Precursors of fluorocarbon film growth studied by mass spectrometry

The precursor species of fluorocarbon film growth at the reactor wall irradiated by an electron cyclotron resonance C₄F₈ plasma have been studied by using a quadrupole mass spectrometer. The amount of polymeric neutral species [C_mF_n (m≥2)] and absolute densities of CF_x (x=1-3) radicals in the vicinity of the wall were measured by electron attachment and threshold ionization mass spectrometry, respectively. The trends in the film growth rate as a function of gas residence time, diluted hydrogen concentration, and microwave power were well accounted for by the competition between the incorporation of CF_x radicals and positive ions and the removal by F and H atoms. The fluxes of CF_x radicals and positive ions incident upon the wall were shown to be comparable with the net condensed carbon flux derived from the growth rate. In contrast, the trends in the amount of polymeric neutrals were not well correlated to the growth rate.