JPH03112850A - Sintered oxide, its production and use thereof - Google Patents

Abstract

PURPOSE:To form a transparent conductive film having low electric resistance by a sputtering process using a sintered indium-tin oxide by suppressing the dissolution of added tin oxide into indium oxide in solid state to a specific dissolution level and increasing the density of the sintered material to a specific level. CONSTITUTION:The objective sintered indium-tin oxide contains <25% of tin oxide dissolved in indium oxide in solid phase and has an apparent sintered density of >=5.5g/cm<3>. A transparent conductive film having low electric resistance (<0.2mOMEGA.cm) can be produced by a sputtering process using the sintered material as a target. A uniform film can be produced without causing the problems such as abnormal discharge during the operation. The ratio of solid solution should be suppressed to <25%, especially preferably <20% because the resistance of transparent conductive film increases according to the progress of the dissolution of tin oxide into indium oxide in solid phase. The surface reduction of the target can be suppressed and a film having low resistance and high stability can be produced by increasing the sintered density to the abovementioned level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a sintered body of indium-tin oxide (abbreviated as ITO) used as a raw material in producing a transparent conductive film. More specifically, ITO is produced by sputtering method.
The present invention relates to an ITO sintered body suitable for forming a transparent conductive film.

[Prior Art] In recent years, there has been an increasing demand for transparent conductive thin films as transparent electrodes for solar cells and display devices, and as conductive coatings for antistatic purposes. Such a transparent conductive thin film is
It is formed by sputtering method, CVD method, ion blating method, etc., but in particular industrially, methods of sputtering an alloy of indium and tin and methods of sputtering an ITO sintered body are mainstream; The most common method is to sputter an ITO sintered body because of its ease of operation.

Conventionally, the ITO sintered sputtering target uses a sintered body of a uniform mixture of indium oxide and tin oxide.This is a mixture of indium oxide and tin oxide dispersed relatively uniformly. 25 of tin oxide
% or more is composed of solid solution in indium oxide.

However, the specific resistance of films sputtered using such conventional ITO sintered body sputtering targets is at most 0.2 mΩ・C11. There is a need for an ITO sputtering target that provides a film.

[Means for Solving the Problem] As a result of intensive studies on the sputtering film formation characteristics of indium oxide doped with tin oxide, the inventors of the present invention found that solid solution of tin oxide progresses in the indium oxide constituting the sputtering target. However, the resistance of the transparent conductive film obtained using this material tends to increase. By using a target in which tin oxide is not solidly dissolved in indium oxide, such as by embedding a sintered body, we can create a transparent conductive film with a resistance that is 10% or more lower than when using a conventional target. The present invention was completed based on the discovery that the following can be obtained.

That is, the present invention uses indium oxide powder and an average secondary particle size of 5.
The present invention relates to a method for producing an indium-tin oxide sintered body, characterized by sintering a mixture with tin oxide powder of μm or more at a temperature of less than 1450° C. The present invention relates to an indium-tin oxide sintered body in which less than % of the indium-tin oxide sintered body is solid-dissolved tin oxide and has an apparent sintered density of 5.5 g/c+s3 or more, and a sputtering target using the same.

It is thought that the tin oxide diffused and solid-solved in the indium oxide lattice in the ITO sintered body is already in a dopant state in the sintered body, and releases excess valence electrons as free electrons. Such tin oxide does not have excess valence electrons in the sputtered film and is considered inactive as a dopant.

On the other hand, tin oxide, which exists in the form of SnO□ particles in the sintered body and is not diffused and dissolved in the indium oxide lattice, does not function as a dopant in the sintered body and does not fully absorb the tetravalent valence electrons. I have it. This type of tin oxide diffuses into the indium oxide lattice as a solid solution only after it is formed by sputtering, and releases excess valence electrons as free electrons for the first time in the film, so it is thought to act as an active dopant in the film. .

The allowable solid solution range of tin oxide in the present invention is less than 25%, and particularly preferably less than 20%.

The solid solution rate of tin oxide in the ITO sintered body can be confirmed by dissolving the sintered body in concentrated hydrochloric acid. Tin oxide generally does not dissolve in concentrated hydrochloric acid, but tin oxide diffused as a solid solution in indium oxide easily dissolves in concentrated hydrochloric acid. The solid solution rate of tin oxide can be confirmed by chemically analyzing the ratio of tin oxide and indium oxide dissolved in this manner.

According to the method described above, it is found that the solid solution rate of tin oxide in indium oxide in the conventional ITO sintered body is 30% or more.

The content of tin oxide in the ITO sintered body is suitably in the range of 5 to 15% by weight, particularly 7 to 12% by weight.

If the amount of tin oxide is too small, the resulting film will have a low electron density and will not have a low resistance. On the other hand, if the amount of tin oxide is too large, the electron density will be saturated and the electron mobility will decrease due to scattering by tin oxide, so that a film with low resistance will still not be obtained.

In order to relatively reduce the amount of inert tin oxide dissolved in the ITO sintered body, it is possible to increase the total amount of tin oxide added to supplement the original effect of tin oxide. Even if such a sintered body is used, a low-resistance film cannot be obtained because of a decrease in electron mobility due to the scattering of tin oxide.

The preparation of the ITO sintered body of the present invention in which such solid solution of tin oxide is suppressed is possible by using tin oxide having an average secondary particle size of 5 μm or more, particularly 10 μm or more.

There is no particular restriction on the primary particle size of the tin oxide used here, but coarse particles with as small a surface area as possible are preferred. Since such coarse-grained tin oxide has a small surface area, diffusion of tin oxide into indium oxide during sintering is suppressed, and the effects of the present invention can be obtained.

In order to obtain such coarse particles of tin oxide, it can be prepared by a conventional method of heat treating tin oxide powder at 1000° C. or higher, or by an oxalate pyrolysis method that easily produces coarse particles.

There is no particular restriction on the particle size of the indium oxide used to prepare the ITO sintered body of the present invention, but since the sintered body preferably has a high density, it is possible to obtain a high sintered density by sintering. It is preferable to use a fine and highly dispersed powder of less than

The sintered density of the ITO sintered body of the present invention is 5.5 g/cm'
(approximately 80% of theoretical density) or more, approximately 6.3g/c+a
3 (approximately 90% of the theoretical density) or more. Such a high-density sintered body suppresses surface reduction of the target due to sputtering, and a stable transparent conductive film with lower resistance can be obtained.

Conventionally, tin oxide acted as an impurity for indium oxide, making it difficult to sinter ITO, but in the present invention, sintering of indium oxide progresses easily in order to suppress the solid solution of tin oxide in indium oxide. However, high sintered density is easily achieved.

The ITO sintered body of the present invention is preformed by a conventional method at a temperature below 1450°C, particularly between 1350°C and 1430°C.
Sinter at a sintering temperature in the range of . If this temperature is less than 1,350°C, it is difficult to obtain the high sintered density of the present invention, while at a high temperature of 1,450°C or higher, the diffusion of tin oxide into the indium oxide lattice progresses during sublimation of tin oxide, and the present invention Therefore, it becomes difficult to suppress the diffusion and solid solution of tin oxide, which is the objective. Also, the sintering time is 2 to 10 hours.

By suppressing the diffusion and solid solution of tin oxide in the ITO sintered body, there is a concern that the resistance of the sintered body increases, which may cause problems when using this for DC sputtering. However, indium oxide has a high density of 0.1Ω・c by itself.
The ITO sintered body has sufficient conductivity even when the solid solution rate of tin oxide in the ITO sintered body is suppressed to less than 25%, and there is no problem in using it in DC sputtering.

On the other hand, in the high-frequency sputtering method, which allows sputtering even when using an insulator, a target with no solid solution of tin oxide is used, such as by embedding a sintered chip of tin oxide in a high-density sintered body of indium oxide alone. is effective. In the case of sputtering using such a method, a controlled film composition can be obtained by using a material in which the surface areas of indium oxide and tin oxide are adjusted from 95=5 to 85:15. However, when there is a difference in the sputtering rate on the target surface as in magnetron sputtering, further appropriate adjustment is required so that the indium oxide/tin oxide ratio in the resulting film is about 9278 to 88712.

The high-density sintered body of indium oxide alone used in the above method is produced by a normal method, for example, by sintering indium oxide powder with a particle size of 0.1 to several μm at the same sintering temperature as in the case of ITO described above. obtain.

[Effects of the present invention] By using the ITO sintered body of the present invention as a sputtering target, a transparent conductive film with lower resistance than before, that is, 0. ．． It became possible to form a low resistance film of less than 2 mΩ·effi. -Also, there are no problems such as abnormal discharge during operation, and a uniform film can be obtained.

[Examples] The present invention will be described below based on Examples, but the present invention is not limited to the Examples in any way.

Example 1 A commercially available tin oxide powder was heat-treated at 1300° C. to grow grains, thereby preparing coarse-grained tin oxide powder having an average grain size of about 10 μm.

Such tin oxide was mixed with indium oxide with an average particle size of 0.2 μm at a mW ratio of 90:10, and
Sintered at ℃ for 5 hours. The sintered density of the obtained ITO sintered body was 8.0 g/cm3, and the solid solution rate of tin oxide by dissolving in concentrated hydrochloric acid was 15%.

Using this sintered body as a sputtering target,
A transparent conductive film was formed by C magnetron sputtering method. The sputtering conditions are input power 4v/Cr
a2, argon atmosphere, 0.5 Pa, substrate temperature 250
It is ℃.

The obtained transparent conductive film had a light transmittance of 85% or more at 550 nm and a specific resistance of 0.17 rRΩ·cm.

Example 2 A stoichiometric amount of ammonium oxalate was added to an aqueous tin chloride solution to precipitate tin oxalate, and the tin oxalate was heated at 800°C.
By thermally decomposing the powder, a dice-shaped tin oxide powder having an average particle size of 10 μI was prepared.

This tin oxide was mixed with fine indium oxide with an average particle size of 0.2 μm in a weight ratio of 90:10,
Sintered at ℃ for 5 hours. The sintered density of the obtained ITO sintered body was 6.2 g/c++3, and the analysis value of the solid solution rate of tin oxide by dissolving in concentrated hydrochloric acid was 14%.

Using this sintered body as a sputtering target,
A transparent conductive film was formed by C magnetron sputtering method. The sputtering conditions are input power 4vlC1
12. Argon atmosphere, 0.5 Pa, substrate temperature 250
It is ℃.

The obtained transparent conductive film had a light transmittance of 85% or more at 550 nm and a specific resistance of O.1BIIΩ·cm.

Example 3 Indium oxide with an average particle size of 0.2 μ
A high-density sintered body with a sintered density of 6.5 g/cg3 was prepared by sintering for a time. A hole with a diameter of 5 mm was made in this sintered body, and a sintered body chip of tin oxide was embedded in the hole so that the area ratio of the target surfaces of indium oxide and tin oxide was 90:10.

Using this sintered body as a sputtering target, R
A transparent conductive film was formed by F sputtering method. The sputtering conditions were an input power of 4 W/cm2, an argon atmosphere, 0.5 Pa, and a substrate temperature of 250°C.

The obtained transparent conductive film had a light transmittance of 85% or more at 550 nm and a specific resistance of 0.15 mΩ·ell.

Comparative Example 1 Commercially available tin oxide having an average particle size of 1 μm was mixed with fine indium oxide having an average particle size of 0.2 μm in a weight ratio of 90:10, and sintered at 1400° C. for 5 hours. Obtained IT
The sintered density of the O sintered body was 5.4 g/cm3, and the analysis value of the solid solution rate of tin oxide by dissolving in concentrated hydrochloric acid was 32%.

Using this sintered body as a sputtering target,
A transparent conductive film was formed by C magnetron sputtering method. Sputtering conditions are input power 4v/cf
l12, argon atmosphere, 0.5 Pa, substrate temperature 25
It is 0°C.

The sputtering conditions were an input power of 4 w/Cl112, an argon atmosphere, 0.5 Pa, and a substrate temperature of 250°C.

The obtained transparent conductive film had a light transmittance of 85% or more at 550 na+, but a specific resistance of 0.23 mΩ・cra.
Met.

Comparative Example 2 Commercially available tin oxide having an average particle size of 1 μm was mixed with fine indium oxide having an average particle size of 0.2 μm in a weight ratio of 90:10, and sintered at a high temperature of 1500° C. for 5 hours. The sintered density of the obtained ITO sintered body was 6.0 g/ca+3, and the analysis value of the solid solution rate of tin oxide by dissolving in concentrated hydrochloric acid was 100%.

Using this sintered body as a sputtering target,
A transparent conductive film was formed by C magnetron sputtering method. Sputtering conditions are input power 4v/cr
a2, argon atmosphere, 0.5 Pa, substrate temperature 250
It is ℃.

The obtained transparent conductive film had a light transmittance of 85% or more at 55On11, but a specific resistance of 0.851! lΩ・C
It had a high resistance of rl1.

Comparative Example 3 Indium and tin hydroxide were coprecipitated from an aqueous solution of tin chloride and indium chloride, and the coprecipitate was heated at 800° C. to prepare a coprecipitated ITO powder. The coprecipitated ITO powder was prepared so that the ratio of indium oxide to tin oxide was 90:10.

This co-precipitated ITO powder was sintered at 1400°C for 5 hours to obtain a sintered body weighing 5°4g/C13. The tin oxide solid solution rate analysis value of this sintered body by dissolving it in concentrated hydrochloric acid was 85%.

Using this sintered body as a sputtering target,
A transparent conductive film was formed by C magnetron sputtering method. The sputtering conditions are input power 4vlcI.
52, Argon atmosphere, 0.5 Pa, substrate temperature 250
It is ℃.

The obtained transparent conductive film had a light transmittance of 85% or more at 550 r+m, but a specific resistance of 0.45 mΩ・el.
It had a high resistance of ll3.

Claims (1)

[Claims] [1] Less than 25% of the tin oxide in indium oxide is solid solution tin oxide, and the apparent sintered density is 5.5 g/c
An indium-tin oxide sintered body having a particle diameter of m^3 or more. [2] A method for producing an indium-tin oxide sintered body, which comprises sintering a mixture of indium oxide powder and tin oxide powder having an average secondary particle size of 5 μm or more at a temperature below 1450°C. [3] Less than 25% of the tin oxide in indium oxide is solid-dissolved tin oxide, and the apparent sintered density is 5.5 g/c
A sputtering target made of an indium-tin oxide sintered body having a diameter of m^3 or more. [4] An indium-tin oxide sintered body sputtering target in which a tin oxide sintered body is embedded in an indium oxide sintered body having an apparent sintered density of 5.5 g/cm^3 or more.