Incorporation of nitrogen in sputtered carbon films

The possibility of depositing carbon nitride with a planar magnetron sputter system has been evaluated. The deposition parameters were varied with the aim of optimising the nitrogen content and the hardness of the films. Both d.c. and r.f. magnetron power sources were used to deposit films on zirconium, yttria-stabilised zirconia and sapphire substrates. The films were studied by electron microscopy (SEM and TEM), Rutherford backscattering and electron energy loss spectroscopy (EELS). The hardnesses of the films were measured by both traditional and depth-sensing methods. Special attention was paid to the nitrogen content of the films, which depended strongly on the sputtering conditions. Films containing up to 58 at.% nitrogen were made, close to the stoichiometry expected for C3N4. However, all the nitrogen-containing films were amorphous. The films suffered from high deposition stresses, which in combination with high elastic relaxation also complicated the hardness measurements. It was found that the fraction of sp2 hybridisation of the carbon increased with nitrogen content and ion bombardment of the films.