Growth precursors for a-C:H film deposition in pulsed inductively coupled methane plasmas

Abstract

Film deposition in pulsed inductively coupled plasmas is investigated using methane as precursor gas. The densities of neutrals as well as ion and radical fluxes are quantified using mass spectrometry. Plasma composition is uniquely determined by the mean dissipated energy per source gas molecule in the plasma, Emean. Film growth rates are measured by in situ real-time ellipsometry. The contributions of individual precursors to film growth are discussed quantitatively by comparing absolute net growth fluxes of reactive species with deposited carbon atoms. It is shown that chemisorption of CH3 or implantation of energetic carbonaceous ions cannot explain the observed growth rates. Instead, film deposition occurs either by incorporation of CH radicals at small values of Emean(<10eV) or by incorporation of unsaturated hydrocarbon radicals such as C2H3 or C2H at intermediate values of Emean(10<Emean<100eV). Film growth depends strongly on incorporation of carbonaceous ions only at larger values of Emean(>100eV).