Effect of nitridation on the electrical properties of W:Ti resistors

The electrical properties of tungsten-titanium (W:Ti) thin film resistors sputtered in an argon-nitrogen atmosphere were investigated. The resistivity ρ and the thermal coefficient of resistivity α were calculated as a function of film thickness and nitrogen content. A bulk resistivity of 70±4 μΩ-cm and the mean free path λ_o), of 0.8±0.1 μm were obtained for samples sputtered without nitrogen. The authors believe this to be the first report for the value of the λ_o in sputtered W:Ti. By appropriately controlling the nitrogen content during sputtering, it is possible to vary the value of α from positive to negative. It was found that α decreases with the nitrogen content and is zero at 0.5% N₂. This added degree of freedom in controlling α allows the integrated circuit designer to compensate the thermal effects within a circuit by customizing the resistor parameters without significant layout modifications.