Amorphous hydrogenated fluorinated carbon films produced by PECVD

Films were deposited from discharges of acetylene-helium-carbon tetrafluoride mixtures. Actinometric optical emission spectrometry (AGES) revealed trends in the concentrations of the plasma species H, CH, F and CF2 as a function of the proportion of CF4 in the feed, R(c). The influence of plasma/polymer surface interactions on the plasma concentrations of such species was investigated using a dynamic form of AGES. Plasma H, CH and F species were possibly produced by the following mechanisms: the gas phase fragmentation of their parent molecules (C2H2 and CF4) or H- or F-containing species; the release of H, CH and F units from the deposited polymer surface upon interaction with energetic plasma particles (helium metastables or electrons). Film composition and structure were probed using transmission infra-red spectrophotometry (IRS) and X-ray photoelectron spectroscopy (XPS). The groups -CH, -C=O, and -CF were present in each fluorinated film. As revealed by IRS and XPS, methyl groups in the films were steadily replaced by CFx groups (x = 1-3) as R(c) was increased. Similarly, as revealed by XPS and AOES, the degree of fluorination of the films was positively correlated with the plasma F concentration.