Influence of RF Power on Chemical Bonding Composition on a-CNx Thin Films as Humidity Sensor

The a-CNx thin film has chemical bonding of C-N (sp(3)), C=N (sp(2)) and C=N (sp(1)). C=N and C equivalent to N bonds are easily resolved by hydrogen attack during the film deposition process to form C-H and N-H bonds. The formation of graphite sp2 components in the a-CNx thin film caused by the presence of nitrogen atom contributes to the reduction of the electrical resistance and enhances the electrical conductivity. These features are essential for a-CNx thin film application as a humidity sensor. In this study, amorphous carbon nitride films (a-CNx) are deposited on the quartz and silicon (111) substrate using PECVD techniques. The samples were deposited at different RF power at 40, 50, 60, 70 and 80 W and analyzed their effects on film chemical composition and films morphology as well as their ability as humidity sensor. D (sp(2)C) peak and G (sp(3)C) peak are clearly observed using Raman spectroscopy in all a-CNx thin films with the highest intensity obtained at RF 70 W. Films micrograph observed by field emission scanning electron microscopy (FESEM) show that surface morphology of all samples have a uniform structural shape of cauliflower. X-ray photoelectron spectroscopy (XPS) confirmed the presence of C-C/C=C, C=N and C equivalent to N bonds in the a-CNx thin film. All the a-CNx thin films showed a response to different humidity with sensitivity between 60-70%. The a-CNx thin film deposited at RF 70 W power indicates the highest sensitivity due to carbon disorder and higher sp(3)C content.