The mechanism for the growth of tungsten films on silicon substrates with the use of low-pressure chemical-vapor deposition from WF6 was studied with soft-x-ray photoemission by growing films in situ. The dissociative chemisorption of WF6 on Si(111) was found to be complete, even at room temperature. The reaction is self-poisoning at room temperature, however, as the fluorine liberated from WF6 ties up the active Si sites responsible for the dissociation. The mechanism for continued growth of tungsten films at elevated temperature was determined to proceed via Si diffusion through the layer towards the surface. Post-fluorination of these films via XeF2 was employed as a means for illustrating their morphology.