Capacitively coupled radio-frequency hydrogen discharges:The role of kinetics

This paper presents a systematic characterization of capacitively coupled radio-frequency hydrogen discharges, produced within a parallel plate cylindrical setup at different rf applied voltages ( V rf = 50 - 600 V ) , frequencies ( f = 13.56 - 40.68 MHz ) , and pressures ( p = 0.2 - 1 torr ) . A two-dimensional, time-dependent fluid model for charged particle transport is self-consistently solved coupled to a homogeneous kinetic model for hydrogen, including vibrationally excited molecular species and electronically excited atomic species. Numerical simulations are compared with experimental measurements of various plasma parameters. A good quantitative agreement is found between simulations and experiment for the coupled electrical power and the plasma potential. The model underestimates the values of the electron density, the self-bias potential, and the H ( n = 1 ) atom density with respect to measurements, but agrees with experiment when predicting that all these parameters increase with either V rf , f , or p . The dissociation degree is about 10 − 3 for the work conditions considered. Simulations adopt a wall recombination probability for H atoms that was experimentally measured, thus accounting for surface modification with discharge operating conditions. Results show the key role played by the atomic wall recombination mechanism in plasma description.