On the induced microstructure changes of the amorphous carbon nitride films during annealing

Abstract

The analysis of the stress release and structural changes caused by postdeposition thermal annealing of amorphous carbon nitride thin films (a-CNx) has been carried out. The a-CNx films were deposited on Si (100) using reactive radio frequency (rf) magnetron sputtering of a high-purity graphite target in a pure nitrogen plasma under various different rf powers. Combined Fourier transform infrared (FTIR), Raman spectroscopy, transmission spectroscopy, photothermal deflexion spectroscopy, and residual stress measurements were used to fully characterize the films. Annealing of the samples in vacuum at temperature up to 600°C produces changes in their structural properties and the intrinsic stress. These changes are found to be strongly dependent on both the deposition conditions and microstructure changes occurring within the films during heating. FTIR spectra showed the existence of N–C sp3, NC sp2, and CN triple bonds in the deposited films. The analysis of the spectra versus annealing temperature (TA) reveals that the major microstructure changes are the reorganization of the C–N and C–C configurations, without significant densification of the deposited films. The Raman features combined to the optical measurements reveal that this progressive graphitization of the material, with increasing TA, is accompanied by a higher disorder form of C sp2 sites. These results are used to describe the stress variation that accompanies the nitrogen evolution within the deposited films.