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 ${\text{O}}_3$, negative ${\text{O}}^{-}$ and positive ${\text{O}}_2^{+}$ ions, metastable singlet delta-state ${\text{O}}_2\left(a^1{\Delta }_g\right)$ 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 ${\text{O}}_3$, negative ${\text{O}}^{-}$ and positive ${\text{O}}_2^{+}$ ions decrease when the gas pressure increases. However, the density of the metastable singlet delta-state ${\text{O}}_2\left(a^1{\Delta }_g\right)$ 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 $40.68\text{MHz}$, and then it drops almost linearly at frequencies greater than $40.68\text{MHz}$. However, the negative ions ${\text{O}}^{-}$ density increases over a range of frequencies from 27.12 to $67.80\text{MHz}$, then it decreases slightly as $f_{hf}$ increases further. Therefore, when $f_{hf}$ increases, it does enhance the production of the metastable ${\text{O}}_2\left(a^1{\Delta }_g\right)$ and the oxygen O atoms, whereas the ${\text{O}}_2^{+}$ 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 ${\text{O}}_2\left(a^1{\Delta }_g\right)$ densities is displayed as $V_{hf}$ increases. Comparisons are made with recent simulation models and experimental data, and a qualitative agreement is obtained.