Silicon carbide films were deposited onto crystalline silicon substrates from a sintered SiC target using a RF magnetron sputtering system. The influence of substrate temperature (150-500 degreesC) and polarization (0-100 V), Ar pressure (0.05-4 Pa) and RF power (50-400 W) on the mechanical properties (hardness and stress) of the resulting films was studied. Films with hardness values larger than 40 GPa could be obtained, provided that Si and C sputtered atoms can reach the surface of the growing film with sufficient high energy and low deposition rates in order to guarantee a high surface mobility. At high deposition rates the surface mobility is limited, but the increase in substrate temperature can contribute to stress relief. Upon thermal annealing at high temperatures, completely stress-free films could be produced without affecting the material hardness. This effect is accompanied by an increased structural and chemical order. Substrate bias was found not to be beneficial to the film properties, since it leads to substantial argon incorporation into the material.