JP7203088B2 - Oxide sintered body, sputtering target and transparent conductive film - Google Patents

Description

The disclosed embodiments relate to oxide sintered bodies, sputtering targets, and transparent conductive films.

Conventionally, a sputtering target for forming a transparent conductive film in which niobium or the like is added to ITO (Indium Tin Oxide) to improve the transmittance in the violet region (for example, a wavelength of 400 nm) is known (for example, Patent Document 1).

WO2011/052375

However, transparent conductive films formed using conventional sputtering targets have room for improvement in transmittance in short wavelength regions such as the ultraviolet region (eg, wavelength 300 nm) and violet region (eg, 400 nm).

One aspect of the embodiment has been made in view of the above, and in a transparent conductive film formed using a sputtering target, it is possible to improve the transmittance in the short wavelength region such as the ultraviolet region and the violet region. An object of the present invention is to provide an oxide sintered body capable of

An oxide sintered body according to one aspect of an embodiment is an oxide sintered body containing indium, niobium, tin, and oxygen, and contains 90.0% by mass or more of the indium in terms of In ₂ O ₃ , It contains 3.5 to 6.5% by mass of niobium in terms of Nb ₂ O ₅ and 0.5 to 2% by mass of tin in terms of SnO ₂ .

According to one aspect of the embodiment, it is possible to improve the transmittance of the formed transparent conductive film in a short wavelength region such as an ultraviolet region and a violet region.

FIG. 1 is a graph showing the wavelength dependence of transmittance of transparent conductive films according to Example 2 and Comparative Examples 1 and 4 before heat treatment. FIG. 2 is a graph showing the wavelength dependence of the transmittance of the transparent conductive films according to Example 2 and Comparative Examples 1 and 4 after heat treatment.

Hereinafter, embodiments of an oxide sintered body, a sputtering target, and a transparent conductive film disclosed in the present application will be described with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

The oxide sintered body of the embodiment contains indium (In), niobium (Nb), tin (Sn) and oxygen (O), and can be used as a sputtering target. The oxide sintered body of the embodiment contains 90.0% by mass or more of indium in terms of In ₂ O ₃ , 3.5 to 6.5% by mass of niobium in terms of Nb ₂ O ₅ , tin contains 0.5 to 2% by mass in terms of SnO ₂ . That is, the oxide sintered body of the embodiment contains indium as a main component and niobium, tin and oxygen as other components.

This makes it possible to improve the transmittance of a transparent conductive film formed by using such an oxide sintered body as a sputtering target in a short wavelength region such as an ultraviolet region and a violet region.

In addition, the transparent conductive film of the embodiment contains indium, niobium, tin, and oxygen, contains 90.0% by mass or more of indium in terms of In ₂ O ₃ , and contains 3.5 to 6% of niobium in terms of Nb ₂ O ₅ . 0.5% by mass, and 0.5 to 2% by mass of tin in terms of SnO ₂ . That is, the transparent conductive film of the embodiment contains indium as a main component and niobium, tin and oxygen as other components.

This makes it possible to improve the transmittance of the transparent conductive film in the short wavelength region such as the ultraviolet region and the violet region. Therefore, according to the embodiment, for example, when such a transparent conductive film is applied to a transparent electrode of a solar cell, light in the ultraviolet region (i.e., ultraviolet rays) incident on the solar cell can also be utilized for power generation. , the power generation efficiency of the solar cell can be improved.

The oxide sintered body of the embodiment contains 90.0% by mass or more of indium in terms of In ₂ O ₃ . Thereby, the conductivity and transmittance of the transparent conductive film formed by using such an oxide sintered body as a sputtering target can be maintained satisfactorily.

The oxide sintered body of the embodiment preferably contains 91.5 to 96.0% by mass of indium in terms of In ₂ O ₃ , more preferably 92.5 to 95.0% by mass. , 93.6 to 94.4% by mass.

Further, the oxide sintered body of the embodiment preferably contains 4.0 to 6.0% by mass of niobium in terms of Nb ₂ O ₅ and 0.5 to 2% by mass of tin in terms of SnO ₂ . . Thereby, the conductivity of the transparent conductive film formed by using such an oxide sintered body as a sputtering target can be maintained satisfactorily.

The oxide sintered body of the embodiment preferably contains 4.5 to 5.5% by mass of niobium in terms of Nb ₂ O ₅ and 0.5 to 2% by mass of tin in terms of SnO ₂ . It preferably contains 4.8 to 5.2% by mass of niobium in terms of Nb ₂ O ₅ and more preferably 0.8 to 1.2% by mass of tin in terms of SnO ₂ .

The transparent conductive film of the embodiment contains 90.0% by mass or more of indium in terms of In ₂ O ₃ . Thereby, the conductivity and transmittance of the transparent conductive film can be favorably maintained.

The transparent conductive film of the embodiment preferably contains 91.5 to 96.0% by mass, more preferably 92.5 to 95.0% by mass of indium in terms of In ₂ O ₃ . 0.6 to 94.4% by mass is more preferable.

Further, the transparent conductive film of the embodiment preferably contains 4.0 to 6.0% by mass of niobium in terms of Nb ₂ O ₅ and 0.5 to 2% by mass of tin in terms of SnO ₂ . Thereby, the conductivity of such a transparent conductive film can be maintained satisfactorily.

The transparent conductive film of the embodiment more preferably contains 4.5 to 5.5% by mass of niobium in terms of Nb ₂ O ₅ and 0.5 to 2% by mass of tin in terms of SnO ₂ . It is more preferable to contain 4.8 to 5.2% by mass of niobium in terms of Nb ₂ O ₅ and 0.8 to 1.2% by mass of tin in terms of SnO ₂ .

Further, the oxide sintered body and the transparent conductive film of the embodiment are more preferably composed of indium as a main component and niobium, tin and oxygen as other components.

In addition, the oxide sintered body and the transparent conductive film of the embodiment may contain unavoidable impurities derived from raw materials and the like. Inevitable impurities in the oxide sintered body of the embodiment include Fe, Cr, Ni, Si, W, Zr, etc., and their contents are usually 100 ppm or less.

Further, the oxide sintered body of the embodiment preferably has a specific resistance of 7.0×10 ⁻⁴ Ω·cm or less. Thereby, when such an oxide sintered body is used as a sputtering target, sputtering using an inexpensive DC power supply becomes possible, and the film formation rate can be improved.

The oxide sintered body of the embodiment preferably has a specific resistance of 5.0×10 ⁻⁴ Ω·cm or less, more preferably 4.0×10 ⁻⁴ Ω·cm or less. , 3.0×10 ⁻⁴ Ω·cm or less.

Further, the oxide sintered body of the embodiment has a relative density of 95% or more. Thereby, when such an oxide sintered body is used as a sputtering target, the discharge state of DC sputtering can be stabilized. The oxide sintered body of the embodiment preferably has a relative density of 97% or more, more preferably 99% or more.

When the relative density is 95% or more, when such an oxide sintered body is used as a sputtering target, voids can be reduced in the sputtering target, and it is easy to prevent gas components from being taken into the atmosphere. In addition, during sputtering, abnormal discharge originating from such gaps, cracking of the sputtering target, and the like are less likely to occur.

Further, the transparent conductive film of the embodiment preferably has a transmittance at a wavelength of 300 nm of 52% or more, more preferably 55% or more, even more preferably 58% or more, and 60% or more. is more preferred.

<Each manufacturing process of the oxide sputtering target>
The oxide sputtering target of the embodiment can be manufactured, for example, by the method shown below. First, raw material powders are mixed. Raw material powders _are usually _In2O3 powder _{, Nb2O5} powder and _SnO2 powder. The average particle size of each raw material powder is preferably 5 μm or less, and the difference in average particle size between each raw material powder is preferably 2 μm or less. The average particle size of the raw material powder is the volume cumulative particle size _D50 at a cumulative volume of 50% by volume measured by a laser diffraction/scattering particle size distribution measurement method.

The mixing ratio of each raw material powder is appropriately determined so as to achieve a desired ratio of constituent elements in the oxide sintered body.

Since particles of each raw material powder are usually agglomerated, it is preferable to crush and mix them in advance, or to crush them while mixing.

There are no particular restrictions on the method of pulverizing or mixing the raw material powders. For example, the raw material powders can be put in a pot and pulverized or mixed with a ball mill.

The mixed powder thus obtained can be molded as it is to form a molded body, which can be sintered. As this binder, binders used for obtaining molded bodies in known powder metallurgy methods, such as polyvinyl alcohol and acrylic emulsion binders, can be used. Alternatively, a slurry may be prepared by adding a dispersion medium to the mixed powder, the slurry may be spray-dried to prepare granules, and the granules may be molded.

As a molding method, a method conventionally employed in powder metallurgy, such as cold pressing or CIP (Cold Isostatic Pressing), can be used.

Alternatively, the mixed powder may be temporarily pressed to produce a temporary molded body, and the pulverized powder obtained by pulverizing this may be subjected to main pressing to produce a molded body.

In addition, you may produce a molded object using wet molding methods, such as a slip casting method. The relative density of the compact is usually 50-75%.

Next, the obtained molded body is fired to produce a sintered body. A firing furnace for producing such a sintered body is not particularly limited, and a firing furnace that can be used for producing a ceramic sintered body can be used.

The firing temperature is preferably 1300°C to 1600°C, more preferably 1400°C to 1600°C. While the higher the firing temperature is, the higher the density of the sintered body can be obtained, it is preferable to control the temperature below the above temperature from the viewpoint of suppressing enlargement of the structure of the sintered body and preventing cracks.

The retention time at such a firing temperature is preferably 3 to 30 hours, more preferably 5 to 20 hours. A high-density sintered body can be obtained when the holding time is within the above range. The heating rate is preferably 100 to 500° C./h from the viewpoint of increasing the density and preventing cracks. An oxygen atmosphere is preferable as the firing atmosphere.

Next, the obtained sintered body is cut. Such cutting is performed using a surface grinder or the like. Further, the surface roughness Ra after cutting can be appropriately controlled by selecting the size of abrasive grains of the grindstone used for cutting.

A sputtering target is produced by bonding the cut sintered body to a substrate. Stainless steel, copper, titanium, or the like can be appropriately selected as the material of the base material. A low melting point solder such as indium can be used as the joining material.

[Example 1]
In ₂ O ₃ powder with an average particle size of 0.7 μm, Nb ₂ O ₅ powder with an average particle size of 1.2 μm, and SnO ₂ powder with an average particle size of 0.9 μm were mixed with zirconia in a pot. A mixed powder was prepared by ball mill dry mixing with balls.

The average particle size of the raw material powder was measured using a particle size distribution analyzer HRA manufactured by Nikkiso Co., Ltd. In this measurement, water was used as a solvent, and the refractive index of the substance to be measured was 2.20.

When preparing such a mixed powder, indium is 94.5% by mass in terms of In ₂ O ₃ , niobium is 5.0% by mass in terms of Nb ₂ O ₅ , and tin is 0.5 mass in terms of SnO ₂ . %.

Next, 6% by mass of polyvinyl alcohol diluted to 4% by mass was added to the mixed powder, and the polyvinyl alcohol was well blended with the powder using a mortar and passed through a 5.5 mesh sieve. Then, the obtained powder was temporarily pressed under the condition of 200 kg/cm ² , and the obtained temporary compact was pulverized in a mortar. Next, the obtained pulverized powder was filled into a press mold and molded at a press pressure of 1 t/cm ² for 60 seconds to obtain a molded body.

Next, this molded body was fired to produce a sintered body. The firing was performed in an oxygen flow atmosphere in which oxygen was flowed at 10 L/min in the furnace at a firing temperature of 1550°C, a firing time of 9 hours, a heating rate of 350°C/h and a cooling rate of 100°C/h.

Next, the obtained sintered body was cut to obtain an oxide sintered body having a width of 210 mm, a length of 710 mm, and a thickness of 6 mm with a surface roughness Ra of 1.0 μm. A #170 whetstone was used for this cutting.

[Examples 2 to 7]
Using the same method as in Example 1, an oxide sintered body was obtained. In Examples 2 to 7, when the mixed powder was prepared, the contents of indium, niobium and tin were adjusted to be the contents shown in Table 1 in terms of In ₂ O ₃ , Nb ₂ O ₅ and SnO ₂ . Each raw material powder was blended in.

[Comparative Examples 1 to 6]
Using the same method as in Example 1, an oxide sintered body was obtained. In Comparative Examples 1 to 6, when the mixed powder was prepared, the contents of indium, niobium and tin were adjusted to be the contents shown in Table 1 in terms of In ₂ O ₃ , Nb ₂ O ₅ and SnO ₂ . Each raw material powder was blended in.

In Examples 1 to 7 and Comparative Examples 1 to 6, it was confirmed that the content of each element weighed when preparing each raw material powder was equal to the content of each element in the obtained oxide sintered body. It was confirmed by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy).

Subsequently, the relative densities of the oxide sintered bodies of Examples 1 to 7 and Comparative Examples 1 to 6 obtained above were measured. Such relative density was measured based on the Archimedes method.

Specifically, the air mass of the oxide sintered body is divided by the volume (the mass of the sintered body in water/the specific gravity of water at the measurement temperature), and the percentage value with respect to the theoretical density ρ (g/cm ³ ) is the relative density ( unit: %).

Moreover, the theoretical density ρ (g/cm ³ ) was calculated from the mass % and density of the raw material powder used in the production of the oxide sintered body. Specifically, it was calculated by the following formula.
ρ={(C ₁ /100)/ρ ₁ +(C ₂ /100)/ρ ₂ +(C ₃ /100)/ρ ₃ } ⁻¹

Note that C ₁ to C ₃ and ρ ₁ to ρ ₃ in the above formula respectively indicate the following values.
・C ₁ : % by mass of the In ₂ O ₃ powder used in the production of the oxide sintered body
・ρ ₁ : Density of In ₂ O ₃ (7.18 g/cm ³ )
・C ₂ : % by mass of the Nb ₂ O ₅ powder used in the production of the oxide sintered body
・ρ ₂ : Density of Nb ₂ O ₅ (4.47 g/cm ³ )
・C ₃ : % by mass of the SnO ₂ powder used in the production of the oxide sintered body
・ρ ₃ : Density of SnO ₂ (6.95 g/cm ³ )

Subsequently, specific resistance (bulk resistance) was measured for each of the oxide sintered bodies for sputtering targets of Examples 1 to 7 and Comparative Examples 1 to 6 obtained above.

Specifically, using Loresta (registered trademark) HP MCP-T410 (series 4-probe probe TYPE ESP) manufactured by Mitsubishi Chemical Corporation, a probe is applied to the surface of the oxide sintered body after processing, and AUTO RANGE mode was measured. Measurement points were five points in total, near the center and four corners of the oxide sintered body, and the average value of the measured values was taken as the bulk resistance value of the sintered body.

Here, for Examples 1 to 7 and Comparative Examples 1 to 6 described above, Table 1 shows the content of each element contained in the mixed powder and the measurement results of relative density and specific resistance (bulk resistance). .

It can be seen that the oxide sintered bodies of Examples 1 to 7 all have a specific resistance of 7.0×10 ⁻⁴ Ω·cm or less. Therefore, according to the embodiment, when the oxide sintered body is used as a sputtering target, sputtering using an inexpensive DC power supply becomes possible, and the film formation rate can be improved.

Subsequently, sputtering targets of Examples 1 to 7 and Comparative Examples 1 to 6 were produced from the oxide sintered bodies of Examples 1 to 7 and Comparative Examples 1 to 6 obtained above. Such a sputtering target was produced by using indium, which is a low melting point solder, as a bonding material, and bonding the oxide sintered body obtained above to a base material made of copper.

Subsequently, using the sputtering targets of Examples 1 to 7 and Comparative Examples 1 to 6, sputtering was performed under the following conditions to form a thin film having a thickness of 100 nm.
・Deposition device: EX-3013M (DC sputtering device) manufactured by Vacuum Equipment Industry Co., Ltd.
・Ultimate vacuum: less than 1×10 ⁻⁴ Pa ・Sputtering gas: Ar/O ₂ mixed gas ・Sputtering gas pressure: 0.4 Pa
・ O ₂ gas flow rate: 0 to 2.0 sccm
・ Substrate: glass substrate (EAGLE XG (registered trademark) manufactured by Corning)
・Substrate temperature: room temperature ・Sputtering power: 3 W/cm ²

In Examples 1 to 7 and Comparative Examples 1 to 6, the content of each element in the oxide sintered body used for the sputtering target was equal to the content of each element in the formed transparent conductive film. was confirmed by ICP-AES.

Subsequently, each glass substrate was cut into a predetermined size, and the transparent conductive films of Examples 1 to 7 and Comparative Examples 1 to 6 were formed by sputtering on the cut glass substrate. was measured.

Furthermore, the cut glass substrate was heat-treated in the atmosphere at 200° C. for 1 hour, and the wavelength dependence of the transmittance of the transparent conductive film after the heat treatment was also measured. The measurement conditions for the wavelength dependence of the transmittance before and after the above heat treatment are as follows.
・Measuring device: Ultraviolet-visible-near-infrared spectrophotometer UH4150 manufactured by Hitachi High-Tech Science Co., Ltd.
・Scan speed: 600 nm/min
・Wavelength range: 200 to 2600 nm

In the measurement of the transmittance of the transparent conductive film, first, a plain glass substrate on which no film was formed was set in the apparatus, the baseline was measured, and then the transmittance of each film-formed sample was measured.

FIG. 1 is a graph showing the wavelength dependence of the transmittance of transparent conductive films according to Example 2 and Comparative Examples 1 and 4 before heat treatment. FIG. 2 shows the transmittance of the same transparent conductive films after heat treatment. It is a graph showing wavelength dependence. As shown in FIGS. 1 and 2, the transmittance of the transparent conductive film can be improved as a whole by subjecting the transparent conductive film formed by sputtering to a predetermined heat treatment.

Subsequently, the specific resistance of each transparent conductive film heat-treated after film formation was measured. The specific resistance of the transparent conductive film was measured using a four-probe K-705RS manufactured by Kyowa Riken Co., Ltd.

Here, for the transparent conductive films of Examples 1 to 7 and Comparative Examples 1 to 6 described above, the results of transmittance measurement at wavelengths of 300 nm, 400 nm and 550 nm before and after heat treatment and the results of resistivity measurement after heat treatment are shown. 2. In addition, the evaluation criteria in the specific resistance measurement shown in Table 2 are as follows.
A: Specific resistance is 4.5×10 ⁻⁴ Ω·cm or less.
B: The specific resistance exceeds 4.5×10 ⁻⁴ Ω·cm and is 6.0×10 ⁻⁴ Ω·cm or less.
C: The specific resistance exceeds 6.0×10 ⁻⁴ Ω·cm.

The transparent conductive film after the heat treatment contains 90.0% by mass or more of indium in terms of In ₂ O ₃ , 3.5 to 6.5% by mass of niobium in terms of Nb ₂ O ₅ , and tin in terms of SnO ₂ . By comparison between Examples 1 to 7 containing 0.5 to 2% by mass of indium and Comparative Examples 1 to 6 containing no niobium or tin at such a content, 90.0% by mass of indium in terms of In ₂ O ₃ By containing 3.5 to 6.5% by mass of niobium in terms of Nb ₂ O ₅ and 0.5 to 2% by mass of tin in terms of SnO ₂ , It can be seen that the transmittance is improved to 52% or more.

In addition, in the transparent conductive films after the heat treatment, as shown in Table 2 and FIG. 2, in Examples 1 to 7, not only the ultraviolet region but also the visible region (for example, wavelengths of 400 nm to 800 nm) are equivalent to those of Comparative Examples 1 to 6. or higher transmittance. That is, in the embodiment, when such a transparent conductive film is applied to a transparent electrode of a solar cell, light in a wide wavelength range incident on such a solar cell can be utilized for power generation.

Therefore, according to the embodiment, it is possible to further improve the power generation efficiency of a solar cell to which such a transparent conductive film is applied.

Further, it contains 90.0% by mass or more of indium in terms of In ₂ O ₃ , 4.0 to 6.0% by mass of niobium in terms of Nb ₂ O ₅ , and 0.5 to 2% by mass of tin in terms of SnO ₂ . By comparison between Examples 1 to 3, 5, and 6 containing % by mass and Examples 4 and 7 containing no niobium at such a content rate, it was found that the indium content was 90.0% by mass or more in terms of In ₂ O ₃ , By containing 4.0 to 6.0% by mass of niobium in terms of Nb ₂ O ₅ and 0.5 to 2% by mass of tin in terms of SnO ₂ , the conductivity of the transparent conductive film is well maintained. I know there is.

Furthermore, it contains 90.0% by mass or more of indium in terms of In ₂ O ₃ , 4.5 to 5.5% by mass of niobium in terms of Nb ₂ O ₅ , and 0.5 to 2% by mass of tin in terms of SnO ₂ . By comparison between Examples 1 to 3 containing niobium at such a content rate and Examples 1 to 3 containing no niobium at such a content rate, it was found that 90.0% by mass or more of indium is contained in terms of In ₂ O ₃ and niobium is contained in Nb ₂ By containing 4.5 to 5.5% by mass in terms of O ₅ and 0.5 to 2% by mass in terms of SnO ₂ of tin, the transmittance in the violet region (wavelength 400 nm) is 93.2% or more. It can be seen that there is an improvement in

Furthermore, it contains 90.0% by mass or more of indium in terms of In ₂ O ₃ , 4.8 to 5.2% by mass of niobium in terms of Nb ₂ O ₅ , and 0.8 to 0.8% by mass of tin in terms of SnO ₂ . By comparing Example 2 containing 1.2% by mass with Examples 1 and 3 to 7 containing no niobium or tin at such a content, 4.8 to 5.2 masses of niobium converted to Nb ₂ O ₅ % and containing 0.8 to 1.2% by mass of tin in terms of SnO ₂ , the transmittance in the ultraviolet region (wavelength 300 nm) is improved to 61.4% or more, and the violet region (wavelength 400 nm ) is improved to 94.6% or more.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in the embodiments, an example in which the transparent conductive film is applied to a solar cell has been described, but the device to which the transparent conductive film according to the embodiments is applied is not limited to the solar cell.

For example, when the transparent conductive film according to the embodiment is applied to a transparent electrode in an image display device such as liquid crystal or organic EL (electro-luminescence), the transmittance in the short wavelength region such as the ultraviolet region and the violet region is high. Emission efficiency in the short wavelength region can be improved.

In addition, by applying the transparent conductive film according to the embodiment to an antistatic film of an optical system in an ultraviolet light source such as an ultraviolet lamp, it is possible to improve the luminous efficiency in the ultraviolet region and stably emit ultraviolet light without charging. be able to.

Further, in the embodiments, an example in which a sputtering target is produced using a plate-shaped oxide sintered body is shown, but the shape of the oxide sintered body is not limited to a plate-like shape, and may be any shape such as a cylindrical shape. It may be in shape.

Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the invention are not limited to the specific details and representative embodiments so shown and described. Accordingly, various changes may be made without departing from the spirit or scope of the general inventive concept defined by the appended claims and equivalents thereof.

Claims (7)

An oxide sintered body containing indium, niobium, tin and oxygen,
90.0% by mass or more of indium in terms of In ₂ O ₃ , 4.8 to 6.5% by mass of niobium in terms of Nb ₂ O ₅ , and 0.5 to 6.5% by mass of tin in terms of SnO ₂ Oxide sintered body containing 2% by mass. The oxide sintered body according to claim 1, containing 4.8 to 6.0% by mass of niobium in terms of Nb ₂ O ₅ . 3. The oxide sintered body according to claim 1, having a specific resistance of 7.0×10 ⁻⁴ Ω·cm or less. The oxide sintered body according to any one of claims 1 to 3, having a relative density of 95% or more. A sputtering target using the oxide sintered body according to any one of claims 1 to 4 as a target material. A transparent conductive film containing indium, niobium, tin and oxygen,
90.0% by mass or more of indium in terms of In ₂ O ₃ , 4.8 to 6.5% by mass of niobium in terms of Nb ₂ O ₅ , and 0.5 to 6.5% by mass of tin in terms of SnO ₂ A transparent conductive film containing 2% by mass. 7. The transparent conductive film according to claim 6, which has a transmittance of 52% or more at a wavelength of 300 nm.

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