Particle in cell Monte Carlo collision simulations of capacitive Ar/Cl2 discharges: Pressure and voltage dependence

Chlorine plasma discharges and their mixtures are often used for etching semiconductors and metals. Here, the capacitive Ar/Cl2 discharge is studied using one-dimensional particle-in-cell/Monte Carlo collision simulations as the pressure, driving voltage amplitude, and the chlorine fraction in the feedstock are varied. By adding chlorine to an argon discharge, the discharge can be varied from being electropositive to become strongly electronegative, depending on the chlorine fraction in the feedstock. We analyze how the electron power absorption mechanisms, the electronegativity, the electron energy distribution function, and the discharge composition evolve with changes in pressure as well as with increasing chlorine admixture. Furthermore, the impact of the voltage amplitude on the Ar/Cl2 discharge at constant pressure for various Cl2 admixtures is studied. We show how the electron power absorption mechanism transitions from the α-mode, to the mixed α-drift-ambipolar-mode to drift-ambipolar-mode and finally to the drift-ambipolar-striation mode as the pressure and the chlorine fraction in the feedstock are increased. Furthermore, we find that meeting the critical ion density condition, derived from the ion-ion plasma resonance model, by itself, is not a sufficient condition for striations to form, as in addition, a sufficiently high electronegativity is required. For the present simulation setup and operating conditions, striations are observed only when the electronegativity is α≳50.