Hybrid simulation of a dc-enhanced radio-frequency capacitive discharge in hydrogen

A PIC-MCC/fluid hybrid model was employed to study a parallel-plate capacitively coupled radio-frequency discharge in hydrogen, under the application of a dc bias voltage. When a negative dc voltage was applied to one of the electrodes of a continuous wave (cw) plasma, a ‘beam’ of secondary electrons was formed that struck the substrate counter-electrode at nearly normal incidence. The energy distribution of the electrons striking the substrate extended all the way to VRF + |Vdc|, the sum of the peak RF voltage and the absolute value of the applied dc bias. Such directional, energetic electrons may be useful for ameliorating charging damage in etching of high aspect ratio nano-features. The vibrational distribution function of molecular hydrogen was calculated self-consistently, and was found to have a characteristic plateau for intermediate values of the vibrational quantum number, v. When a positive dc bias voltage was applied synchronously during a specified time window in the afterglow of a pulsed plasma, the ion energy distributions (IEDs) of positive ions acquired an extra peak at an energy equivalent of the applied dc voltage. The electron energy distribution function was slightly and temporarily heated during the application of the dc bias pulse. The calculated IEDs of H+ 3 and H+ 2 ions in a cw plasma without dc bias were found to be in good agreement with published experimental data.