JP2013014502A - Method for producing nitride crystal, nitride crystal and apparatus for producing the same - Google Patents

Abstract

The present invention provides a method capable of efficiently and safely producing low-cost, high-purity nitride crystals using a generally available mineralizer.
In a reaction vessel for crystal growth or in a closed circuit connected to the reaction vessel 1, a mineralizer sublimation purification step in which the mineralizer is sublimated and then precipitated, and in the reaction vessel 1, a solvent is added. In the presence of the refined mineralizer, a crystal growth step is performed in which a nitride crystal is grown from the nitride crystal growth raw material 8 placed in the reaction vessel 1 by the solvothermal method.
[Selection] Figure 3

Description

  The present invention relates to a method for manufacturing a nitride crystal by a solvothermal method, a nitride crystal, and an apparatus for manufacturing the nitride crystal.

  The solvothermal method is a method for producing a desired material using a solvent in a supercritical state and / or a subcritical state and utilizing a dissolution-precipitation reaction of raw materials. When applied to crystal growth, this is a method in which a crystal is precipitated by generating a supersaturated state due to a temperature difference utilizing the temperature dependence of the solubility of a raw material in a solvent. For example, in order to precipitate a nitride crystal such as gallium nitride, an ammonothermal method using a nitrogen-containing solvent such as ammonia as a solvent is mainly employed. In order to grow a single crystal by the solvothermal method, it is necessary to deposit a sufficient amount of raw material in a supersaturated state, and for this purpose, it is necessary that the raw material for crystal growth is sufficiently dissolved in a solvent. . However, for example, nitrides such as gallium nitride have a problem that the amount necessary for practical crystal growth cannot be dissolved because the solubility in pure ammonia is extremely low in a temperature and pressure range that can be employed.

  In order to solve such a problem, a mineralizer that improves the solubility of nitrides such as gallium nitride is generally added to the reaction system. Since the mineralizer can form a complex with a nitride (solvate), more nitride can be dissolved in a nitrogen-containing solvent such as ammonia. Mineralizers include basic mineralizers and acidic mineralizers. Typical examples of basic mineralizers include alkali metal amides. Typical examples of acidic mineralizers include ammonium halides. (See Patent Document 1).

  These mineralizers are sold as reagents and are usually handled as powdered solids. After such a solid mineralizer is sufficiently dried, it is put into a reaction vessel containing a raw material for crystal growth and a seed crystal and covered. Next, liquid ammonia is injected into the reaction vessel through a valve, and then the temperature is raised by a heater to generate an internal pressure by volume expansion of the internal ammonia. A nitride crystal can be obtained by maintaining a set temperature condition for a predetermined time and growing the crystal, and then cooling and taking out the crystal from the reaction vessel (see Patent Documents 2 to 4).

However, the nitride crystal thus grown by the solvothermal method with the addition of the solid mineralizer has a problem that the oxygen concentration contained in the crystal is relatively high. This is presumably because the mineralizer easily adsorbs water and oxygen, so that oxygen atoms derived from the mineralizer used in the reaction are taken into the crystal. That is, the nitride crystal obtained by the conventional method contains oxygen in the order of 10 ¹⁸ to 10 ²⁰ atom / cm ³ (see Non-Patent Document 1 and Non-Patent Document 2). Compared to nitride crystals grown by the method, this value is extremely high.

  When the oxygen concentration is high, the crystals are colored black to brown, and when used as an optoelectronic substrate such as an LED or LD (Laser Diode), light absorption occurs and the light extraction efficiency decreases. In addition, since oxygen functions as a donor, if the crystal contains an amount of oxygen that is not controlled as an unintended impurity, doping for controlling the electrical characteristics of the substrate becomes difficult.

  In order to deal with these and other various problems, it is possible to select a mineralizer with a low water concentration and fill it in a reaction vessel so that it does not adsorb moisture. Since it requires a large-scale facility to be applied to a large reaction vessel, it is not realistic. Therefore, in the reaction vessel, a reactive gas that reacts with ammonia to produce a mineralizer is brought into contact with ammonia to produce a mineralizer, and a nitride is formed by a solvothermal method using the produced mineralizer. A method of growing a crystal has been proposed (see Patent Document 5). According to this method, a high-purity nitride crystal having a low oxygen concentration can be grown.

JP 2003-277182 A Japanese Patent Laying-Open No. 2005-8444 JP 2007-238347 A JP 2007-290921 A JP 2011-68545 A

Journal of Crystal Growth, 310, 2008, 3902-3906 Journal of Crystal Growth, 310, 2008, 876-880

  According to the method described in Patent Document 5, it is possible to grow a high-purity nitride crystal with a low oxygen concentration. However, in this method, a high purity reactive gas must be introduced into the reaction vessel in order to react with ammonia to produce a mineralizer. For this reason, it is necessary to construct a high purity gas line in the production facility. In addition, it is necessary to control the reaction for generating the mineralizer from the reactive gas and ammonia that require careful handling, and the process of vacuum degassing and gas introduction for removing moisture in the gas line is complicated. For this reason, there existed a subject that cost and an effort were required rather than the conventional method using a solid mineralizer. Moreover, according to the method described in Patent Document 5, it is possible to prevent oxygen from being mixed into the reaction vessel by the mineralizer, but oxygen introduced by other materials or reaction vessel It is not possible to deal with oxygen in the pipes and pipes.

  Considering such problems of the prior art, the present invention uses a mineralizer that is generally available in the same manner as the conventional method, and can efficiently produce a low-cost, high-purity nitride crystal at a low cost. In order to provide a method that can be manufactured in the future, the study was advanced.

  As a result of diligent studies to solve the above problems, the present inventors have refined the mineralizer by a method that has not been studied in the conventional method, and thereby a nitride having a low oxygen concentration by the solvothermal method. It has been found that crystals can be obtained efficiently. The present invention has been made based on such findings, and the specific contents of the present invention are as follows.

[1] A mineralizer sublimation purification step in which a mineralizer is sublimated after precipitation in a reaction vessel for crystal growth or in a closed circuit connected to the reaction vessel;
A crystal growth step of growing a nitride crystal from a nitride crystal growth raw material placed in the reaction vessel by a solvothermal method in the presence of the solvent and the refined mineralizer in the reaction vessel. A method for producing a nitride crystal.
[2] The method for producing a nitride crystal according to [1], wherein in the mineralizer sublimation purification step, the pressure is set to 1 Torr or less.
[3] In the mineralizer sublimation purification step, the temperature (T1) of the mineralizer heating sublimation region for heating and sublimating the mineralizer, and the temperature of the mineralizer precipitation region for precipitating the sublimated mineralizer. The method for producing a nitride crystal according to [1] or [2], wherein the temperature difference (T1−T2) of (T2) is set to 5 ° C. or more.
[4] The method for producing a nitride crystal according to [3], wherein the temperature difference is controlled by a heater.
[5] The method for producing a nitride crystal according to [3] or [4], wherein the temperature (T1) of the mineralizer heating sublimation region is 80 ° C to 350 ° C.
[6] The method for producing a nitride crystal according to any one of [3] to [5], wherein the temperature (T2) of the mineralizer precipitation region is 30 ° C to 300 ° C.
[7] In the mineralizer sublimation purification step, a mineralizer heating sublimation region for heating and sublimating the mineralizer and a mineralizer precipitation region for precipitating the sublimated mineralizer are both contained in the reaction vessel. The method for producing a nitride crystal according to any one of [1] to [6] to be set.
[8] The method for producing a nitride crystal according to [7], wherein the sublimation purification step of the mineralizer is performed in the reaction vessel in which at least a raw material, a mineralizer, and a seed crystal are present.
[9] In the mineralizer sublimation purification step, a mineralizer heating sublimation region for heating and sublimating the mineralizer and a mineralizer precipitation region for precipitating the sublimated mineralizer are both outside the reaction vessel. The method for producing a nitride crystal according to any one of [1] to [6] to be set.
[10] The method for producing a nitride crystal according to [9], wherein both the mineralizer heating sublimation region and the mineralizer precipitation region are set in a mineralizer purification vessel provided separately from the reaction vessel. .
[11] The mineralizer heating sublimation region is set in a mineralizer heating sublimation vessel, and the mineralizer precipitation region is set in a mineralizer precipitation vessel provided separately from the mineralizer heating sublimation vessel. The method for producing a nitride crystal according to [9].

[12] The production of the nitride crystal according to any one of [1] to [11], wherein the mineralizer purified by the sublimation purification step is mixed with ammonia and introduced into the reaction vessel. Method.
[13] The purified mineralizer obtained by precipitation in the mineralizer precipitation vessel is introduced into the reaction vessel, and the mineralizer remaining in the mineralizer heating sublimation vessel is the reaction vessel. The method for producing a nitride crystal according to [12], wherein the nitride crystal is not introduced.
[14] The method for producing a nitride crystal according to any one of [1] to [13], wherein the mineralizer used in the mineralizer sublimation purification step is sublimated and purified in advance.
[15] The method for producing a nitride crystal according to any one of [1] to [14], wherein the mineralizer contains a halogen element.
[16] The method for producing a nitride crystal according to any one of [1] to [15], wherein the solvent is ammonia.
[17] The method for producing a nitride crystal according to any one of [1] to [16], wherein the nitride crystal is gallium nitride.
[18] The nitride crystal according to any one of [1] to [17], wherein the reaction vessel or the closed circuit is replaced with nitrogen gas before the mineralizer sublimation purification process is started. Manufacturing method.
[19] Any of [1] to [18], wherein the reaction vessel is composed of one or more metals or alloys selected from the group consisting of Pt, Ir, W, Ta, Rh, Ru, and Re. A method for producing a nitride crystal according to claim 1.
[20] Any of [1] to [18], wherein the reaction vessel is lined with one or more metals or alloys selected from the group consisting of Pt, Ir, W, Ta, Rh, Ru, and Re. A method for producing a nitride crystal according to claim 1.
[21] The method for producing a nitride crystal according to any one of [1] to [20], wherein the reaction vessel is an autoclave.
[22] The method for producing a nitride crystal according to any one of [1] to [20], wherein the reaction vessel is a capsule inserted in an autoclave.

[23] A nitride crystal produced by the method for producing a nitride crystal according to any one of [1] to [22].
[24] The nitride crystal according to [23], wherein the nitride crystal is a nitride crystal of Group 13 metal of the periodic table.
[25] The nitride crystal according to [23], wherein the nitride is gallium nitride.
[26] A reaction vessel capable of growing a nitride crystal by a solvothermal method, a mineralizer sublimation precipitation vessel for sublimating and precipitating the mineralizer, and a sublimation-purified mineralizer are introduced into the reaction vessel. And an apparatus for producing a nitride crystal.
[27] The mineralizer sublimation deposition container has both a mineralizer heating sublimation region for heating and sublimating the mineralizer and a mineralizer precipitation region for depositing the sublimated mineralizer. [26] The nitride crystal manufacturing apparatus described in 1.
[28] A reaction vessel capable of growing a nitride crystal by a solvothermal method, a mineralizer heating sublimation vessel for sublimating the mineralizer, a mineralizer precipitation vessel for depositing the mineralizer, and the precipitated mineral An apparatus for producing a nitride crystal, comprising: an introduction means for introducing an agent into the reaction vessel.
[29] The nitride crystal production apparatus according to [28], wherein the introduction unit does not introduce the mineralizer remaining in the mineralizer heating sublimation vessel into the reaction vessel.
[30] The nitride crystal production apparatus according to any one of [26] to [29], further comprising means for introducing a solvent into each of the reaction vessels.
[31] The nitride crystal production apparatus according to any one of [26] to [30], wherein a pipe is attached to the reaction vessel and pressure reduction is possible through the pipe.

  According to the method for producing a nitride crystal of the present invention (hereinafter referred to as the solvothermal method of the present invention), a high purity nitride crystal having a low oxygen concentration can be efficiently and safely grown at a low cost. Further, since the nitride crystal of the present invention has a low oxygen concentration and a high purity, it is difficult to cause coloring. Furthermore, if the manufacturing apparatus of this invention is used, the nitride crystal which has such a characteristic can be manufactured efficiently at low cost safely.

It is the schematic of the crystal manufacturing apparatus used by this invention. It is the schematic of another crystal manufacturing apparatus used by this invention. It is the schematic of the crystal manufacturing apparatus of this invention. It is the schematic of another crystal manufacturing apparatus of this invention. It is the schematic of the apparatus used in the mineralizer sublimation purification process of this invention.

  Hereinafter, a method for producing a nitride crystal by the solvothermal method of the present invention, a nitride crystal and an apparatus for producing the same 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.

<Sublimation process of mineralizer>
The method for producing a nitride crystal of the present invention is characterized by including a mineralizer sublimation purification step in which a mineralizer is sublimated and purified in a reaction vessel or in a closed circuit connected to the reaction vessel. Usually, it is preferable that the mineralizer sublimation purification process is completed before the nitride crystal is grown.

(Mineralizer)
When the mineralizer is purified by sublimation in the reaction vessel, the mineralizer is first placed in the reaction vessel. The mineralizer used here may be a commercially available one, a synthesized one, or one in which they are stored. In the present invention, the effect of the invention can be obtained without using a mineralizer that has been refined to increase its purity. However, if the purification according to the present invention is further performed using a purified mineralizer, the purity can be improved. This is preferable because a high nitride crystal can be produced. When the mineralizer is put into the reaction vessel, the mineralizer can be put in by opening the reaction vessel according to a conventional method. The mineralizer may be placed in the reaction vessel under an atmosphere that does not contain moisture such as nitrogen gas, but when the production method of the present invention is adopted, it may be performed in the air without performing such an operation. Absent.

The mineralizer used in the present invention is selected from mineralizers used when producing nitride crystals by the solvothermal method. A basic mineralizer such as alkali metal amide may be used, or an acidic mineralizer such as ammonium halide may be used. Among them, it is preferable to use ammonium halide because the effects of the present invention can be enjoyed better. Examples of ammonium halides include ammonium hydrogen fluoride, ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, etc. Adopting ammonium hydrogen fluoride, ammonium chloride, ammonium bromide, ammonium iodide It is preferable to employ ammonium bromide or ammonium iodide. These mineralizers may be used alone or in combination.
When purifying the mineralizer, only the mineralizer may be placed in the reaction vessel, but raw materials and seed crystals used for the growth of nitride crystals to be performed later may coexist. The types and details of raw materials and seed crystals will be described later.

(Pressure and temperature)
When purifying the mineralizer in the reaction vessel, the reaction vessel is heated under reduced pressure while degassing. Deaeration can be performed by a vacuum pump or the like through a pipe connected to the reaction vessel. The pressure is preferably ¹ Torr or less, more preferably 1 × 10 ⁻¹ Torr or less, and further preferably 1 × 10 ⁻² Torr or less. The lower limit of the pressure is preferably 1 × 10 ⁻⁷ Torr or more, more preferably 1 × 10 ⁻⁶ Torr or more, and further preferably 1 × 10 ⁻⁵ Torr or more. Although it is preferable to gradually reduce the pressure, it may be difficult to lower the pressure due to vaporization of water during purification. In such a case, the pressure can be further lowered after degassing the gas vaporized at a substantially constant pressure. In addition, after the mineralizer is precipitated by refining, it is preferable to gradually lower the temperature and complete the mineralizer sublimation purification process.

  At the time of refining the mineralizer, the mineralizer is sublimated by heating at least a part of the region containing the mineralizer in the reaction vessel to a temperature higher than the sublimation temperature of the mineralizer. In this specification, the area | region which heats a mineralizer and sublimates is called a mineralizer heating sublimation area | region. While providing such a mineralizer heating sublimation region, any other region is set to a temperature lower than the sublimation temperature of the mineralizer to precipitate the mineralizer. In this specification, the area | region which deposits a mineralizer is called a mineralizer precipitation area | region.

  The sublimation temperature of the mineralizer is determined by the type of mineralizer and the pressure in the reaction vessel. Usually, the temperature (T1) of the mineralizer heating sublimation region is set to a temperature that is 1 ° C or higher than the sublimation temperature, preferably set to a temperature that is 3 ° C or higher, and set to a temperature that is 5 ° C or higher. Is more preferable. The upper limit may be, for example, 200 ° C. higher than the sublimation temperature, preferably 150 ° C. higher than the sublimation temperature, and more preferably 100 ° C. higher than the sublimation temperature. The temperature (T2) of the mineralizer precipitation region is usually set to a temperature lower by 0.1 ° C or more than the sublimation temperature, preferably set to a temperature lower by 1 ° C or more, and set to a temperature lower by 3 ° C or more. More preferred. About a lower limit, it can be set as a temperature 100 degreeC lower than sublimation temperature, for example, Preferably it is 50 degreeC temperature lower than sublimation temperature, More preferably, it is 30 degreeC temperature lower than sublimation temperature. If these temperatures employed in the mineralizer sublimation purification process are too high, the energy efficiency will deteriorate, and if it is too low, the purification efficiency will deteriorate. For this reason, it is preferable to heat to moderate temperature, controlling along with conditions, such as a pressure.

  The temperature (T1) of the mineralizer heating sublimation region is preferably set to 80 ° C. or higher, more preferably set to 100 ° C. or higher, and further preferably set to 120 ° C. or higher. Further, the temperature (T1) of the mineralizer heating sublimation region is preferably set to 350 ° C. or lower, more preferably set to 300 ° C. or lower, and further preferably set to 250 ° C. or lower. The temperature (T2) of the mineralizer precipitation region is preferably set to 30 ° C. or higher, more preferably set to 40 ° C. or higher, and further preferably set to 50 ° C. or higher. Moreover, it is preferable to set the temperature (T2) of the mineralizer heating precipitation area | region to 300 degrees C or less, It is more preferable to set to 250 degrees C or less, It is further more preferable to set to 200 degrees C or less. The temperature difference between the mineralizer heating sublimation region and the mineralizer precipitation region is preferably 5 ° C. or more, more preferably 10 ° C. or more, and further preferably 15 ° C. or more. Further, the temperature difference is preferably 200 ° C. or less, more preferably 170 ° C. or less, and further preferably 150 ° C. or less. Note that the temperature difference condition here is considered to be satisfied if there is a portion satisfying the temperature difference in part of the mineralizer heating sublimation region and the mineralizer precipitation region. The set temperature in the mineralizer sublimation purification process is preferably adjusted in consideration of the type of mineralizer to be purified. For example, in the case of ammonium chloride, the mineralizer heating sublimation region is set in the range of 80 to 250 ° C. In the case of ammonium bromide, the mineralizer heating sublimation region is set in the range of 100 to 300 ° C. In the case of ammonium chloride, it is preferable to set the mineralizer heating sublimation region within the range of 120 to 350 ° C. The temperature (T2) of the mineralizer precipitation region is preferably set to a temperature 5 ° C. or more lower than the temperature (T1) of these mineralizer heating sublimation regions.

The temperature of the mineralizer heating sublimation region may be set to the same temperature throughout the region, or there may be a temperature distribution within the region. The same applies to the temperature of the mineralizer precipitation region. As an aspect in which the temperature distribution is present in the mineralizer precipitation region, for example, the temperature is higher at the mineralizer heating sublimation region side. Further, the set temperature and temperature distribution may be kept constant during the mineralizer sublimation purification process, or may be changed according to the deposition state of the mineralizer. Usually, a time for maintaining a constant temperature is secured during the process.
When purifying the mineralizer in the reaction vessel, the mineralizer heating sublimation region is set in the reaction vessel. Usually, when the mineralizer is added, the lower part of the reaction vessel in which the mineralizer accumulates is the mineralizer heating sublimation region. On the other hand, the mineralizer precipitation region may be set inside the reaction vessel or outside the reaction vessel. The mineralizer heating sublimation region and the mineralizer precipitation region can be set according to the installation position of the temperature control mechanism such as a heater and the manner of temperature control. When set in the reaction vessel, the region from the upper part of the reaction vessel or from the upper part to the central part is preferably used as the mineralizer precipitation region.

  In addition, when setting a mineralizer precipitation area | region in reaction container, you may change the width of a mineralizer precipitation area | region and a mineralizer precipitation area | region with progress of a mineralizer sublimation refinement | purification process. As the refining progresses, the amount of mineralizer in the mineralizer heating sublimation region decreases and the amount of precipitation mineralizer in the mineralizer precipitation region increases, so by adjusting the temperature control range gradually mineralization The agent heating sublimation region may be controlled to be narrow, or the mineralizer precipitation region may be controlled to be wide. At that time, a part of the portion that was the mineralizer heating sublimation region at the beginning of the purification may be incorporated into a part of the mineralizer precipitation region at the end of the purification.

  The mineralizer precipitation region can be set outside the reaction vessel. That is, conditions can be set so that the mineralizer does not substantially precipitate in the reaction vessel, and can be set to precipitate outside the reaction vessel. For example, it is possible to set a mineralizer precipitation vessel installed outside the reaction vessel in the mineralizer precipitation region and deposit the mineralizer in the mineralizer precipitation vessel. Moreover, without providing such a mineralizer precipitation container, a part of piping can be set to a mineralizer precipitation area | region, and a mineralizer can also be deposited in piping. In that case, the inner diameter of the pipe is made thicker, or a precipitation auxiliary tool is installed in the pipe to make it easy for the mineralizer to precipitate intensively. It is preferable to devise so that the flow path is not excessively narrowed.

(Precipitation aid)
The deposition aid can be installed in the mineralizer deposition region regardless of inside or outside the reaction vessel. For example, a rod-like body or a plate-like body having the same material surface as the reaction vessel or the inner wall of the pipe can be exemplified. The rod-like body may be a fence-like body or a stitch-like body in which a plurality of bars are combined. The diameter of such a rod-shaped body is preferably 0.1 mm or more, and more preferably 0.2 mm or more. Moreover, it is preferable that it is 3 mm or less, and it is more preferable that it is 2 mm or less. These precipitation aids may be installed so as to cross the mineralizer precipitation region, or may be installed in a part thereof. Moreover, you may use the member used in the reaction container for another purpose as a precipitation auxiliary tool. For example, a seed crystal holding frame or a seed crystal holding wire may function as a deposition aid. If the deposition aid occupies a very large area with respect to the cross-sectional area in the container or pipe to be installed, the risk of clogging the container or pipe with the deposited mineralizer increases. For this reason, it is preferable not to exceed 98% of the cross-sectional area in a container or piping, and it is more preferable not to exceed 95% of the area which a precipitation auxiliary tool occupies.

(Purification of mineralizer outside the reaction vessel and equipment used therefor)
The purification of the mineralizer can also be performed outside the reaction vessel. In this case, a mineralizer purification vessel is provided in a closed circuit separately from the reaction vessel, and the mineralizer can be purified there in the same manner as described above. The closed circuit here means a flow path or container that can form a sealed state together with the reaction container when isolated from the outside air when connected to the reaction container, and can suppress contamination of impurities such as oxygen and moisture. . In addition, the closed circuit does not always need to be connected to the reaction vessel, and may have a structure that can be separated from the reaction vessel while maintaining a function of sealing with the reaction vessel by using a valve or other structure. As an example of connection between such a closed circuit and a reaction vessel, for example, a vessel (mineralizer sublimation deposition vessel) separate from the reaction vessel and the reaction vessel is connected by piping, and a valve is attached to each vessel. The thing which becomes a structure which can be sealed is mentioned. A specific example is the apparatus shown in FIG. Here, the mineralizer is put in the mineralizer sublimation precipitation container 15, the mineralizer is sublimated by heating the lower part of the container with the heater 26, and the upper part of the container is set to the sublimation temperature or less with the heater 25. Then, the mineralizer can be deposited. The inside of the mineralizer sublimation precipitation container 15 is deaerated by the vacuum pump 11 during the mineralizer sublimation purification process. After refining the mineralizer, ammonia is introduced into the mineralizer sublimation precipitation vessel 15 from the ammonia cylinder 12 to form a mixture of ammonia and mineralizer, and the mixture is further passed through the valve 10 to autoclave. 1 can be introduced.

  In the present invention, it is preferable that the precipitated mineralizer is introduced into the reaction vessel while maintaining as high purity as possible. For this purpose, for example, a high-purity solvent used during the growth of nitride crystals is introduced into the mineralizer precipitation region, the purified mineralizer and the solvent are mixed, and the mixture is reacted through the pipe without touching the outside air. It is preferable to employ a method of injecting into the container. At this time, as in the case of using the apparatus of FIG. 3, the mineralizer remaining in the mineralizer heating sublimation region is also introduced into the reaction vessel so that the solvent passes through the mineralizer heating sublimation region. However, it is more preferable that piping is made so as not to pass through the mineralizer heating sublimation region so that only the mineralizer deposited in the mineralizer deposition region is introduced into the reaction vessel. A specific example of such an embodiment is shown in FIG. Here, a mineralizer heating sublimation container 17 and a mineralizer precipitation container 16 are provided separately from the reaction container 1. The mineralizer filled in the lower part of the mineralizer heating sublimation container 17 is heated by the heater 26 to a temperature higher than the sublimation temperature, and the heater 25 controls the temperature so that the mineralizer does not precipitate in the mineralizer heating sublimation container. The mineralizer is controlled to be deposited in the mineralizer deposition vessel 16 by the heater 24. During the sublimation purification of the mineralizer, vacuum deaeration is performed by the vacuum pump 11. When the sublimation purification of the mineralizer is completed, ammonia is introduced into the mineralizer precipitation vessel 16, and a mixture of ammonia and mineralizer is introduced into the autoclave 1 via the valve 10. Details of such a series of devices can be modified as appropriate according to the use situation and purpose of use.

<Crystal growth process>
(Seed crystal)
When growing a nitride crystal according to the present invention, it is preferable to use a seed crystal. As a seed crystal, it is desirable to use a single crystal of nitride grown by the manufacturing method of the present invention, but it is not always necessary to use the same nitride. 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. As specific examples of seed crystals, for example, when growing gallium nitride (GaN), in addition to a single crystal of GaN, a single crystal of nitride such as aluminum nitride (AlN), a single crystal of zinc oxide (ZnO), silicon carbide ( SiC) single crystal, sapphire (Al ₂ O ₃ ), and the like.

  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 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.

(solvent)
In the present invention, the solvent is not particularly limited, but a nitrogen-containing solvent is usually used. Examples of the nitrogen-containing solvent include solvents that do not impair the stability of the nitride single crystal to be grown. Specifically, ammonia, hydrazine, urea, amines (for example, methylamine) Primary amines, secondary amines such as dimethylamine, tertiary amines such as trimethylamine, diamines such as ethylenediamine, and melamine. These solvents may be used alone or in combination. In the present invention, it is particularly preferable to use ammonia as a solvent.
The amount of water and oxygen contained in the solvent used in the present invention is desirably as small as possible, and the content thereof is preferably 1000 ppm or less, more preferably 10 ppm or less, and preferably 0.1 ppm or less. Further preferred. When ammonia is used as a solvent, the purity is usually 99.9% or more, preferably 99.99% or more, more preferably 99.999% or more, and particularly preferably 99.9999% or more. .

(material)
In the present invention, a raw material containing an element constituting the nitride crystal to be grown is used. For example, when a nitride crystal of a periodic table 13 group metal is to be grown, a raw material containing a periodic table 13 group metal is used. Preferred is a polycrystalline raw material of group 13 nitride crystal and / or gallium, and more preferred is gallium nitride and / or gallium. The polycrystalline raw material does not need to be a complete nitride, and may contain a metal component in which the group 13 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 manufacturing method of the polycrystalline raw material used as a raw material in the present invention 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, a nitride polycrystal produced by reacting a metal such as Ga with nitrogen at a high temperature and a high 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 polycrystalline raw material used in the present invention is preferably one having an oxygen concentration of 1 × 10 ¹⁸ atom / cm ³ or less, preferably 1 × 10 ¹⁷ atom / cm ³ or less, preferably 1 × It is more preferable to use one having a density of 10 ¹⁶ atom / cm ³ or less.

(Reaction vessel)
In the production method of the present invention, the crystal growth step is carried out in a reaction vessel.
The reaction vessel used in the present invention is selected from those capable of withstanding the high temperature and high pressure conditions when growing nitride crystals. The reaction vessel is formed from the outside of the reaction vessel as described in JP-T-2003-511326 (International Publication No. 01/024921 pamphlet) and JP-T-2007-509507 (International Publication No. 2005/043638 pamphlet). It may be provided with a mechanism for adjusting the pressure applied to the reaction vessel and its contents, or may be an autoclave not having such a mechanism.
The reaction vessel used in the present invention is preferably composed of a material having pressure resistance and corrosion resistance. In particular, a Ni-based alloy having excellent corrosion resistance against a solvent such as ammonia, Stellite (from Deloro Stellite Company, Inc.) It is preferable to use a Co-based alloy such as a registered trademark. More preferably, it is an Ni-based alloy. Specifically, Inconel 625 (Inconel is a registered trademark of Huntington Alloys Canada Limited, the same shall apply hereinafter), Nimonic 90 (Nimonic is a registered trademark of Special Metals Wiggin Limited, hereinafter the same), RENE41 (Teledyne Allvac, Inc.), Inconel 718 (Inconel is a registered trademark of Huntington Alloys Canada Limited), Hastelloy (registered trademark of Haynes International, Inc.), Waspaloy (registered trademark of United Technologies, Inc.).

  The composition ratio of these alloys depends on the temperature and pressure conditions of the solvent in the reaction vessel, and the reactivity with mineralizers and their reactants used in the reaction vessel and / or the oxidizing power / reducing power and pH. It may be selected as appropriate. In order to use these as materials constituting the inner surface of the reaction vessel, the reaction vessel itself may be manufactured using these alloys, or a thin film may be formed as an inner cylinder (capsule) and installed in the reaction vessel. In addition, the inner surface of the material of any reaction vessel may be plated.

  In order to further improve the corrosion resistance of the reaction vessel, the inner surface of the reaction vessel may be lined or coated using the excellent corrosion resistance of the noble metal. Moreover, the material of the reaction vessel can be a noble metal. Examples of the noble metal herein include Pt, Au, Ir, Ru, Rh, Pd, Ag, and alloys containing these noble metals as main components, and among these, it is preferable to use Pt having excellent corrosion resistance.

  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. Here, crystal growth is performed in the capsule 20 loaded as an inner cylinder in the autoclave 1. The capsule 20 includes a raw material dissolution region 9 for dissolving the raw material and a crystal growth region 6 for growing crystals. A solvent and a mineralizer can be placed in the raw material dissolution region 9 together with the raw material 8, and the seed crystal 7 can be installed in the crystal growth region 6 by suspending it with a wire. Between the raw material dissolution region 9 and the crystal growth region 6, 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 is preferably the same as the material of the capsule 20 that is a reaction vessel. Further, in order to provide more corrosion resistance and to purify the crystal to be grown, the surface of the baffle plate is preferably Ni, Ta, Ti, Nb, Pd, Pt, Au, Ir, pBN, Pd, Pt, Au, Ir, and pBN are more preferable, and Pt is particularly preferable.

  In the crystal manufacturing apparatus of FIG. 1, the gap between the inner wall of the autoclave 1 and the capsule 20 can be filled with the second solvent. Here, ammonia can be filled as the second solvent while filling the nitrogen gas from the nitrogen cylinder 13 through the valve 10 or confirming the flow rate from the ammonia cylinder 12 with the mass flow meter 14. In addition, the vacuum pump 11 can perform necessary pressure reduction. In addition, a valve, a mass flow meter, and a conduit are not necessarily installed in the crystal manufacturing apparatus used when the manufacturing method of the present invention is carried out.

A specific example of another crystal manufacturing apparatus that can be used in the manufacturing method of the present invention is shown in FIG. In this crystal manufacturing apparatus, crystals are grown in an autoclave without using capsules.
Lining can also be used to provide corrosion resistance by autoclaving. The lining material is preferably at least one metal or element of Pt, Ir, Ag, Pd, Rh, Cu, Au and C, or an alloy or compound containing at least one metal, More preferably, it is an alloy or compound containing at least one or more kinds of metals or elements of Pt, Ag, Cu and C, or at least one kind of metals because they are easily lined. For example, Pt simple substance, Pt-Ir alloy, Ag simple substance, Cu simple substance, graphite, etc. are mentioned.

(Crystal growth process)
When growing a nitride crystal, sealing is performed in a state where a seed crystal, a solvent, a raw material, and a mineralizer are placed in a reaction vessel. When purifying the mineralizer in the reaction vessel, it is preferable to purify the mineralizer in a state where components other than the solvent are added, and then introduce the solvent. When the mineralizer is purified outside the reaction vessel, it is preferable to introduce the purified mineralizer and solvent into the reaction vessel containing the seed crystal and the raw material. The mineralizer and the solvent may be introduced by mixing or may be introduced separately. The seed crystal is preferably fixed to a noble metal jig similar to the noble metal constituting the inner surface of the reaction vessel. After loading, heat deaeration may be performed as necessary.

  When the production apparatus shown in FIG. 1 is used, seed capsules, a solvent, a raw material, and a mineralizer are put in a capsule 20 that is a reaction vessel and sealed, and then the capsule 20 is placed in an autoclave (pressure-resistant vessel) 1. The pressure-resistant container is preferably sealed by filling the space between the pressure-resistant container and the reaction container with a second solvent.

  Thereafter, the whole is heated to bring the inside of the reaction vessel into a supercritical state and / or a subcritical state. In the supercritical state, the viscosity is generally low and it is more easily diffused than the liquid, but has the same solvating power as the liquid. The subcritical state means a liquid state having a density substantially equal to the critical density near the critical temperature. For example, in the raw material filling part, the raw material is melted as a supercritical state, and in the crystal growth part, the temperature is changed so as to be in the subcritical state, and crystal growth utilizing the difference in solubility between the supercritical state and the subcritical state raw material is also performed. Is possible.

  When in the supercritical state, the reaction mixture is generally maintained at a temperature above the critical point of the solvent. When an ammonia solvent is used, the critical point is a critical temperature of 132 ° C. and a critical pressure of 11.35 MPa. However, if the filling rate with respect to the volume of the reaction vessel 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.

  Under supercritical conditions, a sufficient growth rate of nitride crystals can be obtained. The reaction time depends in particular on the reactivity of the mineralizer and the thermodynamic parameters, ie temperature and pressure values. During the synthesis or growth of the nitride crystal, the pressure in the reaction vessel is preferably 120 MPa or more, more preferably 150 MPa or more, and further preferably 180 MPa or more. The pressure in the reaction vessel is preferably 700 MPa or less, more preferably 500 MPa or less, further preferably 350 MPa or less, and particularly preferably 300 MPa or less. The pressure is appropriately determined depending on the filling rate of the solvent volume with respect to the temperature and the volume of the reaction vessel. Originally, the pressure in the reaction vessel is uniquely determined by the temperature and the filling rate, but in reality, the raw materials, additives such as mineralizers, temperature heterogeneity in the reaction vessel, and free volume Depending on the presence of

  The lower limit of the temperature range in the reaction vessel is preferably 500 ° C or higher, more preferably 515 ° C or higher, and further preferably 530 ° C or higher. The upper limit value is preferably 700 ° C. or lower, more preferably 650 ° C. or lower, and further preferably 630 ° C. or lower. In the production method of the present invention, the temperature of the raw material dissolution region in the reaction vessel is preferably higher than the temperature of the crystal growth region. The temperature difference is preferably 5 ° C. or more, more preferably 10 ° C. or more, preferably 100 ° C. or less, and more preferably 80 ° C. or less. The optimum temperature and pressure in the reaction vessel can be appropriately determined depending on the type and amount of mineralizer and additive used during crystal growth.

  In order to achieve the above temperature range and pressure range in the reaction vessel, the injection rate of the solvent into the reaction vessel, that is, the filling rate is the free volume of the reaction vessel, that is, the polycrystalline raw material and the seed crystal are used in the reaction vessel. In this case, subtract the volume of the seed crystal and the structure where it is installed from the volume of the reaction vessel, and if a baffle plate is installed, subtract the volume of the baffle plate from the volume of the reaction vessel. Based on the liquid density at the boiling point of the remaining volume of solvent, it is usually 20 to 95%, preferably 30 to 80%, and more preferably 40 to 70%.

The growth of nitride crystals in the reaction vessel is maintained in a subcritical or supercritical state of a solvent such as ammonia by heating and heating the reaction vessel using an electric furnace having a thermocouple. Is done. 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. It can also be heated while being partially cooled.
The above “reaction temperature” is measured by a thermocouple provided so as to be in contact with the outer surface of the reaction vessel and / or a thermocouple inserted into a hole having a certain depth from the outer surface. It can be estimated in terms of temperature. The average value of the temperatures measured with these thermocouples is taken as the average temperature. Usually, an average value of the temperature of the raw material melting region and the temperature of the crystal growth region is defined as the average temperature.

  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. The temperature lowering method is not particularly limited, but the heating may be stopped while the heating of the heater is stopped and the reaction vessel is installed in the furnace as it is, or the reaction vessel may be removed from the electric furnace and air cooled. If necessary, quenching with a refrigerant is also preferably used.

  After the temperature of the outer surface of the reaction vessel or the estimated temperature inside the reaction vessel is below a predetermined temperature, the reaction vessel 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. Here, the valve may be opened by connecting a pipe to the pipe connection port of the valve attached to the reaction vessel, leading to a vessel filled with water or the like. Furthermore, if necessary, remove the ammonia solvent in the reaction vessel sufficiently by applying a vacuum, etc., then dry, open the reaction vessel lid, etc., and generate nitride crystals and unreacted raw materials and mineralization. Additives such as agents can be removed.

  In addition, when manufacturing gallium nitride according to the manufacturing method of this invention, Unexamined-Japanese-Patent No. 2009-263229 can be referred preferably for the detail of materials other than the above, manufacturing conditions, a manufacturing apparatus, and a process. The entire disclosure of this publication is incorporated herein by reference.

(Nitride crystals)
When the mineralizer purified according to the present invention is used, the oxygen concentration of the nitride crystal obtained after crystal growth is significantly lower than when the mineralizer is used without purification according to the conventional method. The oxygen concentration of the nitride crystal obtained by the solvothermal method of the present invention is usually 1 × 10 ¹⁹ atom / cm ³ or less, preferably 5 × 10 ¹⁸ atom / cm ³ or less, more preferably 5 × 10 10. ¹⁷ atom / cm ³ or less, more preferably 5 × 10 ¹⁶ atom / cm ³ or less. Such a low oxygen concentration is a level that has been difficult to achieve by the solvothermal method in which a conventional solid mineralizer is added.

The nitride crystal obtained by the solvothermal method of the present invention is also characterized by a lower silicon concentration than the nitride crystal obtained by the conventional solvothermal method. The silicon concentration of the nitride crystal obtained by the solvothermal method of the present invention is usually 5 × 10 ¹⁸ atom / cm ³ or less, preferably 1 × 10 ¹⁸ atom / cm ³ or less, more preferably 5 × 10 10. ¹⁷ atom / cm ³ or less.
Furthermore, the nitride crystal obtained by the solvothermal method of the present invention is also characterized by a low threading dislocation density. Further, the nitride crystal obtained by the solvothermal method of the present invention has a feature that the warpage of the lattice plane is small.

The type of nitride crystal obtained by the solvothermal method of the present invention depends on the type of crystal growth raw material to be selected. According to the present invention, a nitride crystal of Group 13 metal of the periodic table can be preferably grown, and a gallium-containing nitride crystal can be more preferably grown. Specifically, it can be preferably used for the growth of gallium nitride crystals.
According to the solvothermal method of the present invention, a crystal having a relatively large diameter can be obtained. For example, it is possible to obtain a nitride crystal having a maximum diameter of 50 mm or more, more preferably a nitride crystal having a maximum diameter of 76 mm or more, and even more preferably a nitride crystal having a maximum diameter of 100 mm or more. Since it grows in an environment with fewer impurities than before, uniform growth can be realized in a larger area.

  The features of the present invention will be described more specifically with reference to test examples, 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.

<Test Example> Mineralizer Sublimation Purification Test A GaN crystal was manufactured using the manufacturing apparatus of FIG.
A sublimation experiment of ammonium iodide was performed using a capsule 20 made of Pt—Ir alloy having an inner diameter of 60 mm and a length of 900 mm. In order to approach the actual growth conditions, 2000 g of polycrystalline GaN 8 was filled at the bottom of the capsule, and 58.42 g of 4N purity ammonium iodide reagent was added. The reagent was dark yellow to light orange, suggesting that it was adsorbing moisture. A baffle plate 5 was installed at a substantially middle position, and a seed crystal holding frame made of Pt was installed at the top. Finally, a Pt—Ir alloy cap was attached by welding. A tube for gas injection and evacuation is attached to the upper part of the cap. In order to confirm the sealing property of the capsule, nitrogen gas was filled and the pressure was increased to about 0.2 MPa. Subsequently, a capsule was put in a water tank, and the presence or absence of bubbles was confirmed to confirm that there was no gas leakage. Subsequently, the tube was connected to the vacuum pump 11 and the pressure reduction and dry nitrogen purge were repeated several times until 1 × 10 ⁻¹ Torr, and then the pressure was reduced to 1 × 10 ⁻³ Torr. A rubber heater was wound around the upper and lower halves around the capsule, and the temperature was raised to 120 ° C. for the upper part (T2) and 150 ° C. for the lower part (T1) over about 15 minutes. During the temperature increase, the degree of vacuum, which was considered to be due to the vapor pressure of moisture, was reduced, and the degree of vacuum deteriorated to 1 × 10 ⁻¹ Torr. After that, moisture decreased with the passage of time, and the degree of vacuum started to recover. After maintaining at this temperature for 2 hours, the lower temperature (T1) was raised to 180 ° C. over about 15 minutes while maintaining the upper temperature. After holding at this temperature for 19 hours, the degree of vacuum had reached 1 × 10 ⁻³ Torr. In this state, the valve was closed, and it was naturally cooled down to room temperature in a sealed state. When the cap was opened and the inside of the capsule was observed, a transparent ammonium iodide crystal of about 0.1 mm to 1 mm was sublimated and deposited so as to cover the inner wall of the capsule and the surface of the seed crystal holding frame. The weight of ammonium iodide sublimated and precipitated on the inner wall of the capsule and the surface of the seed crystal holding frame was 35.16 g. This corresponds to about 60% of 58.42 g of ammonium iodide charged. Further, when ammonium iodide remaining in the lower part without observing sublimation was observed, what was dark yellow to light orange before the experiment was almost completely white (transparent). This indicates that the moisture was reduced by heating without sublimation.

<Example> Production of GaN Crystal A GaN crystal was produced using the production apparatus of FIG. The mineralizer sublimation purification process was performed in the apparatus format shown in FIG.
Crystal growth was carried out using a RENE41 autoclave 1 (internal volume of about 345 cm ³ ) having an inner diameter of 30 mm and a length of 450 mm as a pressure resistant container, and a Pt—Ir capsule 20 as a reaction container. As raw material 8, 140 g of polycrystalline GaN particles were weighed and placed in the capsule lower region (raw material dissolution region 9). The polycrystalline GaN particles used as the raw material were analyzed by SIMS (secondary ion mass spectrometer) before use, and as a result, the oxygen concentration was 5 × 10 ¹⁸ atoms / cm ³ . Next, NH ₄ I having a purity of 99.999% and GaF ₃ having a purity of 99.999% were charged into the capsule as mineralizers. It was confirmed that the supplied mineralizer was deposited in the lower raw material dissolution zone.

  Further, a platinum baffle plate 5 was installed between the lower raw material melting region 9 and the upper crystal growth region 6. Two wafers (10 mm x 5 mm x 0.3 mm) of the hexagonal GaN single crystal grown by the HVPE method as the seed crystal 7 having a principal surface of C and a wafer having a principal surface of the M surface (5 mm x 7.5 mm x 0.3 mm) ) Two sheets were used. The main surface of the seed crystal was subjected to CMP (chemical mechanical polishing), and the surface roughness was confirmed to be Rms of 0.5 nm or less by measurement with an atomic force microscope. These seed crystals 7 were suspended from a platinum seed crystal support frame by a platinum wire having a diameter of 0.2 mm, and placed in the crystal growth region 6 above the capsule.

Next, a cap made of Pt—Ir was connected to the upper portion of the capsule 20 by TIG welding, and the weight was measured. A valve similar to the valve 10 in FIG. 1 was connected to the tube attached to the upper part of the cap as shown in FIG. 5, and the valve was operated so as to communicate with the vacuum pump 11 to perform vacuum deaeration. Thereafter, the valve was operated so as to pass through the nitrogen cylinder 13 and the inside of the capsule was purged with nitrogen gas. The vacuum degassing and nitrogen purging were carried out five times, and then the degree of vacuum was increased to 1 × 10 ⁻² Torr while connected to the vacuum pump, and the vacuum pump was kept operating. A rubber heater was wound around each of the lower raw material dissolution zone and the upper crystal growth zone of the capsule to enable independent temperature control. The upper part (T2) was heated to 120 ° C. and the lower part (T1) was heated to 150 ° C. over about 15 minutes, and then held for 2 hours. Subsequently, with the upper part (T2) kept at 120 ° C., the lower part (T1) was heated to 170 ° C. over about 15 minutes, and then kept for 14 hours. After holding for 14 hours, the degree of vacuum reached 1 × 10 ⁻³ Torr. After closing the valve and naturally cooling the capsule to room temperature, the capsule was cooled with a dry ice ethanol solvent while maintaining the vacuum state. Subsequently, the valve of the conduit was operated so as to communicate with the NH ₃ cylinder 12, the valve was opened again, NH ₃ was filled without touching the outside air, and then the valve was closed again. The filling amount was confirmed from the difference in weight before and after NH ₃ filling.

Subsequently, after the capsule 20 was inserted into the autoclave 1 to which the valve 10 was attached, the lid was closed and the weight of the autoclave 1 was measured. Subsequently, the conduit was connected to the vacuum pump 11 through the valve 10 attached to the autoclave, and the valve was opened to perform vacuum deaeration. Nitrogen gas purging was performed several times as in the capsule. Thereafter, the autoclave 1 was cooled with a dry ice ethanol solvent while maintaining the vacuum state, and the valve 10 was once closed. Next, after the conduit was operated to lead to the NH ₃ cylinder 12, the valve 10 was opened again, and NH ₃ was filled in the autoclave 1 without continuously touching the outside air, and then the valve 10 was closed again. The temperature of the autoclave 1 was returned to room temperature, the outer surface was sufficiently dried, and the weight of the autoclave 1 was measured. The weight of NH ₃ was calculated from the difference from the weight before filling with NH ₃ to confirm the filling amount.

Subsequently, the autoclave 1 was housed in an electric furnace composed of a heater divided into two parts in the vertical direction. The temperature was raised to an average temperature of 610 ° C. over 9 hours so that the crystal growth region was about 20 ° C. lower than the raw material dissolution region, and after reaching the set temperature, the temperature was maintained for 11 days. The pressure in the autoclave was 215 MPa. Further, the variation in the control temperature of the outer surface of the autoclave during the holding was ± 0.3 ° C. or less.
Then, it cooled naturally until the temperature of the outer surface of the autoclave 1 returned to room temperature, the valve 10 attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave 1 was weighed to confirm the discharge of NH ₃ , the lid of the autoclave was opened, and the capsule 20 was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule. When the inside of the capsule was confirmed, gallium nitride crystals were uniformly deposited on the entire surface of the seed crystal on either the C plane or the M plane. When the oxygen concentration in the crystal was measured by SIMS, it was 5 × 10 ¹⁷ atoms / cm ³ .

Comparative Example Production of GaN Crystal A GaN crystal was produced using the production apparatus of FIG.
Crystal growth was carried out using a RENE41 autoclave 1 (internal volume of about 345 cm ³ ) having an inner diameter of 30 mm and a length of 450 mm as a pressure resistant container, and a Pt—Ir capsule 20 as a reaction container. As raw material 8, 100 g of polycrystalline GaN particles were weighed and placed in the capsule lower region (raw material dissolution region 9). Next, NH ₄ I having a purity of 99.999% was charged into the capsule as a mineralizer. It was confirmed that the supplied mineralizer was deposited in the lower raw material dissolution zone.

A seed crystal and a baffle were arranged in the same manner as in the above example, and a cap made of Pt—Ir was connected to the top of the capsule 20 by TIG welding, and then the weight was measured. A valve similar to the valve 10 in FIG. 1 was connected to the tube attached to the upper part of the cap, and the valve was operated so as to communicate with the vacuum pump 11 to perform vacuum deaeration. Thereafter, the valve was operated so as to pass through the nitrogen cylinder 13 and the inside of the capsule was purged with nitrogen gas. The vacuum degassing and nitrogen purging were performed 5 times, and the degree of vacuum was raised to 1 × 10 ⁻² Torr while connected to a vacuum pump. All the above steps were performed at room temperature. The capsule was cooled with dry ice ethanol solvent while maintaining the vacuum state. Subsequently, the valve of the conduit was operated so as to communicate with the NH ₃ cylinder 12, the valve was opened again, NH ₃ was filled without touching the outside air, and then the valve was closed again. The filling amount was confirmed from the difference in weight before and after NH ₃ filling.

In the subsequent steps, the capsule was inserted into the autoclave in the same manner as in the above example, NH ₃ was filled outside the capsule, and then the autoclave was set in an electric furnace for crystal growth. The crystal growth period was 5 days.
The oxygen concentration in the crystal grown by SIMS was measured and found to be 1.1 × 10 ¹⁹ atoms / cm ³ .

  As is clear from the comparison of the results of the above Examples and Comparative Examples, the oxygen concentration in the produced nitride crystal is increased by purifying the mineralizer according to the present invention and then growing the nitride crystal. It can be greatly reduced.

  According to the method for producing a nitride crystal by the solvothermal method of the present invention, a high-purity nitride crystal having a low oxygen concentration can be efficiently grown. Moreover, since the apparatus of the present invention capable of producing such a nitride crystal can be enlarged and mass-produced, the industrial applicability is high. Further, since the nitride crystal of the present invention has a low oxygen concentration and a high purity, it is difficult to cause coloring, and can be applied to various uses such as optoelectronic substrates such as LEDs and LDs. Therefore, the present invention has high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Autoclave 2 Autoclave inner surface 3 Lining 4 Lining inner surface 5 Baffle plate 6 Crystal growth area 7 Seed crystal 8 Raw material 9 Raw material melting area 10 Valve 11 Vacuum pump 12 Ammonia cylinder 13 Nitrogen cylinder 14 Mass flow meter 15 Mineralizer sublimation precipitation container 16 Mineralization Agent precipitation container 17 Mineralizer heating sublimation container 20 Capsule 21 Capsule inner surface 22-26 Heater

Claims (31)

A mineralizer sublimation purification step in which the mineralizer is sublimated after being sublimated in a reaction vessel for crystal growth or in a closed circuit connected to the reaction vessel;
A crystal growth step of growing a nitride crystal from a nitride crystal growth raw material placed in the reaction vessel by a solvothermal method in the presence of the solvent and the refined mineralizer in the reaction vessel. A method for producing a nitride crystal.   2. The method for producing a nitride crystal according to claim 1, wherein in the sublimation purification step of the mineralizer, the pressure is set to 1 Torr or less.   In the mineralizer sublimation purification step, the temperature (T1) of the mineralizer heating sublimation region for heating and sublimating the mineralizer, and the temperature (T2) of the mineralizer precipitation region for depositing the sublimated mineralizer. The method for producing a nitride crystal according to claim 1, wherein the temperature difference (T1−T2) is set to 5 ° C. or more.   The method for producing a nitride crystal according to claim 3, wherein the temperature difference is controlled by a heater.   The manufacturing method of the nitride crystal | crystallization of Claim 3 or 4 whose temperature (T1) of the said mineralizer heating sublimation area | region is 80 to 350 degreeC.   The manufacturing method of the nitride crystal as described in any one of Claims 3-5 whose temperature (T2) of the said mineralizer precipitation area | region is 30 to 300 degreeC.   In the mineralizer sublimation purification step, a mineralizer heating sublimation region for heating and sublimating the mineralizer and a mineralizer precipitation region for precipitating the sublimated mineralizer are both set in the reaction vessel. The manufacturing method of the nitride crystal as described in any one of Claims 1-6.   The method for producing a nitride crystal according to claim 7, wherein the sublimation purification step of the mineralizer is performed in the reaction vessel in which at least a raw material, a mineralizer, and a seed crystal are present.   In the mineralizer sublimation purification step, a mineralizer heating sublimation region for heating and sublimating the mineralizer and a mineralizer precipitation region for precipitating the sublimated mineralizer are both set outside the reaction vessel. The manufacturing method of the nitride crystal as described in any one of Claims 1-6.   The method for producing a nitride crystal according to claim 9, wherein both the mineralizer heating sublimation region and the mineralizer precipitation region are set in a mineralizer purification vessel provided separately from the reaction vessel.   The mineralizer heating sublimation area is set in a mineralizer heating sublimation container, and the mineralizer precipitation area is set in a mineralizer precipitation container provided separately from the mineralizer heating sublimation container, Item 10. A method for producing a nitride crystal according to Item 9.   The method for producing a nitride crystal according to any one of claims 1 to 11, wherein the mineralizer purified by the mineralizer sublimation purification step is mixed with ammonia and introduced into the reaction vessel.   The refined mineralizer obtained by precipitation in the mineralizer precipitation vessel is introduced into the reaction vessel, and the mineralizer remaining in the mineralizer heating sublimation vessel is not introduced into the reaction vessel. The method for producing a nitride crystal according to claim 12.   The manufacturing method of the nitride crystal as described in any one of Claims 1-13 by which the mineralizer used for the said mineralizer sublimation purification process is sublimated and refined previously.   The method for producing a nitride crystal according to claim 1, wherein the mineralizer contains a halogen element.   The method for producing a nitride crystal according to any one of claims 1 to 15, wherein the solvent is ammonia.   The method for producing a nitride crystal according to any one of claims 1 to 16, wherein the nitride crystal is gallium nitride.   The method for producing a nitride crystal according to any one of claims 1 to 17, wherein the reaction vessel or the closed circuit is replaced with nitrogen gas before the mineralizer sublimation purification step is started.   The said reaction container is comprised by the 1 or more types of metal or alloy selected from the group which consists of Pt, Ir, W, Ta, Rh, Ru, and Re. A method for producing a nitride crystal.   19. The reaction container according to claim 1, wherein the reaction vessel is lined with one or more metals or alloys selected from the group consisting of Pt, Ir, W, Ta, Rh, Ru, and Re. A method for producing a nitride crystal.   The method for producing a nitride crystal according to any one of claims 1 to 20, wherein the reaction vessel is an autoclave.   The method for producing a nitride crystal according to any one of claims 1 to 20, wherein the reaction vessel is a capsule inserted in an autoclave.   The nitride crystal manufactured by the manufacturing method of the nitride crystal as described in any one of Claims 1-22.   The nitride crystal according to claim 23, wherein the nitride crystal is a nitride crystal of a group 13 metal of the periodic table.   The nitride crystal according to claim 23, wherein the nitride is gallium nitride.   A reaction vessel capable of growing a nitride crystal by a solvothermal method, a mineralizer sublimation precipitation vessel for sublimating and precipitating the mineralizer, and means for introducing the sublimation-purified mineralizer into the reaction vessel. An apparatus for producing a nitride crystal, comprising:   The said mineralizer sublimation precipitation container has both the mineralizer heating sublimation area | region which heats and sublimates the said mineralizer, and the mineralizer precipitation area | region which precipitates the sublimated mineralizer. Nitride crystal manufacturing equipment.   A reaction vessel capable of growing a nitride crystal by a solvothermal method, a mineralizer heating sublimation vessel for sublimating the mineralizer, a mineralizer precipitation vessel for depositing the mineralizer, and the deposited mineralizer An apparatus for producing a nitride crystal, comprising an introduction means for introducing the reaction vessel.   29. The apparatus for producing a nitride crystal according to claim 28, wherein the introduction means does not introduce the mineralizer remaining in the mineralizer heating sublimation vessel into the reaction vessel.   The apparatus for producing a nitride crystal according to any one of claims 26 to 29, further comprising means for introducing a solvent into each of the reaction vessels.   The apparatus for producing a nitride crystal according to any one of claims 26 to 30, wherein a pipe is attached to the reaction vessel, and the pressure can be reduced through the pipe.