JP2005179138A - Method for producing nitride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for obtaining a nitride with less impurity, for example, high-quality gallium nitride by an industrially applicable method. <P>SOLUTION: The method for producing a nitride of group 4 to 14 metal is carried out by allowing a nitrogen-containing compound adduct of a halogenated group 4 to 14 metal to react with a compound of alkali metal or alkaline earth metal (for example, a nitride of alkali metal or alkaline earth metal). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a nitride, and more particularly, to a method for manufacturing a nitride of a periodic table group 4-14 metal.

  In recent years, nitrides, particularly nitrides of specific metals, are useful as substances applied to basic catalysts, photocatalysts, phosphors, raw materials for semiconductor materials, and the like. The most common method for producing such a metal nitride is to use a metal, oxide, or hydroxide as a starting material and to synthesize ammonia at a high temperature. However, since this method is a process in which a large amount of ammonia is distributed and used at a high temperature around 1000 ° C., the production efficiency is low. In addition, the use of ammonia, which is a reducing substance, at a high temperature has the disadvantage of including defects and reduced metal components, and it is not sufficiently suitable as a raw material used for some purposes.

Therefore, in recent years, establishment of a new production technique for high-quality nitrides, which replaces the above method, has been strongly desired, and various proposals have been made.
For example, H.M. Yamane et al. Obtained metal nitride crystals from the target metal and dissolved nitrogen using metal sodium or metal lithium as a flux (see Patent Document 1).
X. Chen et al. Have obtained a nitride by reacting a target metal with lithium nitride (see Non-Patent Document 2).
Moreover, Hara et al. Obtains a metal nitride by first reacting a metal with hydrochloric acid to form a metal chloride, and reacting it with ammonia (see Patent Document 1).
On the other hand, Kanar et al. Have obtained a nitride by a self-heating reaction by mixing metal halide and alkali nitride and igniting them (see Non-Patent Document 3). Further, Gillan et al. And Hu et al. Obtain nitrides by reacting metal halides with sodium azide (see Non-Patent Documents 4 and 5).

J. Crystal Growth 218 (2000) 7-12 J. Crystal Growth 247 (2003) 275-278 J.Phys.Chem.B 105 (2001) 11922-11927 Nano Lett. 2 (2002) 899-902 Chem. Phys. Lett. 351 (2002) 229-234 JP2003-63810

  However, in these methods, a flammable alkali metal that is difficult to handle or dispose of is used in large quantities as a solvent, or a compound that easily generates hydrogen by reacting with a metal raw material is used. Become. In addition, in the synthesis method using metal halides, it is difficult to handle, and it is necessary to ignite to start a reaction when using another nitride as a nitrogen source, and an explosive compound sensitive to impact. There are problems such as using azide as a nitrogen source, and it is expected to be difficult to implement industrially.

  In view of the above problems, the present inventor has conducted earnest studies on a method capable of efficiently producing high-quality nitrides by a method that can be industrially sufficiently applied. The inventors have reached the present invention comprising a method for producing a nitride of a group 4-14 metal, characterized by reacting a nitrogen-containing compound adduct with an alkali metal or alkaline earth metal compound.

  According to the present invention, high-quality nitrides can be efficiently obtained by a simpler and safer method than before. In the present invention, in the production of nitride, the reaction conditions such as temperature are relaxed, and a nitrogen source such as ammonia is not used in large quantities, and it is also possible to avoid using a highly dangerous substance. High and efficient industrial implementation is easy.

  Hereinafter, the present invention will be described in detail. In the nitride manufacturing method of the present invention, the nitride to be manufactured is a nitride of a metal element of Groups 4 to 14 of the periodic table, and is not particularly limited as long as it belongs to the classification of the metal element. The production of nitrides particularly useful in the group 13 elements B, Al, Ga, In, or Ti, Zr, Ta is expected. Examples of such nitrides include single metal nitrides (eg, GaN, AlN), alloy composition nitrides (eg, GaInN, GaAlN), etc., but the present invention is not limited to gallium nitride (GaN). Suitable for manufacturing. In addition, the nitride to be manufactured is not limited to pure nitride, and may include nitride containing oxygen and oxynitride.

In the production of such a nitride, first, a nitrogen-containing compound adduct of a group 4-14 metal halide is prepared as a raw material. Examples of the halide in this case include chloride, bromide, etc. In addition, ammonia is generally used as the nitrogen-containing compound, but a lower alkylamine having about 1 to 6 carbon atoms that can easily form an adduct. It may be.
Ammonia or an amine adduct is produced and reacted with an alkali metal or alkaline earth metal compound.
There is no particular limitation on the method for producing the target nitrogen-containing compound adduct of group 4-14 metal halide, but various methods are known for ammonia. Since metal halide is a typical Lewis acid, it is considered that an adduct is easily formed with an electron donating molecule such as a Lewis base.

  The method for producing the metal halide is not particularly limited, but it is usually obtained by directly reacting a metal, oxide or hydroxide with hydrogen halide or a halogen element. The metal halide is preferably sufficiently removed of impurities by operations such as distillation and sublimation purification. The amount of oxygen and moisture (OH component) in the metal halide is important for obtaining the desired high-quality nitride. In other words, in order to obtain a nitride having a low oxygen impurity content, it is necessary to thoroughly remove oxygen from the raw material metal halide. Conversely, intentionally hydrolyzing or alcoholyzing a part of the obtained metal halide to introduce oxygen or OH component into the system, the desired target oxygen, It is also possible to obtain a nitrogen-containing nitride or oxynitride.

  In addition, metal halides are often solid or liquid at room temperature. Therefore, when adding a nitrogen-containing compound, the metal halide may be reacted in a solid or liquid state, or may be reacted in a dissolved or suspended state by adding a solvent. The solvent here is not particularly limited, but usually an organic solvent such as benzene or ether is used. Nitrogen-containing compounds are introduced into the reaction system as a gas, liquid, or solution. The nitrogen-containing compound to be supplied is usually 0.5 mol times or more with respect to the halide, and there is no particular upper limit, and it may be a large excess. In the addition reaction, the temperature at which the raw materials are introduced and mixed is usually preferably in the range of about 100 ° C. or less. Thereafter, the temperature of the addition reaction is generally raised, but from the viewpoint of suppressing the decomposition of the metal halide and the generated adduct, it is usually 300 ° C. or lower, preferably 200 ° C. or lower, more preferably 100 ° C. or lower. Done in Usually, the reaction proceeds rapidly and a nitrogen-containing compound adduct of metal halide is obtained.

After the addition reaction, it can be directly subjected to the reaction with the next alkali metal or alkaline earth metal compound to obtain the desired nitride, but when performing the addition reaction in a solvent, the solvent is removed, or The adduct can be recovered once by filtration and washing. If an excess of nitrogen-containing compounds remains after the reaction, they may be removed and the target adduct may be dried. Although depending on the reaction method and the degree of drying, usually 1 to 12 moles of adduct are obtained per mole of metal halide. For example, in the case of gallium (Ga), GaCl _3. (NH ₃ ) ₆ is obtained by an addition reaction between GaCl ₃ and a large excess of ammonia. The N-containing compound adduct of the metal halide thus obtained has a low reactivity with water, deliquescence and volatility compared to the metal halide, and is an easy-to-handle powder, so that the desired nitride is obtained. Is very advantageous as starting material for the reaction.

Next, in the present invention, the nitrogen-containing compound adduct of the group 4-14 metal obtained as described above is converted into an alkali metal or alkaline earth metal compound (hereinafter referred to as “nitriding agent” in the present specification). It is characterized by the fact that it may be called.
The nitriding agent is preferably a compound capable of supplying nitrogen that can be a nitrogen source of the target group 4-14 metal nitride, preferably an alkaline metal such as lithium or sodium, or an alkaline earth such as magnesium. Metal nitrides, amides, and imides are preferable, and lithium nitride is particularly preferable. A plurality of such nitriding agents may be used in combination.

The amount of the nitriding agent used in this reaction is 0.5 to 5 times equivalent to the amount of group 4-14 metal contained in the nitrogen-containing compound adduct of group 4-14 metal halide, preferably 1-3. Double equivalent. When the amount of the nitriding agent is small, the reaction is incomplete, and the unreacted metal halide N-containing compound adduct remains, so that it reacts with moisture in the subsequent washing process, etc. It becomes easy to generate. Moreover, even if too much, a yield may worsen. The reason for this is that compounds such as MM′Nx and MM ′ (NH ₂ ) x (M is the intended group 4-14 metal, M ′ is an alkali metal, alkaline earth metal) and the like are formed, and moisture is similarly produced. It can be considered that it becomes easy to disassemble by, for example.

The target metal nitride can be efficiently obtained by the above reaction. The reaction mode is basically considered to be a substitution reaction between the halogen part of the adduct and the anion part of the nitriding agent. In the present invention, since the raw material adduct contains an additional component such as ammonia, the raw material can be easily handled, and the rapid progress of the reaction can be suppressed, and a nitrogen-containing compound can be used as the additional component. The coexistence is considered to be related to the suppression of decomposition of the N ³⁻ group and NH ₂ ⁻ group which are the sources of the nitriding agent. Also, by using a nitrogen-containing compound adduct of a metal halide, unlike the case of reacting only the metal halide itself, there is no special operation such as ignition, and the reaction proceeds promptly by raising the temperature. be able to.

  In addition, an alkali metal or alkaline earth metal nitride that is one of the nitriding agents can be easily produced by a reaction between a metal element alone and nitrogen because alkali metal and alkaline earth metal are highly electropositive. Taking lithium as an example, nitrogen reacts slowly even at 25 ° C, but reacts rapidly at 400 ° C. Therefore, it can be said that the nitrides of alkali metals and alkaline earth metals are easier to produce than the intended group 4-14 metal nitrides, but because they have highly reactive nitrogen, It is believed that the metal halide adduct can be converted to nitride.

The adduct and nitriding agent may be reacted in the absence of a solvent, or may be reacted in a dissolved or suspended state by adding a solvent. By using these as a solvent, the reactivity between the adduct and the nitriding agent can be improved, and as a result, a high-quality nitride with high crystallinity can be obtained. The solvent is preferably a solvent capable of dissolving the raw material, and may be one that dissociates itself into a cation and an anion and is ionically solvated with respect to the raw material to dissolve the raw material. May be dissolved. Solvents include ammonia (NH ₃ ), hydrazine (NH ₂ NH ₂ ), urea, alkali halide salts, ammonium halides, alkali nitrides and alkali amides, organic amines as primary amines such as methylamine, Secondary amines such as dimethylamine, tertiary amines such as trimethylamine, diamines such as ethylenediamine or melamine, and nitrogen-containing cyclic compounds such as imidazole and pyridine can be used. A solvent in which a plurality of compounds are used in combination may be used. Furthermore, in consideration of avoiding mixing of carbon and the like into the crystal of the target metal nitride to be produced, particularly preferred solvents are ammonia or hydrazine, alkali halide salts, ammonium halides, alkali nitrides and alkali amides. It is.

  The above solvents may be used in a subcritical state or even a supercritical state during the reaction. A supercritical fluid means a concentrated gas that is maintained above its critical temperature, and the critical temperature is a temperature at which the gas cannot be liquefied by pressure. Supercritical fluids generally have lower viscosities and are more easily diffused than liquids, but have solvating power similar to liquids. Of course, unlike water used as a solvent in hydrothermal synthesis methods, it is difficult to say that the properties of nitrogen-containing solvents have been clarified, so the dissolution and reaction of raw materials and the like are accelerated in the subcritical or supercritical state. However, if the concept of ionic product known in water is applied to a nitrogen-containing solvent, it increases with increasing temperature, such as an amylolysis equivalent to hydrolysis in water. There is also a possibility that the increase in action contributes.

  When used in a supercritical state, the reaction mixture is generally maintained at a temperature above 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 of the reaction vessel is high, the pressure far exceeds the critical pressure even at a temperature below the critical temperature. The supercritical state here includes a state exceeding the critical pressure. Since the reaction mixture is enclosed in a constant volume container, an increase in temperature increases the pressure of the fluid. In general, if T> Tc (critical temperature of one solvent) and P> Pc (critical pressure of one solvent), it can be said that the fluid is in a supercritical state.

In the reaction method, an adduct and a nitriding agent are charged into a reaction vessel and the reaction is started. It is desirable to dry it sufficiently by circulating an inert gas through the reaction vessel before filling. In particular, when the adduct or the nitriding agent easily absorbs moisture, it is necessary to dry it sufficiently by heating and degassing before filling.
In addition, when a highly decomposable nitriding agent is used, mixing and filling with the adduct are performed quickly in an atmosphere in which oxygen and moisture are eliminated as much as possible. For example, after the inside of the reaction vessel is replaced with an inert gas, a nitriding agent is introduced, and after the introduction, the whole reaction vessel is heated and deaerated to dry. In addition, a method in which a substance that functions as a scavenger that selectively absorbs oxygen and moisture (for example, a metal piece such as titanium) can be employed in the reaction vessel.

The reaction temperature generally tends to be higher in order to obtain a nitride having high crystallinity, but is usually 200 ° C. or higher, preferably 400 ° C. or higher, particularly preferably 500 ° C. or higher, and the upper limit is usually 1200 ° C. Hereinafter, it is preferably 1000 ° C. or less.
The pressure in the reaction vessel is usually 20 MPa or more, preferably 40 MPa or more, particularly preferably 50 MPa or more as the lower limit, and the upper limit is usually 500 MPa or less, preferably 400 MPa or less. Preferably, it is kept at 200 MPa or less.

Also, depending on the amount of N compound contained in the adduct and the presence or absence of the use of a solvent, pressure may be generated when they are desorbed at a high temperature and the reactor is closed. It is also preferable to use a pressure vessel and apply pressure from the outside of the reactor. Depending on the target compound, positive pressure is also preferably used to suppress the formation of metastable substances.
The material of the reaction vessel is not particularly limited, but depending on the type of N-containing compound and solvent contained in the adduct, BN, quartz, alumina, nickel (Ni), tantalum (Ta), titanium (Ti), tungsten (W ), Palladium (Pd), platinum (Pt), gold (Au) or niobium (Nb) is preferably used. A reaction vessel made of these materials or a reaction vessel coated and coated with these is used.

  The reaction between the adduct and the nitriding agent is usually carried out for several hours to several tens of hours. After the reaction is completed, the temperature is lowered and the reactor is opened. In some cases, a special heating process or cooling process is preferably used. When using a solvent, if it can be removed, remove it, then wash with water, alcohol, ammonia, acid, aqueous alkali solution to remove unreacted nitrides, alkali halide salts, etc. Get things. If the solvent cannot be removed, the mixture containing the solvent is washed to obtain a nitride as well.

In the above reaction, by controlling the amount of the solvent, it is possible to synthesize nitride and simultaneously perform crystal growth based on the dissolution and precipitation mechanism of the product. In that case, a temperature gradient can be provided in the reaction vessel, or a seed crystal can be used. When crystal growth is performed simultaneously, the synthesized nitride is once dissolved in a solvent by raising the temperature or the like, and the temperature is gradually lowered to precipitate crystals.
When growing a crystal using a seed crystal or a temperature gradient, it is usually performed over several hours to several hundred days. If necessary, it is also preferable to perform multi-stage temperature rise or change the temperature rise speed in the temperature range. Further, the reaction vessel can be partially heated with a temperature difference, or partially heated while being cooled. During the reaction, the reaction temperature may be constant or may be gradually raised or lowered. After a reaction time to produce the desired crystals, the temperature is lowered. When the temperature drops, depending on the partial precipitation of crystals and certain additives such as mineralizers, the reaction vessel can be cooled with a partial temperature difference or cooled while partially heating. You can also do it.

  Thus, in the case where nitride synthesis and crystal growth are performed simultaneously, more strict control of reaction conditions is required. When it is very difficult and it is desired to obtain larger lump crystals, it is preferable to use a multistage production method. That is, first, nitride is synthesized, and then a bulk crystal is grown using the nitride as a raw material. The multi-stage method facilitates the production of the bulk crystals. At this time, the reaction divided into multiple stages may be performed as it is without removing the solvent in the same reaction vessel, or may be performed by replacing with the same or another solvent. The synthesized raw material may be taken out once and subjected to treatment such as washing, and then filled in the same reaction vessel or another reaction vessel to grow crystals. At that time, it is also preferable to install a temperature gradient or a seed crystal as described above.

Hereinafter, specific embodiments for carrying out the present invention will be described with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
Example 1
In a high purity nitrogen gas atmosphere, 10 g of gallium chloride (GaCl ₃ ) was filled in the flask and evacuated. Next, the flask was cooled with a refrigerant at −72 ° C., and about 40 g of liquid ammonia purified by dehydration through a KOH column was introduced. While stirring, the temperature (about −40 ° C.) was raised to near the boiling point of ammonia, and the reaction was stirred for 1 hour. After removing the refrigerant and removing ammonia, the flask was evacuated for 1 h and then closed. When the generated white powder was analyzed under an inert gas atmosphere, it was GaCl ₃ (NH ₃ ) ₆ .
In a high-purity nitrogen gas atmosphere, the adduct GaCl ₃ (NH ₃ ) ₆ and the nitriding agent lithium nitride were mixed at a molar ratio of 1: 1, sealed in a metal container, and reacted at 530 ° C. for 12 hours. . At this time, the internal pressure was kept at 70 MPa. After the reaction, the temperature was returned to room temperature, the reaction mixture was suspended in water, filtered, washed with water, and vacuum dried at room temperature. The nitride yield based on Ga was 90%. When the obtained off-white powder was analyzed by XRD, it was h-GaN.

Example 2
GaCl ₃ (NH ₃ ) ₆ and lithium nitride, which is a nitriding agent, are mixed at a molar ratio of 1: 1 in a high-purity nitrogen gas atmosphere, and a mixed salt of LiCl—KCl (molar ratio 3: 2) as a solvent is further mixed. The mixture was mixed at a ratio of 5, sealed in a metal container, and reacted at 530 ° C. for 12 hours. At this time, the internal pressure was kept at 60 MPa. The temperature was returned to room temperature, the mixture was suspended in water, filtered, washed with water, and vacuum dried at room temperature. The nitride yield based on Ga was 62%. When the obtained off-white powder was analyzed by XRD, it was h-GaN.

Example 3
GaCl ₃ (NH ₃ ) ₆ and lithium nitride, which is a nitriding agent, are mixed at a molar ratio of 1: 1 in a high-purity nitrogen gas atmosphere, and a mixed salt of LiCl—KCl (molar ratio 3: 2) as a solvent is further mixed. The mixture was mixed at a ratio of 7, sealed in a metal container, and reacted at 530 ° C. for 12 hours. At this time, the system internal pressure was maintained at 30 MPa. The temperature was returned to room temperature, the mixture was suspended in water, filtered, washed with water, and vacuum dried at room temperature. The nitride yield based on Ga was 35%. When the obtained off-white powder was analyzed by XRD, it was c-GaN.

Example 4
GaCl ₃ (NH ₃ ) ₆ and lithium nitride, which is a nitriding agent, are mixed at a molar ratio of 1: 1 in a high-purity nitrogen gas atmosphere, and a mixed salt of LiCl—KCl (molar ratio 3: 2) as a solvent is further mixed. The mixture was mixed at a ratio of 7.5, sealed in a metal container, and reacted at 450 ° C. for 12 hours. At this time, the internal pressure was kept at 70 MPa. The temperature was returned to room temperature, the mixture was suspended in water, filtered, washed with water, and vacuum dried at room temperature. The yield of nitride based on Ga was 40%. When the obtained off-white powder was analyzed by XRD, it was c-GaN.

Example 5
GaCl ₃ (NH ₃ ) ₆ and lithium amide, which is a nitriding agent, were mixed at a molar ratio of 1: 3 in a high purity nitrogen gas atmosphere, sealed in a metal container, and reacted at 450 ° C. for 12 hours. At this time, the internal pressure was kept at 70 MPa. The temperature was returned to room temperature, the mixture was suspended in water, filtered, washed with water, and vacuum dried at room temperature. The yield of nitride based on Ga was 50%. When the obtained off-white powder was analyzed by XRD, it was c-GaN.

Example 6
In a high-purity nitrogen gas atmosphere, GaCl ₃ (NH ₃ ) ₆ and lithium amide as a nitriding agent are mixed in a molar ratio of 1: 3, and a mixed salt of LiCl—KCl (molar ratio 3: 2) as a solvent is further added The mixture was mixed at a ratio of 10, sealed in a metal container, and reacted at 530 ° C. for 12 hours. At this time, the internal pressure was kept at 75 MPa. The temperature was returned to room temperature, the mixture was suspended in water, filtered, washed with water, and vacuum dried at room temperature. The nitride yield based on Ga was 78%. When the obtained off-white powder was analyzed by XRD, it was a mixture of h-GaN and c-GaN.

Comparative Example 1
The reaction was performed under the same conditions as in Example 1 except that no nitriding agent was used. The resulting mixture was suspended in water, washed with filtered water, and dried in vacuo. When the obtained substance was analyzed by XRD, it was GaO (OH) and GaN was not produced.

Comparative Example 2
GaCl ₃ (NH ₃ ) ₆ and ammonium chloride were mixed at a molar ratio of 1: 8 in a high-purity nitrogen gas atmosphere, sealed in a metal container, and reacted at 530 ° C. for 12 hours. The pressure at that time was maintained at 70 MPa. The temperature was returned to room temperature, and the mixture was suspended in water, filtered, washed with water, and vacuum dried at room temperature. When the obtained substance was analyzed by XRD, it contained a large amount of GaO (OH).

Claims (8)

A method for producing a nitride of a group 4-14 metal, comprising reacting a nitrogen-containing compound adduct of a group 4-14 metal halide with an alkali metal or alkaline earth metal compound. The method for producing a nitride according to claim 1, wherein a halide containing a group 4-14 metal is added with a nitrogen-containing compound and then reacted with an alkali metal or alkaline earth metal compound. The method for producing a nitride according to claim 1 or 2, wherein the Group 4-14 metal is any one of B, Al, Ga, In, Ge, Ti, Zr, and Ta. The method for producing a nitride according to any one of claims 1 to 3, wherein the nitrogen-containing compound is ammonia. The method for producing a nitride according to any one of claims 1 to 4, wherein the alkali metal or alkaline earth metal compound is any one of an alkali metal, an alkaline earth metal nitride, an amide, and an imide. 6. The method for producing a nitride according to claim 1, wherein the alkali metal compound is lithium nitride. The method for producing a nitride according to any one of claims 1 to 6, wherein the reaction temperature is 200 ° C or higher and 1000 ° C or lower. The method for producing a nitride according to any one of claims 1 to 7, wherein the reaction pressure is 20 MPa or more and 500 MPa or less.