Characterization of ion beam deposited refractory WNx films on GaAs

Abstract

An ion beam assisted deposition (IBAD) technique has been explored for the growth of refractory W and WNx films on n-GaAs as candidate gate materials for GaAs integrated circuits. Tungsten was deposited by Ar-ion beam sputtering, and simultaneously low energy nitrogen ions were introduced directly onto the GaAs substrate, using a Kaufman-type ion gun, for nitridation of the W deposits. The deposited films were characterized by electrical resistivity measurements, x-ray diffraction, and x-ray photoelectron spectroscopy analyses. The results showed that the composition and the electrical resistivity could be controlled with the nitrogen-ion dose. Thermal stability of the WNx /GaAs interfaces was also investigated by examining Schottky diode characteristics and microstructures. The WNx contacts investigated in the composition range from x=0 to 0.47 were electrically stable up to 850 °C and showed remarkable enhancements in the Schottky barrier height through high temperature annealing. Such annealing induced barrier enhancements were attributed to the dissociation of a thin native oxide layer which was observed between the as-grown film and the GaAs substrate. Comparisons of our results with previous works on conventional sputter-deposited WNx films led to a conclusion that the IBAD technique generates much less ion damage in the substrate and the film, and therefore, is promising for growing refractory compounds on GaAs.