Spectroscopic investigations of the microstructure changes induced by substrate temperature in nitrogen-substituted amorphous carbon thin films

The effect of substrate temperature (T_S) on the microstructure of amorphous nitrogen-substituted carbon thin films (a-C_1−xN_x) has been studied. The a-C_1−xN_x films were deposited on Si(1 0 0) using reactive radio-frequency (RF) magnetron sputtering of a high-purity graphite target in a pure nitrogen plasma using different RF powers and different substrate temperatures T_S. Combined Fourier transform infrared (FTIR), Raman spectroscopy and residual stress measurements are used to fully characterise the films in the as-deposited state. FTIR spectra showed the existence of NCsp² and CN triple bonding, and suggested the presence of N-Csp³ bonding in the deposited films. The analysis of the spectra versus T_S reveals two rearrangement mechanisms of the microstructure. Up to 150 °C, the reversion of NCsp² to N-Csp³ and CCsp²respectively, and the increase the connectivity of the C-C network for higher T_S. The Raman features reveals that this progressive graphitisation of the material, with increasing T_S, is accompanied by a high disorder form of Csp² sites. These results are used to describe the stress variation that accompanies nitrogen evolution within the deposited films.