The structure and stability of thin tungsten films prepared by radio frequency magnetron sputter deposition have been studied by x-ray diffraction and x-ray photoelectron spectroscopy. The structure of these films has been found to systematically evolve from the metastable A15 β-W phase to the equilibrium A2 α-W phase with decreasing oxygen impurity concentration. Within the β-W phase a decrease in the concentration of incorporated oxygen results in a monotonic decrease in the lattice parameter of the unit cell until the β-W phase eventually becomes unstable, and the α-W phase is formed.
Thin W films have been deposited by dual ion beam sputtering using a sputtering ion gun and an assisting ion gun. The crystal structure of the deposited films was strongly dependent on the energy of the assisting ions, substrate temperature, and the thickness of the film. All these variables were found to affect the oxygen concentration of the film which in turn, determines whether the film will have an A-2 body-centered-cubic α-W phase, an A-15 face-centered-cubic-like β-W phase, or a mixture of the two. Assisting ions and substrate temperature both increase the diffusivities of W and O resulting in a decreased oxygen concentration in the film which makes the α-W phase more stable. Films deposited at low substrate temperatures and without any ion bombardment show only the β-W phase.
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