Hydrogen plasma etching mechanism at the a-C:H/a-SiCx:H interface: A key factor for a-C:H adhesion

Abstract Hydrogenated amorphous carbon thin films (a-C:H) do not show good adhesion on ferrous alloys. When a silicon-containing intermediate thin film is chosen, deposition temperatures of at least 300 °C are necessary to provide adequate adhesion. However, a new approach is introduced to achieve similar results at lower temperatures: a selective chemical hydrogen plasma etching before the carbonaceous film deposition. The effect is known but its physicochemical mechanism and kinetics remain open. We have investigated the role of hydrogen etching in the modification of the outermost and innermost interfaces of a-SiCx:H interlayers. The results show that hydrogen radically modifies the interlayer thickness in the outermost region and increases the C/Si ratio in the innermost. Moreover, the hydrogen etching allows the formation of more C C bonds at the outermost interface, which is correlated to better adhesion. Finally, we proposed a mechanism in order to explain physical and chemical changes caused by hydrogen etching.