Effect of Nitridation on the Electrical Properties of Tungsten-Titanium Resistors

The electrical properties of tungsten-titanium (W:Ti) thin film resistors sputtered in an argon-nitrogen atmosphere were investigated. The resistivity rho and the thermal coefficient of resistivity alpha were calculated as a function of film thickness and N content. A bulk resistivity of 70 plus/minus 4 mu Omega -cm and the mean free path lambda sub o ), of 0.8 plus/minus 0.1 mu m were obtained for samples sputtered without N. The authors believe this to be the first report for the value of the lambda sub o in sputtered W:Ti. By appropriately controlling the N content during sputtering, it is possible to vary the value of alpha from positive to neagative. It was found that alpha decreases with the N content and is zero at 0.5% N sub 2 . This added degree of freedom in controlling alpha allows the integrated circuit designer to compensate the thermal effects within a circuit by customizing the resistor parameters without significant layout modificaations.