Evolution under annealing and nitrogen implantation of the mechanical properties of amorphous carbon films

The functionality and lifetime of thin film/substrate set depend mainly on its mechanical properties. Probing and improving the thermo-mechanical behaviour (stability) are then of utmost importance. Amorphous carbon thin films, 320 nm thick, have been deposited by a sputtering technique on silicon wafers, 500 and 200 μm thick. The microstructure and the mechanical properties (hardness, indentation reduced modulus and average in-plane stresses) have been investigated using Raman and infrared spectroscopies, silicon curvature and nanoindentation experiments. In particular, the evolution of global stress in the film has been analysed in situ during an annealing treatment while the evolution of the mechanical response (elastic and plastic) induced by nitrogen post irradiations was surveyed by nanoindentation. We observed a rather good thermal stability of the film/substrate set and the presence of hydrogen in the film is discussed. Further, nitrogen irradiation and incorporation were observed to induce a dramatic decrease of the mechanical performance of the films. These behaviours are discussed in view of the thin film structure.