JP2013067530A - Method and apparatus for manufacturing gallium nitride powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing gallium nitride powder capable of producing gallium nitride powder suitable for use as a raw material in synthesizing bulk crystals of gallium nitride by the ammonothermal method with a low cost and highly productivity by using a vapor-phase method.SOLUTION: Gallium chloride is produced by reacting hydrogen chloride with gallium powder at a temperature of 800 to 1,000°C, and the gallium nitride is synthesized by reacting the obtained gallium chloride with ammonia at a temperature of 800 to 1,200°C. By controlling the temperature of the gas atmosphere containing the obtained gallium nitride to 185°C or more and 337.5°C or less the gallium nitride powder not containing the ammonium chloride of a reaction by-product is separately recovered.

Description

  The present invention relates to a method for producing gallium nitride (GaN) powder, and more particularly to a method for mass-producing and efficiently recovering GaN powder.

Among several issues to be solved in the future for the survival of humankind, energy saving and CO ₂ reduction are extremely important. One of the main energy consumption in homes and offices is lighting. In Europe and the United States, there is a movement to ban the use of incandescent bulbs. It is out. Nevertheless, while further energy saving is desired, the use of white LEDs (light emitting diodes) for illumination is considered an essential direction.

  Conventionally, when manufacturing a white LED, a sapphire (aluminum oxide) substrate is generally used, and a GaN film is formed on the sapphire (aluminum oxide) substrate by a vapor phase method such as an MOCVD method to form a device. However, since the difference in lattice constant between sapphire and GaN is as high as 16%, even if a GaN film is formed using a high-quality sapphire substrate, there are many dislocations that are a kind of lattice defects due to the large difference in lattice constant. This is unavoidable, and this is a cause of low efficiency or short life of the LED or semiconductor laser as a device.

  Even if a large number of dislocations are introduced as described above, a certain amount of light emission is realized in the case of a blue LED because the indium added at the time of device fabrication is moderately distributed to alleviate lattice distortion. ing. However, the longer wavelength green and the shorter wavelength purple or ultraviolet light are wavelengths where light can be emitted strongly from GaN in principle, but in reality the light emission efficiency is extremely low and the lifetime is long. There is a drawback of being short. Although it is such a situation, since the sapphire substrate is inexpensive, whitening is realized by using a blue LED and combining it with an appropriate phosphor even if it is not very efficient.

  On the other hand, the use of a GaN substrate is ideal for increasing the efficiency of white LEDs, but GaN itself is a material that can be synthesized only at a high temperature and high pressure of 1500 ° C. or higher and 10,000 atm. Recently, however, several methods for obtaining a GaN substrate have been tried. For example, a GaN free-standing substrate is manufactured by forming a thick GaN film on a base material such as sapphire or GaAs by a vapor phase method such as MOCVD or HVPE, and then dissolving or physically peeling the base material. It is commercially available. However, it is expensive because it takes a lot of time to produce by a vapor phase method and to remove the base material, and is difficult to apply to general LEDs, and is limited to use in special applications.

  As another approach for obtaining a GaN substrate, there is a method of growing a bulk crystal of GaN. However, since it is impossible to dissolve and pull up the raw material as in the Czochralski method, an ammonothermal method, which is a kind of solution method using a solvent such as ammonia, has been studied. Recently, as shown in Non-Patent Document 1, it has become possible to grow a bulk crystal by an ammonothermal method. If this method enables mass production of GaN bulk crystal ingots with high yield, it will be possible to significantly reduce the substrate price compared to the conventional vapor phase method, and to provide an inexpensive and highly efficient LED using a GaN substrate. It becomes possible.

  The ammonothermal method is based on the same principle as hydrothermal synthesis, which is a crystal growth method. However, in the hydrothermal synthesis of quartz, water is used as a solvent, and 1500 atm is applied at a temperature of about 400 ° C. to realize a supercritical state. The supercritical state is a state in which, when a temperature and pressure above the critical point are applied, a fluid that is neither a liquid nor a gas is obtained, the atoms are separated and the reactivity is very high. In the specific hydrothermal synthesis of quartz, the quartz piece that is the raw material is placed in the high temperature part at the bottom of the autoclave (high temperature high pressure furnace) and dissolved in a solvent to bring it into a saturated solubility state. It reaches the seed crystal in the low temperature part and crystallizes.

  The synthesis of bulk crystals of GaN by the ammonothermal method differs from quartz in that ammonia is used as a solvent, but other conditions such as temperature and pressure can be used under almost the same conditions as in quartz. Production of inexpensive GaN substrates comparable to substrates has become realistic. For this reason, it is an important issue to provide a large amount of GaN material as a raw material at a low cost when considering mass production by the ammonothermal method in the future.

  In order to produce a large amount of GaN material at low cost, it is considered advantageous to manufacture it as a powder. For example, in Patent Document 1, gallium hydroxide obtained by dripping ammonia into gallium nitrate hydrate is rapidly heated at 800 ° C. to obtain porous gallium oxide, and then this gallium oxide is placed in an ammonia atmosphere. Describes a method for obtaining a GaN powder by heat treatment with a glass. However, this method has a problem in terms of safety, such as rapidly heating gallium hydroxide at 800 ° C.

Further, in Patent Document 2, a gallium nitride crystal nucleus is generated by reacting gallium vapor and ammonia gas, and a gallium nitride crystal is grown on the gallium nitride crystal nucleus by reacting gallium halide with ammonia gas. A method for producing a gallium nitride powder is disclosed. However, since the produced gallium nitride powder is heated to about 500 ° C. so that the by-product NH ₄ Cl is not individualized and adhered, it is necessary to lower the temperature when collecting the gallium nitride powder. Therefore, there are concerns about the problem of energy consumption due to excessive heating and the decrease in productivity due to the time loss required for recovery of gallium nitride powder.

Special table 2008-521745 JP 2003-063810 A

Effective promotion and ex-post evaluation of industry-academia-government joint research "Semiconductor substrate crystal manufacturing technology that brings next-generation lighting", Research Institute for Multidisciplinary Research for Advanced Materials, Tohoku University (Research representative: Fumiyoshi Saito), From 2004 to 2006

  In view of the above-described conventional circumstances, an object of the present invention is to provide a method for producing a gallium nitride powder suitable as a raw material for an ammonothermal method at low cost and with high productivity by a vapor phase method.

  In order to achieve the above object, a method for producing a gallium nitride powder provided by the present invention comprises reacting a hydrogen chloride gas introduced by a carrier gas with a gallium powder at a temperature of 800 to 1000 ° C., and using the resulting gallium chloride as a carrier. After reacting with ammonia gas at a temperature of 800 to 1200 ° C. while transporting with gas, gallium nitride is generated, and then the temperature of the gas atmosphere containing the obtained gallium nitride is controlled to 185 ° C. or more and less than 337.5 ° C. Thus, the gallium nitride powder is separated and recovered.

  According to the present invention, gallium nitride powder can be manufactured at low cost and with high productivity by a vapor phase method, and in particular, the temperature at the time of separating and recovering gallium nitride powder from a gas atmosphere can be made significantly lower than before. The recovery of gallium nitride powder containing no reaction by-products can be facilitated and the amount of energy used can be reduced. Therefore, the present invention can be manufactured in a large amount and at a low cost for a gallium nitride powder suitable as a raw material for an ammonothermal method for synthesizing a bulk crystal for a gallium nitride substrate, and thus is extremely useful for providing an inexpensive and highly efficient LED. .

It is a schematic block diagram which shows the manufacturing apparatus of the GaN powder of this invention. It is a graph which shows the relationship between the temperature of the gas atmosphere of a powder collection | recovery chamber, and the collection amount of ammonium chloride.

  The method for producing gallium nitride powder according to the present invention will be specifically described with reference to FIG. First, hydrogen chloride (HCl) gas is introduced into the first reaction chamber 1 by a carrier gas such as hydrogen, and reacted with gallium powder in the first reaction chamber 1 controlled to a temperature of 800 to 1000 ° C. by the heater 1a to gallium chloride. (GaCl) is generated. The gallium powder is placed in the first reaction chamber 1 in a container opened at the top, and when the volume of the first reaction chamber 1 is large, the flow of hydrogen chloride gas and carrier gas as shown in FIG. It is desirable to control the reaction zone by surrounding the vessel except the path.

  Gallium chloride generated in the first reaction chamber 1 is introduced into the second reaction chamber 2 together with the carrier gas. At the same time, ammonia gas is introduced into the second reaction chamber 2 by a carrier gas such as hydrogen from another flow path. The second reaction chamber 2 is controlled to a temperature of 800 to 1200 ° C. by a heater 2a. In this second reaction chamber 2, gallium chloride and ammonia react to synthesize gallium nitride (GaN).

The amount of ammonia gas introduced into the second reaction chamber 2 should be at least about 1:50 in terms of a molar ratio to gallium (Ga), that is, a molar ratio of Ga: NH ₃ . Also, a large amount of hydrogen chloride gas is supplied when gallium chloride is produced from gallium powder in the first reaction chamber 1. Therefore, as represented by the following reaction formula 1, in the reaction for obtaining gallium nitride from gallium powder, a large amount of ammonium chloride (NH ₄ Cl) is generated as a reaction byproduct. Although gallium powder can be directly reacted with ammonia, it is not preferable because of poor reaction efficiency.
[Reaction Formula 1] 2Ga + 3NH ₃ + HCl → 2GaN + NH ₄ Cl + 3H ₂

  As described above, the gallium nitride synthesized in the second reaction chamber 2 is introduced into the powder recovery chamber 3 together with a gas atmosphere made of carrier gas, ammonium chloride, or the like. In the present invention, the temperature of the powder recovery chamber 3, that is, the temperature of the gas atmosphere containing gallium nitride is controlled to a temperature in the range of 185 ° C. or more and less than 337.5 ° C. by the heater 3 a. It has been found that ammonium chloride as a reaction by-product can maintain a gaseous state in a gas atmosphere controlled within this temperature range, so that only the gallium nitride powder can be efficiently separated and recovered in the powder recovery chamber 3.

That is, the synthesized GaN powder is deposited in the powder collection chamber 3 at the bottom of the reaction apparatus, and is collected after the reaction is completed and the operation is stopped. In that case, the temperature of the powder recovery chamber 3 is kept at 337.8 ° C. or higher, which is the sublimation temperature of NH ₄ Cl, so that ammonium chloride (NH ₄ Cl), which is a reaction by-product in the past, does not become impurities of the GaN powder. As a result, NH ₄ Cl was discharged out of the system as an exhaust gas together with a carrier gas. Therefore, when recovering the GaN powder after completion of the reaction, it takes a long time to lower the temperature of the powder recovery chamber 3 from a high temperature of 337.8 ° C. or more to room temperature. It had an adverse effect.

However, according to the study by the present inventors, the NH ₄ Cl sublimation temperature is 337.8 ° C. as described above, but the NH ₄ Cl is actually at a temperature lower than 337.8 ° C. I found that it was sublimating. That is, when the temperature of the powder collection chamber 3 was changed and the relationship between the weight of NH ₄ Cl collected together with the GaN powder in the powder collection chamber 3 and the temperature was examined, the result shown in FIG. 2 was obtained. From this result, it was found that when the temperature is lower than 185 ° C., NH ₄ Cl does not sublime completely and remains in the GaN powder, but at a temperature of 185 ° C. or higher, substantially sublimation of NH ₄ Cl occurs. .

The sublimation temperature normally reported in literature etc. is a value at equilibrium, and when flowing a large amount of carrier gas or the like as in the reaction system represented by the above reaction formula 1, it differs from the value at equilibrium. It is considered that the value is at the time of non-equilibrium. This agrees with the experimental result that the amount of NH ₄ Cl recovered is reduced when the gas flow rate is increased. From the above results, the temperature of the powder recovery chamber in the present invention, that is, the temperature of the gas atmosphere containing gallium nitride is set to 185 ° C. or higher and lower than 337.8 ° C. which is the sublimation temperature of NH ₄ Cl, and preferably Is in the range of 200 to 250 ° C, more preferably in the range of 200 to 230 ° C.

As described above, after the GaN powder is separated and deposited in the powder recovery chamber 3 at the bottom of the reaction apparatus, the gas atmosphere is discharged from the reaction apparatus through the exhaust gas flow path as shown in FIG. NH ₄ Cl is recovered as a liquid.

  As shown in FIG. 1, for example, a manufacturing apparatus used in a method for manufacturing a gallium nitride powder according to the present invention includes a first reaction chamber 1 for reacting gallium powder with hydrogen chloride gas, and a gallium chloride obtained in the first reaction chamber 1. Is provided with a second reaction chamber 2 that reacts with ammonia gas, and a powder recovery chamber 3 that recovers the gallium nitride obtained in the second reaction chamber 2. Further, the outer periphery of the first reaction chamber 1, the second reaction chamber 2 and the powder recovery chamber 3 is provided with heaters 1a, 2a and 3a, respectively, and the temperature of the first reaction chamber 1 is set to 800 to 1000 ° C. by the heater 1a. The temperature of the second reaction chamber 2 is controlled to 800 to 1200 ° C. by the heater 2a, and the temperature of the powder recovery chamber 3 is controlled to 185 ° C. or more and less than 337.5 ° C. by the heater 3a.

  As the reactor, a hot wall type reactor can be used. However, since hydrogen chloride gas having a high temperature exceeding 1000 ° C. and strong corrosiveness is introduced, generally even at a high temperature. It is desirable to use ceramics such as quartz, which is stable and excellent in corrosion resistance, as a constituent material. The synthesis reaction of gallium nitride in the reaction apparatus is usually carried out at normal pressure.

  Moreover, in the reaction apparatus of this invention, it is preferable to make it the structure which can isolate | separate a powder recovery chamber from the reaction container part comprised by a 1st reaction chamber and a 2nd reaction chamber. By having such a structure, when the temperature of the powder recovery chamber drops to a certain extent, it becomes possible to immediately separate the powder recovery chamber from the reaction vessel portion of the reactor and recover the GaN powder. Even in this case, the lower the temperature of the powder recovery chamber during the operation of the reactor, the shorter the time required for cooling, and the easier the recovery of GaN powder.

[Example 1]
A hot wall type furnace made of SUS306 having an inner diameter of 300 mm was prepared, and heaters were arranged on the outer circumferences of the upper part, middle part and lower part, respectively. With each heater, the temperature in the upper part of the furnace (first reaction chamber with the Ga powder container) is set to 900 ° C., the temperature in the middle part (second reaction chamber) is set to 1100 ° C., and the temperature in the lower part (powder recovery chamber). The temperature was adjusted to 300 ° C. Further, a tube having an inner diameter of 20 mm was joined to the furnace side surface approximately 50 cm from the powder recovery chamber to form an exhaust gas flow path.

HCl gas was introduced into the first reaction chamber by a hydrogen carrier gas and reacted with Ga powder in the container to generate GaCl. The produced GaCl was introduced into the second reaction chamber together with the carrier gas, and at the same time, ammonia gas was introduced into the second reaction chamber by the hydrogen carrier gas, thereby reacting GaCl and ammonia gas to synthesize GaN. Carrier gas, unreacted gas, and NH ₄ Cl, which is a reaction byproduct, were exhausted from the exhaust gas flow path, and GaN powder was deposited in the powder recovery chamber.

After completion of the reaction, while replacing the gas atmosphere in the furnace with nitrogen gas, the temperature of the powder recovery chamber was lowered to room temperature, and the GaN powder deposited in the powder recovery chamber was recovered. It took about 1 hour for the temperature of the powder recovery chamber to drop from 300 ° C. to room temperature, and analysis of the recovered GaN powder revealed no NH ₄ Cl.

[Example 2]
A GaN powder was produced in the same manner as in Example 1 except that the temperature of the powder recovery chamber was 185 ° C. After completion of the reaction, the temperature of the powder recovery chamber was lowered to room temperature in the same manner as in Example 1 above, and the GaN powder was recovered because it was deposited in the powder recovery chamber. It took about 0.5 hours for the temperature of the powder recovery chamber to drop from 185 ° C. to room temperature, and analysis of the recovered GaN powder revealed no NH ₄ Cl.

[Comparative Example 1]
A GaN powder was produced in the same manner as in Example 1 except that the temperature of the powder recovery chamber was 180 ° C. After completion of the reaction, the temperature of the powder recovery chamber was lowered to room temperature in the same manner as in Example 1 above, and the GaN powder was recovered because it was deposited in the powder recovery chamber. The temperature in the powder recovery chamber was as short as about 20 minutes until the temperature decreased from 180 ° C. to room temperature, but NH ₄ Cl was contained in the obtained GaN powder.

[Comparative Example 2]
A GaN powder was produced in the same manner as in Example 1 except that the temperature of the powder recovery chamber was 350 ° C. After completion of the reaction, the temperature of the powder recovery chamber was lowered to room temperature in the same manner as in Example 1 above, and the GaN powder was recovered because it was deposited in the powder recovery chamber. Analysis of the recovered GaN powder revealed no NH ₄ Cl, but it took about 1.5 hours for the temperature of the powder recovery chamber to drop from 350 ° C. to room temperature.

DESCRIPTION OF SYMBOLS 1 1st reaction chamber 2 2nd reaction chamber 3 Powder recovery chamber 1a, 2a, 3a Heater 4 Liquid recovery part

Claims (2)

  The hydrogen chloride gas introduced by the carrier gas is reacted with gallium powder at a temperature of 800 to 1000 ° C., and the resulting gallium chloride is reacted with ammonia gas at a temperature of 800 to 1200 ° C. while being conveyed by the carrier gas. , And then the gallium nitride powder is separated and recovered by controlling the temperature of the obtained gas atmosphere containing gallium nitride to 185 ° C. or higher and lower than 337.5 ° C. .   2. The method for producing gallium nitride powder according to claim 1, wherein the temperature of the gas atmosphere is controlled to 200 to 250 ° C. to separate and recover the gallium nitride powder.

Images