Aluminum nitride single crystal manufacturing method and aluminum nitride single crystal manufacturing apparatus

Abstract

To provide a manufacturing method of an aluminum nitride single crystal and a manufacturing apparatus of the aluminum nitride single crystal capable of easily controlling a temperature and manufacturing the aluminum nitride single crystal at a relatively large growth rate.SOLUTION: An aluminum nitride single crystal is deposited on a surface of an object to be deposited by arranging the object to be deposited having aluminum nitride in an atmosphere containing nitrogen and generating an Al vapor in the atmosphere. It is preferable to generate the Al vapor by heating an alloy melt containing Al to a temperature higher than the lowest temperature in a temperature range in which an aluminum nitride crystal is decomposed in the melt.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aluminum nitride single crystal and an apparatus for producing an aluminum nitride single crystal. [Background technology]

[0002] Ultraviolet light-emitting devices are next-generation light sources that are expected to be used in a wide range of applications, such as sterilization light sources, high-brightness white light sources combined with phosphors, light sources for high-density information recording, and light sources for resin curing. These ultraviolet light-emitting devices are made of AlGaN-based nitride semiconductors.

[0003] Candidate substrate materials for AlGaN-based nitride semiconductors include SiC, GaN, and AlN (aluminum nitride) due to their high lattice match with AlGaN. However, SiC and GaN absorb light with wavelengths shorter than 380 nm and 365 nm (high energy), respectively, limiting the wavelength range that can be extracted. On the other hand, AlN has a wider bandgap than AlGaN and is not limited by the wavelength range that SiC and GaN are, making it the most suitable substrate material for ultraviolet light-emitting devices. However, AlN exhibits a high dissociation pressure at high temperatures, so it does not become molten at normal pressure. This makes it extremely difficult to produce AlN single crystals from their own melt, as is the case with silicon single crystals.

[0004] Therefore, in the past, to produce bulk AlN single crystals, crystals have been produced by sublimation (see, for example, Non-Patent Document 1). However, producing AlN crystals by sublimation requires high temperatures exceeding 2448 K in the source material, which poses the problem of making AlN crystals that are suitable for practical use in terms of size and cost.

[0005] To solve this problem, the present inventors have developed a liquid phase growth method for AlN single crystals, which involves bringing a N-containing gas into contact with the surface of an Al-containing alloy melt, thereby growing a crystal on the surface of the melt, as a method for obtaining inexpensive, high-quality aluminum nitride (AlN) crystals at low temperatures and atmospheric pressures (see, for example, Patent Document 1).This method does not require a template substrate, and therefore can also prevent the occurrence of threading dislocations, misfit dislocations, and distortion in the grown AlN crystal.

[0006] The inventors have also developed an AlN single crystal growth method that includes a heating step in which an alloy melt containing Al is brought into contact with a sintered body containing AlN, such as a crucible that holds the melt, and heated to a temperature at which AlN becomes thermodynamically unstable in the alloy melt, thereby dissolving a portion of the AlN sintered body into the melt, and a precipitation step in which, after the heating step, the alloy melt is cooled to a thermodynamically stable temperature, thereby precipitating AlN crystals in the alloy melt (see Patent Application No. 2020-141981).

[0007] Also, a method has been developed for producing AlN whiskers with a cross-sectional width of 0.1 to 50 μm by heating a material containing Al—Ti—Si as a main component in a nitrogen atmosphere (see, for example, Patent Document 2). [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Carsten Hartmann et. al., “Preparation of Bulk AlN Seeds by Spontaneous Nucleation of Freestanding Crystals”, Jpn. J. Appl. Phys., 2013, 52, 08JA06 [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2019-194133 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-73951 Summary of the Invention [Problem to be solved by the invention]

[0010] The liquid phase growth method for AlN single crystals described in Patent Document 1 can produce very high-quality AlN single crystals at low cost, but has the drawback of a somewhat slow growth rate because crystal growth occurs only on the surface of the melt. The method of Patent Application No. 2020-141981 can produce very high-quality AlN single crystals at low cost and more quickly than the method of Patent Document 1, but requires precise temperature control, making temperature control complicated. The method described in Patent Document 2 also has the drawback of producing polycrystalline, rather than single-crystalline, AlN whiskers.

[0011] The present invention has been made in light of these problems, and aims to provide a method and apparatus for producing aluminum nitride single crystals that are easy to control the temperature and that are capable of producing aluminum nitride single crystals at a relatively high growth rate. [Means for solving the problem]

[0012] In order to achieve the above-mentioned objectives, the inventors conducted extensive research into the growth process of AlN single crystals based on the manufacturing methods of AlN crystals described in Patent Document 1 and Patent Application No. 2020-141981. As a result, they discovered that AlN single crystals are generated and grow not only in the molten alloy but also in the gas phase near the molten alloy, leading to the present invention.

[0013] That is, the method for producing aluminum nitride single crystal according to the present invention is characterized in that an object to be deposited, which has aluminum nitride, is placed in an atmosphere containing nitrogen, and Al vapor is generated in the atmosphere, thereby precipitating aluminum nitride single crystal on the surface of the object to be deposited.

[0014] The method for producing aluminum nitride single crystal according to the present invention can precipitate aluminum nitride single crystal by reacting generated Al vapor with nitrogen in the atmosphere. The method for producing aluminum nitride single crystal according to the present invention can produce aluminum nitride single crystal simply by generating Al vapor in a nitrogen-containing atmosphere, making precise temperature control unnecessary and facilitating temperature control. Furthermore, aluminum nitride single crystal can be produced in a nitrogen-containing atmosphere, and the growth rate can be increased compared to conventional methods of growing aluminum nitride crystal only on the surface of a melt.

[0015] In the method for producing aluminum nitride single crystal according to the present invention, it is preferable to generate the Al vapor by heating a melt of an Al-containing alloy to a temperature higher than the lowest temperature in the temperature range at which aluminum nitride crystals decompose in the melt. In this case, by heating to the temperature at which aluminum nitride crystals decompose in the melt of an Al-containing alloy, i.e., the temperature at which aluminum nitride becomes thermodynamically unstable and aluminum nitride is not produced, it is possible to generate Al vapor while suppressing the production of aluminum nitride on the surface of the melt.

[0016] In this case, the temperature at which the formation of aluminum nitride at the melt surface is suppressed can be controlled by the Al composition ratio (activity) in the melt and the nitrogen partial pressure in the atmosphere. That is, Al vapor can be generated while suppressing the formation of aluminum nitride at the melt surface according to the following principle. First, when a melt of an alloy containing Al is maintained at a high temperature to generate Al vapor, the evaporation reaction of Al is expressed by equation (1). Al(l) → Al(g) (1)

[0017] The reaction formula (2) shows the reaction when aluminum vapor generated by formula (1) reacts with nitrogen gas in the atmosphere to form aluminum nitride crystals. 2Al(g)+N2(g)→2AlN(s) (2)

[0018] Next, to continuously maintain the evaporation of Al in the melt as shown in equation (1), it is necessary to maintain conditions that prevent the reaction of Al with nitrogen gas on the melt surface from forming aluminum nitride crystals. At this time, the reaction of Al with nitrogen gas on the melt surface is shown in equation (3). 2Al(l) + N2(g) → 2AlN(s) (3)

[0019] The activity of AlN when the reaction of aluminum nitride crystal formation expressed by equation (3) is equilibrium is a eq. AlN , the activity of Al in the melt is a eq. Al , the partial pressure of nitrogen is p eq. N2 Then, the equilibrium constant K in equation (3) is expressed by equation (4).

number

[0020] Here, since AlN is a nearly pure solid, the activity of AlN a eq. AlN The driving force for the growth of AlN crystals, Δμ, is expressed as p N2 If the Boltzmann constant is k and the absolute temperature is T, the chemical potential of nitrogen in the atmosphere is given by the difference between the chemical potential of nitrogen when equation (3) is in equilibrium, and is expressed by equation (5).

number

[0021] From equation (5), the driving force Δμ for the growth of AlN crystals in the melt is determined by the partial pressure p N2 , equilibrium constant K, activity of Al in the melt a eq. Aland temperature. This shows that the driving force Δμ for AlN crystal growth in the melt can be controlled by the partial pressure of nitrogen in the atmosphere, the temperature, and the alloy composition of the melt. In the method for producing aluminum nitride single crystal according to the present invention, by maintaining the melt under conditions where the driving force Δμ for AlN crystal growth is negative, the reaction for AlN formation at the melt surface can be suppressed, and the generation of Al vapor from the melt can be continuously maintained.

[0022] The temperature at which Δμ = 0 is the lowest temperature within the temperature range at which aluminum nitride crystal decomposes in the melt. Furthermore, it is preferable that the position at which aluminum nitride crystal forms is at a temperature lower than the melt, and that the driving force Δμ for AlN crystal growth be positive.

[0023] In the method for producing aluminum nitride single crystal according to the present invention, the alloy of the melt preferably contains Al and a metal element that is less likely to form nitrides than Al as its main components, and the melting point or liquidus temperature of the alloy preferably is lower than the temperature at which aluminum nitride becomes thermodynamically unstable. In this case, bulk AlN crystal can be produced efficiently and inexpensively at a temperature lower than that achieved by sublimation. The alloy of the melt may contain, for example, at least one element selected from Fe, Ni, Cu, Co, and Si as its main component, as an alloy component other than Al.

[0024] The method for producing an aluminum nitride single crystal according to the present invention can grow a bulk aluminum nitride single crystal, for example, by continuously maintaining evaporation of Al in the melt and continuously precipitating aluminum nitride crystal.

[0025] In the method for producing an aluminum nitride single crystal according to the present invention, the substrate preferably has, at least on its surface, a sintered body containing aluminum nitride or a single-crystal aluminum nitride seed crystal, in which case a high-quality aluminum nitride single crystal can be precipitated and grown on the surface of the substrate.

[0026] The aluminum nitride single crystal manufacturing apparatus according to the present invention comprises a reaction vessel, a heating vessel arranged inside the reaction vessel and capable of storing a melt of an alloy containing Al, a heating means arranged to heat the melt stored in the heating vessel, and an atmospheric gas supply means arranged to supply an atmospheric gas containing nitrogen into the reaction vessel, wherein the atmospheric gas supply means is configured to be able to adjust the partial pressure of the nitrogen in the atmospheric gas being supplied.

[0027] The aluminum nitride single crystal manufacturing apparatus according to the present invention can supply the atmospheric gas after adjusting the nitrogen partial pressure in the atmospheric gas using the atmospheric gas supply means, and therefore can manufacture aluminum nitride single crystals in atmospheric gases having various nitrogen partial pressures, thereby enabling the manufacture of aluminum nitride single crystals by various methods utilizing formula (5), for example.

[0028] In the aluminum nitride single crystal manufacturing apparatus according to the present invention, the atmospheric gas supply means may have a nitrogen gas supply unit that adjusts the flow rate of the nitrogen and supplies it, and a mixing gas supply unit that adjusts the flow rate of a gas other than the nitrogen in the atmospheric gas and supplies it, and may be configured to mix the nitrogen supplied from the nitrogen gas supply unit and the gas supplied from the mixing gas supply unit and supply the mixed gas into the reaction vessel. In this case, the partial pressure of nitrogen in the atmospheric gas can be controlled by adjusting the flow rate of nitrogen and the flow rate of the other gas.

[0029] In the aluminum nitride single crystal manufacturing apparatus according to the present invention, the heating means may be configured to heat the melt to a temperature higher than the lowest temperature within the temperature range at which the aluminum nitride crystal decomposes in the melt, thereby generating the Al vapor. In this case, the aluminum nitride single crystal can be manufactured by the aluminum nitride single crystal manufacturing method according to the present invention. [Effects of the Invention]

[0030] According to the present invention, it is possible to provide a method and an apparatus for producing an aluminum nitride single crystal, which allows easy temperature control and enables production of an aluminum nitride single crystal at a relatively high growth rate. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a graph showing the relationship between the driving force Δμ for the generation of AlN crystal and the temperature T in an Fe-20 mol % Al alloy melt under various nitrogen partial pressures, in connection with a manufacturing method of an aluminum nitride single crystal according to an embodiment of the present invention. [Figure 2] 1 is a front view showing the overall configuration of an AlN single crystal manufacturing apparatus used in a manufacturing method of an aluminum nitride single crystal according to an embodiment of the present invention. [Figure 3] 3(a) is a front view showing the atmospheric gas supply portion of the AlN single crystal manufacturing apparatus shown in FIG. 2, and FIG. 3(b) is a front view showing the atmospheric gas supply means of the aluminum nitride single crystal manufacturing apparatus according to an embodiment of the present invention. [Figure 4] 1A is a cross-sectional view showing the principle of a method for producing an aluminum nitride single crystal according to an embodiment of the present invention, and FIG. 1B is a graph showing the relationship between the driving force Δμ for generating an AlN crystal and temperature T. FIG. [Figure 5] (a) A plan view showing the inside of a crucible when a bulk AlN single crystal is grown by a manufacturing method of an aluminum nitride single crystal according to an embodiment of the present invention, (b) an SEM image of one AlN single crystal, (c) an SEM image of the end (base) of the AlN single crystal shown in (b), (d) an SEM image of the center of the AlN single crystal shown in (b), and (e) an SEM image of the tip (near the growth starting point) of the AlN single crystal shown in (b). [Figure 6] Among the bulk AlN single crystals grown by the manufacturing method of aluminum nitride single crystals in Figure 5, (a) a bird's-eye SEM image of a cross section of an AlN single crystal different from the bulk AlN single crystal shown in Figure 5(b), (b) a (0002) pole figure obtained by X-ray diffraction, and (c) a (10-10) pole figure. [Figure 7]Of the bulk AlN single crystals grown by the aluminum nitride single crystal manufacturing method shown in Figure 5, (a) is an SEM image of a cross section of an AlN seed crystal held above a crucible, and (b) is an enlarged SEM image of a portion of (a). [Figure 8] FIG. 6A is a plan view showing the inside of a crucible, and FIG. 6B is a plan view showing an overall view of two AlN single crystals when a bulk AlN single crystal is grown using a manufacturing method of an aluminum nitride single crystal according to an embodiment of the present invention, with the supply pattern of the atmospheric gas changed from that shown in FIG. 5. [Figure 9] (a) Bird's-eye SEM image of a cross section of one of the bulk AlN single crystals grown by the manufacturing method for aluminum nitride single crystals in Figure 8, (b) a (0002) pole figure obtained by X-ray diffraction, and (c) a (10-10) pole figure. [Figure 10] FIG. 8 shows (a) a plan view showing the state inside a crucible, (b) an SEM image of one AlN single crystal, and (c) an SEM image of the tip of the AlN single crystal shown in (b) when a bulk AlN single crystal is grown using a manufacturing method for an aluminum nitride single crystal according to an embodiment of the present invention, with the temperature rise and fall patterns of the crucible being changed. [Figure 11] Figure 10 shows (a) a plan view showing the inside of a crucible, (b) an SEM image of one AlN single crystal, (c) an SEM image of the end (base) of the AlN single crystal shown in (b), and (d) an SEM image of the tip of the AlN single crystal shown in (b) when bulk AlN single crystals were grown using a manufacturing method for aluminum nitride single crystals according to an embodiment of the present invention, with the temperature rise and fall patterns of the crucible being changed. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, embodiments of the present invention will be described with reference to the drawings and examples. The method for producing aluminum nitride single crystal according to an embodiment of the present invention can produce AlN single crystal as follows. First, a deposition target containing aluminum nitride is placed in a nitrogen-containing atmosphere. The deposition target may be any material from which an aluminum nitride single crystal can be deposited. The deposition target may be, for example, a crucible made of a sintered body containing aluminum nitride or a single-crystal aluminum nitride seed crystal, or may have, at least on its surface, a sintered body containing aluminum nitride or a single-crystal aluminum nitride seed crystal.

[0033] Next, after placing the deposition target body, Al vapor is generated in the atmosphere. At this time, Al vapor is generated by heating a melt of an alloy containing Al to a predetermined temperature. Here, the predetermined temperature for generating Al vapor can be determined as follows.

[0034] When an Fe-20 mol% Al alloy is used as the melt, for example, the relationship between the driving force Δμ for the formation of AlN crystals in the Fe-Al alloy melt at each atmospheric nitrogen partial pressure and the temperature T can be determined from equation (5). The relationship thus determined is shown in Figure 1. Note that the low-temperature end points of the lines corresponding to each atmospheric nitrogen partial pressure shown in Figure 1 indicate the liquidus temperatures of the Fe-20 mol% Al alloy. Furthermore, the element that constitutes the melt alloy together with Al as the main component may be any element that is less likely to form nitrides than Al and has a melting point lower than the dissociation temperature or melting point of AlN, and is not limited to Fe, but may also be Cu, Ni, Co, Si, etc.

[0035] At each atmospheric nitrogen partial pressure, the temperature at which the driving force for AlN crystal growth, Δμ, becomes 0 is the lowest temperature (minimum decomposition temperature) within the temperature range at which AlN crystals become thermodynamically unstable (do not form) in that alloy melt; when Δμ > 0, AlN crystals form on the melt surface, and when Δμ < 0, AlN crystals do not form. As shown in Figure 1, at each atmospheric nitrogen partial pressure, the value of the driving force for AlN crystal growth, Δμ, can be adjusted by the melt temperature; by maintaining the melt at a temperature where Δμ < 0, it is possible to generate Al vapor from the melt while suppressing the formation of AlN crystals on the melt surface.

[0036] The reaction between the generated Al vapor and the nitrogen in the atmosphere allows AlN single crystal to be deposited on the surface of the deposition target. Furthermore, by continuously maintaining the evaporation of Al and continuously precipitating aluminum nitride crystal, bulk AlN single crystal can be grown. To effectively grow AlN crystal, it is preferable that the temperature at the deposition target is lower than that of the melt and that the driving force Δμ for AlN crystal growth is positive.

[0037] Thus, the AlN crystal manufacturing method of the embodiment of the present invention is capable of producing aluminum nitride single crystal simply by generating Al vapor in a nitrogen-containing atmosphere, i.e., by simply heating an Al-containing melt to a temperature higher than the minimum decomposition temperature, making temperature control easy. Furthermore, by being able to produce aluminum nitride single crystal in a nitrogen-containing atmosphere, the growth rate can be increased compared to conventional methods of growing aluminum nitride crystal solely on the surface of a melt.

[0038] Furthermore, in the AlN single crystal manufacturing method according to the embodiment of the present invention, by appropriately selecting the type and composition of the Al-containing alloy, the melting point or liquidus temperature of the alloy can be made lower than the temperature at which AlN becomes thermodynamically unstable, making it possible to manufacture AlN crystals at lower temperatures and at lower cost than with sublimation methods.

[0039] Below, an experiment was carried out to grow an AlN single crystal using the AlN single crystal manufacturing method according to the embodiment of the present invention.

[0040] [AlN single crystal manufacturing equipment] An AlN single crystal production experiment was conducted using the apparatus shown in Figure 2. As shown in Figure 2, the AlN single crystal production apparatus comprises a reaction vessel 1, a heater 2, a heat insulator 3, a gas inlet pipe 4, and a gas exhaust pipe 5. The heater 2 is provided inside the reaction vessel 1 so as to house a crucible 6 inside and cover the sides of the housed crucible 6. The heater 2 is capable of heating the crucible 6. The heat insulator 3 is provided inside the reaction vessel 1 so as to surround the heater 2 and the crucible 6. The gas inlet pipe 4 is provided so as to be able to supply atmospheric gas into the reaction vessel 1. The gas exhaust pipe 5 is provided so as to be able to exhaust gas from inside the reaction vessel 1. The heater 2 corresponds to the heating means, and the crucible 6 corresponds to the heating vessel.

[0041] In the experiment, the crucible 6 was made of an AlN sintered body, and contained a melt 7 of an alloy containing Al inside the crucible 6. Note that the crucible 6 may be made entirely of an AlN sintered body, with only the inner surface being made of the AlN sintered body. In the experiment, a gas containing nitrogen was used as the atmospheric gas. In the experiment, as shown in FIG. 3(a), the atmospheric gas (atmospheric gas; Ar-4 vol% N2 gas) was supplied into the reaction vessel 1 from a cylinder 11 containing the nitrogen-containing gas, while the flow rate was adjusted using a mass flow controller 12.

[0042] The method for supplying the atmospheric gas into the reaction vessel 1 is not limited to a method in which atmospheric gas whose mixture ratio has been adjusted in advance is supplied into the reaction vessel 1 as shown in Fig. 3(a), but may also be a method in which atmospheric gas whose mixture ratio is adjusted is supplied by an atmospheric gas supply means configured to adjust the mixture ratio of the atmospheric gas. For example, as shown in Fig. 3(b), this atmospheric gas supply means may have a nitrogen gas supply unit 21 that supplies nitrogen and a mixing gas supply unit 22 that supplies a gas other than nitrogen, and may be configured to mix the nitrogen supplied from the nitrogen gas supply unit 21 and the gas supplied from the mixing gas supply unit 22, or to supply the nitrogen and the gas other than nitrogen separately (indicated by the dashed lines in the figure) into the reaction vessel 1. In this case, the nitrogen gas supply unit 21 has a cylinder 23 containing nitrogen gas and a mass flow controller 24 that adjusts the flow rate of nitrogen from the cylinder 23, and is configured to adjust the flow rate of nitrogen before supplying it. The mixed gas supply unit 22 has a cylinder 25 storing a gas other than nitrogen (for example, Ar) and a mass flow controller 26 that adjusts the flow rate of the gas from the cylinder 25, and is configured to adjust the flow rate of the gas before supplying it. This allows the flow rate of nitrogen and the flow rates of other gases to be adjusted, thereby controlling the partial pressure of nitrogen in the atmospheric gas.

[0043] As shown in Figure 4, in the experiment, the inside of reaction vessel 1 was first evacuated, and then atmospheric gas was supplied through gas supply pipe 4 to fill reaction vessel 1 with the atmospheric gas. Next, electricity was applied to heater 2, and melt 7 was heated to a temperature at which the driving force for AlN crystal growth, Δμ, became negative. By maintaining this temperature, Al vapor was generated from the melt without AlN crystals forming on the melt surface. As a result, the Al vapor reacted with nitrogen in the atmosphere at a position above the melt where Δμ became positive, and bulk AlN single crystal 8 was precipitated on the inner wall surface of crucible 6. [Example]

[0044] The Al-containing alloy used was Fe-20 mol% Al. The inside of the reaction vessel 1 was purged with Ar-4 vol% N gas at atmospheric pressure. An AlN bulk single crystal (hereinafter referred to as the AlN seed crystal) attached to one end of an alumina tube was held above the melt 7 inside the crucible 6. In the experiment, the Fe-Al alloy melt 7 was heated to 2053 K, at which Δμ<0 (Figure 1) was achieved. Ar-4 vol% N gas was supplied to the reaction vessel 1 at a flow rate of 1.5 L / min for 5.5 hours, 0.9 L / min for 15 hours, and 0.6 L / min for 3.5 hours. The reaction vessel 1 was then cooled to room temperature. The deposition of a bulk AlN single crystal was confirmed at the top of the crucible 6.

[0045] Figure 5(a) shows the state of the crucible 6 observed from above after the AlN seed crystal was removed, Figure 5(b) shows an SEM image of one of the precipitated crystals, and Figures 5(c) to 5(e) show SEM images of the end (base), center, and tip (near the growth starting point) of the crystal, respectively. As shown in Figure 5(b), the precipitated bulk AlN single crystal was confirmed to be in the shape of a hexagonal column, with a length of 13 mm, a thickness of 140 μm at the base, 36 μm at the tip, and a maximum thickness of 220 μm at the center.

[0046] Figure 6(a) shows a bird's-eye view SEM image of a cross section of a bulk AlN single crystal, different from the one shown in Figure 5(b). Figures 6(b) and 6(c) show the (0002) and (10-10) pole figures obtained by X-ray diffraction, respectively. In these pole figures, the direction of χ = 89° and φ = 353.8° corresponds to the longitudinal direction of the crystal. The results in Figures 6(b) and 6(c) confirmed that the longitudinal direction of this hexagonal prism-shaped AlN crystal was the

[0002] direction, and the side surface of the AlN crystal was the (10-10) plane. Furthermore, when the X-ray rocking curve of the AlN single crystal shown in Figure 6(a) was measured, the half-width of the rocking curve for the (0002) plane was 18.0 arcsec, and the half-width of the rocking curve for the (10-10) plane was 32.4 arcsec, confirming that it was a highly oriented single crystal.

[0047] Figure 7 shows an SEM image of the cross section of the AlN seed crystal removed from the crucible 6. The AlN seed crystal had a thickness of 560 μm before the experiment, but as shown in Figure 7, it was confirmed that the thickness had increased by 61 μm to 621 μm after the experiment. This is thought to be because AlN single crystals precipitated and grew on the surface of the AlN seed crystal during the experiment. [Example]

[0048] Fe-20 mol% Al was used as the Al-containing alloy, and the inside of the reaction vessel 1 was replaced with Ar-4 vol% N2 gas at atmospheric pressure. In the experiment, the Fe-Al alloy melt 7 was heated to 2053 K, the temperature at which Δμ<0 as shown in Figure 1, and held for 24 hours while Ar-4 vol% N2 gas was supplied into the reaction vessel 1 at a flow rate of 1.1 L / min. The inside of the reaction vessel 1 was then cooled to room temperature. As a result, it was confirmed that bulk AlN single crystals had precipitated in the upper part of the crucible 6.

[0049] Figure 8(a) shows the crucible 6 observed from above after the experiment, and Figure 8(b) shows an overall image of two of the precipitated crystals. As shown in Figure 8(b), the precipitated bulk AlN single crystal was confirmed to be approximately 25 mm in length.

[0050] Figure 9(a) shows a cross-sectional SEM image of one of the bulk AlN single crystals shown in Figure 8(b), and Figures 9(b) and 9(c) show the (0002) and (10-10) pole figures obtained by X-ray diffraction, respectively. In these pole figures, the directions of χ = 87° and φ = 5.2° correspond to the longitudinal direction of the crystal. As shown in Figure 9(a), it was confirmed that the precipitated bulk AlN single crystal had a triangular prism shape. Furthermore, the results in Figures 9(b) and 9(c) confirmed that the longitudinal direction of this triangular prism crystal was the

[0100] direction. [Example]

[0051] The Al-containing alloy used was Fe-20 mol% Al, and the inside of the reaction vessel 1 was purged with Ar-4 vol% N2 gas at atmospheric pressure. In the experiment, the Fe-Al alloy melt 7 was heated to 2053 K, the temperature at which Δμ<0 (Figure 1) is met. Ar-4 vol% N2 gas was supplied to the reaction vessel 1 at a flow rate of 1.1 L / min and maintained at this temperature for 5 hours. The temperature of the crucible 6 was then lowered to 1900 K and maintained there for 1 hour. The temperature was then raised again to 2053 K and maintained there for 5 hours. This heating and cooling process was repeated three times. The inside of the reaction vessel 1 was then cooled to room temperature. The precipitation of bulk AlN single crystals was confirmed in the upper part of the crucible 6.

[0052] Figure 10(a) shows the state of the crucible 6 observed from above after the experiment, Figure 10(b) shows an SEM image of one of the precipitated crystals, and Figure 10(c) shows an SEM image of the tip of that crystal. As shown in Figure 10(b), the precipitated bulk AlN single crystal was confirmed to be 7.5 mm long and 90 μm thick. [Example]

[0053] The Al-containing alloy used was Fe-15 mol% Al, and the inside of the reaction vessel 1 was purged with Ar-4 vol% N2 gas at atmospheric pressure. In the experiment, the Fe-Al alloy melt 7 was heated to 2000 K, the temperature at which Δμ<0 (Figure 1) is achieved, and held for 5 hours while Ar-4 vol% N2 gas was supplied into the reaction vessel 1 at a flow rate of 1.1 L / min. After that, the temperature of the crucible 6 was lowered to 1849 K and held for 1 hour, and then raised again to 2000 K and held for 5 hours. This heating and cooling process was repeated three times. The inside of the reaction vessel 1 was then cooled to room temperature. This confirmed the precipitation of bulk AlN single crystals in the upper part of the crucible 6.

[0054] Figure 11(a) shows the state of the crucible 6 observed from above after the experiment, Figure 11(b) shows an SEM image of one of the precipitated crystals, and Figures 11(c) and (d) show SEM images of the end (base) and tip of the crystal, respectively. As shown in Figure 11(b), the precipitated bulk AlN single crystal was confirmed to be 6.5 mm long and 53 μm thick at the base.

[0055] From the above experimental results, it can be said that the method for producing aluminum nitride single crystals according to the embodiment of the present invention makes it possible to produce AlN single crystals at lower temperatures and at lower cost than the sublimation method, which requires heating to approximately 2448 K to grow AlN single crystals. [Explanation of symbols]

[0056] 1 reaction vessel 2 heaters 3. Insulation 4 Gas supply pipe 5 Gas exhaust pipe 6. Crucible 7 Melt 8. Bulk AlN single crystal 11 Cylinder 12 Mass flow controller 21 Nitrogen gas supply unit 23 Cylinder 24 Mass flow controller 22 Mixing gas supply unit 25 Cylinder 26 Mass flow controller

Claims

1. A method for producing an aluminum nitride single crystal, comprising: placing a deposition target body having aluminum nitride in a nitrogen-containing atmosphere; heating a melt of an alloy containing Al in said atmosphere to a temperature higher than the lowest temperature within a temperature range at which aluminum nitride crystals decompose in said melt; generating Al vapor; and precipitating an aluminum nitride single crystal on the surface of said deposition target body.

2. The activity of AlN when the reaction of forming the aluminum nitride crystals represented by formula (3) is in equilibrium is expressed as a eq. AlN , the activity of Al in the melt is a eq. Al , the partial pressure of nitrogen is p eq. N2 The partial pressure of nitrogen in the atmosphere is p N2 , where the equilibrium constant of the above equation (3) is K, the Boltzmann constant is k, and the absolute temperature is T, The minimum temperature is the temperature at which the value of the driving force Δμ for growth of the aluminum nitride crystal, expressed by formula (5), becomes 0. The method for producing an aluminum nitride single crystal according to claim 1. 221(1)+8 ２ (g)→22Al8(s) (3) [Equation 1] [Equation 2]

3. 3. The method for producing an aluminum nitride single crystal according to claim 1, wherein a bulk aluminum nitride single crystal is grown by reaction between the Al vapor and nitrogen in the atmosphere.

4. 4. The method for producing an aluminum nitride single crystal according to claim 1, wherein the substrate has, at least on its surface, a sintered body containing aluminum nitride or a single-crystal aluminum nitride seed crystal.

5. A reaction vessel; a heating vessel disposed inside the reaction vessel and configured to accommodate a melt of an alloy containing Al; a heating means provided so as to be able to heat the melt contained in the heating vessel; an atmospheric gas supply means provided so as to be able to supply an atmospheric gas containing nitrogen into the reaction vessel; The atmospheric gas supply means is configured to be able to adjust the partial pressure of the nitrogen in the atmospheric gas that is supplied. This is a special aluminum nitride single crystal manufacturing device.

6. 6. The aluminum nitride single crystal manufacturing apparatus according to claim 5, wherein the atmospheric gas supply means comprises a nitrogen gas supply unit that adjusts the flow rate of the nitrogen and supplies it, and a mixing gas supply unit that adjusts the flow rate of a gas other than the nitrogen in the atmospheric gas and supplies it, and is configured to mix the nitrogen supplied from the nitrogen gas supply unit and the gas supplied from the mixing gas supply unit and supply the mixed gas into the reaction vessel.

7. 7. The aluminum nitride single crystal manufacturing apparatus according to claim 5, wherein the heating means is configured to heat the melt to a temperature higher than the lowest temperature within a temperature range at which the aluminum nitride crystal decomposes in the melt, thereby generating Al vapor.

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