A method of forming a conformal dielectric film having Si—N bonds on a semiconductor substrate by plasma enhanced chemical vapor deposition (PECVD) includes: introducing a nitrogen- and hydrogen-containing reactive gas and a rare gas into a reaction space inside which a semiconductor substrate is placed; applying RF power to the reaction space; and introducing a hydrogen-containing silicon precursor as a first precursor and a hydrocarbon gas as a second precursor in pulses into the reaction space wherein a plasma is excited, thereby forming a conformal dielectric film doped with carbon and having Si—N bonds on the substrate.