JP2007238343A - Method of growing group iii nitride single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deposition or mixing of impurity crystals generated by natural nucleus production into a grown single crystal in a method of growing a group III nitride single crystal using a flux. <P>SOLUTION: A group III nitride single crystal 4 is grown by immersing a seed crystal 3 in a growth source melt 5 containing a flux. A deposition preventing means 6 to prevent impurity crystals 2 generated by natural nucleus production from depositing on the seed crystal 3 is provided between a gas-liquid interface 5A of the growth source melt 5 containing the flux and the seed crystal 3. The deposition preventing means 6 is, for example, a mesh, a punched plate or a porous body. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for growing a group III nitride single crystal such as a gallium nitride single crystal by a so-called flux method. The term “single crystal” as used herein does not mean a single crystal in scientific terms, but means a single crystal that is used to broadly classify the state of a solid substance such as polycrystal or amorphous (amorphous). Including those including crystal defects such as voids, twins, low-angle grain boundaries, and grain boundaries.

  Gallium nitride single crystal substrates are attracting attention as excellent blue light emitting device substrates and are expected as blue-violet semiconductor laser devices for optical pickups, high-speed electronic devices, and power device substrates. Aluminum nitride has a large band gap of 6.2 eV and high thermal conductivity, and is therefore excellent as a substrate material for light emitting elements (LEDs, LDs) in the ultraviolet region, and development of single crystal wafer manufacturing technology is desired. ing.

In Patent Document 1, a crystal growth vessel is provided in a reaction vessel, and a Group III metal and an alkali metal melt are accommodated in the crystal growth vessel. Then, the crystal growth container is divided into an upper part and a lower part by a mesh. GaN is accommodated on the upper side of the mesh, and a mixed melt of an alkali metal melt and a Group III metal is accommodated on the lower part of the mesh. And if the temperature in a container is raised, GaN will decompose | disassemble into Ga and N on a mesh. The produced Ga and N pass through the mesh, are supplied to the Na melt at the bottom of the container, react in the Na melt, and grow GaN crystals.
JP 2003-160399 A

Patent Document 2 discloses that the density of a mixed melt containing an alkali metal and Ga is larger than the density of a GaN crystal to be grown. Thus, when a GaN crystal generated in the melt grows, the GaN crystal is prevented from sinking into the melt, thereby trying to grow a large crystal near the melt surface.
JP2003-313097

  The present inventor uses a flux containing a Group III raw material and an alkali metal or an alkaline earth metal to seed a Group III nitride single crystal such as a GaN crystal on a template substrate or a Group III nitride single crystal free-standing substrate. Tried to nurture. However, when the crystal size is increased, unnecessary crystals called so-called miscellaneous crystals generated by the generation of natural nuclei may adhere to the single crystal. The miscellaneous crystal is a crystal that is made of, for example, a GaN single crystal but cannot be used because the crystal orientation and shape are different from the desired single crystal. The miscellaneous crystals, for example, not only adhere to a predetermined single crystal, but may be embedded in the single crystal, and for this reason, it is difficult to remove from the single crystal by processing such as polishing. Single crystal becomes defective.

  An object of the present invention is to prevent adhesion and mixing of miscellaneous crystals into a grown single crystal in a method of growing a group III nitride single crystal using a seed crystal by a flux method.

  The present invention is a method for growing a group III nitride single crystal using a seed crystal by a flux method, and prevents adhesion of miscellaneous crystals generated by the generation of natural nuclei to the seed crystal around the seed crystal. The present invention relates to a method for growing a group III nitride single crystal, characterized in that a prevention means is provided.

  The present inventor has examined the reason why miscellaneous crystals are attached or included in a single crystal grown on a seed crystal. As a result, for example, as shown in FIG. 1, even when the seed crystal 3 is immersed in the bottom of the crucible 1, the miscellaneous crystal 2 generated by the generation of natural nuclei is in the vicinity of the gas-liquid interface 5A of the melt 5. It was discovered that it descended as shown by arrow A. The miscellaneous crystals 2 generated by the generation of natural nuclei descending from the vicinity of the gas-liquid interface 5A toward the bottom adhere to the growing crystal 4.

  Based on such knowledge, the present inventor has provided the means 6 for preventing adhesion of crystals generated by the generation of natural nuclei to the single crystal around the seed crystal 3, so that the single crystal of the miscellaneous crystal 2 generated by the generation of natural nuclei is provided. It was conceived to prevent adhesion to the crystal 4. In such an invention, the discovery of the problem of adhesion of miscellaneous crystals 2 generated by the generation of natural nuclei on the single crystal 4 and the occurrence location of miscellaneous crystals 2 generated by the generation of natural nuclei adhering to the single crystal 4 are, for example, flux This is possible only after the gas-liquid interface 5A in the vicinity of 5 is found out.

  In Patent Document 1, the mesh is disposed in a space on the surface of the melt, and is not in contact with the melt. Then, Ga and N generated in the space above the mesh pass through the mesh and flow into the melt below the mesh. In Patent Document 2, the density of the mixed melt containing an alkali metal and Ga is made larger than the density of the GaN crystal to be grown, thereby growing a large single crystal in the vicinity of the gas-liquid interface. I'm trying to do it. No seed crystal is used, and the crystal itself generated by the generation of natural nuclei generated near the gas-liquid interface is the target single crystal.

Hereinafter, the present invention will be described in more detail with reference to the drawings as appropriate.
Typically, as schematically shown in FIG. 1, a flux 5 is generated in the crucible 1 and a predetermined seed crystal 3 is immersed therein. Then, an adhesion preventing means 6 is provided between the seed crystal 3 and the gas-liquid interface 5A to prevent the miscellaneous crystal 2 from adhering to the single crystal 4 caused by the generation of natural nuclei generated near the gas-liquid interface.

  The seed crystal 3 only needs to be immersed in the flux 5. That is, the seed crystal 3 may be suspended in the flux 5 or may be held in the flux 5 by some holding means. Moreover, the seed crystal 3 may be sunk in the bottom part of the flux 5, as shown in FIG.

  The means 6 for preventing the adhering of the miscellaneous crystal 2 caused by the generation of natural nuclei on the seed crystal 3 is not particularly limited. In a preferred embodiment, the adhesion preventing means 6 has a shape that does not permeate crystals formed by natural nucleation through the melt. As such a material, a perforated plate such as a net or punching metal, or a porous body is preferable.

  Further, the material of the adhesion preventing means is not limited, but it is desirable that the adhesion preventing means does not react with the melt at the reaction temperature. From this point of view, refractory metals such as tantalum, tungsten, and molybdenum and two or more alloys of these refractory metals can be cited. A metal coated with a carbide such as tantalum carbide or tungsten carbide can also be used. In addition, ceramics such as alumina, yttria, titanium nitride, and zirconium nitride can also be used. Platinum melted into the flux.

  When the adhesion preventing means is a mesh, the diameter of the opening of the mesh is preferably 5 mm or less in order to prevent adhesion of miscellaneous crystals, and more than 100 microns for the passage of the melt. Preferably there is. When the adhesion preventing means is a perforated plate such as punching metal, the diameter of the opening of the hole is preferably 5 mm or less to prevent adhesion of miscellaneous crystals, and also for the passage of the melt. Is preferably 0.1 mm or more.

In the present invention, a seed crystal composed of a group III nitride single crystal is used. This seed crystal may be a single crystal, or a base film 3 made of a group III nitride single crystal formed on the substrate 10 may be used. The material of the substrate 10 is not particularly limited, but perovskite-type composites such as sapphire, SiC single crystal, MgO single crystal, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , LaAlO ₃ , LaGaO ₃ , NdGaO _3, etc. An oxide can be illustrated. The composition formula _{[A 1-y (Sr 1-} x Ba x) y ] _{[(Al 1-z Ga z)} 1-u · D u ] _O 3 (A is a rare earth element; D is niobium and One or more elements selected from the group consisting of tantalum; y = 0.3-0.98; x = 0-1; z = 0-1; u = 0.15-0.49; x + z = 0 .1 to 2) cubic perovskite structure composite oxides can also be used. SCAM (ScAlMgO ₄ ) can also be used.

  The seed crystal, particularly the group III nitride single crystal constituting the base film, is a nitride of one or more metals selected from Ga, Al, and In, such as GaN, AlN, AlGaN, and GaAlInN. Preferred are GaN, AlN, AlGaN, and GaN / AlN multilayer films.

  The group III nitride single crystal for the purpose of growth is a nitride of one or more metals selected from Ga, Al, and In, such as GaN, AlN, GaAlN, and GaAlInN. Particularly preferred are GaN, AlGaN, and AlN.

  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.

  As the aluminum raw material, an aluminum simple metal, an aluminum alloy, and an aluminum compound can be applied, but an aluminum simple metal is also preferable in terms of handling.

  As the indium raw material, indium simple metal, indium alloy, and indium compound can be applied, but indium simple metal is preferable from the viewpoint of handling.

Moreover, the following elements can be contained in the flux.
Sodium, lithium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, tin, silicon (Si)
Moreover, these nitrides can be used.
The flux is not limited to a metal flux, and may be a non-metallic flux such as sodium azide or calcium nitride.

  Gases other than nitrogen in the growing atmosphere are not limited, but inert gases are 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.

  The actual training method in the present invention is not particularly limited. For example, the template substrate can be immersed in a flux in a crucible, the crucible can be accommodated in a pressure resistant container, and heated while supplying a nitrogen-containing atmosphere in the pressure resistant container.

  The growth temperature in the reaction vessel of the present invention is not particularly limited, and is appropriately set according to the type of single crystal to be grown.

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.

  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 can be grown under an atmosphere composed of a mixed gas containing nitrogen gas, for example, 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. Moreover, by setting the total pressure of the atmosphere to 300 atm or more and 2000 atm or less, it is easy to suppress evaporation of the flux and hold the growing solution in the crucible. However, it is not essential that the total pressure is within this range.

  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.

  There is no particular upper limit on the growth temperature of the gallium nitride single crystal, but if the growth temperature is too high, the evaporation of the flux becomes violent, so it is preferably set to 1200 ° C. or lower.

By providing the means for preventing the adhesion of miscellaneous crystals, the diffusion of nitrogen dissolved in the flux may be hindered or the group III metal raw material may not be mixed uniformly in the flux. In this case, it takes time to grow a single crystal. There is a possibility that it will be hindered and growth will be hindered. In such a case, forcibly mixing the growth materials solves problems such as inhibiting the diffusion of nitrogen dissolved in the growth materials and reducing the crystal growth rate due to the fact that Group III metal materials are not mixed uniformly in the flux. can do. As means for forcibly mixing the growing raw materials, the following is preferable.
(1) Stirring means such as a stir bar, stirring blade, baffle plate and the like are placed in a container in which the raw material is placed and mechanically driven to stir the raw material.
(2) The raw materials in the container are mixed by rotating the container.
(3) The materials in the container are mixed by swinging the container.
(4) The raw materials in the container are mixed by applying vibration to the container.
(5) By providing a temperature difference in the raw material container, the raw materials are mixed by generating thermal convection in the growing raw material in the container.
(6) The raw materials in the container are mixed by blowing an air current on the raw material container.

(Growth of AlN single crystal)
The present invention is also useful when growing an AlN single crystal by pressurizing a flux melt containing at least aluminum in a nitrogen-containing atmosphere under specific conditions.

Example 1
As schematically shown in FIG. 1, a GaN single crystal was grown on a seed substrate. Specifically, metal Na, metal Ga, and metal Li were weighed in a glove box so that the molar ratio was Na: Ga: Li = 73: 27: 1. These raw materials were filled in an alumina crucible having an inner diameter of φ80 mm. The height of the raw material melt was about 15 mm. As the seed crystal, a φ2 inch AlN template substrate, GaN template substrate, or GaN single crystal free-standing substrate was used. The crucible 1 was placed horizontally at the bottom of the crucible 1 so that the single crystal thin film of the template faced up or the Ga surface of the GaN single crystal free-standing substrate faced up. The AlN template substrate is a substrate obtained by epitaxially growing an AlN single crystal thin film on a sapphire substrate by 1 micron, and the GaN template substrate is a substrate obtained by epitaxially growing a GaN single crystal thin film on a sapphire substrate by 3 microns.

  A metal tantalum mesh 6 (aperture size 1 mm: wire diameter φ0.2 mm) was placed so as to cover the template substrate 3. The crucible 1 was placed in a stainless steel pressure vessel, heated and pressurized to 900 ° C. and 100 atm for 1 hour using nitrogen gas, and held at 900 ° C. for 100 hours. Subsequently, after naturally cooling to room temperature, the crucible 1 was taken out from the pressure vessel and treated in ethanol to dissolve Na and Li. Thereafter, it was immersed in hot water of about 35 ° C., the remaining Ga was removed, and the GaN single crystal 4 was taken out. The GaN single crystal 4 had a size of φ2 inches, a thickness of about 3 mm, and a substantially circular shape. On the GaN single crystal 4, uptake and adhesion of microcrystals were not observed, and macro defects such as cracks were not observed. FIG. 4 shows a schematic external view of the obtained single crystal 4.

(Example 2)
The experiment was conducted in the same manner as in Example 1. However, the material of the mesh 6 was tungsten metal. As a result, a GaN single crystal having substantially the same shape and size as in Example 1 was obtained. On the GaN single crystal 4, uptake and adhesion of microcrystals were not observed, and macro defects such as cracks were not observed.

(Example 3)
The experiment was conducted in the same manner as in Example 1. However, the material of the mesh 6 was molybdenum metal. As a result, a GaN single crystal having substantially the same shape and size as in Example 1 was obtained. On the GaN single crystal 4, uptake and adhesion of microcrystals were not observed, and macro defects such as cracks were not observed.

Example 4
The experiment was conducted in the same manner as in Example 1. However, the crystal was grown while the reaction vessel was swung. As a result, a GaN single crystal having substantially the same shape and size was obtained in a shorter time than Example 1. On the GaN single crystal 4, uptake and adhesion of microcrystals were not observed, and macro defects such as cracks were not observed.

(Example 5)
As schematically shown in FIG. 2, a GaN single crystal was grown on a seed substrate. Specifically, metal Na, metal Ga, and metal Li were weighed in a glove box so that the molar ratio was Na: Ga: Li = 73: 27: 1. These raw materials were filled in an alumina crucible having an inner diameter of 180 mm. The height of the raw material melt 5 was about 60 mm. Ten AlN templates having a diameter of 2 inches were used as seed crystals, and 10 sheets were arranged in a direction substantially perpendicular to the gas-liquid interface 5A. The periphery of the seed crystal was covered with punching metal 6 (made of metal Ta, hole diameter 5 mm, hole period 7 mm). The growth temperature was 1100 ° C., the partial pressure of nitrogen was 300 atmospheres, and the total pressure was 800 atmospheres using argon. When held for 20 hours, a GaN single crystal 4 of about 0.5 mm grew on the entire surface of the seed crystal substrate. Adhesion and uptake of miscellaneous crystals were not seen in all 10 sheets.

(Example 6)
As schematically shown in FIG. 3, a GaN single crystal was grown on a seed substrate. Specifically, metal Na, metal Ga, and metal Li were weighed in a glove box so that the molar ratio was Na: Ga: Li = 73: 27: 1. These raw materials were filled into an alumina crucible having an inner diameter of 100 mm. The height of the raw material melt 5 was about 15 mm. A 2 inch diameter AlN template or GaN single crystal free-standing substrate is used as a seed crystal, and is horizontally in the vicinity of the gas-liquid interface 5A. In the case of a template, the single crystal thin film surface is faced down. Arranged. The periphery of the seed crystal was surrounded by porous yttria ceramic. When the seed crystal substrate was held at 950 ° C. and 100 atm for 50 hours while rotating at a speed of 20 rpm, a GaN single crystal of about 2 mm grew on the entire surface of the seed crystal substrate. There was no adhesion or uptake of miscellaneous crystals.

(Comparative Example 1)
The experiment was performed in the same manner as in Example 1 except that the mesh 6 was not arranged. As a result, a GaN single crystal having substantially the same shape and size as in Example 1 was obtained. However, as shown in the schematic schematic diagram of FIG. 5, several to ten microcrystals 12 (crystals generated by the generation of natural nuclei) are attached to the surface of the GaN single crystal. The microcrystals 11 were taken in and integrated. .

It is a schematic diagram for demonstrating the cultivation method Example 1 of this invention. It is a schematic diagram for demonstrating the cultivation method Example 4 of this invention. It is a schematic diagram for demonstrating the cultivation method Example 5 of this invention. It is a schematic diagram which shows the external appearance of the single crystal obtained in the Example of this invention. It is a schematic diagram which shows the external appearance of the single crystal obtained by the comparative example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Crucible 2 The miscellaneous crystal generated by the natural nucleus generation | occurrence | production in the gas-liquid interface 5A vicinity 2A The miscellaneous crystal generated by the natural nucleus capture | acquired by the adhesion prevention means 6 3 Seed crystal 4 The grown single crystal 5 Flux 5A Gas-liquid Interface 6 Adhesion prevention means 10 Substrate 11 Crystal generated by natural nucleation introduced into the grown single crystal 12 Crystal generated by natural nucleation attached to the surface of the grown single crystal A Miscellaneous miscellaneous generated by natural nucleation Settling direction of crystals

Claims (15)

A method for growing a group III nitride single crystal using a flux,
A method for growing a group III nitride single crystal, characterized in that an adhesion preventing means for preventing adhesion of a crystal generated by generation of natural nuclei to the seed crystal is provided around the seed crystal. The method according to claim 1, wherein the seed crystal is a group III nitride single crystal.   3. The method according to claim 1, wherein the seed crystal is a group III nitride single crystal formed on a substrate.   The said adhesion prevention means has a shape which does not allow the crystal | crystallization produced by the said natural nucleus generation | occurrence | production to pass the said flux, The Claim 1 characterized by the above-mentioned. Method.   The method according to any one of claims 1 to 4, wherein the adhesion preventing means is selected from the group consisting of a net, a perforated plate, and a porous body.   6. The grown Group III nitride single crystal is selected from the group consisting of gallium nitride, aluminum nitride, and a solid solution of gallium nitride and aluminum nitride. The method of claim. The method according to any one of claims 1 to 6, further comprising means for preventing diffusion inhibition of nitrogen in the growing raw material due to the provision of the adhesion preventing means.   The method according to claim 1, wherein a growing raw material is mixed when growing the group III nitride single crystal. 9. The method according to claim 8, wherein the growing raw material is mixed by rocking a container in which the growing raw material is placed.   The method according to claim 8, wherein the growing raw material is mixed by rotating a container containing the growing raw material. The method according to claim 8, wherein the growing raw material is mixed by thermal convection. The method according to claim 8, wherein the growing raw material is mixed by disposing a stirring means in a container containing the growing raw material. The method according to claim 8, wherein the growing raw material is mixed by an air flow. The method according to claim 8, wherein the growing raw material is mixed by vibration.   A group III nitride single crystal grown by the method according to any one of claims 1 to 14.

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