JP2001072470A - Production of ito sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-density and large-sized ITO sintered compact with no density unevenness by designing the respective particle sizes of indium oxide powder and tin oxide powder in a feedstock slurry and the pH of the slurry to be within respective specific ranges. SOLUTION: This ITO sintered compact is obtained by designing the respective particle sizes of indium oxide powder and tin oxide ponder in a feedstock slurry to be <=0.8 μm and the pH of the slurry to be >=8.0; wherein if the above particle sizes exceed 0.8 μm, the particles become subject to sedimentation in the slurry, leading to being subject to the density unevenness in a molded form obtained by cast molding of the slurry; and if the pH of the slurry is <8.0, the particles in the slurry become subject to mutual flocculation, leading to forming a molded form through the mutual impression of particles flocculated during the cast molding, therefore decreasing the density of the resultant molded form. Furthermore, by conducting a vacuum defoaming treatment prior to the slurry cast molding or by adding a defoaming agent to a dispersion medium for the slurry, a high-density molded form is obtained through reducing cells contained therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a high-density, high-density ITO sintered body sputtering target used for manufacturing a low-resistance transparent conductive film used for a solar cell or a liquid crystal display device by a sputtering method. The present invention relates to a method for producing a uniform ITO sintered body.

[0002]

2. Description of the Related Art A transparent conductive film has high conductivity and high transmittance in a visible light region. It is used for electrodes of solar cells, liquid crystal display devices, and other light-receiving devices, as well as for transparent heat generation for various types of anti-fog such as heat ray reflective films, antistatic films, and freezer showcases for automobiles and buildings. It is also used as a body.

A transparent conductive film is made of tin oxide (S) containing dopants of antimony or fluorine deposited on a glass substrate.
nO ₂ ), zinc oxide (ZnO) containing aluminum or gallium as a dopant, indium oxide (In ₂ O ₃ ) containing tin as a dopant, and the like are known. In particular, the indium oxide film containing tin as a dopant is made of ITO.
(Indium tin oxide) film, which is often used because a low resistance film can be easily obtained.

As a method for producing the ITO transparent conductive film, a sputtering method is often used. The sputtering method is an effective technique when film formation of a material having a low vapor pressure or precise control of the film thickness is required, and the operation is extremely simple, so that it is widely used industrially.

[0005] In the sputtering method, a target is used as a raw material. In this method, generally, under a gas pressure of about 10 Pa or less, a substrate is used as an anode, and a target is used as a cathode, and a glow discharge is generated therebetween to generate argon plasma. When argon cations in the plasma collide with the cathode target, particles of the target component that are repelled are deposited on the substrate to form a film. This method is classified according to the method of generating argon plasma. A method using high frequency plasma is called a high frequency sputtering method, and a method using DC plasma is called a DC sputtering method.

[0006] The ITO film formed by the sputtering method is greatly affected by the characteristics of the sputtering target. In particular, the influence of the density and the microstructure of the target is great, and the higher the density and the more uniform the composition of the target, the better the quality of the film. When a target having a low density or a non-uniform composition is sputtered, black protrusions called “nodules” increase on the surface of the target with an increase in the cumulative input power. When the target is in such a state, problems such as occurrence of arcing during sputtering, a decrease in film formation rate, an increase in specific resistance, and a deterioration in light transmission characteristics occur.

To avoid these problems, it is necessary to take measures such as replacing the target before the target is completely consumed or mechanically removing and removing nodules on the surface of the target. This has been a major obstacle to inexpensively producing a large amount of transparent conductive films.

Therefore, a higher density and uniform target is demanded from the viewpoint of improving the characteristics of the manufactured ITO film and the film manufacturing cost. It is generally said that a target that hardly generates nodules even after sputtering for a long time has a relative density of 98% or more, preferably 99% or more.

Recently, with the increase in the size of the sputtering apparatus, a large-sized target is required. As a conventional method for producing an ITO sintered body, there is a method in which an ITO powder is press-molded in a mold and the obtained molded body is fired. With this method, it is difficult to obtain a large sintered body. This is because uniform press molding becomes difficult when the size is large. Therefore, when a large target is obtained by this method, a large number of small sintered bodies are bonded together.

[0010] However, when sputtering is performed using a target produced by lamination, nodules are apt to be generated in a minute step portion of the lamination part, and there has been a problem that the characteristics of the film are impaired.

[0011] To solve this problem, Japanese Patent Publication No. 6-659 discloses a slurry containing an indium oxide powder and a tin oxide powder, which is formed by slurry casting, and firing the obtained compact to form a large sintered body. It states that it can be manufactured.

[0012]

However, in the method described in Japanese Patent Publication No. 6-659, the obtained ITO
The relative density of the sintered body is about 60 to 63%, which is very low. In addition, there is a problem that the obtained ITO sintered body has a large density unevenness. Nodules are easily generated in a target manufactured from such a sintered body, and it is difficult to stably manufacture a high-quality transparent conductive film.

Accordingly, the present invention solves the above-mentioned conventional problems and provides a uniform large-sized ITO having a relative density of 98% or more and a uniform density by a slurry casting method.
An object is to provide a method for manufacturing a sintered body.

[0014]

Means for Solving the Problems A method for producing an ITO sintered body according to the present invention for achieving the above object is characterized by the following.

That is, according to the present invention, in a slurry obtained by mixing a raw material powder containing indium oxide powder and tin oxide powder as main components in a dispersion medium, the particle diameter of each of the indium oxide powder and tin oxide powder is set to 0.8 μm or less, And,
After the molded body is manufactured by the slurry casting method with the pH being 8.0 or more (10.0 or less), the molded body is fired. The dispersion medium is water or a mixture of water and a dispersant, a binder, and, if necessary, a lubricant, a thickener, a pH adjuster, and a humectant.

[0016]

Embodiments of the present invention will be described below.

The slurry used in the present invention comprises, for example, a mixture of indium oxide powder and tin oxide powder comprising a dispersant and a binder, and if necessary, a dispersion medium containing a lubricant, followed by vacuum defoaming or defoaming. Air bubbles are sufficiently removed by adding the agent.

In the present invention, when the particles of the indium oxide powder or the tin oxide powder in the slurry are larger than 0.8 μm in size, according to experiments by the inventors, the density of the sintered body after firing is low. . This means that the particles are 0.8μ
If it is larger than m, particles tend to settle in the slurry, and the molded product obtained by casting tends to have uneven density.

The particle size of the particles in the slurry is 0.8 μm.
According to experiments by the inventors, even if the pH is less than m, a high-density ITO sintered body cannot be obtained if the pH of the slurry is less than 8.0. This is because if the pH of the slurry is less than 8.0, the particles are likely to aggregate in the slurry, and the aggregated particles deposit during casting to form a molded body, so that the density of the molded body is low. It is because it becomes.

Therefore, the conditions of the slurry for producing a high-density ITO sintered body are as follows:
μm or less, and the pH of the slurry is 8.0 or more,
Preferably it is 8.7 or more.

However, the pH is actually set to 10 or less. This is because it is difficult to adjust the pH more than this. As the dispersant, a polycarboxylic acid-based dispersant or the like can be used. In addition, an acrylic emulsion-based binder or the like can be used as the binder.

The pH of the slurry can be adjusted by the amount of the dispersant added. The amount of the binder to be added is preferably 0.5 to 2.0% by weight based on the total weight of the powder in terms of solid content.

If air bubbles are contained in the slurry used for the casting, a molded article having a high density cannot be obtained. Therefore, if the vacuum defoaming process is sufficiently performed before casting the slurry,
Bubbles can be reduced in the molded body, and a molded body with high density can be obtained. An antifoaming agent may be added to the dispersion medium.

[0024]

The present invention will be described more specifically with reference to the following examples.

Indium oxide powder (22,500 g), tin oxide powder (2500 g), polycarboxylic acid dispersant having a solid content of 40% by weight (20 to 2800 g), and acrylic emulsion binder having a solid content of 40% by weight (1250)
g), a predetermined amount of water was prepared, and pulverized and mixed with a high-speed medium stirring mill to prepare a slurry having a concentration of 80% by weight. In this case, the indium oxide powder and the tin oxide powder used had substantially the same particle size distribution.

The pH of the slurry can be changed by the amount of the polycarboxylic acid-based dispersant added. Therefore, by adjusting the amount of the dispersant added, slurries of various pHs including the pH according to the present invention were produced. Water was added in such an amount that the slurry concentration became 80% by weight.

Since the particle size of the raw material powder in the slurry depends on the time of pulverization and mixing by a high-speed medium stirring mill, by adjusting the time of pulverization and mixing, various particles including the particle size according to the present invention can be obtained. A slurry of diameter raw material powder was prepared. Microtrac (UPA150) was used to measure the particle size.

After the obtained slurry is subjected to vacuum defoaming treatment,
A phenolic resin having an inner size of 750 mm × 920 mm × 10 mm thick was poured into a casting mold (ceraplast manufactured by Nikko) and cast at a pressure of 5 kg / cm ² . After drying the compact, the dimensions and weight were measured to calculate the compact density.

The dried compact was heated to 600 ° C. to remove the binder, and then calcined at 1500 ° C. for 15 hours.
A TO sintered body was obtained. After grinding the surface of the sintered body, the density was measured by the Archimedes method to determine the relative density. The presence of pores in the sintered body was observed with a scanning electron microscope.

Table 1 shows the maximum particle size of the powder in the slurry, the pH of the slurry, the density of the compact after drying, and the relative density of the sintered compact after the grinding treatment, as measured by Microtrack.

Table 1 Kinds of Invention Maximum Slurry of Powder pH of Particle Size (μm) of Sintered Molded Product Relative Density (%) Relative Density (%) Example 1 0.3 8.7 50 99 Example 2 0.3 8.0 50 98 Comparative Example 1 0.3 7.5 43 94 Example 3 0.5 9.0 50 99 Comparative Example 2 0.5 7.5 42 90 Comparative Example 3 0.5 7.0 42 90 Example 4 0.5 9.0 49 99 Example 5 0.6 9.0 49 99 Example 6 0.8 9.0 49 99 Example 7 0.8 8.7 49 99 Example 80 8.8 8.0 49 98 Comparative Example 4 0.8 7.5 43 92 Comparative Example 5 0.8 7.0 43 90 Comparative Example 6 0.9 8.5 43 93 Comparative Example 7 0.9 7.5 41 90 Comparative Example 8 1.0 9.0 39 90 Comparative Example 9 1.6 8.5 37 80 Comparative Example 10 2.0 FIG. 1 shows the measurement results of the particle size distribution of the slurry used in Example 5.
Shown in FIG. 2 shows the measurement results of the particle size distribution of the slurry used in Comparative Example 9.

According to Table 1, according to the present invention, the relative density 98
% Or more of a high-density ITO sintered body can be obtained.

The molded article produced according to the comparative example in Table 1
Since the density was low, the strength was weak, and cracking during handling and cracking and warping during firing were easy to occur. On the other hand, the molded article of the present invention had a high density and a high strength, and did not crack during handling or crack or warp during firing. When the structure inside the sintered body was observed with a scanning electron microscope, a large number of air bubbles were observed in the whole of the sintered body obtained in the comparative example in Table 1, or some of the sintered body was observed. Bubbles were observed intensively, resulting in uneven density. On the other hand, in the sintered body according to the example of the present invention, almost no air bubbles were observed, and there was no density unevenness.

[0034]

As described in detail above, according to the present invention, the particle size of the indium oxide powder and the tin oxide powder in the slurry is 0.8 μm or less, and the pH of the slurry is 8.0 or more, preferably 8.7 or more. By doing so, it is possible to maintain a state in which the particles hardly settle in the slurry and are monodispersed. Slurry casting using such a slurry can produce a high-density compact, which is fired to produce a high-density I with a relative density of 98% or more and no density unevenness.
A TO sintered body can be manufactured.

This sintered body is very useful as a large-sized ITO sintered body sputtering target for producing a transparent electrode film such as a solar cell or a liquid crystal display element. For these reasons, the present invention is extremely valuable industrially.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of measuring the particle size distribution of a slurry powder used in Example 5, which is an example of the present invention, with a microtrack.

FIG. 2 is a graph showing the results of measuring the particle size distribution of the slurry powder used in Comparative Example 9 with a microtrack.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/285 301 C04B 35/00 R (72) Inventor Yoshiharu Kurihara 3-18 Chugoku, Ichikawa, Chiba −5 Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Yuji Takatsuka 3-18-5 China, Ichikawa City, Chiba Prefecture Sumitomo Metal Mining Co., Ltd. Central Research Laboratory F term (reference) 2H092 HA04 MA05 MA35 4G030 AA34 AA39 BA15 GA04 GA11 GA18 GA20 GA23 4K029 BA10 BA15 BA43 BA50 BC09 CA05 DC05 DC09 4M104 BB36 DD40 HH20

Claims (2)

[Claims] 1. A slurry obtained by mixing a raw material powder containing indium oxide powder and tin oxide powder as a main component in a dispersion medium is poured into a molding mold, and the obtained compact is sintered.
In the method for producing a TO sintered body, the particle size of each of the indium oxide powder and the tin oxide powder in the slurry is set to 0.8 μm or less, and the pH of the slurry is set to 8.
A method for producing an ITO sintered body, which is set to 0 or more. 2. A method for producing an ITO sintered body, wherein the slurry has a pH of 8.7 or more.