Characterization of Sputtered Gold-Tungsten and Gold-Molybdenum Metallizations for Microwave Power Transistors

The stability and hence reliability of sputtered gold-tungsten and gold-molybdenum films has been determined as a function of anneal temperature up to 650°c. Isothermal and isochronal resistivity experiments have yielded an activation energy for particle growth in 3000 Å gold films of 0.4 eV below 200oc and 0.7 eV about 200oc. The activation energy for the refractory layer was calculated to be 1.8 eV from particle size measurements. Annealing the films up to 500oc for 24 h resulted in a decrease of internal stress in gold from 2.5 x 109 dyn/cm2 to 0.2 x 109 dyn/cm2. Similar decreases in internal stress were observed for tungsten and molybdenum. The observed results are discussed in terms of microstructural changes.