JP2005179139A - Method for refining nitride - Google Patents

Abstract

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

Description

  The present invention relates to a method for purifying a highly crystalline nitride with few oxygen impurities, and relates to a method for purifying a nitride of a group 4-14 metal of the periodic table.

  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.
Furthermore, when metal nitride is used for semiconductor applications, it is necessary to increase the crystallinity and suppress the introduction of impurities and defects. However, the conventional method facilitates the use of highly crystalline metal nitride with few oxygen impurities. In addition, there is no known effective method for purifying metal nitrides containing oxygen impurities, which cannot be produced easily.

  In view of the above-mentioned problems, the present inventor has obtained an easy acquisition as a result of earnestly examining a method capable of producing or refining a high-quality metal nitride with low oxygen impurities by a method that is sufficiently applicable industrially. Metal nitrides or oxynitrides with poor crystallinity containing oxygen impurities (hereinafter sometimes referred to as crude nitrides) and nitrogen-containing compounds of alkali metals or alkaline earth metals (hereinafter referred to as nitriding agents) It has been found that the desired high-quality metal nitride can be efficiently obtained by reacting with (A). That is, the present invention provides a method for purifying a group 4-14 metal nitride comprising reacting a group 4-14 metal nitride containing an oxygen impurity with an alkali metal or alkaline earth metal nitrogen-containing compound. About.

  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 purification method of the present invention, the target nitride is a nitride of a metal element belonging to Group 4 to 14 of the periodic table, and is not particularly limited as long as it belongs to the classification of the metal element. Purification of nitrides that are particularly useful in the group 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. Further, the nitride to be manufactured is not limited to pure nitride, but can be oxynitride.

  As a nitride (crude nitride) of a group 4-14 metal containing oxygen impurities, a crude nitride of the metal or oxynitride is used. There are no particular limitations on the method for producing these compounds as raw materials. For example, the metal can be reacted with an acid and dissolved as an aqueous solution, then neutralized with a basic aqueous solution to precipitate a hydroxide, and the hydroxide can be separated and recovered. If the hydroxide is baked in an oxygen atmosphere, an oxide can be obtained. When these hydroxides and oxides are heated in an atmosphere of a nitrogen-containing compound such as ammonia, a nitride or oxynitride that is a crude nitride of the metal can be obtained. In addition, a crude nitride can also be obtained by reacting the hydroxide or oxide with an alkali metal or alkaline metal earth nitride or amide. Furthermore, it is also possible to use a metal halide obtained by directly reacting the metal with hydrogen halide or halogen, or a crude nitride produced using a nitrogen-containing compound adduct thereof.

  The form of oxygen impurities contained in these crude nitrides is not particularly limited, and may be a form that is not detected by X-ray diffraction, or may be mixed as an oxide or hydroxide. The amount of oxygen impurities contained in these crude nitrides is not particularly limited as long as it is within a range in which the purification effect can be recognized by the method of the present invention, but generally, the upper limit is usually 20 % By weight or less, preferably 10% by weight or less, and the lower limit is usually 0.1% by weight or more, preferably 0.3% by weight or more. Needless to say, the smaller the amount of oxygen contained in the raw material, the lower the amount of oxygen impurities in the resulting nitride. However, for example, even if the crude nitride contains 0.5% by weight of oxygen, this method is applied. Thus, the amount of oxygen impurities in the resulting nitride is reduced. Further, a crude nitride obtained by nitriding a hydroxide or oxide with ammonia at a temperature of about 800 ° C. usually contains about 5% by weight of oxygen, for example, when gallium is used. When the product is used as a raw material, the effect of the present invention is remarkable.

In the present invention, the above-described crude nitride is reacted with a nitrogen-containing compound (nitriding agent) of an alkali metal or alkaline earth metal. As a result, the metal nitriding agent having higher crystallinity and less oxygen impurities than before the reaction can be obtained efficiently. The reason for this is not clear, but anions such as N ³⁻ groups and NH ₂ ⁻ groups generated by activating the nitrogen-containing compound of a highly positive alkali metal constituting the nitriding agent are used as crude nitrides of the metal. It is presumed that the oxygen anion and hydroxide anion are substituted to improve the crystallinity, and at the same time, oxygen is trapped to give the desired metal nitride with low crystallinity and oxygen impurity.

The nitriding agent is not particularly limited as long as it is a compound capable of supplying nitrogen that can be a nitrogen source of the target group 4-14 metal nitride, but preferably, an alkali metal such as lithium or sodium, magnesium or the like Alkali earth metal nitrides, amides, and imides are preferable, and lithium nitride is particularly preferable. A plurality of such nitriding agents may be used in combination.
In this reaction, the amount of the nitriding agent reacted with the coarse nitride of the group 4-14 metal depends on the oxygen impurity contained in the crude nitride and the crystallinity, but with respect to the amount of the group 4-14 metal, Usually, 0.01 to 10 times equivalent, preferably 0.1 to 2 times equivalent, particularly preferably 0.5 to 1 equivalent is reacted. When the amount of oxygen contained in the raw material crude nitride is small, the amount of the nitriding agent may be small. When the amount of oxygen contained in the raw material crude nitride or oxynitride is large, if the amount of the nitriding agent is small, the reaction will be incomplete and the hydroxide or oxide will be easily mixed. Moreover, even if there is too much quantity of a nitriding agent, 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.

  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, they are group 4-14 metals. It is considered that this crude nitride can be converted into high-purity nitride with high crystallinity.

The crude nitride and the 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 of the crude nitride 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, crude nitride and a nitriding agent are filled in 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 crude nitride or nitriding agent tends to absorb 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 crude nitride 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 nitrogen-containing compounds and the presence or absence of solvent use, they may be detached at high temperatures, and pressure may be generated when the reactor is closed. It is also preferred to use and apply pressure from outside 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 crude nitride 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 a solvent is used, if it can be removed, it is removed and then washed with water, alcohol, ammonia, acid, or an aqueous alkali solution to obtain the desired highly crystalline high-purity nitride. 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 simultaneously purify the 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 purified 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.

  As described above, when the purification of the nitride and the crystal growth are performed simultaneously, more strict control of the reaction conditions is required. When it is very difficult and it is desired to obtain larger lump crystals, a multi-stage method is preferably used. That is, first, nitride is purified, 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)
Ga ₂ O ₃ was treated in a stream of ammonia at 800 ° C. for 6 hours to obtain a wild-colored rough GaN. The crude GaN contained 5.2% by weight of oxygen and 13.5% by weight of nitrogen as measured by an LECO oxygen nitrogen analyzer. The crude GaN was found to be h-GaN by XRD measurement. The peak height of the (100) diffraction line was 2400, and the half width of the peak was 2 theta 0.53 degrees.
Under a high purity nitrogen gas atmosphere, the crude GaN and lithium nitride were mixed at a molar ratio of 2: 1, sealed in a metal reaction vessel, and reacted at 530 ° C. for 12 hours. The pressure at that time was kept at 70 MPa. The temperature was returned to room temperature, and the resulting mixture was suspended in water, washed with filtered water, and dried in vacuo at room temperature. The yield based on Ga was 65%. When the obtained off-white powder was analyzed by XRD, it was h-GaN. The peak height of the (100) diffraction line was 11400, and the half-width of the peak was 2-theta 0.18 degrees. The oxygen was 0.2 wt% and nitrogen was 16.7 wt% on a LECO oxygen nitrogen analyzer. Therefore, it can be seen that the crystallinity is increased by the reaction with lithium nitride, the amount of oxygen impurities is reduced, and h-GaN is purified.

(Example 2)
Ga ₂ O ₃ was treated in an ammonia stream at 1000 ° C. for 6 hours to obtain lemon-colored crude GaN. When measured with a LECO oxygen nitrogen analyzer, this crude GaN contained 0.5 wt% oxygen and 16.1 wt% nitrogen. The crude GaN was found to be h-GaN by XRD measurement, and the half-value widths of the diffraction line peaks of (213) and (220) were 2-theta 1.026 degrees and 1.597 degrees, respectively. Met.
Under a high purity nitrogen gas atmosphere, the crude GaN and lithium nitride were mixed at a molar ratio of 2: 1, sealed in a metal reaction vessel, and reacted at 530 ° C. for 12 hours. The pressure at that time was kept at 70 MPa. The temperature was returned to room temperature, and the resulting mixture was suspended in water, washed with filtered water, and dried in vacuo at room temperature. The yield based on Ga was 70%. When the obtained off-white powder was analyzed by XRD, it was h-GaN. The half widths of the peaks of the diffraction lines (213) and (220) were 2-theta 0.288 degrees and 0.483 degrees, respectively. It was 0.2 wt% oxygen and 16.7 wt% nitrogen using a LECO oxygen nitrogen analyzer. Therefore, it can be seen that the crystallinity is increased by the reaction with lithium nitride, the amount of oxygen impurities is reduced, and h-GaN is purified.

(Example 3)
In a high-purity nitrogen gas atmosphere, the crude GaN of Example 1 and lithium nitride were mixed at a molar ratio of 2: 1, and a mixed salt of LiCl-KCl (molar ratio 3: 2) was further mixed at a molar ratio of 1: 3. Then, it was sealed in a metal reaction vessel and reacted at 530 ° C. for 12 hours. The pressure at that time was kept at 70 MPa. The temperature was returned to room temperature, and the resulting mixture was suspended in water, washed with filtered water, and dried in vacuo at room temperature. The yield based on Ga was 70%. When the obtained off-white powder was analyzed by XRD, it was h-GaN. The peak height of the (100) diffraction line was 8000, and the half-width of the peak was 2-theta 0.23 degrees. According to a LECO oxygen nitrogen analyzer, the oxygen content was 0.4% by weight. Therefore, it can be seen that the crystallinity is increased by the reaction with lithium nitride, the amount of oxygen impurities is reduced, and h-GaN is purified.

Example 4
In a high purity nitrogen gas atmosphere, the crude GaN of Example 1 and lithium amide were mixed at a molar ratio of 2: 3, and a mixed salt of LiCl—KCl (molar ratio 3: 2) was further mixed at a molar ratio of 1: 3. Then, it was sealed in a metal reaction vessel and reacted at 530 ° C. for 12 hours. The pressure at that time was kept at 70 MPa. The temperature was returned to room temperature, and the resulting mixture was suspended in water, washed with filtered water, and dried in vacuo at room temperature. The yield based on Ga was 60%. When the obtained off-white powder was analyzed by XRD, it was h-GaN. The peak height of the (100) diffraction line was 5000, and the half width of the peak was 2-theta 0.34 degrees. According to LECO oxygen nitrogen analyzer, oxygen was 0.5% by weight. Therefore, it can be seen that the crystallinity is increased by the reaction with lithium amide, the amount of oxygen impurities is reduced, and h-GaN is purified.

(Comparative Example 1)
In Example 2, ammonium chloride was mixed in a molar ratio of 2: 1 instead of lithium nitride and 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, the crystallinity of h-GaN was not improved and GaO (OH) was also generated.

Claims (6)

A method for purifying a nitride of a group 4-14 metal comprising reacting a nitride of a group 4-14 metal containing an oxygen impurity with a nitrogen-containing compound of an alkali metal or an alkaline earth metal. The method for purifying a nitride according to claim 1, wherein the Group 4-14 metal is any one of B, Al, Ga, In, Ge, Ti, Zr, and Ta. The method for purifying a nitride according to claim 1 or 2, wherein the oxygen content of the nitride of a group 4-14 metal containing oxygen impurities is 0.1 wt% or more and 20 wt% or less. The method for purifying a nitride according to any one of claims 1 to 3, wherein the nitrogen-containing compound of the alkali metal is lithium nitride. The method for purifying a nitride according to any one of claims 1 to 4, 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 5, wherein the reaction pressure is 20 MPa or more and 500 MPa or less.