Thermal Stability of RuO₂ Thin Films and Effects of Annealing Ambient on Their Reduction Process

Abstract

RuO 2 films prepared by reactive sputtering were annealed in air and vacuum and the changes of their crystal structure, chemical binding state and resistivity were studied. In air, the RuO 2 films maintain a rutile structure below 800°C. Crystal grain growth was found above 600°C and the minimum resistivity of 46 µΩcm was obtained at 800°C. The vacuum annealing was conducted with two types of annealing systems, one using an oil diffusion pump and the other using a turbomolecular pump as the main pump. The RuO 2 films annealed in the system using the turbomolecular pump were not reduced below 500°C, however, the surface of the films was reduced as low as 200°C in the system using the oil diffusion pump. The difference in the reduction processes was examined on the basis of the thermodynamics of RuO 2 and the influence of reducing residual gases in vacuum.