Annealing effects on the structural and electrical properties of sputtered tungsten thin films

We report on the structural and electrical characterization of sputter-deposited tungsten (W) films, having thicknesses between 1.5 and 100 nm, before and after annealing in the temperature range between 200 and 800 °C. In the as-deposited the β-W phase prevails, for all the thicknesses studied. A β-W to α-W transition occurs upon annealing at a temperature that depends on film thickness and it is accompanied by a corresponding resistivity drop. Films with thickness lower or equal to 8 nm are composed predominately of β-W phase after annealing at 300 °C, while the α-W phase prevails after annealing at 450 °C. Films with thickness higher or equal to 10 nm remain at the β-W phase after annealing at 200 °C, but the α-W phase prevails after annealing at 300 °C. The resistivity behavior as a function of film thickness and annealing temperature are discussed. The minimum film resistivity is obtained for the 100 nm thick film after annealing at 800 °C and it is 17.0 μΩ ⋅cm.