Thermal stability of RuO2 thin films and effects of annealing ambient on their reduction process

RuO2 films prepared by reactive sputtering were annealed in air and vacuum and the changes of their crystal structure, chemical binding slate and resistivity were studied. In air, the RuO2 films maintain a rutile structure below 800 degrees C. Crystal grain growth was found above 600 degrees C and the minimum resistivity of 46 mu Ohm cm was obtained at 800 degrees 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 RuO2 films annealed in the system using the turbomolecular pump were not reduced below 500 degrees C however, the surface of the films was reduced as low as 200 degrees C in the system using the oil diffusion pump. The difference in the reduction processes was examined on the basis of the thermodynamics of RuO2 and the influence of reducing residual gases in vacuum.