JP5318803B2 - Method and apparatus for producing nitride crystal - Google Patents

Description

  The present invention relates to a method and an apparatus for producing a nitride crystal.

  Gallium nitride III-V nitride has attracted attention as an excellent blue light emitting device, and has been put into practical use as a material for light emitting diodes and semiconductor laser diodes. Each organization reports a method for growing a group III nitride crystal using a flux.

  For example, the growth rate of gallium nitride single crystals by the sodium flux method is slow. Methods for improving the growth rate are described in Patent Document 1 (WO 2005/095681 A1) and Patent Document 2 (Japanese Patent Laid-Open No. 11-292679).

  In Patent Document 1 (WO 2005/095681 A1), a raw material preparation container is provided separately from the growth container. In the raw material preparation container, nitrogen is supplied to the raw material and the melt of the flux, and at this time, the temperature is set slightly higher than that of the growth container, thereby bringing the nitrogen into an unsaturated state and promoting dissolution of the nitrogen into the melt. To do. Then, the melt in which nitrogen is sufficiently dissolved is sent to the growth container. In the growth vessel, the temperature is relatively lowered to bring the nitrogen supersaturated state, and a nitride single crystal is grown on the single crystal substrate (particularly FIGS. 8 and 0043 to 0047).

  In the case where such a raw material preparation container is not provided, crystal growth begins only after nitrogen is sufficiently dissolved in the melt and becomes supersaturated in the growth container. Therefore, the time until the nitrogen is sufficiently dissolved in the melt is lost, and the productivity of crystals is reduced. In Patent Document 1, the productivity of nitride crystals is improved by separately performing a step of dissolving nitrogen in the melt in a raw material preparation container separate from the growth container.

  In Patent Document 2 (Japanese Patent Application Laid-Open No. 11-292679), the growth container and the raw material preparation container are divided, and the melt in the growth container and the melt in the raw material preparation container are circulated (particularly in FIG. 3 and FIG. 3). 0027-0030). By allowing the raw material to be supplied to the raw material preparation container at any time, the raw material consumed with the crystal growth is replenished.

WO 2005/095681 A1 JP-A-11-292679

  In the methods described in Patent Documents 1 and 2, the crystal productivity per unit time of the entire apparatus is improved. However, it is a method of increasing the productivity of crystals in the growth vessel by performing the step of dissolving nitrogen in the melt in a vessel different from the growth vessel. Therefore, compared with the conventional method, the crystal growth rate in the growth vessel does not change at all. For example, in the data described in Embodiments 2, 3, and 4 (0040 to 0042) of Patent Document 1, the crystal growth rate is 15 to 25 μm / hr, which is the same level as the conventional method.

  An object of the present invention is to improve the growth rate of a crystal when growing the crystal in a melt containing a flux and a raw material so that a large crystal of high quality can be grown in a short time.

The present invention is an apparatus for growing a nitride crystal by heating and pressurizing a melt containing a flux and a group III element raw material in a nitrogen-containing atmosphere,
A growth vessel for growing a nitride crystal by containing a melt and maintaining a supersaturated state;
A first nitrogen dissolution vessel that dissolves nitrogen in the melt by heating and maintaining the melt in an unsaturated state;
A second nitrogen dissolution vessel that dissolves nitrogen in the melt by heating and maintaining the melt in an unsaturated state;
A first connecting portion for connecting the growth vessel and the first nitrogen dissolution vessel to communicate the melt in the growth vessel with the melt in the first nitrogen dissolution vessel;
A second connecting portion for connecting the growth vessel and the second nitrogen dissolution vessel to communicate the melt in the growth vessel with the melt in the second nitrogen dissolution vessel; and the growth vessel and the first nitrogen dissolution vessel A drive means for moving the container, the second nitrogen dissolving container, the first connecting portion and the second connecting portion is provided.

Further, the present invention is a method for growing a nitride crystal by heating and pressurizing a melt containing a flux and a raw material in a nitrogen-containing atmosphere,
A growth vessel for growing a nitride crystal by containing a melt and maintaining a supersaturated state;
A first nitrogen dissolution vessel that dissolves nitrogen in the melt by heating and maintaining the melt in an unsaturated state;
A second nitrogen dissolution vessel that dissolves nitrogen in the melt by heating and maintaining the melt in an unsaturated state;
A first connecting portion for connecting the growth container and the first nitrogen dissolution container to communicate the melt in the growth container with the melt in the first nitrogen dissolution container; and the growth container and the second nitrogen dissolution The first connecting unit is connected to the container, and the second connecting part is used to communicate the melt in the growth container with the melt in the second nitrogen dissolving container. The dissolution container, the second nitrogen dissolution container, the first connection part and the second connection part are moved.

  According to the present invention, at least two nitrogen dissolution containers are provided separately from the growth container, and the melts in each of them are communicated with each other. Then, by driving the entire growth container and each nitrogen dissolution container, convection of the melt is generated between the growth container and each nitrogen dissolution container, and nitrogen is sufficiently transferred from each nitrogen dissolution container to the growth container. The dissolved melt could be supplied stably. This succeeded in improving the crystal growth rate in the growth vessel and reached the present invention.

It is a figure which shows typically the crystal manufacturing apparatus which concerns on one Embodiment of this invention, and shows the time of the container inclining. It is a top view which shows the apparatus of FIG. 1 typically. It is a figure which shows typically the crystal manufacturing apparatus which concerns on one Embodiment of this invention, and shows the time when a container is horizontal.

  Inside the pressure vessel 17 shown in FIG. 2, the growth vessel 2, the first nitrogen dissolving vessel 1, and the second nitrogen dissolving vessel 3 are accommodated. A vacuum suction pipe and a gas pipe 19 are attached to the pressure vessel 17. By suctioning from the vacuum suction tube as indicated by an arrow H, the inside of the pressure vessel 17 can be maintained in a vacuum state. Further, by supplying nitrogen from the gas pipe 19 as indicated by an arrow J, the gas pressure in the inner space of the pressure vessel 17 can be controlled.

  In the growth container 2, the raw material and flux of the melt 27 are accommodated, and the melt 27 is generated by heating and pressurizing. By pressurizing the space 2 a in the growth vessel 2 with a nitrogen-containing gas, nitrogen is supplied into the melt 17 to be in a nitrogen supersaturated state, and the crystal 14 is grown on the seed crystal substrate 13.

  On one side of the growth container 2, the first nitrogen dissolving container 1 is attached by a first connecting portion 4. A second nitrogen dissolving container 3 is attached to the other side of the growing container 2 by a second connecting portion 5. The first nitrogen dissolving container 1, the growing container 2 and the second nitrogen dissolving container 3 are preferably arranged in a straight line via the first connecting part 4 and the second connecting part 5. This is because the convection of the melt can be generated more efficiently by driving described later. More preferably, it is arranged so as to be substantially perpendicular to the swing axis during driving (see FIG. 2).

  A gas pipe 8 and a raw material pipe 9 are attached to the first nitrogen dissolving container 1 and the second nitrogen dissolving container 3, respectively. The gas pipe 8 is connected to the cylinder 11 via the mass flow meter 10, and the raw material pipe 9 is connected to the tank 12 via the mass flow meter 10. The outlet of the raw material pipe 9 is provided near the bottom of the container, and the outlet of the gas pipe 8 is provided on the melt.

  Predetermined raw materials and flashes are accommodated in the inner spaces 1a and 3a of the nitrogen dissolving containers 1 and 3, respectively, and heated under predetermined pressure and temperature conditions to generate melts 6 and 28. .

  In this example, the drive shaft 16 can swing as indicated by an arrow K. When the drive shaft 16 is swung as indicated by an arrow K, the entire growth container 2 and nitrogen dissolving containers 1 and 3 are swung as indicated by arrows A and B. Since the melt 27 in the growth vessel 2 and the melts 6 and 28 in the nitrogen dissolution vessels 1 and 3 are in communication with each other, if the whole swings as indicated by the arrow K, convection occurs in each melt. And the movement of the melt between the containers is promoted.

  That is, during the period when the whole moves as indicated by the arrow B, the container 1 is raised and the container 3 is lowered. As a result, the fresh melt 6 in which the nitrogen in the container 1 is dissolved passes through the connecting portion 4 as shown by the arrow D and is supplied into the growing container 2. At the same time, the melt 27 depleted by crystal growth in the container 2 passes through the connecting portion 5 and flows into the container 3 as indicated by an arrow F. This depleted melt 27 is again supplied with raw materials and nitrogen in the container 3 to become a fresh, undepleted melt 28.

During the period when the whole is moving as indicated by the arrow A, the container 1 is lowered and the container 3 is raised. As a result, the fresh melt 28 in which the nitrogen in the container 3 is dissolved passes through the connecting portion 5 and is supplied into the growth container 2. At the same time, the melt 27 depleted by crystal growth in the container 2 passes through the connecting portion 4 and flows into the container 1. The depleted melt 27 is supplied with the raw material and nitrogen again in the container 1 and becomes a fresh undepleted melt 6.
In the middle of the swing, as shown in FIG. 3, there is a point in time when each container becomes horizontal. At this point, the container 1 and the container 3 are at the same height.

  With such a method, a fresh melt in which nitrogen is dissolved is always supplied into the growth vessel, and the depleted melt in the growth vessel is efficiently discharged to again dissolve nitrogen and raw materials. Provided. Furthermore, the melt can be convected without stagnation, so to speak, it can create a laminar flow or a state similar to laminar flow. Therefore, it is possible to remarkably improve the growth rate in the growth container itself.

In a preferred embodiment, the raw material supply unit 9 is provided in a nitrogen dissolution vessel. As a result, the raw material can be continuously supplied into the growth vessel 2 and crystals can be continuously grown. This raw material is convected in the container as indicated by arrows C and G and mixed with the flux.
In the above embodiment, the connecting portion has a pipe shape. However, the connecting portion is not particularly limited as long as the melt can flow between the containers. In this case, a plate-shaped flow hole can be formed in the plate-shaped connecting portion, or a plurality of flow holes can be formed in the plate-shaped connecting portion.

  In this case, by additionally supplying the raw material at the time of crystal growth, the height of the melt 27 in the growth container can be increased as the crystal growth proceeds.

  In addition, by providing a cooling mechanism at the bottom of the growth vessel 2, the temperature of the seed crystal can be kept constant. This prevents the temperature of the seed crystal from rising even when a solution hotter than the growing section from the raw material supply section is convected.

  In the nitrogen melting containers 1 and 3, the temperature and pressure are set so that the nitrogen is not saturated. Preferably, the temperature of the melt in the nitrogen dissolution vessel is set higher than the temperature of the melt in the growth vessel. In this case, the pressure in each container can be the same.

  The temperature of the melt in the nitrogen dissolution vessel varies depending on the flux and crystal composition ratio, and is thus selected as appropriate. For example, when Na flux is used and a GaN crystal is grown, 850-1000 ° C. is preferable. When an AlN crystal is grown using Sn—Mg flux, 1200 to 1500 ° C. is preferable.

  In a preferred embodiment, the temperature of the melt in the growth vessel is lower than the temperature of the melt in the nitrogen dissolution vessel, thereby making the melt supersaturated. Although this temperature difference is not limited, it is preferably 10 ° C. or higher and more preferably 30 ° C. or higher from the viewpoint of promoting precipitation of nitride crystals. Further, if this difference is too large, the crystal quality tends to be lowered. From this viewpoint, 100 ° C. or lower is preferable, and 70 ° C. or lower is more preferable.

  When driving the growth vessel, the nitrogen dissolution vessel, etc., it is preferable to swing or rotate as described above. In this case, the angle is preferably 5 to 15 °.

  Also, the melt can be moved between the growth container and each nitrogen dissolution container by reciprocating the growth container, the nitrogen dissolution container, and the like in the horizontal direction.

  In the crystal (preferably single crystal) growing apparatus of the present invention, an apparatus for heating the raw material mixture to generate a melt is not particularly limited. This apparatus is preferably a hot isostatic pressing apparatus, but other atmospheric pressure heating furnaces may be used.

Examples of Group III element materials include metal gallium, metal gallium-sodium alloy (Ga4Na), metal aluminum, metal indium, metal gallium-aluminum alloy, metal gallium-germanium alloy, and metal gallium-indium alloy.
The flux for generating the melt is not particularly limited, but one or more metals selected from the group consisting of alkali metals and alkaline earth metals or alloys thereof are preferable. Examples of the metal include lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, and barium. Lithium, sodium, and calcium are particularly preferable, and sodium is most preferable.

  The material of the growth vessel and the nitrogen dissolution vessel is not particularly limited as long as the material is durable under the intended heating and pressurizing conditions. Examples of such materials include refractory metals such as tantalum, tungsten, and molybdenum, oxides such as alumina, sapphire, and yttria, nitride ceramics such as aluminum nitride, titanium nitride, zirconium nitride, and boron nitride, tungsten carbide, tantalum carbide, and the like. And pyrolytic products such as p-BN (pyrolytic BN) and p-Gr (pyrolytic graphite).

  Using the present invention, a gallium nitride 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.

  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 material of the growth substrate for epitaxially growing the crystal is not limited, but sapphire, AlN template, GaN template, silicon crystal, iC crystal, MgO crystal, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , LaAlO ₃ , Examples thereof include perovskite complex oxides such as 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.

A gallium nitride single crystal was grown according to the method and apparatus described with reference to FIGS.
Specifically, 400 g of metallic sodium and 500 g of metallic gallium were filled in the nitrogen dissolution vessels 1 and 3 in advance. In the growth vessel 2, four seed substrates having a diameter of 2 inches (3 micron GaN thin film formed on a sapphire substrate) were placed on the bottom of the vessel, and 400 g of metallic sodium and 500 g of metallic gallium were placed thereon. This is an amount such that the height of the melt in the growth container is about 1.5 cm.

  Using the heater 18 and the pressure regulator, the nitrogen dissolution containers 1 and 3 and the growth container 2 were pressurized with nitrogen gas up to 4 MPa, and then heated to prepare mixed melts 6, 27, and 28. At this time, the temperature of the nitrogen dissolving containers 1 and 3 was set to 900 ° C., and the temperature of the growing container 2 was set to 860 ° C.

  Next, by bubbling nitrogen gas through the gas pipe 9, nitrogen was dissolved in the melt in the melts 6 and 28 in the nitrogen dissolving containers 1 and 3 to prepare a raw material solution. Then, the melt was continuously moved between the nitrogen dissolving containers 1 and 3 and the growth container 2 by swinging the drive shaft 16 as indicated by an arrow K. The swing angle is ± 10 ° when viewed from the vertical axis.

  The temperature of the seed substrate was maintained at 855 ° C. by the cooling mechanism. After starting crystal growth, 15 hours later, Ga melt was additionally supplied to the nitrogen dissolution vessel at a rate of 1 g / hr. This ratio can be appropriately changed according to the nitriding rate of the raw material. By holding for 100 hours as a whole, a crystal having a thickness of about 4.0 mm was obtained. The growth rate, calculated by simply dividing the growth thickness by the holding time, was about 40 μm / hr.

The sapphire on the seed substrate was peeled off naturally during the cooling to room temperature. Neither the sapphire substrate nor the grown GaN crystal had cracks. The half width of the X-ray diffraction peak at the center of the grown crystal was (0002) reflection for 30 seconds and (10-12) reflection for 40 seconds. The etch pit density (EPD) when etched using a mixed solution of phosphoric acid: sulfuric acid = 3: 1 at 250 ° C. for 140 minutes was 5 × 10 ³ / cm ² .

Claims (10)

An apparatus for growing a nitride crystal by heating and pressurizing a melt containing a flux and a Group III element raw material in a nitrogen-containing atmosphere,
A growth vessel for growing the nitride crystal by containing the melt and maintaining a supersaturated state;
A first nitrogen dissolution vessel for dissolving nitrogen in the melt by heating and maintaining the melt in an unsaturated state;
A second nitrogen dissolution vessel for dissolving nitrogen in the melt by heating and maintaining the melt in an unsaturated state;
A first connecting portion for connecting the growth vessel and the first nitrogen dissolution vessel to communicate the melt in the growth vessel with the melt in the first nitrogen dissolution vessel;
A second connecting portion that connects the growth vessel and the second nitrogen dissolution vessel to communicate the melt in the growth vessel with the melt in the second nitrogen dissolution vessel; and the growth Nitride crystal growth comprising: a container, the first nitrogen dissolving container, the second nitrogen dissolving container, the first connecting part, and a driving means for moving the second connecting part. apparatus.   The apparatus according to claim 1, wherein the growing container, the first nitrogen dissolving container, the second nitrogen dissolving container, the first connecting part, and the second connecting part are swung.   The temperature of the melt in the first nitrogen dissolution vessel and the temperature of the melt in the second nitrogen dissolution vessel are higher than the temperature of the melt in the growth vessel. The apparatus according to 1 or 2.   The apparatus according to any one of claims 1 to 3, further comprising raw material supply means for supplying the raw material into the first nitrogen dissolution vessel.   The apparatus according to any one of claims 1 to 4, further comprising a raw material supply means for supplying the raw material into the second nitrogen dissolution vessel. A method for growing a nitride crystal by heating and pressurizing a melt containing a flux and a Group III element raw material in a nitrogen-containing atmosphere,
A growth vessel for growing the nitride crystal by containing the melt and maintaining a supersaturated state;
A first nitrogen dissolution vessel for dissolving nitrogen in the melt by heating and maintaining the melt in an unsaturated state;
A second nitrogen dissolution vessel for dissolving nitrogen in the melt by heating and maintaining the melt in an unsaturated state;
A first connecting portion that connects the growth vessel and the first nitrogen dissolution vessel, and communicates the melt in the growth vessel with the melt in the first nitrogen dissolution vessel; and the growth Using a second connecting part for connecting the container and the second nitrogen dissolution container, and communicating the melt in the growth container and the melt in the second nitrogen dissolution container; Nitride crystal characterized by moving said growth container, said first nitrogen dissolution container, said second nitrogen dissolution container, said first connection part and said second connection part at the time of growth of a product single crystal How to train.   The method according to claim 6, wherein the growth container, the first nitrogen dissolution container, the second nitrogen dissolution container, the first connection part, and the second connection part are rocked.   The temperature of the melt in the first nitrogen dissolution vessel and the temperature of the melt in the second nitrogen dissolution vessel are higher than the temperature of the melt in the growth vessel. The method according to 6 or 7.   The method according to any one of claims 6 to 8, wherein the raw material is supplied from a raw material supply means into the first nitrogen dissolution vessel.   The method according to any one of claims 6 to 9, wherein the raw material is supplied from a raw material supply means into the second nitrogen dissolution vessel.

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