Investigation of reactively sputtered tungsten nitride as high temperature stable Schottky contacts to GaAs

Abstract

Tungsten nitride (WNx) was deposited onto 2‐in.‐GaAs substrates by reactively sputtering a tungsten target in a N2/Ar plasma. The films were deposited at a power density of 5.4 W/cm2 and total pressure of 1.33 Pa (10 mTorr). The partial pressure of N in Ar was varied from 0 to 0.5. Auger analysis of the WNx films indicated the nitrogen content varied between 0 and 20 at. %. The films were also found to contain between 0.5 and 2 at. % of oxygen. Resistivity measurements of the as‐deposited films indicate a linear relationship between film resistivity and atomic percent of nitrogen in the film. Stress measurements were erratic and showed no correlation with atomic percent of N in the film. The average interfacial stress was 2.4 GPa, with a standard deviation of 0.9 GPa. Schottky contacts were patterned on ion‐implanted 2‐in.‐GaAs wafers by reactive ion etching (RIE) the WNx film in a CF4/O2 plasma. The diodes were then capped with chemical vapor deposited (CVD) SiO2 and annealed at temperatures up to 850 °C. The temperature stability of WNx films is maximized at 4 at. % of nitrogen, and the postanneal (810 °C for 20 min) ideality factor (n) and barrier height (φB) for WN0.04 films are excellent: n=1.18, σn=0.008, φB=0.727 eV, and σφB=0.005 eV. State‐of‐the‐art self‐aligned gate field‐effect transistors (FET’s) were fabricated using WN0.04 as the gate metallization.