Oxide sintered body and transparent conductive oxide film

Abstract

An oxide sintered body containing indium, hafnium, tantalum, and oxygen as constituent elements, in which when indium, hafnium, and tantalum are designated as In, Hf, and Ta, respectively, the atomic ratio of Hf/(In+Hf+Ta) is equal to 0.002 to 0.030, and the atomic ratio of Ta/(In+Hf+Ta) is equal to 0.0002 to 0.013.

Claims

1. A transparent conductive oxide film, comprising: an oxide including indium, hafnium, tantalum, and oxygen as constituent elements, wherein the oxide satisfies that an atomic ratio of Hf/(In+Hf+Ta) is equal to 0.002 to 0.030, and that an atomic ratio of Ta/(In+Hf+Ta) is equal to 0.0002 to 0.013, where In, Hf and Ta are indium, hafnium, and tantalum, respectively.

2. The transparent conductive oxide film according to claim 1, wherein the atomic ratio of Hf/(In+Hf+Ta) is equal to 0.005 to 0.025.

3. The transparent conductive oxide film according to claim 1, wherein the atomic ratio of Hf/(In+Hf+Ta) is equal to 0.007 to 0.021.

4. The transparent conductive oxide film according to claim 1, wherein the atomic ratio of Ta/(In+Hf+Ta) is equal to 0.001 to 0.010.

5. The transparent conductive oxide film according to claim 1, wherein the atomic ratio of Ta/(In+Hf+Ta) is equal to 0.003 to 0.010.

6. The transparent conductive oxide film according to claim 1, wherein the atomic ratio of Hf/(In+Hf+Ta) is equal to 0.005 to 0.025, and the atomic ratio of Ta/(In+Hf+Ta) is equal to 0.001 to 0.010.

Description

EXAMPLE

(1) The present invention will be described more specifically by referring to the following Examples; however, the present invention is not intended to be limited to these Examples.

Examples 1 to 20

(2) Sintered bodies, sputtering targets, and transparent conductive films were produced according to the compositions indicated in Table 1 by the following methods.

(3) <Production of Oxide Sintered Body>

(4) As raw material powders, an indium oxide powder having a purity of 99.99% by weight and an average particle size of 0.5 μm, a hafnium oxide powder having a purity of 99.9% by weight and an average particle size of 0.2 μm, and a tantalum oxide powder having a purity of 99.9% by weight and an average particle size of 0.2 μm were prepared. These raw material powders were weighed so as to obtain the atomic ratio described in Table 1, the powders were mixed in a dry type ball mill, and thus a mixed powder for molding was obtained. The average particle size of the mixed powder was 0.2 μm.

(5) This mixed powder was molded by the following procedure, and a molded body was produced. First, the mixed powder was molded using a mold having a diameter of 150 mm by applying pressure at 0.3 ton/cm.sup.2. Next, CIP molding of applying pressure at 3.0 ton/cm.sup.2 was performed, and thus a cylindrical-shaped molded body was obtained. This molded body was disposed in a sintering furnace conditioned to have a pure oxygen atmosphere, and the molded body was sintered under the following conditions. Thus, a disc-shaped oxide sintered body was produced. In this manner, the oxide sintered bodies of the various Examples, various Comparative Examples, and various Reference Examples were obtained. The retention time is the time for which the molded body was maintained at the sintering retention temperature.

(6) (Firing Conditions) Rate of temperature increase: 50° C./hour Sintering retention temperature: 1,600° C. Retention time: 5 hours Sintering atmosphere: From before the initiation of temperature increase (room temperature) to the temperature reached 100° C. upon temperature decrease, pure oxygen gas was introduced into the furnace. Rate of temperature decrease: 100° C./hour Weight of molded body/oxygen flow rate: 0.9 [kg/(L/min)]

(7) <Evaluation of Oxide Sintered Body>

(8) (Composition)

(9) The compositions of the oxide sintered bodies of the various Examples, various Comparative Examples, and various Reference Examples were quantitatively determined by ICP emission spectrometry using a commercially available ICP emission spectrometer. Then, the atomic ratio was determined. The results are shown in Table 1.

(10) Meanwhile, the compositions of the oxide sintered bodies were respectively almost identical with the compositions of the mixed powders for molding.

(11) (Relative Density)

(12) The relative densities of the oxide sintered bodies of the various Examples, various Comparative Examples, and various Reference Examples were determined. The relative density is a value that is determined by the following formula, when the theoretical density of the oxide sintered body is designated as A and the sintered density is designated as B. The methods for measuring the theoretical density A and the sintered density B are as described above. The measurement results are shown in Table 1.
Relative density (%)=(B/A)×100

(13) (Average Crystal Grain Size)

(14) The average crystal grain sizes of the crystal grains that constituted the oxide sintered bodies of the various Examples, various Comparative Examples, and various Reference Examples were measured. The method for measuring the average crystal grain size is as described above. However, an observation photograph (magnification ratio: 1,000 to 5,000 times) of a polished surface of an oxide sintered body was taken using a scanning electron microscope. In this observation photograph, the lengths of the major axes of 500 particles were determined. The arithmetic mean length of the major axes thus determined was designated as the average crystal grain size. The measurement results are shown in Table 1.

(15) (Three-Point Flexural Strength)

(16) Regarding the strength of a sintered body, the three-point flexural strength was measured according to JIS-R-1601.

(17) <Production of Sputtering Target and Transparent Conductive Oxide Film>

(18) The oxide sintered bodies produced in the various Examples, various Comparative Examples, and various Reference Examples were processed into a disc shape (diameter: 4 inches=101.6 mm) The surface that will be served as a sputtering surface when the oxide sintered body was used as a sputtering target was polished using a flat surface grinding machine and a diamond grinding wheel. The center line average roughness (Ra) was adjusted by changing the mesh size of the grinding wheel at the time of polishing. In this manner, a sputtering target was produced. Ra of the sputtering surface of the sputtering target thus produced was measured using a commercially available surface property analyzer (apparatus name: SURFTEST SV-3100, manufactured by Mitutoyo Corporation). The results were as shown in Table 1.

(19) A film was formed on a substrate under the following conditions by a DC magnetron sputtering method using the sputtering target thus obtained. After the film-forming, a post-treatment was carried out under the following conditions, and a transparent conductive oxide film was obtained.

(20) (Film-Forming Conditions) Apparatus: DC magnetron sputtering apparatus Magnetic field intensity: 1,000 Gauss (right above the target, horizontal component) Substrate temperature: Room temperature (25° C.) Attained degree of vacuum: 8×10.sup.−5 Pa Atmosphere at the time of film-forming: Argon Gas pressure at the time of sputtering: 0.5 Pa DC power: 200 W Film thickness: 30 nm Substrate used: Alkali-free glass (EAGLE XG glass manufactured by Corning Incorporated, thickness: 0.7 mm)

(21) (Post-Treatment Conditions after Film-Forming)

(22) After the film-forming, the transparent conductive film-attached substrate was subjected to a heat treatment of heating for 60 minutes at 150° C. in air. The rate of temperature increase at this time was set to 50° C./min.

(23) <Evaluation of Transparent Conductive Oxide Film>

(24) (Film Thickness)

(25) The thickness of the thin film was measured using DEKTAK 3030 (manufactured by Sloan Technology Corp.).

(26) (Resistivity)

(27) The resistivity of the thin film was measured using HL5500 (manufactured by Japan Bio-Rad Laboratories, Inc.).

(28) (Light Transmittance)

(29) The light transmittance of a sample having a transparent conductive oxide film formed on a substrate was measured using a spectrophotometer (trade name: U-4100, manufactured by Hitachi High-Technologies Corporation) in a wavelength range of from 240 nm to 2,600 nm, and the average value of the light transmittances at a wavelength of 400 nm to 800 nm, which is important for display devices, was determined.

(30) The measurement results for the resistivity and the light transmittance of the transparent conductive films thus obtained are shown in Table 1.

Comparative Examples 1 to 10

(31) Sintered bodies, sputtering targets, and transparent conductive films were produced by methods similar to those used in Examples 1 to 20, according to the compositions indicated in Table 1.

Reference Example 1

(32) A sintered body, a sputtering target, and a transparent conductive film were produced according to the composition indicated in Table 1 by methods similar to those used in Examples 1 to 20, except that the retention time during firing was set to 15 hours.

Reference Example 2

(33) A sintered body, a sputtering target, and a transparent conductive film were produced according to the composition indicated in Table 1 by methods similar to those used in Examples 1 to 20, except that the retention time during firing was set to 25 hours.

(34) The measurement results are shown in Table 1.

(35) TABLE-US-00001 TABLE 1 Final composition of Average Three- Light powder and composition Relative crystal point transmittance in of sintered body density of grain size of flexural Ra of Annealing wavelength range Hf/(In + Ta/(In + sintered body sintered body strength target temperature Resistivity of 400 to 800 nm Hf + Ta) Hf + Ta) (%) (μm) (MPa) (μm) (° C.) (μΩ .Math. cm) (%) Example 1 0.0110 0.0012 99.2 5.2 195 0.42 150 259 88.0 Example 2 0.0157 0.0018 99.2 5.2 196 0.48 150 233 88.2 Example 3 0.0120 0.0018 99.2 5.6 190 0.47 150 253 88.3 Example 4 0.0150 0.0015 99.1 5.2 191 0.47 150 231 88.4 Example 5 0.0160 0.0018 99.1 5.3 191 0.42 150 237 88.4 Example 6 0.0200 0.0022 99.1 5.2 193 0.42 150 268 88.3 Example 7 0.0180 0.0017 99.1 5.1 196 0.42 150 260 88.1 Example 8 0.0235 0.0018 99.2 5.4 189 0.42 150 279 87.5 Example 9 0.0235 0.0018 99.2 5.2 190 0.42 150 273 87.3 Example 10 0.0072 0.0018 99.3 5.7 189 0.42 150 266 88.4 Example 11 0.0072 0.0035 99.4 4.8 200 0.45 150 284 88.3 Example 12 0.0055 0.0010 99.1 3.5 280 0.41 150 299 88.4 Example 13 0.0280 0.0050 99.3 5.2 189 0.42 150 294 87.3 Example 14 0.0235 0.0033 99.3 5.0 193 0.43 150 282 87.3 Example 15 0.0150 0.0040 99.3 5.2 189 0.42 150 224 87.0 Example 16 0.0148 0.0050 99.3 4.8 200 0.42 150 226 87.0 Example 17 0.0190 0.0060 99.3 5.0 203 0.45 150 218 87.3 Example 18 0.0190 0.0070 99.3 4.2 230 0.42 150 220 86.9 Example 19 0.0190 0.0093 99.3 4.5 212 0.42 150 214 85.9 Example 20 0.0170 0.0090 99.3 4.9 204 0.42 150 212 86.3 Comparative 0.0320 0.0018 99.0 5.3 190 0.47 150 314 87.2 Example 1 Comparative 0.0240 0.0140 99.4 4.8 200 0.42 150 362 87.4 Example 2 Comparative 0.0004 0.0010 99.1 5.3 189 0.45 150 462 88.8 Example 3 Comparative 0.0310 0.0080 99.2 5.9 178 0.42 150 518 87.2 Example 4 Comparative 0.0070 — 98.8 4.9 200 0.38 150 345 88.2 Example 5 Comparative 0.0120 — 99.1 5.5 189 0.38 150 301 87.5 Example 6 Comparative 0.0300 — 99.1 5.2 200 0.40 150 309 86.4 Example 7 Comparative — 0.0020 99.3 5.3 192 0.41 150 441 88.4 Example 8 Comparative — 0.0145 98.8 5.1 198 0.40 150 323 87.5 Example 9 Comparative — 0.0230 99.0 5.1 203 0.40 150 385 87.4 Example 10 Reference 0.0150 0.0040 99.8 9.0 110 0.40 150 227 87.4 Example 1 Reference 0.0190 0.0050 99.8 15.0 96 0.40 150 227 87.4 Example 2

Reference Example 3

(36) A sintered body, a sputtering target, and a transparent conductive film were produced by methods similar to those used in Examples 1 to 20, except that the additive element was changed to Sn. The evaluation results are shown in Table 2. From these results, it is understood that the present invention can achieve low resistance at a low-temperature process, even when compared to In.sub.2O.sub.3 (ITO) having added Sn, which is currently generally used.

(37) TABLE-US-00002 TABLE 2 Final composition of Average Three- Light powder and composition Relative crystal point transmittance in of sintered body density of grain size of flexural Ra of Annealing wavelength range Additive sintered body sintered body strength target temperature Resistivity of 400 to 800 nm element M M/(In + M) (%) (μm) (MPa) (μm) (° C.) (μΩ .Math. cm) (%) Reference Sn 0.0270 99.0 3.9 215 0.42 150 331 86.7 Example 3

(38) The present invention has been explained in detail with reference to particular embodiments; however, it is clearly known to those having ordinary skill in the art that various modifications or corrections can be added without deviating from the essence and scope of the present invention.

(39) Meanwhile, the entire disclosures of the specifications, claims, drawings, and abstracts of Japanese Patent Application No. 2016-031403, filed on Feb. 22, 2016, and Japanese Patent Application No. 2016-223540, filed on Nov. 16, 2016, are incorporated herein by reference as disclosures of the specification of the present invention.

INDUSTRIAL APPLICABILITY

(40) According to the present invention, a sputtering target and an oxide sintered body that is suitably used as a sputtering target can be provided. By sputtering using the sputtering target, a transparent conductive oxide film can be produced while target damage during film-forming is suppressed. The transparent conductive oxide film of the present invention can realize low resistance in a production process in which the maximum temperature of a process for film-forming of the transparent conductive oxide film or device fabrication is suppressed to a low temperature. Therefore, for example, when the transparent conductive oxide film is used in a solar cell, optical losses and heat generation caused by light absorption can be suppressed compared to conventional cases. Furthermore, since the transparent conductive oxide film of the present invention has low resistivity and high transmittance when produced in a low-temperature film-forming process, the transparent conductive oxide film can be suitably used in touch panel applications where flexible substrates such as films are used, in addition to glass substrates. Furthermore, since the transparent conductive oxide film of the present invention has high durability, the transparent conductive oxide film can be suitably used for various device usage applications.