Influence of sheath collisions on the ion angular distributions in a dual-frequency capacitively coupled plasma

Abstract The energy-resolved angular distributions of ions impinging on a radio-frequency electrode were measured in a dual-frequency capacitively coupled Ar/Kr admixture and pure Ar plasma. Using a microchannel plate, energy-resolved ion angular distributions (IADs) were measured using a time-of-flight technique and an optimization-based image reconstruction. The results indicate that the measured IADs comprise a narrow main-component and a broad tail-component. In the Ar/Kr plasma, Ar and Kr ions exhibit similar main-component angular widths (AWs), which their thermal motion can explain. The results demonstrate that not only energy-resolved measurements but also ion mass-resolved measurements can be performed in this experimental setup. In the pure Ar plasma, ion AWs are measured at different pressures while keeping the same sheath thickness by controlling the plasma density. The main-to-total component ratio in IADs at the maximum-energy decreases exponentially with pressure, indicating that tail-components originate from Ar⁺ collisions with Ar atoms in the sheath.