A one-dimensional fluid model for radio-frequency glow discharges is presented which describes silane/hydrogen discharges that are used for the deposition of amorphous silicon (a-Si:H). The model is used to investigate the relation between the external settings (such as pressure, gas inlet, applied power, and frequency) and the resulting composition of the gas and the deposition rate. In the model, discharge quantities such as the electric field, densities, and fluxes of the particles are calculated self-consistently. Look-up tables of the rates of the electron impact collisions as a function of the average electron energy are obtained by solving the Boltzmann equation in a two term approximation for a sequence of values of the reduced electric field. These tables are updated as the composition of the background neutral gas evolves under the influence of chemical reactions and pumping. Pumping configuration and gas inlet are taken into account by adding source terms in the density balance equations. The effect of pumping is represented by an average residence time. The gas inlet is represented by uniformly distributed particle sources. Also the radial transport of neutrals from the discharge volume into the discharge-free volume is important. As the fluid model is one dimensional, this radial transport is taken into account by an additional source term in the density balance equations. Plasma–wall interaction of the radicals (i.e., the growth of a-Si:H) is included through the use of sticking coefficients. A sensitivity study has been used to find a minimum set of different particles and reactions needed to describe the discharge adequately and to reduce the computational effort. This study has also been used to identify the most important plasma-chemical processes and resulted in a minimum set of 24 species, 15 electron-neutral reactions, and 22 chemical reactions. In order to verify the model, including the chemistry used, the results are compared with data from experiments. The partial pressures of silane, hydrogen, disilane, and the growth rate of amorphous silicon are compared for various combinations of the operating pressure (10–50 Pa), the power (2.5–10 W), and the frequency (13.56–65 MHz). The model shows good agreement with the experimental data in the dust free α regime. Discharges in the γ′ regime, where dust has a significant influence, could not be used to validate the model.

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The growth of amorphous, microcrystalline, and polymorphous silicon has been investigated by studying the species contributing to the growth and resulting film structure. The surface reaction probability of the radicals and the contribution of ions to the growth have been determined. In a-Si:H deposition by hot wire chemical vapor deposition, the surface reaction probability (β=0.29) of the depositing radical is compatible with SiH3, whereas the surface reaction probability in microcrystalline silicon growth is higher (0.36⩽β⩽0.54). On the contrary, the deposition of amorphous silicon by plasma enhanced chemical vapor deposition indicates the contribution of more reactive radicals than SiH3. The deposition of polymorphous and microcrystalline silicon by plasma is dominated by ions, which can contribute up to 70% of the deposited film. This is attributed to efficient ionization of silane in charge exchange reactions with hydrogen ions. The surface reaction probability in the case of polymorphous silicon deposition (β≈0.30) is intermediate between that of a-Si:H deposition (β≈0.40) and that of microcrystalline silicon deposition (β≈0.20). Etching of amorphous silicon by means of a hydrogen plasma shows that ions may hinder the process.

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