Numerical investigation on fundamental properties in capacitively-coupled methane plasmas for deposition of diamond-like carbon films*

Capacitively-coupled methane (CH$_4$) plasmas for deposition of diamond-like carbon films have been simulated using a self-consistent one-dimensional fluid model, incorporating the mass balance equations for electrons, ions, radicals and non-radicals, the electron energy balance equation, coupled with the Poisson equation. Despite of low-pressure CH$_4$ gas condition, many positive-ion species, such as C$_2$H$_4^+$, CH$_4^+$, C$_2$H$_2^+$, CH$_5^+$ etc., have been found in the plasmas. The non-radical neutrals, such as C$_2$H$_4$, C$_3$H$_8$, C$_2$H$_2$ and C$_2$H$_6$, have also found with higher densities comparable to the source gas density. This result indicates that this complexity of background gas in CH$_4$ plasmas is strongly affected to the electron energy distribution function, which is important for the determination of plasmas properties.