Chemical kinetics and energy transfer in moderate pressure H₂ plasmas used in diamond MPACVD processes

A kinetic model for moderate-pressure microwave H₂ plasmas obtained in diamond deposition reactors is presented. This model involves three groups of reactions which describe the vibrational kinetics of H₂, the chemistry of H₂ and H electronically excited states and the groundstate species kinetics, respectively. The set of species kinetic equations resulting from this model, coupled to the electron Boltzmann equation and the total energy equation were solved under a quasi-homogenous plasma assumption. This enables the estimation of the species densities, the electron distribution function and related electron properties, as well as the gas temperature. The results show that the most important ionization channel is that due to the quenching of H (n = 2) excited states by H₂. The production of the H-atom is mainly due to electron impact dissociation at low microwave power density and to thermal dissociation at high power density. A simplified physical model which may be used for describing the non-equilibrium H₂ plasma flow in diamond deposition microwave plasmas reactors is also proposed.