Surface induced effects in the ion energy distribution of a symmetric capacitively coupled plasma

Secondary electron emission (SEE) coefficients are available from particle beam experiments but its determination in a plasma experiment is more difficult since ions, neutrals, metastables, electrons and photons can initiate SEE. Therefore, in-situ approaches typically determine an effective SEE coefficient based on the ratio of emitted electrons per incoming ion. To our knowledge, only two approaches are currently available: The γ-CAST method determines SEE coefficients from the ratio of α and γ electron excitation maximum in PROES measurements and a method that analyzes the plasmas I-V-characteristics. Here, we critically discuss the potentials and challenges of an alternative method that estimates the SEE coefficient from changes in the ion energy distribution function (IEDF) of a symmetric capacitively coupled plasma (CCP).

We use Al and Al₂O­₃ coated electrodes to investigate the impact of changed surface properties on the IEDF of Ar⁺ ions. The comparison of measured and 1D-PIC/MCC simulated IEDFs should in principle provide an estimation of the SEE coefficient. In reality, the measured IEDFs depend on many parameters like pressure, electrode distance and gas temperature that need to be sufficiently precise determined. A critical study of these factors will be presented.