A phenomenological model for surface deposition kinetics during plasma and sputter deposition of amorphous hydrogenated silicon

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Abstract
The surface processes during the plasma-enhanced chemical vapor deposition and reactive sputter deposition of amorphous hydrogenated silicon (a-Si:H) are investigated by use of a phenomenological model. The model consists of an accounting, in rate equation form, of adsorption of radicals from the plasma onto the surface, surface diffusion, incorporation into the lattice, interconnection of bonds in the lattice, and burial of species on the surface, thereby constituting film growth. By accounting for the coordination partners of Si atoms in the film, the atomic fraction of hydrogen in the film is computed for the lattice and for hydrogen in polymeric or isolated configurations. Results from the model are discussed while parametrizing the probability for hydrogen elimination during incorporation and the probability for saturation of dangling bonds by gas phase species. We find that the mode of hydrogen elimination during incorporation distinguishes films grown dominantly from SiH2 or SiH3 radicals. Characteristics of films grown by sputter deposition are investigated as a function of the composition of the radical flux. We find that films grown from hydrogen-rich fluxes are composed dominantly of dihydride (Si HH) configurations, whereas hydrogen-lean mixtures are composed of dominantly hydride ( 3/4 Si–H) configurations.