Influence of External Input Parameters on Species Production in a Dual-Frequency Capacitively Coupled Radio-frequency Oxygen Plasma

The impact of some external input parameters on electron, ozone \(\hbox {O}_3\), negative \(\hbox {O}^{-}\) and positive \(\hbox {O}_2^{+}\) ions, metastable singlet delta-state \(\hbox {O}_{2}(a^{1}\varDelta _{g})\) molecule and atomic oxygen O formation is investigated using a numerical simulation. A one-dimensional, self-consistent fluid model of a dual radio-frequency capacitively coupled discharge operating on pure oxygen is developed to explore the evolution of the species density profiles as functions of gas pressure \(p_g\), driving high-frequency \(f_{hf}\), inter-electrode gap distance d and driving voltage waveform \(V_{hf}\). The proposed model incorporates five main species and 24 dominant reaction channels. Simulation results show that the time-averaged density profiles of electron, ozone \(\hbox {O}_3\), negative \(\hbox {O}^{-}\) and positive \(\hbox {O}_2^{+}\) ions decrease when the gas pressure increases. However, the density of the metastable singlet delta-state \(\hbox {O}_{2}(a^{1}\varDelta _{g})\) molecule and atomic oxygen O increase when the gas pressure increases. The electron density significantly increases with increased \(f_{hf}\) until a maximum peak is reached at \(40.68~ \hbox {MHz}\), and then it drops almost linearly at frequencies greater than \(40.68~\hbox {MHz}\). However, the negative ions \(\hbox {O}^{-}\) density increases over a range of frequencies from 27.12 to \(67.80~ \hbox {MHz}\), then it decreases slightly as \(f_{hf}\) increases further. Therefore, when \(f_{hf}\) increases, it does enhance the production of the metastable \(\hbox {O}_{2}(a^{1}\varDelta _{g})\) and the oxygen O atoms, whereas the \(\hbox {O}_2^{+}\) density is decreased. It is also shown that an increase in the inter-electrode gap distance causes a noticeably decrease in the formation of the various species in the discharge. Furthermore, a significant increase in the atomic oxygen O and the metastable singlet delta-state \(\hbox {O}_{2}(a^{1}\varDelta _{g})\) densities is displayed as \(V_{hf}\) increases. Comparisons are made with recent simulation models and experimental data, and a qualitative agreement is obtained.