Hydrogen/Argon Plasma-Amorphous Carbon Near-Surface Interactions

Interactions between low temperature, hydrogen-containing plasmas and a-C:H are complicated by the fact that the plasma generally strongly alters the near-surface region, and material from the surface will enter, and alter the plasma. In the present study, we report on the effects of H2- and Ar plasma-containing species on the near-surface region of an amorphous carbon film. H from the plasma will often insert into C-C bonds, creating hydrocarbon (HC) chains with varying degrees of cross-linking. HC has a lower density than C and so the near-surface region can expand and soften when exposed to H2-containing plasma. The depth and characteristics of the altered region depend on the composition and energy of the impinging species. Energetic positive ions can penetrate the surface, and fast, light H-containing ions are especially able to penetrate significant distances. The near-surface film structure and composition under steady state conditions is the result of a competition between erosion and insertion processes. A striking feature is the formation and ejection of HC clusters from the surface. These species can act as nuclei to form particles in the plasma. We report on the role of ion energy, composition and neutral-ion flux ratio on near-surface structure and composition and compare these predictions with the available experimental data.