Amorphous to nanocrystalline transition in hydrofluorinated silicon films from helium diluted SiF4-H2 plasmas

Nowadays, there is a renewed interest in the investigation of the silicon plasma deposition processes because in many electronic devices better performances can be achieved with nanocrystalline silicon (nc-Si) as active layers instead of amorphous films (a-Si:H). In this work, we focused our interest on how to favour the amorphous to crystalline transition during silicon deposition from SiF4-H2-He plasmas. Nanocrystalline phase increases, when He is added to SiF4-H2 mixture because the F atom etching of the amorphous phase is enhanced. The r.f. power variation is used as external parameter to determine the relative importance of F and SiFx radicals for etching and deposition, respectively.