PTFE as a masking material for MEMS fabrication

In the present study, radio frequency (RF) sputtered polytetrafluoro ethylene (PTFE) films deposited on silicon substrates are evaluated as masking material for anisotropic etching of silicon in aqueous KOH solution. Sputtered PTFE films were characterized by FTIR, x-ray photoelectron spectroscopy (XPS) and contact angle to know the bonding, the elemental composition and adhesion of the film with the substrate. FTIR and XPS data show the presence of PTFE-like film on the silicon substrate. From the contact angle value, interfacial tension was calculated, which gave a value of 0.7 dyne cm(-1) which confirms good adhesion of the film and the substrate. A pattern was lithographically transferred through the masking material on the silicon substrate and the etch rate of the masking layer was calculated. The etch rate was calculated from the masking time data of the films. The etch rate value of 4 angstrom min(-1) is low as compared to the etch rate of the conventional masking materials (60 angstrom min(-1) for SiO2 and 8 angstrom min(-1) for Si3N4).