X-ray reflectivity study of tetrahedral amorphous carbon films

Hydrogen-free amorphous carbon films were deposited at different deposition bias voltage on a single silicon wafer by a process known as Filtered Cath odic Vacuum Are (FCVA). The influences of different deposition bias voltage s on the microstructure and the properties of thin tetrahedral amorphous ca rbon (ta-C) Films, such as surface roughness, film mass density and thickne ss, have been studied by means of the x-ray reflectivity technique (XRR) fo r the first time. The microstructure of these films deposited on silicon wa fers was simulated by a four-layer model consisting of a ta-C layer, a mixe d ta-C:Si layer, Si-O layer and the silicon substrate. The mixed ta-C:Si la yer consisting of the mixture of ta-C and silicon simulates the carbon ion impinging / diffusion into the surface of the silicon substrate. The mass d ensity and the roughness of the film are found to be dependent on the impin ging ion bombardment energy. The mass density increases with increase in io n bombardment energy up to 100 eV. Beyond 100 eV, the mass density decrease s with further increase in ion bombardment energy. The surface roughness de creases with increasing ion bombardment energy to a minimum value at 100 eV , after which it increases with further increase in ion bombardment energy. The thickness of the films obtained by XRR technique correlates well with the thickness measurement obtained by spectral reflectometry. The existence of the Si-O layer was verified by Auger depth profiling.