Silicon nitride (SiNx) is a material with many applications and can be deposited with various deposition techniques. Series of SiNx films were deposited with HWCVD, RF PECVD, MW PECVD and LF PECVD. The atomic densities are quantified using RBS and ERD. The influence of the atomic densities on the Si¿N and Si¿Si bond structure is studied. The density of N¿N bonds is found to be negligible. New Si¿N FTIR proportionality factors are determined which increase with increasing N/Si ratio from 1.2 · 1019 cm¿ 1 for Si rich films (N/Si = 0.2) to 2.4 · 1019 cm¿ 1 for N rich films (N/Si = 1.5). The peak position of the Si¿H stretching mode in the FTIR spectrum is discussed using the chemical induction model. It is shown that especially for Si-rich films the hydrogen content affects the Si¿H peak position. The influence of the composition on the refractive index of the films is discussed on the basis of the Lorentz¿Lorenz equation and the Kramers¿Kronig relation. The decreasing refractive index with increasing N/Si ratio is primarily caused by an increase of the band gap. Keywords: Hot Wire CVD; Silicon nitride@en