JP3381328B2 - Manufacturing method of ITO sintered body - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of a composite oxide sintered body for an ITO sputtering target used in producing a transparent conductive film. 2. Description of the Related Art ITO (Indium Tin Oxi)
de) The thin film has characteristics such as high conductivity and high transmittance,
Further, since fine processing can be easily performed, it is widely used in a wide range of fields such as display electrodes for flat panel displays, window materials for solar cells, and antistatic films. In particular, in the field of flat panel displays such as liquid crystal display devices, in recent years, the size and definition have been advanced, and the demand for ITO thin films as display electrodes has been rapidly increasing. The method of producing such an ITO thin film can be roughly classified into a chemical film forming method such as a spray pyrolysis method and a CVD method, and a physical film forming method such as an electron beam evaporation method and a sputtering method. Above all, the sputtering method is used in various fields because it is a film forming method that can easily increase the area and obtain a high-performance film. I by sputtering method
In the case of manufacturing a TO thin film, an alloy target composed of metal indium and tin (hereinafter abbreviated as IT target) or a composite oxide target composed of indium oxide and tin oxide (hereinafter abbreviated as ITO target) is used as a sputtering target. Can be But I
The TO target is the mainstream of ITO thin film targets because the resistance and transmittance of the film obtained as compared with the IT target are less changed with time and the control of film forming conditions is easy. As such an oxide sintered body for an ITO target, an indium oxide powder and a tin oxide powder or an ITO powder are usually formed by press molding or casting at room temperature, and this is formed in the air or in an oxygen atmosphere at normal pressure. A medium sintered at 1300 to 1700 ° C. has been used. In the case where an ITO thin film is manufactured by a sputtering method, as the sintering density of a target increases, the film forming rate increases. Generation of particles that cause defects in the film is suppressed. The target life is extended. There are advantages such as. For this reason, a high-density ITO target has generally been strongly desired. [0006] When sintering ITO, tin oxide contained in the molded body undergoes a reaction represented by the following equation with an increase in temperature, and shows the sintering behavior of the evaporative condensation mechanism. It is known that the sinterability is poor and, as a result, sintering of ITO itself is hindered. SnO ₂ (s) = SnO (g) + ／ O ₂ (g) As a result, in general sintering methods such as sintering in the air, S
Even in the case of ITO having an nO ₂ content of 10 wt%, the sintering density is only about 5.7 g / cm ³ , and there is a problem that the sintering density cannot be increased. As a means for solving such a problem,
An oxygen pressure sintering method in which sintering is performed in a pressurized state in an oxygen atmosphere (for example, Japanese Patent Application Laid-Open No. 3-207858) has been proposed. In this method, sintering is performed under pressure,
Evaporation of tin oxide, which is a cause of inhibiting sintering, is suppressed, and a high-density sintered body can be obtained. However, even in the case of using this method, the furnace pressure had to be as high as 9.9 atm in order to obtain a sintered body having a high sintering density. Therefore, the structure of the sintering apparatus must be a pressure-tight container with high airtightness, and the apparatus structure is complicated, and there is a problem that the apparatus cost cannot be reduced. Further, production by the high-pressure process has a problem in terms of safety, and further has a problem that it is difficult to increase productivity. [0009] An object of the present invention is to solve the problem of I
An object of the present invention is to enable a sintered body having a high sintering density to be obtained inexpensively with good productivity while maintaining safety in pressure sintering of TO. Means for Solving the Problems In view of the above-mentioned current situation, the present inventors have conducted intensive studies and as a result, have found that when sintering ITO in a pressurized state in an oxygen atmosphere, additional processing is required. The inventors have found that the sintering density can be easily increased by setting the temperature at which the pressure is started to 800 ° C. or higher, and have completed the present invention. That is, according to the present invention, when pressure-sintering a compact formed by press-molding or casting at room temperature of a powder comprising indium oxide and tin oxide under pressure in an oxygen atmosphere, the temperature at which pressurization is started is determined. The present invention relates to a method for producing an ITO sintered body, wherein the temperature is 800 ° C. or higher. Hereinafter, the present invention will be described in detail. The powder of indium oxide and tin oxide referred to in the present invention is a mixed powder obtained by mixing predetermined amounts of indium oxide powder and tin oxide powder by a ball mill or the like, and a coprecipitation method or indium / tin powder. I containing a predetermined amount of tin oxide obtained by oxidizing the alloy
Means TO powder. Although the mixing ratio of tin oxide varies depending on the sputtering conditions and the like, generally, the resistance of the manufactured ITO film is reduced by 5 to 15%.
It is preferably about wt%. As a method for mixing the powder, a mixing method such as a dry method or a wet method can be appropriately used. [0014] The mixed powder thus produced is molded to obtain a molded body. Examples of the molding method include press molding and cast molding. In the case of producing a molded body by press molding, after filling the mixed powder into a mold of a predetermined size, 100 to 300 k using a press machine.
Pressing is performed at a pressure of g / cm ² to produce a molded body. Thereafter, if necessary, a CIP treatment may be further performed at a pressure of 1 to 5 ton / cm ² to increase the density of the compact. On the other hand, when a molded body is manufactured by casting, the raw material powder is mixed with water, a binder and a dispersant to form a slurry, and the slurry having a viscosity of 50 to 5000 centipoise is cast into a mold for casting. It is poured into the mold to produce a molded article. Since the molded body obtained by the casting contains water, a binder and a dispersant, a drying treatment and a debinding treatment at a temperature of 300 to 500 ° C. for about 5 to 20 hours are performed to remove these. It is necessary to perform it appropriately. The molded body thus obtained may be subjected to a CIP treatment at a pressure of 1 to 5 ton / cm ^{2 in} the same manner as in the case of the press molded body to obtain a molded body having a higher density. Next, the compact thus obtained is put into a pressure sintering furnace and sintered. After setting the compact in the furnace, the inside of the furnace is once evacuated and then oxygen gas is introduced to bring the pressure to atmospheric pressure (gauge pressure: 0 atm). In this state, heating is started. At this time, if the heating rate is too high, cracks may occur in the molded body due to thermal shock. Therefore, the heating rate is preferably 100 ° C./Hr or less. When the temperature rise is started, the volume of the oxygen gas in the furnace increases due to thermal expansion. Therefore, it is necessary to appropriately adjust the pressure so as to keep the furnace pressure at atmospheric pressure. When the temperature in the furnace reaches at least 800 ° C., oxygen gas is further introduced to start pressurization. According to the present invention, by starting pressurization at a temperature of 800 ° C. or higher, a sufficient density improving effect appears, but it is more preferable to start pressurization at a temperature of 1100 ° C. or higher. Once pressurization is started, the pressure is maintained until the process is completed. It is desirable that oxygen gas be continuously supplied from the start of pressurization to the end of the process. The sintering temperature is 1300-1700
C is preferred. If the sintering temperature is lower than 1300 ° C., the solid solution of tin oxide in indium oxide does not progress, so that the sintering density does not increase.
When the temperature exceeds ℃, the molded body starts reacting with the surrounding furnace material, so that the sintering furnace may be damaged. The sintering time is desirably 3 hours or more in order to sufficiently increase the sintering density. The pressure in the furnace at the time of sintering is desirably 1.5 atmospheres or more (absolute pressure) in order to obtain a sufficient density increasing effect on the sintered body. The ITO manufactured by the above method
The sintered body exhibits a higher sintering density at a lower pressurized pressure than a sintered body manufactured by a conventional sintering method in which the pressurization is started from normal temperature. EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. EXAMPLE 1 180 g (purity 99.99%) of indium oxide powder and 20 g (purity 99.99%) of tin oxide powder were put into a ball mill pot having a capacity of 2 L, and 1 kg of nylon balls having a diameter of 10 mm was added thereto. Dry ball mill mixing was performed at 50 rpm for 5 hours. Next, 32 g of the obtained mixed powder
Into a 30 mm square press mold, and press pressure 3
Pressed at 00 kg / cm ² and 30 mm square with a thickness of 11.
A 5 mm compact was produced. Next, 3ton
CIP treatment was performed at a pressure of / cm ² . The molded body density of the obtained molded body was 4.3 g / cm ³ . Next, this compact was put into an oxygen pressure sintering furnace and sintered. The sintering conditions were as follows. (Sintering conditions) Sintering temperature: 1600 ° C. Heating rate: 100 ° C./Hr Sintering pressure: 4.5 atm (gauge pressure: 3.5 atm) Sintering time: 10 hours Pressing start temperature: 1150 ° C. Oxygen gas flow rate: 350 ml / min. (2 of furnace volume
%) When the sintered density of the sintered body manufactured under the above conditions was measured by the Archimedes method, the sintered density was 6.7 g / cm ^3.
Met. Example 2 Using the same method as described in Example 1, a 30 mm square molded article having a thickness of 11.5 mm was manufactured. Sintering was performed under the sintering conditions. (Sintering Conditions) Sintering temperature: 1600 ° C. Heating rate: 100 ° C./Hr Sintering pressure: 6.0 atm (gauge pressure: 5.0 atm) Sintering time: 10 hours Pressing start temperature: 1300 ° C. Oxygen gas flow rate: 350 ml / min. (2 of furnace volume
%) When the sintered density of the sintered body manufactured under the above conditions was measured by the Archimedes method, the sintered density was 6.9 g / cm ^3.
Met. COMPARATIVE EXAMPLE 1 Using the same method as described in Example 1, a 30 mm square molded article having a thickness of 11.5 mm was produced, and the molded article was placed in an oxygen pressurizing furnace and then fired. Sintering was performed under the sintering conditions.
The pressurization was started from room temperature and kept at that pressure until the end of the process. (Sintering conditions) Sintering temperature: 1600 ° C. Heating rate: 100 ° C./Hr Sintering pressure: 6.0 atm (gauge pressure: 5.0 atm) Sintering time: 10 hours Oxygen gas flow rate: 350 ml / min . (2 of furnace volume
%) When the sintered density of the sintered body manufactured under the above conditions was measured by the Archimedes method, the sintered density was 6.5 g / cm ^3.
Met. COMPARATIVE EXAMPLE 2 A 30 mm square, 11.5 mm thick molded body was manufactured using the same method as described in Example 1, and the molded body was placed in an oxygen pressurizing furnace and fired in the next firing step. Sintering was performed under the sintering conditions. (Sintering Conditions) Sintering temperature: 1600 ° C. Heating rate: 100 ° C./Hr Sintering pressure: 4.5 atm (gauge pressure: 3.5 atm) Sintering time: 10 hours Pressing start temperature: 700 ° C. Oxygen gas flow rate: 350 ml / min. (2 of furnace volume
%) When the sintered density of the sintered body manufactured under the above conditions was measured by the Archimedes method, the sintered density was 6.4 g / cm ^3.
Met. According to the present invention, when sintering is performed in a pressurized state in an oxygen atmosphere, the temperature at which the pressurization is started is set to 800 ° C. or more, so that the sintering process is performed. Since fine closed pores are more effectively eliminated from the sintered body, a high-density sintered body can be obtained. Therefore, even when the furnace pressure during sintering is lower than before, it is possible to obtain a sufficient density increasing effect, and it is possible to safely and efficiently produce a sintered body having a high sintering density. Become. [0027]

Claims (1)

(57) [Claims 1] A molded body obtained by molding a powder composed of indium oxide (In ₂ O ₃ ) and tin oxide (SnO ₂ ) under pressure in an oxygen atmosphere. A method for producing an ITO sintered body, characterized in that, when producing an ITO sintered body, the temperature at which pressurization is started is set to 800 ° C. or higher.