Studies of density and surface roughness of ultrathin amorphous carbon films with regards to thickness with x-ray reflectometry and spectroscopic ellipsometry

Specular x-ray reflectivity (XRR) measurements were used to study the density and surface roughness of ultrathin hydrogen-free amorphous carbon films deposited by sputtering, of thickness varying from 25 to 325 Å. The film thickness and surface roughness obtained from XRR measurements are in good agreement with that found by spectroscopic ellipsometry (SE) and atomic force microscopy. The results for the film composition obtained from SE and XRR are supported by stress measurements. Films (especially those with thickness below 100 Å) deposited with positive substrate bias voltage were found to exhibit a reduction in density, sp3 C–C bonding, and internal compressive stresses and an increase in surface roughness by increasing film thickness.