Mass spectrometric study of discharges produced by a large-area dual-frequency-dual-antenna inductively coupled plasma source

An energy-resolved quadrupole mass spectrometer is used to investigate the time-averaged ion energy distribution (IED) of positive ionic species in an Ar/CF ₄ (90%/10%) discharge produced by dual-frequency-dual-antenna, next-generation large-area inductively coupled plasma source. The operating pressure is 10mTorr. Two radio frequencies of 2MHz (low frequency) and 13.56MHz (high frequency) are used to initiate and sustain the discharge. The orifice of the mass spectrometer was 100μm in diameter and placed at 30mm below the ICP source and 20mm outside the discharge volume. It is observed that both of the frequencies have significant effect on IEDs of all prominent discharge species. The evolution of IEDs with power shows that the discharge undergoes a mode transition (E to H) as the applied power is increased. At a fixed value of P _13.56MHz (250 and 500W), the energy spread and the energy separation between two peaks of IEDs increase illustrating enhanced E-mode. Above P _{13.56 MHz}=500W, the IEDs show opposite trends, i.e. decreasing energy spread and energy separation between two peaks, showing the strengthening of H-mode. Increasing P _13.56MHz at a fixed value of P ₂MHz has similar effects. A comparison of IEDs sampled at a fixed total power (P _13.56MHz+P _2MHz) demonstrates that an IED can be tailored by changing the power ratio (P _13.56MHz/P ₂MHz).