Measurements of ion energy distributions in a dual-frequency capacitively coupled plasma for Ar/O₂discharges

Ion energy distributions (IEDs) of Ar+ and bombarding the grounded electrode are measured by an energy resolved quadrupole mass spectrometer in a dual-frequency capacitively coupled plasma (DF-CCP) operated in a gas mixture of Ar and O2 (90%/10%). The effects of external discharge parameters, such as the frequency and power of the low frequency (LF) source and the gas pressure, on the IEDs are investigated in detail. With the increase in the LF power, the high-energy peak shifts towards the high-energy region and the energy width ΔE between high- and low-energy peaks in the IEDs also increases. However, the increase in the LF frequency leads to the shift of the high-energy peak towards the low-energy region as well as a narrow energy width ΔE. The increase in the gas pressure results in the bimodal structure being unobvious because of intensive momentum transfer and charge exchange collisions between ions and background molecules. In addition, the distinctions between Ar+ and IEDs are also discussed. Finally, some experimental results are compared with numerical ones obtained from the particle-in-cell/Monte Carlo (PIC/MC) method and both results are in general agreement.

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