Aluminum nitride single crystal, and method for manufacturing aluminum nitride single crystal

Abstract

To provide a single crystal of aluminum nitride with excellent crystallinity. [Solution] The aluminum nitride single crystal contains boron and one or more additive elements selected from the group consisting of rare earth elements and alkaline earth metal elements.

Description

Technical Field

[0001] The present disclosure relates to a single crystal of aluminum nitride and a method for manufacturing the single crystal of aluminum nitride.

Background Art

[0002] For example, a single crystal of aluminum nitride (AlN) is manufactured by a sublimation method. However, it is difficult to improve the crystallinity of the single crystal by the sublimation method. Further, it is also difficult to increase the size of the single crystal by the sublimation method. In order to solve these problems, as a method for manufacturing a single crystal of aluminum nitride, a liquid phase method (flux method) has been proposed (see Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional liquid phase method, a liquid phase (flux) composed of an alloy containing aluminum and a transition metal element is used as a raw material for a single crystal. The liquid phase can be paraphrased as a molten alloy. The conventional liquid phase method brings the surface of a seed crystal made of silicon carbide (SiC) or the like into contact with the liquid phase. Further, the conventional liquid phase method supplies nitrogen gas (N2) into the liquid phase or dissolves nitrogen in a nitride in contact with the liquid phase into the liquid phase. As a result, a single crystal of aluminum nitride grows on the surface of the seed crystal.

[0005] According to conventional liquid-phase methods, it is possible to grow a single substrate made of single crystal on the surface of a seed crystal in each step. However, it is difficult to manufacture multiple substrates made of single crystals in a short time using conventional liquid-phase methods. In other words, it is difficult to increase the productivity of aluminum nitride single crystals using conventional liquid-phase methods. Furthermore, in conventional liquid-phase methods, fine crystal grains made of aluminum nitride tend to precipitate in the liquid phase. These fine crystal grains in the liquid phase degrade the crystallinity of the single crystal growing on the surface of the seed crystal.

[0006] One aspect of this disclosure is to provide a single crystal of aluminum nitride with excellent crystallinity, and a method for manufacturing the single crystal of aluminum nitride. [Means for solving the problem]

[0007] For example, one aspect of this disclosure relates to a single crystal of aluminum nitride as described in any one of [1] to [9] below, and to a method for producing a single crystal of aluminum nitride as described in any one of

[10] to

[16] below.

[0008] [1] Boron and, One or more additive elements selected from the group consisting of rare earth elements and alkaline earth metal elements, including, A single crystal of aluminum nitride.

[0009] [2] The boron content is 0.05 ppm by mass or more and 0.45 ppm by mass or less. [1] Single crystal of aluminum nitride.

[0010] [3] The content of the rare earth elements is 0.20 ppm by mass or more and 2.20 ppm by mass or less. A single crystal of aluminum nitride as described in [1] or [2].

[0011] [4] The content of the alkaline earth metal element is 0.20 ppm by mass or more and 1.50 ppm by mass or less. The single crystal of aluminum nitride according to any one of [1] to [3].

[0012] [5] The rare earth element is yttrium. The single crystal of aluminum nitride according to any one of [1] to [4].

[0013] [6] The alkaline earth metal element is calcium. The single crystal of aluminum nitride according to any one of [1] to [5].

[0014] [7] Further comprising one or more transition metal elements. The single crystal of aluminum nitride according to any one of [1] to [6].

[0015] [8] The one or more transition metal elements include one or more elements selected from the group consisting of vanadium and chromium. The single crystal of aluminum nitride according to [7].

[0016] [9] It is a substrate or an ingot. The single crystal of aluminum nitride according to any one of [1] to [8].

[0017]

[10] A method for producing the single crystal of aluminum nitride according to any one of [1] to [9], A melting step of melting a metal material in contact with a sintered material to obtain a liquid phase, A growth step of bringing the surface of a seed crystal into contact with the liquid phase and growing the single crystal of aluminum nitride on the surface of the seed crystal, comprising, The sintered body is made of aluminum nitride containing one or more additive elements selected from the group consisting of rare earth elements and alkaline earth metal elements, The metal material contains boron and one or more transition metal elements, The liquid phase contains the additive element, nitrogen, aluminum, the boron, and the one or more transition metal elements, The additive element, the nitrogen, and the aluminum in the liquid phase are derived from the sintered body, The boron and the one or more transition metal elements in the liquid phase are derived from the metal material, The seed crystal is a single crystal of aluminum nitride. A method for producing a single crystal of aluminum nitride.

[0018]

[11] The rare earth element is yttrium. The method for producing a single crystal of aluminum nitride according to

[10] .

[0019]

[12] The alkaline earth metal element is calcium. The method for producing a single crystal of aluminum nitride according to

[10] or

[11] .

[0020]

[13] The one or more transition metal elements include one or more elements selected from the group consisting of vanadium and chromium. The method for producing a single crystal of aluminum nitride according to any one of

[10] to

[12] .

[0021]

[14] The single crystal of aluminum nitride grown on the surface of the seed crystal becomes an ingot. The method for producing a single crystal of aluminum nitride according to any one of

[10] to

[13] .

[0022]

[15] After the start of the melting step, the melting step and the growth step are carried out in parallel. The method for producing a single crystal of aluminum nitride according to any one of

[10] to

[14] .

[0023]

[16] At least a part of the sintered body is dissolved in the molten metal material to obtain the liquid phase. A method for producing a single crystal of aluminum nitride as described in any one of

[10] to

[15] . [Effects of the Invention]

[0024] According to one aspect of this disclosure, a single crystal of aluminum nitride with excellent crystallinity and a method for manufacturing the single crystal of aluminum nitride are provided. [Brief explanation of the drawing]

[0025] [Figure 1] Figure 1 is a perspective view of the unit cell that constitutes the crystal structure (wurtzite structure) of aluminum nitride. [Figure 2] Figure 2(a) is a perspective view of a unit cell showing the (0001) plane of aluminum nitride, and Figure 2(b) is a perspective view of a unit cell showing the (1-102) plane of aluminum nitride. [Figure 3] Figure 3 is a schematic cross-sectional view illustrating a specific example of a method for manufacturing an aluminum nitride single crystal. The cross-section in Figure 3 is perpendicular to the surface 5s (principal plane) of the seed crystal 5. [Figure 4] Figure 4 is a schematic cross-sectional view illustrating a specific example of a method for manufacturing an aluminum nitride single crystal. The cross-section in Figure 4 is perpendicular to the surface 5s (principal plane) of the seed crystal 5. [Figure 5] Figure 5 is a schematic cross-sectional view illustrating a specific example of a method for manufacturing an aluminum nitride single crystal, and the cross-section in Figure 5 is perpendicular to the surface 5s (principal plane) of the seed crystal 5. [Modes for carrying out the invention]

[0026] Preferred embodiments of the present disclosure will be described below with reference to the drawings. In the drawings, equivalent components are denoted by the same reference numerals. The present disclosure is not limited to the embodiments described below. X, Y, and Z shown in Figures 3-5 represent three mutually orthogonal coordinate axes. The directions of the X, Y, and Z axes are common to Figures 3-5.

[0027] (Aluminum nitride single crystal) The aluminum nitride (AlN) single crystal according to this embodiment contains boron (B) and one or more additive elements (E). The one or more additive elements are selected from the group consisting of rare earth elements and alkaline earth metal elements. The ionic radii of each of the rare earth elements and alkaline earth metal elements tend to be larger than the ionic radius of aluminum (Al). Furthermore, the ionic radius of boron is smaller than that of aluminum. Since the aluminum nitride single crystal contains boron and additive elements with ionic radii different from those of aluminum, strain and stress within the single crystal during growth are easily suppressed (or relieved). Therefore, the aluminum nitride single crystal according to this embodiment is superior in crystallinity to aluminum nitride single crystals produced by conventional liquid-phase methods. Furthermore, since the aluminum nitride single crystal contains boron and additive elements with ionic radii different from those of aluminum, the aluminum nitride single crystal tends to be more uniform in crystallinity.

[0028] The crystal structure of aluminum nitride is a hexagonal wurtzite-type structure. Figure 1 shows the unit cell uc of the aluminum nitride crystal structure. Some of the aluminum atoms in the single crystal (unit cell uc) may be substituted with boron (B) and one or more additive elements (E). Figure 2(a) shows the (0001) plane of aluminum nitride. Figure 2(b) shows the (1-102) plane of aluminum nitride. The a1, a2, a3, and c shown in Figure 2(a) and Figure 2(b), respectively, may be the fundamental translation vectors (crystal axes) that constitute the unit cell uc of the wurtzite-type structure. The orientation of a1 is

[1000] . The orientation of a2 is

[0100] . The orientation of a3 is

[0010] . The orientation of c is

[0001] . The lengths of a1, a2, and a3 may be equal to each other. Any of a1, a2, and a3 may be perpendicular to c. The angles a1, a2, and a3 to each other may be 120°. The crystal structure of aluminum nitride (unit cell uc) has rotational symmetry with respect to c. At each of the 12 vertices of the unit cell uc (hexagonal prism) shown in Figure 2(a) and Figure 2(b), one of the elements (E) of aluminum, boron (B), and one or more additive elements may be placed. However, in order to represent the basic translation vectors, crystal orientations, and each lattice plane, atoms are omitted in Figure 2(a) and Figure 2(b).

[0029] For example, the crystal structure of aluminum nitride may be determined by X-ray diffraction (XRD). Whether or not aluminum nitride is a single crystal may be confirmed by the symmetry (rotational symmetry) of the pole figure measured by X-ray diffraction. Each lattice plane in the single crystal of aluminum nitride may be determined by out-of-plane diffraction or in-plane diffraction.

[0030] For example, a single crystal of aluminum nitride may consist only of nitrogen, aluminum, boron, and one or more alloying elements E. For example, a single crystal of aluminum nitride may consist only of nitrogen, aluminum, boron, and one or more rare earth elements. For example, a single crystal of aluminum nitride may consist only of nitrogen, aluminum, boron, and one or more alkaline earth metal elements. For example, a single crystal of aluminum nitride may consist only of nitrogen, aluminum, boron, one or more rare earth elements, and one or more alkaline earth metal elements.

[0031] As long as the crystallinity of the aluminum nitride single crystal is not impaired, the aluminum nitride may further contain trace amounts of other elements other than nitrogen, aluminum, boron, and one or more additive elements E. For example, the other elements may be one or more transition metal elements derived from the liquid phase (metallic material) described later. For example, the other element may be oxygen (O). For example, the other element may be silicon (Si).

[0032] The boron content in an aluminum nitride single crystal may be between 0.05 ppm by mass and 0.45 ppm by mass. When the boron content in the single crystal is within the above range, strain and stress within the single crystal are easily suppressed, the crystallinity of the single crystal is easily improved, and the single crystal is easily made uniform in terms of crystallinity. The boron in the aluminum nitride single crystal originates from the liquid phase obtained in the melting process described later. Then, as the crystallinity of the single crystal improves during the growth process described later, boron becomes less likely to be incorporated from the liquid phase into the single crystal. Therefore, the boron content in an aluminum nitride single crystal is unlikely to exceed 0.45 ppm by mass.

[0033] For example, the total content of one or more additive elements E in an aluminum nitride single crystal may be between 0.20 ppm by mass and 2.20 ppm by mass. When the total content of one or more additive elements E in the single crystal is within the above range, strain and stress within the single crystal are easily suppressed, the crystallinity of the single crystal is easily improved, and the single crystal is easily made uniform in terms of crystallinity.

[0034] When an aluminum nitride single crystal contains rare earth elements as alloying element E, the content of rare earth elements in the aluminum nitride single crystal may be between 0.20 ppm by mass and 2.20 ppm by mass. When the content of rare earth elements in the single crystal is within the above range, strain and stress within the single crystal are easily suppressed, the crystallinity of the single crystal is easily improved, and the single crystal is easily made uniform in terms of crystallinity. The rare earth elements in the aluminum nitride single crystal originate from the liquid phase obtained in the melting process described later. The higher the content of rare earth elements in the liquid phase, the more rare earth elements vaporize from the liquid phase as nitrides. In other words, the higher the content of rare earth elements in the liquid phase, the easier it is to suppress the content of rare earth elements in the liquid phase to a certain value or less due to the vaporization of rare earth elements from the liquid phase. For these reasons, the content of rare earth elements in an aluminum nitride single crystal is unlikely to exceed 2.20 ppm by mass.

[0035] When an aluminum nitride single crystal contains an alkaline earth metal element as an additive element E, the content of the alkaline earth metal element in the aluminum nitride single crystal may be between 0.20 ppm by mass and 1.50 ppm by mass. When the content of the alkaline earth metal element in the single crystal is within the above range, strain and stress within the single crystal are easily suppressed, the crystallinity of the single crystal is easily improved, and the single crystal is easily made uniform in terms of crystallinity. The alkaline earth metal element in the aluminum nitride single crystal originates from the liquid phase obtained in the melting process described later. The higher the content of the alkaline earth metal element in the liquid phase, the more alkaline earth metal elements vaporize from the liquid phase as nitrides. In other words, the higher the content of the alkaline earth metal element in the liquid phase, the easier it is to suppress the content of the alkaline earth metal element in the liquid phase to a certain value or less by vaporization of the alkaline earth metal element from the liquid phase. For these reasons, the content of the alkaline earth metal element in an aluminum nitride single crystal is unlikely to exceed 1.50 ppm by mass.

[0036] If one or more additive elements E include one or more rare earth elements, the rare earth elements may be one or more elements selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadollium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). If one or more additive elements E include one or more alkaline earth metal elements, the alkaline earth metal elements may be one or more elements selected from the group consisting of calcium (Ca), strontium (Sr), and barium (Ba). For the reasons that strain and stress within the single crystal are easily suppressed, the crystallinity of the single crystal is easily improved, and the single crystal is easily made uniform in terms of crystallinity, the rare earth element may be yttrium, and the alkaline earth metal element may be calcium.

[0037] As described above, a single crystal of aluminum nitride may further contain one or more transition metal elements. For example, the one or more transition metal elements contained in a single crystal of aluminum nitride may be one or more elements selected from the group consisting of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). For example, the one or more transition metal elements contained in a single crystal of aluminum nitride may include one or more elements selected from the group consisting of vanadium and chromium. For example, if an aluminum nitride single crystal contains one or more transition metal elements derived from the liquid phase (metallic material) described later, the total content of one or more transition metal elements in the aluminum nitride single crystal may be between 1.0 ppm and 100.0 ppm by mass, or between 3.7 ppm and 92.0 ppm by mass. When the total content of one or more transition metal elements is within the above range, strain and stress within the single crystal are easily suppressed, the crystallinity of the single crystal is easily improved, and the single crystal is easily made uniform in terms of crystallinity.

[0038] For example, if an aluminum nitride single crystal contains vanadium as a transition metal element, the vanadium content in the aluminum nitride single crystal may be between 0.2 ppm by mass and 2.8 ppm by mass. For example, if an aluminum nitride single crystal contains chromium as a transition metal element, the chromium content in the aluminum nitride single crystal may be between 0.2 ppm by mass and 34.0 ppm by mass. For example, if an aluminum nitride single crystal contains nickel as a transition metal element, the nickel content in the aluminum nitride single crystal may be between 3.5 ppm by mass and 28.0 ppm by mass. For example, if an aluminum nitride single crystal contains iron as a transition metal element, the iron content in the aluminum nitride single crystal may be between 4.3 ppm by mass and 58.0 ppm by mass. When the content of V, Cr, Ni, and Fe is within the above range, strain and stress within the single crystal are easily suppressed, the crystallinity of the single crystal is easily improved, and the single crystal is more likely to be uniform in terms of crystallinity.

[0039] For example, the content of each element in a single crystal of aluminum nitride may be measured by at least one of the following analytical methods: secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS).

[0040] A single crystal of aluminum nitride may be a substrate or an ingot. For example, multiple substrates may be manufactured by dividing a single ingot. In other words, an ingot can be rephrased as a single crystal before it is divided into multiple substrates.

[0041] (Method for manufacturing aluminum nitride single crystals) The method for manufacturing aluminum nitride single crystals according to this embodiment is the method for manufacturing the single crystal described above. Figures 3 to 5 schematically show one example of the method for manufacturing aluminum nitride single crystals according to this embodiment. The method for manufacturing aluminum nitride single crystals according to this embodiment uses at least a sintered body 2 and a metal material 3 as raw materials. The method for manufacturing aluminum nitride single crystals according to this embodiment includes a melting step and a growth step.

[0042] The sintered body 2 may be described as a ceramic or a polycrystalline aluminum nitride. The sintered body 2 is made of aluminum nitride containing one or more additive elements E selected from the group consisting of rare earth elements and alkaline earth metal elements. For example, the sintered body 2 may contain only one or more rare earth elements as one or more additive elements E. The sintered body 2 may contain only one or more alkaline earth metal elements as one or more additive elements E. The sintered body 2 may contain both one or more rare earth elements and one or more alkaline earth metal elements as one or more additive elements E. The one or more additive elements E contained in the sintered body 2 may be the same as the one or more additive elements E contained in the single crystal (product) described above. The sintered body 2 may consist only of one or more additive elements E, nitrogen, and aluminum. The sintered body 2 may further contain trace amounts of other elements other than one or more additive elements E, nitrogen, and aluminum, as long as the crystallinity of the aluminum nitride single crystal 1 (product) is not impaired. For example, the sintered body 2 may contain trace amounts of oxygen (O). However, the sintered body 2 does not need to contain oxygen.

[0043] Metal material 3 may be referred to as an alloy. For example, metal material 3 may be in the form of an ingot. Metal material 3 contains boron and one or more transition metal elements. Metal material 3 may consist only of boron and one or more transition metal elements. As long as the crystallinity of single crystal 1 (product) is not impaired, metal material 3 may further contain other elements other than boron and one or more transition metal elements. For example, metal material 3 may contain aluminum (Al). However, metal material 3 does not need to contain aluminum. For example, metal material 3 may contain silicon (Si). However, metal material does not need to contain silicon.

[0044] Metal material 3 may be manufactured in advance before the melting process. The raw materials for metal material 3 may be elemental boron and one or more elemental transition metal elements (elemental metals). For example, a mixture consisting of each weighed raw material is melted by heating in an inert atmosphere (non-oxidizing atmosphere). The molten mixture is stirred and mixed. By cooling the mixture after stirring and mixing to room temperature, metal material 3 (ingot) is obtained.

[0045] The sintered body 2 and the metal material 3 are housed in a crucible 6 with excellent heat resistance. For example, the crucible 6 may be made of carbon. The sintered body 2 and the metal material 3 are in direct contact with each other within the crucible 6. The positions of the sintered body 2 and the metal material 3 within the crucible 6 are not limited, as long as they are in contact with each other within the crucible 6 and the metal material 3 is exposed within the crucible 6. For example, the sintered body 2 may be placed on the bottom surface of the crucible 6, and the metal material 3 may be placed on top of the sintered body 2. The crucible 6 containing the sintered body 2 and the metal material 3 may be placed in a vacuum chamber. That is, the melting process and the growth process may be carried out in a vacuum chamber.

[0046] The seed crystal 5 used in the production of the aluminum nitride single crystal 1 is an aluminum nitride single crystal. As described below, the surface 5s (main surface) of the seed crystal 5 comes into contact with the liquid phase 4 during the growth process. As a result, the aluminum nitride single crystal 1 grows on the surface of the seed crystal 5. For example, the surface 5s of the seed crystal 5 may be planar. For example, the seed crystal 5 may be a plate such as a wafer (disk). The lattice plane of the seed crystal 5 (e.g., the (0001) plane) may be substantially or perfectly parallel to the surface 5s of the seed crystal 5. The lattice plane (e.g., the (0001) plane) of the single crystal 1 that grows on the surface 5s of the seed crystal 5 during the growth process tends to be substantially or perfectly parallel to the surface 5s of the seed crystal 5. If the lattice plane of the seed crystal 5 (e.g., the (0001) plane) is substantially or perfectly parallel to the surface 5s of the seed crystal 5, then the lattice plane of the single crystal 1 that grows on the surface of the seed crystal 5 during the growth process (e.g., the (0001) plane) is likely to be substantially or perfectly parallel to the lattice plane of the seed crystal 5 (e.g., the (0001) plane). The (0001) plane may be referred to as the C plane.

[0047] The seed crystal 5 may be manufactured by sublimation, halide vapor deposition, or flux deposition. The orientation (normal direction) of each lattice plane in the seed crystal 5 is predetermined. Therefore, by cutting the seed crystal 5, the desired lattice plane of the seed crystal 5 can be selected in advance as a lattice plane parallel to the surface 5s (principal plane) of the seed crystal 5.

[0048] If the seed crystal 5 is not a single crystal of aluminum nitride (for example, if the seed crystal 5 is made of silicon carbide (SiC)), lattice mismatch is likely to occur between the seed crystal 5 and the single crystal 1, and stress caused by the lattice mismatch is likely to act on the single crystal 1. As a result, the crystallinity of the single crystal 1 is likely to deteriorate, and the crystallinity of the single crystal 1 is likely to fluctuate during the growth process. Needless to say, if the seed crystal 5 is made of a single crystal of aluminum nitride, lattice mismatch and stress caused by the lattice mismatch are suppressed. As a result, the crystallinity of the single crystal 1 during the growth process is stable, the crystallinity of the single crystal 1 during the growth process is likely to remain constant, the crystallinity of the completed single crystal 1 is improved, and the crystallinity of the completed single crystal 1 is likely to be uniform.

[0049] The seed crystal 5 may be fixed to the end face (tip) of the column 7. For example, the column 7 may be a cylinder. For example, if the seed crystal 5 is a disk and the column 7 is a cylinder, the center of the circular surface 5s (main surface) of the seed crystal 5 may be located on the central axis of the column 7 (cylinder), and the diameter of the surface 5s of the seed crystal 5 may be greater than the thickness of the column 7 (cylinder). During the growth process, heat may be conducted from the seed crystal 5 to the column 7. For example, the column 7 may be made of a material with excellent heat resistance and thermal conductivity. For example, the column 7 may be made of a sintered aluminum nitride body. However, the column 7 is not the sintered body 2 (raw material for the aluminum nitride single crystal 1) described above. The column 7 may rotate freely (spin on its own axis) with respect to a rotation axis parallel to the longitudinal direction (Z-axis direction) of the column 7. The seed crystal 5 during the growth process may also rotate freely (rotate) in the in-plane direction of its surface 5s in accordance with the rotation of the column 7. The column 7 may move freely in a direction perpendicular to the surface 5s of the seed crystal 5 (Z-axis direction). The seed crystal 5 during the growth process may also move freely in a direction perpendicular to the surface 5s of the seed crystal 5 in accordance with the movement of the column 7. For example, the seed crystal 5 may move during the growth process so that it gradually moves away from the liquid phase 4 as the single crystal 1 grows.

[0050] The method for fixing the seed crystal 5 to the end face (tip) of the column 7 is not limited. For example, after the sintering aid is sandwiched between the seed crystal 5 and the column 7, the sintering aid, seed crystal 5, and column 7 may be heated at a temperature of 1800°C to 2000°C. As a result, the seed crystal 5 may be fixed to the end face (tip) of the column 7 via the sintering aid. For example, the sintering aid may be a powder made of one or more oxides selected from the group consisting of aluminum nitride, yttrium oxide, and calcium oxide.

[0051] In the melting process, the metal material 3 (and sintered body 2) is heated, causing all of the metal material 3 in contact with the sintered body 2 to melt. For example, the sintered body 2 and metal material 3 contained within the crucible 6 may be heated by the heat generation (heating) of the crucible 6 based on high-frequency induction heating. As the metal material 3 melts, at least a portion of the sintered body 2 is gradually dissolved into the molten metal material 3. As a result, a liquid phase 4 is obtained. The liquid phase 4 may be referred to as flux. The liquid phase 4 contains one or more additive elements E, nitrogen, aluminum, boron, and one or more transition metal elements. The additive elements E, nitrogen, and aluminum in the liquid phase 4 originate from the sintered body 2. The aluminum nitride (AlN) in the sintered body 2 may decompose in the liquid phase 4. That is, the aluminum and nitrogen originating from the sintered body 2 are converted into aluminum ions (AlN). 3+ ) and nitrogen ions (N 3- ) may exist in the liquid phase 4 as such. One or more additive elements E derived from the sintered body 2 may also exist in the liquid phase 4 as ions. For example, if the sintered body 2 contains one or more rare earth elements as additive elements E, the rare earth elements may be trivalent cations (e.g., Y 3+ ) may exist in the liquid phase 4 as such. For example, if the sintered body 2 contains one or more alkaline earth metal elements as additive elements E, the alkaline earth metal elements may exist as divalent cations (e.g., Ca 2+ ) may exist in the liquid phase 4 as boron ions (B 3+ ) may exist in liquid phase 4. The solubility of nitrogen and aluminum in liquid phase 4 may be saturated. The saturation of the solubility of nitrogen and aluminum in liquid phase 4 facilitates the growth of single crystal 1 in the growth process. Liquid phase 4 may be heated at all times during the melting and growth processes to prevent solidification of liquid phase 4.

[0052] During the growth process, the surface 5s of the seed crystal 5 is brought into contact with the liquid phase 4. As a result, one or more additive elements E, nitrogen, aluminum, and boron from the liquid phase 4 are supplied to the surface 5s of the seed crystal 5. The surface of the liquid phase 4 tends to become curved (convex) due to the surface tension of the liquid phase 4 itself. In other words, the surface 5s of the seed crystal 5 may be pressed against the curved (convex) surface of the liquid phase 4. Due to heat conduction from the seed crystal 5 to the column 7 and heat dissipation in the column 7 (cooling of the column 7), the temperature of the seed crystal 5 is lower than the temperature of the liquid phase 4. Due to the temperature difference between the seed crystal 5 and the liquid phase 4, one or more additive elements E, nitrogen, aluminum, and boron from the liquid phase 4 are continuously deposited on the surface 5s of the seed crystal 5 as single crystals 1 of aluminum nitride. As a result, single crystals 1 grow on the surface 5s of the seed crystal 5. One or more transition metal elements from the liquid phase 4 may also be supplied to the surface 5s of the seed crystal 5. In other words, one or more transition metal elements in the liquid phase 4 may be incorporated into the single crystal 1 growing on the surface 5s of the seed crystal 5, to the extent that the crystallinity of the single crystal 1 is not impaired. In the initial stages of the growth process, the single crystal 1 covers the surface 5s of the seed crystal 5. After the single crystal 1 covers the surface 5s of the seed crystal 5, one or more additive elements E, nitrogen, aluminum, and boron in the liquid phase 4 precipitate on the surface of the single crystal 1. As a result, the single crystal 1 grows in a direction perpendicular to the surface 5s of the seed crystal 5 (the Z-axis direction). The crystal structure of the single crystal 1 is continuous with the crystal structure of the seed crystal 5. In other words, the single crystal 1 and the seed crystal 5 may be integrated and constitute a single single crystal.

[0053] The sintered body 2 supplies multiple elements (one or more additive elements E, nitrogen, and aluminum) that are the raw materials for the single crystal 1 to the liquid phase 4 as solutes. Therefore, the more the single crystal 1 grows during the growth process, the more sintered body 2 is dissolved into the liquid phase 4 during the growth process. In other words, as the single crystal 1 grows, the sintered body 2 is consumed and decreases.

[0054] The longer the growth process continues, the greater the length (thickness) of the single crystal 1 growing on the surface 5s of the seed crystal 5. The length (thickness) of the single crystal 1 can be rephrased as the width of the single crystal 1 in the direction perpendicular to the surface 5s of the seed crystal 5 (Z-axis direction). Depending on the degree of growth of the single crystal 1 (length of the single crystal 1), the seed crystal 5 may move in the direction perpendicular to the surface 5s of the seed crystal 5 (Z-axis direction). In other words, the position of the seed crystal 5 in the direction perpendicular to the surface 5s of the seed crystal 5 may be constantly adjusted so that the surface of the growing single crystal 1 is always in contact with the liquid phase 4.

[0055] The growth process may be started after the melting process has begun. The melting process and the growth process may be carried out simultaneously and in parallel after the melting process has begun. When the melting process and the growth process are carried out simultaneously and in parallel, the sintered body 2 may be gradually dissolved into the liquid phase 4 as the single crystal 1 grows. In other words, it is not necessary for the entire sintered body 2 to be dissolved into the liquid phase 4 before the growth process. When the melting process and the growth process are carried out simultaneously and in parallel, the multiple elements that are the raw materials for the single crystal 1 are supplied stably and continuously as solutes from the sintered body 2 to the liquid phase 4, and the multiple elements supplied from the sintered body 2 are supplied stably and continuously from the liquid phase 4 to the growing single crystal 1 (near the surface of the seed crystal 5). In other words, according to this embodiment, it is easy to continue the growth process stably for a long time. As a result, the single crystal 1 that grows on the surface 5s of the seed crystal 5 is likely to become a long ingot (bulk). Due to the effects described above, which are attributed to one or more additive elements E and boron, the crystallinity of the ingot during the growth process is stabilized, the crystallinity of the ingot during the growth process tends to remain constant, the crystallinity of the finished ingot is improved, and the crystallinity of the finished ingot tends to be uniform. In other words, according to this embodiment, long ingots with excellent crystallinity and uniform crystallinity can be easily manufactured. However, instead of an ingot, a substrate made of a single crystal 1 may be manufactured in the growth process. That is, a substrate made of a single crystal 1 may be grown on the surface 5s of the seed crystal 5.

[0056] For example, the sintered body 2 may be placed on the bottom surface of the crucible 6, and the metal material 3 may be placed in the center of the surface of the sintered body 2. As the metal material 3 placed in the center of the surface of the sintered body 2 melts, the center of the surface of the sintered body 2 dissolves into the molten metal material 3 and disappears. As a result, a depression may be formed in the center of the surface of the sintered body 2, and the liquid phase 4 formed from the sintered body 2 and the metal material 3 may accumulate in the depression formed on the surface of the sintered body 2. In other words, when the metal material 3 is placed in the center of the surface of the sintered body 2, the sintered body 2 with the depression may function as a container for the liquid phase 4. When the sintered body 2 functions as a container for the liquid phase 4, the sintered body 2 is always in contact with the liquid phase 4 in the depression. As a result, one or more additive elements E, nitrogen, and aluminum are easily supplied continuously from the sintered body 2 to the liquid phase 4, and one or more additive elements E, nitrogen, and aluminum in the liquid phase 4 are easily supplied stably and continuously to the growing single crystal 1 (near the surface of the seed crystal 5). In other words, when the sintered body 2 functions as a container for the liquid phase 4, the melting process and the growth process can be stably continued in parallel for a long time, and long ingots can be easily manufactured. As the single crystal 1 grows, the sintered body 2 is consumed and decreases. Therefore, as the single crystal 1 grows, the depressions formed on the surface of the sintered body 2 may become deeper.

[0057] The sintered body 2 contains numerous crystalline grains (fine AlN grains) containing aluminum nitride. The sintered body 2 is manufactured from a mixed powder containing powder made of oxides of one or more additive elements E and powder made of aluminum nitride. For example, the sintered body 2 is manufactured by sintering a compact formed from the mixed powder. During the sintering process of the mixed powder (compact), one or more additive elements E fuse multiple adjacent AlN grains together at grain boundaries. In other words, one or more additive elements E in the sintered body 2 strongly bond the numerous AlN grains in the sintered body 2 together. As a result, each AlN grain in the sintered body 2 is less likely to detach (peel off) from the sintered body 2 during the melting process, and nitrogen, aluminum, and one or more additive elements E in the sintered body 2 are easily dissolved directly from the sintered body 2 into the liquid phase 4 as ions. Therefore, when the aluminum nitride in the sintered body 2 contains one or more additive elements E, the phenomenon of one or more AlN grains being incorporated into the growing single crystal 1 as solids is suppressed. As a result, the crystallinity of single crystal 1 is improved. During the manufacturing process of sintered body 2 (the firing process of the mixed powder), after multiple additive elements E in the mixed powder fuse together multiple adjacent AlN grains at the grain boundaries, most of the multiple additive elements E in sintered body 2 may become nitride gas and disappear from the multiple grain boundaries in sintered body 2.

[0058] If the aluminum nitride in the sintered body 2 does not contain one or more additive elements E, at least some of the multiple AlN grains in the sintered body 2 are easily detached from the sintered body 2 during the melting process. The AlN grains detached from the sintered body 2 are not easily dissolved in either the molten metal material 3 or the liquid phase 4, and are easily incorporated into the liquid phase 4 as solids. The AlN grains in the liquid phase 4 are easily suspended in the liquid phase 4 and can move to the surface 5s of the seed crystal 5. When one or more AlN grains in the liquid phase 4 are incorporated into the growing single crystal 1 as solids, the crystallinity of the single crystal 1 is easily degraded.

[0059] For the reason that the detachment of each AlN grain from the sintered body 2 is easily suppressed, the one or more rare earth elements E included in the sintered body 2 may be yttrium. For the same reason, the one or more alkaline earth metal elements E included in the sintered body 2 may be calcium.

[0060] The total content of one or more additive elements E in the manufactured single crystal 1 depends on the total content of one or more additive elements E in the sintered body 2. For example, the total content of one or more additive elements E in the sintered body 2 may be between 1.0 mass% and 3.0 mass%. When the total content of one or more additive elements E in the sintered body 2 is within the above range, the manufactured single crystal 1 is likely to contain one or more additive elements E, and the total content of one or more additive elements E in the single crystal 1 is easily controlled to a value between 0.20 mass ppm and 2.20 mass ppm. As shown in several examples described later, the content of any one additive element E in the manufactured single crystal 1 may also be controlled based on the content of any one additive element E in the sintered body 2.

[0061] If the liquid phase 4 does not contain boron derived from the metal material 3 (i.e., if the metal material 3 does not contain boron), aluminum nitride microcrystals tend to precipitate irregularly in the liquid phase 4. The crystallinity of the single crystal 1 tends to deteriorate as it incorporates these microcrystals. In contrast, if the liquid phase 4 contains boron derived from the metal material 3, the irregular precipitation of microcrystals in the liquid phase 4 is suppressed, and a single crystal 1 with excellent crystallinity tends to grow. If boron is not contained in the metal material 3 but is contained in the sintered body 2, there will be insufficient boron in the liquid phase 4, and the precipitation of aluminum nitride microcrystals in the liquid phase 4 will not be suppressed. As a result, the crystallinity of the single crystal 1 tends to deteriorate.

[0062] For example, one or more transition metal elements in the metal material 3 may be one or more elements selected from the group consisting of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, and copper. One or more transition metal elements in the metal material 3 may include one or more elements selected from the group consisting of vanadium and chromium. When one or more transition metal elements in the metal material 3 include one or more elements selected from the group consisting of vanadium and chromium, the sintered body 2 dissolves quickly into the molten metal material 3. In other words, the solubility of nitrogen and aluminum in the liquid phase 4 tends to increase. As a result, the continuous growth of the single crystal 1 is easily promoted. In addition to one or more elements selected from the group consisting of vanadium and chromium, the metal material 3 may further contain other transition metal elements. For example, in addition to one or more elements selected from the group consisting of vanadium and chromium, the metal material 3 may further contain one or more elements selected from the group consisting of titanium, manganese, iron, cobalt, nickel, and copper. For example, the main component of metal material 3 may be one or more elements selected from the group consisting of iron and nickel. The main component of metal material 3 can be rephrased as the element that has the highest content (unit: mass% or mass ppm) in metal material 3 among all the elements contained in metal material 3.

[0063] The total amount of substance of one or more transition metal elements in the metallic material 3 may be expressed as [T] (unit: moles). The amount of vanadium in metal material 3 may be expressed as [V] (unit: moles). The amount of chromium in metal material 3 may be expressed as [Cr] (unit: moles). The amount of iron in metal material 3 may be expressed as [Fe] (unit: moles). The amount of nickel in metal material 3 may be expressed as [Ni] (unit: moles). The amount of boron in metal material 3 may be expressed as [B] (unit: moles). The boron content in the manufactured single crystal 1 depends on the ratio of the amount of boron in the metal material 3. For example, [B] / [T] may be between 0.04 and 0.20. For example, [B] / [T] may be [B] / ([Fe]+[V]), [B] / ([Fe]+[Cr]), [B] / ([Ni]+[V]), or [B] / ([Ni]+[Cr]). When [B] / [T] is within the above range, the manufactured single crystal 1 is likely to contain boron, and the boron content in the single crystal 1 is easily controlled to a value between 0.05 mass ppm and 0.45 mass ppm. The content of any one transition metal element in the manufactured single crystal 1 depends on the ratio of the amount of substance of any one transition metal element in the metallic material 3. For example, [V] / [T] may be between 0.06 and 0.40. For example, [V] / [T] may be [V] / ([Fe]+[V]) or [V] / ([Ni]+[V]). When [V] / [T] is within the above range, the manufactured single crystal 1 is likely to contain vanadium, and the vanadium content in single crystal 1 is easily controlled to a value between 0.2 mass ppm and 2.8 mass ppm. For example, [Cr] / [T] may be between 0.06 and 0.40. For example, [Cr] / [T] may be [Cr] / ([Fe]+[Cr]) or [Cr] / ([Ni]+[Cr]). When [Cr] / [T] is within the above range, the manufactured single crystal 1 is likely to contain chromium, and the chromium content in single crystal 1 is easily controlled to a value between 0.2 mass ppm and 34.0 mass ppm.

[0064] The temperature of the liquid phase 4 can be rephrased as the temperature of the molten metal material 3. For example, the temperature of the liquid phase 4 may be such that all of the metal material 3 is melted and no solid matter (undissolved matter) remains on the surface of the liquid phase 4. For example, the temperature of the liquid phase 4 may be between 1600°C and 1900°C. When the temperature of the liquid phase 4 is within the above range, the solubility of nitrogen and aluminum in the liquid phase 4 is more likely to saturate, and the precipitation and growth of the single crystal 1 are more likely to be promoted. In order to ensure that all of the metal material 3 is melted, the temperature of the liquid phase 4 before the growth process may be higher than the temperature of the liquid phase 4 during the growth process. The temperature of the liquid phase 4 during the growth process may be constant, or it may change within the above range. While the melting process and the growth process are carried out in parallel (simultaneously), the temperature of the liquid phase 4 may be constant, or it may change within the above range.

[0065] When crucible 6 is heated by a high-frequency induction heating device, it is difficult to accurately measure the temperature of the liquid phase 4 inside crucible 6 using a thermocouple. This is because the thermocouple itself generates heat due to the action of the high-frequency current. Therefore, the temperature of the liquid phase 4 may be controlled based on the following preliminary experiments.

[0066] A crucible 6 containing the sintered body 2 and the metal material 3 is placed inside the heating section (coil) of a high-frequency induction heating device. By increasing the power output of the high-frequency induction heating device, the sintered body 2 and the metal material 3 in the crucible 6 are heated and melted, and a liquid phase 4 is obtained. The liquid phase 4 is stirred. After the stirred liquid phase 4 is rapidly cooled to room temperature, the liquid level of the liquid phase 4 is monitored. If there are undissolved particles on the liquid level of the liquid phase 4, the power output is increased until there are no more undissolved particles on the liquid level of the liquid phase 4. The temperature at which there are no more undissolved particles on the liquid level of the liquid phase 4 is measured with a thermometer other than a thermocouple, and the power output at that temperature is determined. After there are no more undissolved particles on the liquid level of the liquid phase 4, the power output is gradually reduced, and the temperature at which the single crystal 1 begins to precipitate on the surface 5s of the seed crystal 5 (saturation temperature) is measured with a thermometer other than a thermocouple, and the power output at the saturation temperature is determined. Based on the preliminary experiments described above, the temperature of liquid phase 4 can be indirectly controlled by adjusting the power supply output.

[0067] After degassing in the vacuum chamber, nitrogen gas (N2), or a mixed gas consisting of nitrogen gas and a noble gas, may be continuously supplied to the vacuum chamber during the melting and growth processes. In other words, the melting and growth processes may be carried out in nitrogen gas or the mixed gas. The nitrogen gas or mixed gas suppresses oxidation of the metal material 3, liquid phase 4, seed crystal 5, and single crystal 1, and improves the crystallinity of the single crystal 1. For example, the noble gas constituting the mixed gas may be argon (Ar). At least a portion of the nitrogen gas may be dissolved in the liquid phase 4.

[0068] The liquid phase 4 may be stirred during the melting process. The liquid phase 4 may also be stirred during the growth process. Stirring the liquid phase 4 makes it easier for the composition of the liquid phase 4 to become uniform, and thus easier for the composition of the single crystal 1 to become uniform.

[0069] The time required for the growth process (i.e., the time during which the growth of single crystal 1 continues) may be changed and is not limited to the desired length (thickness) of single crystal 1. For example, the time required for the growth process may be between a few hours and several hundred hours.

[0070] The area of ​​the surface 5s (main surface) of the seed crystal 5 is not limited. For example, the area of ​​the surface 5s of the seed crystal 5 is 1 cm². 2 More than 730cm 2 The following is possible: The area of ​​the cross-section of the single crystal 1 in a direction parallel to the surface 5s of the seed crystal 5 may be approximately or exactly equal to the area of ​​the surface 5s of the seed crystal 5.

[0071] After the growth process, the seed crystal 5 and single crystal 1 are separated from the liquid phase 4 and cooled to room temperature in a vacuum chamber. After the seed crystal 5 and single crystal 1 have cooled, the metal (raw material) adhering to their surfaces is removed by acid washing. Through these steps, single crystal 1 is completed.

[0072] The single crystal 1 may be used as a substrate for a deep ultraviolet light-emitting diode such as a UVC LED or a DUV LED. For example, a light-emitting diode may be manufactured by laminating a nitride semiconductor layer (such as a gallium nitride layer) and an electrode layer on the main surface of a substrate made of the single crystal 1. The substrate made of the single crystal 1 may be used as a substrate for a semiconductor laser oscillator such as an ultraviolet laser. The substrate made of the single crystal 1 may be used in a power transistor. The single crystal 1 integrated with the seed crystal 5 may be used as a single substrate.

[0073] This disclosure is not necessarily limited to the embodiments described above. Various modifications to this disclosure are possible and are included in this disclosure, without departing from the spirit of this disclosure. [Examples]

[0074] The present disclosure will be illustrated in detail by the following examples and comparative examples. The present disclosure is not limited to the following examples.

[0075] (Example 1) Pellets were manufactured by pressure molding of an AlN powder containing 5% by mass of yttrium oxide (Y2O3). The pellets were cylindrical (disc-shaped), with a diameter of 55 mm and a thickness of 12 mm. The pellets were placed in a boron nitride (BN) container. The container containing the pellets was placed in the chamber of a carbon heater (furnace), and the pellets inside the container were fired at 2000°C for 10 hours. The atmosphere inside the carbon heater was nitrogen gas.

[0076] By the method described above, four sintered bodies 2 made of AlN containing only yttrium (Y) as the additive element E were obtained. The Y content in each sintered body 2 was 2.0 mass%. Each sintered body 2 was cylindrical (disc). The thickness (diameter) of each sintered body 2 was 45 mm. The thickness of each sintered body 2 was 10 mm.

[0077] A disc (wafer) made of a pure AlN single crystal was used as the seed crystal 5. The diameter of the surface 5s (circular principal surface) of seed crystal 5 was 15 mm. The thickness of seed crystal 5 was 400 μm. The (0001) plane of AlN in seed crystal 5 was parallel to the surface 5s (principal surface) of seed crystal 5.

[0078] A cylinder was used as the column 7 on which the seed crystal 5 was fixed. The column 7 was a sintered body (ceramic) made only of AlN. The thickness (diameter) of the column 7 was 10 mm. The end face of the column 7 was covered with a sintering aid. The seed crystal 5 was placed on the end face of the column 7 that was covered with the sintering aid. In other words, the sintering aid was sandwiched between the seed crystal 5 and the column 7. The position of the seed crystal 5 on the end face of the column 7 was determined so that the center of the surface 5s (main surface) of the seed crystal 5 coincided with the center of the circular end face of the column 7. As the sintering aid, a powder made of AlN containing 5 mass% Y2O3 was used.

[0079] Seed crystals 5 and columns 7, stacked via a sintering aid, were placed in a carbon heater chamber. After the chamber was evacuated by a pump, nitrogen gas was filled into the chamber. After the chamber was filled with nitrogen gas, the seed crystals 5 and columns 7, stacked via the sintering aid, were heated at 2000°C for 4 hours.

[0080] By the method described above, the seed crystal 5 was fixed to the end face of the column 7.

[0081] As the raw material for metal material 3, a mixture consisting of elemental boron (powder), elemental iron (powder), and elemental chromium (powder) was obtained. The elemental boron, elemental iron, and elemental chromium were mixed in a predetermined molar ratio. The mass of the mixture was 50 g. The mixture was placed in an alumina crucible. The mixture in the crucible was heated in a nitrogen atmosphere at 1550°C and melted. The molten mixture was cooled to room temperature.

[0082] Using the method described above, a metallic material 3 (a lump of alloy) consisting of boron, iron, and chromium was produced. [Cr] / ([Fe]+[Cr]) was adjusted to the value shown in Table 1 below. [B] / ([Fe]+[Cr]) was adjusted to the value shown in Table 1 below. The definitions of [Cr] / ([Fe]+[Cr]) and [B] / ([Fe]+[Cr]) are as described above. The maximum width of metallic material 3 was smaller than the diameter of the surface (circle) of the sintered body 2 described above.

[0083] A carbon crucible 6 was used to house four sintered bodies 2 and a metal material 3. The crucible 6 was a cylinder with a closed bottom. The inner diameter of the crucible 6 was 50 mm. The outer diameter of the crucible 6 was 80 mm. The height of the crucible 6 was 80 mm. The four sintered bodies 2 (discs) were stacked on the bottom surface of the crucible 6. Furthermore, the metal material 3 was placed in the center of the surface (circle) of the sintered body 2 furthest from the bottom surface of the crucible 6.

[0084] The heating section (coil) of the high-frequency induction heating furnace was installed inside the vacuum chamber, and a crucible 6 containing four sintered bodies 2 and metal material 3 was placed inside the heating section (coil) of the high-frequency induction heating furnace. A column 7 and seed crystals 5 fixed to the column 7 were also installed inside the vacuum chamber. The position of the seed crystals 5 was adjusted so that the surface 5s of the seed crystals 5 faced the metal material 3 inside the crucible 6, and the surface 5s of the seed crystals 5 was parallel to the bottom surface of the crucible 6. In other words, the sintered bodies 2, metal material 3, crucible 6, seed crystals 5, and column 7 were arranged as shown in Figure 3.

[0085] The inside of a sealed vacuum chamber was evacuated by a vacuum pump. The pressure inside the vacuum chamber was less than 0.1 Pa. After the vacuum chamber was evacuated, nitrogen gas was supplied to the vacuum chamber until the pressure inside the vacuum chamber reached 0.1 MPa. A small amount of nitrogen gas was continuously supplied to the vacuum chamber to maintain the pressure inside the vacuum chamber at approximately 0.1 MPa during the melting and growth processes.

[0086] In the melting process, the heating element of the high-frequency induction heating furnace heated the crucible 6, maintaining its temperature at 1700°C. The heat generated by the crucible 6 melted the entire metal material 3 in contact with the sintered body 2 within the crucible 6. The central part of the surface of the sintered body 2 (the part of the sintered body 2 in contact with the molten metal material 3) dissolved into the molten metal material 3, yielding a liquid phase 4. The temperature of the liquid phase 4 was equal to the temperature of the crucible 6. By allowing the liquid phase 4 to stand at 1700°C for 24 hours, the solubility of nitrogen ions and aluminum ions in the liquid phase 4 became saturated. As the central part of the surface of the sintered body 2 melted, a depression formed in the center of the sintered body 2, and the liquid phase 4 accumulated in the depression.

[0087] After the liquid phase 4 was left to stand at 1700°C for 24 hours, the following growth process was initiated. The temperature of the liquid phase 4 was maintained at 1700°C during the growth process. Even after the start of the growth process, the sintered body 2 was gradually dissolved into the liquid phase 4 as the single crystal 1 grew. In other words, after the liquid phase 4 was obtained in the melting process, the melting process and the growth process were carried out simultaneously in parallel.

[0088] During the growth process, the seed crystal 5 was constantly rotated (rotated) in the in-plane direction of its surface 5s. The rotation speed of the seed crystal 5 was maintained at 20 rpm. During the growth process, the rotating surface 5s of the seed crystal 5 was brought into contact with the surface (convex surface) of the liquid phase 4 in the crucible 6. Due to the heat dissipation from the column 7 to which the seed crystal 5 was fixed, the temperature of the seed crystal 5 was always maintained at a value lower than the temperature of the liquid phase 4. Due to the temperature difference between the seed crystal 5 and the liquid phase 4, a single crystal 1 precipitated on the surface 5s of the seed crystal 5, and the single crystal 1 further grew in a direction perpendicular to the surface 5s of the seed crystal 5. As the single crystal 1 grew, the seed crystal 5 was moved during the growth process so that it gradually moved away from the liquid phase 4. However, the movement speed (upward speed) of the seed crystal 5 was adjusted so that the tip (end face) of the growing single crystal 1 was always in contact with the liquid phase 4. After the growth of single crystal 1, it was separated from the liquid phase 4 and cooled to room temperature in a vacuum chamber. The time required for the growth of single crystal 1 (growth time) was 125 hours. The growth time is defined as the time from when the surface 5s of seed crystal 5 was brought into contact with the surface of liquid phase 4 until single crystal 1 was separated from liquid phase 4.

[0089] After cooling of single crystal 1, single crystal 1, seed crystal 5, and column 7 were removed from the vacuum chamber. The single crystal 1 (ingot) grown on the surface 5s of seed crystal 5 was cylindrical. The thickness of single crystal 1 (cylinder) was the same as the diameter (15 mm) of the surface 5s (circle) of seed crystal 5. The length of single crystal 1 in the direction perpendicular to the surface 5s of seed crystal 5 was the value shown in Table 2 below.

[0090] Single crystal 1 (ingot) was divided into multiple substrates by cutting it with a wire saw in a direction parallel to the surface 5s of seed crystal 5. Each substrate had a thickness of 1.0 mm. In other words, single crystal 1 (cylinder) with a length of 10 mm was divided into 10 substrates (disks) with a thickness of 1.0 mm. The circular main surface of each substrate was polished to a mirror finish.

[0091] The crystal structure of all substrates was analyzed by X-ray diffraction. The principal plane of each substrate was parallel to the (0001) plane of AlN within each substrate. The diffraction angle 2θ and tilt angle χ were fixed so that the diffracted X-ray peaks originating from the (1-102) plane of AlN were detected on the principal plane of each substrate. Furthermore, the pole figures of the (1-102) plane diffracted X-rays were measured by φ scanning (360° rotation of each substrate in the in-plane direction of the principal plane) on the principal plane of each substrate. The pole figures measured for each substrate contained six diffracted X-ray peaks from the (1-102) plane and showed the symmetry (threefold symmetry) inherent to the AlN single crystal.

[0092] The "substrate A" described below is one of several substrates obtained by splitting a single crystal 1. The "substrate B" described below is another one of the multiple substrates obtained by splitting single crystal 1. Substrate A is a substrate that includes the portion of single crystal 1 that was in contact with seed crystal 5. Substrate B is the substrate consisting of the portion furthest from the seed crystal 5. In other words, substrate B consists only of the tip portion of the single crystal 1 that grew from the surface 5s of the seed crystal 5, and does not include the portion that was in contact with the seed crystal 5. Substrate A corresponds to a single crystal formed in the early stages of single crystal 1's growth. Substrate B corresponds to a single crystal formed in the final stages of single crystal 1's growth.

[0093] The rocking curve of diffracted X-rays originating from the (1-102) plane of AlN in substrate A was measured on the main surface of substrate A. The range of variation of the tilt angle ω of substrate A during the measurement of the rocking curve was ±1.0°. The full width at half maximum (FWHM) of the rocking curve measured on substrate A is denoted as "FWHMa". FWHMa (unit: arcsecone) is shown in Table 2 below. The rocking curve of diffracted X-rays originating from the (1-102) plane of AlN in substrate B was measured on the main surface of substrate B using the same method as in substrate A. The full width at half maximum of the rocking curve measured on substrate B is denoted as "FWHMb". FWHMb (unit: arcsecones) is shown in Table 2 below. As the crystallinity of single crystal 1 improves, both FWHMa and FWHMb decrease. The more constant the crystallinity of single crystal 1 during growth, the smaller the absolute difference between FWHMa and FWHMb. In other words, the more uniform the crystallinity of the completed single crystal 1, the smaller the absolute difference between FWHMa and FWHMb.

[0094] The content (in mass ppm) of each element at 10 randomly selected locations on a single substrate was measured by secondary ion mass spectrometry (SIMS). The average of the elemental content measured at the 10 locations was considered to be the content of each element in single crystal 1. The content of each element in single crystal 1 of Example 1 is shown in Table 2 below. <e>This is the total content of all additive elements E (Y and Ca) shown in Table 2. <t>This represents the total content of all transition metal elements shown in Table 2. The only elements detected in single crystal 1 were nitrogen, aluminum, and the elements shown in Table 2 (excluding elements with zero content).

[0095] The results of the above analysis and measurements demonstrate that single crystal 1 of Example 1 is an AlN single crystal containing the elements shown in Table 2 below.

[0096] (Examples 2-9, Comparative Examples 1 and 2) The sintered bodies 2 in Examples 5, 6, and 9 were each manufactured from a powder consisting of AlN containing calcium oxide (CaO). In other words, the only additive element E in the sintered bodies 2 of Examples 5, 6, and 9 was Ca. The Ca content in the sintered bodies 2 of Examples 5, 6, and 9 was adjusted to the values ​​shown in Table 1 below.

[0097] The sintered body 2 of Example 7 was manufactured from a powder consisting of AlN containing Y2O3 and CaO. In other words, the additive element E contained in the sintered body 2 of Example 7 was Y and Ca. The respective contents of Y and Ca in the sintered body 2 of Example 7 were adjusted to the values ​​shown in Table 1 below.

[0098] Sintered body 2 of Comparative Example 2 was manufactured from a powder consisting solely of pure AlN. In other words, the sintered body of Comparative Example 2 did not contain the additive element E.

[0099] Metal material 3 in Examples 3 and 4 was prepared from a mixture consisting of elemental boron (powder), elemental nickel (powder), and elemental vanadium (powder). The [V] / ([Ni]+[V]) in Examples 3 and 4 was adjusted to the values ​​shown in Table 1 below. The [B] / ([Ni]+[V]) in Examples 3 and 4 was adjusted to the values ​​shown in Table 1 below. The definitions of [V] / ([Ni]+[V]) and [B] / ([Ni]+[V]) are as described above.

[0100] Metal material 3 of Comparative Example 1 was manufactured from a mixture consisting of elemental iron (powder) and elemental chromium (powder). In other words, metal material 3 of Comparative Example 1 did not contain boron. The [Cr] / ([Fe]+[Cr]) of Comparative Example 1 was adjusted to the value shown in Table 1 below. The definition of [Cr] / ([Fe]+[Cr]) is as described above.

[0101] The temperature of liquid phase 4 in each of Examples 2-9 and Comparative Examples 1 and 2 was adjusted to the values ​​shown in Table 1 below.

[0102] By adjusting various conditions such as the temperature of the liquid phase 4 and the growth time of the single crystal 1, the length of the single crystal 1 in Examples 2 to 9 and Comparative Examples 1 and 2 was adjusted to the values ​​shown in Table 2 below.

[0103] Except for the matters mentioned above, single crystal 1 of Examples 2-9 and Comparative Examples 1 and 2 were manufactured in the same manner as in Example 1.

[0104] Substrates A and B for each of Examples 2-9 were manufactured using the same method as in Example 1. Analysis and measurements of substrates A and B for each of Examples 2-9 were performed using the same method as in Example 1. Since the length (thickness) of single crystal 1 in Comparative Examples 1 and 2 was small, in the cases of Comparative Examples 1 and 2, seed crystal 5 and single crystal 1 were not divided, and the entire seed crystal 5 and single crystal 1 were considered as a single substrate A. In other words, substrate B was not manufactured for Comparative Examples 1 and 2. Analysis and measurements of substrate A for Comparative Examples 1 and 2 were performed in the same manner as in Example 1.

[0105] The FWHMa and FWHMb values ​​for each of Examples 2 to 9 are shown in Table 2 below. The FWHMa values ​​for Comparative Examples 1 and 2 are shown in Table 2 below.

[0106] The content of each element in single crystal 1 of Examples 2-9 and Comparative Examples 1 and 2 is shown in Table 2 below. The only elements detected in single crystal 1 of Examples 2-9 and Comparative Examples 1 and 2 were nitrogen, aluminum, and the elements shown in Table 2 (excluding elements with zero content). As shown in Table 2 below, single crystal 1 of Comparative Example 1 did not contain boron. As shown in Table 2 below, single crystal 1 of Comparative Example 2 did not contain yttrium or calcium.

[0107] In each of Examples 2 to 9, single crystal 1 was an AlN single crystal containing the elements shown in Table 2 below. In all of Examples 2 to 9, the main surfaces of substrates A and B were parallel to the (0001) plane of AlN in each substrate. Single crystal 1 in each of Comparative Examples 1 and 2 consisted of an AlN single crystal containing the elements shown in Table 2 below. In both Comparative Examples 1 and 2, the main surface of substrate A was parallel to the (0001) plane of AlN in substrate A.

[0108] [Table 1]

[0109] [Table 2] [Industrial applicability]

[0110] For example, the aluminum nitride single crystal relating to this disclosure may be used as a substrate for a deep ultraviolet light-emitting diode. [Explanation of Symbols]

[0111] 1... Single crystal of aluminum nitride, 2... Sintered body, 3... Metallic material, 4... Liquid phase, 5... Seed crystal, 5s... Surface of seed crystal, 6... Crucible, 7... Column, uc... Unit cell of the crystalline structure of aluminum nitride.< / t> < / e>

Claims

1. Boron and, One or more additive elements selected from the group consisting of rare earth elements and alkaline earth metal elements, including, A single crystal of aluminum nitride.

2. The boron content is 0.05 ppm by mass or more and 0.45 ppm by mass or less. A single crystal of aluminum nitride according to claim 1.

3. The content of the aforementioned rare earth elements is 0.20 ppm by mass or more and 2.20 ppm by mass or less. A single crystal of aluminum nitride according to claim 1.

4. The content of the aforementioned alkaline earth metal element is 0.20 ppm by mass or more and 1.50 ppm by mass or less. A single crystal of aluminum nitride according to claim 1.

5. The aforementioned rare earth element is yttrium. A single crystal of aluminum nitride according to claim 1.

6. The aforementioned alkaline earth metal element is calcium. A single crystal of aluminum nitride according to claim 1.

7. Further comprising one or more transition metal elements, A single crystal of aluminum nitride according to claim 1.

8. The one or more transition metal elements include one or more elements selected from the group consisting of vanadium and chromium. A single crystal of aluminum nitride according to claim 7.

9. It is a substrate or an ingot. A single crystal of aluminum nitride according to claim 1.

10. A method for producing an aluminum nitride single crystal according to claim 1, A melting step in which a metal material in contact with the sintered body is melted to obtain a liquid phase, A growth step in which the surface of a seed crystal is brought into contact with the liquid phase to grow the single crystal of aluminum nitride on the surface of the seed crystal, Equipped with, The sintered body is made of aluminum nitride containing one or more additive elements selected from the group consisting of rare earth elements and alkaline earth metal elements. The aforementioned metallic material comprises boron and one or more transition metal elements. The liquid phase comprises the additive element, nitrogen, aluminum, boron, and one or more of the transition metal elements. The additive element, nitrogen, and aluminum in the liquid phase originate from the sintered body. The boron and the one or more transition metal elements in the liquid phase originate from the metal material. The seed crystal is a single crystal of aluminum nitride. A method for producing single crystals of aluminum nitride.

11. The aforementioned rare earth element is yttrium. A method for producing a single crystal of aluminum nitride according to claim 10.

12. The aforementioned alkaline earth metal element is calcium. A method for producing a single crystal of aluminum nitride according to claim 10.

13. The one or more transition metal elements include one or more elements selected from the group consisting of vanadium and chromium. A method for producing a single crystal of aluminum nitride according to claim 10.

14. The single crystal of aluminum nitride that grows on the surface of the seed crystal becomes an ingot. A method for producing a single crystal of aluminum nitride according to claim 10.

15. After the start of the melting process, the melting process and the growth process are carried out in parallel. A method for producing a single crystal of aluminum nitride according to claim 10.

16. The liquid phase is obtained by dissolving at least a portion of the sintered body in the molten metal material. A method for producing a single crystal of aluminum nitride according to claim 10.

Images