Nanoscale characterization of the dielectric charging phenomenon in PECVD siliconnitride thin films with various interfacial structures based on Kelvin probe forcemicroscopy

Abstract

This work presents a novel characterization methodology for the dielectric chargingphenomenon in electrostatically driven MEMS devices using Kelvin probe force microscopy(KPFM). It has been used to study plasma-enhanced chemical vapor deposition (PECVD)silicon nitride thin films in view of application in electrostatic capacitive RF MEMSswitches. The proposed technique takes the advantage of the atomic force microscope(AFM) tip to simulate charge injection through asperities, and then the induced surfacepotential is measured. The impact of bias amplitude, bias polarity, and bias durationemployed during charge injection has been explored. The influence of various parameters onthe charging/discharging processes has been investigated: dielectric film thickness,SiNx material deposition conditions, and under layers. Fourier transform infrared spectroscopy(FT-IR) and x-ray photoelectron spectroscopy (XPS) material characterization techniqueshave been used to determine the chemical bonds and compositions, respectively, of theSiNx films being investigated. The required samples for this technique consist only of thindielectric films deposited over planar substrates, and no photolithography steps arerequired. Therefore, the proposed methodology provides a low cost and quitefast solution compared to other available characterization techniques of actualMEMS switches. Finally, the comparison between the KPFM results and thedischarge current transients (DCT) measurements shows a quite good agreement.