Amorphous nitrogenated carbon films: Structural modifications induced by thermal annealing

Hard amorphous nitrogenated carbon films [a‐C:H(N)] deposited by self‐bias glow discharge were annealed in vacuum in the temperature range of 300–800 °C. The annealing time was 30 min. The structural and compositional modifications induced by thermal annealing were followed by several analytical techniques: secondary ion mass spectrometry (SIMS), Raman spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection (ERDA), and nuclear reaction analysis. The internal stress of the films was also measured. Nuclear analyses indicate that both nitrogen and hydrogen losses occur for annealing temperatures higher than 300 °C. ERDA and SIMS results suggest that hydrogen and nitrogen out‐diffusion occurs by molecular transport through an interconnect network of voids. In the same temperature range, Raman scattering reveals an increase of the number and/or the size of the graphite domains. Internal stress is compressive for the as‐deposited films and changes to tensile for samples annealed at 800 °C, indicating the progressive graphitization of films. A comparison with amorphous carbon films (a‐C:H) is also made.