Influence of metastable atoms in radio-frequency argon discharges

A planar one-dimensional (1-D) particle-in-cell (PIC) simulation with Monte Carlo collisions (MCC) has been used to study the effect of including metastable argon on the characteristics of a 13.56-MHz argon discharge. Reactions such as metastable creation, ionization from the metastable state, metastable quenching to resonant level, and metastable pooling were taken into account. At low pressure (0.05 torr), metastables were found to have little influence on the discharge. However, at a pressure of 1 torr, ionization from the metastable state and collisions between two metastables represent a significant percentage of the total ionization rate, strongly influencing the electron heating and the discharge potential. The effect of pressure and applied voltage on the discharge parameters is studied and a comparison between discharges with and without metastables is presented. A PIC-MCC simulation was compared to the fluid model of Lymberopoulos and Economu (1993) using their published parameters, showing that using PIC simulation the main process of metastable loss is metastable pooling.