Dual-mode plasma-enhanced chemical vapor deposition (PECVD) of polymer-like a-C:H films: Vibrational and optical properties

A dual-mode microwave (MW)-radio frequency (RF) plasma reactor has been used for the deposition of hydrogenated amorphous carbon (a-C:H) thin films. Butane is injected and decomposed in the post-discharge of a helium-argon MW plasma, assisted by an RF plasma of variable power (0-100 W). It has been observed that the energy of the ion bombardment on the substrate, monitored by the RF power, controls the optical properties. The dielectric function is parametrized using either a single classical oscillator or a three-phase effective medium approximation. The deposition rate and the extinction coefficient of a-C:H increase with the RF power, indicating an increase of the trigonal sp(2) bonding configurations. Simultaneously, the IR absorption spectroscopy gives evidence of a decreasing H content and increasing C=CH2 configurations.