Stopping power dependence of nitrogen sputtering yields in copper nitride films under swift-ion irradiation: exciton model approach

Nitrogen sputtering yields as high as 2×10³ N / ion are obtained by irradiating N-rich-Cu₃N films (N concentration (33±2) at.%) with Cu ions at energies in the range 10-42 MeV. The kinetics of N sputtering as a function of ion fluence is determined at several energies (stopping powers) for films deposited on both, glass and silicon substrates. The kinetic curves show a three stage-behaviour: an initial inhibition stage I of low sputtering yield, followed by a more extended linear region II that finally reaches a saturation stage III at a low remaining nitrogen fraction (5-10 %). For the case of silicon substrates the contribution of the initial stage is not significant. The sputtering rate of stage II is found to be independent of the substrate and to linearly increase with electronic stopping power (S_e). A S_e threshold for nitrogen depletion of ~3.4 keV/nm is estimated. Experimental kinetic data are successfully analysed within the bulk molecular recombination model. All features are in accordance with electronic excitation mechanisms, showing for the first time evidence of the excitonic model.