Studies with nondestructive techniques of the composition, initial stages of growth and surface topography of thin amorphous carbon films

Amorphous carbon (a-C) films. free of hydrogen, were prepared by magnetron sputtering. The films were deposited either with positive or negative bias voltages (V-b) onto a c-Si substrate and from a few monolayers to 400 Angstrom thick. The film composition during deposition was estimated by in-situ spectroscopic ellipsometry (SE), a nondestructive technique, in the energy region 1.5-5.5 eV. It was found that films deposited with negative bias are rich in sp(3) C-C sites from the initial stages of growth to the final thickness of the film. All films were also examined by X-ray reflectometry and atomic force microscopy in order to study the surface morphology versus V-b and the film thickness. The results show that films deposited with negative bias are atomically smooth and independent on their thickness, whereas those deposited with positive bias exhibit spherical elements with size depending on the film thickness. Their RMS surface roughness is about 5 Angstrom at the first 30 Angstrom and increases linearly to 9 k for films 400 A thick. These results support that two type of growth take place in a-C films deposited by sputtering and are discussed in view of reported models for the development of films rich in sp(3) C-C sites. (C) 1998 Elsevier Science S.A.