Characterization of DLC films obtained at room temperature by pulsed-dc PECVD

摘要

Diamond-like carbon films were prepared at room temperature from asymmetric bipolar pulsed-dc methane glow discharges, up to 1600 V of negative voltage pulse and 50-200 kHz of pulse frequency. Plasma parameters within a pulse cycle and at different peak voltage amplitudes were characterized by a Langmuir probe, which measured the I-V characteristics and the electron energy distribution function. Electron and ion density, electron temperature and averaged electron energy are found to increase along with negative peak voltage. Moreover, variations of electron temperature and density of charged species are registered between high- and low-pulse level. Meta-stable dissociation of methane was detected at electron energies of approximately 12 eV. Properties of the films are discussed as a function of the growth parameters obtained by plasma diagnostics, in order to establish their influence on film features. The deposition rate and residual stress of the film, which reached 50 nm/ min and was minor than 1 GPa, respectively, were correlated to the enhancement of the degree of ionization at high power values. Surface topography shows an increase of roughness, up to 1 nm of RMS value, for films deposited at high peak voltages, whereas the friction coefficient, measured by atomic force microscopy in contact mode, is approximately constant. Surface energy was characterized by contact angle measures with water, which value is approximately 85 deg , and shows no dependence with deposition conditions. This deposition technique has an application in industry for deposition of large area coatings and it is especially indicated to process materials with plasma involving a great number of technological parameters.