REACTIVE ION ETCHING OF POLY(TETRAFLUOROETHYLENE) IN O2-CF4 PLASMAS

Films of poly(tetrafluoroethylene) (PTFE) were etched in O2-CF4 rf plasmas. The dependence of the etching rate of PTFE on the relative concentrations of these two gases was compared with data from optical emission spectra and measurements of peak-to-peak rf voltages V(pp) indicative of relative sheath potentials. At a constant rf power (V(pp) varied), etching rates were the greatest when using pure O2 and decreased with the addition of CF4. For V(pp) held fixed (rf power varied), rates were invariant over a wide range of gas compositions. Ion bombardment-induced polymer radical generation is proposed as the initiating step in the PTFE etching sequence. Increases in etching rates with load size, contrary to conventional loading effect behavior, is attributed to a corresponding increase in V(pp) for larger loads. Surface roughening induced by etching is more pronounced in oxygen-rich gas mixtures.