High-purity gallium trioxide and its manufacturing method

Abstract

This high-purity digallium trioxide comprises digallium trioxide, and one or more impurity elements other than gallium and oxygen, wherein in glow discharge mass spectrometry, the total concentration of the impurity elements is at most 1 mass ppm, and the concentration of silicon, which is one of the impurity elements, is 0.01 mass ppm to 0.1 mass ppm.

Description

[Technical Field]

[0001] The present disclosure relates to high-purity gallium trioxide and methods for producing the same. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2011-153054 (Patent Document 1) discloses a technique for densifying a gallium oxide raw material, which is used as a raw material for producing a gallium oxide single crystal, for the purpose of efficiently producing the gallium oxide single crystal. Examples of the gallium oxide raw material include commercially available gallium oxide or gallium carbonate, oxides or salts of gallium, hydrates thereof, and mixtures thereof. Non-Patent Document 1 below discloses gallium oxide containing 6.6 ppm by mass of silicon (Si) as a raw material for producing a gallium oxide single crystal. Non-Patent Document 2 below discloses the production of a gallium oxide single crystal containing 1.0 to 10 ppm by mass of Si using the so-called VB method. Non-Patent Document 3 below discloses gallium oxide containing 1.7 ppm by mass of silicon (Si) as a raw material for producing a gallium oxide single crystal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-153054 [Non-patent literature]

[0004] [Non-Patent Document 1] M. Saleh et al., Semiconductor Science and Technology, Volume 35, Issue 4, id.04LT01 [Non-patent document 2] K. Hoshikawa et al., Journal of Crystal Growth, Volume 447, 1 August 2016, pages 36-41 [Non-patent document 3] Kuramata Akito et al., Journal of the Japanese Society for Crystal Growth, Vol.44, No.4(2017) 44-4-02 Summary of the Invention

[0005] The high-purity digallium trioxide according to the present disclosure contains digallium trioxide and one or more impurity elements other than gallium and oxygen, and in glow discharge mass spectrometry, the total concentration of the impurity elements is 1 ppm by mass or less, and the concentration of silicon, one of the impurity elements, is 0.01 ppm by mass or more and 0.1 ppm by mass or less.

[0006] A method for producing high-purity digallium trioxide according to the present disclosure includes the steps of preparing molten metallic gallium, filling a crucible with the molten metallic gallium, placing solid boron oxide on the molten metallic gallium in the crucible, heating the crucible to obtain molten boron oxide, sealing the molten metallic gallium with the molten boron oxide, heating the crucible to a temperature of 1200 K or higher and 1600 K or lower, and blowing a gas containing oxygen into the crucible to produce digallium trioxide, and washing the contents of the crucible containing the boron oxide and digallium trioxide with ultrapure water at 60°C or higher to obtain the digallium trioxide. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a flowchart showing an example of a method for producing high-purity digallium trioxide according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating a manufacturing apparatus used in the method for manufacturing high-purity digallium trioxide according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Problem to be solved by this disclosure] The gallium oxide single crystals disclosed in Patent Document 1 and Non-Patent Documents 1-3, etc., particularly the gallium oxide (hereinafter referred to as "digallium trioxide or Ga2O3" in this specification) used as the raw material for digallium trioxide single crystals, have traditionally been Ga2O3 sintered compacts for sputtering targets produced by thermal decomposition of gallium hydroxide. However, since the Ga2O3 sintered compacts are intended for sputtering targets, they must have good sinterability, i.e., fine grains. In other words, because the Ga2O3 sintered compacts are fine grains, they are prone to contamination by impurities adsorbed to the Ga2O3 particle surface or coprecipitation. For example, the Ga2O3 disclosed in Patent Document 1 and Non-Patent Documents 1-3, etc., contain a large amount of Si. According to the inventors' research, the upper limit of the purity of such Ga2O3 is 99.999% by mass.

[0009] In recent years, new applications of Ga2O3 as a semiconductor material have been explored, potentially requiring Ga2O3 with higher purity than conventional materials. However, Ga2O3 with extremely low impurity element concentrations, exceeding the 99.9999 mass% purity generally required for compound semiconductors, has not yet been obtained, and its development is eagerly awaited.

[0010] In view of the above, an object of the present disclosure is to provide high-purity gallium trioxide having an extremely low concentration of impurity elements and thus high purity, and a method for producing the same.

[0011] [Effects of this disclosure] According to the above, it is possible to provide high-purity gallium trioxide having an extremely low concentration of impurity elements and thus high purity, and a method for producing the same.

[0012] [Outline of the embodiment] The following is an overview of embodiments of the present disclosure. The present inventors have conducted extensive research to solve the above-mentioned problems and have completed the present disclosure. First, the present inventors focused on obtaining high-purity Ga2O3 by reacting high-purity metallic gallium (Ga) (hereinafter also referred to as "high-purity Ga") with oxygen (O) in an environment substantially free of foreign matter contamination. Specifically, GaAs polycrystalline bodies used as raw materials in the production of gallium arsenide (GaAs) single crystals have traditionally been produced by reacting high-purity Ga with arsenic, with a purity of approximately 99.9999% by mass. Therefore, the inventors conceived the use of such high-purity Ga as a raw material for obtaining high-purity Ga2O3. Furthermore, the inventors conceived the idea of ​​preventing the introduction of foreign matter by sealing the high-purity Ga filled in a container with boron oxide (BO3), which is virtually unreactive with metallic Ga. This finding led to the discovery that high-purity Ga2O3 with a purity exceeding 99.9999% by mass can be produced from high-purity Ga, leading to the present disclosure.

[0013] Next, embodiments of the present disclosure will be listed and described. [1] High-purity digallium trioxide according to one embodiment of the present disclosure contains digallium trioxide and one or more impurity elements other than gallium and oxygen, and by glow discharge mass spectrometry, the total concentration of the impurity elements is 1 ppm by mass or less, and the concentration of silicon, one of the impurity elements, is 0.01 ppm by mass or more and 0.1 ppm by mass or less. Ga2O3 with these characteristics has an extremely low concentration of impurity elements, and therefore can be highly pure.

[0014] [2] In the glow discharge mass spectrometry, the concentration of boron, which is another of the impurity elements, is preferably 0.01 mass ppm or more and 0.5 mass ppm or less, and the concentrations of lithium, sodium, magnesium, aluminum, phosphorus, sulfur, potassium, calcium, chromium, manganese, iron, nickel, copper, zinc, niobium, molybdenum, silver, cadmium, tin, tungsten, lead, and bismuth are each preferably less than 0.01 mass ppm. This makes it possible to provide Ga2O3 with extremely low concentrations of various impurity elements, including boron (B), and with higher purity.

[0015] [3] The purity of the high-purity gallium trioxide is preferably 99.99995% by mass or more, thereby providing Ga2O3 with even higher purity.

[0016] [4] The high-purity gallium trioxide is preferably polycrystalline, which makes it possible to provide high-purity Ga2O3 as a polycrystalline substance.

[0017] [5] In the glow discharge mass spectrometry, the silicon concentration is preferably 0.01 mass ppm or more and 0.05 mass ppm or less, thereby providing high-purity Ga2O3 with an extremely low Si concentration.

[0018] [6] In the glow discharge mass spectrometry, the concentration of boron, which is another of the impurity elements, is preferably 0.01 mass ppm or more and 0.2 mass ppm or less, thereby providing high-purity Ga2O3 with an extremely low B concentration.

[0019] [7] A method for producing high-purity digallium trioxide according to one embodiment of the present disclosure includes the steps of preparing molten metallic gallium, filling a crucible with the molten metallic gallium, disposing solid boron oxide on the molten metallic gallium in the crucible, heating the crucible to obtain molten boron oxide, sealing the molten metallic gallium with the molten boron oxide, heating the crucible to a temperature of 1200 K or higher and 1600 K or lower, and blowing an oxygen-containing gas into the crucible to produce digallium trioxide, and rinsing the contents of the crucible containing the boron oxide and digallium trioxide with ultrapure water at 60° C. or higher to obtain the digallium trioxide. This production method has the following characteristics: Ga2O3 with extremely low impurity element concentrations and therefore high purity can be obtained.

[0020] [8] The high-purity gallium trioxide is preferably polycrystalline, which allows for the production of high-purity Ga2O3 polycrystalline bodies.

[0021] [9] In the step of producing digallium trioxide, the crucible is preferably heated to a temperature of 1200 K or more and 1400 K or less. This makes it possible to obtain Ga2O3 with higher purity.

[0022]

[10] The oxygen-containing gas is preferably a mixed gas consisting of 10 mass % or more of oxygen and the remainder nitrogen, or pure oxygen, which allows for the production of high-purity Ga2O3 with good yield.

[0023]

[11] The purity of the metallic gallium is preferably 99.9999% by mass or more, which allows high-purity Ga2O3 to be obtained with good yield.

[0024]

[12] The purity of the boron oxide is preferably 99.999% by mass or more, which allows high-purity Ga2O3 to be obtained in good yield.

[0025] [Details of the embodiment] An embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described in further detail below, but the present disclosure is not limited thereto. The following description may be made with reference to the drawings, and the same or corresponding elements in the present specification and drawings will be designated by the same reference numerals, and the same description will not be repeated. Furthermore, the scale of the drawings has been adjusted appropriately to facilitate understanding of each component, and the scale of each component shown in the drawings does not necessarily coincide with the scale of the actual component.

[0026] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and only a unit is specified for B, the unit of A and the unit of B are the same. Furthermore, when compounds and the like are expressed in this specification by chemical formulas, unless the atomic ratio is particularly limited, it is understood that any conventionally known atomic ratios are included, and they should not necessarily be limited to only those within a stoichiometric range.

[0027] [High-purity gallium trioxide (Ga2O3)] The high-purity gallium trioxide (Ga2O3) according to this embodiment has the following characteristics. Specifically, the high-purity Ga2O3 contains Ga2O3 and one or more impurity elements other than gallium (Ga) and oxygen (O). In glow discharge mass spectrometry (GDMS), the total concentration of the impurity elements is 1 mass ppm or less, and the concentration of silicon (Si), one of the impurity elements, is 0.01 mass ppm or more and 0.1 mass ppm or less. In particular, the purity of the high-purity Ga2O3 is preferably 99.99995 mass% or more. The purity of the high-purity Ga2O3 is more preferably 99.99998 mass% or more. High-purity Ga2O3 with these characteristics has an extremely low concentration of impurity elements, and therefore can be highly pure. High-purity Ga2O3 contains Ga2O3 at an extremely high purity, or in other words, it can be said to be a composition containing Ga2O3 and one or more impurity elements other than Ga and O.

[0028] <Polycrystalline> The high-purity Ga2O3 is preferably polycrystalline. This is because the high-purity Ga2O3 has coarse particles, which can prevent contamination due to an increase in specific surface area. Specifically, the high-purity Ga2O3 preferably has at least a crystal grain having an average grain size of 1 μm or more, constituting the polycrystalline body. Furthermore, the high-purity Ga2O3 may be single crystal. When the purity of the high-purity Ga2O3 exceeds 99.9999% by mass, the average grain size may be less than 1 μm.

[0029] When the high-purity Ga2O3 is polycrystalline, the average grain size of the crystal grains constituting the polycrystalline body can be directly measured using a scanning electron microscope (SEM). First, a powder of high-purity Ga2O3 to be measured is obtained, for example, according to the manufacturing method of high-purity Ga2O3 described below. Next, the powder is directly attached to conductive tape, and the particle size of the high-purity Ga2O3 on the conductive tape is observed using SEM. In this case, the measurement conditions can be an acceleration voltage of 5 kV and an observation magnification of 10,000 times. The particle sizes of at least 100 Ga2O3 particles present on the conductive tape are measured, and the average value can be determined as the average grain size of the crystal grains constituting the polycrystalline body.

[0030] <Concentration of impurity elements other than gallium (Ga) and oxygen (O)> The high-purity GaO contains GaO as described above and one or more impurity elements other than gallium (Ga) and oxygen (O). In the high-purity GaO, the total concentration of impurity elements other than Ga and O is 1 ppm by mass or less, and the concentration of Si, one of the impurity elements, is 0.01 ppm by mass or more and 0.1 ppm by mass or less in GDMS. If the total concentration of impurity elements other than Ga and O exceeds 1 ppm by mass, or if the concentration of Si exceeds 0.1 ppm by mass, it becomes difficult to obtain the high-purity GaO as intended by the present disclosure.

[0031] The high-purity Ga2O3 preferably further has the following characteristics: In the GDMS, the concentration of Si is preferably 0.01 mass ppm or more and 0.05 mass ppm or less. In the GDMS, the concentration of boron (B), which is another of the impurity elements, is preferably 0.01 mass ppm or more and 0.5 mass ppm or less, and the concentrations of lithium (Li), sodium (Na), magnesium (Mg), aluminum (Al), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), niobium (Nb), molybdenum (Mo), silver (Ag), cadmium (Cd), tin (Sn), tungsten (W), lead (Pb), and bismuth (Bi) are each preferably less than 0.01 mass ppm. In particular, the B concentration in the GDMS is preferably 0.01 mass ppm or more and 0.2 mass ppm or less, which allows the high-purity Ga2O3 to have extremely low concentrations of various impurity elements, including Si and B, and therefore achieve a higher purity.

[0032] In the high-purity GaO, the concentrations of the above-mentioned various impurity elements other than Ga and O being less than 0.01 ppm by mass means that they are below the lower detection limit in the GDMS. In other words, a preferred embodiment of the high-purity GaO means that Li, Na, Mg, Al, P, S, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Nb, Mo, Ag, Cd, Sn, W, Pb, and Bi are not detected in the GDMS. In the above high purity Ga2O3, cesium (Cs), barium (Ba), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Yb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), hafnium (Hf), gold (Au), mercury (Hg), It is further preferred that the various impurity elements, thorium (Th), uranium (U), beryllium (Be), scandium (Sc), titanium (Ti), vanadium (V), cobalt (Co), germanium (Ge), arsenic (As), selenium (Se), strontium (Sr), yttrium (Y), zirconium (Zr), antimony (Sb), iodine (I), and tellurium (Te), are also below the lower detection limit in the GDMS.

[0033] Glow Discharge Mass Spectrometry (GDMS) The following describes a method for analyzing the composition of the high-purity Ga2O3 using glow discharge mass spectrometry (GDMS). GDMS involves generating a glow discharge plasma in a high-purity argon atmosphere using the sample as the cathode, sputtering the surface of the sample in the plasma, and then measuring the ionized constituent elements of the sample using a mass spectrometer. This technique allows for the qualitative and quantitative analysis of impurity elements other than Ga and O contained in the high-purity Ga2O3. It also allows for the determination of the purity of the high-purity Ga2O3. Two types of ion sources can be used for the GDMS: a flat cell and a pin-shaped cell. The pin-shaped cell is suitable for samples that can be formed into strips approximately 2 mm square and 20 mm long. Specifically, it is used for analyzing Si single crystals, gallium arsenide (GaAs) single crystals, and indium phosphide (InP) single crystals, which can be prepared by cleavage. The flat cell is suitable for samples that can be formed into discs approximately 10 mm in diameter, and is used for analyzing polycrystalline materials, for example. In the composition analysis of the high-purity Ga2O3, it is preferable to use a flat cell. When using a flat cell, by using an auxiliary electrode made of high-purity indium (In) as described below, discharge plasma can be generated even in insulating oxide polycrystalline bodies, making it possible to perform GDMS.

[0034] The GDMS can be prepared, for example, as follows: First, high-purity Ga2O3 is obtained by the manufacturing method described below. This high-purity Ga2O3 can be, for example, polycrystalline. Next, the high-purity Ga2O3 polycrystalline body is applied to a sample placement area (a circle with a diameter of 10 mm, i.e., corresponding to the discharge area) on a high-purity indium auxiliary electrode attached to an analytical device described below. Before applying the high-purity Ga2O3 polycrystalline body to the sample placement area, it is preferable to clean the sample placement area using a conventional method to prevent and remove foreign matter, and then perform pre-sputtering for 60 minutes. The analytical value obtained during pre-sputtering serves as the background.

[0035] Next, GDMS can be performed on the high-purity Ga2O3 polycrystalline body coated on the sample placement surface of the high-purity indium under the following conditions. Regarding impurity elements other than Ga and O, which are constituent elements of the analysis sample, and In, which is the element of the auxiliary electrode, semi-quantitative values ​​can be calculated by correcting the ion intensity ratio between Ga and each element in the impurity element by the relative sensitivity factor (RSF). In this specification, "impurity elements" refers to all elements other than Ga and O that can be analyzed by GDMS. Apparatus: Glow discharge mass spectrometer (product name (product number): VG-9000, manufactured by VG Elemental) Ion source: Flat cell (cooled with liquid nitrogen during analysis) Discharge area: diameter 10mm Discharge gas: High-purity argon (6N grade) Discharge conditions: 2mA, 1kV (constant current mode) Detector: Faraday cup and multiplier Mass resolution: 4000 m / Δm or more (high resolution mode).

[0036] The composition of the high-purity Ga2O3 can be analyzed as described above, thereby enabling qualitative and quantitative analysis of impurity elements other than Ga and O contained in the high-purity Ga2O3. Furthermore, the purity of the high-purity Ga2O3 can be determined based on the quantitative analysis of the impurity elements. In this specification, the "purity" of high-purity Ga2O3 is expressed as a numerical value to the fifth decimal point by rounding off the sixth decimal point, since the detection limit of this GDMS is 0.01 ppm. The purities of metallic gallium and boron oxide, described below, can also be determined using the same method as the composition analysis method for high-purity Ga2O3. Note that the GDMS for metallic gallium does not require a high-purity indium auxiliary electrode; analysis can be performed by casting a 20 mm diameter disk-shaped analytical sample.

[0037] [Method for producing digallium trioxide] The method for producing high-purity digallium trioxide (GaO) according to this embodiment can be, for example, a method for producing high-purity GaO having the above-described characteristics. That is, the method for producing high-purity GaO includes the steps of preparing molten metallic gallium (metallic Ga), filling a crucible with the molten metallic Ga, placing solid boron oxide (BO) on the molten metallic Ga in the crucible, heating the crucible to obtain molten BO, sealing the molten metallic Ga with the molten BO, heating the crucible to a temperature of 1200 K or higher and 1600 K or lower, and blowing a gas containing oxygen (O) into the crucible to produce GaO, and washing the contents of the crucible containing the BO and GaO with ultrapure water at 60°C or higher to obtain the GaO. This manufacturing method has the above characteristics, and therefore it is possible to obtain highly pure Ga2O3 with extremely low concentrations of impurity elements.

[0038] Specifically, the above-mentioned production method preferably includes steps as shown in the flowchart of Fig. 1. Fig. 1 is a flowchart showing an example of a method for producing high-purity digallium trioxide according to this embodiment. 1, the method for producing high-purity GaO includes a step S10 (first step) of preparing molten metallic Ga, a step S20 (second step) of filling a crucible with the molten metallic Ga, a step S30 (third step) of disposing solid BO on the molten metallic Ga in the crucible, a step S40 (fourth step) of heating the crucible to obtain molten BO, a step S50 (fifth step) of sealing the molten metallic Ga with the molten BO, heating the crucible to a temperature of 1200 K or more and 1600 K or less, and blowing a gas containing O into the crucible to produce GaO, and a step S60 (sixth step) of washing the contents of the crucible containing BO and GaO with ultrapure water at 60°C or more to obtain GaO.

[0039] In particular, in the method for producing high-purity GaO, the crucible is preferably heated to a temperature of 1200 K or higher and 1400 K or lower in step S50 of producing GaO. Furthermore, the O-containing gas is preferably a mixed gas consisting of 10% by mass or higher of O and the remainder of nitrogen (N), or pure oxygen. The high-purity GaO obtained by the method is preferably polycrystalline. The inventors conceived the idea of ​​obtaining high-purity GaO by sealing high-purity Ga, which is used as a raw material for GaAs polycrystalline material for producing GaAs single crystals, with approximately 99.9999 mass% purity, sealed with GaO, which does not react with metallic Ga, and then reacting it with O. They discovered that this method enables the production of high-purity GaO with a purity exceeding 99.9999 mass% from the high-purity Ga. Below, an overview of the production apparatus used in the method and details of the method for producing high-purity GaO are described with reference to FIGS. 1 and 2.

[0040] <Manufacturing equipment> FIG. 2 is a schematic diagram illustrating a manufacturing apparatus used in the manufacturing method of high-purity gallium trioxide according to this embodiment. In the manufacturing method of high-purity GaO according to this embodiment, high-purity GaO can be manufactured by using, for example, the manufacturing apparatus shown in FIG. 2. The manufacturing apparatus shown in FIG. 2 includes at least a crucible 4, a crucible-holding stage 8 for holding the crucible 4, a lower shaft 9 for supporting the crucible 4 and the crucible-holding stage 8, a load cell 10 for detecting the weight of the contents in the crucible 4 to monitor the progress of the GaO synthesis reaction, and a heater 1 for heating the crucible 4. The manufacturing apparatus also includes a gas inlet pipe 2 for introducing an O-containing gas 5 into the crucible 4 from the outside. The manufacturing apparatus may include a container 11 for housing the crucible 4, its contents, the crucible-holding stage 8, and the lower shaft 9 to prevent the introduction of foreign matter from the outside. The container 11 can be used without any particular restrictions on size, etc., as long as it can prevent foreign matter from entering from the outside, can accommodate the above-mentioned components such as the crucible 4, and is made of a material that has good heat permeability to the heater 1.

[0041] (crucible) The crucible 4 can function as a reaction site between molten Ga metal and O-containing gas 5 to obtain high-purity GaO. Various materials that can withstand the temperature (specifically, 1200 to 1600 K, i.e., 927 to 1327°C) required for the reaction between molten Ga metal and O-containing gas 5 can be used for the crucible 4. For example, pyrolytic boron nitride (pBN) can be used as the material for the crucible 4. Specifically, the crucible 4 is cylindrical and can contain molten Ga metal. Furthermore, by placing solid BO on the molten Ga metal, solid BO can be contained. The inner diameter of the crucible 4 can be, for example, 75 mm to 150 mm. The solid BO can be converted into molten BO by heating the crucible 4 with a heater 1, which will be described later.

[0042] (Crucible holding stage) The crucible-holding stage 8 is in contact with the bottom of the crucible 4 and holds the crucible 4. The crucible-holding stage 8 may have a cylindrical appearance. The material of the crucible-holding stage 8 is not particularly limited, but may be, for example, quartz, alumina, or silicon carbide.

[0043] (lower axis) Lower shaft 9 supports crucible 4 and crucible-holding stage 8 from below. Lower shaft 9 may be rod-shaped, for example, circular or rectangular in horizontal cross section. Materials that can be used for lower shaft 9 include molybdenum, carbon, and silicon carbide.

[0044] (load cell) Load cell 10 is disposed so as to support lower shaft 9 from below. As a result, load cell 10 can detect an increase in the weight of the contents in crucible 4 due to the production of GaO from molten metal Ga in step S50 of producing GaO, which will be described later. By detecting the weight of the contents with load cell 10, the progress of the GaO synthesis reaction can be monitored in the manufacturing apparatus. Load cell 10 can be prepared, for example, by purchasing it from a commercial source.

[0045] (heater) Heater 1 is installed for the purpose of heating crucible 4. Two heaters 1 are arranged to surround the outer periphery of crucible 4. The output of each heater 1 can be controlled independently. In particular, heater 1 may be configured in multiple stages by dividing each heater 1 into multiple sections perpendicular to the axis of crucible 4. In this case, the output of heater 1 can be controlled independently for each section configured in multiple stages, thereby adjusting the temperature of the content in crucible 4 along the axial direction of crucible 4. Heater 1 can be, for example, a known electric heater.

[0046] Although not shown in the drawings, the manufacturing apparatus may include a thermocouple capable of measuring the temperature of the crucible 4 heated by the heater 1. A plurality of thermocouples may be arranged outside the crucible 4 along the axial direction. For example, a known temperature monitor may be used as the thermocouple.

[0047] (gas introduction pipe) The gas inlet tube 2 is a tube for introducing O-containing gas 5 into the crucible 4 from the outside. By introducing O-containing gas 5 into the crucible 4 through the gas inlet tube 2, metallic Ga molten in the crucible 4 reacts with the O-containing gas 5, thereby obtaining high-purity Ga2O37. The material of the gas inlet tube 2 is not particularly limited, but is preferably a material that does not react with oxygen and metallic Ga, and examples of materials that can be used include quartz and pBN-coated carbon.

[0048] <Details of the manufacturing method for high-purity Ga2O3 (each step included in the manufacturing method for high-purity Ga2O3)> (First step: Step S10 of preparing molten Ga metal) According to the method for producing high-purity GaO according to this embodiment, high-purity GaO can be obtained by carrying out the following steps as shown in FIG. 1. In the method, the first step is step S10 of preparing molten metallic Ga. Specifically, in step S10, commercially available solid metallic Ga is melted in a thermostatic bath at a temperature equal to or higher than the melting point of Ga (e.g., 30°C or higher), thereby preparing the molten metallic Ga. In particular, in this step, commercially available 6N-grade high-purity metallic Ga is preferably used. In other words, the purity of the metallic gallium is preferably 99.9999% by mass or higher. 6N-grade high-purity metallic Ga is commercially available, for example, in a polyethylene container. Therefore, the molten metallic Ga can be prepared by placing the polyethylene container in the thermostatic bath.

[0049] (Second step: Step S20 of filling the crucible with molten Ga metal) Next, in the second step, step S20 is performed to fill the crucible with molten metal Ga. Specifically, in the second step, the molten metal Ga 6 in the polyethylene container prepared in the first step can be filled into the crucible 4 while avoiding the inclusion of foreign matter from the outside. As such a filling method, a conventionally known method can be used.

[0050] (Third step: Step S30 of placing solid B2O3) Next, in the third step, step S30 is performed to place solid B2O3 on the molten metallic Ga in the crucible. Specifically, in the third step, solid B2O3 can be placed on the molten metallic Ga6 filled in the crucible 4 in the second step. Conventionally known methods can be used to place the solid B2O3. It is preferable to use 5N-grade solid B2O3 to obtain high-purity Ga2O3. In other words, the purity of B2O3 is preferably 99.999% by mass or higher. Such high-purity B2O3 is commercially available and can be produced by conventionally known methods.

[0051] (Fourth step: Step S40 of obtaining molten B2O3) Next, in the fourth step, step S40 is performed to obtain molten B2O3 by heating the crucible. Specifically, in the fourth step, the crucible 4 is heated by the heater 1, and the temperature inside the crucible 4 is set to a temperature equal to or higher than the melting point of B2O3 (for example, 500°C or higher), thereby melting B2O3. This results in molten B2O33, which can function as a liquid sealant in the next step.

[0052] (Fifth step: Step S50 of producing Ga2O3) Next, in step S50, the molten Ga metal is sealed with molten B2O3, the crucible is heated to a temperature of 1200 K or higher and 1600 K or lower, and a gas containing O is blown into the crucible to produce Ga2O3. In step S50, the molten Ga metal is sealed with molten B2O33, which acts as a liquid sealant. This prevents foreign matter from entering the Ga metal in the crucible 4 from the outside. Next, the gas introduction tube 2 is inserted into the crucible 4 until its tip penetrates the molten B2O33 and reaches the Ga metal. Furthermore, the crucible 4 is heated by a heater 1 so that the temperature inside the crucible 4 is 1200 K or higher and 1600 K or lower, i.e., 927 to 1327°C, at which point by-products other than Ga2O3 produced by the reaction between metallic Ga and O are unlikely to be produced. Also, a gas 5 containing O is blown into the crucible 4 from the outside via a gas inlet pipe 2. This causes metallic Ga and O to react with each other in the crucible 4 to produce Ga2O3. In step S50 of producing Ga2O3, the crucible is preferably heated to a temperature of 1200 K or higher and 1400 K or lower.

[0053] For the purpose of efficiently producing Ga2O3, the O-containing gas 5 is preferably a mixed gas consisting of 10% or more by mass of oxygen and the remainder nitrogen, or pure oxygen. The flow rate of the O-containing gas 5 blown into the crucible 4 through the gas inlet tube 2 is preferably 10 to 1,000 mL / min. In this process, the molten B2O3 acts as a liquid sealant on the molten metal Ga6, so the O in the O-containing gas 5 can be consumed in the reaction with the metal Ga without leaking outside the crucible 4. In particular, by using the load cell 10 to detect the weight increase in the contents of the crucible 4 due to the production of Ga2O3 and monitoring the progress of the reaction between the metal Ga and O, the O in the O-containing gas 5 can react with 99% or more by mass of the metal Ga, thereby efficiently producing Ga2O37. For example, this process can produce Ga2O37 from molten metal Ga6 with a yield of 99% or more by mass. In this specification, the "yield" of Ga2O3 means the ratio of the amount of Ga2O3 actually obtained to the amount of Ga2O3 theoretically obtained when Ga2O3 is obtained by a chemical reaction from metallic Ga, and is expressed as a percentage.

[0054] (Sixth step: Step S60 of obtaining Ga2O3) Finally, in step S60, the contents of the crucible containing B2O3 and Ga2O3 are washed with ultrapure water at 60°C or higher to obtain Ga2O3. In step S60, the load cell 10 is used to confirm that the reaction between metallic Ga and O has progressed to 99% or more, for example. Then, the introduction of O-containing gas 5 into the crucible 4 via the gas inlet tube 2 is stopped. The crucible 4 heated in step S5 is then cooled to room temperature by an appropriate method so that it can be handled by hand. The crucible 4 containing the Ga2O37 and B2O3-containing contents produced in step S5 is then immersed in ultrapure water at 60°C or higher to wash the Ga2O37 and B2O3-containing contents. Since B2O3 dissolves in the ultrapure water, the ultrapure water can be removed to recover only Ga2O37. In this manner, Ga2O37 can be obtained from the content in the crucible 4. In this specification, "ultrapure water" refers to pure water having an electrical resistivity (specific resistance) of 15 MΩ·cm or more, a TOC (total organic carbon) of less than 50 μg / L, and a particle count of less than 100 particles / L.

[0055] <Action and effect> By performing each of the above steps, high-purity Ga2O37 can be produced. In particular, in the fifth step, the method for producing high-purity Ga2O3 according to this embodiment includes sealing the metallic Ga6 melted in the molten B2O33 and heating the crucible 4 to 1200 to 1600 K, a temperature at which by-products other than Ga2O3 are unlikely to be produced. Then, O-containing gas 5 is blown into the crucible 4 to react the metallic Ga with O, thereby producing Ga2O37. This effectively produces high-purity Ga2O3 (e.g., Ga2O3 having a total impurity element concentration other than Ga and O of 1 ppm by mass or less and an Si concentration of 0.01 ppm by mass or more and 0.1 ppm by mass or less) from the high-purity metallic Ga while preventing the incorporation of foreign matter from the outside. Therefore, this production method allows for the production of high-purity Ga2O3 with extremely low impurity element concentrations and high purity. [Example]

[0056] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. In these examples, high-purity gallium trioxide (high-purity Ga2O3) was produced using a production apparatus such as that shown in Figure 2 and according to the flowchart shown in Figure 1. In the following description, Samples 1 and 2 are examples, and Samples 11 to 14 are comparative examples.

[0057] [Production of Ga2O3] <Sample 1> (1st step) This was prepared by purchasing 10 kg of commercially available 6N grade (purity: 99.99995% by mass or more) high-purity metallic Ga (manufactured by Rasa Kogyo Co., Ltd.) This high-purity metallic Ga was contained in a polyethylene container, and the polyethylene container was placed in a constant temperature bath at 60°C to obtain molten metallic Ga.

[0058] (2nd process) The molten Ga6 metal in the polyethylene container was filled into a crucible 4 having an inner diameter of 100 mm by a known method, taking care to avoid the inclusion of foreign matter from the outside. The height of the molten Ga6 metal in the crucible 4 was 209 mm.

[0059] (3rd step) Subsequently, 500 g of commercially available solid B2O3 (manufactured by Rasa Kogyo Co., Ltd.) was placed by a conventionally known method on top of the molten metal Ga6 in the crucible 4. The purity of this solid B2O3 was confirmed to be 99.999 mass% based on the product label.

[0060] (4th step) Next, the crucible 4 was heated with the heater 1 to a temperature of 800°C, which is higher than the melting point of B2O3, thereby melting the solid B2O3. As a result, molten B2O3 was obtained on the molten metal Ga6 in the crucible 4.

[0061] (5th step) First, the molten Ga metal was sealed with the molten B2O33 in the fourth step. The tip of the gas inlet tube 2 was then inserted into the molten Ga metal, penetrating the molten B2O33. The crucible 4 was heated by the heater 1 so that the temperature inside the crucible 4 was 1200 K. Furthermore, pure oxygen was blown into the crucible 4 from the outside via the gas inlet tube 2 at a flow rate of 10 mL / min as the O-containing gas 5, causing the O in the O-containing gas 5 to react with the Ga metal to produce Ga2O37. As the amount of Ga2O37 produced increased, the position of the tip of the gas inlet tube 2 inserted into the molten Ga metal was adjusted to maximize the reaction between the O in the O-containing gas 5 and the Ga metal.

[0062] (6th step) First, after confirming that the reaction rate of Ga2O3, i.e., the progress of the reaction between O in the O-containing gas 5 and metallic Ga6, had reached 99% or more based on the detection by the load cell 10, the introduction of the O-containing gas 5 into the crucible 4 via the gas inlet tube 2 was stopped. The crucible 4, heated in the fifth step, was cooled by air at a rate of 200 °C / hour until its temperature reached room temperature. Next, the crucible 4 containing the Ga2O37 produced in the fifth step and the contents containing the molten B2O33 was immersed in ultrapure water at 60 °C to wash the contents containing the Ga2O37 and molten B2O33. The ultrapure water was then removed to recover the Ga2O37. This resulted in the production of polycrystalline Ga2O3 (sample 1).

[0063] <Sample 2> In the fifth step, Ga2O3 of sample 2 was obtained in the same manner as sample 1, except that crucible 4 was heated by heater 1 so that the temperature inside crucible 4 reached 1600K.

[0064] <Sample 11> Polycrystalline Ga2O3 for sample 11 was obtained by purchasing commercially available Ga2O3 (purity 99.999 mass%, manufactured by Zhuzhou Keneng New Materials Co., Ltd.).

[0065] <Sample 12> In the fifth step, polycrystalline Ga2O3 of sample 12 was obtained in the same manner as sample 1, except that crucible 4 was heated by heater 1 so that the temperature inside crucible 4 reached 1150K.

[0066] <Sample 13> In the fifth step, polycrystalline Ga2O3 of sample 13 was obtained in the same manner as sample 1, except that crucible 4 was heated by heater 1 so that the temperature inside crucible 4 reached 1650K.

[0067] <Sample 14> Polycrystalline Ga2O3 of sample 14 was obtained in the same manner as sample 1, except that in step 3, solid B2O3 (manufactured by Rasa Kogyo Co., Ltd.) was not placed on the molten metallic Ga6 in the crucible 4, and steps 4, 5, and 6 were performed.

[0068] [Composition analysis by GDMS] The Ga2O3 of Samples 1 to 2 and Samples 11 to 14 was subjected to the composition analysis method using GDMS described above to identify impurity elements other than Ga and O contained in the Ga2O3 and measure their concentrations. The results are shown in Table 1. The concentration of each element shown in Table 1 is in ppm by mass. In Table 1, "<0.01" means that the concentration was below the lower detection limit.

[0069] [Table 1]

[0070] [Consideration] According to Table 1, the Ga2O3 of Samples 1 and 2 had a total concentration of impurity elements other than Ga and O of 1 ppm by mass or less (Sample 1: 0.14 ppm by mass, Sample 2: 0.55 ppm by mass). Furthermore, the concentration of silicon, one of the impurity elements, was 0.01 ppm by mass or more and 0.1 ppm by mass or less (Sample 1: 0.02 ppm by mass, Sample 2: 0.05 ppm by mass). Therefore, the purity of Ga2O3 of Samples 1 and 2 was 99.99995% by mass or more.

[0071] On the other hand, the Ga2O3 of samples 11 to 12 and sample 14 had a total concentration of impurity elements other than Ga and O exceeding 1 mass ppm, or a concentration of silicon, one of the impurity elements, exceeding 0.1 mass ppm. The Ga2O3 of sample 13 was produced by reacting metallic Ga with O at a temperature exceeding 1600 K, and some of the Ga2O3 produced dissolved in B2O3 and disappeared, resulting in a lower yield than samples 1 and 2. As a result, the content of impurity elements increased, and the concentration of silicon, one of the impurity elements, reached 0.43 mass ppm.

[0072] Although the embodiments and examples of the present disclosure have been described above, it is also planned from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined.

[0073] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0074] 1 heater, 2 gas inlet tube, 3 molten boron oxide (B2O3), 4 crucible, 5 gas containing oxygen (O), 6 molten metallic gallium (Ga), 7 digallium trioxide (Ga2O3), 8 crucible holding stage, 9 lower shaft, 10 load cell, 11 container, S10 step of preparing molten metallic Ga, S20 step of filling the crucible with molten metallic Ga, S30 step of arranging solid B2O3, S40 step of obtaining molten B2O3, S50 step of generating Ga2O3, S60 step of obtaining Ga2O3.

Claims

1. containing gallium trioxide and one or more impurity elements other than gallium and oxygen, In glow discharge mass spectrometry, the total concentration of the impurity elements is 1 ppm by mass or less, the concentration of silicon, which is one of the impurity elements, is 0.01 ppm by mass or more and 0.1 ppm by mass or less, and the concentration of boron, which is another of the impurity elements, is 0.01 ppm by mass or more and 0.5 ppm by mass or less.

2. In the glow discharge mass spectrometry, the concentrations of lithium, sodium, magnesium, aluminum, phosphorus, sulfur, potassium, calcium, chromium, manganese, iron, nickel, copper, zinc, niobium, molybdenum, silver, cadmium, tin, tungsten, lead, and bismuth, which are further elements of the impurity elements, are all less than 0.01 mass ppm. The high-purity digallium trioxide according to claim 1.

3. The high-purity digallium trioxide according to claim 1 or claim 2, wherein the purity of the high-purity digallium trioxide is 99.99995% by mass or more.

4. The high-purity digallium trioxide according to claim 1 or 2, wherein the high-purity digallium trioxide is a polycrystalline body.

5. The high-purity gallium trioxide according to claim 1 or 2, wherein, in the glow discharge mass spectrometry, the concentration of silicon is 0.01 mass ppm or more and 0.05 mass ppm or less.

6. 3. The high-purity gallium trioxide according to claim 1 or 2, wherein, in the glow discharge mass spectrometry, the concentration of boron, which is another of the impurity elements, is 0.01 ppm by mass or more and 0.2 ppm by mass or less.

7. providing molten metallic gallium; Filling a crucible with the molten metallic gallium; disposing solid boron oxide on the molten gallium metal in the crucible; heating the crucible to obtain molten boron oxide; a step of sealing the molten metallic gallium with the molten boron oxide, heating the crucible to a temperature of 1200 K or more and 1600 K or less, and blowing a gas containing oxygen into the crucible to produce digallium trioxide; and washing the contents of the crucible containing the boron oxide and the digallium trioxide with ultrapure water at 60°C or higher to obtain the digallium trioxide.

8. The method for producing high-purity digallium trioxide according to claim 7, wherein the high-purity digallium trioxide is a polycrystalline body.

9. The method for producing high-purity digallium trioxide according to claim 7 or 8, wherein the crucible is heated to a temperature of 1200 K or more and 1400 K or less in the step of producing digallium trioxide.

10. The method for producing high-purity gallium trioxide according to claim 7 or 8, wherein the oxygen-containing gas is a mixed gas consisting of 10 mass% or more of oxygen and the remainder nitrogen, or pure oxygen.

11. The method for producing high-purity digallium trioxide according to claim 7 or 8, wherein the purity of the metallic gallium is 99.9999% by mass or more.

12. The method for producing high-purity gallium trioxide according to claim 7 or 8, wherein the purity of the boron oxide is 99.999% by mass or more.

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