JP5496071B2 - Method for regenerating reaction vessel for single crystal growth and method for growing single crystal - Google Patents

Description

  The present invention relates to a method for growing a single crystal by a so-called Na flux method and a method for regenerating a reaction vessel used therefor.

  Gallium nitride thin film crystals are attracting attention as an excellent blue light-emitting device, put into practical use in light-emitting diodes, and expected as a blue-violet semiconductor laser device for optical pickups.

  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.

  Furthermore, the applicant of the present invention, in Patent Document 4 (Japanese Patent Application No. 2009-1737), uses a crucible made of yttrium / aluminum garnet, thereby significantly increasing the amount of impurities such as oxygen and silicon incorporated into the obtained single crystal. Disclosed that it can be reduced.

JP2004-300024 JP-A-2005-263622 JP 2005-263535 A Japanese Patent Application No. 2009-1737

  However, alumina crucibles are basically disposable and difficult to reuse because they are corroded by high temperature sodium during single crystal growth. The crucible made of yttria or yttrium / aluminum garnet is not as much as the crucible made of alumina, but it tends to be corroded by high-temperature sodium, and when reused, the resulting single crystal is easily colored and becomes defective. Reuse was difficult.

  An object of the present invention is to grow a single crystal by a flux method in a state where a melt containing sodium is contained in a reaction vessel made of alumina, yttria or yttrium aluminum garnet, and then regenerate the reaction vessel to A transparent single crystal can be grown at the time of crystal growth.

The present invention is a method for regenerating a reaction vessel after growing a single crystal by a flux method in a state where a melt containing sodium is contained in a reaction vessel made of alumina, yttria or yttrium aluminum garnet,
It has the washing | cleaning process which ultrasonically cleans a reaction container, and then the heat processing process which heats a reaction container at 1300-1600 degreeC under oxidizing atmosphere for 5 to 20 hours.

Moreover, the method for growing a single crystal according to the present invention includes:
A first growth step of growing a single crystal by a flux method in a state in which a melt containing sodium is contained in a reaction vessel made of alumina, yttria or yttrium aluminum garnet;
Next, a cleaning step of ultrasonically cleaning the reaction vessel,
Next, a heat treatment step in which the reaction vessel is heated at 1300 to 1600 ° C. for 5 to 20 hours in an oxidizing atmosphere, and then a single crystal is grown by a flux method in a state in which a melt containing sodium is contained in the reaction vessel. Second training process,
It is characterized by having.

  Alumina, yttria, and aluminum / yttrium garnet are reduced and deprived of oxygen by hot sodium during growth. As a result, the surface of the reaction vessel changes from gray to black. When growing for a long time, discoloration progresses to the inside of the reaction vessel. When the reaction vessel material is reduced to contain many oxygen defects, it becomes brittle. When flux treatment with ethanol or the like is performed after single crystal growth, an alkali component (such as sodium hydroxide) is further mixed into the deteriorated portion. In the case of washing with water or ultrasonic cleaning, the alkali component mixed in the deteriorated part cannot be removed, and therefore, it cannot be reused.

  We have found a regeneration method that removes the alkali components mixed in the deteriorated part containing many oxygen defects, repairs the oxygen defects, and maintains the strength. As a result, the reaction vessel made of the specific material used for single crystal growth by the flux method can be reused, and the manufacturing cost is significantly reduced. And the coloring of the single crystal at the time of reuse can also be prevented.

It is a photograph which shows the new growth container before use, the growth container after use, and the growth container after a regeneration process. It is a photograph which shows the external appearance of the alumina crucible which the crack generate | occur | produced. The upper left photograph shows the appearance of the crucible lid after single crystal growth is repeated five times. The upper right photo shows the appearance after the reproduction process. The lower left photograph shows the external appearance of the crucible lid after single crystal growth. The photograph on the lower right shows the appearance of the crucible lid after the reproduction process.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the method of the present invention will be described in the order of steps.
(First training process and second training process)
First, the growth process of the single crystal will be described.
In the growth step, a single crystal is grown by a flux method in a state in which a melt containing sodium is contained in a reaction vessel made of alumina, yttria or yttrium / aluminum / garnet.

  The reaction container referred to in the present invention means all containers that come into contact with a flux liquid or vapor, and is a concept including, for example, a crucible, a crucible lid, a pressure container, and an outer reaction container that accommodates the crucible. The present invention is particularly effective when applied to a crucible for directly containing and melting a flux.

  Alumina, yttria, yttrium / aluminum / garnet 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 alumina polycrystal, yttria polycrystal, yttrium / aluminum / garnet polycrystal is particularly preferably 1 μm or more and 100 μm or less from the viewpoint of corrosion resistance to the flux. More preferably, the particle size is 0.1 μm or more and 10 μm or less.
The Young's modulus of the material constituting the reaction vessel is preferably 100 GPa or more, and more preferably 200 GPa or more. This further improves the durability of the reaction vessel.

  Further, the relative density of the material constituting the reaction vessel is preferably 98% or more from the viewpoint of corrosion resistance to the flux.

  The production method of alumina, yttria, yttrium / aluminum / garnet constituting the reaction vessel is not limited. In order to manufacture each ceramic, 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 thereof include atmospheric pressure sintering, hot pressing, hot isostatic pressing, and discharge plasma sintering in a reducing atmosphere. The firing temperature is not limited, and can be 1700 to 2000 ° C., for example.

When alumina, yttria, yttrium, aluminum, and garnet are single crystals, the Czochralski method, the Cairo porous method, the EFG method (Edge-defined)
Film-fed growth method) is preferable.

  The yttrium portion of the yttrium, aluminum, and garnet constituting the reaction vessel may be partially substituted by a rare earth other than yttrium. Examples of such rare earths include gadolinium, cerium, ytterbium, neodymium, lanthanum, erbium, and scandium. Further, the substitution ratio of the yttrium site with another element is preferably 50 mol% or less, and more preferably 10 mol% or less.

  The aluminum part of the yttrium / aluminum / garnet constituting the reaction vessel may be partially substituted by a transition metal other than aluminum. Examples of such transition metals include iron, gallium, and chromium. Further, the substitution ratio of the aluminum part with other elements is preferably 50 mol% or less, and more preferably 10 mol% or less.

  The purity of alumina, yttria, yttrium / aluminum / garnet constituting the reaction vessel is preferably 99.0% by weight or more, and 99.9% by weight in order to minimize the risk of doping into a single crystal during growth. % Or more is more preferable.

  In the first and second growth steps, a single crystal is grown by a flux method in a state where a melt containing sodium is accommodated in the reaction vessel.

  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, for example, gallium, 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.
GaN, AlN, InN, mixed crystals thereof (AlGaInN), 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.

Hereinafter, more specific single crystals and their growth procedures will be exemplified.
(Gallium nitride single crystal)
Using the present invention, a gallium nitride single crystal can be grown using a flux containing at least sodium metal. In this flux, the gallium source material is dissolved. 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. By setting the nitrogen partial pressure to 1 MPa or more, for example, in a high temperature region of 800 ° C. or more, it was possible to promote the dissolution of nitrogen in the flux and to grow a high-quality gallium nitride single crystal. From this viewpoint, it is more preferable that the nitrogen partial pressure of the atmosphere is 2 MPa or more. Moreover, it is preferable that nitrogen partial pressure shall be 100 Mpa or less practically.

  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 single crystal is 800 ° C. or higher, and more preferably 850 ° C. or higher. Even in such a high temperature region, a good quality gallium nitride single crystal can be grown. Moreover, there is a possibility that productivity can be improved by growing at high temperature and high pressure.

  The upper limit of the growth temperature of the gallium nitride single crystal is not particularly limited. However, if the growth temperature is too high, the crystal is difficult to grow. Therefore, the temperature is preferably set to 1500 ° C. or lower. From this viewpoint, the temperature is further set to 1200 ° C. or lower. preferable.

The material of the growth substrate for epitaxially growing the gallium nitride crystal 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.

(Example of growing AlN single crystal)
An AlN single crystal can be grown by pressurizing a melt containing a flux containing at least aluminum and alkaline earth in a nitrogen-containing atmosphere under specific conditions.

(Process to process flux with organic solvent)
After the first growth step, it is necessary to remove sodium from the flux and separate the single crystal. In this case, the single crystal can be mechanically separated, but the sodium is preferably removed by treating the flux with an organic solvent. In this step, sodium enters the reaction vessel deteriorated in the growing step, and removal of sodium becomes more difficult, so the regeneration method of the present invention is particularly effective.

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.

(Washing process to ultrasonically clean the reaction vessel)
The reaction vessel is subjected to ultrasonic cleaning before the heat treatment step described later. Without this step, some coloring remains in the growth vessel after the heat treatment, and an impurity peak may be observed in the single crystal obtained in the next second growth step.

As a medium for performing this ultrasonic cleaning, the following is preferable.
Pure water (ion exchange water), dilute hydrochloric acid (concentration 10% or less).
When the metal gallium residue of the flux component is visually confirmed, dilute hydrochloric acid is preferably used.

  Further, the temperature of the medium when performing ultrasonic cleaning is preferably 50 ° C. or higher from the viewpoint of the present invention. Further, the temperature of the medium at the time of ultrasonic cleaning is not higher than the boiling point of the medium, and more preferably not higher than (the boiling point of the medium minus 10 ° C.). Practically, it is more preferably 100 ° C. or lower.

(Heat treatment step of heating the reaction vessel at 1300 to 1600 ° C. for 5 to 20 hours in an oxidizing atmosphere)
By setting the treatment temperature to 1300 ° C. or higher, removal of sodium infiltrated into the reaction vessel can be promoted. In addition, by setting the treatment temperature to 1600 ° C. or less, it is possible to prevent the fine structure of the material of the reaction vessel from growing, thereby preventing a decrease in the strength of the reaction vessel.

  By setting the holding time at the treatment temperature to 5 hours or longer, the removal of sodium infiltrated into the reaction vessel can be promoted, and coloring of the grown single crystal can be prevented. Further, by setting the holding time at the treatment temperature to 20 hours or less, it is possible to prevent the grain growth of the fine structure of the reaction vessel material, thereby preventing the strength reduction of the reaction vessel.

  The atmosphere during the heat treatment is an oxidizing atmosphere. The oxidizing atmosphere may be only oxygen or a mixture of oxygen and an inert gas. The pressure in the oxidizing atmosphere is preferably 0.01 to 100 MPa. The inert gas is preferably nitrogen, helium or argon. The proportion of oxygen in the oxidizing atmosphere is preferably 1% by weight or more, and may be 100% by weight. Also, the atmosphere can be used suitably.

Example 1
99.9999% purity metal gallium (Ga) in a glove box in an argon atmosphere
30g, 99.95% pure metallic sodium (Na)
40 g, 0.08 g of 99% pure carbon as additive, and a 2 inch diameter gallium nitride free-standing substrate, an alumina cylindrical round bottom crucible (outer diameter 86 mm, inner diameter 80 mm, height 50 mm) with a relative density of 99% and purity of 99.99% ) And weighed and filled. The crucible was covered with an alumina disk having a relative density of 99% and a purity of 99.99% as 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, the average temperature was 875 ° C., and the crystal growth was performed for 100 hours (first growth step).

  After cooling the crucible to room temperature 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). The GaN crystal was colorless and transparent and grew about 1.5 mm. At this time, the alumina crucible and the lid were discolored from gray to black. (See the center of Fig. 1)

  The crucible after the ethanol treatment was subjected to ultrasonic cleaning with hot water (95 ° C.) for 30 minutes (ultrasonic cleaning step). Next, the crucible was dried and heat-treated at 1500 ° C. for 15 hours in an atmospheric furnace (heater material: Kanthal Super). The temperature rise and cooling rate were 300 ° C./hr (heat treatment step). The alumina crucible after the heat treatment was white and hardly deformed. (See right in Fig. 1)

The crucible after this heat treatment was reused, and a GaN single crystal was grown under the same conditions as in the first growth step described above. As a result, as in the first growth step, a transparent GaN crystal grew about 1.5 mm. Almost no impurity emission band emission was observed in the crystal. When SIMS analysis of the GaN crystal was performed, the oxygen concentration was 5 × 10 ¹⁶ / atoms / cm ³ , which was the same level as when a new alumina crucible was used. The Si concentration was 1 × 10 ¹⁵ / atoms / cm ³ , the same level as when a new alumina crucible was used.

(Examples 2 to 6)
The growth test and crucible regeneration were performed in the same manner as in Example 1. However, the heating temperature and heating time were changed as shown in Table 1. Table 1 shows the crystal state obtained in the second growth step and the presence or absence of impurity band emission.

(Comparative Example 1)
The experiment was conducted in the same manner as in Example 1. However, the heating temperature was 1100 ° C. and the heating time was 15 hours. When this crucible was reused, a white substance floated on the surface of the raw material. The GaN single crystal grew only to a thickness of 0.5 mm and was colored dark brown. This white material was analyzed and found to be sodium hydroxide.

(Comparative Example 2)
The experiment was conducted in the same manner as in Example 1. However, the heating temperature was 1700 ° C. and the heating time was 15 hours. As a result, the crucible became brittle and deformed into an irregular shape, making it difficult to reuse.

(Comparative Example 3)
The experiment was conducted in the same manner as in Example 1. However, the heating temperature was 1500 ° C. and the heating time was 1 hour. The crucible after the heat treatment partially returned to white, but there was an area that remained gray. When this crucible was reused, a white substance floated on the surface of the raw material. The GaN crystal grew 1 mm, but the area of about 0.5 mm at the initial stage of growth was colored black. When this black colored region was analyzed by EDX, several hundred ppm of sodium, oxygen, and silicon were detected.

(Comparative Examples 4 and 5)
The experiment was conducted in the same manner as in Example 1. However, the heating temperature was 1500 ° C., and the heating time was 50 hours or 25 hours. Since the heating time was long, the crucible contracted, and as a result, cracks occurred in the crucible (see FIG. 2). In addition, even if the crucible was not deformed, it became brittle, so when it was reused, the crucible cracked at the time of temperature rise, and the growth material leaked, and the growth experiment failed.

(Comparative Example 6)
The experiment was conducted in the same manner as in Example 1. However, the crucible after the flux treatment was not ultrasonically cleaned. As a result, a large number of brown or green-colored parts, which seem to be affected by the flux residue, were observed on the inner surface of the crucible. This discolored portion did not change even after heat treatment. When this crucible was reused, a transparent crystal grew 1.5 mm, but the intensity of impurity band emission was strong. (Band edge emission intensity / impurity band emission intensity was approximately 1)
(Comparative Example 7)
The experiment was conducted in the same manner as in Example 1. However, the heating temperature was 1200 ° C. and the heating time was 15 hours. The crucible after the heat treatment partially returned to white, but there was an area that remained gray. When this crucible was reused, a white substance floated on the surface of the raw material. The GaN crystal grew 1 mm, but the area of about 0.5 mm at the initial stage of growth was colored black. When this black colored region was analyzed by EDX, several hundred ppm of sodium, oxygen, and silicon were detected.

(Examples 7 to 12: Comparative Examples 8 to 14)
99.9999% purity metal gallium (Ga) in a glove box in an argon atmosphere
3g, 99.95% pure metallic sodium (Na)
4.4 g, 99% purity carbon 0.015 g as an additive, and a 13 × 18 mm gallium nitride free-standing substrate with a relative density of 98% and purity 99.99% yttria cylindrical round bottom crucible (outer diameter 19.5 mm, inner diameter 17 mm, high 50 mm) and weighed and filled. 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, the average temperature was 875 ° C., and the crystal growth was performed for 100 hours (first growth step).

  After cooling the crucible to room temperature 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). The GaN crystal was colorless and transparent and grew about 1.5 mm. At this time, the crucible was discolored from gray to ultramarine blue.

  The crucible after the ethanol treatment was subjected to ultrasonic cleaning with hot water (95 ° C.) for 30 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). Table 2 shows the heat treatment temperature and time. However, in Comparative Example 13, ultrasonic cleaning is not performed. The results of each example are shown in Table 2.

(Examples 13 to 18: Comparative Examples 15 to 21)
99.9999% purity metal gallium (Ga) in a glove box in an argon atmosphere
30g, 99.95% pure metallic sodium (Na)
40g, 0.08g of 99% pure carbon as an additive, and a 2 inch diameter gallium nitride free-standing substrate, cylindrical round bottom crucible made of yttrium aluminum garnet ceramics with a relative density of 98% and purity of 99.99% (outer diameter 86mm, inner diameter 80 mm, height 50 mm) and weighed and filled. The crucible was covered with a yttrium / aluminum / garnet ceramic disk with a relative density of 98% and purity of 99.99% as 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, the average temperature was 875 ° C., and the crystal growth was performed for 100 hours (first growth step).

  After cooling the crucible to room temperature 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). The GaN crystal was colorless and transparent and grew about 1.5 mm. At this time, the crucible and the lid had been changed to dull light blue (see the lower left photograph in FIG. 3 (after one use)).

  The crucible after the ethanol treatment was subjected to ultrasonic cleaning with hot water (95 ° C.) for 30 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 and time are shown in Table 3. However, in Comparative Example 20, ultrasonic cleaning is not performed. The results of each example are shown in Table 3. Further, a photograph of the crucible lid after the heat treatment of Example 7 is shown in FIG. 3 (lower right photograph: first-recycled product). The part that turned dull light blue returned to the original white color.

  A photograph of the crucible lid after the series of steps of Example 13 was repeated five times is shown in FIG. In the photograph at the upper left of FIG. 3 (5th use repeatedly), significant discoloration is seen. In the upper right photo of FIG. 3 (after the fifth reproduction), a slight reddish brown color was seen even after the regeneration treatment, but it could be used without any problem for crystal growth and a transparent crystal was obtained. The impurity band emission of the crystal was almost the same as the first time.

Claims (7)

A method of regenerating the reaction vessel after growing a single crystal by a flux method in a state in which a melt containing sodium is contained in a reaction vessel made of alumina, yttria or yttrium / aluminum / garnet,
A reaction for growing a single crystal, comprising: a washing step for ultrasonically washing the reaction vessel; and a heat treatment step for heating the reaction vessel at 1300 to 1600 ° C. for 5 to 20 hours in an oxidizing atmosphere. Container recycling method.   The method according to claim 1, wherein the reaction vessel is made of alumina.   The method according to claim 1, wherein the single crystal is a nitride single crystal. A first growth step of growing a single crystal by a flux method in a state in which a melt containing sodium is contained in a reaction vessel made of alumina, yttria or yttrium aluminum garnet;
Next, a washing step of ultrasonically washing the reaction vessel,
Next, a heat treatment step of heating the reaction vessel at 1300 to 1600 ° C. for 5 to 20 hours in an oxidizing atmosphere, and then growing a single crystal by a flux method in a state where a melt containing sodium is contained in the reaction vessel A second training process,
A method for growing a single crystal, comprising:   The method according to claim 4, wherein the reaction vessel is made of alumina.   The method according to claim 4, wherein the single crystal is a nitride single crystal. The sodium chloride is removed by bringing the flux in the reaction vessel into contact with an organic solvent after the first growth step and before the washing step. The method described in 1.

Images