Crystal substrate and method for manufacturing the same

Abstract

To provide a technique for further reducing a dislocation density in a crystal substrate composed of a group III nitride.SOLUTION: A crystal substrate is a substrate composed of a group III nitride single crystal, a low-index crystal plane most proximate to a principal surface of the substrate is a c-plane, a threading dislocation included in the single crystal and penetrating the c-plane extends in a thickness direction without bending in a direction orthogonal to the thickness direction of the substrate, and a ratio of edge dislocations in the threading dislocations is less than 60%.SELECTED DRAWING: Figure 12

Description

[Technical field]

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

[0002] Crystal substrates made of Group III nitrides such as gallium nitride (GaN) are used as substrates for manufacturing semiconductor devices such as light-emitting elements, transistors, etc. Various techniques have been proposed for reducing the dislocation density in the crystal substrates (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Yuichi Oshima et al., "GaN Substrates by Void Formation and Separation Method," Hitachi Cable, No. 26 (2007-1), pp. 31-36 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a technique for further reducing the dislocation density in a crystal substrate made of a Group III nitride. [Means for solving the problem]

[0005] According to one aspect of the present invention a first crystal body composed of a single crystal of a Group III nitride; a second crystal body grown on the first crystal body and composed of a single crystal of a Group III nitride; having the second crystal body has an intermediate layer including a plurality of closed spaces containing an alkali metal; the intermediate layer has a plurality of closed space rows formed by arranging a plurality of the closed spaces on each of a plurality of linear crystal defects included in the second crystal body, a crystal substrate, wherein a certain closed space row is selected from the plurality of closed space rows, a first closed space and a second closed space included in the closed space row are selected, and heights from the first closed space and the second closed space to the first crystal body are set to h1 and h2, respectively, and there are a plurality of other closed space rows having closed spaces at the same heights as h1 and h2. is provided.

[0006] According to another aspect of the present invention, A substrate made of a single crystal of a Group III nitride, A crystal substrate, in which the ratio of edge dislocations among the threading dislocations contained in the single crystal is less than 60%. is provided.

[0007] According to yet another aspect of the present invention, preparing a first crystal body composed of a single crystal of a Group III nitride; growing a second crystal body composed of a single crystal of a Group III nitride on the first crystal body in a mixed melt containing an alkali metal and a Group III element; having In the step of growing the second crystal body, the second crystal body has an intermediate layer including a plurality of closed spaces containing the alkali metal; a plurality of closed space rows are formed by arranging a plurality of the closed spaces on each of a plurality of linear crystal defects included in the second crystal body in the intermediate layer, a method for manufacturing a crystal substrate, comprising: selecting a certain closed space row from the plurality of closed space rows; selecting a first closed space and a second closed space included in the closed space row; and growing the second crystal body so that there are a plurality of other closed space rows having closed spaces at the same heights as h1 and h2, when the heights from the first closed space and the second closed space to the first crystal body are h1 and h2, respectively. is provided. Effect of the Invention

[0008] A technique is provided for further reducing dislocation density in a crystal substrate composed of a group III nitride. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a flow chart showing an overall method for manufacturing a crystal substrate according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a flowchart showing details of step S100 in the method for manufacturing a crystal substrate according to one embodiment. [Diagram 3] 3(a) to 3(g) are schematic cross-sectional views illustrating the process of preparing a seed substrate 21 in step S100 of one embodiment. [Figure 4] 4(a) to 4(c) are schematic cross-sectional views illustrating the process of producing the substrate 31 in step S200 according to one embodiment. [Diagram 5] 5(a) and 5(b) are fluorescence microscope images of a crystal 30 produced as an experimental example of one embodiment. [Figure 6] 6(a) and 6(b) are MPPL images of a crystal 30 produced as an experimental example of one embodiment. [Figure 7] FIG. 7 is an MPPL image of a crystal 30 produced as an experimental example of one embodiment. [Figure 8] FIG. 8 is a flowchart showing an overall method for manufacturing a crystal substrate according to a modified embodiment. [Figure 9] 9(a) to 9(c) are schematic cross-sectional views illustrating the process of producing a substrate 41 in step S300 according to a modified example of the embodiment. [Figure 10] FIG. 10 is a schematic diagram illustrating an example of an HVPE apparatus. [Figure 11] FIG. 11 is a schematic diagram illustrating a flux liquid phase growth apparatus. [Figure 12] FIG. 12 is a schematic perspective view of a crystal 30 according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <One embodiment of the present invention>

[0011] An embodiment of the present invention will be described below. In this embodiment, a technique for growing a crystal substrate 31 (hereinafter also referred to as substrate 31) using a seed crystal substrate 21 (hereinafter also referred to as seed substrate 21) as a seed crystal will be described. The seed substrate 21 and the substrate 31 are each composed of a single crystal of a group III nitride. An example of the group III nitride that constitutes the seed substrate 21 and the substrate 31 is gallium nitride (GaN).

[0012] In this embodiment, a GaN substrate grown by a void-assisted separation (VAS) method is exemplified as the seed substrate 21, but a GaN substrate grown by another method may be used as the seed substrate 21. However, from the viewpoint of forming the closed space array 25C in a dispersed state within the plane as described later, the GaN substrate used as the seed substrate 21 is required to have a low dislocation density region (dislocation density of 1×10, for example) in which the dislocation density is not excessively high on the main surface 21s serving as the base for the growth of the substrate 31. 7 / cm 2 It is preferable to have a dislocation concentrated region where the dislocation density is excessively high (a region where the dislocation density is, for example, 1×10 7 / cm 2 In other words, it is more preferable that the maximum dislocation density in the main surface 21s is not more than 1×10 7 / cm 2 In the VAS method, the maximum dislocation density in the main surface 21s is, for example, 1×10 7 / cm 2 This method is preferably used as one method for obtaining a seed substrate 21 having a thickness of less than 100 nm. In this specification, the term "dislocation" refers to a threading dislocation, and in order to avoid complication of expression, the threading dislocation may be simply referred to as a "dislocation."

[0013] (1) Method for manufacturing crystal substrate A method for manufacturing a substrate 31 according to the present embodiment will be described. Fig. 1 is a flowchart showing the entire method for manufacturing a substrate 31 according to the present embodiment. This manufacturing method includes step S100 of preparing a seed substrate 21, and step S200 of fabricating a substrate 31 by a liquid phase method, specifically, a flux method.

[0014] (S100: Prepare seed crystal substrate) In step S100, a seed substrate 21 is prepared. Fig. 2 is a flowchart showing details of step S100 in an example of the VAS method. Figs. 3(a) to 3(g) are schematic cross-sectional views showing the process of producing the seed substrate 21 in step S100 in an example of the VAS method.

[0015] (S110: Prepare a void-forming substrate) Step S100 includes steps S110 to S140. In step S110, a void-formed substrate 15 is prepared. More specifically, step S110 includes steps S111 to S114. In step S111, as shown in Fig. 3(a), a base substrate 10 is prepared. An example of the base substrate 10 is a sapphire substrate.

[0016] In step S112, as shown in FIG. 3(b), an underlayer 11 is formed on the undersubstrate 10. The underlayer 11 is, for example, a stack of a buffer layer made of low-temperature grown GaN and a single crystal layer of GaN. The buffer layer and the single crystal layer are formed by, for example, metal-organic vapor phase epitaxy (MOVPE). For example, trimethylgallium (TMG) is used as the group III raw material, and for example, ammonia (NH3) is used as the group V raw material. The thickness of the buffer layer and the single crystal layer are, for example, 20 nm and 0.5 μm, respectively.

[0017] 3(c), a metal layer 12 is formed on the underlayer 11. The metal layer 12 is formed, for example, by vapor-depositing titanium (Ti) to a thickness of 20 nm.

[0018] In step S114, as shown in FIG. 3(d), the metal layer 12 is nitrided by heat treatment to form a nanomask 14, and voids are formed in the underlayer 11 to form a void-containing layer 13. The heat treatment is performed, for example, as follows. The undersubstrate 10 on which the underlayer 11 and the metal layer 12 are formed is placed in an electric furnace and placed on a susceptor having a heater. Then, the undersubstrate 10 is heated in an atmosphere containing hydrogen gas (H2 gas) or a hydride gas. Specifically, for example, the heat treatment is performed for 20 minutes at a predetermined temperature, for example, a temperature of 850° C. or more and 1100° C. or less, in a flow of H2 gas containing 20% ​​NH3 gas as a nitriding gas.

[0019] The heat treatment nitrides the metal layer 12, forming a nanomask 14 having a high density of fine holes on the surface. Also, a part of the base layer 11 is etched through the fine holes of the nanomask 14, causing voids in the base layer 11, forming the void-containing layer 13. In this manner, in step S110, a void-formed substrate 15 is prepared, which has the void-containing layer 13 and the nanomask 14 formed on the base substrate 10.

[0020] It is preferable that the heat treatment is performed so that the distribution of the micropores in the nanomask 14 and the distribution of the voids in the void-containing layer 13 are uniform in the plane. For this reason, for example, it is preferable that the heating condition of the heater is adjusted so that the temperature distribution becomes closer to uniform in the plane, and it is also preferable that the heat treatment is performed while rotating the susceptor.

[0021] (S120: Crystal growth by HVPE) In step S120, as shown in Fig. 3(e), a crystal 20 is grown on the nanomask 14 of the void-formed substrate 15. The crystal 20 is grown by a vapor phase method, specifically, a hydride vapor phase epitaxy (HVPE) method. Here, an HVPE apparatus 200 will be described. Fig. 10 is a schematic diagram illustrating the configuration of the HVPE apparatus 200.

[0022] The HVPE apparatus 200 is made of a heat-resistant material such as quartz, and includes an airtight container 203 in which a film formation chamber 201 is formed. A susceptor 208 for holding a substrate 250 to be processed is provided in the film formation chamber 201. The susceptor 208 is connected to a rotating shaft 215 of a rotating mechanism 216, and is configured to be freely rotatable. Gas supply pipes 232a to 232c for supplying hydrochloric acid (HCl) gas, NH3 gas, and nitrogen gas (N2 gas) into the film formation chamber 201 are connected to one end of the airtight container 203. A gas supply pipe 232d for supplying hydrogen (H2) gas is connected to the gas supply pipe 232c. The gas supply pipes 232a to 232d are provided with flow rate controllers 241a to 241d and valves 243a to 243d, respectively, in this order from the upstream side. A gas generator 233a that contains Ga melt as a raw material is provided downstream of the gas supply pipe 232a. A nozzle 249a that supplies gallium chloride (GaCl) gas generated by the reaction between HCl gas and Ga melt toward the substrate 250 held on the susceptor 208 is connected to the gas generator 233a. Nozzles 249b and 249c that supply various gases supplied from these gas supply pipes toward the substrate 250 held on the susceptor 208 are connected to the downstream sides of the gas supply pipes 232b and 232c, respectively. An exhaust pipe 230 that exhausts the inside of the film formation chamber 201 is provided at the other end of the airtight container 203. A pump 231 is provided to the exhaust pipe 230. A zone heater 207 for heating the inside of the gas generator 233a and the substrate 250 held on the susceptor 208 to a desired temperature is provided on the outer periphery of the airtight container 203, and a temperature sensor 209 for measuring the temperature inside the film formation chamber 201 is provided inside the airtight container 203. Each member of the HVPE apparatus 200 is connected to a controller 280 configured as a computer, and the processing procedures and processing conditions described below are controlled by a program executed on the controller 280.

[0023] Step S120 can be performed using the HVPE apparatus 200, for example, in the following procedure. First, Ga is accommodated as a raw material in the gas generator 233a. Also, the void-forming substrate 15 is held on the susceptor 208 as the substrate 250 to be processed. Then, a mixed gas of H2 gas and N2 gas is supplied into the film formation chamber 201 while the film formation chamber 201 is heated and evacuated. Then, when the film formation temperature and pressure in the film formation chamber 201 reach the desired film formation temperature and pressure, and the atmosphere in the film formation chamber 201 becomes the desired atmosphere, gas is supplied from the gas supply pipes 232a and 232b to supply GaCl gas and NH3 gas as film formation gas to the void-forming substrate 15.

[0024] The processing conditions for carrying out step S120 are exemplified as follows. Growth temperature Tg: 980 to 1100°C, preferably 1050 to 1100°C Pressure in the film formation chamber 201: 90 to 105 kPa, preferably 90 to 95 kPa GaCl gas partial pressure: 0.2 to 15 kPa Partial pressure of NH3 gas / partial pressure of GaCl gas: 4~20 N2 gas flow rate / H2 gas flow rate: 1~20

[0025] In this growth process, GaN crystals that start growing from the void-containing layer 13 pass through the fine holes in the nanomask 14 and appear on the surface, forming initial nuclei on the nanomask 14. The initial nuclei grow in the thickness direction (vertical direction) and in-plane direction (horizontal direction) and bond to each other within the plane, forming a crystal 20 of a continuous film made of a GaN single crystal. Since a mutual attractive force acts between the bonded initial nuclei, a tensile stress is introduced into the crystal 20. Furthermore, in areas where no initial nuclei are formed, gaps 16 due to the voids in the void-containing layer 13 are formed between the nanomask 14 and the crystal 20.

[0026] It is preferable that the growth process is performed so that the distribution of the initial nuclei and the distribution of the voids 16 are uniform within the plane. For this reason, for example, it is preferable that the heating condition of the zone heater 207 is adjusted so that the temperature distribution approaches uniformity within the plane, and it is also preferable that the growth process is performed while rotating the susceptor 208. It is preferable that the distribution of the fine holes in the nanomask 14 and the distribution of the voids in the void-containing layer 13 are uniform within the plane so that the distribution of the initial nuclei and the distribution of the voids 16 are uniform within the plane. The uniform distribution of the initial nuclei prevents the formation of dislocation concentrated regions with locally very high dislocation density within the plane (dislocation density of, for example, 1×10 7 / cm 2 Since no region where the initial nuclei are greater than or equal to the initial dislocation density is generated, the distribution of dislocation density becomes uniform. In addition, the uniform distribution of initial nuclei makes the tensile stress uniform within the plane.

[0027] The thickness of the crystal 20 to be grown is preferably a thickness that allows at least one free-standing seed substrate 21 to be obtained from the crystal 20, for example, a thickness of 0.2 mm or more. There is no particular upper limit to the thickness of the crystal 20 to be grown.

[0028] (S130: Peeling) In step S130, as shown in Fig. 3(f), the crystal 20 is peeled off from the void-forming substrate 15. This peeling is performed by the crystal 20 naturally peeling off from the void-forming substrate 15 at the gaps 16 formed between the crystal 20 and the nanomask 14 during the growth of the crystal 20 or in the process of cooling the inside of the film formation chamber 201 after the growth of the crystal 20. The gaps 16 are uniformly distributed, so that peeling is performed in a state where stress concentration in a specific area is unlikely to occur.

[0029] After the crystal 20 has grown to a predetermined thickness, the temperature inside the film-forming chamber 201 is lowered to a temperature at which the unloading operation can be performed, and the void-formed substrate 15 and the crystal 20 are unloaded from the film-forming chamber 201 .

[0030] Due to the tensile stress introduced during the growth of the crystal 20, the exfoliated crystal 20 warps so that the growth side surface is concave. In the crystal 20, the tensile stress is uniform within the plane, so that the warp occurs uniformly. As a result, the c-plane 120 of the GaN single crystal constituting the exfoliated crystal 20 curves in a concave spherical shape toward the inside of the crystal 20 when the main surface 20s is viewed from the +c side. Here, "spherical" means a curved surface that is approximated by a spherical surface. In addition, "spherical approximation" means approximation within a predetermined error range to a perfect circular sphere (true sphere) or an elliptical sphere (prolate spheroid).

[0031] In addition, in a plan view seen from the normal direction of the center of the main surface 20s, the uniformity of the growing crystal is likely to decrease in the outermost peripheral part of the crystal 20. For this reason, the above-mentioned "c-plane 120 is spherically curved" may not be true in the outermost peripheral part of the crystal 20. The above-mentioned "c-plane 120 is spherically curved" may be true in a region (hereinafter also referred to as a main region) that accounts for 80% or more of the area on the center side of the main surface 20s in a plan view. This also applies to the c-plane 121 of the seed substrate 21, the c-plane 130 of the crystal 30, the c-plane 131 of the substrate 31, the c-plane 140 of the crystal 40, and the c-plane 141 of the substrate 41, which will be described later.

[0032] To avoid complication, the c-face 120 of crystalline body 20 is simply expressed as "curved in a concave spherical shape toward the inside of crystalline body 20 when main surface 20s is viewed from the +c side in the main region," but this is also expressed as "curved in a concave spherical shape." Similar expressions are used for c-face 121 of seed substrate 21, c-face 130 of crystalline body 30, c-face 131 of substrate 31, c-face 140 of crystalline body 40, and c-face 141 of substrate 41, which will be described later.

[0033] The off angle of crystalline mass 20 is defined as the angle between the c-axis direction of the GaN single crystal constituting crystalline mass 20 and the normal direction to the center of main surface 20s. The off angles of seed substrate 21, crystalline mass 30, substrate 31, crystalline mass 40, and substrate 41, which will be described later, are similarly defined.

[0034] The off-angle of the crystal 20 varies depending on the position on the main surface 20s because the c-plane 120 is curved. In other words, the peeled crystal 20 has an off-angle distribution. The off-angle at the center of the main surface 20s is the central off-angle. The central off-angle can be controlled by adjusting the off-angle of the base substrate 10, and may be set so as to be inclined in a specified direction (e.g., the a-axis direction or the m-axis direction).

[0035] When the central off-angle is inclined in a specific direction, the radius of curvature of the c-surface 120 may differ between a direction parallel to the inclination direction and a direction perpendicular to the inclination direction. In other words, the curved shape of the c-surface 120 may be approximated not only by a perfect circular sphere, but also by an elliptical sphere. When approximated by a perfect circular sphere, the shape of the c-surface 120 is represented by one radius of curvature. When approximated by an elliptical sphere, the shape of the c-surface 120 is represented by two radii of curvature.

[0036] In addition, in crystals grown by a method that generates dislocation-concentrated regions by unevenly distributing the density of initial nuclei, such as ELO (Epitaxially Lateral Overgrowth) using a stripe mask, the shape of the c-plane is distorted. In other words, in such crystals, the radius of curvature of the c-plane varies within the plane. The direction of the unevenness of the c-plane may even be reversed depending on the location. For this reason, the shape of the c-plane in such crystals cannot be appropriately approximated as a sphere with a constant radius of curvature.

[0037] (S140: Machining and polishing) In step S140, as shown in FIG. 3(g), the crystal body 20 peeled off in step S130 is mechanically processed and / or polished as necessary to obtain a seed substrate 21 (crystal body 20 as a free-standing substrate). The mechanical processing is, for example, cutting with a wire saw. For example, one seed substrate 21 may be obtained from the entire crystal body 20. Also, for example, a plurality of seed substrates 21 may be obtained from the entire crystal body 20 by slicing the crystal body 20 into a plurality of pieces. The obtained seed substrate 21 may or may not be polished as necessary. One of the two main surfaces may be polished. The crystal body 20 peeled off in step S130 may be used as the seed substrate 21 as it is.

[0038] The radius of curvature of the c-plane 121 of the seed substrate 21 may vary from the radius of curvature of the c-plane 120 of the exfoliated crystal mass 20 due to the machining or polishing in step S140.

[0039] 3(g) illustrates a seed substrate 21 configured in a flat plate shape. The seed substrate 21 is configured such that the crystal plane with a low index closest to the main surface 21s is the c-plane 121, and the c-plane 121 is curved in a concave spherical shape relative to the main surface 21s (relative to either one of the main surfaces 21s of the seed substrate 21). The c-plane 121 has a constant radius of curvature (in the main region) because distortion from the spherical shape is suppressed. In this manner, in step S100, the seed substrate 21 (crystal mass 20) is prepared.

[0040] The fact that the c-plane 121 of the seed substrate 21 has a shape that is approximated to a spherical shape means that the in-plane distribution of dislocation density is uniform (i.e., there is no region where the dislocation density is locally very high). The maximum dislocation density on the main surface 21s of the seed substrate 21 is 1×10 7 / cm 2 less than, for example, 5×10 6 / cm 2 The average dislocation density is preferably 3×10 6 / cm 2 The following is the result.

[0041] The dislocation density is evaluated, for example, by emission intensity mapping near the band edge of GaN using multiphoton excited photoluminescence (hereinafter abbreviated as MPPL). Since dislocation defects are non-radiative recombination centers, the emission intensity is weak around the dislocation defects, and the dislocation defects are observed as dark spots in the emission intensity mapping image. By utilizing this, the dislocation density can be evaluated. Specifically, for example, an image is taken of an observation area of ​​250 μm square in one field of view at any location on the sample, and the dark spot density obtained as the evaluation result can be treated as the dislocation density. In this specification, the dark spot density measured by MPPL is treated as the dislocation density.

[0042] (S200: Crystal substrate preparation using liquid phase method) After the seed substrate 21 is prepared in step S100, the substrate 31 is fabricated by a liquid phase method, specifically a flux method, in step S200. Figures 4(a) to 4(c) are schematic cross-sectional views showing the process of fabricating the substrate 31 in step S200. Figure 4(a) shows the seed substrate 21 prepared in step S100.

[0043] (S210: Crystal growth by flux method) Step S200 includes steps S210 and S220. In step S210, as shown in FIG. 4(b), a crystal 30 is grown on a seed substrate 21 by a flux method. In the flux method, a group III nitride (GaN in this example) is grown in a mixed melt containing an alkali metal used as a flux (solvent) and a group III element (Ga in this example). As the alkali metal to be the flux, sodium (Na) is preferably used, but other alkali metal elements such as lithium (Li) and potassium (K) may be used. These elements may also be mixed and used. The metal used as the flux may be an alkali metal plus an alkaline earth metal. As the alkaline earth metal, magnesium (Mg), calcium (Ca), etc. may be used alone or in a mixture. Here, a flux liquid phase growth apparatus 300 will be described. FIG. 11 is a schematic configuration diagram illustrating the flux liquid phase growth apparatus 300.

[0044] The flux liquid phase epitaxy apparatus 300 includes a pressure vessel 303. The pressure vessel 303 is made of stainless steel (SUS) or the like, and a pressurizing chamber 301 capable of increasing the pressure to a high pressure state of, for example, about 10 MPa is configured inside the pressure vessel 303. The pressurizing chamber 301 includes a crucible 308, a lid for the crucible 308, a reaction vessel 310, a heater 307 for heating the inside of the crucible 308, and a temperature sensor 309 for measuring the temperature inside the pressurizing chamber 301. The crucible 308 is configured to accommodate a mixed melt composed of Na and Ga, for example, with Na as a flux, and to allow a substrate 350 to be processed to be immersed in the mixed melt with its main surface (base surface for crystal growth) facing upward. The reaction vessel 310 is composed of a reaction vessel body and a reaction vessel lid, and the crucible 308 is accommodated inside the reaction vessel 310. A heater 307 is provided on the outside of the reaction vessel 310. The flux liquid phase epitaxy apparatus 300 also includes a rotation mechanism 320, which can rotate the reaction vessel 310, i.e., the crucible 308 accommodated therein. A gas supply pipe 332 for supplying N2 gas into the pressurizing chamber 301 is connected to the pressure-resistant vessel 303. The gas supply pipe 332 is provided with a pressure control device 333, a flow rate controller 341, and a valve 343 in this order from the upstream side. Each member of the flux liquid phase epitaxy apparatus 300 is connected to a controller 380 configured as a computer, and is configured to control the processing procedure and processing conditions described later by a program executed on the controller 380.

[0045] Step S210 is performed, for example, by the following procedure using the flux liquid phase epitaxy apparatus 300. First, the seed substrate 21, which is the substrate 350 to be processed, and the raw materials (Na and Ga) of the mixed melt are placed in the crucible 308, and additives are placed as necessary, and the pressure-resistant container 303 is sealed. Then, N2 gas is supplied into the pressurizing chamber 301, and heating is started after a predetermined gas pressure is reached. By starting heating by the heater 307, the Na and Ga in the crucible 308 melt, and a mixed melt (a Ga melt with Na as a medium, a mixed melt containing Na and Ga) is formed. After raising the temperature to the crystal growth temperature, the gas pressure is adjusted to the crystal growth pressure. Nitrogen (N) is dissolved in the mixed melt, and this state is maintained for a predetermined time. In this specification, the "mixed melt" is not limited to one in which nitrogen is not dissolved, but also includes one in which nitrogen is dissolved.

[0046] The processing conditions for performing step S210 are exemplified as follows. Growth temperature (temperature of mixed melt): 700 to 1000°C, preferably 800 to 900°C, more preferably 870 to 890°C Growth pressure (pressure in the pressure chamber): 0.1 to 10 MPa, preferably 1 to 6 MPa, more preferably 2.5 to 4.0 MPa Na concentration in the mixed melt [[Na] / ([Na]+[Ga])]: 10 to 90%, preferably 40 to 85%, more preferably 70 to 85% (the Na concentration is a molar concentration) Here, for example, the number of moles of Na is represented as [Na]. This notation of the number of moles is also used for other elements in the same way. In this embodiment, the mixed molten liquid used is one in which another metal M, which will be described below, is added to Na (an example of an alkali metal used as a flux) and Ga (an example of a group III element, i.e., a group 13 typical metal element). The concentration (molar concentration) of the other metal M is defined as the ratio of the content of the other metal M to the combined content of Ga and the other metal M in the mixed molten liquid. Concentration of other metal M [[M] / ([M]+[Ga])]: 3 to 15%, preferably 4 to 12% In this case, the other metal M may be a single element or multiple elements. In the case of multiple elements, the combination of the multiple elements is called M. [M] is the total number of moles of the metal elements added other than sodium and gallium. As another additive to the mixed melt, for example, carbon (C) may be added. C concentration [[C] / ([C]+[Ga]+[Na])]: for example, 0.1 to 1.0% Distance between the gas-liquid interface of the mixed melt and nitrogen gas and the main surface of the seed substrate 21: 3 to 70 mm, preferably 5 to 40 mm, and more preferably 20 to 35 mm Rotation speed: 1 to 30 rpm, preferably 5 to 20 rpm, more preferably 7 to 15 rpm

[0047] The other metal M added to the mixed melt includes at least one metal selected from group 4 transition metals, group 5 transition metals, group 6 transition metals, group 7 transition metals, group 8 transition metals, group 9 transition metals, group 10 transition metals, group 11 transition metals, group 12 typical metals, group 14 typical metals, and group 15 typical metals. Specifically, the other metal M may be, for example, one of Ti, Nb, Cr, Fe, Ni, Zn, Ge, Sn, Sb, and Bi, or a combination thereof. The other metal M added to the mixed melt may include a group 13 typical metal element (for example, Al or In in the case of growing GaN) different from the group III element contained in the group III nitride to be grown. Even when the other group III element is added in this way, if the concentration is low as described above, it will not become a mixed crystal.

[0048] 4(b), a GaN single crystal is grown on the primary surface 21s of the seed substrate 21, thereby forming a crystal 30. In the crystal 30, an alkali metal (Na in this example) contained in the mixed molten liquid is incorporated as an inclusion 22 near the interface 27 between the crystal 30 and the seed substrate 21, thereby forming an intermediate layer 24 including (at least) a plurality of closed spaces 23 containing the alkali metal. An upper layer 26 is formed above the intermediate layer 24, which is made of crystals 30 that do not include closed spaces 23 (inclusions 22).

[0049] Fig. 12 is a schematic perspective view of the crystal 30 according to this embodiment. This schematic perspective view is a hypothetical model inferred from findings obtained from experiments shown in Figs. 5(a) to 7 described later. Starting from threading dislocations in the seed substrate 21, linear crystal defects 51 extending in the growth direction (thickness direction) are formed in the intermediate layer 24 of the crystal 30, and multiple closed spaces 23 (inclusions 22) are formed discretely on each linear crystal defect 51, thereby forming a closed space array 25C. (For example, in a seed substrate 21 produced by the VAS method) Since threading dislocations are randomly distributed on the main surface, the closed space array 25C is randomly distributed within the surface.

[0050] As will be understood from the growth method of the crystal 30 described later, the closed spaces 23 are formed multiple times at predetermined intervals in the growth direction (thickness direction). Therefore, the closed spaces 23 formed simultaneously are arranged at the same height in each closed space row 25C. FIG. 12 shows a virtual plane 52 that is approximately parallel to the interface 27 between the seed substrate 21 and the crystal 30, that is, has a substantially constant height from the interface 27. Here, "a certain surface is approximately parallel to another surface" means that the angle between the normal direction of the certain surface and the normal direction of the other surface is 2° C. or less. The closed spaces 23 formed simultaneously are arranged on the same virtual plane 52.

[0051] When the closed spaces 23 included in each closed space column 25C are projected onto a cross section 53 perpendicular to the interface 27, the projected closed spaces 23 are aligned on the line where the cross section 53 intersects with the virtual plane 52, that is, aligned in a direction approximately parallel to the interface 27, forming a closed space row 25R. Therefore, the closed spaces 23 projected onto the cross section 53 form a matrix structure 25 consisting of the closed space rows 25R and the closed space columns 25C. FIG. 4(b) shows a schematic diagram of the matrix structure 25 formed by the closed spaces 23 projected onto a cross section (paper surface) perpendicular to the interface 27.

[0052] The inventors of the present application have found that the density of threading dislocations 54 in the upper layer 26 is lower than the density of threading dislocations in the seed substrate 21, as described below. From this, it is considered that the closed space array 25C formed on the linear crystal defect 51 in the intermediate layer 24 has a function of terminating threading dislocations (a function of preventing the threading dislocations in the seed substrate 21 from extending to the upper layer 26). For ease of understanding, threading dislocations 55 in the case where it is assumed that the threading dislocations terminated by the intermediate layer 24 extend to the upper layer 26 (i.e., the amount reduced by the intermediate layer 24) are shown by dashed lines.

[0053] More specifically, in step S210, the crystal 30 is grown, for example, as follows: Using the above-mentioned mixed melt containing another metal M, the temperature of the mixed melt, which is the growth temperature, is set to, for example, 880° C., and the nitrogen gas pressure, which is the growth pressure, is set to, for example, 3.4 MPa, and these are maintained for, for example, 10 hours, to grow an initial layer of the crystal 30 on the seed substrate 21.

[0054] Thereafter, the intermediate layer 24 having the closed space array 25C is formed. As a method for forming the intermediate layer 24, for example, a method for controlling the growth temperature and a method for controlling the growth pressure can be mentioned. Note that these methods may be used in appropriate combination.

[0055] In the method of controlling the growth temperature, after the growth of the initial layer, the temperature of the mixed melt is lowered to, for example, 875°C while keeping the nitrogen gas pressure at, for example, 3.4 MPa, and maintained for, for example, 1 hour. This allows the crystal 30 to grow so that the alkali metal (Na in this example) contained in the mixed melt is incorporated as the inclusions 22, that is, so that closed spaces 23 containing the alkali metal are formed. Thereafter, the temperature of the mixed melt is again raised to, for example, 880°C while keeping the nitrogen gas pressure at, for example, 3.4 MPa, and maintained for, for example, 1 hour. This allows the crystal 30 to grow so that the closed spaces 23 (inclusions 22) are not formed. By alternately lowering and raising the growth temperature in this way, an intermediate layer 24 having a closed space row 25C is formed.

[0056] In the method of controlling the growth pressure, after the growth of the initial layer, the nitrogen gas pressure is lowered to, for example, 3 MPa while keeping the temperature of the mixed melt at, for example, 880°C, and maintained for, for example, one hour. This allows the crystal 30 to grow so that the closed spaces 23 (inclusions 22) are formed. Thereafter, the nitrogen gas pressure is increased to, for example, 3.4 MPa while keeping the temperature of the mixed melt at, for example, 880°C, and maintained for, for example, one hour. In this manner, the crystal 30 is grown so that the closed spaces 23 (inclusions 22) are not formed. By alternately lowering and raising the growth pressure in this way, an intermediate layer 24 having a closed space row 25C is formed.

[0057] After the intermediate layer 24 is formed, similarly to the growth of the initial layer, the temperature of the mixed molten liquid is set to, for example, 880°C, the nitrogen gas pressure is set to, for example, 3.4 MPa, and these are held for, for example, 100 hours, thereby growing a crystal 30 in which no closed space 23 (inclusions 22) is formed, thereby forming an upper layer 26.

[0058] In this manner, in step S210, the crystal 30 having the intermediate layer 24 is grown. Specifically, for example, the growth of the crystal 30 in which the closed space 23 is formed and the growth of the crystal 30 in which the closed space 23 is not formed are alternately performed, so that the intermediate layer 24 is formed, by alternately decreasing and increasing the growth temperature or alternately decreasing and increasing the growth pressure.

[0059] 5(a) and 5(b) are fluorescence microscope images of a crystal 30 produced as an experimental example of this embodiment, showing a cross section perpendicular to an interface 27 between the seed substrate 21 and the crystal 30. FIG. 5(b) is an enlarged image of a portion of FIG. 5(a). The bright region at the bottom indicates the seed substrate 21, and the dark region at the top indicates the crystal 30. A linear interface 27 is observed as the boundary between the seed substrate 21 and the crystal 30. FIGS. 5(a) and 5(b) show a region of about 700 μm and a region of about 100 μm in the direction along the interface, respectively.

[0060] A matrix structure 25, in which a plurality of brightly indicated closed spaces 23 are arranged in a matrix, i.e., an intermediate layer 24, is observed in the crystal 30 slightly above the interface 27. The plurality of closed spaces 23 are arranged in rows in a direction along (parallel to) the interface, and in columns in a direction intersecting (perpendicular to) the interface. Note that in the matrix structure 25, closed spaces 23 do not necessarily exist at all positions in the rows, and similarly, closed spaces 23 do not necessarily exist at all positions in the columns. In other words, the matrix structure 25 (each closed space column 25C) may have a missing closed space 23.

[0061] In the example shown in Fig. 5(a), the matrix structure 25 is arranged in rows, for example, over 500 μm or more. As can be seen from Fig. 5(a), the matrix structure 25 is formed over almost the entire surface of the crystal body 30, for example, over 80% or more of the area, in a plan view seen from a direction perpendicular to the interface. In the example shown in Fig. 5(a) or Fig. 5(b), the multiple closed spaces 23 are arranged in rows, for example, three or more rows, for example, four or more rows, or further, for example, five or more rows, and the multiple closed spaces 23 are arranged in columns, for example, three or more columns, for example, four or more columns, or further, for example, five or more columns.

[0062] As can be seen from Figure 5(a), the matrix structure 25, i.e., the intermediate layer 24, is formed in a region within a predetermined height from the interface 27, and above the intermediate layer 24 is formed an upper layer 26, which is a region that does not contain a closed space 23 (inclusions 22).

[0063] 6(a) and 6(b) are MPPL images (multiphoton microscope images) of a crystal 30 produced as an experimental example of this embodiment, showing a cross section perpendicular to the interface 27 between the seed substrate 21 and the crystal 30. The dark region at the bottom represents the seed substrate 21, and the bright region at the top represents the crystal 30. FIG. 6(a) and FIG. 6(b) are MPPL images of the same region displayed with different contrasts. FIG. 6(a) is an MPPL image displayed with a contrast that makes it easier to observe the structure of the crystal 30 than the seed substrate 21, and FIG. 6(b) is an MPPL image displayed with a contrast that makes it easier to observe the structure of the seed substrate 21 than the crystal 30.

[0064] 6(a), a plurality of closed spaces 23 (inclusions 22) are arranged on (along) a linear crystal defect 51 contained in the crystalline body 30, thereby forming a closed space row 25C. The linear crystal defect 51 extends in the growth direction (in a direction roughly perpendicular to the interface 27). Moreover, a plurality of such closed space rows 25C are arranged in a line in a direction along the interface 27, thereby forming a matrix structure 25 of the closed spaces 23.

[0065] 6(b), threading dislocations extending in the thickness direction (vertical direction) are present in seed substrate 21, and closed space arrays 25C are formed on extensions of the threading dislocations in crystalline body 30. In other words, linear crystal defects 51 contained in crystalline body 30 are formed with threading dislocations contained in seed substrate 21 as starting points, and it can be seen that closed space arrays 25C are formed on such linear crystal defects 51.

[0066] FIG. 7 is a diagram in which a straight line (i.e., a line intersecting the observed cross section and the virtual plane 52) at a certain height from the interface 27 between the seed substrate 21 and the crystal mass 30 is added to the same MPPL image as FIG. 6(b). FIG. 7 exemplarily shows three closed space columns 25C1, 25C2, and 25C3. For example, the heights to the three closed spaces 23 included in the closed space column 25C1 are h1, h2, and h3, respectively. Among the closed spaces 23 included in the closed space columns 25C1 to 25C3, the closed space row 25R1 is constituted by the closed spaces 23 arranged at the height h1, the closed space row 25R2 is constituted by the closed spaces 23 arranged at the height h2, and the closed space row 25R3 is constituted by the closed spaces 23 arranged at the height h3.

[0067] Based on the contents described with reference to FIG. 4(b), FIG. 5(a) to FIG. 7, and FIG. 12, the following can be said about the closed space row 25C of the intermediate layer 24 according to this embodiment.

[0068] For example, when a certain closed space row 25C is selected from the multiple closed space rows 25C, a first closed space 23 and a second closed space 23 included in the closed space row 25C are selected, and the heights from the first closed space 23 and the second closed space 23 to the seed substrate 21 are set to h1 and h2, respectively, there are multiple other closed space rows 25C that have closed spaces 23 at the same heights as h1 and h2.

[0069] For example, when a certain closed space row 25C is selected from the multiple closed space rows 25C, a first closed space 23 and a second closed space 23 included in the closed space row 25C are selected, and a first virtual plane 52 and a second virtual plane 52 are considered that pass through the first closed space 23 and the second closed space 23, respectively, and are approximately parallel to the interface 27 between the seed substrate 21 and the crystal body 30, there are multiple closed space rows 25C including the closed spaces 23 arranged on the first virtual plane 52, and there are multiple closed space rows 25C including the closed spaces 23 arranged on the second virtual plane 52.

[0070] Furthermore, for example, when the closed spaces 23 included in the multiple closed space rows 25C are projected onto a cross section 53 perpendicular to the interface 27 between the seed substrate 21 and the crystal body 30, there are multiple closed space rows 25R within the cross section 53, each of which is formed by the projected multiple closed spaces 23 being arranged in a direction approximately parallel to the interface 27.

[0071] 4(b), in a cross section perpendicular to the interface 27 (in a cross section parallel to the thickness direction) of the laminated crystal substrate 100 constituted by the seed substrate 21 and the crystal 30, the intermediate layer 24 contains a plurality of spatially scattered closed spaces 23 (inclusions 22), and the intermediate layer 24 serves as a transition region for the GaN single crystal constituting the crystal 30 to grow uniformly by the flux method from the GaN single crystal constituting the seed substrate 21. For example, by performing the growth process under the above-mentioned processing conditions, the closed spaces 23 (inclusions 22) can be distributed uniformly or in a dispersed state without localization within the surface of the intermediate layer 24.

[0072] The crystal 30 grows in a manner that reflects the crystallinity of the seed substrate 21, thereby obtaining a GaN single crystal as the crystal 30. The present inventors have discovered that by growing the crystal 30 so as to form an intermediate layer 24 having a series of closed spaces 25C, the dislocation density in the upper layer 26 of the crystal 30 can be significantly reduced compared to the dislocation density in the seed substrate 21. For example, when the dislocation density in the primary surface 21s of the seed substrate 21 is 3×10 6 / cm 2 The average dislocation density of about 3×10 on the main surface 30s of the upper layer 26 of the crystal 305 / cm 2 It has been confirmed that the average dislocation density can be significantly reduced to about 5×10 on the main surface 30s of the upper layer 26 of the crystal body 30. 5 / cm 2 The average dislocation density is preferably 3×10 5 / cm 2 The minimum dislocation density in the main surface 30s is not particularly limited. The ratio of the maximum dislocation density to the minimum dislocation density can be larger as the minimum dislocation density is lower, but as a guideline, it is, for example, 100 times or less, or, for example, 10 times or less.

[0073] The inventors of the present application have also found that the ratio of types of dislocations (threading dislocations) (ratio of edge dislocations, mixed dislocations, and screw dislocations) changes between the seed substrate 21 grown by the VAS method (hereinafter, in the explanation of the types of dislocations, the seed substrate 21 means the seed substrate 21 grown by the VAS method) and the crystal body 30 (of the upper layer 26). In the main surface 21s of the seed substrate 21, the ratio of edge dislocations, mixed dislocations, and screw dislocations is, for example, 64:36:0. In contrast, in the main surface 30s of the upper layer 26 of the crystal body 30 according to this embodiment, the ratio of edge dislocations, mixed dislocations, and screw dislocations is, for example, 56:44:0. No screw dislocations have been detected in the seed substrate 21 and the crystal body 30 (of the upper layer 26).

[0074] It is speculated that the growth of the crystal 30 accompanied by the formation of the intermediate layer 24 having the closed space array 25C reduces dislocations (threading dislocations) overall, with edge dislocations being preferentially reduced among them.

[0075] The crystal 30 is characterized in that the ratio of edge dislocations is lower than that of the seed substrate 21. The crystal 30 is characterized in that the ratio of mixed dislocations is higher than that of the seed substrate 21. Characteristics of dislocations contained in the seed substrate 21 (grown by the VAS method) include, for example, a ratio of edge dislocations of 60% or more, and, for example, a ratio of mixed dislocations of less than 40%. In contrast, in the crystal 30 grown in this embodiment, characteristics of dislocations contained in the crystal 30 constituting the upper layer 26 include, for example, a ratio of edge dislocations of less than 60%, and, for example, a ratio of mixed dislocations of 40% or more.

[0076] The type of dislocations (threading dislocations) contained in the crystal can be evaluated, for example, as follows. The main surface (surface) of the crystal is treated with, for example, a mixed molten alkaline solution of potassium hydroxide and sodium hydroxide to form etch pits at positions corresponding to each dislocation. The main surface on which the etch pits are formed is observed, for example, with a differential interference microscope, and the etch pits are classified into a plurality of groups according to the size of the etch pits. In addition, the cross section of the etch pits in each group is observed, for example, with a transmission electron microscope (TEM), to confirm what type of dislocation the etch pits in each group correspond to. By utilizing the confirmed correspondence, the type of dislocation contained in the crystal can be evaluated from the size of each etch pit observed with the differential interference microscope.

[0077] More specifically, the type of dislocations contained in the crystal 30 was evaluated as follows. On the substrate 31 obtained from the upper layer 26 of the crystal 30, a GaN single crystal was epitaxially grown by the HVPE method in the same manner as in the modified example (see FIG. 8) described later, to form the crystal 40. The type of dislocations was then evaluated for the crystal 40. This is to accurately compare and evaluate the ratio of the types of dislocations in the seed substrate 21 and the crystal 40, which are formed by the same HVPE method, by evaluating the types of dislocations. Since the crystal 40 is epitaxially grown inheriting the dislocations of the crystal 30, the dislocation densities of the crystal 40 and the crystal 30 are approximately the same, and the ratio of the types of dislocations does not change. For this reason, it can be said that the evaluation result of the ratio of the types of dislocations in the crystal 40 is similar to the evaluation result of the ratio of the types of dislocations in the crystal 30.

[0078] By growing the crystal 30 using the flux method, the hydrogen concentration and oxygen concentration in the crystal 30 can be suppressed. The hydrogen concentration in the crystal 30 is, for example, 1×10 17 / cm 3 less than 5×10 16 / cm 3 The oxygen concentration in the crystal 30 is, for example, 1×10 17 / cm 3 less than 8 x 10 16 / cm 3 The following is the result.

[0079] The c-plane 130 of the GaN single crystal constituting the crystal 30 is curved in a concave spherical shape with respect to the main surface 30s of the crystal 30. The inventors of the present application have also found that by using a seed substrate 21 grown by the VAS method as a seed crystal and growing the crystal 30 by the flux method, the radius of curvature of the c-plane 130 of the crystal 30 can be made larger than the radius of curvature of the c-plane 121 of the seed substrate 21. The reason for this is presumably that the intermediate layer 24 present near the interface between the seed substrate 21 and the crystal 30 weakens the force that binds the crystal 30 to the seed substrate 21, thereby mitigating the compressive stress generated in the crystal 30 as the crystal 30 grows.

[0080] The thickness of the crystal 30 to be grown is not particularly limited, but in this embodiment, the thickness is set to a thickness that allows at least one free-standing substrate 31 to be obtained from the crystal 30, for example, a thickness of 0.2 mm or more. After the crystal 30 of a predetermined thickness has been grown, the pressure-resistant vessel 303 is returned to room temperature and atmospheric pressure, and the seed substrate 21 on which the crystal 30 has been formed is removed from the crucible 308.

[0081] (S220: Machining and polishing) In step S220, as shown in FIG. 4(c), the crystal 30 grown in step S210 is cut by mechanical processing, for example, a wire saw, to separate it from the seed substrate 21. By cutting at a position appropriately away from the interface 27 between the seed substrate 21 and the crystal 30, it is possible to prevent the separated crystal 30 from including the root portion of the crystal 30 including the intermediate layer 24. In other words, it is possible to selectively separate the crystal 30 of the upper layer 26 that does not include the closed space 23 (inclusions 22). The layered crystal substrate 110 consisting of the seed substrate 21 and the root portion of the crystal 30 including the intermediate layer 24 that remains after the separation of the crystal 30 may be reused as a seed crystal for crystal growth by the flux method or the like.

[0082] The separated crystal 30 (upper layer 26) is subjected to machining and / or polishing as necessary to obtain a substrate 31 (crystal 30 as a free-standing substrate). For example, one substrate 31 may be obtained from the entire crystal 30. Also, for example, a plurality of substrates 31 may be obtained from the entire crystal 30 by slicing the crystal 30 into a plurality of pieces. The obtained substrate 31 may or may not be polished as necessary. One of the two main surfaces may be polished. The separated crystal 30 may be used as the substrate 31 as it is.

[0083] Due to the separation of the crystal 30 from the seed substrate 21, the radius of curvature of the c-face 130 of the crystal 30 may change from the radius of curvature of the c-face 130 of the crystal 30 before separation. Furthermore, due to machining or polishing of the separated crystal 30, the radius of curvature of the c-face 131 of the substrate 31 may change from the radius of curvature of the c-face 130 of the separated crystal 30. However, even if such a change in the radius of curvature occurs, the tendency that the radius of curvature of the c-face 130 of the separated crystal 30 and the radius of curvature of the c-face 131 of the substrate 31 are larger than the radius of curvature of the c-face 121 of the seed substrate 21 is maintained.

[0084] 4(c) illustrates a substrate 31 configured in a flat plate shape. The substrate 31 is configured such that the crystal plane with a low index closest to the main surface 31s is the c-plane 131, and the c-plane 131 is curved in a concave spherical shape relative to the main surface 31s (relative to one of the main surfaces 31s of the substrate 31). The c-plane 131 has a constant radius of curvature (in the main region) because distortion from the spherical shape is suppressed. As described above, in step S200, the substrate 31 (crystal 30) is produced by the flux method using the seed substrate 21 (crystal 20) as a seed crystal.

[0085] (2) Effects Obtained by the Present Embodiment According to this embodiment, one or more of the following advantages can be obtained.

[0086] (a) By growing crystal 30 on seed substrate 21 so that an intermediate layer 24 having a closed space array 25C is formed (or so that an intermediate layer 24 having a matrix structure 25 is formed), the dislocation density of the GaN single crystal constituting crystal 30 of upper layer 26 formed on the upper side of intermediate layer 24 can be significantly reduced compared to the dislocation density of the GaN single crystal constituting seed substrate 21.

[0087] The substrate 31 made of the crystal 30 has a dislocation density of, for example, 3×10 5 / cm 2The substrate 31 is of high quality and has a very low resistance to chemical attack. Therefore, the substrate 31 is expected to contribute to improving the performance of semiconductor devices manufactured using the substrate, and is expected to be used, for example, as a substrate for manufacturing power devices that have a higher energy saving effect than existing devices.

[0088] By growing the crystal 30 with the formation of an intermediate layer 24 having a closed space array 25C (a matrix-like structure 25) (i.e., reflecting the formation of the crystal 30 by such growth), a crystal 30 having a changed ratio of dislocation types is obtained as the crystal 30 of the upper layer 26 relative to the seed substrate 21 (grown by the VAS method).

[0089] (b) The intermediate layer 24 having the closed space array 25C (the matrix structure 25) can be formed over almost the entire surface of the crystal 30, for example, over an area of ​​80% or more, in a plan view seen from a direction perpendicular to the interface between the seed substrate 21 and the crystal 30. This makes it possible to obtain the above-mentioned effect of reducing dislocation density uniformly over almost the entire surface of the crystal 30.

[0090] The closed spaces 23 constituting the closed space array 25C of the intermediate layer 24 are aligned on linear crystal defects 51 of the crystal body 30 originating from threading dislocations in the seed substrate 21. In order for the closed space arrays 25C to be formed in a dispersed state within the plane to the extent that a matrix structure 25 is formed, it is considered preferable that the intervals between dislocations on the main surface 21s of the seed substrate 21 are relatively wide. This is because if the intervals between dislocations are excessively narrow, the closed spaces 23 (inclusions 22) formed on adjacent dislocations collide with each other and are not aligned properly. Therefore, the seed substrate 21 has a low dislocation density region where the dislocation density is not excessive (dislocation density of, for example, 1×10 6) as a region on the main surface 21s where the closed space arrays 25C are likely to be formed in a dispersed state. 7 / cm 2 It is preferred to have a region where the .lambda.

[0091] In addition, the seed substrate 21 has a dislocation concentrated region in the main surface 21s where the dislocation density is excessively high (for example, a dislocation density of 1×10 7 / cm2 That is, the maximum dislocation density in the main surface 21s is, for example, 1×10 7 / cm 2 This makes it easy to form the closed space array 25C (the matrix structure 25) uniformly in-plane over a wide area above the main surface 21s of the seed substrate 21.

[0092] (c) By growing the substrate 31 by the flux method using the seed substrate 21 grown by the VAS method as a seed crystal, the radius of curvature of the c-plane 131 in the substrate 31 can be made larger than the radius of curvature of the c-plane 121 in the seed substrate 21. The larger the radius of curvature of the c-plane 131, the more the curvature of the c-plane 131 is reduced, and the width of the off-angle distribution in the substrate 31 can be made smaller. In other words, the substrate 31 with improved uniformity of the off-angle in the plane can be obtained. The spherical c-plane 131 of the substrate 31 is obtained by enlarging the radius of curvature from the spherical c-plane 121 of the seed substrate 21. Therefore, the substrate 31 has a gentler change in the off-angle overall in the plane than the seed substrate 21. The substrate 31 has a gentler change in the off-angle overall in the plane than the seed substrate 21, and therefore the width of the off-angle distribution can be made smaller.

[0093] The larger the diameter of the substrate 31, the larger the width of the off-angle distribution tends to be. Therefore, the present technology, which can reduce the width of the off-angle distribution, is particularly preferably applied to a substrate 31 with a large diameter. The radius of curvature of the c-face 121 of the seed substrate 21 is, for example, 3 m or more, and, for example, 15 m or less. The radius of curvature of the c-face 131 of the substrate 31 is larger than the radius of curvature of the c-face 121 of the seed substrate 21, and is preferably 15 m or more, more preferably 20 m or more, and further preferably 30 m or more. In response to market demands for large-diameter substrates, the size of the substrate 31 is preferably, for example, 4 inches (10.16 cm) or more in diameter. Correspondingly, the size of the seed substrate 21 is also preferably, for example, 4 inches or more in diameter. Since the c-face 131 is spherical, the off-angle does not change irregularly within a certain region of the main surface 31s (for example, within a region corresponding to one semiconductor device), and the change in the off-angle is gradual. In addition, since the c-plane 131 is spherical, the overall off-angle distribution within the main surface 31s can be easily grasped. That is, since the radius of curvature of the c-plane 131 is large, the off-angle distribution within the plane can be made small even for a large-diameter substrate, and since the c-plane 131 is spherical, the change in the off-angle changes regularly.

[0094] By utilizing the phenomenon in which inclusions 22 are incorporated near the interface between seed substrate 21 and crystal 30 during crystal growth by the flux method, intermediate layer 24 can be formed and the radius of curvature of c-face 131 of substrate 31 can be increased. By distributing inclusions 22, that is, closed spaces 23, uniformly or in a non-localized, dispersed state within the interface plane between seed substrate 21 and crystal 30, the effect of increasing the radius of curvature can be obtained uniformly within the plane.

[0095] The concave spherical c-face 131 of the substrate 31 is obtained by enlarging the radius of curvature of the concave spherical c-face 121 of the seed substrate 21. Therefore, the c-face 131 does not have a locally convex curvature, and local distortion is suppressed within the substrate 31. As a result, the substrate 31 is less susceptible to cracks and chipping, and is easy to process. This improves the yield in the manufacturing process of the substrate 31 and in the device manufacturing process using the substrate 31.

[0096] <Modification> A modified example of the above embodiment will be described. In the embodiment, the manufacturing method for producing substrate 31 using seed substrate 21 as a seed crystal has been described. In this modified example, a manufacturing method for producing crystal substrate 41 (hereinafter also referred to as substrate 41) using substrate 31 as a seed crystal will be further described.

[0097] 8 is a flowchart showing a method for manufacturing substrate 41 according to this modification. This manufacturing method includes step S100 of preparing seed substrate 21, step S200 of fabricating substrate 31 by a liquid phase method, specifically a flux method, and step S300 of fabricating substrate 41 by a gas phase method, for example, an HVPE method. Steps S100 and S200 are similar to those described with reference to FIG. 1 in the above embodiment.

[0098] (S300: Crystal substrate production by vapor phase method) After the substrate 31 is prepared in step S200, the substrate 41 is fabricated by a vapor phase method, for example, an HVPE method, in step S300. Figures 9(a) to 9(c) are schematic cross-sectional views showing the process of fabricating the substrate 41 in step S300. Figure 9(a) shows the substrate 31 prepared in step S200.

[0099] (S310: Crystal growth by HVPE method) Step S300 includes steps S310 and S320. In step S310, as shown in FIG. 9(b), a GaN single crystal is epitaxially grown on a substrate 31 by the HVPE method to form a crystal 40. Step S310 can be performed by the HVPE apparatus 200 using the substrate 31 as the substrate 250 to be processed, in a similar procedure to that of step S120 for producing the seed substrate 21. The processing conditions for the crystal growth process in step S310 are exemplified by the same conditions as those of step S120. Note that the substrate 31 used for the seed crystal of the crystal 40 may be the crystal 30 (the laminated crystal substrate 100 shown in FIG. 4(b)) laminated on the seed substrate 21.

[0100] The thickness of the crystal 40 to be grown is preferably a thickness that allows at least one free-standing substrate 41 to be obtained from the crystal 40, for example, a thickness of 0.2 mm or more. There is no particular upper limit to the thickness of the crystal 20 to be grown.

[0101] By growing the crystal 40 using the HVPE method, the hydrogen concentration and oxygen concentration in the crystal 40 can be suppressed. The hydrogen concentration in the crystal 40 is, for example, 1×10 17 / cm 3 less than 5×10 16 / cm 3 The oxygen concentration in the crystal 40 is, for example, 5×10 16 / cm 3 ≦3×10 16 / cm 3 or less, and more preferably 1×10 16 / cm 3 The following is the result.

[0102] (S320:machined and polished) 9(c), in step S320, the crystal 40 grown in step S310 is cut by mechanical processing, for example, a wire saw, and separated from the substrate 31. The layered crystal substrate 130 consisting of the substrate 31 and the base portion of the crystal 40 that remains after the separation of the crystal 40 may be reused as a seed crystal for crystal growth by the HVPE method or the like.

[0103] The separated crystal 40 is machined and / or polished as necessary to obtain a substrate 41 (crystal 40 as a free-standing substrate). For example, one substrate 41 may be obtained from the entire crystal 40. Alternatively, for example, multiple substrates 41 may be obtained from the entire crystal 40 by slicing the crystal 40 into multiple pieces. The obtained substrate 41 may or may not be polished as necessary. One of the two main surfaces may be polished. The separated crystal 40 may be used as the substrate 41 as it is.

[0104] Due to the separation of the crystal 40 from the substrate 31, the radius of curvature of the c-face 140 of the crystal 40 may change from the radius of curvature of the c-face 140 of the crystal 40 before separation. Also, due to machining or polishing of the separated crystal 40, the radius of curvature of the c-face 141 of the substrate 41 may change from the radius of curvature of the c-face 140 of the separated crystal 40.

[0105] 9(c) illustrates a substrate 41 configured in a flat plate shape. The substrate 41 is configured such that the crystal plane with a low index closest to the main surface 41s is the c-plane 141, and the c-plane 141 is curved in a concave spherical shape relative to the main surface 41s (relative to one of the main surfaces 41s of the substrate 41). The c-plane 141 has a constant radius of curvature (in the main region) because distortion from the spherical shape is suppressed.

[0106] As described above, in step S300, the substrate 41 is produced by a vapor phase method, for example, the HVPE method, using the substrate 31 as a seed crystal. The HVPE method can grow a crystal at a higher growth rate than the flux method. Therefore, this modification is preferably used as a technique for obtaining a thick crystal 40 using the substrate 31 as a seed crystal after obtaining the substrate 31 with enhanced crystallinity by the flux method.

[0107] The crystallinity of substrate 41 (crystal 40) is as high as that of substrate 31 (crystal 30). The radius of curvature of c-face 141 of substrate 41 is at least as large as the radius of curvature of c-face 131 of substrate 31, and is larger than the radius of curvature of c-face 121 of seed substrate 21. As an experimental example of this modification, free-standing substrate 41 was fabricated by the HVPE method. In substrate 41 of the experimental example, the entire substrate surface was covered with a 3×10 5 / cm 2 It has been confirmed that an extremely low dislocation density of about 100 nm can be obtained. It has also been confirmed that, in the substrate 41 of the experimental example, the radii of curvature in the m-axis direction and the a-axis direction of the c-plane are 20 m or more (preferably 30 m or more), for example, very large values ​​of 76.4 m and 65.5 m, respectively.

[0108] <Other embodiments> The embodiment and the modified examples of the present invention have been specifically described above. However, the present invention is not limited to the above-mentioned embodiment and modified examples, and various modifications can be made without departing from the gist of the present invention.

[0109] For example, in a modified example, one or more substrates may be obtained from a laminated crystal substrate 120 of the substrate 31 and the crystal 40, without separating the crystal 40 from the substrate 31. Also, for example, when growing the crystal 20, 30 or 40, impurities such as conductivity-determining impurities may be added as necessary.

[0110] <Preferred embodiment of the present invention> Preferred aspects of the present invention will be described below.

[0111] (Appendix 1) a first crystal body composed of a single crystal of a Group III nitride; a second crystal body grown on the first crystal body and composed of a single crystal of a Group III nitride; having the second crystal body has an intermediate layer including a plurality of closed spaces (inclusions) containing an alkali metal; the intermediate layer has a plurality of closed space rows formed by arranging a plurality of the closed spaces on (along) each of a plurality of linear crystal defects included in the second crystal body, A crystal substrate in which a certain row of closed spaces is selected from the plurality of rows of closed spaces, a first closed space and a second closed space included in the row of closed spaces are selected, and when the heights from the first closed space and the second closed space to the first crystal body are h1 and h2, respectively, there are a plurality of other rows of closed spaces having closed spaces at the same heights as h1 and h2.

[0112] (Appendix 2) the second crystal body has an upper layer that is disposed above the intermediate layer and does not include the closed space, 2. The crystal substrate of claim 1, wherein the threading dislocation density in the main surface of the second crystal body of the upper layer is lower than the threading dislocation density in the main surface of the first crystal body that serves as the base for growth of the second crystal body.

[0113] (Appendix 3) 3. The crystal substrate according to claim 1, wherein the linear crystal defect contained in the second crystal body of the intermediate layer is formed with a threading dislocation contained in the first crystal body as an origin.

[0114] (Appendix 4) The main surface of the first crystal body, which serves as a base for the growth of the second crystal body, has a threading dislocation density of 1×10 7 / cm 2 4. The crystal substrate of claim 1, having a region where the thickness is less than 100 nm.

[0115] (Appendix 5) The main surface of the first crystal body, which serves as a base for the growth of the second crystal body, has a threading dislocation density of 1×10 7 / cm 2 (The maximum dislocation density is 1×10 7 / cm 2 The crystal substrate according to any one of claims 1 to 4, wherein the thickness of the crystal substrate is less than 100 nm.

[0116] (Appendix 6) The second crystal body has an upper layer that is disposed above the intermediate layer and does not include the closed space, and a maximum threading dislocation density in a main surface of the second crystal body of the upper layer is 5×10 5 / cm 2 6. A crystal substrate according to any one of claims 1 to 5 below.

[0117] (Appendix 7) The second crystal body has an upper layer that is disposed above the intermediate layer and does not include the closed space, and an average threading dislocation density in a main surface of the second crystal body of the upper layer is 3×10 5 / cm 2 The crystal substrate according to any one of claims 1 to 6, wherein:

[0118] (Appendix 8) the c-plane of the single crystal constituting the first crystal body is curved into a concave spherical shape with a predetermined curvature; the second crystal body has an upper layer that is disposed above the intermediate layer and does not include the closed space, 9. The crystal substrate according to any one of claims 1 to 8, wherein the radius of curvature of the c-plane of the single crystal constituting the second crystal body of the upper layer is greater than the radius of curvature of the c-plane of the single crystal constituting the first crystal body.

[0119] (Appendix 9) the second crystal body has an upper layer that is disposed above the intermediate layer and does not include the closed space, the second crystal body of the upper layer does not have screw dislocations; 9. The crystal substrate according to any one of claims 1 to 8, wherein a ratio of edge dislocations among threading dislocations contained in the second crystal body of the upper layer is lower than a ratio of edge dislocations among threading dislocations contained in the first crystal body.

[0120] (Appendix 10) 10. The crystal substrate of claim 9, wherein the ratio of edge dislocations among the threading dislocations contained in the second crystal body of the upper layer is less than 60%, and the ratio of edge dislocations among the threading dislocations contained in the first crystal body is 60% or more.

[0121] (Appendix 11) a first crystal body composed of a single crystal of a Group III nitride; a second crystal body grown on the first crystal body and composed of a single crystal of a Group III nitride; having the second crystal body has an intermediate layer including a plurality of closed spaces (inclusions) containing an alkali metal; the intermediate layer has a plurality of closed space rows formed by arranging a plurality of the closed spaces on (along) each of a plurality of linear crystal defects included in the second crystal body, A crystal substrate in which, when a certain row of closed spaces is selected from the plurality of rows of closed spaces, a first closed space and a second closed space included in the row of closed spaces are selected, and a first imaginary plane and a second imaginary plane are considered which pass through the first closed space and the second closed space, respectively, and are approximately parallel to the interface between the first crystal body and the second crystal body, there are a plurality of rows of closed spaces including closed spaces arranged on the first imaginary plane, and there are a plurality of rows of closed spaces including closed spaces arranged on the second imaginary plane.

[0122] (Appendix 12) a first crystal body composed of a single crystal of a Group III nitride; a second crystal body grown on the first crystal body and composed of a single crystal of a Group III nitride; having the second crystal body has an intermediate layer including a plurality of closed spaces (inclusions) containing an alkali metal; the intermediate layer has a plurality of closed space rows formed by arranging a plurality of the closed spaces on (along) each of a plurality of linear crystal defects included in the second crystal body, A crystal substrate in which, when the closed spaces included in the multiple closed space rows are projected onto a cross section perpendicular to the interface between the first crystal body and the second crystal body, there are multiple closed space rows in the cross section, each of which is formed by the multiple projected closed spaces being aligned in a direction approximately parallel to the interface.

[0123] (Appendix 13) a first crystal body composed of a single crystal of a Group III nitride; a second crystal body grown on the first crystal body and composed of a single crystal of a Group III nitride; having the second crystal body has an intermediate layer including a plurality of closed spaces (inclusions) containing an alkali metal; The intermediate layer is a crystal substrate having a matrix structure of closed spaces formed by arranging a plurality of the closed spaces in rows in a direction along the interface between the first crystal body and the second crystal body, and arranging a plurality of the closed spaces in a direction intersecting the interface, in a cross section intersecting the interface.

[0124] (Appendix 14) 14. The crystal substrate according to claim 13, wherein in the matrix structure, the closed spaces are arranged in three or more rows (four or more, five or more rows).

[0125] (Appendix 15) 15. The crystal substrate according to claim 13, wherein in the matrix structure, the closed spaces are arranged in three or more rows (four or more, five or more rows).

[0126] (Appendix 16) 16. The crystal substrate according to any one of claims 13 to 15, wherein the matrix structure is formed over 500 μm or more in the direction along the interface.

[0127] (Appendix 17) 17. The crystal substrate according to any one of claims 13 to 16, wherein the matrix structure is formed over 80% or more of the area of ​​the second crystal mass in a plan view.

[0128] (Appendix 18) A substrate made of a single crystal of a Group III nitride, A crystal substrate, wherein the ratio of edge dislocations among the threading dislocations contained in the single crystal is less than 60%.

[0129] (Appendix 19) 19. The crystal substrate of claim 18, wherein the threading dislocations contained in the single crystal are free of screw dislocations.

[0130] (Appendix 20) Has a diameter of 4 inches or more; 20. The crystal substrate according to claim 18 or 19, wherein the c-plane of the single crystal is curved inwardly of the substrate with a radius of curvature of 15 nm or more in a concave spherical shape when the main surface of the substrate is viewed from the +c side, and has a constant radius of curvature over a region of 80% or more of the main surface in a planar view.

[0131] (Appendix 21) 21. The crystal substrate according to any one of claims 18 to 20, wherein both the radius of curvature of the c-plane of the single crystal in the a-axis direction and the radius of curvature of the c-plane of the single crystal in the m-axis direction are 20 m or more (preferably 30 m or more).

[0132] (Appendix 22) The maximum threading dislocation density on the main surface of the single crystal is 5×10 5 / cm 2 22. The crystal substrate according to any one of claims 18 to 21 below.

[0133] (Appendix 23) The average threading dislocation density on the main surface of the single crystal is 3×10 5 / cm 2 23. The crystal substrate according to any one of claims 18 to 22 below.

[0134] (Appendix 24) 24. The crystal substrate according to any one of claims 18 to 23, wherein the ratio of the maximum dislocation density to the minimum threading dislocation density in the main surface of the single crystal is 100 times or less.

[0135] (Appendix 25) The hydrogen concentration in the single crystal is 1×10 17 / cm 3 Less than (preferably 5 × 10 16 / cm 3 25. The crystal substrate according to any one of claims 18 to 24, wherein

[0136] (Appendix 26) The oxygen concentration in the single crystal is 1×10 17 / cm 3 Less than (preferably 8 × 10 16 / cm 3 Less than or equal to 5×10 16 / cm 3 Less than 3×10, more preferably 16 / cm 3 Less than 1×10, more preferably 16 / cm 3 26. The crystal substrate according to any one of claims 18 to 25, wherein

[0137] (Appendix 27) preparing a first crystal body composed of a single crystal of a Group III nitride; growing a second crystal body composed of a single crystal of a Group III nitride on the first crystal body in a mixed melt containing an alkali metal and a Group III element; having In the step of growing the second crystal body, the second crystal body has an intermediate layer including a plurality of closed spaces (inclusions) containing the alkali metal; In the intermediate layer, a plurality of the closed spaces are arranged on (along) each of a plurality of linear crystal defects included in the second crystal body, thereby forming a plurality of closed space rows; A method for manufacturing a crystal substrate, comprising the steps of: selecting a certain row of closed spaces from the plurality of rows of closed spaces; selecting a first closed space and a second closed space included in the row of closed spaces; and growing the second crystal body so that there are a plurality of other rows of closed spaces having closed spaces at the same heights as h1 and h2, when the heights from the first closed space and the second closed space to the first crystal body are h1 and h2, respectively.

[0138] (Appendix 28) The mixed molten liquid contains other metals in addition to the alkali metal and the Group III element which is a Group 13 typical metal element, the other metal includes at least one metal selected from among group 4 transition metals, group 5 transition metals, group 6 transition metals, group 7 transition metals, group 8 transition metals, group 9 transition metals, group 10 transition metals, group 11 transition metals, group 12 typical metals, group 13 typical metal elements other than the group III elements, group 14 typical metals, and group 15 typical metals; In the step of growing the second crystal body, A method for producing a crystal substrate as described in Appendix 27, wherein the growth temperature is alternately decreased and increased, or the growth pressure is alternately decreased and increased, so that the intermediate layer is formed by alternately growing the second crystal body in which the closed space is formed and growing the second crystal body in which the closed space is not formed.

[0139] (Appendix 29) 29. The method for producing a crystal substrate according to claim 28, wherein the other metal includes at least one of Ti, Nb, Cr, Fe, Ni, Zn, Ge, Sn, Sb, and Bi.

[0140] (Appendix 30) 30. The method for producing a crystal substrate according to claim 28 or 29, wherein a concentration of the other metal, which is a ratio of a content of the other metal to a combined content of the Group III element and the other metal in the mixed molten liquid, is set to 3% or more and 15% or less (preferably 4% or more and 12% or less).

[0141] (Appendix 31) In the step of growing the second crystal body, 31. The method for producing a crystal substrate according to any one of claims 28 to 30, wherein after the intermediate layer is formed, the second crystal body is grown in such a way that the closed space is not formed, thereby forming an upper layer that is disposed above the intermediate layer and does not include the closed space.

[0142] (Appendix 32) 32. The method for producing a crystal substrate according to any one of claims 28 to 31, further comprising the step of growing a third crystal body composed of a single crystal of a Group III nitride on the second crystal body by a vapor phase method. [Explanation of symbols]

[0143] 10...underlying substrate, 11...underlying layer, 12...metal layer, 13...void-containing layer, 14...nanomask, 15...void-formed substrate, 16...void, 20, 30, 40...crystal, 21, 31, 41...substrate, 20s, 21s, 30s, 31s, 40s, 41s...main surface, 120, 121, 130, 131, 140, 141...c-plane, 100, 110, 120, 130...laminated crystal substrate, 22...inclusion, 23...closed space, 24...intermediate layer, 25...matrix-like structure, 25R...closed space row, 25C...closed space column, 26...upper layer, 27...interface (between seed substrate 21 and crystal 30), 51...linear crystal defect, 52...virtual plane, 53...cross section, 54...threading dislocation (in upper layer)

Claims

1. A substrate made of a single crystal of a Group III nitride, the low-index crystal plane closest to a primary surface of the substrate being a c-plane; A crystal substrate, wherein threading dislocations penetrating the c-plane contained in the single crystal extend in the thickness direction of the substrate without bending in a direction perpendicular to the thickness direction of the substrate, and a ratio of edge dislocations among the threading dislocations is less than 60%.

2. The oxygen concentration in the single crystal is 1×10 １７ / cm ３ The crystalline substrate of claim 1 , wherein the crystalline substrate has a thickness of less than 100 nm.

3. The crystal substrate according to claim 1 , wherein the threading dislocations contained in the single crystal do not include screw dislocations.

4. 4. The crystal substrate according to claim 1, wherein both the radius of curvature of the c-plane of the single crystal in the a-axis direction and the radius of curvature of the c-plane of the single crystal in the m-axis direction are 20 m or more.

5. The maximum threading dislocation density in the main surface of the single crystal is 5×10 ５ / cm ２ The crystal substrate according to any one of claims 1 to 4, wherein:

6. The average threading dislocation density on the main surface of the single crystal is 3×10 ５ / cm ２ The crystal substrate according to any one of claims 1 to 5, wherein:

7. 7. The crystal substrate according to claim 1, wherein the ratio of the maximum dislocation density to the minimum threading dislocation density in the main surface of the single crystal is 100 times or less.

8. The hydrogen concentration in the single crystal is 1×10 １７ / cm ３ The crystal substrate according to any one of claims 1 to 7, wherein the crystal substrate has a thickness of less than 100 nm.

9. a first crystal body composed of a single crystal of a Group III nitride; a second crystal body grown on the first crystal body and composed of a single crystal of a Group III nitride; having the second crystal body has an intermediate layer including a plurality of closed spaces containing an alkali metal; the intermediate layer has a plurality of closed space rows formed by arranging a plurality of the closed spaces on each of a plurality of linear crystal defects included in the second crystal body, A crystal substrate, in which a certain row of closed spaces is selected from the plurality of rows of closed spaces, a first closed space and a second closed space included in the row of closed spaces are selected, and when the heights from the first closed space and the second closed space to the first crystal body are h1 and h2, respectively, there are a plurality of other rows of closed spaces having closed spaces at the same heights as h1 and h2.

10. the second crystal body has an upper layer that is disposed above the intermediate layer and does not include the closed space, 10. The crystal substrate of claim 9, wherein the threading dislocation density in the main surface of the second crystal body of the upper layer is lower than the threading dislocation density in the main surface of the first crystal body that serves as the base for growth of the second crystal body.

11. 11. The crystal substrate according to claim 9, wherein the linear crystal defect contained in the second crystal body of the intermediate layer is formed with a threading dislocation contained in the first crystal body as an origin.

12. the second crystal body has an upper layer that is disposed above the intermediate layer and does not include the closed space, the second crystal body of the upper layer is free of screw dislocations; 12. The crystal substrate according to claim 9, wherein a ratio of edge dislocations among threading dislocations contained in the second crystal body of the upper layer is lower than a ratio of edge dislocations among threading dislocations contained in the first crystal body.

13. preparing a first crystal body composed of a single crystal of a Group III nitride; growing a second crystal body composed of a single crystal of a Group III nitride on the first crystal body in a mixed melt containing an alkali metal and a Group III element; having In the step of growing the second crystal body, the second crystal body has an intermediate layer including a plurality of closed spaces containing the alkali metal; a plurality of closed space rows are formed by arranging a plurality of the closed spaces on each of a plurality of linear crystal defects included in the second crystal body in the intermediate layer, A method for manufacturing a crystal substrate, comprising the steps of: selecting a certain row of closed spaces from the plurality of rows of closed spaces; selecting a first closed space and a second closed space included in the row of closed spaces; and growing the second crystal body so that, when the heights from the first closed space and the second closed space to the first crystal body are h1 and h2, respectively, there are a plurality of other rows of closed spaces having closed spaces at the same heights as h1 and h2.

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