Oxide sintered body

Abstract

Provided is an oxide sintered body containing: cubic MgO with Zn in solid solution; hexagonal ZnO with Mg in solid solution; and ZnGa2O4 with Mg in solid solution.

Description

Sintered oxide

[0001] The present invention relates to an oxide sintered body and a film-forming material used to form a thin film.

[0002] MgO-ZnO-based oxides have been applied to translucent ceramics for color liquid crystal projectors (Patent Document 1), oxide semiconductors (Patent Document 2), transparent electrodes (Patent Document 3), and the like. The above-mentioned sintered body is a material that emphasizes electrical conductivity, but because it contains ZnO as the main component, there is a problem with its translucency in the ultraviolet region. In response to the above problem, the present inventors have disclosed an oxide sintered body that contains zinc, magnesium, a positive trivalent or positive tetravalent metal element X, and oxygen as constituent elements, and by adjusting the ratio of these elements, it is possible to obtain a film that has high translucency in the ultraviolet region and also has high electrical conductivity (Patent Document 4).

[0003] JP 2009-184898 A JP 2012-066968 A JP 2011-063866 A International Publication No. 2020 / 262433

[0004] As a result of further investigation, the inventors have found that cubic MgO containing Zn as a solid solution, hexagonal ZnO containing Mg as a solid solution, and ZnGa containing Mg as a solid solution are ２ O ４ It has been found that when a film is formed using an oxide sintered body containing the above compound, a film having high light transmittance in the ultraviolet region and high electrical conductivity can be obtained. One of the objects of the present invention is to provide an oxide sintered body from which a film having high light transmittance in the ultraviolet region and high electrical conductivity can be obtained.

[0005] According to the present invention, the following oxide sintered bodies are provided: 1. Cubic MgO with Zn dissolved therein, hexagonal ZnO with Mg dissolved therein, and ZnGa with Mg dissolved therein. ２ O ４2. The oxide sintered body according to claim 1, wherein the atomic ratio of the gallium to the total of zinc, magnesium, and gallium [Ga / (Zn+Mg+Ga)] is 0.0001 or more and 0.090 or less. 3. The oxide sintered body according to claim 2, wherein the atomic ratio [Ga / (Zn+Mg+Ga)] is 0.007 or more and 0.070 or less. 4. The oxide sintered body according to claim 2, wherein the atomic ratio [Ga / (Zn+Mg+Ga)] is 0.008 or more and 0.060 or less. 5. The oxide sintered body according to claim 2, wherein the atomic ratio [Ga / (Zn+Mg+Ga)] is 0.010 or more and 0.050 or less. 6. The oxide sintered body according to any one of claims 2 to 5, wherein the atomic ratio of the magnesium to the total of the zinc and the magnesium [Mg / (Zn+Mg)] is 0.25 or more and 0.80 or less. 7. 8. The oxide sintered body according to claim 6, wherein the atomic ratio [Mg / (Zn+Mg)] is 0.30 or more and 0.70 or less. 8. A film-forming material comprising the oxide sintered body according to any one of claims 1 to 7. 9. The film-forming material according to claim 8, which is a film-forming tablet. 10. The film-forming material according to claim 8, which is a sputtering target. 11. A thin film obtained by using the film-forming material according to any one of claims 8 to 10.

[0006] According to the present invention, it is possible to provide an oxide sintered body from which a film having high light transmittance in the ultraviolet region and high electrical conductivity can be obtained.

[0007] FIG. 2 is a diagram showing the analysis results of an XRD chart of the oxide sintered body of Example 1.

[0008] The oxide sintered body according to one embodiment of the present invention is made of cubic MgO with Zn dissolved therein, hexagonal ZnO with Mg dissolved therein, and ZnGa with Mg dissolved therein. ２ O ４ This results in an oxide sintered body that can be used to form a film that is both transparent in the ultraviolet range and electrically conductive.

[0009] In the oxide sintered body of this embodiment, the atomic ratio of gallium to the total of zinc, magnesium, and gallium [Ga / (Zn+Mg+Ga)] is preferably 0.0001 or more and 0.090 or less. This results in an oxide sintered body that can form a film with improved transmittance in the ultraviolet region and high conductivity. The atomic ratio [Ga / (Zn+Mg+Ga)] is more preferably 0.007 or more and 0.070 or less, even more preferably 0.008 or more and 0.060 or less, and particularly preferably 0.010 or more and 0.050 or less.

[0010] Furthermore, in the oxide sintered body of this embodiment, the atomic ratio of magnesium to the total of zinc and magnesium [Mg / (Zn+Mg)] is preferably 0.25 or more and 0.80 or less. This results in an oxide sintered body that has improved transmittance in the ultraviolet region and can form a film with high conductivity. It is more preferable that the atomic ratio [Mg / (Zn+Mg)] is 0.30 or more and 0.70 or less. Note that if the atomic ratio exceeds 0.80, a highly conductive film cannot be obtained even if the film obtained from the oxide sintered body is annealed. On the other hand, if it is less than 0.25, the ultraviolet transmittance of the film will be low.

[0011] In this embodiment, in addition to gallium, another positive trivalent or positive tetravalent metal element X may be added. Examples of the metal element X include Al, In, Sc, and Y. Preferably, it is Al.

[0012] The atomic ratios of zinc, magnesium, and gallium can be controlled by adjusting the atomic ratios of the starting materials. The atomic ratio of the oxide sintered body tends to be higher in zinc than in the starting materials, and the atomic ratio of gallium tends to be approximately the same.

[0013] The atomic ratio of each element contained in an oxide sintered body can be determined by analyzing the contained elements using an inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, when a solution sample is atomized using a nebulizer and introduced into argon plasma (approximately 5000–8000°C), the elements in the sample absorb thermal energy and become excited, causing their orbital electrons to move from the ground state to a higher energy level orbital, and then to a lower energy level orbital. During this process, the elements emit light corresponding to the energy difference. This light exhibits element-specific wavelengths (spectral lines), and the presence or absence of these spectral lines can be used to confirm the presence of the element (qualitative analysis). Furthermore, because the magnitude of the spectral lines (emission intensity) is proportional to the number of elements in the sample, the sample concentration can be determined by comparing it with a standard solution of known concentration (quantitative analysis). After identifying the elements contained in the sample through qualitative analysis, quantitative analysis is used to determine their content, and the atomic ratio of each element can be determined from the results.

[0014] The constituent elements of the oxide sintered body of this embodiment may consist essentially of Mg, Zn, Ga, and O. For example, 70 mol % or more, 80 mol % or more, or 90 mol % or more of the constituent elements of the oxide sintered body of this embodiment may be Mg, Zn, Ga, and O. Furthermore, the constituent elements of the oxide sintered body of this embodiment may consist only of Mg, Zn, Ga, and O. In this case, inevitable impurities may be contained.

[0015] It can be confirmed that the oxide sintered body contains each of the above oxides by comparing an XRD chart obtained by an X-ray diffraction (XRD) method with the database (PDF: Powder Diffraction File) of the ICDD (International Center for Diffraction Data).

[0016] The presence of other metal elements in each crystal can be determined by comparing the lattice constant (measured value) determined by XRD with the lattice constant (PDF value) listed in the PDF. For example, in the case of a crystal containing Zn as a solid solution, the measured value will be larger than the PDF value. If the state of the solid solution cannot be determined by XRD, it can be determined by mapping the position of each element using characteristic X-rays of each element using, for example, an energy dispersive X-ray analyzer (EDS) attached to a scanning electron microscope (SEM).

[0017] The oxide sintered body of this embodiment can be produced, for example, by a process of mixing raw material powders to prepare a mixed powder, a process of molding the mixed powder into a molded body, and a process of firing the molded body. As starting materials, powders of compounds containing Mg, Zn, and Ga can be used. The compounds are preferably oxides. For example, MgO, ZnO, Ga ２ O ３ The mixing ratio of the raw material powders can be adjusted, for example, taking into consideration the atomic ratio of the oxide sintered body to be obtained.

[0018] The average particle size of the raw material powder is preferably 0.1 to 1.2 μm, more preferably 0.5 to 1.0 μm. The average particle size of the raw material powder can be measured using a laser diffraction particle size distribution analyzer or the like.

[0019] The method for mixing and molding the raw materials is not particularly limited, and known methods can be used. A binder may be added during mixing. The raw materials can be mixed using known devices such as a ball mill, a bead mill, a jet mill, or an ultrasonic device. The mixing time can be adjusted as appropriate, but is preferably about 6 to 100 hours.

[0020] For example, the mixed powder can be molded under pressure to form a molded body. This process allows the powder to be molded into the shape of the product (for example, a shape suitable for a sputtering target).

[0021] The mixed powder is filled into a mold and pressed, for example, at 1000 kg / cm by die pressing or cold isostatic pressing (CIP). ２By applying pressure in the above manner, a molded body can be obtained. During molding, a molding aid such as polyvinyl alcohol, polyethylene glycol, methyl cellulose, polywax, oleic acid, or stearic acid may be used.

[0022] The resulting molded body can be heated, for example, at a temperature of 1200 to 1650°C for 2 hours or more to obtain an oxide sintered body. The heating temperature is preferably 1350 to 1600°C, more preferably 1400 to 1600°C, and even more preferably 1450 to 1500°C. The heating time is preferably 2 to 72 hours, more preferably 3 to 48 hours, and even more preferably 4 to 24 hours.

[0023] The firing is usually carried out by heating the molded body in an air atmosphere or an oxygen gas atmosphere, preferably an oxygen gas atmosphere having an oxygen concentration of, for example, 10 to 50% by volume.

[0024] The oxide sintered body of the present embodiment can be suitably used as a film-forming material for forming a thin film having the composition of the oxide sintered body, for example, as a tablet or sputtering target used when forming a film by a vacuum deposition method or an ion plating method. A thin film obtained from the film-forming material of the present embodiment can be used as a transparent conductive film used in an electrode substrate for an ultraviolet light-emitting diode, an ultraviolet light-emitting laser diode, or the like.

[0025] Furthermore, by heat-treating the film at a high temperature after film formation, the UV transmittance and conductivity of the film are improved. The film immediately after film formation is in a state in which zinc oxide, magnesium oxide, etc. are uniformly mixed. Heat-treating the film in this state causes aggregation and separation of the oxides, resulting in the formation of a zinc oxide network, which exhibits conductivity. Meanwhile, it is presumed that magnesium oxide aggregates in the gaps of the zinc oxide network, allowing UV light to pass through. The heat-treatment temperature for the electrode layer is preferably 750°C or higher, more preferably 900°C or higher.

[0026] Tablets can be produced, for example, by cutting or polishing an oxide sintered body obtained by molding raw materials into a desired shape and firing it. Sputtering targets can be produced, for example, by cutting or polishing an oxide sintered body and bonding it to a backing plate. By cutting, uneven surfaces can be removed and the target can be made to a specified size. The surface may be polished to #200, #400, or even #800 grit. This can suppress abnormal discharge and particle generation during sputtering.

[0027] The polished oxide sintered body is washed as necessary, and then a bonding material such as metal indium solder is applied to the bonding surface, followed by bonding to a backing plate, thereby obtaining a sputtering target.

[0028] Example 1 (A) Preparation of Oxide Sintered Body Zinc oxide (ZnO) powder having an average particle size of 1 μm or less, magnesium oxide (MgO) powder having an average particle size of 1 μm or less, and gallium oxide (GaO) powder having an average particle size of 1 μm or less were used. ２ O ３ The metals (ZnO, MgO, Ga, and ZnO powders) were weighed and mixed so that the atomic ratio of each metal was as shown in Table 1. The mass fraction of the mixed powder was 60.9 mass % for ZnO, 31.6 mass % for MgO, and 1.0 mass % for Ga. ２ O ３ The mixed powder was placed in a resin pot, water was added, and hard ZrO ２ The mixture was mixed in a wet ball mill for 20 hours using balls. The resulting mixed slurry was taken out, filtered, dried, and granulated. The resulting granules were placed in a mold and cold isostatically pressed at 3 ton / cm. ２ It was pressed and molded.

[0029] The obtained molded body was placed in a sintering furnace with an internal volume of 0.1 m ３The molded body was fired while inflowing oxygen at a rate of 5 L / min per sintering furnace. The temperature in the sintering furnace was increased from room temperature to 1000°C at 1°C / min, then increased from 1000°C to 1470°C at 3°C / min, and fired at 1470°C for 5 hours. Thereafter, the inflow of oxygen was stopped, and the temperature in the furnace was decreased from 1470°C to 1300°C at 10°C / min. Next, the furnace was sintered in a furnace with an internal volume of 0.1 m. ３ The temperature inside the furnace was maintained at 1300° C. for 3 hours while Ar was flown in at a rate of 10 L / min per furnace. Thereafter, the furnace was allowed to cool to obtain an oxide sintered body.

[0030] The composition and relative density of the obtained oxide sintered body were evaluated. The results are shown in Table 2.

[0031]

[0032]

[0033] The evaluation methods are as follows. (1) Atomic ratio of metal elements in oxide sintered body A part of the obtained oxide sintered body was cut out, dissolved in acid, and then analyzed by an inductively coupled plasma emission spectrometer. (2) Relative density The relative density was calculated by measuring the actual density of the oxide sintered body by the Archimedes method using water and dividing it by the theoretical density calculated from the composition. The theoretical density was calculated by dividing the density of MgO without oxygen defects by 3.59 g / cm. ３ , the density of ZnO is 5.61 g / cm ３ , Ga ２ O ３ The density is 5.88 g / cm ３ and the average value was calculated based on the composition ratio (mass fraction) of the sintered body.

[0034] (3) XRD Measurement Measurement was carried out using the following apparatus and conditions: Apparatus: Ultima-III manufactured by Rigaku Corporation X-ray: Cu-Kα ray (wavelength 1.5406 Å, monochromatized with a graphite monochromator) 2θ-θ reflection method, continuous scan (1.0° / min) Sampling interval: 0.02° Slits DS, SS: 2 / 3°, RS: 0.6 mm

[0035] The results of the XRD measurement were analyzed using integrated powder X-ray analysis software (PDXL2, manufactured by Rigaku Corporation) to determine the crystal structure and lattice constant of the oxide sintered body. The crystal structure was confirmed using the following ICDD (PDF) card. ZnO: 36-1451 (hexagonal crystal) MgO: 45-0946 (cubic crystal) ZnGa ２ O ４ :38-1240

[0036] The analysis results of the XRD chart are shown in Figure 1. From Figure 1, it can be seen that the oxide sintered body has a crystal structure consisting of ZnO, MgO, and ZnGa. ２ O ４ The results are shown in Table 3. In the table, cases where the sample contains the compound are marked with an ◯, and cases where the sample does not contain the compound are marked with an X.

[0037]

[0038] (B) Preparation of a sputtering target The surface of the obtained oxide sintered body to be sputtered was polished with a cup grindstone to have a diameter of 100 mm and a thickness of 5 mm. A backing plate was attached to the polished oxide sintered body using an In-based alloy to prepare a sputtering target.

[0039] A thin film was actually formed and evaluated using a sputtering target made from an oxide sintered body. The film formation conditions were as follows: A sapphire substrate (thickness: 0.5 mm) was placed in an ultrasonic cleaner and washed with trichloroethylene for 5 minutes, acetone for 5 minutes, methanol for 5 minutes, and finally distilled water for 5 minutes. This substrate was set in a sputtering device (ULVAC: ACS-4000), and film formation was carried out at 25°C using Ar as the sputtering gas, forming a film with a thickness of 100 nm on the substrate.

[0040] (2) Heat Treatment The substrate on which the film was formed in (1) above was heat treated (activation annealing) at 950°C for 5 minutes in a nitrogen atmosphere. The surface resistance of the heat-treated film was measured using a Loresta FP manufactured by Mitsubishi Chemical. In addition, the ultraviolet transmittance was evaluated using a spectrophotometer (UV-2600 manufactured by Shimadzu Corporation). The evaluation results are shown in Table 4.

[0041]

[0042] Examples 2 and 3, Comparative Examples 1 and 2 Oxide sintered bodies and sputtering targets were produced and evaluated in the same manner as in Example 1, except that the raw materials were weighed and mixed so that the atomic ratios of each metal element were the values ​​shown in Table 1. The results are shown in Tables 2 to 4. Examples 1 to 3 obtained favorable values ​​for both UV transmittance and resistance. On the other hand, Comparative Example 1 had a higher resistance and a lower UV transmittance than Examples 1 to 3. Furthermore, Comparative Example 2 had a lower resistance than Examples 1 to 3, but a lower UV transmittance.

[0043] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention. Accordingly, these numerous modifications are within the scope of the present invention. The contents of all documents cited in this specification and of the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims

1. Cubic MgO solid-solved with Zn, hexagonal ZnO solid-solved with Mg, and ZnGa solid-solved with Mg ２ O ４ An oxide sintered body containing the above components.

2. The oxide sintered body according to claim 1, wherein the atomic ratio of gallium to the total of zinc, magnesium and gallium [Ga / (Zn + Mg + Ga)] is 0.0001 or more and 0.090 or less.

3. The oxide sintered body according to claim 2, wherein the atomic ratio [Ga / (Zn + Mg + Ga)] is 0.007 or more and 0.070 or less.

4. The oxide sintered body according to claim 2, wherein the atomic ratio [Ga / (Zn + Mg + Ga)] is 0.008 or more and 0.060 or less.

5. The oxide sintered body according to claim 2, wherein the atomic ratio [Ga / (Zn + Mg + Ga)] is 0.010 or more and 0.050 or less.

6. The oxide sintered body according to any one of claims 2 to 5, wherein the atomic ratio of magnesium to the total of zinc and magnesium [Mg / (Zn + Mg)] is 0.25 or more and 0.80 or less.

7. The oxide sintered body according to claim 6, wherein the atomic ratio [Mg / (Zn + Mg)] is 0.30 or more and 0.70 or less.

8. A film-forming material comprising the oxide sintered body according to any one of claims 1 to 5.

9. The film-forming material according to claim 8, which is a film-forming tablet.

10. The film-forming material according to claim 8, which is a sputtering target.

11. A thin film obtained by using the film-forming material according to claim 8.