To enhance the electrical properties of dielectric film by improving the interface related problems such as second phase formation and surface roughening at the dielectric film-bottom electrode interface, suppression of abnormal grain growth in the Ru film was investigated by N2O plasma treatment. When the Ru film was annealed by rapid thermal processing in oxygen ambient, grains grew heterogeneously, leading to an increase in surface roughness. Where the Ru film was oxidized by N2O plasma, however, the surface of the Ru film was smooth. The suppression of abnormal grain growth can be attributed to the faster reactivity of oxygen ions than the growth rate of some grains in the Ru film during N2O plasma oxidation. The Ru film oxidized at the surface by N2O plasma significantly improved the leakage current property due to suppression of heterogeneous grain growth during oxidation.