We have investigated the role of hydrogen in hydrogenated microcrystalline silicon (&mgr;c-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-Si:H). It is demonstrated that the hydrogen plasma treatment ofa-Si:Hfilm on the anode using a cathode covered bya-Si:Hfilm, which is inevitably coated during the deposition period, gives rise to the deposition of&mgr;c-Si:Hover thea-Si:Hlayer, i.e., chemical transport takes place. It is also found that the pure hydrogen plasma treatment using a clean cathode induces only etching of thea-Si:Hlayer. These results imply that the present hydrogen plasma condition does not cause crystallization ofa-Si:Hbut only etching, and that careful experimentation is required to determine the real subsurface reaction due to atomic hydrogen. ©1997 American Institute of Physics.