PLASMA PROCESSES IN METHANE DISCHARGES DURING RF PLASMA-ASSISTED CHEMICAL-VAPOR-DEPOSITION OF A-CH THIN-FILMS

Methane-hydrogen capacitively coupled r.f. (13.56 MHz) discharges were studied using a mass spectrometer. The relative concentrations of neu tral species (CH4, C2Hx) were investigated in a broad range of dischar ge parameters (pressure 1.5-50 Pa, residence time 1-45 s, and r.f. pow er 0-120 W) and correlated with deposition rate measurements. It is sh own that the chemical plasma processes (C2H, formation) and deposition characteristics (deposition rate) are strongly correlated with the de gree of methane dissociation. These observations are interpreted in te rms of the occurrence of dominant CH(y)-CH4 reaction pathways for the production of C2Hx and a simple growth model based on a combined mecha nism of CH3 radical adsorption and ion bombardment. The pressure depen dence of the degree of dissociation of methane is correlated with the existence of various discharge regimes (alpha and gamma).