Role of the hydrogen plasma treatment in layer-by-layer deposition of microcrystalline silicon

We have investigated the role of hydrogen in hydrogenated microcrystalline silicon ($\mathrm{\mu c}\mathrm{-Si:H}$ ) formation using hydrogen plasma treatments, in particular examining the possibility of subsurface reaction due to permeating hydrogen atoms, which leads to the crystallization of hydrogenated amorphous silicon ($a\mathrm{-Si:H}$ ). It is demonstrated that the hydrogen plasma treatment of $a\mathrm{-Si:H}$ film on the anode using a cathode covered by $a\mathrm{-Si:H}$ film, which is inevitably coated during the deposition period, gives rise to the deposition of $\mathrm{\mu c}\mathrm{-Si:H}$ over the $a\mathrm{-Si:H}$ layer, i.e., chemical transport takes place. It is also found that the pure hydrogen plasma treatment using a clean cathode induces only etching of the $a\mathrm{-Si:H}$ layer. These results imply that the present hydrogen plasma condition does not cause crystallization of $a\mathrm{-Si:H}$ but only etching, and that careful experimentation is required to determine the real subsurface reaction due to atomic hydrogen.