TiW nitride thermally stable Schottky contacts to GaAs: Characterization and application to self-aligned gate field-effect transistor fabrication

Abstract

The thin-film properties and temperature stability of titanium–tungsten nitride (TiWNx) Schottky contacts to GaAs have been investigated as a function of x, the atomic percent of nitrogen in the film. A Ti30W70 composite target was reactively sputtered onto GaAs substrates in nitrogen using argon as the diluent gas. The partial pressure of nitrogen was varied from 0% to 100%. This resulted in x varying from 0 to 27 at. %; however, the films contained a constant Ti–W atomic ratio of 0.18, regardless of x. The film stress and resistivity were well-behaved and reproducible functions of x. Schottky contact characteristics were measured after annealing at several temperatures. After an 810 °C furnace anneal, the ideality factor (n) and barrier height (φB) displayed well-defined, broad extrema as a function of x. Both the best average values of n and φB and their smallest standard deviations occurred for x=10 at. % of nitrogen. Thus the most stable and uniform TiWNx–GaAs Schottky contact was obtained from TiWN10. TiWN10 has been used as the refractory metal in ITT’s self-aligned gate digital GaAs integrated circuit process to obtain gate delays as low as 19 ps at a power-delay product per gate of 19 fJ.