Plasma processing and chemistry*

Plasma deposition and plasma conversion can be characterized by five steps: production by ionization, transfer of chemistry to precursors, transport of radicals to the surface, surface interactions with deposition, recirculation and generation of new monomers. For very fast deposition, large flows of radicals are needed and a regime is reached, in which monolayer coverage is reached in a very short time. Such large flows of radicals can be obtained by ion-induced interactions, as the C2H radical from acetylene for a-C:H deposition, or by H atom abstraction as the SiH3 radical from SiH4 for a-Si:H deposition. These radicals with intermediate sticking coefficient are advantageous as they are mobile and have a finite dwelling time at the surface. By such a pure radical mechanism, good layers can be formed with very high growth rates, if large radical fluxes can be reached. This regime of high fluence is also interesting for conversion, of which ammonia formation from hydrogen and nitrogen atoms is given as an example. These new approaches offer new possibilities for further development of the field in close connection with surface science, catalysis, and materials science.