A high-permittivity dielectric capacitor and a fabrication method thereof are provided. The capacitor uses a tantalum oxynitride film as a high-permittivity dielectric film. The tantalum oxynitride film is deposited by chemical vapor deposition using tantalum ethoxide gas as a source of tantalum and oxygen and ammonia gas as a source of nitrogen. The tantalum oxynitride film has a high permittivity, a high thermal stability and a low interface heterogeneity between upper and lower electrodes. Thus, the current leakage due to oxygen vacancy in the film can be reduced.