Hydrogenation kinetics and defect termination of post-plasma-treated chemical-vapor-deposited amorphous silicon film

In order to study hydrogenation kinetics of post-plasma-treated chemical-vapor-deposited amorphous Si film, changes in bonding of Si and H, content of bonded hydrogen, the hydrogen profile in the depth direction of the film, and spin elimination were measured as functions of plasma exposure time and temperature (Tp) and film thickness. The activation energy of hydrogen diffusion estimated from the change of hydrogen content with Tp and exposure time was small, i.e., 0.2–0.4 eV in comparison with that of bond breaking diffusion (∼1.5 eV). Accordingly, bond breaking diffusion was minor for the post-hydrogenation of Si film by hydrogen plasma. All the observed physical quantities in this study could be explained by the fast diffusion of atomic hydrogen through weakly bound sites such as interstitials and its capture by reactive sites such as dangling bonds and weak SiSi bonds. For the capture process, preferential capture of the hydrogen by dangling bonds always occurred. The surface etching of the film, often observed in plasma hydrogenation experiments, was attributable to the evaporation of hydrosilane molecules created by adding hydrogen to the SiSi bond in the surface region.