Capacitively Coupled Hydrogen Discharges: Modeling vs. Experiment

Abstract

This paper presents a systematic characterization of hydrogen capacitively coupled very high frequency discharges, produced within a parallel plate cylindrical setup, by comparing numerical simulations to experimental measurements for various plasma parameters. A good quantitative agreement is found between calculation and experiment for the coupled electrical power and the plasma potential, at various frequencies, pressures and applied voltages. However, the model generally underestimates the electron density and the self-bias potential with respect to measured values. Model predictions for the absolute density of H(n=1) atoms are compared to first diagnostic results, obtained by two-photon absorption laser-induced fluorescence diagnostics at various pressures and frequencies.

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

“…I-III or the simplified kinetic model previously mentioned (where H atoms are not considered). 33 The experimental values reported were obtained either by Langmuir probe measurements 34,88 or semi-empirically, using a simplified electric description of the discharge combined with electrical measurements of the plasma bulk resistance R b . The latter can be written as 94…”

“…The coupling between the different calculation modules follows the usual procedure adopted in the kinetic modeling of such gas discharges. 34,87 The crm runs typically every 5 rf periods, knowing the space-time average values of the charged particle densities and of the rate coefficients for the production/destruction of each neutral species. The crm nonlinear equations are solved using a semi-implicit Gauss-Seidel relaxation technique, which searches for the stationary solution (∂n b i /∂t) → 0.…”

“…Figure 4 also compares simulation results with experimental measurements obtained using either a cylindrical Langmuir probe or a planar probe. 34,88 The electron temperature and density were derived from the cylindrical probe characteristics following the techniques described in Refs. 89,90.…”

“…Usually, fluid-type simulations of ccrf discharges yield electron densities that are systematically underestimated with respect to measurements, yet predicting values for the power coupled to the plasma that agree with experiment. [32][33][34] The reason for this discrepancy is probably associated with an incomplete description of charge separation regions, as will be also investigated here by comparing measured values and calculation results for the timeaverage thickness of the rf space-charge sheath.…”

Electrical Characterization of Capacitively Coupled Radio Frequency Discharges in Hydrogen

“…In previous works,10–12 we have presented a systematic study on the variation of several plasma parameters with the rf applied voltage, the excitation frequency and the gas pressure, in hydrogen CCRF discharges. In this paper, we complement these works by presenting unpublished results for the current–voltage characteristics and for the distribution, between electrons and ions, of the electrical power coupled to the plasma, which can contribute to a better understanding of the physical features in plasma‐assisted surface processing.…”