JPH08198677A - Ito sintered compact for forming transparent electrically conductive film - Google Patents

Abstract

PURPOSE: To obtain an ITO sintered compact capable of giving a low resistance ITO film by sputtering at a low temp. by compacting a mixture of In2 O3 powder with SnO2 powder and firing the resultant compact in an oxygen-contg. atmosphere. CONSTITUTION: A powdery mixture prepd. by uniformly mixing In2 O3 powder with >=7wt.% SnO2 powder is compacted by uniaxial pressing, isostatic pressing or other method and the resultant compact is heated to 1,300-1,700 deg.C at >=0.5 deg.C/min heating rate in the temp. range of >=1,000 deg.C in an atmosphere having >=25vol.% concn. of oxygen. After holding at the temp., the compact is cooled at >=0.5 deg.C/min cooling rate to obtain the objective ITO sintered compact. contg. >=80% by area of a principal phase in which the molar ratio of In:Sn is 10:1 to 22:1. The principal phase has 3-50μm average grain diameter, >=1.0121nm lattice constant and >=6.5g/cm<3> density.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an IT for forming a transparent conductive film.
More particularly, the present invention relates to a low temperature substrate, that is, an ITO sintered body for forming a transparent conductive film having a low resistance at a substrate temperature of 200 ° C. or lower to room temperature.

[0002]

2. Description of the Related Art In recent years, the demand for transparent conductive films has increased with the development of display devices centered on liquid crystals. For the transparent conductive film, an indium tin oxide film (hereinafter referred to as an ITO film) having low resistance and high transparency is optimal. As a method for obtaining an ITO film, a mixed powder of indium oxide powder and tin oxide powder is molded and sintered to produce an indium / tin oxide sintered body (hereinafter referred to as ITO sintered body), which is used as a target. As an ITO film is formed. The ITO film formation method includes a sputtering method, a vacuum deposition method, a CVD method, and the like. Among them, the sputtering method has an advantage that a large area can be formed and a low resistance film can be obtained with good reproducibility. Therefore, the method of forming the ITO film is currently the mainstream. The sputtering method is a method in which a target is sputtered with an inert gas ion and a film is formed on a substrate heated to about 300 ° C. It is known that the ITO film thus obtained has a resistivity of about 2.0 × 10 −4 Ω · cm.

[0003]

However, recently, due to colorization of liquid crystals, miniaturization of display elements, adoption of an active matrix system, and introduction of a thin film transistor, a resin substrate such as a film having a heatable temperature of 200 ° C. or less. It is desired to form an ITO film having a low resistance on the above, and it has become necessary to use a target that can be used for film formation at a low temperature. In the conventional target, the main phase has a composition of In: Sn = 23: 1 to 98: 1, and the resistivity has a limit of 5 × 10 −4 Ω · cm at a film forming temperature of 200 ° C. In order to use it as a liquid crystal electrode, a resistivity of less than 4 × 10 −4 Ω · cm is required at a film forming temperature of 200 ° C. Therefore, the present invention is an IT for forming a transparent conductive film that can obtain an ITO film having a low resistance even by low-temperature film formation.
The purpose is to obtain an O sintered body.

[0003]

Means for Solving the Problems The inventors of the present invention have conducted various studies in order to solve the above-mentioned object, and as a result, have found that an ITO sintering having a main phase containing In2O3 as a main component and a phase containing more SnO2 than the main phase. It has been found that, by newly defining the composition of the main phase in the body, it can be used as a target that can obtain a low-resistance film even by low-temperature film formation. That is, the transparent conductive film forming target of the present invention is substantially composed of In, S
In an ITO sintered body composed of n and O, the molar ratio is I
It is characterized in that the main phase composed of n: Sn = 10: 1 to 22: 1 is contained in an area ratio of 80% or more. In the present invention, the average crystal grain size of the main phase is preferably 3 to 50 μm. Further, the lattice constant of the main phase is preferably 1.0121 nm or more. Furthermore, it is desirable that the density is 6.5 g / cm3 or more. Further, it is desirable that the amount of SnO2 in the ITO sintered body is 7 wt% or less.

[0004]

In the present invention, the main phase is In: Sn in molar ratio.
= 10: 1 to 22: 1 is because the composition of the main phase is In / Sn <10
When the composition of the main phase is In / Sn> 22, the Sn content becomes insufficient, and the Sn content becomes insufficient.
This is because oxygen resistance is not generated in the TO film, so that sufficient low resistance is not exhibited. In addition, In: Sn = 14: 1 to
By setting the ratio to 21: 1, the rate of resistance change of the film becomes smaller and stable sputtering can be performed, and 18: 1 to 21:
More preferably, it is 1. In addition, In:
When the area ratio of the main phase of Sn = 10: 1 to 22: 1 is less than 80%, a low resistance film cannot be obtained due to the existence of phases other than the main phase. The area ratio of the main phase is preferably as high as possible, and may be substantially 100% of the main phase area ratio. The ITO sintered body of the present invention may contain a phase other than the main phase in an area ratio of less than 20%,
For example, a phase having a larger Sn content than the main phase may be included as a phase other than the main phase. Further, if the SnO2 content of the sintered body is 7 wt% or less, the phases other than the main phase can be minimized, which is desirable.

In order to obtain a stable film resistivity, the ITO sintered body of the present invention preferably has an average crystal grain size of the main phase of 3 to 50 μm and a density of 6.5 g / cm 3 or more. Is desirable. Further, in the present invention, if the lattice constant of the main phase is less than 1.0121 nm, oxygen defects are less likely to occur and sufficient low resistance is difficult to develop, so 1.0121 nm or more is desirable, and it is 1.0121 to 1.0140 nm. More desirable.

In the present invention, the composition of each phase and the composition of the bulk are determined by SEM-EDX analysis (Scanning electron micr
oscopy-Energy dispersive Xray spectrometer) to analyze the composition of In and Sn, and the area ratio of the phases is determined by determining the area ratio of the SEM micrograph with light gray as the main phase and dark gray as the second phase. You can check. The lattice constant of the main phase is determined by an X-ray diffractometer (for example,
It can be confirmed by refining the lattice constant of Rigaku RINT1000).

In producing the target of the present invention, for example, In2O3 powder and SnO2 powder may be uniformly mixed at a predetermined ratio, and a mixed powder or a composite powder such as a solid solution powder or a coprecipitated powder may be used. . It is also possible to use a mixed powder in which one or two kinds of In2O3 powder and SnO2 powder are mixed with the composite powder as the main component. The mixed powder is molded by uniaxial pressing or hydrostatic pressing, etc., and the obtained molded product is heated at 1300 ° C to 17 ° C in an atmosphere having an oxygen concentration of 25 vol% or more.
Keep heating at a temperature of 00 ° C.

In the present invention, the sintering atmosphere is set to the oxygen atmosphere because it is necessary to suppress the decomposition of In2O3 and SnO2, but the oxygen concentration is preferably 25% or more, more preferably 50% or more. It is more desirable to be in a pressurized oxygen atmosphere. If the sintering temperature is less than 1300 ° C, a sintered body with a relative density of 85% or more cannot be obtained, while if it exceeds 1700 ° C, the density decreases due to the decomposition of tin oxide and indium oxide.
It is desirable to set the temperature to 1200-1700 ℃. In addition, the ITO sintered body is composed of a main phase composed of In: Sn = 10: 1 to 22: 1 at an area ratio of 8
In order to obtain a sintered body containing 0% or more, the temperature rising rate at 1000 ° C or higher is 0.5 ° C / min or more, and the cooling rate at cooling is 0.
It is preferably set to 5 ° C / min or more.

[0009]

【Example】

(Example 1) In2O3 powder having an average particle size of 50 nm and an average particle size
150 nm SnO2 powder was blended in a predetermined ratio and mixed by a ball mill for 24 hours. Molding is carried out by adding 1% of polyvinyl alcohol (PVA) to these powders and granulating them, and molding pressure with a cold isostatic press at 3000 kg / c.
Molded at m2. The compact was sintered by holding it at 1550 ° C., 1 atm and 70% oxygen atmosphere for 5 hours. Sample Nos. 1 to 11 were sintered under the sintering conditions of a temperature rising rate of 2 ° C./min at 1000 ° C. or higher and a cooling rate of 2 ° C./min during cooling. No.12 ~
For No. 16, sintering was performed under the condition of the temperature decreasing rate during cooling of 0.2 ° C./min. The average crystal grain size of the obtained sintered body is 5
The density was 6.5 g / cm @ 3 or more. The composition, area ratio and lattice constant of each phase of the obtained sintered body were measured and are shown in Table 1. Table 1 shows the resistivity and the rate of change in resistance when the obtained sintered body was formed into a film by using a target processed into a shape having a diameter of 100 mm and a thickness of 5 mm. The resistivity is the resistivity of the film after sputtering for 2 hours at a substrate temperature of 200 ° C. The rate of change in resistance is the rate of change (ba) in the resistance (b) of the film after 30 hours with respect to the resistance (a) of the film after 2 hours (ba) x 100 / a. In Table 1, Nos. 1 to 11 are the present invention, and Nos. 12 to 16 are comparative examples. 1, 2, and 3 are SEM microstructure photographs of the microstructures of the No. 3, No. 5, and No. 12 ITO sintered bodies in Table 1 observed by SEM after mirror finishing. In addition, No. 1, 8, 12, 14, 1 in Table 1
Table 2 shows the resistivity (μΩ · cm) of the ITO film when the substrate temperature during film formation was changed for the 6 samples. Furthermore, for the sample prepared in the same manner as the sample No. 3 in Table 1 except for the sintering conditions, the film resistivity (substrate temperature) of the ITO film obtained when the average crystal grain size and density were controlled by changing the sintering conditions. 200 ° C) is shown in Table 3. The film forming conditions are as follows. Spatter method DC magnetron spattering target-distance between substrates 60mm Sputtering power 1.0W / cm2 Sputtering gas composition 99% Argon + 1% Oxygen mixed gas Sputtering gas pressure 1Pa Film thickness 150nm Substrate Corning # 7059 glass

From Table 1, the molar ratio of In: Sn = 10: 1
It can be seen that by setting the area ratio of the main phase composed of 22: 1 to 80% or more, a transparent conductive film having a low resistance can be obtained even by low temperature film formation. Further, since the resistance change rate of the film is small, stable sputtering is possible. As shown in Table 2, sample No. 1 to sample No. 8 of the target of the present invention
Compared with Nos. 11 and 14 of Comparative Example, showed a lower resistance value especially in low temperature film formation at 200 ° C. or lower. As shown in Table 3, when the average crystal grain size is 5 to 30 μm and the density is 6.5 g / cm 3 or more, low film resistivity is obtained.

[0011]

By using the ITO sintered body for forming a transparent conductive film of the present invention as a target, it is possible to obtain an ITO film having a low resistance value even by sputtering at a low temperature.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

[Table 3]

[Brief description of drawings]

FIG. 1 is a photograph of a micro metallographic structure of Sample No. 3, which is an ITO sintered body of the present invention.

FIG. 2 is a photograph of the micro metallographic structure of Sample No. 5, which is an ITO sintered body of the present invention.

FIG. 3 is a photograph of a micro metallographic structure of Sample No. 12, which is an ITO sintered body of a comparative example.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01B 13/00 503 Z // H01B 5/14 A

Claims (5)

[Claims] 1. I consisting essentially of In, Sn and O
In To Sn sintered body, molar ratio of In: Sn = 10: 1 to 22: 1
An ITO sintered body for forming a transparent conductive film, comprising the main phase consisting of 80% or more in area ratio. 2. The ITO sintered body for forming a transparent conductive film according to claim 1, wherein the main phase has an average crystal grain size of 3 to 50 μm. 3. The ITO sintered body for forming a transparent conductive film according to claim 1, wherein the main phase has a lattice constant of 1.0121 nm or more. 4. The density is 6.5 g / cm3 or more.
4. The ITO sintered body for forming a transparent conductive film according to any one of 1 to 3. 5. The ITO sintered body for forming a transparent conductive film according to claim 1, wherein the amount of SnO 2 in the ITO sintered body is 7 wt% or less.