Si-C-N films of maximum 65 at.% of Si and maximum 40 at.% of N were prepared by reactive magnetron sputtering and their fine structure was investigated by high-resolution transmission electron microscopy. For compositions, where C-C and C-N bonds prevail, the films had anisotropic structure on the atomic scale, composed of curved graphitic layers, aligned parallel to the substrate normal. An isotropic structure was detected in the middle of the compositional triangle. On a larger scale, a columnar morphology, aligned in the direction of the deposition flux was formed in films containing more than 15 at.% of Si. Singular or simultaneous appearance of the above structures depended on film composition. (C) 2003 Elsevier B.V. All rights reserved.