Growth and erosion of hydrocarbon films investigated by in situ ellipsometry

The growth of hydrocarbon films (C:H films) from a methane plasma and their erosion by a hydrogen plasma are investigated by means of in situ ellipsometry. The kinetic energy of the ions impinging on the surface during deposition and erosion is varied by applying a rf bias resulting in a dc self-bias ranging from floating potential up to 100 V. In addition, the substrate temperature is varied from room temperature up to 600 K. The direct comparison between the growth and erosion indicates that the temperature dependence of the growth rate during deposition from a methane plasma is caused by the temperature-dependent erosion due to reactions with the abundant atomic hydrogen. Furthermore, the synergistic effects between hydrogen ions and atomic hydrogen on the etch rate of C:H films are investigated. The underlying surface reactions during the erosion show up in the optical response of the deposited films as measured by ellipsometry. These results are compared with findings in the literature on the elementary steps of the erosion of C:H films by atomic hydrogen.