Nanoporosity in plasma deposited amorphous carbon films investigated by small-angle X-ray scattering

Amorphous carbon films were deposited by plasma enhanced chemical vapor deposition (PECVD) and d.c.-magnetron sputtering and their porosity was investigated by small-angle X-ray scattering (SAXS). In the case of sputtered films, the X-ray scattering intensity increased with the argon pressure used for the film deposition, while the atomic density decreased. The analysis of the SAXS results was performed using the GNOM code assuming a distribution of spherical pores. This analysis suggested that the maximum of these distributions occur for a radius value below 1 nm. The films deposited at 0.17 Pa were essentially pore-free. As the Ar pressure increases, the pore size distribution widens and the volume occupied by the pores increases. A direct relation between the atomic density of carbon films deposited by sputtering and the pore volume fraction was also obtained. The low scattering intensity observed for the films deposited by PECVD showed that they were compact and homogeneous regardless of the self-bias voltage employed in the range between - 100 V and -500 V. (C) 2002 Published by Elsevier Science B.V.