Diagnostics and modelling of a methane plasma used in the chemical vapour deposition of amorphous carbon films

Abstract

In an RF-discharge methane plasma, the dissociation rate of CH 4 in collisions with electrons has been measured using a laser absorption technique. The measured rate increases as the RF power increases and as the gas pressure decreases. The electron energy distribution function f( epsilon ) and the electron density n e have also been measured by a heated electrical probe. The measured f( epsilon ) is quite different from the Maxwellian distribution and rather close to the Druyvesteynian distribution. The dissociation rate constant deduced from f( epsilon ) and the reported cross-section when multiplied by the measured n e is consistent with the results of the laser absorption method. Based on these measurements a modelling of the plasma has been performed using a set of rate equations for CH 4 and the various neutral and ionic species produced in the plasma. The calculated degree of dissociation for CH 4 in the plasma agrees well with the measured results. The most abundant neutral radical in the plasma predicted by the model is CH 3 , while CH 5 + is the most abundant ionic species.