JP2003277182A - Method for manufacturing nitride single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a lumpy single crystal of a nitride of an element of the group 13 in the Periodic Table, which is based on an ammonothermal method and comprises a simple and inexpensive process, and by which contamination with impurities is prevented and a large lumpy single crystal is obtained in a good yield. <P>SOLUTION: A polycrystalline nitride of at least one of elements of the group 13 in the Periodic Table as a raw material and a solvent containing a mineralizer including nitrogen atom are supplied to a raw material filling part of a high temperature and pressure reaction vessel which is constituted of an alloy containing nickel and chromium. Thereafter, the crystal is ammonothermally grown by providing a temperature gradient between a seed crystal placed at a growing section in the reaction vessel and the polycrystalline nitride. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a bulk single crystal of a nitride of a group 13 element of the periodic table, especially a bulk single crystal of GaN.

[0002]

2. Description of the Related Art GaN is useful as a material applied to electronic devices such as light emitting diodes and laser diodes. At present, gallium nitride (G
The aN) crystal size and growth is sufficient for some applications, but in many other applications the crystal size and quality of gallium nitride is not sufficient. So far, practical crystallization of GaN has been reported by S. Nakamura et al. In J. Appl. Phys. 37 (1998) L309 etc. on MOCVD (Metal-Orga) on a substrate such as sapphire or silicon carbide.
A method of performing vapor phase epitaxial growth by the nic chemical vapor deposition method has been proposed. However, in this method, since the substrate and GaN are heteroepitaxially grown with different lattice constants and thermal expansion coefficients, the obtained G
Problems such as aN lattice defects have been pointed out. In particular,
At least one of high-concentration transition, vacancies, and impurities. These defects have undesired effects and adverse effects on epitaxially grown gallium nitride and can adversely affect the operation of the resulting gallium nitride-based electronic device. For this reason, the GaN obtained by these methods cannot exhibit satisfactory performance when used in applications such as blue lasers. Currently, the heteroepitaxial gallium nitride growth method requires complicated and long steps to reduce the defect concentration in gallium nitride. Therefore, in recent years, establishment of a technique for producing a GaN massive single crystal has been strongly desired. Regarding the crystallization of GaN by such homoepitaxy growth, three methods are currently being largely divided and developed. First, SP
Method of reacting nitrogen with Ga under a pressure in the range of about 10 to about 20 kbar and at a temperature in the range of about 1200 ° C. to about 1500 ° C. disclosed by orowski et al. in J. Crystal Growth 178 (1997) 174. (High-pressure method), which requires high equipment cost and complicated reaction process. Moreover, the quality of gallium nitride crystals produced by this method may be sufficient in terms of dislocation density for some gallium nitride applications. However, the quality of gallium nitride crystals formed by this method exhibits a high concentration of unwanted nitrogen vacancies, which adversely affects gallium nitride crystal applications. Second is Ma
As disclosed in J. Crystal Growth 218 (2000) 7-12 by sato Aoki et al., a method of reacting gallium and NaN ₃ under elevated pressure, atmospheric pressure flux growth, and metathesis reaction (GaI ₃ + Li ₃ N), etc., Gallium nitride grown from other methods has also been proposed. It is difficult to control the growth area, and there is concern about contamination by flux, and this growth method is considered to be expensive,
It is not believed to produce high quality, defect-free, bulky gallium nitride single crystals. Although these methods have succeeded in crystallization to some extent, they have not yet been able to obtain larger single crystals. On the other hand, as the third method, R. D
wilinski et al. by ACTA PHYSICA POLONICA A Vol.88 (1
995), a GaN crystal synthesis method by an ammonothermal method has been reported. Here, KNH is used as a mineralizer for crystallization in supercritical ammonia at high temperature.
_A method for obtaining a single crystal of GaN using ₂ is disclosed. After that, J. Crystal Gro by JWKOLIS et al.
In wth222 (2001) 431-434, it was also proposed to use KNH ₂ and KI as mineralizers by the ammonothermal method to synthesize crystals. Also, Andrew.P.Purdy and others
In Chem. Master 1999, 11, 1648-1651, it was proposed to use ammonium halide as a mineralizer in the ammonothermal method. And XL Chen et al.
In J. Crystal Growth 209 (2000) 208-212, the use of a platinum liner in the stainless autoclave of the reaction vessel in the ammonothermal method also suppresses the generation of quadrangular prismatic GaN crystals, and suppresses hexagonal GaN. It was said that it could be selectively crystallized. These documents propose to crystallize GaN by the ammonothermal method, but the crystal growth is random because no seed crystal is used, and it is assumed that it is difficult to control the crystal growth orientation and size. However, it has not been possible to obtain crystals of a size applicable to industrial products such as blue lasers. In addition, the ammonothermal method using these supercritical ammonia shows a slow growth rate, and therefore bulky or large gallium nitride crystals cannot be easily produced. Also, pressure vessels limit the growth of these gallium nitrides. The pressure vessel limits the supercritical ammonia growth process to pressures less than about 5 kbar, and thus limits the temperature and reaction rate of the supercritical ammonia growth process. In addition, these documents include:
Since the detailed conditions for crystal growth are not described, whether the crystal growth rate is diffusion-controlled in the ammonothermal method G
It has not been clarified that the reaction is governed by the production reaction of aN.

On the other hand, French patent publication FR 2796657 A1
Proposes to first prepare a polycrystal of nitride and grow the crystal by the solvothermal method using this as a raw material. This document describes the growth of a GaN single crystal by the solution growth method. According to this growth method, a GaN polycrystal nitride is placed in the lower part of the crystal growth apparatus, while a GaN seed crystal is grown in the growth apparatus. Each is placed on top and then filled with the nitride solvent. In this state, 10
The operation is carried out at a growth temperature of 0 to 600 ° C. and a pressure of 5 MPa to 2 GPa. Here, the operation is performed so that the temperature of the lower part is 10 to 100 ° C. higher than the temperature of the upper part in the crystal growth device. As a result, a GaN single crystal is grown.

[0004] Furthermore, International Patent Application Publication WO 01/24
In 921 A1, a GaN seed crystal is used, the reaction vessel is sealed, and the inside of the reaction vessel is heated to a high temperature and high pressure by using the HPHT method.
A method of growing a single crystal of GaN using a reaction of aN polycrystalline nitride or Ga and a nitride solvent has been proposed. Further, in this document, it is proposed to use copper or platinum as a material for a reaction vessel which has a low permeability of hydrogen, which is harmful to the HPHT reactor, and which has a desirable cold pressure welding property that is not easily corroded by the HPHT reaction. Has been done.
Further, the same document discloses that a raw material having relatively low crystallinity, a raw material having high crystallinity, an amorphous raw material, etc. is used as a raw material GaN crystal. It is described that it is supplied to the crystal growth step as it is.

[0005]

In such a GaN growth method, an ammonothermal method using a seed crystal or an HPHT method is used. Therefore, although crystal growth is improved, a sufficient crystal is still available. You can't get one in size. In the ammonothermal method, the solubility of the nitride raw material in the nitriding solvent, the ion transportability in the solvent convection, the control of the recrystallization factor to the seed crystal, etc. are important factors, and these should be controlled comprehensively. However, in the method described in the above literature, the basic conditions for crystal growth are only examined, and the actual situation is that improvement is still desired. For example, when a seed crystal is used, the seed crystal falls due to the elution of the seed crystal, the problem of adhesion or precipitation of the microcrystals on the seed crystal, the adhesion and crystal growth of the microcrystals contained in the raw material at the reaction vessel end, No effective countermeasures have been taken for various kinds of inhibiting factors related to the growth of large lump crystals such as the supply of raw materials to seed crystals and the deviation of crystal growth. Also, in an environment in which crystal growth is performed by the ammonothermal method using supercritical ammonia as a solvent, the reaction vessel or the vessel may be mixed depending on the combination of various conditions such as oxidizing power, reducing power, acidity, and alkalinity in the system. It is extremely important to provide each of the members such as the baffle plate with sufficient corrosion resistance, from the viewpoint of industrial stable production and from the influence on the crystal purity and characteristics. Therefore, it is industrially strongly desired to establish a method for obtaining a larger and higher-performance massive single crystal with high yield, at low cost, and stably.

[0006]

[Means for Solving the Problems]
In view of the problem, 10-
For a method that can produce single crystals in the size range of 100 mm
As a result of intensive studies, the present invention has been achieved. That is,
The gist of Ming is as follows. (1) Manufacturing a bulk single crystal of a nitride of Group 13 element of the periodic table
The alloy containing nickel and chromium
In a reaction vessel composed of
Supply the nitride as a raw material to the raw material charging section of the reaction vessel,
A seed crystal is installed in the growing section, and the crystal grows ammonothermally.
Mass of a nitride of a group 13 element of the periodic table, characterized in that
Of producing a crystalline single crystal. (2) Group 13 element of the periodic table is gallium (Ga) or
1. The above-mentioned item 1 characterized in that it is aluminum (Al)
Manufacturing method. (3) The alloy containing nickel and chromium is nickel
・ Chromium alloy or nickel ・ chromium ・ molybdenum
The above-mentioned item (1) or (2) characterized by being an alloy
Manufacturing method. (4) The reaction vessel contains a mineralizer having a nitrogen atom.
The above (1), (2) or (3) characterized in that
The manufacturing method described. (5) The mineralizer having a nitrogen atom is an alkali metal amide.
Or ammonium halide, alkali metal nitride or
At least one selected from the group consisting of alkaline earth metal nitrides
The above (4) is also characterized in that it is also one compound
Manufacturing method. (6) The alkali metal amide is potassium amide (KNH
₂(5) The manufacturing method according to (5). (7) Ammonium halide is ammonium bromide
(NH_Four(6) above, which is Br) or the like.
Manufacturing method. (8) Ammonia (N
H₃), Hydrazine (NH₂NH ₂), Urea, etc., amine
, At least one selected from the group consisting of melamine
(1) or (1), which is characterized by containing a compound
(7) The production method described in (9) It is characterized in that the solvent is used in a supercritical state
The manufacturing method according to (8). (10) Seal the reaction vessel and increase the temperature and pressure inside the reaction vessel.
The above-mentioned items (1) to (9) characterized by reacting
Manufacturing method. (11) Between the raw material filling section and the growing section in the reaction vessel, a bag
(1) to (1) characterized in that a full plate is provided
0) The production method described. (12) The surface material of the baffle plate is nickel or black.
(11) characterized in that it is an alloy containing aluminum
The manufacturing method described. (13) Nickel and chromium containing alloy is nickel
Le-chromium alloy or nickel-chromium-molybdenum
Production according to the above (12), characterized by being a system alloy
Method.

According to the present invention, even in a reaction system under a severe condition for a reaction vessel such as an ammonothermal method using ammonia in a supercritical state as a solvent, sufficient corrosion resistance is exhibited for a long period of time and a lump crystal is formed. (EN) Provided is a process for producing a bulk crystal of a nitride, which is capable of preventing contamination of impurities which causes a disadvantage, is industrially stable to a high-performance bulk crystal, and is inexpensive and simple.

Hereinafter, the present invention will be described with reference to the synthesis of a GaN single crystal, but the present invention is not limited to the synthesis of the above substances, of course, and an element of Group 13 of the periodic table and alloys thereof (for example, , GaInN, GaAlN). Thus, whenever in doubt, gallium may be replaced by an element of one of the above elements or an alloy of the above elements, in view of its appropriate characteristics (particularly if it is a solid or a liquid). .

According to the invention, the method for synthesizing this kind of nitride comprises two steps: in the first step, a fine polycrystalline nitride, for example gallium nitride (hereinafter referred to as "microcrystalline raw material"). ) Is prepared, and in the second step, single crystal growth is realized from the microcrystalline raw material. This source is often GaN
The average grain size of the microcrystalline raw material is preferably 5 μm or less.

When the average particle size is in such a small range, the specific surface area becomes large and the reactivity with the solvent becomes good. As a grain size of the fine crystal raw material in a better mode, a GaN fine crystal raw material having a small average grain size, that is, a high dissolution rate is used. In this case, the preferable average grain size of the GaN microcrystalline raw material is 1 μm or more. When a fine crystal raw material having an average grain size of 1 μm or less is used, it may be transported to the crystal growing portion by thermal convection and adhere to the seed crystal, so it is necessary to take a avoidance measure.

By using two kinds of fine crystal raw materials having different average particle diameters, a fast dissolution rate of a fine crystal raw material having a small particle diameter and a material having a slow dissolution rate of a large particle diameter are mixed in the system. It is also possible to prevent the supply of (containing) ions from being supplied to the crystal growth portion, and as a result, to prevent the disadvantage of growing the bulk single crystal, which is the elution of the seed crystal.
Further, the shape of the GaN microcrystal is not particularly limited, but if the uniformity of dissolution in a solvent is taken into consideration,
A spherical shape is preferable.

The method of the present invention can be used with other nitrides (eg, A
The first step of the method may be developed in different ways, since it is applied to 1N, InN or nitrides of other elements of group III), but the conditions for preparing the microcrystalline raw material are common. In the case of gallium, for example, the first step is performed as follows. At a temperature slightly above the transition temperature to the liquid state, gallium is mixed with one or more finely divided materials to prepare a powder that is easy to work with, and thus with gallium, one or more of the above materials (minerals). Called agent). Such mineralizers (or solubilizers) are well known in the art for enhancing the solubility of solutes in the reaction medium and for transporting the solutes to nucleation sites. A mineralizer is understood to be a "catalyst" as it is consumed when the solute is dissolved in the reaction medium and is regenerated when crystals are formed. Examples of suitable mineralizers are those containing fluoride or nitrogen atoms. Examples of fluorides include ammonium fluoride, hydrogen fluoride, sodium difluoride, ammonium hexafluorosilicate, and hydrocarbyl ammonium fluoride such as tetramethyl ammonium fluoride, tetraethyl ammonium fluoride, benzyltrimethyl ammonium fluoride, dipropyl fluoride. Ammonium fluoride and isopropyl ammonium fluoride. Alternatively, a fluoroalkyl metal salt such as sodium fluoride may be used as long as it is reactive in the reaction mixture. Preferably, the fluoride source is ammonium fluoride, hydrogen fluoride, sodium fluoride, sodium difluoride, or ammonium hexafluorosilicate. More preferably, the fluoride source is ammonium fluoride.

As a mineralizer having a nitrogen atom, it can be decomposed.
Can have a nitriding ability or increase the nitriding ability of the solvent
It is a fine, all-compound compound. For example, Natri
Umamide (NaNH₂), Potassium amide (KN
H₂), Lithium amide (LiNH ₂), Lithium die
Lamide ((C₂H_Five)₂Alkali metals such as NLi))
Amide and ammonium chloride (NH_FourCl), ammonium fluoride
Monium (NH_FourF), ammonium bromide (NH_FourBr)
Ammonium halides such as Li₃N, Mg₃N₂, C
a₃N₂, Na₃Alkali metal nitride such as N or aluminum nitride
Potassium earth metal, NH₂NH ₃Cl or NH₃NH₃C
l₂, NHI, chromium nitride (CrN), niobium nitride (N
bN), silicon nitride (Si₃N_Four), Zinc nitride (Zn nitride
₃N₃), Ammonium carbonate ((NH_Four)₂CO₃) Is listed
To be Other mineralizers include NaCl and KI
Alkali metal halide, Li₂S, KNO₃, Phosphorus nitride
(P−N, P = N) and the like. In addition, the following solvents
When using small amounts of various nitrogen compounds exemplified as
May serve as a mineralizer.

If an appropriate mineralizer is selected from these,
Nitriding rate in the presence of NH ₃ in the supercritical state is much larger than in the case of use of only the solvent NH _3. The above nitriding rate can be improved if the mineralizer or co-mineralizer used further forms a hydrogen atmosphere during its decomposition. In general, it is preferred to select the mineralizer from materials that can activate gallium and promote nitridation of gallium.
In particular, it is important to select a mineralizer that separates Ga contained in the raw material of the present invention from GaN. Gallium
For example, NH ₂ NH ₃ Cl is preferably used as a co-mineralizer when the content of Ga in the polycrystalline nitride is high, since NH ₂ NH ₃ Cl can be divided by NH ₂ NH ₃ Cl.

In the case of gallium, the amount of gallium and the amount of mineralizing agent are optimized in order to reliably perform the first step.
For example, as NH ₂ NH ₃ Cl / Ga molar ratio, 1-10
You can select a ratio in the range of. The reaction is carried out in a container into which a solvent and reagents have been introduced. The solvent is, for example, ammonia (NH ₃ ), hydrazine (NH ₂ NH ₂ ), urea and the like, amines such as primary amines such as methylamine, secondary amines such as dimethylamine and trimethylamine. It is possible to use all other solvents which do not impair the stability of the nitride III-V, such as tertiary amines, diamines such as ethylenediamine or melamine. These solvents may be used alone or as a mixture.

These solvents are preferably used in a supercritical state. A supercritical fluid means a concentrated gas that is maintained at or above its critical temperature, which is the temperature at which the gas cannot be liquefied by pressure. Supercritical fluids generally have lower viscosities and diffuse more easily than liquids,
However, it has a solvating power similar to that of liquids. The reaction mixture is kept above the critical temperature of the solvent (400 <T <800 ° C.). Since the reaction mixture is enclosed in a constant volume (vessel volume), increasing the temperature increases the pressure of the fluid. Generally, the pressure is in the range of 40-400 MPa. T> Tc (critical temperature of one solvent) and P
> Pc (the critical pressure of one solvent), the fluid is
It is in a supercritical condition. Under the above conditions, generation of GaN microcrystals is observed. In fact, the solubility of the reagents introduced into the solvent is very different between subcritical and supercritical conditions, so that under supercritical conditions sufficient seed crystal formation of GaN is induced, thus forming microcrystals. To be done. On the other hand, in the subcritical state, it may be more disadvantageous than the supercritical state in terms of corrosion of the reaction vessel, so the supercritical state is desirable. Although the reaction vessel in the present invention will be described in detail later, it is an alloy containing nickel and chromium, but the corrosion resistance of these materials shows different characteristics depending on the oxidizing power, reducing power, and pH in the supercritical state. The reaction time is in particular the reactivity and thermodynamic parameters of the mineralizer or co-mineralizer, ie
Depends on temperature and pressure figures. G thus obtained
Microcrystals of aN (or one of its alloys) are suitable for single crystal growth by the ammonothermal method in the second step.

In addition, the polycrystalline raw material of the present invention can be prepared by heat-treating a gallium compound in an ammonia gas stream in a temperature range of 600 ° C. or higher to cause a nitriding reaction. In such a nitriding reaction, the gallium compound is preferably reacted in the solid phase, and when it is necessary to increase the surface area of the solid phase gallium compound to increase the reaction rate, the solid phase gallium compound is mortar or crusher. It is desirable to sufficiently pulverize it into a fine powder. Such finely powdered gallium compound may be molded into pellets by pressurization for the purpose of facilitating its handling, and a liquid having a high viscosity such as glycerin or ethylene glycol and having a certain degree of hydrophilicity is used as a binder. You can knead them. The heat treatment temperature range of the gallium compound in the ammonia gas flow is adjusted by the thermal decomposition temperature of the gallium compound used, but the grain size controllability and crystallinity of the product, or heating required for production is economically performed. In this respect, it is usually 600 ° C to 1200 ° C, preferably 700 ° C to 1100 ° C, more preferably 750 ° C to
It is about 1050 ° C. If this temperature is too low, the progress of the nitriding reaction and the crystallinity of gallium nitride may be extremely hindered. Such heating is carried out by placing a gallium compound used as a raw material in the reactor and raising the temperature to a predetermined temperature while passing an ammonia gas stream there. Although there is no particular limitation on the rate of temperature increase, for example, 1 to 50 ° C./min, preferably 3 to 30 ° C./min, more preferably 5 to 20 ° C./min from the viewpoint of productivity and temperature controllability. Is. The ammonia gas stream means a stream of gas containing ammonia. The ammonia content in the gas is usually 10 to 100 mol%,
The reaction rate is preferably 30 to 100 mol%, more preferably about 50 to 100 mol%, and the gas mixed with ammonia does not cause a chemical reaction that adversely affects the nitriding reaction of the production method of the present invention. It is desirable to use an inert gas such as nitrogen gas or argon gas.

Further, in order to suppress the production of oxides as impurities, it is desirable to make the oxygen gas concentration in the ammonia gas flow as low as possible.
It is 0 ppm or less, preferably 1 ppm or less, and more preferably about 0.1 ppm or less. Typical examples of the gallium compound include gallium salts of anions and gallium chalcogenides containing an element belonging to Group 15 or Group 16 of the periodic table, and those containing crystallization water. It does not matter, but anhydrous is preferable. Specific examples include gallium salts of strong acid anions such as gallium sulfate and gallium nitrate, gallium salts of low-oxidation anions such as gallium sulfite and gallium nitrite, and gallium chalcogenides such as gallium oxide. Gallium and gallium oxide are preferably used from the viewpoint of crystallinity of the product, and gallium sulfate is more preferably used from the viewpoint of suitable thermal decomposition temperature. The thermal decomposition temperature of the gallium compound is preferably within the above heat treatment temperature range, for example, 600 ° C. to 1 as in gallium sulfate.
A gallium compound having a thermal decomposition temperature within a temperature range of about 000 ° C. is preferably used in the present invention. The thermal decomposition temperature is more preferably in the range of 650 ° C to 900 ° C, and further preferably in the range of 700 ° C to 850 ° C. The thermal decomposition temperature referred to here is defined as the temperature at which 50% of the total weight of the state in which low-molecular-weight substances such as water of crystallization and adsorbed water are removed is lost by heating in air. Also,
The gallium compound preferably has a low water content in the present invention, and it is desirable to use, as a raw material, any form of water molecule such as crystallization water or adsorbed water, which does not contain water as much as possible. When the water content is high, the crystallinity and purity of the product may be extremely reduced. Therefore, the water content in the gallium compound is usually not more than 3 times, preferably not more than 2 times, more preferably not more than 1.6 times as much as the weight of water with respect to the weight of gallium contained as an element. The supply amount and speed of the ammonia gas flow are not limited and are adjusted depending on the amount of the gallium compound used as a raw material, the cross-sectional area of the reaction vessel, etc. Is preferable in terms of reaction rate and completion of the reaction. The progress of the nitriding reaction can be confirmed by, for example, analyzing the crystal structure of the product by an X-ray diffraction method using a copper Kα ray as an X-ray source to determine the crystal structure of each of the raw material gallium compound and the generated gallium nitride. This is possible by comparing the known diffraction patterns from

The microcrystalline raw material of GaN (or one of its alloys) thus obtained is present in the mixture of unreacted Ga and by-products because it is difficult to make the reaction efficiency 100%. Is normal. In this case, unreacted Ga and by-product components must be removed after the first step,
If the particle size of the microcrystalline raw material is small, it is difficult to remove it. In order to remove unreacted Ga and by-products remaining on the surface of the microcrystalline raw material, treatment in an acid solution for several hours to tens of hours is required in some cases. In order to increase the removal rate, it is effective to perform heat treatment, for example, to use hydrochloric acid in a boiling state. On the other hand, if this removal treatment is performed excessively, on the contrary, a surface with excessive N may be formed on the surface of the particles, so caution is required. Performing such a treatment is disadvantageous in terms of production efficiency, and the present inventors have found that unreacted G remaining on the surface of the microcrystalline raw material is not reacted.
Starting for use in bulk GaN single crystal growth in the second step including the microcrystalline raw material obtained in the first step by removing a and by-products or by actively adding Ga to hybridize It has been found that it is effective to use it as a raw material (hereinafter referred to as "starting raw material"). With respect to the hybrid ratio of the starting material, it is preferably up to about 50%.
If residual oxide remains and there is concern about single crystal growth by the ammonothermal method, deaeration heating is effective.

In the second step, a massive GaN single crystal is grown. This step is performed in a closed reaction vessel and is a so-called ammonothermal method. The drawing shows a schematic representation of an apparatus comprising a reaction vessel in the form of a vertically arranged long cylindrical vessel. The top of the container is closed by a nozzle connected to a pressure control device (not shown). The vessel is provided in a furnace that encloses the vessel over its entire height and can apply a temperature gradient to the vessel along the vessel axis.

The container is divided into two overlapping zones, that is, a lower raw material charging section and an upper growing section separated by a baffle plate. The temperature gradient ΔT between these two zones is 10-100 ° C. The direction of the gradient depends, among other things, on the solubility of the raw materials as a function of temperature. The raw material prepared in the first step is charged in the raw material charging section, and the seed crystal is set in the growing section. Seed crystal is G
Single crystal material pieces or polycrystals having size parameters that match those of the aN crystal lattice (single crystal) or coordinated to ensure heteroepitaxy (ie, coincidence of crystallographic positions of some atoms). Composed of pieces of material. The seed crystal is GaN, InN, AI.
It can be composed of all materials having a crystal structure extremely close to that of N or GaN. For example, in the case of GaN, a single crystal of GaN, a single crystal of zinc oxide (ZnO), a single crystal of silicon carbide (SiC). Crystal, lithium gallate (LiGaO ₂ ), zirconium diboride (ZrB ₂ )
And a single crystal thereof.

The seed crystal is held by the noble metal wire and can be fixed by fastening the noble metal wire to the frame. The noble metal wire is preferably an element of Group 13 of the periodic table, for example, nickel (Ni), tantalum (Ta), titanium (Ti), palladium (Pd), platinum (Pt), niobium (Nb). The seed crystal may be installed in any direction, but the angle between the c-axis of the seed crystal and the convection direction of the nitride solvent is 0 to 180 ° (where 0 ° and 1
(Excluding 80 °), and more preferably 60 ° to 120 °. By using the seed crystal thus arranged, the obtained GaN single crystal is eccentrically grown with respect to the seed crystal, and a large single crystal can be obtained.

The reason for the eccentric growth is not clear, but in the side surface of the seed crystal whose height direction is the c-axis direction, the portion where the convection directly contacts and the portion where the convection makes a detour contact. , Ga (contained) transported by convection
Ion supply rate is different. On the other hand, the GaN single crystal has a hexagonal system (wurtzite) and has a 6-fold symmetry axis. Therefore, when growing a GaN single crystal by the ammonothermal method, G
When the c-axis direction of the aN (or other) seed crystal is arranged in parallel to the convection direction of the nitride solvent, it is considered that the seed crystal grows almost uniformly, but according to this method. , By providing a portion where the supply rate of Ga (containing) ions is small and a portion where the supply rate of Ga ions is large, a surface where crystal growth is slower than other surfaces is intentionally created, and this slow surface has higher growth efficiency than other fast surfaces. It is conjectured that this may lead to the advantage that large crystals can be obtained.

The seed crystals can also be used by joining the seed crystals together. In this case, the c-axis polarities are brought into contact with each other and brought into contact with each other, and the bonding is carried out by the ammonothermal method of the present invention or by using the vapor phase method such as the MOCVD method and utilizing the homoepitaxy action. It is possible to reduce dislocations in the area. By joining the seed crystals to each other in this way, a large seed crystal can be obtained in the c-axis direction even when selective growth in the a-axis direction occurs. In this case, it is preferable to bond not only the c-axis polarities but also the a-axis polarities so that the seed crystals having the same shape are bonded.

When the seed crystals are bonded to each other, it is preferable to polish the bonding surface to a smooth surface at a mirror surface level. It is more preferable to polish the surface smoothly at the atomic level. Although the polishing method is not particularly limited, for example, EEM processing (Elastic Emission Machine) is used.
g). The polishing agent used for this purpose is not particularly limited, and SiO ₂ , Al ₂ O ₃ ,
ZrO _{2 and the} like are exemplified, but colloidal silica is preferable. The reason why the c-plane is smoothed in this way is that if the c-plane is rough, the rate of crystal growth increases, and the matching between the c-planes to be bonded is likely to be impaired.

In the present invention, ultrasonic waves may be further applied to the growing portion on which the seed crystal is arranged. The seed crystal will be subjected to vibration due to applied ultrasonic waves in addition to normal thermal vibration according to the temperature of the growing portion. Therefore, the seed crystal vibrates at a frequency determined in proportion to the frequency of the applied ultrasonic wave. Since this vibration has a shape in which the space where the atoms of the crystal lattice are located is relatively widened, the probability that raw material compounds that contact the surface of the seed crystal will enter the crystal lattice is relatively large compared to the conventional state. Become. In addition, even if crystal nuclei or other particles that cause polycrystals are generated, the bond strength is weak and the crystals are incorporated into the crystal because the lattice matching with the crystal interface, which was grown up to now in single crystals, is poor. I can't. . That is, only the crystal nuclei that have a strong bond and are lattice-matched are taken into the crystal to grow a single crystal. That is, the generation of polycrystals can be suppressed by ultrasonic vibration.
As a result, the atoms accurately located in the proper part of the crystal lattice realize a relatively good crystal quality, and the electrical and optical characteristics of the substance formed thereby are improved.

The reason for this is not clear, but it is considered as follows. That is, ultrasonic waves have a sound frequency of 20.
It is a sound wave having a frequency of kHz or higher, and when ultrasonic waves are applied to a substance, changes in pressure, temperature, density, etc. occur within the substance.
Such an ultrasonic wave has a feature that ultrasonic waves are transmitted to the atoms constituting a substance, the vibration of the atoms is promoted, and the two substances are melted so that they can be bonded. Therefore, by using such performance of ultrasonic waves, when the ultrasonic wave is applied to the surface of the seed crystal during the growth of the gallium nitride single crystal, the material forming the seed crystal and the incident material are easily welded to each other. As a result, a high quality massive single crystal can be grown even at a lower crystal growth temperature as compared with the conventional method.

Further, as will be described later, the activation rate can be increased by simultaneously applying ultrasonic waves to the raw material compounds, so that the crystal growth efficiency of the growth system can be increased. The container contains a nitride solvent (eg, hydrazine N ₂ H ₄
Alternatively, fill with any solvent that is miscible with Animonia NH ₃ ) or Nitride III-V. The container is about 5 MPa
Hold at a pressure in the range of -2 GPa. The rate of injection of the nitride solvent is set to be about 60 to 85% of the free volume of the container, that is, the volume remaining when the raw material containing the GaN polycrystalline nitride, the baffle plate and the like are installed in the container. preferable.
The compounding ratio with the nitrogen source is adjusted according to the weight of the residual Ga mixed with the microcrystals.

In order to ensure the transport of gallium and nitrogen from the raw material to the seed crystal, an intermediate compound capable of supplying an anion (for example, all other compounds containing N ^{3 −} or nitrogen or all compounds containing a halogen anion) is selected. It is advantageous if it is generated in the raw material filling section. The above compound is a raw material GaN
Results in a chemical reaction between at least one other compound called a "precursor". In the present invention, as the precursor, in addition to the polycrystalline raw material, Ga metal contained in the polycrystalline, GaX (X = Cl, Br, I), GaX ₂ (X = C)
l, Br, I), GaX ₃ (X = Cl, Br, I), G
A compound such as a ₂ S or Ga ₂ O may be supplied to the reaction system.

Compounds of this kind improve the solubility of GaN (very little, even in the form of very fine particles), due to the production of ionic species which promote the above-mentioned transport of gallium and nitrogen. For example, the halide is initially GaN
To form a halogen complex, which is substituted with an amide to form a complex Ga (NH ₃ ) _x ³⁺ , Ga amide, Ga imide, GaN amine, etc., which is converted into a transportable substance. Can be considered.

In all cases, the intermediate complex compound is decomposed into GaN and N ^{3 −} (or NH ₃ ) and the nitride is deposited on the seed crystal so that the intermediate compound is produced and the raw material filling part and seed are formed. It is necessary to maintain a temperature gradient with the crystal. By controlling the temperature and pressure conditions of the container, taking into account the special properties of the solvent placed in the supercritical state (temperature and pressure), the complex Ga (NH ₃ ) complex (relatively limited in stability) _It is preferable to avoid the _x ³⁺ generation region.

If the above crystal growth conditions are satisfied, it is advantageous to generate the intermediate species M _x GaN _y (soluble in the nitride solvent) between the raw material GaN and the additive, in an advantageous manner, the above temperature gradient is obtained. Can generate chemical ionic species that can transport gallium and nitrogen depending on The good solubility of the intermediate compound M _x GaN _y , ie the ionic species GaN ₂₊ δ ⁽¹⁺ δ), which serves for the chemical transport of the constituents of GaN (ie Ga ³⁺ and N ^{3 −} ).
^{) 3-} to ensure the solubility essential for the formation of Ga-N
The body M can be selected from all elements that increase the ionization degree of the bond. It is advantageous if M is an alkaline element, especially lithium), in which case the precursor is Li ₃ N. The parameters that influence the transport of the raw material species to the seed crystal are, inter alia, the properties of the intermediate compound M _x GaN _y , the properties of the solvent, the properties of the seed crystal, the temperature gradient between the raw material and the seed crystal Δ.
T, the temperature of the raw material, and the pressure value in the container 2. Intermediate compound (in this case, M is an alkali element or an alkaline earth element), liquid NH ₃ as a solvent, 100-600 ° C.
Using a feed temperature in the range of 5 MPa, a pressure in the range of 5 MPa-2 GPa and a temperature gradient in the range of 10-100 ° C.
It is possible to synthesize GaN single crystals with a size in the range of 0-100 mm (but not limited to this size). The duration of the crystal growth process depends on material throughput, chemical parameters (solvent properties, properties and amounts of additives or co-additives, temperature gradients), thermodynamic parameters (temperature and pressure) that can control material transport Furthermore, it depends on the size of the desired single crystal. In particular, depending on the latter parameter above, a period of 1-10 weeks is required.

Further, in the present invention, it is possible to promote the chemical reaction between GaN and at least one other compound called "precursor" by applying ultrasonic waves. This type of compound is based on the formation of Ga species that promotes the transport of gallium and nitrogen from the source to the seed crystal.
It improves the solubility of N, but promotes the diffusion of ionic species generated by the application of ultrasonic waves, and the effect of ultrasonic waves being transmitted to the atoms that make up the substance to promote the vibration of the polycrystals. It is considered that this is because the reactivity of the grain boundaries of the raw material is increased. Further, it is possible to reduce the amount of the curing agent added, which is required by applying ultrasonic waves.

The GaN single crystal is a hexagonal crystal.
However, depending on the growing conditions, it may have a square columnar shape.
It When growing as a hexagonal crystal, it grows especially in the c-axis direction
It is necessary to select the conditions to do. Growth in the c-axis direction is
By doping with lithium (K) or a Group 2 element
Will be achieved. Magnesium as a Group 2 element
(Mg), beryllium (Be), calcium (Ca), etc.
Is achieved by doping Dope K
The above KNH₂By using as a mineralizer
Can be done. As a mineralizer for doping Mg and Ca,
The above Mg₃N₂, Ca ₃N₂Can be achieved by using
It

If it is necessary to promote the growth in the a-axis direction, it is preferable to dope lithium (Li). To dope Li, as a mineralizer, LiN
In addition to using H ₂ , an embodiment using Li ₃ N as a precursor is also included. The major feature of the present invention is that the above G
The inner surface of the reaction container of the aN polycrystalline nitride is made of an alloy containing nickel and chromium. The above-mentioned alloys are nickel-chromium alloys such as MC alloy (Chromium content is 45% by weight and molybdenum content is 1% by weight) manufactured by Mitsubishi Materials, or nickel-chromium-molybdenum alloys such as MAT21 manufactured by Mitsubishi Materials. (Chromium content is 19% by weight, molybdenum content is 19% by weight) and alloys described in JP-A-1-50936. The lower limit of the chromium content in the alloy containing nickel and chromium used in the present invention is preferably 10% by weight, more preferably 20% by weight, and particularly preferably 30% by weight.
%, Most preferably 40% by weight, and the upper limit is preferably 55% by weight or less, more preferably 50% by weight.
It is preferably not more than 45% by weight, particularly preferably not more than 45% by weight. If the chromium content is too low, the corrosiveness tends to increase as the oxidizing conditions become stronger, and if the chromium content is too high, the workability tends to deteriorate. Further, the content of chromium in the case of the nickel-chromium-molybdenum alloy is the same as that in the case of the nickel-chromium alloy in the ratio to nickel, but the lower limit of the content of molybdenum with respect to the entire alloy is preferable. Is 1% by weight or more, more preferably 5% by weight, further preferably 10% by weight, particularly preferably 15% by weight or more, and the upper limit value is preferably 35% by weight or less, more preferably 30% by weight or less, further preferably Is 25% by weight or less, particularly preferably 20% by weight or less. If the molybdenum content is too low, the corrosiveness tends to increase as the reducing power becomes stronger, and if the molybdenum content is too high, not only will the solid solution limit for nickel be exceeded, but the workability will also tend to be poor. is there. The composition ratio of these alloys depends on the conditions of the temperature and pressure of the solvent in the system, the reactivity with the various mineralizing agents and their reactants contained in the system, and / or the oxidizing power, the reducing power, and the pH. It may be appropriately selected according to the conditions. As a method of using these as a material for forming the inner surface of the reaction vessel, the reaction vessel itself may be manufactured using these alloys, or a method of forming a thin film as an inner cylinder and installing it in the reaction vessel,
A method of plating the inner surface of the material of any reaction vessel may be used. The preferable composition range of the alloy containing nickel and chromium of the present invention is as described above, but the more detailed composition of the material is not limited thereto, and the alloy containing nickel and chromium of the present invention has It does not prevent inclusion of other metal components such as manganese, silicon, titanium, tantalum, carbon, aluminum, magnesium, calcium, etc. as long as the characteristics are not impaired. In the present invention, by using an alloy containing nickel and chromium as the material of the inner surface of the reaction vessel, in the reaction system using the ammonia solvent in the supercritical state, for example, as the above mineralizer, N
Even when H ₄ X (X represents halogen such as Cl and Br) is used, it is possible to reduce the influence of halogen ions such as Cl ^{− and the} like on the corrosion of the neutral region. The use of the alloy containing nickel and chromium used in the present invention has high weldability and enables the reactor to be manufactured at a lower cost than other metals having corrosion resistance, which is industrially advantageous. In the present invention, a method of sealing the reaction vessel inner cylinder and installing it in the reaction vessel can also be used, if necessary. As described above, it is possible to suppress the mixing of impurities from the reaction container. Then, if necessary, a baffle plate is installed in the container to divide into a raw material filling portion filled with a raw material made of GaN polycrystalline nitride and a crystal growth portion in which a GaN seed crystal is arranged. The baffle plate preferably has a porosity of 2 to 5% (not including 5%), and the material of the surface of the baffle plate is the same as the material of the reaction vessel. preferable. As described above, by controlling the opening ratio of the baffle plate, it becomes easy to properly control the supersaturation degree of GaN in the crystal growth portion under the solution growth condition.

In the present invention, the raw material can be further supplied onto the baffle plate. Thus, by further interposing the raw material on the baffle plate, that is, between the raw material filling portion and the seed crystal arrangement portion, the transition speed of the crystal growth portion to the supersaturated state can be increased, and the seed crystal elution It is possible to prevent various disadvantages in the above. In this case, the supply amount of the raw material onto the baffle plate is preferably 0.3 to 3 times the dissolution amount of GaN in the crystal growth portion.

In addition, the reaction vessel of the present invention may be provided with a precipitate collecting net above the seed crystal installation location, that is, in the vicinity of the convection focusing point of the solvent. The role of this deposit collection net is as follows. That is, as it goes to the upper part of the reaction vessel, the convection of the solvent, that is, the transport flow of the solute, goes to a lower temperature region, but the solute supersaturated at such a low temperature portion is only on the seed crystal. In addition, there is a problem that the noble metal wire suspending the seed crystal, the frame for fastening the noble metal wire, and the inner wall of the reaction vessel are also precipitated as precipitates. In such a case, by providing a precipitate collecting net near the convection focusing point, the residual solute not completely precipitated on the seed crystal is inverted downward by the top inner wall, and then the It is possible to capture fine crystals or precipitates and selectively deposit the fine crystals on this collection net.

The material of this collecting net is preferably the same as the material of the above-mentioned reaction vessel. Further, in the present invention, in order to appropriately control the supersaturation degree in this manner, it is preferable to set the ratio of the volume of the crystal growth portion to the volume of the raw material filling portion within a range of 1 to 5 times. If the degree of supersaturation exceeds 1.50, the rate of precipitation on the seed crystal is too high, which deteriorates the internal consistency of the grown crystal and introduces defects, which is not preferable. Furthermore, since the amount of precipitation on the inner wall of the growth container and on the frame increases, if the precipitate enlarges, it may come into contact with the GaN single crystal and hinder the growth of the single crystal, which is not preferable.

Here, "supersaturation" means a state in which the amount of dissolution increases more than the saturated state, and "supersaturation" means
It refers to the ratio between the amount of dissolution in the supersaturated state and the amount of dissolution in the saturated state.
In the solution growth method, the amount of GaN dissolved in the crystal growth part that is in a supersaturated state due to the transport of GaN by thermal convection from the material filling part and the GaN in the crystal growth part in the saturated state.
It refers to the ratio with the dissolved amount of. Supersaturation degree = (dissolved amount in supersaturated state of crystal growth part) /
(Dissolved amount in saturated state of crystal growing portion) In the present invention, the degree of supersaturation is determined by appropriately determining the density of the polycrystalline nitride, the porosity of the baffle plate, the temperature difference between the raw material filling portion and the crystal growing portion, and the like. It can be controlled by changing or selecting.

In the present invention, the obtained bulk single crystal can be washed with hydrochloric acid (HCl), nitric acid (HNO ₃ ) or the like. Specific embodiments for carrying out the present invention will be described below, but the present invention is not limited to these methods. High-purity 6N metallic gallium and NH ₄ Br are put into a reactor whose inner surface is made of nickel-molybdenum alloy, and then NH ₃ is injected as a solvent into the reactor at a filling rate of about 60%. It is sealed with a cap made of a system alloy. The reactor is installed in an electric furnace and the temperature is raised to about 500 ° C. The pressure of the reactor at this time is preferably about 350 MPa. This state is 1
After holding for about 20 hours, it is cooled to room temperature and GaN polycrystal is taken out. As a result, the particle size is 0.1 μm to 1.2 μm.
A predetermined amount of m GaN polycrystal is obtained. The reactor was filled with the GaN polycrystal obtained above, and Ga
And GaN are adjusted and added so that the hybridization rate is 10%. Next, a baffle plate which is also made of a nickel-molybdenum alloy and has an opening ratio of about 4% is installed, and the inside of the reactor is divided into a raw material charging part and a crystal growth part.
Then, as a seed crystal, a plate-shaped GaN single crystal of about 30 mm × 50 mm cut out in a plane perpendicular to the C-axis direction and mirror-polished was hung in a Pt frame in about 5 steps vertically so that the C-axis was oriented in the horizontal direction. Are arranged in the crystal growth portion. A solvent consisting of KNH2 and NH3 of about 3 mol / l is injected into the pressure vessel at a filling rate of about 80%, and the autoclave is sealed with a cap also made of a nickel-molybdenum alloy.

The reactor was installed in an electric furnace composed of heaters divided into upper and lower parts by about 5 divisions, and the raw material charging part was kept while keeping the temperature of the crystal growing part always lower than the temperature of the raw material charging part. About 350 ° C, crystal growth part at 300 ° C
Increase the temperature. The pressure in the reactor at this time is 800 MPa
A degree is preferable. After maintaining this state for about 60 days, it is cooled to room temperature and the GaN single crystal is taken out. G taken out
After slicing an aN single crystal in a plane perpendicular to the C-axis to a thickness of about 350 μm, it was mirror-polished with colloidal silica and 50 sheets of 3
A square wafer of about 0 mm × 50 mm is obtained.

[0042]

According to the method for producing a bulk single crystal of a nitride of a group 13 element of the periodic table of the present invention, contamination of impurities is prevented and a large bulk single crystal is collected by a simpler and more economical process than ever before. Efficient, cheap and stable.

[Brief description of drawings]

FIG. 1 is a diagram showing a crystal growth container used in a single crystal growth manufacturing method according to the present invention.

[Explanation of symbols]

1 GaN polycrystalline raw material 2 GaN seed crystal 3 baffle board 4 frames 5 Crystal growth department 6 Raw material filling section 7 Thermocouple insertion part 7'thermocouple insert 8 growth containers 9 precious metal wire

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Wada             2-5-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi             Gaku Co., Ltd. F-term (reference) 4G077 AA02 BE13 BE15 CB04 EG25                       EJ09 KA01 KA03 KA11 KA12

Claims (13)

[Claims] 1. A method for producing a bulk single crystal of a nitride of a group 13 element of the periodic table, in which a polycrystalline nitride of a group 13 element of the periodic table is placed in a reaction vessel composed of an alloy containing nickel and chromium. Production of a bulk single crystal of a nitride of a Group 13 element of the periodic table, characterized in that it is supplied as a raw material to a raw material charging section of the reaction vessel, a seed crystal is set in a growing section, and crystal growth is performed ammonothermally. Method. 2. The method according to claim 1, wherein the Group 13 element of the periodic table is gallium (Ga) or aluminum (Al). 3. The manufacturing method according to claim 1, wherein the alloy containing nickel and chromium is a nickel-chromium alloy or a nickel-chromium-molybdenum alloy. 4. The method according to claim 1, 2 or 3, wherein the reaction vessel contains a mineralizer having a nitrogen atom. 5. The mineralizer having a nitrogen atom is at least one compound selected from the group consisting of alkali metal amides, ammonium halides, alkali metal nitrides and alkaline earth metal nitrides. Item 4
The manufacturing method described. 6. The method according to claim 5, wherein the alkali metal amide is potassium amide (KNH ₂ ). 7. The ammonium halide is ammonium bromide (NH ₄ Br) or the like.
The manufacturing method described. 8. Ammonia (N
H ₃ ), hydrazine (NH ₂ NH ₂ ), urea and the like, and at least one compound selected from the group consisting of amines and melamine is contained.
The manufacturing method described. 9. The method according to claim 8, wherein the solvent is used in a supercritical state. 10. The production method according to claim 1, wherein the reaction vessel is sealed and the inside of the reaction vessel is reacted at high temperature and high pressure. 11. The manufacturing method according to claim 1, wherein a baffle plate is provided between the raw material charging section and the growing section in the reaction vessel. 12. The manufacturing method according to claim 11, wherein the material of the surface of the baffle plate is an alloy containing nickel and chromium. 13. An alloy containing nickel and chromium,
The manufacturing method according to claim 12, which is a nickel-chromium alloy or a nickel-chromium-molybdenum alloy.