Self-diffusion of silicon in magnetron sputtered silicon carbide films deposited on different substrates (crystalline silicon and glassy carbon) is investigated. Since crystallization of amorphous silicon carbide films strongly depends on the substrate, the diffusivity of silicon is expected to depend on the substrate as well. Isotope hetero-structures and secondary ion mass spectrometry were used for analysis. For amorphous samples an upper limit of the diffusivity of 1 x 10(-21) m(2)/S is derived at 1100 C degrees. For crystallized films diffusivities between 1350 degrees C and 1600 degrees C are found to be not significantly different for the two types of substrates. For samples deposited on glassy carbon substrates an activation enthalpy Delta H(D) = (8.7 +/- 0.9) eV was found for the self-diffusion of Si. The consequences of our findings for crystallization are discussed. (C) 2009 Elsevier B.V. All rights reserved.