In order to make polycrystalline silicon films at low temperature, hydrogen radicals have been utilized in the rf sputtering process. The films were prepared in gas mixtures containing argon and hydrogen. They were investigated by reflection electron diffraction and Raman spectroscopy. Furthermore, optical emission spectroscopy was employed to study the quantity of hydrogen radicals in the plasma, and the plasma potential was measured to decide the substrate bias voltage under realistic plasma condition for the deposition of silicon films. The results showed that polycrystalline silicon films were grown even at the substrate temperature of less than 200°C. It was also found from the optical emission spectroscopy that there existed atomic hydrogen radicals with high energy of about 10eV. They are expected to be able to restructure the silicon atoms on the substrate. Thus the crystallization at such low temperature is considered to be mainly due to hydrogen radicals in the plasma.