RF sputtered polytetrafluoroethylene—a potential masking material for MEMS fabrication process

Abstract

Microsystems technology has received great attention lately, creating new fields of application. Many new smart materials have been proposed and investigated, and many processing methods for ultrafine fabrication have been developed. Polymers have attracted much attention as promising masking materials due to their inherent properties. Polytetrafluoroethylene (PTFE) is a very unique polymeric material in this category. The present study deals with the deposition of PTFE by RF (13.56 MHz) sputtering on silicon substrate. The deposited polymer film is characterized for stoichiometry and adhesion after deposition by Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and contact angle measurements and more importantly test of masking (masking properties). The masking properties include the measurement of etch rate of PTFE film (at various deposition conditions) in KOH and TMAH anisotropic etchants at various temperatures and concentrations of the etchant solution. The masking properties are then compared with the conventional and widely used masking materials such as SiO2 and Si3N4. For confirmation of the presence of PTFE film on the silicon substrate after etching in KOH and TMAH, FTIR and XPS characterizations were again done. Also, a diaphragm structure is realized in the silicon by anisotropic etching in KOH (40 wt% at 90 °C) using sputtered PTFE film as the masking material.