Structural, optical and electrical properties of Si-rich and N-rich PECVD silicon nitride films

Silicon nitride (SiN_x) thin films play a crucial role in the semiconductor industry due to their controllable properties, which make them suitable for various applications. In this study, SiN_x films, with varying composition ratios (x=[N]/[Si]), were fabricated under different conditions using plasma-enhanced chemical vapor deposition (PECVD). The composition significantly affects the structural, optical and electrical properties of the films. We investigate the characteristics that depend on the stoichiometric composition of amorphous hydrogenated SiN_x films (ranging from N-rich to Si-rich) through techniques such as X-ray photoelectron spectroscopy (XPS), electron microprobe microscopy (EMP), ellipsometry, Fourier transform infrared spectroscopy (FTIR), secondary ion mass spectroscopy (SIMS), and high-voltage broadband dielectric spectroscopy (HVBDS). Key parameters, including refractive index, bonding structure, permittivity, loss factor and AC conductivity are analyzed and discussed in relation to the x=[N]/[Si] ratio. The presence of hydrogen in PECVD SiN_x is also examined with Si-H and N-H bonds varying based on the x ratio. These variations influence the film electrical conduction properties with low-frequency HVBDS accurately identifying the structural transitions between N-rich and Si-rich compositions. These results show the key role of the Si-N bonding and hydrogenation (mainly through Si-H bonding) in controlling nonlinear conduction of SiN_x films.