Numerical modeling of capacitively coupled hydrogen plasmas: Effects of frequency and pressure

In the field of plasma deposition of amorphous and microcrystalline silicon, the increase of the excitation frequency has often been considered as a way to enhance the deposition rate. Moreover, the increase of pressure has also been shown to enhance the deposition rate and improve the film properties. We attempt to clarify the effects of frequency in the 13.56–40.68 MHz range and to compare them to those of the pressure in the range of 0.5–1.5 Torr. For that purpose we use a numerical modeling of capacitively coupled hydrogen plasma, particularly relevant for the deposition of microcrystalline silicon. We use a one-dimensional time-dependent fluid model for the description of neutrals, positive and negative ions, and electrons, which involves a chemistry model taking into account 32 reactions in the gas phase and on the surface of the electrodes. The results of the model for the symmetrical system show that both pressure and frequency have pronounced influence on the parameters of the discharge: sheath t...