Nitride semiconductor substrate

Abstract

To provide a nitride semiconductor substrate that improves crystal quality of a nitride semiconductor substrate, and to provide a laminate structure and a method for manufacturing a nitride semiconductor substrate.SOLUTION: This nitride semiconductor substrate has a diameter of 2 inches or more and has a principal plane in which a crystal plane having the nearest low index is a (0001) plane, where the ratio of FWHM2{10-12} to FWHM1{10-12} is 80% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nitride semiconductor substrate, a stacked structure, and a method for manufacturing a nitride semiconductor substrate. [Background technology]

[0002] A known technique is to use a substrate made of a single crystal of a group III nitride semiconductor as a base substrate (seed substrate), and further grow a crystal layer made of a single crystal of a group III nitride semiconductor on a primary surface of the base substrate whose closest low-index crystal plane is the (0001) plane. According to this technique, at least one nitride semiconductor substrate can be obtained by slicing the crystal layer grown to a predetermined thickness (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-60349 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to improve the crystal quality of a nitride semiconductor substrate. [Means for solving the problem]

[0005] According to one aspect of the present invention, A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 {10-12} FWHM2 {10-12} The ratio is over 80% A nitride semiconductor substrate is provided. However, FWHM1 {10-12} and FWHM2 {10-12}are the half-widths of the {10-12} plane diffraction measured by X-ray rocking curve measurement, respectively, FWHM1 {10-12} Under the incident conditions for measuring the above, Cu Kα1 X-rays are irradiated onto the center of the main surface from a Cu X-ray source through, in this order, an X-ray mirror that converts the X-rays into parallel light, a monochromator with two reflections on Ge (220), and an entrance-side opening having a width of 1.4 mm in the ω direction, which is the rotation angle direction around the rotation axis of the goniometer, and a length of 12 mm in the direction parallel to the rotation axis; FWHM1 {10-12} The receiving conditions for measuring are as follows: the receiving slit is open, and X-rays are received by a detector having an opening with a width of 14.025 mm in the ω direction without passing through an analyzer crystal; FWHM2 {10-12} The incident condition when measuring is FWHM1 {10-12} The incident conditions are the same as when measuring FWHM2 {10-12} In the light receiving condition for measuring the X-rays, the detector receives the X-rays through a Ge(220) triple-reflection analyzer crystal having an entrance aperture with a width of 6.54 mm in the ω direction.

[0006] According to another aspect of the present invention, A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 was measured by measuring the diffraction of the equivalent crystal plane represented by the {10-12} plane from three directions rotated by 60° in the circumferential direction around the normal line at the center of the main surface. {10-12} The maximum and minimum difference is less than 9 arcsec. A nitride semiconductor substrate is provided.

[0007] According to yet another aspect of the present invention, A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 {10-12} is less than 50 arcsec A nitride semiconductor substrate is provided.

[0008] According to yet another aspect of the present invention, a base substrate made of a single crystal of a group III nitride semiconductor, having a mirror-finished primary surface, the lowest-index crystal plane closest to the primary surface being the (0001) plane; a lamination unit including: a low oxygen concentration region formed above the primary surface of the base substrate and made of a single crystal of a Group III nitride semiconductor; and a high oxygen concentration region formed on the low oxygen concentration region and made of a single crystal of a Group III nitride semiconductor; an uppermost low oxygen concentration region formed of a single crystal of a Group III nitride semiconductor and provided above the stacked unit; Equipped with the oxygen concentration in the high oxygen concentration region is higher than the oxygen concentrations in the low oxygen concentration region and the uppermost low oxygen concentration region, The lamination unit is repeatedly provided in a thickness direction between the base substrate and the uppermost low oxygen concentration region. A laminate structure is provided.

[0009] According to yet another aspect of the present invention, A method for manufacturing a nitride semiconductor substrate using a vapor phase growth method, comprising the steps of: (a) preparing a base substrate made of a single crystal of a group III nitride semiconductor, having a mirror-finished primary surface, and the lowest-index crystal plane closest to the primary surface being the (0001) plane; (b) homoepitaxially growing a single crystal of a Group III nitride semiconductor flatly above the primary surface; (c) growing a three-dimensional growth layer characterized by generating a plurality of recesses on the surface of a flat homoepitaxially grown crystal, each recess being composed of an inclined interface other than the (0001) plane, and gradually expanding the inclined interface as the crystal growth progresses, until the (0001) plane disappears at least once from the crystal growth interface; (d) further epitaxially growing a single crystal of a Group III nitride semiconductor on the three-dimensional growth layer to eliminate the inclined interface and grow a planarization layer having a mirror-finished surface consisting of a (0001) plane; and A cycle including steps (c) and (d) is performed multiple times. A method for manufacturing a nitride semiconductor substrate is provided. [Effects of the Invention]

[0010] According to the present invention, the crystal quality of the nitride semiconductor substrate can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a flowchart showing a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention. [Figure 2] 1(a) to 1(g) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to one embodiment of the present invention. [Figure 3] 1(a) to 1(c) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to one embodiment of the present invention. [Figure 4] 1 is a schematic perspective view showing a part of a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention. [Figure 5] 1(a) and 1(b) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to one embodiment of the present invention. [Figure 6] 1(a) and 1(b) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to one embodiment of the present invention. [Figure 7] 1A to 1C are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to one embodiment of the present invention. [Figure 8] 1A to 1C are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to one embodiment of the present invention. [Figure 9] 1A to 1C are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to one embodiment of the present invention. [Figure 10](a) is a schematic cross-sectional view showing the growth process under the reference growth condition, in which the inclined interface and the c-plane do not expand or contract, and (b) is a schematic cross-sectional view showing the growth process under the first growth condition, in which the inclined interface expands and the c-plane contracts. [Figure 11] FIG. 10 is a schematic cross-sectional view showing the growth process under the second growth conditions in which the inclined interface shrinks and the c-plane expands. [Figure 12] FIG. 1(a) is a schematic top view showing a nitride semiconductor substrate according to one embodiment of the present invention; FIG. 1(b) is a schematic cross-sectional view along the m-axis of the nitride semiconductor substrate according to one embodiment of the present invention; and FIG. 1(c) is a schematic cross-sectional view along the a-axis of the nitride semiconductor substrate according to one embodiment of the present invention. [Figure 13] (a) is a schematic cross-sectional view showing the diffraction of X-rays on a curved c-plane, and (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. [Figure 14] FIG. 1 is a schematic perspective view showing an X-ray rocking curve measurement of an asymmetric reflecting surface in one embodiment of the present invention. [Figure 15] FIG. 2 is a schematic plan view showing an X-ray rocking curve measurement of an asymmetric reflecting surface in one embodiment of the present invention. [Figure 16] FIG. 2 is a view showing an image of a cross section of the laminated structure of Sample 1 observed with a fluorescence microscope. [Figure 17] 1 is a view of the main surface of the nitride semiconductor substrate of Sample 1 observed using a multiphoton excitation microscope. [Figure 18] 1 is a view of the main surface of the nitride semiconductor substrate of Sample 1 observed using a multiphoton excitation microscope. [Figure 19] 1 is a view of the main surface of the nitride semiconductor substrate of Sample 2 observed using a multiphoton excitation microscope. [Figure 20] 10 is a view of the principal surface of the nitride semiconductor substrate of Sample 3 observed using a multiphoton excitation microscope. [Figure 21]1(a) and 1(b) are diagrams showing normalized X-ray diffraction patterns obtained when X-ray rocking curve measurements of (0002) plane diffraction were performed on the nitride semiconductor substrates of Sample 1 and Sample 4, respectively, with different entrance-side slits. [Figure 22] FIG. 10 shows normalized X-ray diffraction patterns when X-ray rocking curve measurements of {10-12} plane diffraction were performed on the nitride semiconductor substrate of Sample 1 under different measurement conditions. [Figure 23] FIG. 10 shows normalized X-ray diffraction patterns when X-ray rocking curve measurements of {10-12} plane diffraction were performed on the nitride semiconductor substrate of Sample 3 under different measurement conditions. [Figure 24] FIG. 10 shows normalized X-ray diffraction patterns when X-ray rocking curve measurements of {10-12} plane diffraction were performed on the nitride semiconductor substrate of Sample 4 under different measurement conditions. DETAILED DESCRIPTION OF THE INVENTION

[0012] <One embodiment of the present invention> Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] (1) Method for manufacturing nitride semiconductor substrate A method for manufacturing a nitride semiconductor substrate according to this embodiment will be described with reference to FIGS. 1 to 9. FIG. 1 is a flowchart showing a method for manufacturing a nitride semiconductor substrate according to this embodiment. FIGS. 2(a) to 2(g), 3(a) to 3(c), 5(a) to 6(b), and 7 to 9 are schematic cross-sectional views showing a part of the method for manufacturing a nitride semiconductor substrate according to this embodiment. FIG. 4 is a schematic perspective view showing a part of the method for manufacturing a nitride semiconductor substrate according to this embodiment. FIG. 4 corresponds to the perspective view at the time of FIG. 3(b), and shows a part of a three-dimensionally grown layer 30 grown on an undersubstrate 10. In FIG. 5(b), thin solid lines indicate crystal planes during growth, and dotted lines indicate dislocations in FIGS. 3(c) to 6(b) and 7 to 9.

[0014] The method for manufacturing a nitride semiconductor substrate according to this embodiment includes the steps of: A method for manufacturing a nitride semiconductor substrate using a vapor phase growth method, comprising the steps of: (a) preparing a base substrate made of a single crystal of a group III nitride semiconductor, having a mirror-finished primary surface, and the lowest-index crystal plane closest to the primary surface being the (0001) plane; (b) epitaxially growing a single crystal of a Group III nitride semiconductor having a top surface in which the (0001) plane is exposed above the primary surface of the base substrate, generating a plurality of recesses on the top surface composed of inclined interfaces other than the (0001) plane, gradually expanding the inclined interfaces upwardly of the primary surface of the base substrate, causing the (0001) plane to disappear at least once from the top surface, and growing a three-dimensionally grown layer; (c) epitaxially growing a single crystal of a Group III nitride semiconductor on the three-dimensional growth layer to eliminate the inclined interface and grow a planarization layer having a mirror-finished surface; and A cycle including (b) and (c) is performed multiple times.

[0015] Specifically, as shown in FIG. 1, the method for manufacturing a nitride semiconductor substrate according to this embodiment includes, for example, a base substrate preparation step S100, a three-dimensional growth step S200, a planarization step S300, an implementation count determination step S400, a main growth step S500, a slicing step S600, and a polishing step S700.

[0016] (S100: Base board preparation process) First, in the base substrate preparation step S100, a base substrate 10 made of a single crystal of a group III nitride semiconductor is prepared. In this embodiment, for example, a gallium nitride (GaN) freestanding substrate is prepared as the base substrate 10.

[0017] In the following, in a group III nitride semiconductor crystal having a wurtzite structure, <0001> The axis (e.g., the

[0001] axis) is called the "c-axis," and the (0001) plane is called the "c-plane." The (0001) plane is sometimes called the "+c-plane (Group III element polar plane)," and the (000-1) plane is sometimes called the "-c-plane (nitrogen (N) polar plane)." The <1-100> axis (e.g., the [1-100] axis) is called the "m-axis," and the {1-100} plane is called the "m-plane." The m-axis may also be written as the <10-10> axis. The <11-20> axis (e.g., the [11-20] axis) is called the "a-axis," and the {11-20} plane is called the "a-plane."

[0018] In the base substrate preparation step S100 of this embodiment, the base substrate 10 is produced by, for example, a VAS (Void-Assisted Separation) method.

[0019] Specifically, the base substrate preparation step S100 includes, for example, a crystal growth substrate preparation step S110, a first crystal layer formation step S120, a metal layer formation step S130, a void formation step S140, a second crystal layer formation step S150, a peeling step S160, a slicing step S170, and a polishing step S180.

[0020] (S110: Crystal growth substrate preparation process) First, as shown in FIG. 2(a), a crystal growth substrate 1 (hereinafter sometimes abbreviated as "substrate 1") is prepared. The substrate 1 is, for example, a sapphire substrate. The substrate 1 may also be, for example, a Si substrate or a gallium arsenide (GaAs) substrate. The substrate 1 has, for example, a primary surface 1s that serves as a growth surface. The low-index crystal plane closest to the primary surface 1s is, for example, the c-plane 1c.

[0021] In this embodiment, 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 θ0 with respect to the normal to the main surface 1s. The off-angle θ0 within the main surface 1s of the substrate 1 is uniform over the entire main surface 1s. The off-angle θ0 within the main surface 1s of the substrate 1 affects the off-angle θ3 at the center of the main surface 10s of the base substrate 10, which will be described later.

[0022] (S120: First crystal layer formation step) 2(b), for example, by metalorganic vapor phase epitaxy (MOVPE), a low-temperature-grown GaN buffer layer and a Si-doped GaN layer are grown in this order as a first crystal layer (underlying growth layer) 2 on the primary surface 1s of the substrate 1 by supplying trimethylgallium (TMG) gas as a group III source gas, ammonia gas (NH3) as a nitrogen source gas, and monosilane (SiH4) gas as an n-type dopant gas to the substrate 1 heated to a predetermined growth temperature. The thicknesses of the low-temperature-grown GaN buffer layer and the Si-doped GaN layer are set to, for example, 20 nm and 0.5 μm, respectively.

[0023] (S130: Metal layer formation process) 2(c), a metal layer 3 is vapor-deposited on the first crystal layer 2. The metal layer 3 is, for example, a titanium (Ti) layer. The thickness of the metal layer 3 is, for example, 20 nm.

[0024] (S140: Void formation process) Next, the substrate 1 is placed in an electric furnace and placed on a susceptor equipped with a predetermined heater. After the substrate 1 is placed on the susceptor, the heater heats the substrate 1, and heat treatment is performed in an atmosphere containing hydrogen gas or a hydride gas. Specifically, the heat treatment is performed for 20 minutes at a predetermined temperature in a hydrogen (H) gas stream containing 20% ​​NH gas. The heat treatment temperature is, for example, 850°C or higher and 1,100°C or lower. This heat treatment nitrides the metal layer 3, forming a metal nitride layer 5 with a high density of fine holes on its surface. Furthermore, the heat treatment etches a portion of the first crystal layer 2 through the holes in the metal nitride layer 5, forming a high density of voids in the first crystal layer 2.

[0025] As a result, a void-containing first crystal layer 4 is formed as shown in FIG. 2(d).

[0026] (S150: Second crystal layer formation step) Next, for example, by hydride vapor phase epitaxy (HVPE), gallium chloride (GaCl) gas, NH3 gas, and dichlorosilane (SiH2Cl2) gas as an n-type dopant gas are supplied to the substrate 1 heated to a predetermined growth temperature, thereby epitaxially growing a Si-doped GaN layer as a second crystal layer (full-grown layer) 6 on the void-containing first crystal layer 4 and the metal nitride layer 5. Note that a Ge-doped GaN layer may also be epitaxially grown as the second crystal layer 6 by supplying tetrachlorogermane (GeCl4) gas or the like as the n-type dopant gas instead of SiH2Cl2 gas.

[0027] At this time, the second crystal layer 6 grows from the void-containing first crystal layer 4 through the holes in the metal nitride layer 5 onto the void-containing first crystal layer 4 and the metal nitride layer 5. Some of the voids in the void-containing first crystal layer 4 are filled by the second crystal layer 6, but other voids in the void-containing first crystal layer 4 remain. 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 the second crystal layer 6 to peel off in the peeling step S160 described below.

[0028] At this time, the second crystal layer 6 is grown while inheriting the orientation of the substrate 1. That is, the off-angle θ1 in the main surface of the second crystal layer 6 becomes uniform over the entire main surface, similar to the off-angle θ0 in the main surface 1s of the substrate 1.

[0029] In this case, the thickness of the second crystal layer 6 is set to, for example, 600 μm or more, preferably 1 mm or more. Although there is no particular upper limit to the thickness of the second crystal layer, from the viewpoint of improving productivity, the thickness of the second crystal layer 6 is preferably set to 50 mm or less.

[0030] (S160: Peeling process) After the growth of the second crystal layer 6 is completed, during the process of cooling the HVPE apparatus used to grow the second crystal layer 6, the second crystal layer 6 naturally peels off from the substrate 1 at the boundaries of the void-containing first crystal layer 4 and the metal nitride layer 5.

[0031] At this time, tensile stress is introduced into the second crystal layer 6 due to the mutual attraction of initial nuclei generated during the growth process. Therefore, due to the tensile stress generated in the second crystal layer 6, internal stress acts on the second crystal layer 6 so that the surface side thereof is recessed. Furthermore, the dislocation density on the main surface (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 due to the difference in dislocation density in the thickness direction of the second crystal layer 6, internal stress acts on the second crystal layer 6 so that the surface side thereof is recessed.

[0032] 2(f), after being peeled off from the substrate 1, the second crystalline layer 6 warps so that its surface side is concave. Therefore, the c-plane 6c of the second crystalline layer 6 is curved into a concave spherical shape with respect to a plane perpendicular to the normal direction to the center of the main surface 6s of the second crystalline layer 6. The off-angle θ2 that the c-axis 6ca makes with respect to the normal to the center of the main surface 6s of the second crystalline layer 6 has a predetermined distribution.

[0033] (S170: Slicing process) Next, as shown in FIG. 2(f), for example, the second crystalline layer 6 is sliced ​​by a wire saw along a cutting plane SS that is approximately perpendicular to the normal direction at the center of the main surface 6s of the second crystalline layer 6.

[0034] 2(g), the base substrate 10 is formed as an as-sliced ​​substrate. At this time, the thickness of the base substrate 10 is set to, for example, 450 μm. Note that the off-angle θ3 of the base substrate 10 may vary from the off-angle θ2 of the second crystal layer 6 due to slice direction dependency.

[0035] (S180: Polishing process) Next, both surfaces of the base substrate 10 are polished using a polishing device, thereby making the main surface 10s of the base substrate 10 mirror-finished.

[0036] The above-described base substrate preparation step S100 provides a base substrate 10 made of single crystal GaN.

[0037] The diameter of the starting substrate 10 is, for example, 2 inches or more, and the thickness of the starting substrate 10 is, for example, 300 μm or more and 1 mm or less.

[0038] The primary surface 10s of the base substrate 10 has, for example, a primary surface (base surface) 10s that serves as an epitaxial growth surface. In this embodiment, the lowest-index crystal plane closest to the primary surface 10s is, for example, the c-plane (+c-plane) 10c.

[0039] The c-plane 10c of the base substrate 10 is curved into a concave spherical shape relative to the main surface 10s. Here, "spherical" refers to a curved surface that is approximated to a spherical surface. Furthermore, "spherical approximation" refers to an approximation to a perfect spherical surface or an ellipsoidal spherical surface within a predetermined error range.

[0040] In this embodiment, the c-plane 10f of the starting substrate 10 has a curved surface that is approximated as a sphere in both the cross section along the m-axis and the cross section along the a-axis. The radius of curvature of the c-plane 10c of the starting substrate 10 is, for example, not less than 1 m and less than 10 m.

[0041] The off-angle θ3 that the c-axis 10ca makes with respect to the normal to the center of the main surface 10s of the base substrate 10 has a predetermined distribution.

[0042] In this embodiment, the magnitude of the off-angle θ3 at the center of the main surface 10s of the base substrate 10 is, for example, 1° or less, preferably 0.4° or less. If the magnitude of the off-angle θ3 at the center of the main surface 10s exceeds 1°, it may be difficult to achieve three-dimensional growth of the three-dimensionally grown layer 30 in the three-dimensional growth step S200 (described later) depending on the first growth conditions. This makes it difficult to eliminate the c-plane 30c. In contrast, in this embodiment, by setting the magnitude of the off-angle θ3 at the center of the main surface 10s to 1° or less, the three-dimensionally grown layer 30 can be easily three-dimensionally grown in the three-dimensional growth step S200 (described later). This makes it easy to eliminate the c-plane 30c. Furthermore, by setting the magnitude of the off-angle θ3 at the center of the main surface 10s to 0.4° or less, the three-dimensionally grown layer 30 can be three-dimensionally grown under a relatively wide range of growth conditions, and the c-plane 30c can be stably eliminated.

[0043] Note that, from the viewpoint of three-dimensional growth of the three-dimensionally grown layer 30, the smaller the magnitude of the off-angle θ3 at the center of the main surface 10s, the better. However, if the magnitude of the off-angle θ3 at the center of the main surface 10s is too close to 0°, the surface of the three-dimensionally grown layer 30 may become excessively rough. For this reason, the magnitude of the off-angle θ3 at the center of the main surface 10s is preferably, for example, 0.1° or greater.

[0044] The magnitude and direction of the off-angle θ3 at the center of the main surface 10s of the base substrate 10 can be adjusted, for example, by the magnitude and direction of the off-angle θ0 of the crystal growth substrate 1 used in the above-mentioned VAS method and the slice angle and slice direction in the slice step S170.

[0045] In this embodiment, 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.

[0046] Furthermore, in this embodiment, the base substrate 10 is fabricated by the above-mentioned VAS method, and therefore the dislocation density is low on the main surface 10s of the base substrate 10. Specifically, the dislocation density on the main surface 10s of the base substrate 10 is, for example, 3×106 cm -2 More than 1×10 7 cm -2 is less than.

[0047] (S200: 3D growth process) After preparing the base substrate 10 as shown in Figure 3(a), a single crystal of a Group III nitride semiconductor having a top surface 30u with the c-plane 30c exposed is epitaxially grown above the primary surface 10s of the base substrate 10, as shown in Figures 3(b), 3(c), and 4. This allows a three-dimensionally grown layer 30 to grow.

[0048] At this time, multiple recesses 30p surrounded by inclined interfaces 30i other than the c-plane are formed on the top surface 30u of the single crystal, and the inclined interfaces 30i are gradually enlarged and the c-plane 30c is gradually reduced upwardly toward the main surface 10s of the base substrate 10. This causes the c-plane 30c to disappear at least once from the top surface 30u. As a result, a three-dimensionally grown layer 30 is formed in which the inclined interfaces 30i are widely present on the surface.

[0049] In the three-dimensional growth step S200 of the first cycle, as shown in FIG. 3(a), the base substrate 10 is used in a state where neither a mask layer nor a concave-convex pattern has been formed on the main surface 10s. The term "mask layer" as used herein refers to a mask layer having predetermined openings, as used in, for example, the so-called ELO (Epitaxial Lateral Overgrowth) method. The term "convex-convex pattern" as used herein refers to at least one of trenches and ridges, as used in, for example, the so-called pendeoepitaxy method, which are directly patterned on the main surface of the base substrate. The height difference of the concave-convex pattern referred to here is, for example, 100 nm or more. In the three-dimensional growth step S200 of the first cycle, a single crystal of a group III nitride semiconductor is epitaxially grown directly on the main surface 10s of the base substrate 10, which does not have the above-described structure.

[0050] In the three-dimensional growth step S200 of the first cycle, the three-dimensionally grown layer 30 is grown three-dimensionally so as to intentionally roughen the main surface 10s of the base substrate 10. Even if the three-dimensionally grown layer 30 has such a growth form, it is grown as a single crystal as described above. In this respect, the three-dimensionally grown layer 30 differs from a so-called low-temperature grown buffer layer that is formed as an amorphous or polycrystalline layer on a heterogeneous substrate such as sapphire prior to epitaxial growth of a Group III nitride semiconductor on the heterogeneous substrate.

[0051] At this time, an inclined interface growth region 70 (gray part in the figure) is formed in the three-dimensional growth layer 30 by growing the inclined interface 30i other than the c-plane as the growth plane. As will be described later, the area occupied by the inclined interface growth region 70 in the three-dimensional growth layer 30 in a cross section along the main surface 10s of the base substrate 10 is set to, for example, 80% or more.

[0052] In this embodiment, for example, a layer made of the same Group III nitride semiconductor as that constituting the base substrate 10 is epitaxially grown as the three-dimensional growth layer 30. Specifically, for example, the base substrate 10 is heated by the HVPE method, and GaCl gas and NH gas are supplied to the heated base substrate 10, thereby epitaxially growing a GaN layer as the three-dimensional growth layer 30.

[0053] Here, in the three-dimensional growth step S200, in order to realize the above-mentioned growth process, for example, the three-dimensional growth layer 30 is grown under a predetermined first growth condition.

[0054] First, a reference growth condition in which the inclined interface 30i and the c-plane 30c do not expand or contract will be described with reference to Fig. 10(a). Fig. 10(a) is a schematic cross-sectional view showing the growth process under the reference growth condition in which the inclined interface and the c-plane do not expand or contract.

[0055] In FIG. 10(a), the thick solid line indicates the surface of the three-dimensionally grown layer 30 per unit time. The inclined interface 30i shown in FIG. 10(a) is the inclined interface that is most inclined with respect to the c-plane 30c. In FIG. 10(a), the growth rate of the c-plane 30c of the three-dimensionally grown layer 30 is expressed as G c0 The growth rate of the inclined interface 30i of the three-dimensional growth layer 30 is G i 10(a), the angle between the c-plane 30c and the inclined interface 30i is defined as α. In addition, in FIG. 10(a), the three-dimensionally grown layer 30 is grown while maintaining the angle α between the c-plane 30c and the inclined interface 30i. It is also assumed that the off-angle of the c-plane 30c of the three-dimensionally grown layer 30 is negligible compared to the angle α between the c-plane 30c and the inclined interface 30i.

[0056] 10(a), when the inclined interface 30i and the c-plane 30c do not expand or contract, the locus of intersections between the inclined interface 30i and the c-plane 30c is perpendicular to the c-plane 30c. Therefore, the reference growth condition under which the inclined interface 30i and the c-plane 30c do not expand or contract satisfies the following formula (a). G c0 =G i / cosα (a)

[0057] Next, a first growth condition under which the inclined interface 30i expands and the c-plane 30c shrinks will be described with reference to Fig. 10(b). Fig. 10(b) is a schematic cross-sectional view showing the growth process under the first growth condition under which the inclined interface expands and the c-plane shrinks.

[0058] 10(b), as in FIG. 10(a), the thick solid line indicates the surface of the three-dimensionally grown layer 30 per unit time. The inclined interface 30i shown in FIG. 10(b) is also the inclined interface that is most inclined with respect to the c-plane 30c. In FIG. 10(b), the growth rate of the c-plane 30c of the three-dimensionally grown layer 30 is expressed as G c1 The rate of progression of the locus of intersections between the inclined interface 30i and the c-plane 30c in the three-dimensional growth layer 30 is R1. The narrower angle between the locus of intersections between the inclined interface 30i and the c-plane 30c and the c-plane 30c is αR1 R1 direction and G i If the angle between the direction is α', then α' = α + 90 - α R1 It is assumed that the off-angle of the c-plane 30c of the three-dimensionally grown layer 30 is negligible compared to the angle α formed between the c-plane 30c and the inclined interface 30i.

[0059] As shown in FIG. 10(b), the progression rate R1 of the locus of intersections between the inclined interface 30i and the c-plane 30c is expressed by the following formula (b). R1=G i / cosα' (b)

[0060] In addition, the growth rate G of the c-plane 30c of the three-dimensional growth layer 30 c1 is expressed by the following equation (c). G c1 = R1 sin α R1 (c)

[0061] By substituting equation (b) into equation (c), G c1 is G i Using this, it is expressed by the following equation (d). G c1 =G i sin α R1 / cos(α+90-α R1 ) (d)

[0062] In order for the inclined interface 30i to expand and the c-plane 30c to shrink, α R1 Therefore, the first growth condition under which the inclined interface 30i expands and the c-plane 30c shrinks is expressed by the formula (d) and α R1 <90°, it is preferable that the following formula (1) is satisfied. G c1 >G i / cosα (1) However, as mentioned above, G i is the growth rate of the inclined interface 30i that is most inclined with respect to the c-plane 30c, and α is the angle between the inclined interface 30i that is most inclined with respect to the c-plane 30c and the c-plane 30c.

[0063] Or, G under the first growth condition c1 is G under standard growth conditions. c0 It can also be considered that it is preferable that G c1 >G c0 By substituting equation (a) into equation (1), equation (1) can be derived.

[0064] Since the growth conditions for expanding the inclined interface 30i that is most inclined with respect to the c-plane 30c are the most stringent conditions, if the first growth condition satisfies formula (1), it becomes possible to expand the other inclined interfaces 30i as well.

[0065] Specifically, for example, when the inclined interface 30i most inclined with respect to the c-plane 30c is the {10-11} plane, α=61.95°. Therefore, it is preferable that the first growth condition satisfies, for example, the following formula (1′). G c1 >2.13G i (1')

[0066] Alternatively, as will be described later, when the inclined interface 30i is a {11-2m} plane where m≧3, the inclined interface 30i most inclined with respect to the c-plane 30c is the {11-23} plane, and therefore α=47.3°. Therefore, it is preferable that the first growth condition satisfies, for example, the following formula (1″). G c1 >1.47G i (1")

[0067] As a first growth condition in this embodiment, for example, the growth temperature in the three-dimensional growth step S200 is set lower than the growth temperature in the planarization step S300 described below. Specifically, the growth temperature in the three-dimensional growth step S200 is set to, for example, 980°C or higher and 1,020°C or lower, preferably 1,000°C or higher and 1,020°C or lower.

[0068] Furthermore, as a first growth condition of this embodiment, for example, the ratio of the partial pressure of the flow rate of NH gas as the nitrogen source gas to the partial pressure of GaCl gas as the Group III source gas in the three-dimensional growth step S200 (hereinafter also referred to as the "V / III ratio") may be set to be larger than the V / III ratio in the planarization step S300 described later. Specifically, the V / III ratio in the three-dimensional growth step S200 is set to, for example, 2 or more and 20 or less, preferably 2 or more and 15 or less.

[0069] In practice, at least one of the growth temperature and the V / III ratio is adjusted within the above ranges as the first growth condition so as to satisfy the formula (1).

[0070] Other conditions among the first growth conditions of this embodiment are, for example, as follows. Growth pressure: 90 to 105 kPa, preferably 90 to 95 kPa GaCl gas partial pressure: 1.5 to 15 kPa N2 gas flow rate / H2 gas flow rate: 0 to 1

[0071] Here, the three-dimensional growth step S200 of this embodiment is classified into two steps, for example, based on the morphology of the three-dimensional growth layer 30 during growth. Specifically, the three-dimensional growth step S200 of this embodiment includes, for example, an inclined interface expansion step S220 and an inclined interface maintenance step S240. Through these steps, the three-dimensional growth layer 30 includes, for example, an inclined interface expansion layer 32 and an inclined interface maintenance layer 34.

[0072] (S220: Inclined interface expansion process) First, as shown in Figures 3(b) and 4, 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 directly on the main surface 10s of the base substrate 10 under the first growth conditions described above.

[0073] In the initial stage of growth of the inclined interface expansion layer 32, the inclined interface expansion layer 32 is grown to a predetermined thickness by step-flow growth (two-dimensional growth) in the normal direction (direction along the c-axis) of the primary surface 10s of the base substrate 10, with the c-plane 30c serving as the growth plane. That is, the single-crystal inclined interface expansion layer 32 is homoepitaxially grown to a flat surface. Here, a portion of the inclined interface expansion layer 32 grown with the c-plane 30c as the growth plane is also referred to as the "initial layer." This growth results in an initial layer with a mirror-finished surface and a predetermined thickness. At this time, the initial layer is grown continuously in a direction along the primary surface 10s of the base substrate 10, i.e., across the entire primary surface 10s of the base substrate 10. At this time, the thickness of the initial layer is, for example, 1 μm to 100 μm, preferably 1 μm to 20 μm.

[0074] Then, by gradually growing the inclined interface expansion layer 32 under the first growth conditions, as shown in Figures 3(b) and 4, a plurality of recesses 30p formed of inclined interfaces 30i other than the c-plane are formed on the top surface 30u of the inclined interface expansion layer 32, where the c-plane 30c is exposed. The plurality of recesses 30p formed of inclined interfaces 30i other than the c-plane are formed randomly on the top surface 30u. This results in the formation of an inclined interface expansion layer 32 in which the c-plane 30c and inclined interfaces 30i other than the c-plane are mixed on the surface.

[0075] The term "inclined interface 30i" used here refers to a growth interface inclined relative to the c-plane 30c, and includes low-index facets other than the c-plane, high-index facets other than the c-plane, and inclined faces that cannot be expressed by a plane index. Examples of facets other than the c-plane include {11-2m} and {1-10n}, where m and n are integers other than 0.

[0076] In this embodiment, by using the above-described base substrate 10 and adjusting the first growth conditions to satisfy formula (1), it is possible to generate, for example, a {11-2m} plane, where m≧3, as the inclined interface 30i. This makes it possible to make the inclination angle of the {11-2m} plane relative to the c-plane 30c gentle. Specifically, the inclination angle can be set to 47.3° or less.

[0077] 3(b) and 3(c), by further growing the inclined interface expansion layer 32 under the first growth conditions, the inclined interfaces 30i other than the c-plane gradually expand and the c-plane 30c gradually shrinks upward in the inclined interface expansion layer 32 toward the major surface 10s of the base substrate 10. Note that, at this time, the inclination angle of the inclined interfaces 30i relative to the major surface 10s of the base substrate 10 gradually decreases upward in the inclined interface expansion layer 32. As a result, most of the inclined interfaces 30i eventually become the {11-2m} planes where m≧3 as described above.

[0078] As the inclined interface expansion layer 32 continues to grow, the c-plane 30c of the inclined interface expansion layer 32 disappears from the top surface 30u, and the outermost surface (top surface) of the inclined interface expansion layer 32 is composed of only the inclined interface 30i.

[0079] In this way, by forming multiple recesses 30p consisting of inclined interfaces 30i other than the c-plane on the top surface 30u of the inclined interface expansion layer 32 and eliminating the c-plane 30c, multiple valleys 30v and multiple peaks 30t are formed on the surface of the inclined interface expansion layer 32, as shown in FIG. 3(c). Each of the multiple valleys 30v is an inflection point on the surface of the inclined interface expansion layer 320 that is convex downward, and is formed above the position where each inclined interface 30i other than the c-plane is generated. Meanwhile, each of the multiple peaks 30t is an inflection point on the surface of the inclined interface expansion layer 320 that is convex upward, and is formed at or above the position where the c-plane 30c (finally) disappears and terminates, sandwiching a pair of inclined interfaces 30i that expand in opposite directions. The valleys 30v and peaks 30t are alternately formed in a direction along the major surface 10s of the base substrate 10.

[0080] In this embodiment, in the initial stage of growth of the inclined interface expansion layer 32, the inclined interface expansion layer 32 is grown to a predetermined thickness on the main surface 10s of the base substrate 10 using the c-plane 30c as the growth plane without generating the inclined interface 30i, and then the inclined interface 30i other than the c-plane is generated on the surface of the inclined interface expansion layer 32. As a result, the multiple valleys 30v are formed at positions spaced upward from the main surface 10s of the base substrate 10.

[0081] Due to the above-described growth process of the inclined interface expansion layer 32, dislocations propagate while bending as follows. Specifically, as shown in FIG. 3( c), multiple dislocations that extended along the c-axis in the undersubstrate 10 propagate from the undersubstrate 10 toward the c-axis of the inclined interface expansion layer 32. In the region of the inclined interface expansion layer 32 grown using the c-plane 30c as the growth plane, dislocations propagate from the undersubstrate 10 toward the c-axis of the inclined interface expansion layer 32. However, when the growth interface where dislocations are exposed in the inclined interface expansion layer 32 changes from the c-plane 30c to the inclined interface 30i, the dislocations propagate while bending toward a direction substantially perpendicular to the inclined interface 30i. That is, the dislocations propagate while bending toward a direction inclined with respect to the c-axis. As a result, in the inclined interface expansion step S220 and subsequent steps, dislocations are locally collected above the approximate center between the pair of apexes 30t. As a result, the dislocation density on the surface of the planarizing layer 40, which will be described later, can be reduced.

[0082] In this embodiment, when viewing an arbitrary cross section perpendicular to the main surface 10s of the base substrate 10, the average distance L (also referred to as the "average distance between nearest apices") between the pair of nearest apices 30t sandwiching one of the plurality of valleys 30v in the direction along the main surface 10s of the base substrate 10 is set to, for example, more than 100 μm. Note that the average distance L between nearest apices is the distance when viewing the cross section when the c-plane 30c has disappeared from the crystal growth interface.

[0083] When the average distance L between nearest apexes is 100 μm or less, such as when fine hexagonal pyramidal crystal nuclei are generated on the main surface 10s of the base substrate 10 from the initial stage of the inclined interface expansion step S220, the distance over which dislocations bend and propagate is shortened in the steps following the inclined interface expansion step S220. Therefore, dislocations are not sufficiently collected above the approximate center between the pair of apexes 30t of the inclined interface expansion layer 32. As a result, the dislocation density on the surface of the planarization layer 40 (described later) may not be sufficiently reduced. In contrast, in this embodiment, by setting the average distance L between nearest apexes to greater than 100 μm, the distance over which dislocations bend and propagate in the steps following the inclined interface expansion step S220 can be ensured to be at least 50 μm or more. This allows dislocations to be sufficiently collected above the approximate center between the pair of apexes 30t of the inclined interface expansion layer 32. As a result, the dislocation density on the surface of the planarization layer 40 (described later) can be sufficiently reduced.

[0084] On the other hand, in this embodiment, the average distance L between the nearest apexes is set to less than 800 μm. If the average distance L between the nearest apexes is 800 μm or more, the height from the major surface 10s of the base substrate 10 to the valleys 30v to the peaks 30t of the inclined interface expansion layer 32 becomes excessively large. As a result, in the planarization step S300 described below, the thickness of the planarization layer 40 becomes large until it is mirror-finished. In contrast, in this embodiment, by setting the average distance L between the nearest apexes to less than 800 μm, the height from the major surface 10s of the base substrate 10 to the valleys 30v to the peaks 30t of the inclined interface expansion layer 32 can be reduced. This allows the planarization layer 40 to be mirror-finished more quickly.

[0085] At this time, based on the difference in the growth plane during the growth process, the inclined interface expansion layer 320 is formed with a c-plane growth region 60 grown using the c-plane 30c as the growth plane, and an inclined interface growth region 70 (gray area in the figure) grown using an inclined interface 30i other than the c-plane as the growth plane.

[0086] At this time, in c-plane growth region 60, valleys 60a are formed at positions where inclined interfaces 30i are generated, and peaks 60b are formed at positions where c-plane 30c disappears and terminates. In c-plane growth region 60, a pair of inclined portions 60i are formed on both sides of peak 60b as loci of intersections between c-plane 30c and inclined interfaces 30i.

[0087] In addition, in this case, when the first growth condition satisfies formula (1), the angle formed by the pair of inclined portions 60i when viewed in a cross section passing through the centers of the two adjacent valley portions 60a is, for example, 70° or less.

[0088] These areas will be described in more detail below.

[0089] (S240: Inclined interface maintenance process) After the c-plane 30c has disappeared from the surface of the inclined interface expansion layer 32, the growth conditions in the inclined interface maintaining step S240 are maintained at the first growth conditions described above, similar to the inclined interface expanding step S220.

[0090] 5(a), the growth of the three-dimensionally grown layer 30 continues over a predetermined thickness while maintaining a state in which the inclined interface 30i occupies more of the surface than the c-plane 30c. As a result, an inclined interface maintaining layer 34 is formed on the inclined interface enlarging layer 32.

[0091] Here, in the three-dimensional growth step S200, in order to reliably bend the propagation direction of dislocations and reduce the dislocation density as described above, it is important that the c-plane 30c has disappeared at least once when looking at the history of the growth interface at any position in the three-dimensional growth layer 30. For this reason, it is desirable that the c-plane 30c disappears at least once in an early stage of the three-dimensional growth step S200 (for example, the above-mentioned inclined interface expansion step S220).

[0092] However, in the inclined interface maintaining step S240, after the c-plane 30c has disappeared at least once, the c-plane 30c may reappear in part of the surface of the inclined interface maintaining layer 34. However, it is preferable to expose mainly the inclined interface 30i on the surface of the inclined interface maintaining layer 34 so that the area proportion occupied by the inclined interface growth region 70 is 80% or more in the cross-sectional surface along the main surface 10s of the base substrate 10. The higher the area proportion occupied by the inclined interface growth region 70 in the cross-sectional surface, the better, and 100% is preferable.

[0093] Furthermore, at this time, by growing the inclined interface maintaining layer 34 under the first growth conditions with the inclined interface 30i as the growth surface, the dislocations that have propagated while bending in a direction inclined with respect to the c-axis at the position where the inclined interface 30i is exposed in the inclined interface enlarging layer 32 as described above continue to propagate in the same direction in the inclined interface maintaining layer 34.

[0094] At this time, the inclined interface maintaining layer 34 grows using the inclined interface 30i as a growth surface, so that substantially the entire inclined interface maintaining layer 34 becomes part of the inclined interface growth region 70.

[0095] By the above three-dimensional growth step S200, a three-dimensionally grown layer 30 having a gradient interface enlarging layer 32 and a gradient interface maintaining layer 34 is formed.

[0096] In one cycle of the three-dimensional growth step S200, the height from the main surface 10s of the base substrate 10 to the top 30t of the three-dimensionally grown layer 30 (the maximum height in the thickness direction of the three-dimensionally grown layer 30) is, for example, more than 100 μm and less than 1.5 mm.

[0097] (S300: Flattening process) After the three-dimensionally grown layer 30 in which the c-plane 30c has disappeared is grown, a single crystal of a group III nitride semiconductor is further epitaxially grown on the three-dimensionally grown layer 30, as shown in FIG. 5(b).

[0098] At this time, the inclined interface 40i is gradually reduced and the c-plane 40c is gradually expanded upwardly toward the main surface 10s of the base substrate 10. This causes the inclined interface 30i formed on the surface of the three-dimensionally grown layer 30 to disappear. As a result, a planarization layer 40 having a mirror-finished surface is grown. Note that the "mirror surface" referred to here refers to a surface in which the maximum difference in height between adjacent concaves and convexes is equal to or less than the wavelength of visible light.

[0099] In this embodiment, the planarization layer 40 is formed by epitaxial growth of a layer whose main component is the same group III nitride semiconductor as that constituting the three-dimensional growth layer 30. In the planarization step S300, GaCl gas, NH gas, and dichlorosilane (SiH2Cl2) gas as an n-type dopant gas are supplied to the base substrate 10 heated to a predetermined growth temperature, thereby epitaxially growing a silicon (Si)-doped GaN layer as the planarization layer 40. Instead of SiH2Cl2 gas, GeCl4 gas or the like may be supplied as the n-type dopant gas.

[0100] Here, in the planarization step S300, in order to realize the above-mentioned growth process, the planarization layer 40 is grown under, for example, predetermined second growth conditions.

[0101] The second growth condition, in which the inclined interface 40i is reduced and the c-plane 40c is expanded, will be described with reference to Fig. 11. Fig. 11 is a schematic cross-sectional view showing the growth process under the second growth condition, in which the inclined interface is reduced and the c-plane is expanded. Fig. 11 shows the process of growing the planarization layer 40 on the three-dimensional growth layer 30 in which the inclined interface 30i most inclined relative to the c-plane 30c is exposed.

[0102] 11, similarly to FIG. 10(a), the thick solid line indicates the surface of the planarization layer 40 per unit time. In addition, in FIG. 11, the growth rate of the c-plane 40c of the planarization layer 40 is expressed as G c2 The growth rate of the inclined interface 40i of the planarization layer 40 is G iThe rate of progression of the path of intersections between the inclined interface 40i and the c-plane 40c in the planarization layer 40 is R2. The narrower angle between the path of intersections between the inclined interface 40i and the c-plane 40c and the c-plane 30c is α R2 R2 direction and G i When the angle between the direction is α”, α” = α-(90-α R2 11, the planarizing layer 40 is grown while maintaining the angle α between the c-plane 30c and the inclined interface 30i in the three-dimensionally grown layer 30. It is assumed that the off-angle of the c-plane 40c of the planarizing layer 40 is negligible compared to the angle α between the c-plane 30c and the inclined interface 30i.

[0103] As shown in FIG. 11, the progression rate R2 of the locus of intersections between the inclined interface 40i and the c-plane 40c is expressed by the following formula (e). R2=G i / cosα” ···(e)

[0104] In addition, the growth rate G c2 is expressed by the following formula (f). G c2 =R2sinα R2 (f)

[0105] By substituting equation (e) into equation (f), G c2 is G i Using this, it is expressed by the following formula (g). G c2 =G i sin α R2 / cos(α+α R2 -90) ···(g)

[0106] In order for the inclined interface 40i to shrink and the c-plane 40c to expand, α R2 Therefore, the second growth condition under which the inclined interface 40i is reduced and the c-plane 40c is expanded is expressed by the formula (g) and α R2 <90°, it is preferable to satisfy the following formula (2). G c2 <G i / cosα (2) However, as mentioned above, G i is the growth rate of the inclined interface 40i that is most inclined with respect to the c-plane 40c, and α is the angle between the inclined interface 40i that is most inclined with respect to the c-plane 40c and the c-plane 40c.

[0107] Alternatively, the growth rate of the c-plane 30c of the planarization layer 40 under the reference growth conditions is G c0 When G under the second growth condition is c2 is G under standard growth conditions. c0 It can also be considered that it is preferable that G c2 <G c0 By substituting equation (a) into equation (2), equation (2) can be derived.

[0108] Since the growth conditions for reducing the inclined interface 40i that is most inclined with respect to the c-plane 40c are the most stringent conditions, if the second growth conditions satisfy formula (2), it becomes possible to reduce the other inclined interfaces 40i as well.

[0109] Specifically, when the inclined interface 40i most inclined with respect to the c-plane 40c is the {10-11} plane, the second growth condition preferably satisfies the following formula (2'). G c2 <2.13G i (2')

[0110] Alternatively, for example, when the inclined interface 30i is a {11-2m} plane where m≧3, the inclined interface 30i most inclined with respect to the c-plane 30c is the {11-23} plane, and therefore, it is preferable that the second growth condition satisfies, for example, the following formula (2″): G c2 <1.47G i (2")

[0111] As the second growth condition of this embodiment, the growth temperature in the planarization step S300 is set to be higher than the growth temperature in the three-dimensional growth step S200. Specifically, the growth temperature in the planarization step S300 is set to be, for example, 990°C or higher and 1,120°C or lower, preferably 1,020°C or higher and 1,100°C or lower.

[0112] Furthermore, as a second growth condition of this embodiment, the V / III ratio in the planarization step S300 may be adjusted. For example, the V / III ratio in the planarization step S300 may be set smaller than the V / III ratio in the three-dimensional growth step S200. Specifically, the V / III ratio in the planarization step S300 is set to, for example, 1 or more and 10 or less, preferably 1 or more and 5 or less.

[0113] In practice, at least one of the growth temperature and the V / III ratio is adjusted within the above ranges as the second growth condition so as to satisfy the formula (2).

[0114] Other conditions among the second growth conditions of this embodiment are, for example, as follows. Growth pressure: 90 to 105 kPa, preferably 90 to 95 kPa GaCl gas partial pressure: 1.5 to 15 kPa N2 gas flow rate / H2 gas flow rate: 1 to 20

[0115] By epitaxially growing the planarization layer 40 made of a single crystal of a Group III nitride semiconductor on the three-dimensional growth layer 30 under the above-described second growth conditions, as shown in FIG. 5(b), it is possible to expand the c-plane 40c while reducing the inclined interface 40i other than the c-plane toward the top of the three-dimensional growth layer 30.

[0116] Specifically, by growing under the second growth conditions, the planarizing layer 40 grows from the inclined interface 30i of the inclined interface maintaining layer 34 in a direction perpendicular to the c-axis (i.e., in the longitudinal direction or lateral direction) with the inclined interface 40i as the growth plane. As the planarizing layer 40 grows laterally, the c-plane 40c of the planarizing layer 40 begins to be exposed again above the top portion 30t of the inclined interface maintaining layer 34. This results in the formation of a planarizing layer 40 in which the c-plane 40c and inclined interfaces 40i other than the c-plane are mixed on the surface.

[0117] As the planarization layer 40 continues to grow laterally, the c-plane 40c gradually expands and the inclined interfaces 40i of the planarization layer 40 gradually shrink. As a result, the recesses 30p formed by the multiple inclined interfaces 30i on the surface of the three-dimensionally grown layer 30 are gradually filled.

[0118] Thereafter, when the planarizing layer 40 is further grown, the inclined interfaces 40i of the planarizing layer 40 completely disappear, and the recesses 30p formed by the multiple inclined interfaces 30i on the surface of the three-dimensionally grown layer 30 are completely filled in. As a result, the surface of the planarizing layer 40 becomes a mirror surface (flat surface) formed only by the c-plane 40c.

[0119] In this case, dislocations are locally collected during the growth process of the three-dimensional growth layer 30 and the planarization layer 40, thereby reducing the dislocation density. Specifically, dislocations that propagate while bending in a direction inclined relative to the c-axis in the three-dimensional growth layer 30 continue to propagate in the same direction in the planarization layer 40. As a result, dislocations are locally collected at the meeting point of adjacent inclined interfaces 40i above the approximate center between a pair of apexes 30t in the planarization layer 40. Among the multiple dislocations collected at the meeting point of adjacent inclined interfaces 40i in the planarization layer 40, dislocations with opposite Burgers vectors disappear when they meet. In addition, some of the multiple dislocations collected at the meeting point of adjacent inclined interfaces 40i form loops, which suppress their propagation along the c-axis (i.e., toward the surface of the planarization layer 40). The remaining dislocations collected at the meeting points of adjacent inclined interfaces 40i in the planarizing layer 40 change their propagation direction again from a direction inclined with respect to the c-axis to a direction along the c-axis, and propagate to the surface side of the planarizing layer 40. By eliminating some of the dislocations in this way or suppressing the propagation of some of the dislocations toward the surface side of the planarizing layer 40, the dislocation density on the surface of the planarizing layer 40 can be reduced. Furthermore, by locally collecting dislocations, a low-dislocation density region can be formed above the portion of the planarizing layer 40 where the dislocations propagate in a direction inclined with respect to the c-axis.

[0120] At this time, in the planarization layer 40, the c-plane 40c gradually expands, and the c-plane growth region 60, which has grown using the c-plane 40c as the growth plane, is again formed while gradually expanding upward in the thickness direction.

[0121] On the other hand, in the planarization layer 40, as the inclined interface 40i gradually shrinks, the inclined interfacial growth region 70 gradually shrinks upward in the thickness direction and terminates at a predetermined position in the thickness direction. Due to this growth process of the planarization layer 40, valley portions 70a of the inclined interfacial growth region 70 are formed at positions where the c-plane 40c appears again in a cross-sectional view. Furthermore, as the recesses formed by the inclined interface 40i are gradually filled, peak portions 70b of the inclined interfacial growth region 70 are formed at positions where the inclined interface 40i disappeared in a cross-sectional view.

[0122] In the planarization process S300, the surface of the planarization layer 40 becomes a mirror surface composed only of the c-plane 40c, so that the height in the thickness direction of the planarization layer 40 (maximum height in the thickness direction) is, for example, equal to or greater than the height from the valley 30v to the peak 30t of the inclined interface maintaining layer 34.

[0123] A single cycle including the three-dimensional growth step S200 and the planarization step S300 forms a stacked unit 50 having a three-dimensional growth layer 30 and a planarization layer 40. In the following, the portion including the c-plane growth region 60 below the inclined interfacial growth region 70 and the inclined interfacial growth region 70, excluding the c-plane growth region 60 above the inclined interfacial growth region 70, may also be referred to as the stacked unit 50. The stacked unit 50 formed in the first cycle may also be referred to as the "first stacked unit 51."

[0124] (S400: execution count determination process) After the first cycle is completed, the number of times the cycle including the three-dimensional growth step S200 and the planarization step S300 has been performed is determined.

[0125] When the number of times of execution is less than the predetermined number N (No in S400), the cycle including the three-dimensional growth step S200 and the planarization step S300 is repeated as follows.

[0126] (S200: 3D growth process) In the second and subsequent cycles, as shown in Fig. 6(a), a three-dimensionally grown layer 30 is grown again on the planarizing layer 40 of the first stack unit 51. At this time, the three-dimensionally grown layer 30 is grown under the same first growth conditions as those in the three-dimensional growth step S200 of the first cycle.

[0127] In the three-dimensional growth step S200 of the second or subsequent cycles, similarly to the three-dimensional growth step S200 of the first cycle, for example, the inclined interface expansion step S220 and the inclined interface maintenance step S240 are performed.

[0128] (S220: Inclined interface expansion process) As shown in FIG. 6( a ), 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 planarization layer 40 of the first stack unit 51 .

[0129] In the second and subsequent cycles, in the initial stage of growth of the inclined interface expansion layer 32, the inclined interface expansion layer 32 is grown with the c-plane 30c as the growth plane in the normal direction (direction along the c-axis) to the surface of the planarization layer 40 of the first stack unit 51. That is, in the initial stage of the cycle as well, the above-mentioned initial layer is grown over the entire planarization layer 40 of the first stack unit 51 with the c-plane 30c as the growth plane.

[0130] Then, by gradually growing the inclined interface expansion layer 32 under the first growth conditions, a plurality of recesses 30p consisting of inclined interfaces 30i other than the c-plane are formed on the top surface 30u of the inclined interface expansion layer 32, which exposes the c-plane 30c, and the c-plane 30c is eliminated at least once. As a result, a plurality of valleys 30v and a plurality of peaks 30t are formed on the surface of the inclined interface expansion layer 32.

[0131] In the second and subsequent cycles, the recesses 30p are also formed randomly on the top surface 30u of the inclined interface expansion layer 32. For this reason, in a plan view, the positions of the valleys 30v and peaks 30t on the surface of the inclined interface expansion layer 32 in the second and subsequent cycles do not necessarily coincide with the positions of the valleys 30v and peaks 30t on the surface of the inclined interface expansion layer 32 in the first cycle.

[0132] Due to the above-described growth process of the inclined interface expansion layer 32, dislocations again bend and propagate as follows. Specifically, as shown in FIG. 6( a), the multiple dislocations remaining on the surface of the planarization layer 40 of the first stack unit 51 propagate from the planarization layer 40 of the first stack unit 51 in a direction along the c-axis of the inclined interface expansion layer 32. In the region of the inclined interface expansion layer 32 grown using the c-plane 30c as the growth plane, dislocations propagate from the planarization layer 40 of the first stack unit 51 in a direction along the c-axis of the inclined interface expansion layer 32. However, when the growth interface where the dislocations are exposed in the inclined interface expansion layer 32 changes from the c-plane 30c to the inclined interface 30i, the dislocations bend and propagate in a direction approximately perpendicular to the inclined interface 30i. That is, the dislocations again bend and propagate in a direction inclined with respect to the c-axis. As a result, in the second and subsequent cycles, dislocations are locally collected above the approximate center between the pair of apexes 30t.

[0133] In this case, in the inclined interface expansion step S220 of the second or subsequent cycle, the average distance L between nearest-neighbor apexes is set longer than that in the inclined interface expansion step S220 of the first cycle when viewed in any cross section perpendicular to the main surface 10s of the base substrate 10. This makes it possible to make the distance over which dislocations bend and propagate longer in the second or subsequent cycle than in the first cycle. As a result, non-overlapping 50 μm square dislocation-free regions can be easily formed on the surface of the flattening layer 40 in the second or subsequent cycle, thereby increasing the density of the dislocation-free regions.

[0134] Furthermore, in the inclined interface expansion step S220 in each of the multiple cycles, the average distance L between the nearest apexes is gradually increased, for example, as the multiple cycles are repeated. This allows the distance over which dislocations bend and propagate to gradually increase as the multiple cycles are repeated. As a result, the dislocation-free region on the surface of the planarizing layer 40 can be gradually widened, or the density of the dislocation-free region on the surface of the planarizing layer 40 can be gradually increased as the multiple cycles are repeated.

[0135] Also, in the inclined interface expansion step S220 in each of the second and subsequent cycles, similar to the first cycle, the average distance L between the nearest apexes is set to, for example, at least 100 μm when viewing any cross section perpendicular to the main surface 10s of the base substrate 10. This allows dislocations to be sufficiently concentrated above the approximate center between a pair of apexes 30t of the three-dimensionally grown layer 30, similar to the first cycle.

[0136] Furthermore, in the inclined interface expansion step S220 of at least the last cycle among the multiple cycles, it is preferable to set the average distance L between nearest apexes to, for example, more than 200 μm when viewing any cross section perpendicular to the main surface 10s of the base substrate 10. This ensures that the distance over which dislocations bend and propagate is at least more than 100 μm in the steps following the inclined interface expansion step S220 of the last cycle. As a result, a dislocation-free region measuring at least 100 μm square can be formed on at least a portion of the surface of the planarization layer 40 in the last cycle.

[0137] In this case, it is preferable that the average distance L between the nearest apexes is set to, for example, less than 800 μm in the inclined interface expansion step S220 of the second or subsequent cycles, so that the planarization layer 40 can be quickly mirror-finished in the planarization step S300 of the second or subsequent cycles.

[0138] (S240: Inclined interface maintenance process) In the second and subsequent cycles, after the c-plane 30c disappears from the surface of the inclined interface expansion layer 32, the growth conditions in the inclined interface maintaining step S240 are maintained at the first growth conditions described above, similar to the inclined interface expansion step S220.

[0139] 6(b), the three-dimensional growth layer 30 continues to grow to a predetermined thickness while maintaining the inclined interface growth region 70 occupying 80% or more of the surface cross section. As a result, an inclined interface maintaining layer 34 is formed on the inclined interface enlarging layer 32.

[0140] By the three-dimensional growth step S200 of the second and subsequent cycles, the three-dimensional growth layer 30 having the gradient interface enlarging layer 32 and the gradient interface maintaining layer 34 is formed again.

[0141] (S300: Flattening process) In the second and subsequent cycles, once the three-dimensionally grown layer 30 has been grown with the c-plane 30c having disappeared at least once, a planarization layer 40 made of a single crystal of a Group III nitride semiconductor is epitaxially grown on the three-dimensionally grown layer 30, as shown in Fig. 7. At this time, the planarization layer 40 is grown under the same second growth conditions as in the planarization step S300 of the first cycle. As a result, the c-plane 40c expands upward in the three-dimensionally grown layer 30, while the inclined interface 40i other than the c-plane shrinks.

[0142] Thereafter, when the planarizing layer 40 is further grown, the inclined interfaces 40i of the planarizing layer 40 completely disappear, and the recesses 30p formed by the multiple inclined interfaces 30i on the surface of the three-dimensionally grown layer 30 are completely filled in. As a result, the surface of the planarizing layer 40 becomes a mirror surface (flat surface) formed only by the c-plane 40c.

[0143] At this time, in the second and subsequent cycles, the dislocation density can be further reduced by locally collecting dislocations during 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 below the dislocation density on the surface of the flattening layer 40 in the first cycle.

[0144] In this way, by repeating the cycle including the three-dimensional growth step S200 and the planarization step S300 multiple times, the dislocation density can be gradually reduced depending on the number of times the cycle is repeated.

[0145] By the second or subsequent cycles including the three-dimensional growth step S200 and the planarization step S300, a stacked unit 50 having a three-dimensional growth layer 30 and a planarization layer 40 is again formed. Note that, hereinafter, the stacked unit 50 formed by the second cycle may also be referred to as a "second stacked unit 52."

[0146] (S400: execution count determination process) After the second cycle is completed, the number of times the cycle including the three-dimensional growth step S200 and the planarization step S300 has been performed is determined again.

[0147] When the number of times of execution reaches a predetermined N times (Yes in S400), the cycle including the three-dimensional growth step S200 and the planarization step S300 is ended.

[0148] The number of cycles performed is, for example, between two and five. By performing the cycle two or more times, the dislocation reduction effect due to repeated cycles can be sufficiently obtained. On the other hand, the dislocation reduction effect is not dramatically observed until the third cycle, and after the third cycle, the dislocation reduction effect becomes more difficult to obtain with each increase in the number of cycles. For this reason, it is preferable to perform the cycle five or less times.

[0149] In this embodiment, the cycle ends when N=2, for example.

[0150] In the final cycle, the c-plane growth region in which the c-plane 40c of the planarizing layer 40 gradually expands and grows becomes part of an uppermost c-plane growth region 80, which will be described later.

[0151] (S500: Main growth process (c-plane growth process)) After the planarization step S300 of the final cycle, as shown in FIG. 8, a main growth layer 44 is formed to a predetermined thickness on the planarization layer 40 whose surface has been mirror-finished, with the c-plane as the growth surface.

[0152] At this time, the growth conditions in the main growth step S500 are maintained at the second growth conditions described above, similar to the planarization step S300 in each cycle described above, thereby enabling the main growth layer 44 to be grown by step flow growth using the c-plane as the growth surface.

[0153] In this case, 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 underlying substrate 10. This makes it possible to make the variation in the off-angle of the c-axis of the main growth layer 44 relative to the normal to the surface smaller than the variation in the off-angle of the c-axis 10ca of the underlying substrate 10 relative to the normal to the main surface 10s.

[0154] At this time, the main growth layer 44 is grown using only the c-plane as the growth surface without exposing the inclined interface 40i, so that the entire main growth layer 44 becomes an uppermost c-plane growth region 80, which will be described later.

[0155] In the main growth step S500, the thickness of the main growth layer 44 is set to, for example, 300 μm or more and 10 mm or less. By setting the thickness of the main growth layer 44 to 300 μm or more, at least one substrate 100 can be sliced ​​from the main growth layer 44 in the slicing step S600 described below. On the other hand, by setting the thickness of the main growth layer 44 to 10 mm, the final thickness is set to 650 μm, and when slicing 700 μm-thick substrates 100 from the main growth layer 44, at least 10 substrates 100 can be obtained, even taking into account a kerf loss of approximately 200 μm.

[0156] Through the steps from the three-dimensional growth step S200 to the main growth step S500 in the first cycle, the laminated structure 90 of this embodiment is formed.

[0157] The steps from the three-dimensional growth step S200 to the main growth step S500 of the first cycle are performed continuously in the same chamber without exposing the base substrate 10 to the atmosphere. This makes it possible to prevent the formation of unintended high-oxygen concentration regions (regions having an oxygen concentration excessively higher than that of the inclined interface growth region 70) at the interface between the three-dimensional growth layer 30 and the planarization layer 40, the interface between each stacking unit 50, the interface between the planarization layer 40 and the main growth layer 44, and the like.

[0158] (S600: Slicing process) 9, the main growth layer 44 is sliced ​​using, for example, a wire saw along a cutting plane substantially parallel to the surface of the main growth layer 44. This forms at least one nitride semiconductor substrate 100 (also referred to as substrate 100) as an as-sliced ​​substrate. At this time, the thickness of the substrate 100 is set to, for example, 300 μm or more and 700 μm or less.

[0159] At this time, 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 underlying substrate 10. Note that at this time, 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. This makes it possible to make the variation in the off-angle θ of the c-axis 100ca with respect to the normal to the main surface 100s of the substrate 100 smaller than the variation in the off-angle of the c-axis 10ca of the underlying substrate 10.

[0160] (S700: Polishing process) Next, a polishing device is used to polish both surfaces of the substrate 100. At this time, the final thickness of the substrate 100 is set to, for example, 250 μm or more and 650 μm or less.

[0161] Through the above steps S100 to S700, the substrate 100 according to this embodiment is manufactured.

[0162] (Process for manufacturing semiconductor laminates and process for manufacturing semiconductor devices) After the substrate 100 is manufactured, a semiconductor functional layer made of, for example, a Group III nitride semiconductor is epitaxially grown on the substrate 100 to produce a semiconductor laminate. After the semiconductor laminate is produced, electrodes and the like are formed using the semiconductor laminate, and the semiconductor laminate is diced to cut out chips of a predetermined size. In this way, a semiconductor device is produced.

[0163] (2) Laminated structure Next, a laminated structure 90 according to this embodiment will be described with reference to FIG.

[0164] The stacked structure 90 of this embodiment includes, for example, a base substrate 10, a plurality of stacked units 50, and an uppermost c-plane growth region (uppermost low oxygen concentration region) 80.

[0165] A plurality of stacked units 50 are provided repeatedly in the thickness direction, for example, between the base substrate 10 and the uppermost c-plane growth region 80. Each of the plurality of stacked units 50 has, for example, a c-plane growth region (low oxygen concentration region 60) and an inclined interface growth region (high oxygen concentration region) 70.

[0166] The c-plane growth region 60 is a region grown using the c-plane 30c as the growth plane. In the c-plane growth region 60, oxygen uptake is suppressed compared to 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 Less than or equal to 3 x 10 16 cm -3 The following is the result.

[0167] 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 during 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.

[0168] The c-plane growth region 60 has, for example, multiple valleys 60a and multiple peaks 60b in a cross-sectional view. The valleys 60a and peaks 60b herein refer to portions of the shape observed based on differences in luminescence intensity when the cross-section of the stacked structure 90 is observed with a fluorescent microscope or the like, and do not refer to portions of the shape of the outermost surface generated during the growth of the three-dimensionally grown layer 30. Each of the multiple valleys 60a is a downwardly convex inflection point in the c-plane growth region 60 in a cross-sectional view, and is formed at a position where an inclined interface 30i occurs. At least one of the multiple valleys 60a is located above and spaced apart from the major surface 10s of the base substrate 10. Meanwhile, each of the multiple peaks 60b is an upwardly convex inflection point in the c-plane growth region 60 in a cross-sectional view, and is formed at a position where the c-plane 30c (finally) disappears and terminates, sandwiching a pair of inclined interfaces 30i that expand in opposite directions. The valleys 60a and peaks 60b are formed alternately in a direction along the major surface 10s of the base substrate 10.

[0169] When viewing any cross section perpendicular to the main surface 10s of the base substrate 10, the average distance between the pair of closest peaks 60b, sandwiching one of the valleys 60a, in a direction along the main surface 10s of the base substrate 10 corresponds to the average distance L between the closest peaks of the three-dimensionally grown layer 30 described above, and is, for example, greater than 100 μm. Hereinafter, this distance will also be referred to as the "average distance between closest peaks."

[0170] The c-plane growth region 60 has a pair of inclined portions 60i on either side of one of the multiple peaks 60b, the inclined portions 60i being provided as the locus of intersections between the c-plane 30c and the inclined interfaces 30i. Note that the inclined portions 60i here refer to a part of the shape observed based on the difference in luminescence intensity when the cross section of the stacked structure 90 is observed with a fluorescent microscope or the like, and do not refer to the inclined interfaces 30i on the outermost surface that are generated during the growth of the three-dimensional growth layer 30.

[0171] The angle formed by the pair of inclined portions 60i when viewed from a cross section passing through the center of each of two adjacent valleys 60a is, for example, 70° or less, preferably 20° to 65°. The angle formed by the pair of inclined portions 60i being 70° or less is a factor that, under the first growth condition, the growth rate G i The growth rate G of the c-plane 30c of the three-dimensional growth layer 30 c1 The ratio G c1 / G i This means that the angle between the pair of inclined portions 60i and the c-plane was high. This facilitates the formation of inclined interfaces 30i other than the c-plane. As a result, dislocations can be easily bent at the positions where the inclined interfaces 30i are exposed. Furthermore, by setting the angle between the pair of inclined portions 60i to 70° or less, multiple valleys 30v and multiple peaks 30t can be easily formed above the major surface 10s of the base substrate 10. Furthermore, by setting the angle between the pair of inclined portions 60i to 65° or less, inclined interfaces 30i other than the c-plane can be more easily formed, and multiple valleys 30v and multiple peaks 30t can be more easily formed above the major surface 10s of the base substrate 10. Note that by setting the angle between the pair of inclined portions 60i to 20° or more, the height from the valleys 30v to the peaks 30t of the three-dimensionally grown layer 30 can be prevented from increasing, and the thickness of the planarization layer 40 required to achieve a mirror finish can be prevented from increasing.

[0172] On the other hand, the inclined interface growth region 70 is a region grown using the inclined interface 30i or the inclined interface 40i as a growth surface. The inclined interface growth region 70 is more likely to take in oxygen than the c-plane growth region 60 and the uppermost c-plane growth region 80 described below. Therefore, the oxygen concentration in the inclined interface growth region 70 is higher than the oxygen concentrations in the c-plane growth region 60 and the uppermost c-plane growth region 80, respectively. Note that the oxygen taken in the inclined interface growth region 70 may be, for example, oxygen unintentionally mixed into the vapor phase growth apparatus or oxygen released from components (such as quartz components) constituting the vapor phase growth apparatus. Specifically, the oxygen concentration in the inclined interface growth region 70 may be, for example, 9×10 17 cm -3 5x10 or more 19cm -3 The following is the result.

[0173] The inclined interfacial growth region 70 is provided, for example, on the c-plane growth region 60 in the stack unit 50 of the same layer. The inclined interfacial growth region 70 is provided continuously along the main surface 10s of the base substrate 10. That is, when multiple cross sections of the three-dimensional growth layer 30 cut along the main surface 10s of the base substrate 10 are viewed, it is desirable that at least a portion of the three-dimensional growth layer 30 in the thickness direction does not include a c-plane growth region grown using the c-plane 30c as the growth surface.

[0174] 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 stack unit 50 of the same layer.

[0175] The upper surface of the inclined interfacial growth region 70 has, for example, a plurality of valleys 70a and a plurality of peaks 70b in a cross-sectional view. The valleys 70a and peaks 70b herein refer to portions of the shape observed based on differences in luminescence intensity when the cross section of the stacked structure 90 is observed with a fluorescent microscope or the like, and do not refer to portions of the shape of the outermost surface generated during the growth of the planarization layer 40. As described above, the plurality of valleys 70a of the inclined interfacial growth region 70 are formed at positions where the c-plane 40c reappears in a cross-sectional view. Furthermore, the plurality of valleys 70a of the inclined interfacial growth region 70 are each formed above the plurality of peaks 60b of the c-plane growth region 60 in a cross-sectional view. Meanwhile, the plurality of peaks 70b of the inclined interfacial growth region 70 are each formed at positions where the inclined interface 40i disappears and terminates in a cross-sectional view. Furthermore, the plurality of peaks 70b of the inclined interfacial growth region 70 are each formed above the plurality of valleys 60a of the c-plane growth region 60 in a cross-sectional view.

[0176] Furthermore, the boundary surface along the main surface 10s of the base substrate 10 at the upper end of the inclined interfacial growth region 70 is the boundary surface between the laminate units 50, and is the boundary surface at the position where the inclined interface 40i disappears and terminates. Hereinafter, the boundary surface along the main surface 10s of the base substrate 10 at the upper end of the inclined interfacial growth region 70 of a given laminate unit 50 will also be simply referred to as the "boundary surface of the laminate unit 50."

[0177] The c-plane growth region 60 in the second or higher layer stack unit 50 is provided on, for example, the inclined interface growth region 70 in the lower layer stack unit 50.

[0178] The top c-plane growth region 80 is provided, for example, on the graded interfacial growth region 70 in the top stack unit 50 .

[0179] The uppermost c-plane growth region 80 is a region grown using the c-plane as the growth plane. In the uppermost c-plane growth region 80, oxygen uptake is suppressed compared to 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, similar to the oxygen concentration in the c-plane growth region 60. 16 cm -3 Less than or equal to 3 x 10 16 cm -3 The following is the result.

[0180] Here, in this embodiment, when viewing any cross section perpendicular to the main surface 10s of the base substrate 10, the average distance between the nearest neighboring peaks in the second or higher layer stacked units 50 among the multiple stacked units 50 is longer than that of the first layer stacked unit 50, for example.

[0181] Furthermore, in this embodiment, when viewing any cross section perpendicular to the main surface 10s of the base substrate 10, the average distance between the closest peaks in each of the multiple stacked units 50 gradually increases, for example, as one moves toward the upper layers of the multiple stacked units 50.

[0182] Furthermore, in this embodiment, during the growth process of the three-dimensionally grown layer 30 in each cycle, dislocations bend and propagate in a direction approximately perpendicular to the inclined interface 30i at positions where the inclined interface 30i other than the c-plane is exposed, so that in the flattening layer 40, some of the multiple dislocations disappear or are suppressed from propagating toward the surface side of the c-plane expansion layer 42. As a result, the dislocation density at the boundary surface of each stacking unit 50 is reduced compared to the dislocation density at the main surface 10s of the base substrate 10.

[0183] Furthermore, in this embodiment, even in the second and subsequent cycles, dislocations are locally collected during the growth process of the three-dimensional growth layer 30 and the planarization layer 40, so that the dislocation density at the interface of the second or higher layer stacking unit 50 is lower than the dislocation density at the interface of the first layer stacking unit 50.

[0184] In this embodiment, the cycle including the three-dimensional growth step S200 and the planarization step S300 is repeated multiple times, so that the dislocation density is gradually reduced according to the number of times the cycle is repeated. Specifically, the dislocation density at the interface between each of the multiple stacked units 50 is gradually reduced toward the upper layer of the multiple stacked units 50.

[0185] As a result, in this embodiment, the dislocation density is rapidly reduced in the thickness direction.

[0186] Here, the dislocation density at the main surface 10s of the base substrate 10 is set to N0, and the dislocation density (average dislocation density) at the boundary surface of the uppermost stacked unit 50 is set to N. On the other hand, when a crystal layer of a Group III nitride semiconductor is epitaxially grown on the main surface 10s of the base substrate 10 using only the c-plane as the growth plane to a thickness equal to the thickness from the main surface 10s of the base substrate 10 of this embodiment to the boundary surface of the uppermost stacked unit 50 (hereinafter also referred to as "c-plane thick film growth (c-plane limited growth)"), the dislocation density at the surface of the crystal layer is set to N'.

[0187] In the case of c-plane thick film growth, the dislocation density at the surface of the crystal layer tended to be inversely proportional to the thickness of the crystal layer. Specifically, in the case of c-plane thick film growth, the reduction rate of dislocation density calculated as N' / N0 was approximately 0.5 when the crystal layer thickness was 2 mm.

[0188] In contrast, in this embodiment, the reduction rate of dislocation density calculated by N / N0 is smaller than the reduction rate of dislocation density calculated by N' / N0 in the case of c-plane thick film growth, for example.

[0189] Specifically, in this embodiment, the thickness per layer of the multilayer unit 50 is, for example, more than 200 μm and 1.5 mm or less, preferably 1.2 mm or less. When the number of layers in the multilayer unit 50 is two, the thickness from the main surface 10s of the base substrate 10 to the boundary surface of the second multilayer unit 52 is, for example, 3 mm or less, preferably 2.4 mm or less. In this case, the reduction rate of dislocation density calculated by the above-mentioned N / N0 is, for example, 0.15 or less, preferably 0.10 or less, and more preferably 0.08 or less.

[0190] In this embodiment, the lower limit of the reduction rate of dislocation density is not limited, as the smaller the reduction rate, the better. 6 cm -2 When the base substrate 10 is used, the average dislocation density at the interface of the second stacked unit 52 is set to 10 3 cm -2 Therefore, the reduction rate of dislocation density is, for example, 3 × 10 -4 That's all.

[0191] Additionally, in this embodiment, the entire surface of the stacked structure 90 is configured to be aligned to the +c-plane, and each stacked unit 50 and the uppermost c-plane growth region 80 do not include inversion domains. In this respect, the stacked structure 90 of this embodiment differs from stacked structures formed by the so-called DEEP (Dislocation Elimination by the Epitaxial-growth with inverse-pyramidal pits) method, i.e., from stacked structures that include inversion domains in the cores located at the centers of the pits.

[0192] (3) Nitride semiconductor substrates (freestanding nitride semiconductor substrates, nitride crystal substrates) Next, a nitride semiconductor substrate 100 according to this embodiment will be described with reference to Figure 12. Figure 12(a) is a schematic top view showing the nitride semiconductor substrate according to this embodiment, (b) is a schematic cross-sectional view of the nitride semiconductor substrate according to this embodiment taken along the m-axis, and (c) is a schematic cross-sectional view of the nitride semiconductor substrate according to this embodiment taken along the a-axis. The direction along the m-axis is defined as the x-direction, and the direction along the a-axis is defined as the y-direction.

[0193] In this embodiment, the substrate 100 obtained by slicing the main growth layer 44 by the above-described manufacturing method is, for example, a free-standing substrate made of a single crystal of a group III nitride semiconductor. In this embodiment, the substrate 100 is, for example, a free-standing GaN substrate.

[0194] The diameter of the substrate 100 is, for example, 2 inches or more, and the thickness of the substrate 100 is, for example, 300 μm or more and 1 mm or less.

[0195] The conductivity of the substrate 100 is not particularly limited. However, when the substrate 100 is used to manufacture a semiconductor device as a vertical Schottky barrier diode (SBD), the substrate 100 is, for example, n-type, and 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 Over 1.0 x 1020 cm -3 The following is the result.

[0196] The substrate 100 has, for example, a primary surface 100s that serves as an epitaxial growth surface. In this embodiment, the crystal plane with a low index closest to the primary surface 100s is, for example, the c-plane 100c.

[0197] The main surface 100s of the substrate 100 is, for example, mirror-finished, and the root mean square roughness RMS of the main surface 100s of the substrate 100 is, for example, less than 1 nm.

[0198] Furthermore, in this embodiment, the impurity concentration in the substrate 100 obtained by the above-described manufacturing method is lower than that of a substrate obtained by the flux method or ammonothermal method.

[0199] Specifically, the hydrogen concentration in the substrate 100 is, for example, 1×10 17 cm -3 Less than 5 x 10 16 cm -3 The following is the result.

[0200] In this embodiment, the substrate 100 is formed by slicing the main growth layer 44 grown using the c-plane 40c as the growth plane, and therefore does not include the inclined interface growth region 70 grown using the inclined interface 30i or the inclined interface 40i as the growth plane. In other words, the entire substrate 100 is composed of a low-oxygen concentration region.

[0201] Specifically, the oxygen concentration in the substrate 100 is, for example, 5×10 16 cm -3 Less than or equal to 3 x 10 16 cm -3 The following is the result.

[0202] In this embodiment, the substrate 100 does not include, for example, an inversion domain, as described above.

[0203] (Curving of the c-plane and variation in off-angle) As shown in Figures 12(b) and (c), in this embodiment, the c-plane 100c, which is the low-index crystal plane closest to the primary surface 100s of the substrate 100, is curved in a concave spherical shape relative to the primary surface 100s, for example, due to the manufacturing method of the substrate 100 described above.

[0204] In this embodiment, the c-plane 100c of the substrate 100 has a curved surface that is approximated as a sphere in both the cross section along the m-axis and the cross section along the a-axis.

[0205] In this embodiment, since the c-plane 50f of the substrate 100 is curved into a concave spherical shape as described above, at least a portion of the c-axes 100ca are inclined with respect to the normal to the main surface 100s. The off-angle θ, which is the angle that the c-axis 100ca makes with respect to the normal to the main surface 100s, has a predetermined distribution within the main surface 100s.

[0206] Of the off-angle θ of the c-axis 100ca relative to the normal to the main surface 100s, the directional component along the m-axis is referred to as "θ m " and the direction component along the a-axis is "θ a ". Note that θ 2 =θ m 2 +θ a 2 is.

[0207] In this embodiment, since the c-plane 100c of the substrate 100 is curved into a concave spherical shape as described above, the off-angle m-axis component θ m and the off-axis component θ a can be approximately expressed as a linear function of x and a linear function of y, respectively.

[0208] Specifically, for example, X-ray rocking curves of the (0002) plane are measured at each position on a line passing through the center of the main surface 100s. When the peak value of the angle ω between the X-rays incident on the main surface 100s and the main surface 100s (hereinafter also referred to as the peak angle ω) is plotted against the position on the line, the peak angle ω can be approximated by a linear function of the position. Note that the "peak angle ω" here refers to the angle between the X-rays incident on the main surface 100s and the main surface 100s, and is the angle at which the diffraction intensity is maximized. The radius of curvature of the c-plane 100c can be calculated from the reciprocal of the slope of the linear function approximated as described above.

[0209] In this embodiment, the radius of curvature of the c-face 100c of the substrate 100 is greater than, for example, the radius of curvature of the c-face 10c of the base substrate 10 used in the method for manufacturing the substrate 100 described above.

[0210] Specifically, 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.

[0211] For reference, even in the case of c-plane thick film growth, the radius of curvature of the c-plane of a substrate sliced ​​from a crystal layer having the same thickness as the thickness from main surface 10s of base substrate 10 of this embodiment to the boundary surface of the uppermost stack unit 50 may be larger than the radius of curvature of c-plane 10c of base substrate 10. However, in the case of c-plane thick film growth, when the crystal layer is 2 mm thick, the radius of curvature of the c-plane of a substrate sliced ​​from the crystal layer is approximately 11 mm, which is about 1.4 times the radius of curvature of c-plane 10c of base substrate 10.

[0212] In this embodiment, the upper limit of the radius of curvature of the c-face 100c of the substrate 100 is not particularly limited, and the larger the radius, the better. When the c-face 100c of the substrate 100 is substantially flat, the radius of curvature of the c-face 100c can be considered to be infinite.

[0213] In addition, in this embodiment, since the radius of curvature of the c-plane 100c of the substrate 100 is large, the variation in the off-angle θ of the c-axis 100ca relative to the normal to the main surface 100s of the substrate 100 can be made smaller than the variation in the off-angle of the c-axis 10ca of the base substrate 10.

[0214] Specifically, when an X-ray rocking curve measurement is performed on the (0002) plane of the substrate 100 and the off-angle θ of the c-axis 100ca relative to the normal to the main surface 100s is measured based on the diffraction peak angle of the (0002) plane, the variation calculated as the maximum and minimum difference in the magnitude of the off-angle θ within a diameter of 2 inches (50.8 mm) from the center of the main surface 100s is, for example, 0.127° or less, preferably 0.097° or less, and more preferably 0.073° or less.

[0215] For reference, in base substrate 10 produced by the above-mentioned VAS method, the variation in the off-angle of c-axis 10ca determined by the above-mentioned measurement method is approximately 0.38°. Furthermore, in the case of c-plane thick film growth, when the thickness of the crystal layer is set to the same thickness (e.g., 2 mm) as the thickness from main surface 10s of base substrate 10 of this embodiment to the boundary surface of the uppermost stack unit 50, the variation in the off-angle of the c-axis determined by the above-mentioned measurement method in nitride semiconductor substrates obtained from that crystal layer is approximately 0.26°.

[0216] In this embodiment, the lower limit of the variation in the off-angle θ of the c-axis 100ca of the substrate 100 is not particularly limited, and the smaller the better. When the c-plane 100c of the substrate 100 is substantially flat, the variation in the off-angle θ of the c-axis 100ca of the substrate 100 can be considered to be 0°.

[0217] Furthermore, in this embodiment, the curvature of the c-plane 100c is isotropically reduced relative to the main surface 100s of the substrate 100, so the directional dependency of the radius of curvature of the c-plane 100c is small.

[0218] Specifically, the difference between the absolute value of the radius of curvature of the c-face 100c in the direction along the a-axis, as determined by the above-mentioned measurement method, and the absolute value of the radius of curvature of the c-face 100c in the direction along the m-axis, is, for example, 90% or less, preferably 50% or less, and more preferably 20% or less of the larger of these values.

[0219] Furthermore, in this embodiment, when the peak angle ω is approximated by a linear function of the position on the main surface 100s in an X-ray rocking curve measurement of the c-plane 100c, the error of ω relative to the linear function of the position is small. The error of ω in this embodiment can be made smaller than that of a substrate obtained from a crystal layer grown on a base substrate patterned by an ELO method using a mask layer, or a substrate obtained from a planarized layer when the c-plane is not lost in a three-dimensional growth process with a single cycle.

[0220] Specifically, the error of the measured peak angle ω relative to the linear function approximated as described above is, for example, 0.05° or less, preferably 0.02° or less, and more preferably 0.01° or less. Note that, since at least some peak angles ω may coincide with the linear function, the minimum value of the error is 0°.

[0221] (scotoma) Next, a description will be given of dark spots on the main surface 100s of the substrate 100 of this embodiment. Note that the term "dark spots" used here refers to points of low luminescence intensity observed in an observation image of the main surface 100s using a multiphoton excitation microscope or in a cathodoluminescence image of the main surface 100s, and includes not only dislocations but also non-luminescent centers caused by foreign matter or point defects. Note that a "multiphoton excitation microscope" is sometimes called a two-photon excitation fluorescence microscope.

[0222] In this embodiment, substrate 100 is manufactured using base substrate 10 made of high-purity GaN single crystal produced by the VAS method, and therefore there are few non-radiative centers caused by foreign matter or point defects in substrate 100. Therefore, when the primary surface of substrate 100 is observed using a multiphoton excitation microscope or the like, 95% or more, preferably 99% or more, and more preferably 100% of the dark spots are dislocations rather than non-radiative centers caused by foreign matter or point defects.

[0223] Furthermore, in this embodiment, the above-described manufacturing method reduces the dislocation density on the surface of the main growth layer 44 compared to the dislocation density on the main surface 10s of the base substrate 10. As a result, dislocations are also reduced on the main surface 100s of the substrate 100 formed by slicing the main growth layer 44.

[0224] Furthermore, in this embodiment, the three-dimensional growth process S200 and the like are performed using the base substrate 10 in an unpatterned state by the above-described manufacturing method, so that on the main surface 100s of the substrate 100 formed by slicing the growth layer 44, no regions with excessively high dislocation density are formed due to the patterning of the base substrate 10, and regions with low dislocation density are uniformly formed.

[0225] Specifically, in this embodiment, when the main surface 100s of the substrate 100 is observed with a multiphoton excitation microscope in a field of view of 250 μm square and the dislocation density is calculated from the dark spot density, the dislocation density is 3×10 6 cm -2 There is no region where the dislocation density exceeds 1×10 6 cm -2 The area where this is less than 80% or more of the main surface 100s, preferably 90% or more, and more preferably 95% or more.

[0226] In addition, when the manufacturing method of this embodiment is used, the dislocation density is 1×10 6 cm -2 The upper limit for the percentage of regions that are less than this is 100%.

[0227] Furthermore, in this embodiment, by repeating a cycle including the three-dimensional growth step S200 and the planarization step S300 multiple times, the dislocation density in the main surface 100s of the substrate 100 is reduced in accordance with the number of times the cycle is repeated. That is, the dislocation density in the main surface 100s of the substrate 100 in this embodiment is reduced compared to the dislocation density in the main surface of a substrate formed by slicing the grown layer when only one cycle is performed.

[0228] Specifically, in this embodiment, when the main surface 100s of the substrate 100 is observed with a multiphoton excitation microscope in a field of view of 250 μm square and the dislocation density is calculated from the dark spot density, the dislocation density is 1×10 6 cm -2 There is no region where the dislocation density is 7×10 5 cm -2 The area where this is less than 80% or more of the main surface 100s, preferably 90% or more, and more preferably 95% or more.

[0229] In addition, when the manufacturing method of this embodiment is used, the dislocation density is 7×10 5 cm -2 The upper limit for the percentage of regions that are less than this is 100%.

[0230] In this embodiment, the dislocation density averaged over the entire main surface 100s of the substrate 100 is, for example, 7×10 5 cm -2 less than 5.5 x 10 5 cm -2 and more preferably less than 3×10 5 cm -2 The following is the result.

[0231] Furthermore, the main surface 100s of the substrate 100 of this embodiment includes dislocation-free regions of at least 50 μm square, for example, based on the average distance L between nearest apexes in the above-mentioned three-dimensional growth step S200.

[0232] In this embodiment, the dislocation density is reduced over the entire main surface 100s of the substrate 100, so that 50 μm square dislocation-free regions are scattered over the entire main surface 100s of the substrate 100, for example.

[0233] In this embodiment, multiple cycles are performed, and the average distance L between the nearest apexes in each cycle is made longer than that in the first cycle, thereby increasing the density of dislocation-free regions. Specifically, the main surface 100s of the substrate 100 has, for example, 100 dislocation-free regions of 50 μm square that do not overlap each other at a density of 100 / cm. 2 More than 1000 particles / cm 2 More preferably, 1600 particles / cm 2 More preferably, 4800 particles / cm 2 More than 10,000 particles / cm, most preferably 10,000 particles / cm 2 It has a density of more than 10 ...

[0234] The upper limit of the density of dislocation-free regions in a 50 μm square that do not overlap is 40,000 / cm based on the measurement method. 2 is.

[0235] In this embodiment, by setting the average distance L between nearest apexes to more than 200 μm in at least the last cycle of the inclined interface expansion step S220 among the multiple cycles, at least a portion of the main surface 100s of the substrate 100 has, for example, dislocation-free regions of at least 100 μm square. The main surface 100s of the substrate 100 has, for example, 100 dislocation-free regions of non-overlapping 100 μm squares at a density of 100 / cm. 2 More than 250 particles / cm 2 It has a density of more than 10 ...

[0236] The upper limit of the density of dislocation-free regions in a 100 μm square that do not overlap is 10,000 / cm based on the measurement method. 2 is.

[0237] Furthermore, in this embodiment, even in regions other than the dislocation-free regions (for example, between a pair of adjacent dislocation-free regions), dislocations are not excessively concentrated, and the dislocation density is low. Specifically, the number of dislocations present in the quadrangular region sandwiched between the opposing sides of the closest pair of 50-μm square dislocation-free regions is, for example, 330 or less, preferably 90 or less, more preferably 70 or less, even more preferably 33 or less, and most preferably 18 or less.

[0238] For reference, in substrates obtained by conventional manufacturing methods that do not involve any special process for collecting dislocations, the size of the dislocation-free region is smaller than 50 μm square, or the density of the dislocation-free region of 50 μm square is 100 / cm. 2 Because the density of dislocation-free regions of 50 μm square is low, the number of dislocations between a pair of dislocation-free regions increases. Furthermore, there is a high possibility that a dislocation-free region of 100 μm square will not be formed.

[0239] Next, the Burgers vector of dislocations in the substrate 100 of this embodiment will be described.

[0240] In this embodiment, the dislocation density is low on the primary surface 10s of the base substrate 10 used in the above-described manufacturing method, and therefore, there is little bonding (mixing) of multiple dislocations when the three-dimensional growth layer 30 and the planarization layer 40 are grown on the base substrate 10. This makes it possible to suppress the generation of dislocations with a large Burgers vector in the substrate 100 obtained from the planarization layer 40.

[0241] Specifically, in the substrate 100 of this embodiment, for example, the Burgers vector is <11-20> / 3, <0001> Many dislocations have either <11-23> / 3 or <11-23> / 3. The "Burgers vector" here can be measured, for example, by large angle convergent beam electron diffraction (LACBED) using a transmission electron microscope (TEM). Dislocations with a Burgers vector of <11-20> / 3 are edge dislocations, and Burgers vectors of <0001> A dislocation with a Burgers vector of <11-23> / 3 is a mixed dislocation that is a mixture of an edge dislocation and a screw dislocation.

[0242] In this embodiment, when 100 dislocations are randomly sampled on the main surface 100s of the substrate 100, the Burgers vector is <11-20> / 3, <0001> or <11-23> / 3 is, for example, 50% or more, preferably 70% or more, and more preferably 90% or more. Note that dislocations with a Burgers vector of 2<11-20> / 3 or <11-20> may be present in at least a portion of the main surface 100s of the substrate 100.

[0243] (X-ray rocking curve measurement of c-plane diffraction with different ω-direction widths of the entrance slit) Here, the inventors discovered that by performing X-ray rocking curve measurements of c-plane diffraction while varying the width of the entrance slit in the ω direction, it is possible to simultaneously evaluate both the crystal quality elements constituting the substrate 100 of this embodiment and the curvature (warpage) of the c-plane 100c described above.

[0244] First, we explain the influence of crystal quality factors on X-ray rocking curve measurements.

[0245] The half-width of the diffraction pattern in X-ray rocking curve measurements is significantly affected by crystal quality factors such as dislocation density, mosaicity, stacking fault density, basal plane dislocation density, point defect (vacancy, etc.) density, in-plane fluctuation of the lattice constant, and impurity concentration distribution. If these crystal quality factors are poor, the fluctuation of the diffraction angle in X-ray rocking curve measurements will be large, and the half-width of the diffraction pattern will be large.

[0246] Next, the influence of the curvature of the c-plane 100c on X-ray rocking curve measurement will be described with reference to Fig. 13(a), which is a schematic cross-sectional view showing the diffraction of X-rays with respect to the curved c-plane.

[0247] The width of the incident slit in the ω direction is dI, the irradiation width (footprint width) of the X-rays irradiated onto the main surface of the substrate is b, and the Bragg angle of the crystal is θ B Then, the irradiation width b of the X-ray on the main surface of the substrate can be calculated by the following formula (h): b=dI / sinθ B (h) Note that "ω" and "ω direction" respectively refer to the "rotation angle" and "rotation angle direction" around the rotation axis of the goniometer in X-ray rocking curve measurement. Note that in the c-plane diffraction measurement, "ω" and "ω direction" can also be considered as the substrate rotation angle and substrate rotation direction when the substrate 100 placed on the substrate stage is rotated around a central axis that passes through the center of the substrate stage and is parallel to the mounting surface of the substrate stage.

[0248] 13(a), when the c-plane of the substrate is curved, the radius of curvature of the c-plane is R, and half the central angle formed by the curved c-plane within the range of the X-ray irradiation width b is γ, then the radius of curvature R of the c-plane is very large compared to the X-ray irradiation width b. Therefore, the angle γ can be calculated using the following formula (i): γ=sin -1 (b / 2R) ≒ b / 2R (i)

[0249] At this time, at the end of the c-plane of the substrate on the incident side of the region irradiated with X-rays (the right end in the figure), the diffraction angle with respect to the main surface of the substrate is θ B +γ=θ B It becomes +b / 2R.

[0250] On the other hand, at the end of the c-plane of the substrate on the light-receiving side of the region irradiated with X-rays (the left end in the figure), the diffraction angle with respect to the main surface of the substrate is θ B -γ=θ B It becomes -b / 2R.

[0251] Therefore, the fluctuation in the diffraction angle of X-rays with respect to the curved c-plane is b / R, which is the difference between the diffraction angle with respect to the main surface of the substrate at the end of the c-plane on the incident side and the diffraction angle with respect to the main surface of the substrate at the end of the c-plane on the light-receiving side.

[0252] Figures 13(b) and (c) show the fluctuation of the diffraction angle of the (0002) plane with respect to the radius of curvature of the c-plane. Note that the vertical axis in Figure 13(b) is a logarithmic scale, while the vertical axis in Figure 13(c) is a linear scale.

[0253] As shown in Figures 13(b) and 13(c), when the width dI of the ω-direction of the X-ray incident slit is increased, i.e., when the X-ray irradiation width b is increased, the fluctuation of the diffraction angle of the (0002) plane increases according to the X-ray irradiation width b. Furthermore, as the curvature radius R of the c-plane decreases, the fluctuation of the diffraction angle of the (0002) plane gradually increases. Furthermore, the difference in the fluctuation of the diffraction angle of the (0002) plane when the X-ray irradiation width b is changed increases as the curvature radius R of the c-plane decreases.

[0254] For example, when the width dI of the entrance slit in the ω direction is narrow, the influence of the c-plane curvature on the fluctuation of the diffraction angle of the (0002) plane is small, and the influence of the above-mentioned crystal quality factors becomes dominant. In contrast, when the width dI of the entrance slit in the ω direction is wide, the influence of the crystal quality factors and the influence of the c-plane curvature on the fluctuation of the diffraction angle of the (0002) plane are both superimposed. Therefore, by performing X-ray rocking curve measurements with different widths dI of the entrance slit in the ω direction, it becomes possible to simultaneously evaluate both the above-mentioned crystal quality factors and the c-plane curvature (warpage) across the entire area irradiated with X-rays.

[0255] Here, the characteristics of the substrate 100 of this embodiment when an X-ray rocking curve measurement of c-plane diffraction is performed will be described.

[0256] In the following, when Cu Kα1 X-rays are irradiated onto the main surface 100s of the substrate 100 through a Ge (220) plane double crystal monochromator and an entrance side slit, and an X-ray rocking curve measurement of the (0002) plane diffraction is performed, the half-width of the (0002) plane diffraction when the entrance side slit has a width of 1 mm in the ω direction is defined as "FWHMa," and the half-width of the (0002) plane diffraction when the entrance side slit has a width of 0.1 mm in the ω direction is defined as "FWHMb."

[0257] In the substrate 100 of this embodiment, all of the above-mentioned crystal quality factors, such as the dislocation density, mosaicity, stacking fault density, basal plane dislocation density, point defect (vacancy, etc.) density, in-plane fluctuation of lattice constant, and impurity concentration distribution, are excellent.

[0258] As a result, in the substrate 100 of this embodiment, when the width of the entrance side slit in the ω direction is set to 0.1 mm and an X-ray rocking curve measurement of the (0002) plane diffraction is performed, the half-width FWHMb of the (0002) plane diffraction is, for example, 80 arcsec or less, preferably 50 arcsec or less, and more preferably 32 arcsec or less.

[0259] In addition, in the substrate 100 of the present embodiment, as described above, all of the above-described crystal quality elements are good over a wide range of the main surface 100s.

[0260] As a result, at a plurality of measurement points set at intervals of 5 mm within the main surface 100s of the substrate 100 of the present embodiment (between the center and the outer edge), when X-ray rocking curve measurement of (0002) plane diffraction is performed with the width in the ω direction of the incident-side slit being 0.1 mm, for example, in 90% or more, preferably 95% or more, more preferably 100% of all the measurement points, the full width at half maximum FWHMb of (0002) plane diffraction is 80 arcsec or less, preferably 50 arcsec, more preferably 32 arcsec or less.

[0261] [[ID='7]] In addition, in the substrate 100 of the present embodiment, the in-plane variation of the above-described crystal quality elements is small. For this reason, when X-ray rocking curve measurement is performed with the width in the ω direction of the incident-side slit widened, the diffraction pattern of the (0002) plane tends to be less likely to become narrower than the diffraction pattern of the (0002) plane when X-ray rocking curve measurement is performed with the width in the ω direction of the incident-side slit narrowed.

[0262] As a result, in the substrate 100 of the present embodiment, the full width at half maximum FWHMa of (0002) plane diffraction when the width in the ω direction of the incident-side slit is 1 mm can be, for example, not less than the full width at half maximum FWHMb of (0002) plane diffraction when the width in the ω direction of the incident-side slit is 0.1 mm.

[0263] Note that even when the crystal quality elements of the substrate 10 are good, there may be a case where FWHMa < FWHMb in a state where FWHMb is very small.

[0264] In addition, in the substrate 100 of the present embodiment, as described above, over a wide range of the main surface 100s, not only are there few dislocations, but all of the above-described 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. Due to these, in the substrate 100 of the present embodiment, even when the width in the ω direction of the incident-side slit is widened and the X-ray rocking curve measurement of (0002) plane diffraction is performed, over the region irradiated with X-rays, the above-described crystal quality elements are well-balanced and good, and due to the large radius of curvature of the c-plane, the fluctuation of the diffraction angle of the (0002) plane does not increase so much. Therefore, even when the X-ray rocking curve measurement is performed with different widths in the ω direction of the incident-side slit, the difference in the fluctuation of the diffraction angle of the (0002) plane becomes small.

[0265] As a result, at a predetermined measurement point (for example, the center of the main surface) of the substrate 100 of the present embodiment, the difference FWHMa - FWHMb obtained by subtracting the full width at half maximum FWHMb of (0002) plane diffraction when the width in the ω direction of the incident-side slit is 0.1 mm from the full width at half maximum FWHMa of (0002) plane diffraction when the width in the ω direction of the incident-side slit is 1 mm is, for example, 30% or less (0% or more) of FWHMa, preferably 22% or less.

[0266] Also, when the X-ray rocking curve measurement of (0002) plane diffraction is performed with different widths in the ω direction of the incident-side slit at a plurality of measurement points set at 5 mm intervals within the main surface 100s of the substrate 100 of the present embodiment (between the center and the outer edge), for example, at 95% or more, preferably 100% of all the measurement points, FWHMa - FWHMb is, for example, 30% or less of FWHMa, preferably 22% or less.

[0267] Note that in the substrate 100 of the present embodiment, even if FWHMa < FWHMb, |FWHMa - FWHMb| / FWHMa is 30% or less. Also, in the substrate 100 of the present embodiment, FWHMa may be substantially equal to FWHMb and |FWHMa - FWHMb| / FWHMa may be 0%.

[0268] Furthermore, in the substrate 100 of this embodiment, even if the width of the entrance slit in the ω direction is widened and an X-ray rocking curve measurement is performed, the diffraction pattern will have a single peak because the variation in the above-mentioned crystal quality factors is small across the region irradiated with X-rays.

[0269] For reference, a substrate manufactured by a conventional manufacturing method (hereinafter also referred to as a conventional substrate) will be described. The conventional manufacturing methods referred to here include, for example, the conventional VAS method, a method of growing a thick film using the c-plane as the growth surface, the above-mentioned DEEP method, the THVPE (Tri-halide vapor phase epitaxy) method, the ammonothermal method, and the flux method.

[0270] In the conventional substrate, at least one of the above crystal quality factors is not better than that of the substrate 100 of this embodiment. Therefore, the FWHMb of the conventional substrate is larger than that of the substrate 100 of this embodiment.

[0271] In conventional substrates, there is a possibility that at least one of the above crystal quality factors may vary within the plane. For this reason, when an X-ray rocking curve measurement is performed with the width of the entrance slit in the ω direction widened, the diffraction pattern of the (0002) plane may be broader than the diffraction pattern of the (0002) plane when the X-ray rocking curve measurement is performed with the width of the entrance slit in the ω direction narrowed. As a result, in conventional substrates, the FWHMa <FWHMbとなることがある。

[0272] In the conventional substrate, the radius of curvature of the c-plane is smaller than that of the substrate 100 of this embodiment. When the width of the entrance slit in the ω direction is increased, at least a portion of the region irradiated with X-rays inevitably includes a location where at least one of the crystal quality factors is inferior to that of the substrate 100 of this embodiment. For this reason, the difference FWHMa-FWHMb in the conventional substrate is larger than that in the substrate 100 of this embodiment.

[0273] In conventional substrates, there is a possibility that in-plane variations in at least one of the above-mentioned crystal quality factors may occur. When the width of the entrance slit in the ω direction is widened, there may be areas where the fluctuations in the diffraction angle of the (0002) plane are different in at least a part of the area irradiated with X-rays. Therefore, when the width of the entrance slit in the ω direction is widened, the diffraction pattern of the (0002) plane may have multiple peaks.

[0274] As described above, conventional substrates may not satisfy the above-mentioned (0002) plane diffraction requirements defined for the substrate 100 of this embodiment.

[0275] (X-ray rocking curve measurements of asymmetric reflecting surfaces under different measurement conditions) Furthermore, the inventors have found that the crystal quality of the substrate 100 of this embodiment can be appropriately evaluated by measuring the X-ray rocking curve of the asymmetric reflecting surface under different measurement conditions.

[0276] First, the measurement area MA when an X-ray rocking curve measurement of an asymmetric reflecting surface is performed will be described with reference to Figures 14 and 15. Figures 14 and 15 are a schematic perspective view and a schematic plan view, respectively, showing the X-ray rocking curve measurement of an asymmetric reflecting surface in this embodiment. Note that a portion of the main surface 100s of the substrate 100 is tentatively shown as a rectangle.

[0277] In the drawings and the following description, two directions that are perpendicular to each other along the main surface 100s of the substrate 100 are referred to as the "X direction" and the "Y direction," respectively, and the normal direction to the main surface 100s of the substrate 100 is referred to as the "Z direction." Furthermore, the direction of the rotation axis of the goniometer is referred to as the "y direction," the direction that is perpendicular to the rotation axis of the goniometer and coincides with the X direction of the substrate 100 is referred to as the "x direction," and the direction that is perpendicular to the x and y directions is referred to as the "z direction."

[0278] As described above, the rotation angle and rotation angle direction around the rotation axis of the goniometer are defined as "ω" and "ω direction," respectively. The angle at which the rotation axis of the goniometer is tilted with respect to the major surface of the substrate 100 (i.e., the tilt angle in the y direction with respect to the Y direction) is defined as "χ."

[0279] The width of the entrance aperture in the ω direction is defined as "d I ” and the length of the entrance aperture in the direction parallel to the rotation axis of the goniometer is “L I On the other hand, the width of the light receiving side opening in the ω direction is set to "d D ” and the length of the light-receiving aperture in the direction parallel to the rotation axis of the goniometer is “L D In the measurements described below, the light-receiving aperture corresponds to the aperture of the detector or the entrance aperture of the analyzer crystal.

[0280] Furthermore, the region where X-rays are irradiated from the X-ray source onto the substrate 100 is referred to as the "X-ray irradiation region IA," the region where the detector can receive X-rays from the substrate 100 is referred to as the "light-receiving region DA," and the region where information on the crystal quality of the substrate 100 can actually be obtained is referred to as the "measurement region MA." In each figure, the trajectory of the X-ray from the incident side to the main surface 100s and the virtual X-ray trajectory from the detector side to the main surface 100s are each shown in light gray, the X-ray irradiation region IA and light-receiving region DA are each shown in gray, and the measurement region MA is shown in dark gray.

[0281] 14 and 15, in the X-ray rocking curve measurement of the asymmetric reflecting surface, the rotation axis of the goniometer is tilted at an angle χ with respect to the main surface 100s of the substrate 100. Therefore, in this measurement, the X-ray irradiation area IA on the main surface 100s of the substrate 100 extends along a direction tilted with respect to the Y-axis of the main surface 100s. As a result, the irradiation area IA in this measurement is wider than the measurement area along the Y-axis in the X-ray rocking curve measurement of the c-plane diffraction described above.

[0282] 14 and 15, the light-receivable area DA, which is the area where the detector can receive X-rays from the substrate 100, can be obtained as a virtual X-ray irradiation area when it is assumed that X-rays are irradiated from the detector side toward the substrate 100. In this measurement, the light-receivable area DA on the main surface 100s of the substrate 100 extends in a direction symmetrical to the X-ray irradiation area IA across the Y axis of the main surface 100s.

[0283] As a result, as shown in Figures 14 and 15, the measurement area MA from which information regarding the crystalline quality of the substrate 100 can actually be obtained is the area where the X-ray irradiation area IA based on the incident conditions and the light-receiving area DA based on the light-receiving conditions overlap.

[0284] Here, the influence of imperfections in the crystals of the substrate 100 (i.e., fluctuations in the diffraction angle) is measured by the width of the component corresponding to the ω direction on the main surface 100s of the substrate 100, that is, the width W in the X direction of the measurement area MA. MA Depends on.

[0285] As shown in FIG. 15, the width W in the X direction of the measurement area MA MA is calculated using the following formula (j).

[0286]

number

[0287] Width of the entrance aperture in the ω direction, d I When fixed, the width W in the X direction of the measurement area MA MA For example, the width d of the light receiving aperture in the ω direction is D When the width W of the measurement area MA in the X direction is narrow, MA Therefore, the influence of the curvature of the crystal plane on the fluctuation of the diffraction angle of the asymmetric reflecting surface is small, and the influence of the above-mentioned crystal quality factors becomes dominant. D When the measurement area MA is wide, the width W in the X direction MATherefore, the fluctuation of the diffraction angle of the asymmetric reflecting surface is influenced by both the influence of the crystal quality factor and the influence of the curvature of the crystal surface. D By performing X-ray rocking curve measurements with different beam widths, it becomes possible to simultaneously evaluate both the above-mentioned crystal quality factors and the curvature of the crystal plane over the entire measurement area MA.

[0288] Next, the characteristics of the substrate 100 of this embodiment when an X-ray rocking curve measurement of the {10-12} plane diffraction is carried out as an asymmetric reflecting surface will be described.

[0289] In the following, FWHM1 {10-12} and FWHM2 {10-12} are the half-widths of the {10-12} plane diffraction measured by X-ray rocking curve measurement. FWHM1 {10-12} The incident conditions for measuring are: a Cu X-ray source, an X-ray mirror that converts X-rays into parallel light, a monochromator with two reflections on Ge(220), and a goniometer with a width d in the ω direction as the rotation angle direction around the rotation axis. I is 1.4 mm and the length L in the direction parallel to the rotation axis I The center of the main surface 100s of the substrate 100 is irradiated with Cu Kα1 X-rays through the entrance side openings having a diameter of 12 mm in this order. FWHM1 {10-12} The light receiving conditions for measuring are as follows: the light receiving slit is open and the width in the ω direction is d D The X-rays are received by a detector having an aperture (receiving aperture) with a diameter of 14.025 mm. FWHM2 {10-12} The incident condition when measuring is FWHM1 {10-12} The incidence conditions shall be the same as when measuring. FWHM2 {10-12} The light receiving conditions for measuring the width d D The detector receives the X-rays through a Ge(220) triple-reflection analyzer crystal with an entrance aperture (i.e., receiving aperture) of 6.54 mm.

[0290] When X-ray rocking curve measurement of {10-12} plane diffraction was performed on the substrate 100 of this embodiment, the theoretical diffraction angles were χ=43.19° and ω=24.05°.

[0291] Under the above conditions, the width W in the X direction of the measurement area MA MA will have the following value: FWHM1 {10-12} When measuring W MA : Approx. 18.92 mm FWHM2 {10-12} When measuring W MA :Approx. 9.74mm

[0292] In the following, FWHM1 {10-12} When measuring the width W in the X direction of the measurement area MA, MA The condition for making the FWHM2 relatively wide is sometimes abbreviated as "wide measurement area condition." {10-12} When measuring the width W in the X direction of the measurement area MA, MA The condition for making the measurement area relatively narrow is sometimes abbreviated as "narrow measurement area condition."

[0293] As described above, in substrate 100 of this embodiment, all of the above-mentioned crystal quality elements are well-balanced and excellent over a wide range of main surface 100s, and there is little curvature of the crystal plane of substrate 100. Even when X-ray rocking curve measurement of {10-12} plane diffraction is performed on substrate 100 of this embodiment under wide measurement area conditions, fluctuations in the diffraction angle of the {10-12} plane do not become very large because the above-mentioned crystal quality elements are well-balanced and excellent over the entire measurement area MA, and there is little curvature of the crystal plane.

[0294] As a result, in the substrate 100 of this embodiment, FWHM1 {10-12} is, for example, 50 arcsec or less, preferably 40 arcsec or less.

[0295] Furthermore, in the substrate 100 of this embodiment, all of the above-mentioned crystal quality elements are well-balanced and excellent, regardless of the crystal orientation, and the curvature of the crystal planes of the substrate 100 is small. Even when X-ray rocking curve measurements are performed on the substrate 100 of this embodiment under wide measurement area conditions, with diffraction from equivalent crystal planes from different directions, the fluctuation in the diffraction angle of the {10-12} plane does not vary significantly.

[0296] As a result, in the substrate 100 of this embodiment, the FWHM1 was obtained by measuring the diffraction of the equivalent crystal plane represented by the {10-12} plane from three directions rotated by 60° in the circumferential direction around the normal to the center of the main surface 100s. {10-12} The maximum and minimum difference is, for example, 9 arcsec or less.

[0297] Furthermore, as described above, in the substrate 100 of this embodiment, 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 X-ray rocking curve measurements of the {10-12} plane diffraction are performed under different measurement conditions, the fluctuation in the diffraction angle of the {10-12} plane is small.

[0298] As a result, at the center of the main surface 100s of the substrate 100 of this embodiment, FWHM1 {10-12} FWHM2 {10-12} The ratio is, for example, 80% or more.

[0299] In addition, the term "FWHM1 {10-12} FWHM2 {10-12} The "FWHM2 {10-12} / FWHM1 {10-12} ) × 100.

[0300] On the other hand, even if the above-mentioned crystal quality factors and the curvature of the crystal plane satisfy the above-mentioned requirements, if a surface defect such as a pit occurs in a part of the main surface 100s of the substrate 100, the FWHM1 {10-12} is better than FWHM2 under narrow measurement area conditions. {10-12}That is, the FWHM can be smaller than 1 {10-12} FWHM2 {10-12} The ratio can exceed 100%.

[0301] In contrast, in this embodiment, it is preferable that the main surface 100s of the substrate 100 is free from defects in the surface state, i.e., FWHM1 {10-12} FWHM2 {10-12} The ratio is preferably, for example, 100% or less.

[0302] For reference, in the conventional substrate, at least one of the above-mentioned crystal quality factors is not good. Therefore, when measurements are performed under wide measurement area conditions, at least a part of the measurement area MA inevitably includes a portion where at least one of the crystal quality factors is not good. Furthermore, in the conventional substrate, the curvature of the crystal plane is larger than that of the substrate 100 of this embodiment. As a result, the FWHM1 of the conventional substrate is {10-12} is larger than that of the substrate 100 of this embodiment.

[0303] Furthermore, in the conventional substrate, there is a possibility that at least one of the above crystal quality factors may vary within the surface. For this reason, the FWHM1 of the equivalent crystal plane diffraction measured from three directions in the conventional substrate {10-12} The maximum and minimum difference is larger than that of the substrate 100 of this embodiment.

[0304] Furthermore, as described above, the conventional substrate has poor crystal quality and exhibits greater curvature of the crystal plane than the substrate 100 of this embodiment. {10-12} FWHM2 {10-12} The ratio is smaller than that of the substrate 100 of this embodiment.

[0305] As described above, conventional substrates may not satisfy the requirements for the {10-12} plane diffraction specified for the substrate 100 of this embodiment.

[0306] (4) Effects Obtained by the Present Embodiment According to this embodiment, one or more of the following effects can be obtained.

[0307] (a) In the three-dimensional growth step S200, by forming an inclined interface 30i other than the c-plane on the surface of the single crystal constituting the three-dimensional growth layer 30, dislocations can be bent and propagated in a direction substantially perpendicular to the inclined interface 30i at the exposed position of the inclined interface 30i. This allows dislocations to be locally collected. By locally collecting dislocations, dislocations with opposite Burgers vectors can be eliminated. Alternatively, the locally collected dislocations can form a loop, which can suppress the propagation of dislocations toward the surface of the planarization layer 40. In this way, the dislocation density on the surface of the planarization layer 40 can be reduced. As a result, a substrate 100 can be obtained that has a lower dislocation density than the base substrate 10.

[0308] (b) In the three-dimensional growth step S200, the c-plane 30c is removed at least once from the top surface 30u of the three-dimensional growth layer 30. This allows a plurality of valleys 30v and a plurality of peaks 30t to be formed on the surface of the three-dimensional growth layer 30. As a result, dislocations propagating from the base substrate 10 can be reliably bent at positions where the inclined interfaces 30i in the three-dimensional growth layer 30 are exposed.

[0309] Here, let us consider the case where the c-plane remains in the three-dimensional growth process. In this case, in the part where the c-plane remains, dislocations propagating from the base substrate propagate almost vertically upward without being bent, and reach the surface of the second layer. Therefore, above the part where the c-plane remains, dislocations are not reduced, and a high dislocation density region is formed.

[0310] In contrast, according to the present embodiment, in the three-dimensional growth step S200, the c-plane 30c is eliminated at least once from the top surface 30u of the three-dimensional growth layer 30, thereby allowing the surface of the three-dimensional growth layer 30 to be composed only of inclined interfaces 30i other than the c-plane, and multiple valleys 30v and multiple peaks 30t can be formed on the surface of the three-dimensional growth layer 30. This ensures that dislocations propagating from the base substrate 10 are bent over the entire surface of the three-dimensional growth layer 30. By ensuring that dislocations are bent, some of the dislocations can be easily eliminated or some of the dislocations can be made less likely to propagate toward the surface of the planarization layer 40. As a result, the dislocation density can be reduced over the entire main surface 1s of the substrate 100 obtained from the main growth layer 44.

[0311] (c) In this embodiment, a cycle including the three-dimensional growth step S200 and the planarization step S300 is repeated multiple times. As described above, one cycle including the three-dimensional growth step S200 and the planarization step S300 bends dislocations propagating from the base substrate 10 side, allowing the dislocations to be locally collected. By performing a subsequent cycle, the dislocations remaining in the planarization layer 40 from the previous cycle can be further bent and locally collected. This allows the dislocation density on the surface of the planarization layer 40 in the next cycle to be reduced below the dislocation density on the surface of the planarization layer 40 in the previous cycle. By repeating the cycle in this manner, the dislocation density can be gradually reduced depending on the number of times the cycle is repeated.

[0312] (d) Even if the c-plane 30c remains in the three-dimensional growth step S200 of any of the multiple cycles, the c-plane 30c can be eliminated at least once above the remaining c-plane 30c in the next or subsequent cycles. This ensures that dislocations are bent above the remaining c-plane 30c. As a result, the dislocation density can be stably reduced.

[0313] (e) In the inclined interface expansion step S220 of the second or subsequent cycle, the average distance L between nearest-neighbor apexes is made longer when viewing any cross section perpendicular to the main surface 10s of the base substrate 10 than in the inclined interface expansion step S220 of the first cycle. This makes it possible to make the distance over which dislocations bend and propagate longer in the second or subsequent cycle than in the first cycle. As a result, it is possible to easily form non-overlapping 50 μm square dislocation-free regions on the surface of the flattening layer 40 in the second or subsequent cycle, thereby increasing the density of the dislocation-free regions.

[0314] (f) In the inclined interface expansion step S220 in each of the multiple cycles, the average distance L between nearest apexes is gradually increased, for example, as the multiple cycles are repeated. This allows the distance over which dislocations bend and propagate to gradually increase as the multiple cycles are repeated. As a result, the dislocation-free region on the surface of the planarizing layer 40 can be gradually widened, or the density of the dislocation-free region on the surface of the planarizing layer 40 can be gradually increased as the multiple cycles are repeated.

[0315] (g) In the inclined interface expansion step S220 in each of the multiple cycles, by setting the average distance L between nearest vertices to be greater than 100 μm when viewing any cross section perpendicular to the main surface 10s of the base substrate 10, the distance over which dislocations bend and propagate can be ensured to be at least greater than 50 μm. This allows dislocations to be sufficiently concentrated above the approximate center between a pair of vertices 30t of the three-dimensionally grown layer 30. As a result, the dislocation density on the surface of the planarization layer 40 can be sufficiently reduced.

[0316] (h) Furthermore, in at least the final inclined interface expansion step S220 of the multiple cycles, it is preferable to set the average distance L between nearest-neighbor apexes to, for example, more than 200 μm when viewing any cross section perpendicular to the main surface 10s of the base substrate 10. This ensures that the distance over which dislocations bend and propagate is at least more than 100 μm in the steps following the final inclined interface expansion step S220. As a result, a dislocation-free region measuring at least 100 μm square can be formed on at least a portion of the surface of the planarization layer 40 in the final cycle.

[0317] (i) In the three-dimensional growth step S200 in each of the multiple cycles, the first growth conditions are adjusted to satisfy formula (1), thereby generating {11-2m} planes, where m≧3, as the inclined interfaces 30i. This allows the inclination angle of the {11-2m} planes relative to the c-plane 30c to be gentle. Specifically, the inclination angle can be set to 47.3° or less. By gentle the inclination angle of the {11-2m} planes relative to the c-plane 30c, the period of the multiple apexes 30t can be lengthened. Specifically, when viewed in any cross section perpendicular to the major surface 10s of the base substrate 10, the average distance L between the nearest apexes can be set to greater than 100 μm.

[0318] For reference, when etch pits are typically formed on a nitride semiconductor substrate using a specific etchant, etch pits composed of {1-10n} planes are formed on the surface of the substrate. In contrast, in this embodiment, {11-2m} planes, where m≧3, can be formed on the surface of the three-dimensionally grown layer 30 grown under specific conditions. Therefore, compared to typical etch pits, in this embodiment, it is believed that an inclined interface 30i specific to the manufacturing method is formed.

[0319] (j) In the three-dimensional growth step S200 in each of the multiple cycles, after the c-plane 30c has disappeared from the surface of the three-dimensional growth layer 30, the growth of the three-dimensional growth layer 30 is continued over a predetermined thickness while maintaining a state in which the inclined interfaces 30i predominate on the surface. This ensures that the c-plane 30c disappears over the entire surface of the three-dimensional growth layer 30. For example, even if the timing at which the c-plane 30c disappears on the surface of the three-dimensional growth layer 30 in the inclined interface expansion step S220 is shifted and the c-plane 30c remains in part of the inclined interface expansion layer 32, the c-plane 30c can be ensured to disappear.

[0320] Furthermore, by continuing growth of the three-dimensional growth layer 30 along the inclined interface 30i after the c-plane 30c disappears, sufficient time is ensured for dislocation bending at the position where the inclined interface 30i is exposed. If c-plane growth were to occur immediately after the c-plane disappears, dislocations would not be sufficiently bent and may propagate in a substantially vertical direction toward the surface of the second layer. In contrast, in this embodiment, sufficient time is ensured for dislocation bending at the position where the inclined interface 30i other than the c-plane is exposed. This ensures that dislocations, particularly those near the top 30t of the three-dimensional growth layer 30, are bent reliably, thereby preventing dislocations from propagating in a substantially vertical direction from the base substrate 10 toward the surface of the planarization layer 40. This prevents dislocations from concentrating above the top 30t of the three-dimensional growth layer 30.

[0321] (k) The manufacturing method of this embodiment allows the radius of curvature of the c-plane 100c of the substrate 100 to be greater than the radius of curvature of the c-plane 10c of the base substrate 10. This allows the variation in the off-angle θ of the c-axis 100ca relative to the normal to the main surface 100s of the substrate 100 to be smaller than the variation in the off-angle of the c-axis 10ca of the base substrate 10.

[0322] One of the reasons why the radius of curvature of the c-plane 100c of the substrate 100 can be increased is, for example, as follows.

[0323] As described above, in the three-dimensional growth step S200, the three-dimensional growth layer 30 is three-dimensionally grown using an inclined interface 30i other than the c-plane as the growth plane, thereby forming the inclined interface growth region 70. The inclined interface growth region 70 is more likely to take in oxygen than 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. In other words, the inclined interface growth region 70 can be considered as a high-oxygen concentration region.

[0324] In this way, by incorporating oxygen into the high-oxygen-concentration region, the lattice constant of the high-oxygen-concentration region can be made larger than the lattice constant of other regions (see Chris G. Van de Walle, Physical Review B vol. 68, 165209 (2003)). The c-plane growth region 60 of the three-dimensional growth layer 30, grown using the c-plane 30c as the growth plane, is subjected to stress concentrated toward the center of curvature of the c-plane due to the curvature of the c-plane 10c of the base substrate 10. In contrast, by increasing the lattice constant of the high-oxygen-concentration region relatively, stress that spreads the c-plane 30c outward in the lateral direction can be generated in the high-oxygen-concentration region. This allows the stress concentrated toward the center of curvature of the c-plane 30c below the high-oxygen-concentration region and the stress that spreads the c-plane 30c of the high-oxygen-concentration region outward in the lateral direction to be offset.

[0325] By obtaining this stress-cancelling effect from the three-dimensional growth layer 30, the radius of curvature of the c-plane 100c of the substrate 100 obtained from the planarization layer 40 can be made larger than the radius of curvature of the c-plane 10c of the base substrate 10 obtained by the conventional VAS method.

[0326] (l) In the substrate 100 obtained by the manufacturing method of this embodiment, not only can the dislocation density be reduced and the off-angle variation be reduced, but also all of the above-mentioned crystal quality factors that determine the half-width in X-ray rocking curve measurement can be well balanced.

[0327] As a result, in X-ray rocking curve measurement of (0002) plane diffraction, the substrate 100 of this embodiment can achieve an FWHMb of 32 arcsec or less. Furthermore, with the substrate 100 of this embodiment, even if the width of the entrance slit in the ω direction is 1 mm, the radius of curvature of the c-plane is large over the entire region irradiated with X-rays, and the above-mentioned crystal quality factors are well balanced, so that (FWHMa-FWHMb) / FWHMa can be reduced to 30% or less.

[0328] Furthermore, with respect to the X-ray rocking curve measurement of the {10-12} plane diffraction, the substrate of this embodiment has a FWHM of 1 {10-12} In addition, in the substrate of this embodiment, the FWHM1 measured by diffraction of an equivalent crystal plane represented by the {10-12} plane from three directions can be set to 50 arcsec or less. {10-12} The maximum and minimum difference between the FWHM1 and FWHM2 can be set to 9 arcsec or less. {10-12} FWHM2 {10-12} The ratio can be 80% or more.

[0329] <Other embodiments> Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present invention.

[0330] In the above embodiment, the case where the base substrate 10 is a GaN freestanding substrate has been described. However, the base substrate 10 is not limited to a GaN freestanding substrate, and may be, for example, a group III nitride semiconductor such as aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium nitride (InN), indium gallium nitride (InGaN), or aluminum indium gallium nitride (AlInGaN). x In y Ga 1-x-y The substrate may be a free-standing substrate made of a Group III nitride semiconductor represented by the composition formula N(0≦x≦1, 0≦y≦1, 0≦x+y≦1).

[0331] In the above embodiment, the substrate 100 is a GaN freestanding substrate. However, the substrate 100 is not limited to a GaN freestanding substrate. For example, the substrate 100 may be a group III nitride semiconductor such as AlN, AlGaN, InN, InGaN, or AlInGaN. x In y Ga 1-x-y The substrate may be a free-standing substrate made of a Group III nitride semiconductor represented by the composition formula N(0≦x≦1, 0≦y≦1, 0≦x+y≦1).

[0332] In the above embodiment, the substrate 100 is described as being n-type, but the substrate 100 may be p-type or semi-insulating. For example, when the substrate 100 is used to manufacture a semiconductor device such as a high electron mobility transistor (HEMT), the substrate 100 preferably has semi-insulating properties.

[0333] In the above-described embodiment, the polishing step S180 of the base substrate preparation step S100 is described as mirror-finishing the primary surface 10s of the base substrate 10. However, in the polishing step S180, the primary surface 10s of the base substrate 10 may be roughly polished while maintaining the primary surface 10s in a so-called epi-ready state in which a single crystal of a Group III nitride semiconductor can be epitaxially grown. Specifically, the root-mean-square roughness (RMS) of the primary surface 10s of the base substrate 10 is set to, for example, 1 nm or more and 10 nm or less. By setting the RMS of the primary surface 10s of the base substrate 10 within this range, when a three-dimensionally grown 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 an inclined interface 30i other than the c-plane on the surface of the three-dimensionally grown layer 30. Furthermore, by keeping the RMS of the main surface 10s of the base substrate 10 within the above range, the surface of the three-dimensional growth layer 30 can be prevented from becoming excessively rough in the three-dimensional growth step S200 of the first cycle, and the average distance L between the nearest apexes in the three-dimensional growth layer 30 can be prevented from becoming shorter.

[0334] Alternatively, for example, while maintaining good crystal quality in the bulk portion of the base substrate 10, crystal strain introduced by processing the base substrate 10, such as the slicing step S170 or polishing step S180, may remain on the main surface 10s side of the base substrate 10. Specifically, when an X-ray rocking curve is measured with an incident angle of 2° with respect to the main surface 10s of the processed base substrate 10, the full width at half maximum (FWHM) of the (10-10) plane diffraction is set to be greater than the full width at half maximum of the base substrate 10 before processing, for example, to be 60 arcsec or more and 200 arcsec or less. By setting the FWHM of the (10-10) plane diffraction within this range, the stable crystal plane appearing on the surface of the three-dimensionally grown layer 30 can be changed in the three-dimensional growth step S200 of the first cycle due to crystal strain on the main surface 10s side of the base substrate 10. As a result, an inclined interface 30i other than the c-plane can be generated on the surface of the three-dimensionally grown layer 30. Furthermore, by keeping the FWHM of the (10-10) plane diffraction within the above range, it is possible to suppress the occurrence of excessively large numbers of dislocations in the three-dimensional growth layer 30 due to crystal distortion on the main surface 10s side of the base substrate 10 in the three-dimensional growth step S200 of the first cycle.

[0335] In the above-described embodiment, the first cycle of the three-dimensional growth step S200 is performed immediately after the base substrate preparation step S100. However, this is not limited to this. In the initial step S190, which is performed after the base substrate preparation step S100 and before the first cycle of the three-dimensional growth step S200, an initial layer may be grown directly on the main surface 10s of the base substrate 10, using the c-plane as the growth surface. In this case, the growth rate of the initial layer in the initial step S190 is set lower than the growth rate of the three-dimensionally grown layer 30 in the three-dimensional growth step S200. This allows the initial layer to be grown by step-flow growth on the main surface 10s of the base substrate 10. By growing the initial layer by step-flow growth, even if there are abnormalities, such as rough areas or areas with different crystallinity, on part of the main surface 10s of the base substrate 10, the surface morphology and crystallinity of the initial layer can be made substantially uniform across the entire surface, regardless of the condition of the main surface 10s of the base substrate 10. By making the surface morphology and crystallinity of the initial layer substantially uniform, in the three-dimensional growth step S200 of the first cycle, the state of occurrence of the inclined interfaces 30i, such as the inclination angle of the inclined interfaces 30i with respect to the c-plane 30c, can be made substantially uniform over the entire surface of the three-dimensionally grown layer 30. Specifically, it is possible to prevent a region with a short nearest-neighbor apex distance from being formed in a part of the surface of the three-dimensionally grown layer 30, and to make the nearest-neighbor apex distance substantially uniform over the entire surface of the three-dimensionally grown layer 30. As a result, it is possible to prevent a region with a high dislocation density from being formed in a part of the surface of the planarizing layer 40, and to reduce the dislocation density over the entire surface of the planarizing layer 40.

[0336] In the above-described embodiment, in the three-dimensional growth step S200 of each cycle, the case where the growth temperature is mainly adjusted as the first growth condition has been described. However, as long as the first growth condition satisfies formula (1), the first growth condition may be adjusted by adjusting a growth condition other than the growth temperature, or by combining the growth temperature with a growth condition other than the growth temperature.

[0337] In the above-described embodiment, in the planarization step S300 of each cycle, the second growth condition is mainly adjusted as the growth temperature. However, as long as the second growth condition satisfies the formula (2), the second growth condition may be adjusted by adjusting a growth condition other than the growth temperature, or by combining the growth temperature with a growth condition other than the growth temperature.

[0338] In the above-described embodiment, the growth conditions in the inclined interface maintaining step S240 of each cycle are maintained at the first growth conditions described above, similar to the inclined interface expanding step S220. However, the growth conditions in the inclined interface maintaining step S240 may be different from the growth conditions in the inclined interface expanding step S220, as long as the growth conditions in the inclined interface maintaining step S240 satisfy the first growth conditions.

[0339] In the above embodiment, the case where the cycle is ended when the number of times of implementation reaches two in the implementation number determination step S400 has been described, but the number of times of implementation may be more than two.

[0340] In the above-described embodiment, the three-dimensional growth step S200 of the second or subsequent cycle is described as growing the three-dimensional growth layer 30 under the same first growth conditions as those of the three-dimensional growth step S200 of the first cycle. However, as long as the growth conditions of the three-dimensional growth step S200 of the second or subsequent cycle satisfy the first growth conditions, the growth conditions of the step may be different from those of the three-dimensional growth step S200 of the first cycle.

[0341] In the above-described embodiment, the planarization step S300 of the second or subsequent cycle is described as growing the planarization layer 40 under the same second growth conditions as those of the planarization step S300 of the first cycle. However, as long as the growth conditions of the planarization step S300 of the second or subsequent cycle satisfy the second growth conditions, the growth conditions of the step may be different from those of the planarization step S300 of the first cycle.

[0342] In the above embodiment, the growth conditions in the main growth step S500 are maintained at the second growth conditions, similar to the planarization step S300 of each cycle. However, as long as the growth conditions in the main growth step S500 satisfy the second growth conditions, the growth conditions in this step may be different from the growth conditions in the planarization step S300 of each cycle.

[0343] In the above-described embodiment, the slicing step S170 and the slicing step S600 are described as using a wire saw to slice the second crystal layer 6 or the main growth layer 44, but for example, an outer diameter blade slicer, an inner diameter blade slicer, an electric discharge machine, etc. may also be used.

[0344] In the above-described embodiment, the substrate 100 is obtained by slicing the primary growth layer 44 of the laminated structure 90. However, this is not a limitation. For example, the laminated structure 90 may be used as is to manufacture a semiconductor laminate for fabricating a semiconductor device. Specifically, after fabricating the laminated structure 90, a semiconductor functional layer is epitaxially grown on the laminated structure 90 in a semiconductor laminate fabrication process to fabricate the semiconductor laminate. After fabricating the semiconductor laminate, the back side of the laminated structure 90 is polished, and the base substrate 10 and the multiple laminated units 50 of the laminated structure 90 are removed. As a result, a semiconductor laminate having the primary growth layer 44 and the semiconductor functional layer is obtained, as in the above-described embodiment. In this case, the slicing step S600 and the polishing step S700 for obtaining the substrate 100 can be omitted.

[0345] In the above embodiment, the manufacturing process is terminated once the substrate 100 is manufactured. However, the substrate 100 may be used as the base substrate 10, and steps S200 to S700 may be repeated. This allows for the production of a substrate 100 with a further reduced dislocation density. Furthermore, it allows for the production of a substrate 100 with a further reduced variation in the off-angle θ of the c-axis 100ca. Furthermore, steps S200 to S700 using the substrate 100 as the base substrate 10 constitute one cycle, and this cycle may be repeated multiple times. This allows for the dislocation density of the substrate 100 to be gradually reduced depending on the number of times the cycle is repeated. Furthermore, it is also possible to gradually reduce the variation in the off-angle θ of the c-axis 100ca in the substrate 100 depending on the number of times the cycle is repeated. [Example]

[0346] Various experimental results that support the effects of the present invention will be described below. Note that, hereinafter, the term "nitride semiconductor substrate" may be abbreviated to simply "substrate."

[0347] (1) Experiment 1 (1-1) Fabrication of nitride semiconductor substrate The substrates of Samples 1 to 4 were fabricated as follows: For Sample 1, a laminated structure was also fabricated.

[0348] <Conditions for producing nitride semiconductor substrate of Sample 1> For Sample 1, the cycle including the three-dimensional growth step and the planarization step was performed twice. (Base substrate) Material: GaN Preparation method: VAS method Diameter: 2 inches Thickness: 400 μm The closest low-index crystal plane to the main plane: c-plane No patterning of the main surface, such as a mask layer, is required. Off-angle of the center of the main surface: 0.4° in the m direction

[0349] [First Cycle] (3D growth layer) Material: GaN Growth method: HVPE method First growth condition: The growth temperature was set to 980°C or higher and 1,020°C or lower, and the V / III ratio was set to 2 or higher and 20 or lower. At least one of the growth temperature and the V / III ratio was adjusted within the above ranges so that the first growth condition satisfied formula (1). (flattening layer) Material: GaN Growth method: HVPE method Growth temperature: 1,050℃ V / III ratio: 2 The second growth condition satisfies the formula (2). Thickness from the main surface of the base substrate to the boundary surface of the first laminate unit (thickness of the first laminate unit): Approximately 800 μm

[0350] [Second cycle] (3D growth layer) Growth conditions similar to those of the first cycle 3D growth layer (flattening layer) Growth conditions similar to the planarization layer of the first cycle Thickness from the boundary surface of the first laminate unit to the boundary surface of the second laminate unit (thickness of the second laminate unit): Approximately 800 μm (main growth layer) The growth conditions were the same as for the planarization layer of each cycle. Thickness: Approx. 2mm In the laminated structure for observation, the thickness of the main growth layer was set to about 200 μm. (Slicing conditions) Substrate thickness: 400 μm Kerf loss: 200 μm

[0351] <Conditions for producing nitride semiconductor substrate of sample 2> In Sample 2, the cycle including the three-dimensional growth step and the planarization step was performed once, i.e., the cycle was not repeated. (Base substrate) Equivalent to the base substrate used in Sample 1 (3D growth layer) The growth conditions were similar to those of the first cycle of the 3D growth layer of Sample 1. (flattening layer) Growth conditions similar to the planarization layer of the first cycle of Sample 1 Thickness from the main surface of the base substrate to the interface on the planarization layer: Approximately 800 μm (main growth layer) The same growth conditions as for the planarization layer described above Thickness: Approx. 2mm (Slicing conditions) Same as sample 1.

[0352] <Conditions for producing nitride semiconductor substrate of sample 3> The method described above, "c-plane thick film growth," was used. (Base substrate) Material: GaN Preparation method: VAS method Diameter: 62mm Thickness: 400 μm The closest low-index crystal plane to the main plane: c-plane Off-angle of the center of the main surface: m-axis direction 0.5° No patterning of the main surface, such as a mask layer, is required. (crystalline layer) Material: GaN Growth method: HVPE method Growth temperature: 1050℃ V / III ratio: 2.8 Growth time: 15 hours (processing) Grinding: The cylindrical region was removed to obtain a cylindrical region with a diameter of 56 mm. Slices: 630 μm thick, 5 slices Beveling processing: diameter 50.8 mm. Polishing: The thickness was 400 to 450 μm.

[0353] <Production conditions of nitride semiconductor substrate for sample 4> The substrate for Sample 4 was prepared using the same conventional VAS method as the undersubstrate. Note that for Sample 4, the absolute value of the off-angle and the off-direction differed from those of the undersubstrate, but the radius of curvature of the c-plane and the dislocation density were the same as those of the undersubstrate.

[0354] (1-2) Evaluation (Observation by fluorescence microscope) A cross section of the laminated structure of Sample 1 before the substrate was sliced ​​was observed using a fluorescence microscope.

[0355] (Observation by multiphoton excitation microscope) Using a multiphoton excitation microscope, the main surfaces of the substrates of Samples 1 to 3 and the substrate of Sample 4, which corresponds to the base substrate, were observed. At this time, the dislocation density was measured by measuring the density of dark spots over the entire main surface at 250 μm field of view. It was confirmed that all of the dark spots in these substrates were dislocations by measuring with the focus shifted in the thickness direction. In addition, at this time, the dislocation density for the total number of measurement areas in the field of view of 250 μm square was 1×10 6 cm -2 Less than or 7 x 10 5 cm -2 The percentage of the number of regions where the value was less than 1 was calculated.

[0356] (X-ray rocking curve measurement of (0002) plane diffraction) The following two types of X-ray rocking curve measurements of (0002) plane diffraction were carried out for each of the substrates of Samples 1 to 3 and the substrate of Sample 4, which corresponds to the base substrate.

[0357] The X-ray rocking curve measurements were performed using a Spectris X'Pert-PRO MRD, with the company's hybrid monochromator serving as the input monochromator. The hybrid monochromator consists of, from the X-ray source side, an X-ray mirror and two Ge(220) crystals. In this measurement, the X-rays emitted from the X-ray source are first collimated by the X-ray mirror. This increases the number of X-ray photons (i.e., X-ray intensity) used. The collimated light from the X-ray mirror is then converted into monochromatic Cu Kα1 light by two Ge(220) crystals. The monochromatic light from the two Ge(220) crystals is then narrowed to a predetermined width through an input slit and incident on the substrate. The half-width (FWHM) of the rocking curve measured for the (0002) plane of perfectly crystalline GaN using this hybrid monochromator was calculated by simulation to be 25.7 arcsec. This FWHM is the theoretical measurement limit for the optical system described above.

[0358] In this measurement, the X-rays incident on the substrate are parallel rays directed toward the substrate in a cross section perpendicular to the rotation axis of the goniometer (i.e., a cross section along the ω direction). However, the incident X-rays are not parallel rays in a cross section along the rotation axis of the goniometer. Therefore, while the width of the X-rays in the ω direction is almost constant from the slit to the substrate, the width of the X-rays in the direction perpendicular to the ω direction increases. Therefore, in X-ray rocking curve measurement, the half-width of the X-rays diffracted by a given crystal plane depends on the width of the incident slit in the ω direction where the X-rays become parallel rays.

[0359] On the other hand, the light-receiving side was left open. The window width of the detector on the light-receiving side in the ω direction was set to 14.025 mm. In the above optical system, the gonioradius is 420 mm, so it is possible to measure a Bragg angle fluctuation of ±0.95°.

[0360] (X-ray rocking curve measurement 1) The width of the entrance slit in the ω direction was set to 0.1 mm, and X-ray rocking curve measurements were performed on the (0002) plane of each of the substrates of Samples 1 to 3 and the substrate of Sample 4, which corresponds to the base substrate. The measurements were performed at multiple measurement points set at 5 mm intervals on a line passing through the center of the main surface of each substrate along the m-axis direction, and on a line passing through the center along the a-axis direction perpendicular to the m-axis. The X-rays were incident from the side defined as the positive position within the main surface of the substrate. The peak angle ω between the X-rays incident on the main surface and the main surface was plotted against the position on the line, and the peak angle ω was approximated by a linear function of the position. The radius of curvature of the c-plane was calculated as the inverse of the slope of the linear function.

[0361] At each measurement point, the half-width FWHMb of the (0002) plane diffraction was also determined when the width of the entrance slit in the ω direction was set to 0.1 mm.

[0362] (X-ray rocking curve measurement 2) The width of the entrance slit in the ω direction was set to 1 mm, and X-ray rocking curve measurements were performed on the substrates of Samples 1 to 3 and the substrate of Sample 4, which corresponds to the base substrate. The measurements were performed at multiple measurement points set at 5 mm intervals on a line passing through the center and along the m-axis direction within the main surface of each substrate, and on a line passing through the center and along the a-axis direction perpendicular to the m-axis. As a result of the measurements, the half-width FWHMa of the (0002) plane diffraction was calculated at each measurement point when the width of the entrance slit in the ω direction was set to 1 mm. Furthermore, the ratio of FWHMa - FWHMb to FWHMa was calculated at each measurement point.

[0363] In X-ray rocking curve measurements 1 and 2, when X-rays are incident on the main surface of each substrate at a Bragg angle of 17.28° on the (0002) plane, the X-ray footprint is approximately 0.337 mm when the slit width in the ω direction is 0.1 mm, and approximately 3.37 mm when the slit width in the ω direction is 1 mm.

[0364] (1-3) Results The results are shown in Tables 1 to 5.

[0365] [Table 1]

[0366] [Table 2]

[0367] [Table 3]

[0368] [Table 4]

[0369] [Table 5]

[0370] <Sample 4: Equivalent to base substrate> With reference to Tables 1 and 5 and Figure 21(b), the results for Sample 4, which corresponds to a base substrate fabricated by the conventional VAS method, will be described. Figure 21(b) shows the normalized X-ray diffraction pattern obtained when X-ray rocking curve measurements of (0002) plane diffraction were performed on the nitride semiconductor substrate of Sample 4 with different entrance slits. Note that Figure 21(b) shows the measurement results in the direction along the a-axis. In addition, in this figure, "Line width" refers to the X-ray footprint mentioned above.

[0371] (dislocation) As shown in Table 1, the substrate of sample 4, which corresponds to the base substrate, has an average dislocation density of 1 × 10 6 cm -2 The dislocation density in the main surface of the substrate of Sample 4 was 1×10 6 cm -2 There were no areas where it was less than

[0372] Although not shown, dislocations were uniformly dispersed within the surface of the substrate of Sample 4. As a result, the size of the dislocation-free regions was smaller than 50 μm square throughout the entire substrate of Sample 4, and no 50 μm square dislocation-free regions were formed.

[0373] (X-ray rocking curve measurement results) As shown in Table 1, the radius of curvature of the c-plane of the substrate of Sample 4 was less than 10 m.

[0374] As shown in Table 5, in the substrate of Sample 4, the variation in the off-angle of the c-axis within a diameter of 40 mm was about ±0.24°.

[0375] Furthermore, as shown in Table 5, in the substrate of Sample 4, the FWHMb was greater than 32 arcsec at all measurement points when the width of the entrance side slit in the ω direction was 0.1 mm.

[0376] As shown in Figure 21(b), for the substrate of Sample 4, the X-ray diffraction pattern when the width of the incident-side slit in the ω direction was 1 mm was wider than the X-ray diffraction pattern when the width of the incident-side slit in the ω direction was 0.1 mm.

[0377] Therefore, as shown in Table 5, in the substrate of Sample 4, (FWHMa-FWHMb) / FWHMa exceeded 30% at all measurement points.

[0378] <Sample 3: c-plane thick film growth> The results for the substrate of Sample 3 obtained by c-plane thick film growth will be described with reference to Tables 1 and 4 and Fig. 20. Fig. 20 is a view of the main surface of the nitride semiconductor substrate of Sample 3 observed using a multiphoton excitation microscope.

[0379] (dislocation) As shown in Table 1, in the substrate of Sample 3 obtained by c-plane thick film growth, the dislocation density decreased in inverse proportion to the thickness of the crystal layer, and therefore the average dislocation density was lower than that of Sample 4, which was equivalent to the underlying substrate.

[0380] However, in the substrate of sample 3, the dislocation density was 1 × 10 6 cm -2 The percentage of the area where the dislocation density is less than 7×10 cm is less than 90%. -2 The percentage of areas where the luminance was less than 80% was less than 100%.

[0381] Furthermore, as shown in Fig. 20, dislocations were uniformly dispersed within the surface of the substrate of Sample 3. The dislocation distribution was similar to that shown in Fig. 20 even in regions not shown. Therefore, the size of the dislocation-free regions was smaller than 50 µm square throughout the entire substrate of Sample 3, and no 50 µm square dislocation-free regions were formed.

[0382] Thus, even when the method of Sample 3, which is a conventional method for obtaining high-quality substrates, was used, the obtained substrate did not have the above-mentioned low dislocation density region and no 50-μm square dislocation-free region. For this reason, it is thought that even substrates produced by other conventional manufacturing methods that do not involve any special process for collecting dislocations would not have the 50-μm square dislocation-free region.

[0383] (X-ray rocking curve measurement results) As shown in Table 1, in the substrate of Sample 3, the radius of curvature of the c-plane was slightly larger than that of the underlying substrate due to the effect of the thickened crystal layer.

[0384] Furthermore, as shown in Table 4, the variation in the c-axis off-angle within a diameter of 40 mm for the substrate of Sample 3 obtained by c-plane thick film growth was improved to about ±0.074° compared to the substrate of Sample 4. Furthermore, the FWHMb of the substrate of Sample 3 was improved compared to the FWHMb of the substrate of Sample 4.

[0385] However, there were several portions where FWHMb exceeded 32 arcsec on the substrate of Sample 3. Also, on the substrate of Sample 3, (FWHMa-FWHMb) / FWHMa greatly exceeded 30% at all measurement points.

[0386] Thus, the substrate of Sample 3, which is of relatively high quality as a conventional substrate, had improved dislocation density and off-angle variation compared to Sample 4, which was equivalent to the base substrate. However, the substrate of Sample 3 did not have any points that satisfied the half-width conditions of FWHMb≦32 arcsec and (FWHMa−FWHMb) / FWHMa≦30%. This is thought to be because the substrate of Sample 3 did not have at least one of the above-mentioned crystal quality elements as good as the substrates of Samples 1 and 2.

[0387] For this reason, even the substrate of Sample 3, which is a relatively high quality substrate as a conventional substrate, does not satisfy the above-mentioned half-width condition, and it is therefore considered that substrates manufactured by other conventional manufacturing methods also do not satisfy the above-mentioned half-width condition.

[0388] <Sample 2: 1 cycle> The results for the substrate of Sample 2, which was subjected to one cycle, will be described with reference to Tables 1 and 3 and Fig. 19. Fig. 19 is a view of the main surface of the nitride semiconductor substrate of Sample 2 observed using a multiphoton excitation microscope.

[0389] (dislocation) As shown in Table 1, the substrate of Sample 2, which was cycled once, had a lower average dislocation density than the substrates of Samples 3 and 4. The substrate of Sample 2 had a dislocation density of 1×10 6 cm -2 The percentage of areas where the area was less than 90% was over.

[0390] However, in the substrate of sample 2, the dislocation density was 1 × 10 6 cm -2 The area where the dislocation density was 7×10 or more was present in about 5% of the main surface. 5 cm-2 The percentage of areas where the luminance was less than 80% was less than 100%.

[0391] 19, the main surface of the substrate of Sample 2 contained dislocation-free regions measuring at least 50 μm square. Furthermore, in the substrate of Sample 2, dislocation-free regions measuring 50 μm square were scattered over the entire main surface.

[0392] In addition, in the substrate of Sample 2, at least one 50 μm square dislocation-free region was present within the entire 250 μm square field of view. The main surface of the substrate of Sample 2 had non-overlapping 50 μm square dislocation-free regions at a density of 1000 / cm. 2 It had a density of more than 1000.

[0393] However, in the main surface of the substrate of Sample 2, no dislocation-free region of 100 μm square was present.

[0394] (X-ray rocking curve measurement results) As shown in Table 1, the substrate of Sample 2 had a larger radius of curvature of the c-plane than the substrates of Samples 3 and 4, being 23 m or more.

[0395] Furthermore, as shown in Table 3, in the substrate of Sample 2, the variation in the off-angle of the c-axis within a diameter of 40 mm was smaller than in the substrates of Samples 3 and 4, being about ±0.03°.

[0396] Furthermore, for the substrate of Sample 2, FWHMb was 32 arcsec or less at all measurement points. Furthermore, for the substrate of Sample 2, (FWHMa-FWHMb) / FWHMa was 30% or less at all measurement points.

[0397] <Sample 1: 2 cycles> The results of the substrate of Sample 1, which underwent two cycles, will be described with reference to Table 1, Table 2, FIGS. 16, 17, 18, and 21(a). FIG. 16 shows an image of the cross section of the stacked structure of Sample 1 observed with a fluorescence microscope. FIGS. 17 and 18 show images of the main surface of the nitride semiconductor substrate of Sample 1 observed with a multiphoton excitation microscope. In FIGS. 17 and 18, the white solid squares indicate 50-μm square dislocation-free regions, and the white dotted squares indicate 100-μm square dislocation-free regions. FIG. 21(a) shows a normalized X-ray diffraction pattern obtained by measuring the X-ray rocking curve of (0002) plane diffraction for the nitride semiconductor substrate of Sample 1 with different entrance slits. The measurement conditions for FIG. 21(a) were the same as those for FIG. 21(b).

[0398] (Laminated structure) 16, 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 growth surface. Each of the two laminated units had a low oxygen concentration region and a high oxygen concentration region.

[0399] The low oxygen concentration region was not continuous in the thickness direction from the undersubstrate side to the uppermost low oxygen concentration region.

[0400] The low-oxygen concentration region of the first stack unit had a portion corresponding to an initial layer grown on the base substrate with the c-plane as the growth surface during the initial growth stage. The initial layer was formed to a predetermined thickness over the entire main surface of the base substrate.

[0401] The low oxygen concentration region of the first laminate unit had a plurality of valleys and a plurality of peaks in a cross-sectional view, and the average distance between the nearest peaks in the first laminate unit was approximately 135 μm.

[0402] The high oxygen concentration region of the first stacked unit was provided on the low oxygen concentration region of the first stacked unit. The high oxygen concentration region of the first stacked unit was provided continuously 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 first stacked unit.

[0403] The low oxygen concentration region of the second laminate unit was provided above the high oxygen concentration region of the first laminate unit.

[0404] The low-oxygen concentration region of the second stack unit also had multiple valleys and multiple peaks in a cross-sectional view. The average distance between nearest peaks in the second stack unit was approximately 209 μm, which was longer than the average distance between nearest peaks in the first stack unit.

[0405] The high oxygen concentration region of the second stacked unit was provided on the low oxygen concentration region of the second stacked unit. The high oxygen concentration region of the second stacked unit was provided continuously along the main surface of the base substrate. In other words, it was confirmed that the c-plane disappeared at least once during the growth process of the second stacked unit.

[0406] In the laminated structure of Sample 1, the thickness from the main surface of the base substrate to the boundary surface of the second laminated unit was 1690 μm. From the results in Table 1, the reduction rate of dislocation density calculated by the above-mentioned N / N0 was 0.07.

[0407] (dislocation) As shown in Table 1, the substrate of Sample 1, which had undergone two cycles, had a lower average dislocation density than the substrates of Samples 2 to 4.

[0408] In the substrate of sample 1, the dislocation density was 1×10 6 cm -2 The percentage of the region where the dislocation density was less than 1×10 was 100%. 6 cm -2 No area where this was the case existed on the main surface.

[0409] In addition, the dislocation density of the substrate of Sample 1 is 7 × 10 5 cm -2 The percentage of areas where the area was less than 80% was more than 80%.

[0410] 17 and 18, the main surface of the substrate of Sample 1 contained dislocation-free regions measuring at least 50 μm square. Furthermore, in the substrate of Sample 1, multiple dislocation-free regions measuring 50 μm square were scattered across the entire main surface.

[0411] Furthermore, in the substrate of Sample 1, multiple 50 μm square dislocation-free regions were present within the entire 250 μm square field of view. In other words, the density of non-overlapping 50 μm square dislocation-free regions 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 contained non-overlapping 50 μm square dislocation-free regions at a density of 10,000 / cm. 2 It had a density of more than 1000.

[0412] In addition, in the substrate of Sample 1, the number of dislocations present in the quadrangular region sandwiched between the opposing sides of the closest pair of dislocation-free regions was 90 or less.

[0413] 17 and 18, the main surface of the substrate of Sample 1 contained dislocation-free regions of 100 μm square. The main surface of the substrate of Sample 1 contained non-overlapping dislocation-free regions of 100 μm square at a density of 100 dislocations / cm. 2 It had a density of more than 1000.

[0414] (X-ray rocking curve measurement results) As shown in Table 1, the substrate of Sample 1 had a larger radius of curvature of the c-plane than the substrates of Samples 3 and 4, being 23 m or more.

[0415] Furthermore, as shown in Table 2, in the substrate of Sample 1, the variation in the off-angle of the c-axis within a diameter of 40 mm was smaller than in the substrates of Samples 3 and 4, being about ±0.006°.

[0416] Furthermore, in the substrate of Sample 1, the FWHMb was 32 arcsec or less at all measurement points when the width of the entrance slit in the ω direction was 0.1 mm.

[0417] As shown in FIG. 21(a), in the substrate of Sample 1, the spread of the X-ray diffraction pattern was small even when the width of the incident-side slit in the ω direction was increased from 0.1 mm to 1 mm.

[0418] As a result, as shown in Table 2, in the substrate of Sample 1, (FWHMa-FWHMb) / FWHMa was 30% or less at all measurement points.

[0419] That is, in the X-ray rocking curve measurement of the (0002) plane diffraction in the substrate of Sample 1, results equivalent to or better than those in the substrate of Sample 2 were obtained.

[0420] (2) Experiment 2 (2-1) Preparation of nitride semiconductor substrate Samples 1, 3 and 4 in the above-mentioned Experiment 1 were prepared and evaluated as follows.

[0421] (2-2) Evaluation (X-ray rocking curve measurement of {10-12} plane diffraction) The substrate of Sample 1, the substrate of Sample 3, and the substrate of Sample 4 corresponding to the base substrate were each subjected to the following two types of X-ray rocking curve measurements for {10-12} plane diffraction.

[0422] The same equipment as in Experiment 1 was used for the X-ray rocking curve measurement. As described in the above embodiment, FWHM1 {10-12} Measure FWHM2 under narrow measurement area conditions. {10-12} was measured.

[0423] FWHM1 {10-12}The incident conditions for measuring are: a Cu X-ray source, an X-ray mirror that converts X-rays into parallel light, a monochromator with two reflections on Ge(220), and a goniometer with a width d in the ω direction as the rotation angle direction around the rotation axis. I is 1.4 mm and the length L in the direction parallel to the rotation axis I The center of the main surface 100s of the substrate 100 was irradiated with Cu Kα1 X-rays through the entrance side opening having a diameter of 12 mm in this order. That is, the measurement in Experiment 2 was carried out by removing the entrance side slit used in Experiment 1. FWHM1 {10-12} The receiving conditions for measuring were that the receiving slit was open and the X-rays were received without passing through the analyzer crystal. Note that the width of the aperture in the ω direction (width of the receiving aperture in the ω direction) d D , and the length of the aperture parallel to the rotation axis (length of the aperture on the light receiving side) L D Both were set to 14.025 mm. FWHM2 {10-12} The incident condition when measuring is FWHM1 {10-12} The incident conditions were the same as those when measuring FWHM2 {10-12} The receiving conditions for measuring X-rays were set to a triple-reflection analyzer crystal of Ge(220). The width of the entrance aperture in the ω direction (the width of the receiving aperture in the ω direction) of the analyzer crystal was d D , and the length of the entrance opening in the direction parallel to the rotation axis (length of the light-receiving side opening) L D were set to 6.54 mm and 14.025 mm, respectively.

[0424] (2-3) Results The results are shown in Table 6.

[0425] [Table 6]

[0426] <Sample 4: Equivalent to base substrate> The results for the substrate of Sample 4, which corresponds to the base substrate, will be described with reference to Table 6 and Fig. 24. Fig. 24 shows normalized X-ray diffraction patterns obtained when X-ray rocking curve measurements of {10-12} plane diffraction were performed on the nitride semiconductor substrate of Sample 4 under different measurement conditions.

[0427] As shown in Table 6 and Figure 24, the substrate of Sample 4 has a FWHM of 1 {10-12} In addition, for the substrate of sample 4, the FWHM1 {10-12} The variation was large, with the maximum and minimum difference exceeding 150 arcsec.

[0428] As shown in FIG. 24, for the substrate of Sample 4, the {10-12} diffraction pattern under the wide measurement area condition was broader than the {10-12} diffraction pattern under the narrow measurement area condition.

[0429] Therefore, as shown in Table 6, the substrate of Sample 4 has a FWHM of 1 {10-12} FWHM2 {10-12} The proportion of patients with HIV was less than 40%.

[0430] <Sample 3: c-plane thick film growth> The results for the substrate of Sample 3 will be described with reference to Table 6 and Fig. 23. Fig. 23 shows normalized X-ray diffraction patterns obtained when X-ray rocking curve measurements of {10-12} plane diffraction were performed on the nitride semiconductor substrate of Sample 3 under different measurement conditions.

[0431] As shown in Table 6 and Figure 23, when the substrate of Sample 3 was measured from a direction of 150° to the a-axis, the FWHM1 {10-12} In addition, for the substrate of sample 3, the FWHM1 {10-12} The maximum and minimum variations were more than 20 arcsec.

[0432] As shown in Figure 23, when the substrate of Sample 3 was measured from a direction at 150° to the a-axis, the {10-12} diffraction pattern under the wide measurement area condition was wider than the {10-12} diffraction pattern under the narrow measurement area condition.

[0433] Therefore, as shown in Table 6, in the substrate of Sample 3, when measured from the direction of 150° to the a-axis, FWHM1 {10-12} FWHM2 {10-12} The ratio was less than 80%.

[0434] <Sample 1: 2 cycles> The results for the substrate of Sample 1 will be described with reference to Table 6 and Fig. 22. Fig. 22 shows normalized X-ray diffraction patterns obtained when X-ray rocking curve measurements of {10-12} plane diffraction were performed on the nitride semiconductor substrate of Sample 1 under different measurement conditions.

[0435] As shown in Table 6 and Figure 22, the substrate of Sample 3 has a FWHM1 {10-12} In addition, for the substrate of Sample 3, the FWHM1 {10-12} The variation was small, with the maximum and minimum difference being less than 9 arcsec.

[0436] As shown in FIG. 22, in the substrate of Sample 1, the spread of the {10-12} diffraction pattern was small even under the wide measurement area condition.

[0437] Therefore, as shown in Table 6, the substrate of Sample 1 has a FWHM of 1 {10-12} FWHM2 {10-12} The ratio was over 80%.

[0438] In addition, the substrate of Sample 1 had no defects on the main surface, so FWHM1 {10-12} FWHM2 {10-12} The ratio was less than 100%.

[0439] (3) Summary of results for Samples 1 and 2 For Samples 1 and 2 described above, the first growth conditions were adjusted to satisfy formula (1) in the three-dimensional growth process. This ensured that the c-plane disappeared during the growth of the three-dimensional growth layer. By ensuring that the c-plane disappeared, dislocations were reliably bent at positions where the inclined interface in the three-dimensional growth layer was exposed. As a result, it was confirmed that the dislocation density on the main surface of the substrate was efficiently reduced.

[0440] Furthermore, in Sample 1, a cycle including a three-dimensional growth process and a planarization process was repeated multiple times. As a result, in the second cycle, the dislocations remaining in the planarization layer in the first cycle were further bent and the dislocations were locally collected. As a result, it was confirmed that the dislocation density of Sample 1, which underwent two cycles, was reduced more than that of Sample 2, which underwent one cycle.

[0441] In addition, in Sample 1, the average distance between nearest neighboring peaks in the second stack unit was longer than the average distance between nearest neighboring peaks in the first stack unit. This enabled the distance over which dislocations bent and propagated to be longer in the second cycle than in the first cycle. As a result, it was confirmed that the density of dislocation-free regions in a 50 μm square could be increased.

[0442] Furthermore, in Sample 1, the average distance between the nearest neighboring peaks in the second stack unit was approximately 209 μm. This ensured that the distance over which dislocations bend and propagate in the second cycle was at least 100 μm. As a result, it was confirmed that dislocation-free regions of at least 100 μm square could be formed on at least a portion of the surface of the planarizing layer in the second cycle. Furthermore, the density of non-overlapping 100 μm square dislocation-free regions on the main surface was 100 / cm. 2 It was confirmed that this could be achieved.

[0443] In Samples 1 and 2, it was confirmed that the stress-cancelling effect of the high oxygen concentration region enabled the radius of curvature of the c-plane of the substrate to be larger than the radius of curvature of the c-plane of the base substrate, thereby reducing the variation in the off-angle of the c-axis of the substrate.

[0444] Furthermore, with samples 1 and 2, not only was it possible to reduce the dislocation density and the off-angle variation, but it was also possible to achieve a good balance between all of the above-mentioned crystal quality factors that determine the half-width.

[0445] As a result, it was confirmed that, in terms of X-ray rocking curve measurements of (0002) plane diffraction, FWHMb could be reduced to 32 arcsec or less for the substrates of Samples 1 and 2. Furthermore, in Samples 1 and 2, even when the width of the entrance slit in the ω direction was set to 1 mm, the radius of curvature of the c-plane was large over the entire area irradiated with X-rays, and the above-mentioned crystal quality factors were well balanced, so it was confirmed that (FWHMa-FWHMb) / FWHMa could be reduced to 30% or less.

[0446] Furthermore, regarding the X-ray rocking curve measurement of the {10-12} plane diffraction, the substrate of sample 1 had a FWHM of 1 {10-12} It was confirmed that the FWHM1 of the substrate of Sample 1, which was measured by measuring the diffraction of the equivalent crystal plane represented by the {10-12} plane from three directions, was 50 arcsec or less. {10-12} It was confirmed that the maximum and minimum difference between the FWHM and FWHM values ​​could be reduced to 9 arcsec or less. {10-12} FWHM2 {10-12} It was confirmed that the ratio of

[0447] <Preferred embodiment of the present invention> Preferred embodiments of the present invention will be described below.

[0448] (Appendix 1) A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 {10-12} FWHM2 {10-12} The ratio is over 80% Nitride semiconductor substrate. However, FWHM1 {10-12} and FWHM2 {10-12} are the half-widths of the {10-12} plane diffraction measured by X-ray rocking curve measurement, respectively, FWHM1 {10-12} Under the incident conditions for measuring the above, Cu Kα1 X-rays are irradiated onto the center of the main surface from a Cu X-ray source through, in this order, an X-ray mirror that converts the X-rays into parallel light, a monochromator with two reflections on Ge (220), and an entrance-side opening having a width of 1.4 mm in the ω direction, which is the rotation angle direction around the rotation axis of the goniometer, and a length of 12 mm in the direction parallel to the rotation axis; FWHM1 {10-12} The receiving conditions for measuring are as follows: the receiving slit is open, and X-rays are received by a detector having an opening with a width of 14.025 mm in the ω direction without passing through an analyzer crystal; FWHM2 {10-12} The incident condition when measuring is FWHM1 {10-12} The incident conditions are the same as when measuring FWHM2 {10-12} In the light receiving condition for measuring the X-rays, the detector receives the X-rays through a Ge(220) triple-reflection analyzer crystal having an entrance aperture with a width of 6.54 mm in the ω direction.

[0449] (Appendix 2) FWHM1 {10-12} FWHM2 {10-12} The ratio is 100% or less. 2. The nitride semiconductor substrate according to claim 1.

[0450] (Appendix 3) FWHM1 was measured by measuring the diffraction of the equivalent crystal plane represented by the {10-12} plane from three directions rotated by 60° in the circumferential direction around the normal line at the center of the main surface. {10-12} The maximum and minimum difference is less than 9 arcsec. 3. The nitride semiconductor substrate according to claim 1 or 2.

[0451] (Appendix 4) A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 was measured by measuring the diffraction of the equivalent crystal plane represented by the {10-12} plane from three directions rotated by 60° in the circumferential direction around the normal line at the center of the main surface. {10-12} The maximum and minimum difference is less than 9 arcsec. Nitride semiconductor substrate. However, FWHM1 {10-12} is the half-width of the {10-12} plane diffraction measured by X-ray rocking curve measurement, FWHM1 {10-12} Under the incident conditions for measuring the above, Cu Kα1 X-rays are irradiated onto the center of the main surface from a Cu X-ray source through, in this order, an X-ray mirror that converts the X-rays into parallel light, a monochromator with two reflections on Ge (220), and an entrance-side opening having a width of 1.4 mm in the ω direction, which is the rotation angle direction around the rotation axis of the goniometer, and a length of 12 mm in the direction parallel to the rotation axis; FWHM1 {10-12} In the light receiving conditions for measuring, the light receiving slit is open and X-rays are received by a detector having an opening with a width of 14.025 mm in the ω direction without passing through an analyzer crystal.

[0452] (Appendix 5) FWHM1 {10-12} is less than 50 arcsec 5. The nitride semiconductor substrate according to any one of claims 1 to 4.

[0453] (Appendix 6) A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 {10-12} is less than 50 arcsec Nitride semiconductor substrate. However, FWHM1 {10-12} is the half-width of the {10-12} plane diffraction measured by X-ray rocking curve measurement, FWHM1 {10-12} Under the incident conditions for measuring the above, Cu Kα1 X-rays are irradiated onto the center of the main surface from a Cu X-ray source through, in this order, an X-ray mirror that converts the X-rays into parallel light, a monochromator with two reflections on Ge (220), and an entrance-side opening having a width of 1.4 mm in the ω direction, which is the rotation angle direction around the rotation axis of the goniometer, and a length of 12 mm in the direction parallel to the rotation axis; FWHM1 {10-12} In the light receiving conditions for measuring, the light receiving slit is open and X-rays are received by a detector having an opening with a width of 14.025 mm in the ω direction without passing through an analyzer crystal.

[0454] (Appendix 7) When the main surface of the nitride semiconductor substrate is observed with a multiphoton excitation microscope in a field of view of 250 μm square and the dislocation density is calculated from the dark spot density, the dislocation density is 1×10 6 cm -2 and there is no region on the main surface where the dislocation density is 7×10 5 cm -2 an area where the area is less than 80% of the main surface; The main surface has non-overlapping 50 μm square dislocation-free regions at 1000 / cm 2 With a density of more than 7. The nitride semiconductor substrate according to any one of claims 1 to 6.

[0455] (Appendix 8) A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, When the main surface of the nitride semiconductor substrate is observed with a multiphoton excitation microscope in a field of view of 250 μm square and the dislocation density is calculated from the dark spot density, the dislocation density is 1×10 6 cm -2 and there is no region on the main surface where the dislocation density is 7×10 5 cm -2 an area where the area is less than 80% of the main surface; The main surface has non-overlapping 50 μm square dislocation-free regions at 1000 / cm 2 With a density of more than Nitride semiconductor substrate.

[0456] (Appendix 9) The number of dislocations present in the rectangular region sandwiched between the opposing sides of the closest pair of dislocation-free regions is 90 or less. 9. The nitride semiconductor substrate according to claim 7 or 8.

[0457] (Appendix 10) The main surface has 100 μm square dislocation-free regions with no overlapping at 100 counts / cm 2 With a density of more than 10. The nitride semiconductor substrate according to any one of claims 7 to 9.

[0458] (Appendix 11) When Cu Kα1 X-rays were irradiated onto the principal surface through a Ge (220) plane double crystal monochromator and an entrance side slit, and the X-ray rocking curve of the (0002) plane diffraction was measured, When the width of the entrance-side slit in the ω direction is 0.1 mm, the half-width FWHMb of the (0002) plane diffraction is 32 arcsec or less, When the width of the entrance side slit in the ω direction is 1 mm, the difference FWHMa-FWHMb obtained by subtracting FWHMb from FWHMa of the (0002) plane diffraction is 30% or less of FWHMa. 11. The nitride semiconductor substrate according to any one of claims 1 to 10.

[0459] (Appendix 12) A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, When Cu Kα1 X-rays were irradiated onto the principal surface through a Ge (220) plane double crystal monochromator and an entrance side slit, and the X-ray rocking curve of the (0002) plane diffraction was measured, When the width of the entrance-side slit in the ω direction is 0.1 mm, the half-width FWHMb of the (0002) plane diffraction is 32 arcsec or less, When the width of the entrance side slit in the ω direction is 1 mm, the difference FWHMa-FWHMb obtained by subtracting FWHMb from FWHMa of the (0002) plane diffraction is 30% or less of FWHMa. Nitride semiconductor substrate.

[0460] (Appendix 13) 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 within the principal surface. 13. The nitride semiconductor substrate according to claim 11 or 12.

[0461] (Appendix 14) When X-ray rocking curve measurements of the (0002) plane diffraction are performed at a plurality of measurement points set at 5 mm intervals on the principal surface with the width of the entrance side slit in the ω direction set to 0.1 mm, the half width FWHMb of the (0002) plane diffraction is 32 arcsec or less at 90% or more of all measurement points. 14. The nitride semiconductor substrate according to any one of claims 11 to 13.

[0462] (Appendix 15) a base substrate made of a single crystal of a group III nitride semiconductor, having a mirror-finished primary surface, the lowest-index crystal plane closest to the primary surface being the (0001) plane; a lamination unit including: a low oxygen concentration region formed above the primary surface of the base substrate and made of a single crystal of a Group III nitride semiconductor; and a high oxygen concentration region formed on the low oxygen concentration region and made of a single crystal of a Group III nitride semiconductor; an uppermost low oxygen concentration region formed of a single crystal of a Group III nitride semiconductor and provided above the stacked unit; Equipped with the oxygen concentration in the high oxygen concentration region is higher than the oxygen concentrations in the low oxygen concentration region and the uppermost low oxygen concentration region, The lamination unit is repeatedly provided in a thickness direction between the base substrate and the uppermost low oxygen concentration region. Laminated structure.

[0463] (Appendix 16) an upper surface of the low oxygen concentration region in each of the plurality of stacked units has a plurality of valleys and a plurality of peaks, In the second or higher layer laminate units among the plurality of laminate units, When viewing an arbitrary cross section perpendicular to the main surface, the average distance between a pair of peaks that are closest to each other among the plurality of peaks, sandwiching one of the plurality of valleys, in a direction along the main surface is longer than that of a first laminate unit among the plurality of laminate units. 16. The laminate structure of claim 15.

[0464] (Appendix 17) In each of the plurality of stacked units, The average distance between the pair of closest peaks gradually increases toward the upper layers of the plurality of laminate units. 17. The laminate structure according to claim 15 or 16.

[0465] The manufacturing method of the present invention may be embodied, for example, in the following additional notes.

[0466] (Appendix 18) A method for manufacturing a nitride semiconductor substrate using a vapor phase growth method, comprising the steps of: (a) preparing a base substrate made of a single crystal of a group III nitride semiconductor, having a mirror-finished primary surface, and the lowest-index crystal plane closest to the primary surface being the (0001) plane; (b) epitaxially growing a single crystal of a Group III nitride semiconductor having a top surface with an exposed (0001) plane above the primary surface of the base substrate, generating a plurality of recesses on the top surface composed of inclined interfaces other than the (0001) plane, gradually expanding the inclined interfaces upward on the primary surface of the base substrate, causing the (0001) plane to disappear at least once from the top surface, and growing a three-dimensionally grown layer; (c) epitaxially growing a single crystal of a Group III nitride semiconductor on the three-dimensional growth layer to eliminate the inclined interface and grow a planarization layer having a mirror-finished surface; and A cycle including steps (b) and (c) is performed multiple times. A method for manufacturing a nitride semiconductor substrate.

[0467] (Appendix 19) In (b) in each of the plurality of cycles, generating the plurality of recesses on the top surface of the single crystal and eliminating the (0001) plane, thereby forming a plurality of valleys and a plurality of peaks on the surface of the three-dimensionally grown layer; In the (b) of the second or subsequent cycles of the plurality of cycles, When viewed in any cross section perpendicular to the main surface, the average distance between a pair of closest peaks among the plurality of peaks across one of the plurality of valleys in a direction along the main surface is made longer than that of (b) in a first cycle among the plurality of cycles. 19. A method for manufacturing a nitride semiconductor substrate according to claim 18.

[0468] (Appendix 20) In (b) in each of the plurality of cycles, The average distance between the pair of closest apexes is gradually increased as the cycles are repeated. 20. A method for manufacturing a nitride semiconductor substrate according to claim 19.

[0469] (Appendix 21) In (b) in each of the plurality of cycles, The average distance between the pair of closest apexes is set to more than 100 μm. 21. A method for producing a nitride semiconductor substrate according to claim 19 or 20.

[0470] (Appendix 22) In (b) of at least the last cycle of the plurality of cycles, The average distance between the pair of closest apexes is set to more than 200 μm. 22. A method for producing a nitride semiconductor substrate according to any one of claims 19 to 21.

[0471] (Appendix 23) In (b) in each of the plurality of cycles, The average distance between the pair of closest apexes is less than 800 μm. 23. The method for producing a nitride semiconductor substrate according to claim 21 or 22.

[0472] (Appendix 24) In the above (a), The root mean square roughness of the main surface of the base substrate is set to 1 nm or more. 24. A method for producing a nitride semiconductor substrate according to any one of claims 18 to 23.

[0473] (Appendix 25) In the above (a), leaving crystal strains introduced by processing the base substrate on the main surface side of the base substrate; When an X-ray rocking curve measurement is performed with an incident angle of 2° with respect to the main surface of the processed base substrate, the half-width of the (10-10) plane diffraction is made larger than the half-width of the base substrate before processing, and is set to 60 arcsec or more and 200 arcsec or less. 25. A method for producing a nitride semiconductor substrate according to any one of claims 18 to 24.

[0474] (Appendix 26) In (b) in each of the plurality of cycles, After the (0001) plane disappears from the surface, the three-dimensional growth layer is continued to grow to a predetermined thickness while maintaining a state in which the inclined interface occupies more of the surface than the (0001) plane. 26. A method for producing a nitride semiconductor substrate according to any one of claims 18 to 25.

[0475] (Appendix 27) (d) after the step (c) in the last cycle of the plurality of cycles, forming a main growth layer on the planarization layer, the surface of which has been mirror-finished, with the (0001) plane as a growth surface and having a predetermined thickness; (e) slicing at least one nitride semiconductor substrate from the grown layer; Further having 27. A method for producing a nitride semiconductor substrate according to any one of claims 18 to 26.

[0476] (Appendix 28) In the above (a), preparing a base substrate in which the (0001) plane is curved in a concave spherical shape relative to the main surface; In the above (e), The radius of curvature of the (0001) plane of the nitride semiconductor substrate is made larger than the radius of curvature of the (0001) plane of the base substrate. 28. A method for manufacturing a nitride semiconductor substrate according to claim 27.

[0477] (Appendix 29) In (b) in each of the plurality of cycles, The inclined interface is a {11-2m} plane where m≧3. A method for producing a nitride semiconductor substrate according to any one of claims 18 to 28.

[0478] Further, other aspects of the manufacturing method of the present invention may include, for example, the following additional features.

[0479] (Appendix 30) A method for manufacturing a nitride semiconductor substrate using a vapor phase growth method, comprising the steps of: (a) preparing a base substrate made of a single crystal of a group III nitride semiconductor, having a mirror-finished primary surface, and the lowest-index crystal plane closest to the primary surface being the (0001) plane; (b) homoepitaxially growing a single crystal of a Group III nitride semiconductor flatly above the primary surface; (c) growing a three-dimensional growth layer characterized by generating a plurality of recesses on the surface of a flat homoepitaxially grown crystal, each recess being composed of an inclined interface other than the (0001) plane, and gradually expanding the inclined interface as the crystal growth progresses, until the (0001) plane disappears at least once from the crystal growth interface; (d) further epitaxially growing a single crystal of a Group III nitride semiconductor on the three-dimensional growth layer to eliminate the inclined interface and grow a planarization layer having a mirror-finished surface consisting of a (0001) plane; and A cycle including steps (c) and (d) is performed multiple times. A method for manufacturing a nitride semiconductor substrate.

[0480] (Appendix 31) In the (c) of the second or subsequent cycles of the plurality of cycles, When viewing an arbitrary cross section perpendicular to the main surface when the (0001) plane disappears from the crystal growth interface, the average distance between a pair of closest peaks among a plurality of peaks sandwiching one valley among a plurality of valleys and a plurality of peaks present on the surface of the three-dimensional growth layer in a direction along the main surface is made longer than the average distance in (c) of the previous cycle. 31. A method for manufacturing a nitride semiconductor substrate according to claim 30.

[0481] The above-mentioned Appendices 20 to 29 can be made subordinate to the above-mentioned Appendices 30 or 31 by replacing (b) with (c), (c) with (d), (d) with (e), and (e) with (f). [Explanation of symbols]

[0482] 10 Base substrate 30 1st layer 40 2nd layer 50 Nitride semiconductor substrate (substrate)

Claims

1. A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 ｛１０－１２｝ FWHM2 for ｛１０－１２｝ The ratio is over 80% Nitride semiconductor substrate. However, FWHM1 ｛１０－１２｝ and FWHM2 ｛１０－１２｝ are the half-widths of the {10-12} plane diffraction measured by X-ray rocking curve measurement, FWHM1 ｛１０－１２｝ Under the incident conditions for measuring the above, Cu Kα1 X-rays are irradiated onto the center of the main surface from a Cu X-ray source via, in this order, an X-ray mirror that converts the X-rays into parallel light, a monochromator with two reflections on Ge (220), and an entrance-side opening having a width of 1.4 mm in the ω direction, which is the rotation angle direction around the rotation axis of the goniometer, and a length of 12 mm in a direction parallel to the rotation axis; FWHM1 ｛１０－１２｝ Under the light receiving conditions for measuring, the light receiving side slit is opened and X-rays are received by a detector having an opening with a width of 14.025 mm in the ω direction without passing through an analyzer crystal, FWHM2 ｛１０－１２｝ The incident condition when measuring is FWHM1 ｛１０－１２｝ The incident conditions are the same as when measuring FWHM2 ｛１０－１２｝ In the light receiving conditions for measuring the X-rays, the detector receives the X-rays through a Ge(220) triple-reflection analyzer crystal having an entrance aperture with a width of 6.54 mm in the ω direction.

2. FWHM1 ｛１０－１２｝ FWHM2 for ｛１０－１２｝ The ratio is 100% or less. The nitride semiconductor substrate according to claim 1 .

3. FWHM1 was measured by measuring the diffraction of an equivalent crystal plane represented by the {10-12} plane from three directions rotated 60° in the circumferential direction around the normal line at the center of the main surface. ｛１０－１２｝ The maximum and minimum difference is 9 arcsec or less. The nitride semiconductor substrate according to claim 1 or 2.

4. A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 was measured by measuring the diffraction of an equivalent crystal plane represented by the {10-12} plane from three directions rotated 60° in the circumferential direction around the normal line at the center of the main surface. ｛１０－１２｝ The maximum and minimum difference is 9 arcsec or less. Nitride semiconductor substrate. However, FWHM1 ｛１０－１２｝ is the half-width of the {10-12} plane diffraction measured by X-ray rocking curve measurement, FWHM1 ｛１０－１２｝ Under the incident conditions for measuring the above, Cu Kα1 X-rays are irradiated onto the center of the main surface from a Cu X-ray source via, in this order, an X-ray mirror that converts the X-rays into parallel light, a monochromator with two reflections on Ge (220), and an entrance-side opening having a width of 1.4 mm in the ω direction, which is the rotation angle direction around the rotation axis of the goniometer, and a length of 12 mm in a direction parallel to the rotation axis; FWHM1 ｛１０－１２｝ In the light receiving conditions for measuring , the light receiving side slit is open and X-rays are received by a detector having an opening with a width of 14.025 mm in the ω direction without passing through an analyzer crystal.

5. FWHM1 ｛１０－１２｝ is less than or equal to 50 arcsec The nitride semiconductor substrate according to any one of claims 1 to 4.

6. A nitride semiconductor substrate having a diameter of 2 inches or more and a primary surface in which the nearest low-index crystal plane is the (0001) plane, FWHM1 ｛１０－１２｝ is less than or equal to 50 arcsec Nitride semiconductor substrate. However, FWHM1 ｛１０－１２｝ is the half-width of the {10-12} plane diffraction measured by X-ray rocking curve measurement, FWHM1 ｛１０－１２｝ Under the incident conditions for measuring the above, Cu Kα1 X-rays are irradiated onto the center of the main surface from a Cu X-ray source via, in this order, an X-ray mirror that converts the X-rays into parallel light, a monochromator with two reflections on Ge (220), and an entrance-side opening having a width of 1.4 mm in the ω direction, which is the rotation angle direction around the rotation axis of the goniometer, and a length of 12 mm in a direction parallel to the rotation axis; FWHM1 ｛１０－１２｝ In the light receiving conditions for measuring , the light receiving side slit is open and X-rays are received by a detector having an opening with a width of 14.025 mm in the ω direction without passing through an analyzer crystal.

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