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

摘要

Polymer-like hydrogenated amorphous carbon films have been deposited in a microwave-assisted radiofrequency plasma reactor. Vivratioal properties are investigated in-situ by infrared ellipsometry as a function of ion bonbardment. By choosing either hyddrogen 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 freqfuencies, widths and intensities as a function of macroscopic properties like density and optical gap. Hydrogen atoms attached to sp~2-carbon are detected even in highly s aturated films. The sensitivity of the vibrational oscillator strength to the matrix effect is used to probe the local environmemt of hydrogenated carbon atoms. Quanutiative determination of CH_n group densities in the different configurations indicates that sp~3 CH groups are dominant and that the local structure evolves with atomic hydrogen concentration.