JP5213899B2 - Method for producing nitride crystal - Google Patents

Description

  The present invention relates to a method for producing a nitride crystal, and more particularly to a method for producing a high-quality bulk crystal of a Group 13 element (hereinafter referred to as “Group 13 element”) nitride represented by gallium nitride. The present invention also relates to a production apparatus used for carrying out the method for producing the nitride crystal.

  Gallium nitride (GaN) is useful as a material applied to electronic devices such as light emitting diodes and laser diodes. The most common method for producing this gallium nitride crystal is a method of performing vapor phase epitaxial growth by MOCVD (Metal-Organic Chemical Vapor Deposition) on a substrate such as sapphire or silicon carbide. However, in this method, GaN crystals are heteroepitaxially grown on substrates having different lattice constants and thermal expansion coefficients of GaN, so that dislocations and lattice defects are likely to occur in the obtained GaN crystals, and a quality applicable to a blue laser or the like is obtained. There was a problem that it was difficult.

Therefore, in recent years, there has been a strong demand for establishment of a new manufacturing technique for high-quality gallium nitride massive single crystals for homoepitaxial substrates, which can replace the above method. As one of such new methods for producing gallium nitride crystals, a nitride solution growth method using ammonia as a solvent has been proposed. R. Dwilinski et al. Have obtained a gallium nitride crystal using ammonia in a supercritical state as a solvent under high pressure of 100 to 500 MPa and using KNH ₂ as a mineralizer for crystallization (see Non-Patent Document 1). . Kolis et al. Have obtained gallium nitride crystals using KNH ₂ and KI as mineralizers for crystallization using ammonia in a supercritical state as a solvent under a high pressure of 240 MPa (see Non-Patent Document 2). Chen et al. Also used a reaction vessel lined with Pt, using ammonia in a supercritical state as a solvent under a high pressure of about 200 MPa, NH ₄ Cl as a mineralizer for crystallization, and gallium nitride crystals. (See Non-Patent Document 3).

R. Dwilinski etal., ACTA PHYSICA POLONICA A Vol.88 (1995) 833 Kolis etal., J. Crystal Growth 222 (2001) 431 Chen etal., J. Crystal Growth 209 (2000) 208

  However, the gallium nitride crystal production method based on the solution growth method based on the principle of dissolution and precipitation of gallium nitride in the above ammonia solvent is generally an oxide produced by hydrothermal synthesis (growing) method using water as a solvent. It was limited to elementary conditions within a range restricted by operations and equipment in crystal production. For this reason, the details of the crystal growth mechanism of nitride using ammonia as a solvent are still unclear, and a method for obtaining a high-quality single crystal with high crystallinity and large size has yet to be established. There wasn't. Moreover, in the said manufacturing method, the yield of the crystal | crystallization was also inadequate and it was difficult to obtain high production efficiency. Furthermore, the manufacturing method does not sufficiently disclose an index related to the quality of crystals such as impurities. In particular, in applications as a semiconductor substrate, it is necessary to avoid the inclusion of transition metal components and oxygen that can cause the formation of lattice defects, dislocation density, and impurity levels in the band gap. In addition, in order to carry out industrial nitride crystal growth, safety issues must be fully considered when using ammonia, which is more toxic, dangerous and corrosive than water as a solvent. .

That is, the object of the present invention is achieved by the following method for producing a nitride crystal.
(1) After sealing the reaction vessel was filled with the raw material and ammonia solvent in a counter-reaction container unit, further inserting the reaction vessel pressure resistance container, the gap between the reaction vessel and the pressure vessel A method for producing a nitride crystal, comprising filling a second solvent and sealing the pressure-resistant container, and then obtaining a nitride crystal by heating.
(2) At least the inner surface is filled with a raw material and an ammonia solvent in a corrosion-resistant reaction vessel and the reaction vessel is sealed, and then the reaction vessel is inserted into the pressure-resistant vessel, and the reaction vessel and the pressure-resistant vessel A nitride crystal is obtained by filling a space between the second solvent and sealing the pressure-resistant container and then raising the temperature.
(3) The production method according to any one of (1) and (2) , wherein the reaction vessel is provided with at least one valve.
(4) Said 2nd solvent is ammonia solvent, water, alcohol, or a carbon dioxide, The manufacturing method as described in any one of (1)-(3) characterized by the above-mentioned.
(5) The method according to any one of (1) to (3) , wherein the second solvent is an ammonia solvent.
(6) The production method according to any one of (1) to (5) , wherein the ammonia solvent in the reaction vessel is maintained in a subcritical state or a supercritical state.
(7) The method for producing a nitride crystal according to any one of (1) to (6) , wherein at least the pressure-resistant container is maintained at 20 to 500 MPa.
(8) The method for producing a nitride crystal according to any one of (1) to (6), wherein at least the pressure-resistant container is maintained at 20 to 400 MPa.
(9) The method according to any one of (1) to (8) , wherein the temperature of at least the pressure-resistant container is increased to 200 to 700 ° C.
(10) The production method according to any one of (1) to (9) , wherein at least one kind of additive is added to the reaction vessel.
(11) The production method according to (10) , wherein the additive contains at least one kind of halogen atom.
(12) The production method according to any one of (1) to (11) , wherein an oxygen content in the raw material is 5% by mass or less.
(13) The manufacturing method according to any one of (1) to (12) , wherein the raw material contains gallium nitride.
(14) At least one kind of seed crystal is placed in the reaction vessel, and a raw material dissolved in an ammonia solvent is deposited on the seed crystal. (1) to (13) The manufacturing method of the nitride crystal of description.

That is, the object of the present invention is achieved by the following method for producing a nitride crystal.
(1) At least the inner surface is filled with a raw material and an ammonia solvent in a reaction vessel made of a noble metal, and the reaction vessel is sealed. Then, the reaction vessel is further inserted into a pressure resistant vessel, and the reaction vessel and the pressure resistant property are sealed. A method for producing a nitride crystal, comprising filling a space between the container and a second solvent, sealing the pressure-resistant container, and then obtaining a nitride crystal by raising the temperature.
(2) The method according to (1), wherein the noble metal contains at least one kind of noble metal selected from the group consisting of Rh, Pd, Ag, Ir, Pt and Au as a main component.
(3) The production method according to (2), wherein the reaction vessel is a vessel mainly composed of Pt or an alloy containing Pt.
(4) The production method according to any one of (1) to (3), wherein the reaction vessel is provided with at least one valve.
(5) The production method according to any one of (1) to (4), wherein the second solvent is an ammonia solvent.
(6) The production method according to any one of (1) to (5), wherein the ammonia solvent in the reaction vessel is maintained in a subcritical state or a supercritical state.
(7) The method for producing a nitride crystal according to any one of (1) to (6), wherein at least the pressure-resistant container is maintained at 20 to 500 MPa.
(8) The production method according to any one of (1) to (7), wherein the temperature in at least the pressure-resistant container is increased to 200 to 700 ° C.
(9) The production method according to any one of (1) to (8), wherein at least one kind of additive is added to the reaction vessel.
(10) The production method according to (9), wherein the additive contains at least one kind of halogen atom.
(11) The production method according to any one of (1) to (10), wherein an oxygen content in the raw material is 5% by mass or less.
(12) The manufacturing method according to any one of (1) to (11), wherein the raw material contains gallium nitride.
(13) In any one of (1) to (12), at least one kind of seed crystal is placed in the reaction vessel, and a raw material dissolved in an ammonia solvent is deposited on the seed crystal. The manufacturing method of the nitride crystal of description.
(14) A nitride crystal manufacturing apparatus having a structure in which a sealable nitride crystal growth reaction vessel is inserted into a sealable pressure-resistant vessel,
The apparatus for producing a nitride crystal, wherein at least the inner surface of the reaction vessel is made of a noble metal and has a gap that can be filled with a solvent between the reaction vessel and the pressure-resistant vessel.
(15) The nitride crystal production apparatus according to (14), wherein the reaction vessel is provided with at least one valve.

  In the production method of the present invention, at least the inner surface is filled with a raw material and an ammonia solvent in a noble metal reaction vessel represented by Pt and sealed, and then the reaction vessel is placed in a pressure-resistant vessel different from the reaction vessel. Then, the space between the reaction vessel and the pressure vessel is filled with a second solvent to seal the pressure vessel, and then the temperature is raised. With this configuration, according to the present invention, it is possible to efficiently produce a high-quality massive nitride crystal having good crystallinity and few impurities, more easily and safely than the conventional production method.

  Further, according to the present invention, using a pressure-resistant container having a reaction container having an inner surface made of a noble metal typified by Pt on the inside, a so-called double container is used, and ammonia is contained inside the reaction container. By performing a solution growth reaction of nitride crystals using as a solvent, it is possible to avoid mixing of transition metal components derived from the reaction vessel into the nitride crystals, solubility of the nitride raw material in the ammonia solvent, ions in the solvent convection The portability and the control of the recrystallization factor to the seed crystal can be easily controlled, and further, the accumulation of transition metal impurity components in the generated massive nitride crystal and the deterioration of the crystallinity can be avoided.

  The manufacturing apparatus of the present invention has a structure in which a sealable nitride crystal growth reaction vessel having at least an inner surface made of a noble metal is inserted into a sealable pressure-resistant vessel, There is a gap that can be filled with the second solvent between the reaction vessel and the pressure-resistant vessel. If this manufacturing apparatus is used, the above-described method for manufacturing a nitride crystal can be easily carried out. In particular, by using a reaction vessel equipped with at least one valve, it can be sealed after filling with ammonia without contacting with the outside air through the valve, so that nitridation of impurities such as oxygen derived from the outside air Incorporation into physical crystals can also be avoided.

It is a schematic sectional drawing of the manufacturing apparatus of this invention. It is a schematic sectional drawing which shows the valve shape of the reaction container which comprises the manufacturing apparatus of this invention. It is a schematic sectional drawing which shows another valve shape of the reaction container which comprises the manufacturing apparatus of this invention. It is a schematic sectional drawing which shows another valve shape of the reaction container which comprises the manufacturing apparatus of this invention. It is a schematic sectional drawing which shows another valve shape of the reaction container which comprises the manufacturing apparatus of this invention.

  Below, the manufacturing method and manufacturing apparatus of the nitride crystal of this invention are demonstrated in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

  The present invention uses a reaction vessel having at least an inner surface made of a noble metal typified by Pt, and fills the reaction vessel with raw materials (additives such as a mineralizer as necessary) and an ammonia solvent. After sealing the reaction vessel from above, it is inserted into a pressure-resistant vessel installed outside the reaction vessel, sealed with a predetermined second solvent in the gap between the reaction vessel and the pressure-resistant vessel, and then heated. Then, the pressure inside and outside the reaction vessel is made substantially the same, and the dissolution and precipitation of the raw material is promoted in the presence of the supercritical ammonia solvent in the reaction vessel to obtain a nitride crystal.

First, the raw material, solvent, container used in the present invention and the nitride crystal obtained in the present invention will be described with reference to the drawings as appropriate.
FIG. 1 is a schematic cross-sectional view of a manufacturing apparatus used in the manufacturing method of the present invention. 2-5 is a schematic sectional drawing which shows the specific example of the valve | bulb shape of the reaction container which comprises the manufacturing apparatus of this invention. Reference numeral 1 is a valve, reference numeral 2 is a pressure gauge, reference numeral 3 is a pressure-resistant container, reference numeral 4 is a valve, reference numeral 5 is a crystal growing section, reference numeral 6 is a reaction vessel, reference numeral 7 is a raw material filling section, reference numeral 8 is an electric furnace, reference numeral 9 represents a thermocouple, 10 represents a seed crystal, and 11 represents a pipe connection port.

  In the present invention, a nitride crystal to be manufactured depends on a raw material to be used, but is mainly a crystal of a single metal nitride of a group 13 element such as B, Al, Ga, In (for example, GaN, AlN). Alternatively, a crystal of an alloy nitride (eg, GaInN, GaAlN) is preferable, and a gallium nitride crystal is more preferable.

  In the present invention, the noble metal that forms the reaction vessel 6 is at least one selected from the group consisting of Group 9 to 11 elements in the fifth and sixth periods of the periodic table, that is, Rh, Pd, Ag, Ir, Pt, and Au. Examples include various types of noble metals and alloys containing the noble metals as a main component. Among them, it is preferable to use Pt having excellent corrosion resistance.

  Conventionally, it is known to line or coat Pt on the inside of a reaction vessel by utilizing the excellent corrosion resistance of Pt (see Non-Patent Document 3). However, when the reaction vessel is lined or coated, it is practically difficult to line or coat all portions of the reaction vessel that come into contact with the ammonia solvent with a noble metal. In particular, in the method for producing a nitride crystal using an ammonia solvent, pipes and valves are attached to the reaction vessel in order to fill the ammonia solvent. It was difficult to line or coat all with precious metals.

  The present inventors, when there is a portion that is not lined or coated with a noble metal in the reaction vessel and its accessory parts, erosion by ammonia or the like occurs from that portion, and as a result, the obtained nitride crystal is contained in the reaction vessel. It has been found that the transition metals that have been used can be mixed. Furthermore, the present inventors show that the mixing of the transition metal component into the nitride crystal due to the erosion of the reaction vessel is particularly remarkable when an additive for promoting dissolution precipitation called a mineralizer described later is added. I also found out.

  In the present invention, the reaction vessel itself is made of a noble metal, so that the portion where the raw materials and additives come into contact with each other through the ammonia solvent can be limited to the noble metal. Accordingly, it is possible to avoid mixing of transition metal components such as Cr, Ni and Fe into the raw material and the nitride crystal to be produced, which have been problematic in the conventional reaction vessel, and a high quality nitride crystal can be obtained. In the present invention, it is particularly preferable to use a reaction vessel having at least an inner surface as a main component of Pt or an alloy containing Pt.

  When the precious metal reaction vessel 6 is used alone, it is difficult to withstand the ultra-high pressure generated accompanying the reaction conditions. Therefore, in the present invention, the pressure resistant container 3 is provided outside the noble metal reaction vessel 6, and the second solvent is put into the space between the outer pressure resistant vessel 3 and the inner reaction vessel 6 to react at the time of temperature rise. By trying to balance the pressure inside and outside the container 6, the reaction container 6 can be prevented from being ruptured or crushed. That is, in the present invention, the pressure inside and outside the reaction vessel 6 sealed during the temperature rising reaction can be substantially equalized, so that the reaction vessel 6 can be set to an ultrahigh pressure of supercritical ammonia during the temperature rising reaction. The pressure resistance that can withstand is not required. On the other hand, in an operation process for filling with an ammonia solvent, the container is required to be able to withstand at least the vapor pressure of the ammonia solvent at the temperature at the time of operation and the reduced pressure state when the reaction vessel 6 is evacuated and dried. Therefore, the reaction vessel 6 of the present invention has a thickness of at least 0.1 mm, preferably 0.2 mm, more preferably 0.3 mm, particularly preferably 0.5 mm at the thinnest part. .

  The shape of the reaction vessel 6 can be any shape including a cylindrical shape. In addition, the reaction vessel 6 may be used standing upright, horizontally or diagonally. The reaction vessel 6 can be provided with a valve 4 for filling ammonia, a pipe connection port 11 and the like (FIGS. 2 to 5). A structure such as a frame may be provided outside the reaction vessel 6 in advance for the purpose of ensuring stability when the reaction vessel 6 is inserted into the pressure-resistant vessel 3 and installed. The structure such as the frame is also preferably made of a noble metal or coated or lined with the noble metal.

  In the present invention, the reaction vessel 6 is preferably provided with at least one valve communicating with the inside of the reaction vessel. By providing the valve, the reaction vessel can be filled and sealed with ammonia without touching the outside air through the valve. In addition, an exhaust valve may be provided separately.

  The valve is preferably made of a material exhibiting high corrosion resistance against ammonia. In particular, it is preferable that a portion leading to the inside of the reaction vessel when the valve is sealed is made of a noble metal, or the surface is coated or lined with the noble metal. Thereby, unwanted impurities can be prevented from being mixed into the reaction system due to corrosion of the valve or the like.

  Any shape of the valve can be used. The position at which the valve 4 is attached to the reaction vessel 6 is also arbitrary. For example, as shown in FIGS. 2 to 5, when a cylindrical reaction vessel 6 is used, the valve 4 smaller than the cross-sectional circle is connected to the reaction vessel 6. If it is attached to the upper part or the lower part, it is preferable because it can be easily inserted into and installed in the pressure-resistant container 3 and the space can be used effectively.

  Further, as shown in FIGS. 3 to 5, the valve may be integrated with the reaction vessel. With such an integrated structure, when the reaction vessel 6 is inserted into the pressure resistant vessel 3, the gap generated between the pressure resistant vessel 3 can be reduced. The valve 4 and the reaction vessel 6 may be made of the same noble metal and have an integrated structure excellent in corrosion resistance.

  2 to FIG. 5 will be described in more detail. The aspect of FIG. 2 is characterized in that it is not an integral type, and there is an advantage that the replacement of the valve is easy. The aspect of FIG. 3 is characterized in that it is an integral type, and has the advantage that it is structurally excellent in strength. The aspect of FIG. 4 is characterized in that a packing ring is used in combination, and has an advantage that it can be easily closed. The aspect of FIG. 5 is characterized in that it is a body-embedded type, and has the advantages of excellent strength and effective use of space.

  The type and shape of the valve are not particularly limited, but gate valves, ball valves, angle valves, needle valves, ball valves, diaphragm valves, and the like are used. The type and shape of the valve body are not particularly limited, but a needle type, a wedge type, a drum type, a round type and the like are used. A gasket, packing or seal may be used in combination. The material of the valve body, the valve seat, the gasket, the packing, and the seal may be made of precious metal, or may be coated or lined with precious metal.

  The valve may be provided with a plurality of valves having the same shape or different shapes. By attaching a plurality of valves, ammonia can be efficiently charged and discharged efficiently. For example, it is possible to discharge the gas in the reaction vessel while filling the reaction vessel with ammonia, or to discharge the ammonia in the reaction vessel while introducing an inert gas into the reaction vessel.

  A method for attaching the valve to the reaction vessel is not particularly limited, but welding or the like can be used as an example.

  In the present invention, as described above, at least the inner surface is filled with a solvent in the space between the pressure vessel 3 and the reaction vessel 6 made of a noble metal typified by Pt. The pressure difference can be minimized. Therefore, the pressure resistance performance of the valve 4 is only required to withstand the pressure difference between the inside and outside when the reaction vessel 6 is kept at a high temperature. However, in view of performance required at the time of filling the raw material and ammonia, for example, it is necessary to be able to withstand the pressure resistance performance that can withstand the vapor pressure of ammonia at room temperature and the reduced pressure state when the reaction vessel 6 is heated and evacuated and dried. is there.

  On the other hand, the pressure-resistant container 3 installed outside the reaction container 6 is preferably a container that can withstand a pressure corresponding to the super-high pressure of supercritical ammonia during the temperature rising reaction. The material for forming the pressure-resistant container 3 is not particularly limited as long as it is a pressure-resistant material, but Ni-based materials such as Inconel, Nimonic, and Rene materials that can withstand high temperature and pressure and have high corrosion resistance to ammonia. It is preferable to use alloys, stellite, and the like.

  The structure of the pressure-resistant container 3 is not particularly limited, but in many cases, the shape of the pressure-resistant container 3 is a cylindrical shape, and when used upright, the solvent-filling valve 1 and the piping for the upper part are used. Or a pressure gauge 2 can be provided. A plurality of valves 1 and pipes may be installed, or may be installed in a portion corresponding to the lid of the pressure-resistant container 3.

  The thickness of the body portion of the pressure-resistant container 3 can be appropriately determined according to the material, the body diameter, the length, and the like. Since the pressure-resistant container 3 needs to withstand the ultra-high pressure generated according to the reaction conditions for the solution growth, depending on the reaction conditions, it is usually at least 2 mm or more, preferably 5 mm or more in the thinnest part. More preferably, it has a thickness of 10 mm or more, particularly preferably 20 mm or more.

  In the present invention, since the reaction vessel 6 is used in a sealed state, additives such as raw materials and mineralizers for crystal growth in the reaction vessel 6 do not come into contact with the pressure resistant vessel 3. However, after the sealed reaction vessel 6 is inserted into the pressure-resistant vessel 3, in the unlikely event that the raw material or mineralizer filled from the reaction vessel 6 leaks, the inner wall and internal structure of the pressure-resistant vessel 3 and the pressure gauge 2 In addition, the inside of the valve 1 and the inside of the piping extending from the inside of the pressure-resistant container 3 may corrode severely. As countermeasures, the inner wall and internal structure of the pressure-resistant container 3, the inside of the pressure gauge 2 and the valve 1, and the inside of the piping leading from the inside of the pressure-resistant container 3 to the above-mentioned precious metal or other highly corrosion-resistant material Can be coated or lined with.

  The raw material for producing a nitride crystal used in the present invention is usually a nitride polycrystalline powder raw material (hereinafter referred to as “polycrystalline raw material”), preferably a raw material containing gallium nitride. The polycrystalline raw material does not need to be a complete nitride, and may contain a metal component in a metal state (that is, zero valence) depending on conditions. The reason why the metal-like metal component can be contained is not clear, but when a small amount of oxygen is mixed in the reaction system, the metal-like metal component is an oxygen trap agent that prevents oxygen from diffusing in the nitrogen-containing solvent. It is presumed that they play such a role. The content of the metal-like metal component is not particularly limited, but if it is too much, the content is determined considering that generation of hydrogen from ammonia accompanying the oxidation of the metal component during nitride crystal growth cannot be ignored. It is preferable to do.

  The manufacturing method of the polycrystalline raw material used as the raw material is not particularly limited. For example, a nitride polycrystal produced by reacting a metal or an oxide or hydroxide thereof with ammonia in a reaction vessel in which ammonia gas is circulated can be used. In addition, as a metal compound raw material having higher reactivity, a compound having a covalent MN bond such as a halide, an amide compound, an imide compound, or galazan can be used. Furthermore, nitride polycrystal (for example, GaN) produced by reacting a metal such as Ga with nitrogen at a high temperature and a high pressure can also be used.

  In order to obtain high quality crystals by crystal growth of the polycrystalline raw material, mixing of water and oxygen should be avoided as much as possible. Therefore, the oxygen content in the polycrystalline raw material is usually 5% by mass or less, preferably 2% by mass or less, and particularly preferably 0.5% by mass or less. The ease with which oxygen is mixed into the polycrystalline raw material is related to the reactivity with water or the absorption capacity. This is because the worse the crystallinity of the polycrystalline raw material, the more active groups such as NH groups exist on the surface and the like, and this may react with water to generate some oxides or hydroxides. For this reason, it is generally desirable to use a polycrystalline material having as high crystallinity as possible, and the crystallinity can be estimated by the half-value width of powder X-ray diffraction. The preferred polycrystalline raw material has a half-width of (100) diffraction line (2θ = about 32.5 ° for hexagonal gallium nitride), usually 0.25 ° or less, preferably 0.20 ° or less, more preferably 0. .17 ° or less.

  The primary particles of the polycrystalline raw material preferably have an average particle size in the range of 1 to 100 μm. The smaller the particle size, the larger the specific surface area and the higher the rate of dissolution in the solvent, which is preferable. If so, it may adhere to the seed crystal.

  In addition, by using two types of polycrystalline raw materials having different average particle diameters, Ga (( It is also possible to suppress the supply of ions and the like to the crystal growth section, and as a result, it is possible to suppress the disadvantage of growing the bulk single crystal, such as elution of the seed crystal, particularly when a seed crystal is used.

  The shape of the polycrystalline raw material is not particularly limited, but it is usually preferable that the shape of the secondary particles is spherical when considering the solubility uniformity in the solvent. Further, in order to increase the filling amount or prevent the movement of particles due to thermal convection, the polycrystalline raw material can be formed into a pellet shape or a block shape.

  The polycrystalline raw material is usually subjected to a crystallization process based on solution growth after being mixed with an additive called a mineralizer. A mineralizer is an additive that can increase the solubility of a polycrystalline raw material in a solvent. In addition to using one kind of mineralizer, it is possible to use another kind as a co-mineralizer or to use a mixture of two or more kinds as necessary. For example, in the case of GaN, the ratio of the addition amount of the polycrystalline raw material and the mineralizer is within the range of 0.001 to 100 as the mineralizer / Ga molar ratio. In addition, it can be appropriately selected in consideration of the size of the target crystal.

  The mineralizer is usually a compound containing a halogen atom or an alkali metal, alkaline earth metal, or rare earth metal. Among them, the mineralizer preferably contains a nitrogen atom in the form of ammonium ion or amide. Examples of mineralizers containing a halogen atom include ammonium halide, hydrogen halide, ammonium hexahalosilicate, and hydrocarbyl ammonium fluoride, tetramethylammonium halide, tetraethylammonium halide, benzyltrimethylammonium halide, halogen Illustrative examples include alkylammonium salts such as dipropylammonium halide and isopropylammonium halide, and alkylmetal halides such as sodium alkyl fluoride.

  Examples of the mineralizer containing alkali metal, alkaline earth metal, and rare earth metal include alkali metal metal, alkaline earth metal metal, alkali halide, alkaline earth, rare earth halide, and the like. Oxo acid salts such as alkali, alkaline earth, and rare earth carbonates can be used, but from the viewpoint of preventing the generated crystals from containing oxygen, they contain nitrogen atoms in the form of ammonium ions or amides. It is preferable to use those as mineralizers. In order to prevent impurities from being mixed into the nitride crystal, the mineralizer is purified and dried if necessary. The purity of the mineralizer is usually 95% or more, preferably 98% or more, more preferably 99% or more, and particularly preferably 99.5% or more. It is desirable that the mineralizer contains water and oxygen as little as possible, preferably 1000 ppm or less, more preferably 100 ppm or less.

Specific examples of mineralizers containing alkali metals and nitrogen atoms include sodium amide (NaNH ₂ ), potassium amide (KNH ₂ ), lithium amide (LiNH ₂ ), lithium diethylamide ((C ₂ H ₅ ) ₂ NLi) Alkali metal amides such as Mg (NH ₂ ) ₂ , rare earth amides such as La (NH ₂ ) ₃ , Li ₃ N, Mg ₃ N ₂ , Ca ₃ N ₂ , Na ₃ N, etc. Alkali metal nitride or alkaline earth metal nitride, azide compounds such as NaN ₃ , zinc nitride (Zn ₃ N ₂ ) and the like. Other examples include hydrazine salts such as NH ₂ NH ₃ Cl, ammonium carbonate ((NH ₄ ) ₂ CO ₃ ), and ammonium carbamate (NH ₂ COONH ₄ ).

  Of these, the halogen halide-containing additive (mineralizer) is preferably an alkali halide, alkaline earth halide, ammonium halide, or hydrogen halide, more preferably an alkali halide or ammonium halide. And particularly preferred is ammonium halide. These additives have high solubility in a supercritical ammonia solvent, have nitriding ability in ammonia, and have low reactivity with noble metals such as Pt. One kind of these additives may be used, or two or more kinds of compounds may be used in combination. By using these additives, dissolution of the raw material is promoted, and high-quality large-sized nitride massive crystals can be obtained in a short period of time by appropriately controlling the reaction conditions.

  In the present invention, the polycrystalline raw material and the additive such as the mineralizer mixed as described above are filled in a noble metal reaction vessel 6 as shown in FIG. Alternatively, the polycrystalline raw material and one or more additives such as mineralizer may be separately charged in the reaction vessel 6. Depending on the types of additives such as raw materials and mineralizers, after the reaction vessel 6 is sealed, the reaction vessel 6 is dissolved in a gas, liquid or solvent through the pipe 4 connected to the pipe connection port 11 and the valve 4. It can also be filled.

  When there is a reason that additives such as polycrystalline raw materials and mineralizers easily absorb moisture, it is desirable that the polycrystalline raw materials and mineralizers are sufficiently dried by heating and degassing before filling. Furthermore, when a highly decomposable mineralizer and a polycrystalline raw material are mixed and filled, it is desirable to carry out promptly in an atmosphere in which oxygen and moisture are excluded as much as possible. For example, in a container or room filled with an inert gas, the inside of the reaction vessel can be sufficiently replaced with an inert gas, and then a mineralizer and a polycrystalline raw material with high decomposability can be filled.

  After the polycrystalline raw material and an additive such as a mineralizer are mixed and filled into the reaction vessel 6 or separately filled into the reaction vessel 6, the reaction vessel 6 is sealed. Thereafter, it is also preferable to heat and deaerate the reaction vessel 6 and the piping section through the piping connected to the piping connection port 11 and the valve 4. In addition, it is also preferable to mix in the reaction vessel 6 a substance that functions as a scavenger that selectively absorbs oxygen and moisture (for example, a metal piece such as titanium).

  As shown in FIG. 1, additives such as raw materials and mineralizers are usually filled so as to be accommodated in a raw material filling portion 7 provided at the lower part of the reaction vessel 6. This is because, by giving a temperature difference between the lower part of the reaction vessel 6 and the upper part of the reaction vessel 6, the dissolved crystals can be deposited on the crystal growing part 5 at the upper part of the reaction vessel 6. Thus, by obtaining crystals through the process of dissolution and precipitation of raw materials, it is possible to obtain high-quality, high-quality bulk crystals with high crystallinity.

  In the present invention, the seed crystal 10 is further installed in the crystal growth section 5 above the reaction vessel 6, thereby promoting the generation of the single crystal and obtaining a larger single crystal. The seed crystal 10 is usually loaded at the same time as or after filling with additives such as raw materials and mineralizers, and is usually placed in a noble metal jig similar to the noble metal constituting the inner surface of the reaction vessel 6. The seed crystal 10 is fixed. If necessary, heating and deaeration after loading into the reaction vessel 6 is also effectively used.

The seed crystal 10 is desirably a single crystal of the target nitride, but is not necessarily the same nitride as the target, and may be an oxide single crystal in some cases. However, in that case, it is a seed crystal having a lattice constant, crystal lattice size parameter that matches or matches the target nitride, or heteroepitaxy (ie, coincidence of crystallographic positions of some atoms) It is necessary to use a seed crystal composed of a single crystal material piece or a polycrystalline material piece coordinated so as to guarantee the above. Specific examples of the seed crystal include, for example, gallium nitride (GaN), a single crystal of GaN, a single crystal of nitride such as AlN, a single crystal of zinc oxide (ZnO), a single crystal of silicon carbide (SiC), Examples include lithium gallate (LiGaO ₂ ) and zirconium diboride (ZrB ₂ ).

  The seed crystal 10 can be determined in consideration of the solubility in the ammonia solvent and the reactivity with the mineralizer. For example, as a seed crystal of GaN, a single crystal obtained by epitaxial growth on a dissimilar substrate such as sapphire by MOCVD method or HVPE method and then exfoliated, and obtained by crystal growth of Na, Li, Bi from metal Ga as a flux. In addition, single crystals grown by homo / heteroepitaxial growth using the LPE method, single crystals prepared based on the solution growth method including the method of the present invention, and crystals obtained by cutting them can be used.

  In the present invention, an ammonia solvent is used as a solvent for dissolving the raw material in the reaction vessel 6. The purity of ammonia to be used is usually 99.9% or more, preferably 99.99% or more, more preferably 99.999% or more, and particularly preferably 99.9999% or more. Since ammonia generally has a high affinity with water, when ammonia solvent is charged into the reaction vessel 6, oxygen derived from water is likely to be brought into the reaction vessel 6 and the resulting crystals are mixed in. There is a possibility that the amount of oxygen increases and the crystallinity of the nitride deteriorates. From such a viewpoint, it is desirable to reduce the amount of water and oxygen contained in the ammonia solvent as much as possible, preferably 1000 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less.

  The type of the second solvent filled in the gap between the reaction vessel 6 and the pressure-resistant vessel 3 in the present invention is not limited as long as it is a solvent that can bring the inside and outside of the reaction vessel 6 to substantially the same pressure. As such a second solvent, for example, an ammonia solvent, water, alcohol, carbon dioxide and the like can be used. In order to reduce the pressure difference between the inside and the outside of the reaction vessel 6, the second solvent is preferably an ammonia solvent used as a solvent for the reaction vessel 6. The reason for this is that when solvents having different properties are used, the pressure inside and outside the reaction vessel 6 is kept substantially the same when the temperature is raised in order to carry out the crystal growth reaction by dissolution and precipitation of the raw materials, especially during the temperature raising process. Because it is difficult. Usually, it is preferable to use the same solvent on the inner side and the outer side of the reaction vessel 6 so that the filling ratio to the gaps is almost the same.

  When the second solvent filled in the space between the reaction vessel 6 and the pressure-resistant vessel 3 is an ammonia solvent, the ammonia solvent does not come into direct contact with the raw material and the like, so there is no particular problem with respect to physical properties such as impurities. However, in order to make the physical properties of the ammonia solvent in the reaction vessel 6 and the ammonia solvent filled in the gap between the reaction vessel 6 and the pressure-resistant vessel 3 substantially equal, water and oxygen contained in the ammonia solvent It is desirable to reduce the amount as much as possible, preferably 1000 ppm or less, more preferably 100 ppm or less.

Next, the procedure in the manufacturing method of the present invention will be described.
In the present invention, the reaction vessel 6 is closed after filling the reaction vessel 6 with raw materials, additives such as mineralizers (if necessary, seed crystals 10) and the like. This step can be performed in an inert gas atmosphere if necessary. When the reaction vessel 6 is closed, the reaction vessel 6 may be closed in advance by a screwing method using packing together, or may be closed by welding or the like. Subsequently, ammonia solvent is filled into the closed reaction vessel 6 through the valve 4 for opening and closing the reaction vessel 6 and the pipe connected to the pipe connection port 11. By making the inside of the valve 4 leading to the reaction vessel 6 side made of the same noble metal as the material of the reaction vessel 6, the nitride crystals obtained can be obtained except for raw materials, additives such as mineralizers and those brought in from an ammonia solvent Incorporation of transition metals, etc. into can be virtually eliminated.

The ammonia solvent is charged into the reaction vessel 6 from the tank through the piping of the ammonia filling facility through the valve 4 and the pipe connection port 11 attached to the reaction vessel 6 without touching the outside air. At that time, the ammonia solvent is preferably filled in a gas or liquid state. If necessary, a part of the plurality of valves 4 can be used to escape the gas in the reaction vessel 6.
The ammonia solvent can be charged into the reaction vessel 6 as a liquid without cooling even when the room temperature is higher than the boiling point of ammonia because of its latent heat, but the reaction vessel 6 is previously filled with the boiling point of the ammonia solvent. It is also preferable to fill in the cooled state below. Further, when additives such as raw materials and mineralizers are sufficiently soluble in the ammonia solvent, they can be dissolved in advance, and the raw materials and the ammonia solvent can be charged into the reaction vessel 6 simultaneously. When filling ammonia as a gas or liquid, a flow rate control device (not shown) may be provided in the middle to fill a predetermined amount.

  When the reaction vessel 6 is filled with the ammonia solvent, filling time is required. However, it is generally possible to avoid mixing impurities from the piping and the like into the reaction vessel 6 when filling in the gaseous state. Since the gas contained therein can be completely replaced with the ammonia solvent, it is possible to fill the ammonia solvent with extremely high purity. Further, a method of filling the reaction vessel 6 with an ammonia solvent having a small amount of impurities through a purification device (not shown) using an adsorbent or the like is also preferably used.

  After filling the reaction vessel 6 with the ammonia solvent, the valve 4 attached to the reaction vessel 6 is closed to seal the reaction vessel 6, and then the piping of the ammonia filling facility (not shown) is removed. Sealing the reaction vessel 6 is important in order to prevent water and oxygen from entering the air. In particular, when the reaction vessel 6 is opened after the ammonia solvent is filled in the reaction vessel 6, the reaction vessel 6 is cooled by the large latent heat of the ammonia solvent, so that water in the air tends to condense. If the valve 4 for closing the reaction vessel 6 and the piping connection port 11 for filling ammonia are attached to the reaction vessel 6 in advance, it is possible to continuously fill the ammonia solvent without contacting with the outside air. After filling the reaction vessel 6 with the ammonia solvent, the reaction vessel 6 can be easily sealed.

The reaction vessel 6 is filled with an additive such as raw materials and mineralizers and an ammonia solvent and sealed, and then inserted into the standing pressure-resistant vessel 3. The insertion method and the installation method are not particularly limited, but it is preferable to install the reaction vessel 6 at the bottom of the pressure-resistant vessel 3 so that it can stand on its own. In the present invention, in order to make the pressure inside and outside the reaction vessel 6 approximately equal during the reaction, the second solvent is put into the gap between the reaction vessel 6 and the pressure vessel 3, so that the reaction vessel 6 and the pressure vessel It is necessary to provide a predetermined gap between the three. When the pressure resistant container 3 has a constant size, the smaller the gap between the side surface of the reaction container 6 and the side surface of the pressure resistant container 3, the larger the size of the reaction container 6 can be. Space can be secured and production efficiency is improved. However, if the gap between the two containers is too small, if the pressure inside the reaction vessel 6 becomes larger than the pressure outside the reaction vessel 6, the reaction vessel 6 expands and adheres closely to the inner surface of the pressure-resistant vessel 3, and after the reaction is completed. It may be difficult to take out the reaction vessel 6 from the pressure-resistant vessel 3.
Therefore, in the present invention, the gap between the side surface of the reaction vessel 6 and the side surface of the pressure-resistant vessel 3 (when both are cylindrical, the difference between the outer diameter of the reaction vessel 6 and the inner diameter of the pressure-resistant vessel 3) is In at least a part, it is 0.1 mm or more, preferably 0.2 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.5 mm or more.

  After returning the reaction vessel 6 to room temperature and sufficiently removing condensed water adhering to the outer surface of the reaction vessel 6, the reaction vessel 6 is inserted into the pressure-resistant vessel 3. At this time, a frame or the like for facilitating the installation and sitting of the reaction vessel 6 may be provided in advance as the outer structure of the reaction vessel 6 or the internal structure of the pressure-resistant vessel 3. Subsequently, the second solvent is filled in the gap between the reaction vessel 6 and the pressure-resistant vessel 3. It is preferable to use the same solvent on the inner side and the outer side of the reaction vessel 6 so that the filling ratios for the gaps are almost the same. When filling the space between the reaction vessel 6 and the pressure-resistant vessel 3 with an ammonia solvent, water or water is filled in the same manner as when filling the reaction vessel 6 through piping, the valve 1 attached to the pressure-resistant vessel 3 or the like. It is possible to suppress mixing of air and the like. Moreover, the method of cooling the pressure | voltage resistant container 3 below to the boiling point of an ammonia solvent is also used suitably.

  After filling the reaction vessel 6 with raw materials, additives such as mineralizer and ammonia solvent, and the second solvent (in many cases, ammonia) between the reaction vessel 6 and the pressure-resistant vessel 3 by the above operation. The pressure-resistant container 3 is operated such as closing the attached valve 1, the pressure-resistant container 3 is sealed, and the outer pressure-resistant container 3 including the reaction container 6 is installed using an electric furnace 8 having a thermocouple 9. The temperature is raised by heating.

  Here, the ammonia solvent in the reaction vessel 6 is preferably in a subcritical state or even a supercritical state during nitride crystal synthesis or growth. A supercritical fluid means a concentrated gas that is maintained above its critical temperature, and the critical temperature is a temperature at which the gas cannot be liquefied by pressure. Supercritical fluids generally have a lower viscosity and are more easily diffused than liquids, but have solvating power similar to liquids. The physical properties of ammonia solvent, unlike water used as a solvent in hydrothermal synthesis (growth) methods, are not clarified. Therefore, dissolution of raw materials and nitride crystals in subcritical or supercritical states The reason why the formation and dissolution precipitation is promoted cannot be determined, but if the concept of ionic product known in water is applied to a nitrogen-containing solvent, the ionic product increases as the temperature rises, resulting in hydrolysis in water. It is considered that an increase in the corresponding action such as amylolysis contributes.

  When using the solvent in a supercritical state, the reaction mixture is generally maintained at a temperature above the critical point of the solvent. In the case of an ammonia solvent, the critical point is a critical temperature of 132 ° C. and a critical pressure of 11.35 MPa. However, if the filling rate of the reaction vessel 6 is high, the pressure far exceeds the critical pressure even at a temperature below the critical temperature. In the present invention, the “supercritical state” includes such a state exceeding the critical pressure. Since the reaction mixture is enclosed in a constant volume reaction vessel, the increase in temperature increases the pressure of the fluid. In general, if T> Tc (critical temperature of one solvent) and P> Pc (critical pressure of one solvent), the fluid is in a supercritical state.

  In fact, since the solubility of the nitride polycrystalline raw material in the solvent is very different between the subcritical state and the supercritical state, a sufficient growth rate of the nitride crystal can be obtained under the supercritical condition. The reaction time depends in particular on the reactivity of the mineralizer or co-mineralizer and on the thermodynamic parameters, ie temperature and pressure values. During nitride crystal synthesis or growth, the pressure-resistant vessel 3 is held in a pressure range of about 5 MPa to 2 GPa, and the reaction vessel 6 is also held at a pressure equivalent to that in the pressure-resistant vessel 3. The pressure is appropriately determined depending on the temperature and the filling rate of the solvent volume with respect to the volume of the reaction vessel 6. Originally, the pressure in the reaction vessel 6 is uniquely determined by the temperature and the filling rate, but in practice, additives such as raw materials and mineralizers, temperature heterogeneity in the reaction vessel 6, and Varies slightly depending on the presence of dead volume.

  In the case of an ammonia solvent, the dissociation equilibrium is greatly inclined to nitrogen and hydrogen at a high temperature, so that a change in pressure due to the high temperature may not be negligible. In general, the dissociation reaction is catalyzed by a metal component, and there is a possibility of reaching an equilibrium depending on the types of additives such as raw materials and mineralizers. In the present invention, since the second solvent is filled in the gap between the reaction vessel 6 and the pressure-resistant vessel 3, by adjusting the temperature and pressure in the pressure-resistant vessel 3, the inside and outside of the reaction vessel 6 can be adjusted. The temperature difference and the pressure difference can be reduced as much as possible to approximate both. In consideration of this point, at least the temperature range in the heat-resistant vessel 6 (that is, the temperature range in the reaction vessel 3) is usually 150 ° C. or higher, preferably 200 ° C. or higher, particularly preferably 300 ° C. or higher, as the lower limit. The temperature is usually 800 ° C. or lower, preferably 700 ° C. or lower, particularly preferably 650 ° C. or lower. Further, at least the pressure range in the heat-resistant container 3 (that is, the pressure range in the reaction container 6) is usually 20 MPa or more as a lower limit, preferably 30 MPa or more, particularly preferably 50 MPa or more, and usually 500 MPa or less, preferably 400 MPa or less as an upper limit. It is particularly desirable to keep the pressure at 200 MPa or less.

  The ratio of the injection of the ammonia solvent into the reaction vessel 6 for achieving the temperature range and pressure range of the reaction vessel 6 described above, that is, the filling rate, is the free volume of the reaction vessel 6, that is, the polycrystalline raw material in the reaction vessel 6, In the case where a seed crystal is used, the volume remaining after subtracting the volume of the seed crystal and the structure on which the seed crystal is installed from the volume of the reaction vessel 6, or known to those who are involved in the production of bulk single crystal products by the hydrothermal growth method When installing a baffle plate, subtract the volume of the baffle plate from the volume of the reaction vessel 6 to determine the liquid density in the standard state of the remaining volume of ammonia (the liquid density at the boiling point in the case of gas in the standard state). As a reference, it is usually 20 to 95%, preferably 40 to 90%, more preferably 50 to 85%. The filling rate of the second solvent in the gap between the reaction vessel 6 and the pressure-resistant vessel 3 is also based on the volume remaining after subtracting the volume of the structure such as the frame and the reaction vessel, like the ammonia solvent. The solvent is preferably filled at a filling rate determined so that the pressure inside and outside the reaction vessel 6 becomes substantially equal when the temperature is raised. In consideration of dead volume and temperature distribution, it is also preferably used to finely adjust the pressure inside and outside the reaction vessel 6 in the temperature rising process to be the same.

  The solution growth reaction of nitride crystals in the reaction vessel 6 inside the double vessel as described above is performed by using an electric furnace 8 having a thermocouple 9 and the like including the reaction vessel 6 outside. By heating and heating the pressure-resistant vessel 3, the inside reaction vessel 6 is maintained in a subcritical or supercritical state of ammonia. The heating method and the rate of temperature increase to a predetermined reaction temperature are not particularly limited, but are usually performed over several hours to several days. If necessary, the temperature can be raised in multiple stages, or the temperature raising speed can be changed in the temperature range. Furthermore, the outer pressure-resistant container 3 can be heated by partially providing a temperature difference, or can be heated while being partially cooled.

  The “reaction temperature” is measured by the thermocouple 9 provided so as to be in contact with the outer surface of the pressure-resistant vessel 3 and can be approximated to the internal temperature of the reaction vessel 6. The temperature gradient in the inner direction of the reaction vessel 6 varies depending on the shape of the reaction vessel 6, the shape of the electric furnace 8 to be stored, and the heating and heat retention conditions represented by the positional relationship. As for the reaction temperature, a temperature gradient in the inner direction of the reaction vessel 6 is estimated using a hole opened inward from the outer surface of the pressure-resistant vessel 3 for the thermocouple 9 and does not penetrate to the cavity in the pressure-resistant vessel 3. Alternatively, it can be extrapolated and estimated from the temperature inside the reaction vessel 6. Similarly, the temperature in the vertical direction of the reaction vessel 6 also varies depending on the shape of the reaction vessel 6, the shape of the electric furnace 8 to be stored, and the heating and heat insulation conditions represented by the positional relationship. Therefore, as shown in FIG. 1, it is desirable to measure the temperature at several points above and below the outer surface of the pressure-resistant vessel 3 and to estimate the temperature inside the reaction vessel 6 at each position and perform temperature control. For example, depending on the shape of the reaction vessel 6 and the temperature maintaining condition, even if the temperature of the outer surface of the pressure-resistant vessel 3 is the same up and down, or the upper part is several tens of degrees Celsius, the temperature inside the reaction container 6 is several tens of degrees Celsius at the upper part. It can be low. In addition, as described above, in order to promote the transportation and folding of the raw materials by melting and thermal convection, when a vertical temperature gradient is provided in advance during the reaction, the temperature of several points on the outer surface of the pressure-resistant vessel 3 is measured. It is also effective to perform temperature control mainly divided in the vertical direction of the reaction vessel 6 using heaters divided in multiple stages.

  The reaction time after reaching a predetermined temperature varies depending on the type of nitride crystal, the raw material used, the type of mineralizer, and the size and amount of the crystal to be produced, but is usually several hours to several hundred days. be able to. During the reaction, the reaction temperature may be constant, or the temperature may be gradually raised or lowered. After a reaction time for producing desired crystals, the temperature is lowered. Although the temperature lowering method is not particularly limited, the heating may be stopped while the heater is stopped and the pressure-resistant vessel 3 containing the reaction vessel 6 is installed in the furnace as it is, or the pressure-resistant vessel containing the reaction vessel 6 may be used. 3 may be removed from the electric furnace 8 and air-cooled. If necessary, quenching with a refrigerant is also preferably used. In addition, depending on the partial precipitation of crystals at the time of cooling and additives such as a specific mineralizer, the pressure-resistant vessel 3 can be cooled with a partial temperature difference or partially fine to prevent the partial precipitation. It can also be cooled while heating.

  After the temperature of the outer surface of the pressure-resistant vessel 3 or the estimated temperature inside the reaction vessel 6 becomes equal to or lower than a predetermined temperature, the pressure-resistant vessel 3 is opened. The predetermined temperature at this time is not particularly limited, and is usually −80 ° C. to 200 ° C., preferably −33 ° C. to 100 ° C. When the solvent filled in the space between the reaction vessel 6 and the pressure-resistant vessel 3 is ammonia, first, the tip of the valve 1 attached to the outer pressure-resistant vessel 3 on the opposite side to the vessel side is first washed with water or the like. Open the attached valve 1 through a filled container. At this time, it may be performed through an inert gas. When the temperature in the pressure-resistant container 3 is sufficiently high, the ammonia solvent moves as a gas and is absorbed by water or the like. At this time, it is also preferable to heat the pressure-resistant container 3 again in order to shorten the moving time. It is also preferable to cool without filling water or the like in the container on the side where ammonia is moved. When a method of absorbing in a solvent such as water is not used, the recovered ammonia solvent can be easily reused. Further, after opening the attached valve 1, the solvent may be directly extracted and removed by a pump or the like.

  Further, if necessary, the solvent filled between the pressure-resistant vessel 3 and the reaction vessel 6 is sufficiently removed by making a vacuum or the like, and after drying, the lid of the pressure-resistant vessel 3 is opened and the reaction vessel 6 is taken out. You can also. Next, a pipe is connected to the pipe connection port 11 of the valve 4 attached to the reaction vessel 6, and the valve 4 is opened by passing through a vessel filled with water or the like. At this time, an inert gas may be used. When the temperature in the reaction vessel 6 is sufficiently high, the ammonia solvent moves as a gas and is absorbed by water or the like. At this time, it is also preferable to reheat the reaction vessel 6 in order to shorten the moving time. It is also preferable to cool the container on the moving side without filling it with water or the like. When the method of absorbing in a solvent such as water is not used, the recovered ammonia solvent can be easily reused. Alternatively, after the attached valve 4 is opened, the ammonia solvent may be directly extracted and removed by a pump or the like. In this method, when the ammonia solvent is removed, additives such as mineralizers dissolved in ammonia and unreacted raw materials can be removed at the same time.

  Further, if necessary, the ammonia solvent in the reaction vessel 6 is sufficiently removed by making a vacuum or the like, and then dried, and the nitride crystal produced by opening the lid of the reaction vessel 6 and the unreacted raw materials, Additives such as mineralizers can be removed.

As described above, the production method of the present invention has been described by taking as an example the case where nitride polycrystal is used as a raw material, but in principle, even if nitride polycrystal is not used as a raw material, a similar compound or a similar compound, In addition, it is possible to carry out the above method using a precursor that can be converted into them as a raw material. Examples of such compounds or precursors include compounds having a covalent MN bond such as galazane already listed in the production raw materials, metal amides such as Ga (NH ₂ ) _3, and alkalis such as KGa (NH ₂ ) _4. Examples include metal amides, metal imides, halogen salts such as GaCl ₃ , halide ammonia adducts, and halo metal salts such as ammonium halogallate. In addition, in the sense of avoiding the mixing of oxygen impurities, hydroxides, oxides, oxoacid salts, and the like can be used, although they should not be used actively.

  When trying to obtain a bulk nitride crystal using a raw material that is not the nitride polycrystal itself, it is necessary to simultaneously perform nitride synthesis and dissolution and precipitation of the nitride in a nitrogen-containing solvent. Stricter control of reaction conditions is required. When it is very difficult and it is desired to obtain larger lump crystals, a multistage production method can be suitably used. That is, similar to the nitride polycrystalline raw material as described above by a manufacturing method using a double container including an inner reaction container 6 made of noble metal represented by Pt of the present invention and an outer pressure-resistant container 3. Alternatively, a polycrystalline nitride is first produced under certain reaction conditions using a similar compound and a precursor that can be converted into the raw material, and then the polycrystalline nitride is used as a raw material in the same manner according to the production method of the present invention. Grow nitride crystals. In the case of using such a raw material, it is easy to produce a massive nitride crystal by this multi-stage method. At this time, the reaction divided into multiple stages may be performed as it is without removing ammonia or the like in the same reaction vessel, or may be performed by replacing with the same or different ammonia or mineralizer. The synthesized nitride polycrystalline raw material may be taken out once, subjected to treatment such as washing, and then filled into the same reaction vessel or another reaction vessel to grow nitride crystals. At that time, it is also possible to suitably use a seed crystal as described above.

As described above, impurities such as transition metals can be efficiently and safely mixed by a manufacturing method using a double vessel comprising a reaction vessel 6 and a pressure-resistant vessel 3 having at least an inner surface made of a noble metal. It is possible to produce a nitride crystal with a small amount. By the production method of the present invention, the inclusion of transition metal impurities in the produced nitride crystal can be normally suppressed to 0.1% by weight or less in terms of oxide. The bulk nitride crystals obtained by the present invention can be washed with hydrochloric acid (HCl), nitric acid (HNO ₃ ) or the like, if necessary. Also, the reaction vessel after removing the produced crystals and unreacted raw materials and additives such as mineralizers can be similarly washed when necessary.

  The cleaned nitride crystal is further sliced perpendicularly to a specific crystal plane depending on its orientation, and if necessary, it can be etched or polished to produce a nitride free-standing single crystal substrate. . The obtained nitride single crystal substrate has few impurities and high crystallinity, so that lattice defects and dislocation density are reduced and impurity levels are not formed, and in manufacturing various devices by VPE, MOCVD, etc. Excellent substrate for epitaxial growth. In particular, in the case of gallium nitride, industrial production of a high-quality single crystal substrate for homoepitaxial growth is not known. After epitaxial growth on the sapphire via a buffer layer or the like by a method such as VPE, a gallium nitride single crystal free-standing substrate can be manufactured even if the sapphire and the buffer layer are removed, but gallium nitride has a lattice constant and thermal expansion coefficient. Due to so-called heteroepitaxial growth on different substrates, lattice defects are likely to occur in the obtained gallium nitride, and in that respect, the gallium nitride crystal produced according to the present invention is from the viewpoint of lattice defects and dislocation density. Is also excellent.

  Furthermore, the nitride crystal produced according to the present invention and the one obtained by cutting, slicing, etching, and polishing the crystal are various kinds of solution growth methods including a solution growth method using an ammonia solvent, sublimation methods, and melt growth methods. A crystal is excellent because it has few impurities and high crystallinity.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. Materials, usage amounts, ratios, processing contents, processing procedures, processing apparatuses, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

Example 1
In this example, the manufacturing apparatus shown in FIG. 1 was used. Further, the valve attached to the reaction vessel has the structure shown in FIG.
A Pt reaction vessel (about 40 ml) with a valve, which is divided into upper and lower parts, is sufficiently dried, and in an inert gas atmosphere, a XRD (100) diffraction line (2θ = Approximately 32.5 °) half-width (2θ) is 0.17 ° or less, and the oxygen amount measured by LECO oxygen-nitrogen analyzer TC-436 is 0.2% by weight. 1.0 g of h-GaN (hexagonal gallium nitride) raw material was added. Further, 0.2 g of 99.995% NH ₄ Cl sufficiently dried as a mineralizer was placed in the reaction vessel 6. After installing a crystal growing part such as a Pt baffle plate, the upper and lower parts of the reaction vessel were quickly closed. Next, connect the pipe to the pipe connection port of the valve attached to the reaction vessel, operate the reaction vessel to communicate with the vacuum pump through the valve, open the valve and degas the vacuum, then react while maintaining the vacuum state The vessel was cooled with dry ice ethanol solvent and the valve was once closed. Then, after operating as leading to NH ₃ tank, again opening the valve, it was charged with 99.999% of NH ₃ without touching the open air continuously to the reaction vessel. Based on the flow rate control, NH ₃ was filled as a liquid corresponding to 60% of the hollow portion inside the reaction vessel (converted with an NH ₃ density of −33 ° C.), and then the valve was closed to seal the reaction vessel. Then, after returning the temperature of the reaction vessel to room temperature, the outer surface was sufficiently dried.

Subsequently, the reaction vessel was removed from the piping and placed in a pressure vessel made of Inconel, and the lid of the pressure vessel equipped with a valve was closed. Next, the pipe is connected to a vacuum pump through a valve attached to the pressure-resistant container, and after opening the valve and vacuum degassing, the pressure-resistant container is cooled with dry ice ethanol solvent while maintaining the vacuum state. Once the valve was closed. Then, after operating as leading to NH ₃ tank, again opening the valve, he was charged with NH ₃ without touching the open air continuously in the gap between the reaction vessel and the pressure vessel. Based on the flow rate control, NH ₃ was filled as a liquid corresponding to about 60% of the gap between the reaction vessel and the pressure-resistant vessel (converted to the NH ₃ density at −33 ° C.), and then the valve was closed to The temperature of the container was returned to room temperature, and the outer surface was sufficiently dried.

Subsequently, the pressure-resistant vessel including the reaction vessel therein was removed from the pipe and housed in an electric furnace composed of a heater that was divided into two vertically. The temperature was increased over 6 hours so that the temperature of the lower outer surface of the pressure-resistant container reached 530 ° C., and after the temperature of the lower outer surface of the pressure-resistant container reached 530 ° C., the temperature was further maintained for 72 hours. The pressure in the pressure resistant container was about 130 MPa. The temperature range during holding was ± 10 ° C. or less. Thereafter, heating by the heater was stopped and the mixture was naturally cooled in an electric furnace. After confirming that the temperature of the lower outer surface of the pressure-resistant container had dropped to almost room temperature, piping was connected to a valve attached to the pressure-resistant container. Then, after flowing the inert gas into the pipe portion not reactive vessel side of the valve, it opens the valve to remove NH ₃ in the gap portion between the reaction vessel and the pressure vessel. The valve was once closed and operated so as to be connected to the vacuum pump, and then the valve was opened again, so that NH _{3 in} the gap between the reaction vessel and the pressure-resistant vessel was almost completely removed. Thereafter, the pressure-resistant container was opened and the reaction container was removed.

Next, piping was connected so as to communicate with the inside of the reaction vessel through a valve attached to the reaction vessel, and after flowing an inert gas into the piping portion, the valve was opened, and NH ₃ in the reaction vessel was removed. Once the valve was closed and operated to communicate with the vacuum pump, the valve was opened again, and NH ₃ inside the reaction vessel was almost completely removed. Then, when the reaction container was opened and the inside was confirmed, about 0.3 g of massive gallium nitride crystals were deposited on the upper part of the reaction container.
The obtained gallium nitride crystal was taken out and subjected to X-ray diffraction measurement. As a result, the crystal form was hexagonal. The obtained gallium nitride crystal was finely pulverized, and the amount of oxygen measured with an oxygen-nitrogen analyzer TC-436 manufactured by LECO was 0.5% by weight or less. Moreover, when elemental analysis was performed with the Shimadzu EDX700 X-ray fluorescence spectrometer, only Ga was detected, and metal components heavier than Na other than Ga were below the detection limit.

(Example 2)
Precipitation of gallium nitride crystals was attempted in the same manner as in Example 1 except that the following conditions in Example 1 were changed. That is, a point where the weight of the polycrystalline h-GaN raw material is 3.0 g, a point where the weight of the mineralizer NH ₄ Cl is 0.96 g, and NH ₃ is 70% of the cavity inside the reaction vessel based on the flow rate control. % As liquid (corresponding to NH ₃ density of −33 ° C.) and NH ₃ as liquid corresponding to about 70% of the gap between the reaction vessel and pressure-resistant vessel based on flow rate control (converted as NH ₃ density at −33 ° C.) After conversion to the NH ₃ density of −33 ° C., the temperature of the lower outer surface of the pressure-resistant container is raised to 500 ° C. over 6 hours, and the temperature of the lower outer surface of the pressure-resistant container reaches 500 ° C. The conditions were changed for the point held at that temperature for a further 72 hours.
As a result, as in Example 1, about 0.3 g of massive gallium nitride crystals were deposited on the top of the reaction vessel.
As in Example 1, the obtained gallium nitride crystal was taken out and subjected to X-ray diffraction measurement. As a result, the crystal form was a hexagonal type. The obtained gallium nitride crystal was finely pulverized, and the amount of oxygen measured with an oxygen-nitrogen analyzer TC-436 manufactured by LECO was 0.5% by weight or less. Moreover, when elemental analysis was performed with the Shimadzu EDX700 X-ray fluorescence spectrometer, only Ga was detected, and metal components heavier than Na other than Ga were below the detection limit.

(Comparative Example 1)
As a comparative example of Example 1, in order to demonstrate the effect of using a Pt reaction vessel, only an Inconel pressure resistant vessel was used without using a Pt reaction vessel. The polycrystalline h-GaN (hexagonal gallium nitride) raw material sufficiently dried as in the examples as a raw material in the lower part of the pressure resistant container in an inert gas atmosphere after sufficiently drying the pressure resistant container 1.0 g was added. Furthermore, 0.2 g of 99.995% NH ₄ Cl sufficiently dried as a mineralizer was added. After a structure such as a Pt baffle plate was installed, the pressure resistant container was closed.

Subsequently, piping was connected to a valve attached to the pressure resistant container, and 99.999% NH ₃ was filled in the pressure resistant container in the same procedure as in the example. Based on the flow rate control, NH ₃ was filled as a liquid corresponding to 60% of the cavity of the pressure-resistant container (converted with an NH ₃ density of −33 ° C.), and then the valve was closed to seal the pressure-resistant container. Next, the temperature of the pressure-resistant container was returned to room temperature, and the outer surface was sufficiently dried.

The temperature was raised and the reaction was carried out under the same conditions as in the examples, and the mixture was naturally cooled in the furnace. After confirming that the temperature of the outer surface of the lower part of the pressure-resistant container had dropped to substantially room temperature, NH ₃ inside the pressure-resistant container was almost completely removed by the same procedure as in the example. Thereafter, when the pressure resistant container was opened and the inside was confirmed, about 0.2 g of massive gallium nitride crystals were deposited on the pressure resistant container.

  When the X-ray diffraction was measured, the crystal form was hexagonal, but it became a broad peak and the crystallinity was lowered. When elemental analysis was performed with Shimadzu EDX700 X-ray fluorescence spectrometer, Cr, Fe, Ni, and Ta were detected as metal components heavier than Na other than Ga, and in particular, Cr was detected as 0.1% by weight in terms of oxide. It was done.

(Comparative Example 2)
As a comparative example of Example 2, in order to demonstrate the effect of using a Pt reaction vessel, Example 2 was used except that only a Inconel pressure vessel was used without using a Pt reaction vessel. In the same manner as described above, precipitation of gallium nitride crystals was attempted.
As a result, as in Comparative Example 1, about 0.2 g of massive gallium nitride crystal was deposited on the top of the pressure resistant container.
Further, as in Comparative Example 1, the crystal form was a hexagonal type, but it became a broad peak and the crystallinity was lowered. When elemental analysis was performed with Shimadzu EDX700 X-ray fluorescence spectrometer, Cr, Fe, Ni, and Ta were detected as metal components heavier than Na other than Ga, and in particular, Cr was detected as 0.1% by weight in terms of oxide. It was done.

From the results of Examples 1 and 2 and Comparative Examples 1 and 2, the nitride crystals (Examples 1 and 2) obtained by the method of the present invention are nitride crystals obtained by the methods of Comparative Examples 1 and 2. It can be seen that the crystallinity is higher and the quality is lower with less impurities.
Further, the gallium nitride crystal obtained by the method of the present invention is 1) the content of transition metal components such as Cr, Fe, Ni and Ta is 0.1% by weight or less, and 2) the oxygen content is 0.5% by weight. It can also be seen that it has a characteristic of less than

  The nitride crystal obtained by the manufacturing method of the present invention has few impurities and high crystallinity, so that lattice defects and dislocation density are reduced and impurity levels are not formed, and various devices are manufactured by VPE, MOCVD, etc. In doing so, it can be used as a substrate for epitaxial growth.

DESCRIPTION OF SYMBOLS 1 Valve 2 Pressure gauge 3 Pressure-resistant container 4 Valve 5 Crystal growth part 6 Reaction container 7 Raw material filling part 8 Electric furnace 9 Thermocouple 10 Seed crystal 11 Pipe connection port 12 Packing ring

Claims (11)

At least the inner surface is made of precious metal, and the reaction vessel with at least one valve is filled with raw materials and ammonia solvent, and the reaction vessel is sealed, and then the reaction vessel is inserted into the pressure-resistant vessel And filling the space between the reaction vessel and the pressure-resistant vessel with a second solvent selected from ammonia solvent, water, alcohol, or carbon dioxide , sealing the pressure-resistant vessel, and then raising the temperature. A method for producing a nitride crystal, comprising obtaining a nitride crystal by:   The manufacturing method according to claim 1, wherein the second solvent is an ammonia solvent. 3. The method according to claim 1, wherein the ammonia solvent in the reaction vessel is maintained in a subcritical state or a supercritical state. The manufacturing method according to any one of claims 1 to 3 , wherein at least the inside of the pressure-resistant container is held at 20 to 500 MPa. The process according to any one of claims 1 to 4, characterized in that to hold at least the pressure-resistant vessel 20～400MPa. The manufacturing method according to any one of claims 1 to 5 , wherein at least the inside of the pressure-resistant container is heated to 200 to 700 ° C. The process according to any one of claims 1 to 6, wherein adding at least one additive into said reaction vessel. The manufacturing method according to claim 7 , wherein the additive contains at least one halogen atom. The process according to any one of claims 1 to 8, characterized in that the oxygen content in said raw material is not more than 5 wt%. The manufacturing method according to any one of claims 1 to 9 , wherein the raw material contains gallium nitride. The nitride crystal according to any one of claims 1 to 10 , wherein at least one kind of seed crystal is installed in the reaction vessel, and a raw material dissolved in an ammonia solvent is deposited on the seed crystal. Manufacturing method.

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