C-H bonding of polymer-like hydrogenated amorphous carbon films investigated by in-situ infrared ellipsometry

Polymer-like hydrogenated amorphous carbon films have been deposited in a m icrowave-assisted radiofrequency plasma reactor. Vibrational properties are investigated in-situ by infrared ellipsometry as a function of ion bombard ment. By choosing either hydrogen or helium in the microwave gas mixture, f ilms ranging from nearly purely saturated polymer to olefinic/aromatic film s can be obtained. Both absorption bands and transparent regions are studie d, leading to a determination of the dielectric constant as well as the vib rational frequencies, widths and intensities as a function of macroscopic p roperties like density and optical gap. Hydrogen atoms attached to sp(2)-ca rbon are detected even in highly saturated films. The sensitivity of the vi brational oscillator strength to the matrix effect is used to probe the loc al environment of hydrogenated carbon atoms. Quantitative determination of CHn group densities in the different configurations indicates that sp(3) CH groups are dominant and that the local structure evolves with atomic hydro gen concentration. (C) 1999 Elsevier Science Ltd. All rights reserved.