Effect of niobium and tantalum alloying on the microstructure and film structure of molybdenum alloy target

Thin films prepared by Molybdenum (Mo) sputtering targets are widely used in electronic products and components, such as thin film transistor-liquid cerystal display ,TFT-LCD), back electrode of thin film solar cell module, diffusion barrier layer in large and very large scale semiconductor integrated circuit and gate material in organic light-emitting diode, etc. The purity, density, grain size and distribution, grain orientation and other characteristics of target material will have a certain impact on film quality and product performance. For example, as the raw material of the back electrode in TFT-LCD, the quality of molybdenum target directly affects the performance of TFT-LCD. With the rapid development of electronic information industry, the demand for molybdenum sputtering target is increasing year by year, and its technical requirements are also improving. Molybdenum sputtering target is developing towards the direction of high purity, high density and fine grain. With the increase of the target density, the particle size on the film surface becomes larger, the distribution density increases, and the critical current decreases. However, this study only discusses the effect of the target density.

Alloying has a certain effect on the microstructure and properties of target and sputtering films, which has gradually attracted people's attention and become one of the important development directions of target materials in the future. At present, most molybdenum target manufacturers at home and abroad use conventional powder metallurgy to produce the target material. The raw material is obtained through powder mixing, billet pressing, sintering, multi-pass rolling forming, stress relieving annealing, mechanical processing, surface treatment and other processes. Conventional production process is long, grain refinement and non-preferred orientation are difficult to ensure.

The research results show that both niobium and tantalum alloying can refine the target grains, and the target grains have no obvious preferred orientation. The average grain sizes of Mo-Ni and Mo-Ta alloy targets are 70.02 μm and 34.43 μm, respectively. Under the same sputtering process parameters, the thickness of molybdenum-niobium and molybdenum-tantalum alloy films are about 200 nm and 240 nm, respectively. The average square resistance of the molybdenum-niobium alloy film is 15.680Ω/□, and the average square resistance of the aluminum-tantalum alloy film is 22.00Ω/□. After tantalum alloying, the grain refinement of the molybdenum target material is more significant, the grain size distribution is more uniform, the film deposition speed is faster, and the surface roughness is smaller, which leads to a larger increase in the square resistance of the molybdenum-tantalum alloy film.