JP2013203652A - Method for producing nitride single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a nitride single crystal capable of obtaining a high-purity crystal, while preventing corrosion of a member used for the reaction vessel surface and the reaction vessel interior.SOLUTION: When a crystal is grown in a reaction vessel in a supercritical state and/or in a subcritical state under a nitrogen-containing solvent atmosphere, Ni is used for at least a part of the surface of a member used for the reaction vessel surface and the reaction vessel interior, and a fluorine-based mineralizing agent, which is a mineralizing agent not containing a halogen atom other than fluorine, is used as the mineralizing agent.

Description

  The present invention relates to a method for producing a nitride single crystal. In particular, the present invention relates to a production method useful when producing a nitride crystal of Group 13 element of the periodic table.

  The ammonothermal method is a method of producing a desired material using a dissolution-precipitation reaction of raw materials using a nitrogen-containing solvent such as ammonia in a supercritical state and / or a subcritical state. When applied to crystal growth, a crystal is precipitated by generating a supersaturated state due to a temperature difference using the temperature dependence of the raw material solubility in an ammonia solvent. Specifically, raw materials and seed crystals are placed in a reaction container such as a pressure-resistant container such as an autoclave or a capsule and sealed, and heated with a heater or the like installed inside or outside the reaction container, so that a high temperature region and a low temperature are contained in the reaction container. A desired crystal can be produced by forming a zone, dissolving the raw material on one side, and growing the crystal on the other side.

For example, gallium nitride (GaN) crystal growth by the ammonothermal method is a reaction in a supercritical state at high temperature and high pressure (500 ° C. or higher, 150 MPa or higher). Are naturally limited. Moreover, since the solubility of gallium nitride in a nitrogen-containing solvent such as pure ammonia in a supercritical state is extremely small, a mineralizer is generally added to improve the solubility and promote crystal growth. Mineralizers are acidic mineralizers typified by ammonium halide NH ₄ X (X = F, Cl, Br, I) and basic minerals typified by alkali amide XNH ₂ (X = Li, Na, K). It is classified as an agent. The environment of the nitrogen-containing solvent in the supercritical state and / or subcritical state containing these mineralizers is an extremely severe corrosive environment. For this reason, it is necessary to design an apparatus and select a material having sufficient corrosion resistance even in such an environment.

  For example, in GaN crystal growth by an ammonothermal method using an acidic mineralizer, it is possible to increase the purity of the crystal by using Pt in the reaction vessel. However, since Pt is expensive, it is necessary to design an apparatus using other materials in order to manufacture at a reduced cost industrially. Therefore, it has been proposed to use Cu, Ag, Mo, Fe, Ta as the lining material of the capsule used in the apparatus, and to use Ti, Fe, Co, Cr, Ni as the autoclave material (Patent Document 1). To 6).

JP-T-2006-513122 JP 2010-222247 A International Publication WO2003 / 97906 JP 2007-56320 A Japanese Patent Laid-Open No. 2004-2152 JP 2010-222152 A

  As described above, various materials have been proposed as materials constituting autoclaves and capsules. However, mineralization is possible even if GaN crystal growth is attempted by the ammonothermal method by selecting materials as described in the patent literature. It was found that corrosion of the autoclave and capsules could not be prevented sufficiently depending on the type of agent and growth conditions. Accordingly, the present inventors proceeded with studies for the purpose of providing a method capable of obtaining a high-purity nitride single crystal while preventing corrosion of the reaction vessel surface and the members used inside the reaction vessel. It was.

  As a result of intensive studies to solve the above problems, the present inventors have formed at least a part of the surface inside the reaction vessel used for crystal growth and the surface of the member used inside the reaction vessel with a metal containing Ni. Furthermore, by limiting the halogen contained in the mineralizer to be used to those containing only fluorine, a fluorine-containing film is formed on the surface of the reaction vessel and the surface of the member used inside the reaction vessel. It was found that corrosion of the container surface and the like was prevented, and high purity of the crystal was achieved. In particular, the manufacturing method of the present invention is advantageous in terms of cost compared to a manufacturing method using Pt because impurities can be reduced without using a noble metal such as Pt.

  That is, said subject is solved by the manufacturing method of the nitride single crystal of the following this invention.

[1] A crystal growth step in which crystal growth is performed using a mineralizer in a nitrogen-containing solvent atmosphere in a supercritical state and / or a subcritical state in a reaction vessel, which is used on the reaction vessel surface and inside the reaction vessel A method for producing a nitride single crystal characterized in that Ni is contained in at least a part of the surface of a member to be formed, and the mineralizer is a fluorine-based mineralizer and does not contain a halogen atom other than fluorine. .
[2] The nitride single crystal according to [1], wherein at least a part of the surface of the reaction vessel and the surface of a member used inside the reaction vessel is a Ni-based alloy having a Ni content exceeding 40% by mass. Manufacturing method.
[3] The nitride single crystal according to [1], wherein at least a part of the surface of the reaction vessel and the surface of a member used inside the reaction vessel is a Ni-based alloy having a Ni content exceeding 50% by mass. Manufacturing method.
[4] In any one of [1] to [3], the carbon content of at least a part of the surface of the reaction vessel and the surface of a member used inside the reaction vessel is 0.2% by mass or less. The manufacturing method of the nitride single crystal of description.
[5] In any one of [1] to [4], the Fe content of at least a part of the surface of the reaction vessel and the surface of a member used inside the reaction vessel is 2.5% by mass or less. The manufacturing method of the nitride single crystal of description.
[6] At least a part of the surface of the reaction vessel and the surface of a member used inside the reaction vessel contains at least one selected from Cr, Al, Ti, Nb, V, W, and Mo. The method for producing a nitride single crystal according to any one of [5].
[7] The method for producing a nitride single crystal according to any one of [1] to [6], wherein the crystal growth step is performed a plurality of times.

[8] A method for producing a nitride single crystal including a crystal growth step in which crystal growth is performed using a mineralizer in a supercritical and / or subcritical nitrogen-containing solvent atmosphere in a reaction vessel, the reaction vessel A method for producing a nitride single crystal, wherein the surface and at least a part of the surface of a member used inside the reaction vessel are coated with a fluorine-containing film.
[9] The method for producing a nitride single crystal according to [8], wherein the fluorine-containing coating has a thickness of 5 nm to 50 μm.
[10] At least part of the surface of the reaction vessel and the surface of the member used inside the reaction vessel is a Ni-based alloy having a Ni content exceeding 40% by mass, according to [8] or [9]. A method for producing a nitride single crystal.
[11] The surface of the reaction vessel and at least a part of the surface of a member used inside the reaction vessel are a Ni-based alloy having a Ni content exceeding 50% by mass, according to [8] or [9]. A method for producing a nitride single crystal.
[12] In any one of [8] to [11], the carbon content of at least a part of the surface of the reaction vessel and the surface of a member used inside the reaction vessel is 0.2% by mass or less. The manufacturing method of the nitride single crystal of description.
[13] In any one of [8] to [12], the Fe content of at least a part of the surface of the reaction vessel and the surface of a member used inside the reaction vessel is 2.5% by mass or less. The manufacturing method of the nitride single crystal of description.
[14] At least part of the surface of the reaction vessel and the surface of the member used inside the reaction vessel contains at least one selected from Cr, Al, Ti, Nb, V, W, and Mo. [13] The method for producing a nitride single crystal according to any one of [13].
[15] The method for producing a nitride single crystal according to any one of [8] to [14], wherein the crystal growth step is performed a plurality of times.
[16] The method for producing a nitride single crystal according to any one of [8] to [15], wherein the film forming step is simultaneously performed in at least a part of the crystal growth step.

  According to the production method of the present invention, it is possible to prevent corrosion of the reaction vessel surface and the members used inside the reaction vessel, and to obtain high purity crystals.

It is a schematic diagram of the crystal manufacturing apparatus which can be used by this invention.

  Hereinafter, a method for producing a nitride single crystal of the present invention, and a crystal production apparatus and members used therefor will be described 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 method for producing a nitride single crystal according to the first aspect of the present invention (hereinafter simply referred to as “first production method”) comprises a mineral in a nitrogen-containing solvent atmosphere in a supercritical state and / or a subcritical state in a reaction vessel. A crystal growth step of performing crystal growth using an agent, Ni is included in at least a part of the reaction vessel surface and the surface of a member used inside the reaction vessel, and the mineralizer is a fluorine-based mineral. It is an agent and does not contain a halogen atom other than fluorine.
In addition, the method for producing a nitride single crystal of the second aspect of the present invention (hereinafter simply referred to as “second production method”) includes a nitrogen-containing solvent atmosphere in a supercritical state and / or a subcritical state in a reaction vessel. A crystal growth step in which crystal growth is performed using a mineralizer, and a film formation step of forming a fluorine-containing film on at least a part of the reaction vessel surface and the surface of a member used inside the reaction vessel, Ni is contained in at least a part of the surface of the reaction vessel and the surface of the member used inside the reaction vessel.
Further, the third method for producing a nitride single crystal of the present invention (hereinafter simply referred to as “third production method”) is a mineral containing nitrogen in a supercritical and / or subcritical nitrogen-containing solvent atmosphere in a reaction vessel. A method for producing a nitride single crystal including a crystal growth step in which crystal growth is performed using an agent, wherein at least a part of the reaction vessel surface and the surface of a member used inside the reaction vessel is a fluorine-containing film. It is covered.
Hereinafter, unless otherwise specified, the “production method of the present invention” means that includes all of the first production method, the second production method, and the third production method.

The first production method includes at least a crystal growth step, but by using only a fluorine-based mineralizer containing no halogen atom other than fluorine as the mineralizer, the reaction vessel surface containing Ni and the reaction vessel A fluorine-containing film can be formed on at least a part of the surface of the member used inside.
Similarly, in the second manufacturing method, in addition to the crystal growth step, a film forming step of forming a fluorine-containing film on at least part of the surface of the reaction vessel containing Ni and the surface of a member used inside the reaction vessel. Is included. As described above, the fluorine-containing coating is a coating formed on the reaction vessel surface containing Ni or the like. Each of these steps may be performed separately and sequentially. Further, as a method for producing a nitride single crystal, it is preferable to simultaneously perform the film forming step in at least a part of the crystal growth step because the time required for the entire step can be shortened.
In the third production method, the crystal growth is performed in a reaction vessel in which at least a part of the reaction vessel surface and the surface of a member used inside the reaction vessel is coated with the fluorine-containing coating.
Moreover, in the manufacturing method of this invention, you may implement a crystal growth process and / or a film formation process in multiple times. Even if the crystal growth step and / or the film formation step are performed a plurality of times, the fluorine-containing coating formed on at least a part of the surface inside the reaction vessel and the surface of the member used inside the reaction vessel exists stably. Therefore, since the reaction vessel and / or member can be used for a long time without being corroded, the productivity is greatly improved.

  The production method of the present invention is a method for producing a desired material using a dissolution-precipitation reaction of raw materials using a nitrogen-containing solvent in a supercritical state and / or a subcritical state, and is generally an ammonothermal method. (Hereinafter, also referred to as ammonothermal method in this specification). Specifically, when applied to crystal growth, it is a method in which crystals are precipitated by generating a supersaturated state due to a temperature difference utilizing the temperature dependence of the raw material solubility in a nitrogen-containing solvent such as ammonia.

  The nitride single crystal obtained by the production method of the present invention is not particularly limited, but a single metal nitride single crystal of a group 13 element of the periodic table such as Al, Ga, In or the like is preferable. Examples of the periodic table group 13 metal nitride single crystal include GaN, AlN, InN, and the like, and alloy group nitride single crystals such as GaInN and GaAlN are also included. Of these, the present invention is particularly suitable for obtaining a metal nitride single crystal containing Ga.

(Crystal production equipment)
Each step of the present invention is performed using a crystal production apparatus in which a reaction vessel for crystal growth is installed in a nitrogen-containing solvent atmosphere in a supercritical state and / or a subcritical state at least in a pressure resistant vessel. Is called. At least a part of the surface inside the reaction vessel and the surface of the member used inside the reaction vessel is coated with a fluorine-containing coating. The details of the fluorine-containing coating will be described in detail in the section of the coating forming process.

(Reaction vessel)
“Reaction vessel” means a vessel for producing a nitride crystal in a state in which a nitrogen-containing solvent in a supercritical state and / or a subcritical state can be in direct contact with its inner wall surface. Preferred examples include the structure itself and capsules installed in a pressure-resistant container.

The pressure-resistant container used in the present invention is selected from those that can withstand high-temperature and high-pressure conditions when a nitride crystal is grown by an ammonothermal method. In the production method of the present invention, Ni is contained in at least a part of the surface of the reaction vessel and the surface of the member used inside the reaction vessel. That is, the reaction vessel or the like is preferably made of a metal containing Ni, and is preferably made of a Ni-based alloy having excellent corrosion resistance against a nitrogen-containing solvent such as ammonia. More preferred is a Ni-based alloy. As the metal containing Ni, pure Ni (Ni200, Ni201, etc.) having a carbon content of 0.2% by mass or less; Fe and Co as impure elements having a Ni content of 40% by mass or more and 5% by mass The following Ni-based alloys (for example, Inconel 625, etc. (Inconel is a registered trademark of Huntington Alloys Canada Limited, the same shall apply hereinafter); Ni-Cu alloys having a Ni content of 40% by mass or more (Monel 400, etc.) may be mentioned. The base alloy may contain Cr, Al, Ti, Nb, and V that form nitrides in a supercritical NH ₃ environment, and may further contain W and Mo as solid solution strengthening elements.

  The pure Ni includes “Ni200” having a carbon content of 0.2% by mass or less, “Ni201” having an extremely low carbon content, and the like. The Ni used in the present invention is preferably a very low carbon grade. Ni having a low carbon content is preferable because it is difficult for age-induced embrittlement to occur, and even when the temperature is about 500 to 600 ° C., carbon does not precipitate as a graphite at grain boundaries and tends to be brittle as a material.

  Examples of the Ni-based alloy include Ni—Cr, Ni—Cr—Mo, and Ni—Cr—W alloys in which the Fe content is preferably limited to 7% by mass or less, and more preferably 5% by mass or less. . In addition, the Ni-based alloy is a Ni-based alloy having an Fe content of 5.0% by mass or less and a Co content of 2.0% by mass or less from the viewpoint of suppressing selective elution of Fe and Co in a fluorine environment. Is preferred.

  From the above viewpoint, the Ni-containing metal is preferably a Ni-based alloy with a Ni content exceeding 40% by mass, more preferably a Ni-based alloy with a Ni content exceeding 45% by mass, A Ni-based alloy having a content exceeding 50% by mass is particularly preferable.

  The carbon content of at least part of the metal containing Ni, that is, the surface of the reaction vessel containing the metal and the surface of the member used inside the reaction vessel is 0.2% by mass or less from the viewpoint of embrittlement. Preferably, it is preferably 0.1% by mass or less, particularly preferably 0.05% by mass or less.

  The Fe content of the metal containing Ni, that is, the surface of the reaction vessel containing the metal and the surface of the member used inside the reaction vessel is 8.0 mass from the viewpoint of reactivity with fluorine. % Or less, more preferably 5.0% by mass or less, and particularly preferably 2.0% by mass or less.

  Co content of at least part of the metal containing Ni, that is, the surface of the reaction vessel containing the metal and the surface of the member used inside the reaction vessel is 8% by mass or less from the viewpoint of reactivity with fluorine. It is preferably 5% by mass or less, more preferably 3% by mass or less.

For example, the metal containing Ni used for the surface of the reaction vessel or the like preferably has a Fe concentration of 1 × 10 ¹⁹ atoms / cc by SIMS analysis, and the purity of Ni is preferably on the 17th power.

At least a part of the metal containing Ni, that is, the surface of the reaction vessel containing the metal and the surface of the member used inside the reaction vessel is selected from Cr, Al, Ti, Nb, V, W, and Mo. It is preferable to include at least one kind. That is, when the Ni-based alloy is used, it may contain Cr, Al, Ti, Nb, and V that form nitrides in a supercritical NH ₃ environment, and further, W, You may contain Mo.

  The composition ratio of these alloys depends on the temperature and pressure conditions of the solvent in the system, and the reactivity with mineralizers contained in the system and their reactants and / or the oxidizing power / reducing power, pH, etc. It may be selected as appropriate. Although the alloys used for these pressure resistant containers have high corrosion resistance, they do not have such high corrosion resistance that they have no influence on the crystal quality. In these alloys, Ni, Cr, Fe and other components are dissolved in the solution and incorporated into the crystals in a supercritical and / or subcritical nitrogen-containing solvent atmosphere, particularly in a more severe corrosive environment containing a mineralizer. Will be. Therefore, in the present invention, in order to suppress internal corrosion of these pressure-resistant containers, the inner surface of the reaction container is covered with a fluorine-containing coating by limiting the mineralizer used to a mineralizer containing only fluorine as a halogen.

  The form of the reaction vessel is not particularly limited, but in the method of directly lining or coating the inner surface of the pressure resistant vessel, it is difficult to line or coat all surfaces that can come into contact with the nitrogen-containing solvent inside the reaction vessel. Therefore, a method in which capsules made of a material having excellent corrosion resistance are arranged in a pressure resistant container is mentioned as a more preferable embodiment. However, since pure Ni is soft and rich in workability, a reaction vessel can be easily formed by lining the inner surface of the vessel to a thickness of about 0.5 mm. It is also possible to change the lining once every few years.

  The shape of the reaction vessel can be any shape including a cylindrical shape. Further, the reaction vessel may be used standing upright, horizontally or diagonally.

(Element)
The production method of the present invention is generally performed in a state where members are installed inside the reaction vessel. The “member” as used herein means a member that is installed in a container when producing a nitride crystal by the ammonothermal method and can be separated from the reaction container. For example, a growth frame for holding the seed crystal, a baffle plate for controlling the convection of the solution, a raw material basket, a wire for hanging the seed crystal, and the like can be used. In the present invention, the surfaces of these members are also preferably covered with the material having excellent corrosion resistance as described above.

A specific example of a crystal production apparatus including a reaction vessel that can be used in the production method of the present invention is shown in FIG. FIG. 1 is a schematic view of a crystal manufacturing apparatus that can be used in the present invention. The crystal manufacturing apparatus shown in FIG. 1 is an apparatus that performs crystal growth in an autoclave, but an apparatus that performs crystal growth in a capsule (reaction vessel) loaded as an inner cylinder in the autoclave may be adopted. The autoclave shown in FIG. 1 includes a raw material melting region 1 for melting raw materials and a crystal growth region 2 for growing crystals. A solvent and a mineralizer can be placed in the raw material dissolution region 1 together with the raw material 4, and a seed crystal 6 can be installed in the crystal growth region 2 by suspending it with a wire. Between the raw material melting region 1 and the crystal growth region 2, a partition baffle plate 5 is installed in two regions. The baffle plate 5 has a hole area ratio of preferably 2 to 60%, more preferably 3 to 40%. The material of the surface of the baffle plate 5 is preferably the same as the material of the capsule 20 that is a reaction vessel. Further, in order to give more corrosion resistance and to purify the crystal to be grown, the surface of the baffle plate 5 is made of Ni, Ta, W, Mo, Ti, Nb, Pd, Pt, Au, Ir, and pBN. It is preferable that Ni, Pd, Pt, Au, Ir, and pBN are more preferable, and a metal containing Ni is particularly preferable.
When crystal growth is performed in a capsule (reaction vessel) loaded as an inner cylinder in the autoclave, the gap between the inner wall of the autoclave and the outer wall of the capsule can be filled with the second solvent. Then, it is possible to fill with ammonia as the second solvent while filling nitrogen gas from a nitrogen cylinder through a valve or checking the flow rate from an ammonia cylinder with a mass flow meter. Moreover, the required pressure reduction can be performed by a vacuum pump. It should be noted that a valve, a mass flow meter, and a conduit do not necessarily have to be installed in the crystal manufacturing apparatus used when the nitride single crystal manufacturing method is carried out.

Hereafter, each process of the manufacturing method of this invention is demonstrated in detail.
The crystal growth step is a step of performing crystal growth in a nitrogen-containing solvent atmosphere in a supercritical state and / or a subcritical state in a reaction vessel.

(Crystal growth process)
The “ammonothermal method” is a method for producing a desired material using a dissolution-precipitation reaction of raw materials using a nitrogen-containing solvent such as ammonia in a supercritical state and / or a subcritical state. When the ammonothermal method is applied to crystal growth, a crystal is precipitated by generating a supersaturated state due to a temperature difference utilizing the temperature dependence of the solubility of the raw material in a nitrogen-containing solvent such as ammonia.
Crystal growth by the ammonothermal method is a reaction in a high-temperature and high-pressure supercritical nitrogen-containing solvent environment, and the solubility of gallium nitride and the like in a nitrogen-containing solvent such as pure ammonia in a supercritical state is extremely small. Mineralizers can be used to improve solubility and promote crystal growth. The crystal growth is performed, for example, by placing a raw material, a seed crystal, and a solvent containing nitrogen in a reaction vessel, and raising the temperature in the reaction vessel to the growth temperature of the nitride single crystal.

(Seed crystal)
As the seed crystal, a single crystal of nitride grown as a growth crystal can be used. Specific examples of the seed crystal include nitride single crystals such as gallium nitride (GaN) and aluminum nitride (AlN).
The seed crystal can be determined in consideration of solubility in a solvent and reactivity with a mineralizer. For example, as a seed crystal of GaN, a single crystal obtained by epitaxial growth on a heterogeneous substrate such as sapphire and then exfoliated, a single crystal obtained by crystal growth of Na, Li, and Bi from metal Ga as a flux, a liquid phase A single crystal obtained by homo / heteroepitaxial growth obtained by using an epitaxy method (LPE method), a single crystal produced based on a solution growth method, a crystal obtained by cutting them, and the like can be used. The specific method of the epitaxial growth is not particularly limited, and for example, a hydride vapor phase growth method (HVPE) method, a metal organic chemical vapor deposition method (MOCVD method), a liquid phase method, an ammonothermal method, or the like is adopted. be able to.

(Mineralizer)
The mineralizer is a fluorine-based mineralizer and does not contain halogen atoms other than fluorine. That is, only a mineralizer containing only a fluorine atom as a halogen element is used. Examples of mineralizers that contain only fluorine atoms as halogen elements include ammonium fluoride, hydrogen fluoride, and hydrocarbyl ammonium fluoride, tetramethylammonium fluoride, tetraethylammonium fluoride, and benzyltrimethylammonium fluoride. And alkyl ammonium salts such as dipropylammonium fluoride and isopropylammonium fluoride, alkyl fluoride metals such as sodium alkyl fluoride, alkaline earth metal fluorides, metal fluorides and the like. Of these, alkali fluoride, alkaline earth metal fluoride, metal fluoride, ammonium fluoride, and hydrogen fluoride are preferred, and alkali fluoride, ammonium fluoride, and group 13 metal fluoride of the periodic table are more preferred. Particularly preferred are ammonium fluoride (NH ₄ F) and gallium fluoride.

  The amount of the mineralizer used in the ammonothermal method is preferably such that the molar concentration of fluorine contained in the mineralizer with respect to the nitrogen-containing solvent is 0.1 mol% or more, more preferably 0.3 mol% or more, and 0.5 mol. % Or more is more preferable. The molar concentration of fluorine contained in the mineralizer with respect to the nitrogen-containing solvent is preferably 30 mol% or less, more preferably 20 mol% or less, and even more preferably 10 mol% or less. If the concentration is too low, the solubility tends to decrease and the growth rate tends to decrease. On the other hand, when the concentration is too high, the solubility tends to be too high and the generation of spontaneous nuclei increases, or the degree of supersaturation becomes too high and control tends to be difficult.

In addition, the fluorine concentration in the crystal in the crystal growth step is preferably 1 × 10 ¹⁷ atoms / cc or less because the fluorine does not corrode the apparatus when the obtained crystal is used as a device manufacturing substrate. 5 × 10 ¹⁶ atoms / cc or less atoms / cc or less is more preferable, but 1 × 10 ¹⁶ atoms / cc or less is particularly preferable.

(solvent)
As the solvent used in the ammonothermal method, a nitrogen-containing solvent can be used. Examples of the nitrogen-containing solvent include solvents that do not impair the stability of the grown nitride single crystal. Examples of the solvent include ammonia, hydrazine, urea, amines (for example, primary amines such as methylamine, secondary amines such as dimethylamine, tertiary amines such as trimethylamine, and ethylenediamine. Diamine) and melamine. These solvents may be used alone or in combination.
The amount of water and oxygen contained in the solvent is desirably as small as possible, and the content thereof is preferably 1000 ppm or less, more preferably 10 ppm or less, and further preferably 0.1 ppm or less. When ammonia is used as a solvent, the purity is usually 99.9% or more, preferably 99.99% or more, and more preferably 99.999% or more.

(material)
As a raw material, a raw material containing an element constituting a nitride single crystal to be grown on a seed crystal can be used. Preferred is a polycrystalline raw material of nitride single crystal and / or a metal to be nitrided, and more preferred is gallium nitride and / or metallic gallium. The polycrystalline raw material does not need to be a complete nitride, and may contain a metal component in which the group III element is in a metal state (zero valence) depending on conditions. For example, when the crystal is gallium nitride Is a mixture of gallium nitride and metal gallium.
The method for producing the polycrystalline raw material is not particularly limited. For example, a metal 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, a metal nitride polycrystal produced by reacting a metal such as Ga with nitrogen at high temperature and pressure can also be used.
The amount of water and oxygen contained in the polycrystalline raw material used as the raw material in the present invention is preferably small. The oxygen content in the polycrystalline raw material is usually 10,000 ppm or less, preferably 1000 ppm or less, particularly preferably 1 ppm or less. The ease of mixing oxygen into the polycrystalline raw material is related to the reactivity with water or the absorption capacity. The worse the crystallinity of the polycrystalline raw material, the more active groups such as NH groups exist on the surface, which may react with water and partially generate oxides or hydroxides. For this reason, it is usually preferable to use a polycrystalline material having as high crystallinity as possible. The crystallinity can be estimated by the half width of powder X-ray diffraction. The half width of the (100) diffraction line (2θ = about 32.5 ° for hexagonal gallium nitride) is usually 0.25 ° or less, preferably It is 0.20 ° or less, more preferably 0.17 ° or less.

The growth rate of crystal growth is preferably 50 μm / day or more, more preferably 100 μm / day or more, and particularly preferably 150 μm / day or more from the viewpoint of cost reduction by mass production.
The oxygen concentration in the reaction vessel in the crystal growth step is about the 18th power, which is about 1/100 of that in the case of using the same autoclave containing iodine as a mineralizer. That is, as described above, the purity of the grown crystal can be improved by using only the fluorine-containing mineralizer containing only fluorine as the halogen as the mineralizer.

  In the crystal growth step, as the reaction time when growing the nitride single crystal by the ammonothermal method, since the seed crystal may be dissolved at the initial stage of the crystal growth step, the growth of a crystal larger than the seed crystal, From the viewpoint of use as a substrate for various devices, the lower limit can be 6 hours or more, further 12 hours or more, and further 24 hours or more. Similarly, from the viewpoint of preventing dissolution of seed crystals due to depletion of raw materials, the upper limit of the growth temperature can be 2400 hours or less, can be further 2160 hours or less, and can be further 1440 hours or less. .

  In the crystal growth step, as the growth pressure when growing the nitride single crystal by the ammonothermal method, the lower limit can be set to 3 MPa or more from the viewpoint that the growth rate can be increased. It can be set to 5 MPa or more, and further can be set to 10 MPa or more. Similarly, the upper limit of the reaction pressure can be 250 Pa or less, more preferably 200 Pa or less, from the viewpoint of facilitating the production of a pressure-resistant container or easy handling in production. It can be 150 Pa or less.

  In the crystal formation step, the growth temperature for growing a nitride single crystal by the ammonothermal method is that crystal growth can be performed in a region where the crystal growth region is 300 ° C. or higher. And the lower limit is preferably set to 500 ° C. or higher, more preferably 550 ° C. or higher, and 580 ° C. or higher. It is preferable to set it as ° C or more. Similarly, the upper limit of the growth temperature can be set to 650 ° C. or lower and can be further set to 630 ° C. or lower from the viewpoint of easy manufacture of the pressure-resistant container and easy handling in manufacturing. Furthermore, it can be set to 620 ° C. or lower.

(Film formation process)
The coating forming step is a step of forming a fluorine-containing coating on at least a part of the surface inside the reaction vessel and the surface of the member used inside the reaction vessel. In the first production method, a fluorine-containing film can be formed on the surface of the reaction vessel or the like by using only a fluorine-based mineralizer containing only fluorine as a halogen in the growth step. In this case, when replaced with the second manufacturing method, the film forming process is simultaneously performed in the crystal growth process as described above.

  When a fluorine-containing film is formed on the surface inside the reaction vessel containing Ni in the film formation step, it is presumed that it functions as a passive film, and the surface inside the reaction vessel is supercritical and / or subcritical. It is possible to effectively suppress corrosion underneath. Thus, the growth crystal can be highly purified by preventing the corrosion of the surface in the reaction vessel. For this reason, the crystal | crystallization (semiconductor) obtained by the manufacturing method of this invention has high transparency.

The thickness of the fluorine-containing coating is preferably 5 nm to 50 μm. In particular, since the fluorine-containing film is stable in the crystal growth process and the like, and is performed in an automatic repair environment, a thick film is not particularly required, and the film may be about the outermost surface (10-100 nm) of the material. That's fine. Further, for example, a fluorine-containing film such as NiF ₂ has an extremely low vapor pressure in a high temperature range as compared with fluorinated Fe, fluorinated Cr and fluorinated Co, and is stably present as a solid NiF ₂ film. Is unlikely to occur. In contrast, Ni chloride, Cr chloride, Fe chloride, or Ni iodide, Fe iodide, Cr iodide produced in a chlorine or iodine environment has a high vapor pressure and is selected in the solvent NH ₃ environment side. Leaching out, causing corrosion thinning of the reaction vessel and contamination of the resulting crystals.
Also, since the operating environment is always a fluorinated atmosphere, it is operated in an environment where the fluorine-containing film can self-repair, so the ammonothermal method of the fluorinated atmosphere does not require fluorination treatment in advance, and self-repair The manufacturing method can be carried out while forming a film.

  As described above, the fluorine-containing film is extremely stable against a nitrogen-containing solvent in a supercritical state and / or a subcritical state, and a solution in which a mineralizer and raw materials are dissolved. When at least a part of the surface of the member used inside the reaction vessel is coated, the reaction vessel and the member are not corroded, and impurities in the obtained nitride crystal can be reduced. Since impurities are further reduced, it is preferable that 50% or more of the total surface area of the surface inside the reaction vessel and the surface made of a material containing Ni of the member used inside the reaction vessel is covered. More preferably, it is 70% or more, more preferably 80% or more, particularly preferably 90% or more, and 100% may be coated.

  The fluorine-containing film is not particularly limited as long as it contains fluorine, and may contain a metal other than Ni as long as the effects of the present invention are exhibited. For example, a metal that functions as a dopant for a nitride crystal, such as Si, Ca, Mg, or Zn, may be included.

  In addition, when a film formation process is implemented in multiple times, a fluorine-containing film tends to become thicker every time it repeats.

(Method for forming film)
The formation method of a fluorine-containing film is not specifically limited, For example, it can form by raising temperature and pressure in the environment where the metal which can react with a fluorine and fluorine exists in reaction container. Specifically, it can be formed by increasing the temperature and pressure in an environment where a fluorine-based mineralizer and a metal such as Ni, Fe, Cr, and Co are present.
When forming the film, there may be a supercritical and / or subcritical nitrogen-containing solvent, mineralizer, etc. in the reaction vessel, and at least part of the crystal growth process, the film formation process Since the steps can be simplified if the steps are performed simultaneously, it is preferable to use the same conditions as the crystal growth step.

  The film forming step may be performed in a state where a fluorine-containing film is already formed on the surface inside the reaction vessel and the surface of the member used inside the reaction vessel.

  When forming the film, it is preferable to remove substances other than those necessary for the crystal growth step such as oxygen and water from the reaction vessel. Specifically, the concentration of these substances is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 10 ppm or less. Specific methods for reducing these substances include nitrogen purge in the reaction vessel and evacuation. Nitrogen purging and evacuation are preferably performed in combination. The reaction vessel may be heated together with evacuation.

  In this invention, it is preferable to implement combining the formation conditions of said fluorine-containing film. For example, it is preferable to adopt an embodiment in which the reaction vessel is set to a temperature of 400 to 700 ° C. and a pressure of 100 to 700 MPa in the presence of a nitrogen-containing solvent and a fluorine-based mineralizer in a supercritical state and / or a subcritical state. it can.

  The nitride single crystal obtained as described above has few impurities, and since the crystal is grown in a high temperature region, the quality of the crystal is good and the PL strength is strong. Moreover, according to the manufacturing method of the present invention, it is possible to produce a transparent bulk crystal under conditions that allow an increase in size.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate 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.

<Examples 1 and 2>
(Corrosion test with test piece)
Dimensions of 22mm diameter inner lined with Pt, the baffle plate is placed inside an autoclave (volume approximately 119 ml) of length 293 mm, NH ₃ loading the NH ₄ F of the well-dried 99.99% pure as a mineralizer 0.5 mol% was added. Next, Inconel 625 test pieces (10 mm × 10 mm) were placed on the top and bottom. Thereafter, the lid of the autoclave equipped with the valve was quickly closed and the autoclave was weighed. Next, the conduit was connected to the vacuum pump through a valve attached to the autoclave, and the valve was opened to evacuate the inside of the autoclave. Thereafter, while maintaining the vacuum state, the autoclave was cooled with dry ice / methanol, and the valve was once closed. Next, after the conduit was operated to lead to the NH ₃ cylinder through the valve, the valve was opened again, and NH ₃ was continuously filled in the autoclave without touching the outside air. After controlling the flow rate and filling NH ₃ as a liquid in the autoclave, the valve was closed again. The temperature of the autoclave was returned to room temperature, and the increased amount of NH ₃ filled after the outer surface was sufficiently dried was measured.

Subsequently, the autoclave was housed in an electric furnace composed of a heater divided into two parts in the vertical direction. The temperature was raised so that the temperature in the lower region in the autoclave was 588 ° C. and the temperature in the upper region was 508 ° C., and the temperature was maintained for 96 hours. The pressure in the autoclave was 150 MPa. Further, the temperature range during holding was controlled to ± 5 ° C. or less. Thereafter, the temperature was lowered over about 9 hours until the temperature of the lower outer surface of the autoclave reached 50 ° C., and then the heating by the heater was stopped, followed by natural cooling in the electric furnace. After confirming that the temperature of the lower outer surface of the autoclave had dropped to about room temperature, first, the valve attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave was weighed to confirm the discharge of NH ₃ . Thereafter, the valve was once closed, the conduit was operated so as to communicate with the vacuum pump, the valve was opened again, and NH ₃ in the autoclave was almost completely removed.
Thereafter, the lid of the autoclave was opened and the test piece was taken out. No corrosion marks such as roughness were found on the surface of the test piece. Moreover, the weight increase of 0.001g was confirmed by formation of a fluorine-containing film.

<Examples 3 to 6>
The test was performed in the same manner as in Examples 1 and 2 except that the material, mineralizer, and temperature of the test piece shown in Table 1 were changed. In addition, the temperature shown in Table 1 is the temperature in the area | region which installed the test piece, respectively. After completion of the test, no corrosion marks such as roughness were found on the surface of the test piece. Moreover, the weight increase of 0.001-0.015g was confirmed by formation of the fluorine-containing film in any case.

  Incone 625 and Ni-12Cr-14Mo have a Ni content exceeding 50%. In addition, the fact that the weight change is positive indicates that a film is formed on the surface.

<Comparative Examples 1-22>
The test was performed in the same manner as in Example 1 except that the material, mineralizer, and temperature shown in Table 1 were changed. When a mineralizer having a positive solubility characteristic with respect to ammonia as a solvent was used, seed crystals and raw materials were arranged with the upper part of the autoclave as the crystal growth region and the lower part of the autoclave as the raw material dissolution region. In addition, the temperature shown in Table 1 is the temperature in the area | region which installed the test piece, respectively. After completion of the test, some test pieces were observed to lose weight or disappear. In other cases, there was no increase or decrease in weight, and it was confirmed that a Ni-F fluorine-containing film was not formed.

  From the above results, in the example using a test piece containing a Ni-based alloy and using a mineralizer containing no halogen other than fluorine, the weight change is positive, and a film containing fluorine is formed on the surface of the sample piece. It was. On the other hand, in the test piece of the comparative example, the weight change was negative, and the sample piece was corroded. From the examples using the above test pieces, a nitride single crystal was formed by an ammonothermal method using a mineralizer containing only fluorine as a mineralizer in a reaction vessel made of a metal containing Ni on the inner wall of the reaction vessel. When manufactured, the reaction vessel is covered with a fluorine-containing film, and it can be seen that corrosion of members used inside the reaction vessel and inside the reaction vessel can be suppressed.

<Example 7>
A GaN crystal produced by the HVPE method was placed as a seed crystal in the lower part of an autoclave (volume: about 119 ml) having a diameter of 22 mm and a length of 293 mm lined with Pt. Next, a baffle plate was installed inside the autoclave, and 44.5 g of polycrystalline GaN produced by the HVPE method as a raw material was placed above the baffle plate. Next, 0.5 mol% of NH ₄ F having a purity of 99.99% and sufficiently dried as a mineralizer was added to the NH ₃ filling amount. Thereafter, a gasket made of Inconel 625 was attached, the lid of the autoclave where the valve was quickly attached was closed, and the autoclave was weighed. Next, the conduit was connected to the vacuum pump through a valve attached to the autoclave, and the valve was opened to evacuate the inside of the autoclave. Thereafter, while maintaining the vacuum state, the autoclave was cooled with dry ice / methanol, and the valve was once closed. Next, after the conduit was operated to lead to the NH ₃ cylinder through the valve, the valve was opened again, and NH ₃ was continuously filled in the autoclave without touching the outside air. After controlling the flow rate and filling NH ₃ as a liquid in the autoclave, the valve was closed again. The temperature of the autoclave was returned to room temperature, and the increased amount of NH ₃ filled after the outer surface was sufficiently dried was measured.

Subsequently, the autoclave was housed in an electric furnace composed of a heater divided into two parts in the vertical direction. The temperature was raised so that the temperature of the crystal growth region (lower part) in the autoclave was 638 ° C. and the temperature of the upper raw material dissolution region was 558 ° C., and the temperature was maintained for 96 hours. The pressure in the autoclave was 147 MPa. Thereafter, the temperature was lowered over about 9 hours until the temperature of the lower outer surface of the autoclave reached 50 ° C., and then the heating by the heater was stopped, followed by natural cooling in the electric furnace. After confirming that the temperature of the lower outer surface of the autoclave had dropped to about room temperature, first, the valve attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave was weighed to confirm the discharge of NH ₃ . Thereafter, the valve was once closed, the conduit was operated so as to communicate with the vacuum pump, the valve was opened again, and NH ₃ in the autoclave was almost completely removed.

Thereafter, the lid of the autoclave was opened and the seed crystal was taken out. When impurities contained in the GaN crystal on the seed crystal after crystal growth were analyzed by SIMS, the Fe concentration was 1 × 10 ¹⁹ atoms / cc and Ni was in the 15th power range. From this, it is considered that a fluorine-containing film is formed on the gasket made of Inconel 625 containing Ni, thereby reducing impurities in the crystal.

<Comparative Example 23>
It carried out similarly to Example 7 except having changed the kind of mineralizer.
When SIMS analysis of the obtained growth was performed, it was found that the impurity concentrations of Ni, Fe, and O were higher than in Example 7.

  The present invention is useful for growing a bulk single crystal of a group 13 element nitride, particularly a bulk single crystal of GaN. According to the production method of the present invention, it is possible to reduce impurities derived from reaction vessels and members in the obtained crystal, and it is possible to use a reaction vessel having a stable surface in crystal growth more than once, Significant improvements can be expected in both time and cost. Therefore, the present invention has very high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Raw material melt | dissolution area | region 2 Crystal growth area | region 3 Outer wall 4 Raw material 5 Baffle plate 6 Seed crystal

Claims (11)

  A member used in the reaction vessel surface as well as in the reaction vessel, including a crystal growth step for carrying out crystal growth using a mineralizer in a nitrogen-containing solvent atmosphere in a supercritical state and / or a subcritical state in the reaction vessel A method for producing a nitride single crystal, wherein Ni is contained in at least a part of the surface of the metal, and the mineralizer is a fluorine-based mineralizer and does not contain a halogen atom other than fluorine.   A crystal growth step in which crystal growth is performed using a mineralizer in a nitrogen-containing solvent atmosphere in a supercritical state and / or a subcritical state in the reaction vessel, and a surface of the reaction vessel and a member used inside the reaction vessel A film forming step of forming a fluorine-containing film on at least a portion of the surface, and Ni is contained in at least a portion of the surface of the reaction vessel and the surface of a member used inside the reaction vessel. A method for producing a single crystal.   The method for producing a nitride single crystal according to claim 2, wherein the film forming step is simultaneously performed at least in a part of the crystal growth step.   A method for producing a nitride single crystal comprising a crystal growth step in which crystal growth is performed using a mineralizer in a nitrogen-containing solvent atmosphere in a supercritical and / or subcritical state in a reaction vessel, the surface of the reaction vessel and the A method for producing a nitride single crystal, wherein at least a part of the surface of a member used inside the reaction vessel is coated with a fluorine-containing film.   The manufacturing method of the nitride single crystal of any one of Claims 2-4 whose thickness of the said fluorine-containing film is 5 nm-50 micrometers.   At least one part of the surface of the said reaction container surface and the member used inside the said reaction container is a Ni base alloy in which Ni content exceeds 40 mass%, It is any one of Claims 1-5. A method for producing a nitride single crystal.   6. The method according to claim 1, wherein at least a part of the surface of the reaction vessel and the surface of a member used inside the reaction vessel is a Ni-based alloy having a Ni content exceeding 50 mass%. A method for producing a nitride single crystal.   The nitride unit according to any one of claims 1 to 7, wherein a carbon content of at least a part of a surface of the reaction vessel and a surface of a member used inside the reaction vessel is 0.2 mass% or less. Crystal production method.   The nitride single crystal according to any one of claims 1 to 8, wherein Fe content of at least a part of a surface of the reaction vessel and a surface of a member used inside the reaction vessel is 5 mass% or less. Production method.   10. The method according to claim 1, wherein at least a part of the reaction vessel surface and the surface of a member used inside the reaction vessel contains at least one selected from Cr, Al, Ti, Nb, V, W, and Mo. A method for producing a nitride single crystal according to claim 1.   The method for producing a nitride single crystal according to any one of claims 1 to 10, wherein the crystal growth step is performed a plurality of times.