It has been known that thermal stability of the silicide/silicon system can be improved by fluorine incorporation. Two mechanisms have been proposed - the fluorine buffer model and the grain growth retardation model. This communication examines the validity of these two mechanisms. Fluorine ions are introduced into the PtSi/Si structure by implantation at various energies and to various dosages. If the fluorine ions are confined in the silicide layer, the grain growth is retarded, however, no improvement of the thermal stability can be obtained. On the other hand, if most of the implanted fluorine ions are located near the PtSi/Si interface, the grains of the fluorinated silicide film can grow to be larger than those of the unfluorinated silicide film without becoming discontinuous to the film. It is thus concluded that the fluorine accumulation at the interface, i.e., the fluorine buffer model, plays the dominant role on the thermal stability of the fluorinated PtSi/Si structure.