JP6389424B2 - Method for regenerating reaction vessel for crystal growth and method for crystal growth - Google Patents

Description

  The present invention relates to a method for regenerating a reaction vessel for crystal growth.

  A method for growing a gallium nitride single crystal using the Na flux method has been studied. At this time, since highly reactive sodium or the like is put in the crucible and heated at a high temperature for a long time, a crucible material that can withstand this is required.

  Patent Document 1 (Japanese Patent Laid-Open No. 2004-300024) discloses a crucible made of boron nitride or alumina. Patent Document 2 (Japanese Patent Laid-Open No. 2005-263622) also discloses an alumina crucible. Patent Document 3 (Japanese Patent Laid-Open No. 2005-263535) discloses a crucible made of yttria.

  However, in the Na flux method, an alkali metal flux and metal gallium are put in a crucible and a growth process is performed at a high temperature and a high pressure. For this reason, during crystal growth, the crucible was corroded by high-temperature sodium, and an impurity emission band was sometimes observed in the grown crystal. For this reason, Patent Document 4 has been proposed as a method for regenerating crucibles.

  In the regeneration method described in Patent Document 4, a used crucible is ultrasonically cleaned and then heated at a temperature of 1300 to 1600 ° C. in an oxygen-containing atmosphere. This is because alumina is reduced by contact between high-temperature sodium and an alumina crucible in the crystal growth process, which causes impurities to accumulate. Therefore, the reduced alumina is re-oxidized by high-temperature heat treatment at 1300 ° C. or higher. And restore it. Patent Document 4 describes ultrasonic cleaning with pure water or dilute hydrochloric acid having a concentration of 10% or less before oxidizing a used crucible at a high temperature of 1300 ° C. or higher in an oxygen atmosphere.

JP2004-300024 JP-A-2005-263622 JP 2005-263535 A JP2011-136898A

  However, when the present inventor regenerated the crucible by the method described in Patent Document 4 and grew the crystal, the following problems occurred. In other words, I tried to grow a crystal such as gallium nitride on the seed crystal substrate, but even if the external appearance of the crucible was regenerated without any problems, impurities easily collect along the interface between the seed crystal substrate and the grown crystal. In some cases, rate fluctuations and crystal defects near the interface occurred.

  The problem of the present invention is that, when a crystal is grown in a state in which a melt containing sodium and gallium is accommodated in a reaction vessel made of alumina, the initial growth rate of the crystal to be grown varies when the reaction vessel is regenerated. It is to suppress crystal defects.

The present invention is a method for regenerating the reaction vessel after growing a crystal in a state in which a melt containing sodium and gallium is contained in a reaction vessel made of alumina,
A dipping step in which the purity of the alumina is 99.9% by weight or more, the bulk density of the alumina is 99.5% or more, and the reaction vessel is dipped in an acid solution or an alkali solution and left standing. And a cleaning step of ultrasonically cleaning the reaction vessel, and setting the immersion time of the reaction vessel in the acid solution or alkali solution to 30 ° C. or less while the environmental temperature during regeneration of the reaction vessel is 300 ° C. or less. And the gallium hydroxide adhering to the reaction vessel is removed.

Further, the present invention is a first growth step of growing a crystal in a state in which a melt containing sodium and gallium is contained in a reaction vessel made of alumina,
Next, a regeneration step for regenerating the reaction vessel, and a second growth step for growing crystals in a state in which a melt containing sodium and gallium is accommodated in the reaction vessel, and the purity of the alumina is 99 9.9% by weight or more, and the bulk density of the alumina is 99.5% or more, and the regeneration step comprises:
A dipping step in which the reaction vessel is immersed in an acid solution or an alkaline solution and left standing, and then a washing step in which the reaction vessel is ultrasonically cleaned, and the second growing step from the first growing step. While the ambient temperature is 300 ° C. or lower , the immersion time of the reaction vessel in the acid solution or alkaline solution is 30 minutes or longer, and gallium hydroxide adhering to the reaction vessel is removed.

  In the regeneration method described in Patent Document 4, oxygen defects on the crucible surface are compensated by heat treatment at a high temperature to maintain the strength, and alkali components attached to the oxygen defect portion on the crucible surface are removed. This is because the alkaline component mixed in the oxygen defect portion cannot be removed by simple ultrasonic cleaning or acid cleaning.

  However, when a gallium nitride crystal or the like was actually grown on a seed crystal substrate using the regenerated crucible, variations in the initial growth rate of the crystal and crystal defects occurred.

  As a result of searching for the cause, the present inventor found the following. That is, the reaction vessel in which the initial crystal defect of the grown crystal or the variation in the growth rate occurred was subjected to ultrasonic cleaning of the surface and elemental analysis of the cleaning solution. As a result, Ga and a small amount of Fe and Na were detected. Next, when this washing solution was neutralized with an acid, a Ga salt was precipitated. This indicates that gallium hydroxide is produced and remains on the surface or inside of the reaction vessel.

  Although gallium hydroxide is a stable substance, it is easily reduced to a strong reducing substance such as Na, and oxygen constituting the gallium hydroxide dissolves into the growth solution, so that oxygen in the flux solution It is considered that the concentration increases and inhibits the initial nitriding. Since the amount of gallium hydroxide remaining in such a reaction vessel is very small, it is not easy to detect, and it is considered that the crystallinity was deteriorated at the initial stage of crystal growth, resulting in variations in the growth rate.

  Further, in the regeneration method described in Patent Document 4, since bulk crystals were grown, it is considered that the influence of a small amount of gallium hydroxide remaining in the crucible could not be found.

  For this reason, the present inventor first examined the material of alumina constituting the reaction vessel. As a result, after suppressing impurities by using alumina having a purity of 99.9% or more, the reaction vessel is composed of highly dense alumina having a bulk density of 99.5% or more, so that the surface of the reaction vessel after crystal growth It was found that no coloring or deteriorated layer was observed, that is, almost no surface oxygen defects were observed. As a result, it is no longer necessary to fill oxygen defects by high-temperature heating in an oxygen atmosphere.

  In addition, since gallium hydroxide is soluble in acid and alkali, an attempt was made to remove the reaction vessel by ultrasonic cleaning in an acid solution or an alkali solution. However, in actual trials, gallium hydroxide not only adheres to the reaction vessel, but is also protected and included by entering the grain boundaries in the ceramics and miscellaneous crystals, and contact with chemicals in general cleaning operations The reaction becomes limited in time. For this reason, it has been found that a longer contact time with the chemical solution is required than a general cleaning operation.

  For this reason, this inventor provided the immersion process which hold | maintains the said precise | minute reaction container in the state immersed in the acid solution or the alkali solution. While the reaction vessel is immersed in the acid solution or alkali vessel, dissolution of gallium hydroxide protected and encapsulated by the grain boundaries and miscellaneous crystals proceeds in the vicinity of the reaction vessel surface. In addition, by further washing the reaction vessel, the acid and alkali adhered to the reaction vessel surface and the dissolved gallium hydroxide were successfully removed.

  Furthermore, in the present invention, the reaction vessel can be regenerated by immersing the reaction vessel in an acid solution or an alkali solution and then washing. Therefore, it is possible to avoid the surface of the reaction vessel from becoming rough due to the high temperature treatment. For this reason, gallium hydroxide is difficult to be included in the rough surface of the reaction vessel, and it can be surely dissolved to minimize the influence on the next growth process. Crystal nucleation and crystal nucleation at a location away from the seed substrate can be suppressed.

(Reaction vessel)
The reaction container referred to in the present invention means all containers that come into contact with the liquid or vapor of the flux, and includes a crucible, a lid that covers the crucible, a pressure container, and an outer reaction container that houses the crucible. The present invention is particularly effective when applied to a crucible for directly containing and melting a flux.

The bulk density of the alumina constituting the reaction vessel is 99.5% or more, and more preferably 99.9% or more. In the example described in Patent Document 4, alumina having a bulk density of 99% is used.
The bulk density is measured by the Archimedes method.

  The purity of the alumina constituting the reaction vessel is 99.9% by weight or more, and more preferably 99.95% by weight or more in order to minimize the risk of doping into the single crystal during growth.

  The alumina constituting the reaction vessel may be single crystal or polycrystalline (ceramics). Ceramics may be a so-called translucent material having a high relative density, such as HIP treatment.

  The average particle size of the alumina polycrystal is particularly preferably 10 μm or more and 100 μm or less from the viewpoint of corrosion resistance to the flux. From this viewpoint, the particle size of the raw material powder is 0.1 μm or more and 10 μm or less. Further preferred. The Young's modulus of the material constituting the reaction vessel is preferably 100 GPa or more, and more preferably 200 GPa or more.

  The method for producing alumina constituting the reaction vessel is not limited. For example, raw material powders are mixed and molded. Examples of this forming method include a uniaxial pressing method, a cold isostatic pressing method, and a casting method. Also, a binder such as PVA (polyvinyl alcohol) or PVB (polyvinyl butyral) can be used at the time of molding.

  Degreasing can also be performed after the molding step. The degreasing temperature is not particularly limited, but may be, for example, 300 ° C. or higher, and further 400 ° C. or higher. The upper limit of the degreasing temperature is not particularly limited, but may be 600 ° C. or lower, and further 500 ° C. or lower.

  The firing method is not particularly limited, and examples include hot pressing, hot isostatic pressing, and discharge plasma sintering. The firing temperature is not limited, and can be 1700 to 2000 ° C., for example.

  When the alumina is a single crystal, it is preferably produced by the Czochralski method, the Cairoporous method, or the EFG method (Edge-defined Film-fed Growth Method).

  An example of a method for increasing the bulk density of the reaction vessel is to reduce the primary particles of the raw material powder. By using a small raw material powder, the bulk density can be increased because densification proceeds at a low temperature.

(Temperature conditions during regeneration)
In the present invention, the regeneration process may consist only of a cleaning process described later, but may also include a process other than the cleaning process (for example, an immersion process). Throughout the regeneration process, the ambient temperature remains below the evaporation temperature of the acid or alkaline solution solvent. This temperature is more preferably practically 100 ° C. or less. Further, there is no particular lower limit to the temperature at which the regeneration step is performed, but from the viewpoint of promoting the dissolution of gallium hydroxide, 0 ° C. or higher is preferable, and 10 ° C. or higher is more preferable.

(Regeneration process)
In the present invention, the reaction vessel used for crystal growth is immersed and held in an acid solution or an alkali solution, and then washed.

  The acid or alkali is not particularly limited as long as it is a substance that has low erosion with respect to alumina constituting the reaction vessel and can etch gallium hydroxide. Specific examples include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, citric acid, acetic acid, oxalic acid, sodium hydroxide, potassium hydroxide and the like.

  The acid and alkali are in the form of a solution, and an aqueous solution is particularly preferable. A water-soluble organic solvent may be contained in the aqueous solution.

  From the viewpoint of gallium hydroxide removal efficiency, the pH of the acid solution is preferably 5 or less, and more preferably 3 or less. Further, the pH of the alkaline solution is preferably 9 or more, and more preferably 12 or more.

  In the dipping process, the reaction vessel is left in an acid solution or an alkaline solution.

  In the washing step, the acid, alkali and gallium hydroxide dissolved in the reaction vessel surface are removed by washing.

  From the viewpoint of the present invention, the temperature of the solution when performing ultrasonic cleaning is preferably 0 ° C. or higher, more preferably 10 ° C. or higher, still more preferably 20 ° C. or higher, and particularly preferably 30 ° C. or higher. Further, the temperature at the time of ultrasonic cleaning is not higher than the boiling point of the solvent, and more preferably not higher than (the boiling point of the solvent minus 10 ° C.). Practically, 100 ° C. or lower is preferable.

  Further, in the cleaning step, the cleaning medium can be made into droplets, and cleaning can be performed by spraying the droplets toward the reaction vessel.

  An acid solution or an alkali solution can be used as a cleaning medium at the time of cleaning, but neutral pure water or an organic solvent can also be used.

  By immersing the reaction vessel in an acid solution or an alkali solution for 0.5 hour or more, it is possible to ensure contact with the gallium hydroxide that has penetrated into the reaction vessel and has been adhered and contained. From this viewpoint, the immersion time of the reaction vessel in the acid solution or alkali solution is more preferably 1.0 hour or more. Moreover, although there is no upper limit in particular in this contact time, from a viewpoint of productivity, immersion time may be 24 hours or less.

The immersion time of the reaction vessel in the acid solution or alkali solution is the sum of the time of the immersion step and the time during which the reaction vessel is immersed in the acid solution or alkali solution in the cleaning step.
For example, when the reaction vessel is ultrasonically cleaned in an acid solution or an alkaline solution, the reaction vessel is immersed in the acid solution or the alkaline solution during the ultrasonic cleaning step. On the other hand, when a cleaning medium other than an acid solution or an alkaline solution is used in the cleaning step, the immersion time of the reaction vessel in the acid solution or alkaline solution is the time of the immersion step.

After carrying out the regeneration step, the organic matter adhering to the reaction vessel can be scattered by heating the reaction vessel at a relatively low temperature. Also in this case, the heating temperature of the reaction vessel is preferably 300 ° C. or less, and more preferably 200 ° C. or less. In this heat treatment step, reoxidation of alumina constituting the reaction vessel does not occur, the surface of the reaction vessel is not roughened, and gallium hydroxide removal is not hindered.
For the same reason, the maximum temperature of the environment is preferably 300 ° C. or less, and more preferably 200 ° C. or less, throughout the first and second growth steps.

(First training process and second training process)
In each growth step, crystals are grown using a melt containing sodium and gallium.

  In a preferred embodiment, the crucible containing the flux is housed in a pressure vessel and heated under high pressure using a hot isostatic press. At this time, the atmospheric gas containing nitrogen is compressed to a predetermined pressure, supplied into the pressure vessel, and the total pressure and the nitrogen partial pressure in the pressure vessel are controlled.

  Although the flux contains sodium and gallium, for example, aluminum, indium, boron, zinc, silicon, tin, antimony, and bismuth can be added. Further, the target nitride raw material is contained in the flux.

For example, the following single crystals can be suitably grown by each growing method. Further, different single crystals can be grown in the first growth step and the second growth step.
Gallium nitride, aluminum nitride, indium nitride, mixed crystals thereof (such as aluminum gallium nitride), BN.

  The heating temperature and pressure in the single crystal growth step are not particularly limited because they are selected depending on the type of single crystal. The heating temperature can be set to, for example, 800 to 1500 ° C. Preferably it is 800-1200 degreeC, More preferably, it is 800-1100 degreeC. The pressure is not particularly limited, but the pressure is preferably 1 MPa or more, and more preferably 2 MPa or more. The upper limit of the pressure is not particularly defined, but can be, for example, 200 MPa or less, and preferably 100 MPa or less.

  When growing the gallium nitride crystal, the gallium source material is dissolved in the flux. As the gallium source material, a gallium simple metal, a gallium alloy, and a gallium compound can be applied, but a gallium simple metal is also preferable in terms of handling.

  This flux can contain metals other than sodium, such as lithium. The use ratio of the gallium source material and the flux source material such as sodium may be appropriate, but in general, it is considered to use an excess amount of sodium. Of course, this is not limiting.

  In this embodiment, a gallium nitride single crystal is grown under a pressure of a total pressure of 1 MPa or more and 200 MPa or less in an atmosphere composed of a mixed gas containing nitrogen gas. By setting the total pressure to 1 MPa or more, it was possible to grow a good quality gallium nitride single crystal in a high temperature region of, for example, 800 ° C. or higher, more preferably in a high temperature region of 850 ° C. or higher.

In a preferred embodiment, the nitrogen partial pressure in the growth atmosphere is 1 MPa or more and 200 MPa or less.
A gas other than nitrogen in the atmosphere is not limited, but an inert gas is preferable, and argon, helium, and neon are particularly preferable. The partial pressure of a gas other than nitrogen is a value obtained by subtracting the nitrogen gas partial pressure from the total pressure.

  In a preferred embodiment, the growth temperature of the gallium nitride crystal is 800 ° C. or higher, and more preferably 850 ° C. or higher. The upper limit of the growth temperature of the gallium nitride crystal is not particularly limited, but is preferably 1500 ° C. or lower, more preferably 1200 ° C. or lower.

The material of the growth substrate for epitaxially growing the crystal of the present invention is not limited, but sapphire, AlN template, GaN template, GaN free-standing substrate, silicon single crystal, SiC single crystal, MgO single crystal, spinel (MgAl ₂ O ₄ ) Examples thereof include perovskite complex oxides such as LiAlO ₂ , LiGaO ₂ , LaAlO ₃ , LaGaO ₃ , and NdGaO ₃ . The composition formula _{[A 1-y (Sr 1-} x Ba x) y ] _{[(Al 1-z Ga z)} 1-u · D u ] _O 3 (A is a rare earth element; D is niobium and One or more elements selected from the group consisting of tantalum; y = 0.3-0.98; x = 0-1; z = 0-1; u = 0.15-0.49; x + z = 0 .1 to 2) cubic perovskite structure composite oxides can also be used. SCAM (ScAlMgO ₄ ) can also be used.

  The method for producing the seed crystal film is not particularly limited, but the metal organic chemical vapor deposition (MOCVD) method, the hydride vapor deposition (HVPE) method, the pulse excitation deposition (PXD) method, the MBE method, and the sublimation method. Examples thereof include a vapor phase method such as a liquid phase method such as a flux method. Further, the material of the seed crystal film is preferably a group 13 element nitride, and particularly preferably gallium nitride or gallium aluminum nitride.

(Process to process flux with organic solvent)
After the first growth step, it is necessary to remove sodium from the flux and separate the crystals. At this time, the crystals can be mechanically separated, but the sodium is preferably removed by treating the flux with an organic solvent.
Examples of such organic solvents include the following.
Ethanol, isopropanol (IPA), kerosene, acetone The treatment temperature with an organic solvent is preferably -15 to 30 ° C.

(Comparative Example 1)
A cylindrical round bottom crucible (outer diameter 86 mm, inner diameter 80 mm, height 50 mm) made of an alumina sintered body was prepared. The material of alumina is as follows.
Purity: 99.99% by weight
Bulk density: 99.0% by weight
Average crystal grain size: 1.0 μm

In a glove box in an argon atmosphere, 30 g of 99.9999% pure metal gallium (Ga), 40 g of 99.95% pure metal sodium (Na), 0.08 g of 99% pure carbon as an additive, and a 2-inch diameter seed crystal substrate Was housed in a crucible.
Here, the seed crystal substrate is obtained by forming a seed crystal film made of gallium nitride crystal on a support substrate made of sapphire by MOCVD.

  Next, the crucible body was covered with a lid. These were sealed in a stainless steel container, removed from the glove box, and transferred to a growing apparatus. The growth conditions were such that the nitrogen pressure was 4.5 MPa and the average temperature was 875 ° C., and the crystals were grown for 20 hours (first growth step).

  After cooling the crucible to 25 ° C. over 10 hours, the crucible was recovered, the residue of the growing material was removed using ethanol, and the crystals were recovered (step of treating the flux with an organic solvent). Although the obtained GaN crystal was partially colored at the interface between the seed crystal and the LPE part (crystal grown by the flux method), the main body was colorless and transparent and grew 300 μm. At this time, the crucible had turned gray.

  The crucible after the ethanol treatment was subjected to ultrasonic cleaning with ethanol at 25 ° C. for 10 minutes (ultrasonic cleaning step). Next, the crucible was dried and heat-treated in an atmospheric furnace (heater material: Kanthal Super). The temperature rise and cooling rate were 300 ° C./hr (heat treatment step). The heat treatment temperature was 1500 ° C., and the holding time at 1500 ° C. was 15 hours. It was then cooled to 25 ° C.

  As a result, neither the crucible body nor the lid was discolored. Then, the 2nd crystal growth process was implemented on the same conditions as the 1st crystal growth process. Then, the variation of 110 to 450 μm was observed in the thickness of the grown crystal. In addition, the crystallinity of the grown crystal was lowered.

  Therefore, the regenerated crucible surface was ultrasonically cleaned with diluted hydrochloric acid, and the cleaning liquid was analyzed by ICP-AES. As a result, Al and Ga, and trace amounts of Na and Fe were detected. When this cleaning solution was neutralized with an alkaline solution, GaCl was deposited. This suggests that GaOH is included in the crucible and affects the crystal growth.

(Comparative Example 2)
The first crystal growth step was performed in the same manner as in Comparative Example 1.
Next, the crucible after the ethanol treatment was subjected to ultrasonic cleaning at 25 ° C. for 10 minutes using a 5% hydrochloric acid aqueous solution (ultrasonic cleaning step). Next, the crucible was dried and heat-treated in an atmospheric furnace (heater material: Kanthal Super). The temperature rise and cooling rate were 300 ° C./hr (heat treatment step). The heat treatment temperature was 1500 ° C., and the holding time at 1500 ° C. was 15 hours. It was then cooled to 25 ° C.

  As a result, neither the crucible body nor the lid was discolored. Then, the 2nd crystal growth process was implemented on the same conditions as the 1st crystal growth process. Then, the variation of 150 to 420 μm was observed in the thickness of the grown crystal. In addition, the crystallinity of the grown crystal was lowered.

(Comparative Example 3)
The first crystal growth step was performed in the same manner as in Comparative Example 1.
However, the alumina constituting the crucible was changed to alumina having the following physical properties.
Purity: 99.99% by weight
Bulk density: 99.5% by weight
Average crystal grain size: 0.3 μm

  The obtained GaN crystal was colored at the interface between the seed crystal and the LPE, but the LPE crystal body was colorless and transparent and grew about 280 mm. Moreover, no discoloration of the crucible was seen in appearance.

  Next, the ethanol-treated crucible was ultrasonically washed with another ethanol at 25 ° C. for 30 minutes, and then rinsed with pure water to remove ethanol adhering to the crucible. (Ultrasonic cleaning process).

  Next, the second crystal growth step was performed under the same conditions as the first crystal growth step. Then, the variation of 150 to 370 μm was observed in the thickness of the grown crystal. In addition, the crystallinity of the grown crystal was lowered.

  Therefore, the surface of the crucible immediately before the second crystal growth step was washed with a dilute hydrochloric acid aqueous solution, and the washing solution was analyzed by ICP-AES. As a result, Al and Ga, and trace amounts of Na and Fe were detected. When this cleaning solution was neutralized with alkali, GaCl was deposited. This suggests that GaOH is included in the crucible and affects the crystal growth.

Example 1
The first crystal growth step was performed in the same manner as in Comparative Example 1.
However, the alumina constituting the crucible was changed to alumina having the following physical properties.
Purity: 99.99% by weight
Bulk density: 99.5% by weight
Average crystal grain size: 0.3 μm

  The obtained GaN crystal was colorless and transparent and grew about 220 mm. Moreover, no discoloration of the crucible was seen in appearance.

  Next, the crucible after the ethanol treatment was immersed in a 15% hydrochloric acid aqueous solution (less than pH 1) at 25 ° C. for 50 minutes, then ultrasonically washed with a 15% hydrochloric acid aqueous solution for 10 minutes, and then rinsed with pure water, Hydrochloric acid adhering to the base material was removed.

  Next, the second crystal growth step was performed under the same conditions as the first crystal growth step. Then, the variation in the thickness of the grown crystal was 190 to 250 μm. Moreover, the crystallinity of the grown crystal was not lowered.

  Therefore, the regenerated crucible surface was ultrasonically cleaned with pure water and the cleaning solution was analyzed by ICP-AES. As a result, Al was detected, but Ga, Na, and Fe were not detected.

(Example 2)
The first crystal growth step was performed in the same manner as in Example 1.
Next, the ethanol-treated crucible is immersed in a 20% aqueous citric acid solution (pH 2.5) at 25 ° C. for 50 minutes, then ultrasonically washed with a 20% aqueous citric acid solution for 10 minutes, and then rinsed with pure water. The citric acid adhering to the reaction vessel was removed.

  Next, the second crystal growth step was performed under the same conditions as the first crystal growth step. Then, the variation in the thickness of the grown crystal was 190 to 280 μm. Moreover, the crystallinity of the grown crystal was not lowered.

  Therefore, when the surface of the crucible after the regeneration was ultrasonically cleaned with pure water and the cleaning liquid was analyzed by ICP-AES, Al was detected, but Ga, Na, and Fe were not detected.

(Example 3)
The first crystal growth step was performed in the same manner as in Example 1.
Next, the ethanol-treated crucible was immersed in a 48% aqueous sodium hydroxide solution (pH 14) at 25 ° C. for 50 minutes, then ultrasonically washed with a 48% aqueous sodium hydroxide solution for 10 minutes, and then rinsed with pure water. The sodium hydroxide was removed.

  Next, the second crystal growth step was performed under the same conditions as the first crystal growth step. Then, the variation in the thickness of the grown crystal was 170 to 270 μm. Moreover, the crystallinity of the grown crystal was not lowered.

  Therefore, when the surface of the crucible after the regeneration was ultrasonically cleaned with pure water and the cleaning liquid was analyzed by ICP-AES, Al was detected, but Ga, Na, and Fe were not detected.

(Example 4)
The first crystal growth step was performed in the same manner as in Example 1.
Next, the ethanol-treated crucible was immersed in a 3% aqueous hydrochloric acid solution (pH <1) at 25 ° C. for 1 hour and 50 minutes, then ultrasonically washed with a 3% aqueous hydrochloric acid solution for 10 minutes, and then rinsed with pure water. Then, hydrochloric acid was removed.

  Next, the second crystal growth step was performed under the same conditions as the first crystal growth step. Then, the variation in the thickness of the grown crystal was 190 to 260 μm. Moreover, the crystallinity of the grown crystal was not lowered.

(Example 5)
The first crystal growth step was performed in the same manner as in Example 1.
However, the alumina constituting the crucible was changed to alumina having the following physical properties.
Purity: 99.99% by weight
Bulk density: 99.9% by weight
Average crystal grain size: 0.3 μm

  The obtained GaN crystal was colorless and transparent and grew about 260 mm. Moreover, no discoloration of the crucible was seen in appearance.

  Next, the ethanol-treated crucible was immersed in a 15% aqueous hydrochloric acid solution (pH <1) at 25 ° C. for 50 minutes, then ultrasonically washed with a 15% aqueous hydrochloric acid solution for 10 minutes, then rinsed with pure water, Was removed.

  Next, the second crystal growth step was performed under the same conditions as the first crystal growth step. Then, a variation of 160 to 230 μm was observed in the thickness of the grown crystal. Moreover, the crystallinity of the grown crystal was not lowered.

(Comparative Example 4)
The first crystal growth step was performed in the same manner as in Example 1.
Next, ultrasonic cleaning was started immediately without providing a step of immersing and holding the crucible after ethanol treatment in a 15% aqueous hydrochloric acid solution (pH <1). Then, it was ultrasonically washed with a 15% hydrochloric acid aqueous solution for 10 minutes, and then rinsed with pure water to remove hydrochloric acid.

  Next, the second crystal growth step was performed under the same conditions as the first crystal growth step. Then, the variation of 120 to 300 μm was observed in the thickness of the grown crystal. Moreover, the crystallinity of the grown crystal was lowered.

(Example 6)
The first crystal growth step was performed in the same manner as in Example 1. Next, the ethanol-treated crucible is immersed in a 15% aqueous hydrochloric acid solution (less than pH 1) at 25 ° C. for 20 minutes, then ultrasonically washed with a 15% aqueous hydrochloric acid solution for 10 minutes, and then rinsed with pure water. The hydrochloric acid adhering to the material was removed.

Next, the second crystal growth step was performed under the same conditions as the first crystal growth step. Then, the variation in the thickness of the grown crystal was 150 to 270 μm. Moreover, the crystallinity of the grown crystal was not lowered.
Therefore, the regenerated crucible surface was ultrasonically cleaned with pure water and the cleaning solution was analyzed by ICP-AES. As a result, Al was detected, but Ga, Na, and Fe were not detected.

Claims (10)

A method for regenerating the reaction vessel after growing a crystal in a state in which a melt containing sodium and gallium is contained in a reaction vessel made of alumina,
A dipping process in which the purity of the alumina is 99.9% by weight or more, the bulk density of the alumina is 99.5% or more, and the reaction vessel is dipped in an acid solution or an alkali solution and left standing; A washing step of ultrasonically washing the reaction vessel, and setting the environmental temperature during regeneration of the reaction vessel to 300 ° C. or less, and setting the immersion time of the reaction vessel in the acid solution or alkali solution to 30 minutes or more A method for regenerating a crystal growth reaction vessel, wherein gallium hydroxide adhering to the reaction vessel is removed. Wherein in the washing step by the reaction vessel wherein the acid solution or an alkaline solution, characterized in that ultrasonic cleaning method of claim 1, wherein. The crystals, gallium nitride, characterized in that it is a gallium aluminum or gallium indium nitride nitride, The method of claim 1 or 2. The method according to any one of claims 1 to 3 , wherein the acid is hydrochloric acid or citric acid, and the alkali is sodium hydroxide. The method according to any one of claims 1 to 4 , wherein the crystal is grown by a flux method. A first growth step for growing a crystal in a state in which a melt containing sodium and gallium is contained in a reaction vessel made of alumina;
Next, a regeneration step for regenerating the reaction vessel, and a second growth step for growing crystals in a state in which a melt containing sodium and gallium is accommodated in the reaction vessel, and the purity of the alumina is 99 9.9% by weight or more, and the bulk density of the alumina is 99.5% or more, and the regeneration step comprises:
A dipping step in which the reaction vessel is immersed in an acid solution or an alkaline solution and left standing, and then a washing step in which the reaction vessel is ultrasonically cleaned, and the second growing step from the first growing step. The immersion time in the acid solution or alkali solution of the reaction vessel is 30 minutes or more while the ambient temperature is 300 ° C. or less, and gallium hydroxide attached to the reaction vessel is removed. Single crystal growth method. The method according to claim 6 , wherein the crystal is grown on a seed crystal substrate in the first growing step and the second growing step. The method according to claim 6 or 7 , characterized in that the crystal is gallium nitride, gallium aluminum nitride or gallium indium nitride. 9. A method according to any one of claims 6 to 8 , characterized in that the acid is hydrochloric acid or citric acid and the alkali is sodium hydroxide. The method according to any one of claims 6 to 9 , wherein the crystal is grown by a flux method.