JP4919949B2 - Method for growing single crystal and single crystal growing apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for growing a nitride single crystal by a so-called Na flux method.

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, Non-Patent Document 1 ( Jpn. J. Appl. Phys. Vol. 42, (2003) pages L4-L6) uses an atmosphere containing only nitrogen. In this case, the atmospheric pressure is 50 atm. When a mixed gas atmosphere of 40% ammonia and 60% nitrogen is used, the total pressure is 5 atm.

For example, in patent document 1 ( Unexamined-Japanese-Patent No. 2002-293696), it is set to 10 to 100 atmospheres using the mixed gas of nitrogen and ammonia. Also in patent document 2 ( Unexamined-Japanese-Patent No. 2003-292400), 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.

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. Moreover, the manufacturing technology of AlN by the flux method (solution method) is disclosed in Patent Document 3 ( Japanese Patent Laid-Open No. 2003-1119099) and Non-Patent Document 2 ( Mat. Res. Bull. Vol. 9 (1974) pages 331 to 336). It is disclosed. In JP2003-1119099, a transition metal is used as a flux. Mat. Res. Bull. Vol. 9 (1974) pp. 331 to 336, an AlN single crystal is obtained from Ca ₃ N ₂ and AlN powder.

Recently, it has been reported that a high-quality bulk gallium nitride single crystal can be synthesized at a low temperature and low pressure by using Na as a catalyst ( Patent Document 4: Japanese Patent Laid-Open No. 2000-327495). The raw materials are gallium and sodium azide.

Further, according to Non-Patent Document 3 ( Phys. Stat. Sol. Vol. 188 (2001) p415-419), Na flux is produced using sodium azide, gallium and aluminum as raw materials, and this Na flux is used. AlGaN solid solution single crystals have been successfully grown at 750 ° C. or 800 ° C. and a pressure of about 100 to 110 atm.

Jpn. J. Appl. Phys. Vol. 42, (2003) Page L4-L6 Mat. Res. Bull. Vol. 9 (1974) 331-336 Phys. Stat. Sol. Vol.188 (2001) p415-419

JP 2002-293696 A JP 2003-292400 A JP2003-1119099 JP 2000-327495 A Japanese Patent Application No. 2004-103093

The present inventor has attempted to grow a gallium nitride single crystal or an aluminum nitride single crystal in a high temperature and high pressure region using a hot isostatic press (HIP) apparatus than in the above document ( Patent Document 5: Special Application 2004-103093).

  When crystal growth is performed by a flux method using an HIP apparatus, it is necessary to accommodate structural parts such as a heater, a heat insulating material (furnace material), and a movable mechanism inside the pressure vessel. In the region, it has been found that these are subject to corrosion by flux metal vapors generated from the flux in the crucible.

  An object of the present invention is to grow a single crystal using a flux containing an alkali or an alkaline earth metal, and to heat a structural metal component such as a heater, a furnace material or a movable mechanism using a flux metal vapor generated from a flux in a crucible. It is to prevent corrosion.

  The present invention is a method for growing a single crystal using a flux containing at least an alkali or an alkaline earth metal, the crucible for containing the flux, a lid for the crucible, a crucible, and at least nitrogen gas And a flux metal vapor absorber disposed inside the pressure vessel and outside the crucible to grow a single crystal.

  Further, the present invention is an apparatus for growing a single crystal using a flux containing at least an alkali or alkaline earth metal, and contains a crucible for containing the flux, a lid for the crucible, and a crucible. A single crystal growth apparatus comprising: a pressure vessel for filling an atmosphere containing at least nitrogen gas; and a flux metal vapor absorber disposed inside the pressure vessel and outside the crucible. is there.

  The inventor accommodates a crucible for accommodating a flux, and provides a flux metal vapor absorber in a pressure vessel for filling an atmosphere containing at least nitrogen gas, thereby removing the gap between the crucible and the lid. It absorbed the leaked flux metal vapor and succeeded in preventing corrosion of heaters, heat insulating materials and moving parts. Thus, a single crystal can be grown using an apparatus suitable for processing at high temperature and high pressure using an alkali or alkaline earth-containing flux.

FIG. 1 is a cross-sectional view schematically showing a reaction vessel that can be used in an embodiment of the present invention. FIG. 2 is a view showing a state in which the reaction container of FIG. 1 is set in the HIP apparatus.

  The details of the present invention will be described below by taking gallium nitride crystal growth by the Na flux method as an 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. 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 an 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 the generated Na vapor. In the present invention, in order to prevent such corrosion of each member in the pressure vessel, a sodium vapor absorber is installed inside the pressure vessel.

  In a preferred embodiment, a reaction vessel for housing the crucible is provided in the pressure vessel, and a sodium vapor absorber is provided in the reaction vessel. As a result, members that are susceptible to corrosion, such as heaters and heat insulating materials, can be installed outside the reaction vessel, which is further advantageous in terms of preventing corrosion of these members.

  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 sodium vapor absorber. Thereby, the sodium 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. In addition, the discharge path forming member is a bottomed container, a crucible is accommodated in the bottomed container, one or more discharge paths are provided on the upper surface or side surface of the bottomed container, and sodium vapor is absorbed at the outlet of each discharge path. Materials can be installed.

  FIG. 1 is a cross-sectional view schematically showing a reaction vessel 16, a discharge channel forming member 20, a sodium vapor absorber 19 and a crucible 25 for installation in a pressure vessel according to the present invention. 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 sodium constituting the flux is accommodated in the 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 sodium. 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. A circular protrusion 23 a is formed on the lid 23. The lid 23 is fitted to the main body 17 to form the reaction vessel 16. A discharge passage forming means 20 is installed in the space 18 of the reaction vessel 16. A circular protrusion 22 a is formed on the lid 22. The discharge path forming means 20 of this example is a bottomless container, in which a crucible 25 is accommodated. The Na flux 8 and the substrate 7 are accommodated in the inner space 24 of the crucible 25.

  In this example, Na vapor generated from the Na flux 8 passes through the gap between the lid and the crucible 25 from the space 24 as shown by an arrow C, and has a cylindrical shape formed between the crucible 25 and the discharge path forming means 20. The gap 28 is lowered as indicated by an arrow D. The Na vapor further rises as indicated by an arrow E through a gap 29 between the discharge path forming means 20 and the reaction vessel body 17.

  Here, a sodium vapor absorber 19 is installed between the reaction vessel main body 17 and the discharge path forming means 20, and the vapor discharged along the discharge path forming means is a sodium vapor absorber as indicated by arrow F. 19 leads to contact. Here, after the Na vapor is absorbed from the exhaust gas, the gas passes through the gap 30 between the lid 23 and the reaction vessel main body 17 as indicated by an arrow G, and is released into the pressure vessel 2 as indicated by an arrow H.

  The flux metal vapor absorber refers to a member having a property of absorbing one or more metal vapors among the metals constituting the flux. This absorbent material preferably has at least the ability to absorb alkali metal or alkaline earth metal constituting the flux. Particularly preferably, it has an absorption capacity of sodium or lithium or calcium metal.

The kind of flux metal vapor | steam absorber is not specifically limited, For example, the following may be sufficient.
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

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 quite 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 this 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. 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, 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. Further, 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 to 0.98; x = 0 to 1; z = 0 to 1; u = 0.15 to 0.49; x + z = A cubic perovskite structure composite oxide of 0.1 to 2) can also be used. SCAM (ScAlMgO ₄ ) can also be used.

(Example of growing 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. In this pressure vessel 2, as shown in FIG. 1, a reaction vessel 16, a sodium vapor absorber 19, a discharge path forming means 20, a crucible 25, and a lid 22 were installed.

  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 an alumina crucible 25. The crucible 25 has a cylindrical shape with a diameter of 100 mm and a height of 120 mm. 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.

Next, after cooling to room temperature, the weight of the crucible 25 containing the raw material, the weight of the reaction vessel main body 17 with the crucible 25 still contained, and the weight of the lid 23 were measured. The weight of the crucible 25 was reduced by about 1%, which is thought to be due to evaporation of metallic sodium in the flux. The weight of the reaction vessel main body 17 (including the crucible) and the weight of the lid 23 were not changed. Therefore, it can be seen that the evaporated sodium was trapped by the absorbent material 19. Moreover, no leakage of metallic sodium to the outside of the reaction vessel was observed, and no corrosion was observed in the heater or heat insulating material in the pressure vessel.
As a result, a GaN single crystal having a thickness of about 5 mm and a diameter of 2 inches grew.

(Comparative Example 1)
In Example 1, a comparative experiment was performed with the exception of the sodium vapor absorber 19. However, it was the same as the above except that the sodium vapor absorber 19 was omitted.

  After cooling to room temperature, the weight of the crucible 25 containing the raw material, the weight of the reaction vessel main body 17 with the crucible 25 still contained, and the weight of the lid 23 were measured. The weight of the crucible was reduced by about 1%, which is believed to be due to evaporation of metallic sodium in the flux. The weight of the reaction vessel main body 17 (including the crucible) was also reduced by 1%. Therefore, it was confirmed that sodium evaporated from the crucible leaked into the space outside the reaction vessel 17. Furthermore, when the heater and heat insulating material in the pressure vessel were confirmed, some corrosion was observed.

(Example 2)
An AlN single crystal was grown in the same manner as in Example 1. In this example, the flux raw material containing Al and Ca was weighed in a glove box. The alumina crucible 25 was filled with the weighed raw material. 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.

  Next, after cooling to room temperature, the weight of the crucible 25 containing the raw material, the weight of the reaction vessel main body 17 with the crucible 25 still contained, and the weight of the lid 23 were measured. The weight of the crucible 25 was reduced by about 0.1%. The weight of the reaction vessel main body 17 (including the crucible) and the weight of the lid 23 were not changed. Moreover, corrosion was not seen in the heater and heat insulating material in the pressure vessel.

  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.

  The amount of flux evaporated from the crucible is considered to be determined by the vapor pressure at the growth temperature. Table 2 shows vapor pressures of sodium, lithium, and calcium, which are typical flux raw materials, compared with vapor pressures of aluminum and gallium.

Claims (11)

A method of growing a single crystal using a flux containing at least an alkali or alkaline earth metal,
A crucible for containing the flux;
This crucible lid,
Growing the single crystal using a pressure vessel that contains the crucible and is filled with an atmosphere containing at least nitrogen gas, and a flux metal vapor absorber disposed in the pressure vessel and outside the crucible A method for growing a single crystal characterized by the above.   The method according to claim 1, wherein a reaction vessel provided in the pressure vessel and containing the crucible is used, and the flux metal vapor absorber is provided in the reaction vessel.   The discharge path forming means for guiding the steam leaked from the opening between the crucible and the lid to contact with the flux metal vapor absorber is used. Method.   The method according to claim 1, wherein the single crystal is a nitride single crystal.   5. The method according to claim 4, wherein the nitride single crystal is grown under an atmosphere of a mixed gas containing nitrogen gas under a pressure of a total pressure of 300 to 2000 atm.   The method according to claim 1, wherein the single crystal is grown using a hot isostatic pressing apparatus. An apparatus for growing a single crystal using a flux containing at least an alkali or alkaline earth metal,
A crucible for containing the flux;
This crucible lid,
A pressure vessel for containing the crucible and filling an atmosphere containing at least nitrogen gas, and a flux metal vapor absorber disposed inside the pressure vessel and outside the crucible, Single crystal growth equipment. The apparatus according to claim 7 , further comprising a reaction vessel provided in the pressure vessel and containing the crucible, wherein the flux metal vapor absorber is provided in the reaction vessel. Characterized in that it comprises a discharge path forming means for guiding the leaked vapor from the opening between the crucible and the lid, the contact between the flux metal vapor absorption material, according to claim 7 or 8 The device described. The device according to claim 7 , wherein the single crystal is a nitride single crystal. . 11. A device according to any one of claims 7 to 10 , characterized in that it comprises a hot isostatic pressing mechanism for heating and pressing.

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