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.