A detailed structural analysis and dielectric property measurements of silicon nitride films fabricated using atmospheric pressure (AP) plasma were carried out, and the results were compared to those of nitride films fabricated using a radio frequency plasma. Using AP plasma, 1.8-nm-thick silicon nitride films composed of Si3N3.5O0.7 were obtained at nitridation temperatures ranging from 25to500°C. X-ray photoelectron spectroscopy using a monochromatic AlKα source at 1486.6eV and high-resolution Rutherford backscattering spectrometry revealed approximately 10% more nitrogen atoms corresponding to the N–Si3 bond in the film using AP plasma than those using rf plasma. In the range of 25–500°C, the nitridation temperature did not affect the leakage current densities of the films fabricated using AP plasma. Films fabricated at 25°C showed leakage current density of as low as 7×10-2A/cm2 at 5MV/cm. This value was one order of magnitude lower than that using rf plasma. The direct-tunneling current simulation analysis with the Wentzel-Kramers-Brillouin approximation revealed that the effective tunneling mass of holes increased due to the nitrogen atoms incorporated in the films. From deep-level transient spectroscopy, signals attributed to defects generated by plasma irradiation in the silicon substrate were not observed.