JP5454828B2 - Crystal manufacturing method and crystal manufacturing apparatus using supercritical solvent - Google Patents

Description

  The present invention relates to a crystal manufacturing method and a crystal manufacturing apparatus by a solvothermal method, and in particular, using a solid mineralizer and a nitrogen-containing solvent such as ammonia, gallium nitride (hereinafter referred to as the chemical formula “GaN” A crystal having excellent crystallinity by an ammonothermal method or the like for crystal growth of a nitride such as a group 13 element (hereinafter referred to as “group 13 element”) of the periodic table represented by The present invention relates to a crystal manufacturing method and a crystal manufacturing apparatus that can be manufactured.

  The solvothermal method is a general term for crystal manufacturing methods using a solvent in a supercritical state and / or a subcritical state, and is called a hydrothermal method (hydrothermal synthesis method) or ammonothermal method depending on the type of solvent used. The

  In the solvothermal method, a temperature difference is provided in a high-temperature and high-pressure system containing raw materials, a solvent, a seed crystal, a mineralizer, and the like, and crystal growth is performed by utilizing the difference in crystal solubility of the raw materials in the solvent due to this temperature difference. Is what you do. In order to perform single crystal growth with good crystallinity by the solvothermal method, it is necessary to maintain an appropriate crystal growth rate. It is known that the concentration of the mineralizer dissolved in the solvent affects the crystal growth rate (see, for example, Non-Patent Document 1). According to such knowledge, when the concentration of the mineralizer in the solvent is large, the solubility of the raw material is increased and the crystal growth rate is also increased.

  The hydrothermal method uses an acid or alkali solution in which a mineralizer is previously dissolved in a solvent. In the hydrothermal method, since the dissolved mineralizer contributes purely as a catalyst, the concentration of the mineralizer does not change greatly from the start of crystal growth to the end of growth, and stable crystals are obtained. It is possible to sustain the growth rate.

  On the other hand, among the solvothermal methods, for example, in the ammonothermal method, a solid mineralizer is used. In the case of the ammonothermal method in which the mineralizer is placed in an autoclave as a solid, the raw material is charged into a reaction vessel such as an autoclave, and then the mineralizer starts to dissolve at the time of temperature rise or pressure increase until the start of crystal growth. . However, in the ammonothermal method, since the concentration of the mineralizer in the solvent changes depending on the dissolution rate of the mineralizer, it is difficult to control the solubility of the raw material affected by the concentration.

  For example, when the dissolution rate of the mineralizer is slow, the raw material dissolution rate is slowed accordingly, and the raw material becomes difficult to dissolve. For this reason, a sufficient crystal growth rate cannot be obtained. On the other hand, when the dissolution rate of the mineralizer is extremely high, the dissolution rate of the raw material is increased, and the crystal growth rate is also promoted. At this time, the dissolution of the seed crystal is promoted with the improvement of the dissolution rate of the raw material. However, if the dissolution rate of the mineralizer is too fast, the seed crystals will be dissolved more than necessary, and so-called seed crystals will be melted back more than necessary. If the meltback goes too far, the seed crystal disappears and the yield decreases. Here, meltback means that the seed crystal surface is slightly etched in order to remove the seed crystal, scratches on the surface of the seed crystal, and impurities during crystal growth using the seed crystal, and to grow a good crystal. Say.

  In the case of the ammonothermal method, metal gallium (Ga) or the like can be used as a raw material in addition to GaN. In this case, metal Ga reacts with nitrogen in the mineralizer to form GaN, and it is known that the mineralizer itself is consumed during this reaction (see, for example, Patent Document 1). . That is, when metal Ga is used as a raw material, the concentration of the mineralizer in the solvent changes from the start of crystal growth to the end of growth due to consumption of the mineralizer. As a result, it is difficult to control the crystal growth rate, and it has been difficult to obtain a single crystal with good crystallinity by such a method.

The problems described above are problems inherent to the ammonothermal method using a solid mineralizer, and the mineralizer is dissolved in a solvent at normal temperature and pressure (as an acid or alkali solution). In the hydrothermal method, such a problem did not occur. Further, there is room for improvement in the filling method of the solid mineralizer and the configuration of the mineralizer filling portion of the autoclave used for such ammonothermal method.
Japanese Patent Laid-Open No. 2004-2152 Mineralogical Journal Vol. 8 No. 6 pages 383-396 (1968)

  The present invention controls the dissolution rate of the solid mineralizer, which is a problem in the prior art as described above, in the solvent, and controls the solubility of the mineralizer in the solvent, so that the crystal growth rate is suitably adjusted. An object of the present invention is to provide a crystal production method and a crystal production apparatus capable of maintaining and extending the lifetime of mineralizers, seed crystals, and the like.

  As a result of intensive investigations to solve the above-mentioned problems, the present inventors set the contact area of the mineralizer to the solvent within a certain range with respect to the internal horizontal cross-sectional area of the reaction vessel. The present invention has been found. The gist of the present invention is as follows.

(1) in a reaction vessel, a solvent in a supercritical state and / or subcritical state, the raw material, and, using a solid-like of mineralizer, a crystal manufacturing method for growing crystals,
In the state in which the mineralizer is arranged in the reaction vessel so that the total contact area of the mineralizer with the solvent is 2 to 80% of the internal horizontal cross-sectional area of the reaction vessel. A method for producing a crystal, characterized in that:

(2) The crystal production method according to (1), wherein the reaction vessel has a mineralizer filling portion for filling the mineralizer in the vessel.

(3) The method for producing a crystal according to (2), wherein the total opening area of the mineralizer filling portion is 2 to 80% of the internal horizontal cross-sectional area of the reaction vessel.

(4) The crystal production method according to (2) or (3), wherein a horizontal cross-sectional area of the mineralizer filling portion is 2 to 80% of an internal horizontal cross-sectional area of the reaction vessel.

(5) The crystal production method according to any one of (2) to (4), wherein the mineralizer filling part is provided integrally with a container inner bottom part of the reaction container.

(6) The crystal production method according to any one of (2) to (4), wherein the mineralizer filling part is a crucible separately installed in the reaction vessel.

(7) The crystal production method according to any one of (1) to (6), wherein the mineralizer is formed.

(8) The crystal production method according to any one of (1) to (7), wherein the obtained crystal is a single crystal.

(9) The crystal production method according to any one of (1) to (8), wherein the obtained crystal is a periodic table group 13 element nitride.

(10) The crystal production method according to any one of (1) to (9), wherein the solvent is a nitrogen-containing solvent.

(11) The crystal production method according to any one of (1) to (10), wherein the reaction vessel is an autoclave.

(12) comprises a reaction vessel, in the reaction vessel, the supercritical state and / or solvent subcritical state, the raw material, and, using a solid-like of mineralizer, a crystal manufacturing apparatus for growing a crystal ,
The reaction vessel has a mineralizer filling part for filling the mineralizer in the vessel,
The total contact area of the mineralizer filled in the mineralizer filling portion with the solvent during the growth of the crystal is designed to be 2 to 80% of the internal horizontal cross-sectional area of the reaction vessel. The crystal manufacturing apparatus characterized by the above-mentioned.

(13) The crystal production apparatus according to (12), wherein the reaction vessel includes a mineralizer filling unit that fills the vessel with the mineralizer.

(14) The crystal manufacturing apparatus according to (13), wherein the total opening area of the mineralizer filling portion is 2 to 80% of the internal horizontal sectional area of the reaction vessel.

(15) The crystal manufacturing apparatus according to (13) or (14), wherein a horizontal cross-sectional area of the mineralizer filling portion is 2 to 80% of an internal horizontal cross-sectional area of the reaction vessel.

(16) The crystal production apparatus according to any one of (13) to (15), wherein the mineralizer filling part is provided integrally with a container inner bottom part of the reaction container.

(17) The crystal manufacturing apparatus according to any one of (13) to (15), wherein the mineralizer filling unit is a crucible separately installed in the reaction vessel.

(18) The crystal production apparatus according to any one of (12) to (17), wherein the reaction vessel is an autoclave.

  By controlling the dissolution rate of the solid mineralizer in the solvent and controlling the solubility of the mineralizer in the solvent by the crystal production method and the crystal production apparatus of the present invention, the crystal growth rate is suitably maintained. In addition, the lifetime of mineralizers and seed crystals can be extended. Thereby, the crystal | crystallization excellent in crystallinity can be manufactured efficiently.

  Hereinafter, the crystal production method and the crystal production apparatus of the present invention 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.

  In the reaction vessel, the present invention uses (1) a supercritical and / or subcritical solvent, and (2) a solid mineralizer, and the total contact area of the mineralizer with the solvent Is 2 to 80% of the internal horizontal cross-sectional area of the reaction vessel. The crystal production method of the present invention and the crystal production apparatus used in the method are as follows. The contact area of the mineralizer with respect to the solvent is 2 to 80% of the internal horizontal cross-sectional area of the reaction vessel. The contact area with respect to can be reduced. For this reason, the melt | dissolution rate with respect to the solvent of a mineralizer can be suppressed, and the melt | dissolution density | concentration of the mineralizer in a solvent can be controlled in connection with this. Thus, by controlling the dissolution concentration of the mineralizer in the solvent, the dissolution rate of the raw material for forming the target crystal (especially a single crystal) in the solvent can be maintained within a desired range. The crystal growth rate can be suitably maintained. Furthermore, by maintaining the crystal growth rate, the generation of polynuclear nuclei can be prevented, and a single crystal having excellent crystallinity can be produced.

  The present invention is suitable for a method using a solid mineralizer in the solvothermal method, and particularly suitable for an ammonothermal method. The reaction vessel in the present invention is not particularly limited as long as it can be applied to crystal growth using a solvent in a supercritical state and / or a subcritical state (hereinafter referred to as “supercritical solvent”). For example, an autoclave is preferable.

  First, the reference in the present invention will be described with reference to FIGS. 1 and 2 taking as an example the case where an autoclave is used as the crystal manufacturing apparatus of the present invention and the apparatus used in the manufacturing method of the present invention. However, the present invention is not limited to these embodiments.

  FIG. 1 is a cross-sectional view showing a crystal production apparatus of the present invention using a crucible, and FIG. 2 is an explanatory view showing a contact area of a mineralizer with a solvent in the present invention and an internal horizontal cross-sectional area of a reaction vessel. is there. In FIG. 1, a crystal production apparatus 1 has an autoclave used for an ammonothermal method, and is composed of a reaction vessel (autoclave) 2 and a conduit 3. The reaction vessel 2 has a crystal growth region 4 and a raw material filling region 5, and a baffle plate 6 is provided at the boundary. Inside the reaction vessel 2, two crucibles 8A and 8B in which a solid mineralizer 7 is filled in a crystal filling region 5 are placed, and further, a crystal raw material (polycrystalline raw material to be manufactured) ) 10 is filled to fill between crucibles 8A and 8B. The crystal growth region 4 of the reaction vessel 2 is provided with a plurality of seed crystals 9. 1 and 2, the reaction vessel 2 and the crucibles 8A and 8B are assumed to be cylindrical. In the following drawings, the direction from the top to the bottom of the page is the direction of gravity.

  A plurality of heaters 11 and thermocouples 12 are provided in the vicinity of the outside of the reaction vessel 2 in order to provide a temperature difference in the high-temperature and high-pressure system. The autoclave 1 is configured such that the temperature can be controlled by dividing the reaction vessel 2 into a plurality of zones by a heater 11 and a thermocouple 12 (in FIG. 1, it is divided into two zones, upper and lower with respect to the paper surface). The output can be changed every time. This temperature difference is set so that the solubility curve becomes a lower temperature as it goes to the upper part of the autoclave 1 when the solubility curve has a positive slope (the higher the temperature, the higher the solubility).

In the autoclave 1, after vacuum degassing from the state shown in FIG. 1, a supercritical solvent such as NH ₃ is filled into the reaction vessel 2 through the conduit 3, and the temperature is increased between the crystal growth region 4 and the raw material filling region under high pressure. Raise the temperature while making a difference. Furthermore, after the temperature of the reaction vessel 2 reaches a predetermined temperature, a desired single crystal can be deposited in the form of a seed crystal by holding for a certain period of time.

  In the crystal production method of the present invention, the total contact area of the mineralizer 7 with the solvent is 2 to 80% of the internal horizontal cross-sectional area of the reaction vessel 2. If the total contact area of the mineralizer is less than 2% of the internal horizontal cross-sectional area of the reaction vessel, the dissolution rate of the mineralizer becomes too slow, and as a result, the dissolution rate of the raw material decreases and the raw material becomes a solvent. Therefore, a sufficient crystal growth rate of the raw material cannot be obtained. Further, if the total contact area of the mineralizer exceeds 80% of the internal horizontal cross-sectional area of the reaction vessel, the dissolution rate of the mineralizer becomes too fast, and the dissolution of not only the raw material but also the seed crystal is promoted. An excessive meltback of crystals and disappearance of seed crystals are caused, and the yield of crystals is lowered.

  From the viewpoint of dissolution of the mineralizer in the solvent, the total contact area of the mineralizer is preferably 10%, more preferably 20%, with respect to the internal horizontal cross-sectional area of the reaction vessel. On the other hand, the upper limit is preferably 70%, more preferably 50%.

  Here, “the sum of the total contact area with the solvent of the mineralizer” means an area in contact with the solvent of the mineralizer in the reaction vessel, and when a plurality of mineralizers are installed. Means the sum of these contact areas. For example, when the mineralizer is filled in the mineralizer filling portion and installed in the reaction vessel, it comes into contact with the solvent only at the opening of the filler filling portion. The total area corresponds to the total contact area of the mineralizer. Mineralization, especially when an opening is provided only above the paper surface, such as a crucible, that is, when the contact area of the mineralizer can be regarded as only the surface area when the mineralizer is observed from above the paper surface. You may calculate the sum total of all the contact areas on the basis of the horizontal cross-sectional area of an agent.

  The “inner horizontal cross-sectional area of the reaction vessel” means the horizontal cross-sectional area of the inner diameter when the reaction vessel is cut in the horizontal direction with respect to the direction of gravity at the maximum inner diameter of the raw material filling region of the reaction vessel.

  That is, in FIG. 1, the mineralization in the case where the reaction vessel is cut in the horizontal direction with respect to the direction of gravity at any portion (for example, broken lines L1 to L3) where the mineralizer 7 of the reaction vessel 2 is installed. The sum of the horizontal cross-sectional areas of the agent and the internal horizontal cross-sectional area of the reaction vessel are the criteria of the present invention.

  Specifically, when the reaction vessel 2 is cut in the horizontal direction at the position of the broken line L1 in FIG. 1, the total contact area of the mineralizer 7 is shown in FIG. 2 where each of the arrows SA1 and SA2 has a diameter. This is the sum of the areas of the circles S1 and S2. Circles S1 and S2 correspond to the opening areas of crucibles 8A and 8B, respectively. On the other hand, the internal horizontal cross-sectional area of the reaction vessel 2 at the position of the broken line L1 in FIG. 1 is the area of a circle SB shown in FIG. 2 having the diameter of the arrow SB1.

  Further, in FIG. 1, since the reaction vessel 2 and the crucibles 8A and 8B are cylindrical, even when the reaction vessel 2 is cut in the horizontal direction along the broken lines L2 and L3, the contact with the mineralizer 7 respectively. The total area is the sum of the areas of the circles S1 and S2, and the internal horizontal cross-sectional area of the reaction vessel 2 is the area of the circle SB.

  That is, in the crystal manufacturing apparatus shown in FIG. 1 and FIG. 2, the dissolution rate of the mineralizer is suitably maintained by setting the total area of the circle S1 and the circle S2 to 2 to 80% of the area of the circle SB. can do. In FIGS. 1 and 2, since the cylindrical reaction vessel and the crucible were used, the contact area of the mineralizer and the internal horizontal cross-sectional area of the reaction vessel were the same at any position. When shapes having different areas are adopted, it is necessary to satisfy the requirements of the present invention in all other parts.

  Moreover, as shown in FIG. 3, the crystal production apparatus 1 of the present invention may have a mode in which the mineralizer filling portion 13 is provided integrally with the inner bottom portion of the reaction vessel 2. FIG. 3 is a cross-sectional view showing the crystal manufacturing apparatus of the present invention having an integrated mineralizer filling portion. In this case, the total contact area of the mineralizer 7 corresponds to the area of a circle whose diameter is the arrow SA3, and the internal horizontal cross-sectional area of the reaction vessel 2 corresponds to the area of the circle whose diameter is the arrow SB1.

  Furthermore, as shown in FIG. 4, the crystal manufacturing apparatus 1 of the present invention may use a laminate in which pelletized mineralizers are stacked. FIG. 4 is a cross-sectional view showing a crystal production apparatus of the present invention using a pelletized mineralizer. In FIG. 4, a pelletized mineralizer laminate 14 is placed on the bottom of the reaction vessel 2 of the crystal production apparatus 1. In this embodiment, the total contact area of the mineralizers in the laminate 14 of the mineralizer corresponds to the sum of the area of the circle having the diameter of the arrow SA4 and the area of the side surface, and the internal horizontal cross-sectional area of the reaction vessel 2 Corresponds to the area of a circle having the diameter of the arrow SB1.

  Hereinafter, the present invention will be described with reference to the drawings as appropriate, taking as an example an ammonothermal method of growing a group 13 nitride crystal using a nitrogen-containing solvent such as ammonia.

[Crystal production equipment]
(Reaction vessel)
The crystal production apparatus of the present invention has at least the reaction vessel of the present invention. An autoclave is suitable as the reaction vessel.
The structure of the autoclave (reaction vessel in the present invention) will be described. The autoclave is usually separated like a lid and a container and sealed with a gasket or the like. Moreover, you may have a recessed part for inserting a thermocouple etc. As shown in FIG. 1, the reaction vessel in the present invention includes an autoclave having a conduit.

  The autoclave is preferably capable of withstanding a pressure corresponding to the ultrahigh pressure of a supercritical solvent (for example, supercritical ammonia) during the temperature rising reaction. The material for forming the autoclave is not particularly limited as long as it has pressure resistance and erosion resistance. In particular, it is preferable to use a Ni-based alloy that can withstand high temperature and high pressure and has high erosion resistance against ammonia, and a Co-based alloy such as Stellite (registered trademark of Deloro Stellite Company, Inc.). It is particularly preferable to use an alloy. Specific examples of the material include Inconel 625 (Inconel is a registered trademark of Huntington Alloys Canada Limited, the same applies hereinafter), Nimonic 90 (Nimonic is a registered trademark of Special Metals Wiggin Limited, the same applies hereinafter), RENE41, and the like.

  The composition ratio of these alloys depends on the temperature / pressure conditions of the solvent in the system, the reactivity with the various mineralizers contained in the system and their reactants, and / or the oxidizing power / reducing power, pH. What is necessary is just to select suitably according to conditions. As a method of using these as a material constituting the inner surface of the autoclave, a method of manufacturing the autoclave itself using these alloys, a method of forming a thin film as an inner cylinder and installing it in the autoclave may be used. A method of plating the inner surface of the material may also be used.

  In order to further improve the erosion resistance of the autoclave, the inner surface of the autoclave may be lined or coated using the superior erosion resistance of the noble metal. Further, the material of the autoclave itself can be a noble metal. Examples of the noble metal include Pt, Au, Ir, Ru, Rh, Pd, Ag, Os, and alloys containing these noble metals as main components. Among them, it is preferable to use Pt having excellent erosion resistance.

  When the inner surface of the autoclave is lined or coated with a noble metal, if it is difficult to line or coat the entire inner surface, it may be lined or coated on the upper part and / or the lower part of the autoclave. There may be parts that cannot be done.

  The autoclave is a crystal in which a baffle plate (baffle plate 6 in FIG. 1) is installed inside as required, and a raw material filling region filled with a raw material made of GaN polycrystalline nitride or the like and a seed crystal such as GaN are arranged. It is divided into growth regions. Hereinafter, the present invention may be described by taking GaN polycrystalline nitride as a raw material and GaN as a seed crystal as an example, but the present invention is not limited to this.

(Mineralizer filling part)
In this invention, the mineralizer filling part which fills a mineralizer with a reaction container can be provided. The mineralizer filling portion may be provided integrally with the bottom of the reaction vessel, or the mineralizer filling portion may be installed in the reaction vessel as a crucible separately from the reaction vessel (not integrally). May be. Moreover, only one mineralizer filling portion may be provided, or two or more mineralizer filling portions may be provided. Furthermore, the size and capacity of the mineralizer filling portion can be appropriately selected according to the purpose.

  Moreover, although the site | part and the number of the opening part of a mineralizer filling part are not specifically limited, What has one opening part upwards is preferable. Moreover, the shape of the mineralizer filling portion is not particularly limited, but is preferably cylindrical. Furthermore, the cross-sectional shape of the mineralizer filling portion may be polygonal or circular, but is preferably a perfect circle. Moreover, after installing a mineralizer in a raw material filling area | region, it compresses by pushing a mineralizer from the top etc., and you may eliminate the space | gap between mineralizers.

  When the mineralizer filling part is integrally installed at the bottom of the reaction vessel, for example, at the stage of producing the autoclave, the inner diameter of the bottom is made smaller than the top of the autoclave to provide a concave part, or the bottom part has a concave shape. One or more indentations may be provided.

  Moreover, when using a crucible as a mineralizer filling part, the number of crucibles is not specifically limited, According to the objective, 1 or several crucibles can be used. The material of the crucible is not particularly limited as long as it has contact resistance to a supercritical solvent such as supercritical ammonia, and examples thereof include pBN (Pyrolitic Boron Nitride), platinum, and iridium. The shape of the crucible is not particularly limited, but is preferably a cylindrical shape. Furthermore, the cross-sectional shape of the crucible may be polygonal or circular, but is preferably a perfect circle.

  Further, the crucible may be a basket (cage shape) having pores smaller than the particle size of the mineralizer, but a box shape having one opening is preferable.

(Baffle plate)
The crystal manufacturing apparatus of the present invention may include at least one baffle plate to partition the crystal growth region and the raw material filling region. The baffle plate preferably has a hole area ratio of 2 to 10%. By controlling the aperture ratio of the baffle plate, the convection of the supercritical solvent is controlled, a temperature difference is formed between the crystal growth region and the raw material filling region, and the supersaturation degree of GaN in the crystal growth region under the growth conditions is increased. Proper control becomes easy.

  Here, “supersaturation” means a state in which the amount of dissolution has increased more than the saturation state, and “supersaturation degree” means that the amount of dissolution in the supersaturated state and the saturation state as expressed in the following formula (1). The ratio to the amount dissolved. In the solution growth method, it refers to the ratio between the amount of GaN dissolved in the crystal growth region that is supersaturated by GaN transport by convection from the raw material filling region and the amount of GaN dissolved in the saturation state of the crystal growth region. .

なお、本発明において、過飽和度は、原料窒化物の充填量、バッフル板の開孔率、原料充填領域と結晶成長領域との温度差等を適宜変更・選定することにより制御できる。

In the present invention, the degree of supersaturation can be controlled by appropriately changing and selecting the filling amount of the raw material nitride, the baffle plate opening ratio, the temperature difference between the raw material filling region and the crystal growth region, and the like.

  The baffle plate may be made of the same material as that of the autoclave. However, the surface of the baffle plate is made of nickel (Ni) or tantalum (Ta) in order to provide further erosion resistance and to refine the crystal. , Titanium (Ti), niobium (Nb) or pBN. More preferred is a noble metal such as iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), and most preferred is platinum (Pt).

[Crystal production]
In the case of the ammonothermal method, the crystal to be manufactured is a group 13 nitride crystal, which depends on the group 13 element in the raw material. It is preferable that the crystal to be manufactured is mainly a crystal of a single metal nitride of a group 13 element such as B, Al, Ga, In or a crystal of an alloy nitride (for example, GaInN, GaAlN), More preferred are gallium nitride crystals and aluminum nitride.

  In addition, the manufactured crystal is a single crystal. The size of the single crystal obtained by the ammonothermal method depends on conditions such as the size of the autoclave and the size of the seed crystal, but an autoclave having an inner diameter of 100 mm can have a size of φ3 inches.

(material)
When the target product is a Group 13 nitrogen compound crystal, a polycrystalline material of Group 13 nitride crystal is usually used as the material. As the raw material, a raw material containing gallium nitride is preferable. The polycrystalline raw material does not need to be a complete nitride, and depending on the conditions, the group 13 element may contain a metal component in a metal state (that is, zero valence). For example, the crystal is gallium nitride. In some cases, a mixture of gallium nitride and metal gallium may be mentioned.

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

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

  The average particle size of the secondary particles of the polycrystalline raw material is preferably 5 μm or less. When such an average particle diameter is in a small range, the specific surface area is increased and the reactivity with the solvent is improved. The grain size of the polycrystalline raw material in a better mode is to use a GaN polycrystalline raw material having a small average grain size, that is, a high dissolution rate. In this case, the average grain size of the desired GaN polycrystalline material is 1 μm or more. When a polycrystalline raw material having an average particle size of less than 1 μm is used, this may be transported to the crystal growth region by thermal convection and adhere to the seed crystal.

  In addition, by using two types of polycrystalline raw materials having different average particle diameters, Ga (( It is possible to suppress the supply of ions to the crystal growth region, and as a result, it is possible to suppress the disadvantage of the growth of the bulk single crystal, elution of the seed crystal. Moreover, the shape of the GaN microcrystal is not particularly limited, but a spherical shape is preferable in consideration of the uniformity of dissolution in a solvent.

(solvent)
When the crystal growth is growth of a nitride crystal by an ammonothermal method, the solvent is a nitrogen-containing solvent (for example, at least one compound selected from the group consisting of hydrazine N ₂ H ₄ , ammonia NH ₃ , amines, melamine) or can be filled with any solvent miscible with the nitride III-V, it is preferable to use ammonia NH ₃ in the solvent.

  In addition, before putting the nitrogen-containing solvent into the autoclave, it is also preferable to degas the autoclave or to put the nitrogen-containing solvent while circulating an inert gas such as nitrogen. At that time, the reaction vessel may be cooled below the boiling point of the nitrogen-containing solvent. Further, the concentration of water or oxygen contained in these solvents is preferably low, and these concentrations are preferably 1000 ppm or less, more preferably 100 ppm or less, and further preferably 10 ppm or less. The solvent may be used alone or in combination of two or more.

  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. Ammonia generally has a high affinity with water, so when ammonia is charged into an autoclave, it is easy to bring oxygen derived from water into the autoclave, resulting in an increase in the amount of mixed oxygen in the crystals produced and the resulting nitrogen. There is a possibility that the crystallinity of the compound crystal is deteriorated. Also from such a viewpoint, it is desirable to reduce the amount of water and oxygen contained in the ammonia solvent as much as possible, preferably 1000 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less.

  These solvents are used in the subcritical and / or supercritical state during crystal production. The supercritical state means a concentrated gas that is maintained above its critical temperature, and the critical temperature is a temperature at which the gas cannot be liquefied by pressure. 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 refers to a liquid state having a density substantially equal to the critical density near the critical temperature. For example, in the raw material filling region, the raw material is melted as a supercritical state, and the crystal growth region is used to change the temperature so that it becomes a subcritical state. Is possible.

(Mineralizer)
In the present invention, a solid mineralizer is used to increase the crystal growth rate during crystal growth. A mineralizer (or also called a solubilizer) is a substance for increasing the solubility of a raw material in a solvent and transferring the crystal raw material to a crystal growth region, and is well known in the art. The dissolution in this specification includes both physical dissolution and chemical dissolution.

  The mineralizer is usually a compound containing a halogen atom or an alkali metal, alkaline earth metal, or rare earth metal. Among these, from the viewpoint of preventing the generated crystals from containing oxygen, it is preferable to use those containing nitrogen atoms in the form of ammonium ions or amides as mineralizers. These mineralizers may be used alone or in combination of two or more. In order to prevent impurities from being mixed into the nitride crystal, the mineralizer is purified and dried if necessary. The purity of the mineralizer is usually 95% or more, preferably 98% or more, more preferably 99% or more, and particularly preferably 99.5% or more. It is desirable to reduce the water and oxygen contained in the mineralizer as much as possible. These concentrations are preferably 1000 ppm or less, and more preferably 100 ppm or less.

Mineralizers are divided into acidic mineralizers and basic mineralizers. Examples of the basic mineralizer include alkali metals, alkaline earth metals, rare earth metals and compounds containing nitrogen atoms, alkaline earth metal amides, rare earth amides, alkali nitride metals, alkaline earth metal nitrides, azide compounds, etc. Examples thereof include hydrazine salts. Preferably, it is an alkali metal amide, and specific examples include sodium amide (NaNH ₂ ), potassium amide (KNH ₂ ), and lithium amide (LiNH ₂ ). The acidic mineralizer is a compound containing a halogen atom, and examples thereof include ammonium halides, such as ammonium chloride (NH ₄ Cl), ammonium iodide (NH ₄ I), ammonium bromide (NH ₄ Br). Of these, ammonium chloride (NH ₄ Cl) is preferred.

  In the case of the ammonothermal method using ammonia as a solvent, the acidic mineralizer is highly soluble in a supercritical ammonia solvent, has nitriding ability in ammonia, and reacts with noble metals such as Pt. An acidic mineralizer is more preferable because of its low nature.

  As for the use ratio of the mineralizer and the raw material, the mineralizer / group 13 metal element (molar ratio) is usually 0.001 to 100. For example, in the case of GaN, the mineralizer / Ga molar ratio is usually preferably in the range of 0.001 to 20, taking into consideration the types of additives such as raw materials and mineralizers and the target crystal size. Can be selected as appropriate.

  Further, if the mineralizer is not present above the baffle plate (crystal growth region), it may be arranged separately from the raw material, or the mineralizer and the raw material may be mixed. Furthermore, after the mineralizer is installed in the raw material filling region, the mineralizer can be compressed from above by compressing it to eliminate voids between the mineralizers.

  In the present invention, the mineralizer may be in a powder form as long as it is solid, or may be a molded one. Here, “molded” includes compression molding and the like such as “pelletizing”, and may be sintered after compression molding. At this time, the size and shape of the molded mineralizer can be appropriately selected according to the purpose.

(Seed crystal)
In the present invention, it is preferable to use a seed crystal in order to grow the crystal at a predetermined position. When a seed crystal is used, generation of a single crystal on the seed crystal is promoted, and a larger single crystal can be obtained. The seed crystal is usually loaded at the same time as or after filling with additives such as raw materials and mineralizers, and the seed crystal is fixed to a precious metal jig similar to the precious metal constituting the inner surface of the autoclave. If necessary, heating and deaeration after loading in an autoclave is also effectively used.

  When a single crystal of nitride is grown by an ammonothermal method, it is desirable to use the target single crystal of nitride, but it is not necessarily the same nitride as the target. However, in that case, it is a seed crystal having a lattice constant and / or crystal lattice that matches or matches the target nitride, or heteroepitaxy (ie, coincidence of crystallographic positions of some atoms). It is preferable to use a seed crystal composed of a single crystal material piece or a polycrystalline material piece coordinated so as to guarantee. Specific examples of the seed crystal include, for example, gallium nitride (GaN), a single crystal of GaN, a single crystal of nitride such as AlN, a single crystal of silicon carbide (SiC), and the like.

  The seed crystal can be determined in consideration of solubility in an ammonia 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 (Hydride Vapor Phase Epitaxy), and then separated from metal Ga to Na A single crystal obtained by crystal growth using Li, Bi and flux as a flux, a single crystal obtained by homo / heteroepitaxial growth obtained by using the LPE method, a single crystal produced based on the solution growth method including the method of the present invention, and those A cut crystal or the like can be used.

[Production conditions]
Next, each condition for crystal growth in the present invention will be described. In the present invention, in order to produce crystals in a supercritical state and / or a subcritical state, the temperature is generally kept higher than the critical point of the solvent. When ammonia is used as a solvent, the critical point is a critical temperature of 132 ° C. and a critical pressure of 11.35 MPa. However, if the filling rate into the autoclave 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 a state exceeding such a critical pressure. Since the reaction mixture is enclosed within a constant volume (container volume), an increase in temperature increases the pressure of the fluid. In general, the temperature T is in a supercritical state if T> Tc (Tc: critical temperature of the solvent) and pressure P> Pc (Pc: critical pressure of the solvent). Under the above conditions, formation of GaN microcrystals is observed. Actually, since the solubility of the polycrystalline raw material introduced into the solvent is very different between the subcritical condition and the supercritical condition, a sufficient growth rate of the GaN single crystal can be obtained under the supercritical condition. The reaction time depends in particular on the reactivity of the mineralizer and the thermodynamic parameters, ie temperature and pressure values.

  In the case of an ammonia solvent, the lower limit of the temperature range in the autoclave is usually 150 ° C. or higher, preferably 200 ° C. or higher, and particularly preferably 300 ° C. or higher. The upper limit is usually 800 ° C. or lower, preferably 700 ° C. or lower, and particularly preferably 650 ° C. or lower.

  The autoclave is divided into two overlapping zones, that is, a lower raw material filling region and an upper crystal growth region separated by a baffle plate. The temperature gradient ΔT between these two zones is 10-100 ° C. The direction of the gradient depends in particular on the solubility of the raw material as a function of temperature.

  During crystal growth, the autoclave is preferably maintained at a pressure in the range of about 15 MPa to 600 MPa. When the solvent is ammonia, the pressure range in the autoclave is usually 20 MPa or more as the lower limit, preferably 30 MPa or more, particularly preferably 50 MPa or more, and the upper limit is usually 500 MPa or less, preferably 400 MPa or less, particularly preferably 200 MPa or less. It is desirable to hold.

  The rate of injection of the ammonia solvent to achieve the above temperature range and pressure range in the autoclave, that is, the filling rate, is the free volume of the autoclave, i.e., when the raw material and seed crystal are used in the autoclave, Subtract the volume of the structure where it will be installed from the total volume of the autoclave, and if a baffle plate is to be installed, subtract the volume of the baffle plate to obtain the remaining volume of ammonia in the standard state. It is usually 20 to 95%, preferably 30 to 85%, more preferably 40 to 75%, based on the density (liquid density at the boiling point in the case of gas in the standard state).

  The reaction time after reaching a predetermined temperature depends 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 it is usually several hours to several months. Can do. 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 method for lowering the temperature is not particularly limited, but the heating of the heater may be stopped and the autoclave may be allowed to cool as it is installed in the furnace, or the autoclave may be removed from the electric furnace and air cooled. If necessary, quenching with a refrigerant is also preferably used.

  After draining the solvent from the conduit, if necessary, remove the solvent in the autoclave sufficiently by vacuuming, etc., then dry and open the autoclave to grow nitrogen compound crystals and unreacted raw materials and Additives such as mineralizers can be removed.

  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.

[Example 1]
Using an autoclave made of Inconel 625 (approx. 110 ml) with an inner dimension of 20 mm in diameter and 350 mm in length with platinum lined, NH ₄ Cl with a purity of 4N, which was sufficiently dried as a mineralizer, 1.5 g of each was put in a pBN crucible having a length of 50 mm without any gap and set in an autoclave. Next, 18 g of HVPE GaN polycrystal as a raw material was filled so as to fill the gap between crucibles, and further filled from above. Here, since the cylindrical reaction vessel and the crucible are used, the contact area of the mineralizer and the horizontal cross-sectional area of the reaction vessel are the same at any position, and the horizontal cross-sectional area of the mineralizer filling part (crucible) The total was 48% of the internal horizontal cross-sectional area of the autoclave.

Next, a baffle plate was set at a position 180 mm from the bottom, and GaN was installed as five 10 mm square 300 μm thick seed crystals at 25 mm intervals in the crystal growth region on the top, and then the autoclave equipped with a valve was quickly installed. The lid was closed and the autoclave was weighed. Next, the conduit was connected to a vacuum pump through a valve attached to the autoclave, and the valve was opened to evacuate the inside of the autoclave. Thereafter, the autoclave was cooled with a dry ice methanol solvent while maintaining the vacuum state, and the valve was once closed. Subsequently, after the conduit was operated to lead to the NH ₃ cylinder, the valve was opened again, and NH ₃ was filled into the autoclave without continuously touching the outside air. Based on the flow rate control, NH ₃ was filled as a liquid corresponding to about 65% of the cavity of the autoclave (converted to an NH ₃ density of −33 ° C.), and then 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 of the lower outer surface of the autoclave is increased to 490 ° C. and the temperature of the upper outer surface is increased to 410 ° C. over 12 hours with a temperature difference, and the temperature of the lower outer surface of the autoclave is increased to 490 ° C. After reaching 410 ° C., it was held at that temperature for an additional 240 hours. The pressure in the autoclave was about 130 MPa. Further, the temperature range during holding was ± 5 ° C. or less. Thereafter, the temperature was lowered for about 8 hours until the temperature of the lower outer surface of the autoclave reached 150 ° C., and then the heating by the heater was stopped and the mixture was naturally cooled in an electric furnace. After confirming that the temperature of the lower outer surface of the 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 and operated so as to be connected to a 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 inside was confirmed. As a result, 245 μm, 227 μm, 203 μm, 190 μm, and 172 μm gallium nitride (GaN) crystals were deposited on the seed crystal in this order. Further, the thickness of the original seed crystal hardly changed.

  Moreover, the undissolved residue of the mineralizer was not seen in each crucible. When the obtained gallium nitride crystal was taken out and the crystal plane state was first observed with an SEM (scanning electron microscope), no acicular crystals or grain clusters were found. Further, as a result of X-ray diffraction measurement, it was found that the crystal form was hexagonal, and was C-axis oriented in the same orientation as the seed crystal, and the crystallinity was extremely good.

[Example 2]
Using an Autoclave made of Inconel 625 (approx. 210 ml) with an inner dimension of 30 mm in diameter and 300 mm in length with platinum lined, a total of 1.2 g of NH ₄ Cl with a purity of 4N pelletized into a disk shape of φ15 mm thickness 1.7 mm In an autoclave. Further, 12 g of HVPE GaN polycrystal as a raw material was put in the autoclave. The contact area of the mineralizer was the sum of the area of the side surface and the area of the upper surface of the pelletized mineralizer stacked in a columnar shape, and was 70% of the internal horizontal cross-sectional area of the autoclave.

A baffle plate is set at a position 150 mm from the bottom of the autoclave, and 5 pieces of 6 mm sq. 250 μm thick GaN are set as seed crystals at 20 mm intervals in the crystal growth part on the baffle plate, and then held in the same procedure as in Example 1. The gallium nitride was grown for only 120 hours. Then, after cooling to room temperature and discharging NH ₃ , the autoclave lid was opened and the inside was confirmed. As a result, the gallium nitride crystals of 119 μm, 105 μm, 99 μm, 88 μm, and 79 μm were formed in order from the top of the seed crystal. It was precipitated. Further, the thickness of the original seed crystal hardly changed. About 6 g of undissolved raw material GaN polycrystals remained in the autoclave. The discoid mineralizer was not completely dissolved. Moreover, the undissolved residue of the mineralizer was not seen in each crucible. When the obtained gallium nitride crystal was taken out and the crystal plane state was first observed with an SEM (scanning electron microscope), no acicular crystals or grain clusters were found. Further, as a result of X-ray diffraction measurement, it was found that the crystal form was hexagonal, and was C-axis oriented in the same orientation as the seed crystal, and the crystallinity was extremely good.

[Comparative Example 1]
Using the same autoclave as in Example 1, 24 g of HVPE GaN polycrystal (raw material 10) as a raw material was placed in the autoclave 2 as shown in FIG. 6 g of purity 4N NH ₄ Cl (mineralizer 7) was added. When measured at a site 50 to 60 mm in height from the bottom of the autoclave, the horizontal sectional area of the mineralizer 7 (contact area of the mineralizer) was 100% of the internal horizontal sectional area of the autoclave.

A baffle plate is set at a position 180 mm from the bottom of the autoclave, and 5 pieces of 10 mm square 300 μm thick GaN are set as seed crystals at 25 mm intervals on the crystal growth region on the baffle plate. Then, the same growth is performed in the same procedure as in Example 1. Went. Next, after cooling to room temperature and discharging NH ₃ , the autoclave lid was opened and the inside was confirmed. As a result, 202 μm, 193 μm, 181 μm, 169 μm, and 165 μm gallium nitride crystals were deposited in this order from the top of the seed crystal. However, in both cases, the thickness of the original seed part was about 40 μm thinner in the upper seed crystal and about 180 μm thinner in the lower seed crystal. Thereby, it was confirmed that the original seed crystal was dissolved before the gallium nitride crystal was deposited on the seed crystal. Moreover, the undissolved residue of the mineralizer was not seen in the raw material filling area. The obtained gallium nitride crystal was taken out and observed with an SEM (scanning electron microscope), and as a result, it was found that a part of the crystal growth layer contained needle-like crystals and the crystallinity was poor.

From the above, in Comparative Example 1 in which the contact area with NH _{3 as} the solvent of the mineralizer deviated from 2 to 80% of the internal horizontal cross-sectional area of the autoclave, only the mineralizer was first dissolved in the initial stage of growth. It seems that it takes time for the solvent to reach supersaturation due to the dissolution of the raw material with a delay, and it can be seen that the seed crystal is dissolved as well as the raw material. On the other hand, by delaying the dissolution of the mineralizer by the method as in Example 1 and Example 2, and maintaining the state almost always supersaturated, unnecessary dissolution of the seed crystal is prevented, and gallium nitride A sufficient growth rate could be obtained.

  Since the nitrogen compound crystal obtained by the crystal production method and the crystal production apparatus of the present invention has good crystallinity, it can be used as an epitaxial growth substrate when various devices are produced by VPE, MOCVD or the like.

It is sectional drawing which shows the crystal manufacturing apparatus of this invention using a crucible. It is explanatory drawing which shows the contact area with respect to the solvent of the mineralizer in this invention, and the internal horizontal cross-sectional area of reaction container. It is sectional drawing which shows the crystal manufacturing apparatus of this invention provided with the integrated mineralizer filling part. It is sectional drawing which shows the crystal manufacturing apparatus of this invention using the pelletized mineralizer. It is sectional drawing for showing the structure of the crystal manufacturing apparatus of a comparative example.

Explanation of symbols

1 Crystal production equipment 2 Reaction vessel (autoclave)
DESCRIPTION OF SYMBOLS 3 Conduit 4 Crystal growth area | region 5 Raw material filling area | region 6 Baffle board 7 Mineralizer 8A, 8B Crucible 9 Seed crystal 10 Raw material 11 Heater 12 Thermocouple 13 Mineralizer filling part 14 Laminate of mineralizer

Claims (9)

In a cylindrical reaction vessel, using a nitrogen-containing solvent in a supercritical state and / or a subcritical state, a raw material, and a solid mineralizer , a periodic table Group 13 element nitride single crystal is formed on a seed crystal. A crystal production method by a solvothermal method of growing,
The reaction vessel has a cylindrical crucible for filling the mineralizer in the vessel,
The mineralizer is adjusted so that the total opening area of the crucible corresponding to the total contact area of the mineralizer with the solvent is 2 to 80% of the internal horizontal cross-sectional area of the reaction vessel. A method for producing a crystal, the method comprising growing the crystal in a state of being arranged in the reaction vessel. The crystal manufacturing method according to claim 1 , wherein the crucible is provided integrally with an inner bottom portion of the reaction vessel. Crystal manufacturing method according to claim 1 or 2, wherein the mineralizer is molded. The use molar ratio of mineralizer to the raw material (mineralizer / feedstock) of crystal manufacturing method according to any one of claim 1 to 3, characterized in that a 0.001. Crystal manufacturing method according to any one of claims 1 to 4, wherein the mineralizer is an acidic mineralizer. The crystal production method according to any one of claims 1 to 5 , wherein the reaction vessel is an autoclave. A columnar reaction vessel, wherein a supercritical and / or subcritical nitrogen-containing solvent, a raw material, and a solid mineralizer are used, and a periodic table group 13 is formed on a seed crystal. A crystal manufacturing apparatus by a solvothermal method for growing an element nitride single crystal,
The reaction vessel has a cylindrical crucible for filling the mineralizer in the vessel,
The total opening area of the crucible corresponding to the total contact area of the mineralizer filled in the crucible with the solvent during the growth of the crystal is 2-80 of the internal horizontal cross-sectional area of the reaction vessel. %. The crystal manufacturing apparatus, wherein the crucible is designed to be%. The crystal manufacturing apparatus according to claim 7 , wherein the crucible is provided integrally with an inner bottom portion of the reaction vessel. The crystal production apparatus according to claim 7 or 8 , wherein the reaction vessel is an autoclave.

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