Silicon and its related alloys deposited by catalytic chemical vapor deposition (Cat-CVD), takes place upon thermo-catalytic decomposition of the reactant gases, i.e. silane (SiH ₄ ) and hydrogen (H ₂ ), at the surface of a hot filament. Tantalum (Ta) has been used as catalyst which resulted with better controllability from amorphous to crystalline-phase transition. Process for depositing hydrogenated nanocrystalline silicon (nc-Si:H) embedded in hydrogenated amorphous silicon oxide (a-Si:O:H) matrix, as a function of both, Ta-catalyst, and substrate-temperatures are reported. The deposited samples were characterized by X-ray diffraction and micro-Raman spectroscopy. Crystalline sizes were determined using a Sherrer's formula and Raman spectra for its size-related tendencies. As preliminary results, the range of crystallite formation starts at the catalyst temperature of 1700 ~ 1750°C.