I. An et al., CHEMICAL EQUILIBRATION OF PLASMA-DEPOSITED AMORPHOUS-SILICON WITH THERMALLY GENERATED ATOMIC-HYDROGEN, Physical review. B, Condensed matter, 48(7), 1993, pp. 4464-4472
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 w
ithin the top 200 angstrom of the film without significant etching; su
rface roughening, or coordination defect generation. Real-time spectro
scopic ellipsometry is applied to study the kinetics of near-surface S
i-H bond formation at 250-degrees-C in order to improve our understand
ing of the effects of excess atomic H in the a-Si:H growth environment
. Atomic H entering the film surface exhibits an effective diffusion c
oefficient > 3 X 10(-15) cm2/s and is trapped within the top 200 angst
rom 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 equ
ilibration between the gas and solid phases.