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

Abstract

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.