nitride crystal substrate

Abstract

To obtain a nitride crystal substrate having excellent crystal quality.SOLUTION: A method for manufacturing a nitride crystal substrate using a vapor phase growth method includes steps of: preparing a base structure consisting of a group III nitride semiconductor single crystal having at least a surface layer including manganese; epitaxially growing a main growth layer consisting of a group III nitride semiconductor single crystal having a manganese concentration lower than that of the surface layer of the base structure on the base structure ; and acquiring at least one self-standing nitride crystal substrate from the main growth layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A method has been disclosed for obtaining at least one nitride crystal substrate from a crystal layer made of a single crystal of a Group III nitride semiconductor epitaxially grown on a base substrate (for example, Patent Document 1). [Prior art documents] [Patent documents]

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

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

[0005] According to one aspect of the present invention, A method for manufacturing a nitride crystal substrate using a vapor phase growth method, comprising the steps of: preparing an underlayer structure made of a single crystal of a Group III nitride semiconductor, at least a surface layer of which contains manganese; epitaxially growing, on the underlayer structure, a main growth layer made of a single crystal of a Group III nitride semiconductor having a manganese concentration lower than the manganese concentration in the surface layer of the underlayer structure; obtaining at least one free-standing nitride crystal substrate from the main growth layer; have A method for manufacturing a nitride crystal substrate is provided.

[0006] According to another aspect of the present invention, preparing an underlayer structure made of a single crystal of a Group III nitride semiconductor, at least a surface layer of which contains manganese; epitaxially growing, on the underlayer structure, a main growth layer made of a single crystal of a Group III nitride semiconductor having a manganese concentration lower than the manganese concentration in the surface layer of the underlayer structure; and In the step of epitaxially growing the main growth layer, The growth layer is grown by vapor phase epitaxy to a thickness that allows for obtaining at least one freestanding nitride crystal substrate. A method for manufacturing a laminate structure is provided.

[0007] According to yet another aspect of the present invention, A nitride crystal substrate configured as a freestanding substrate made of a single crystal of a Group III nitride semiconductor, having a primary surface in which the nearest low-index crystal plane is the (0001) plane, having a plurality of threading dislocations propagating in the thickness direction; Among the set of the plurality of threading dislocations, a dislocation line formed by at least some of the threading dislocations has a curved portion. A nitride crystal substrate is provided.

[0008] According to yet another aspect of the present invention, a base structure having at least a surface layer made of a single crystal of a group III nitride semiconductor containing manganese; a main growth layer provided on the understructure and made of a single crystal of a Group III nitride semiconductor having a manganese concentration lower than the manganese concentration in the surface layer of the understructure; and The growth layer has a thickness that allows at least one freestanding nitride crystal substrate to be obtained. A laminate structure is provided. [Effects of the Invention]

[0009] According to the present invention, a nitride crystal substrate with good crystal quality can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flowchart showing a method for manufacturing a nitride crystal substrate according to a first embodiment of the present invention. [Figure 2] 1(a) to 1(g) are schematic cross-sectional views showing part of a method for manufacturing a nitride crystal substrate according to a first embodiment of the present invention. [Figure 3] 1(a) to 1(c) are schematic cross-sectional views showing a part of a method for manufacturing a nitride crystal substrate according to a first embodiment of the present invention. [Figure 4] 1(a) and 1(b) are schematic cross-sectional views showing a part of a method for manufacturing a nitride crystal substrate according to a first embodiment of the present invention. [Figure 5] FIG. 1(a) is a schematic top view showing a nitride crystal substrate according to a first embodiment of the present invention, FIG. 1(b) is a schematic cross-sectional view taken along the m-axis of the nitride crystal substrate according to the first embodiment of the present invention, and FIG. 1(c) is a schematic cross-sectional view taken along the a-axis perpendicular to the m-axis of the nitride crystal substrate according to the first embodiment of the present invention. [Figure 6] 1 is a schematic diagram showing an image of a nitride crystal substrate according to a first embodiment of the present invention, observed from a direction along the main surface, while changing the focus using a multiphoton excitation microscope. FIG. [Figure 7] 10(a) and 10(b) are schematic cross-sectional views showing a part of a method for manufacturing a nitride crystal substrate according to a second embodiment of the present invention. [Figure 8] 1 is an image of a cross section of a laminated structure of Sample 1 observed with a fluorescence microscope in Experiment 1. [Figure 9] 1(a) shows the results of X-ray diffraction rocking curve measurements taken in the direction along the m-axis of each sample in Experiment 1, and FIG. 1(b) shows the results of X-ray diffraction rocking curve measurements taken in the direction along the a-axis, which is perpendicular to the m-axis of each sample in Experiment 1. [Figure 10] FIG. 2 is a diagram showing an image of the main surface of the substrate of Sample 1 observed using a multiphoton excitation microscope. [Figure 11] FIG. 1 is a perspective view of an image obtained by observing the substrate of sample 1 while changing the focus using a multiphoton excitation microscope. [Figure 12]1A and 1B are images of an underlying substrate observed using a multiphoton excitation microscope while changing the focus, viewed from a direction along the main surface. [Figure 13] 10 is an image of a cross section of the laminated structure of Sample 2 observed with a fluorescence microscope in Experiment 2. [Figure 14] 1(a) shows the results of X-ray diffraction rocking curve measurements taken in the direction along the m-axis of each sample in Experiment 2, and FIG. 1(b) shows the results of X-ray diffraction rocking curve measurements taken in the direction along the a-axis, which is perpendicular to the m-axis of each sample in Experiment 2. [Figure 15] FIG. 10 is a diagram showing an image of the main surface of the substrate of Sample 2 observed using a multiphoton excitation microscope. [Figure 16] FIG. 10 is a perspective view of an image obtained by observing the substrate of sample 2 while changing the focus using a multiphoton excitation microscope. DETAILED DESCRIPTION OF THE INVENTION

[0011] <First embodiment of the present invention> A first embodiment of the present invention will be described below with reference to the drawings.

[0012] (1) Method for manufacturing nitride crystal substrate and method for manufacturing laminated structure The method for manufacturing a nitride crystal substrate and a method for manufacturing a layered structure according to this embodiment will be described with reference to Figures 1 to 4. Figure 1 is a flowchart showing the method for manufacturing a nitride crystal substrate according to this embodiment. Figures 2(a) to 4(b) are schematic cross-sectional views showing part of the method for manufacturing a nitride crystal substrate according to this embodiment.

[0013] In the following, in a group III nitride semiconductor crystal having a wurtzite structure, <0001> The axis (e.g., the

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

[0014] 1, the method for manufacturing a nitride crystal substrate according to this embodiment includes, for example, a base structure preparation step S100, a main growth step S300, a slicing step S400, and a polishing step S500. The method for manufacturing a nitride crystal substrate according to this embodiment uses, for example, a vapor phase growth method.

[0015] (S100: Base structure preparation process) First, an underlayer structure 30 is prepared, which is made of a single crystal of a group III nitride semiconductor containing manganese (Mn) at least in its surface layer. In this embodiment, for example, the underlayer structure 30 includes a underlayer substrate 10, an initial layer 22, and a Mn-doped layer 24.

[0016] As shown in FIG. 1, the base structure preparing step S100 of this embodiment includes, for example, a base substrate preparing step S110, an initial step S120, and a Mn doping step S140.

[0017] (S110: Base board preparation process) First, in the base substrate preparation step S110, a base substrate 10 made of a single crystal of a group III nitride semiconductor is prepared. Specifically, for example, a gallium nitride (GaN) freestanding substrate is fabricated as the base substrate 10 by the VAS (Void-Assisted Separation) method.

[0018] Specifically, first, as shown in FIG. 2(a), a crystal growth substrate 1 (hereinafter sometimes abbreviated as "substrate 1") is prepared. The substrate 1 is, for example, a sapphire substrate. The low-index crystal plane closest to the primary surface 1s of the substrate 1 is, for example, the c-plane 1c. The c-axis 1ca of the substrate 1 is inclined at a predetermined off-angle θ0 with respect to the normal to the primary surface 1s. Next, as shown in FIG. 2(b), a first semiconductor layer 2 made of GaN is grown on the primary surface 1s of the substrate 1 by, for example, metalorganic vapor phase epitaxy (MOVPE). Next, as shown in FIG. 2(c), a metal layer 3 is vapor-deposited on the first semiconductor layer 2. The metal layer 3 is, for example, a titanium (Ti) layer.

[0019] 2(d), the substrate 1 is heat-treated in an atmosphere containing at least one of hydrogen gas, hydrogen-containing gas, nitrogen gas, and nitrogen-containing gas (e.g., NH3 gas). This nitrides the metal layer 3, forming a metal nitride layer 5 having a high density of fine holes on its surface. Furthermore, a portion of the first semiconductor layer 2 is etched through the holes in the metal nitride layer 5, forming a high density of voids in the first semiconductor layer 2. This forms a void-containing first semiconductor layer 4.

[0020] 2(e), for example, by hydride vapor phase epitaxy (HVPE), a second semiconductor layer 6 made of GaN is epitaxially grown on the void-containing first semiconductor layer 4 and the metal nitride layer 5. At this time, some of the voids in the void-containing first semiconductor layer 4 are filled with the second semiconductor layer 6 through the holes in the metal nitride layer 5, but other parts of the voids in the void-containing first semiconductor layer 4 remain.

[0021] During the cooling process after the growth of the second semiconductor layer 6 is completed, the second semiconductor layer 6 naturally peels off from the substrate 1 at the boundaries of the void-containing first semiconductor layer 4 and the metal nitride layer 5. At this time, the second semiconductor layer 6 is subjected to internal stress that causes the surface side to become depressed due to the tensile stress caused by the attraction between the initial nuclei during the growth process and the difference in dislocation density in the thickness direction of the second semiconductor layer 6.

[0022] As a result, as shown in FIG. 2(f), after being peeled off from the substrate 1, the second semiconductor layer 6 warps so that its front surface side is concave. Therefore, the c-plane 6c of the second semiconductor layer 6 is curved into a concave spherical shape with respect to a plane perpendicular to the normal direction of the center of the major surface 6s of the second semiconductor layer 6. Next, as shown in FIG. 2(f), the base substrate 10 is sliced ​​from the second semiconductor layer 6 along the cutting surface SS. After slicing, both surfaces of the base substrate 10 are polished.

[0023] As a result of the above, a base substrate 10 made of single crystal GaN is obtained, as shown in FIG. 2(g).

[0024] The diameter of the starting substrate 10 is, for example, 2 inches or more, and preferably 4 inches or more. The thickness of the starting substrate 10 is, for example, 300 μm or more and 1 mm or less.

[0025] The base substrate 10 has a base surface (main surface, base surface) 10s. In this embodiment, the low-index crystal plane closest to the base surface 10s is, for example, the c-plane (+c-plane) 10c.

[0026] The c-plane 10c of the base substrate 10 is curved, for example, into a concave spherical shape with respect to the base surface 10s. Here, "spherical" means a curved surface that is approximated to a spherical surface. Furthermore, "spherical approximation" here means approximation to a perfect sphere or an ellipsoidal sphere within a predetermined error range. The radius of curvature of the c-plane 10c of the base substrate 10 is, for example, not less than 1 m and not more than 10 m. The magnitude of the off-angle θ3 at the center of the base surface 10s of the base substrate 10 is, for example, more than 0° and not more than 1°.

[0027] The root mean square roughness RMS of the base surface 10s of the base substrate 10 is, for example, less than 1 nm.

[0028] The dislocation density in the base surface 10s of the base substrate 10 is reduced by the VAS method described above, and is, for example, 3×10 6 cm -2 More than 1×10 7 cm -2 is less than.

[0029] (S120: Initial process (initial layer formation process, non-doped layer formation process)) After preparing the base substrate 10, as shown in FIG. 3(b), for example, HVPE is used to start with the supply of GaCl gas, ensuring that the GaCl gas reaches the base surface 10s of the base substrate 10 before the manganese chloride gas described below. This allows an initial layer 22 made of a single crystal of a group III nitride semiconductor not containing Mn (e.g., non-doped GaN) to be epitaxially grown on the base surface 10s of the base substrate 10. The initial layer 22 is grown (step flow growth) over the entire base surface 10s of the base substrate 10, using the c-plane as the growth surface, to form a mirror-finished surface of the initial layer 22. Note that the term "mirror-finished" here refers to a surface in which the maximum difference in height between adjacent asperities on the surface is equal to or less than the wavelength of visible light.

[0030] Here, for example, consider the case where a Mn-doped layer 24 containing Mn, which will be described later, is epitaxially grown directly on the underlying surface 10s of the underlying substrate 10 without performing the initial step S120. In this case, if MnCl gas is flowed together with GaCl from the initial stage of growth of the Mn-doped layer 24, Mn alone may adhere to a portion of the underlying surface 10s of the underlying substrate 10. The portion to which only Mn adheres acts as an antisurfactant (growth-inhibiting portion) that inhibits crystal growth of the group III nitride semiconductor. Therefore, Mn acting as an antisurfactant may cause three-dimensional growth (island-like growth) of the Mn-doped layer 24.

[0031] In contrast, by forming a Mn-free initial layer 22 on the base surface 10s of the base substrate 10 before the Mn doping step S140 described below, it is possible to prevent only Mn from adhering to a portion of the base surface 10s of the base substrate 10 at the initial stage of growth of the Mn-doped layer 24 in the Mn doping step S140. This prevents Mn from becoming an anti-surfactant. As a result, it is possible to prevent three-dimensional growth of the Mn-doped layer 24.

[0032] In the initial step S120, the growth conditions are set, for example, as follows: Growth temperature: 990°C or higher and 1,120°C or lower, preferably 1,020°C or higher and 1,100°C or lower V / III ratio: 1 or more and 10 or less, preferably 1 or more and 5 or less Growth pressure: 90 to 105 kPa, preferably 90 to 95 kPa GaCl gas partial pressure: 1.5 to 15 kPa Ratio of H2 gas flow rate / N2 gas flow rate: 1 to 20 The "V / III ratio" is the ratio of the partial pressure of NH3 gas to the partial pressure of GaCl gas as a group III source gas.

[0033] As described above, the purpose of forming the initial layer 22 is to ensure that the GaCl gas reaches the underlying surface 10s of the underlying substrate 10 before the manganese chloride gas does. For this reason, the initial layer 22 may be grown in a short time (about several minutes) depending on the growth rate, and the thickness of the initial layer 22 is not particularly limited.

[0034] (S140: Mn doping process) After the growth of the predetermined initial layer 22 is completed, as shown in FIG. 3(c), a Mn-doped layer 24 made of a single crystal of a group III nitride semiconductor containing Mn is epitaxially grown above the base surface 10s of the base substrate 10 (on the initial layer 22).

[0035] In this embodiment, Mn is accommodated in a gas generation vessel made of quartz via an intervening part (e.g., a liner) that is resistant to HCl gas. While preventing direct contact between the quartz and Mn, HCl gas is introduced into the gas generation vessel to generate manganese chloride gas, which is then added to the Mn-doped layer 24. This prevents the decomposition of quartz caused by the catalytic action of Mn in an atmosphere containing HCl gas. By preventing the decomposition of quartz, it is possible to prevent silicon (Si) and oxygen (O) originating from the quartz from being mixed into the Mn-doped layer 24. As a result, a Mn-doped layer 24 with a low background impurity level can be obtained.

[0036] Hereinafter, the gas line that produces manganese chloride gas will be referred to as the "Mn line." At this time, manganese chloride gas (MnCl x The gas) is, for example, MnCl2 gas.

[0037] As described above, the intermediate portion used in the gas generation vessel of the Mn line must be resistant to HCl gas. Additionally, the intermediate portion must not melt or vaporize, for example, at the growth temperature of the Mn-doped layer 24. Furthermore, the intermediate portion must be highly pure (99.9% or higher) so as not to release impurities at the growth temperature of the Mn-doped layer 24. Furthermore, the intermediate portion must not exhibit catalytic activity that decomposes quartz in an atmosphere containing HCl gas. Furthermore, the intermediate portion must not directly react with quartz and Mn in an atmosphere containing at least one of H gas, N gas, and HCl gas. By having the intermediate portion satisfy these requirements, it is possible to suppress the generation of impurities caused by the intermediate portion itself and to suppress the decomposition of quartz caused by the catalytic activity of Mn.

[0038] Specifically, the intermediate portion contains at least one of tungsten (W), boron nitride (BN), silicon carbide (SiC), and molybdenum (Mo). Examples of BN include pyrolitic boron nitride (PBN). The above requirements can be met by using these materials for the intermediate portion.

[0039] At this time, at least a part of the group III element sites of the Mn-doped layer 24 is substituted with Mn.

[0040] Furthermore, at this time, the Mn-doped layer 24 is grown (step flow growth) over the entire base surface 10s of the base substrate 10, using the c-plane as the growth surface. This makes it possible to suppress the occurrence of facets other than the c-plane on the surface of the Mn-doped layer 24. Here, the "facets other than the c-plane" refers to, for example, {11-2m} or {1-10n}, where m and n are integers other than 0. Regions grown using facets other than the c-plane as the growth surface are more likely to incorporate oxygen (O) than regions grown using the c-plane as the growth surface. In this embodiment, by performing growth using the c-plane as the growth surface and suppressing growth using facets other than the c-plane as the growth surface as described above, it is possible to suppress the incorporation of O into the Mn-doped layer 24. As a result, a Mn-doped layer 24 with good crystal quality can be obtained.

[0041] Furthermore, by growing the Mn-doped layer 24 using the c-plane as the growth plane, the Mn-doped layer 24 with a mirror finish can be stably obtained.

[0042] The growth conditions for the Mn doping step S140 are set, for example, as follows: Growth temperature: 990°C or higher and 1,120°C or lower, preferably 1,020°C or higher and 1,100°C or lower Temperature near the gas generation vessel of the Mn line: 600℃ to 850℃ V / III ratio: 1 or more and 10 or less, preferably 1 or more and 5 or less Growth pressure: 90 to 105 kPa, preferably 90 to 95 kPa GaCl gas partial pressure: 1.5 to 15 kPa Partial pressure of HCl gas supplied to the Mn line: 1.6 x 10 -2 kPa or more and 0.8 kPa or less Ratio of H2 gas flow rate / N2 gas flow rate: 1 to 20

[0043] The growth conditions other than the conditions related to Mn doping in the Mn doping step S140 may be the same as or different from the growth conditions in the initial step S120.

[0044] Furthermore, the thickness of the Mn-doped layer 24 is set to, for example, 100 μm or more. By setting the thickness of the Mn-doped layer 24 to 100 μm or more, the effect of correcting the c-plane warpage (curvature) described below can be sufficiently exhibited. On the other hand, the upper limit of the thickness of the Mn-doped layer 24 is not particularly limited, but is preferably 10 mm from the viewpoint of preventing the total thickness from the initial layer 22 to the main growth layer 40 described below from becoming excessively thick.

[0045] The base structure 30 of this embodiment is formed by the base structure preparing step S100 described above.

[0046] (S300: Main growth step (non-doped layer growth step)) 4(a), after the base structure 30 is prepared, a main growth layer 40 made of a single crystal of a Group III nitride semiconductor having a Mn concentration lower than the Mn concentration in the surface layer (i.e., the Mn-doped layer 24) of the base structure 30 is epitaxially grown on the base structure 30. Following the base structure preparation step S100, the main growth layer 40 is grown by the HVPE method.

[0047] Specifically, for example, the main growth layer 40 is grown without supplying HCl gas to the Mn line, thereby making it possible to obtain the main growth layer 40 having a Mn concentration lower than the Mn concentration in the Mn-doped layer 24.

[0048] However, in the initial stage of the main growth step S300, an effect due to the so-called memory effect may occur. Specifically, the following cases may occur: In the above-described Mn doping step S140, the generation rate of MnCl2 on the surface of the Mn source material in the gas generation vessel of the Mn line is higher than the evaporation rate based on the saturated vapor pressure of the MnCl2 gas. Therefore, even if the supply of HCl gas to the Mn line is stopped after the completion of the Mn doping step S140, MnCl2 formed on the surface of the Mn source material in the Mn line may remain. If MnCl2 remains on the surface of the Mn source material, MnCl2 gas is generated from the MnCl2 remaining on the surface of the Mn source material in the initial stage of the main growth step S300. MnCl2 gas continues to be emitted at a constant saturated vapor pressure until the MnCl2 remaining on the surface of the Mn source material dries up. In this case, as the main growth step S300 progresses, the MnCl2 remaining on the surface of the Mn source material gradually dries up, and the amount of MnCl2 gas released gradually decreases. For this reason, the Mn concentration in the primary growth layer 40 gradually decreases, for example, from the Mn-doped layer 24 side toward the surface side of the primary growth layer 40. Therefore, in this embodiment, it is preferable to grow the non-doped primary growth layer 40 to a predetermined thickness after the Mn concentration in the primary growth layer 40 has sufficiently decreased.

[0049] In addition, at this time, the main growth layer 40 is grown (step flow growth) over the entire surface of the base structure 30 (Mn-doped layer 24) using the c-plane as the growth plane. This makes it possible to suppress the occurrence of facets other than the c-plane on the surface of the main growth layer 40. By suppressing the occurrence of facets other than the c-plane, it is possible to suppress the incorporation of O into the main growth layer 40. As a result, a main growth layer 40 with good crystal quality can be obtained.

[0050] Furthermore, by growing the main growth layer 40 on the Mn-doped layer 24, the radius of curvature of the c-plane of the main growth layer 40 can be made larger than the radius of curvature of the c-plane 10c of the underlying substrate 10.

[0051] The growth conditions for the main growth step S300 are set, for example, as follows. Growth temperature: 990°C or higher and 1,120°C or lower, preferably 1,020°C or higher and 1,100°C or lower V / III ratio: 1 or more and 10 or less, preferably 1 or more and 5 or less Growth pressure: 90 to 105 kPa, preferably 90 to 95 kPa GaCl gas partial pressure: 1.5 to 15 kPa Ratio of H2 gas flow rate / N2 gas flow rate: 1 to 20

[0052] The growth conditions in the main growth step S300 may be the same as or different from the growth conditions in the Mn doping step S140 other than the conditions related to Mn doping.

[0053] Furthermore, when the primary growth layer 40 is to be n-type, Si or Ge may be added to the primary growth layer 40. On the other hand, when the primary growth layer 40 is to be p-type, magnesium (Mg) may be added to the primary growth layer 40.

[0054] Furthermore, at this time, the main growth layer 40 is grown to a thickness that allows for the production of at least one free-standing nitride crystal substrate 50. The "thickness that allows for the production of at least one free-standing nitride crystal substrate 50" referred to here is, for example, 300 μm or more.

[0055] It is preferable that the thickness of the main growth layer 40 is set to a thickness that allows obtaining at least one substrate 50 that is self-supporting as a single layer. The term "single layer" as used herein means, for example, a layer obtained only from the main growth layer 40, and does not include a growth interface such as a growth initiation interface between the base structure 30 and the main growth layer 40.

[0056] Furthermore, in this embodiment, the thickness of the growth layer 40 is preferably, for example, 600 μm or more and 10 mm or less. By making the growth layer 40 thicker than 600 μm, at least one substrate 50 can be obtained from the non-doped region of the growth layer 40 in the slicing step S400 described below, even after removing the region where Mn is mixed due to the memory effect. On the other hand, by making the growth layer 40 thicker than 10 mm, at least ten substrates 50 can be obtained, even taking kerf loss into consideration. Furthermore, by making the growth layer 40 thicker than 10 mm, the occurrence of cracks in the growth layer 40 can be suppressed.

[0057] The above steps from the initial step S120 to the main growth step S300 are performed consecutively in the same vapor phase growth apparatus without exposing the base substrate 10 to the atmosphere. This makes it possible to prevent the formation of unintended high oxygen concentration regions (regions having an oxygen concentration excessively higher than that of facet growth regions other than the c-plane) at the interface between the initial layer 22 and the Mn-doped layer 24 and the interface between the Mn-doped layer 24 and the main growth layer 40.

[0058] In this manner, the laminated structure 90 of this embodiment is obtained.

[0059] (S400: Slicing process (substrate acquisition process)) 4(b), for example, the main growth layer 40 is sliced ​​using a wire saw along a cutting plane substantially parallel to the surface of the main growth layer 40. This forms at least one nitride crystal substrate 50 (also referred to as substrate 50) as an as-sliced ​​substrate. At this time, the thickness of the substrate 50 is set to, for example, 300 μm or more and 700 μm or less.

[0060] At this time, the radius of curvature of the c-plane 50c of the substrate 50 can be made larger than the radius of curvature of the c-plane 10c of the underlying substrate 10. Note that at this time, the radius of curvature of the c-plane 50c of the substrate 50 can be made larger than the radius of curvature of the c-plane 40c of the actual growth layer 40 before slicing. This makes it possible to make the variation in the off-angle θ of the c-axis 50ca with respect to the normal to the main surface 50s of the substrate 50 smaller than the variation in the off-angle of the c-axis 10ca of the underlying substrate 10.

[0061] (S500: Polishing process) Next, a polishing device is used to polish both surfaces of the substrate 50. At this time, the final thickness of the substrate 50 is set to, for example, 250 μm or more and 650 μm or less.

[0062] Through the above steps S100 to S500, the substrate 50 according to this embodiment is manufactured.

[0063] (Process for manufacturing semiconductor laminates and process for manufacturing semiconductor devices) After the substrate 50 is manufactured, a semiconductor functional layer made of, for example, a Group III nitride semiconductor is epitaxially grown on the substrate 50 to produce a semiconductor laminate. After the semiconductor laminate is produced, electrodes and the like are formed using the semiconductor laminate, and the semiconductor laminate is diced to cut out chips of a predetermined size. In this way, a semiconductor device is produced.

[0064] (2) Laminated structure Next, a laminated structure 90 according to this embodiment will be described with reference to FIG.

[0065] The stacked structure 90 of this embodiment includes, for example, an underlayer structure 30 and a main growth layer 40 .

[0066] At least the surface layer of the base structure 30 is made of, for example, a single crystal of a group III nitride semiconductor containing Mn. Specifically, the base structure 30 of this embodiment includes, for example, a base substrate 10 and a Mn-doped layer 24.

[0067] The Mn-doped layer 24 is provided above the underlying surface 10s of the underlying substrate 10, for example.

[0068] The Mn-doped layer 24 may be provided on the underlying surface 10s of the underlying substrate 10 via, for example, the above-described initial layer 22. In this case, the initial layer 22 is, for example, in contact with the underlying surface 10s of the underlying substrate 10 and is made of a single crystal of a group III nitride semiconductor that does not contain Mn.

[0069] The Mn-doped layer 24 is made of, for example, a single crystal of a group III nitride semiconductor containing Mn. Specifically, the Mn concentration in the Mn-doped layer 24 is, for example, 1×10 18 cm -3 or more, preferably 5 x 10 18 cm -3 The upper limit of the Mn concentration in the Mn-doped layer 24 is not limited, but from the viewpoint of yield, that is, maintaining normal crystal quality, it is set to, for example, 1×10 20 cm -3 is.

[0070] In this embodiment, the Mn-doped layer 24 is grown while suppressing the decomposition of quartz due to the catalytic action of Mn, so that the Si concentration and O concentration in the Mn-doped layer 24 are low. Specifically, the Si concentration in the Mn-doped layer 24 is, for example, 5×10 16 cm -3 Less than or equal to 3 x 10 16 cm -3 Less than or equal to 2 × 10 16 cm -3 The following is the result. The O concentration in the Mn-doped layer 24 is, for example, 1×10 16 cm -3 Less than or equal to 6 x 10 15 cm -3 Less than or equal to 5 × 10 15 cm -3 The following is the result.

[0071] In the Mn-doped layer 24, the c-plane is the crystal plane with a low index that is closest to the interface between the Mn-doped layer 24 and the main growth layer 40. The c-plane of the Mn-doped layer 24 is curved, for example, in a concave (or convex) spherical shape with respect to the interface.

[0072] In this embodiment, the radius of curvature of the c-plane of the Mn-doped layer 24 is, for example, larger than the radius of curvature of the c-plane 10c of the underlying substrate 10. Specifically, the absolute value of the radius of curvature of the c-plane of the Mn-doped layer 24 is, for example, greater than 6 m, preferably 10 m or greater.

[0073] The main growth layer 40 is provided on, for example, the base structure 30. The main growth layer 40 is made of, for example, a single crystal of a group III nitride semiconductor having a Mn concentration lower than the Mn concentration in the surface layer of the base structure 30.

[0074] In this embodiment, the Mn concentration in the main growth layer 40 gradually decreases from the Mn-doped layer 24 side toward the surface side of the main growth layer 40, as described above. The Mn concentration averaged over the entire main growth layer 40 is lower than the Mn concentration in the Mn-doped layer 24. The Mn concentration in the surface layer of the main growth layer 40 is, for example, 5×10 16 cm -3 Less than 1 × 10 16 cm -3 The following is the result.

[0075] Since the main growth layer 40 is grown on the c-plane, oxygen incorporation is suppressed. Therefore, the O concentration in the main growth layer 40 is, for example, 5×10 16 cm -3 Less than or equal to 3 x 10 16 cm -3 The following is the result.

[0076] The growth layer 40 has a surface in which the nearest low-index crystal plane is the c-plane. In this embodiment, the entire surface of the growth layer 40 is oriented to the +c-plane and does not include inversion domains. The c-plane of the growth layer 40 is curved, for example, into a concave (or convex) spherical shape relative to the surface.

[0077] In this embodiment, the radius of curvature of the c-plane of the growth layer 40 is, for example, larger than the radius of curvature of the c-plane 10c of the base substrate 10. Furthermore, the radius of curvature of the c-plane of the growth layer 40 is preferably larger than the radius of curvature of the c-plane of the Mn-doped layer 24. Specifically, the absolute value of the radius of curvature of the c-plane of the growth layer 40 is, for example, greater than 6 m, preferably 10 m or greater.

[0078] As described above, the main growth layer 40 has a thickness that allows for obtaining, for example, at least one freestanding nitride crystal substrate 50. In this embodiment, the thickness of the main growth layer 40 is, for example, 300 μm or more, and preferably 600 μm or more and 10 mm or less.

[0079] Furthermore, the grown layer 40 has the following characteristics regarding dislocations, for example.

[0080] The growth layer 40 has, for example, a plurality of threading dislocations. The term "threading dislocations" as used herein refers to dislocations that propagate in the thickness direction of the growth layer 40, in other words, dislocations that penetrate the c-plane (intersect with the c-plane). Note that, because threading dislocations originating from the interface between two different layers of the stacked structure 90 exist, the term "threading dislocations" as used herein does not refer to dislocations that propagate (penetrate) throughout the entire thickness direction of the stacked structure 90, but rather refers to dislocations that propagate at least within the growth layer 40 in the thickness direction.

[0081] In this embodiment, dislocation lines formed by at least some of the threading dislocations among the collection of threading dislocations in the growth layer 40 have curved portions. This feature will be described in detail later as a feature of the substrate 50 obtained by slicing from the growth layer 40.

[0082] (3) Nitride crystal substrates (freestanding nitride crystal substrates, nitride semiconductor substrates) Next, a nitride crystal substrate 50 according to this embodiment (hereinafter sometimes abbreviated as "substrate 50") will be described with reference to Figures 5 and 6. Figure 5(a) is a schematic top view showing the nitride crystal substrate according to this embodiment, (b) is a schematic cross-sectional view of the nitride crystal substrate according to this embodiment taken along the m-axis, and (c) is a schematic cross-sectional view of the nitride crystal substrate according to this embodiment taken along the a-axis, which is orthogonal to the m-axis. The direction along the m-axis is defined as the x-direction, and the direction along the a-axis is defined as the y-direction.

[0083] In this embodiment, the substrate 50 is configured as a free-standing substrate made of a single crystal of a group III nitride semiconductor, for example, a GaN free-standing substrate.

[0084] The diameter of the substrate 50 is, for example, 2 inches or more, and preferably 4 inches or more. The thickness of the substrate 50 is such that it can stand on its own, for example, 300 μm or more and 1 mm or less.

[0085] It is preferable that the substrate 50 is, for example, a single-layer that can stand on its own. As mentioned above, the term "single-layer" means a layer that does not include a growth interface.

[0086] The substrate 50 has a primary surface 50s whose nearest low-index crystal plane is, for example, a c-plane (+c-plane) 50c. The primary surface 50s of the substrate 50 is, for example, mirror-finished, and the root-mean-square roughness RMS of the primary surface 50s of the substrate 50 is, for example, less than 1 nm.

[0087] Additionally, in this embodiment, the substrate 50 does not include, for example, an inversion domain, as described above.

[0088] (Impurity concentration) The substrate 50 is obtained, for example, from a region of the growth layer 40 where the Mn concentration is sufficiently low. Specifically, the Mn concentration in the substrate 50 is, for example, 5×10 16 cm -3 Less than 1 × 10 16 cm -3 The following is the result.

[0089] The substrate 50 is obtained from the grown layer 40 grown on the c-plane, for example, and has a low O concentration. Specifically, the O concentration in the substrate 50 is, for example, 5×10 16 cm -3 Less than or equal to 3 x 10 16 cm -3 The following is the result.

[0090] The conductivity of the substrate 50 is not particularly limited. However, when the substrate 50 is of n-type, the n-type impurity in the substrate 50 is, for example, Si or Ge, and the n-type impurity concentration in the substrate 50 is, for example, 1.0×10 18 cm -3 Over 1.0 x 10 20 cm -3 When the substrate 50 is p-type, the p-type impurity in the substrate 50 is, for example, Mg, and the p-type impurity concentration in the substrate 50 is, for example, 1.0×10 18 cm -3 Over 1.0 x 10 20 cm -3 Furthermore, when the conductive impurity is not intentionally added to the substrate 50, the concentration of the conductive impurity in the substrate 50 is, for example, 5×10 17 cm -3 Less than 1 × 10 17 cm -3 The following is the result.

[0091] Furthermore, in this embodiment, the hydrogen (H) concentration in the substrate 50 is lower than that of a substrate obtained by a flux method or an ammonothermal method, and is, for example, 1×10 17 cm -3 Less than 5 x 10 16 cm -3 The following is the result.

[0092] (c-plane curvature) As shown in Figures 5(b) and (c), in this embodiment, the c-plane 50c, which is the low-index crystal plane closest to the primary surface 50s of the substrate 50, is curved, for example, in a concave (or convex) spherical shape with respect to the primary surface 50s.

[0093] In this embodiment, the c-plane 50c of the substrate 50 has a curved surface that is approximated as a sphere in both the cross section along the m-axis and the cross section along the a-axis.

[0094] In this embodiment, since the c-plane 50c of the substrate 50 is curved as described above, at least a portion of the c-axes 50ca is inclined with respect to the normal to the main surface 50s. The off-angle θ, which is the angle that the c-axis 50ca makes with respect to the normal to the main surface 50s, has a predetermined distribution within the main surface 50s.

[0095] The component of the off angle θ of the c-axis 50ca relative to the normal to the main surface 50s along the m-axis is referred to as "θ m " and the direction component along the a-axis is "θ a ". Note that θ 2 =θ m 2 +θ a 2 is.

[0096] In this embodiment, since the c-plane 50c of the substrate 50 is curved into a spherical shape as described above, the m-axis component of the off-angle θ m and the off-angle a-axis component θ a can be approximately expressed as a linear function of x and a linear function of y, respectively.

[0097] Specifically, for example, X-ray rocking curves of the (0002) plane are measured at each position on a line passing through the center of the main surface 50s. When the peak angle ω between the X-rays incident on the main surface 50s and the main surface 50s is plotted against the position on the line (distance from the center), the peak angle ω can be approximated by a linear function of the position. Note that the "peak angle ω" here refers to the angle between the X-rays incident on the main surface 50s and the main surface 50s, and is the angle at which the diffraction intensity is maximized. The radius of curvature of the c-plane 50c can be calculated from the reciprocal of the slope of the linear function approximated as described above.

[0098] In this embodiment, the radius of curvature of the c-plane 50c of the substrate 50 is, for example, larger than the radius of curvature of the c-plane 10c of the base substrate 10, and is also larger than the radius of curvature of the c-plane of the main growth layer 40 described above.

[0099] Specifically, when the peak angle ω is approximated by a linear function of position in an X-ray rocking curve measurement of the c-plane 50c, the radius of curvature of the c-plane 50c calculated as the reciprocal of the slope of the linear function is, for example, 10 m or more, preferably 12 m or more, more preferably 15 m or more, and even more preferably 18 m or more.

[0100] In this embodiment, the upper limit of the radius of curvature of the c-face 50c of the substrate 50 is not particularly limited, and the larger the radius, the better. When the c-face 50c of the substrate 50 is substantially flat, the radius of curvature of the c-face 50c can be considered to be infinite.

[0101] Furthermore, in this embodiment, the growth layer 40 is grown without patterning the base substrate 10, and therefore the c-plane of the growth layer 40 does not have any irregularities resulting from patterning the base substrate 10. That is, the c-plane 50c of the substrate 50 is, for example, close to a perfect sphere. Therefore, when the peak angle ω in an X-ray rocking curve measurement of the c-plane 50c is approximated by a linear function of position, the error of ω relative to the linear function of position is small. The error of ω in this embodiment can be made smaller than that of, for example, a substrate obtained from a crystal layer grown on a patterned base substrate.

[0102] Specifically, the error of the measured peak angle ω relative to the linear function approximated as described above is, for example, 0.05° or less, preferably 0.02° or less, and more preferably 0.01° or less. Note that, since at least some peak angles ω may coincide with the linear function, the minimum value of the error is 0°.

[0103] In this embodiment, the curvature of the c-plane 50c in the off-axis direction of the substrate 50 is easily corrected to be flat. Specifically, for example, the m-axis component θ of the off-axis angle at the center of the main surface 50s mand the a-axis component of the off-angle perpendicular to the m-axis, θ a In this case, the m-axis component θ m and the a-axis component θ a The absolute value of the radius of curvature of the c-face 50c in either direction is greater than the absolute value of the radius of curvature of the c-face 50c in the other direction.

[0104] However, in this embodiment, the directional dependency of the radius of curvature of the c-plane 50c is small compared to a substrate obtained from a crystal layer grown on a patterned base substrate.

[0105] Specifically, the difference between the absolute value of the radius of curvature of c-face 50c in the direction along the m-axis and the absolute value of the radius of curvature of c-face 50c in the direction along the a-axis is, for example, 90% or less of the larger of these radii of curvature, preferably 50% or less, and more preferably 20% or less.

[0106] (dislocation) Next, dislocations in substrate 50 of this embodiment will be described with reference to Figure 6. Figure 6 is a schematic diagram of an observation image of the nitride crystal substrate of this embodiment, observed from a direction along the main surface while changing the focus using a multiphoton excitation microscope. In Figure 6, solid lines extending substantially vertically in substrate 50 indicate threading dislocations.

[0107] As shown in FIG. 6, the substrate 50 of this embodiment has, for example, a plurality of threading dislocations. The term "threading dislocations" as used herein refers to dislocations that propagate in the thickness direction of the substrate 50, in other words, dislocations that penetrate the c-plane 50c (intersect with the c-plane 50c). That is, multiple threading dislocations propagate (extend) from, for example, the back surface of the substrate 50 opposite the main surface 50s toward the main surface 50s.

[0108] The threading dislocations may include dislocations that do not reach at least one of the main surface 50s and the back surface of the substrate 50.

[0109] The manufacturing method of this embodiment does not use any special method for collecting dislocations. Therefore, the dislocation density on the main surface 50s of the substrate 50 of this embodiment is, for example, approximately equal to or slightly lower than the dislocation density on the base surface 10s of the base substrate 10. Specifically, the dislocation density (average dislocation density) on the main surface 50s of the substrate 50 is, for example, 1×10 5 cm -2 More than 1×10 7 cm -2 Less than 5 x 10 6 cm -2 The following is the result.

[0110] Here, the present inventors have found that dislocations in the substrate 50 have unique characteristics resulting from the manufacturing method of this embodiment.

[0111] Specifically, as shown in Fig. 6, when an image of the substrate 50 is observed from a direction along the main surface while changing the focus using a multiphoton excitation microscope, the dislocation line formed by at least some of the threading dislocations among a set of multiple threading dislocations has a curved portion. Hereinafter, a threading dislocation having a curved portion will be referred to as a "curved dislocation cdl."

[0112] The "curved portion" referred to here means a portion curved with respect to an imaginary line connecting the starting point of a threading dislocation at a predetermined depth and the ending point of the threading dislocation on the main surface 50s. The curved portion of the threading dislocation may extend over the entire thickness direction of the substrate 50, or may be a partial region in the thickness direction of the substrate 50. Furthermore, the curved portion of the threading dislocation may be in one place (in one threading dislocation) or in multiple places.

[0113] At least one curved dislocation cdl in the substrate 50 has, for example, the following characteristics. For example, the inclination of the dislocation line of the curved dislocation cdl with respect to the normal to the main surface 50s on a side that is relatively shallower from the main surface 50s is greater than that on a side that is relatively deeper from the main surface 50s. For example, the inclination of the dislocation line of the curved dislocation cdl with respect to the normal to the main surface 50s gradually increases from the back surface opposite the main surface 50s toward the main surface 50s. Note that the multiple curved dislocations cdl may include curved dislocations cdl that do not satisfy the above characteristics.

[0114] Here, we consider the case where a dislocation whose maximum distance d from an imaginary line connecting the starting point of the dislocation at a depth of 200 μm from the main surface 50s and the end point of the dislocation on the main surface 50s (in a direction perpendicular to the line) is 5 μm or more is defined as a "curved dislocation cdl," and the number of curved dislocations cdl is measured.

[0115] In this embodiment, the proportion of curved dislocations cdl among the plurality of dislocations is, for example, 10% or more and 90% or less, and preferably 20% or more and 80% or less.

[0116] In this embodiment, the density of the curved dislocations cdl on the main surface 50s of the substrate 50 is, for example, 5×10 4 cm -2 Over 4.5 x 10 6 cm -2 The following is the result.

[0117] (4) Effects Obtained by the Present Embodiment According to this embodiment, one or more of the following effects can be obtained.

[0118] (a) In this embodiment, the main growth layer 40 is epitaxially grown on an underlayer structure 30, at least the surface layer of which contains Mn. At this time, the main growth layer 40 is grown to a thickness that allows slicing into at least one freestanding nitride crystal substrate 50. The inclusion of Mn in at least the surface layer of the underlayer structure 30 has the effect of correcting c-plane warpage (curvature), although the detailed mechanism is unknown.

[0119] Specifically, the radius of curvature of the c-plane of the growth layer 40 can be made larger than the radius of curvature of the c-plane 10c of the underlying substrate 10. Furthermore, when at least one substrate 50 is sliced ​​from the growth layer 40, the radius of curvature of the c-plane 50c of the substrate 50 can be made larger than both the radius of curvature of the c-plane 10c of the underlying substrate 10 and the radius of curvature of the c-plane of the growth layer 40 before slicing. This makes it possible to obtain substrates 50 with small variations in the off-angle θ of the c-axis 50ca with respect to the normal to the main surface 50s.

[0120] (b) By simply growing the main growth layer 40 on the base structure 30, at least the surface layer of which contains Mn, the c-plane warpage can be corrected more quickly than by other manufacturing methods.

[0121] Here, for example, consider the case where a thick crystal layer is grown using the c-plane as the growth plane (hereinafter referred to as c-plane thick film growth). Even in this case of c-plane thick film growth, the warpage of the c-plane is gradually corrected as the crystal layer is grown thicker. However, in the case of c-plane thick film growth, the rate at which the warpage of the c-plane is corrected is slow. Specifically, even if a crystal layer is grown to a thickness of 1 mm using the c-plane as the growth plane on an undersubstrate with a c-plane curvature radius of 6 m, the radius of curvature of the c-plane of the crystal layer will be larger than that of the undersubstrate, but will not exceed 10 m. For this reason, in the case of c-plane thick film growth, it may be difficult to mass-produce substrates with a large c-plane curvature radius.

[0122] Another method is to consider flattening the crystal layer after three-dimensionally growing it using a facet other than the c-plane as the growth plane (hereinafter referred to as the three-dimensional growth method). The warpage of the c-plane of the crystal layer can also be corrected in the three-dimensional growth method. However, this method may result in wasted crystal regions or a decrease in the yield of the substrate.

[0123] In contrast, in this embodiment, the warpage of the c-plane can be immediately corrected by simply growing the primary growth layer 40 on the base structure 30, at least the surface layer of which contains Mn. That is, the radius of curvature of the c-plane can be increased at any position in the thickness direction of the primary growth layer 40, without growing the primary growth layer 40 excessively thick. As a result, it becomes possible to easily mass-produce substrates 50 having a large radius of curvature of the c-plane 50c.

[0124] (c) In this embodiment, unlike the three-dimensional growth described above, it is possible to suppress the formation of pits in the main growth layer 40 due to changes in growth conditions. As a result, it is possible to improve the yield of obtaining substrates 50 from the main growth layer 40.

[0125] (d) In this embodiment, the base structure 30 is formed by epitaxially growing an Mn-doped layer 24 made of a single crystal of a group III nitride semiconductor containing Mn above the base substrate 10. This allows the Mn doping step S140 to the main growth step S300 to be performed continuously in the same vapor phase growth apparatus. As a result, the manufacturing process for the substrate 50 is simplified, and it becomes possible to easily mass-produce the substrate 50.

[0126] (e) In this embodiment, the Mn doping step S140 through the main growth step S300 are performed consecutively within the same vapor phase growth apparatus, thereby allowing Mn to adhere to the inner wall of the chamber. While the detailed mechanism is unclear, this makes it possible to suppress the adhesion of by-products (e.g., parasitic growth of polycrystalline nitrides) to the inner wall of the chamber during the main growth step S300. As a result, particle generation during the main growth step S300 can be suppressed.

[0127] (f) In the substrate 50, at least some of the dislocations (curved dislocations cdl) among the multiple dislocations have curved portions. When an epitaxial layer is grown on the substrate 50, dislocation propagation from the curved dislocations cdl in the substrate 50 to the epitaxial layer can occur, just like other dislocations. However, the propagation direction of dislocations propagating from the curved dislocations cdl in the substrate 50 to the epitaxial layer can be significantly tilted. This can suppress the appearance of dislocations on the surface of the epitaxial layer. For example, in the epitaxial layer, dislocations propagating from the curved dislocations cdl can be actively caused to meet with other dislocations, dislocations propagating from the curved dislocations cdl can be made to form loops, or dislocations propagating from the curved dislocations cdl can be caused to propagate toward the side of the epitaxial layer. As a result, the dislocation density on the surface of the epitaxial layer can be reduced.

[0128] <Second embodiment of the present invention> Next, a second embodiment of the present invention will be described.

[0129] In the first embodiment described above, the base structure 30 has the base substrate 10 and the Mn-doped layer 24, but the present invention is not limited to this. As in the present embodiment described below, the base structure 30 may be modified. In this embodiment, the base structure preparation step S100 and the like are different from those in the first embodiment described above.

[0130] Hereinafter, only elements different from the above-described embodiment will be described, and elements that are substantially the same as the elements described in the above-described embodiment will be assigned the same reference numerals and descriptions thereof will be omitted.

[0131] (1) Method for manufacturing nitride crystal substrate The method for manufacturing a nitride crystal substrate according to this embodiment will be described with reference to Figure 7. Figures 7(a) and (b) are schematic cross-sectional views showing part of the method for manufacturing a nitride crystal substrate according to this embodiment.

[0132] (S100: Base structure preparation process) First, as shown in FIG. 7(a), in this embodiment, a Mn-doped substrate 26 in which Mn is added to the entire surface is prepared as the base structure 30.

[0133] The method for producing the Mn-doped substrate 26 is not particularly limited, but may be, for example, the following method. First, the base substrate preparation step S110, initial step S120, and Mn doping step S140 of the first embodiment are performed. Next, the Mn-doped layer 24 is sliced ​​to obtain the Mn-doped substrate 26. Thereafter, both surfaces of the Mn-doped substrate 26 are polished. In this manner, the Mn-doped substrate 26 as the base structure 30 can be obtained.

[0134] The Mn-doped substrate 26 obtained by the above-described method is, for example, a free-standing substrate made of a single crystal of a group III nitride semiconductor containing Mn. In this embodiment, the Mn-doped substrate 26 is, for example, a Mn-doped GaN free-standing substrate.

[0135] The diameter of the Mn-doped substrate 26 is, for example, 2 inches or more, preferably 4 inches or more. The thickness of the Mn-doped substrate 26 is, for example, 300 μm or more and 1 mm or less.

[0136] The Mn concentration in the Mn-doped substrate 26 is, for example, 1×10 18 cm -3 or more, preferably 5 x 10 18 cm -3 The upper limit of the Mn concentration in the Mn-doped substrate 26 is not limited, but from the viewpoint of the yield mentioned above, it is set to, for example, 1×10 20 cm -3 is.

[0137] The concentrations of other impurities in the Mn-doped substrate 26 are not particularly limited. However, in the Mn-doped substrate 26 obtained by the above-described manufacturing method, the Si concentration is, for example, 5×10 17 cm -3 Less than 1 × 10 17 cm -3 and the O concentration is less than, for example, 5 x 10 16 cm -3 Less than or equal to 3 x 10 16 cm -3 The following is the result.

[0138] The Mn-doped substrate 26 has a base surface (principal surface, base surface) 26s. The crystal plane with a low index closest to the base surface 26s is, for example, a c-plane (+c-plane) 26c. The c-plane 26c of the Mn-doped substrate 26 is, for example, curved in a concave spherical shape with respect to the base surface 26s.

[0139] The radius of curvature of the c-plane 26c of the Mn-doped substrate 26 is larger than the radius of curvature of the c-plane of a substrate obtained by a conventional VAS method (e.g., the base substrate 10 of the first embodiment), and is, for example, 10 m or more, preferably 12 m or more, more preferably 15 m or more, and even more preferably 18 m or more.

[0140] (S300: Main growth process) 7(b), a main growth layer 40 made of a single crystal of a Group III nitride semiconductor is epitaxially grown on the Mn-doped substrate 26 by, for example, the HVPE method without supplying MnCl gas. This allows the main growth layer 40 to have a Mn concentration lower than that of the Mn-doped substrate 26.

[0141] In addition, the main growth layer 40 is grown to a thickness that allows slicing into at least one freestanding substrate 50. Since the memory effect described above does not occur in this embodiment, the main growth layer 40 in this embodiment may be thinner than that in the first embodiment.

[0142] The growth conditions for the main growth step S300 in this embodiment can be, for example, the same as those in the first embodiment.

[0143] (S400: Slicing process) 7(c), the grown layer 40 is sliced ​​to form at least one substrate 50. At this time, the radius of curvature of the c-plane 50c of the substrate 50 can be made larger than the radius of curvature of the c-plane 26c of the Mn-doped substrate 26.

[0144] (S500: Polishing process) Thereafter, the polishing step S500 is carried out in the same manner as in the first embodiment.

[0145] Through the above steps S100 to S500, the substrate 50 according to this embodiment is manufactured.

[0146] In the stacked structure 90 of this embodiment, the Mn concentration in the main growth layer 40 is uniformly lower throughout the thickness direction than the Mn concentration in the Mn-doped substrate 26. Other features of the stacked structure 90 of this embodiment are the same as those of the first embodiment described above.

[0147] The characteristics of the substrate 50 of this embodiment can be equivalent to those of the first embodiment described above.

[0148] (2) Effects Obtained by the Present Embodiment (a) In this embodiment, a Mn-doped substrate 26, which is entirely doped with Mn, is prepared as the base structure 30, and the main growth layer 40 is epitaxially grown on the Mn-doped substrate 26. This has the effect of correcting the warpage of the c-plane. Specifically, the radius of curvature of the c-plane 50c of the sliced ​​substrate 50 can be made larger than the radius of curvature of the c-plane 26c of the Mn-doped substrate 26.

[0149] (b) In the main growth step S300 of this embodiment, the main growth layer 40 is grown without supplying MnCl gas as a step independent of the base structure preparation step S100, which prepares the Mn-doped substrate 26. This makes it possible to suppress the incorporation of Mn into the main growth layer 40 due to the memory effect described above in the main growth step S300. By suppressing the incorporation of Mn into the main growth layer 40, the Mn concentration in the main growth layer 40 can be made uniformly lower throughout the thickness direction than the Mn concentration in the Mn-doped substrate 26. As a result, many Mn-free substrates 50 can be efficiently obtained from the main growth layer 40 of a predetermined thickness.

[0150] <Other embodiments> The above is a specific description of the embodiments of the present invention. However, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. Note that "the above-described embodiments" includes the first and second embodiments.

[0151] In the first embodiment described above, the case where the base substrate 10 is a GaN freestanding substrate has been described. However, the base substrate 10 is not limited to a GaN freestanding substrate, and may be, for example, a Group III nitride semiconductor such as aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium nitride (InN), indium gallium nitride (InGaN), or aluminum indium gallium nitride (AlInGaN). x In y Ga 1-x-y The substrate may be a free-standing substrate made of a Group III nitride semiconductor represented by the composition formula N(0≦x≦1, 0≦y≦1, 0≦x+y≦1).

[0152] In the first embodiment described above, the steps from the initial step S120 to the main growth step S300 are performed consecutively in the same vapor phase growth apparatus. However, the present invention is not limited to this case, and the following method may also be applied. Specifically, after the Mn doping step S140, the base structure 30 is removed from the vapor phase growth apparatus, and the Mn source material with MnCl2 remaining on its surface is removed from the gas generation vessel of the Mn line. Thereafter, the base structure 30 is loaded into the vapor phase growth apparatus, and the main growth step S300 is performed. This method can suppress the incorporation of Mn into the main growth layer 40 in the main growth step S300, which is caused by the memory effect described above.

[0153] In the above embodiment, the case where the substrate 50 is a GaN freestanding substrate has been described. However, the substrate 50 is not limited to a GaN freestanding substrate. For example, the substrate 50 may be a group III nitride semiconductor such as AlN, AlGaN, InN, InGaN, or AlInGaN. x In y Ga 1-x-y The substrate may be a free-standing substrate made of a Group III nitride semiconductor represented by the composition formula N(0≦x≦1, 0≦y≦1, 0≦x+y≦1).

[0154] In the above embodiment, the substrate 50 is described as being a single layer that can stand on its own. However, the substrate 50 may contain Mn on the back side due to, for example, the memory effect described above. In such a case, the substrate 50 can be considered to be a single layer as described above if it does not include a growth interface. However, in this case, the substrate 50 may also be considered to include a Mn-doped layer, i.e., the substrate 50 may be considered to be one aspect of a "laminated structure."

[0155] In the above embodiment, the case where a wire saw is used in the slicing step S400 has been described, but for example, an outer diameter blade slicer, an inner diameter blade slicer, an electric discharge machine, or the like may also be used.

[0156] In the above-described embodiment, the case where the substrate 50 is obtained by slicing the main growth layer 40 of the laminated structure 90 has been described, but this is not limited to this. For example, the laminated structure 90 may be used as is to manufacture a semiconductor laminate for fabricating a semiconductor device. Specifically, after fabricating the laminated structure 90, a semiconductor functional layer is epitaxially grown on the laminated structure 90 in a semiconductor laminate fabrication process to fabricate the semiconductor laminate. After fabricating the semiconductor laminate, the back side of the laminated structure 90 is polished, and the base structure 30 is removed. As a result, a semiconductor laminate having a substrate 50 and a semiconductor functional layer is obtained, as in the above-described embodiment. In this case, the slicing step S400 and the polishing step S500 for obtaining the substrate 50 can be omitted. [Example]

[0157] Various experimental results that support the effects of the present invention will be described below. In the following, "nitride crystal substrate" may be abbreviated to "substrate."

[0158] (1) Experiment 1 (1-1) Fabrication of laminated structures and nitride crystal substrates The laminated structure and substrate of Sample 1 were fabricated as follows.

[0159] [Conditions for preparing the laminated structure and substrate of Sample 1] <Base structure> (Base substrate) Material: Undoped GaN Manufacturing method: VAS method Diameter: 2 inches Thickness: 400 μm The closest low-index crystal plane to the main plane: c-plane No patterning of the main surface, such as a mask layer, is required. (initial layer) Before the growth of the Mn-doped layer, GaCl gas was supplied without supplying MnCl 2 gas to form an initial layer. Thickness: 30 μm (Mn-doped layer) Material: GaN Growth method: HVPE method Growth temperature: 1040℃ GaCl partial pressure: 9.5 kPa V / III ratio: 1.67 Temperature near the gas generation vessel of the Mn line: 650℃ HCl gas partial pressure on the Mn line: 1.6×10 -2 kPa Thickness: Approximately 220 μm <Main growth layer> Material: GaN Growth method: HVPE method Growth temperature: 1040℃ GaCl partial pressure: 9.5 kPa V / III ratio: 1.67 Thickness: Approximately 500 μm <Slicing and polishing conditions> The substrate was sliced ​​to a predetermined thickness from the surface side of the main growth layer. Double-sided polishing Final thickness of the substrate: 400 μm

[0160] (1-2) Evaluation (Observation by fluorescence microscope) The cross section of the laminated structure of Sample 1 was observed using a fluorescent microscope.

[0161] (X-ray rocking curve measurement) X-ray rocking curve measurements of the (0002) plane were performed on the base substrate, the laminated structure of Sample 1, and the substrate of Sample 1. The measurements were performed at multiple measurement points set at 5 mm intervals on a line passing through the center of the main surface of each substrate along the m-axis direction, and on a line passing through the center of the main surface along the a-axis direction perpendicular to the m-axis. The X-rays were incident from the side defined as the positive side within the main surface of the substrate. The peak angle ω between the X-rays incident on the main surface and the main surface was plotted against the position on the line, and the peak angle ω was approximated by a linear function of the position. The radius of curvature of the c-plane was calculated as the inverse of the slope of the linear function.

[0162] (Secondary Ion Mass Spectrometry (SIMS)) After slicing the substrate of Sample 1, SIMS was performed on the surface side of the Mn-doped layer of Sample 1 and on the main surface side of the substrate of Sample 1.

[0163] (Observation by multiphoton excitation microscope) A multiphoton excitation microscope was used to observe the main surface of the substrate of Sample 1. Also, the base substrate and the substrate of Sample 1 were each observed using the multiphoton excitation microscope while changing the focus in the thickness direction.

[0164] (1-3) Results <Cross section of the laminated structure of Sample 1> The cross section of the laminated structure of Sample 1 will be described with reference to Fig. 8. Fig. 8 is an image of the cross section of the laminated structure of Sample 1 observed in Experiment 1 using a fluorescent microscope.

[0165] As shown in FIG. 8, it was confirmed based on the difference in color that the layered structure of Sample 1 had a base substrate, an initial layer, a Mn-doped layer, and a main growth layer.

[0166] The Mn-doped layer was reddish-brown due to the inclusion of Mn. The Mn-doped layer side of the growth layer was also slightly reddish-brown, and the color of the growth layer gradually became lighter from the Mn-doped layer side toward the surface side of the growth layer. This confirmed that the Mn concentration in the growth layer of Sample 1 gradually decreased from the Mn-doped layer side toward the surface side of the growth layer.

[0167] Furthermore, there was no evidence of three-dimensional growth (facet growth) of the growth layer, and the surface of the growth layer was flat without pits, confirming that in Sample 1, the growth layer was successfully grown over the entire surface of the Mn-doped layer, with the c-plane as the growth plane.

[0168] <Impurity concentration> The SIMS results showed that the Mn concentration on the surface side of the Mn-doped layer of Sample 1 was approximately 5 × 10 19 cm -3 In the Mn-doped layer of sample 1, the Si concentration was approximately 2 × 10 16 cm -3 The O concentration is approximately 5 × 10 15 cm -3 This confirmed that the incorporation of Si and O into the Mn-doped layer was suppressed during growth.

[0169] On the other hand, the Mn concentration on the main surface side of the substrate of Sample 1 was 1×10 16 cm -3 In addition, the Si concentration in the substrate of Sample 1 was also about 2 × 10 16 cm -3 The O concentration is approximately 5 × 10 15 cm -3 It was.

[0170] (X-ray rocking curve measurement) Next, the results of X-ray rocking curve measurements for Sample 1 will be described with reference to Figures 9(a) and (b). Figure 9(a) shows the results of X-ray diffraction rocking curve measurements performed in the direction along the m-axis of each sample in Experiment 1, and Figure 9(b) shows the results of X-ray diffraction rocking curve measurements performed in the direction along the a-axis, which is perpendicular to the m-axis of each sample in Experiment 1. In the figures, "As-grown" refers to the laminated structure, and "Backlapped" refers to the substrate after slicing and polishing.

[0171] 9(a) and (b), the radius of curvature of the c-plane of the grown layer in the laminate structure of Sample 1 was larger than that of the base substrate, being 7 m or more. Furthermore, the radius of curvature of the c-plane of the substrate of Sample 1 was larger than those of the base substrate and the grown layer in the laminate structure, being 10 m or more.

[0172] In addition, when the peak angle ω was approximated by a linear function of position in the X-ray rocking curve measurement of the c-plane substrate of Sample 1, the error with respect to the linear function was small. Specifically, the error of the measured peak angle ω with respect to the linear function approximated as described above was 0.01° or less.

[0173] 9(a) and (b), the a-axis component of the off-angle at the center of the substrate of Sample 1 was larger (absolute value) than the m-axis component of the off-angle. The theoretical value of the peak angle ω of the (0002) plane is approximately 17.28°.

[0174] In addition, in the substrate of Sample 1, the absolute value of the radius of curvature of the c-plane in the a-axis direction was larger than the absolute value of the radius of curvature of the c-plane in the m-axis direction.

[0175] However, the directional dependence of the radius of curvature of the c-plane was small for the substrate of Sample 1. That is, the difference between the absolute value of the radius of curvature of the c-plane in the a-axis direction and the absolute value of the radius of curvature of the c-plane in the m-axis direction was 30% of that in the a-axis direction.

[0176] (dislocation) Dislocations in the substrate of Sample 1 will be described with reference to FIGS. 10 to 13. FIG. 10 is a diagram showing an image of the main surface of the substrate of Sample 1 observed using a multiphoton excitation microscope. FIG. 11 is a perspective view of an image of the substrate of Sample 1 observed using a multiphoton excitation microscope while changing the focus. FIG. 12 is a diagram showing an image of the base substrate observed using a multiphoton excitation microscope while changing the focus, viewed from a direction along the main surface. Note that in FIGS. 11 and 12 (as well as FIG. 16 described below), black and white are inverted, and dislocations are shown in white.

[0177] Note that Figure 10 is an observation image focused on the main surface of the substrate. On the other hand, the "observation images" in Figures 11 and 12 are superimposed images in the thickness direction, in which unit images observed by focusing at predetermined depths are superimposed. In Figure 11, the horizontal and vertical lengths are approximately 64 μm and approximately 300 μm, respectively. In Figure 12, the horizontal and vertical lengths are approximately 64 μm and approximately 200 μm, respectively.

[0178] Observation using a multiphoton excitation microscope revealed that the dislocation density on the surface of the substrate was 3.0 × 10 6 cm -2 In contrast, the dislocation density on the main surface of the substrate of Sample 1 was slightly lower than that of the underlying substrate, at 1.3 × 10 6 cm -2 (See Figure 10).

[0179] As shown in FIG. 12, in the base substrate, each of the multiple dislocations extended in a substantially straight line from the rear surface toward the surface of the base.

[0180] In contrast, as shown in FIG. 11, it was confirmed that the dislocations in the substrate of Sample 1 had unique characteristics.

[0181] Specifically, at least some of the dislocations had curved portions in the substrate of Sample 1. In Figure 11, one of the dislocations having a curved portion is designated as "curved dislocation A."

[0182] The curved dislocation A in Figure 11 had the following characteristics. The inclination of the curved dislocation A with respect to the normal to the main surface on the side that was relatively shallower from the main surface was larger than that on the side that was relatively deeper from the main surface. The inclination of the curved dislocation A with respect to the normal to the main surface gradually increased from the back surface opposite the main surface toward the main surface.

[0183] Here, using the observation image of Sample 1 viewed from the main surface side of the substrate and the observation image of Sample 1 viewed from the direction along the main surface of the substrate, the number of curved dislocations was counted, defining as a "curved dislocation" a dislocation whose maximum distance from an imaginary line connecting the start point of the dislocation at a depth of 200 μm from the main surface and the end point of the dislocation on the main surface was 5 μm or more.

[0184] In this case, the proportion of curved dislocations among the multiple dislocations in Sample 1 was 43%. In addition, in Sample 1, the density of curved dislocations on the main surface of the substrate was 5.6 × 10 5 cm -2 It was.

[0185] (2) Experiment 2 (2-1) Fabrication of laminated structures and nitride crystal substrates The laminated structure and substrate of Sample 2 were fabricated as follows.

[0186] [Conditions for preparing the laminated structure and substrate of Sample 2] <Base structure: Mn-doped substrate> A Mn-doped substrate was fabricated as the base structure using the following procedure. Specifically, an initial layer and a Mn-doped layer were formed in this order on the base substrate under the same conditions as those for the base structure of Sample 1, except that the thickness of the Mn-doped layer was set to 500 nm. Next, the Mn-doped layer was sliced ​​to obtain the Mn-doped substrate. Both sides of the Mn-doped substrate were then polished to a thickness of 400 nm. <Main growth layer> The main growth layer was grown on a Mn-doped substrate under conditions similar to those for the main growth layer of Sample 1. <Slicing and polishing conditions> The slicing and polishing conditions were the same as those for Sample 1.

[0187] (2-2) Evaluation (Observation by fluorescence microscope) The cross section of the laminated structure of Sample 2 was observed using a fluorescent microscope.

[0188] (X-ray rocking curve measurement) Under the same conditions as those in Experiment 1, X-ray rocking curve measurements were performed on the (0002) plane for the Mn-doped layer before slicing, the Mn-doped substrate, the (mainly grown layer) of the stacked structure of Sample 2, and the substrate of Sample 2.

[0189] (SIMS) SIMS was performed on the surface side of the Mn-doped substrate and on the main surface side of the substrate of Sample 2.

[0190] (Observation by multiphoton excitation microscope) A multiphoton excitation microscope was used to observe the main surface of the substrate of Sample 2. The substrate of Sample 2 was also observed using the multiphoton excitation microscope while changing the focus in the thickness direction.

[0191] (2-3) Results <Cross section of the laminated structure of Sample 2> The cross section of the laminated structure of Sample 2 will be described with reference to Fig. 13. Fig. 13 is an image of the cross section of the laminated structure of Sample 2 observed with a fluorescent microscope in Experiment 2.

[0192] As shown in FIG. 13, it was confirmed based on the difference in color that the layered structure of Sample 2 had a Mn-doped substrate and a main growth layer.

[0193] The Mn-doped substrate was reddish-brown. On the other hand, the actual growth layer was not reddish-brown, and the interface between the Mn-doped substrate and the actual growth layer was clearly observed. This confirmed that in Sample 2, the Mn concentration in the growth layer was uniformly lower than the Mn concentration in the Mn-doped substrate throughout the entire thickness direction. It also confirmed that Mn did not diffuse from the Mn-doped substrate to the actual growth layer.

[0194] Furthermore, in Sample 2, similar to Sample 1, there was no evidence of three-dimensional growth of the main growth layer, and the surface of the main growth layer was flat without pits. This confirmed that in Sample 2 as well, the main growth layer was able to grow over the entire surface of the Mn-doped substrate, with the c-plane as the growth surface.

[0195] <Impurity concentration> The SIMS results showed that the Mn concentration on the surface side of the Mn-doped substrate of Sample 2 was approximately 5 × 10 19 cm -3 In the Mn-doped substrate of sample 2, the Si concentration was approximately 2 × 10 16 cm -3 The O concentration is approximately 5 × 10 15 cm -3 It was.

[0196] On the other hand, the Mn concentration on the main surface side of the substrate of Sample 2 was below the detection limit of 1 × 10 15 cm -3 The Si concentration in the substrate of Sample 1 was also about 2 × 10 16 cm -3 The O concentration is approximately 5 × 10 15 cm -3 It was.

[0197] (X-ray rocking curve measurement) 14(a) and (b), the results of the X-ray rocking curve measurement for Sample 2 will be described. Fig. 14(a) shows the results of X-ray diffraction rocking curve measurement in the direction along the m-axis of each sample in Experiment 2, and Fig. 14(b) shows the results of X-ray diffraction rocking curve measurement in the direction along the a-axis, which is perpendicular to the m-axis of each sample in Experiment 2.

[0198] 14(a) and (b), the radius of curvature of the c-plane of the Mn-doped substrate was larger than that of the Mn-doped layer before slicing. Furthermore, the radius of curvature of the c-plane of the substrate of Sample 2 was larger than that of the Mn-doped substrate, being 20 m or more.

[0199] In addition, when the peak angle ω was approximated by a linear function of position in the X-ray rocking curve measurement of the c-plane substrate of Sample 2, the error with respect to the linear function was small. Specifically, the error of the measured peak angle ω with respect to the linear function approximated as described above was 0.01° or less.

[0200] Furthermore, as shown in FIGS. 14(a) and (b), the a-axis component of the off-angle at the center of the substrate of Sample 2 (its absolute value) was larger than the m-axis component of the off-angle.

[0201] In addition, in the substrate of Sample 2, the absolute value of the radius of curvature of the c-plane in the a-axis direction was larger than the absolute value of the radius of curvature of the c-plane in the m-axis direction.

[0202] However, the directional dependence of the radius of curvature of the c-plane was small for the substrate of Sample 2. That is, the difference between the absolute value of the radius of curvature of the c-plane in the a-axis direction and the absolute value of the radius of curvature of the c-plane in the m-axis direction was 25% of that in the a-axis direction.

[0203] (dislocation) Dislocations in the substrate of Sample 2 will be described with reference to Figures 15 and 16. Figure 15 is a diagram showing an image of the main surface of the substrate of Sample 2 observed using a multiphoton excitation microscope. Figure 16 is a perspective view of an image of the substrate of Sample 2 observed using a multiphoton excitation microscope while changing the focus.

[0204] In FIG. 16, the horizontal length and vertical length are also approximately 64 μm and approximately 300 μm, respectively.

[0205] Observation using a multiphoton excitation microscope revealed that the dislocation density on the main surface of the substrate of Sample 2 was slightly lower than that of the underlying substrate, at 1.2 × 10 6 cm -2 (See Figure 15).

[0206] As shown in FIG. 16, in the substrate of Sample 2, similar to the substrate of Sample 1, at least some of the dislocations among the plurality of dislocations had curved portions.

[0207] At least one of the curved dislocations in the substrate of Sample 2 had the same characteristics as curved dislocation A in the substrate of Sample 1. That is, in the substrate of Sample 2, the inclination of the curved dislocation with respect to the normal to the main surface on the side relatively shallower from the main surface was larger than that on the side relatively deeper from the main surface. The inclination of the curved dislocation with respect to the normal to the main surface gradually increased from the back surface opposite the main surface toward the main surface.

[0208] In addition, when the number of curved dislocations in Sample 2 was measured using the same method as in Sample 1, the proportion of curved dislocations among the multiple dislocations was 45%. In addition, in Sample 1, the density of curved dislocations on the main surface of the substrate was 5.2 × 10 5 cm -2 It was.

[0209] (3) Summary of Experiments 1 and 2 According to the above-mentioned Experiments 1 and 2, it was confirmed that the effect of correcting the c-plane warpage can be achieved by epitaxially growing the growth layer on a base structure whose surface layer contains Mn.

[0210] Furthermore, it was confirmed that in each of the substrates of Samples 1 and 2, at least some of the dislocations among the plurality of dislocations had curved portions due to the above-mentioned manufacturing method.

[0211] <Preferred embodiment of the present invention> Preferred embodiments of the present invention will be described below.

[0212] (Appendix 1) A method for manufacturing a nitride crystal substrate using a vapor phase growth method, comprising the steps of: preparing an underlayer structure made of a single crystal of a Group III nitride semiconductor, at least a surface layer of which contains manganese; epitaxially growing, on the underlayer structure, a main growth layer made of a single crystal of a Group III nitride semiconductor having a manganese concentration lower than the manganese concentration in the surface layer of the underlayer structure; obtaining at least one free-standing nitride crystal substrate from the main growth layer; have A method for manufacturing a nitride crystal substrate.

[0213] (Appendix 2) In the step of epitaxially growing the main growth layer, The main growth layer is grown by hydride vapor phase epitaxy. A method for producing the nitride crystal substrate described in Appendix 1.

[0214] (Appendix 3) The step of preparing the base structure includes: preparing a base substrate made of a single crystal of a Group III nitride semiconductor; epitaxially growing a manganese-doped layer made of a single crystal of a group III nitride semiconductor containing manganese above the base substrate; have 3. A method for producing a nitride crystal substrate according to claim 1 or 2.

[0215] (Appendix 4) The radius of curvature of the (0001) plane of the nitride crystal substrate is made larger than the radius of curvature of the (0001) plane of the manganese-doped layer. A method for producing the nitride crystal substrate according to Appendix 3.

[0216] (Appendix 5) In the step of preparing a base substrate, preparing a base substrate having a principal surface in which the nearest low-index crystal plane is a concave, spherically curved (0001) plane; In the step of obtaining the nitride crystal substrate, The nitride crystal substrate is obtained, the radius of curvature of the (0001) plane of which is greater than the radius of curvature of the (0001) plane of the starting substrate. 5. A method for producing a nitride crystal substrate according to claim 3 or 4.

[0217] (Appendix 6) The steps from the step of epitaxially growing the manganese-doped layer to the step of epitaxially growing the main growth layer are carried out continuously in the same vapor phase growth apparatus. 6. A method for producing a nitride crystal substrate according to any one of appendixes 3 to 5.

[0218] (Appendix 7) In the step of preparing the base structure, As the base structure, a manganese-doped substrate in which manganese is added to the entire surface is prepared. 3. A method for producing a nitride crystal substrate according to claim 1 or 2.

[0219] (Appendix 8) In the step of preparing the base structure, preparing the manganese-doped substrate having a primary surface in which the nearest low-index crystal plane is a concave, spherically curved (0001) plane; In the step of obtaining the nitride crystal substrate, The nitride crystal substrate is obtained, the radius of curvature of the (0001) plane of which is larger than the radius of curvature of the (0001) plane of the manganese-doped substrate. A method for producing a nitride crystal substrate according to Supplementary Note 7.

[0220] (Appendix 9) In the step of preparing the base structure, At least a portion of the Group III element sites in the surface layer is substituted with manganese. A method for producing a nitride crystal substrate according to any one of appendices 1 to 8.

[0221] (Appendix 10) In the step of epitaxially growing the main growth layer, The main growth layer is grown over the entire main surface of the base structure, with the (0001) plane as the growth plane. 10. A method for producing a nitride crystal substrate according to any one of appendices 1 to 9.

[0222] (Appendix 11) preparing an underlayer structure made of a single crystal of a Group III nitride semiconductor, at least a surface layer of which contains manganese; epitaxially growing, on the underlayer structure, a main growth layer made of a single crystal of a Group III nitride semiconductor having a manganese concentration lower than the manganese concentration in the surface layer of the underlayer structure; and In the step of epitaxially growing the main growth layer, The growth layer is grown by vapor phase epitaxy to a thickness that allows for obtaining at least one freestanding nitride crystal substrate. A method for manufacturing a laminated structure.

[0223] (Appendix 12) A nitride crystal substrate configured as a freestanding substrate made of a single crystal of a Group III nitride semiconductor, having a primary surface in which the nearest low-index crystal plane is the (0001) plane, having a plurality of threading dislocations propagating in the thickness direction; Among the set of the plurality of threading dislocations, a dislocation line formed by at least some of the threading dislocations has a curved portion. Nitride crystal substrate.

[0224] (Appendix 13) The inclination of the dislocation line of the curved threading dislocation with respect to the normal to the main surface on a side that is relatively shallower from the main surface is greater than that on a side that is relatively deeper from the main surface. 13. The nitride crystal substrate according to claim 12.

[0225] (Appendix 14) The inclination of the dislocation line of the curved threading dislocation with respect to the normal to the main surface gradually increases from the side opposite to the main surface toward the main surface. 14. The nitride crystal substrate according to claim 12 or 13.

[0226] (Appendix 15) Among the set of threading dislocations, the proportion of curved threading dislocations is 10% or more and 90% or less. 15. The nitride crystal substrate according to any one of claims 12 to 14.

[0227] (Appendix 16) The dislocation density on the main surface is 1×10 5 cm -2 5x10 or more 6 cm -2 is 16. The nitride crystal substrate according to any one of claims 12 to 15.

[0228] (Appendix 17) The density of curved threading dislocations on the primary surface is 5×10 4 cm -2 Over 4.5 x 10 6 cm -2 is 17. The nitride crystal substrate according to any one of claims 12 to 16.

[0229] (Appendix 18) The radius of curvature of the (0001) plane is 10 m or more. 18. The nitride crystal substrate according to any one of claims 12 to 17.

[0230] (Appendix 19) At the center of the main surface <0001> the axis is inclined with respect to the normal to the main surface at a predetermined off angle; one of a component of the off angle in the <1-100> axis direction and a component of the off angle in the <11-20> axis direction perpendicular to the <1-100> axis is larger than the other, The absolute value of the radius of curvature of the (0001) plane in the larger of the <1-100> axial component and the <11-20> axial component is larger than the absolute value of the radius of curvature of the (0001) plane in the other direction. 19. The nitride crystal substrate according to any one of claims 12 to 18.

[0231] (Appendix 20) The difference between the absolute value of the radius of curvature of the (0001) plane in a direction along the <1-100> axis and the absolute value of the radius of curvature of the (0001) plane in a direction along the <11-20> axis perpendicular to the <1-100> axis is 90% or less of the larger one of them. 20. The nitride crystal substrate according to any one of claims 12 to 19.

[0232] (Appendix 21) Have a diameter of 2 inches or more 21. The nitride crystal substrate according to any one of claims 12 to 20.

[0233] (Appendix 22) Has a diameter of 4 inches or more 22. The nitride crystal substrate according to any one of claims 12 to 21.

[0234] (Appendix 23) a base structure having at least a surface layer made of a single crystal of a group III nitride semiconductor containing manganese; a main growth layer provided on the understructure and made of a single crystal of a Group III nitride semiconductor having a manganese concentration lower than the manganese concentration in the surface layer of the understructure; and The growth layer has a thickness that allows at least one freestanding nitride crystal substrate to be obtained. Laminated structure. [Explanation of symbols]

[0235] 10 Base substrate 24 Mn-doped layer 26 Mn-doped substrate 30 Base structure 40 growth layers 50 Nitride crystal substrate (substrate)

Claims

1. A nitride crystal substrate configured as a free-standing substrate made of a single crystal of a Group III nitride semiconductor, having a primary surface whose nearest low-index crystal plane is the (0001) plane, and a back surface opposite to the primary surface, the nitride crystal substrate includes a plurality of curved dislocations having curved portions in which the inclination of the dislocation line relative to the normal to the main surface changes continuously; the (0001) plane in the nitride crystal substrate is curved in a concave spherical shape relative to the main surface, The manganese concentration on the back surface of the nitride crystal substrate is higher than the manganese concentration on the main surface. Nitride crystal substrate.

2. A nitride crystal substrate configured as a freestanding substrate made of a single crystal of a Group III nitride semiconductor, having a primary surface in which the nearest low-index crystal plane is the (0001) plane, the nitride crystal substrate includes a plurality of curved dislocations having curved portions in which the inclination of the dislocation line relative to the normal to the main surface changes continuously; the (0001) plane in the nitride crystal substrate is curved in a concave spherical shape relative to the main surface, At the center of the main surface, one of a component of an off angle formed by a <0001> axis with respect to a normal to the main surface in a direction along a <1-100> axis and a component of the off angle in a direction along a <11-20> axis is larger than the other, The absolute value of the radius of curvature of the (0001) plane in either the component of the off-angle in the direction along the <1-100> axis or the component of the off-angle in the direction along the <11-20> axis is larger than the absolute value of the radius of curvature of the (0001) plane in the other direction. Nitride crystal substrate.

3. The difference between the absolute value of the radius of curvature of the (0001) plane in the direction along the <1-100> axis and the absolute value of the radius of curvature of the (0001) plane in the direction along the <11-20> axis is 90% or less of the larger of the two radii of curvature of the (0001) plane. The nitride crystal substrate according to claim 2 .

4. A nitride crystal substrate configured as a freestanding substrate made of a single crystal of a Group III nitride semiconductor, having a primary surface in which the nearest low-index crystal plane is the (0001) plane, the nitride crystal substrate includes a plurality of curved dislocations having curved portions in which the inclination of the dislocation line relative to the normal to the main surface changes continuously; the (0001) plane in the nitride crystal substrate is curved in a concave spherical shape relative to the main surface, The difference between the absolute value of the radius of curvature of the (0001) plane in the direction along the <1-100> axis and the absolute value of the radius of curvature of the (0001) plane in the direction along the <11-20> axis is 90% or less of the larger of the two radii of curvature of the (0001) plane. Nitride crystal substrate.

5. In the nitride crystal substrate, the oxygen concentration in a region including the curved portions of the plurality of curved dislocations is equal to the oxygen concentration in a region not including the curved portions of the plurality of curved dislocations. The nitride crystal substrate according to any one of claims 1 to 4.

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