The effects of RuO2 addition on the electrical properties of a Ta-RuO2 diffusion barrier for capacitor bottom electrodes were investigated as a function of the composition ratio of Ta:RuO2 and contact size, at a temperature range of 650-800 degrees C in air. When the Ta film was deposited without RuO2 addition, it exhibited a higher total resistance and a nonohmic behavior with increasing annealing temperature, originating from the formation of a nonconductive Ta2O5 phase by reaction between the Ta film and the external ambient oxygen after annealing. For both the Ta + RuO2/n(++)-poly-SiSiO2/Si and the Pt/Ta + RuO2/n(++)-poly-SiSiO2/Si contact system, no other phase, such as Ta2O5, Pt-silicides, and Pt-Ta compounds, was observed except for the formation of a conductive RuO2 crystalline phase after annealing, followed by the prevention of surface oxidation of the diffusion barrier itself as well as the retention of the bottom electrode structure up to 800 degrees C. This resulted in a lower total resistance and an ohmic characteristic. Therefore, it can be concluded that ohmic behavior does not depend on contact size for both contact systems and all compositions in this study.