Etching of tungsten with XeF2: An x-ray photoelectron spectroscopy study

I n situ x-ray photoelectron spectroscopy measurements of both W(100) crystals and sputter-deposited tungsten films exposed to a molecular beam of XeF2 with and without an accompanying argon ion beam have yielded the fluorine coverage and the chemical states of the adsorbed fluorine as a function of temperature, exposure, and ion dose. WF, WF2, WF3, and WF4 were found to exist on the tungsten surfaces. Room and elevated temperature exposures of clean tungsten resulted in the surface population of mainly WF species with WF4 observed on nonannealed samples. Ion dose promoted the formation of higher fluorine coordination species from the WF leading to the formation of volatile WF6 and thus resulting in ion-enhanced etching of tungsten.