Tantalum Nitride (TaN) thin films were deposited onto n-type Si(100) and (111) substrates with SiO 2 films at room temperature by radio frequency (RF) magnetron sputtering under Ar-N 2 plasma using a tantalum target. We observed the formation of TaN thin films with a wide range of the electrical resistivity as a function of the N 2 gas flow ratio, working pressure and the sputtering power, and their origins are discussed based upon the structural properties and chemical compositions of TaN thin films before Cu films deposition. In this study, we first observed that the TaN thin films with lower resistivity exhibited TaN (200) preferentially oriented structures and had larger grain sizes. It was also found that the formation of TaO(002) made the resistivity of TaN thin films higher because of the diffusion of oxygen from SiO 2 films during deposition.