Silicon nitride (SIN,) ultrathin gate dielectric films for ultralarge-scale integrated circuits have been successfully formed by radical chemical vapor deposition (R-CVD) at 300 degreesC. In this process, charged species incident on the silicon (Si) substrate during the growth were eliminated with the magnetic field in electron cyclotron resonance plasma-enhanced CVD employing nitrogen and silane (N-2/SiH4) gases. By using R-CVD, SiNx films with very low leakage current and near-ideal dielectric constant (is an element of =7.2) have been obtained. III situ Fourier transform infrared reflection absorption spectroscopy (FT-IR RAS) has confirmed that the Si-N bonds are increased and the voids in films are reduced by eliminating charged species. A key factor for forming ultrathin SiNlambda films of high quality at 300 degreesC is discussed, based on characterization of films synthesized with and without charged species on the substrate using in situ: x-ray photoelectron spectroscopy, ill situ FT-IR RAS, and in situ atomic force microscopy.