JP4493427B2 - Method for producing group III nitride single crystal - Google Patents

Description

  The present invention relates to a method and apparatus for producing a group III nitride single crystal.

  Group III nitride semiconductors centered on GaN-based compound semiconductors are characterized by higher electron mobility and a larger band gap than silicon semiconductors. For this reason, group III nitride semiconductors have been the subject of much research as materials for HEMTs (High Electron Mobility Transistors) and blue LEDs (Light Emitting Diodes) with excellent high frequency characteristics. It was.

  Such a GaN-based compound is often produced by heteroepitaxial growth on a substrate such as sapphire or SiC using MOCVD (Metal Organic Chemical Vapor Deposition). However, since the lattice mismatch and thermal expansion coefficient difference between GaN-based compounds and these substrates are large, a high-quality epitaxial layer can be obtained even if the desired GaN-based compound is directly formed on these substrates. I can't.

  For this reason, it has been studied to produce a group III nitride semiconductor device by adopting a group III nitride single crystal itself as a substrate and homoepitaxially growing the group III nitride on the substrate. For this purpose, various methods for growing high-quality group III nitride single crystals have been studied. For example, Patent Document 1 discloses a technique for growing a GaN single crystal by pressure control in a high-pressure solution growth method using Ga melt.

WO99 / 34037

  However, in the technique of Patent Document 1, the size and growth rate of the GaN single crystal are industrially insufficient, which contributes to the short life and cost increase of the GaN-based compound semiconductor element.

  The present invention has been made to solve this problem, and an object thereof is to provide a manufacturing method and a manufacturing apparatus for growing a high-quality GaN single crystal at a high speed and in a large area.

In order to solve the above-mentioned problems, the invention of claim 1 is a method for producing a group III nitride single crystal that is crystal-grown on a flat substrate by a liquid phase epitaxial growth method. A generating step for generating a combined financial solution by heating, a dissolving step for dissolving the nitrogen element-containing gas in the combined financial solution using a nitrogen element-containing gas pressurized to 2000 atm or more, and the holding container are arranged The atmosphere in the apparatus is replaced with nitrogen gas, and the atmosphere replacement process for bringing the inside of the apparatus into an airtight state, and sapphire, AlN, GaN, AlGaN, at any timing before, after, and simultaneously with the melting process, A dipping step of immersing a base material made of any of SiC in the compound financial solution and a growth step of epitaxially growing a group III nitride single crystal on the base material after the dipping step are provided. The combined liquid is composed of a first melt component containing one or more group III metals and one alkali metal or one alkaline earth metal, and a flux that lowers the melting point of the first melt component. The second melt component is contained.

  According to a second aspect of the present invention, in the method for producing a group III nitride single crystal according to the first aspect, the second melt component is sodium.

  The invention according to claim 3 is the method for producing a group III nitride single crystal according to claim 1 or claim 2, wherein the combined financial liquid includes the first melt component and the second melt component. Contains a third melt component containing one or more different metals.

  The invention of claim 4 is the method for producing a group III nitride single crystal according to any one of claims 1 to 3, wherein the surface of the base material on which the group III nitride single crystal is epitaxially grown is III. The group nitride layer is epitaxially formed in advance.

  Further, the invention of claim 5 is the method for producing a group III nitride single crystal according to claim 4, wherein the group III nitride layer contains Al at 50 atomic% or more in all group III elements. It is a layer.

According to the first to fifth aspects of the present invention, a high-quality, large-area group III nitride single crystal can be grown at high speed.

  Moreover, according to the invention of claim 5, it is possible to suppress the crack of the group III nitride single crystal.

The method for producing a group III nitride single crystal according to the present embodiment is a liquid phase epitaxial growth method in which a group III nitride single crystal is grown on a substrate immersed in a melt. In the present embodiment, the melt is a combined financial liquid composed of at least two components,
a) a first component serving as a supply source of the group III metal constituting the group III nitride single crystal;
b) It contains a second component made of an alkali metal or alkaline earth metal that serves as a flux that lowers the melting point of the Group III metal.

  The first component is a group III metal (more specifically, one or more metals selected from gallium, aluminum, and indium). In particular, gallium is also used for efficiently melting aluminum in the flux. Is preferably contained in a molar fraction of 50% or more.

  The second component is one kind of alkali metal or alkali metal, typically sodium.

In addition, a nitrogen element-containing gas serving as a nitrogen supply source constituting the group III nitride single crystal is dissolved in the combined financial liquid by pressurization. Nitrogen (N ₂ ), ammonia (NH ₃ ), or the like is preferably used as the nitrogen element-containing gas. Further, the nitrogen element-containing gas is pressurized to 2000 atm or more and dissolved in the combined financial liquid. More preferably, the solubility of the nitrogen element-containing gas can be further increased by pressurizing to 5000 atm or higher.

  Further, the solubility of the nitrogen element-containing gas is remarkably improved by adding the third component metal. Therefore, the growth rate of the group III nitride single crystal can be remarkably improved by pressurizing the nitrogen element-containing gas to 2000 atm or more with the third component added. The third component is a metal other than the first component and the second component, and is typically an alkaline earth metal such as calcium or copper. Note that the metal added as the third component added here has no effect when used in a small amount to be used for impurity gettering.

  Here, when the flux as the third component is introduced, the molar ratio of the second component to the third component in the flux is in the range of second component: third component = 99.9: 0.1-50: 50. It is desirable that the molar ratio between the first component and the second component + third component (flux component) in the combined financial liquid is: first component: (second component + third component) = 0.1: It is desirable to be within the range of 99.9-50: 50. This is because by selecting such a melt composition, it is possible to grow a particularly high-quality group III nitride single crystal at a high speed.

In this embodiment, sapphire, ZnO, LiAlO ₂ , LiGaO ₂ , MgAl ₂ O ₄ , MgO, (La, Sr) (Al, Ta) O ₃ are used as the surface for epitaxial growth of the group III nitride single crystal. Group IV or IV-IV single crystal typified by oxide single crystal Si, SiC, representative compound semiconductor single crystal typified by GaAs, Group III nitride typified by AlN, GaN, AlGaN Surfaces such as single crystal substrates such as crystals and boride single crystals represented by ZrB ₂ , and substrates obtained by epitaxially growing a predetermined single crystal layer on these single crystal substrates in advance can be used. The selection of the single crystal substrate is appropriately selected according to the growth conditions of the single crystal. However, the higher the growth temperature, the higher the growth rate and the higher the crystallinity. It is desirable to select a material having a higher melting point, such as AlN, GaN, AlGaN, or SiC. From the viewpoint of increasing the size, a sapphire substrate or a SiC substrate is most desirable because a substrate having a diameter of 2 inches or more can be easily obtained commercially.

It is desirable to use a group III nitride single crystal layer as the single crystal layer epitaxially grown on the single crystal substrate. This is because the lattice constant mismatch existing between the single crystal substrate and the group III nitride single crystal to be grown can be effectively relaxed and the crystal quality can be improved. For example, an (Al _x Ga _y ) N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y = 1) layer (with a crystallinity of 20 nm to 30 nm) formed at 400 ° C. to 600 ° C. by MOCVD. A low-temperature buffer layer), a GaN layer formed at 1000 ° C. or higher by the MOCVD method on the low-temperature buffer layer, or (Al _x Ga _y ) N having a thickness of 0.2 μm or more formed at 1100 ° C. or higher by the MOCVD method. (0.5 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, x + y = 1) layer (high-temperature buffer layer with high crystallinity) can be employed. In this case, from the viewpoint of improving the surface flatness, it is desirable that the main surface of the group III nitride single crystal layer is a (0001) plane (C plane).

In particular, among the epitaxially grown single crystal layers, the latter high crystallinity high temperature (Al _x Ga _y ) N buffer layer can be used to effectively suppress the occurrence of group III nitride single crystal cracks, The quality can be improved more easily. This is because the tensile stress generated in the single crystal can be suppressed as the Al composition of the layer to be epitaxially grown is larger than that of the single crystal to be grown. In particular, when a high temperature AlN buffer layer is employed, this effect can be utilized to the maximum. (In the case of x = 1 in the above formula) In order to improve the quality of a single crystal to be grown, a high temperature grown directly or via a surface nitride film using a sapphire single crystal or a SiC single crystal for the substrate 2 It is desirable to use an (Al _x Ga _y ) N buffer layer (x + y = 1, 1 ≧ x ≧ 0.5). In this case, the half width of the X-ray rocking curve of the (002) plane of the single crystal layer to be epitaxially grown can be easily set to 200 seconds or less, and the crystal quality of the single crystal grown thereon can be improved. Note that the half width of this X-ray rocking curve cannot be easily realized when the low-temperature buffer layer having low crystallinity is used.

Further, when a high temperature (Al _x Ga _y ) N buffer layer is used, the thickness is preferably 0.4 μm or more. It is possible to effectively suppress pits, which are defects generated on the surface, and furthermore, a film having a surface flatness that allows atomic steps to be clearly confirmed (surface roughness ra: 3 mm), which is desirable for group III nitride single crystal growth. This is because the following can be realized. Below, the specific Example of the manufacturing apparatus used for the manufacturing method of the group III nitride single crystal which concerns on this Embodiment, and the said manufacturing method is demonstrated.

<Manufacturing equipment>
-1st aspect of manufacturing apparatus;
A first aspect of the apparatus for producing a group III nitride single crystal according to the embodiment will be described with reference to the cross-sectional view of FIG.

  The manufacturing apparatus 1 includes a bottomed cylindrical high-pressure vessel 4 having a gas introduction port 2 and a gas exhaust port 3. The stainless steel high-pressure vessel 4 can maintain an airtight state even when the internal pressure becomes 2000 atmospheres or more. A nitrogen gas supply source 6 is connected to the gas inlet 2 via a pressurizing device 5. The pressurizing device 5 has the ability to pressurize the internal pressure of the high-pressure vessel 4 to 2000 atmospheres or more. The gas exhaust port 3 is connected to an exhaust treatment device (not shown) via a valve 7. When the valve 7 is open, the gas inside the high-pressure vessel 4 is naturally exhausted.

  Inside the high-pressure vessel 4 is provided a reaction vessel 8 capable of holding the melt M used during the growth of the group III nitride single crystal. The reaction vessel 8 is made of boron nitride ceramics and has a heat resistant temperature of 1000 ° C. or higher.

  Furthermore, an electric heater 9 for heating the contents of the reaction vessel 8 is provided inside the high-pressure vessel 4.

  Moreover, in the manufacturing apparatus 1, the upper cover part 4a and the main-body part 4b of the high pressure container 4 are detachable. Then, operations such as charging the contents into the reaction vessel 8 are performed in a state where the upper lid portion 4a and the main body portion 4b are separated. Further, when the upper lid portion 4a and the main body portion 4b are joined, the gap portion 4c between the upper lid portion 4a and the main body portion 4b is sealed with a metal gasket. Even if it rises, the airtight state of the high pressure vessel 4 is maintained.

  An elevating mechanism 11 that elevates and lowers the jig 10 that holds the base materials S1 to S4 is provided inside the high-pressure vessel 4. The elevating mechanism 11 is installed in a fixed state with respect to the high-pressure vessel 4. The jig 10 connected to the elevating mechanism 11 can be immersed in the melt M inside the reaction vessel 8 and pulled up from the melt M according to an instruction from the outside of the high-pressure vessel 4. ing. In FIG. 1, a state in which the jig 10 is immersed in the melt M is illustrated.

  The jig 10 includes base material bases 10a to 10d on which the base materials S1 to S4 are placed. The bases 10a to 10d are held at a predetermined distance L in the vertical direction by the support pillar 10e. Thus, industrial productivity can be remarkably improved by enabling several base material S1-S4 to be immersed in the melt M simultaneously. The predetermined distance interval L is not particularly limited as long as it is within a range that does not hinder the growth of the single crystal on the base materials S1 to S4. Further, the number of substrate bases is not limited to four, and may be three or less or five or more.

○ Second aspect of the manufacturing apparatus;
A second mode of the group III nitride single crystal manufacturing apparatus according to the embodiment will be described with reference to the cross-sectional view of FIG.

  The manufacturing apparatus 21 includes a covered cylindrical high-pressure vessel 24 having a gas introduction port 22 and a gas exhaust port 23. A pressure piston 25 is provided at the bottom of the high-pressure vessel 24 and can slide in the cylindrical axis direction while maintaining airtightness. In the manufacturing apparatus 21, the internal pressure of the high-pressure vessel 24 can be increased by moving the pressure piston 25 in the inner direction DI of the high-pressure vessel 24. A nitrogen gas supply source 28 is connected to the gas inlet 22 via a valve 26 and a pressurizing device 27. The pressurizing device 27 also has the ability to pressurize the internal pressure of the high-pressure vessel 24 to 2000 atmospheres or more, like the pressurizing device 5 of the manufacturing apparatus 1. The gas exhaust port 23 is connected to an exhaust processing device (not shown) via a valve 29. And in the manufacturing apparatus 21, when the valve | bulb 29 is an open state, the gas inside the high pressure vessel 24 is naturally exhausted.

  Inside the high-pressure vessel 24, boards 29a to 29d capable of holding the melt M used when the group III nitride single crystal is grown are provided. The boards 29a to 29d are made of boron nitride ceramics and have a heat resistant temperature of 1000 ° C. or higher. The boards 29 a to 29 d are held inside the high-pressure vessel 24 using the support member 31. When the group III nitride single crystal is grown, the substrates S5 to S8 are placed in the melts M inside the boards 29a to 29d.

  Furthermore, an electric heater 30 for heating the entire high-pressure vessel 24 is provided outside the high-pressure vessel 24.

<Example>
Embodiments according to the present invention will be described below.

○ Preparation of the substrate;
Here, preparation of various base materials (seed crystals) for growing a group III nitride single crystal will be described with reference to a cross-sectional view of the base material in FIG.

-About the base material Sa-
First, a substantially circular (0001) 6H—SiC single crystal substrate (400 μm thick) 100 having a diameter of 2 inches was prepared. Prior to the formation of the buffer layer 101 on the Si surface which is the main surface of the 6H—SiC single crystal substrate 100 (the surface on which the group III nitride single crystal is formed), the 6H—SiC single crystal substrate 100 is formed using buffered hydrofluoric acid. Was washed. Next, thermal cleaning was performed by heating the 6H—SiC single crystal substrate 100 to 1200 ° C. and holding it for 10 minutes in hydrogen gas having an average flow velocity of 2 m / sec (FIG. 3A).

Subsequently, an AlN buffer layer 101 is formed on the clean surface of the 6H—SiC single crystal substrate 100 obtained by cleaning and thermal cleaning by MOCVD. Prior to the formation of the buffer layer, the substrate surface is nitrided in ammonia gas, and the buffer layer 101 is formed by trimethylaluminum gas (Al (CH ₃ ) ₃ ) and ammonia gas (NH ₃ ) having an average flow rate of 2 m / sec. The 6H—SiC single crystal substrate 100 was heated to 1200 ° C. at a molar ratio of trimethylaluminum gas to ammonia gas of 1: 100 in a mixed gas of hydrogen gas. As a result, an AlN buffer layer 101 having a layer thickness of 0.5 μm was formed on the 6H—SiC single crystal substrate 100. Hereinafter, the base material S thus obtained is referred to as a base material Sa. In addition, when the base material Sa prepared in this way was evaluated, the half width of the X-ray rocking curve of the (0002) plane of the AlN layer was 100 seconds, and the arithmetic surface roughness (Ra) of a square area of 5 μm square. Was 1.5 Å. Further, when the surface of the substrate Sa was observed with an atomic force microscope, the presence of atomic steps was confirmed.

-About the substrate Sb-
A substantially circular (0001) plane sapphire single crystal substrate (430 μm thick) 200 having a diameter of 2 inches was prepared. Next, thermal cleaning was performed by heating the sapphire single crystal substrate 200 to 1200 ° C. and holding it for 10 minutes in hydrogen gas having an average flow velocity of 2 m / sec (FIG. 3A).

Subsequently, an AlN buffer layer 201 is formed on the clean surface of the sapphire single crystal substrate 200 obtained by cleaning and thermal cleaning by MOCVD. Prior to the formation of the buffer layer, the substrate surface is nitrided in ammonia gas, and the buffer layer 201 is formed by trimethylaluminum gas (Al (CH ₃ ) ₃ ) and ammonia gas (NH ₃ ) having an average flow rate of 2 m / sec. The sapphire single crystal substrate 200 was heated to 1200 ° C. with a molar ratio of trimethylaluminum gas and ammonia gas of 1: 100 in a mixed gas of hydrogen gas. As a result, an AlN buffer layer 201 having a layer thickness of 1.0 μm was formed on the sapphire single crystal substrate 200. Hereinafter, the base material S thus obtained is referred to as a base material Sb. In addition, when the base material Sb prepared in this way was evaluated, the half width of the X-ray rocking curve of the (0002) plane of the AlN layer was 70 seconds, and the arithmetic surface roughness (Ra) of a 5 μm square area. Was 1.5 Å. Further, when the surface of the substrate Sb was observed with an atomic force microscope, the presence of atomic steps was confirmed.

-About the base material Sc-
A substantially circular (0001) plane sapphire single crystal substrate (430 μm thick) 300 having a diameter of 2 inches was prepared. Next, thermal cleaning was performed by heating the sapphire single crystal substrate 300 to 1200 ° C. and holding it for 10 minutes in hydrogen gas having an average flow velocity of 2 m / sec (FIG. 3A).

Subsequently, a GaN buffer layer 301 is formed on the clean surface of the sapphire single crystal substrate 300 obtained by cleaning and thermal cleaning by MOCVD. Prior to formation of the buffer layer, trimethylgallium gas (Ga (CH ₃ ) ₃ ), trimethylaluminum gas (Al (CH ₃ ) ₃ ), ammonia gas (NH ₃ ), and hydrogen gas at an average flow rate of 2 m / sec at 600 ° C. A buffer layer made of AlGaN having a low crystallinity of 25 nm is once formed in the mixed gas of GaN, and the GaN buffer layer 301 is formed in a mixed gas of trimethylgallium gas, ammonia gas, and hydrogen gas having an average flow velocity of 2 m / sec. The sapphire single crystal substrate 300 was heated to 1080 ° C. with a molar ratio of trimethylgallium gas and ammonia gas of 1: 1000. As a result, a GaN buffer layer 301 having a layer thickness of 3.0 μm was formed on the sapphire single crystal substrate 300. Hereinafter, the base material S thus obtained is referred to as a base material Sc. When the base material Sc thus prepared was evaluated, the half-value width of the X-ray rocking curve of the (0002) plane of the GaN layer was 250 seconds, and the arithmetic surface roughness (Ra) of a square area of 5 μm square. Was 3.5 angstroms. Moreover, when the surface of the base material Sc was observed with an atomic force microscope, the presence of atomic steps was confirmed.

○ Liquid phase epitaxial growth;
Hereinafter, Examples 1 to 4 relating to liquid phase epitaxial growth will be described.

<Example 1>
In Example 1, a procedure for liquid phase epitaxial growth of a GaN single crystal using the manufacturing apparatus 1 and the base materials Sa, Sb, and Sc described above will be described.

  First, the atmosphere inside and around the manufacturing apparatus 1 was replaced with dry nitrogen gas. Thereafter, the upper lid portion 4a and the main body portion 4b of the high-pressure vessel 4 were separated, and the jig 10 was pulled up to the uppermost end using the lifting device 11.

  Next, metal gallium and metal sodium (first flux) were weighed so as to have a molar ratio of 90:10 and charged into the reaction vessel 8 as contents. The base material S (S1 to S4) was placed on the base material bases 10a to 10d of the jig 10. At this time, the substrate S is placed on the substrate tables 10a to 10d so that the epitaxial growth surface of the substrate S is on the upper side, that is, the surface opposite to the epitaxial growth surface is in contact with the substrate table. .

  Subsequently, while continuing the atmosphere replacement with nitrogen gas, the upper lid portion 4a and the main body portion 4b were joined to bring the high-pressure vessel 4 into an airtight state. Then, the internal pressure of the nitrogen gas inside the high-pressure vessel 4 was increased to 3000 atmospheres using the pressurizing device 5. Subsequently, electric power was supplied to the heater 9, and the temperature of the contents of the reaction vessel 8 was heated from near room temperature to 900 ° C., and metal gallium and metal sodium were melted to produce a combined financial liquid.

  After the formation of the combined financial liquid, the lifting / lowering device 11 was driven again to immerse the jig 10 in the melt M. Thereby, the epitaxial growth surface of the base materials S1 to S4 and the melt M are brought into contact with each other. In this state, the temperature was kept at 900 ° C. for 24 hours, and then the lifting / lowering device 11 was driven again to lift the jig 10 from the melt M.

  After the completion of the pulling up, power supply to the heater 9 was stopped to naturally cool the high-pressure vessel 4 to room temperature, and the valve 7 was opened to reduce the internal pressure of the high-pressure vessel 4 to 1 atmosphere. Thereafter, the upper lid portion 4a and the main body portion 4b of the high-pressure vessel 4 were separated, and the base materials S1 to S4 were collected. When the recovered base materials S1 to S4 were observed, a GaN single crystal having an average thickness of about 5 mm was grown on the base material.

<Example 2>
In Example 1, a procedure for liquid phase epitaxial growth of a GaN single crystal using the manufacturing apparatus 1 and the base materials Sa, Sb, and Sc described above will be described.

  First, the atmosphere inside and around the manufacturing apparatus 1 was replaced with dry nitrogen gas. Thereafter, the upper lid portion 4a and the main body portion 4b of the high-pressure vessel 4 were separated, and the jig 10 was pulled up to the uppermost end using the lifting device 11.

  Next, metallic gallium, metallic sodium (first flux) and metallic calcium (second flux) are weighed so as to have a molar ratio of 80:10:10 and charged into the reaction vessel 8 as contents. did. The base material S (S1 to S4) was placed on the base material bases 10a to 10d of the jig 10. At this time, the substrate S is placed on the substrate tables 10a to 10d so that the epitaxial growth surface of the substrate S is on the upper side, that is, the surface opposite to the epitaxial growth surface is in contact with the substrate table. .

  Subsequently, while continuing the atmosphere replacement with nitrogen gas, the upper lid portion 4a and the main body portion 4b were joined to bring the high-pressure vessel 4 into an airtight state. Then, the internal pressure of the nitrogen gas inside the high-pressure vessel 4 was increased to 3000 atmospheres using the pressurizing device 5. Subsequently, electric power was supplied to the heater 9, and the temperature of the contents of the reaction vessel 8 was heated from near room temperature to 900 ° C., and the combined liquid was produced by melting metallic gallium, metallic sodium and metallic calcium.

  After the formation of the combined financial liquid, the lifting / lowering device 11 was driven again to immerse the jig 10 in the melt M. Thereby, the epitaxial growth surface of the base materials S1 to S4 and the melt M are brought into contact with each other. In this state, the temperature was kept at 900 ° C. for 24 hours, and then the lifting / lowering device 11 was driven again to lift the jig 10 from the melt M.

  After the completion of the pulling up, power supply to the heater 9 was stopped to naturally cool the high-pressure vessel 4 to room temperature, and the valve 7 was opened to reduce the internal pressure of the high-pressure vessel 4 to 1 atmosphere. Thereafter, the upper lid portion 4a and the main body portion 4b of the high-pressure vessel 4 were separated, and the base materials S1 to S4 were collected. As a result of observing the recovered base materials S1 to S4, a GaN single crystal having an average thickness of about 10 mm was grown on the base material.

<Example 3>
In Example 3, a procedure of liquid phase epitaxial growth of a GaN single crystal using the manufacturing apparatus 21 and the base materials Sa, Sb, and Sc described above will be described.

  First, the atmosphere inside and around the manufacturing apparatus 21 was replaced with dry nitrogen gas. Thereafter, the pressure piston 25 was once separated from the high pressure vessel 24, and the base material S (S5 to S8) was placed on the bottoms of the boards 29a to 29d. At this time, the substrate S is placed so that the epitaxial growth surface of the substrate S is on the upper side, that is, the surface opposite to the epitaxial growth surface is in contact with the bottoms of the boards 29a to 29d.

  Further, metallic gallium, metallic sodium (first flux) and metallic calcium (second flux) are weighed so that the molar ratio is 80:10:10, and are put into the boards 29a to 29d as contents. did.

  Subsequently, the pressure piston 25 was reattached to the high-pressure vessel 24 while continuing the atmosphere replacement with nitrogen gas, and the inside of the high-pressure vessel 24 was made airtight. Then, the internal pressure of the nitrogen gas inside the high-pressure vessel 24 was increased to about 10,000 atmospheres using the pressurizing device 27. Subsequently, electric power was supplied to the heater 30 to heat the contents of the boards 29a to 29d from near room temperature to 900 ° C., and metallic gallium, metallic sodium and metallic calcium were dissolved to produce a combined financial liquid. . As a result, the epitaxial growth surfaces of the base materials S5 to S8 and the melt M are brought into contact with each other. In this state, the pressure piston 25 is moved in the inner direction DI of the high-pressure vessel 24 to further increase the internal pressure of the high-pressure vessel 24, and a GaN single crystal is deposited on the epitaxial growth surfaces of the base materials S5 to S8 over 12 hours. .

  After completion of these series of steps, the power supply to the heater 30 was stopped to naturally cool the high-pressure vessel 4 to room temperature, and the valve 29 was opened to reduce the internal pressure of the high-pressure vessel 24 to 1 atm. Thereafter, the pressure piston 25 was separated from the high-pressure vessel 24 again, and the base materials S5 to S8 were collected. When the recovered base materials S5 to S8 were observed, an average of about 10 mm of GaN single crystal was grown on the base material.

<Example 4>
In Example 4, the procedure of liquid phase epitaxial growth of an AlGaN single crystal using the manufacturing apparatus 21 and the base materials Sa, Sb, and Sc described above will be described.

  First, the atmosphere inside and around the manufacturing apparatus 21 was replaced with dry nitrogen gas. Thereafter, the pressure piston 25 was once separated from the high pressure vessel 24, and the base material S (S5 to S8) was placed on the bottoms of the boards 29a to 29d. At this time, the substrate S is placed so that the epitaxial growth surface of the substrate S is on the upper side, that is, the surface opposite to the epitaxial growth surface is in contact with the bottoms of the boards 29a to 29d.

  Further, Group III metal, metallic sodium (first flux) and metallic calcium (second flux) are weighed so that the molar ratio is 80:10:10, and are contained in the boards 29a to 29d as contents. I put it in. In the group III metal, the composition of Al and Ga is appropriately changed in accordance with the composition of the finally formed AlGaN single crystal.

  Subsequently, the pressure piston 25 was reattached to the high-pressure vessel 24 while continuing the atmosphere replacement with nitrogen gas, and the inside of the high-pressure vessel 24 was made airtight. Then, the internal pressure of the nitrogen gas inside the high-pressure vessel 24 was increased to about 10,000 atmospheres using the pressurizing device 27. Subsequently, power is supplied to the heater 30 to heat the contents of the boards 29a to 29d from near room temperature to 1000 ° C., and the metallic gallium, metallic aluminum, metallic sodium and metallic calcium are dissolved to form a combined financial liquid. Was generated. As a result, the epitaxial growth surfaces of the base materials S5 to S8 and the melt M are brought into contact with each other. In this state, the pressurizing piston 25 is moved in the inner direction DI of the high-pressure vessel 24 to further increase the internal pressure of the high-pressure vessel 24, and AlGaN single crystals were deposited on the epitaxial growth surfaces of the substrates S5 to S8 over 12 hours. .

  After completion of these series of steps, the power supply to the heater 30 was stopped to naturally cool the high-pressure vessel 4 to room temperature, and the valve 29 was opened to reduce the internal pressure of the high-pressure vessel 24 to 1 atm. Thereafter, the pressure piston 25 was separated from the high-pressure vessel 24 again, and the base materials S5 to S8 were collected. When the recovered base materials S5 to S8 were observed, an average AlGaN single crystal of about 10 mm was grown on the base material. At this time, good single crystals could be grown on the substrates Sa and Sb, but cracks were generated in the single crystals on the substrate Sc.

<Comparative Example 1>
Comparative examples outside the scope of the present invention will be described below.

  In Comparative Example 1, a GaN single crystal was produced in the same manner as in Example 1 except that the nitrogen gas pressure in Example 1 was reduced from 3000 atmospheres to 50 atmospheres. In this case, an average of about 1 mm thick GaN single crystal was grown on the substrate.

<Comparative example 2>
In Comparative Example 2, a GaN single crystal was produced in the same manner as in Example 1 except that only Ga was used as the molten metal in Example 1 described above. In this case, an average of about 1 mm thick GaN single crystal was grown on the substrate.

<Contrast between Example and Comparative Example>
As described above, in Example 1, Example 2 and Example 3 according to the present invention, each of the GaN single crystals is about five times as compared with Comparative Examples 1 and 2 outside the scope of the present invention. It was possible to grow at a speed of about 10 times or about 20 times. Moreover, in Example 4, it was possible to grow an AlGaN single crystal at a rate substantially the same as that of Example 3, and using an AlN epitaxial film at that time was effective in suppressing cracks. As shown in Example 1 and Comparative Example 1, by making the pressure of nitrogen gas from 50 atm to 2000 atm or more, it is possible to significantly improve the growth rate, and as shown in Example 1 and Comparative Example 2, By adding the first flux, it was possible to significantly improve the growth rate. Further, as shown in Examples 2 and 3 and Comparative Example 1, by adding the flux as the third component, it was possible to further improve the growth rate.

<Modification>
In the above-described embodiment, following the pressurization of nitrogen gas, generation of the combined financial liquid by heating and immersion of the base material S in the combined financial liquid were performed, but the execution order of each step is limited to this. Absent. For example, when the flux component is room temperature at room temperature, such as sodium potassium (NaK) alloy, before the formation of a combined liquid by pressurization and heating of nitrogen gas, or the combined financial by pressurization and heating of nitrogen gas Substantially simultaneously with the generation of the liquid, the substrate S may be immersed in the flux.

  Further, prior to the pressurization of the nitrogen gas or almost simultaneously with the pressurization of the nitrogen gas, the combined financial liquid may be generated by heating.

2 is a cross-sectional view of the manufacturing apparatus 1. FIG. 3 is a cross-sectional view of the manufacturing apparatus 21. FIG. It is sectional drawing for demonstrating a process flow.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,21 Manufacturing apparatus 4,24 High pressure vessel 5,27 Pressurization device 8 Reaction vessel 9,30 Heater 11 Lifting device 100 6H-SiC single crystal 200 Sapphire single crystal substrate 101, 201, 301 Buffer layer S, Sa to Sc, S1-S8 Base material M Melt

Claims (5)

A method for producing a group III nitride single crystal, wherein a crystal is grown on a flat substrate by a liquid phase epitaxial growth method,
A generation step of heating the contents of a predetermined holding container to generate a combined financial liquid;
A dissolving step of dissolving the nitrogen element-containing gas in the combined financial liquid using a nitrogen element-containing gas pressurized to 2000 atmospheres or more;
An atmosphere replacement step of replacing the atmosphere in the apparatus in which the holding container is arranged with nitrogen gas to make the inside of the apparatus airtight;
An immersion step of immersing a base material made of any of sapphire, AlN, GaN, AlGaN, and SiC in the combined financial solution at any timing before, after, and simultaneously with the dissolution step;
A growth step of epitaxially growing a group III nitride single crystal on the substrate after the immersion step;
With
The joint financial liquid is
A first melt component containing one or more Group III metals;
A group III nitride unit comprising a second melt component comprising a single alkali metal or a single alkaline earth metal and serving as a flux that lowers the melting point of the first melt component. Crystal production method. In the manufacturing method of the group III nitride single crystal of Claim 1,
The method for producing a group III nitride single crystal, wherein the second melt component is sodium. In the method for producing a group III nitride single crystal according to claim 1 or 2,
The joint financial liquid is
A method for producing a group III nitride single crystal comprising a third melt component containing at least one metal different from the first melt component and the second melt component. In the manufacturing method of the group III nitride single crystal in any one of Claims 1 thru | or 3,
A method for producing a group III nitride single crystal, wherein a group III nitride layer is epitaxially formed in advance on a surface of the base material on which a group III nitride single crystal is epitaxially grown.   5. The method for producing a group III nitride single crystal according to claim 4, wherein the group III nitride layer is a group III nitride layer containing 50 atomic% or more of Al in all group III elements. A method for producing a group nitride single crystal.

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