JPH0668935B2 - Oxide sintered body, method for producing the same, and target using the same - Google Patents

Description

The present invention relates to a sintered body of indium oxide / tin oxide (hereinafter referred to as ITO), a method for producing the same, and an application thereof.
The ITO sintered body according to the present invention has extremely excellent performance as a sputtering target when forming a transparent conductive film by a sputtering method.

[Prior Art] In recent years, there has been a rapid increase in demand for ITO thin films as transparent conductive films used for transparent electrodes of solar cells and liquid crystal displays, touch panels and the like. The method of forming such an ITO thin film is a method of applying ITO fine particles to a base material, a method of applying an ITO precursor to a base material and then thermally decomposing it, or a sputtering method using an ITO alloy target or an ITO sintered body target. Although a method of forming an ITO film on the material surface is known, at present, a method of sputtering an ITO sintered body is the most general method.

Conventionally, an ITO sintered body is manufactured by press-molding a mixture of indium oxide and tin oxide powders and sintering it. However, since the indium oxide and tin oxide powders are originally difficult to sinter. It was extremely difficult to manufacture a high density ITO sintered body. The sintered density of the ITO sintered body is
The sintered density at a theoretical density of 100% is about 7.1 g / cm ^{3, although} it depends on the tin content.

Many of the conventional ITO sintered bodies have many pores in the sintered body, and the sintered density is at most about 60% of the theoretical density (up to 4.3 g /
cm ³ ), the conductivity was low, the specific resistance was 2 × 10 ⁻³ or more, and the color tone was yellowish green. ITO like this
Since the sintered body has low electrical conductivity and thermal conductivity, and weak mechanical strength, cracks easily occur when the input power during film formation by sputtering becomes excessive, and the film formation rate by sputtering is slow. The discharge state was very unstable. In addition, a reducing substance (black substance) is generated on the surface of the sintered body during sputtering, and this substance is mixed with the transparent conductive film generated on the surface of the base material and causes deterioration of the film quality. Each time it was produced, it had to be shut down and removed. And this has been a serious obstacle to the continuous operation of sputtering.

Therefore, in order to solve such a problem in the past, ITO
Various studies have been made to increase the density and reduce the resistance of the sintered body.

For example, a method of improving the sintering density by using as raw materials indium oxide or tin oxide powder having a relatively large particle diameter of 3 to 6 μm, which has been temporarily calcined at a high temperature (Japanese Patent Laid-open No. Sho 61-206).
62-21751) has been proposed. However, the density of the ITO sintered body obtained from such a material having a relatively large particle size is at most 5 g / cm ^{3 as} can be seen from the examples described in the publication.
And it can't be said that the density is high enough. Further, a method of using a coprecipitated ITO powder containing a precipitating agent as a raw material for a sintered body (Japanese Patent Laid-Open No. 62-1200).
9) is proposed. However, the sintered density of the sintered body obtained by this method is about 70% (5 g / cm ³ ) of the theoretical density, which is not sufficiently high. On the other hand, a method of introducing oxygen defects into the ITO sintered body to reduce the resistance has also been proposed (JP-A-63-4075).
6). However, although such a method is effective in reducing the resistance of the sintered body, it is insufficient in terms of high density.

Furthermore, special high-density IT by pressure sintering (hot pressing)
Although a method for producing an O sintered body has also been proposed, it is said that the apparatus is expensive and the operation is complicated, and a relatively high density sintered body can be obtained, but it was not an industrial method.

Further, in hot pressing, there is also a problem that the sintered body is inevitably reduced in strength.

[Problems to be Solved by the Invention] As described above, the present situation is that an ITO sintered body having high density and low resistance has not been obtained by an industrial method so far.

The object of the present invention is a high density and low resistance ITO sintered body, that is, a sintered density of 5.3 g / cm ³ or more, and a sintered density of 6 g / cm ³
It is intended to provide an ITO sintered body having a high density and a specific resistance of 2 × 10 ⁻³ Ω · cm or less, a manufacturing method thereof, and a use as a sputtering target utilizing the characteristics of the ITO sintered body. .

[Means for Solving the Problems] As a result of intensive studies made by the present inventors on increasing the density and lowering the resistance of an ITO sintered body, the present invention was achieved by using a certain ITO powder as a raw material for the sintered body. It was found that the purpose of was achieved.

That is, in the sintering of ITO powder having a primary particle size of 1 μm or less, a BET surface area of 15 m ² / g or more, and a specific surface area of 2 m ² / g or more obtained from the particle size distribution, in the sintering reaction, pores inside the sintered body are formed. Due to the remarkable volume shrinkage due to the reduction, the sintered body becomes high density,
It was also found that the resistance was low.

Furthermore, this high-density ITO target has extremely excellent performance as a sputtering target, and when this is used as a sputtering target, it was found that a transparent conductive film with extremely uniform and low resistance can be formed, and the present invention was completed. did.

Next, the present invention will be described in more detail.

Any ITO powder may be used in the present invention as long as it satisfies the conditions defined in the present invention.

That is, it may be a mixture of indium oxide powder and tin oxide powder, or may be a coprecipitated oxide powder of indium and tin by a coprecipitation method.

A general method for producing indium oxide powder and tin oxide powder is, for example, a method of heat dehydration or thermal decomposition of each metal hydroxide, organic metal salt or inorganic metal salt powder, or each sol or gel, or As a method for producing a coprecipitated powder of ITO, a method of using a precipitating agent in a mixed solution of indium salt and tin salt (JP-A-60-186416 and 62-7627), hydrolysis of a mixed solution of indium salt and tin salt Method (JP-A-63-19510
1) etc., but we have proposed indium and /
Alternatively, a method of thermally decomposing a high-purity organic acid salt obtained from an aqueous solution of tin with an organic acid (JP-A-63-195101) is also a method of obtaining a very excellent powder.

The particle size of the powder in the present invention is 1 μm to 0.01 μm, and particularly preferably 0.5 μm to 0.3 μm.
Those with a large primary particle size have high dispersibility but poor sinterability,
On the other hand, if the primary particle size is less than 0.01 μm, it is difficult to suppress agglomeration within the particles, and it is extremely difficult to obtain a powder having high sinterability.

On the other hand, indium oxide, tin oxide or
The primary particle size of the ITO powder is generally from several μm to 0.01 μm, and the size of the primary particle size satisfies the range of the present invention, but since these particles are strongly aggregated, the present invention does not have such a size. It cannot be a raw material for a sintered body.

The indium oxide powder and the ITO powder used in the present invention are characterized by using such a fine primary particle size and high dispersion, that is, not agglomerated.

BET surface area is a means of evaluating the dispersibility of the powder, there is a particle size distribution, powder used in the present invention is a BET surface area of 15 m ² / g or more, preferably, yet the particle size distribution at 15m ² / g~50m ² / g the specific surface area obtained from the 2m ² / g or more, preferably, 2m ² / g~5m
² / g, more preferably 3.5 m ² / g or more.

Even if the above BET surface area becomes too large, the powder becomes porous or has a poor surface condition, and if it is unnecessarily small, the sinterability is still poor, so the BET surface area is 50 m ² / g.
The above-mentioned range is preferable.

The ITO powder satisfying the above conditions has a primary particle size of 1 μm.
It can be prepared by producing ITO powder of m or less and then mechanically pulverizing it.

Mechanically pulverizing is generally known as a method for improving the sinterability of ceramic powder, but in the case of indium oxide and ITO powder, the sinterability is improved by mechanically pulverizing any powder. Do not mean.

As a method for mechanically pulverizing indium oxide and ITO powder, there are generally a ball mill, a dyno mill, a sand mill, a homogenizer, a vibration mill, and the like. It is to grind by using a high grinder such as a vibration mill.
It is not possible to obtain, with a low pulverization efficiency, for example, a rotary ball mill that satisfies the conditions of the present invention.

Further, the grinding medium used for grinding is important, and it is preferable to use one having a high specific gravity from the viewpoint of grinding efficiency. In addition, since the mixing of impurities into the powder during such a pulverizing treatment brings about a decrease in the conductivity of the ITO sintered body using the same, the pulverizing medium used in the present invention has a high specific gravity and is resistant to abrasion. It is preferable to use excellent ones. As a dispersion medium having a high specific gravity and excellent abrasion resistance, for example, zirconia beads, hard carbon coated beads, diamond coated beads and the like are excellent. In particular, even if the hard carbon-coated beads and the diamond-coated beads are worn, no problem occurs because the carbon impurities are removed as carbon dioxide gas at the sintering temperature of the ITO powder. On the other hand, alumina beads and glass beads pose a problem of impurities due to abrasion, and resin beads are too light to obtain a crushing effect. The size of the crushing medium used in the present invention is preferably 5 mm or less, and particularly preferably 2 mm or less, which enables fine pulverization. Further, in order to improve the pulverization efficiency and the dispersibility of the powder, it is preferable to add a liquid to the powder to be pulverized to form a slurry state. As the liquid to be added here, it is possible to use water and various organic solvents, but it is particularly preferable to use water in terms of abrasion resistance of the dispersion medium. Furthermore, adding various dispersants to the slurry is also effective for pulverization. From the viewpoint of pulverization efficiency, it is preferable that the amount of water added to form the above slurry is such that the viscosity of the slurry is in the range of 50 cps to 5000 cps. If the viscosity of this slurry is higher or lower, the pulverization efficiency will decrease. The amount of water added to prepare such a slurry varies depending on the properties such as the particle size of the powder to be treated and the grinding medium used for grinding, but generally powder / water = 80:20 to 10:90. . The crushing time is about 1 hour to 100 hours, and particularly preferably 5 hours to 30 hours.

Also, the most important point in crushing using a vibration crusher is
The diameter of the crushing container is less than 10 times the amplitude of the vibration crusher. If the diameter of the crushing container becomes larger than 10 times the amplitude, not only the operation of the crushing medium inside the crushing container becomes irregular, but also many of the crushing media cause small vibration or sliding at the lower part of the crushing container during crushing. Just by doing so, the pulverization efficiency is significantly reduced. This phenomenon occurs especially when the grinding medium is small, for example, a diameter of 2 mm used in a grinder.
This is remarkable when using a grinding medium of a certain degree. Further, when the powder is pulverized in such a state, the powder becomes amorphous rather than dispersed, that is, the crystal is broken, so that the sinterability of the powder in the pulverization process is rather lowered.

On the other hand, when the diameter of the crushing container is less than 10 times the amplitude of the oscillating crusher, when the crushing process is performed, the motion of the crushing medium inside the crushing container is extremely uniform, and the agglomeration of the powder is efficiently eliminated. . In addition, such a crushing treatment also suppresses crystal destruction due to crushing.

In addition, such efficient pulverization treatment suppresses abrasion of the pulverization medium, and the powder to be treated can be kept in high purity.

By performing such a pulverization process, the ITO powder becomes highly dispersed and satisfies the conditions limited by the present invention.
ITO powder is obtained. That is, the primary particle size is 1 μm to 0.01 μm
In m, BET surface area of 15m ² / g~50m ² / g, the specific surface area determined from the particle size distribution becomes of 2m ² / g~5m ² / g.

In the case of ITO powder in the powder of the present invention, the ratio of indium oxide to tin oxide in the powder is indium oxide / weight ratio.
Tin oxide = 98: 2 to 80:20, particularly preferably 92: 8 to 85:15. When the content of tin oxide is less than 2% or more than 20%, a sintered body made of this cannot have a high conductivity.

Further, the ITO powder used in the present invention is obtained by crushing the coprecipitate obtained by coprecipitating these solutions from a solution containing indium and tin used as the raw material, into an oxide, by the method described above. It has a uniform composition and thus when sintered and used as a target, it forms a uniform film. The coprecipitation method may be the general method described above,
The calcination temperature is 300 to 800 ° C.

In the sintered body of the present invention, the raw material powder is molded and sintered as in the general sintered body manufacturing method, but any method can be applied to the molding method of the ITO powder. For example, pressure molding,
There are cast molding, injection molding, etc. The ITO powder compact obtained by any of these molding methods has a compact density of 3 g / cm.
The range of ³ to 4.5 g / cm ³ , and most of the range is 3.5 g / cm ³ to 4.5 g / cm ³ , but in the present invention, 75% or more of the theoretical density is sufficiently obtained from such a low-density molded article. , 5.3 g / cm ³ or more, and in many cases 85% or more of the theoretical density, that is, 6 g / cm ³ or more of high density sintered body can be obtained.

Next, such an ITO powder compact is sintered, but any atmosphere can be applied to the sintering atmosphere of the ITO powder compact. For example, in air, in an inert atmosphere, in vacuum, etc. can be considered. A sintered body that has been sintered in an inert atmosphere or in vacuum has more oxygen lattice defects than one sintered in air, so a lower resistance can be obtained. A sintered body obtained by sintering in 1. is preferable.

Sintering of ITO starts from approximately 1050 ° C, but the sintering density does not improve below 1300 ° C, and the conductivity of the sintered body is insufficient, so the sintering temperature is 1300 ° C or higher, especially 1350 ° C. C. or higher is preferable. On the other hand, when the sintering temperature exceeds 1450 ° C, the tin component volatilizes.

Therefore, the sintering temperature in the present invention is optimally 1300 ° C or higher, particularly preferably 1400 ° C or higher and 1450 ° C or lower.

The holding time at the sintering temperature is several hours to several tens hours, particularly 5 hours to 20 hours. Further, the rate of temperature increase and the rate of temperature decrease are preferably 200 ° C./hour or less, particularly preferably 100 ° C./hour or less. The sintered particle size of the thus obtained sintered body is 5 μm to 15 μm.

[Effects of the Invention] As described above, the ITO sintered body of the present invention has a high density and low resistance, and thus has an extremely excellent performance as a sputtering target for forming a transparent conductive film. The conventional ITO sintered body is porous and has a low resistance, so that the transverse rupture strength is at most 5 kg / mm ² , whereas the high-density sintered body of the present invention has a bending strength of 5 kg / mm ² or more, and most of it is 10 kg / mm ^2. Since it is more than mm ² and has high thermal conductivity, cracking due to heat shock is unlikely to occur, and since there are few holes in the sintered body, the etching rate of the target surface of argon ions, that is, the sputtering rate is improved, resulting in sputtering. Speed up. Furthermore, the specific resistance is 2 × 10 ^-3 Ω in the conventional low density ITO sintered body.
· Those having a size of at least cm are 2 × 10 ⁻³ Ω · cm to 2 × 10 ⁻⁴ Ω · cm in the high density ITO sintered body of the present invention, and most of them are 1 × 10 ⁻³ Ω ·.
Since it is cm to 2 × 10 ⁻⁴ Ω · cm, the power that can be applied is significantly increased and the discharge characteristics are improved. In addition, in the high-density sintered body, selective sputtering of oxygen is less likely to occur, and reduction blackening of the target surface that causes deterioration of the quality of the transparent conductive film is suppressed, which is extremely advantageous in continuous operation of transparent conductive film production. .

From these properties, the high density, low resistance ITO of the present invention
The sintered body can be expected to have extremely excellent performance as a sputtering target for forming a transparent conductive film.

[Examples] Hereinafter, the present invention will be described based on Examples, but the present invention is not limited thereto.

Example 1 An indium / tin mixed acetic acid solution containing indium / tin at a ratio of 90/10 was concentrated to obtain an indium / tin mixed acetic acid salt, and the acetic acid salt was thermally decomposed to prepare an ITO powder. Water was added to this powder to make a 50% slurry, which was then ground for 20 hours in a vibration mill (vibration amplitude 10 mm, grinding container diameter 50 mm) using hard carbon-coated metal beads having a diameter of 2 mm as a grinding medium. The powder had a primary particle size of 0.3 μm as observed by an electron microscope, a BET surface area of 17 m ² / g, and a specific surface area determined from a particle size distribution of 3.5 m ² / g.

The powder was pressure-molded with a mold to obtain a 3.7 g / cm ³ molded body, which was then sintered at 1400 ° C. in atmospheric air.

The temperature rising rate in sintering was 100 ° C./hour, the temperature holding rate was 1400 ° C. for 10 hours, and the temperature lowering rate was 100 ° C./hour.

Under these sintering conditions, the sintered density is 5.7 g / cm ³ and the specific resistance is 3 ×.
A sintered body of 10 ⁻⁴ Ω · cm was obtained.

Electron micrograph showing the grain structure on the surface of the sintered body (2000
1) is shown in FIG.

Example 2 The sintered body obtained in Example 1 was used to form a film by DC magnetron sputtering (condition is input power: 4 W).
/ cm ² , pressure: 0.6Pa (5 × 10 ^-3 torr), substrate temperature: 350
As a result, a transparent conductive film having extremely low resistance was obtained as shown in Table 1.

Example 3 Indium acetate and tin acetate were pyrolyzed to prepare indium oxide and tin oxide, respectively, and then mixed so that the indium oxide / tin oxide ratio was 90/10. Thereafter, a powder and a sintered body were prepared under the same conditions as in Example 1 except that zirconia beads were used instead of the carbon-coated beads.

The average primary particle size of the powder is 0.3 μm by electron microscopic observation, B
The ET surface area is 16 m ² / g, the specific surface area obtained from the particle size distribution is 3.5 m ² / g before crushing, while the sintered density of the obtained sintered body is 5.9 g / cm ³ , the specific resistance 9 × It was 10 ⁻⁴ Ω · cm.

Example 4 The sintered body obtained in Example 3 was used to form a film by DC magnetron sputtering (conditions are the same as in Example 2). As a result, as shown in Table 1, it was extremely similar to Example 2. A transparent conductive film having low resistance was obtained.

Comparative Example 1 An indium / tin mixed acetic acid solution having a ratio of 90/10 was concentrated to obtain an indium / tin mixed acetic acid salt, and ITO powder was prepared by thermally decomposing the acetic acid salt.

The primary particle size of this powder was 0.3 μm as observed by an electron microscope.
ET surface area is 9 m ² / g, specific surface area calculated from particle size distribution is 2 m ² / g
Met.

When molded and sintered under the same conditions as in Example 1, the sintered density
A sintered body with 4.7 m ² / g and a specific resistance of 2.4 × 10 ⁻⁴ μm was obtained. Scanning electron microscope image showing the grain structure on the surface of the sintered body (2000
2) is shown in FIG.

The powder used as the raw material has a primary particle size, and the specific surface area obtained from the particle size distribution is within the range of the powder used in the present invention, but the BET surface area is low, that is, the sinterability is poor because it is an agglomerated powder, and the sintered density No high sintered body was obtained.

Comparative Example 2 Using the sintered body obtained in Comparative Example 1, a film was formed by DC magnetron sputtering under the same conditions as in Example 2. Table 1 shows the specific resistance of the formed film. As shown in Table 1, a transparent conductive film having a low resistance as in Examples was not obtained.

Further, the results of Auger electron spectroscopy analysis of the surface of the sintered sputtering target before and after sputtering are shown in FIG. 3, the relationship between the applied power and the film formation rate is shown in FIG. 4, and the relationship between the density of the sintered body and the bending force is shown in FIG. The relationship between the sintered density and the thermal conductivity is shown in FIG.

From FIG. 3, no reduction (oxygen reduction) was observed on the surface of the high density ITO sintered body. Further, from FIG. 4, extremely high-speed film formation was possible with the high-density sintered body. From FIG. 5, it was shown that the high-density sintered body has a high bending strength and is difficult to crack.
In addition, FIG. 6 shows that the high-density ITO sintered body has high thermal conductivity and cracks due to heat shock are suppressed.

[Brief description of drawings]

FIG. 1 and FIG. 2 are scanning electron micrographs as substitutes for drawings showing the particle structures on the surfaces of the sintered bodies obtained in Examples and Comparative Examples. FIG. 3 is a diagram showing the results of analysis by Auger electron spectroscopy, FIG. 4 is a diagram showing the relationship between the input power and the film formation rate, and FIG. 5 is a diagram showing the relationship between the density of the sintered body and the bending force (FIG. 4). 5 out of 5
Indicates the result of Example 2, □ indicates the result of Example 4 and Δ indicates the result of Comparative Example 2), and FIG. 6 shows the relationship between the sintered density and the thermal conductivity (in the figure, ○ indicates the example and Δ indicates the comparative example). The results are shown).

Claims (4)

[Claims] 1. A sintered density of 5.3 g / cm ³ or more and a specific resistance of 2 × 10 ^-3.
Indium oxide / tin oxide sintered body with Ω · cm or less. 2. The primary particle size is 1 μm or less and the BET surface area is 15 m ² /
Sintering density characterized by using indium oxide / tin oxide with a specific surface area of 2 m ² / g or more determined by particle size distribution
A method for producing an indium oxide / tin oxide sintered body having a specific resistance of 5.3 g / cm ³ or more and a specific resistance of 2 × 10 ⁻³ Ω · cm or less. 3. The production method according to claim 2), wherein the indium oxide / tin oxide powder is obtained by a coprecipitation method. 4. A sintered density of 5.3 g / cm ³ or more and a specific resistance of 2 × 10 ^-3.
Sputtering target consisting of indium oxide / tin oxide sintered body with Ω · cm or less.