JP2006265069A - Reaction vessel for growing single crystal and method for growing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent swelling and infiltration of a reaction vessel due to the flux within the reaction vessel even when a single crystal is grown at high temperature, in growing the single crystal by using the flux containing sodium metal etc. <P>SOLUTION: In the reaction vessel 25 used for growing the single crystal by using flux containing at least either of alkali metal and alkaline earth metal, there is provided the reaction vessel 25 composed of ceramics containing either or both of titanium nitride and zirconium nitride as a principal component. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for growing a single crystal by a so-called Na flux method and 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. As a method for growing a gallium nitride single crystal by the Na flux method, for example, in Non-Patent Document 1, when an atmosphere containing only nitrogen is used, the atmospheric pressure is 50 atm, and 40% ammonia and 60% nitrogen are mixed. When a gas atmosphere is used, the total pressure is 5 atmospheres.
Jpn. J. Appl. Phys. Vol.42, (2003) Page L4-L6

For example, in patent document 1, it is set to 10 to 100 atmospheres using the mixed gas of nitrogen and ammonia. Also in patent document 2, the atmospheric pressure at the time of a cultivation is 100 atmospheres or less, and is 2, 3, 5 MPa (about 20 atmospheres, 30 atmospheres, 50 atmospheres) in an Example. In any of the conventional techniques, all the growth temperatures are 1000 ° C. or less, and in the examples, all are 850 ° C. or less.
JP 2002-293696 A JP 2003-292400 A

In addition, aluminum nitride has a large band gap of 6.2 eV and high thermal conductivity. Therefore, aluminum nitride is excellent as a substrate material for light emitting elements (LED, LD) in the ultraviolet region, and development of single crystal wafer manufacturing technology is desired. It is rare. Until now, the manufacturing technique of the AlN single crystal by the sublimation method and the HVPE method has been proposed. In addition, Patent Document 3 and Non-Patent Document 2 disclose AlN production techniques using a flux method (solution method). In Patent Document 3, a transition metal is used as a flux. In Non-Patent Document 2, an AlN single crystal is obtained from Ca ₃ N ₂ and AlN powder.
JP2003-1119099 Mat.Res. Bull. Vol. 9 (1974) 331-336

Recently, it has been reported that high-quality bulk gallium nitride single crystals can be synthesized at low temperature and low pressure by using Na as a catalyst (Patent Document 4). The raw materials are gallium and sodium azide.
JP 2000-327495 A

Further, according to Patent Document 5, AlN and pyrolytic BN are disclosed as crucibles for growing gallium nitride and the like.
JP 2002-326898 A

  The present inventor attempted to grow a gallium nitride single crystal or an aluminum nitride single crystal in a higher temperature region than that described in the above document under a pressurized state using, for example, an HIP apparatus. Here, for example, when the reaction temperature is 1000 ° C. or higher, it has been found that the alumina crucible containing the flux swells and infiltrates and deteriorates significantly. When the crucible swells and infiltrates in this way, the life of the crucible is short, and it is considered necessary to prevent contamination in the HIP device by frequently replacing the crucible. In addition, there is a concern that the crucible component elutes into the raw material melt and is taken into the crystal as an impurity.

  The object of the present invention is to swell the reaction vessel due to the flux in the reaction vessel even when the single crystal is grown at a high temperature when the single crystal is grown using a flux containing an alkali or alkaline earth metal. And to prevent infiltration.

  The present invention is a reaction vessel used for growing a single crystal using a flux containing at least one of an alkali metal and an alkaline earth metal, and one or both of titanium nitride and zirconium nitride as a main component The present invention relates to a reaction vessel characterized by comprising ceramics contained as

  The present invention is also a method for growing a single crystal using a flux containing at least one of an alkali and an alkaline earth metal, from a ceramic containing one or both of titanium nitride and zirconium nitride as a main component. The present invention relates to a method for growing a single crystal, wherein the flux is accommodated in a reaction vessel.

  The present inventor, when growing a single crystal using a flux containing at least one of an alkali and an alkaline earth metal, is a reaction vessel made of a ceramic containing one or both of titanium nitride and zirconium nitride as a main component. It was found that when a single crystal is used, the reaction vessel is less likely to swell or infiltrate due to the flux even when a single crystal is grown at a high temperature.

  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 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.

  The nitride constituting the reaction vessel may be a single crystal or a powder sintered body. In the case of a powder sintered body, a titanium nitride powder, a zirconium nitride powder, or a mixed powder of a titanium nitride powder and a zirconium nitride powder is used as a raw material powder, and a powder sintered body is obtained by sintering.

  At this time, the particle size of the raw material powder is particularly preferably 0.2 μm or more and 3 μm or less from the viewpoint of corrosion resistance to the flux. From this viewpoint, the particle size of the raw material powder is 0.5 μm or more and 2 μm or less. Is more preferable.

Further, the Young's modulus of the ceramic constituting the reaction vessel is preferably 200 GPa or more, and more preferably 300 GPa or more. This further improves the durability of the reaction vessel.
The relative density of the nitride is not particularly limited, but is preferably 96% or more and more preferably 97% or more from the viewpoint of corrosion resistance to the flux.

  In addition, the ceramic constituting the reaction vessel may contain zirconium nitride as a main component, titanium nitride as a main component, or titanium nitride and zirconium nitride as main components. Components other than zirconium nitride and titanium nitride can also be added within a range that does not affect the corrosion resistance of the reaction vessel of the present invention to an alkali metal or alkaline earth metal flux. Examples of such other components include rare earth oxides such as yttria. The ceramics constituting the reaction vessel contain one or both of zirconium nitride and titanium nitride as a main component. The ratio of these main components (the total value when both are included) is preferably 80% by weight or more, more preferably 90% by weight or more, and most preferably 95% by weight or more. The ratio of other components is preferably 10% by weight or less, and more preferably 5% by weight or less.

  The method for producing nitride is not particularly 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 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.

  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. This crucible can be formed of the ceramic material of the present invention. 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.

  However, for example, when a gallium nitride single crystal is grown by the Na flux method using such a HIP apparatus, corrosion occurs in the heater, the drive mechanism, the heat insulating material of the inner wall of the pressure vessel, and the like. It was confirmed that this was due to Na vapor generated from. In a preferred embodiment, in order to prevent corrosion of each member in such a pressure vessel, a sodium vapor absorber is installed inside the pressure vessel.

  In a preferred embodiment, an outer reaction vessel for housing the crucible is provided in the pressure vessel, and an alkali metal or alkaline earth metal vapor absorber is provided in the outer reaction vessel. As a result, members that are susceptible to corrosion, such as heaters and heat insulating materials, can be installed outside the outer reaction vessel, which is further advantageous in terms of preventing corrosion of these members. This outer reaction vessel can be formed of the nitride according to the present invention.

  Further, in a preferred embodiment, there is provided a discharge path forming means for guiding the vapor leaking from the opening between the crucible and the lid to contact with the alkali metal or alkaline earth metal vapor absorber. Thereby, the alkali metal or alkaline earth metal vapor leaking from the crucible can be surely guided to contact with the absorbent.

  The form of the discharge path forming member is not particularly limited. For example, the discharge channel forming member can be a container without a bottom, and a crucible can be accommodated in the bottomless container so that gas can escape from the gap between the bottomless container and the bottom surface of the reaction container. Further, the discharge path forming member is a bottomed container, a crucible is accommodated in the bottomed container, one or a plurality of discharge paths are provided on the upper surface or the side surface of the bottomed container, and an alkali metal or Alkaline earth metal vapor absorbers can be installed.

  FIG. 1 is a cross-sectional view schematically showing an outer reaction vessel 16, a discharge passage forming member 20, an alkali metal or alkaline earth metal vapor absorber 19 and a crucible 25 for installation in a pressure vessel. FIG. 2 is a diagram schematically showing a single crystal growth apparatus 1 that can be used in the present invention.

  For example, when the reaction vessel 16 of FIG. 1 is accommodated in the pressure vessel 2 of a HIP (hot isostatic press) apparatus, the state schematically shown in FIG. 2 is obtained. The jacket 3 is fixed in the pressure vessel 2 of the HIP (hot isostatic press) apparatus, and the reaction vessel 16 is installed in the jacket 3. A raw material containing at least an alkali metal or an alkaline earth metal constituting the flux is accommodated in the outer reaction vessel 16.

  A gas mixture cylinder (not shown) is provided outside the pressure vessel 2. The mixed gas cylinder is filled with a mixed gas having a predetermined composition. The mixed gas is compressed by a compressor to a predetermined pressure, and is supplied into the pressure vessel 2 through the supply pipe 10 as indicated by an arrow B. Nitrogen in the atmosphere serves as a nitrogen source, and an inert gas such as argon gas suppresses evaporation of alkali metal or alkaline earth metal. This pressure is monitored by a pressure gauge (not shown). A heater 4 is installed around the reaction vessel 16 so that the growth temperature in the crucible can be controlled.

  As shown in FIG. 1, the reaction vessel 16 includes a reaction vessel main body 17 and a lid 23, and the lid 23 is formed with a circular protrusion 23 a. The outer reaction vessel 16 is formed by fitting the lid 23 to the main body 17. A discharge passage forming means 20 is installed in the space 18 of the reaction vessel 16. The discharge path forming means 20 of this example is a bottomless container, in which a crucible 25 is accommodated. A circular protrusion 22 a is formed on the lid 22. In the inner space 24 of the crucible 25, the alkali metal or alkaline earth metal flux 8 and the substrate 7 are accommodated.

  The alkali metal or alkaline earth metal vapor generated from the alkali metal or alkaline earth metal flux 8 passes through the space between the lid and the crucible 25 from the space 24 as shown by the arrow C, and the gap between the crucible 25 and the discharge path forming means 20 A cylindrical gap 28 formed therebetween is lowered as indicated by an arrow D. The alkali metal or alkaline earth metal vapor further rises as indicated by an arrow E through a gap 29 between the discharge path forming means 20 and the reaction vessel main body 17.

  Here, an alkali metal or alkaline earth metal vapor absorber 19 is installed between the reaction vessel main body 17 and the discharge path forming means 20, and the steam discharged along the discharge path forming means is indicated by the arrow F. Thus, it is guided to contact with the alkali metal or alkaline earth metal vapor absorber 19. Here, after the alkali metal or alkaline earth metal vapor is absorbed from the exhaust gas, the gas passes through the gap 30 between the lid 23 and the reaction vessel body 17 as indicated by an arrow G, and is released into the pressure vessel 2 as indicated by an arrow H. Is done.

The kind of alkali metal or alkaline earth metal vapor absorber is not particularly limited, and may be, for example, the following.
Material: Porous material such as carbon, activated carbon, silica gel, zeolite Form: Cotton, fiber, sheet, granule

For example, the following single crystals can be suitably grown by the growing method and apparatus of the present invention.
Gallium nitride, aluminum nitride, boron nitride and their solid solutions

Moreover, the following metal components can be contained in the flux in addition to sodium.
Lithium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, tin

  The reaction temperature of the flux in the reaction container of the present invention is not particularly limited. However, when the reaction temperature is 850 ° C. or higher, the effects of the present invention are particularly remarkable. From this viewpoint, the reaction temperature is preferably 900 ° C. or higher, more preferably 1000 ° C. or higher. The upper limit of the reaction temperature is not particularly limited, but is preferably 1500 ° C. or less, more preferably 1300 ° C. or less, from the viewpoint of the corrosion resistance of the reaction vessel.

Hereinafter, more specific single crystals and their growth procedures will be exemplified.
(Gallium nitride single crystal growth example)
Using the present invention, a gallium nitride single crystal can be grown using a flux containing at least sodium metal. This flux is mixed with a gallium source material. 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 usage ratio of the gallium source material and the flux source material such as sodium may be appropriate, but in general, the use of an excess amount of Na is considered. Of course, this is not limiting.

  In this embodiment, a gallium nitride single crystal is grown under an atmosphere composed of a mixed gas containing nitrogen gas under a total pressure of 300 atm or more and 2000 atm or less. By setting the total pressure to 300 atm or higher, a high-quality gallium nitride single crystal could be grown, for example, in a high temperature region of 900 ° C. or higher, more preferably in a high temperature region of 950 ° C. or higher. The reason for this is not clear, but it is presumed that the nitrogen solubility increases as the temperature rises and nitrogen is efficiently dissolved in the growing solution. Further, if the total pressure of the atmosphere is 2000 atmospheres or more, the density of the high-pressure gas and the density of the growth solution become very close, which is not preferable because it becomes difficult to hold the growth solution in the crucible.

  In a preferred embodiment, the nitrogen partial pressure in the growth atmosphere is set to 100 atm or more and 2000 atm or less. By setting the nitrogen partial pressure to 100 atm or higher, for example, in a high temperature region of 1000 ° C. or higher, dissolution of nitrogen into the flux was promoted, and a high-quality gallium nitride single crystal could be grown. From this viewpoint, it is more preferable that the nitrogen partial pressure of the atmosphere is 200 atm or more. Further, it is preferable that the nitrogen partial pressure is practically 1000 atm 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 single crystal is 950 ° C. or higher, more preferably 1000 ° C. or higher, and a high-quality gallium nitride single crystal can be grown even in such a high temperature region. . In addition, since it can be grown at a high temperature, there is a possibility that productivity can be improved.

  The upper limit of the growth temperature of the gallium nitride single crystal is not particularly limited, but if the growth temperature is too high, the crystal is difficult to grow. Therefore, the temperature is preferably 1500 ° 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, silicon single crystal, SiC single crystal, MgO single crystal, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , perovskite complex oxides such as LaAlO ₃ , LaGaO ₃ , and NdGaO ₃ can be exemplified. 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.

(Growth example of GaN, AlN single crystal)
The present invention has been confirmed to be effective even when growing an AlN single crystal by pressurizing a melt containing a flux containing at least aluminum and an alkaline earth in a nitrogen-containing atmosphere under specific conditions. .

Example 1
A gallium nitride single crystal film was grown on the seed crystal 7 in accordance with the procedure described with reference to FIGS. 1 and 2 using the apparatus shown in FIGS.

  Specifically, a yoke frame type HIP (hot isostatic pressing) apparatus was used. As shown in FIG. 1, an outer reaction vessel 16, an alkali metal or alkaline earth metal vapor absorber 19, a discharge path forming means 20, a crucible 25, and a lid 22 are installed in the pressure vessel 2.

  The crucible 25 and the lid 22 were made of titanium nitride. Specifically, 300 g of titanium nitride powder having a particle size of 1 to 1.5 μm was press-molded into pellets having a diameter of 100 mm and a height of about 110 mm. This was heated to 1800 ° C. in a nitrogen atmosphere while applying a load of 40 KN, and held for 2 hours. As a result, a sintered body having a height of about 55 mm was obtained. A crucible having an outer diameter of 90 mm and a height of 50 mm was produced from the sintered body. The relative density of titanium nitride constituting these lids prepared in the same manner is 97%, and the Young's modulus is 580 GPa.

  A 2 inch diameter AlN template 7 was used as a seed crystal. An AlN template refers to an AlN single crystal epitaxial thin film formed on a sapphire single crystal substrate. The thickness of the AlN thin film at this time was 1 micron. Metal gallium and metal sodium were weighed in a glove box so as to have a molar ratio of 27:73 and placed in the crucible 25. An inert mixed gas having a nitrogen concentration of 50% (remaining argon) was supplied from the cylinder 12, pressurized to 40 MPa (approximately 400 atm) in a compressor, and heated to 1100 ° C. The nitrogen partial pressure at this time is approximately 200 atmospheres. This gas was fed into the pressure vessel. This was maintained for 100 hours.

  As a result, a GaN single crystal having a thickness of about 5 mm and a diameter of 2 inches grew. Little evaporation of metallic sodium was seen. Also, no traces of corrosion, infiltration or swelling were seen on the inner wall of the crucible.

(Example 2)
A single crystal was grown in the same manner as in Example 1. However, the material constituting the crucible 25 and the lid 22 was zirconium nitride. Specifically, 400 g of zirconium nitride powder having a particle size of 1 to 2 μm was press-molded into pellets having a diameter of 100 mm and a height of about 110 mm. This was heated to 1800 ° C. in a nitrogen atmosphere while applying a load of 40 KN, and held for 2 hours. As a result, a sintered body having a height of about 55 mm was obtained. A crucible having an outer diameter of 90 mm and a height of 50 mm was produced from the sintered body. A lid was prepared in the same manner. The relative density of the zirconium nitride constituting them is 97%, and the Young's modulus is 500 GPa.

  As a result, a GaN single crystal having a thickness of about 5 mm and a diameter of 2 inches grew. Little evaporation of metallic sodium was seen. Also, no traces of corrosion, infiltration or swelling were seen on the inner wall of the crucible.

(Example 3)
A single crystal was grown in the same manner as in Example 1. However, the material constituting the crucible and the lid was a mixed ceramic of titanium nitride and zirconium nitride. Specifically, 150 g of titanium nitride powder having a particle size of 1 to 1.5 μm and 200 g of zirconium nitride powder having a particle size of 1 to 2 μm were press-molded into pellets having a diameter of 100 mm and a height of about 110 mm. This was heated to 1800 ° C. in a nitrogen atmosphere while applying a load of 40 KN, and kept for 4 hours. As a result, a sintered body having a height of about 55 mm was obtained. A crucible having an outer diameter of 90 mm and a height of 50 mm was produced from the sintered body. A lid was prepared in the same manner. The relative density of the ceramics constituting these is 97%, and the Young's modulus is 540 GPa.

  As a result, a GaN single crystal having a thickness of about 5 mm and a diameter of 2 inches grew. Little evaporation of metallic sodium was seen. Also, no traces of corrosion, infiltration or swelling were seen on the inner wall of the crucible.

(Comparative Example 1)
A single crystal was grown in the same manner as in Example 1. However, the material constituting the crucible and the lid was aluminum nitride. Specifically, aluminum nitride powder having an average particle size of 1.4 μm was press-molded into pellets having a diameter of 100 mm and a height of about 100 mm. This was heated to 1800 ° C. in a nitrogen atmosphere while applying a load of 40 KN, and kept for 4 hours. As a result, a sintered body having a height of about 55 mm was obtained. A crucible having an outer diameter of 90 mm and a height of 50 mm was produced from the sintered body. A lid was prepared in the same manner. The relative density of the aluminum nitride constituting them is 97%, and the Young's modulus is 300 GPa.

  As a result, a GaN single crystal having a thickness of about 5 mm and a diameter of 2 inches grew. Little evaporation of metallic sodium was seen. Moreover, traces of swelling were seen on the inner wall surface of the crucible, and the ceramic structure was slightly swollen.

Example 4
An AlN single crystal was grown in the same manner as in Example 1. In this example, the flux raw material containing Ga, Al, and Ca was weighed in a glove box. The weighed raw material was filled in the crucible 25. The crucible and the lid were formed from the same titanium nitride sintered body as in Example 1. In addition, AlN template 7 (a 1 μm thick aluminum nitride thin film epitaxially grown on a sapphire single crystal wafer) was used as a seed crystal. A nitrogen-argon mixed gas (nitrogen 10%) was used as an atmosphere, and the mixture was held at a predetermined temperature and pressure for 100 hours.

  As a result, it was confirmed that an aluminum nitride single crystal having a thickness of about 1 mm was grown on the AlN template.

  Moreover, almost no evaporation of metallic sodium was observed. There was no evidence of corrosion, infiltration or swelling on the inner wall of the crucible.

It is sectional drawing which shows schematically the reaction container which can be used in embodiment of this invention. It is a figure which shows the state which set the reaction container of FIG. 1 to the HIP apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Growing apparatus 2 Pressure vessel 7 Seed crystal 8 Flux 10 Supply pipe 16 Reaction vessel 17 Reaction vessel main body 19 Alkali metal or alkaline earth metal vapor absorber 20 Drain passage forming member 21 Drain passage 22 Crucible lid 23 Lid 25 Crucible B Mixing Gas flow C, D, E, F, G, H Gas flow path

Claims (10)

A reaction vessel used for growing a single crystal from a flux containing at least one of an alkali metal and an alkaline earth metal,
A reaction vessel comprising a ceramic containing one or both of titanium nitride and zirconium nitride as a main component.   2. The ceramic according to claim 1, wherein the ceramic is a sintered body using a powder of one kind of nitride selected from the group consisting of titanium nitride and zirconium nitride or a mixed powder of two kinds of nitride as a raw material powder. The reaction vessel as described.   The reaction vessel according to claim 2, wherein the particle size of the raw material powder is 0.2 μm or more and 3 μm or less.   The reaction container according to any one of claims 1 to 3, wherein Young's modulus of the ceramic is 200 GPa or more.   The reaction container according to any one of claims 1 to 4, wherein the ceramic has a relative density of 96% or more. A method for growing a single crystal from a flux containing at least one of an alkali metal and an alkaline earth metal,
A method for growing a single crystal, wherein the flux is accommodated in a reaction vessel made of a ceramic containing one or both of titanium nitride and zirconium nitride as a main component.   7. The ceramic according to claim 6, wherein the ceramic is a sintered body using a powder of one kind of nitride selected from the group consisting of titanium nitride and zirconium nitride or a mixed powder of two kinds of nitride as a raw material powder. The method described.   The method according to claim 7, wherein a particle size of the raw material powder is 0.2 μm or more and 3 μm or less.   The method according to claim 6, wherein the ceramic has a Young's modulus of 200 GPa or more.   The method according to claim 6, wherein the ceramic has a relative density of 96% or more.

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