Electron power absorption mode transition in capacitively coupled Ar/CF4 discharges: hybrid modeling investigation

Abstract

Abstract In this work, the electron power absorption mode transition in capacitively coupled Ar/CF4 discharges is investigated by using a one-dimensional fluid/electron Monte Carlo hybrid model. Different electron power absorption modes are observed under various external discharge conditions, which could be explained by examining the contribution of bulk electrons and secondary electrons respectively. The results indicate that as the gap increases, the electron power absorption mode changes from the drift-ambipolar (DA) mode to a α-γ-DA hybrid mode. This is ascribed to the enhanced ionization process of secondary electrons due to their sufficient collisions when the discharge region expands, as well as the weakened drift and ambipolar electric fields. By increasing the secondary electron emission coefficient, the number density of secondary electrons grows, and thus the discharge experiences a transition from a α-DA hybrid mode over a α-γ-DA hybrid mode and finally into the γ mode. Moreover, when the proportion of CF4 increases, the discharge tends to be more electronegative. As a consequence, the discharge gradually transits from a α-γ hybrid mode over a α-γ-DA hybrid mode, and finally to the DA mode. The results obtained in this work are important for improving the high aspect ratio etching process by secondary electrons.