Model for an inductively coupled Ar/c-C4F8 plasma discharge

This article describes a two-dimensional model for an inductively coupled Ar/c-C4F8 plasma discharge, which is widely used in the microelectronics industry for dielectric etching and polymerization. The chemical mechanism for c-C4F8 incorporates known information about electron impact dissociation, ionization, and attachment processes. Unknown details such as neutral dissociation byproducts have been empirically inferred using energetics analysis or diagnostic experiments. The mechanism also considers electron impact processes for neutral radicals (e.g., CF, CF2, CF3) and stable molecules (e.g., C2F4) produced in a c-C4F8 plasma. It is demonstrated in the article that the resulting neutral species densities, ion flux to the wafer, and electron characteristics are in good agreement with experiments in the Gaseous Electronics Conference reference cell. The validated model is used to understand the dynamics of an inductively coupled Ar/c-C4F8 plasma discharge, and the impact of various control parameters on plasma characteristics. Results indicate that CF2 is the dominant CFx radical in the c-C4F8 discharge and the plasma is mildly electronegative. Enhanced ionization and dissociation of c-C4F8 with increasing inductive power deposition leads to an increase in electron and CFx radical densities, and total ion flux to the wafer. Enhanced dissociative attachment at higher gas pressure decreases the electron density and increases the negative ion density. The plasma becomes more electropositive with decreasing c-C4F8 concentration in the gas mixture, which increases the total positive ion flux to the wafer