Depositions and microstructures of Mg–Si thin film by ion beam sputtering

Mg–Si thin films were deposited on glass substrates by ion beam sputtering from a target composed of Mg and Si plates with area ratios of 25%:75%, 50%:50% and 75%:25%. The Mg concentration in the films increases with the target area ratio of Mg, resulting in control of the film composition by the target area ratio. The Mg–Si films deposited from the targets of Mg/Si = 25%:75% and 75%:25% show amorphous and Mg crystalline peaks in X-ray diffraction patterns, respectively. From the target of area ratio Mg/Si = 50%:50%, films having intermetallic compound magnesium silicide Mg2Si were obtained. Structural, mechanical and electrical properties of the Mg–Si films deposited from a target with Mg/Si area ratio 50%:50% were examined. The films show a two-layer structure; the upper one consists of crystalline Mg2Si with a columnar structure and the lower shows an amorphous structure. For the two-layer structure, the mechanical properties of elastic modulus and hardness in the amorphous lower layer are higher than those in the crystalline upper layer. The electrical properties of the film indicate that they are semiconducting with a variable-range hopping mechanism. Moreover, magnesium concentrations in the crystalline upper layer have been found to be larger than those in the amorphous lower layer. In this paper, the properties of the films are also discussed together with film deposition details.