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 (V rf = 50 − 600 V), frequencies (f = 13.56 − 40.56 MHz), and pressures (p = 0.2 − 1 torr). A twodimensional, 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.

Etching of a-Si:H thin films by hydrogen plasma: A view from in situ spectroscopic ellipsometry

“…[40][41][42] In fact, as more energy is coupled into the plasma, the gas becomes increasingly dissociated, forming more and more atomic hydrogen. Furthermore, increasing the RF power from 5 to 30 W enhances the absolute value of the self-bias voltage by more than 150 V. This effect increases the ion bombardment by accelerating hydrogen ions within the plasma sheathes towards the substrate.…”

The trend of electron temperature and electron density in the process of microcrystalline silicon solar cells

“…The above equation is originated from the plasma conductivity [13], and available when the driving frequency (x) is much smaller than the electron momentum transfer collision frequency ðm m Þ,…”

“…The averaged electron density, n av , and the discharge resistance, R, are related as [13] n av ¼ dm e m m…”

Introduction of a new experimental device for simulating parasitic plasmas such as those expected under the divertor dome

“…One can remark that the excited state temperatures are found (slightly) out-of-equilibrium between atomic and molecular species, as expected in such a low temperature discharge. Hotter Hatoms may be produced depending on the different kinetic paths possible [10] (H 2 dissociative excitation, H 2 dissociative ionisation, or direct electronic impact excitation of H atoms). The dominant path is strongly dependent on the shape of the eedf, which we measure by electrostatic probe characterisation.…”