Nitride semiconductor substrate, laminated structure, and method for manufacturing nitride semiconductor substrate

Abstract

A nitride semiconductor substrate is formed of a single crystal of a group III nitride semiconductor and has a main surface with the nearest low-index crystal plane being a (0001) plane, wherein the nitride semiconductor substrate has an inclined interface growth region that grows with an inclined interface other than the (0001) plane as a growth plane, the area ratio of the inclined interface growth region in the main surface is 80% or more, and when the main surface is observed with a multiphoton excitation microscope with a 250 μm square field of view, when the dislocation density is calculated from the dark spot density, there is no dislocation density exceeding 3×10 6 cm ‑2 The main surface is 100 pieces / cm 2 The above density has non-overlapping dislocation-free regions of 50 μm square.

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 Art

[0002] A method is known in which a substrate formed of a single crystal of a group III nitride semiconductor is used as a base substrate (seed substrate) and a crystal layer formed of a single crystal of a group III nitride semiconductor is further grown on a principal surface of the base substrate whose nearest low-index crystal plane is the (0001) plane. According to this method, at least one nitride semiconductor substrate can be obtained by slicing the crystal layer grown to a predetermined thickness (for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2013-60349 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] An object of the present invention is to provide a technology capable of easily and stably obtaining a nitride semiconductor substrate having good crystal quality.

[0008] Solutions for solving problems

[0009] According to one embodiment of the present invention, there is provided a nitride semiconductor substrate.

[0010] It is formed of a single crystal of a group III nitride semiconductor and has a primary surface whose nearest low-index crystal plane is a (0001) plane.

[0011] The nitride semiconductor substrate has an inclined interface growth region that grows with an inclined interface other than the aforementioned (0001) plane as a growth plane,

[0012] The area ratio of the inclined interface growth region in the main surface is 80% or more,

[0013] When the main surface is observed with a 250 μm square field of view using a multiphoton excitation microscope and the dislocation density is calculated from the dark spot density, there is no dislocation density exceeding 3×10 6 cm -2 area,

[0014] The main surface is 100 / cm 2 The above density has non-overlapping dislocation-free regions of 50 μm square.

[0015] According to another aspect of the present invention, there is provided a laminated structure comprising:

[0016] A base substrate, which is formed of a single crystal of a group III nitride semiconductor and has a mirror-finished main surface, wherein the nearest low-index crystal plane to the main surface is a (0001) plane;

[0017] a low oxygen concentration region which is directly provided on the main surface of the base substrate and is formed of a single crystal of a Group III nitride semiconductor; and

[0018] a high oxygen concentration region, which is provided on the low oxygen concentration region and is formed of a single crystal of a Group III nitride semiconductor,

[0019] The oxygen concentration in the high oxygen concentration region is higher than the oxygen concentration in the low oxygen concentration region.

[0020] When observing any cross section perpendicular to the above main surface,

[0021] The upper surface of the low oxygen concentration region has a plurality of valleys and a plurality of hills.

[0022] An average distance between a pair of closest peaks among the plurality of peaks sandwiching one valley among the plurality of valleys exceeds 100 μm in the direction along the main surface.

[0023] According to another aspect of the present invention, there is provided a method for manufacturing a nitride semiconductor substrate.

[0024] This is a method for manufacturing a nitride semiconductor substrate using a vapor phase growth method, and includes the following steps:

[0025] A step of preparing a base substrate, wherein the base substrate is formed of a single crystal of a group III nitride semiconductor and has a mirror-finished main surface, wherein the nearest low-index crystal plane to the main surface is a (0001) plane;

[0026] A step of epitaxially growing a single crystal of a group III nitride semiconductor having a top surface with the (0001) plane exposed directly on the main surface of the base substrate, causing a plurality of recesses to be formed on the top surface by inclined interfaces other than the (0001) plane, causing the inclined interfaces to gradually expand toward the upper side of the main surface of the base substrate, causing the (0001) plane to disappear from the top surface at least once, and causing a three-dimensional growth layer to grow; and

[0027] The three-dimensional growth layer is sliced ​​to form a nitride semiconductor substrate.

[0028] In the step of forming the three-dimensional growth layer,

[0029] The plurality of concave portions are generated on the top surface of the single crystal, and the (0001) plane is eliminated, thereby forming a plurality of valleys and a plurality of tops on the surface of the three-dimensional growth layer.

[0030] When observing any cross section perpendicular to the main surface, an average distance between a pair of closest tops among the plurality of tops sandwiching one valley among the plurality of valleys in a direction along the main surface is set to exceed 100 μm.

[0031] Effects of the Invention

[0032] According to the present invention, a nitride semiconductor substrate having good crystal quality can be easily and stably obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flowchart showing a method for manufacturing a nitride semiconductor substrate according to one embodiment of the present invention.

[0034] Figure 2 (a) to (g) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention.

[0035] Figure 3 (a) to (c) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention.

[0036] Figure 4 This 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.

[0037] Figure 5 (a) to (b) are schematic cross-sectional views showing a part of a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention.

[0038] Figure 6 (a) is a schematic cross-sectional view showing the growth process under the standard growth conditions where the inclined interface and the c-plane are neither expanded nor reduced. Figure 6 (b) is a schematic cross-sectional view showing the growth process under the first growth condition in which the inclined interface is expanded and the c-plane is reduced.

[0039] Figure 7 (a) is a schematic top view showing a nitride semiconductor substrate according to one embodiment of the present invention, Figure 7 (b) is a schematic cross-sectional view along the m-axis of the nitride semiconductor substrate according to one embodiment of the present invention, Figure 7(c) is a schematic cross-sectional view along the a-axis of the nitride semiconductor substrate according to one embodiment of the present invention.

[0040] Figure 8 This is a schematic diagram showing a cathode luminescence image obtained by observing the main surface of the nitride semiconductor substrate according to one embodiment of the present invention with a scanning electron microscope.

[0041] Fig. 9 (a) is a diagram showing an observed image obtained by observing the surface of the laminated structure of Experiment 1 using an optical microscope. Fig. 9 (b) is a diagram showing an observed image obtained by observing a cross section of the laminated structure of Experiment 1 using a fluorescence microscope.

[0042] Fig.10 This is a schematic diagram showing an observation image obtained by observing the main surface of the nitride semiconductor substrate A obtained in Experiment 1 using a multiphoton excitation microscope.

[0043] Fig.11 (a) is a diagram showing the results of measuring the rocking curve of X-ray diffraction along the m-axis direction of the nitride semiconductor substrate A obtained in Experiment 1, Fig.11 (b) is a diagram showing the results of measuring the rocking curve of X-ray diffraction along the a-axis direction of the nitride semiconductor substrate A obtained in Experiment 1.

[0044] Fig.12 (a) is a diagram showing the results of measuring the rocking curve of X-ray diffraction in a predetermined direction of the nitride semiconductor substrate B obtained in Experiment 1, Fig.12 (b) is an enlarged view of the result of measuring the rocking curve of X-ray diffraction along the a-axis direction of (a). Fig.12 (c) is an enlarged view of the result of measuring the rocking curve of X-ray diffraction along the m-axis in (a).

[0045] Fig.13 (a) is a diagram showing a cathode luminescence image obtained by observing the surface of the semiconductor layer in the laminate of the example in Experiment 2 using a scanning electron microscope. Fig.13 (b) is a diagram showing a cathode luminescence image obtained by observing the surface of the semiconductor layer in the reference laminate of the reference example in Experiment 2 using a scanning electron microscope.

[0046] Fig.14 (a) is a diagram showing the results of photoluminescence mapping measurement in the laminate of the example in Experiment 2, Fig.14(b) is a diagram showing the results of photoluminescence mapping measurement performed on the reference laminate of the reference example in Experiment 2.

[0047] Fig.15 1 and 2 are photoluminescence spectra of the semiconductor layers of the laminate of the example and the reference laminate of the reference example in Experiment 2. DETAILED DESCRIPTION

[0048] <One embodiment of the present invention>

[0049] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0050] (1) Method for manufacturing nitride semiconductor substrate

[0051] use Figure 1 to Figure 6 , a method for manufacturing a nitride semiconductor substrate according to this embodiment is described. Figure 1 This is a flowchart showing the method for manufacturing a nitride semiconductor substrate according to this embodiment. Figure 2 (a)~(g), Figure 3 (a)~(c) Figure 5 (a)~ Figure 5 (b) is a schematic cross-sectional view showing a part of the method for manufacturing a nitride semiconductor substrate according to this embodiment. Figure 4 1 is a schematic perspective view showing a part of the method for manufacturing a nitride semiconductor substrate according to the present embodiment. Figure 4 Equivalent to Figure 3 (b) is a perspective view at this time, showing a portion of the three-dimensional growth layer 30 grown on the base substrate 10. Figure 3 (c)~ Figure 5 In (b), the dotted line represents a dislocation.

[0052] like Figure 1 As shown, the method for manufacturing a nitride semiconductor substrate according to the present embodiment includes, for example, a base substrate preparation step S100 , a three-dimensional growth step S200 , a slicing step S400 , and a polishing step S500 .

[0053] (S100: Base substrate preparation step)

[0054] First, in the base substrate preparation step S100, a base substrate 10 formed of a single crystal of a group III nitride semiconductor is prepared. In the present embodiment, as the base substrate 10, for example, a gallium nitride (GaN) free-standing substrate is prepared.

[0055] It should be noted that, in the crystal of a Group III nitride semiconductor having a wurtzite structure, <0001> The axis (for example, the

[0001] axis) is called the "c-axis", and the (0001) plane is called the "c-plane". It should be noted that the (0001) plane is sometimes called the "+c plane (Group III element polar plane)", and the (000-1) plane is called the "-c plane (nitrogen (N) polar plane)". In addition, the <1-100> axis (for example, the [1-100] axis) is called the "m-axis", and the {1-100} plane is called the "m-plane". It should be noted that the m-axis can be recorded as the <10-10> axis. In addition, the <11-20> axis (for example, the [11-20] axis) is called the "a-axis", and the {11-20} plane is called the "a-plane".

[0056] In the base substrate preparation step S100 of the present embodiment, the base substrate 10 is produced by, for example, a VAS (Void-Assisted Separation) method.

[0057] Specifically, the base substrate preparation step S100 includes, for example, a crystal growth substrate preparation step S110, a first crystal layer forming step S120, a metal layer forming step S130, a pore forming step S140, a second crystal layer forming step S150, a peeling step S160, a slicing step S170 and a grinding step S180.

[0058] (S110: Crystal Growth Substrate Preparation Step)

[0059] First, if Figure 2 As shown in (a), a substrate 1 for crystal growth (hereinafter sometimes abbreviated as "substrate 1") is prepared. Substrate 1 is, for example, a sapphire substrate. It should be noted that substrate 1 may also be, for example, a Si substrate or a gallium arsenide (GaAs) substrate. Substrate 1 has, for example, a principal surface 1s that serves as a growth surface. The low-index crystal plane closest to principal surface 1s is, for example, c-plane 1c.

[0060] In this embodiment, the c-plane 1c of the substrate 1 is tilted relative to the main surface 1s. The c-axis 1ca of the substrate 1 is tilted at a predetermined deviation angle θ0 relative to the normal line of the main surface 1s. The deviation angle θ0 in the main surface 1s of the substrate 1 is uniform throughout the main surface 1s. The deviation angle θ0 in the main surface 1s of the substrate 1 affects the deviation angle θ3 at the center of the main surface 10s of the base substrate 10 described later.

[0061] (S120: First Crystal Layer Formation Step)

[0062] Then, if Figure 2As shown in (b), for example, by using the metal organic vapor phase epitaxy (MOVPE) method, trimethylgallium (TMG) gas as a Group III raw material gas, ammonia (NH3) gas as a nitrogen raw material gas, and monosilane (SiH4) gas as an n-type dopant gas are supplied to the substrate 1 heated to a predetermined growth temperature, thereby causing a low-temperature grown GaN buffer layer and a Si-doped GaN layer as the first crystal layer (base growth layer) 2 to grow in sequence on the main surface 1s of the substrate 1. At this time, the thickness of the low-temperature grown GaN buffer layer and the thickness of the Si-doped GaN layer are set to, for example, 20 nm and 0.5 μm, respectively.

[0063] (S130: Metal Layer Forming Step)

[0064] Then, if Figure 2 As shown in (c) of FIG. 1 , a metal layer 3 is deposited on the first crystal layer 2. A titanium (Ti) layer is used as the metal layer 3, for example. The thickness of the metal layer 3 is set to 20 nm, for example.

[0065] (S140: Hole Forming Step)

[0066] Next, the above-mentioned substrate 1 is put into an electric furnace, and the substrate 1 is placed on a susceptor having a specified heater. After the substrate 1 is placed on the susceptor, the substrate 1 is heated by a heater and heat-treated in an atmosphere containing hydrogen or hydride gas. Specifically, for example, heat treatment is performed at a specified temperature for 20 minutes in a flow of hydrogen (H2) gas containing 20% ​​NH3 gas. It should be noted that the heat treatment temperature is set to, for example, not less than 850°C and not more than 1100°C. By performing such a heat treatment, the metal layer 3 is nitrided to form a metal nitride layer 5 having a high density of fine pores on the surface. In addition, by performing the above-mentioned heat treatment, a portion of the first crystal layer 2 is etched through the pores of the metal nitride layer 5, and a high density of pores is formed in the first crystal layer 2.

[0067] Therefore, if Figure 2 As shown in (d) of FIG. 5 , a first crystal layer 4 containing pores is formed.

[0068] (S150: Second Crystal Layer Formation Step)

[0069] Next, 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, for example, by using the hydride vapor phase epitaxy (HVPE) method, thereby causing the Si-doped GaN layer as the second crystal layer (formal growth layer) 6 to be epitaxially grown on the first crystal layer 4 containing vacancies and the metal nitride layer 5. It should be noted that, as an n-type dopant gas, germanium tetrachloride (GeCl4) gas or the like may be supplied instead of SiH2Cl2 gas, thereby causing the Ge-doped GaN layer as the second crystal layer 6 to be epitaxially grown.

[0070] At this time, the second crystal layer 6 grows from the first crystal layer 4 containing voids through the voids in the metal nitride layer 5 on the first crystal layer 4 containing voids and the metal nitride layer 5. A portion of the voids in the first crystal layer 4 containing voids are filled with the second crystal layer 6, but the other portions of the voids in the first crystal layer 4 containing voids remain. A flat gap is formed between the second crystal layer 6 and the metal nitride layer 5 due to the voids remaining in the first crystal layer 4 containing voids. This gap causes the second crystal layer 6 to be peeled off in the peeling step S160 described later.

[0071] At this time, the second crystal layer 6 grows while inheriting the orientation of the substrate 1. That is, the off angle θ1 in the principal surface of the second crystal layer 6 is uniform over the entire principal surface, similarly to the off angle θ0 in the principal surface 1s of the substrate 1.

[0072] 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. The upper limit of the thickness of the second crystal layer is not particularly limited, but from the viewpoint of improving productivity, the thickness of the second crystal layer 6 is preferably set to 50 mm or less.

[0073] (S160: Peeling Step)

[0074] After the growth of the second crystal layer 6 is completed, while the HVPE apparatus used to grow the second crystal layer 6 is being cooled, the second crystal layer 6 is naturally peeled off from the substrate 1 with the pore-containing first crystal layer 4 and the metal nitride layer 5 as the boundary.

[0075] At this time, in the second crystal layer 6, tensile stress is introduced due to the mutual attraction of the initial nuclei generated during the growth process. Therefore, due to the tensile stress generated in the second crystal layer 6, internal stress acts in the second crystal layer 6 to make the surface side concave. In addition, the dislocation density on the main surface (surface) side of the second crystal layer 6 becomes low, while the dislocation density on the back side of the second crystal layer 6 becomes high. Therefore, also due to the difference in dislocation density in the thickness direction of the second crystal layer 6, internal stress acts in the second crystal layer 6 to make the surface side concave.

[0076] The results, such as Figure 2 As shown in (f), the second crystal layer 6 is warped in a concave manner on its surface side after being peeled off from the substrate 1. Therefore, the c-plane 6c of the second crystal layer 6 is curved into a concave spherical shape relative to the plane perpendicular to the normal direction of the center of the main surface 6s of the second crystal layer 6. The deviation angle θ2 formed by the c-axis 6ca relative to the normal to the center of the main surface 6s of the second crystal layer 6 has a predetermined distribution.

[0077] (S170: Slicing process)

[0078] Then, if Figure 2 As shown in (f) of FIG. 8 , for example, the second crystal layer 6 is sliced ​​using a wire saw along a cut surface SS that is substantially perpendicular to a normal direction of the center of the primary surface 6 s of the second crystal layer 6 .

[0079] Therefore, if Figure 2 As shown in (g), a base substrate 10 is formed as an in-situ sliced ​​substrate. At this time, the thickness of the base substrate 10 is set to, for example, 450 μm. It should be noted that the deviation angle θ3 of the base substrate 10 may change from the deviation angle θ2 of the second crystal layer 6 due to the slicing direction dependency.

[0080] (S180: grinding process)

[0081] Next, both surfaces of the base substrate 10 are polished by a polishing device. Thus, the main surface 10s of the base substrate 10 is mirror-finished.

[0082] Through the above-described base substrate preparation step S100 , the base substrate 10 formed of a GaN single crystal is obtained.

[0083] The diameter of the base substrate 10 is, for example, not less than 2 inches. The thickness of the base substrate 10 is, for example, not less than 300 μm and not more than 1 mm.

[0084] The primary surface 10s of the base substrate 10 has, for example, a primary surface (base surface) 10s that becomes an epitaxial growth surface. In the present embodiment, the low-index crystal plane closest to the primary surface 10s is, for example, a c-plane (+c-plane) 10c.

[0085] The c-plane 10c in the base substrate 10 is curved into a concave spherical shape relative to the main surface 10s. The "spherical shape" mentioned here refers to a curved surface shape that is approximately spherical. In addition, the "approximate spherical surface" mentioned here refers to an approximation within a specified error range relative to a true spherical surface or an ellipsoidal surface.

[0086] In this embodiment, the c-plane 10c of the base substrate 10 has a substantially spherical curved surface in the cross section along the m-axis and the cross section along the a-axis. The curvature radius of the c-plane 10c in the base substrate 10 is, for example, not less than 1 m and less than 10 m.

[0087] Since the c-plane 10 c in the base substrate 10 is curved, the off angle θ3 of the c-axis 10 ca with respect to the normal line to the center of the main surface 10 s of the base substrate 10 has a predetermined distribution.

[0088] In the present embodiment, the magnitude of the off angle θ3 at the center of the main surface 10 s of the base substrate 10 is set to, for example, more than 0° and not more than 1°.

[0089] It should be noted that the size and direction of the off angle θ3 at the center of the main surface 10s of the base substrate 10 can be adjusted by, for example, the size and direction of the off angle θ0 of the crystal growth substrate 1 used in the above-mentioned VAS method, and the slicing angle and slicing direction in the slicing step S170.

[0090] In addition, in the present embodiment, the root mean square roughness RMS of the main surface 10 s of the base substrate 10 is set to, for example, less than 1 nm.

[0091] In addition, in the present embodiment, the base substrate 10 is produced by the VAS method, and therefore the dislocation density in the main surface 10s of the base substrate 10 is low. Specifically, the dislocation density in the main surface 10s of the base substrate 10 is, for example, 3×10 6 cm -2 More than and less than 1×10 7 cm -2 .

[0092] (S200: Three-dimensional growth process)

[0093] After preparing the base substrate 10, Figure 3 As shown in (a), the following three-dimensional growth process S200 is performed using a base substrate 10 in a state where neither a mask layer is formed on the main surface 10s nor a concave-convex pattern is formed on the main surface 10s. It should be noted that the "mask layer" mentioned here refers to a mask layer formed of silicon oxide and having a predetermined opening, for example, as used in the so-called ELO (Epitaxial Lateral Overgrowth) method. In addition, the "concave-convex pattern" mentioned here refers to at least any one of the grooves and ridges obtained by directly patterning the main surface of the base substrate, for example, as used in the so-called suspended epitaxy method. The height difference of the concave-convex pattern mentioned here is, for example, greater than 100 nm. The base substrate 10 of this embodiment is used for the three-dimensional growth process S200 in a state where it does not have the above-mentioned structure.

[0094] First, if Figure 3 (b) Figure 3 (c) Figure 4 and Figure 5 As shown in FIG. 1 (a), a single crystal of a group III nitride semiconductor having a top surface 30 u with a c-plane 30 c exposed is epitaxially grown directly on the main surface 10 s of the base substrate 10 .

[0095] At this time, a plurality of recesses 30p formed by being surrounded by the inclined interfaces 30i other than the c-plane are generated on the top surface 30u of the single crystal, and the inclined interfaces 30i are gradually expanded and the c-plane 30c is gradually reduced as the main surface 10s of the base substrate 10 is moved upward. Thus, the c-plane 30c disappears from the top surface 30u at least once. As a result, a three-dimensional growth layer 30 having the inclined interfaces 30i in a large range on the surface is formed.

[0096] In addition, at this time, an inclined interface growth region 70 (gray portion in the figure) that grows with the inclined interface 30i other than the c-plane as a growth plane is formed in the three-dimensional growth layer 30. In addition, as described later, in the cross section along the main surface 10s of the base substrate 10 in the three-dimensional growth layer 30, the area occupied by the inclined interface growth region 70 is set to, for example, 80% or more.

[0097] In this way, in the three-dimensional growth step S200, the three-dimensional growth layer 30 is three-dimensionally grown in such a manner that the main surface 10s of the base substrate 10 is intentionally roughened. It should be noted that even if the three-dimensional growth layer 30 forms such a growth morphology, it will grow as a single crystal as described above. In this respect, the three-dimensional growth layer 30 is different from a so-called low-temperature growth buffer layer formed in an amorphous or polycrystalline form on a heterogeneous substrate such as sapphire before epitaxially growing a group III nitride semiconductor on the heterogeneous substrate.

[0098] In the present embodiment, as the three-dimensional growth layer 30, for example, a layer formed of the same group III nitride semiconductor as the group III nitride semiconductor constituting the base substrate 10 is epitaxially grown. Specifically, for example, by using the HVPE method, the base substrate 10 is heated, and GaCl gas and NH3 gas are supplied to the heated base substrate 10, thereby epitaxially growing a GaN layer as the three-dimensional growth layer 30.

[0099] Here, in the three-dimensional growth step S200 , in order to express the above-mentioned growth process, for example, the three-dimensional growth layer 30 is grown under a predetermined first growth condition.

[0100] First, use Figure 6 (a) will be described with respect to the reference growth condition in which the inclined interface 30i and the c-plane 30c are neither expanded nor shrunk. Figure 6(a) is a schematic cross-sectional view showing the growth process under the standard growth conditions where the inclined interface and the c-plane neither expand nor shrink.

[0101] exist Figure 6 In (a), the thick solid line represents the surface of the three-dimensional growth layer 30 per unit time. Figure 6 The inclined interface 30i shown in (a) is set to be the most inclined interface relative to the c-plane 30c. Figure 6 In (a), the growth rate of the c-plane 30c in the three-dimensional growth layer 30 is denoted as G c0 , the growth rate of the inclined interface 30i in the three-dimensional growth layer 30 is recorded as G i , the angle between the c-plane 30c in the three-dimensional growth layer 30 and the inclined interface 30i is denoted as α. Figure 6 In (a), the three-dimensional growth layer 30 grows while maintaining the angle α between the c-plane 30c and the inclined interface 30i. It should be noted that the deviation angle of the c-plane 30c of the three-dimensional growth layer 30 is negligible compared to the angle α between the c-plane 30c and the inclined interface 30i.

[0102] like Figure 6 As shown in (a), when the inclined interface 30i and the c-plane 30c are neither expanded nor reduced, the trajectory of the intersection of the inclined interface 30i and the c-plane 30c is perpendicular to the c-plane 30c. Therefore, the baseline growth condition in which the inclined interface 30i and the c-plane 30c are neither expanded nor reduced satisfies the following formula (a).

[0103] G c0 =G i / cosα···(a)

[0104] Next, use Figure 6 (b) will now be described the first growth condition in which the inclined interface 30i is expanded and the c-plane 30c is reduced. Figure 6 (b) is a schematic cross-sectional view showing the growth process under the first growth condition in which the inclined interface is expanded and the c-plane is reduced.

[0105] exist Figure 6 In (b), it is also related to Figure 6 Similarly, the thick solid line represents the surface of the three-dimensional growth layer 30 per unit time. Figure 6 The inclined interface 30i shown in (b) is also set to be the most inclined interface relative to the c-plane 30c. Figure 6 In (b), the growth rate of the c-plane 30c in the three-dimensional growth layer 30 is denoted as G c1, the advancing speed of the trajectory of the intersection of the inclined interface 30i and the c-plane 30c in the three-dimensional growth layer 30 is recorded as R1. In addition, the narrower angle among the angles formed by the trajectory of the intersection of the inclined interface 30i and the c-plane 30c and the c-plane 30c is recorded as α R1 . Align the direction of R1 with G i When the angle between the two directions is denoted as α', α'=α+90-α R1 It should be noted that the deviation angle of the c-plane 30 c of the three-dimensional growth layer 30 can be ignored compared with the angle α formed by the c-plane 30 c and the inclined interface 30 i .

[0106] like Figure 6 As shown in (b), the advancing speed R1 of the trajectory of the intersection of the inclined interface 30i and the c-plane 30c is expressed by the following formula (b).

[0107] R1=G i / cosα'···(b)

[0108] In addition, the growth rate G of the c-plane 30c in the three-dimensional growth layer 30 is c1 It is represented by the following formula (c).

[0109] G c1 =R1sinα R1 ···(c)

[0110] By substituting equation (b) into equation (c), we can get G c1 G i And it is represented by the following formula (d).

[0111] G c1 =G i sinα R1 / cos(α+90-α R1 )···(d)

[0112] In order to expand the inclined interface 30i and reduce the c-plane 30c, it is preferred that α R1 <90°. Therefore, the first growth condition where the inclined interface 30i is enlarged and the c-plane 30c is reduced is preferably obtained by equation (d) and α R1 <90° to satisfy the following formula (1).

[0113] G c1 >G i / cosα···(1)

[0114] Among them, as mentioned above, G i is the growth rate of the inclined interface 30i which is most inclined relative to the c-plane 30c, and α is the angle between the inclined interface 30i which is most inclined relative to the c-plane 30c and the c-plane 30c.

[0115] Alternatively, it can be considered that G under the first growth condition c1 Preferably greater than G under baseline growth conditions c0 Therefore, by substituting formula (a) into G c1 >G c0 In the above equation, we can also derive formula (1).

[0116] It should be noted that the growth condition for expanding the inclined interface 30i most inclined with respect to the c-plane 30c is the most stringent condition. Therefore, if the first growth condition satisfies the formula (1), the other inclined interfaces 30i can also be expanded.

[0117] Specifically, for example, when the most inclined interface 30i with respect to the c-plane 30c is the {10-11} plane, α=61.95°. Therefore, the first growth condition preferably satisfies, for example, the following formula (1′).

[0118] G c1 >2.13G i ···(1')

[0119] Alternatively, as described later, for example, when the inclined interface 30i is a {11-2m} plane with m≥3, the inclined interface 30i most inclined relative to the c-plane 30c is a {11-23} plane, and therefore α=47.3°. Therefore, the first growth condition preferably satisfies, for example, the following formula (1”).

[0120] G c1 >1.47G i ···(1")

[0121] As the first growth condition of the present embodiment, for example, the growth temperature in the three-dimensional growth step S200 is typically lower than the growth temperature when the group III nitride layer is grown with the c-plane as the growth plane. Specifically, the growth temperature in the three-dimensional growth step S200 is set to, for example, 980° C. to 1020° C., preferably 1000° C. to 1020° C.

[0122] In addition, as the first growth condition of the present embodiment, for example, the ratio of the partial pressure of the flow rate of the NH3 gas as the nitrogen source gas to the partial pressure of the GaCl gas as the group III source gas in the three-dimensional growth step S200 (hereinafter also referred to as "V / III ratio") can be typically larger than the V / III ratio when the group III nitride layer is grown with the c-plane as the growth plane. 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.

[0123] In practice, as the first growth condition, at least one of the growth temperature and the V / III ratio is adjusted within the above range so as to satisfy the formula (1).

[0124] It should be noted that other conditions among the first growth conditions in this embodiment are as follows, for example.

[0125] Growth pressure: 90-105 kPa, preferably 90-95 kPa

[0126] Partial pressure of GaCl gas: 1.5~15kPa

[0127] N2 gas flow rate / H2 gas flow rate: 0~1

[0128] Here, the three-dimensional growth step S200 of the present embodiment is classified into two steps, for example, according to the morphology of the three-dimensional growth layer 30 during growth. Specifically, the three-dimensional growth step S200 of the present embodiment includes, for example, a tilted interface expansion step S220 and a tilted interface maintenance step S240. Through these steps, the three-dimensional growth layer 30 includes, for example, a tilted interface expansion layer 32 and a tilted interface maintenance layer 34.

[0129] (S220: Inclined Interface Enlarging Process)

[0130] First, if Figure 3 (b) and Figure 4 As shown, the inclined interface expansion layer 32 of the three-dimensional growth layer 30 formed of a single crystal of a group III nitride semiconductor is epitaxially grown directly on the main surface 10 s of the base substrate 10 under the first growth condition.

[0131] In the initial stage of the growth of the inclined interface expansion layer 32, the inclined interface expansion layer 32 is laminarly grown (two-dimensionally grown) with the c-plane 30c as the growth plane and with a predetermined thickness in the normal direction of the main surface 10s of the base substrate 10 (in the direction along the c-axis). Here, a part 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". Through this growth, an initial layer having a mirrored surface is formed with a predetermined thickness. At this time, the initial layer is continuously grown, for example, in the direction along the main surface 10s of the base substrate 10, that is, throughout the entire main surface 10s of the base substrate 10. In addition, at this time, the thickness of the initial layer is set to, for example, 1 μm or more and 100 μm or less, preferably 1 μm or more and 20 μm or less.

[0132] Thereafter, the inclined interface expansion layer 32 is slowly grown under the first growth condition, so that Figure 3 (b) and Figure 4As shown in FIG. 1 , a plurality of recesses 30p formed by the inclined interfaces 30i other than the c-plane are formed on the top surface 30u where the c-plane 30c is exposed in the inclined interface expansion layer 32. The plurality of recesses 30p formed by the inclined interfaces 30i other than the c-plane are randomly formed on the top surface 30u. Thus, the inclined interface expansion layer 32 having the c-plane 30c and the inclined interfaces 30i other than the c-plane mixed on the surface is formed.

[0133] It should be noted that the "inclined interface 30i" mentioned here refers to a growth interface that is inclined relative to the c-plane 30c, including a small face with a low index other than the c-plane, a small face with a high index other than the c-plane, or an inclined face that cannot be represented by a face index. It should be noted that the small face other than the c-plane is, for example, {11-2m}, {1-10n}, etc., wherein m and n are integers other than 0.

[0134] In this embodiment, by using the above-mentioned base substrate 10 and adjusting the first growth condition in a manner satisfying equation (1), it is possible to generate, for example, a {11-2m} plane with m≥3 as the inclined interface 30i. Thus, the inclination angle of the {11-2m} plane relative to the c-plane 30c can be reduced. Specifically, the inclination angle can be made less than 47.3°.

[0135] By further growing the inclined interface enlarged layer 32 under the first growth condition, Figure 3 As shown in (b) and (c), as the base substrate 10 is moved upward, the inclined interface 30i other than the c-plane is gradually expanded in the inclined interface expansion layer 32, and the c-plane 30c is gradually reduced. It should be noted that at this time, as the base substrate 10 is moved upward, the inclination angle of the inclined interface 30i relative to the main surface 10s of the base substrate 10 is gradually reduced. As a result, most of the inclined interface 30i finally forms the above-mentioned {11-2m} plane with m≥3.

[0136] Furthermore, when the inclined interface expansion layer 32 is gradually grown, the c-plane 30c of the inclined interface expansion layer 32 disappears at least once from the top surface 30u, and the outermost surface (uppermost surface) of the inclined interface expansion layer 32 is composed only of the inclined interface 30i.

[0137] In this way, by forming a plurality of recessed portions 30p composed of the inclined interfaces 30i other than the c-plane on the top surface 30u of the inclined interface expansion layer 32, the c-plane 30c disappears, thereby Figure 3As shown in (c), a plurality of valleys 30v and a plurality of tops 30t are formed on the surface of the inclined interface expansion layer 32. The plurality of valleys 30v are inflection points that protrude downward on the surface of the inclined interface expansion layer 32, and are formed above the positions where the inclined interfaces 30i other than the c-plane appear. On the other hand, the plurality of tops 30t are inflection points that protrude upward on the surface of the inclined interface expansion layer 32, and are formed at or above the position where the c-plane 30c disappears (last) with a pair of inclined interfaces 30i that expand in opposite directions. The valleys 30v and the tops 30t are formed alternately in the direction along the main surface 10s of the base substrate 10.

[0138] In this embodiment, as described above, in the initial stage of the growth of the inclined interface expansion layer 32, the inclined interface expansion layer 32 is grown with a predetermined thickness on the main surface 10s of the base substrate 10 with 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, a plurality of valleys 30v are formed at a position above the main surface 10s of the base substrate 10 at a distance.

[0139] Through the growth process of the inclined interface expansion layer 32 as described above, dislocations propagate in a curved manner as follows. Specifically, Figure 3 As shown in (c), multiple dislocations extending in the direction along the c-axis in the base substrate 10 propagate from the base substrate 10 toward the direction along the c-axis of the inclined interface expansion layer 32. In the region where the inclined interface expansion layer 32 grows with the c-plane 30c as the growth plane, the dislocations propagate from the base substrate 10 toward the direction along the c-axis of the inclined interface expansion layer 32. However, in the inclined interface expansion layer 32, if the growth interface where the dislocation is exposed changes from the c-plane 30c to the inclined interface 30i, the dislocation bends and propagates in a direction substantially perpendicular to the inclined interface 30i at the position where the inclined interface 30i is exposed. That is, the dislocation bends and propagates in a direction inclined relative to the c-axis. As a result, in the inclined interface expansion step S220 and subsequent steps, the dislocations are locally gathered above the approximately center between a pair of tops 30t. As a result, the dislocation density in the surface of the inclined interface maintaining layer 34 described later can be reduced.

[0140] At this time, in the present embodiment, when observing any cross section perpendicular to the main surface 10s of the base substrate 10, the average distance (also referred to as "the average distance between the closest tops") L between the closest pair of tops 30t among the multiple tops 30t sandwiching one valley among the multiple valleys 30v in the direction along the main surface 10s of the base substrate 10 is set to, for example, more than 100 μm. It should be noted that the average distance L between the closest tops is set to the distance when observing the cross section when the c-plane 30c disappears from the crystal growth interface.

[0141] When the average distance L between the closest tops is less than 100 μm, as in the case where fine hexagonal pyramid-shaped 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 of dislocation bending propagation becomes shorter in the inclined interface expansion step S220 and subsequent steps. Therefore, dislocations are not fully gathered above the approximate center between a pair of tops 30t in the inclined interface expansion layer 32. As a result, the dislocation density in the surface of the inclined interface maintenance layer 34 described later may not be sufficiently reduced. In contrast, in the present embodiment, by making the average distance L between the closest tops exceed 100 μm, it is possible to ensure that the dislocation bending propagation distance exceeds at least 50 μm in the inclined interface expansion step S220 and subsequent steps. As a result, dislocations can be fully gathered above the approximate center between a pair of tops 30t in the inclined interface expansion layer 32. As a result, the dislocation density in the surface of the inclined interface maintenance layer 34 described later can be sufficiently reduced.

[0142] On the other hand, in the present embodiment, the average distance L between the closest tops is set to be less than 800 μm. If the average distance L between the closest tops is greater than 800 μm, dislocations will be gathered throughout the entire surface, and it will take time for the c-plane 30c to disappear in the entire surface. Therefore, the productivity of the substrate 50 is reduced. In addition, if the average distance L between the closest tops is greater than 800 μm, the height from the valley 30v of the inclined interface expansion layer 32 to the top 30t sometimes becomes too high. As long as countermeasures such as buried growth are not implemented, the valley 30v on the crystal surface will become the cause of the through pit when the substrate 50 is sliced. Therefore, the acquisition yield of the substrate 50 may be reduced. In contrast, in the present embodiment, by making the average distance L between the closest tops less than 800 μm, the time for the c-plane 30c to disappear as a whole in the surface can be shortened. Thus, the productivity of the substrate 50 can be improved. In addition, by making the average distance L between the closest tops less than 800 μm, the height from the valley 30v to the top 30t of the inclined interface expansion layer 32 can be reduced. This can suppress the formation of the valley 30v that causes the through pit when slicing the substrate 50. As a result, the acquisition yield of the substrate 50 can be improved.

[0143] In addition, at this time, in the inclined interface expansion layer 32, according to the difference in growth surfaces during the growth process, a c-plane growth region (the first c-plane growth region, the base side c-plane growth region) 60 that grows with the c-plane 30c as the growth surface and an inclined interface growth region 70 that grows with the inclined interface 30i other than the c-plane as the growth surface are formed.

[0144] In addition, at this time, in the c-plane growth region 60, a valley portion 60a is formed at the position where the inclined interface 30i is generated, and a mountain portion 60b is formed at the position where the c-plane 30c disappears. In addition, in the c-plane growth region 60, a pair of inclined portions 60i are formed on both sides of the mountain portion 60b as the locus of the intersection of the c-plane 30c and the inclined interface 30i.

[0145] At this time, by making the first growth condition satisfy the formula (1), the angle β formed by the pair of inclined portions 60i when observing a cross section passing through the center of each of two adjacent valley portions 60a is, for example, 70° or less.

[0146] For these areas, see below for details.

[0147] (S240: Inclined Interface Maintaining Step)

[0148] After the c-plane 30 c disappears from the surface of the sloped interface expansion layer 32 , the growth conditions in the sloped interface maintaining step S240 are maintained under the first growth conditions as in the sloped interface expanding step S220 .

[0149] Therefore, if Figure 5 As shown in (a), the inclined interface growth region 70 occupies more than 80% of the area of ​​the surface cross section, and the growth of the three-dimensional growth layer 30 is continued over a predetermined thickness. As a result, the inclined interface maintaining layer 34 is formed on the inclined interface expansion layer 32.

[0150] Here, in the three-dimensional growth step S200, as described above, in order to surely bend the propagation direction of dislocations and reduce the dislocation density, it is important that the c-plane 30c disappears at least once when observing the history of the growth interface at any position of the three-dimensional growth layer 30. Therefore, it is ideal that the c-plane 30c disappears at least once in the early stage of the three-dimensional growth step S200 (for example, the above-mentioned inclined interface expansion step S220).

[0151] However, in the inclined interface maintaining step S240, if the c-face 30c is made to disappear at least once, the c-face 30c may reappear on a part of the surface of the inclined interface maintaining layer 34. Among them, as described above, it is preferred that the inclined interface 30i is mainly exposed on the surface of the inclined interface maintaining layer 34 in such a way that the area ratio of the inclined interface growth region 70 in the surface cross section becomes 80% or more. If the area ratio of the inclined interface growth region 70 in the surface cross section is less than 80%, cracks may be generated during growth. In addition, it may be difficult to perform processing such as slicing and grinding. In contrast, in the present embodiment, by making the area ratio of the inclined interface growth region 70 in the surface cross section be 80% or more, it is possible to suppress the generation of cracks during growth, and it is also possible to easily perform processing such as slicing and grinding.

[0152] It should be noted that the higher the area ratio of the inclined interface growth region 70 in the surface cross section, the better, and is preferably 100%.

[0153] However, as described above, in the three-dimensional growth process 200, for example, the c-plane 30c sometimes reappears on a portion of the surface of the inclined interface maintaining layer 34, resulting in the area ratio of the inclined interface growth region 70 in the surface cross section being less than 100%. At this time, the inclined interface growth region 70 and the c-plane growth region (the second c-plane growth region) 80 are mixed in a portion of the three-dimensional growth layer 30. In the inclined interface growth region 70, oxygen as an n-type impurity is relatively easy to mix in, while in the mixed c-plane growth region 80, the mixing of oxygen is relatively suppressed. Therefore, the oxygen concentration in the c-plane growth region 80 is lower than the oxygen concentration in the inclined interface growth region 70, and the carrier concentration in the c-plane growth region 80 is lower than the carrier concentration in the inclined interface growth region 70. As a result, in the substrate 50 cut out from the region where the inclined interface growth region 70 and the c-plane growth region 80 are mixed, there is a possibility that an in-plane deviation of the carrier concentration will occur.

[0154] Therefore, in the three-dimensional growth process S200 of the present embodiment, for example, it is preferred to add conductive impurities in a concentration greater than or equal to the concentration of oxygen mixed into the inclined interface growth region 70. As the conductive impurities, for example, at least one of Si or Ge as n-type impurities. For example, in at least the inclined interface maintaining process S240 in the three-dimensional growth process S200, when the inclined interface maintaining layer 34 is grown at a predetermined position of the slice of the substrate 50, conductive impurities can be added at the above concentration. It should be noted that conductive impurities can be added to the entire three-dimensional growth layer 30 at the above concentration. By adding such conductive impurities, the carrier concentration in the 2c-plane growth region can be suppressed from being relatively low. As a result, the in-plane deviation of the carrier concentration in the substrate 50 can be suppressed.

[0155] In addition, at this time, the inclined interface maintaining layer 34 is grown mainly with the inclined interface 30i as the growth plane under the first growth condition, so that as described above, at the position where the inclined interface 30i is exposed in the inclined interface expansion layer 32, the dislocations that bend and propagate in the direction inclined relative to the c-axis continue to propagate in the inclined interface maintaining layer 34 along the same direction. As a result, in the inclined interface maintaining layer 34, dislocations are locally gathered at the junction of adjacent inclined interfaces 30i. In the inclined interface maintaining layer 34, among the multiple dislocations gathered at the junction of adjacent inclined interfaces 30i, dislocations with mutually opposite Burgers vectors disappear when they meet. In addition, a part of the multiple dislocations gathered at the junction of adjacent inclined interfaces 30i forms a closed loop, and the propagation in the direction along the c-axis (i.e., the surface side of the inclined interface maintaining layer 34) is suppressed. It should be noted that the propagation direction of other parts of the plurality of dislocations gathered at the junction of the adjacent inclined interfaces 30i in the inclined interface maintaining layer 34 is changed from the direction inclined relative to the c-axis to the direction along the c-axis again, and propagates to the surface side of the inclined interface maintaining layer 34. In this way, by making part of the plurality of dislocations disappear or suppressing part of the plurality of dislocations from propagating to the surface side of the c-plane expansion layer 42, the dislocation density in the surface of the inclined interface maintaining layer 34 can be reduced. In addition, by locally gathering the dislocations, a low dislocation density region can be formed above the portion in the inclined interface maintaining layer 34 where the dislocations propagate in the direction inclined relative to the c-axis.

[0156] In the inclined interface maintaining step S240, the thickness of the inclined interface maintaining layer 34 is set to a thickness obtained by, for example, adding 300 μm or more and 10 mm or less to the height from the valley 30v to the top 30t of the inclined interface expansion layer 32. By setting the thickness of the inclined interface maintaining layer 34 to be 300 μm or more, at least one substrate 50 can be cut out from the inclined interface maintaining layer 34 in the slicing step S400 described later. On the other hand, by setting the thickness of the inclined interface maintaining layer 34 to 10 mm, when the final thickness is set to 650 μm and a substrate 50 of 700 μm thickness is cut out from the inclined interface maintaining layer 34, at least 10 substrates 50 can be obtained even if a cutting loss of about 200 μm is taken into account.

[0157] It should be noted that, at the end of the growth of the inclined interface maintaining layer 34, if the growth with the inclined interface 30i as the growth plane is mainly maintained, the inclined angle of the inclined interface 30i relative to the main surface 10s of the base substrate 10 does not necessarily need to be maintained on the surface of the inclined interface maintaining layer 34. For example, at least a part of the concave portion 30p of the inclined interface maintaining layer 34 may be buried at the end of the growth of the inclined interface maintaining layer 34. At this time, the inclination angle of the inclined interface 30i may be gradually reduced, and the index m of the {11-2m} plane may be gradually increased.

[0158] Through the above three-dimensional growth step S200 , the three-dimensional growth layer 30 including the sloped interface expansion layer 32 and the sloped interface maintaining layer 34 is formed.

[0159] It should be noted that the above-mentioned inclined interface expansion step S220 and inclined interface maintenance step S240 are continuously performed in the same chamber without exposing the base substrate 10 to the atmosphere. Thus, it is possible to suppress the formation of an unexpected high oxygen concentration region (a region having an excessively high oxygen concentration compared to the inclined interface growth region 70) at the interface between the inclined interface expansion layer 32 and the inclined interface maintenance layer 34.

[0160] (S400: Slicing process)

[0161] Then, if Figure 5 As shown in (b), for example, the three-dimensional growth layer 30 is sliced ​​using a wire saw along a cut plane substantially parallel to the main surface 10s of the base substrate 10. Thus, at least one nitride semiconductor substrate 50 (also referred to as substrate 50) serving as an in-situ sliced ​​substrate is formed. At this time, the thickness of the substrate 50 is set to, for example, 300 μm or more and 700 μm or less.

[0162] At this time, for example, the substrate 50 is formed by slicing the inclined interface maintaining layer 34. In addition, for example, the inclined interface maintaining layer 34 is sliced ​​at a position above the position where the c-plane growth region 60 that lasts on the base substrate 10 disappears (i.e., the mountain portion 60b of the c-plane growth region 60). Thus, the substrate 50 with reduced dislocation can be stably obtained.

[0163] In addition, at this time, the curvature radius (absolute value) of the c-plane 50c of the substrate 50 can be made larger than the curvature radius (absolute value) of the c-plane 10c of the base substrate 10. Thus, the deviation of the offset angle θ of the c-axis 50ca of the substrate 50 with respect to the normal line of the main surface 50s can be made smaller than the deviation of the offset angle of the c-axis 10ca of the base substrate 10.

[0164] (S500: grinding process)

[0165] Next, a polishing device is used to polish both surfaces of the substrate 50. In this case, the thickness of the final substrate 50 is set to, for example, 250 μm or more and 650 μm or less.

[0166] Through the above steps S100 to S500 , the substrate 50 according to the present embodiment is manufactured.

[0167] (Process for producing a semiconductor stack and process for producing a semiconductor device)

[0168] After manufacturing the substrate 50, a semiconductor functional layer formed of, for example, a group III nitride semiconductor is epitaxially grown on the substrate 50 to manufacture a semiconductor stack. After manufacturing the semiconductor stack, electrodes are formed using the semiconductor stack, and the semiconductor stack is cut into chips of a predetermined size. Thus, a semiconductor device is manufactured.

[0169] (2) Laminated structure

[0170] Next, use Figure 5 (a) of the present invention will now be described with respect to the stacked structure 90 according to the present embodiment.

[0171] The stacked structure 90 of the present embodiment includes, for example, a base substrate 10 and a three-dimensional growth layer 30 .

[0172] The three-dimensional growth layer 30 grows, for example, on the main surface 10 s of the base substrate 10 .

[0173] The three-dimensional growth layer 30 is formed by, for example, generating a plurality of recesses 30 p formed by inclined interfaces 30 i other than the c-plane on the top surface 30 u of the single crystal of the group III nitride semiconductor and eliminating the c-plane 30 c at least once.

[0174] In addition, the three-dimensional growth layer 30 has a c-plane growth region (first low oxygen concentration region) 60 and an inclined interface growth region (high oxygen concentration region) 70 , for example, based on the difference in growth planes during the growth process.

[0175] The c-plane growth region 60 is a region where the growth is performed with the c-plane 30c as the growth plane. As described above, the mixing of oxygen in the c-plane growth region 60 is suppressed compared to the inclined interface growth region 70. Therefore, the oxygen concentration in the c-plane growth region 60 is lower than that 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 Below, preferably 3×10 16 cm -3 the following.

[0176] Since the c-plane 30 c disappears at least once, the c-plane growth region 60 is discontinuous from the base substrate 10 to the surface (uppermost surface) of the three-dimensional growth layer 30 .

[0177] The c-plane growth region 60 has, for example, a plurality of valleys 60a and a plurality of hills 60b in cross-sectional view. It should be noted that the valleys 60a and hills 60b mentioned here refer to a portion of the shape observed based on the difference in luminous intensity when observing the cross section of the stacked structure 90 using a fluorescent microscope or the like, and do not refer to a portion of the outermost shape generated in the middle of the growth of the three-dimensional growth layer 30. The plurality of valleys 60a are inflection points that protrude downward in the c-plane growth region 60 in cross-sectional view, and are formed at a position where the inclined interface 30i is generated. At least one (or all) of the plurality of valleys 60a is arranged at a position above the main surface 10s of the base substrate 10 at a distance. On the other hand, the plurality of hills 60b are inflection points that protrude upward in the c-plane growth region 60 in cross-sectional view, and are formed at a position where the c-plane 30c disappears (finally) by sandwiching a pair of inclined interfaces 30i that expand in opposite directions. The valley portions 60 a and the peak portions 60 b are alternately formed in a direction along the main surface 10 s of the base substrate 10 .

[0178] When observing any cross section perpendicular to the main surface of the base substrate 10, the average distance between the closest peaks during the growth of the three-dimensional growth layer 30 corresponds to the average distance between the peaks 60b of the c-plane growth region 60. The average distance between the peaks 60b of the c-plane growth region 60 exceeds 100 μm, for example.

[0179] The c-plane growth region 60 has a pair of inclined portions 60i provided as the locus of the intersection of the c-plane 30c and the inclined interface 30i on both sides of one of the plurality of mountain portions 60b. It should be noted that the inclined portion 60i mentioned here refers to a part of the shape observed based on the difference in luminous intensity when observing the cross section of the stacked structure 90 using a fluorescent microscope or the like, and does not refer to the outermost inclined interface 30i generated in the middle of the growth of the three-dimensional growth layer 30.

[0180] The angle β formed by the pair of inclined portions 60i when observing a cross section passing through the center of each of the two adjacent valley portions 60a is, for example, 70° or less, preferably 20° or more and 65° or less. The angle β formed by the pair of inclined portions 60i being 70° or less means that under the first growth condition, the growth rate G of the c-plane 30c in the three-dimensional growth layer 30 is c1 The growth rate G of the inclined interface 30i which is most inclined with respect to the c-plane 30c in the three-dimensional growth layer 30 is i The ratio G c1 / G iHigh. Thus, it is possible to easily generate an inclined interface 30i other than the c-plane. As a result, at the position where the inclined interface 30i is exposed, the dislocation can be easily bent. In addition, by setting the angle β formed by a pair of inclined portions 60i to less than 70°, it is possible to easily generate a plurality of valleys 30v and a plurality of tops 30t above the main surface 10s of the base substrate 10. Furthermore, by setting the angle β formed by a pair of inclined portions 60i to less than 65°, it is possible to further easily generate an inclined interface 30i other than the c-plane, and it is possible to more easily generate a plurality of valleys 30v and a plurality of tops 30t above the main surface 10s of the base substrate 10. It should be noted that by setting the angle β formed by a pair of inclined portions 60i to more than 20°, it is possible to suppress the height from the valley 30v of the three-dimensional growth layer 30 to the top 30t from becoming higher. Thus, it is possible to minimize the area where a qualified substrate cannot be obtained due to the generation of through pits due to the valley 30v when slicing the substrate 50.

[0181] On the other hand, the inclined interface growth region 70 is a region that grows with the inclined interface 30 i other than the c-plane as a growth plane.

[0182] Oxygen is more easily mixed into the inclined interface growth region 70 than in 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. It should be noted that the oxygen mixed into the inclined interface growth region 70 is, for example, oxygen accidentally mixed into the HVPE device or oxygen released from components (quartz components, etc.) constituting the HVPE device.

[0183] Specifically, the oxygen concentration in the inclined interface growth region 70 is, for example, 9×10 17 cm -3 Above and 5×10 19 cm -3 the following.

[0184] The inclined interface growth region 70 is provided on the c-plane growth region 60. The lower surface of the inclined interface growth region 70 is formed along the shape of the c-plane growth region 60, for example.

[0185] At least a portion of the inclined interface growth region 70 is continuously provided along the main surface of the base substrate 10. That is, when observing a plurality of cross sections (surface cross sections) obtained by cutting the three-dimensional growth layer 30 along the main surface 10s of the base substrate 10, it is ideal that at least a portion of the three-dimensional growth layer 30 in the thickness direction has a cross section that does not include a c-plane growth region grown with the c-plane 30c as the growth plane.

[0186] The inclined interface maintaining layer 34 continues to grow mainly with the inclined interface 30 i as the growth plane, so that the area ratio of the inclined interface growth region 70 in the surface cross section obtained by cutting the three-dimensional growth layer 30 along the main surface 10 s of the base substrate 10 is, for example, 80% or more.

[0187] It should be noted that, as described above, in a predetermined surface cross section, the area ratio occupied by the inclined interface growth region 70 is sometimes less than 100%. That is, a surface cross section in which the inclined interface growth region 70 and the second c-plane growth region (equivalent to the c-plane growth region 80 described later) are mixed is sometimes produced. The second c-plane growth region mixed in the surface cross section has, for example, an oxygen concentration equivalent to the oxygen concentration of the c-plane growth region 60 described above.

[0188] During the growth of the three-dimensional growth layer 30 , the c-plane growth region 80 is generated or disappears. Therefore, the size of the c-plane growth region 80 in a plan view randomly changes from the main surface 10 s of the base substrate 10 toward the surface of the three-dimensional growth layer 30 .

[0189] In addition, as described above, during the growth process of the three-dimensional growth layer 30, the c-plane 30c disappears at least once. Therefore, the c-plane growth region 80, like the c-plane growth region 60, is discontinuous from the main surface 10s of the base substrate 10 to the surface (topmost surface) of the three-dimensional growth layer 30.

[0190] In the present embodiment, during the growth of the three-dimensional growth layer 30, at a position where the inclined interface 30i other than the c-plane is exposed, dislocations bend and propagate in a direction substantially perpendicular to the inclined interface 30i, thereby, in the inclined interface maintaining layer 34, a part of the plurality of dislocations disappear or a part of the plurality of dislocations are suppressed from propagating toward the surface side of the inclined interface maintaining layer 34. As a result, the dislocation density in the surface of the inclined interface maintaining layer 34 is reduced compared to the dislocation density in the main surface 10s of the base substrate 10.

[0191] In addition, in the present embodiment, the surface of the three-dimensional growth layer 30 is oriented along the +c plane as a whole, and the three-dimensional growth layer 30 does not contain a polarity inversion domain. In this respect, the stacked structure 90 of the present embodiment is different from a stacked structure formed by the so-called DEEP (Dislocation Elimination by the Epitaxial-growth with inverse-pyramidal Pits) method, that is, a stacked structure including a polarity inversion domain in the core located at the center of the pit.

[0192] (3) Nitride semiconductor substrates (nitride semiconductor self-supporting substrates, nitride crystal substrates)

[0193] Next, use Figure 7 and Figure 8 , the nitride semiconductor substrate 50 according to this embodiment is described. Figure 7 (a) is a schematic top view showing the nitride semiconductor substrate according to the present embodiment, Figure 7 (b) is a schematic cross-sectional view along the m-axis of the nitride semiconductor substrate according to this embodiment, Figure 7 (c) is a schematic cross-sectional view of the nitride semiconductor substrate according to this embodiment along the a-axis. Figure 8 This is a schematic diagram showing a cathode luminescence image obtained by observing the main surface of the nitride semiconductor substrate according to the present embodiment with a scanning electron microscope (SEM).

[0194] In the present embodiment, the substrate 50 obtained by the above-mentioned manufacturing method is, for example, a free-standing substrate formed of a single crystal of a group III nitride semiconductor. In the present embodiment, the substrate 50 is, for example, a GaN free-standing substrate.

[0195] The diameter of the substrate 50 is, for example, not less than 2 inches. The thickness of the substrate 50 is, for example, not less than 300 μm and not more than 1 mm.

[0196] The substrate 50 has, for example, a principal surface 50s that serves as an epitaxial growth surface. In the present embodiment, the low-index crystal plane closest to the principal surface 50s is, for example, the c-plane 50c.

[0197] It should be noted that the main surface 50 s of the substrate 50 is, for example, mirror-finished, and the root mean square roughness RMS of the main surface 50 s of the substrate 50 is, for example, less than 1 nm.

[0198] In addition, in the present embodiment, the substrate 50 does not include a polarity inversion domain as described above, for example.

[0199] (Inclined interface growth region and c-plane growth region)

[0200] Next, use Figure 8 , the characteristics of the main surface 50s of the substrate 50 are described.

[0201] like Figure 8 As shown in the figure, the substrate 50 has, for example, an inclined interface growth region (high oxygen concentration region) 70 where the inclined interface 30i is used as a growth surface. As described above, the oxygen concentration in the inclined interface growth region 70 is, for example, 9×10 17 cm -3 Above and 5×10 19 cm -3 the following.

[0202] As described above, the inclined interface growth region 70 contains a high concentration of oxygen, and therefore, the inclined interface growth region 70 is observed relatively brightly in a cathode luminescence image (CL image) (or a multiphoton excitation microscopy image (2PPL image)) taken within a wavelength range that includes at least a portion of the wavelength of light emitted near the band gap energy of the Group III nitride semiconductor.

[0203] The shape of the inclined interface growth region 70 when viewed from above reflects, for example, the shape of the concave portion 30p generated during the growth process of the three-dimensional growth layer 30 when viewed from above, and has at least a portion of a roughly hexagonal shape. Among the shapes of the inclined interface growth region 70 when viewed from above, one roughly hexagonal shape may intersect with other roughly hexagonal shapes. It should be noted that in the 2PPL image, the ridges of the concave portion 30p generated during the growth process of the three-dimensional growth layer 30 can sometimes be observed in the inclined interface growth region 70.

[0204] In this embodiment, the area ratio of the inclined interface growth region 70 in the main surface 50s is, for example, 80% or more. In other words, in the main surface 50s, the c-plane growth region (the second c-plane growth region, the surface side c-plane growth region, the low oxygen concentration region) 80 can exist with an area ratio of less than 20%.

[0205] As described above, the c-plane growth region 80 is a region where the c-plane 30c appears again in the slope interface sustaining layer 34. The oxygen concentration in the c-plane growth region 80 is, for example, 5×10 16 cm -3 Below, preferably 3×10 16 cm -3 the following.

[0206] The size of the c-plane growth region 80 in a plan view randomly changes from the back surface on the opposite side to the main surface 50 s of the substrate 50 toward the main surface 50 s , for example.

[0207] For example, the c-plane growth region 80 is not continuously connected from the back surface on the opposite side to the main surface 50 s of the substrate 50 toward the main surface 50 s.

[0208] On the other hand, the area ratio of the inclined interface growth region 70 in the main surface 50 s may be 100%, that is, the substrate 50 may not have the c-plane growth region 80 .

[0209] It should be noted that, according to the area ratio of the inclined interface growth region 70 in the main surface 50s, the average oxygen concentration of the entire main surface 50s of the substrate 50 is, for example, 7×10 17 cm -3 Above and 5×10 19 cm -3 the following.

[0210] In this embodiment, the substrate 50 obtained by the above-mentioned manufacturing method is, for example, an n-type substrate. In the substrate 50 of this embodiment, as an n-type impurity, for example, not only the above-mentioned oxygen (O) but also at least one of Si and Ge is contained. The total n-type impurity concentration in the substrate 50 is, for example, 1.0×10 18 cm -3 Above and 1.0×10 20 cm -3 the following.

[0211] In the substrate 50 of the present embodiment, not only at least one of Si and Ge is activated but also O is activated. Therefore, the free electron concentration in the substrate 50 is equivalent to the total concentration of O, Si, and Ge in the substrate 50, for example.

[0212] It should be noted that in the present embodiment, the concentration of impurities other than the n-type impurities (conductive type impurities) in the substrate 50 obtained by the above-mentioned manufacturing method is low.

[0213] For example, the hydrogen concentration in the substrate 50 obtained by the above-mentioned manufacturing method is lower than that of a substrate obtained by a flux method, an ammonothermal method, or the like.

[0214] Specifically, the hydrogen concentration in the substrate 50 is, for example, less than 1×10 17 cm -3 , preferably 5×10 16 cm -3 the following.

[0215] (Dark spot)

[0216] Next, use Figure 8 , the dark spots in the main surface 50s of the substrate 50 of the present embodiment are described. It should be noted that the "dark spots" mentioned here refer to points with low luminescence intensity observed in the observation image of the main surface 50s in the multiphoton excitation microscope, the cathode luminescence image of the main surface 50s, etc., including not only dislocations but also non-luminescent centers caused by foreign matter or point defects. It should be noted that "multiphoton excitation microscope" is sometimes also called two-photon excitation fluorescence microscope.

[0217] In the present embodiment, the substrate 50 is manufactured using the base substrate 10 formed of a high-purity GaN single crystal produced by the VAS method. Therefore, the substrate 50 has few non-luminescent centers caused by foreign matter or point defects.

[0218] Therefore, if Figure 8As shown, in the CL image (or 2PPL image) of the main surface 50s of the substrate 50, more than 95%, preferably more than 99% of the dark spots are not non-luminescent centers caused by foreign matter or point defects, but dislocations (threading dislocations) d.

[0219] In addition, in the present embodiment, by the above-mentioned manufacturing method, dislocations are locally gathered in the inclined interface maintaining layer 34, and the dislocation density on the surface of the inclined interface maintaining layer 34 is reduced compared with the dislocation density on the main surface 10s of the base substrate 10. As a result, the dislocation density is also reduced in the main surface 50s of the substrate 50 formed by slicing the inclined interface maintaining layer 34.

[0220] In addition, in this embodiment, if Figure 8 As shown, by the above manufacturing method, dislocations d are locally concentrated at the center of the roughly hexagonal inclined interface growth region 70. Hereinafter, the region where dislocations d are relatively concentrated in the inclined interface growth region 70 is also referred to as a "dislocation concentration region dca". A low dislocation density region is formed in a large area outside the dislocation concentration region dca.

[0221] In addition, in the present embodiment, by using the above-mentioned manufacturing method, the three-dimensional growth step S200 is performed using the base substrate 10 in a state where the pattern processing is not performed, so that in the main surface 50s of the substrate 50 formed by slicing the three-dimensional growth layer 30, a high dislocation density region that occurs regularly due to the pattern processing of the base substrate 10 is not formed. In other words, in the substrate 50 of the present embodiment, even if there are dislocation concentration regions dca, the dislocation concentration regions dca are randomly arranged. In addition, the dislocation density in the dislocation concentration regions dca of the substrate 50 of the present embodiment is lower than the dislocation density when the base substrate 10 is subjected to pattern processing.

[0222] Specifically, in this embodiment, when the main surface 50s of the substrate 50 is observed with a 250 μm square field of view using a multiphoton excitation microscope and the dislocation density is calculated from the dark spot density, there is no dislocation density exceeding 3×10 6 cm -2 In addition, the dislocation density is less than 1×10 6 cm -2 The region exists in 80% or more of the main surface 50s, preferably exists in 90% or more, and more preferably exists in 95% or more. It should be noted that the same result as that of the multiphoton excitation microscope can be obtained by observing the cathode luminescence image.

[0223] It should be noted that when the manufacturing method of this embodiment is used, the dislocation density is less than 1×10 6 cm -2 The upper limit of the ratio of the area is, for example, 99% of the main surface 50s.

[0224] In other words, in this embodiment, the average dislocation density of the entire main surface 50s of the substrate 50 is, for example, less than 1×10 6 cm -2 , preferably less than 5.5×10 5 cm -2 , more preferably 3×10 5 cm -2 the following.

[0225] In addition, the main surface 50s of the substrate 50 of the present embodiment includes at least a 50 μm square dislocation-free region based on, for example, the average distance L between the closest tops in the above-mentioned three-dimensional growth step S200. In addition, the 50 μm square dislocation-free region is, for example, dispersed throughout the main surface 50s of the substrate 50 except for the above-mentioned dislocation concentration region dca. In addition, the main surface 50s of the substrate 50 of the present embodiment is, for example, 100 / cm 2 More than 800 pieces / cm 2 More preferably, 1600 pieces / cm 2 The density above has non-overlapping 50 μm square dislocation-free areas. The density of non-overlapping 50 μm square dislocation-free areas is 1600 / cm 2 The above situation corresponds to, for example, a case where the main surface 50 s has at least one 50 μm square dislocation-free region in any field of view of 250 μm square.

[0226] It should be noted that the upper limit of the density of non-overlapping 50 μm square dislocation-free regions is, for example, 30,000 / cm 2 about.

[0227] For reference, in a substrate obtained by a conventional manufacturing method without performing a 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 less than 100 / cm 2 In addition, in the substrate obtained by the conventional ELO method, the size of the dislocation-free region is less than 50 μm square or the density of the dislocation-free region of 50 μm square is less than 100 / cm 2 .

[0228] In addition, in this embodiment, as described above, even when the substrate 50 has the c-plane growth region 80, the c-plane 30c disappears at least once during the growth of the three-dimensional growth layer 30, and the dislocation bends below the c-plane growth region 80 on the main surface 50s side. Thus, for example, the c-plane growth region 80 on the main surface 50s sometimes includes the above-mentioned dislocation-free region of at least 50 μm square.

[0229] In addition, in the present embodiment, as described above, the dislocation density of the dislocation concentration region dca is reduced, so that when the main surface 50s is observed with a multiphoton excitation microscope in a 50 μm square field of view including the dislocation concentration region dca and the dislocation density is obtained from the dark spot density, the dislocation density is, for example, less than 3×10 6 cm -2 It should be noted that it is considered that there is at least one dark spot in the 50 μm square field of view including the dislocation concentration area dca. Therefore, the lower limit of the dislocation density in the 50 μm square field of view including the dislocation concentration area dca is, for example, 4×10 4 cm -2 .

[0230] (Basal plane dislocation)

[0231] Next, use Figure 8 , the basal plane dislocation bpd in the primary surface 50s of the substrate 50 according to the present embodiment will be described.

[0232] In this embodiment, due to the stress offset effect of the inclined interface growth region 70 described later, crystal strain is applied to the three-dimensional growth layer 30, which may cause basal plane dislocation. Figure 8 As shown, in the CL image of the main surface 50 s of the substrate 50 formed by slicing the three-dimensional growth layer 30 , a basal plane dislocation bpd is sometimes observed.

[0233] However, in the present embodiment, the basal plane dislocation bpd in the main surface 50 s of the substrate 50 is smaller than that of a substrate obtained by the ELO method or the like using a mask layer.

[0234] Specifically, in the CL image of the main surface 50s, when an arbitrary imaginary line segment ls with a length of 200 μm is drawn, the number of intersections between the line segment ls and the basal plane dislocation bpd is, for example, 10 or less, preferably, 5 or less. It should be noted that the minimum number of intersections between the line segment ls and the basal plane dislocation bpd is, for example, 0.

[0235] (Burger vector)

[0236] Next, the Burgers vector of dislocation in the substrate 50 of the present embodiment will be described.

[0237] In this embodiment, the dislocation density in the main surface 10s of the base substrate 10 used in the above-mentioned manufacturing method is low, so when the three-dimensional growth layer 30 is grown on the base substrate 10, there is little combination (mixing) of multiple dislocations. As a result, in the substrate 50 obtained from the three-dimensional growth layer 30, the generation of dislocations having a large Burgers vector can be suppressed.

[0238] Specifically, in the substrate 50 of the present embodiment, for example, the Burgers vector is <11-20> / 3, <0001> or <11-23> / 3. It should be noted that the "Burgers vector" here can be measured by, for example, the large angle convergent beam electron diffraction method (LACBED method) using a transmission electron microscope (TEM). In addition, a dislocation with a Burgers vector of <11-20> / 3 is an edge dislocation, and a Burgers vector of <0001> The dislocation with a Burgers vector of <11-23> / 3 is a mixed dislocation formed by a mixture of edge dislocation and screw dislocation.

[0239] In this embodiment, when 100 dislocations are randomly selected from the primary surface 50s of the substrate 50, the Burgers vectors are <11-20> / 3, <0001> The ratio of the number of dislocations of any one of <11-23> / 3 is, for example, 50% or more, preferably 70% or more, and more preferably 90% or more. It should be noted that dislocations having a Burgers vector of 2<11-20> / 3 or <11-20>, etc., may also exist in at least a portion of the main surface 50s of the substrate 50.

[0240] (Radius of curvature of c-surface)

[0241] Next, use Figure 7 , the curvature radius of the c-plane 50c in the substrate 50 of this embodiment is described.

[0242] like Figure 7 As shown in (b) and (c) of FIG. 5 , in this embodiment, the c-plane 50c, which is the low-index crystal plane closest to the main surface 50s of the substrate 50, becomes flat or curved into a spherical shape, for example, due to the manufacturing method of the above-mentioned substrate 50. It should be noted that the c-plane 50c of the substrate 50 can be curved into a concave spherical shape, or can be curved into a convex spherical shape, for example, relative to the main surface 50s. Alternatively, if the c-plane 50c of the substrate 50 is, for example, roughly flat, it can have a portion curved into a concave spherical shape relative to the main surface 50s and a portion curved into a convex spherical shape relative to the main surface 50s.

[0243] In the present embodiment, the c-plane 50 c of the substrate 50 is flat or has a substantially spherical curved surface in each of the cross section along the m-axis and the cross section along the a-axis, for example.

[0244] Here, among the positions on the principal surface 50s of the substrate 50, the coordinate along the m-axis is set to "x". On the other hand, among the positions on the principal surface 50s of the substrate 50, the coordinate along the a-axis is set to "y". It should be noted that the coordinates (x, y) of the center of the principal surface 50s of the substrate 50 are set to (0, 0). In addition, among the deviation angle θ of the c-axis 50ca with respect to the normal line of the principal surface 50s, the direction component along the m-axis is set to "θ m ”, set the direction component along the a-axis to “θ a "It should be noted that θ 2 =θ m 2 +θ a 2 .

[0245] In this embodiment, since the c-plane 50c of the substrate 50 is flat or curved in a spherical shape as described above, the m-axis component θ of the deviation angle is m and the deviation angle a-axis component θ a It can be approximately expressed by a linear function of x and a linear function of y respectively.

[0246] Specifically, for example, when measuring the X-ray rocking curve of the (0002) plane at each position on a straight line passing through the center of the main surface 50s and plotting the peak angle ω between the X-ray incident on the main surface 50s and the main surface 50s relative to the position on the straight line, the peak angle ω can be approximated by a linear function of the position. It should be noted that the "peak angle ω" mentioned here is the angle between the X-ray incident on the main surface 50s and the main surface 50s, and refers to the angle at which the diffraction intensity becomes the maximum. The radius of curvature of the c-plane 50c can be obtained by taking the inverse of the slope of the linear function approximated as described above.

[0247] In the present embodiment, the curvature radius of the c-plane 50 c of the substrate 50 is, for example, larger than the curvature radius of the c-plane 10 c of the base substrate 10 used in the above-described method of manufacturing the substrate 50 .

[0248] Specifically, in the X-ray rocking curve measurement of the c-face 50c, when the peak angle ω is approximated by a linear function of the position, the curvature radius of the c-face 50c calculated by the inverse of the slope of the linear function is, for example, greater than 15 m, preferably greater than 23 m, more preferably greater than 30 m, and further preferably greater than 40 m.

[0249] In this embodiment, the upper limit of the curvature radius of the c-plane 50c of the substrate 50 is preferably as large as possible, and is therefore not particularly limited. When the c-plane 50c of the substrate 50 is substantially flat, the curvature radius of the c-plane 50c may be considered to be infinite.

[0250] In this embodiment, by increasing the curvature radius of the c-plane 50 c of the substrate 50 , the deviation of the off angle θ of the c-axis 50 ca with respect to the normal to the principal surface 50 s of the substrate 50 can be made smaller than the deviation of the off angle of the c-axis 10 ca of the base substrate 10 .

[0251] In the present embodiment, when the peak angle ω is approximated by a linear function of position in the X-ray rocking curve measurement of the c-plane 50 c , the error of ω with respect to the linear function is smaller than that of a substrate obtained by the ELO method using a mask layer.

[0252] 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. It should be noted that sometimes at least a portion of the peak angle ω is consistent with the linear function, so the minimum value of the error is 0°.

[0253] (Photoluminescence properties of semiconductor stacks)

[0254] Next, the photoluminescence characteristics of the semiconductor layer when a semiconductor stack is produced using the substrate 50 will be described.

[0255] In the present embodiment, as described above, the substrate 50 has the inclined interface growth region 70 showing a high oxygen concentration, but when a semiconductor stack is produced using the substrate 50, almost no crystal strain is generated due to the substrate 50 with respect to the semiconductor layer grown on the substrate 50. Therefore, in the photoluminescence of the semiconductor layer grown on the substrate 50, the peak shift caused by the crystal strain of the semiconductor layer is small or there is no peak shift.

[0256] Specifically, the following characteristics can be obtained. First, a stack is prepared, wherein the stack is obtained by epitaxially growing a semiconductor layer formed of a predetermined undoped single crystal of a group III nitride semiconductor on the main surface 50s of a substrate 50, and the reference stack is obtained by epitaxially growing a semiconductor layer on a substrate formed of a single crystal of a group III nitride semiconductor (i.e., an undoped single crystal of a group III nitride semiconductor that is the same as the substrate 50) except that the inclined interface growth region 70 is not provided. It should be noted that the "undoped" mentioned here means that the semiconductor does not contain intentionally added impurities, including the case where the semiconductor contains unavoidable impurities. Next, the photoluminescence of the semiconductor layer of the stack of the present embodiment and the reference stack is measured under the condition that the temperature difference is less than 1°C (e.g., 27°C). At this time, the difference between the maximum peak wavelength of the semiconductor layer of the stack of the present embodiment and the maximum peak wavelength of the semiconductor layer of the reference stack is, for example, less than 1 nm.

[0257] (4) Effects obtained by this embodiment

[0258] According to this embodiment, one or more of the following effects are obtained.

[0259] (a) In the three-dimensional growth step S200, by causing the surface of the single crystal constituting the three-dimensional growth layer 30 to have an inclined interface 30i other than the c-plane, at the position where the inclined interface 30i is exposed, the dislocation can be bent and propagated in a direction substantially perpendicular to the inclined interface 30i. Thus, the dislocations can be locally gathered. By causing the dislocations to be locally gathered, dislocations with mutually opposite Burgers vectors can be made to disappear. Alternatively, by causing the locally gathered dislocations to form a closed loop, the propagation of dislocations to the surface side of the three-dimensional growth layer 30 can be suppressed. In this way, the dislocation density in the surface of the three-dimensional growth layer 30 can be reduced. As a result, a substrate 50 with a reduced dislocation density compared to the base substrate 10 can be obtained.

[0260] (b) 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 . This allows dislocations propagating from the base substrate 10 to be reliably bent at positions in the three-dimensional growth layer 30 where the inclined interface 30i is exposed.

[0261] Here, in the three-dimensional growth process, the case where the c-plane remains is considered. In this case, in the portion where the c-plane remains, the dislocations propagated from the base substrate propagate in a substantially vertical direction without bending and reach the surface of the three-dimensional growth layer. Therefore, above the portion where the c-plane remains, the dislocations do not decrease, but a high dislocation density region is formed.

[0262] In contrast, according to the present embodiment, in the three-dimensional growth step S200, by making the c-plane 30c disappear at least once from the top surface 30u of the three-dimensional growth layer 30, the surface of the three-dimensional growth layer 30 can be constituted at least once by only the inclined interface 30i other than the c-plane. As a result, the dislocation propagated from the base substrate 10 can be surely bent over the entire surface of the three-dimensional growth layer 30. By surely bending the dislocation, it is easy to make a part of the plurality of dislocations disappear or to make a part of the plurality of dislocations difficult to propagate to the surface side of the three-dimensional growth layer 30. As a result, the dislocation density can be reduced over the entire main surface 50s of the substrate 50 obtained from the three-dimensional growth layer 30.

[0263] (c) In the three-dimensional growth step S200, after the c-plane 30c disappears from the surface of the three-dimensional growth layer 30, the inclined interface growth region 70 is maintained to occupy more than 80% of the area of ​​the cross section along the surface, and the growth of the three-dimensional growth layer 30 is continued over a specified thickness. Thus, it is possible to fully ensure the time for the dislocation to bend at the position where the inclined interface 30i is exposed. Here, if the c-plane is grown immediately after the c-plane disappears, the dislocation may not be fully bent, but propagate in a substantially vertical direction toward the surface of the three-dimensional growth layer. In contrast, in the present embodiment, by fully ensuring the time for the dislocation to bend at the position where the inclined interface 30i other than the c-plane is exposed, it is possible to suppress the dislocation from the base substrate 10 toward the surface of the three-dimensional growth layer 30 in a substantially vertical direction. Thus, the concentration of dislocations in the three-dimensional growth layer 30 can be suppressed.

[0264] (d) In the present embodiment, by slicing the three-dimensional growth layer 30 , the curvature radius of the c-plane 50 c of the substrate 50 can be made larger than the curvature radius of the c-plane 10 c of the base substrate 10 .

[0265] As one reason why the curvature radius of the c-plane 50 c of the substrate 50 increases, for example, the following reason is conceivable.

[0266] As described above, in the three-dimensional growth step S200, the three-dimensional growth layer 30 is grown with the inclined interface 30i other than the c-plane as the growth plane, thereby forming the inclined interface growth region 70. Compared with the c-plane growth region 60, oxygen is easily mixed into the inclined interface growth region 70. 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 regarded as a high oxygen concentration region.

[0267] In this way, by mixing 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 except the high oxygen concentration region (reference: Chris G. Van de Walle, Physical Review B vol. 68, 165209 (2003)). For the c-plane growth region 60 grown with the c-plane 30c as the growth plane in the base substrate 10 or the three-dimensional growth layer 30, stress concentrated toward the center of curvature of the c-plane 30c is applied by the bending of the c-plane 10c of the base substrate 10. In contrast, by relatively increasing the lattice constant of the high oxygen concentration region, stress that causes the c-plane 30c to expand outward in the plane direction can be generated in the high oxygen concentration region. As a result, the stress concentrated toward the center of curvature of the c-plane 30c below the high oxygen concentration region and the stress that causes the c-plane 30c of the high oxygen concentration region to expand outward in the plane direction can be offset (hereinafter also referred to as the "stress offset effect" based on the high oxygen concentration region). As a result, the curvature radius of the c-plane 50 c of the substrate 50 can be made larger than the curvature radius of the c-plane 10 c of the base substrate 10 .

[0268] (e) In the three-dimensional growth step S200, by growing the three-dimensional growth layer 30 with the inclined interface 30i as the growth plane, the growth rate of the three-dimensional growth layer 30 can be increased compared to the case where the semiconductor layer is grown with the c-plane as the growth plane. Thus, the production capacity in the manufacture of the substrate 50 can be improved.

[0269] (f) In the three-dimensional growth step S200, by making the area ratio of the inclined interface growth region 70 in the surface cross section 80% or more, the stress compensation effect of the three-dimensional growth layer 30 can be exhibited as described above. As a result, the generation of cracks in the three-dimensional growth layer 30 during growth can be suppressed. As a result, the three-dimensional growth layer 30 can be easily grown thicker.

[0270] (g) In the three-dimensional growth step S200, by making the area ratio of the inclined interface growth region 70 in the surface cross section 80% or more, it is easier to perform processing such as slicing and grinding compared to the case where the c-plane growth region occupies a larger area.

[0271] As described in (a) to (g) above, in this embodiment, the substrate 50 having good crystal quality can be obtained easily and stably.

[0272] (h) In the three-dimensional growth step S200, in the initial stage of the growth of the inclined interface expansion layer 32, after the inclined interface expansion layer 32 is two-dimensionally grown with the c-plane 30c as the growth plane and a predetermined thickness, a plurality of recesses 30p are generated on the top surface 30u of the inclined interface expansion layer 32. In other words, before the inclined interface expansion layer 32 starts three-dimensional growth, the inclined interface expansion layer 32 (initial layer) having a mirrored surface is formed with a predetermined thickness. Thus, in the three-dimensional growth step S200, the appearance of the inclined interface 30i in the three-dimensional growth layer 30 can be stably uniform within the surface. As a result, the dislocation density can be reduced throughout the surface of the three-dimensional growth layer 30 as a whole.

[0273] In addition, in the initial stage of the three-dimensional growth step S200, after the inclined interface expansion layer 32 is two-dimensionally grown with the c-plane 30c as the growth plane and a predetermined thickness, a plurality of recesses 30p are generated on the top surface 30u of the inclined interface expansion layer 32, thereby making it possible to unify the crystal axis throughout the main surface 10s of the base substrate 10. In this way, the generation of new dislocations caused by the shift of the crystal axis can be suppressed. As a result, the dislocation density can be reduced.

[0274] It should be noted that, as a reference, a case where an amorphous buffer layer is grown on a base substrate at a low temperature, and then the temperature is raised to grow the epitaxial layer in three dimensions is considered. At this time, in the process of heating to the growth temperature of the epitaxial layer, the buffer layer changes from amorphous to polycrystalline. In the subsequent growth of the epitaxial layer, the epitaxial layer grows in an island shape on the polycrystallized buffer layer. The crystal axes of the crystals grown in an island shape on the polycrystalline are scattered. Therefore, when the island crystals grow further and the island crystals meet each other, new dislocations are generated due to the offset of the crystal axis. Therefore, in the epitaxial layer, the dislocation density may become high.

[0275] (i) In the present embodiment, by using the above-mentioned base substrate 10 and adjusting the first growth condition in a manner satisfying formula (1), in the three-dimensional growth step S200, a {11-2m} plane with m≥3 can be generated as an inclined interface 30i. Thus, the inclination angle of the {11-2m} plane relative to the c-plane 30c can be reduced. Specifically, the inclination angle can be made less than 47.3°. By reducing the inclination angle of the {11-2m} plane relative to the c-plane 30c, the period of multiple tops 30t can be extended. Specifically, when observing any cross section perpendicular to the main surface 10s of the base substrate 10, the average distance L between the closest tops can be made to exceed 100μm.

[0276] It should be noted that, for reference, when a predetermined etchant is used to generate an etching pit on a nitride semiconductor substrate, an etching pit consisting of a {1-10n} plane is formed on the surface of the substrate. In contrast, in the present embodiment, a {11-2m} plane with m≥3 can be generated on the surface of the three-dimensional growth layer 30 grown under predetermined conditions. Therefore, it can be considered that, compared with a conventional etching pit, an inclined interface 30i unique to the manufacturing method can be formed in the present embodiment.

[0277] (j) In the present embodiment, when observing any cross section perpendicular to the main surface 10s of the base substrate 10, by making the average distance L between the closest tops exceed 100 μm, it is possible to ensure that the distance over which dislocations bend and propagate is at least more than 50 μm. As a result, dislocations can be fully concentrated above the approximate center between a pair of tops 30t in the three-dimensional growth layer 30. As a result, the dislocation density on the surface of the three-dimensional growth layer 30 can be sufficiently reduced.

[0278] (k) In the slicing step S400, the substrate 50 is formed by slicing the inclined interface maintaining layer 34. In addition, the inclined interface maintaining layer 34 is sliced ​​at a position above the position where the c-plane growth region 60 that continues from the base substrate 10 disappears last. Thus, the portion of the process in which dislocations gather in the three-dimensional growth layer 30 can be avoided. As a result, the substrate 50 with reduced dislocations can be stably obtained.

[0279] <Other Implementation Methods>

[0280] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention.

[0281] In the above embodiment, the base substrate 10 is described as a GaN self-supporting substrate, but the base substrate 10 is not limited to a GaN self-supporting substrate, and can be, for example, a III-group nitride semiconductor such as aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium nitride (InN), indium gallium nitride (InGaN), aluminum indium gallium nitride (AlInGaN), etc., i.e., Al x In y Ga 1-x-y A self-supporting substrate formed of a Group III nitride semiconductor represented by a composition formula of N (0≤x≤1, 0≤y≤1, 0≤x+y≤1).

[0282] In the above embodiment, the substrate 50 is described as a GaN self-supporting substrate, but the substrate 50 is not limited to a GaN self-supporting substrate, and can be, for example, a III-group nitride semiconductor such as AlN, AlGaN, InN, InGaN, AlInGaN, etc., i.e., Al xIn y Ga 1-x-y A self-supporting substrate formed of a Group III nitride semiconductor represented by a composition formula of N (0≤x≤1, 0≤y≤1, 0≤x+y≤1).

[0283] In the above embodiment, the substrate 50 is described as being n-type, but the substrate 50 may be p-type or semi-insulating. For example, when the substrate 50 is used to manufacture a semiconductor device as a high electron mobility transistor (HEMT), the substrate 50 is preferably semi-insulating.

[0284] In the above-mentioned embodiment, the case where the growth temperature is mainly adjusted as the first growth condition in the three-dimensional growth step S200 is described, but as long as the first growth condition satisfies formula (1), then as the first growth condition, growth conditions other than the growth temperature can be adjusted or the growth temperature and growth conditions other than the growth temperature can be adjusted in combination.

[0285] In the above embodiment, the case where the growth conditions in the inclined interface maintaining process S240 are maintained as the above-mentioned first growth conditions in the same manner as the inclined interface expansion process S220 is described, but as long as the growth conditions in the inclined interface maintaining process S240 satisfy the first growth conditions, the growth conditions in the inclined interface maintaining process S240 can also be made different from the growth conditions in the inclined interface expansion process S220.

[0286] In the above embodiment, a wire saw is used to slice the second crystal layer 6 or the sloped interface maintaining layer 34 in the slicing step S170 and the slicing step S400 . However, an outer peripheral blade slicer, an inner peripheral blade slicer, an electric discharge machine, or the like may be used.

[0287] In the above embodiment, the case where the substrate 50 is obtained by slicing the inclined interface maintenance layer 34 in the stacked structure 90 is described, but it is not limited to this case. For example, the stacked structure 90 can also be directly used to manufacture a semiconductor stack for manufacturing a semiconductor device. Specifically, after the stacked structure 90 is manufactured, in the semiconductor stack manufacturing process, the semiconductor functional layer is epitaxially grown on the stacked structure 90 to manufacture the semiconductor stack. After the semiconductor stack is manufactured, the back side of the stacked structure 90 is grinded to remove the base substrate 10 and the inclined interface expansion layer 32 in the stacked structure 90. Thus, a semiconductor stack having a tilted interface maintenance layer 34 and a semiconductor functional layer is obtained in the same manner as in the above embodiment. According to this situation, the slicing step S400 and the grinding step S500 for obtaining the substrate 50 can be omitted.

[0288] Example

[0289] Various experimental results for verifying the effects of the present invention are described below.

[0290] (1) Experiment 1

[0291] (1-1) Preparation of Nitride Semiconductor Substrate

[0292] The nitride semiconductor substrates of the examples and comparative examples were prepared as follows. It should be noted that, for the examples, a stacked structure before slicing the nitride semiconductor substrate was also prepared. Hereinafter, "nitride semiconductor substrate" may be abbreviated as "substrate".

[0293] [Production Conditions of Nitride Semiconductor Substrate in Example]

[0294] (Base substrate)

[0295] Material: GaN

[0296] Production method: VAS method

[0297] Diameter: 2 inches

[0298] Thickness: 550μm

[0299] The closest low-index crystal plane to the main plane: c-plane

[0300] The main surface is not subjected to patterning such as mask layer.

[0301] (3D growth layer)

[0302] Material: GaN

[0303] Growth method: HVPE method

[0304] First growth condition:

[0305] The growth temperature is set to 980°C to 1020°C, and the V / III ratio is set to 2 to 20. At this time, at least one of the growth temperature and the V / III ratio is adjusted within the above ranges so that the first growth condition satisfies the formula (1).

[0306] Thickness of 3D growth layer: about 1.45mm

[0307] (Slicing conditions)

[0308] Thickness of nitride semiconductor substrate: 400 μm

[0309] Cutting loss: 200μm

[0310] It should be noted that, in the embodiment, two substrates (A and B) with different slicing positions are prepared. It should be noted that substrate B is sliced ​​at a side closer to the base substrate than substrate A.

[0311] (Grinding conditions)

[0312] Grinding thickness: 200μm

[0313] [Production Conditions of Nitride Semiconductor Substrate of Comparative Example]

[0314] (Base substrate)

[0315] Material: GaN

[0316] Production method: VAS method

[0317] Diameter: 2 inches

[0318] Thickness: 400μm

[0319] The closest low-index crystal plane to the main plane: c-plane

[0320] The main surface is not subjected to patterning such as mask layer.

[0321] (Crystal layer)

[0322] Material: GaN

[0323] Growth method: HVPE method

[0324] Growth temperature: 1050℃

[0325] V / III ratio: 2

[0326] (That is, the crystal layer grows laminarly with the c-plane as the growth plane.)

[0327] Thickness from the main surface of the base substrate to the surface of the crystal layer: 2 mm

[0328] (Slicing conditions and grinding conditions)

[0329] Same as the embodiment.

[0330] (1-2) Evaluation

[0331] (Observation of laminated structure)

[0332] The cross section of the laminated structure before slicing the substrate of the example was observed using a fluorescence microscope. The surface of the laminated structure was also observed using an optical microscope.

[0333] (Observation of nitride semiconductor substrate using multiphoton excitation microscopy)

[0334] The main surfaces of the base substrate, the comparative example substrate, and the example substrate were observed using a multiphoton excitation microscope. At this time, the dislocation density was measured by measuring the dark spot density over the entire main surface with a 250 μm field of view. It should be noted that the dark spots in these substrates were all through dislocations, which was confirmed by measuring with the focus shifted in the thickness direction. In addition, at this time, the dislocation density was less than 1×10 6 cm -2 The ratio of the number of regions (low dislocation density regions) to the total number of measured regions. It should be noted that the "low dislocation density region" mentioned here refers to a region having a lower dislocation density than the average dislocation density in the main surface of the crystal layer in the comparative example obtained by growing the crystal layer without performing the three-dimensional growth process, as shown in the results described later.

[0335] (X-ray rocking curve measurement)

[0336] The X-ray rocking curves of the (0002) planes of the base substrate, the comparative example substrate, and the example substrate were measured. At this time, the measurement was performed at multiple measurement points set at intervals of 5 mm on a straight line passing through the center of the main surface of each substrate and along the m-axis direction and the a-axis direction. As a result of the measurement, the peak angle ω between the X-ray incident on the main surface and the main surface is plotted relative to the position on the straight line, and the peak angle ω is approximated by a linear function of the position. The inverse of the slope of the linear function is used to calculate the curvature radius of the c-plane. It should be noted that in the above-mentioned configuration of the device used in this experiment, when the slope of the linear function is negative, it means that the c-plane is convex.

[0337] (1-3) Results

[0338] The results are shown in Table 1.

[0339] [Table 1]

[0340] Example Comparative Example Base substrate <![CDATA[Average dislocation density (cm -2 )]]> <![CDATA[1.2×10 5 ]]> <![CDATA[1.5×10 6 ]]> <![CDATA[3.0×10 6 ]]> Ratio of low dislocation density region (%) 93 30 0 Radius of curvature of c surface (m) 38.4～1129 11.3 7.64

[0341] (Observation Results of Laminated Structure)

[0342] Fig. 9 (a) is a diagram showing an observed image obtained by observing the surface of the laminated structure of Experiment 1 using an optical microscope. Fig. 9 (b) is a diagram showing an observed image obtained by observing a cross section of the laminated structure of Experiment 1 using a fluorescence microscope. Fig. 9 (b) is a cross section along the <11-20> axis.

[0343] like Fig. 9As shown in (b), in the stacked structure of the embodiment, the three-dimensional growth layer has a c-plane growth region that grows with the c-plane as the growth plane and an inclined interface growth region that grows with the inclined interface as the growth plane, depending on the difference in growth planes during the growth process (i.e., the difference in oxygen concentration).

[0344] The c-plane growth region has a portion corresponding to an initial layer grown on the base substrate with the c-plane as a growth plane in the initial stage of growth. The initial layer is formed over the entire main surface of the base substrate and has a predetermined thickness.

[0345] Since the c-plane disappears at least once, the c-plane growth region is discontinuous from the base substrate to the surface (uppermost surface) of the three-dimensional growth layer.

[0346] At least a portion of the inclined interface growth region is continuously arranged along the main surface of the base substrate. That is, when observing multiple cross sections obtained by cutting the three-dimensional growth layer along the main surface of the base substrate, it can be confirmed that at least a portion of the three-dimensional growth layer in the thickness direction has a cross section that does not contain a c-plane growth region grown with the c-plane as the growth plane.

[0347] The c-plane growth region has a plurality of valleys and a plurality of peaks. The average value of the angle formed by a pair of inclined portions in the c-plane growth region is about 52°. In addition, the average distance between the closest peaks is about 234 μm.

[0348] like Fig. 9 As shown in (b), there is also a 2c-plane growth region at a position overlapping with the inclined interface growth region in cross-sectional view. During the growth of the three-dimensional growth layer, the 2c-plane growth region is generated or disappears, so the width of the 2c-plane growth region in cross-sectional view (in other words, the size of the 2c-plane growth region in top view) changes randomly from the base substrate toward the surface of the three-dimensional growth layer.

[0349] like Fig. 9 As shown in (a), a plurality of concave portions consisting of inclined interfaces other than the c-plane are generated on the surface of the three-dimensional growth layer. Six luminous visible surfaces are formed in the concave portions generated on the surface of the three-dimensional growth layer, that is, the concave portions have six inclined interfaces.

[0350] Considering the direction of the orientation plane of the base substrate, the ridgeline in the recess is along the <1-100> axis direction. In addition, the inclined interface constituting the recess is a surface with the direction inclined from the <11-20> axis as the normal direction (i.e., the {11-2m} surface).

[0351] exist Fig. 9 In the cross section along the <11-20> axis shown in (b), the angle of the inclined interface in the three-dimensional growth layer with respect to the main surface of the base substrate is about 47° or less.

[0352] Here, the angle of the {11-2m} plane of GaN with respect to the {0001} plane is as follows.

[0353] {11-21} plane: 72.9°

[0354] {11-22} face: 58.4°

[0355] {11-23} plane: 47.3°

[0356] {11-24} face: 39.1°

[0357] From the above, it can be confirmed that the inclined interface generated on the surface of the three-dimensional growth layer is a {11-2m} plane with m ≥ 3. It can also be confirmed that the inclined interface is mostly a {11-23} plane.

[0358] (Observation results of nitride semiconductor substrate using multiphoton excitation microscopy)

[0359] Fig.10 This is a schematic diagram showing an observation image obtained by observing, with a multiphoton excitation microscope, the main surface of the nitride semiconductor substrate A obtained in Experiment 1. It should be noted that the bold square portion represents a 50 μ square dislocation-free region.

[0360] like Fig.10 As shown, the nitride semiconductor substrate of the embodiment has a relatively bright oblique interface growth region. In the main surface of the nitride semiconductor substrate of the embodiment, the area ratio occupied by the oblique interface growth region is 80% or more.

[0361] As shown in Table 1, the average dislocation density of the primary surface of the nitride semiconductor substrate of the example is significantly lower than that of the base substrate and the nitride semiconductor substrate of the comparative example, and is less than 5.5×10 5 cm -2 Even when a thick crystal layer is grown as in the comparative example, the dislocation density of the nitride semiconductor substrate is lower than that of the base substrate. In the nitride semiconductor substrate of the example, the dislocation density is further lower than that of the comparative example.

[0362] In addition, in the nitride semiconductor substrate of the example, there is no 6 cm -2 In addition, in the nitride semiconductor substrate of the embodiment, the dislocation density is less than 1×10 6 cm -2 The region (low dislocation density region) exists in more than 90% of the main surface.

[0363] In addition, if Fig.10As shown in FIG. 1 , the main surface of the nitride semiconductor substrate of the embodiment includes at least a 50 μm square dislocation-free region. 2 The density above has non-overlapping 50 μm square dislocation-free regions. Specifically, in the main surface of the nitride semiconductor substrate of the embodiment, the density of non-overlapping 50 μm square dislocation-free regions is 5000 / cm 2 about.

[0364] Furthermore, when the c-plane growth region that appears dark is magnified and confirmed, the c-plane growth region has a dislocation-free region of at least 50 μm square.

[0365] Furthermore, the main surface of the nitride semiconductor substrate of the embodiment was observed with a multiphoton excitation microscope with a 50 μm square field of view including the dislocation concentration area dca. When the dislocation density was calculated from the dark spot density, the dislocation density was less than 3×10 6 cm -2 .

[0366] It should be noted that if Fig.10 As shown, the substrate of the example has basal plane dislocations. When observing the CL image of the substrate of the example, when an arbitrary imaginary line segment of 200 μm in length is drawn in the CL image of the main surface, the number of intersections between the line segment and the basal plane dislocation is 10 or less.

[0367] (Radius of curvature of c-surface)

[0368] Next, use Table 1, Fig.11 (a)~ Fig.12 (c) describes the curvature radius of the c-plane.

[0369] Fig.11 (a) is a diagram showing the results of measuring the rocking curve of X-ray diffraction along the m-axis direction of the nitride semiconductor substrate A obtained in Experiment 1, Fig.11 (b) is a diagram showing the results of measuring the rocking curve of X-ray diffraction along the a-axis direction of the nitride semiconductor substrate A obtained in Experiment 1. Fig.12 (a) is a diagram showing the results of measuring the rocking curve of X-ray diffraction in a predetermined direction of the nitride semiconductor substrate B obtained in Experiment 1, Fig.12 (b) is an enlarged view of the result of measuring the rocking curve of X-ray diffraction along the a-axis direction of (a). Fig.12(c) is an enlarged view of the result of measuring the rocking curve of X-ray diffraction along the m-axis in (a). It should be noted that R in the figure represents the radius of curvature of the c-plane, and negative R means that the c-plane is curved convexly relative to the main surface as described above.

[0370] In addition, in the above-mentioned Table 1, the c-plane of each of the base substrate and the substrate of the comparative example is curved in a concave spherical shape.

[0371] As shown in Table 1, Fig.11 (a)~ Fig.12 As shown in (c), the radius of curvature (absolute value) of the c-plane in the substrate of the embodiment is larger than the radius of curvature of the c-plane of the base substrate and the substrate of the comparative example, and is greater than 30 μm. Even when the crystal layer is grown thicker as in the comparative example, the radius of curvature of the c-plane in the substrate is larger than the radius of curvature of the c-plane of the base substrate, but the radius of curvature of the c-plane in the substrate of the embodiment is further larger than the radius of curvature of the c-plane in the nitride semiconductor substrate of the comparative example.

[0372] In addition, if Fig.12 As shown in (a) to (c) of FIG. 1 , in the substrate B cut out from the side close to the base substrate in the stacked structure of the embodiment, the c-surface is slightly concave relative to the main surface, but the radius of curvature of the c-surface is large and the c-surface is generally flat. Fig.12 The enlarged measurement results in (b) and (c) show that the c-plane of the substrate B has a portion curved in a concave spherical shape relative to the main surface and a portion curved in a convex spherical shape relative to the main surface.

[0373] On the other hand, Fig.11 (a) and Fig.11 As shown in (b), in the substrate A cut out from the side close to the surface of the stacked structure of the embodiment, the c-surface is curved into a convex spherical shape relative to the main surface. In addition, the absolute value of the curvature radius of the c-surface in the substrate A is smaller than the absolute value of the curvature radius of the c-surface in the substrate B.

[0374] In addition, in the substrates A and B of the examples, when the peak angle ω was approximated by a linear function of position in the measurement of the X-ray rocking curve of the c-plane, the error relative to the linear function was small. Specifically, the error of the measured peak angle ω relative to the linear function approximated as described above was less than 0.01°.

[0375] (Summary of Experiment 1)

[0376] According to the above embodiment, in the three-dimensional growth process, the first growth condition is adjusted in a manner that satisfies formula (1). As a result, the c-plane can be surely eliminated at least once during the growth of the three-dimensional growth layer. By eliminating the c-plane at least once, the dislocation can be surely bent at the position where the inclined interface is exposed in the three-dimensional growth layer. As a result, it can be confirmed that the dislocation density of the main surface of the nitride semiconductor substrate can be reduced.

[0377] In addition, according to the embodiment, by using the above-mentioned base substrate and adjusting the first growth condition in a manner satisfying formula (1), it is possible to generate a {11-2m} plane with m≥3 as an inclined interface. Thus, in the three-dimensional growth layer, the average distance between the closest tops can exceed 100μm. The result can confirm that the dislocation density of the main surface of the nitride semiconductor substrate can be sufficiently reduced. It can also be confirmed that by making the average distance between the closest tops exceed 100μm, a dislocation-free region of at least 50μm square can be formed.

[0378] In addition, according to the embodiment, in the initial stage of the three-dimensional growth process, the inclined interface expansion layer can be grown two-dimensionally with the c-plane as the growth plane and a predetermined thickness, and then three-dimensionally grown. As a result, the crystal axis can be unified throughout the main surface of the base substrate, and the generation of new dislocations caused by the crystal axis shift can be suppressed. As a result, it can be confirmed that the dislocation density can be reduced.

[0379] In addition, according to the embodiments, it can be confirmed that: through the stress cancellation effect of the inclined interface growth region, the curvature radius of the c-plane of the nitride semiconductor substrate can be made larger than the curvature radius of the c-plane of the base substrate, and the deviation of the deviation angle of the c-axis in the nitride semiconductor substrate can be made smaller than the deviation of the deviation angle of the c-axis in the base substrate.

[0380] It should be noted that, in the examples, it can be confirmed that the c-plane changes from concave to convex from the base substrate side of the stacked structure toward the surface side due to the stress offset effect of the inclined interface growth region. Therefore, it can be considered that if the position in the thickness direction of the slice from the stacked structure is optimized, a nitride semiconductor substrate with an extremely flat c-plane can be obtained.

[0381] (2) Experiment 2

[0382] (2-1) Preparation of laminated material

[0383] The following laminated products were produced by using the base substrate and the substrate A of the example.

[0384] [Production Conditions of Laminated Products in Examples]

[0385] (Substrate)

[0386] Substrate A of the embodiment

[0387] (Semiconductor layer)

[0388] Material: GaN

[0389] Growth method: MOVPE method

[0390] Growth conditions: Conditions for laminar growth of undoped GaN with the c-plane as the growth plane

[0391] Thickness of semiconductor layer: 2μm

[0392] [Production Conditions of Reference Laminated Material]

[0393] (Substrate)

[0394] Base substrate used in Experiment 1 (i.e., substrate not containing the inclined interface growth region)

[0395] (Semiconductor layer)

[0396] The conditions are the same as those for the semiconductor layer in the laminate of Example.

[0397] (2-2) Evaluation

[0398] (Observation of laminated materials)

[0399] The CL images of the surfaces of the semiconductor layers of the laminated product of the example and the reference laminated product of the reference example were observed using a SEM.

[0400] (Photoluminescence measurement)

[0401] The photoluminescence (PL) mapping of the semiconductor layers of the laminated products of the embodiment and the reference laminated products of the reference example was measured using LabRAM HR Evolution manufactured by Horiba. At this time, a He-Cd laser with a wavelength of 325 nm and a power of 1.25 mW was used as an excitation light source. In addition, the spot size of the laser was set to a diameter of 5 μm. That is, the irradiation intensity was set to 6.4×10 3 W -2 The measurement interval was 500 μm. The PL mapping measurement of the semiconductor layer of each of the laminate of the example and the reference laminate of the reference example was performed at a temperature of 27° C. and a temperature difference of less than 1° C.

[0402] (2-3) Results

[0403] (Observation results of laminated products)

[0404] Fig.13 (a) is a diagram showing a cathode luminescence image obtained by observing the surface of the semiconductor layer in the laminate of the example in Experiment 2 using a scanning electron microscope. Fig.13(b) is a diagram showing a cathode luminescence image obtained by observing the surface of the semiconductor layer in the reference laminate of the reference example in Experiment 2 using a scanning electron microscope.

[0405] like Fig.13 As shown in (b), a large number of dislocations inherited from the dislocations of the base substrate were observed in the semiconductor layer of the reference example. In addition, microscopic light emission unevenness corresponding to the surface morphology of the semiconductor layer was observed in the semiconductor layer of the reference example.

[0406] In contrast, Fig.13 As shown in (a), in the semiconductor layer of the embodiment, only the dislocations in the dislocation concentration region of the substrate are inherited, and there are few dislocations in the region other than the dislocation concentration region. In addition, the semiconductor layer of the embodiment has at least a 50 μm square dislocation-free region. In addition, no uneven light emission was observed in the semiconductor layer of the embodiment, so it can be confirmed that the surface of the semiconductor layer of the embodiment is flat.

[0407] (PL measurement results)

[0408] Fig.14 (a) is a diagram showing the results of photoluminescence mapping measurement in the laminate of the example in Experiment 2, Fig.14 (b) is a diagram showing the results of photoluminescence mapping measurement performed on the reference laminate of the reference example in Experiment 2.

[0409] like Fig.14 As shown in (a) of FIG. 1 , the results of PL mapping measurement of the entire surface of the laminate of the embodiment are similar to those of FIG. Fig.14 Similarly to the result of the comparative example shown in (b), no macroscopic uneven light emission was observed.

[0410] Fig.15 1 and 2 are photoluminescence spectra of the semiconductor layers of the laminate of the example and the reference laminate of the reference example in Experiment 2.

[0411] like Fig.15 As shown, the difference between the maximum peak wavelength of the semiconductor layer of the laminate of the example and the maximum peak wavelength of the semiconductor layer of the reference laminate of the reference example is 1 nm or less. In other words, the band edge emission of the semiconductor layer of the example does not have a peak shift.

[0412] (Summarize)

[0413] According to the above examples, the surface of the semiconductor layer in the laminate of the example is flat, and the band-end emission of the semiconductor layer does not have a peak drift. It is thus confirmed that: relative to the semiconductor layer grown on the substrate of the example, no crystal strain caused by the substrate occurs. In other words, it has been actually proved that the substrate of the example is fully practical as a substrate for manufacturing a light-emitting element, etc.

[0414] <Preferred Mode of the Invention>

[0415] Hereinafter, preferred embodiments of the present invention will be described.

[0416] (Note 1)

[0417] A nitride semiconductor substrate is formed of a single crystal of a group III nitride semiconductor and has a primary surface whose nearest low-index crystal plane is a (0001) plane.

[0418] The nitride semiconductor substrate has an inclined interface growth region that grows with an inclined interface other than the (0001) plane as a growth plane.

[0419] The area ratio of the inclined interface growth region in the main surface is 80% or more,

[0420] When the main surface is observed with a 250 μm square field of view using a multiphoton excitation microscope and the dislocation density is calculated from the dark spot density, there is no dislocation density exceeding 3×10 6 cm -2 area,

[0421] The main surface is 100 / cm 2 The above density has non-overlapping dislocation-free regions of 50 μm square.

[0422] (Note 2)

[0423] The nitride semiconductor substrate according to Supplementary Note 1, wherein an X-ray rocking curve of the (0002) plane is measured at each position on a straight line passing through the center in the main surface, and a peak angle ω between an X-ray incident on the main surface and the main surface is plotted relative to the position on the straight line, and when the peak angle ω is approximated by a linear function of the position,

[0424] The radius of curvature of the (0001) plane obtained by the inverse of the slope of the linear function is 15 m or more.

[0425] The error of the measured peak angle ω relative to the linear function is 0.05° or less.

[0426] (Note 3)

[0427] The nitride semiconductor substrate according to Supplementary Note 1 or 2, which does not have a c-plane growth region grown with the (0001) plane as a growth plane.

[0428] (Note 4)

[0429] The nitride semiconductor substrate according to Supplement 1 or 2, comprising a c-plane growth region grown with the (0001) plane as a growth plane,

[0430] The c-plane growth region in the main surface includes at least a 50 μm square dislocation-free region.

[0431] (Note 5)

[0432] The nitride semiconductor substrate according to any one of appendices 1 to 4, comprising a dislocation concentrated region where dislocations are relatively concentrated,

[0433] The main surface was observed using a multiphoton excitation microscope with a 50 μm square field of view including the above-mentioned dislocation concentration area. When the dislocation density was calculated from the dark spot density, the dislocation density was less than 3×10 6 cm -2 .

[0434] (Note 6)

[0435] The nitride semiconductor substrate according to any one of Supplementary Notes 1 to 5, wherein when an arbitrary imaginary line segment of 200 μm in length is drawn in the cathode luminescence image of the main surface, the number of intersections between the line segment and the basal plane dislocation is 10 or less.

[0436] (Note 7)

[0437] A nitride semiconductor substrate according to any one of Appendixes 1 to 6, wherein a stacked product is obtained by epitaxially growing a semiconductor layer composed of an undoped single crystal of a specified Group III nitride semiconductor on the aforementioned main surface, and a reference stacked product is obtained by epitaxially growing the aforementioned semiconductor layer on a substrate composed of a single crystal of a Group III nitride semiconductor which is the same as the aforementioned nitride semiconductor substrate except that the aforementioned inclined interface growth region is not present, and the photoluminescence of the aforementioned semiconductor layer of each of the aforementioned stacked product and the aforementioned reference stack is measured under a condition where the temperature difference is less than 1°C,

[0438] A difference between a maximum peak wavelength of the semiconductor layer of the stack and a maximum peak wavelength of the semiconductor layer of the reference stack is 1 nm or less.

[0439] (Note 8)

[0440] A laminated structure comprising:

[0441] A base substrate, which is formed of a single crystal of a group III nitride semiconductor and has a mirror-finished main surface, wherein the nearest low-index crystal plane to the main surface is a (0001) plane;

[0442] a low oxygen concentration region which is directly provided on the main surface of the base substrate and is formed of a single crystal of a Group III nitride semiconductor; and

[0443] a high oxygen concentration region, which is provided on the low oxygen concentration region and is formed of a single crystal of a Group III nitride semiconductor,

[0444] The oxygen concentration in the high oxygen concentration region is higher than the oxygen concentration in the low oxygen concentration region.

[0445] When observing any cross section perpendicular to the above main surface,

[0446] The upper surface of the low oxygen concentration region has a plurality of valleys and a plurality of hills.

[0447] An average distance between a pair of closest peaks among the plurality of peaks sandwiching one valley among the plurality of valleys exceeds 100 μm in the direction along the main surface.

[0448] (Note 9)

[0449] The multilayer structure according to Supplementary Note 8, wherein the low oxygen concentration region is discontinuous from the base substrate to the surface of the high oxygen concentration region.

[0450] (Note 10)

[0451] The stacked structure according to Appendix 8 or 9, wherein when observing a plurality of cross sections obtained by cutting the high oxygen concentration region along the main surface, there is a cross section that does not include the low oxygen concentration region in at least a portion in the thickness direction of the high oxygen concentration region.

[0452] (Note 11)

[0453] A method for manufacturing a nitride semiconductor substrate, which is a method for manufacturing a nitride semiconductor substrate using a vapor phase growth method, has the following steps:

[0454] A step of preparing a base substrate, wherein the base substrate is formed of a single crystal of a group III nitride semiconductor and has a mirror-finished main surface, wherein the nearest low-index crystal plane to the main surface is a (0001) plane;

[0455] A step of epitaxially growing a single crystal of a group III nitride semiconductor having a top surface with the (0001) plane exposed directly on the main surface of the base substrate, causing a plurality of recesses to be formed on the top surface by inclined interfaces other than the (0001) plane, causing the inclined interfaces to gradually expand toward the upper side of the main surface of the base substrate, causing the (0001) plane to disappear from the top surface at least once, and causing a three-dimensional growth layer to grow; and

[0456] The three-dimensional growth layer is sliced ​​to form a nitride semiconductor substrate.

[0457] In the step of forming the three-dimensional growth layer,

[0458] The plurality of concave portions are generated on the top surface of the single crystal, and the (0001) plane is eliminated, thereby forming a plurality of valleys and a plurality of tops on the surface of the three-dimensional growth layer.

[0459] When observing any cross section perpendicular to the main surface, an average distance between a pair of closest tops among the plurality of tops sandwiching one valley among the plurality of valleys in a direction along the main surface is set to exceed 100 μm.

[0460] (Note 12)

[0461] The method for manufacturing a nitride semiconductor substrate according to Supplementary Note 11, wherein in the step of growing the three-dimensional growth layer,

[0462] forming an inclined interface growth region in the three-dimensional growth layer, which grows with the inclined interface as a growth surface;

[0463] In a planar cross section obtained by cutting the three-dimensional growth layer along the main surface, the area ratio occupied by the inclined interface growth region is set to be 80% or more.

[0464] (Note 13)

[0465] The method for manufacturing a nitride semiconductor substrate according to Supplementary Note 12, wherein the step of forming the three-dimensional growth layer comprises the following steps:

[0466] After the (0001) plane disappears from the top surface, the inclined interface growth region is maintained to occupy more than 80% of the area of ​​the surface cross section, and the growth of the single crystal is continued over a predetermined thickness to form an inclined interface maintaining layer.

[0467] (Note 14)

[0468] The method for manufacturing a nitride semiconductor substrate according to Supplementary Note 13, wherein in the step of slicing the three-dimensional growth layer, the slope interface maintaining layer is sliced.

[0469] (Note 15)

[0470] The method for manufacturing a nitride semiconductor substrate according to Supplementary Note 14, wherein in the step of slicing the three-dimensional growth layer,

[0471] The slope interface maintaining layer is sliced ​​at a position above a position spaced apart from a position where the (0001) plane disappears from the top surface.

[0472] (Note 16)

[0473] The method for manufacturing a nitride semiconductor substrate according to any one of Supplementary Notes 11 to 15, wherein in the step of forming the three-dimensional growth layer,

[0474] After the single crystal is grown to a predetermined thickness with the (0001) plane as a growth plane, the plurality of recesses are generated on the top surface of the single crystal.

[0475] (Note 17)

[0476] The method for manufacturing a nitride semiconductor substrate according to any one of Supplementary Notes 11 to 16, wherein in the step of forming the three-dimensional growth layer,

[0477] As the aforementioned inclined interface, a {11-2m} plane with m≥3 is generated.

[0478] (Note 18)

[0479] The method for manufacturing a nitride semiconductor substrate according to any one of Supplementary Notes 11 to 17, wherein in the step of forming the three-dimensional growth layer,

[0480] The average distance between the pair of top portions that are closest to each other is set to be less than 800 μm.

[0481] (Note 19)

[0482] The method for manufacturing a nitride semiconductor substrate according to any one of Supplementary Notes 11 to 18, wherein in the step of preparing the base substrate,

[0483] preparing the base substrate whose (0001) surface is curved into a concave spherical shape relative to the main surface;

[0484] In the step of slicing the three-dimensional growth layer,

[0485] The curvature radius of the (0001) plane of the nitride semiconductor substrate is made larger than the curvature radius of the (0001) plane of the base substrate.

[0486] Description of Reference Numerals

[0487] 10 Base substrate

[0488] 30 Three-dimensional growth layer

[0489] 50 Nitride semiconductor substrate (substrate)

Claims

1. A nitride semiconductor substrate, which is formed of a single crystal of a group III nitride semiconductor and has a primary surface whose nearest low-index crystal plane is a (0001) plane, The nitride semiconductor substrate has an inclined interface growth region that grows with an inclined interface other than the (0001) plane as a growth plane. The inclined interface growth region occupies an area ratio of 80% or more in the main surface. The main surface was observed with a multiphoton excitation microscope in a 250 μm square field of view, and when the dislocation density was calculated from the dark spot density, there was no dislocation density exceeding 3×10 6 cm -2 area, The dislocation density is less than 1×10 6 cm -2 The region exists in more than 80% of the main surface, The main surface has 100 pieces / cm 2 The above density has non-overlapping dislocation-free regions of 50 μm square.

2. The nitride semiconductor substrate according to claim 1, wherein The X-ray rocking curve of the (0002) plane is measured at each position on a straight line passing through the center of the main surface, and the peak angle ω between the X-ray incident on the main surface and the main surface is plotted relative to the position on the straight line. When the peak angle ω is approximated by a linear function of the position, The curvature radius of the (0001) plane obtained by the inverse of the slope of the linear function is greater than 15 m, The error of the measured peak angle ω relative to the linear function is less than 0.05°. 3 . The nitride semiconductor substrate according to claim 1 , which does not have a c-plane growth region grown with the (0001) plane as a growth plane.

4. The nitride semiconductor substrate according to claim 1 or 2, comprising a c-plane growth region grown with the (0001) plane as a growth plane, The c-plane growth region in the primary surface includes at least a 50 μm square dislocation-free region.

5. The nitride semiconductor substrate according to claim 1 or 2, comprising a dislocation concentrated region where dislocations are relatively concentrated, The main surface was observed using a multiphoton excitation microscope with a 50 μm square field of view including the dislocation concentration area. When the dislocation density was calculated from the dark spot density, the dislocation density was less than 3×10 6 cm -2 .

6. The nitride semiconductor substrate according to claim 1 or 2, wherein: When an arbitrary imaginary line segment with a length of 200 μm is drawn in the cathode luminescence image of the main surface, the number of intersection points between the line segment and the basal plane dislocation is 10 or less.

7. The nitride semiconductor substrate according to claim 1 or 2, wherein a stack is prepared by epitaxially growing a semiconductor layer formed of an undoped single crystal of a specified group III nitride semiconductor on the main surface, and a reference stack is prepared by epitaxially growing the semiconductor layer on a substrate formed of a single crystal of a group III nitride semiconductor which is the same as the nitride semiconductor substrate except that the semiconductor layer does not have the inclined interface growth region, and the photoluminescence of the semiconductor layer of each of the stack and the reference stack is measured under a condition where the temperature difference is less than 1°C. A difference between a maximum peak wavelength of the semiconductor layer of the stack and a maximum peak wavelength of the semiconductor layer of the reference stack is 1 nm or less.

8. A method for manufacturing a nitride semiconductor substrate according to claim 1 or 2, which is a method for manufacturing a nitride semiconductor substrate using a vapor phase growth method, comprising the following steps: A step of preparing a base substrate, wherein the base substrate is formed of a single crystal of a group III nitride semiconductor and has a mirror-finished main surface, wherein the nearest low-index crystal plane to the main surface is a (0001) plane; A step of epitaxially growing a single crystal of a group III nitride semiconductor having a top surface with the (0001) plane exposed directly on the main surface of the base substrate, causing a plurality of recesses to be formed on the top surface by inclined interfaces other than the (0001) plane, causing the inclined interfaces to gradually expand toward the upper side of the main surface of the base substrate, causing the (0001) plane to disappear from the top surface at least once, and causing a three-dimensional growth layer to grow; and a step of slicing the three-dimensional growth layer to form a nitride semiconductor substrate, In the step of forming the three-dimensional growth layer, The plurality of recesses are generated on the top surface of the single crystal, and the (0001) plane disappears, thereby forming a plurality of valleys and a plurality of tops on the surface of the three-dimensional growth layer. When observing any cross section perpendicular to the main surface, an average distance between a pair of the closest tops among the plurality of tops sandwiching one of the plurality of valleys in a direction along the main surface exceeds 100 μm.

9. The method for manufacturing a nitride semiconductor substrate according to claim 8, wherein: In the step of growing the three-dimensional growth layer, forming an inclined interface growth region in the three-dimensional growth layer, which grows with the inclined interface as a growth surface, In a surface cross section obtained by cutting the three-dimensional growth layer along the main surface, the area ratio occupied by the inclined interface growth region is set to be 80% or more.

10. The method for manufacturing a nitride semiconductor substrate according to claim 9, wherein: The process of forming the three-dimensional growth layer includes the following steps: After the (0001) plane disappears from the top surface, the inclined interface growth region is maintained to occupy more than 80% of the area of ​​the surface cross section, and the growth of the single crystal is continued over a predetermined thickness to form an inclined interface maintaining layer.

11. The method for manufacturing a nitride semiconductor substrate according to claim 10, wherein: In the step of slicing the three-dimensional growth layer, the slope interface maintaining layer is sliced.

12. The method for manufacturing a nitride semiconductor substrate according to claim 8, wherein: In the step of forming the three-dimensional growth layer, After the single crystal is grown to a predetermined thickness with the (0001) plane as a growth plane, the plurality of recesses are generated on the top surface of the single crystal.

13. The method for manufacturing a nitride semiconductor substrate according to claim 8, wherein: In the step of forming the three-dimensional growth layer, As the inclined interface, a {11-2m} plane with m≥3 is generated.

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