Ion energy for crystallizing metallic compound film in plasma

Typical materials for the actuators in micro machines are shape memory alloys like nickel titanium (TiNi) and piezoelectric compounds like lead zirconate titanate (PZT). For medical application in a future the materials will be required to be deposited directly on surfaces of plastics as thin film in a crystalline structure, since most medical instruments such as catheters for blood vessel surgery are made of polymeric plastics. However, compound material sputter-deposited at room temperature is usually amorphous as it is. The material had needed to be annealed at high temperature over 800K afterwards. In order to resolve this problem a new apparatus was developed which deposited metallic compound film in crystalline structure directly on a substrate at lower temperature than 500 K. The apparatus consisted of a magnetron-sputtering deposition system with multi targets as well as of an ion irradiation system immersed in plasma^{1, 2}. The ion irradiation system was basically similar to the plasma based ion implantation (PBII) system³ in constitution, although the pulse bias voltage was much lower, i.e., below 100 V. In further research regarding TiNi the crystallization temperature was lowered down to 358 K by optimizing the plasma conditions. So long the ion energy irradiating the sputter-deposited film had been considered given only by the bias voltage from the similarity to PBII. In this study we find the ion energy value should be corrected by adding the plasma potential against the plasma chamber to the bias voltage. The plasma potential is usually 5.18 times the electron temperature. Consequently it is experimentally shown that the optimum ion energy for crystallization is almost constant even if the plasma parameters, including electron temperature, change.