Paper PS-MoA7
Will Recombination Reaction Probabilities at Plasma Chamber Walls Ever Be Non-Adjustable Parameters?

Monday, October 20, 2008, 4:00 pm, Room 304

Reactions of neutral species on surfaces immersed in plasmas have been recognized for many years to be an important class of processes that plays a major role in determining the make-up of species in the plasma. The association of radicals on the surfaces of chamber walls and substrates represents a sink for radicals and a source of larger product species. Chemistry-rich models have been developed in recent years for plasmas such as those used to etch silicon and dielectric materials. Heterogeneous reactions are an essential part of these models. With the exception of a few atom recombination reactions, the reaction probabilities for these processes are completely unknown; hence they are usually treated as adjustable parameters, or are guessed at and left constant. Experimental measurements of these reactions are usually carried out in one of two ways, neither is ideal. First, in-situ measurements can made in the plasma. This approach has the advantage of studying the surface that exists during plasma operation - one that is often coated with amorphous deposits of sputtered or etched substrate and reactor materials, and receives high fluxes of neutrals, ions, electrons and photons. This complexity makes it difficult to isolate individual reactions. Consequently, a second approach has been practiced in which the complex plasma environment can be avoided by studying reactions in high vacuum with selected molecular beam impingement. While this approach can provide accurate measurements of reaction probabilities, product identification and surface characterization, it can also lead to misleading predictions when extended to real plasma conditions. This talk will briefly review a few selected studies that highlight the complexity and lack of consensus in this field, and offer prospects for system-non-specific rate parameters for this class of heterogeneous reactions.