Locally enhanced discharges at gas hole outlets of a showerhead in a plasma etching reactor

Process gases are generally supplied through a showerhead into a plasma etching reactor. Mitigating phenomena such as gas hole erosion in showerheads are a significant issue over the life of a plasma etcher. Phenomena at the gas hole plasma interface are difficult to probe experimentally. Using plasma simulation, we found that locally enhanced discharges may occur at gas hole outlets even at the low process pressure ( tens of mTorr). Simulations show that an abnormal discharge may be generated at the gas hole outlet where the gas pressure is much higher than the process pressure. The typical barrel shaped gas hole erosion profile that may evolve over the life of a showerhead can be ascribed to that discharge. Simulations also show that locally enhanced discharges at gas holes of the showerhead can supplement the plasma with energetic electrons resulting in a significant increase in the bulk electron density in the reactor, a fact often ignored in the modelling and simulation of plasma sources containing showerheads.