Thermal stability of carbon nitride thin films

The thermal stability of carbon nitride films, deposited by reactive direct current magnetron sputtering in N-2 discharge, was studied for postdeposition annealing temperatures T-A up to 1000 degreesC. Films were grown at temperatures of 100 degreesC (amorphous structure) and 350 and 550 degreesC (fullerenelike structure) and were analyzed with respect to thickness, composition, microstructure, bonding structure, and mechanical properties as a function of T-A and annealing time. All properties investigated were found to be stable for annealing up to 300 degreesC for long times (> 48 h). For higher T-A, nitrogen is lost from the films and graphitization takes place. At T-A = 500 degreesC the graphitization process takes up to 48 h while at T-A = 900 degreesC it takes less than 2 min. A comparison on the evolution of x-ray photoelectron spectroscopy, electron energy loss spectroscopy and Raman spectra during annealing shows that for T-A > 800 degreesC, preferentially pyridinelike N and -C equivalent toN is lost from the films, mainly in the form of molecular N-2 and C2N2, while N substituted in graphite is preserved the longest in the structure. Films deposited at the higher temperature exhibit better thermal stability, but annealing at temperatures a few hundred degrees Celsius above the deposition temperature for long times is always detrimental for the mechanical properties of the films.