Quenching rates of Ar metastables in radio-frequency glow discharges

Abstract

Although rate coefficients are essential ingredients in modeling chemical processes such as chemical vapor deposition and plasma etching, the values measured as a function of temperature under well-defined equilibrium conditions may be inappropriate for use in models of nonequilibrium systems. For this reason, it is important to have measurements of in situ rates that can be used as input parameters or can provide stringent tests for reactor simulations. Using time-resolved plasma-induced emission and laser-induced fluorescence spectroscopy, we measured quenching rates for Ar metastable states in radio-frequency discharges through mixtures of Ar and the molecular gases SF6, Cl2, BCl3, and N2. After verifying the validity of modulation spectroscopy to measure in situ rates, the effects of discharge power, pressure, and flowrate are investigated. The most important effect occurs when the discharge power is increased; the decline in quenching rates with increased power is attributed to increased molecular dissociation that produces products with lower collision cross sections.