Substrate holder biasing for improvement of microcrystalline silicon deposition process

Application of a dual frequency plasma source for the deposition of microcrystalline silicon thin films from highly diluted SiH4/H2 was investigated in this paper. A positively or negatively biased low frequency voltage was applied on the substrate holder while the conventional frequency of 13.56 MHz was used for the powered electrode. The results show a significant increase of the deposition rate and an improvement of the film crystallinity in the case of the positive biasing. Plasma diagnostics and modeling were used to understand the beneficial effect of positive biasing on the deposition process. The results revealed that the observed changes are not only due to the variation of ion flux and ion bombardment but also depend on the changes in the production and distribution of neutral species in the discharge space.