Nanoscale characterization of the dielectric charging phenomenon in PECVD silicon nitride thin films with various interfacial structures based on Kelvin probe force microscopy

This work presents a novel characterization methodology for the dielectric charging phenomenon 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 MEMS switches. The proposed technique takes the advantage of the atomic force microscope (AFM) tip to simulate charge injection through asperities, and then the induced surface potential is measured. The impact of bias amplitude, bias polarity, and bias duration employed during charge injection has been explored. The influence of various parameters on the charging/discharging processes has been investigated: dielectric film thickness, SiN(x) material deposition conditions, and under layers. Fourier transform infrared spectroscopy (FT-IR) and x-ray photoelectron spectroscopy (XPS) material characterization techniques have been used to determine the chemical bonds and compositions, respectively, of the SiN(x) films being investigated. The required samples for this technique consist only of thin dielectric films deposited over planar substrates, and no photolithography steps are required. Therefore, the proposed methodology provides a low cost and quite fast solution compared to other available characterization techniques of actual MEMS switches. Finally, the comparison between the KPFM results and the discharge current transients (DCT) measurements shows a quite good agreement.