Plasma Dynamics in Low-Pressure Capacitively Coupled Oxygen Plasma Using PIC-MCC/Fluid Hybrid Model

Low-pressure (< 20 mT) capacitively coupled plasmas are now widely used for plasma processing in the semiconductor industry. In particular, O-2 plasmas are being used for etching, photoresist ashing, and chamber cleaning. At low pressure, the electron mean free path increases, making kinetic effects more important. To consider kinetic effects, a hybrid plasma simulation tool has been developed that couples the particle-in-cell/Monte Carlo collision model for charged species with a fluid model for neutral species. Oxygen plasma has been modeled using this hybrid model for a range of pressures. It is observed that the electrons primarily absorb power at the sheath edge during sheath expansion. These energetic beam electrons are responsible for plasma production and sustenance through collisions. The beam electrons are stronger at lower pressure and retain their beam characters for a longer distance. For a constant RF voltage, the electron density increases with pressure.