Ion enhanced reactive etching of tungsten single crystals and films with XeF2

The etching of W(100) single crystals and sputter-deposited tungsten films by XeF2 has been investigated with and without inert gas ion bombardment. The surface fluorine was measured by Auger electron spectroscopy as a function of pressure (from low 10−8 to 10−4 Torr), and temperature (80–1300 K). The fluorine coverage was found to be near one monolayer at 170 K and decreased to 4% coverage at 1300 K. The pressure dependence showed a maximum coverage for sputter-deposited films at 6×10−6 Torr. Quartz-crystal microbalance measurements of etch rates of sputter-deposited W films under different ion fluxes, XeF2 pressures, ion beam angles, and temperatures have been measured and are consistent with a kinetic model of the etch process. The model, which is damage driven, reproduces well both the surface fluorine concentration and the measured etch rates with and without ion bombardment.