CHEMICAL EQUILIBRATION OF PLASMA-DEPOSITED AMORPHOUS-SILICON WITH THERMALLY GENERATED ATOMIC-HYDROGEN

Hydrogenated amorphous silicon (a-Si:H) thin films prepared by plasma-enhanced chemical vapor deposition (PECVD) from SiH4 have been further hydrogenated in situ by exposure to atomic H generated by a filament heated in H-2 gas. Upon equilibration of the network with gas-phase H, as many as approximately 2 X 10(21) cm-3 additional Si-H bonds form within the top 200 angstrom of the film without significant etching; surface roughening, or coordination defect generation. Real-time spectroscopic ellipsometry is applied to study the kinetics of near-surface Si-H bond formation at 250-degrees-C in order to improve our understanding of the effects of excess atomic H in the a-Si:H growth environment. Atomic H entering the film surface exhibits an effective diffusion coefficient > 3 X 10(-15) cm2/s and is trapped within the top 200 angstrom of the film at a rate of approximately 10(-3) s-1. Most of this H is trapped irreversibly on the time scale of deposition with emission rates < 2 X 10(-7) S-1. We also find that monolayer levels of surface oxide are an effective diffusion barrier to H, preventing chemical equilibration between the gas and solid phases.