High-purity gallium trioxide and manufacturing method thereof

Abstract

A high-purity gallium sesquioxide which contains gallium sesquioxide and one or more impurity elements that are elements other than gallium and oxygen, the total concentration of the impurity elements being 1 ppm by mass or less in glow discharge mass spectrometry, and the concentration of silicon as one of the impurity elements being 0.01 ppm by mass or more and 0.1 ppm by mass or less.

Description

Technical Field

[0001] The invention relates to high-purity gallium trioxide and a preparation method thereof. Background Art

[0002] Japanese Patent Publication No. 2011-153054 (Patent Document 1) discloses a technology for making the gallium oxide raw material, which is the raw material of the gallium oxide single crystal, high-density for the purpose of efficiently manufacturing the gallium oxide single crystal. Examples of the gallium oxide raw material include commercially available gallium oxide or gallium carbonate, gallium oxides or salts, their hydrates, and mixtures thereof. The following non-patent document 1 discloses gallium oxide containing 6.6 mass ppm of silicon (Si) as a raw material for manufacturing gallium oxide single crystals. The following non-patent document 2 discloses the use of the so-called VB method to manufacture gallium oxide single crystals containing 1.0 to 10 mass ppm of Si. The following non-patent document 3 discloses gallium oxide containing 1.7 mass ppm of silicon (Si) as a raw material for manufacturing gallium oxide single crystals.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2011-153054.

[0006] Non-patent literature

[0007] Non-patent document 1: M. Saleh et al., Semiconductor Science and Technology, Volume 35, Issue 4, id.04LT01;

[0008] Non-patent document 2: K. Hoshikawa et al., Journal of Crystal Growth, Volume 447, 1 August 2016, pp. 36-41;

[0009] Non-patent document 3: Kuramata Hiroshi, Journal of the Japan Crystal Growth Society, Vol. 44, No. 4 (2017) 44-4-02. Summary of the invention

[0010] The high-purity gallium trioxide of the present invention contains gallium trioxide and one or more impurity elements other than gallium and oxygen, and in glow discharge mass spectrometry analysis, the total concentration of the above impurity elements is less than 1 mass ppm, and the concentration of silicon as one of the above impurity elements is greater than 0.01 mass ppm and less than 0.1 mass ppm.

[0011] The method for producing high-purity gallium trioxide of the present invention includes: a step of preparing molten metal gallium; a step of filling the molten metal gallium into a crucible; a step of disposing solid boron oxide on the molten metal gallium in the crucible; a step of obtaining molten boron oxide by heating the crucible; a step of sealing the molten metal gallium with the molten boron oxide, heating the crucible to a temperature of 1200K to 1600K, and blowing a gas containing oxygen into the crucible to generate gallium trioxide; and a step of washing the contents containing boron oxide and gallium trioxide in the crucible with ultrapure water at a temperature of 60°C or above to obtain gallium trioxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a flow chart showing an example of a method for producing high-purity gallium trioxide according to the present embodiment.

[0013] Figure 2 This is a schematic diagram for explaining a production apparatus used in the method for producing high-purity gallium trioxide according to the present embodiment. DETAILED DESCRIPTION

[0014] [Problems to be Solved by the Invention]

[0015] As the raw material of gallium oxide (hereinafter referred to as "gallium trioxide or Ga2O3" in this specification) used as the raw material of the gallium oxide single crystal disclosed in the above-mentioned Patent Document 1 and Non-Patent Documents 1 to 3, etc., in particular, the Ga2O3 sintered body for sputtering target manufactured by thermal decomposition of gallium hydroxide has been widely used in the past. However, since the above-mentioned Ga2O3 sintered body is used for sputtering target, it is required to have good sintering property, that is, it is required to be fine particles. That is, since the above-mentioned Ga2O3 sintered body is fine particles, it is easy to be contaminated by impurities adsorbed and co-precipitated on the surface of Ga2O3 particles. For example, a large amount of Si is mixed in the Ga2O3 disclosed in the above-mentioned Patent Document 1 and Non-Patent Documents 1 to 3, etc. According to the research of the present inventors, the purity of such Ga2O3 is 99.999% by mass as the upper limit.

[0016] In recent years, new uses of Ga2O3 as a semiconductor material have been studied, and higher purity Ga2O3 than ever before may be required. On the other hand, as a compound semiconductor, Ga2O3 with extremely low concentrations of impurity elements exceeding the generally required purity of 99.9999 mass % has not yet been obtained, and its development is urgently needed.

[0017] In view of the above problems, an object of the present invention 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.

[0018] [Effects of the Invention]

[0019] 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.

[0020] [Overview of Embodiments]

[0021] Hereinafter, an outline of the embodiments of the present invention will be described. The inventors of the present invention have repeatedly conducted in-depth research to solve the above-mentioned problems and have completed the present invention. First, the inventors of the present invention focused on obtaining high-purity Ga2O3 by reacting high-purity metal gallium (Ga) (hereinafter also referred to as "high-purity Ga") with oxygen (O) in an environment where there is substantially no foreign matter mixed in. Specifically, since GaAs polycrystals used as raw materials in the manufacture of gallium arsenide (GaAs) single crystals were previously manufactured by reacting high-purity Ga with a purity of about 99.9999% by mass with arsenic, it was thought of using the high-purity Ga as a raw material for obtaining high-purity Ga2O3. It was further thought of avoiding the mixing of foreign matter by sealing the high-purity Ga filled in a container with boron oxide (B2O3) that hardly reacts with metal Ga. It was thus found that high-purity Ga2O3 with a purity exceeding 99.9999% by mass could be manufactured from high-purity Ga, thereby completing the present invention.

[0022] Next, embodiments of the present invention are listed and described for explanation.

[0023] [1] One embodiment of the high-purity gallium trioxide of the present invention contains gallium trioxide and one or more impurity elements other than gallium and oxygen, wherein the total concentration of the impurity elements is 1 mass ppm or less in glow discharge mass spectrometry, and the concentration of silicon as one of the impurity elements is 0.01 mass ppm or more and 0.1 mass ppm or less. Ga2O3 having such characteristics has an extremely low concentration of impurity elements and can therefore be of high purity.

[0024] [2] In the above-mentioned glow discharge mass spectrometry analysis, it is preferred that the concentration of boron as another of the above-mentioned impurity elements is 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 all less than 0.01 mass ppm. This can provide Ga2O3 with extremely low concentrations of multiple impurity elements, including boron (B), and higher purity.

[0025] [3] The purity of the high-purity gallium trioxide is preferably 99.99995% by mass or more. This can provide Ga2O3 with higher purity.

[0026] [4] The high-purity gallium trioxide is preferably a polycrystalline material. Thus, high-purity Ga2O3 can be provided as a polycrystalline material.

[0027] [5] In the above-mentioned glow discharge mass spectrometry, the concentration of the above-mentioned silicon is preferably not less than 0.01 mass ppm and not more than 0.05 mass ppm. This can provide high-purity Ga2O3 with an extremely low Si concentration.

[0028] [6] In the above-mentioned glow discharge mass spectrometry, the concentration of boron as another impurity element is preferably 0.01 mass ppm or more and 0.2 mass ppm or less. This can provide high-purity Ga2O3 with an extremely low B concentration.

[0029] [7] A method for producing high-purity gallium trioxide according to one embodiment of the present invention includes: preparing molten metal gallium; filling the molten metal gallium into a crucible; placing solid boron oxide on the molten metal gallium in the crucible; heating the crucible to obtain molten boron oxide; sealing the molten metal gallium with the molten boron oxide, heating the crucible to a temperature of 1200K or higher and 1600K or lower, and blowing a gas containing oxygen into the crucible to produce gallium trioxide; and washing the contents containing the boron oxide and gallium trioxide in the crucible with ultrapure water at 60°C or higher to obtain gallium trioxide. By using such a production method, it is possible to obtain Ga2O3 having an extremely low concentration of impurity elements and thus high purity.

[0030] [8] The high-purity gallium trioxide is preferably polycrystalline. Thus, a high-purity Ga2O3 polycrystalline can be obtained.

[0031] [9] In the step of generating gallium trioxide, the crucible is preferably heated to a temperature of 1200 K or higher and 1400 K or lower. This can produce Ga2O3 of higher purity.

[0032]

[10] The oxygen-containing gas is preferably a mixed gas consisting of 10 mass % or more of oxygen and the remainder of nitrogen, or pure oxygen. This allows high-purity Ga2O3 to be obtained in good yield.

[0033]

[11] The purity of the above-mentioned metal gallium is preferably 99.9999% by mass or more. This allows high-purity Ga2O3 to be obtained in good yield.

[0034]

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

[0035] [Details of implementation method]

[0036] Hereinafter, one embodiment of the present invention (hereinafter also referred to as "this embodiment") will be described in more detail, but the present invention is not limited thereto. Figure 1 In the present specification and the drawings, the same or corresponding elements are given the same reference numerals, and the same description is not repeated for them. Furthermore, in the drawings, the scales are appropriately adjusted to facilitate the understanding of each component, and the scales of each component shown in the drawings may not be consistent with the scales of the actual components.

[0037] In this specification, the description in the form of "A to B" refers to the upper and lower limits of the range (i.e., greater than A and less than B). When no unit is described in A and only a unit is described in B, the unit of A is the same as the unit of B. Furthermore, in this specification, when a compound is represented by a chemical formula, when the atomic ratio is not particularly limited, all conventionally known atomic ratios are included, and it is not necessarily limited to the atomic ratio within the stoichiometric range.

[0038] [High-purity gallium trioxide (Ga2O3)]

[0039] The high-purity gallium trioxide (Ga2O3) of this embodiment has the following characteristics. That is, 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 above impurity elements is less than 1 mass ppm, and the concentration of silicon (Si) as one of the above impurity elements is greater than 0.01 mass ppm and less than 0.1 mass ppm. In particular, the purity of the above high-purity Ga2O3 is preferably greater than 99.99995 mass%. The purity of the above high-purity Ga2O3 is more preferably greater than 99.99998 mass%. With regard to the high-purity Ga2O3 having such characteristics, the concentration of its impurity elements is extremely low, so it can be highly pure. Although the high-purity Ga2O3 contains Ga2O3 with extremely high purity, it can be said to be a composition containing Ga2O3 and one or more impurity elements other than Ga and O.

[0040] <Polycrystalline>

[0041] The high-purity Ga2O3 is preferably a polycrystalline. This is because the high-purity Ga2O3 is a coarse particle, which can prevent contamination associated with an increase in specific surface area. Specifically, the high-purity Ga2O3 preferably has an average particle size of at least 1 μm or more of the grains constituting its polycrystalline. Furthermore, the high-purity Ga2O3 may also be a single crystal. When the purity of the high-purity Ga2O3 exceeds 99.9999% by mass, the average particle size may also be less than 1 μm.

[0042] In the case where the above-mentioned high-purity Ga2O3 is a polycrystal, the average particle size of the grains constituting the above-mentioned polycrystal can be directly measured by using a scanning electron microscope (Scanning Electron Microscope: SEM). First, according to the manufacturing method of high-purity Ga2O3, for example, described later, a powder of high-purity Ga2O3 as the measurement object is obtained. Then, the above-mentioned powder is directly pasted on a conductive tape, and the particle size of the high-purity Ga2O3 on the above-mentioned conductive tape is observed by SEM. In this case, the measurement conditions can be set to an acceleration voltage of 5 kV and an observation magnification of 10,000 times. The particle size of at least 100 Ga2O3 present on the above-mentioned conductive tape can be measured, and the average value thereof is calculated as the average particle size of the grains constituting the above-mentioned polycrystal.

[0043] <Concentration of impurity elements other than gallium (Ga) and oxygen (O)>

[0044] As described above, the high-purity Ga2O3 contains Ga2O3 and one or more impurity elements other than gallium (Ga) and oxygen (O). In GDMS, the total concentration of impurity elements other than Ga and O in the high-purity Ga2O3 is 1 mass ppm or less, and the concentration of Si as one of the impurity elements is 0.01 mass ppm or more and 0.1 mass ppm or less. In the high-purity Ga2O3, when the total concentration of impurity elements other than Ga and O exceeds 1 mass ppm, or when the concentration of Si exceeds 0.1 mass ppm, it is difficult to obtain the high purity desired by the present invention.

[0045] The above-mentioned high-purity Ga2O3 preferably also has the following characteristics. That is, in the GDMS, the concentration of Si is preferably greater than 0.01 mass ppm and less than 0.05 mass ppm. In the above-mentioned GDMS, it is preferred that: the concentration of boron (B) as another of the above-mentioned impurity elements is greater than 0.01 mass ppm and less than 0.5 mass ppm, 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 all less than 0.01 mass ppm. In particular, in the above-mentioned GDMS, the concentration of B is preferably greater than 0.01 mass ppm and less than 0.2 mass ppm. Therefore, in the case of high-purity Ga2O3, the concentrations of various impurity elements, led by Si and B, are extremely low, so it can be of higher purity.

[0046] Here, in the high-purity Ga2O3, the concentration of the above-mentioned various impurity elements other than Ga and O is less than 0.01 mass ppm, which means that it is less than the detection limit in the GDMS. In other words, a preferred embodiment of the high-purity Ga2O3 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-mentioned high-purity Ga2O3, various impurity elements such as 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), 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 further preferred, and their contents are also less than the detection limit in the above-mentioned GDMS.

[0047] <Glow Discharge Mass Spectrometry (GDMS)>

[0048] Hereinafter, the composition analysis method of the above-mentioned high-purity Ga2O3 using glow discharge mass spectrometry (GDMS) is described. GDMS refers to a method of generating a glow discharge plasma with an analysis sample as a cathode under a high-purity argon atmosphere, sputtering the surface of the above-mentioned analysis sample in the above-mentioned plasma, and thereby determining the constituent elements in the above-mentioned analysis sample ionized by a mass spectrometer. Thus, it is possible to carry out qualitative and quantitative analysis of impurity elements contained in the above-mentioned high-purity Ga2O3 as elements other than Ga and O. Furthermore, it is also possible to determine the purity of the above-mentioned high-purity Ga2O3. As the ion source of the above-mentioned GDMS, a flat cell and a pin-shaped cell can be used. For the pin-shaped cell, it can be applied to an analysis sample that can be formed into a strip shape of about 2 mm square and 20 mm in length. Specifically, it is used in the case of analyzing Si single crystals, gallium arsenide (GaAs) single crystals, and indium phosphide (InP) single crystals, etc., which can be made by cleavage. The sheet-shaped discharge cell can be applied to the analysis sample that can be formed into a disk shape with a diameter of about 10 mm, and is used in the case of analyzing, for example, polycrystals. In the composition analysis of the above-mentioned high-purity Ga2O3, it is preferable to use a sheet-shaped discharge cell. When using a sheet-shaped discharge cell, by using an auxiliary electrode of high-purity indium (In) described later, discharge plasma can be generated even for oxide polycrystals, which are insulators, so GDMS can be performed.

[0049] The above-mentioned GDMS can be performed, for example, by the following method. First, high-purity Ga2O3 is obtained by the manufacturing method described later. The high-purity Ga2O3 can be, for example, a polycrystalline. Next, the polycrystalline of the above-mentioned high-purity Ga2O3 is coated on the sample configuration part (a circle with a diameter of 10 mm, i.e. corresponding to the discharge area) on the auxiliary electrode of high-purity indium attached to the analysis device described later. Here, for the above-mentioned sample configuration part, it is preferred to clean it according to the conventional method before coating the polycrystalline of high-purity Ga2O3, and perform pre-sputtering for 60 minutes in order to prevent the mixing of foreign matter and remove foreign matter. The analysis value during pre-sputtering is used as the background.

[0050] Next, GDMS can be performed on the polycrystal of the high-purity Ga2O3 coated on the sample configuration surface of the high-purity indium under the following conditions. In addition, for impurity elements other than Ga and O and In of the auxiliary electrode in the constituent elements of the analysis sample, a semi-quantitative value can be calculated by correcting the ion intensity ratio of Ga and each element in the impurity element using the relative sensitivity factor (RSF). In this specification, "impurity elements" refer to elements other than Ga and O and all elements that can be analyzed by the above-mentioned GDMS. Apparatus: Glow discharge mass spectrometer (trade name (model): VG-9000, manufactured by VG Elemental)

[0051] Ion source: sheet discharge cell (cooled with liquid nitrogen during analysis)

[0052] Discharge area: 10mm in diameter

[0053] Discharge gas: high purity argon (6N grade)

[0054] Discharge conditions: 2mA, 1kV (constant current mode)

[0055] Detector: Faraday cup and multiplier

[0056] Mass resolution: more than 4000 m / Δm (high resolution mode).

[0057] According to the above, the composition analysis of the above-mentioned high-purity Ga2O3 is carried out, so the elements other than Ga and O contained in the above-mentioned high-purity Ga2O3, that is, the impurity elements, can be qualitatively and quantitatively determined. Furthermore, based on the quantitative results of the impurity elements, the purity of the above-mentioned high-purity Ga2O3 can be calculated. In this specification, the "purity" of high-purity Ga2O3 is expressed as a numerical value up to the 5th decimal place by rounding off the 6th decimal place because the detection limit concentration of this GDMS is 0.01ppm. In addition, the purity of the later-mentioned metallic gallium and boron oxide can also be calculated by the same method as the composition analysis method of the above-mentioned high-purity Ga2O3. In addition, in the GDMS of metallic gallium, high-purity indium as an auxiliary electrode is not required, and a disc-shaped analysis sample with a diameter of 20mm can be obtained by casting for analysis.

[0058] [Method for producing gallium trioxide]

[0059] The method for producing high-purity gallium trioxide (Ga2O3) of the present embodiment can be a method for producing high-purity Ga2O3 having the above-mentioned characteristics, for example. That is, the method for producing high-purity Ga2O3 includes: a step of preparing molten metal gallium (metal Ga); a step of filling the molten metal Ga into a crucible; a step of placing solid boron oxide (B2O3) on the molten metal Ga in the crucible; a step of obtaining molten B2O3 by heating the crucible; a step of sealing the molten metal Ga with the molten B2O3, heating the crucible to a temperature of 1200K or higher and 1600K or lower, and blowing a gas containing oxygen (O) into the crucible to generate Ga2O3; and a step of washing the contents containing B2O3 and Ga2O3 in the crucible with ultrapure water at 60°C or higher to obtain Ga2O3. By the production method having such characteristics, Ga2O3 having a very low concentration of impurity elements and thus being highly pure can be obtained.

[0060] Specifically, the above-mentioned production method preferably has, for example, Figure 1 The process is shown in the flowchart. Figure 1 FIG. 1 is a flow chart showing an example of a method for producing high-purity gallium trioxide according to the present embodiment. Figure 1 , the method for manufacturing high-purity Ga2O3 may include: step S10 of preparing molten metal Ga (first step); step S20 of filling the molten metal Ga into a crucible (second step); step S30 of configuring solid B2O3 on the molten metal Ga in the crucible (third step); step S40 of obtaining molten B2O3 by heating the crucible (fourth step); step S50 of sealing the molten metal Ga with molten B2O3, heating the crucible to a temperature of not less than 1200K and not more than 1600K, and blowing a gas containing O into the crucible to generate Ga2O3 (fifth step); and step S60 of washing the contents containing B2O3 and Ga2O3 in the crucible with ultrapure water above 60°C to obtain Ga2O3 (sixth step).

[0061] In particular, the method for producing the high-purity Ga2O3 described above preferably heats the crucible to a temperature of not less than 1200K and not more than 1400K in the step S50 of generating Ga2O3. Furthermore, the gas containing O is preferably a mixed gas consisting of not less than 10% by mass of O and the remainder of nitrogen (N), or pure oxygen. The high-purity Ga2O3 obtained by the above-mentioned production method is preferably a polycrystalline. The inventors of the present invention have conceived that, as described above, by sealing high-purity Ga with a purity of about 99.9999% by mass, which is used as a raw material for GaAs polycrystals for producing GaAs single crystals, with Ga2O3 that does not react with metallic Ga, the high-purity Ga with a purity of about 99.9999% by mass is reacted with O to obtain high-purity Ga2O3. It was thus found that high-purity Ga2O3 with a purity exceeding 99.9999% by mass can be produced from the above-mentioned high-purity Ga. Below, with reference to Figure 1 and Figure 2 , while explaining the overview of the manufacturing apparatus used in the above-mentioned manufacturing method and the details of the above-mentioned manufacturing method of high-purity Ga2O3.

[0062] <Manufacturing Equipment>

[0063] Figure 2 Schematic diagram of a manufacturing apparatus used in the method for manufacturing high-purity gallium trioxide of the present embodiment. In the method for manufacturing high-purity Ga2O3 of the present embodiment, by using, for example, Figure 2 The manufacturing apparatus shown is capable of manufacturing high-purity Ga2O3. Figure 2 The manufacturing apparatus shown in the figure has at least a crucible 4, a crucible holding table 8 for holding the crucible 4, a lower shaft 9 for supporting the crucible 4 and the crucible holding table 8, a load sensor 10 capable of monitoring the progress of the synthesis reaction of Ga2O3 by detecting the weight of the content in the crucible 4, and a heater 1 for heating the crucible 4. Furthermore, the manufacturing apparatus has a gas introduction pipe 2 for introducing a gas 5 containing O into the crucible 4 from the outside. In addition, the manufacturing apparatus can have a container 11 for accommodating the crucible 4 and its content, the crucible holding table 8, and the lower shaft 9 in order to prevent the mixing of foreign matter from the outside. The container 11 can be used without any particular limitation in terms of size, etc., as long as it can prevent the mixing of foreign matter from the outside, can accommodate the above-mentioned components such as the crucible 4, and is made of a material with good heat permeability of the heater 1.

[0064] (Crucible)

[0065] In order to obtain high-purity Ga2O37, the crucible 4 can serve as a place for the molten metal Ga6 to react with the gas 5 containing O. The crucible 4 can be made of various materials that can withstand the temperature (specifically 1200-1600K, i.e. 927-1327°C) at which the molten metal Ga6 reacts with the gas 5 containing O. For example, pyrolytic boron nitride (pBN) can be used as the material of the crucible 4. The crucible 4 is specifically cylindrical and can accommodate molten metal Ga6, and can accommodate solid B2O3 by configuring solid B2O3 on the molten metal Ga6. The inner diameter of the crucible 4 can be, for example, greater than 75 mm and less than 150 mm. The above-mentioned solid B2O3 can become molten B2O33 by heating the crucible 4 with the heater 1 described later.

[0066] (Crucible holding table)

[0067] The crucible holding table 8 is in contact with the bottom of the crucible 4 to hold the crucible 4. The crucible holding table 8 may have a cylindrical appearance. The material of the crucible holding table 8 is not particularly limited, and for example, quartz, alumina, silicon carbide, or the like can be used.

[0068] (Lower axis)

[0069] The lower shaft 9 can support the crucible 4 and the crucible holding table 8 by supporting the crucible holding table 8 from below the crucible holding table 8. The lower shaft 9 can be, for example, a rod-shaped shape that is circular or rectangular when viewed horizontally in section. The material of the lower shaft 9 can be, for example, molybdenum, carbon, or silicon carbide.

[0070] (Load sensor)

[0071] The load sensor 10 is arranged so as to support the lower shaft 9 from below the lower shaft 9. Thus, in the step S50 of generating Ga2O3 described later, the load sensor 10 can detect the increase in the weight of the contents in the crucible 4 due to the generation of Ga2O37 from the molten metal Ga6. By detecting the weight of the contents by the load sensor 10, the progress of the synthesis reaction of Ga2O3 can be monitored in the above-mentioned manufacturing device. The load sensor 10 can be prepared by, for example, obtaining it from the market.

[0072] (Heater)

[0073] The heater 1 is provided for heating the crucible 4. The heater 1 is arranged in such a manner that the two heaters surround the outer circumference of the crucible 4. The output of the heater 1 can be controlled independently. In particular, the heater 1 is sometimes divided into a plurality of parts in a direction perpendicular to the axis of the crucible 4 to form a multi-stage structure. In this case, the output of the heater 1 can be independently controlled for each of the multi-stage parts, so that the temperature of the content in the crucible 4 can be adjusted along the axial direction of the crucible 4. The heater 1 can adopt, for example, a well-known electric heater.

[0074] Although not shown in the figure, 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 in the axial direction outside the crucible 4. For example, a known temperature monitor may be used as the thermocouple.

[0075] (Gas inlet pipe)

[0076] The gas introduction tube 2 is a tube for introducing a gas 5 containing O from the outside into the crucible 4. By introducing the gas 5 containing O into the crucible 4 through the gas introduction tube 2, the molten metal Ga6 reacts with the gas 5 containing O in the crucible 4, so that high-purity Ga2O37 can be obtained. The material of the gas introduction tube 2 is not particularly limited, but is preferably a material that does not react with oxygen and metal Ga, and can be, for example, quartz or pBN-coated carbon.

[0077] <Details of the method for producing high-purity Ga2O3 (each step included in the method for producing high-purity Ga2O3)>

[0078] (First step: step S10 of preparing molten metal Ga)

[0079] According to the method for producing high-purity Ga2O3 of this embodiment, by implementing Figure 1 The following steps shown can obtain high-purity Ga2O37. In the above-mentioned manufacturing method, first, as the first step, step S10 of preparing molten metal Ga is carried out. In the first step, specifically, molten metal Ga can be prepared by melting solid metal Ga obtained from the market in a constant temperature bath at a temperature above the melting point of Ga (for example, above 30°C). In particular, in this step, it is preferred to use 6N grade high-purity metal Ga that can be obtained from the market. That is, the purity of the above-mentioned metal gallium is preferably above 99.9999 mass%. 6N grade high-purity metal Ga can be contained in a container made of, for example, polyethylene and obtained from the market, so the molten metal Ga can be prepared by putting it into the above-mentioned constant temperature bath together with the polyethylene container.

[0080] (Second step: step S20 of filling the crucible with molten metal Ga)

[0081] Next, as a second step, a step S20 of filling the crucible with molten metal Ga is performed. In the second step, specifically, the molten metal Ga6 in the polyethylene container prepared in the first step can be filled into the crucible 4 in a manner that prevents the mixing of foreign matter from the outside. As such a filling method, a conventionally known method can be used.

[0082] (Third step: Step S30 of configuring solid B2O3)

[0083] Next, as the third step, step S30 of configuring solid B2O3 on the molten metal Ga in the crucible is performed. In the third step, specifically, solid B2O3 can be configured on the molten metal Ga6 filled into the crucible 4 by the second step. As a method for configuring solid B2O3, a conventionally known method can be used. Here, for solid B2O3, in order to obtain high-purity Ga2O37, it is preferred to use 5N-grade solid B2O3. That is, the purity of B2O3 is preferably 99.999% by mass or more. Such high-purity B2O3 can be obtained from the market and can be produced by conventionally known methods.

[0084] (Fourth step: Step S40 of obtaining molten B2O3)

[0085] Next, as the fourth step, step S40 of obtaining molten B2O3 by heating the crucible is performed. In the fourth step, specifically, by heating the crucible 4 with the heater 1, the temperature in the crucible 4 is made to be a temperature above the melting point of B2O3 (for example, above 500°C), so that B2O3 can be melted. The molten B2O33 obtained in this way can function as a liquid sealing material in the next step.

[0086] (Fifth step: Step S50 of generating Ga2O3)

[0087] Next, as the fifth step, the molten metal Ga is sealed with molten B2O3, the crucible is heated to a temperature of 1200K or more and 1600K or less, and a gas containing O is blown into the crucible, thereby performing the step S50 of generating Ga2O3. In the fifth step, first, the molten metal Ga6 is sealed with the B2O33 melted in the fourth step, so that the molten B2O33 functions as a liquid sealing material. Thus, it is possible to prevent foreign matter from being mixed into the metal Ga6 in the crucible 4 from the outside. Next, the gas introduction pipe 2 is inserted into the crucible 4 until its front end penetrates the molten B2O33 and reaches the molten metal Ga6. Furthermore, the crucible 4 is heated with a heater 1 so that the temperature in the crucible 4 becomes a temperature of 1200K or more and 1600K or less, that is, 927 to 1327°C, at which byproducts other than Ga2O3 generated by the reaction of metal Ga and O are not easily generated. In addition, a gas 5 containing O is blown into the crucible 4 from the outside through the gas introduction pipe 2. Thus, metal Ga and O react in the crucible 4 to generate Ga2O3. In the step S50 of generating Ga2O3, the crucible is preferably heated to a temperature of 1200K or more and 1400K or less.

[0088] In order to efficiently generate Ga2O3, the gas 5 containing O is preferably a mixed gas consisting of more than 10% by mass of oxygen and the remainder of nitrogen, or pure oxygen. The flow rate of the gas 5 containing O blown into the crucible 4 via the gas introduction pipe 2 is preferably 10 to 1000 mL / min. In this process, the molten B2O33 acts as a liquid sealant on the molten metal Ga6, so that the O in the gas 5 containing O can be consumed in the reaction with the metal Ga without leaking to the outside of the crucible 4. In particular, by using the load sensor 10 to detect the increase in the weight of the contents in the crucible 4 due to the generation of Ga2O3, the progress of the reaction between metal Ga and O is monitored, so that the O in the gas 5 containing O reacts with more than 99% by mass of the metal Ga, so that Ga2O37 can be efficiently generated. For example, according to this process, Ga2O37 can be generated from the molten metal Ga6 at a yield of more than 99% by mass. In this specification, the "yield" of Ga2O3 refers to the ratio of the amount of Ga2O3 actually obtained to the amount of Ga2O3 theoretically obtained when Ga2O3 is obtained from metallic Ga by a chemical reaction, and is expressed as a percentage.

[0089] (Sixth step: step S60 of obtaining Ga2O3)

[0090] Finally, as the sixth step, the content of the crucible containing B2O3 and Ga2O3 is washed with ultrapure water at a temperature of 60°C or above, thereby carrying out the step S60 of obtaining Ga2O3. In the sixth step, after first confirming that the reaction of metal Ga and O has reached 99% or more through the load sensor 10, the introduction of the gas 5 containing O into the crucible 4 through the gas introduction pipe 2 is stopped. Furthermore, the crucible 4 heated in the fifth step is cooled by an appropriate method until the temperature of the crucible 4 reaches room temperature so that it can be handled by human hands. Next, the crucible 4 containing the content containing Ga2O37 and B2O3 generated in the fifth step is put into ultrapure water at a temperature of 60°C or above, thereby washing the content containing the above-mentioned Ga2O37 and B2O3. At this time, since B2O3 is dissolved in the ultrapure water, only Ga2O37 can be recovered by removing the above-mentioned ultrapure water. According to the above, Ga2O37 can be obtained from the content in the crucible 4. In this specification, "ultrapure water" refers to pure water having a 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.

[0091] <Effects>

[0092] By carrying out the above-mentioned steps, high-purity Ga2O37 can be manufactured. As for the manufacturing method of high-purity Ga2O3 of the present embodiment, in particular, in the fifth step, the molten metal Ga6 is sealed with molten B2O33, and the crucible 4 is heated to a temperature of 1200-1600K at which byproducts other than Ga2O3 are not easily generated, and then a gas 5 containing O is blown into the crucible 4 to react metal Ga with O, thereby generating Ga2O37. In this way, high-purity Ga2O3 (for example, Ga2O3 in which the total concentration of impurity elements other than Ga and O is less than 1 mass ppm and the concentration of Si is greater than 0.01 mass ppm and less than 0.1 mass ppm) can be efficiently obtained from high-purity metal Ga while preventing foreign matter from being mixed in from the outside. Therefore, according to the present manufacturing method, high-purity Ga2O3 with extremely low concentration of impurity elements and high purity can be obtained.

[0093] Example

[0094] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Figure 2 The manufacturing device shown in Figure 1 The flow chart shown in the figure is for producing high-purity gallium trioxide (high-purity Ga2O3). In the following description, samples 1 and 2 are examples, and samples 11 to 14 are comparative examples.

[0095] [Manufacturing of Ga2O3]

[0096] <Sample 1>

[0097] (First process)

[0098] The preparation was performed by obtaining 10 kg of commercially available 6N grade (purity: 99.99995 mass % or more) high-purity metallic Ga (manufactured by RASA Industries, Ltd.) Since the high-purity metallic Ga was contained in a polyethylene container, the container was placed in a 60° C. thermostatic bath together with the polyethylene container to obtain molten metallic Ga.

[0099] (Second process)

[0100] The molten metal Ga6 in the polyethylene container was filled into the crucible 4 having an inner diameter of 100 mm by a known method so as to prevent the mixing of foreign matter from the outside. The height of the molten metal Ga6 in the crucible 4 was 209 mm.

[0101] (Third process)

[0102] Next, 500 g of commercially available solid B2O3 (manufactured by RASA Industries, Ltd.) was placed on the molten metal Ga6 in the crucible 4 by a conventionally known method. The purity of the solid B2O3 was confirmed to be 99.999% by mass based on the product label.

[0103] (Fourth process)

[0104] Next, crucible 4 is heated by heater 1 to melt solid B2O3 by making the temperature in crucible 4 higher than the melting point of B2O3, that is, 800°C. Thus, molten B2O33 is obtained on molten metal Ga6 in crucible 4.

[0105] (Fifth step)

[0106] First, the molten metal Ga6 is sealed with the B2O33 melted in the fourth step. Then, the front end of the gas introduction tube 2 is inserted into the molten metal Ga6 through the molten B2O33. The temperature in the crucible 4 is heated by the heater 1 so as to reach 1200K. Then, pure oxygen is blown into the crucible 4 from the outside as a gas 5 containing O at a flow rate of 10mL / min through the gas introduction tube 2, so that the O in the gas 5 containing O reacts with the metal Ga6 to generate Ga2O37. In addition, according to the increase in the amount of Ga2O37 generated, the front end position of the gas introduction tube 2 inserted into the molten metal Ga6 is adjusted, so that the O in the gas 5 containing O reacts with the metal Ga6 as much as possible.

[0107] (Sixth step)

[0108] First, after confirming that the reaction rate of Ga2O3, that is, the progress of the reaction between O in the gas 5 containing O and metal Ga6 is 99% or more based on the detection of the load sensor 10, the introduction of the gas 5 containing O into the crucible 4 through the gas introduction pipe 2 is stopped. In addition, the crucible 4 heated in the fifth step is cooled at a rate of 200°C / hour by air cooling until the temperature of the crucible 4 reaches room temperature. Next, the crucible 4 containing the contents including Ga2O37 generated in the fifth step and molten B2O33 is put into ultrapure water at 60°C, thereby washing the contents including the above-mentioned Ga2O37 and molten B2O33. Furthermore, Ga2O37 is recovered by removing the above-mentioned ultrapure water. Based on the above, polycrystalline Ga2O3 of sample 1 is obtained.

[0109] <Sample 2>

[0110] Ga2O3 of sample 2 was obtained by the same method as sample 1 except that in the fifth step, crucible 4 was heated by heater 1 so that the temperature inside crucible 4 reached 1600K.

[0111] <Sample 11>

[0112] The polycrystalline Ga2O3 of sample 11 was obtained by obtaining commercially available Ga2O3 (purity 99.999 mass %, manufactured by Zhuzhou Keneng New Materials Co., Ltd.).

[0113] <Sample 12>

[0114] Polycrystalline Ga2O3 of sample 12 was obtained by the same method as sample 1, except that in the fifth step, crucible 4 was heated by heater 1 so that the temperature inside crucible 4 reached 1150K.

[0115] <Sample 13>

[0116] Polycrystalline Ga2O3 of sample 13 was obtained by the same method as sample 1, except that in the fifth step, crucible 4 was heated by heater 1 so that the temperature inside crucible 4 reached 1650K.

[0117] <Sample 14>

[0118] In the third step, solid B2O3 (produced by RASA Industries, Ltd.) is not arranged on the molten metal Ga6 in the crucible 4, and the fourth, fifth and sixth steps are carried out. Except for this, the polycrystalline Ga2O3 of sample 14 is obtained by the same method as sample 1.

[0119] [Composition analysis based on GDMS]

[0120] By performing the composition analysis method using the above-mentioned GDMS on Ga2O3 of Samples 1 to 2 and Samples 11 to 14, the impurity elements contained in the above-mentioned Ga2O3 as elements other than Ga and O were determined, and their concentrations were measured. The results are shown in Table 1. The unit of the concentration of each element shown in Table 1 is mass ppm. In addition, "<0.01" in Table 1 means below the detection limit.

[0121] [Table 1]

[0122] Table 1

[0123]

[0124] [Investigation]

[0125] According to Table 1, in Ga2O3 of Samples 1 and 2, the total concentration of impurity elements other than Ga and O is less than 1 mass ppm (Sample 1: 0.14 mass ppm, Sample 2: 0.55 mass ppm). Furthermore, the concentration of silicon, which is one of the impurity elements, is greater than or equal to 0.01 mass ppm and less than or equal to 0.1 mass ppm (Sample 1: 0.02 mass ppm, Sample 2: 0.05 mass ppm). Therefore, the purity of Ga2O3 of Samples 1 and 2 is greater than or equal to 99.99995 mass %.

[0126] On the other hand, in Ga2O3 of samples 11 to 12 and 14, the total concentration of impurity elements other than Ga and O exceeded 1 mass ppm, or the concentration of silicon as one of the impurity elements exceeded 0.1 mass ppm. In Ga2O3 of sample 13, part of the generated Ga2O3 was dissolved in B2O3 and disappeared by reacting metal Ga with O at a temperature exceeding 1600K, so the yield was deteriorated compared with samples 1 and 2. As the content of impurity elements increased, the concentration of silicon as one of the impurity elements was 0.43 mass ppm.

[0127] As mentioned above, although embodiment and Example of this invention were demonstrated, it is planned from the outset that the structure of each embodiment and Example mentioned above is combined suitably.

[0128] The embodiments and examples disclosed herein are illustrative in all aspects and are not restrictive. The scope of the present invention is not indicated by the above-mentioned embodiments and examples but by the claims, and is intended to include all modifications within the scope and meaning equivalent to the claims.

[0129] Description of Reference Numerals

[0130] 1: heater; 2: gas inlet pipe; 3: molten boric oxide (B2O3); 4: crucible; 5: gas containing oxygen (O); 6: molten metal gallium (Ga); 7: gallium trioxide (Ga2O3); 8: crucible holding table; 9: lower axis; 10: load sensor; 11: container; S10: process of preparing molten metal Ga; S20: process of filling molten metal Ga into crucible; S30: process of configuring solid B2O3; S40: process of obtaining molten B2O3; S50: process of generating Ga2O3; S60: process of obtaining Ga2O3.

Claims

1. A high-purity gallium trioxide comprising 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 mass ppm or less, and the concentration of silicon as one of the impurity elements is 0.01 mass ppm or more and 0.1 mass ppm or less.

2. The high-purity gallium trioxide according to claim 1, wherein: In the glow discharge mass spectrometry analysis, the concentration of boron as another impurity element is greater than 0.01 mass ppm and less than 0.5 mass ppm, 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 all less than 0.01 mass ppm.

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

4. The high-purity gallium trioxide according to any one of claims 1 to 3, wherein The high-purity gallium trioxide is polycrystalline.

5. The high-purity gallium trioxide according to any one of claims 1 to 4, wherein In the glow discharge mass spectrometry, the concentration of the silicon is 0.01 mass ppm or more and 0.05 mass ppm or less.

6. The high-purity gallium trioxide according to any one of claims 1 to 5, wherein In the glow discharge mass spectrometry, the concentration of boron as another of the impurity elements is 0.01 mass ppm or more and 0.2 mass ppm or less.

7. A method for producing high-purity gallium trioxide, comprising: A process for preparing molten metal gallium; The process of filling the molten metal gallium into a crucible; A step of disposing solid boron oxide on the molten metal gallium in the crucible; A step of obtaining molten boron oxide by heating the crucible; The molten metal gallium is sealed with the molten boron oxide, the crucible is heated to a temperature of 1200 K to 1600 K, and a gas containing oxygen is blown into the crucible to generate gallium trioxide; and The step of washing the content including the boron oxide and the gallium trioxide in the crucible with ultrapure water at 60° C. or higher to obtain the gallium trioxide.

8. The method for producing high-purity gallium trioxide according to claim 7, wherein: The high-purity gallium trioxide is polycrystalline.

9. The method for producing high-purity gallium trioxide according to claim 7 or claim 8, wherein: In the step of generating gallium trioxide, the crucible is heated to a temperature of 1200K or higher and 1400K or lower.

10. The method for producing high-purity gallium trioxide according to any one of claims 7 to 9, wherein: The gas containing oxygen is a mixed gas consisting of 10 mass % or more of oxygen and the remainder of nitrogen, or pure oxygen.

11. The method for producing high-purity gallium trioxide according to any one of claims 7 to 10, wherein: The purity of the metallic gallium is 99.9999 mass % or more.

12. The method for producing high-purity gallium trioxide according to any one of claims 7 to 11, wherein: The purity of the boron oxide is 99.999 mass % or more.

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