Ion bombardment diagnostics in a nitrogen RF magnetron sputtering discharge

Abstract

Abstract The identity, fluxes and kinetic energy distributions of positive ions bombarding the substrate during radio frequency (RF) magnetron sputtering of graphite in a balanced nitrogen plasma have been investigated for various settings of discharge power and pressure by using energy-mass spectrometry analysis and probe measurements. Three prominent groups of ionic species were identified to form the ion bombardment. The first is due to the process gas ions, of which the primary ions of nitrogen are the dominant ones. The two further ionic groups are clearly related to sputtered carbon and its reaction products with nitrogen. The net fluxes of these ionic species respond very sensitively to changes in the discharge conditions. The ratios of the net ion fluxes of C + and N + to their atom deposition rates indicate that nearly all carbon species for film growth arise from the arriving flux of sputtered C atoms, whereas the bombarding N + flux acts as an intense nitrogen source for the film chemistry. The ion kinetic energy distributions measured for predominant ions, such as C + , N + , N + 2 and (CN) + 2 , were observed to be qualitatively similar in their shapes and trends, clearly reflecting the ions' sensitivity to RF modulations and to collision processes while passing the near-substrate sheath. Over the range of power and pressure, the mean kinetic energy of the bombarding ions was from about 25 eV to 45 eV. With the found data, the energy flux density of the ion bombardment and the averaged bombardment energy per condensing carbon and nitrogen atom were calculated, these being fundamental internal process parameters for judging the effect of the bombarding ion flux on carbon nitride formation.