Plasma enhanced chemical vapor deposition (PECVD) with SiH4/NH3 mixtures was used to produce silicon nitride thin films on silicon substrates. These types of films are commonly used as dielectrics in modern semiconductor technology; however, the incorporation of large amounts of hydrogen affects negatively their stability and electrical properties. Therefore, quantifications of the hydrogen content and chemical composition of these films are required. Forward elastic scattering using a 10 MeV 12C3+ beam was used to determine the thickness and stoichiometry of the films. Nuclear reaction analysis (NRA) using a 0.825 MeV deuterium beam was also applied to measure the low concentrations of oxygen and carbon in these films. The chemical structure of the silicon nitride layers was studied using infrared spectroscopy.