Diagnostics of CH4 plasmas used for diamond-like carbon deposition

Spatially resolved optical emission spectroscopy was used to study asymmetric low-frequency (LF) (25-50 kHz) and radio-frequency (RF) (13.56 MHz) discharges in methane used to deposit hard, hydrogenated carbon films. The optical data in conjunction with ion flux, electron density, and deposition rate measurements show that the processes due to fast electrons are of major importance for the deposition of amorphous C:H. Optical monitoring of the spectrum of the species and correlation with the deposition process are effective if the region close to the substrate is sampled. Both discharges lead to hard carbon films if the substrate is on the powered (hot) electrode. Deposition on the ground electrode of the 13.6-MHz discharge leads to highly hydrogenated carbon films as a result of the strong asymmetry, lower ion flux, and absence of fast electron processes