JPH02225366A - Production of oxide sintered compact - Google Patents

Abstract

PURPOSE:To obtain an indium oxide.tin oxide(ITO) sintered compact having plane surface of sintered granules and small reflectivity of light in a visible light region and excellent as a dark green sputtering target by sintering ITO powder at a specific high-temperature. CONSTITUTION:Indium oxide tin oxide(ITO) is sintered at a temperature exceeding 1400 deg.C and crystal thereof is grown until at least part or all of sintered granule surface becomes plane. At this time, when sintering temperature is <=1400 deg.C, growth of characteristic above-mentioned sintering granules do not proceed and when temperature of the composition is raised to 1800 deg.C or above, sintering granules are grown, but tin is volatilized. Therefore, especially preferable temperature is 1450-1700 deg.C. The enough retention time at the sintering temperature is from 5hr to 20hr and raising and lowering rate is especially preferably <=100 deg.C/hr. Highly crystalline ITO sintered compact having <=20% reflectivity of light in light visible light region, showing dark green and having performance excellent as sputtering target for preparing transparent electroconductive film is obtained by the above-mentioned method.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to indium oxide/tin oxide (hereinafter referred to as !TO and 2.
) This relates to the use of %A of sintered bodies.

[Prior Art] In recent years, there has been a rapid increase in demand for ITO thin films as transparent conductive films used in solar cells, suitable electrodes for liquid crystal displays, touch panels, and the like. Methods for forming such an ITo thin film include coating ITO fine particles on the surface of a base material,
Methods such as applying an O precursor to the surface of a base material and then thermally decomposing it, or sputtering an ITO sintered target are known, but sputtering is currently the most commonly used method. The ITO brick body according to the present invention has extremely excellent performance as a sputtering target for forming a transparent conductive film by a sputtering method.

Conventionally, ITO sintered bodies have been manufactured by press-molding a mixture of indium oxide and tin oxide powders and then sintering the mixture. However, since ITO powder is difficult to sinter, it has not been possible to manufacture an ITO sintered body that has excellent film forming operability by sputtering and the quality of the resulting transparent conductive film when using an ITO sintered body. was extremely difficult.

The color tone of conventional ITOa bodies is yellowish green, and the sintered particles are spherical or amorphous with low crystallinity. like this! The 00 sintered body was easily cracked due to its low crystallinity, and the power that could be input during film formation was painfully small, resulting in a slow film formation rate by sputtering, and the discharge state was extremely unstable. Furthermore, in conventional ITO sintered bodies, reducing substances (black substances) are generated on the surface of the sintered bodies during sputtering.
Since this substance deteriorates the quality of the transparent conductive film formed on the surface of material a, the operation had to be stopped and removed every time a reducing substance was formed on the surface of the sintered body. This has been a significant hindrance in the continuous operation of sputtering, and these problems have been a significant constraint on the technology for producing ITOFWIIK by sputtering.

Several methods have been proposed to obtain a high density or low resistance ITO sintered body suitable for use as a sputtering target. has been proposed (Japanese Patent Laid-Open No. 62-21751). However, the sintered density of the ITO sintered body obtained by this method is less than 5 g/cm', and the yellow H
When sputtering using this as a target, the surface of the sintered body turned black, and the quality of the transparent conductive film could not be stabilized. Furthermore, a method has been proposed for reducing the resistance of an ITO sintered body by introducing oxygen lattice defects into the sintered body (Japanese Patent Laid-Open No. 63-40756). However, with ITO, which has many oxygen lattice defects, the sintered body will not have low resistance.
There was a problem in forming a film vertically and uniformly, and this method was not always satisfactory.

[Three Problems to be Solved by the Present Invention] An object of the present invention is to provide a method for manufacturing an ITo sintered body that can improve the above-mentioned disadvantages.

[Means for Solving the Problems] As a result of intensive studies regarding ITO sintered bodies, the present inventors found that when ITO powder is sintered at a high temperature exceeding 1400°C, the obtained ITO sintered bodies have sintered particles. It was discovered that a dark green to black sintered body can be obtained which has crystal growth until the surface becomes flat and has a band structure with absorption in the visible region, and that such a sintered body has low resistance. We also discovered that the transparent conductive film obtained by sputtering using such an IT0 sintered body has low resistance and a visible transmittance IA higher than that of the conventional one, which led us to complete the present invention. It is.

That is, in the present invention, indium oxide/tin oxide powder is
Highly crystalline indium oxide/tin oxide that is sintered at a temperature exceeding 00°C and grown as a crystal until at least a portion of the sintered particle surface becomes flat, reflecting less than 20% of visible wavelength light and exhibiting a dark green color. The present invention relates to a method for manufacturing a sintered body.

Any method can be used to produce the ITO powder used in the present invention, but for example, each metal hydroxide, oxide hydrate, organic metal salt or inorganic metal salt powder, or each sol or gel is heated and dehydrated. Or a method of thermal decomposition. There is also a method of obtaining ITO by a coprecipitation method, but ITO obtained by any of these methods may be used. For example, adding a precipitant to a mixed aqueous solution of indium salt and tin salt (Japanese Patent Application Laid-Open No. 62-762
7, JP-A-6O-IJlfi41B) or a method of thermally decomposing the precipitate after hydrolysis (JP-A-58-38925).

Furthermore, a method for thermally decomposing a mixed organic acid salt obtained from a mixed organic acid aqueous solution of indium and tin (Japanese Unexamined Patent Publication No. 62-195
101) may also provide an ITO co-precipitated powder suitable for use in the present invention.

The primary particle size of indium oxide, tin oxide or ITO powder obtained by these methods is generally from several μm to 0.01 μm.
However, the particle size of these powders used in the present invention is 1 l or less, particularly 0. - A range of 0.05 μm from the μ layer is preferred. The finer the primary particle size, the better the sinterability of the oxide, so a finer ITO powder can yield a sintered body with better crystallinity and higher density.

In the present invention, the sintering temperature of the ITO powder is important.

The sintering temperature for obtaining the sintered body of the present invention needs to be higher than 1400°C, particularly preferably 1450°C or higher. Sintering of lτ0 starts at about 1050°C, but at temperatures below 1400°C, the growth of sintered particles characteristic of the present invention does not proceed, and at temperatures above 1800°C, sintered particles grow but tin volatilizes. Therefore, the sintering temperature in the present invention ranges from a temperature exceeding 1400°C to 18[)D''C1, particularly preferably from 1450°C to 1700°C.

The holding time at the sintering temperature of the present invention ranges from several hours to several + hours.
In particular, 5 to 20 hours is sufficient. The temperature increase rate and temperature decrease rate during sintering, especially the temperature decrease rate, greatly affects the formation of sintered particles, so the temperature increase rate and temperature cross-sectional temperature should be 200℃ or less for 1 hour, especially 100"C/hour or less. is desirable.

In the present invention, the raw material ITO powder is preformed prior to sintering. This uneven molding is carried out by a conventional method, for example, by enclosing the mold in a mold and applying pressure.

In addition, the vI content of indium oxide and tin oxide in the original $41 TO powder is indium oxide and tin oxide 98-2 to 8.
A range of 0/20, particularly 9515 to 90/10 is preferred.

By sintering the raw TO powder under the above conditions, the sintered body defined in the present invention can be obtained.

The sintered density of an ITO sintered body increases somewhat by +A depending on the tin content, but the sintered density of a sintered body with a theoretical density of 100% is
It is about 7.1 g/cm3. The sintered density of the sintered body obtained by the present invention ranges from 4.5g/cs' to 7-0g/cs',
In particular, when the characteristic sintered particles obtained by the present invention are formed, the resulting sintered bodies often have a high density of 5.5 H/c- or more.

The ITO sintered body obtained by the present invention differs from conventional ITO sintered bodies in that each sintered particle has grown until one or all of the surfaces become flat, and this one has a bulk band structure. The color of the sintered body changes, and the color of the sintered body changes from ti-green to black instead of the conventional yellow-green color. Conventional ITO sintered bodies have significant absorption in the infrared and ultraviolet regions due to the light reflectance of the sintered bodies, and while the light reflectance in these wavelength regions is about 10%, in the visible region It has a small absorption of about 40% (reflects.) - The ITO sintered body obtained by the Rikiki invention has infrared and ultraviolet M
The absorption in the I region is similar to that of conventional products, but the absorption in the visible region is extremely large, reflecting less than 20%, often less than 10%, of light in the visible region. These differences are ITO
This is thought to be due to changes in the band structure of the crystal. The transparent conductive film obtained by sputtering the ITO sintered body that absorbs light in the visible region of the present invention has high transparency in the visible light region. Furthermore, due to such a change in band structure, the specific resistance of the sintered body of the present invention is 1Xl0'Ω
・Most of the resistance below cl is 5X10'Ω・01 or below.

[Effects of the Invention] The highly crystalline ITO sintered body according to the present invention has extremely excellent performance as a sputtering target for creating a transparent conductive film. First, a transparent conductive film obtained by sputtering the surface of a sintered particle with very good crystallinity is formed by oxide ions with excellent bonding properties being deposited as a transparent conductive film on a substrate. In particular, it has excellent conductivity, and can have a specific resistance of 2×10-'Ω·cm or less. In addition, in terms of operability, ITO with good crystallinity
The sintered body is difficult to crack, and furthermore, the etching rate of the googet surface of the sintered body with argon ions, that is, the sputtering rate is improved, and as a result, the sputtering rate is increased. In addition, because the surface of the sintered body has good crystallinity, selective sputtering of oxygen during sputtering is difficult to occur, and reduction of the target surface that causes quality deterioration of the transparent conductive film is suppressed, which improves the quality of the transparent conductive film and the continuous operation. This is extremely advantageous. Furthermore, since the color change of the sintered body of the present invention is not due to oxygen enzyme defects, the transparent conductive film obtained by sputtering is very uniform and bright.

In particular, the sintered body obtained using ITO powder obtained by coprecipitation has an extremely uniform composition distribution in the sintered body, so the composition of the resulting transparent conductive film is also more uniform, resulting in a homogeneous transparent film. A conductive film is obtained.

From these properties, the high-density ITO sintered body of the present invention can be expected to have extremely excellent performance as a sputtering target.

[Example] The present invention will be explained below based on Examples, but the present invention is not limited thereto.

Example 1 An acetic acid aqueous solution containing these at an indium/tin ratio of 90,710 was concentrated to obtain an indium/tin mixed acetate, and the acetate was thermally decomposed to prepare an ITO coprecipitated powder.

Pressure mold the second coprecipitated powder with a mold, 3.7g/c+a"
After forming a molded body, it was heated and sintered at 1500° C. in the atmosphere at normal pressure. The temperature increase rate during sintering is 100°C for 1 hour, 15
The temperature was maintained at 00°C for 10 hours, and the temperature drop rate was 100°C for 1 hour. Under these sintering conditions, the sintered density was 64 g/e-1
A sintered body with a specific resistance of 3×10-'Ω·C was obtained.

Observation with a scanning electron microscope shows that the sintered particles of this sintered body have grown until the surface becomes flat, the color tone of the sintered body is dark green to black, and the light reflectance at 550 nm is 9%.
Met. Also Electron Prove Mlc
According to the composition analysis using RO Analyzer (EPMA), it was found to be an oxide like the yellow-green sintered body. The compositional analysis results are shown in Table 1. In addition, an image (5 (100x)) of the sintered particles of the sintered body by a scanning electronic rIL mirror is shown in Figure 1.
The light reflection characteristics are shown in FIG. 2(1).

Example 2 Using the sintered body obtained in Example 1, a film was formed by DC magnetron sputtering. The sputtering conditions are shown in Table 2, and the characteristics of the obtained transparent conductive film are shown in Table 3.

With the highly crystalline ITO sintered body, it was possible to form a film with low resistance and high transparency at extremely high speed.

Example 3 Indium acetate and tin acetate were respectively thermally decomposed to produce indium oxide and tin oxide, and then mixed so that the ratio of indium oxide to tin oxide was 90/10. After that, the sintered body was made under the same conditions as in Example 1: l! sintered density 6.1g/cm", specific resistance 4X10-4Ω・C
- A sintered body was obtained. As in Example 1, scanning electron microscope observation revealed that the sintered particles of the sintered body had grown until the surface became flat, and the color tone of the sintered body was from dark green to black.
The light reflectance at 5on- was 11%. Also EP
According to the composition analysis by MA, it was an oxide like the conventional yellow-green sintered body.

The compositional analysis results are shown in Table 1. A scanning electron microscope image (2000x) of the sintered particles of the sintered body is shown in FIG. 3, and the light reflection characteristics are shown in FIG. 2 (2).

Example 4 Using the sintered body obtained in Example 3, a film was formed by DC magnetron sputtering. The sputtering conditions are shown in Table 2, and the characteristics of the obtained transparent conductive film are shown in Table 3.

As in Example 2, this highly crystalline ITO sintered body could also be formed into a low resistance, highly transparent film at extremely high speed.

Comparative Example 1 The ITO powder used in Example 3 was sintered at 1300°C,
Sintered density 4.5g/cm, specific resistance 2XIO-3Ω"
A sintered body of cm was obtained.

Scanning electron microscope observation revealed that the sintered particles of this sintered body were irregular in shape, the color of the sintered body was yellowish green, and the light reflectance at 550 ns was 45%. Furthermore, compositional analysis by EPMA revealed that this material was an oxide. The compositional analysis results are shown in Table 1, and the scanning electron microscope fl image of the sintered particles of this sintered body (
2000 times) is shown in FIG. 4, and the light reflection characteristics are shown in FIG. 2 (3). Comparative Example 2 Using the sintered body obtained in Comparative Example 1, film formation was performed by DC magnetron sputtering under the same conditions as in Example 2.3.

The sputtering conditions are shown in Table 2, and the characteristics of the obtained transparent conductive film are shown in Table 3. With this ITOfi aggregate, the film formation rate was slow, and only a transparent conductive film with particularly low conductivity could be obtained.

Table 1 Table 2 Table 3

[Brief explanation of the drawing]

Figure 1.3.4 is a scanning electron microscope used as a substitute for a drawing showing the structure of crystal grains of the sintered bodies obtained in Examples and Comparative Examples. 7! FIG. 2 is a diagram showing the light reflection characteristics of the sintered bodies obtained in Examples and Comparative Examples. In the figure, (1), (2), and (3) show the results of Example 1.3 and Comparative Example 1, respectively. Patent applicant: Tosoh Co., Ltd. Page 2 n・Zan (no change in content) Figure 2 Wavelength (nm) 80°I! 13 Procedural amendment (formality) 6. Contents of the amendment “Engraving of the drawing (Figure 2) originally attached to the application dated July 18, 2008 as shown in the attached sheet (no change in content)” Bunkoden 11 Displays 1999 Patent Application No. 45454 2 Name of Invention Method for Manufacturing Oxide Sintered Body 3? ! Relationship with case of person who makes i correction Special 2'E Applicant Address 748 Yamaguchi Prefecture New i! Tosoh Corporation Patent Office 4560 Oaza Tomita, Iyo City Telephone number (505) 4471

Claims (1)

[Claims] 1) Indium oxide/tin oxide powder is sintered at a temperature exceeding 1400°C and crystals are grown until at least a part of the sintered particle surface becomes flat, so that the reflection of light in the visible wavelength range is 20%.
The following describes a method for producing a highly crystalline indium oxide/tin oxide sintered body that exhibits a dark green color. 2) The method according to claim 1, in which the indium oxide/tin oxide powder is obtained by a coprecipitation method.