Kinetic Consequences of Adding Rare Gases to Radio Frequency Glow Discharges Through Boron Trichloride.

Because mixtures of rare and molecular gases are often used in plasma processing (to achieve desired etch or deposition rates, selectivity, anisotropy, etc.), we investigated the kinetic consequences of diluting discharges through BCl sub 3 with the rare gases He, Ar, and Kr. Time-resolved laser- induced fluorescence and plasma-induced emission intensity measurements are used to measure long-lived and short-lived state densities, respectively. From the density waveforms, the primary mechanism for enhanced dissociation of BCl sub 3 in the discharge mixtures is isolated. Energy transfer from rare gas metastable states to BCl sub 3 dissociative states is shown to be dominant; for concentrations of BCl sub 3 greater than 1%, changes in the electron density and energy distribution function play an insignificant role in enhancing dissociation. When the rare gas is changed from He to Ar to Kr, the extent of BCl sub 3 dissociation increases monotonically as the rare gas metastable level comes into resonance with BCl sub 3 dissociation limits. While the conclusions drawn here are based upon experiments with BCl sub 3, similar results should be obtained when any molecular gas is diluted with a rare gas.