Study of volume and surface processes in low pressure radio frequency plasma reactors by pulsed excitation methods. I. Hydrogen–argon plasma

Abstract

In low pressure reactors, for which the mean free paths of reactive particles are of the order of plasma chamber dimensions, the chemical equilibrium of the gas phase is strongly dependent on surface chemistry. Unfortunately data on elementary surface processes are often not available, particularly for surfaces exposed to plasma conditions. In this work such data are obtained through a time resolved analysis of species concentration in a reactor where a square wave modulated rf power is used for excitation. A very short pulse excitation technique, acting as a time resolved ‘‘in situ chemical probe,’’ has been developed in order to follow the radical concentrations in the afterglow where surface processes are dominant. Results for hydrogen–argon plasmas are reported. The surface reactions of hydrogen atoms with reactor walls and silicon surface are studied. The recombination probability on reactor walls is shown to be very sensitive to plasma conditions. These surface properties evolve on time scales as long as few tens minutes, in connection with bulk diffusion process of atomic Hydrogen. For Silicon surface, the measured recombination probability is very high (near unity) while etching appears as an added small effect. In a companion paper determination of F atom reactivity for surfaces submitted to fluorinated plasmas will be described.