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

Abstract

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 (Vrf=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 Vrf, 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.