Magnetron sputtered layers of TiN often show high intrinsic stresses. In addition to the thermal stresses due to the difference in the thermal expansion coefficients of the layer and the substrate, the incorporation of N and Ar atoms in lattice voids contributes essentially to the intrinsic stresses. We used Fe-57 Mossbauer spectroscopy on (Ti,Fe)N model layers to obtain direct information on the occupation of tetrahedral voids in the TiN (B1) structure by excess nitrogen and its diffusion during heat treatment. The results of this investigation are supported by X-ray stress analysis.