Solid-state reactions between Ni1-uPtu (0< u < 0.15 at.%) and Si0.7Ge0.3 after rapid thermal annealing at 280 to 700 degrees C were studied. Numerous physical and chemical characterizations such as sheet resistance analysis, scanning electron microscopy, transmission electron microscopy, Xray diffraction measurement, and atom probe tomography were used to determine the formation and morphological degradation mechanisms of the pure Ni-based germanosilicide. In particular, atom probe tomography was used to quantitatively determine the element distribution in 3D and at the atomic scale. Similar mechanisms for the degradation were found for the Ni mono germanosilicide with and without Pt and led to Ge rich Si1-xGex regions that are etched away by the selective etch. These mechanisms, Ge out-diffusion and agglomeration, have a combined effect on the germanosilicide degradation and occurs through Ge and Ni diffusion, respectively. Adding Pt increases the thermal stability of the layer owing to changes in the phase sequence and texture and strong binding with Ge atoms. Several models are developed to explain the different steps of the film morphological degradation. The thermodynamics description of the equilibrium in the quaternary Ni-Pt-Si-Ge system allows us to rule out a pure thermodynamics explanation for the morphological stabilization due to Pt addition. Published by AIP Publishing.