Effect of Deposition Gas Ratio, RF Power, and Substrate Temperature on the Charging/Discharging Processes in PECVD Silicon Nitride Films for Electrostatic NEMS/MEMS Reliability Using Atomic Force Microscopy

Abstract

The dependence of the electrical properties of silicon nitride, which is a commonly used dielectric in nano- and micro-electromechanical systems (NEMS and MEMS), on the deposition conditions used to prepare it and, consequently, on material stoichiometry has not been fully understood. In this paper, the influence of plasma-enhanced chemical vapor deposition conditions on the dielectric charging of films is investigated. The work targets mainly the dielectric-charging phenomenon which constitutes a major failure mechanism in electrostatically driven NEMS/MEMS devices and particularly in capacitive MEMS switches. The charging/discharging processes are studied using two nanoscale characterization techniques: Kelvin probe force microscopy (KPFM) and, for the first time, force-distance curve (FDC) measurements. KPFM is used to investigate dielectric charging at the level of a single asperity, while FDC is employed to measure the multiphysics coupling between the charging phenomenon and tribological issues, mainly meniscus force. The electrical properties of the films obtained from both techniques show a very good correlation. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy material characterization techniques are also used to determine the compositions and chemical bonds, respectively, of the films. An attempt to correlate between the chemical and electrical properties of films is made.