WO2021075369A1 - 窒化物半導体基板、積層構造体、および窒化物半導体基板の製造方法 - Google Patents
窒化物半導体基板、積層構造体、および窒化物半導体基板の製造方法 Download PDFInfo
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- 239000000758 substrate Substances 0.000 title claims abstract description 687
- 239000004065 semiconductor Substances 0.000 title claims abstract description 186
- 150000004767 nitrides Chemical class 0.000 title claims abstract description 175
- 238000004519 manufacturing process Methods 0.000 title claims description 70
- 239000013078 crystal Substances 0.000 claims abstract description 248
- 238000005259 measurement Methods 0.000 claims description 147
- 238000000034 method Methods 0.000 claims description 106
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 88
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- 229910052760 oxygen Inorganic materials 0.000 claims description 88
- 230000008569 process Effects 0.000 claims description 35
- 238000001947 vapour-phase growth Methods 0.000 claims description 8
- 239000010410 layer Substances 0.000 description 450
- 239000007789 gas Substances 0.000 description 34
- 229910002601 GaN Inorganic materials 0.000 description 25
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 25
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- UPWPDUACHOATKO-UHFFFAOYSA-K gallium trichloride Chemical compound Cl[Ga](Cl)Cl UPWPDUACHOATKO-UHFFFAOYSA-K 0.000 description 5
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- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 2
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- XCZXGTMEAKBVPV-UHFFFAOYSA-N trimethylgallium Chemical compound C[Ga](C)C XCZXGTMEAKBVPV-UHFFFAOYSA-N 0.000 description 2
- NCGICGYLBXGBGN-UHFFFAOYSA-N 3-morpholin-4-yl-1-oxa-3-azonia-2-azanidacyclopent-3-en-5-imine;hydrochloride Chemical compound Cl.[N-]1OC(=N)C=[N+]1N1CCOCC1 NCGICGYLBXGBGN-UHFFFAOYSA-N 0.000 description 1
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 1
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- XOYLJNJLGBYDTH-UHFFFAOYSA-M chlorogallium Chemical compound [Ga]Cl XOYLJNJLGBYDTH-UHFFFAOYSA-M 0.000 description 1
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- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- MROCJMGDEKINLD-UHFFFAOYSA-N dichlorosilane Chemical compound Cl[SiH2]Cl MROCJMGDEKINLD-UHFFFAOYSA-N 0.000 description 1
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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
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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
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
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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
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
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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
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Definitions
- the present invention relates to a nitride semiconductor substrate, a laminated structure, and a method for manufacturing a nitride semiconductor substrate.
- a substrate made of a single crystal of a group III nitride semiconductor is used as a base substrate (seed substrate), and a group III nitride semiconductor is placed on a main surface in which the closest low index crystal plane is the (0001) plane.
- a method for further growing a crystal layer composed of a single crystal of No. 1 is known. According to this method, at least one nitride semiconductor substrate can be obtained by slicing a crystal layer grown to a predetermined thickness (for example, Patent Document 1).
- An object of the present invention is to improve the crystal quality of a nitride semiconductor substrate.
- Nitride semiconductor substrates are provided in which the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ is 80% or more.
- FWHM1 ⁇ 10-12 ⁇ and FWHM2 ⁇ 10-12 ⁇ are half widths of ⁇ 10-12 ⁇ plane diffraction measured by X-ray locking curve measurement, respectively.
- an X-ray mirror that makes X-rays parallel light
- a Ge (220) double-reflection monochrome meter and a goniometer rotation axis.
- the width in the ⁇ direction as the circumference rotation angle direction is 1.4 mm and the length in the direction parallel to the rotation axis is 12 mm through the incident side opening in this order.
- FWHM1 ⁇ 10-12 ⁇ measured the diffraction of the equivalent crystal plane represented by the ⁇ 10-12 ⁇ plane from three directions rotated by 60 ° in the circumferential direction about the normal of the center of the main plane.
- Nitride semiconductor substrates with a maximum and minimum difference of 9 arcsec or less are provided.
- a nitride semiconductor substrate having a length of 50 arcsec or less is provided.
- a base substrate composed of a single crystal of a group III nitride semiconductor, having a mirrored main surface, and having a low index crystal plane closest to the main surface as the (0001) plane.
- a high oxygen concentration region provided above the main surface of the base substrate and composed of a single crystal of a group III nitride semiconductor and a high oxygen concentration region composed of a single crystal of a group III nitride semiconductor provided on the low oxygen concentration region.
- a laminated unit having an oxygen concentration region and The highest oxygen concentration region which is provided above the laminated unit and is composed of a single crystal of a group III nitride semiconductor, With The oxygen concentration in the high oxygen concentration region is higher than the oxygen concentration in each of the low oxygen concentration region and the highest oxygen concentration region.
- a laminated structure is provided in which a plurality of laminated units are repeatedly provided in the thickness direction between the base substrate and the uppermost low oxygen concentration region.
- a method for manufacturing a nitride semiconductor substrate using a vapor phase growth method (A) A step of preparing a base substrate which is composed of a single crystal of a group III nitride semiconductor, has a mirrored main surface, and has a low index crystal plane closest to the main surface as the (0001) plane.
- C A plurality of recesses composed of inclined interfaces other than the (0001) plane are formed on the surface of a flat homoepitaxially grown crystal, and the inclined interface is gradually expanded as the crystal growth progresses to form a crystal growth interface.
- a step of growing a three-dimensional growth layer which comprises eliminating the (0001) plane at least once.
- D By further epitaxially growing a single crystal of a group III nitride semiconductor on the three-dimensional growth layer, the inclined interface disappears and a flattening layer having a mirrored surface composed of (0001) planes is grown.
- Process and Have Provided is a method for manufacturing a nitride semiconductor substrate in which a cycle including the above (c) and the above (d) is performed a plurality of times.
- the crystal quality of a nitride semiconductor substrate can be improved.
- FIG. 1 It is a flowchart which shows the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention.
- (A) to (g) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention.
- (A)-(c) are schematic cross-sectional views which show a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention. It is a schematic perspective view which shows a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention.
- (A)-(b) are schematic cross-sectional views which show a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention.
- (A)-(b) are schematic cross-sectional views which show a part of the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention.
- FIG. 1 is a schematic cross-sectional view showing a growth process under a reference growth condition in which each of the inclined interface and the c-plane does not expand or contract
- (b) is a th-order view in which the inclined interface expands and the c-plane shrinks.
- FIG. 1 is a schematic cross-sectional view which shows the growth process under 1 growth condition.
- FIG. 2nd growth condition shows the growth process under the 2nd growth condition that the inclined interface shrinks and the c-plane expands.
- FIG. 3C is a schematic cross-sectional view taken along the a-axis of the nitride semiconductor substrate according to the embodiment of the present invention.
- (A) is a schematic cross-sectional view showing the diffraction of X-rays with respect to the curved c-plane
- (b) and (c) are diagrams showing the fluctuation of the diffraction angle of the (0002) plane with respect to the radius of curvature of the c-plane. Is.
- FIG. 1 is a flowchart showing a method for manufacturing a nitride semiconductor substrate according to the present embodiment.
- 2 (a) to (g), FIGS. 3 (a) to 3 (c), FIGS. 5 (a) to 6 (b), and FIGS. 7 to 9 show the production of the nitride semiconductor substrate according to the present embodiment.
- FIG. 4 is a schematic perspective view showing a part of the method for manufacturing a nitride semiconductor substrate according to the present embodiment. Note that FIG.
- FIG. 4 corresponds to the perspective view at the time of FIG. 3B, and shows a part of the three-dimensional growth layer 30 that grows on the base substrate 10. Further, in FIG. 5 (b), the fine solid line indicates a crystal plane during growth, and in FIGS. 3 (c) to 6 (b) and FIGS. 7 to 9, the dotted line indicates a dislocation.
- the method for manufacturing a nitride semiconductor substrate according to the present embodiment is as follows.
- a method for manufacturing a nitride semiconductor substrate using a vapor phase growth method (A) A step of preparing a base substrate which is composed of a single crystal of a group III nitride semiconductor, has a mirrored main surface, and has a low index crystal plane closest to the main surface as the (0001) plane. , (B) A single crystal of a group III nitride semiconductor having a top surface with an exposed (0001) plane is epitaxially grown above the main surface of the base substrate, and a plurality of recesses composed of inclined interfaces other than the (0001) plane are formed.
- C A step of epitaxially growing a single crystal of a group III nitride semiconductor on a three-dimensional growth layer, eliminating the inclined interface, and growing a flattening layer having a mirrored surface. Have, The cycle including (b) and (c) is performed a plurality of times.
- the method for manufacturing a nitride semiconductor substrate includes, for example, a base substrate preparation step S100, a three-dimensional growth step S200, a flattening step S300, and the number of times of implementation. It has a determination step S400, a main growth step S500, a slicing step S600, and a polishing step S700.
- the base substrate 10 made of a single crystal of a group III nitride semiconductor is prepared.
- a gallium nitride (GaN) free-standing substrate is prepared as the base substrate 10.
- the ⁇ 0001> axis (for example, [0001] axis) is referred to as "c-axis", and the (0001) plane is referred to as "c-plane".
- the (0001) plane may be referred to as a "+ c plane (Group III element polar plane)", and the (000-1) plane may be referred to as a "-c plane (nitrogen (N) polar plane)”.
- the ⁇ 1-100> axis (for example, the [1-100] axis) is referred to as an "m axis", and the ⁇ 1-100 ⁇ plane is referred to as an "m plane”.
- the m-axis may be expressed as the ⁇ 10-10> axis.
- the ⁇ 11-20> axis (for example, the [11-20] axis) is referred to as an "a axis”
- the ⁇ 11-20 ⁇ plane is referred to as an "a plane”.
- the base substrate 10 is produced by the VAS (Void-Assisted Separation) method.
- the base substrate preparation step S100 includes, for example, a crystal growth substrate preparation step S110, a first crystal layer forming step S120, a metal layer forming step S130, a void forming step S140, and a second crystal layer forming. It has a step S150, a peeling step S160, a slicing step S170, and a polishing step S180.
- a crystal growth substrate 1 (hereinafter, may be abbreviated as “substrate 1”) is prepared.
- the substrate 1 is, for example, a sapphire substrate.
- the substrate 1 may be, for example, a Si substrate or a gallium arsenide (GaAs) substrate.
- the substrate 1 has, for example, a main surface 1s which is a growth surface.
- the crystal plane with the lowest index closest to the main plane 1s is, for example, the c plane 1c.
- the c-plane 1c of the substrate 1 is inclined with respect to the main surface 1s.
- the c-axis 1ca of the substrate 1 is inclined at a predetermined off angle ⁇ 0 with respect to the normal of the main surface 1s.
- the off angle ⁇ 0 in the main surface 1s of the substrate 1 is uniform over the entire main surface 1s.
- the off angle ⁇ 0 in the main surface 1s of the substrate 1 affects the off angle ⁇ 3 at the center of the main surface 10s of the base substrate 10, which will be described later.
- TMG trimethylgallium
- MOVPE organic metal vapor phase growth
- the metal layer 3 is deposited on the first crystal layer 2.
- the metal layer 3 is, for example, a titanium (Ti) layer. Further, the thickness of the metal layer 3 is set to, for example, 20 nm.
- the above-mentioned substrate 1 is put into an electric furnace, and the substrate 1 is placed on a susceptor having a predetermined heater. After the substrate 1 is placed on the susceptor, the substrate 1 is heated by a heater and heat-treated in an atmosphere containing hydrogen gas or hydride gas. Specifically, for example, heat treatment is performed at a predetermined temperature for 20 minutes in a hydrogen (H 2 ) gas stream containing 20% NH 3 gas.
- the heat treatment temperature is, for example, 850 ° C. or higher and 1,100 ° C. or lower.
- the metal layer 3 is nitrided to form a metal nitride layer 5 having high-density fine holes on the surface. Further, by performing the above-mentioned heat treatment, a part of the first crystal layer 2 is etched through the holes of the metal nitride layer 5 to form high-density voids in the first crystal layer 2.
- the void-containing first crystal layer 4 is formed.
- Si-doped GaN layer is epitaxially grown as a second crystal layer (full-scale growth layer) 6 on the void-containing first crystal layer 4 and the metal nitride layer 5.
- HVPE hydride vapor phase epitaxy
- the Ge-doped GaN layer may be epitaxially grown as the second crystal layer 6 by supplying a tetrachlorogerman (GeCl 4 ) gas or the like as the n-type dopant gas instead of the SiH 2 Cl 2 gas.
- a tetrachlorogerman (GeCl 4 ) gas or the like as the n-type dopant gas instead of the SiH 2 Cl 2 gas.
- the second crystal layer 6 grows from the void-containing first crystal layer 4 onto the void-containing first crystal layer 4 and the metal nitride layer 5 through the holes in the metal nitride layer 5.
- a part of the void in the void-containing first crystal layer 4 is embedded by the second crystal layer 6, but the other part of the void in the void-containing first crystal layer 4 remains.
- a flat void is formed between the second crystal layer 6 and the metal nitride layer 5 due to the voids remaining in the void-containing first crystal layer 4. This void causes peeling of the second crystal layer 6 in the peeling step S160 described later.
- the second crystal layer 6 is grown by inheriting the orientation of the substrate 1. That is, the off-angle ⁇ 1 in the main surface of the second crystal layer 6 becomes uniform over the entire main surface, similarly to the off-angle ⁇ 0 in the main surface 1s of the substrate 1.
- the thickness of the second crystal layer 6 is set to, for example, 600 ⁇ m or more, preferably 1 mm or more.
- the upper limit of the thickness of the second crystal layer is not particularly limited, but from the viewpoint of improving productivity, the thickness of the second crystal layer 6 is preferably 50 mm or less.
- the second crystal layer 6 is the void-containing first crystal layer 4 and the metal nitride layer. It naturally peels off from the substrate 1 at the boundary of 5.
- tensile stress is introduced into the second crystal layer 6 by attracting the initial nuclei generated in the growth process to each other. Therefore, due to the tensile stress generated in the second crystal layer 6, an internal stress acts on the second crystal layer 6 so that the surface side thereof is recessed. Further, the dislocation density on the main surface (front surface) side of the second crystal layer 6 is low, while the dislocation density on the back surface side of the second crystal layer 6 is high. Therefore, even if the dislocation density difference in the thickness direction of the second crystal layer 6 is caused, an internal stress acts on the second crystal layer 6 so that the surface side thereof is recessed.
- the c-plane 6c of the second crystal layer 6 is curved in a concave spherical shape with respect to the plane perpendicular to the normal direction of the center of the main surface 6s of the second crystal layer 6.
- the off-angle ⁇ 2 formed by the c-axis 6ca with respect to the normal of the center of the main surface 6s of the second crystal layer 6 has a predetermined distribution.
- the second crystal is used by a wire saw along the cut surface SS substantially perpendicular to the normal direction of the center of the main surface 6s of the second crystal layer 6. Slice layer 6.
- the base substrate 10 as the as-slice substrate is formed.
- the thickness of the base substrate 10 is set to, for example, 450 ⁇ m.
- the off-angle ⁇ 3 of the base substrate 10 may change from the off-angle ⁇ 2 of the second crystal layer 6 due to the slice direction dependence.
- the base substrate 10 made of a single crystal of GaN can be obtained.
- the diameter of the base substrate 10 is, for example, 2 inches or more.
- the thickness of the base substrate 10 is, for example, 300 ⁇ m or more and 1 mm or less.
- the main surface 10s of the base substrate 10 has, for example, a main surface (base surface) 10s which is an epitaxial growth surface.
- the crystal plane having the lowest index closest to the main plane 10s is, for example, the c-plane (+ c-plane) 10c.
- the c-plane 10c of the base substrate 10 is curved in a concave spherical shape with respect to the main surface 10s.
- the term "spherical” as used herein means a curved surface that is approximated by a spherical surface.
- the term “spherical approximation” as used herein means that the sphere is approximated to a perfect circular sphere or an elliptical sphere within a predetermined error range.
- the c-plane 10f of the base substrate 10 has, for example, a curved surface that is approximated by a spherical surface in each of the cross section along the m-axis and the cross-section along the a-axis.
- the radius of curvature of the c-plane 10c on the base substrate 10 is, for example, 1 m or more and less than 10 m.
- the off-angle ⁇ 3 formed by the c-axis 10ca with respect to the normal of the center of the main surface 10s of the base substrate 10 has a predetermined distribution.
- the size of the off angle ⁇ 3 at the center of the main surface 10s of the base substrate 10 is set to, for example, 1 ° or less, preferably 0.4 ° or less. If the magnitude of the off angle ⁇ 3 at the center of the main surface 10s exceeds 1 °, it becomes difficult for the three-dimensional growth layer 30 to develop three-dimensional growth depending on the first growth condition in the three-dimensional growth step S200 described later. There is. Therefore, it becomes difficult to eliminate the c-plane 30c.
- the three-dimensional growth layer 30 can be easily three-dimensionally grown in the three-dimensional growth step S200 described later. Can be made to. As a result, the c-plane 30c can be easily eliminated. Further, by setting the size of the off angle ⁇ 3 at the center of the main surface 10s to 0.4 ° or less, the three-dimensional growth layer 30 can be three-dimensionally grown under relatively wide growth conditions, and the c-plane 30c can be grown three-dimensionally. Can be stably eliminated.
- the size of the off-angle ⁇ 3 at the center of the main surface 10s is preferably 0.1 ° or more, for example.
- the size and direction of the off-angle ⁇ 3 at the center of the main surface 10s of the base substrate 10 are, for example, the size and direction of the off-angle ⁇ 0 of the crystal growth substrate 1 used in the above-mentioned VAS method, and the slicing step. It can be adjusted by the slice angle and the slice direction in S170.
- the root mean square roughness RMS of the main surface 10s of the base substrate 10 is set to, for example, less than 1 nm.
- the dislocation density on the main surface 10s of the base substrate 10 is low.
- the dislocation density on the main surface 10s of the base substrate 10 is, for example, 3 ⁇ 10 6 cm -2 or more and less than 1 ⁇ 10 7 cm -2.
- a plurality of recesses 30p formed by being surrounded by the inclined interface 30i other than the c-plane are formed on the top surface 30u of the single crystal, and the inclined interface 30i goes above the main surface 10s of the base substrate 10. Is gradually enlarged, and the c-plane 30c is gradually reduced. As a result, the c-plane 30c disappears from the top surface 30u at least once. As a result, the three-dimensional growth layer 30 in which the inclined interface 30i is widely present on the surface is formed.
- the base substrate 10 in a state where no pattern processing is performed is used.
- the term "mask layer” as used herein means, for example, a mask layer used in the so-called ELO (Epitaxial Lateral Overgrown) method and having a predetermined opening.
- the "concavo-convex pattern" referred to here means, for example, at least one of a trench and a ridge used in the so-called pendeo epitaxy method in which the main surface of the base substrate is directly patterned.
- the height difference of the uneven pattern referred to here is, for example, 100 nm or more.
- a single crystal of a group III nitride semiconductor is epitaxially grown directly on the main surface 10s of the base substrate 10 in a state not having the above-mentioned structure.
- the three-dimensional growth layer 30 is three-dimensionally grown so as to intentionally roughen the main surface 10s of the base substrate 10. Even if the three-dimensional growth layer 30 forms such a growth form, it is grown as a single crystal as described above. In this respect, the three-dimensional growth layer 30 is different from the so-called low-temperature growth buffer layer formed as an amorphous or polycrystal on the dissimilar substrate before epitaxially growing the group III nitride semiconductor on the dissimilar substrate such as sapphire. Is.
- an inclined interface growth region 70 (gray portion in the figure) is formed in which the inclined interface 30i other than the c-plane is grown as a growth surface. Further, as will be described later, the area occupied by the inclined interface growth region 70 in the creepage cross section of the three-dimensional growth layer 30 along the main surface 10s of the base substrate 10 is set to, for example, 80% or more.
- the three-dimensional growth layer 30 for example, a layer made of the same group III nitride semiconductor as the group III nitride semiconductor constituting the base substrate 10 is epitaxially grown. Specifically, for example, by HVPE, the base substrate 10 is heated, by supplying the GaCl gas and NH 3 gas to the heated base substrate 10, epitaxially growing a GaN layer as a three-dimensional growth layer 30 Let me.
- the three-dimensional growth layer 30 is grown under predetermined first growth conditions.
- FIG. 10A is a schematic cross-sectional view showing a growth process under reference growth conditions in which the inclined interface and the c-plane are neither expanded nor contracted.
- the thick solid line shows the surface of the three-dimensional growth layer 30 for each unit time.
- the inclined interface 30i shown in FIG. 10A is the inclined interface most inclined with respect to the c-plane 30c.
- the growth rate of the c-plane 30c of the three-dimensional growth layer 30 and G c0, the growth rate of the graded interface 30i of the three-dimensional growth layer 30 and G i, 3-dimensional growth Let ⁇ be the angle formed by the c-plane 30c and the inclined interface 30i in the layer 30.
- FIG. 10A it is assumed that the three-dimensional growth layer 30 grows while maintaining the angle ⁇ formed by the c-plane 30c and the inclined interface 30i. It is assumed that the off angle of the c-plane 30c of the three-dimensional growth layer 30 is negligible as compared with the angle ⁇ formed by the c-plane 30c and the inclined interface 30i.
- FIG. 10B is a schematic cross-sectional view showing a growth process under the first growth condition in which the inclined interface expands and the c-plane shrinks.
- the thick solid line indicates the surface of the three-dimensional growth layer 30 for each unit time.
- the inclined interface 30i shown in FIG. 10B is also the inclined interface most inclined with respect to the c-plane 30c.
- the growth rate of the c-plane 30c of the three-dimensional growth layer 30 is set to G c1, and the progress of the locus of the intersection of the inclined interface 30i and the c-plane 30c of the three-dimensional growth layer 30. rate is referred to as R 1.
- the narrower angle between the locus of the intersection of the inclined interface 30i and the c-plane 30c and the c-plane 30c is defined as ⁇ R1 .
- the traveling rate R 1 of the locus of the intersection between the inclined surface 30i and the c-plane 30c is represented by the following formula (b).
- R 1 G i / cos ⁇ ' ⁇ (b)
- the growth rate G c1 of the c-plane 30c of the three-dimensional growth layer 30 is represented by the following formula (c).
- G c1 R 1 sin ⁇ R1 ... (c)
- G c1 G i sin ⁇ R1 / cos ( ⁇ + 90- ⁇ R1) ⁇ (d)
- the first growth condition in which the inclined interface 30i expands and the c-plane 30c shrinks satisfies the following equation (1) according to the equation (d) and ⁇ R1 ⁇ 90 °.
- G i is the growth rate of the inclined surface 30i of the most inclined relative to the c plane 30c
- alpha is an inclined surface 30i of the most inclined relative to the c plane 30c
- the c-plane 30c The angle between the two.
- G c1 under the first growth condition is preferably larger than G c0 under the reference growth condition.
- the equation (1) can be derived by substituting the equation (a) for G c1 > G c0.
- the growth condition for expanding the most inclined inclined interface 30i with respect to the c-plane 30c is the strictest condition, if the first growth condition satisfies the equation (1), the other inclined interface 30i is also expanded. Is possible.
- the first growth condition satisfies, for example, the following formula (1').
- G c1 2.13G i ... (1')
- the inclined interface 30i is a ⁇ 11-2m ⁇ surface with m ⁇ 3
- the growth temperature in the three-dimensional growth step S200 is made lower than the growth temperature in the flattening step S300 described later.
- the growth temperature in the three-dimensional growth step S200 is, for example, 980 ° C. or higher and 1,020 ° C. or lower, preferably 1,000 ° C. or higher and 1,020 ° C. or lower.
- the ratio of the partial pressure of the flow rate of the NH 3 gas as the nitrogen raw material gas to the partial pressure of the GaCl gas as the group III raw material gas in the three-dimensional growth step S200 may be larger than the V / III ratio in the flattening step S300 described later.
- the V / III ratio in the three-dimensional growth step S200 is, for example, 2 or more and 20 or less, preferably 2 or more and 15 or less.
- the first growth condition at least one of the growth temperature and the V / III ratio is adjusted within the above range so as to satisfy the formula (1).
- the other conditions of the first growth condition of the present embodiment are as follows, for example. Growth pressure: 90-105 kPa, preferably 90-95 kPa Partial pressure of GaCl gas: 1.5 to 15 kPa Flow rate of N 2 gas / Flow rate of H 2 gas: 0 to 1
- the three-dimensional growth step S200 of the present embodiment is classified into two steps based on, for example, the growing form of the three-dimensional growth layer 30.
- the three-dimensional growth step S200 of the present embodiment includes, for example, an inclined interface expanding step S220 and an inclined interface maintaining step S240.
- the three-dimensional growth layer 30 has, for example, an inclined interface expanding layer 32 and an inclined interface maintaining layer 34.
- the inclined interface expanding layer 32 has a predetermined thickness in the normal direction (direction along the c-axis) of the main surface 10s of the base substrate 10 with the c-plane 30c as the growth surface.
- step flow growth two-dimensional growth. That is, the inclined interface expansion layer 32 of the single crystal is homoepitaxially grown flat.
- a part of the inclined interface expansion layer 32 grown with the c-plane 30c as the growth plane is also referred to as an "initial layer". This growth forms an initial layer with a mirrored surface to a predetermined thickness.
- the initial layer is grown continuously, for example, in the direction along the main surface 10s of the base substrate 10, that is, over the entire main surface 10s of the base substrate 10.
- the thickness of the initial layer is, for example, 1 ⁇ m or more and 100 ⁇ m or less, preferably 1 ⁇ m or more and 20 ⁇ m or less.
- the inclined interface expansion layer 32 by gradually growing the inclined interface expansion layer 32 under the first growth condition, as shown in FIGS. 3 (b) and 4, the c-plane 30c of the inclined interface expansion layer 32 is exposed.
- a plurality of recesses 30p formed of an inclined interface 30i other than the c-plane are formed in 30u.
- a plurality of recesses 30p formed by the inclined interface 30i other than the c-plane are randomly formed on the top surface 30u.
- the inclined interface expansion layer 32 in which the c-plane 30c and the inclined interface 30i other than the c-plane are mixed on the surface is formed.
- the "inclined interface 30i" here means a growth interface inclined with respect to the c-plane 30c, and has a low index facet other than the c-plane, a high-index facet other than the c-plane, or a surface index. Includes slopes that cannot be represented by.
- the facets other than the c-plane are, for example, ⁇ 11-2m ⁇ , ⁇ 1-10n ⁇ and the like. However, m and n are integers other than 0.
- the inclined interface 30i is set to, for example, m ⁇ 3 ⁇ 11-2m ⁇ .
- a surface can be created.
- the inclination angle of the ⁇ 11-2m ⁇ plane with respect to the c plane 30c can be made gentle.
- the inclination angle can be 47.3 ° or less.
- the inclined interface expansion layer 32 goes above the main surface 10s of the base substrate 10.
- the inclined interface 30i other than the c-plane is gradually enlarged, and the c-plane 30c is gradually reduced.
- the inclination angle formed by the inclined interface 30i with respect to the main surface 10s of the underlying substrate 10 gradually decreases toward the upper side of the underlying substrate 10.
- most of the inclined interface 30i finally becomes the ⁇ 11-2m ⁇ plane of m ⁇ 3 described above.
- the c-plane 30c of the inclined interface expanding layer 32 disappears from the top surface 30u, and the outermost surface (top surface) of the inclined interface expanding layer 32 is composed of only the inclined interface 30i.
- each of the plurality of valleys 30v is an inflection point that is convex downward on the surface of the inclined interface expansion layer 320, and is formed above the position where each of the inclined interfaces 30i other than the c-plane is generated.
- each of the plurality of tops 30t is an inflection point that is convex upward on the surface of the inclined interface expansion layer 320, and is a c-plane sandwiching a pair of inclined interfaces 30i that are enlarged in directions opposite to each other. 30c disappears (finally) and forms at or above the terminated position.
- the valley portion 30v and the top portion 30t are formed alternately in the direction along the main surface 10s of the base substrate 10.
- the inclined interface expanding layer 32 in the initial stage in which the inclined interface expanding layer 32 grows, is defined on the main surface 10s of the base substrate 10 with the c-plane 30c as the growth surface without causing the inclined interface 30i. After growing to a thickness, an inclined interface 30i other than the c-plane is formed on the surface of the inclined interface expansion layer 32. As a result, the plurality of valley portions 30v are formed at positions separated upward from the main surface 10s of the base substrate 10.
- the dislocations are bent and propagated as follows. Specifically, as shown in FIG. 3C, a plurality of dislocations extending in the direction along the c-axis in the base substrate 10 move from the base substrate 10 to the c-axis of the inclined interface expansion layer 32. Propagate in the direction along the line. In the region of the inclined interface expansion layer 32 that has grown with the c-plane 30c as the growth surface, dislocations propagate from the base substrate 10 in the direction along the c-axis of the inclined interface expansion layer 32.
- the dislocations bend and propagate in a direction substantially perpendicular to the inclined interface 30i. .. That is, the dislocations are bent and propagated in a direction inclined with respect to the c-axis.
- the steps after the inclined interface expansion step S220 dislocations are locally collected above the substantially center between the pair of tops 30t. As a result, the dislocation density on the surface of the flattening layer 40 described later can be reduced.
- the average distance L (also referred to as “the average distance between the most recent apex portions”) L in which the pair of top portions 30t are separated from each other in the direction along the main surface 10s of the base substrate 10 is set to, for example, more than 100 ⁇ m.
- the average distance L between the most recent apex portions is the distance when the cross section when the c-plane 30c disappears from the crystal growth interface is viewed.
- the average distance L between the most recent apex parts is 100 ⁇ m or less, such as when a fine hexagonal pyramid-shaped crystal nucleus is generated on the main surface 10s of the base substrate 10 from the initial stage of the inclined interface expansion step S220, the inclination is formed.
- the distance at which dislocations are bent and propagated is shortened. Therefore, dislocations are not sufficiently collected above the substantially center between the pair of tops 30t of the inclined interface expansion layer 32. As a result, the dislocation density on the surface of the flattening layer 40 described later may not be sufficiently reduced.
- the distance at which the dislocations bend and propagate in the steps after the inclined interface expansion step S220 is secured at least more than 50 ⁇ m. be able to.
- dislocations can be sufficiently collected above the substantially center between the pair of tops 30t in the inclined interface expansion layer 32.
- the dislocation density on the surface of the flattening layer 40 described later can be sufficiently reduced.
- the average distance L between the most recent ridges is set to less than 800 ⁇ m.
- the average distance L between the most recent apex portions is 800 ⁇ m or more, the height from the main surface 10s of the base substrate 10 to the valley portion 30v to the apex portion 30t of the inclined interface expansion layer 32 becomes excessively high. Therefore, in the flattening step S300 described later, the thickness of the flattening layer 40 until it is mirrored becomes thicker.
- the average distance L between the most recent apex portions is set to less than 800 ⁇ m, so that the height from the main surface 10s of the base substrate 10 to the valley portion 30v to the apex portion 30t of the inclined interface expansion layer 32 is lowered. can do. As a result, the flattening layer 40 can be quickly mirrored.
- the c-plane growth region 60 grown with the c-plane 30c as the growth plane and the inclined interface 30i other than the c-plane grow on the inclined interface expansion layer 320 based on the difference in the growth planes in the growth process.
- An inclined interface growth region 70 (gray portion in the figure) grown as a surface is formed.
- a valley portion 60a is formed at a position where the inclined interface 30i is generated, and a mountain portion 60b is formed at a position where the c-plane 30c disappears and ends.
- a pair of inclined portions 60i are formed on both sides of the mountain portion 60b as a locus of an intersection between the c-plane 30c and the inclined interface 30i.
- the angle formed by the pair of inclined portions 60i when the cross section passing through the center of each of the two adjacent valley portions 60a is viewed, for example. It shall be 70 ° or less.
- the growth of the three-dimensional growth layer 30 is continued over a predetermined thickness while maintaining the state in which the inclined interface 30i occupies more than the c-plane 30c on the surface.
- the inclined interface maintaining layer 34 is formed on the inclined interface expanding layer 32.
- the three-dimensional growth step S200 in order to reduce the dislocation density by reliably bending the dislocation propagation direction as described above, when the history of the growth interface is viewed at an arbitrary position of the three-dimensional growth layer 30. In addition, it is important that the c-plane 30c disappears at least once. Therefore, it is desirable that the c-plane 30c disappears at least once in the early stage of the three-dimensional growth step S200 (for example, the above-mentioned inclined interface expansion step S220).
- the c-plane 30c may reappear on a part of the surface of the inclined interface maintenance layer 34 after the c-plane 30c has disappeared at least once.
- the inclined interface 30i is mainly exposed on the surface of the inclined interface maintaining layer 34 so that the area ratio occupied by the inclined interface growth region 70 in the creepage cross section along the main surface 10s of the base substrate 10 is 80% or more. Is preferable.
- the area ratio occupied by the inclined interface growth region 70 in the creepage cross section is better, preferably 100%.
- the inclined interface maintenance layer 34 grows with the inclined interface 30i as a growth surface, so that substantially the entire inclined interface maintaining layer 34 becomes a part of the inclined interface growth region 70.
- the three-dimensional growth layer 30 having the inclined interface expanding layer 32 and the inclined interface maintaining layer 34 is formed.
- the height from the main surface 10s of the base substrate 10 to the top 30t of the three-dimensional growth layer 30 (the maximum height in the thickness direction of the three-dimensional growth layer 30) is set, for example. , More than 100 ⁇ m and less than 1.5 mm.
- the inclined interface 40i is gradually reduced and the c-plane 40c is gradually expanded toward the upper side of the main surface 10s of the base substrate 10.
- the inclined interface 30i formed on the surface of the three-dimensional growth layer 30 disappears.
- the flattening layer 40 having a mirrored surface is grown.
- mirror surface as used herein means a surface in which the maximum value of the height difference between adjacent irregularities on the surface is equal to or less than the wavelength of visible light.
- the flattening layer 40 for example, a layer containing the same group III nitride semiconductor as the group III nitride semiconductor constituting the three-dimensional growth layer 30 as a main component is epitaxially grown.
- GaCl gas, NH 3 gas, and dichlorosilane (SiH 2 Cl 2 ) gas as an n-type dopant gas are supplied to the base substrate 10 heated to a predetermined growth temperature.
- a silicon (Si) -doped GaN layer is epitaxially grown.
- the n-type dopant gas GeCl 4 gas or the like may be supplied instead of SiH 2 Cl 2 gas.
- the flattening layer 40 is grown under a predetermined second growth condition.
- FIG. 11 is a schematic cross-sectional view showing a growth process under a second growth condition in which the inclined interface is reduced and the c-plane is expanded.
- FIG. 11 shows a process in which the flattening layer 40 grows on the three-dimensional growth layer 30 in which the inclined interface 30i most inclined with respect to the c-plane 30c is exposed.
- the thick solid line indicates the surface of the flattening layer 40 for each unit time.
- the growth rate of the c-plane 40c of the planarizing layer 40 and G c2 the growth rate of the graded interface 40i of the planarizing layer 40 and G i, the inclination of the planarization layer 40
- R 2 be the progress rate of the locus of the intersection of the interface 40i and the c-plane 40c.
- the narrower angle between the locus of the intersection of the inclined interface 40i and the c-plane 40c and the c-plane 30c is defined as ⁇ R2 .
- the traveling rate R 2 of the locus of the intersection between the inclined surface 40i and the c-plane 40c is represented by the following formula (e).
- R 2 G i / cos ⁇ " ⁇ (e)
- the growth rate G c2 of the c-plane 40c of the flattening layer 40 is represented by the following formula (f).
- G c2 R 2 sin ⁇ R2 ... (f)
- G c2 G i sin ⁇ R2 / cos ( ⁇ + ⁇ R2 -90) ⁇ (g)
- the second growth condition in which the inclined interface 40i is reduced and the c-plane 40c is expanded preferably satisfies the following formula (2) according to the formula (g) and ⁇ R2 ⁇ 90 °.
- G i is the growth rate of the inclined surface 40i of the most inclined relative to the c plane 40c
- alpha is an inclined surface 40i of the most inclined relative to the c plane 40c
- the c-plane 40c The angle between the two.
- the equation (2) can be derived by substituting the equation (a) for G c2 ⁇ G c0.
- the second growth condition preferably satisfies the following formula (2').
- the inclined interface 30i is a ⁇ 11-2m ⁇ plane with m ⁇ 3
- the most inclined inclined interface 30i with respect to the c-plane 30c is the ⁇ 11-23 ⁇ plane, so that the second growth occurs.
- the conditions preferably satisfy, for example, the following equation (2 "). G c2 ⁇ 1.47G i ... (2 ")
- the growth temperature in the flattening step S300 is made higher than, for example, the growth temperature in the three-dimensional growth step S200.
- the growth temperature in the flattening step S300 is, for example, 990 ° C. or higher and 1,120 ° C. or lower, preferably 1,020 ° C. or higher and 1,100 ° C. or lower.
- the V / III ratio in the flattening step S300 may be adjusted.
- the V / III ratio in the flattening step S300 may be smaller than the V / III ratio in the three-dimensional growth step S200.
- the V / III ratio in the flattening step S300 is, for example, 1 or more and 10 or less, preferably 1 or more and 5 or less.
- the second growth condition at least one of the growth temperature and the V / III ratio is adjusted within the above range so as to satisfy the formula (2).
- the other conditions of the second growth condition of the present embodiment are as follows, for example. Growth pressure: 90-105 kPa, preferably 90-95 kPa Partial pressure of GaCl gas: 1.5 to 15 kPa Flow rate of N 2 gas / Flow rate of H 2 gas: 1 to 20
- the three-dimensional growth layer 30 is formed by epitaxially growing the flattening layer 40 made of a single crystal of a group III nitride semiconductor on the three-dimensional growth layer 30 under the above-mentioned second growth condition.
- the inclined interface 40i other than the c-plane can be reduced while expanding the c-plane 40c toward the upper side of the c-plane.
- the flattening layer 40 is directed from the inclined interface 30i of the inclined interface maintaining layer 34 along the direction perpendicular to the c-axis with the inclined interface 40i as the growth surface ( That is, it grows in the creeping direction or the lateral direction).
- the c-plane 40c of the flattening layer 40 begins to be exposed again above the top 30t of the inclined interface maintenance layer 34.
- the flattening layer 40 in which the c-plane 40c and the inclined interface 40i other than the c-plane are mixed on the surface is formed.
- the c-plane 40c gradually expands and the inclined interface 40i of the flattening layer 40 gradually shrinks.
- the recesses 30p formed by the plurality of inclined interfaces 30i are gradually embedded on the surface of the three-dimensional growth layer 30.
- the inclined interface 40i of the flattening layer 40 disappears completely, and the recess 30p composed of the plurality of inclined interfaces 30i is completely embedded on the surface of the three-dimensional growth layer 30. ..
- the surface of the flattening layer 40 becomes a mirror surface (flat surface) composed of only the c-plane 40c.
- the dislocation density can be reduced by locally collecting dislocations in the growth process of the three-dimensional growth layer 30 and the flattening layer 40. Specifically, the dislocations that are bent and propagated in the direction inclined with respect to the c-axis in the three-dimensional growth layer 30 continue to propagate in the same direction in the flattening layer 40. As a result, dislocations are locally collected at the meeting part of the adjacent inclined interface 40i above the center of the flattening layer 40 between the pair of tops 30t. Of the plurality of dislocations collected at the meeting portion of the adjacent inclined interface 40i in the flattening layer 40, the dislocations having Burgers vectors opposite to each other disappear at the time of associating.
- a part of the plurality of dislocations collected at the meeting portion of the adjacent inclined interface 40i forms a loop and is suppressed from propagating in the direction along the c-axis (that is, the surface side of the flattening layer 40). Will be done.
- the other part of the plurality of dislocations collected at the meeting part of the adjacent inclined interface 40i in the flattening layer 40 is again propagated in the direction along the c-axis from the direction inclined with respect to the c-axis. It is changed and propagates to the surface side of the flattening layer 40.
- the dislocation density on the surface of the flattening layer 40 can be increased. It can be reduced. Further, by locally collecting dislocations, a low dislocation density region can be formed above the portion of the flattening layer 40 in which the dislocations propagate in the direction inclined with respect to the c-axis.
- the c-plane 40c gradually expands, so that the c-plane growth region 60 grown with the c-plane 40c as the growth plane gradually expands as it goes upward in the thickness direction again. It is formed while expanding to.
- the inclined interface 40i gradually shrinks, so that the inclined interface growth region 70 gradually shrinks as it goes upward in the thickness direction, and ends at a predetermined position in the thickness direction. Due to the growth process of the flattening layer 40, the valley portion 70a of the inclined interface growth region 70 is formed at the position where the c-plane 40c is generated again in the cross-sectional view. Further, in the process of gradually embedding the recess formed by the inclined interface 40i, a mountain portion 70b of the inclined interface growth region 70 is formed at a position where the inclined interface 40i disappears in a cross-sectional view.
- the height of the flattening layer 40 in the thickness direction is, for example, The height of the inclined interface maintenance layer 34 is equal to or higher than the height from the valley portion 30v to the top portion 30t.
- a laminated unit 50 having a three-dimensional growth layer 30 and a flattening layer 40 is formed by one cycle including the above three-dimensional growth step S200 and flattening step S300.
- the portion having the c-plane growth region 60 below the inclined interface growth region 70 and the inclined interface growth region 70 is designated. It may also be called a stacking unit 50.
- the laminated unit 50 formed by the first cycle may be referred to as a "first laminated unit 51".
- the inclined interface expansion step S220 and the inclined interface maintenance step S240 are performed in the same manner as in the three-dimensional growth step S200 of the first cycle.
- the inclined interface expansion layer 32 of the three-dimensional growth layer 30 made of a single crystal of a group III nitride semiconductor is epitaxially grown on the flattening layer 40 of the first laminated unit 51.
- the c-plane 30c is formed in the normal direction (direction along the c-axis) of the surface of the flattening layer 40 of the first laminated unit 51.
- the inclined interface expansion layer 32 is grown as a growth surface. That is, even in the initial stage of the cycle, the above-mentioned initial layer is grown over the entire flattening layer 40 of the first laminated unit 51 with the c-plane 30c as the growth plane.
- the apex surface 30u of the inclined interface expanding layer 32 in which the c-plane 30c is exposed is composed of the inclined interface 30i other than the c-plane.
- a plurality of recesses 30p are formed, and the c-plane 30c disappears at least once.
- a plurality of valleys 30v and a plurality of tops 30t are formed on the surface of the inclined interface expansion layer 32.
- the plurality of recesses 30p are randomly formed on the top surface 30u of the inclined interface expansion layer 32. Therefore, in a plan view, the positions of the valley portion 30v and the top portion 30t on the surface of the inclined interface expansion layer 32 in the second and subsequent cycles are the valley portion 30v and the top portion on the surface of the inclined interface expansion layer 32 in the first cycle. It does not always match each position of 30t.
- the dislocations are again bent and propagated as follows. Specifically, as shown in FIG. 6A, the plurality of dislocations remaining on the surface of the flattening layer 40 of the first laminated unit 51 are inclined interfaces from the flattening layer 40 of the first laminated unit 51. It propagates in the direction along the c-axis of the expansion layer 32. In the region of the inclined interface expansion layer 32 that has grown with the c-plane 30c as the growth surface, dislocations propagate from the flattening layer 40 of the first laminated unit 51 toward the direction along the c-axis of the inclined interface expansion layer 32.
- the dislocations bend and propagate in a direction substantially perpendicular to the inclined interface 30i. .. That is, the dislocations are again bent and propagated in a direction inclined with respect to the c-axis. As a result, even in the second and subsequent cycles, dislocations are locally collected above the center between the pair of tops 30t.
- the average distance L between the nearest apex portions is set to, for example, the first cycle. It is made longer than that of the inclined interface expansion step S220.
- the distance at which the dislocations bend and propagate can be made longer than in the first cycle.
- the average distance L between the nearest apex portions is gradually increased as, for example, a plurality of cycles are repeated.
- the distance at which the dislocations bend and propagate can be gradually increased.
- the dislocation-free region on the surface of the flattening layer 40 can be gradually widened, and the density of the dislocation-free region on the surface of the flattening layer 40 can be gradually increased. ..
- the interfacial average distance L is, for example, more than 100 ⁇ m at the shortest.
- the average distance L between the nearest apex portions is set.
- the distance at which the dislocations are bent and propagated can be secured at least 100 ⁇ m or more.
- a dislocation-free region of at least 100 ⁇ m square can be formed on at least a part of the surface of the flattening layer 40 in the last cycle.
- the average distance L between the nearest apex portions is, for example, less than 800 ⁇ m.
- the three-dimensional growth layer 30 grows over a predetermined thickness while maintaining a state in which the inclined interface growth region 70 occupies an area of 80% or more of the creepage cross section. Let it continue. As a result, the inclined interface maintaining layer 34 is formed on the inclined interface expanding layer 32.
- the three-dimensional growth layer 30 having the inclined interface expanding layer 32 and the inclined interface maintaining layer 34 is formed again.
- the inclined interface 40i of the flattening layer 40 disappears completely, and the recess 30p composed of the plurality of inclined interfaces 30i is completely embedded on the surface of the three-dimensional growth layer 30. ..
- the surface of the flattening layer 40 becomes a mirror surface (flat surface) composed of only the c-plane 40c.
- the dislocation density can be further reduced by locally collecting dislocations in the growth process of the three-dimensional growth layer 30 and the flattening layer 40. That is, the dislocation density on the surface of the flattening layer 40 in the second and subsequent cycles can be reduced as compared with the dislocation density on the surface of the flattening layer 40 in the first cycle.
- the dislocation density can be gradually reduced according to the number of times the cycle is repeated.
- the laminated unit 50 having the three-dimensional growth layer 30 and the flattening layer 40 is formed again by the second and subsequent cycles including the above three-dimensional growth step S200 and the flattening step S300.
- the laminated unit 50 formed by the second cycle may be referred to as a "second laminated unit 52".
- the number of times the cycle is carried out is, for example, 2 times or more and 5 times or less.
- the number of cycles By setting the number of cycles to be performed twice or more, the effect of reducing dislocations due to repeated cycles can be sufficiently obtained.
- the dislocation reduction effect appears dramatically up to 3 times, and after 3 times, it becomes difficult to obtain the dislocation reduction effect as the number of times increases. Therefore, it is preferable that the number of cycles performed is 5 or less.
- the c-plane growth region in which the c-plane 40c of the flattening layer 40 gradually expands and grows in the final cycle becomes a part of the uppermost c-plane growth region 80 described later.
- the main growth layer 44 is formed on the flattening layer 40 whose surface is mirror-surfaced over a predetermined thickness with the c-plane as the growth surface. To do.
- the growth conditions in the main growth step S500 are maintained under the above-mentioned second growth conditions in the same manner as in the above-mentioned flattening step S300 of each cycle.
- the main growth layer 44 can be step-flow-grown with the c-plane as the growth plane.
- the radius of curvature of the c-plane of the main growth layer 44 can be made larger than the radius of curvature of the c-plane 10c of the base substrate 10.
- the variation in the off-angle of the c-axis with respect to the normal of the surface of the main growth layer 44 can be made smaller than the variation of the off-angle of the c-axis 10ca with respect to the normal of the main surface 10s of the base substrate 10. ..
- the entire main growth layer 44 becomes the uppermost c-plane growth region 80 described later. ..
- the thickness of the main growth layer 44 is set to, for example, 300 ⁇ m or more and 10 mm or less.
- the thickness of the main growth layer 44 is set to 300 ⁇ m or more, at least one or more substrates 100 can be sliced from the main growth layer 44 in the slicing step S600 described later.
- the final thickness is set to 650 ⁇ m, and when slicing the substrate 100 having a thickness of 700 ⁇ m from the main growth layer 44, even if about 200 ⁇ m of carfloss is taken into consideration. , At least 10 substrates 100 can be obtained.
- the laminated structure 90 of the present embodiment is formed by the above steps from the three-dimensional growth step S200 to the main growth step S500 in the first cycle.
- the steps from the three-dimensional growth step S200 to the main growth step S500 of the first cycle are continuously performed in the same chamber without exposing the base substrate 10 to the atmosphere.
- an unintended high oxygen concentration is formed at the interface between the three-dimensional growth layer 30 and the flattening layer 40, the interface between the laminated units 50, the interface between the flattening layer 40 and the main growth layer 44, and the like. It is possible to suppress the formation of a region (a region having an oxygen concentration excessively higher than that of the inclined interface growth region 70).
- the main growth layer 44 is sliced by a wire saw along a cut surface substantially parallel to the surface of the main growth layer 44.
- at least one nitride semiconductor substrate 100 also referred to as substrate 100
- the thickness of the substrate 100 is set to, for example, 300 ⁇ m or more and 700 ⁇ m or less.
- the radius of curvature of the c-plane 100c of the substrate 100 can be made larger than the radius of curvature of the c-plane 10c of the base substrate 10.
- the radius of curvature of the c-plane 100c of the substrate 100 can be made larger than the radius of curvature of the c-plane 40c of the main growth layer 44 before slicing.
- the variation in the off-angle ⁇ of the c-axis 100ca with respect to the normal of the main surface 100s of the substrate 100 can be made smaller than the variation in the c-axis 10ca off-angle of the base substrate 10.
- both sides of the substrate 100 are polished by a polishing device.
- the thickness of the final substrate 100 is set to, for example, 250 ⁇ m or more and 650 ⁇ m or less.
- the substrate 100 according to the present embodiment is manufactured by the above steps S100 to S700.
- semiconductor laminate manufacturing process and semiconductor device manufacturing process After the substrate 100 is manufactured, for example, a semiconductor functional layer made of a group III nitride semiconductor is epitaxially grown on the substrate 100 to produce a semiconductor laminate. After producing the semiconductor laminate, electrodes and the like are formed using the semiconductor laminate, the semiconductor laminate is diced, and a chip having a predetermined size is cut out. As a result, a semiconductor device is manufactured.
- the laminated structure 90 of the present embodiment has, for example, a base substrate 10, a plurality of laminated units 50, and an uppermost c-plane growth region (uppermost low oxygen concentration region) 80.
- a plurality of laminated units 50 are repeatedly provided in the thickness direction between the base substrate 10 and the uppermost c-plane growth region 80, for example.
- Each of the plurality of laminated units 50 has, for example, a c-plane growth region (low oxygen concentration region 60) and a gradient interface growth region (high oxygen concentration region) 70.
- the c-plane growth region 60 is a region that has grown with the c-plane 30c as the growth plane. In the c-plane growth region 60, oxygen uptake is suppressed as compared with the inclined interface growth region 70. Therefore, the oxygen concentration in the c-plane growth region 60 is lower than the oxygen concentration in the inclined interface growth region 70. Specifically, the oxygen concentration in the c-plane growth region 60 is, for example, 5 ⁇ 10 16 cm -3 or less, preferably 3 ⁇ 10 16 cm -3 or less.
- the c-plane growth region 60 is provided above the main surface 10s of the base substrate 10. Since the c-plane 30c disappears at least once in the growth process of the three-dimensional growth layer 30, the c-plane growth region 60 is not continuous from the base substrate 10 side to the uppermost c-plane growth region 80.
- the c-plane growth region 60 has, for example, a plurality of valley portions 60a and a plurality of peak portions 60b in a cross-sectional view.
- Each of the valley portion 60a and the peak portion 60b referred to here means a part of the shape observed based on the difference in emission intensity when the cross section of the laminated structure 90 is observed with a fluorescence microscope or the like, and three-dimensional growth occurs. It does not mean a part of the outermost surface shape that occurs during the growth of the layer 30.
- Each of the plurality of valleys 60a is formed at a position where an inclined interface 30i is generated at a downwardly convex inflection point in the c-plane growth region 60 in a cross-sectional view.
- At least one of the plurality of valley portions 60a is provided at a position separated upward from the main surface 10s of the base substrate 10.
- each of the plurality of mountain portions 60b is an inflection point that is convex upward in the c-plane growth region 60 in a cross-sectional view, and sandwiches a pair of inclined interfaces 30i that are enlarged in directions opposite to each other.
- the c-plane 30c disappears (finally) and is formed at the terminal position.
- the valley portions 60a and the peak portions 60b are formed alternately in the direction along the main surface 10s of the base substrate 10.
- the average distance separated in the direction along the main surface 10s of the base substrate 10 corresponds to the average distance L between the closest apex portions of the above-mentioned three-dimensional growth layer 30, and is, for example, more than 100 ⁇ m.
- the distance is also referred to as "the average distance between the most recent mountainous areas”.
- the c-plane growth region 60 has a pair of inclined portions 60i provided as a locus of an intersection between the c-plane 30c and the inclined interface 30i on both sides of one of the plurality of mountain portions 60b.
- the inclined portion 60i referred to here means a part of the shape observed based on the difference in emission intensity when the cross section of the laminated structure 90 is observed with a fluorescence microscope or the like, and is in the middle of growth of the three-dimensional growth layer 30. It does not mean the sloped interface 30i on the outermost surface.
- the angle formed by the pair of inclined portions 60i when the cross section passing through the center of each of the two adjacent valley portions 60a is viewed is, for example, 70 ° or less, preferably 20 ° or more and 65 ° or less.
- Angle formed pair of inclined portions 60i is 70 ° or less, in the first growth condition, on the growth rate G i of the inclined surface 30i of the most inclined relative to the c plane 30c of the three-dimensional growth layer 30, the ratio G c1 / G i of growth rate G c1 of c plane 30c of the three-dimensional growth layer 30 means that there was high. Thereby, the inclined interface 30i other than the c-plane can be easily generated.
- the dislocations can be easily bent at the position where the inclined interface 30i is exposed. Further, by setting the angle formed by the pair of inclined portions 60i to 70 ° or less, a plurality of valley portions 30v and a plurality of top portions 30t can be easily generated above the main surface 10s of the base substrate 10. Further, by setting the angle formed by the pair of inclined portions 60i to 65 ° or less, an inclined interface 30i other than the c-plane can be more easily generated, and a plurality of valleys can be formed above the main surface 10s of the base substrate 10. The portion 30v and the plurality of tops 30t can be more easily generated.
- the angle formed by the pair of inclined portions 60i By setting the angle formed by the pair of inclined portions 60i to 20 ° or more, it is possible to prevent the height from the valley portion 30v to the top portion 30t of the three-dimensional growth layer 30 to increase, and the flattening layer 40 is mirrored. It is possible to prevent the thickness from becoming thicker.
- the inclined interface growth region 70 is a region where the inclined interface 30i or the inclined interface 40i is used as a growth surface.
- oxygen is easily taken in as compared with the c-plane growth region 60 and the uppermost c-plane growth region 80 described later. Therefore, the oxygen concentration in the inclined interface growth region 70 is higher than the oxygen concentration of each of the c-plane growth region 60 and the uppermost c-plane growth region 80.
- the oxygen taken into the inclined interface growth region 70 is, for example, oxygen unintentionally mixed in the vapor phase growth apparatus, oxygen released from a member (quartz member or the like) constituting the vapor phase growth apparatus, or the like. Is.
- the oxygen concentration in the inclined interface growth region 70 is, for example, 9 ⁇ 10 17 cm -3 or more and 5 ⁇ 10 19 cm -3 or less.
- the inclined interface growth region 70 is provided on the c-plane growth region 60 of the laminated unit 50 of the same layer, for example.
- the inclined interface growth region 70 is continuously provided along the main surface 10s of the base substrate 10. That is, when a plurality of creepage cross sections obtained by cutting the three-dimensional growth layer 30 along the main surface 10s of the base substrate 10 are viewed, the cross section not including the c-plane growth region grown with the c-plane 30c as the growth plane is three-dimensional. It is desirable that it is present in at least a part of the growth layer 30 in the thickness direction.
- the lower surface of the inclined interface growth region 70 is formed, for example, following the shape of the c-plane growth region 60 in the laminated unit 50 of the same layer.
- the upper surface of the inclined interface growth region 70 has, for example, a plurality of valleys 70a and a plurality of peaks 70b in a cross-sectional view.
- Each of the valley portion 70a and the peak portion 70b referred to here means a part of the shape observed based on the difference in emission intensity when the cross section of the laminated structure 90 is observed with a fluorescence microscope or the like, and is a flattening layer. It does not mean a part of the outermost surface shape that occurs during the growth of 40.
- the plurality of valleys 70a of the inclined interface growth region 70 are formed at positions where the c-plane 40c is generated again in the cross-sectional view.
- each of the plurality of valleys 70a of the inclined interface growth region 70 is formed above the plurality of peaks 60b of the c-plane growth region 60 in a cross-sectional view.
- the plurality of mountain portions 70b of the inclined interface growth region 70 are formed at positions where the inclined interface 40i disappears and ends in a cross-sectional view.
- each of the plurality of peaks 70b of the inclined interface growth region 70 is formed above the plurality of valleys 60a of the c-plane growth region 60 in a cross-sectional view.
- boundary surface along the main surface 10s of the base substrate 10 at the upper end of the inclined interface growth region 70 is the boundary surface between the laminated units 50, and becomes the boundary surface at the position where the inclined interface 40i disappears and ends. ..
- boundary surface along the main surface 10s of the base substrate 10 at the upper end of the inclined interface growth region 70 of the predetermined laminated unit 50 is also simply referred to as “boundary surface of the laminated unit 50”.
- the c-plane growth region 60 in the second and higher layer laminated units 50 is provided above, for example, the inclined interface growth region 70 in the lower layer laminated unit 50.
- the top c-plane growth region 80 is provided above, for example, the inclined interface growth region 70 in the top stacking unit 50.
- the uppermost c-plane growth region 80 is a region that has grown with the c-plane as the growth plane. In the uppermost c-plane growth region 80, the uptake of oxygen is suppressed as compared with the inclined interface growth region 70. Therefore, the oxygen concentration in the uppermost c-plane growth region 80 is lower than the oxygen concentration in the inclined interface growth region 70.
- the oxygen concentration in the uppermost c-plane growth region 80 is, for example, 5 ⁇ 10 16 cm -3 or less, preferably 3 ⁇ 10 16 cm -3 or less, similar to the oxygen concentration in the c-plane growth region 60.
- the average between the closest peaks in the second or more laminated units 50 among the plurality of laminated units 50 is, for example, longer than that of the first layer stacking unit 50.
- the average distance between the closest mountain portions in each of the plurality of laminated units 50 is, for example, the plurality of laminated units 50. It gradually becomes longer toward the upper layers.
- dislocations occur at positions where the inclined interface 30i other than the c-plane is exposed, in a direction substantially perpendicular to the inclined interface 30i.
- the flattening layer 40 By bending and propagating, in the flattening layer 40, some of the plurality of dislocations disappear, and some of the plurality of dislocations are suppressed from propagating to the surface side of the c-plane expansion layer 42. There is. As a result, the dislocation density at the boundary surface of each laminated unit 50 is lower than the dislocation density at the main surface 10s of the base substrate 10.
- dislocations are locally collected in the growth process of the three-dimensional growth layer 30 and the flattening layer 40, so that the dislocations are locally collected at the boundary surface of the second and higher laminated units 50.
- the dislocation density is lower than the dislocation density at the interface of the first layer laminated unit 50.
- the dislocation density is gradually reduced according to the number of times the cycle is repeated. Specifically, the dislocation density at each interface of the plurality of laminated units 50 is gradually reduced toward the upper layer of the plurality of laminated units 50.
- the dislocation density is sharply reduced in the thickness direction.
- the dislocation density on the main surface 10s of the base substrate 10 is N 0, and the dislocation density (average dislocation density) on the boundary surface of the uppermost laminated unit 50 is N.
- a crystal layer of a group III nitride semiconductor is formed on the main surface 10s of the base substrate 10 with only the c-plane as a growth surface, from the main surface 10s of the base substrate 10 of the present embodiment to the boundary surface of the uppermost laminated unit 50.
- the dislocation density on the surface of the crystal layer is defined as N'when epitaxially grown to a thickness equal to the thickness of (hereinafter, also referred to as "c-plane thick film growth (c-plane limited growth)").
- the dislocation density on the surface of the crystal layer tended to be inversely proportional to the thickness of the crystal layer.
- the reduction rate of the dislocation density determined by N'/ N 0 was about 0.5 when the thickness of the crystal layer was 2 mm.
- the reduction ratio of the dislocation density obtained by N / N for example, smaller than reduction rate of the dislocation density obtained by N '/ N 0 in the case of c MenAtsumaku growth.
- the thickness of the laminated unit 50 per layer is, for example, more than 200 ⁇ m and 1.5 mm or less, preferably 1.2 mm or less.
- the thickness from the main surface 10s of the base substrate 10 to the boundary surface of the second laminated unit 52 is, for example, 3 mm or less, preferably 2.4 mm or less.
- the reduction rate of the dislocation density obtained by N / N 0 described above is, for example, 0.15 or less, preferably 0.10 or less, and more preferably 0.08 or less.
- the lower limit of the reduction rate of the dislocation density is not limited because the smaller it is, the better.
- the reduction rate of the dislocation density is, for example, 3 ⁇ 10 -4 or more.
- the entire surface of the laminated structure 90 is closed to the + c plane, and each laminated unit 50 and the uppermost c plane growth region 80 each have a polarity reversal zone (inversion domain). Does not include.
- the laminated structure 90 of the present embodiment is different from the laminated structure formed by the so-called DEEP (Dislocation Elimination by the Epitaxyal-growth with inverse-pyramidal Pits) method, that is, it is located at the center of the pit. It is different from the laminated structure in which the core contains a polarity reversal section.
- FIG. 12A is a schematic top view showing the nitride semiconductor substrate according to the present embodiment
- FIG. 12B is a schematic cross-sectional view taken along the m-axis of the nitride semiconductor substrate according to the present embodiment
- (C) is a schematic cross-sectional view along the a-axis of the nitride semiconductor substrate according to the present embodiment.
- the direction along the m-axis is the x-direction
- the direction along the a-axis is the y-direction.
- the substrate 100 obtained by slicing the main growth layer 44 by the above-mentioned manufacturing method is, for example, a self-standing substrate made of a single crystal of a group III nitride semiconductor.
- the substrate 100 is, for example, a GaN free-standing substrate.
- the diameter of the substrate 100 is, for example, 2 inches or more.
- the thickness of the substrate 100 is, for example, 300 ⁇ m or more and 1 mm or less.
- the conductivity of the substrate 100 is not particularly limited, but when a semiconductor device as a vertical Schottky barrier diode (SBD) is manufactured using the substrate 100, the substrate 100 is, for example, n-type.
- the n-type impurity in the substrate 100 is, for example, Si or germanium (Ge), and the n-type impurity concentration in the substrate 100 is, for example, 1.0 ⁇ 10 18 cm -3 or more and 1.0 ⁇ 10 20 cm -3 or less. ..
- the substrate 100 has, for example, a main surface 100s which is an epitaxial growth surface.
- the crystal plane having the lowest index closest to the main plane 100s is, for example, the c plane 100c.
- the main surface 100s of the substrate 100 is mirrored, for example, and the root mean square roughness RMS of the main surface 100s of the substrate 100 is, for example, less than 1 nm.
- the impurity concentration in the substrate 100 obtained by the above-mentioned manufacturing method is lower than that of the substrate obtained by the flux method, the amonothermal method, or the like.
- the hydrogen concentration in the substrate 100 is, for example, less than 1 ⁇ 10 17 cm -3 , preferably 5 ⁇ 10 16 cm -3 or less.
- the substrate 100 is formed by slicing the main growth layer 44 grown with the c-plane 40c as the growth surface, the inclined interface growth grown with the inclined interface 30i or the inclined interface 40i as the growth surface. Does not include region 70. That is, the entire substrate 100 is composed of a low oxygen concentration region.
- the oxygen concentration in the substrate 100 is, for example, 5 ⁇ 10 16 cm -3 or less, preferably 3 ⁇ 10 16 cm -3 or less.
- the substrate 100 does not include the polarity reversal zone (inversion domain) as described above, for example.
- the c-plane 100c as the crystal plane having the lowest index closest to the main plane 100s of the substrate 100 is, for example, the production of the substrate 100 described above. Due to the method, it is curved in a concave spherical shape with respect to the main surface 100s.
- the c-plane 100c of the substrate 100 has, for example, a curved surface that is approximated by a spherical surface in each of the cross section along the m-axis and the cross-section along the a-axis.
- the c-plane 50f of the substrate 100 is curved in a concave spherical shape as described above, at least a part of the c-axis 100ca is inclined with respect to the normal of the main surface 100s. ..
- the off-angle ⁇ which is the angle formed by the c-axis 100ca with respect to the normal of the main surface 100s, has a predetermined distribution within the main surface 100s.
- the off-angle m-axis component ⁇ m and the off-angle a-axis component ⁇ a are 1 of x, respectively. It can be approximately represented by a quadratic function and a linear function of y.
- the X-ray locking curve of the (0002) surface is measured at each position on a straight line passing through the center within the main surface 100s, and the angle formed by the X-ray incident on the main surface 100s and the main surface 100s.
- peak angle ⁇ the peak angle ⁇
- the "peak angle ⁇ " referred to here is an angle formed by an X-ray incident on the main surface 100s and the main surface 100s, and means an angle at which the diffraction intensity is maximized.
- the radius of curvature of the c-plane 100c can be obtained from the reciprocal of the slope of the linear function approximated as described above.
- the radius of curvature of the c-plane 100c of the substrate 100 is larger than, for example, the radius of curvature of the c-plane 10c of the base substrate 10 used in the above-described method for manufacturing the substrate 100.
- the radius of curvature of the c-plane 100c of the substrate 100 is, for example, 23 m or more, preferably 30 m or more, and more preferably 40 m or more.
- the radius of curvature of the c-plane in the sliced substrate may be larger than the radius of curvature of the c-plane 10c of the base substrate 10.
- the radius of curvature of the c-plane in the substrate sliced from the crystal layer is about 11 m, and the c-plane 10c of the base substrate 10 It is about 1.4 times the radius of curvature of.
- the upper limit of the radius of curvature of the c-plane 100c of the substrate 100 is not particularly limited as it is larger.
- the c-plane 100c of the substrate 100 is substantially flat, it may be considered that the radius of curvature of the c-plane 100c is infinite.
- the variation of the off-angle ⁇ of the c-axis 100ca with respect to the normal of the main surface 100s of the substrate 100 is made to be off by the c-axis 10ca of the base substrate 10. It can be smaller than the variation in angle.
- the X-ray locking curve of the (0002) plane of the substrate 100 is measured, and the off angle ⁇ of the c-axis 100ca with respect to the normal of the main plane 100s is measured based on the diffraction peak angle of the (0002) plane.
- the variation obtained by the maximum and minimum difference in the size of the off-angle ⁇ within 2 inches (50.8 mm) in diameter from the center of the main surface 100s is, for example, 0.127 ° or less, preferably 0.097 °. Hereinafter, it is more preferably 0.073 ° or less.
- the variation in the off-angle of the c-axis 10ca obtained by the above-mentioned measurement method is about 0.38 °.
- the thickness of the crystal layer was set to the same thickness as the thickness from the main surface 10s of the base substrate 10 of the present embodiment to the boundary surface of the uppermost laminated unit 50 (for example, 2 mm).
- the variation in the off-angle of the c-axis obtained by the above-mentioned measuring method is about 0.26 °.
- the lower limit of the variation in the off-angle ⁇ of the c-axis 100ca of the substrate 100 is not particularly limited as it is smaller.
- the c-plane 100c of the substrate 100 is substantially flat, it may be considered that the variation of the off-angle ⁇ of the c-axis 100ca of the substrate 100 is 0 °.
- the curvature of the c-plane 100c is isotropically small with respect to the main surface 100s of the substrate 100, the direction dependence of the radius of curvature of the c-plane 100c is small.
- the difference between the absolute value of the radius of curvature of the c-plane 100c in the direction along the a-axis and the absolute value of the radius of curvature of the c-plane 100c in the direction along the m-axis obtained by the above-mentioned measurement method is For example, the larger of these is 90% or less, preferably 50% or less, and more preferably 20% or less.
- the error of ⁇ with respect to the linear function of the position is small.
- the error of ⁇ in this embodiment is set to, for example, a substrate obtained from a crystal layer grown on a base substrate that has been patterned by an ELO method using a mask layer, or in a three-dimensional growth step with one cycle. It can be made smaller than the substrate obtained from the flattening layer when the surface does not disappear.
- the error of the measured peak angle ⁇ with respect to the linear function approximated as described above is, for example, 0.05 ° or less, preferably 0.02 ° or less, more preferably 0.01 ° or less. Is. Since at least a part of the peak angle ⁇ may match the linear function, the minimum value of the error is 0 °.
- the dark spot here means a point where the emission intensity observed in the observation image of the main surface 100s or the cathode luminescence image of the main surface 100s in a multiphoton excitation microscope is low, and only dislocations occur. It also contains non-luminous centers due to foreign matter or point defects.
- the "multiphoton excitation microscope” may also be referred to as a two-photon excitation fluorescence microscope.
- the substrate 100 is manufactured using the base substrate 10 made of a high-purity GaN single crystal produced by the VAS method, a non-emission center due to a foreign substance or a point defect in the substrate 100. Less is. Therefore, 95% or more, preferably 99% or more, more preferably 100% of dark spots when the main surface of the substrate 100 is observed with a multiphoton excitation microscope or the like is a non-emission center caused by a foreign substance or a point defect. There is no dislocation.
- the dislocation density on the surface of the main growth layer 44 is lower than the dislocation density on the main surface 10s of the base substrate 10 by the above-mentioned manufacturing method. As a result, dislocations are also reduced on the main surface 100s of the substrate 100 formed by slicing the main growth layer 44.
- the main growth layer 44 is formed by slicing the main growth layer 44 by performing the three-dimensional growth step S200 or the like by using the base substrate 10 in a state where the pattern processing is not performed by the above-mentioned manufacturing method.
- a region having an excessively high dislocation density is not formed due to pattern processing of the base substrate 10, and a region having a low dislocation density is uniformly formed.
- the dislocation density is 3 ⁇ 10 6 cm ⁇ .
- a region having a dislocation density of less than 1 ⁇ 10 6 cm- 2 is present at 80% or more, preferably 90% or more, more preferably 95% or more of the main surface 100s.
- the upper limit of the proportion of the region where the dislocation density is less than 1 ⁇ 10 6 cm- 2 is 100%.
- the dislocation density on the main surface 100s of the substrate 100 is reduced according to the number of times the cycle is repeated. ing. That is, the dislocation density on the main surface 100s of the substrate 100 of the present embodiment is lower than the dislocation density on the main surface of the substrate formed by slicing the main growth layer when only one cycle is performed. ..
- the dislocation density is 1 ⁇ 10 6 cm ⁇ .
- the dislocation density is 1 ⁇ 10 6 cm ⁇ .
- the upper limit of the ratio of the region where the dislocation density is less than 7 ⁇ 10 5 cm- 2 is 100%.
- the dislocation density obtained by averaging the entire main surface 100s of the substrate 100 is, for example, less than 7 ⁇ 10 5 cm- 2 , preferably less than 5.5 ⁇ 10 5 cm- 2 . More preferably, it is 3 ⁇ 10 5 cm- 2 or less.
- the main surface 100s of the substrate 100 of the present embodiment includes, for example, a dislocation-free region of at least 50 ⁇ m square based on the average distance L between the most recent ridges in the above-mentioned three-dimensional growth step S200.
- the dislocation-free regions of 50 ⁇ m square are scattered over the entire main surface 100s of the substrate 100, for example. There is.
- the main surface 100s of the substrate 100 has, for example, 100 pieces / cm 2 or more, preferably 1000 pieces / cm 2 or more, more preferably 1600 pieces / cm 2 or more of non-overlapping 50 ⁇ m square non-dislocation regions. More preferably, it has a density of more than 4,800 pieces / cm 2 , and most preferably, it has a density of 10,000 pieces / cm 2 or more.
- the upper limit of the density of the non-dislocation-free regions of 50 ⁇ m square that do not overlap is 40,000 pieces / cm 2 based on the measurement method.
- At least a part of the main surface 100s of the substrate 100 is formed by setting the average distance L between the nearest apex portions to exceed 200 ⁇ m in the inclined interface expansion step S220 of at least the last cycle among the plurality of cycles. For example, it has a dislocation-free region of at least 100 ⁇ m square.
- the main surface 100s of the substrate 100 has, for example, 100 ⁇ m square non-dislocation-free regions that do not overlap at a density of 100 pieces / cm 2 or more, preferably 250 pieces / cm 2 or more.
- the upper limit of the density of the non-dislocation-free regions of 100 ⁇ m square that do not overlap is 10,000 pieces / cm 2 based on the measurement method.
- dislocations are not excessively concentrated even in a region other than the dislocation-free region (for example, between a pair of adjacent dislocation-free regions), and the dislocation density is low.
- the number of dislocations existing in the quadrangular region sandwiched between the opposite sides of the pair of 50 ⁇ m square non-dislocation regions that are closest to each other is, for example, 330 or less, preferably 90 or less.
- the number is preferably 70 or less, more preferably 33 or less, and most preferably 18 or less.
- the size of the dislocation-free region is smaller than 50 ⁇ m square, or the density of the dislocation-free region of 50 ⁇ m square is high. It is lower than 100 pieces / cm 2. Since the density of the 50 ⁇ m square dislocation-free region is low, the number of dislocations existing between the pair of dislocation-free regions also increases. Further, there is a high possibility that a 100 ⁇ m square non-dislocation region is not formed.
- the dislocation density on the main surface 10s of the base substrate 10 used in the above-mentioned manufacturing method is low, a plurality of dislocations are generated when the three-dimensional growth layer 30 and the flattening layer 40 are grown on the base substrate 10. Are less likely to combine (mix). This makes it possible to suppress the formation of dislocations having a large Burgers vector in the substrate 100 obtained from the flattening layer 40.
- the Burgers vector is either ⁇ 11-20> / 3, ⁇ 0001>, or ⁇ 11-23> / 3.
- the "Burgers vector” here can be measured by, for example, a large-angle converged electron diffraction method (LACBED method) using a transmission electron microscope (TEM).
- a dislocation having a Burgers vector ⁇ 11-20> / 3 is a blade dislocation
- a dislocation having a Burgers vector ⁇ 0001> is a spiral dislocation
- One dislocation is a mixed dislocation that is a mixture of edge dislocations and spiral dislocations.
- the Burgers vector is any one of ⁇ 11-20> / 3, ⁇ 0001>, and ⁇ 11-23> / 3.
- the ratio of the number of dislocations is, for example, 50% or more, preferably 70% or more, and more preferably 90% or more.
- dislocations having a Burgers vector of 2 ⁇ 11-20> / 3 or ⁇ 11-20> may be present in at least a part of the main surface 100s of the substrate 100.
- the inventor obtains the crystal quality elements constituting the substrate 100 of the present embodiment by measuring the X-ray locking curve of c-plane diffraction with different widths of the slits on the incident side in the ⁇ direction, and the above-mentioned c. It has been found that both the curvature (warp) of the surface 100c and the curvature can be evaluated at the same time.
- the half-value width of the diffraction pattern in the X-ray locking curve measurement is, for example, the high / low dislocation density, the high / low mosaicity, the high / low stacking defect density, the high / low basal plane dislocation density, the high / low point defect (vacancy, etc.) density, and the lattice constant. It is greatly affected by crystal quality factors such as the amount of in-plane fluctuation and the distribution of impurity density. If these crystal quality factors are not good, the fluctuation of the diffraction angle in the X-ray locking curve measurement becomes large, and the half width of the diffraction pattern becomes large.
- FIG. 13A is a schematic cross-sectional view showing the diffraction of X-rays with respect to the curved c-plane.
- the irradiation width of X-rays (footprint width) irradiated on the main surface of the substrate is b
- the Bragg angle of the crystal is ⁇ B
- the " ⁇ " and “ ⁇ direction” mean the “rotation angle” and the "rotation angle direction” around the rotation axis of the goniometer in the X-ray locking curve measurement, respectively.
- the " ⁇ " and the “ ⁇ direction” are respectively mounted on the substrate stage with the axis passing through the center of the substrate stage and parallel to the mounting surface of the substrate stage as the central axis. It can also be considered as the substrate rotation angle and the substrate rotation direction when the substrate 100 is rotated.
- FIG. 13 (b) and 13 (c) are diagrams showing fluctuations in the diffraction angle of the (0002) plane with respect to the radius of curvature of the c plane.
- the vertical axis of FIG. 13B is a logarithmic scale
- the vertical axis of FIG. 13C is a linear scale.
- the influence of the curvature of the c-plane is small in the fluctuation of the diffraction angle of the (0002) plane, and the influence of the above-mentioned crystal quality factor becomes dominant.
- the width dI of the incident side slit in the ⁇ direction is wide, both the influence of the crystal quality element and the influence of the curvature of the c-plane are superimposed on the fluctuation of the diffraction angle of the (0002) plane. It will be.
- the main surface 100s of the substrate 100 is irradiated with X-rays of Cu K ⁇ 1 through the two-crystal monochromator on the Ge (220) surface and the slit on the incident side, and the X-ray locking curve of (0002) surface diffraction is measured.
- the width of the incident side slit in the ⁇ direction is 1 mm
- the half width of the (0002) plane diffraction is set to "FWHMa”
- the width of the incident side slit in the ⁇ direction is 0.1 mm.
- the half width of surface diffraction is defined as "FWHMb”.
- the dislocation density is high and low, the mosaicity is high and low, the stacking defect density is large and small, the basal plane dislocation density is large and small, the point defect (vacancy, etc.) density is large and small, and the amount of in-plane fluctuation of the lattice constant is large and small. All of the above-mentioned crystal quality factors such as the distribution of impurity concentrations are good.
- the half width FWHMb of the (0002) plane diffraction is performed. Is, for example, 80 arcsec or less, preferably 50 arcsec or less, and more preferably 32 arcsec or less.
- the width of the incident side slit in the ⁇ direction is 0.1 mm (0002).
- the half width FWHMb of (0002) surface diffraction is 80 arcsec.
- it is preferably 50 arcsec or less, more preferably 32 arcsec or less.
- the in-plane variation of the above-mentioned crystal quality elements is small. Therefore, the diffraction pattern of the (0002) plane when the X-ray locking curve measurement is performed by widening the width of the incident side slit in the ⁇ direction narrows the width of the incident side slit in the ⁇ direction to obtain the X-ray locking curve. It tends to be less likely to be narrower than the diffraction pattern of the (0002) plane when the measurement is performed.
- the width at half maximum of (0002) plane diffraction can be FWHMb or more.
- FWHMb may be ⁇ FWHMb in a state where the FWHMb is very small.
- the substrate 100 of the present embodiment as described above, not only are there few dislocations over a wide range of the main surface 100s, but all of the above-mentioned crystal quality elements are well-balanced and good. Further, the curvature of the c-plane 100c of the substrate 100 is small, and the radius of curvature of the c-plane 100c is large. As a result, in the substrate 100 of the present embodiment, even if the width of the slit on the incident side in the ⁇ direction is widened (0002) and the X-ray locking curve measurement of the surface diffraction is performed, the X-ray irradiation region is covered.
- the full width at half maximum of (0002) surface diffraction when the width of the slit on the incident side in the ⁇ direction is 1 mm
- the incident side The difference FWHMa-FWHMb obtained by subtracting the full width at half maximum FWHMb of the (0002) plane diffraction when the width of the slit in the ⁇ direction is 0.1 mm is, for example, 30% or less (0% or more) of FWHMa, preferably 22% or less.
- the widths of the incident side slits in the ⁇ direction are different (0002) surfaces.
- FWHMa-FWHMb is, for example, 30% or less, preferably 22% or less of FWHMa.
- FWHMa may be substantially equal to FWHMb, and
- / FWHMa may be 0%.
- the above-mentioned crystal quality elements are present over the region irradiated with X-rays.
- the small variation means that the diffraction pattern has a single peak.
- a substrate manufactured by a conventional manufacturing method (hereinafter, also referred to as a conventional substrate) will be described.
- the conventional manufacturing method referred to here is, for example, a conventional VAS method, a method of growing a thick film using the c-plane as a growth plane, the above-mentioned DEEP method, a THVPE (Tri-halide flux phase epitaxy) method, an analog thermal method, and the like. Flux method, etc.
- the FWHMb in the conventional substrate is larger than that of the substrate 100 of the present embodiment.
- the radius of curvature of the c-plane is smaller than that of the substrate 100 of the present embodiment.
- the width of the incident side slit in the ⁇ direction is widened, it is inevitable that at least one of the crystal quality elements is not better than the substrate 100 of the present embodiment in at least a part of the region irradiated with X-rays. include. Therefore, the difference FWHMa-FWHMb in the conventional substrate is larger than that of the substrate 100 of the present embodiment.
- in-plane variation of at least one of the above-mentioned crystal quality elements may occur.
- the width of the incident side slit in the ⁇ direction is widened, there may be a portion where the fluctuation of the diffraction angle of the (0002) plane is different in at least a part of the region irradiated with X-rays. Therefore, the diffraction pattern of the (0002) plane when the width of the incident side slit in the ⁇ direction is widened may have a plurality of peaks.
- the conventional substrate may not satisfy the above-mentioned (0002) plane diffraction requirement defined for the substrate 100 of the present embodiment.
- FIGS. 14 and 15 are a schematic perspective view and a schematic plan view showing the measurement of the X-ray locking curve of the asymmetric reflective surface in the present embodiment, respectively.
- a part of the main surface 100s of the substrate 100 is tentatively shown as a quadrangle.
- the two directions orthogonal to each other along the main surface 100s of the substrate 100 are defined as the "X direction” and the “Y direction”, respectively, and the normal direction of the main surface 100s of the substrate 100 is “Z”.
- Direction. the direction of the rotation axis of the goniometer is defined as the "y direction”
- the direction orthogonal to the rotation axis of the goniometer and coincident with the X direction of the substrate 100 is defined as the "x direction”
- the directions orthogonal to the x direction and the y direction Is the "z direction”.
- the rotation angle and the rotation angle direction around the rotation axis of the goniometer are defined as “ ⁇ ” and “ ⁇ direction”, respectively.
- the angle at which the rotation axis of the goniometer is tilted with respect to the main surface of the substrate 100 is defined as “ ⁇ ”.
- the width of the ⁇ direction of the input aperture and "d I", and “L I” the length of the parallel direction of the input aperture to the axis of rotation of the goniometer.
- the width of the ⁇ direction of the light receiving side opening and "d D", and “L D” the length of the parallel direction of the light receiving side opening to the axis of rotation of the goniometer.
- the light receiving side opening corresponds to the opening of the detector or the entrance opening of the analyzer crystal.
- the region where the substrate 100 is irradiated with X-rays from the X-ray source is defined as "X-ray irradiation region IA", and the region where the detector can receive X-rays from the substrate 100 is defined as "light-receiving region DA".
- the region where information on the crystal quality of the substrate 100 can be actually obtained is referred to as “measurement region MA”.
- the locus of X-rays from the incident side to the main surface 100s and the locus of virtual X-rays from the detector side to the main surface 100s are shown in light gray, respectively, and the X-ray irradiation area IA and the light receiving area DA are shown. Are shown in gray, and the measurement area MA is shown in dark gray.
- the rotation axis of the goniometer is tilted at an angle ⁇ with respect to the main surface 100s of the substrate 100. Therefore, the X-ray irradiation region IA on the main surface 100s of the substrate 100 in the measurement extends along the direction inclined with respect to the Y axis of the main surface 100s. As a result, the irradiation region IA in the measurement becomes wider than the measurement region along the Y axis in the above-mentioned X-ray locking curve measurement of c-plane diffraction.
- the light receiving region DA as a region where the detector can receive X-rays from the substrate 100 is, for example, irradiating the substrate 100 with X-rays from the detector side. It can be obtained as a hypothetical X-ray irradiation area.
- the light receiving region DA on the main surface 100s of the substrate 100 in the measurement extends in a direction symmetrical to the X-ray irradiation region IA with the Y axis of the main surface 100s interposed therebetween.
- the measurement region MA from which information on the crystal quality of the substrate 100 is actually obtained is the X-ray irradiation region IA based on the incident conditions and the light reception based on the light reception conditions. It is an area where the possible area DA and the possible area DA overlap.
- the influence of the imperfections of the crystals formed by the substrate 100 is the width of the component corresponding to the ⁇ direction on the main surface 100s of the substrate 100, that is, the X direction of the measurement region MA.
- the width WMA of the width of the component corresponding to the ⁇ direction on the main surface 100s of the substrate 100 that is, the X direction of the measurement region MA.
- the width W MA of the measurement region MA in the X direction is calculated by the following equation (j).
- the width W MA in the X direction of the measurement region MA is compared.
- the width W MA of the measurement region MA in the X direction becomes narrow. Therefore, in the fluctuation of the diffraction angle of the asymmetric reflection surface, the influence of the curvature of the crystal plane is small, and the influence of the above-mentioned crystal quality factor becomes dominant.
- the width W MA of the measurement region MA in the X direction becomes wide.
- both the influence of the crystal quality element and the influence of the curvature of the crystal plane are superimposed. Therefore, if the X-ray locking curve measurement is performed with different widths d D in the ⁇ direction of the light receiving side opening, both the above-mentioned crystal quality element and the curvature of the crystal plane can be obtained over the entire measurement region MA. It is possible to evaluate at the same time.
- FWHM1 ⁇ 10-12 ⁇ and FWHM2 ⁇ 10-12 ⁇ are half widths of ⁇ 10-12 ⁇ plane diffraction measured by X-ray locking curve measurement, respectively.
- an X-ray mirror that makes X-rays parallel light
- a Ge (220) double-reflection monochrome meter and a goniometer rotation axis.
- the input aperture length L I of the direction parallel to the ⁇ width d I is 1.4mm and the rotation axis as a rotation angle direction is 12mm around through in this order, the main substrate 100
- the center of the surface 100s is irradiated with X-rays of Cu K ⁇ 1.
- a detector having an opening (light receiving side opening) having a width d D in the ⁇ direction of 14.025 mm without an open light receiving side slit and an analyzer crystal. Receives X-rays.
- the incident conditions when measuring FWHM2 ⁇ 10-12 ⁇ are the same as the incident conditions when measuring FWHM1 ⁇ 10-12 ⁇ .
- a Ge (220) triple-reflection analyzer crystal having an inlet opening (that is, a light-receiving side opening) having a width d D in the ⁇ direction of 6.54 mm is used. Then, the detector receives X-rays.
- the width W MA of the measurement region MA in the X direction has the following values.
- W MA when measuring FWHM1 ⁇ 10-12 ⁇ Approximately 18.92 mm
- W MA when measuring FWHM2 ⁇ 10-12 ⁇ Approximately 9.74 mm
- a condition for making the width W MA of the measurement area MA in the X direction relatively wide may be abbreviated as “wide measurement area condition”, and FWHM2 ⁇ A condition for relatively narrowing the width W MA of the measurement region MA in the X direction, such as when measuring 10-12 ⁇ , may be abbreviated as “narrow measurement region condition”.
- the above-mentioned crystal quality elements are well-balanced and good over a wide range of the main surface 100s, and the curvature of the crystal plane of the substrate 100 is small.
- the above-mentioned crystal quality elements are well-balanced over the entire measurement region MA. Since it is good and the curvature of the crystal plane is small, the fluctuation of the diffraction angle of the ⁇ 10-12 ⁇ plane is not so large.
- the FWHM1 ⁇ 10-12 ⁇ under the wide measurement area condition is, for example, 50 arcsec or less, preferably 40 arcsec or less.
- the substrate 100 of the present embodiment all of the above-mentioned crystal quality elements are well-balanced and good regardless of the crystal orientation, and the curvature of the crystal plane of the substrate 100 is small.
- the variation of the diffraction angle of the ⁇ 10-12 ⁇ plane does not vary. , Doesn't get too big.
- equivalent crystal planes represented by ⁇ 10-12 ⁇ planes are formed from three directions rotated by 60 ° in the circumferential direction about the normal line of the center of the main surface 100s.
- the maximum and minimum difference of FWHM1 ⁇ 10-12 ⁇ in which the diffraction of FWHM1 is measured is, for example, 9 arcsec or less.
- the substrate 100 of the present embodiment as described above, all of the above-mentioned crystal quality elements are well-balanced and good over a wide range of the main surface 100s, and the curvature of the crystal plane of the substrate 100 is small. Therefore, even if the X-ray locking curve of the ⁇ 10-12 ⁇ plane diffraction is measured under different measurement conditions, the fluctuation of the diffraction angle of the ⁇ 10-12 ⁇ plane becomes small.
- the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ at the center of the main surface 100s of the substrate 100 of the present embodiment is, for example, 80% or more.
- the "ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ " here is a value obtained by (FWHM2 ⁇ 10-12 ⁇ / FWHM1 ⁇ 10-12 ⁇ ) ⁇ 100. ..
- the FWHM1 ⁇ 10-12 ⁇ under the condition may be smaller than the FWHM2 ⁇ 10-12 ⁇ under the narrow measurement region condition. That is, the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ may exceed 100%.
- the main surface 100s of the substrate 100 has no surface state defects, that is, the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ is, for example, 100% or less. Is preferable.
- the above-mentioned crystal quality elements is not good in the conventional substrate. Therefore, when the measurement is performed under the condition of a wide measurement region, at least a part of the measurement region MA inevitably includes a portion where at least one of the crystal quality elements is not good. Further, in the conventional substrate, the curvature of the crystal plane is larger than that of the substrate 100 of the present embodiment. As a result, the FWHM1 ⁇ 10-12 ⁇ in the conventional substrate is larger than that of the substrate 100 of the present embodiment.
- the maximum and minimum difference of the equivalent crystal plane diffraction FWHM1 ⁇ 10-12 ⁇ measured from three directions on the conventional substrate is larger than that of the substrate 100 of the present embodiment.
- the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ in the measurement in at least one direction of the conventional substrate is smaller than that of the substrate 100 of the present embodiment.
- the conventional substrate may not satisfy the above-mentioned ⁇ 10-12 ⁇ plane diffraction requirement defined for the substrate 100 of the present embodiment.
- the inclined interface 30i is formed at the position where the inclined interface 30i is exposed.
- Dislocations can be bent and propagated in a direction substantially perpendicular to the direction. This allows dislocations to be collected locally. By locally collecting dislocations, dislocations having Burgers vectors that are opposite to each other can be eliminated. Alternatively, the locally collected dislocations form a loop, so that the dislocations can be suppressed from propagating to the surface side of the flattening layer 40. In this way, the dislocation density on the surface of the flattening layer 40 can be reduced. As a result, it is possible to obtain a substrate 100 having a dislocation density lower than that of the base substrate 10.
- the c-plane 30c disappears from the top surface 30u of the three-dimensional growth layer 30 at least once.
- a plurality of valleys 30v and a plurality of tops 30t can be formed on the surface of the three-dimensional growth layer 30.
- the dislocations propagating from the base substrate 10 can be reliably bent at the position where the inclined interface 30i in the three-dimensional growth layer 30 is exposed.
- the dislocations propagated from the base substrate propagate substantially vertically upward without being bent and reach the surface of the second layer. Therefore, dislocations are not reduced and a high dislocation density region is formed above the portion where the c-plane remains.
- the surface of the three-dimensional growth layer 30 is other than the c-plane. It can be configured only by the inclined interface 30i of the above, and a plurality of valleys 30v and a plurality of tops 30t can be formed on the surface of the three-dimensional growth layer 30. As a result, the dislocations propagating from the base substrate 10 side can be reliably bent over the entire surface of the three-dimensional growth layer 30.
- the cycle including the three-dimensional growth step S200 and the flattening step S300 is repeated a plurality of times.
- the dislocations propagating from the base substrate 10 side can be bent and the dislocations can be locally collected by one cycle including the three-dimensional growth step S200 and the flattening step S300.
- the dislocations remaining in the flattening layer 40 in the previous cycle can be further bent, and the dislocations can be locally collected.
- the dislocation density on the surface of the flattening layer 40 in the next cycle can be reduced from the dislocation density on the surface of the flattening layer 40 in the previous cycle.
- the dislocation density can be gradually reduced according to the number of times the cycle is repeated.
- the average distance L between the nearest apex portions is gradually increased as, for example, the plurality of cycles are repeated.
- the distance at which the dislocations bend and propagate can be gradually increased.
- the dislocation-free region on the surface of the flattening layer 40 can be gradually widened, and the density of the dislocation-free region on the surface of the flattening layer 40 can be gradually increased. ..
- the average distance L between the nearest apex portions is set to more than 100 ⁇ m.
- the distance at which the dislocations bend and propagate can be secured at least over 50 ⁇ m.
- dislocations can be sufficiently collected above the substantially center between the pair of tops 30t of the three-dimensional growth layer 30.
- the dislocation density on the surface of the flattening layer 40 can be sufficiently reduced.
- the average distance L between the nearest apex portions is set.
- the distance at which the dislocations are bent and propagated can be secured at least 100 ⁇ m or more.
- a dislocation-free region of at least 100 ⁇ m square can be formed on at least a part of the surface of the flattening layer 40 in the last cycle.
- the ⁇ 11-2m ⁇ plane in which m ⁇ 3 is set as the inclined interface 30i by adjusting the first growth condition so as to satisfy the equation (1). Can be caused.
- the inclination angle of the ⁇ 11-2m ⁇ plane with respect to the c plane 30c can be made gentle. Specifically, the inclination angle can be 47.3 ° or less.
- the period of the plurality of tops 30t can be lengthened. Specifically, when an arbitrary cross section perpendicular to the main surface 10s of the base substrate 10 is viewed, the average distance L between the nearest apex portions can be set to more than 100 ⁇ m.
- an etch pit composed of ⁇ 1-10n ⁇ planes is formed on the surface of the substrate.
- a ⁇ 11-2m ⁇ surface having m ⁇ 3 can be generated. Therefore, it is considered that the inclined interface 30i peculiar to the manufacturing method is formed in the present embodiment as compared with the normal etch pit.
- the dislocations at the position where the inclined interface 30i is exposed are surely bent. It is possible to prevent dislocations from propagating from the base substrate 10 toward the surface of the flattening layer 40 in a substantially vertical direction. As a result, the concentration of dislocations above the top 30t of the three-dimensional growth layer 30 can be suppressed.
- the radius of curvature of the c-plane 100c of the substrate 100 can be made larger than the radius of curvature of the c-plane 10c of the base substrate 10.
- the variation in the off-angle ⁇ of the c-axis 100ca with respect to the normal of the main surface 100s of the substrate 100 can be made smaller than the variation in the c-axis 10ca off-angle of the base substrate 10.
- the following reasons can be considered as one of the reasons why the radius of curvature of the c-plane 100c of the substrate 100 can be increased.
- the inclined interface growth region 70 is formed by three-dimensionally growing the three-dimensional growth layer 30 with the inclined interface 30i other than the c-plane as the growth surface.
- oxygen is easily taken in as compared with the c-plane growth region 60. Therefore, the oxygen concentration in the inclined interface growth region 70 is higher than the oxygen concentration in the c-plane growth region 60. That is, the inclined interface growth region 70 can be considered as a high oxygen concentration region.
- the lattice constant of the high oxygen concentration region can be made larger than the lattice constant of other regions other than the high oxygen concentration region (Reference: Chris G. Van de Walle, Physical Review B vol.68, 165209 (2003)).
- the c-plane growth region 60 grown with the c-plane 30c as the growth plane in the base substrate 10 or the three-dimensional growth layer 30 is concentrated toward the center of curvature of the c-plane due to the curvature of the c-plane 10c of the base substrate 10. Stress is applied.
- the radius of curvature of the c-plane 100c of the substrate 100 obtained from the flattening layer 40 can be set to the c-plane 10c of the base substrate 10 obtained by the conventional VAS method. It can be larger than the radius of curvature.
- the dislocation density can be lowered, the off-angle variation can be reduced, and the half-value width of the X-ray locking curve measurement is determined. All of the elements can be well-balanced and good.
- the FWHMb can be set to 32 arcsec or less in the substrate 100 of the present embodiment. Further, in the substrate 100 of the present embodiment, even when the width of the incident side slit in the ⁇ direction is 1 mm, the radius of curvature of the c-plane is large over the entire region irradiated with X-rays, and the radius of curvature is large.
- (FWHMa-FWHMb) / FWHMa can be set to 30% or less.
- the FWHM1 ⁇ 10-12 ⁇ can be set to 50 arcsec or less in the substrate of the present embodiment. Further, in the substrate of the present embodiment, the maximum and minimum difference of FWHM1 ⁇ 10-12 ⁇ measured by the diffraction of the equivalent crystal plane represented by the ⁇ 10-12 ⁇ plane from three directions can be set to 9 arcsec or less. .. Further, in the substrate 10 of the present embodiment, the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ can be 80% or more.
- the base substrate 10 is a GaN free-standing substrate
- the base substrate 10 is not limited to the GaN free-standing substrate, and for example, aluminum nitride (AlN), aluminum gallium nitride (AlGaN), and indium gallium nitride are used.
- Group III nitride semiconductors such as (InN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN), that is, Al x In y Ga 1-xy N (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ ) It may be a self-supporting substrate made of a group III nitride semiconductor represented by the composition formula of 1, 0 ⁇ x + y ⁇ 1).
- the substrate 100 is a GaN free-standing substrate
- the substrate 100 is not limited to the GaN free-standing substrate, and for example, group III nitride semiconductors such as AlN, AlGaN, InN, InGaN, and AlInGaN. That is, it is a self-supporting substrate made of a group III nitride semiconductor represented by the composition formula of Al x In y Ga 1-xy N (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ x + y ⁇ 1). You may.
- the substrate 100 is n-type has been described, but the substrate 100 may be p-type or have semi-insulating properties.
- the substrate 100 when a semiconductor device as a high electron mobility transistor (HEMT) is manufactured using the substrate 100, the substrate 100 preferably has semi-insulating properties.
- HEMT high electron mobility transistor
- the main surface 10s of the base substrate 10 is mirror-finished in the polishing step S180 of the base substrate preparation step S100 has been described, but in the polishing step S180, the main surface 10s of the base substrate 10 is formed into a group III.
- Rough polishing may be performed while maintaining a so-called epiready state in which a single crystal of a nitride semiconductor can grow epitaxially.
- the root mean square roughness RMS of the main surface 10s of the base substrate 10 is set to, for example, 1 nm or more and 10 nm or less.
- the three-dimensional growth layer 30 is grown on the base substrate 10 in the three-dimensional growth step S200 of the first cycle. It is possible to promote the generation of the inclined interface 30i other than the c-plane on the surface of the above. Further, by setting the RMS of the main surface 10s of the base substrate 10 within the above range, it is possible to prevent the surface of the three-dimensional growth layer 30 from becoming excessively rough in the three-dimensional growth step S200 of the first cycle, and to prevent the surface of the three-dimensional growth layer 30 from becoming excessively rough. It is possible to suppress the shortening of the average distance L between the nearest apex portions in the growth layer 30.
- the crystal strain introduced by processing such as the slicing step S170 and the polishing step S180 of the base substrate 10 is applied to the main surface 10s of the base substrate 10. It may be left on the side.
- the width at half maximum of the base substrate 10 before processing is set to 60 arcsec or more and 200 arcsec or less.
- the three-dimensional growth layer 30 is caused by the crystal strain on the main surface 10s side of the base substrate 10 in the three-dimensional growth step S200 of the first cycle. It is possible to change the stable crystal plane that appears on the surface of. As a result, an inclined interface 30i other than the c-plane can be generated on the surface of the three-dimensional growth layer 30. Further, by setting the FWHM of the (10-10) plane diffraction within the above range, in the three-dimensional growth step S200 of the first cycle, the three-dimensional growth is caused by the crystal strain on the main surface 10s side of the base substrate 10. It is possible to suppress the occurrence of an excessively large number of dislocations in the layer 30.
- the present invention is not limited to this case.
- the initial step S190 after the base substrate preparation step S100 and before the three-dimensional growth step S200 of the first cycle the initial step C is directly on the main surface 10s of the base substrate 10 with the c-plane as the growth surface. Layers may be grown. At this time, the growth rate of the initial layer in the initial step S190 is made lower than the growth rate of the three-dimensional growth layer 30 in the three-dimensional growth step S200. As a result, the initial layer can be step-flow-grown on the main surface 10s of the base substrate 10.
- the surface morphology and crystallinity of the initial layer can be made substantially uniform over the entire surface.
- the generation state of the inclined interface 30i such as the inclined angle of the inclined interface 30i with respect to the c-plane 30c is three-dimensionally grown. It can be made substantially uniform over the entire surface of the layer 30.
- the growth temperature is mainly adjusted as the first growth condition in the three-dimensional growth step S200 of each cycle, but if the first growth condition satisfies the equation (1), the first growth condition is described.
- a growth condition other than the growth temperature may be adjusted, or the growth temperature and the growth condition other than the growth temperature may be combined and adjusted.
- the growth temperature is mainly adjusted as the second growth condition in the flattening step S300 of each cycle, but if the second growth condition satisfies the equation (2), the second growth condition is described.
- the growth conditions the growth conditions other than the growth temperature may be adjusted, or the growth temperature and the growth conditions other than the growth temperature may be combined and adjusted.
- the case where the growth conditions in the inclined interface maintenance step S240 of each cycle are maintained under the above-mentioned first growth conditions as in the inclined interface expansion step S220 has been described, but the inclined interface maintenance step S240 has been described. If the growth condition in is satisfied with the first growth condition, the growth condition in the inclined interface maintenance step S240 may be different from the growth condition in the inclined interface expansion step S220.
- the number of implementations may be more than two.
- the three-dimensional growth step S200 of the second and subsequent cycles a case where the three-dimensional growth layer 30 is grown under the same first growth conditions as the three-dimensional growth step S200 of the first cycle has been described. However, if the growth conditions in the three-dimensional growth step S200 of the second and subsequent cycles satisfy the first growth condition, the growth conditions of the process are made different from the growth conditions in the three-dimensional growth step S200 of the first cycle. May be good.
- the growth conditions in the flattening step S300 of the second and subsequent cycles satisfy the second growth condition, the growth conditions of the step may be different from the growth conditions in the flattening step S300 of the first cycle.
- the growth conditions in the main growth step S500 are maintained under the second growth conditions as in the flattening step S300 of each cycle, but the growth conditions in the main growth step S500 are the first. 2. If the growth conditions are satisfied, the growth conditions in the step may be different from the growth conditions in the flattening step S300 of each cycle.
- the case where the second crystal layer 6 or the main growth layer 44 is sliced by using a wire saw in the slicing step S170 and the slicing step S600 has been described.
- An electric discharge machine or the like may be used.
- the laminated structure 90 may be used as it is to manufacture a semiconductor laminate for manufacturing a semiconductor device. Specifically, after the laminated structure 90 is produced, the semiconductor functional layer is epitaxially grown on the laminated structure 90 in the semiconductor laminate manufacturing step to prepare the semiconductor laminate. After producing the semiconductor laminate, the back surface side of the laminated structure 90 is polished to remove the base substrate 10 and the plurality of laminated units 50 in the laminated structure 90. As a result, a semiconductor laminate having the main growth layer 44 and the semiconductor functional layer can be obtained as in the above-described embodiment. According to this case, the slicing step S600 and the polishing step S700 for obtaining the substrate 100 can be omitted.
- the substrate 100 may be used as the base substrate 10 and the steps S200 to S700 may be performed again.
- the substrate 100 having a further reduced dislocation density can be obtained.
- the steps S200 to S700 using the substrate 100 as the base substrate 10 may be set as one cycle, and the cycle may be repeated a plurality of times.
- the dislocation density of the substrate 100 can be gradually reduced according to the number of times the cycle is repeated.
- the variation in the off angle ⁇ of the c-axis 100ca on the substrate 100 can be gradually reduced according to the number of times the cycle is repeated.
- the "nitride semiconductor substrate” may be simply abbreviated as the “substrate”.
- the substrate of sample 4 was prepared by the conventional VAS method similar to that of the substrate.
- the radius of curvature of the c-plane and the dislocation density were the same as those of the base substrate, except that the absolute value of the off angle and the off direction were different from those of the base substrate.
- the hybrid monochromator has an X-ray mirror and two crystals on the Ge (220) plane in this order from the X-ray source side.
- the X-rays emitted from the X-ray source are made into parallel light by an X-ray mirror. This makes it possible to increase the number of X-ray photons used (ie, X-ray intensity).
- the parallel light from the X-ray mirror is converted into monochromatic light of K ⁇ 1 of Cu by two crystals on the Ge (220) plane.
- the monochromatic light from the two crystals on the Ge (220) plane is narrowed to a predetermined width through the slit on the incident side and incident on the substrate.
- the full width at half maximum when the locking curve of the (0002) plane of the (0002) plane of the perfect crystal GaN is measured using the hybrid monochromator is 25.7 arcsec. That is, the full width at half maximum is the theoretical measurement limit when measuring with the above-mentioned optical system.
- the X-rays incident on the substrate in the measurement are parallel light toward the substrate in the cross section orthogonal to the rotation axis of the goniometer (that is, the cross section along the ⁇ direction).
- the incident X-rays are not parallel light in the cross section along the rotation axis of the goniometer. Therefore, the width of the X-ray in the ⁇ direction is substantially constant until the X-ray reaches the substrate from the slit, but the width in the direction orthogonal to the ⁇ direction of the X-ray increases. Therefore, in the X-ray locking curve measurement, the full width at half maximum of the X-ray diffracted at the predetermined crystal plane depends on the width of the slit on the incident side in the ⁇ direction in which the X-ray becomes parallel light.
- the light receiving side was open.
- the window width of the detector on the light receiving side in the ⁇ direction was set to 14.025 mm.
- the goniometer radius is 420 mm, it is possible to measure the fluctuation of the Bragg angle of ⁇ 0.95 °.
- X-ray locking curve measurement 1 The width of the slit on the incident side in the ⁇ direction was set to 0.1 mm, and the X-ray locking curve of the (0002) plane of each of the substrate of Samples 1 to 3 and the substrate of Sample 4 corresponding to the base substrate was measured. At this time, among the main surfaces of each substrate, a plurality of sets are set at 5 mm intervals on a straight line passing through the center and along the m-axis direction and on a straight line passing through the center and orthogonal to the m-axis along the a-axis direction. The measurement was performed at the measurement point of. At this time, X-rays were incident from the side positively defined as the position in the main surface of the substrate.
- the peak angle ⁇ formed by the X-ray incident on the main surface and the main surface was plotted with respect to the position on the straight line, and the peak angle ⁇ was approximated by the linear function of the position.
- the radius of curvature of the c-plane was obtained from the reciprocal of the slope of the linear function.
- X-ray locking curve measurement 2 The width of the slit on the incident side in the ⁇ direction was set to 1 mm, and X-ray locking curves were measured for each of the substrates of Samples 1 to 3 and the substrate of Sample 4 corresponding to the base substrate. At this time, a plurality of the main surfaces of each substrate are set at 5 mm intervals on a straight line passing through the center and along the m-axis direction and on a straight line passing through the center and orthogonal to the m-axis along the a-axis direction. The measurement was performed at the measurement point of.
- the width of the slit in the ⁇ direction is 0.1 mm.
- the X-ray footprint is about 0.337 mm, and when the width of the slit in the ⁇ direction is 1 mm, the X-ray footprint is about 3.37 mm.
- FIG. 21B is a diagram showing a standardized X-ray diffraction pattern of the nitride semiconductor substrate of Sample 4 when the X-ray locking curve of surface diffraction was measured with different slits on the incident side (0002). Is. Note that FIG. 21B shows the measurement results in the direction along the a-axis. Further, in the figure, "LINE width" means the above-mentioned X-ray footprint.
- the average dislocation density of the substrate of Sample 4 which corresponds to the substrate, was 1 ⁇ 10 6 cm- 2 or more. There was no region in the main surface of the substrate of sample 4 where the dislocation density was less than 1 ⁇ 10 6 cm- 2.
- the dislocations were uniformly dispersed in the plane on the substrate of sample 4. Therefore, the size of the dislocation-free region was smaller than the 50 ⁇ m square over the entire substrate of the sample 4, and the dislocation-free region of 50 ⁇ m square was not formed.
- the FWHMb was more than 32 arcsec at all the measurement points when the width of the slit on the incident side in the ⁇ direction was 0.1 mm.
- the X-ray diffraction pattern when the width of the incident side slit in the ⁇ direction is 1 mm is set to 0.1 mm in the width of the incident side slit in the ⁇ direction. It was wider than the X-ray diffraction pattern at that time.
- FIG. 20 is a view of observing the main surface of the nitride semiconductor substrate of Sample 3 using a multi-photon excitation microscope.
- the proportion of regions having a dislocation density of less than 1 ⁇ 10 6 cm- 2 is less than 90%, and the proportion of regions having a dislocation density of less than 7 ⁇ 10 cm-2 is less than 80%. there were.
- dislocations were uniformly dispersed in the plane.
- the distribution of dislocations was the same as in FIG. 20 even in the region (not shown). Therefore, the size of the dislocation-free region was smaller than 50 ⁇ m square over the entire substrate of Sample 3, and the dislocation-free region of 50 ⁇ m square was not formed.
- the substrate of sample 3 which has a relatively high quality as a conventional substrate, has improved dislocation density and off-angle variation as compared with sample 4, which is equivalent to the underlying substrate.
- the substrate of sample 3 did not have any point satisfying the half-value width of FWHMb ⁇ 32 arcsec and (FWHMa-FWHMb) / FWHMa ⁇ 30%. It is probable that in the substrate of sample 3, at least one of the above-mentioned crystal quality elements was not as good as that of the substrates of samples 1 and 2.
- FIG. 19 is a view of observing the main surface of the nitride semiconductor substrate of Sample 2 using a multi-photon excitation microscope.
- a region having a dislocation density of 1 ⁇ 10 6 cm- 2 or more was present in about 5% of the main surface. Further, in the substrate of Sample 2, the proportion of the region where the dislocation density was less than 7 ⁇ 10 5 cm- 2 was less than 80%.
- the main surface of the substrate of Sample 2 contained a dislocation-free region of at least 50 ⁇ m square. Further, in the substrate of Sample 2, dislocation-free regions of 50 ⁇ m square were scattered over the entire main surface.
- the substrate of Sample 2 at least one 50 ⁇ m square dislocation-free region was present in all the visual fields of 250 ⁇ m square.
- the main surface of the substrate of Sample 2 had non-overlapping 50 ⁇ m square dislocation-free regions at a density of 1000 pieces / cm 2 or more.
- the FWHMb was 32 arcsec or less at all the measurement points. Further, on the substrate of sample 2, (FWHMa-FWHMb) / FWHMa was 30% or less at all the measurement points.
- FIG. 16 is a diagram showing an observation image obtained by observing a cross section of the laminated structure of Sample 1 with a fluorescence microscope.
- 17 and 18 are views of the main surface of the nitride semiconductor substrate of Sample 1 observed using a multi-photon excitation microscope.
- the white solid line square portion indicates a 50 ⁇ m square non-dislocation region
- the white dotted square portion indicates a 100 ⁇ m square non-dislocation region.
- FIG. 21A shows a standardized X-ray diffraction pattern of the nitride semiconductor substrate of Sample 1 when the X-ray locking curve of surface diffraction was measured with different slits on the incident side (0002). Is.
- the measurement conditions are the same as those in FIG. 21 (b) described above.
- the laminated structure of Sample 1 had two laminated units and an uppermost low oxygen concentration region based on the difference in oxygen concentration due to the difference in the growth surface.
- Each of the two laminated units had a low oxygen concentration region and a high oxygen concentration region.
- the low oxygen concentration region was not continuous from the substrate side to the maximum low oxygen concentration region in the thickness direction.
- the low oxygen concentration region of the first laminated unit had a portion corresponding to the initial layer grown on the base substrate with the c-plane as the growth plane in the initial stage of growth.
- the initial layer was formed to have a predetermined thickness over the entire main surface of the base substrate.
- the low oxygen concentration region of the first laminated unit had a plurality of valleys and a plurality of peaks in a cross-sectional view.
- the average distance between the closest peaks in the first laminated unit was about 135 ⁇ m.
- the high oxygen concentration region of the first laminated unit was provided above the low oxygen concentration region of the first laminated unit.
- the high oxygen concentration region of the first laminated unit was continuously provided along the main surface of the base substrate. That is, it was confirmed that the c-plane disappeared at least once in the growth process of the first laminated unit.
- the low oxygen concentration region of the second laminated unit was provided above the high oxygen concentration region of the first laminated unit.
- the low oxygen concentration region of the second laminated unit also had a plurality of valleys and a plurality of peaks in a cross-sectional view.
- the average distance between the closest peaks in the second laminated unit was longer than the average distance between the closest peaks in the first laminated unit, and was about 209 ⁇ m.
- the high oxygen concentration region of the second laminated unit was provided above the low oxygen concentration region of the second laminated unit.
- the high oxygen concentration region of the second laminated unit was continuously provided along the main surface of the base substrate. That is, it was confirmed that the c-plane disappeared at least once during the growth process of the second laminated unit.
- the thickness from the main surface of the base substrate to the boundary surface of the second laminated unit was 1690 ⁇ m. From the results in Table 1, the reduction rate of the dislocation density obtained at N / N 0 described above was 0.07.
- the proportion of the region where the dislocation density was less than 1 ⁇ 10 6 cm- 2 was 100%. That is, there was no region on the main surface where the dislocation density was 1 ⁇ 10 6 cm- 2 or more.
- the proportion of the region where the dislocation density was less than 7 ⁇ 10 5 cm- 2 was 80% or more.
- the main surface of the substrate of sample 1 contained a dislocation-free region of at least 50 ⁇ m square. Further, in the substrate of Sample 1, a plurality of 50 ⁇ m square dislocation-free regions were scattered over the entire main surface.
- the substrate of Sample 1 a plurality of 50 ⁇ m square dislocation-free regions existed in all the visual fields of 250 ⁇ m square. That is, the density of the 50 ⁇ m square non-dislocation region that does not overlap on the main surface of the substrate of sample 1 was higher than that of sample 2. Specifically, the main surface of the substrate of Sample 1 had non-overlapping 50 ⁇ m square dislocation-free regions at a density of 10,000 pieces / cm 2 or more.
- the number of dislocations existing in the quadrangular region sandwiched between the opposite sides of the pair of the closest pair of non-dislocation regions was 90 or less.
- the main surface of the substrate of Sample 1 contained a 100-square non-dislocation region.
- the main surface of the substrate of Sample 1 had 100 ⁇ m square non-dislocation-free regions that did not overlap at a density of 100 pieces / cm 2 or more.
- the FWHMb was 32 arcsec or less when the width of the slit on the incident side in the ⁇ direction was 0.1 mm at all measurement points.
- the spread of the X-ray diffraction pattern was small even when the width of the incident side slit in the ⁇ direction was widened from 0.1 mm to 1 mm.
- the light receiving side slit was opened and X-rays were received without passing through the analyzer crystal.
- the width of the opening in the ⁇ direction width of the opening on the light receiving side in the ⁇ direction
- the length of the opening in the direction parallel to the rotation axis length of the opening on the light receiving side
- Both D were set to 14.025 mm.
- the incident conditions when measuring FWHM2 ⁇ 10-12 ⁇ were the same as the incident conditions when measuring FWHM1 ⁇ 10-12 ⁇ .
- FIG. 24 is a diagram showing a standardized X-ray diffraction pattern when the X-ray locking curve measurement of ⁇ 10-12 ⁇ plane diffraction is performed on the nitride semiconductor substrate of Sample 4 under different measurement conditions.
- the pattern of ⁇ 10-12 ⁇ diffraction under the wide measurement region condition was wider than the pattern of ⁇ 10-12 ⁇ diffraction under the narrow measurement region condition.
- FIG. 23 is a diagram showing a standardized X-ray diffraction pattern when the X-ray locking curve measurement of ⁇ 10-12 ⁇ plane diffraction is performed on the nitride semiconductor substrate of Sample 3 under different measurement conditions.
- the pattern of ⁇ 10-12 ⁇ diffraction under the wide measurement region condition is the narrow measurement region condition. It was wider than the ⁇ 10-12 ⁇ diffraction pattern.
- the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ is less than 80% when measured from the direction of 150 ° with respect to the a-axis. Met.
- FIG. 22 is a diagram showing a standardized X-ray diffraction pattern when the X-ray locking curve measurement of ⁇ 10-12 ⁇ plane diffraction is performed on the nitride semiconductor substrate of Sample 1 under different measurement conditions.
- FWHM1 ⁇ 10-12 ⁇ under the wide measurement area condition was 40 arcsec or less. Further, in the substrate of sample 3, the variation of FWHM1 ⁇ 10-12 ⁇ in which the diffraction of the equivalent crystal plane was measured from three directions was small, and the maximum and minimum difference was 9 arcsec or less.
- the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ was 100% or less.
- the cycle including the three-dimensional growth step and the flattening step was repeated a plurality of times.
- the dislocations remaining in the flattening layer in the first cycle were further bent, and the dislocations could be locally collected.
- the dislocation density of sample 1 having two cycles could be reduced from the dislocation density of sample 2 having one cycle.
- the average distance between the closest peaks in the second laminated unit was longer than the average distance between the closest peaks in the first laminated unit. This allowed the dislocations to bend and propagate in the second cycle longer than in the first cycle. As a result, it was confirmed that the density of the dislocation-free region of 50 ⁇ m square could be increased.
- the average distance between the closest mountain portions in the second laminated unit was about 209 ⁇ m.
- the second cycle it was possible to secure a distance of at least 100 ⁇ m for the dislocations to bend and propagate.
- a dislocation-free region of at least 100 ⁇ m square could be formed on at least a part of the surface of the flattening layer in the second cycle.
- the density of non-dislocation-free regions of 100 ⁇ m square on the main surface could be 100 pieces / cm 2 or more.
- the radius of curvature of the c-plane of the substrate can be made larger than the radius of curvature of the c-plane of the substrate due to the stress canceling effect of the high oxygen concentration region, and the off angle of the c-axis in the substrate can be increased. It was confirmed that the variation in the off angle of the c-axis in the base substrate could be reduced.
- FWHM1 ⁇ 10-12 ⁇ could be set to 50 arcsec or less on the substrate of Sample 1. Further, in the substrate of sample 1, the maximum and minimum difference of FWHM1 ⁇ 10-12 ⁇ measured by the diffraction of the equivalent crystal plane represented by the ⁇ 10-12 ⁇ plane from three directions could be set to 9 arcsec or less. It was confirmed. Further, it was confirmed that the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ could be 80% or more in the substrate 10 of sample 1.
- FWHM1 ⁇ 10-12 ⁇ and FWHM2 ⁇ 10-12 ⁇ are half widths of ⁇ 10-12 ⁇ plane diffraction measured by X-ray locking curve measurement, respectively.
- an X-ray mirror that makes X-rays parallel light
- a Ge (220) double-reflection monochrome meter and a goniometer rotation axis.
- the width in the ⁇ direction as the circumference rotation angle direction is 1.4 mm and the length in the direction parallel to the rotation axis is 12 mm through the incident side opening in this order.
- Appendix 2 The nitride semiconductor substrate according to Appendix 1, wherein the ratio of FWHM2 ⁇ 10-12 ⁇ to FWHM1 ⁇ 10-12 ⁇ is 100% or less.
- nitride semiconductor substrate having a diameter of 2 inches or more and having a main surface whose closest low index crystal plane is the (0001) plane.
- FWHM1 ⁇ 10-12 ⁇ measured the diffraction of the equivalent crystal plane represented by the ⁇ 10-12 ⁇ plane from three directions rotated by 60 ° in the circumferential direction about the normal of the center of the main plane. The maximum and minimum difference between the two is 9 arcsec or less.
- FWHM1 ⁇ 10-12 ⁇ is the half width of the ⁇ 10-12 ⁇ plane diffraction measured by the X-ray locking curve measurement.
- an X-ray mirror that makes X-rays parallel light
- a Ge (220) double-reflection monochrome meter and a goniometer rotation axis.
- the width in the ⁇ direction as the circumference rotation angle direction is 1.4 mm and the length in the direction parallel to the rotation axis is 12 mm through the incident side opening in this order.
- FWHM1 ⁇ 10-12 ⁇ is the nitride semiconductor substrate according to any one of Supplementary note 1 to 4, which is 50 arcsec or less.
- nitride semiconductor substrate having a diameter of 2 inches or more and having a main surface whose closest low index crystal plane is the (0001) plane.
- FWHM1 ⁇ 10-12 ⁇ is a nitride semiconductor substrate having a length of 50 arcsec or less.
- FWHM1 ⁇ 10-12 ⁇ is the half width of the ⁇ 10-12 ⁇ plane diffraction measured by the X-ray locking curve measurement.
- an X-ray mirror that makes X-rays parallel light, a Ge (220) double-reflection monochrome meter, and a goniometer rotation axis.
- the width in the ⁇ direction as the circumference rotation angle direction is 1.4 mm and the length in the direction parallel to the rotation axis is 12 mm through the incident side opening in this order.
- the region where the dislocation density is 1 ⁇ 10 6 cm- 2 or more is the above.
- a region that does not exist on the main surface and has a dislocation density of less than 7 ⁇ 10 5 cm- 2 exists in 80% or more of the main surface.
- the main surface is a nitride semiconductor substrate having 50 ⁇ m square non-dislocation regions that do not overlap at a density of 1000 pieces / cm 2 or more.
- Appendix 9 The nitride semiconductor substrate according to Appendix 7 or 8, wherein the number of dislocations existing in the quadrangular region sandwiched between the opposite sides of the pair of dislocation-free regions that are closest to each other is 90 or less.
- the difference FWHMa-FWHMb obtained by subtracting FWHMb from the full width at half maximum FWHMa of the (0002) plane diffraction when the width of the incident side slit in the ⁇ direction is 1 mm is any one of Supplementary notes 1 to 10 which is 30% or less of FWHMa.
- (Appendix 12) A nitride semiconductor substrate having a diameter of 2 inches or more and having a main surface whose closest low index crystal plane is the (0001) plane.
- the main surface is irradiated with X-rays of Cu K ⁇ 1 through a two-crystal monochromator on the Ge (220) plane and the slit on the incident side, and X-ray locking curve measurement of (0002) plane diffraction is performed.
- the full width at half maximum FWHMb of the (0002) plane diffraction when the width of the incident side slit in the ⁇ direction is 0.1 mm is 32 arcsec or less.
- FWHMa-FWHMb is 30% or less of FWHMa at a plurality of measurement points set at predetermined intervals in each of the ⁇ 1-100> axial direction and the ⁇ 11-20> axial direction in the main surface.
- a base substrate composed of a single crystal of a group III nitride semiconductor, having a mirrored main surface, and having a low index crystal plane closest to the main surface as the (0001) plane.
- a high oxygen concentration region provided above the main surface of the base substrate and composed of a single crystal of a group III nitride semiconductor and a high oxygen concentration region composed of a single crystal of a group III nitride semiconductor provided on the low oxygen concentration region.
- a laminated unit having an oxygen concentration region and The highest oxygen concentration region which is provided above the laminated unit and is composed of a single crystal of a group III nitride semiconductor, With The oxygen concentration in the high oxygen concentration region is higher than the oxygen concentration in each of the low oxygen concentration region and the highest oxygen concentration region.
- the laminated structure is a laminated structure in which a plurality of laminated units are repeatedly provided in the thickness direction between the base substrate and the uppermost low oxygen concentration region.
- the upper surface of the low oxygen concentration region in each of the plurality of laminated units has a plurality of valleys and a plurality of peaks.
- the second or higher layered unit among the plurality of laminated units When looking at an arbitrary cross section perpendicular to the main surface, a pair of peaks closest to each other across the plurality of valleys along the main surface.
- the laminated structure according to Appendix 15, wherein the average distance separated in the direction is longer than that of the first laminated unit among the plurality of laminated units.
- Examples of the manufacturing method of the present invention include the following appendices.
- (Appendix 18) A method for manufacturing a nitride semiconductor substrate using a vapor phase growth method.
- B A plurality of group III nitride semiconductor single crystals having a top surface with an exposed (0001) plane formed by epitaxially growing above the main surface of the base substrate and having an inclined interface other than the (0001) plane.
- the recessed surface is formed on the top surface, the inclined interface is gradually expanded toward the upper side of the main surface of the base substrate, the (0001) surface is eliminated from the top surface at least once, and three-dimensional growth is performed.
- the process of growing the layer and (C) A step of epitaxially growing a single crystal of a group III nitride semiconductor on the three-dimensional growth layer, eliminating the inclined interface, and growing a flattening layer having a mirrored surface.
- (Appendix 30) A method for manufacturing a nitride semiconductor substrate using a vapor phase growth method.
- B A step of flatly homoepitaxially growing a single crystal of a group III nitride semiconductor above the main surface.
- (C) A plurality of recesses composed of inclined interfaces other than the (0001) plane are formed on the surface of a flat homoepitaxially grown crystal, and the inclined interface is gradually expanded as the crystal growth progresses to form a crystal growth interface.
- a step of growing a three-dimensional growth layer which comprises eliminating the (0001) plane at least once.
- D By further epitaxially growing a single crystal of a group III nitride semiconductor on the three-dimensional growth layer, the inclined interface disappears and a flattening layer having a mirrored surface composed of (0001) planes is grown.
- Process and Have A method for manufacturing a nitride semiconductor substrate in which a cycle including the above (c) and the above (d) is performed a plurality of times.
- Base substrate 30 First layer 40 Second layer 50 Nitride semiconductor substrate (substrate)
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Abstract
Description
2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
FWHM1{10-12}に対するFWHM2{10-12}の比率は、80%以上である
窒化物半導体基板が提供される。
ただし、FWHM1{10-12}およびFWHM2{10-12}は、それぞれ、X線ロッキングカーブ測定により測定した{10-12}面回折の半値幅であり、
FWHM1{10-12}を測定するときの入射条件では、CuのX線源から、X線を平行光とするX線ミラー、Ge(220)の2回反射のモノクロメータ、およびゴニオメータの回転軸周りの回転角方向としてのω方向の幅が1.4mmであり且つ前記回転軸に平行な方向の長さが12mmである入射側開口をこの順で介して、前記主面の中心に対してCuのKα1のX線を照射し、
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずに、前記ω方向の幅が14.025mmである開口を有するディテクタによりX線を受光し、
FWHM2{10-12}を測定するときの入射条件は、FWHM1{10-12}を測定するときの入射条件と同様とし、
FWHM2{10-12}を測定するときの受光条件では、前記ω方向の幅が6.54mmである入口開口を有するGe(220)の3回反射のアナライザ結晶を介して、前記ディテクタによりX線を受光する。
2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
前記主面の中心の法線を軸として周方向に60°ずつ回転させた3つの方向から、{10-12}面で表される等価な結晶面の回折を測定したFWHM1{10-12}の最大最小差は、9arcsec以下である
窒化物半導体基板が提供される。
2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
FWHM1{10-12}は、50arcsec以下である
窒化物半導体基板が提供される。
III族窒化物半導体の単結晶からなり、鏡面化された主面を有し、前記主面に対して最も近い低指数の結晶面が(0001)面である下地基板と、
前記下地基板の前記主面の上方に設けられ、III族窒化物半導体の単結晶からなる低酸素濃度領域と、前記低酸素濃度領域上に設けられ、III族窒化物半導体の単結晶からなる高酸素濃度領域と、を有する積層ユニットと、
前記積層ユニットよりも上方に設けられ、III族窒化物半導体の単結晶からなる最上低酸素濃度領域と、
を備え、
前記高酸素濃度領域の酸素濃度は、前記低酸素濃度領域および前記最上低酸素濃度領域のそれぞれの酸素濃度よりも高く、
前記積層ユニットは、前記下地基板と前記最上低酸素濃度領域との間で、厚さ方向に繰り返し複数設けられている
積層構造体が提供される。
気相成長法を用いた窒化物半導体基板の製造方法であって、
(a)III族窒化物半導体の単結晶からなり、鏡面化された主面を有し、前記主面に対して最も近い低指数の結晶面が(0001)面である下地基板を準備する工程と、
(b)前記主面の上方にIII族窒化物半導体の単結晶を平坦にホモエピタキシャル成長させる工程と、
(c)平坦なホモエピタキシャル成長結晶の表面に、(0001)面以外の傾斜界面で構成される複数の凹部を生じさせ、結晶成長の進行にしたがって該傾斜界面を徐々に拡大させて、結晶成長界面から(0001)面を少なくとも一度消失させることを特徴とする3次元成長層を成長させる工程と、
(d)前記3次元成長層上にIII族窒化物半導体の単結晶を更にエピタキシャル成長させることで、傾斜界面を消失させ、(0001)面からなる鏡面化された表面を有する平坦化層を成長させる工程と、
を有し、
前記(c)と前記(d)とを含むサイクルを複数回行う
窒化物半導体基板の製造方法が提供される。
以下、本発明の一実施形態について図面を参照しながら説明する。
図1~図9を用い、本実施形態に係る窒化物半導体基板の製造方法について説明する。図1は、本実施形態に係る窒化物半導体基板の製造方法を示すフローチャートである。図2(a)~(g)、図3(a)~(c)、図5(a)~図6(b)、図7~図9は、本実施形態に係る窒化物半導体基板の製造方法の一部を示す概略断面図である。図4は、本実施形態に係る窒化物半導体基板の製造方法の一部を示す概略斜視図である。なお、図4は、図3(b)の時点での斜視図に相当し、下地基板10上に成長する3次元成長層30の一部を示している。また、図5(b)において、細実線は、成長途中の結晶面を示し、図3(c)~図6(b)、図7~図9において、点線は、転位を示している。
気相成長法を用いた窒化物半導体基板の製造方法であって、
(a)III族窒化物半導体の単結晶からなり、鏡面化された主面を有し、主面に対して最も近い低指数の結晶面が(0001)面である下地基板を準備する工程と、
(b)(0001)面が露出した頂面を有するIII族窒化物半導体の単結晶を下地基板の主面の上方にエピタキシャル成長させ、(0001)面以外の傾斜界面で構成される複数の凹部を頂面に生じさせ、下地基板の主面の上方に行くにしたがって該傾斜界面を徐々に拡大させ、(0001)面を頂面から少なくとも一度消失させ、3次元成長層を成長させる工程と、
(c)3次元成長層上にIII族窒化物半導体の単結晶をエピタキシャル成長させ、傾斜界面を消失させ、鏡面化された表面を有する平坦化層を成長させる工程と、
を有し、
(b)と(c)とを含むサイクルを複数回行う。
まず、下地基板準備工程S100において、III族窒化物半導体の単結晶からなる下地基板10を準備する。本実施形態では、下地基板10として、例えば、窒化ガリウム(GaN)自立基板を準備する。
まず、図2(a)に示すように、結晶成長用基板1(以下、「基板1」と略すことがある)を準備する。基板1は、例えば、サファイア基板である。なお、基板1は、例えば、Si基板またはガリウム砒素(GaAs)基板であってもよい。基板1は、例えば、成長面となる主面1sを有している。主面1sに対して最も近い低指数の結晶面は、例えば、c面1cである。
次に、図2(b)に示すように、例えば、有機金属気相成長(MOVPE)法により、所定の成長温度に加熱された基板1に対して、III族原料ガスとしてのトリメチルガリウム(TMG)ガス、窒素原料ガスとしてのアンモニアガス(NH3)およびn型ドーパントガスとしてのモノシラン(SiH4)ガスを供給することで、基板1の主面1s上に、第1結晶層(下地成長層)2として、低温成長GaNバッファ層およびSiドープGaN層をこの順で成長させる。このとき、低温成長GaNバッファ層の厚さおよびSiドープGaN層の厚さを、それぞれ、例えば、20nm、0.5μmとする。
次に、図2(c)に示すように、第1結晶層2上に金属層3を蒸着させる。金属層3としては、例えば、チタン(Ti)層とする。また、金属層3の厚さを例えば20nmとする。
次に、上述の基板1を電気炉内に投入し、所定のヒータを有するサセプタ上に基板1を載置する。基板1をサセプタ上に載置したら、ヒータにより基板1を加熱し、水素ガスまたは水素化物ガスを含む雰囲気中で熱処理を行う。具体的には、例えば、20%のNH3ガスを含有する水素(H2)ガス気流中において、所定の温度で20分間熱処理を行う。なお、熱処理温度を、例えば、850℃以上1,100℃以下とする。このような熱処理を行うことで、金属層3を窒化し、表面に高密度の微細な穴を有する金属窒化層5を形成する。また、上述の熱処理を行うことで、金属窒化層5の穴を介して第1結晶層2の一部をエッチングし、該第1結晶層2中に高密度のボイドを形成する。
次に、例えば、ハイドライド気相成長(HVPE)法により、所定の成長温度に加熱された基板1に対して、塩化ガリウム(GaCl)ガス、NH3ガスおよびn型ドーパントガスとしてのジクロロシラン(SiH2Cl2)ガスを供給することで、ボイド含有第1結晶層4および金属窒化層5上に第2結晶層(本格成長層)6としてSiドープGaN層をエピタキシャル成長させる。なお、n型ドーパントガスとして、SiH2Cl2ガスの代わりに、テトラクロロゲルマン(GeCl4)ガスなどを供給することで、第2結晶層6としてGeドープGaN層をエピタキシャル成長させてもよい。
第2結晶層6の成長が終了した後、第2結晶層6を成長させるために用いたHVPE装置を冷却する過程において、第2結晶層6は、ボイド含有第1結晶層4および金属窒化層5を境に基板1から自然に剥離する。
次に、図2(f)に示すように、例えば、第2結晶層6の主面6sの中心の法線方向に対して略垂直な切断面SSに沿って、ワイヤーソーにより、第2結晶層6をスライスする。
次に、研磨装置により下地基板10の両面を研磨する。これにより、下地基板10の主面10sは、鏡面化される。
図3(a)に示すように下地基板10を準備したら、図3(b)、図3(c)、および図4に示すように、c面30cが露出した頂面30uを有するIII族窒化物半導体の単結晶を、下地基板10の主面10sの上方にエピタキシャル成長させる。これにより、3次元成長層30を成長させる。
Gc0=Gi/cosα ・・・(a)
R1=Gi/cosα’ ・・・(b)
Gc1=R1sinαR1 ・・・(c)
Gc1=GisinαR1/cos(α+90-αR1) ・・・(d)
Gc1>Gi/cosα ・・・(1)
ただし、上述のように、Giは、c面30cに対して最も傾斜した傾斜界面30iの成長レートであり、αは、c面30cに対して最も傾斜した傾斜界面30iと、c面30cとのなす角度である。
Gc1>2.13Gi ・・・(1’)
Gc1>1.47Gi ・・・(1”)
成長圧力:90~105kPa、好ましくは、90~95kPa
GaClガスの分圧:1.5~15kPa
N2ガスの流量/H2ガスの流量:0~1
まず、図3(b)および図4に示すように、III族窒化物半導体の単結晶からなる3次元成長層30の傾斜界面拡大層32を、上述の第1成長条件下で、下地基板10の主面10s上に直接エピタキシャル成長させる。
傾斜界面拡大層32の表面からc面30cを消失させた後、傾斜界面維持工程S240での成長条件を、傾斜界面拡大工程S220と同様に、上述の第1成長条件で維持する。
c面30cを消失させた3次元成長層30を成長させたら、図5(b)に示すように、3次元成長層30上に、III族窒化物半導体の単結晶をさらにエピタキシャル成長させる。
R2=Gi/cosα” ・・・(e)
Gc2=R2sinαR2 ・・・(f)
Gc2=GisinαR2/cos(α+αR2-90) ・・・(g)
Gc2<Gi/cosα ・・・(2)
ただし、上述のように、Giは、c面40cに対して最も傾斜した傾斜界面40iの成長レートであり、αは、c面40cに対して最も傾斜した傾斜界面40iと、c面40cとのなす角度である。
Gc2<2.13Gi ・・・(2’)
Gc2<1.47Gi ・・・(2”)
成長圧力:90~105kPa、好ましくは、90~95kPa
GaClガスの分圧:1.5~15kPa
N2ガスの流量/H2ガスの流量:1~20
最初のサイクルが終了したら、3次元成長工程S200と平坦化工程S300とを含むサイクルの実施回数を判定する。
2回目以降のサイクルでは、図6(a)に示すように、第1積層ユニット51の平坦化層40の上に、再度、3次元成長層30を成長させる。このとき、最初のサイクルの3次元成長工程S200と同様の第1成長条件下で、3次元成長層30を成長させる。
図6(a)に示すように、III族窒化物半導体の単結晶からなる3次元成長層30の傾斜界面拡大層32を、第1積層ユニット51の平坦化層40の上にエピタキシャル成長させる。
2回目以降のサイクルにおいても、傾斜界面拡大層32の表面からc面30cを消失させた後、傾斜界面維持工程S240での成長条件を、傾斜界面拡大工程S220と同様に、上述の第1成長条件で維持する。
2回目以降のサイクルにおいても、c面30cを少なくとも一度消失させた3次元成長層30を成長させたら、図7に示すように、3次元成長層30上にIII族窒化物半導体の単結晶からなる平坦化層40をエピタキシャル成長させる。このとき、最初のサイクルの平坦化工程S300と同様の第2成長条件で、平坦化層40を成長させる。これにより、3次元成長層30の上方に行くにしたがって、c面40cを拡大させつつ、c面以外の傾斜界面40iを縮小させる。
2回目のサイクルが終了したら、3次元成長工程S200と平坦化工程S300とを含むサイクルの実施回数を再度判定する。
最後のサイクルの平坦化工程S300の後に、図8に示すように、表面が鏡面化された平坦化層40上に、c面を成長面として所定の厚さに亘って本成長層44を形成する。
次に、図9に示すように、例えば、本成長層44の表面と略平行な切断面に沿ってワイヤーソーにより本成長層44をスライスする。これにより、アズスライス基板としての窒化物半導体基板100(基板100ともいう)を少なくとも1つ形成する。このとき、基板100の厚さを、例えば、300μm以上700μm以下とする。
次に、研磨装置により基板100の両面を研磨する。なお、このとき、最終的な基板100の厚さを、例えば、250μm以上650μm以下とする。
基板100が製造されたら、例えば、基板100上にIII族窒化物半導体からなる半導体機能層をエピタキシャル成長させ、半導体積層物を作製する。半導体積層物を作製したら、半導体積層物を用いて電極等を形成し、半導体積層物をダイシングし、所定の大きさのチップを切り出す。これにより、半導体装置を作製する。
次に、図8を用い、本実施形態に係る積層構造体90について説明する。
次に、図12を用い、本実施形態に係る窒化物半導体基板100について説明する。図12(a)は、本実施形態に係る窒化物半導体基板を示す概略上面図であり、(b)は、本実施形態に係る窒化物半導体基板のm軸に沿った概略断面図であり、(c)は、本実施形態に係る窒化物半導体基板のa軸に沿った概略断面図である。なお、m軸に沿った方向をx方向とし、a軸に沿った方向をy方向とする。
図12(b)および(c)に示すように、本実施形態では、基板100の主面100sに対して最も近い低指数の結晶面としてのc面100cは、例えば、上述した基板100の製造方法に起因して、主面100sに対して凹の球面状に湾曲している。
次に、本実施形態の基板100の主面100sにおける暗点について説明する。なお、ここでいう「暗点」とは、多光子励起顕微鏡における主面100sの観察像や、主面100sのカソードルミネッセンス像などにおいて観察される発光強度が低い点のことを意味し、転位だけでなく、異物または点欠陥を起因とした非発光中心も含んでいる。なお、「多光子励起顕微鏡」とは、二光子励起蛍光顕微鏡と呼ばれることもある。
ここで、発明者は、入射側スリットのω方向の幅を異ならせてc面回折のX線ロッキングカーブ測定を行うことにより、本実施形態の基板100を構成する結晶品質要素と、上述のc面100cの湾曲(反り)と、の両方を同時に評価することができることを見出した。
b=dI/sinθB ・・・(h)
なお、「ω」および「ω方向」とは、それぞれ、X線ロッキングカーブ測定において、ゴニオメータの回転軸周りの「回転角」および「回転角方向」のことをいう。なお、当該c面回折の測定では、「ω」および「ω方向」とは、それぞれ、基板ステージの中心を通り基板ステージの載置面に平行な軸を中心軸として、基板ステージに載置される基板100を回転させたときの基板回転角および基板回転方向と考えることもできる。
γ=sin-1(b/2R)≒b/2R ・・・(i)
さらに、発明者は、測定条件を異ならせて非対称反射面のX線ロッキングカーブ測定を行うことにより、本実施形態の基板100の結晶品質を適切に評価することができることを見出した。
FWHM1{10-12}を測定するときの入射条件では、CuのX線源から、X線を平行光とするX線ミラー、Ge(220)の2回反射のモノクロメータ、およびゴニオメータの回転軸周りの回転角方向としてのω方向の幅dIが1.4mmであり且つ当該回転軸に平行な方向の長さLIが12mmである入射側開口をこの順で介して、基板100の主面100sの中心に対してCuのKα1のX線を照射する。
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずに、ω方向の幅dDが14.025mmである開口(受光側開口)を有するディテクタによりX線を受光する。
FWHM2{10-12}を測定するときの入射条件は、FWHM1{10-12}を測定するときの入射条件と同様とする。
FWHM2{10-12}を測定するときの受光条件では、ω方向の幅dDが6.54mmである入口開口(すなわち受光側開口)を有するGe(220)の3回反射のアナライザ結晶を介して、ディテクタによりX線を受光する。
FWHM1{10-12}を測定する場合のWMA:約18.92mm
FWHM2{10-12}を測定する場合のWMA:約9.74mm
本実施形態によれば、以下に示す1つまたは複数の効果が得られる。
以上、本発明の実施形態を具体的に説明した。しかしながら、本発明は上述の実施形態に限定されるものではなく、その要旨を逸脱しない範囲で種々変更可能である。
(1-1)窒化物半導体基板の作製
以下のようにして、サンプル1~4の基板を作製した。なお、サンプル1については、積層構造体も作製した。
サンプル1では、3次元成長工程および平坦化工程を含むサイクルを2回行った。
(下地基板)
材質:GaN
作製方法:VAS法
直径:2インチ
厚さ:400μm
主面に対して最も近い低指数の結晶面:c面
主面に対するマスク層等のパターン加工なし。
主面の中心のオフ角:m方向に0.4°
(3次元成長層)
材質:GaN
成長方法:HVPE法
第1成長条件:
成長温度を980℃以上1,020℃以下とし、V/III比を2以上20以下とした。このとき、第1成長条件が式(1)を満たすように、成長温度およびV/III比のうち少なくともいずれかをそれぞれ上記範囲のなかで調整した。
(平坦化層)
材質:GaN
成長方法:HVPE法
成長温度:1,050℃
V/III比:2
なお、上記第2成長条件は、式(2)を満たす。
下地基板の主面から第1積層ユニットの境界面までの厚さ(第1積層ユニットの厚さ):約800μm
(3次元成長層)
最初のサイクルの3次元成長層と同様の成長条件
(平坦化層)
最初のサイクルの平坦化層と同様の成長条件
第1積層ユニットの境界面から第2積層ユニットの境界面までの厚さ(第2積層ユニットの厚さ):約800μm
(本成長層)
それぞれのサイクルの平坦化層と同様の成長条件
厚さ:約2mm
なお、観察用の積層構造体では、本成長層の厚さを約200μmとした。
(スライス条件)
基板の厚さ:400μm
カーフロス:200μm
サンプル2では、3次元成長工程および平坦化工程を含むサイクルを1回とした。すなわち、サイクルを繰り返さなかった。
(下地基板)
サンプル1で用いた下地基板と同等
(3次元成長層)
サンプル1の最初のサイクルの3次元成長層と同様の成長条件
(平坦化層)
サンプル1の最初のサイクルの平坦化層と同様の成長条件
下地基板の主面から平坦化層上の境界面までの厚さ:約800μm
(本成長層)
上述の平坦化層と同様の成長条件
厚さ:約2mm
(スライス条件)
サンプル1と同じ。
上述の「c面厚膜成長」による方法を用いた。
(下地基板)
材質:GaN
作製方法:VAS法
直径:62mm
厚さ:400μm
主面に対して最も近い低指数の結晶面:c面
主面の中心のオフ角:m軸方向0.5°
主面に対するマスク層等のパターン加工なし。
(結晶層)
材質:GaN
成長方法:HVPE法
成長温度:1050℃
V/III比:2.8
成長時間:15時間
(加工)
研削:円筒状領域を除去し、直径56mmの円柱状領域を得た。
スライス:630μm厚、5枚
べべリング加工:直径50.8mmとした。
研磨加工:400~450μm厚とした。
下地基板と同様の従来のVAS法により、サンプル4の基板を作製した。なお、サンプル4については、オフ角の絶対値およびオフ方向が下地基板と異なる点を除いて、c面の曲率半径や転位密度などは下地基板と同等とした。
(蛍光顕微鏡による観察)
蛍光顕微鏡を用い、サンプル1の基板をスライスする前の積層構造体の断面を観察した。
多光子励起顕微鏡を用い、サンプル1~3の基板、下地基板に相当するサンプル4の基板のそれぞれの主面を観察した。このとき、視野250μmごとに主面全体に亘って暗点密度を測定することで、転位密度を測定した。なお、これらの基板における暗点の全てが転位であることは、厚さ方向に焦点をずらして測定することにより確認している。また、このとき、視野250μm角での全測定領域数に対する、転位密度が1×106cm-2未満または7×105cm-2未満である領域の数の割合を求めた。
サンプル1~3の基板、下地基板に相当するサンプル4の基板のそれぞれについて、(0002)面回折の以下の2種類のX線ロッキングカーブ測定を行った。
入射側スリットのω方向の幅を0.1mmとし、サンプル1~3の基板、下地基板に相当するサンプル4の基板のそれぞれの、(0002)面のX線ロッキングカーブ測定を行った。このとき、それぞれの基板の主面内のうち、中心を通りm軸方向に沿った直線上、および中心を通りm軸に直交するa軸方向に沿った直線上で、5mm間隔で設定した複数の測定点において、該測定を行った。このとき、基板の主面内の位置として正に定義している側からX線を入射させた。測定の結果、主面へ入射したX線と主面とがなすピーク角度ωを、直線上の位置に対してプロットし、ピーク角度ωを位置の1次関数で近似した。当該1次関数の傾きの逆数により、c面の曲率半径を求めた。
入射側スリットのω方向の幅を1mmとし、サンプル1~3の基板、下地基板に相当するサンプル4の基板のそれぞれについて、X線ロッキングカーブ測定を行った。このとき、それぞれの基板の主面内のうち、中心を通りm軸方向に沿った直線上、および中心を通りm軸に直交するa軸方向に沿った直線上で、5mm間隔で設定した複数の測定点において、該測定を行った。測定の結果、各測定点において、入射側スリットのω方向の幅を1mmとしたときの(0002)面回折の半値幅FWHMaを求めた。さらに、各測定点において、FWHMaに対するFWHMa-FWHMbの割合を求めた。
結果を表1~5に示す。
表1、表5および図21(b)を参照し、従来のVAS法により作製された下地基板に相当するサンプル4の基板の結果について説明する。図21(b)は、サンプル4の窒化物半導体基板について、入射側スリットを異ならせて(0002)面回折のX線ロッキングカーブ測定を行ったときの、規格化したX線回折パターンを示す図である。なお、図21(b)は、a軸に沿った方向の測定結果を示している。また、同図において、「LIne width」は上述のX線のフットプリントを意味している。
表1に示すように、下地基板に相当するサンプル4の基板では、平均転位密度が1×106cm-2以上であった。サンプル4の基板の主面内には、転位密度が1×106cm-2未満である領域が存在しなかった。
表1に示すように、サンプル4の基板におけるc面の曲率半径は、10m未満であった。
表1、表4および図20を参照し、c面厚膜成長により得られたサンプル3の基板の結果について説明する。図20は、多光子励起顕微鏡を用い、サンプル3の窒化物半導体基板の主面を観察した図である。
表1に示すように、c面厚膜成長により得られたサンプル3の基板では、結晶層の厚さに反比例して転位密度が減少するため、平均転位密度が下地基板相当のサンプル4のそれよりも低減されていた。
表1に示すように、サンプル3の基板では、結晶層の厚膜化の効果により、c面の曲率半径が下地基板のそれよりも若干大きくなっていた。
表1、表3および図19を参照し、サイクルを1回としたサンプル2の基板の結果について説明する。図19は、多光子励起顕微鏡を用い、サンプル2の窒化物半導体基板の主面を観察した図である。
表1に示すように、サイクルを1回としたサンプル2の基板では、平均転位密度がサンプル3および4の基板のそれぞれよりも低減されていた。サンプル2の基板では、転位密度が1×106cm-2未満である領域の割合が90%以上であった。
表1に示すように、サンプル2の基板では、c面の曲率半径が、サンプル3および4の基板に比べて大きく、23m以上であった。
表1、表2、図16、図17、図18および図21(a)を参照し、サイクルを2回としたサンプル1の基板の結果について説明する。図16は、サンプル1の積層構造体の断面を蛍光顕微鏡により観察した観察像を示す図である。図17および図18は、多光子励起顕微鏡を用い、サンプル1の窒化物半導体基板の主面を観察した図である。なお、図17および図18において、白実線四角部は、50μm角の無転位領域を示し、白点線四角部は、100μm角の無転位領域を示している。図21(a)は、サンプル1の窒化物半導体基板について、入射側スリットを異ならせて(0002)面回折のX線ロッキングカーブ測定を行ったときの、規格化したX線回折パターンを示す図である。図21(a)についても、測定条件は、上述の図21(b)と同様である。
図16に示すように、サンプル1の積層構造体は、成長面の違いによる酸素濃度の違いに基づいて、2つの積層ユニットと、最上低酸素濃度領域と、を有していた。2つの積層ユニットのそれぞれは、低酸素濃度領域と、高酸素濃度領域と、を有していた。
表1に示すように、サイクルを2回としたサンプル1の基板では、平均転位密度がサンプル2~4の基板のそれぞれよりも低減されていた。
表1に示すように、サンプル1の基板では、c面の曲率半径が、サンプル3および4の基板に比べて大きく、23m以上であった。
(2-1)窒化物半導体基板の準備
上述の実験1におけるサンプル1、サンプル3およびサンプル4を準備し、以下の評価を行った。
({10-12}面回折のX線ロッキングカーブ測定)
サンプル1の基板、サンプル3の基板、および下地基板に相当するサンプル4の基板のそれぞれについて、{10-12}面回折の以下の2種類のX線ロッキングカーブ測定を行った。
上述の実施形態で述べたように、広測定領域条件でFWHM1{10-12}を測定し、狭測定領域条件でFWHM2{10-12}を測定した。
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずにX線を受光した。なお、X線を受光するディテクタにおいて、開口のω方向の幅(受光側開口のω方向の幅)dD、および回転軸に平行な方向の開口の長さ(受光側開口の長さ)LDを、ともに14.025mmとした。
FWHM2{10-12}を測定するときの入射条件は、FWHM1{10-12}を測定するときの入射条件と同様とした。
FWHM2{10-12}を測定するときの受光条件では、Ge(220)の3回反射のアナライザ結晶を介してX線を受光した。なお、アナライザ結晶において、入口開口のω方向の幅(受光側開口のω方向の幅)dD、および回転軸に平行な方向の入口開口の長さ(受光側開口の長さ)LDを、それぞれ、6.54mm、14.025mmとした。
結果を表6に示す。
表6および図24を参照し、下地基板に相当するサンプル4の基板の結果について説明する。図24は、サンプル4の窒化物半導体基板について、異なる測定条件で{10-12}面回折のX線ロッキングカーブ測定を行ったときの、規格化したX線回折パターンを示す図である。
表6および図23を参照し、サンプル3の基板の結果について説明する。図23は、サンプル3の窒化物半導体基板について、異なる測定条件で{10-12}面回折のX線ロッキングカーブ測定を行ったときの、規格化したX線回折パターンを示す図である。
表6および図22を参照し、サンプル1の基板の結果について説明する。図22は、サンプル1の窒化物半導体基板について、異なる測定条件で{10-12}面回折のX線ロッキングカーブ測定を行ったときの、規格化したX線回折パターンを示す図である。
以上のサンプル1および2によれば、3次元成長工程において、式(1)を満たすように第1成長条件を調整した。これにより、3次元成長層の成長過程で、c面を確実に消失させることができた。c面を確実に消失させたことで、3次元成長層における傾斜界面が露出した位置で、転位を確実に屈曲させることができた。その結果、基板の主面における転位密度を効率よく低減することができたことを確認した。
以下、本発明の好ましい態様について付記する。
2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
FWHM1{10-12}に対するFWHM2{10-12}の比率は、80%以上である
窒化物半導体基板。
ただし、FWHM1{10-12}およびFWHM2{10-12}は、それぞれ、X線ロッキングカーブ測定により測定した{10-12}面回折の半値幅であり、
FWHM1{10-12}を測定するときの入射条件では、CuのX線源から、X線を平行光とするX線ミラー、Ge(220)の2回反射のモノクロメータ、およびゴニオメータの回転軸周りの回転角方向としてのω方向の幅が1.4mmであり且つ前記回転軸に平行な方向の長さが12mmである入射側開口をこの順で介して、前記主面の中心に対してCuのKα1のX線を照射し、
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずに、前記ω方向の幅が14.025mmである開口を有するディテクタによりX線を受光し、
FWHM2{10-12}を測定するときの入射条件は、FWHM1{10-12}を測定するときの入射条件と同様とし、
FWHM2{10-12}を測定するときの受光条件では、前記ω方向の幅が6.54mmである入口開口を有するGe(220)の3回反射のアナライザ結晶を介して、前記ディテクタによりX線を受光する。
FWHM1{10-12}に対するFWHM2{10-12}の前記比率は、100%以下である
付記1に記載の窒化物半導体基板。
前記主面の中心の法線を軸として周方向に60°ずつ回転させた3つの方向から、{10-12}面で表される等価な結晶面の回折を測定したFWHM1{10-12}の最大最小差は、9arcsec以下である
付記1又は2に記載の窒化物半導体基板。
2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
前記主面の中心の法線を軸として周方向に60°ずつ回転させた3つの方向から、{10-12}面で表される等価な結晶面の回折を測定したFWHM1{10-12}の最大最小差は、9arcsec以下である
窒化物半導体基板。
ただし、FWHM1{10-12}は、X線ロッキングカーブ測定により測定した{10-12}面回折の半値幅であり、
FWHM1{10-12}を測定するときの入射条件では、CuのX線源から、X線を平行光とするX線ミラー、Ge(220)の2回反射のモノクロメータ、およびゴニオメータの回転軸周りの回転角方向としてのω方向の幅が1.4mmであり且つ前記回転軸に平行な方向の長さが12mmである入射側開口をこの順で介して、前記主面の中心に対してCuのKα1のX線を照射し、
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずに、前記ω方向の幅が14.025mmである開口を有するディテクタによりX線を受光する。
FWHM1{10-12}は、50arcsec以下である
付記1~4のいずれか1つに記載の窒化物半導体基板。
2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
FWHM1{10-12}は、50arcsec以下である
窒化物半導体基板。
ただし、FWHM1{10-12}は、X線ロッキングカーブ測定により測定した{10-12}面回折の半値幅であり、
FWHM1{10-12}を測定するときの入射条件では、CuのX線源から、X線を平行光とするX線ミラー、Ge(220)の2回反射のモノクロメータ、およびゴニオメータの回転軸周りの回転角方向としてのω方向の幅が1.4mmであり且つ前記回転軸に平行な方向の長さが12mmである入射側開口をこの順で介して、前記主面の中心に対してCuのKα1のX線を照射し、
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずに、前記ω方向の幅が14.025mmである開口を有するディテクタによりX線を受光する。
多光子励起顕微鏡により視野250μm角で前記窒化物半導体基板の主面を観察して暗点密度から転位密度を求めたときに、前記転位密度が1×106cm-2以上である領域が前記主面に存在せず、前記転位密度が7×105cm-2未満である領域が前記主面の80%以上存在し、
前記主面は、重ならない50μm角の無転位領域を1000個/cm2以上の密度で有する
付記1~6のいずれか1つに記載の窒化物半導体基板。
2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
多光子励起顕微鏡により視野250μm角で前記窒化物半導体基板の主面を観察して暗点密度から転位密度を求めたときに、前記転位密度が1×106cm-2以上である領域が前記主面に存在せず、前記転位密度が7×105cm-2未満である領域が前記主面の80%以上存在し、
前記主面は、重ならない50μm角の無転位領域を1000個/cm2以上の密度で有する
窒化物半導体基板。
最も接近する一対の前記無転位領域の互いに対向する辺間で挟まれた四角形領域内に存在する転位の数は、90個以下である
付記7又は8に記載の窒化物半導体基板。
前記主面は、重ならない100μm角の無転位領域を100個/cm2以上の密度で有する
付記7~9のいずれか1つに記載の窒化物半導体基板。
Ge(220)面の2結晶モノクロメータおよび入射側スリットを介して前記主面に対してCuのKα1のX線を照射し、(0002)面回折のX線ロッキングカーブ測定を行った場合に、
前記入射側スリットのω方向の幅を0.1mmとしたときの前記(0002)面回折の半値幅FWHMbは32arcsec以下であり、
前記入射側スリットのω方向の幅を1mmとしたときの前記(0002)面回折の半値幅FWHMaからFWHMbを引いた差FWHMa-FWHMbは、FWHMaの30%以下である
付記1~10のいずれか1つに記載の窒化物半導体基板。
2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
Ge(220)面の2結晶モノクロメータおよび入射側スリットを介して前記主面に対してCuのKα1のX線を照射し、(0002)面回折のX線ロッキングカーブ測定を行った場合に、
前記入射側スリットのω方向の幅を0.1mmとしたときの前記(0002)面回折の半値幅FWHMbは32arcsec以下であり、
前記入射側スリットのω方向の幅を1mmとしたときの前記(0002)面回折の半値幅FWHMaからFWHMbを引いた差FWHMa-FWHMbは、FWHMaの30%以下である
窒化物半導体基板。
FWHMa-FWHMbは、前記主面内のうち<1-100>軸方向および<11-20>軸方向のそれぞれに所定の間隔で設定した複数の測定点において、FWHMaの30%以下である
付記11又は12に記載の窒化物半導体基板。
前記主面内に5mm間隔で設定した複数の測定点において、前記入射側スリットのω方向の幅を0.1mmとして前記(0002)面回折のX線ロッキングカーブ測定を行ったときに、全測定点の90%以上において、前記(0002)面回折の半値幅FWHMbは、32arcsec以下である
付記11~13のいずれか1つに記載の窒化物半導体基板。
III族窒化物半導体の単結晶からなり、鏡面化された主面を有し、前記主面に対して最も近い低指数の結晶面が(0001)面である下地基板と、
前記下地基板の前記主面の上方に設けられ、III族窒化物半導体の単結晶からなる低酸素濃度領域と、前記低酸素濃度領域上に設けられ、III族窒化物半導体の単結晶からなる高酸素濃度領域と、を有する積層ユニットと、
前記積層ユニットよりも上方に設けられ、III族窒化物半導体の単結晶からなる最上低酸素濃度領域と、
を備え、
前記高酸素濃度領域の酸素濃度は、前記低酸素濃度領域および前記最上低酸素濃度領域のそれぞれの酸素濃度よりも高く、
前記積層ユニットは、前記下地基板と前記最上低酸素濃度領域との間で、厚さ方向に繰り返し複数設けられている
積層構造体。
前記複数の積層ユニットのそれぞれにおける前記低酸素濃度領域の上面は、複数の谷部および複数の山部を有し、
前記複数の積層ユニットのうちの2層目以上の積層ユニットでは、
前記主面に垂直な任意の断面を見たときに、前記複数の谷部のうちの1つを挟んで前記複数の頂部のうちで最も接近する一対の山部同士が前記主面に沿った方向に離間した平均距離は、前記複数の積層ユニットのうちの1層目の積層ユニットのそれよりも長い
付記15に記載の積層構造体。
前記複数の積層ユニットのそれぞれでは、
最も接近する前記一対の山部同士の前記平均距離は、前記複数の積層ユニットの上層に行くにしたがって徐々に長くなっている
付記15又は16に記載の積層構造体。
気相成長法を用いた窒化物半導体基板の製造方法であって、
(a)III族窒化物半導体の単結晶からなり、鏡面化された主面を有し、前記主面に対して最も近い低指数の結晶面が(0001)面である下地基板を準備する工程と、
(b)(0001)面が露出した頂面を有するIII族窒化物半導体の単結晶を前記下地基板の前記主面の上方にエピタキシャル成長させ、前記(0001)面以外の傾斜界面で構成される複数の凹部を前記頂面に生じさせ、前記下地基板の前記主面の上方に行くにしたがって該傾斜界面を徐々に拡大させ、前記(0001)面を前記頂面から少なくとも一度消失させ、3次元成長層を成長させる工程と、
(c)前記3次元成長層上にIII族窒化物半導体の単結晶をエピタキシャル成長させ、前記傾斜界面を消失させ、鏡面化された表面を有する平坦化層を成長させる工程と、
を有し、
前記(b)と前記(c)とを含むサイクルを複数回行う
窒化物半導体基板の製造方法。
前記複数のサイクルのそれぞれにおける前記(b)では、
前記単結晶の前記頂面に前記複数の凹部を生じさせ、前記(0001)面を消失させることで、前記3次元成長層の表面に、複数の谷部および複数の頂部を形成し、
前記複数のサイクルのうちの2番目以降のサイクルの前記(b)では、
前記主面に垂直な任意の断面を見たときに、前記複数の谷部のうちの1つを挟んで前記複数の頂部のうちで最も接近する一対の頂部同士が前記主面に沿った方向に離間した平均距離を、前記複数のサイクルのうちの最初のサイクルの前記(b)のそれよりも長くする
付記18に記載の窒化物半導体基板の製造方法。
前記複数のサイクルのそれぞれにおける前記(b)では、
最も接近する前記一対の頂部同士の前記平均距離を、前記複数のサイクルを繰り返すにしたがって徐々に長くしていく
付記19に記載の窒化物半導体基板の製造方法。
前記複数のサイクルのそれぞれにおける前記(b)では、
最も接近する前記一対の頂部同士の前記平均距離を、100μm超とする
付記19又は20に記載の窒化物半導体基板の製造方法。
前記複数のサイクルのうち少なくとも最後のサイクルの前記(b)では、
最も接近する前記一対の頂部同士の前記平均距離を、200μm超とする
付記19~21のいずれか1つに記載の窒化物半導体基板の製造方法。
前記複数のサイクルのそれぞれにおける前記(b)では、
最も接近する前記一対の頂部同士の前記平均距離を、800μm未満とする
請求項21又は22に記載の窒化物半導体基板の製造方法。
前記(a)では、
前記下地基板の前記主面の二乗平均粗さを、1nm以上とする
付記18~23のいずれか1つに記載の窒化物半導体基板の製造方法。
前記(a)では、
前記下地基板の加工によって導入される結晶歪みを該下地基板の前記主面側に残存させ、
加工後の前記下地基板の前記主面に対する入射角を2°としてX線ロッキングカーブ測定を行ったときの、(10-10)面回折の半値幅を、加工前の前記下地基板の前記半値幅よりも大きくし、60arcsec以上200arcsec以下とする
付記18~24のいずれか1つに記載の窒化物半導体基板の製造方法。
前記複数のサイクルのそれぞれにおける前記(b)では、
前記(0001)面を前記表面から消失させた後に、前記表面に前記傾斜界面が前記(0001)面よりも多く占める状態を維持しつつ、所定の厚さに亘って前記3次元成長層の成長を継続させる
付記18~25のいずれか1つに記載の窒化物半導体基板の製造方法。
(d)前記複数のサイクルのうちの最後のサイクルの前記(c)の後に、表面が鏡面化された前記平坦化層上に、前記(0001)面を成長面として所定の厚さに亘って本成長層を形成する工程と、
(e)前記本成長層から少なくとも1つの窒化物半導体基板をスライスする工程と、
をさらに有する
付記18~26のいずれか1つに記載の窒化物半導体基板の製造方法。
前記(a)では、
前記(0001)面が前記主面に対して凹の球面状に湾曲した前記下地基板を準備し、
前記(e)では、
前記窒化物半導体基板の前記(0001)面の曲率半径を、前記下地基板の前記(0001)面の曲率半径よりも大きくする
付記27に記載の窒化物半導体基板の製造方法。
前記複数のサイクルのそれぞれにおける前記(b)では、
前記傾斜界面として、m≧3である{11-2m}面を生じさせる
付記18~28のいずれか1つに記載の窒化物半導体基板の製造方法。
気相成長法を用いた窒化物半導体基板の製造方法であって、
(a)III族窒化物半導体の単結晶からなり、鏡面化された主面を有し、前記主面に対して最も近い低指数の結晶面が(0001)面である下地基板を準備する工程と、
(b)前記主面の上方にIII族窒化物半導体の単結晶を平坦にホモエピタキシャル成長させる工程と、
(c)平坦なホモエピタキシャル成長結晶の表面に、(0001)面以外の傾斜界面で構成される複数の凹部を生じさせ、結晶成長の進行にしたがって該傾斜界面を徐々に拡大させて、結晶成長界面から(0001)面を少なくとも一度消失させることを特徴とする3次元成長層を成長させる工程と、
(d)前記3次元成長層上にIII族窒化物半導体の単結晶を更にエピタキシャル成長させることで、傾斜界面を消失させ、(0001)面からなる鏡面化された表面を有する平坦化層を成長させる工程と、
を有し、
前記(c)と前記(d)とを含むサイクルを複数回行う
窒化物半導体基板の製造方法。
前記複数のサイクルのうちの2番目以降のサイクルの前記(c)では、
結晶成長界面から(0001)面が消失したときの前記主面に垂直な任意の断面を見た場合に、前記3次元成長層の表面に存在する複数の谷部および複数の頂部のうち、1つの谷部を挟んだ複数の頂部のうちで最も接近する一対の頂部同士が前記主面に沿った方向に離間した平均距離を、前のサイクルの前記(c)の平均距離よりも長くする
付記30に記載の窒化物半導体基板の製造方法。
30 第1層
40 第2層
50 窒化物半導体基板(基板)
Claims (9)
- 2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
FWHM1{10-12}に対するFWHM2{10-12}の比率は、80%以上である
窒化物半導体基板。
ただし、FWHM1{10-12}およびFWHM2{10-12}は、それぞれ、X線ロッキングカーブ測定により測定した{10-12}面回折の半値幅であり、
FWHM1{10-12}を測定するときの入射条件では、CuのX線源から、X線を平行光とするX線ミラー、Ge(220)の2回反射のモノクロメータ、およびゴニオメータの回転軸周りの回転角方向としてのω方向の幅が1.4mmであり且つ前記回転軸に平行な方向の長さが12mmである入射側開口をこの順で介して、前記主面の中心に対してCuのKα1のX線を照射し、
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずに、前記ω方向の幅が14.025mmである開口を有するディテクタによりX線を受光し、
FWHM2{10-12}を測定するときの入射条件は、FWHM1{10-12}を測定するときの入射条件と同様とし、
FWHM2{10-12}を測定するときの受光条件では、前記ω方向の幅が6.54mmである入口開口を有するGe(220)の3回反射のアナライザ結晶を介して、前記ディテクタによりX線を受光する。 - FWHM1{10-12}に対するFWHM2{10-12}の前記比率は、100%以下である
請求項1に記載の窒化物半導体基板。 - 前記主面の中心の法線を軸として周方向に60°ずつ回転させた3つの方向から、{10-12}面で表される等価な結晶面の回折を測定したFWHM1{10-12}の最大最小差は、9arcsec以下である
請求項1又は2に記載の窒化物半導体基板。 - 2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
前記主面の中心の法線を軸として周方向に60°ずつ回転させた3つの方向から、{10-12}面で表される等価な結晶面の回折を測定したFWHM1{10-12}の最大最小差は、9arcsec以下である
窒化物半導体基板。
ただし、FWHM1{10-12}は、X線ロッキングカーブ測定により測定した{10-12}面回折の半値幅であり、
FWHM1{10-12}を測定するときの入射条件では、CuのX線源から、X線を平行光とするX線ミラー、Ge(220)の2回反射のモノクロメータ、およびゴニオメータの回転軸周りの回転角方向としてのω方向の幅が1.4mmであり且つ前記回転軸に平行な方向の長さが12mmである入射側開口をこの順で介して、前記主面の中心に対してCuのKα1のX線を照射し、
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずに、前記ω方向の幅が14.025mmである開口を有するディテクタによりX線を受光する。 - FWHM1{10-12}は、50arcsec以下である
請求項1~4のいずれか1項に記載の窒化物半導体基板。 - 2インチ以上の直径を有し、最も近い低指数の結晶面が(0001)面である主面を有する窒化物半導体基板であって、
FWHM1{10-12}は、50arcsec以下である
窒化物半導体基板。
ただし、FWHM1{10-12}は、X線ロッキングカーブ測定により測定した{10-12}面回折の半値幅であり、
FWHM1{10-12}を測定するときの入射条件では、CuのX線源から、X線を平行光とするX線ミラー、Ge(220)の2回反射のモノクロメータ、およびゴニオメータの回転軸周りの回転角方向としてのω方向の幅が1.4mmであり且つ前記回転軸に平行な方向の長さが12mmである入射側開口をこの順で介して、前記主面の中心に対してCuのKα1のX線を照射し、
FWHM1{10-12}を測定するときの受光条件では、受光側スリットをオープンとし且つアナライザ結晶を介さずに、前記ω方向の幅が14.025mmである開口を有するディテクタによりX線を受光する。 - III族窒化物半導体の単結晶からなり、鏡面化された主面を有し、前記主面に対して最も近い低指数の結晶面が(0001)面である下地基板と、
前記下地基板の前記主面の上方に設けられ、III族窒化物半導体の単結晶からなる低酸素濃度領域と、前記低酸素濃度領域上に設けられ、III族窒化物半導体の単結晶からなる高酸素濃度領域と、を有する積層ユニットと、
前記積層ユニットよりも上方に設けられ、III族窒化物半導体の単結晶からなる最上低酸素濃度領域と、
を備え、
前記高酸素濃度領域の酸素濃度は、前記低酸素濃度領域および前記最上低酸素濃度領域のそれぞれの酸素濃度よりも高く、
前記積層ユニットは、前記下地基板と前記最上低酸素濃度領域との間で、厚さ方向に繰り返し複数設けられている
積層構造体。 - 前記複数の積層ユニットのそれぞれにおける前記低酸素濃度領域の上面は、複数の谷部および複数の山部を有し、
前記複数の積層ユニットのうちの2層目以上の積層ユニットでは、
前記主面に垂直な任意の断面を見たときに、前記複数の谷部のうちの1つを挟んで前記複数の頂部のうちで最も接近する一対の山部同士が前記主面に沿った方向に離間した平均距離は、前記複数の積層ユニットのうちの1層目の積層ユニットのそれよりも長い
請求項7に記載の積層構造体。 - 気相成長法を用いた窒化物半導体基板の製造方法であって、
(a)III族窒化物半導体の単結晶からなり、鏡面化された主面を有し、前記主面に対して最も近い低指数の結晶面が(0001)面である下地基板を準備する工程と、
(b)前記主面の上方にIII族窒化物半導体の単結晶を平坦にホモエピタキシャル成長させる工程と、
(c)平坦なホモエピタキシャル成長結晶の表面に、(0001)面以外の傾斜界面で構成される複数の凹部を生じさせ、結晶成長の進行にしたがって該傾斜界面を徐々に拡大させて、結晶成長界面から(0001)面を少なくとも一度消失させることを特徴とする3次元成長層を成長させる工程と、
(d)前記3次元成長層上にIII族窒化物半導体の単結晶を更にエピタキシャル成長させることで、傾斜界面を消失させ、(0001)面からなる鏡面化された表面を有する平坦化層を成長させる工程と、
を有し、
前記(c)と前記(d)とを含むサイクルを複数回行う
窒化物半導体基板の製造方法。
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