A one-dimensional ͑1D͒ model for a methane rf plasma consisting of 20 species ͑neutrals, radicals, ions, and electrons͒ is presented. The equations solved are the particle balances, assuming a drift-diffusion approximation for the fluxes, and the electron energy balance equation. The self-consistent electric field is obtained from the simultaneous solution of Poisson's equation. The electron-neutral collision rates are expressed as a function of the average electron energy. These expressions are obtained from the solution of the Boltzmann equation using the Lorentz approximation. The results presented in this article are limited to the alpha regime, hence no secondary electrons are considered. In total, 27 electron reactions ͑vibrational excitation, dissociation, and ionization͒ have been included in the model, as well as seven ion-neutral reactions and 12 neutral-neutral reactions. The 1D fluid model yields, among others, information about the densities of the different species in the plasma. It is found that in a methane plasma C 2 H 6 ,C 3 H 8 , C 2 H 4 ,and C 2 H 2 are also present at high densities, together with CH 4 and H 2 ͑inlet gases͒. The main radical in the plasma is CH 3. At low pressure ͑e.g., 0.14 Torr͒ the most important ion is found to be CH 5 ϩ , at higher pressure ͑e.g., 0.5 Torr͒ C 2 H 5 ϩ becomes the dominant ion.

Functional coating deposition using plasma is broadly used in industrial application working at a pressure ranging from low pressure discharges (a few Pascals) to atmospheric plasmas. The active gas (silane is selected for this study) is often diluted in a gas that helps in stabilizing the discharge like helium or argon. In addition, the discharge can be polluted by uncontrolled external gas source like air or oxygen coming from water adsorbed in reactor walls. In this paper, we study the interactions taking place within the bulk of a capacitively coupled plasma and study the impact of these reactions on the flux of species moving towards the substrate and so the impact on the composition of deposited film. A one-dimensional fluid model is presented for the modelling of radio frequency capacitively coupled plasmas in a mixture of silane/helium, including small concentrations of O2 and N2. In total, 48 different species (electrons, ions, neutrals, radicals and excited species) are considered in the model. After a sensitivity study, 27 electron–neutral and 76 chemical reactions (i.e. ion–neutral and neutral–neutral reactions) were maintained in the fluid model. The fluid model itself consists of a set of mass balance equations (i.e. one for every species), the electron energy equation and the Poisson equation. The reaction rate coefficients of the electron–neutral reactions, as a function of average electron energy, are obtained from a Boltzmann model. The reaction rate coefficients of the ion–neutral and neutral–neutral reactions are assumed to be constant. It is found that helium does not affect the silane plasma chemistry drastically. The incorporation of small amounts of air (containing about 82% N2 and 18% O2) in a silane/helium plasma, however, influences the plasma chemistry to a large extent. A large number of nitrogen species (i.e. N2, N, N2+), and species containing oxygen (i.e. SiH3O SiO, OH and others), are present in the discharge at relatively high densities (i.e. of the order of 1014–1017 m−3).

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A one-dimensional particle-in-cell-Monte Carlo ͑PIC-MC͒ model was developed for a capacitively coupled rf discharge in a mixture of CH 4 and H 2 . The electron behavior is kinetically simulated by solving Newton's equations and treating the electron collisions with the Monte Carlo algorithm, whereas the behavior of the ions and radicals is treated by a set of continuity equations. The distinctive feature of this model is its self-consistency, i.e., the motion of the electrons is considered in the real electric field calculated from the Poisson equation, and not in the time-averaged electric field. The PIC-MC results were compared with the data calculated by means of a pure fluid model. In both models, exactly the same type of species, reactions, and cross sections are used. The results of both models, such as the electron energy distribution function, the average electron energy, and the densities of the various plasma species, are compared at a gas pressure of 0.14 Torr and a discharge frequency of 13.56 MHz, for the power ranging from 0.5 to 25 W. The nonstationary and nonlocal features of the electron energy distribution function are shown in the PIC-MC calculations. The effect of accumulation of low-energy electrons in the center of the discharge at higher input power Pϭ25 W is observed in the PIC-MC model, in contrast with the fluid model. The mechanisms causing the accumulation of low-energy electrons, and the processes defining the stationary state of the discharge are analyzed. The applicability of the fluid model for the calculation of the density of different hydrocarbon radicals is discussed.

A comparison is made between a one-dimensional ͑1D͒ and a two-dimensional ͑2D͒ self-consistent fluid model for a methane rf plasma, used for the deposition of diamond-like carbon layers. Both fluid models consider the same species ͑i.e., 20 in total; neutrals, radicals, ions, and electrons͒ and the same electron-neutral, ion-neutral, and neutral-neutral reactions. The reaction rate coefficients of the different electron-neutral reactions depend strongly on the average electron energy, and are obtained from the simplified Boltzmann equation. All simulations are limited to the alpha regime, hence secondary electrons are not taken into account. Whereas the 1D fluid model considers only the distance between the electrodes ͑axial direction͒, the 2D fluid model takes into account the axial as well as the radial directions ͑i.e., distance between the electrodes and the radius of the plasma reactor, respectively͒. The calculation results ͑species densities and species fluxes towards the electrodes͒ obtained with the 1D and 2D fluid model are in relatively good agreement. However, the 2D fluid model can give additional information on the fluxes towards the electrodes, as a function of electrode radius. It is found that the fluxes of the plasma species towards both electrodes show a nonuniform profile, as a function of electrode radius. This will have an effect on the uniformity of the deposited layer.