Can plasma experiments unravel microscopic surface processes in thin film growth and erosion? Implications of particle–beam experiments on the understanding of a-C:H growth

Abstract

Despite the widespread use of low-temperature plasmas for deposition and erosion of thin films and surface modification the underlying microscopic mechanisms are often not well understood, especially for reactive plasmas. Thorough parameter studies and the use of modern in situ real-time diagnostics of the plasmas as well as of the growing film provide valuable results to optimize the processes. However, they generally allow only an indirect and therefore qualitative or even ambiguous conclusion about the actual film growth processes. One reason is the complexity that is inherently connected to such plasma processes. A vast number of particles with different energy and reactivity is interacting simultaneously with the surface, thus hindering to reveal microscopic growth mechanisms or reliable values of universal constants. One approach to isolate microscopic mechanisms is the use of model experiments with quantified particle beams. In this article model experiments for the example of amorphous hydrogenated carbon film (a-C:H) growth will be motivated and described. The discrepancy between different experimental results and various growth models proposed over the years are briefly reviewed. Recent results of the particle–beam experiment during the last years established at the Max-Planck-Institut für Plasmaphysik are presented. It will be shown, how the sticking probability of thermal methyl radicals is influenced by substrate temperature and how the presence of other radicals such as atomic hydrogen alter the sticking of methyl. Furthermore, it will be shown how ions participate in film growth and the consequences for plasma experiments are discussed.