Effect of deposition reactive gas ratio , RF power and substrate temperature on the charging / discharging processes in PECVD silicon nitride films based on induced surface potential and adhesive force measurements using Atomic force microscopy

The dependence of the electrical properties of silicon nitride on the deposition conditions used to prepare it and consequently on material stoichiometry has not been fully understood. In the present study, the influence of plasma-enhanced chemical vapor deposition (PECVD) conditions on the dielectric charging of SiNx films is investigated. The work targets mainly the dielectric charging phenomenon which constitutes a major failure mechanism in electrostatically driven MEMS devices, particularly in electrostatic capacitive MEMS switches. The charging/discharging processes in the investigated SiNx films have been studied using two different nanoscale characterization techniques based on Kelvin probe force microscopy (KPFM) and, for the first time, force-distance curve (FDC) measurements. The main advantage of the FDC based methodology is that it takes into account the meniscus force between the AFM tip and the SiNx surface which cannot be measured by KPFM. The electrical properties of the SiNx films obtained from both techniques show a very good correlation. X-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red spectroscopy (FT-IR) material characterization techniques have been also used to determine the compositions and chemical bonds, respectively, of the SiNx films. An attempt to correlate between the chemical and electrical properties of SiNx films is made.