Characterization of reactively sputtered WN<i>x</i> film as a gate metal for self-alignment GaAs metal–semiconductor field effect transistors

Abstract

Properties of reactively sputtered WNx films on a GaAs substrate have been investigated by electrical and physical analyses. WNx films were deposited from a pure W target by using three types of sputtering systems: (1) Magnetron sputtering system equipped with rf and dc mode; (2) S-gun sputtering system; (3) rf diode sputtering system. The composition of WNx films was easily and reproducibly controlled by changing the N2 content in Ar–N2 mixed ambient gas. The WNx–GaAs system was both electrically and metallurgically stable even after high-temperature annealing of up to 800 °C. The Schottky barrier height to n-type GaAs was more than 0.8 V, which is the highest value obtained so far among any other refractory metals. Self-aligned GaAs MESFET’s were successfully fabricated using a WNx gate. The transconductance was typically 150 mS/mm for 1.5 μm gate length.