Compositional Properties and High Field Electrical Conduction of PECVD Silicon Nitride Thin Films

The composition of silicon nitride (SiNx) films, varying from N-rich to Si-rich stoichiometries, significantly impacts their structural and electrical properties. In this study, we investigate the composition dependent characteristics of amorphous SiNx films, deposited by plasma-enhanced chemical vapor deposition (PECVD), using electron microprobe microscopy (EMP), Fourier transform infrared spectroscopy (FTIR), secondary ion mass spectroscopy (SIMS), and high-voltage broadband dielectric spectroscopy (HVBDS). It is found that amorphous PECVD SiNx films contain hydrogen bonded to both Si and N atoms, in the form of Si-H and N-H bonds, which vary with the ratio x=[N]/[Si] of SiNx. These films exhibit a wide range of electrical conduction properties such that the low frequency HVBDS is a powerful technique that clearly reveals the structural transition from N-rich to Si-rich types of SiNx films. We present and discuss the influence of the Si-N bonding structure and the hydrogenation process on the low frequency AC conductivity based on different SiNx ratios.