Study On Process Optimization And Performance Of ITO Target Prepared By Atmospheric Pressure Sintering

Indium tin oxide（ITO）,as the most widely used and rapidly developing transparent conductive oxide,has excellent optical and electrical properties.With the rise of the semiconductor industry,the demand for ITO is also increasing.However,China is slow to develop ITO preparation technology for both the traditional ITO with 9:1 mass ratio of indium oxide to tin oxide,and ITO with the new ratio（97:3,95:5,8:2）.For the preparation of low tin oxide content ITO targets such as 97:3,95:5,there has been a problem of its low densification.Therefore,it is of great significance for the development of semiconductor industry to prepare high density ITO targets with the new ratio.In this paper,ITO powders and ITO targets with 97:3 mass ratio of indium oxide to tin oxide were prepared using indium ingots and tin oxide powder as raw materials by mechanical ball milling,molding-cold isostatic pressing secondary molding process and atmospheric pressure sintering method.SEM,XRD,UV and other testing methods were used to characterize the microscopic morphology,phase composition,optical properties,electrical properties and density of the powders and targets,and to investigate the influence of process parameters in the preparation of ITO powders and targets.The main study contents and conclusions are as follows: （1）The ITO powder were prepared by mechanical ball milling method,and the effects of dispersant citric acid content,solid content,ball milling speed,and grinding media diameter on the morphology,phase composition,and optoelectronic properties of ITO powder were analysed.The results showed that the powder dispersion gradually became better with the increase of the citric acid content,and the agglomeration coefficient gradually decreased,and the agglomeration coefficient was only 1.06 when the citric acid content was 5%or 7%.As the solid content increases（from 10%to 70%）,the morphology of ITO powders changes from sphere-like to rod-like,and the optical band gap of ITO powders increasing and then decreasing.The optical band gap decreases with the increase of grinding media diameter.At the same time,with the increase of grinding media diameter,the powder resistance first decrease and then increase.As the ball milling speed increases from 60 r/min to 150 r/min,the optical band gap of the ITO powder increases from 3.36 e V to 3.44 e V,and the resistance value becomes smaller.At a solid content of 30%,a grinding media diameter of 10mm and a ball milling speed of 120 r/min,The sub-micron single cubic phase ITO powder with an average particle size of 130 nm,a resistance of 12.7Ω,a visible light transmission rate of90%,an optical band gap of 3.42 e V,and a high UV absorption rate can be obtained.（2）The ITO target is prepared by the atmospheric pressure sintering method by first pressing,then degreasing and finally sintering.And the effects of sintering temperature,heating rate,oxygen pressure and flow rate,holding time,and granulation method on the microstructure and properties of ITO targets were analyzed,and the results showed that:sintered at 1450°C-1600°C,the targets were all In₂O₃ single-phase structure,and no second phase would be produced.In the higher sintering temperature range,the temperature does not affect the microstructure.However,when the sintering temperature reaches 1600°C,secondary crystallization occurs and the pore pressure difference makes the pores larger and the density smaller.The density of the target gradually decreases with the increase of the heating rate,and the increase of the heating rate reduce the dwell time of the target in the middle of the sintering densification,thus affecting its density.The density of the sintered target is significantly improved under oxygen atmosphere,which can inhibit the decomposition of indium tin oxide.Compared with the traditional powder manufacturing process,the powder fluidity is improved after spray granulation,the particle size becomes larger,and the target density is higher.With the increase of holding time,the target densification increases,but the weight loss rate also increases.When using the atmosphere sintering method with oxygen pressure of 0.02 MPa,holding time of 25 h,sintering temperature of 1550°C,the heating rate of 1°C/min,relative density,resistivity and average particle size of prepared ITO target reached 98.50%,1.1×10^-4Ω·cm and 10.11μm,respectively.（3）The optimal sintering parameters are as follows:oxygen pressure is 0.02 MPa,holding time is 25 h,sintering temperature is 1550°C,and heating rate is 1°C/min,so that the degreasing and sintering are completed in one step and the sintering is carried out with long time atmosphere protection during the oxide decomposition time.Compared with the ITO targets prepared by separate sintering at the same calcination temperature,the stepped sintering process can further increase the density of the targets from 98.50%to 98.82%.The final target weight loss was only1%,although it was held for a period of time during the oxide decomposition time.And in this process the grains get growth time,but the grain size does not increase much,the average grain size grows from 10.11μm to 12.10μm,and the resistivity is 1.1×10^-4Ω·cm.