Effect of O2, Ar/H2 and CF4 plasma treatments on the structural and dielectric properties of parylene-C thin films

Abstract

Plasma treatment of parylene-C surfaces not only causes structural modification of the surface during the plasma exposure, but also leaves active sites on the surfaces, which decreases the dielectric properties. In this work, the effects of oxygen, argon/hydrogen and fluorine plasma treatment on the surface and dielectric properties of parylene-C thin films were investigated using Fourier transform-IR spectroscopy, energy dispersive x-ray analysis and dielectric spectroscopy measurement. The results showed that the plasma treatment successfully introduced fluorine functional groups and decreased the oxygen content on the parylene-C surfaces. It appears that the replacement of oxygen and hydrogen by fluorine atoms led to a decrease in the local orientational polarizability of parylene-C. Consequently, it was found that the atmospheric fluorine plasma-treated parylene-C possessed lower dielectric characteristics, 16% lower than the untreated parylene-C at industrial frequencies (10–104 Hz). The Ar/H2 plasma treatment is also an experimental means to reduce the dielectric properties and to decrease the oxygen content in parylene-C. In contrast, the oxygen plasma increases the dielectric constant and can cause deterioration of the leakage current associated with carbon depletion showing C–O and C=O formation. CF4 and Ar/H2 plasma treatment does not significantly affect the long molecular motion (α-relaxation). Additional extrinsic oxygen content due to O2 plasma treatment in the parylene-C structure reproduces the increase in the time constant of both the short (β-relaxation) and long molecular motion.