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

Polymer-like hydrogenated amorphous carbon films have been deposited in a microwave-assisted radiofrequency plasma reactor. Vibrational properties are investigated in-situ by infrared ellipsometry as a function of ion bombardment. By choosing either hydrogen or helium in the microwave gas mixture, films ranging from nearly purely saturated polymer to olefinic/aromatic films can be obtained. Both absorption bands and transparent regions are studied, leading to a determination of the dielectric constant as well as the vibrational frequencies, widths and intensities as a function of macroscopic properties like density and optical gap. Hydrogen atoms attached to sp2-carbon are detected even in highly saturated films. The sensitivity of the vibrational oscillator strength to the matrix effect is used to probe the local environment of hydrogenated carbon atoms. Quantitative determination of CHn group densities in the different configurations indicates that sp3 CH groups are dominant and that the local structure evolves with atomic hydrogen concentration.