Low-energy ion bombardment effects in reactive rf magnetron sputtering of carbon nitride films

Abstract

Variable unbalanced rf magnetron sputtering of graphite in pure nitrogen and a mixture of nitrogen and helium has been used to prepare carbon nitride films in a wide range of ion bombardment conditions analyzed as to their fluxes and kinetic energies by energy-resolved mass spectrometry and probe measurements. These data were related to the chemical composition, bonding structure, density and Young's modulus of the deposited CN x films which have been studied by several analytical methods. The energy flux density supplied to the growing film by the bombarding positive ions and the bombardment energy per condensing C and N atom were determined to range from below 1×10 −3 to close to 5 Wcm −2 and from about 1 up to 2×10 3 eV, respectively, depending on rf power density, discharge pressure and magnetron magnetic field configuration chosen. With increasing energy flux of the ion bombardment the overall [N]/[C] ratio of the films decreases exponentially from a maximum of about 1 to a final value of nearly 0.3 attributed to a bombardment activated desorption of N atoms as well as to a diminishing formation and/or an increased resputtering of N-H groups. The CN x films were found to consist of an amorphous sp 2/sp 3 hybridized carbon matrix with N substitutions of C atoms and contributions of several C-N and N-H groups. At increasing energy flux density of the ion bombardment the matrix changes from a more graphite-like phase with large sp 2 domains to a predominantly disordered carbon structure. In low-pressure quadrupole magnetic field magnetron sputtering the film density increases with increasing bombardment energy per condensing C and N atom, but remains below that of graphite. This was accompanied by increasing Young's moduli not exceeding 120 GPa.