Hydrogenated microcrystalline silicon (μc-Si:H) thin films have been obtained by plasma decomposition of SiF4-H2-He mixtures at low temperature (120 °C). The size of crystalline grain and their volume fraction with respect to the amorphous phase have been found dependent on the r.f. power as evaluated by grazing incidence X-ray diffraction, microRaman and ellipsometry measurements. Chemical and electrical properties change according to the microcrystallinity. Pure and/or highly microcrystalline silicon has been obtained at temperature and r.f. power as low as 120 °C and 15 Watt.