of metal Na are added to the alumina crucible. The 3-inch polycrystalline alumina support substrate 3 to which the GaN seed crystal layer 2 was bonded was immersed in a melt containing a flux.
  • this alumina crucible is placed in a refractory metal growing container and sealed.
  • the temperature inside the furnace was set to 850 ° C, and nitrogen gas was introduced to set the pressure inside the furnace to 4 MPa.
  • the GaN crystal layer was grown on the polycrystalline alumina support substrate 3 to which the GaN seed crystal layer 2 was bonded by holding the growth container horizontally for 35 hours in a heat-resistant and pressure-resistant crystal growth furnace. .. After cooling to room temperature, when the substrate on which the GaN crystal layer was grown was taken out from the alumina crucible, the GaN seed crystal layer 2 and the support substrate 3 were spontaneously peeled off, and the thick film GaN crystal layer 4 had a diameter of 3 inches and was about. A 5.5 mm thickness was obtained.
  • the front surface and the back surface (peeled surface) of the removed thick film GaN crystal layer 4 were flattened by polishing with diamond abrasive grains so as to have a thickness of 5 mm, and a nitride semiconductor ingot 5 having a diameter of 3 inches was obtained. (FIG. 2 (d)).
  • Example 2 The off-angle of the 3-inch sapphire substrate used in Example 1 was changed to 0.0 degrees, 0.3 degrees, 1 degree, 2 degrees, and 3 degrees to prepare 5 types, and nitrided by the same method as in Example 1.
  • the off angles were 0.0 degrees and 3 degrees, but the off angles were 0.3 degrees, 1 degree, and 2 degrees.
  • a nitride semiconductor ingot having a thickness of 3 inches and a thickness of 5 mm was obtained in the same manner as in Example 1.
  • nitride ingots are designated as #A (0.3 degrees), #B (1 degree), and #C (2 degrees) in ascending order of off angle, and 9 points in the plane of each of the gallium polar plane and the nitrogen polar plane.
  • SIMS analysis was performed at. As schematically shown in FIG. 3, the nine in-plane points are set with a virtual circle C1 having a radius of 30 mm and a virtual circle C2 having a radius of 60 mm around the center O of the surface 5a of the nitride ingot 5. Further, virtual lines P and H that pass through the center O and are orthogonal to each other are set.
  • the measurement points are the center O, the intersections A1, A2, A3, A4 between the virtual circle C1 and the virtual lines P and H, and the intersections B1, B2, B3 and B4 between the virtual circle C2 and the virtual lines P and H.
  • Table 1 shows the results of calculating the average value of the oxygen concentration having a depth of 5 ⁇ m to 25 ⁇ m at 9 points in the plane and obtaining the maximum value and the minimum value, respectively.
  • Example 3 Sputtering target
  • the nitride semiconductor ingot of Example 2 was used to heat a copper plate (backing plate), and the nitride semiconductor ingot was bonded using metallic indium to serve as a sputtering target.
  • Ar 20sccm, N 2 100sccm, pressure 1 Pa, RF power power 400W using a 2-inch sapphire substrate as the base material, the temperature of the substrate was set to 250 ° C, and a GaN film was formed by sputtering. rice field.
  • a GaN film having a thickness of 1 ⁇ m was uniformly formed.
  • the oxygen concentrations were all 1 ⁇ 10 17 (cm -3 ).
  • the same quality GaN film could be stably formed even if the sputtering target was consumed.
  • Example 4 In the same manner as in Example 1, a GaN crystal layer was grown into a thick film by a flux method using a 3-inch polycrystalline alumina-supported substrate bonded with a GaN seed crystal layer.
  • a flux method 2000 g of metal Ga and 4000 g of metal Na are filled in an alumina crucible. Further, this alumina crucible is placed in a refractory metal growing container and sealed. The temperature inside the furnace was set to 850 ° C, and nitrogen gas was introduced to set the pressure inside the furnace to 4 MPa.
  • a GaN crystal layer was grown on a 3-inch polycrystalline alumina support substrate to which a GaN seed crystal layer was bonded by holding the growth container for 300 hours while rotating it horizontally in a heat-resistant and pressure-resistant crystal growth furnace. .. After cooling to room temperature, when the substrate on which the GaN crystal layer was grown was taken out from the alumina crucible, the GaN crystal layer and the polycrystalline alumina support substrate were naturally exfoliated, and the thick film GaN crystal layer was 3 inches and about 52 mm. The thickness was obtained.
  • the front surface and the back surface of the removed thick film GaN crystal layer were flattened by polishing with diamond abrasive grains, and a nitride semiconductor ingot having a thickness of 50 mm was obtained.
  • This nitride semiconductor ingot was sliced to obtain 50 3-inch GaN wafers (nitride semiconductor wafers) having a thickness of 0.5 mm.
  • Three of the obtained GaN wafers were extracted, and the off-angle of the GaN wafer, its distribution and the warp shape were measured.
  • the wafer closest to the gallium polar plane was designated as #D
  • the wafer closest to the nitrogen polar plane was designated as #F
  • the wafer between #D and #F was designated as #E.
  • the off-angle was measured at 9 in-plane points on the gallium polar plane of the GaN wafer.
  • the measurement positions of the nine points in the plane were O, A1, A2, A3, A4, B1, B2, B3 and B4 shown in FIG.
  • a D2 Cryso manufactured by Bruker AXS was used to measure the off-angle, and the difference between the maximum value and the minimum value of the off-angle measured at 9 points in the plane was taken as the width of the off-angle.
  • a Nidec flat nestester FT-17 was used to measure the warpage value. The results are shown in Table 2. From Table 2, a substrate having a smaller off-angle width as it was closer to the nitrogen polar plane was obtained.
  • Example 5 A GaN film grown as a thin film on a substrate by sputtering was used as a seed crystal to produce a GaN wafer having a larger diameter. Specifically, when a sputtering process was performed using the sputtering target obtained in Example 3 using a 200 mm diameter sapphire substrate as a base material, a GaN film having a thickness of 1 ⁇ m was uniformly formed. When the polarity was determined by the CBED method, the surface of the GaN film was a gallium polar surface.
  • a thick GaN crystal layer was grown by the flux method.
  • the alumina crucible is filled with 2000 g of metal Ga and 4000 g of metal Na. Further, this alumina crucible is placed in a refractory metal growing container and sealed. The temperature inside the furnace was set to 850 ° C, and nitrogen gas was introduced to set the pressure inside the furnace to 4 MPa.
  • a GaN crystal layer was grown on a sapphire substrate on which a GaN film was formed by holding the growth container for 200 hours while rotating it horizontally in a heat-resistant and pressure-resistant crystal growth furnace.
  • the GaN crystal layer and the supporting substrate made of polycrystalline alumina were spontaneously peeled off, and the thick film GaN crystal layer had a diameter of about 200 mm. A thickness of 6 mm was obtained.
  • a nitride semiconductor ingot having a diameter of 200 mm and a thickness of 5 mm was obtained.
  • This nitride semiconductor ingot was sliced, and the front surface and the back surface were polished and flattened using diamond abrasive grains to obtain three GaN wafers having a diameter of 200 mm and a thickness of 1 mm.

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