JP7086080B2 - Oxide sintered body and sputtering target - Google Patents

Description

The present invention relates to an oxide sintered body and a sputtering target, and more particularly, it is possible to prepare a sputtering target capable of obtaining a thin film having a high transmittance and a low specific resistance in the visible light region, and such a target. Regarding the oxide sintered body that can be formed.

With the development of display devices centered on liquid crystals, the demand for transparent conductive films is increasing. High transparency is required for the transparent conductive film, and low resistance is also required. Due to the demand for high transparency and low resistance, ITO film is widely used as a transparent conductive film. As a method for forming an ITO transparent conductive film, a method of sputtering an ITO sputtering target to form a film is generally used from the viewpoint of operability.

In particular, recently, with the colorization of liquid crystals, the miniaturization of elements, and the adoption of the active matrix method, there is a demand for a high-performance ITO transparent conductive film having higher transparency and lower resistance.
Patent Document 1 describes a transparent conductive film having a high transmittance and low resistance containing 1 to 20% by weight of tin oxide and 0.05 to 5% by weight of titanium oxide, and a sputtering target at 300 ° C. It is described that it is possible to increase the transmittance and reduce the resistance of the transparent conductive film by heat treatment, so-called annealing.

Patent Document 2 describes a method for producing a transparent conductive film in which a sputtering target made of an oxide such as indium oxide, tin oxide and titanium oxide is sputtered and the obtained indium tin oxide thin film is crystallized by heat treatment. .. In this method, the amorphous indium tin oxide thin film obtained by sputtering is crystallized by a heat treatment at 200 ° C. or higher, so that the specific resistance of the thin film can be reduced and the conductivity characteristics can be improved.

However, the method that requires heat treatment at a high temperature of 200 ° C. or higher cannot be applied when a transparent conductive film is formed on a resin film that is deformed at 200 ° C. or higher.

Japanese Unexamined Patent Publication No. 4-277408 Japanese Patent No. 5726752

An object of the present invention is to provide a sputtering target capable of forming a thin film capable of obtaining a transparent conductive film having high transparency and low resistance without heat treatment at a high temperature.

In the oxide sintered body of the present invention, the constituent elements are In, Sn, Ti and O, and the In content ratio is 88.0 to 98.2% by mass in terms of In ₂ O ₃ , and the Sn content ratio. Is 1.0 to 8.0% by mass in terms of SnO ₂ , and the content ratio of Ti is 0.8 to 4.0% by mass in terms of TiO ₂ .

The oxide sintered body preferably has a specific resistance of 5.0 × 10 ^-4 Ωcm or less, and preferably has a relative density of 95% or more.
The sputtering target material of the present invention comprises the oxide sintered body.
The sputtering target of the present invention is formed by joining the sputtering target material to a base material.

The transparent conductive film of the present invention has an In content ratio of 88.0 to 98.2% by mass in terms of In ₂ O ₃ and a Sn content ratio of 1.0 to 8.0% by mass in terms of Sn O ₂ . Yes, the Ti content ratio is 0.8 to 4.0% by mass in terms of TiO ₂ .

In the method for producing a transparent conductive film of the present invention, a thin film formed by sputtering the sputtering target is heat-treated at 110 to 145 ° C.

The oxide sintered body of the present invention provides a sputtering target capable of forming a thin film capable of obtaining a transparent conductive film having high transparency and a transparent conductive film having low resistance without high-temperature heat treatment. be able to.

FIG. 1 is a diagram showing the light transmittance of the thin film obtained by sputtering and the transparent conductive film obtained by heat-treating the thin film at 125 ° C. in the wavelength range of 300 nm to 800 nm in Example 15. FIG. 2 is a diagram showing the light transmittance of the transparent conductive film obtained by heat-treating the thin film obtained by sputtering in Example 15 and Comparative Examples 1 and 3 at 125 ° C. in the wavelength range of 300 nm to 800 nm. be.

In the oxide sintered body of the present invention, the constituent elements are In, Sn, Ti and O, and the In content ratio is 88.0 to 98.2% by mass in terms of In ₂ O ₃ , and the Sn content ratio. Is 1.0 to 8.0% by mass in terms of SnO ₂ , and the content ratio of Ti is 0.8 to 4.0% by mass in terms of TiO ₂ .

The oxide sintered body has an In content ratio of 88.0 to 98.2% by mass, preferably 90.0 to 97.0% by mass, and more preferably 91.5 to 96.% In terms of In ₂ O ₃ . It is 0% by mass, more preferably 93.0 to 95.5% by mass, and the Sn content ratio is 1.0 to 8.0% by mass, preferably 2.0 to 7.0% by mass in terms of SnO ₂ . It is more preferably 2.7 to 6.0% by mass, further preferably 3.0 to 5.0% by mass, and the Ti content ratio is 0.8 to 4.0% by mass in terms of TiO ₂ , preferably 1. It is 0.0 to 3.0% by mass, more preferably 1.3 to 2.5% by mass, and further preferably 1.5 to 2.0% by mass. It goes without saying that an oxide sintered body as in the present invention may contain unavoidable impurities derived from raw materials and the like, and the oxide sintered body of the present invention may also contain unavoidable impurities. Examples of the unavoidable impurities in the oxide sintered body of the present invention include Fe, Cr, Ni, Si, W, Zr and the like, and their contents are usually 100 ppm or less.

In the present invention, the constituent elements mean constituent elements excluding unavoidable impurities in the oxide sintered body or the transparent conductive film, and the content ratio of each constituent element is applied to the entire oxide sintered body or the transparent conductive film. It means the content ratio of each constituent element.

The specific resistance of the oxide sintered body is preferably 5.0 × 10 ^-4 Ωcm or less, more preferably 4.8 × 10 ^-4 Ωcm or less, and 4.5 × 10 ^-4 Ωcm or less. The following is more preferable. As a result, sputtering using an inexpensive DC power supply becomes possible, the film formation rate can be improved, and the occurrence of abnormal discharge can be suppressed.

The relative density of the oxide sintered body is preferably 95% or more, more preferably 98% or more, still more preferably 99% or more. When the relative density is 95% or more, efficient sputtering without generation of nodules and arcing is possible. The upper limit of the relative density is not particularly limited and may exceed 100%. The relative density is a numerical value measured based on the Archimedes method.

The oxide sintered body can be produced, for example, by the method shown below.
First, the raw material powder is mixed. The raw material powder is usually In ₂ O ₃ powder, SnO ₂ powder and TiO ₂ powder. The In ₂ O ₃ powder, Sn O ₂ powder and TiO ₂ powder are mixed so that the contents of In, Sn and Ti in the obtained sintered body are within the above ranges, respectively. The content ratios of In ₂ O ₃ powder, SnO ₂ powder and TiO ₂ powder in the mixed powder obtained by mixing the raw material powders are the In ₂ O ₃ equivalent In content ratio and SnO in the oxide sintered body. It matches the Sn content ratio converted to ₂ and the Ti content ratio converted to TiO ₂ , respectively.

Since the particles of each raw material powder are usually agglomerated, it is preferable to grind them in advance and mix them, or to grind them while mixing.
The method for crushing and mixing the raw material powder is not particularly limited, and for example, the raw material powder can be placed in a pot and crushed or mixed by a ball mill.

The obtained mixed powder can be molded as it is to form a molded product, which can be sintered, but if necessary, a binder may be added to the mixed powder and molded to form a molded product. As the binder, a binder used for obtaining a molded product in a known powder metallurgy method, for example, polyvinyl alcohol, an acrylic emulsion binder, or the like can be used. Alternatively, a dispersion medium may be added to the mixed powder to prepare a slurry, and the slurry may be spray-dried to prepare granules, and the granules may be formed.
As the molding method, a method conventionally adopted in the powder metallurgy method, for example, cold pressing, CIP (cold isotropic molding), or the like can be used.

Alternatively, the mixed powder may be temporarily pressed to produce a temporary molded product, and the crushed powder obtained by crushing the mixed powder may be subjected to main pressing to produce a molded product.
A molded product may be produced by using a wet molding method such as a slip cast method.
The obtained molded body may be degreased by a method conventionally adopted in the powder metallurgy method, if necessary. The density of the molded product is usually 50 to 75%.

Next, the obtained molded body is fired to prepare an oxide sintered body. The firing furnace used for firing is not particularly limited as long as the cooling rate can be controlled during cooling, and a firing furnace generally used for powder metallurgy may be used. An oxygen atmosphere is suitable as the firing atmosphere.

The rate of temperature rise is usually 100 to 500 ° C./h from the viewpoint of increasing the density and preventing cracking. The firing temperature is 1300 to 1600 ° C, preferably 1400 to 1600 ° C. When the firing temperature is within the above range, a high-density oxide sintered body can be obtained. The holding time at the firing temperature is usually 3 to 30 hours, preferably 5 to 20 hours. When the holding time is within the above range, it is easy to obtain a high-density oxide sintered body.
The cooling rate is usually 300 ° C./hr or less, preferably 50 ° C./hr or less.

The sputtering target material of the present invention comprises the oxide sintered body. Specifically, the sputtering target material can be obtained by cutting the oxide sintered body into a desired shape as needed and performing processing such as grinding.

The composition of the sputtering target material and the physical property values such as specific resistance and relative density are the same as the composition, specific resistance, relative density and the like of the oxide sintered body.
A sputtering target can be obtained by joining the sputtering target material to the substrate. The substrate is usually made of Cu, Al, Ti or stainless steel. As the joining material, a joining material used for joining a conventional ITO target material, for example, In metal can be used. The joining method is also the same as the conventional joining method of the ITO target material.

A thin film can be formed by sputtering the sputtering target. Sputtering can be performed according to the conditions in sputtering using a normal ITO sputtering target.

The thin film thus obtained is usually amorphous. By heat-treating this thin film, so-called annealing, it can be crystallized, and a transparent conductive film having high light transmittance and low resistivity can be obtained. Regarding the light transmittance, the light transmittance can be remarkably increased particularly in a short wavelength region, for example, a wavelength region of 300 to 380 nm.

The temperature required for this heat treatment is 110 ° C. to 145 ° C., preferably 115 to 140 ° C., and more preferably 120 ° C. to 135 ° C. As described above, a temperature of 200 ° C. or higher was required for the heat treatment for increasing the transmittance and lowering the resistance of the conventionally known ITO thin film. On the other hand, the temperature of the heat treatment for increasing the transmittance and lowering the resistance of the thin film obtained by sputtering the sputtering target of the present invention may be as low as 110 to 145 ° C. Therefore, if the sputtering target of the present invention is used, even when a transparent conductive film is formed on a resin film or the like that is deformed at 200 ° C. or higher, the film or the like is deformed. A transparent conductive film having high light transmittance and low resistance can be produced without causing it. On the other hand, when the heat treatment is performed at a temperature exceeding 145 ° C., sufficient high transmittance and low resistivity cannot be obtained, but rather a conventional ITO film (In ₂ O ₃ : SnO ₂ = 90: 10 (mass ratio)). It is not preferable because the transmittance tends to be lower and the specific resistance tends to be higher.

The time required for the heat treatment is usually 0.1 to 2 hours, preferably 0.5 to 1 hour. The heat treatment can be performed in the atmosphere.
By subjecting the thin film obtained by sputtering the sputtering target of the present invention to the heat treatment, the light transmittance and the specific resistance can be improved.

In particular, the light transmittance has been conventionally known in the wavelength range of visible light (for example, 380 to 750 nm), and particularly in the short wavelength range (for example, 300 to 380 nm) by performing the heat treatment at the above temperature. It can be made higher than the ITO thin film (In ₂ O ₃ : SnO ₂ = 90: 10 (mass ratio)).

The transparent conductive film thus obtained has In, Sn, Ti and O as constituent elements, and for example, the content ratio of In is 88.0 to 98.2% by mass in terms of In ₂ O ₃ . It is preferably 90.0 to 97.0% by mass, more preferably 91.5 to 96.0% by mass, still more preferably 93.0 to 95.5% by mass, and the Sn content ratio is in terms of SnO ₂ . It is 1.0 to 8.0% by mass, preferably 2.0 to 7.0% by mass, more preferably 2.7 to 6.0% by mass, and further preferably 3.0 to 5.0% by mass. _The Ti content is 0.8 to 4.0% by mass, preferably 1.0 to 3.0% by mass, more preferably 1.3 to 2.5% by mass, and even more preferably. Is 1.5 to 2.0% by mass. As described above, this transparent conductive film has a high light transmittance and may have a low resistance.

（式中C1～Ciはそれぞれ酸化物焼結体の構成物質の含有量（質量％）を示し、ρ1～ρiはC1～Ciに対応する各構成物質の密度（ｇ／ｃｍ³）を示す。）
下記実施例および比較例において酸化物焼結体の製造に使用する物質（原料）は、Ｉｎ₂Ｏ₃、ＳｎＯ₂、ＴｉＯ₂であるため、例えば
Ｃ１：酸化物焼結体に使用したＩｎ₂Ｏ₃原料の質量％
ρ１：Ｉｎ₂Ｏ₃の密度（７．１８ｇ／ｃｍ³）
Ｃ２：酸化物焼結体に使用したＳｎＯ₂原料の質量％
ρ２：ＳｎＯ₂の密度（６．９５ｇ／ｃｍ³）
Ｃ３：酸化物焼結体に使用したＴｉＯ₂原料の質量％
ρ３：ＴｉＯ₂の密度（４．２６ｇ／ｃｍ³）
を式（Ｘ）に適用することで理論密度ρを算出することができる。The measurement methods used in the following Examples and Comparative Examples are shown below.
1. 1. Relative Density of Oxide Sintered Body The relative density of the oxide sintered body was measured based on the Archimedes method. Specifically, the aerial mass of the oxide sintered body is divided by the volume (mass of the oxide sintered body in water / water specific gravity at the measured temperature), and the theoretical density ρ (g / cm ³ ) based on the following formula (X) is used. ) Relative density (unit:%)
And said.

(In the formula, C1 to Ci each indicate the content (mass%) of the constituent substances of the oxide sintered body, and ρ1 to ρi indicate the density (g / cm ³ ) of each constituent substance corresponding to C1 to Ci. )
In the following Examples and Comparative Examples, the substances (raw materials) used for producing the oxide sintered body are In ₂ O ₃ , SnO ₂ , and TiO _2. Therefore, for example, C1: In ₂ used for the oxide sintered body. O ₃ Raw material mass%
ρ1: In ₂ O ₃ density (7.18 g / cm ³ )
C2: Mass% of SnO ₂ raw material used for oxide sintered body
ρ2: Density of SnO ₂ (6.95 g / cm ³ )
C3: Weight% of TiO ₂ raw material used for the oxide sintered body
ρ3: TIO ₂ density (4.26 g / cm ³ )
Can be applied to the equation (X) to calculate the theoretical density ρ.

2. 2. Specific resistance of oxide sintered body The specific resistance of the oxide sintered body is sintered after processing using Loresta (registered trademark) HP MCP-T410 (series 4-probe probe TYPE ESP) manufactured by Mitsubishi Chemical Corporation. A probe was applied to the body surface and measurement was performed in AUTO RANGE mode. The measurement points were a total of 5 points near the center of the oxide sintered body and at the four corners, and the average value of each measured value was taken as the bulk resistance value of the sintered body.

3. 3. Light transmittance of the film The light transmittance of the film was measured using an ultraviolet-visible near-infrared spectrophotometer UH4150 manufactured by Hitachi High-Tech Science. The measurement conditions were set to scan speed; 600 nm / min and wavelength range; 200 to 2600 nm. First, a bare glass substrate that had not been film-formed was set in the apparatus and the baseline was measured, and then the transmittance of each film-forming sample was measured.

4. Specific resistance of the transparent conductive film The film resistivity of the transparent conductive film was measured using a four-probe measuring instrument K-705RS manufactured by Kyowa Riken Co., Ltd.

[Examples and Comparative Examples]
(Manufacturing of oxide sintered body)
The In ₂ O ₃ powder, the SnO ₂ powder, and the TiO ₂ powder were mixed at the ratios shown in Table 1 using a ball mill to prepare a mixed powder.

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

The obtained molded product is placed in a sintering furnace, oxygen is flowed into the furnace at 10 L / min, the firing atmosphere is an oxygen flow atmosphere, the temperature rise rate is 350 ° C./h, the sintering temperature is 1550 ° C., and sintering. Sintering was performed with the holding time at temperature set to 9 hours.

Then, it was cooled at a temperature lowering rate of 100 ° C./h to obtain an oxide sintered body.
Next, the obtained oxide sintered body was machined to obtain a sputtering target material having a surface roughness Ra of 1.0 μm, a width of 210 mm, a length of 710 mm, and a thickness of 6 mm. A # 170 grindstone was used for cutting.
The relative density and resistivity of the oxide sintered body were measured by the above method. The results are shown in Table 1.
In each Example and Comparative Example, it was confirmed that the content of each element measured when preparing each raw material powder was equal to the content of each element in the obtained oxide sintered body. The content of each element in the oxide sintered body can be measured by, for example, ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy).

(Manufacturing of sputtering target)
A sputtering target was manufactured by joining the sputtering target material to a copper backing plate with In solder.
(Manufacturing of transparent conductive film)
Using the sputtering target, sputtering was performed under the following conditions to form a thin film having a film thickness of 100 nm on a glass substrate.
Equipment: EX-3013M manufactured by Vacuum Equipment Industry Co., Ltd.
(DC magnetron sputtering equipment)
Ultimate vacuum: 1.0 x 10 ^-4 Pa or less Spatter gas: Ar / O ₂ mixed gas Spatter gas pressure: 0.4 Pa
Oxygen flow rate: 0-2.0 sccm
Substrate: Glass substrate (EAGLE XG (registered trademark) manufactured by Corning Inc.)
Substrate temperature: Room temperature Sputtering power: 3 W / cm ²
In each Example and Comparative Example, it was confirmed that the content of each element in the oxide sintered body used for the sputtering target material was equal to the content of each element in the film-formed transparent conductive film. The content of each element in the transparent conductive film can be measured by, for example, ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy).

The obtained thin film was heat-treated in the air at 125 ° C. for 1 hour to produce a transparent conductive film.
The light transmittance and the specific resistance of the transparent conductive film at wavelengths of 350 nm and 550 nm of the thin film and the transparent conductive film were measured by the above methods. The results of light transmittance and specific resistance are shown in Table 1.
Regarding the specific resistance, the specific resistance of the transparent conductive film (In ₂ O ₃ : SnO ₂ = 90:10 (mass ratio)) obtained in Comparative Example 1 which is a conventional ITO thin film is 4.8 × 10 ^-4 Ωcm ( (Hereinafter referred to as reference resistivity), the transparent conductive film having a specific resistance less than 1.0 times the reference specific resistance is "A", and the specific resistance is 1.0 times or more the reference specific resistance. "B" is the transparent conductive film that was less than 1.1 times, "C" is the transparent conductive film whose specific resistance is 1.1 times or more and less than 1.2 times the reference specific resistance, and the specific resistance is the reference specific resistance. The transparent conductive film which was 1.2 times or more of the above was evaluated as "D".

Further, in Example 15, the light transmittance of the thin film obtained by sputtering and the transparent conductive film obtained by heat-treating the thin film at 125 ° C. in the wavelength range of 300 nm to 800 nm is shown in FIG. In Comparative Examples 1 and 3, the light transmittance of the transparent conductive film obtained by heat-treating the thin film obtained by sputtering at 125 ° C. in the wavelength range of 300 nm to 800 nm is shown in FIG. In FIG. 1, “as-depo” means that the heat treatment has not been performed.

Claims (7)

The constituent elements are In, Sn, Ti and O, the content ratio of In is 90.0 to 96.0 % by mass in terms of In ₂ O ₃ , and the content ratio of Sn is 2.0 to 8 in terms of Sn O ₂ . An oxide sintered body having a Ti content of 1.0 % by mass, a Ti content ratio of 1.5 to 2.0 % by mass in terms of TiO ₂ , and a relative density of 95% or more . The oxide sintered body according to claim 1, wherein the specific resistance is 5.0 × 10 ^-4 Ωcm or less. A sputtering target material made of the oxide sintered body according to claim 1 or 2 . A sputtering target obtained by joining the sputtering target material according to claim 3 to a base material. It has In, Sn, Ti and O as constituent elements, the content ratio of In is 90.0 to 96.0 % by mass in terms of In ₂ O ₃ , and the content ratio of Sn is 2.0 to ₂ in terms of Sn O 2. A transparent conductive film having a Ti content of 8.0 % by mass and a Ti content of 1.5 to 2.0 % by mass in terms of TIO ₂ . When a film was formed with a film thickness of 100 nm and heat-treated at 125 ° C in the air for 1 hour, the specific resistance was 4.8 × 10. ^-Four It is less than Ω cm and has a light transmittance of 72.1% or more at a wavelength of 350 nm.
The transparent conductive film according to claim 5. A method for producing a transparent conductive film in which a thin film formed by sputtering a sputtering target according to claim 4 is heat-treated at 110 to 145 ° C.

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