Stability of Schottky barriers at high temperatures for use in GaAs MESFET technology

The stability of Schottky barrier gates in GaAs MESFETS has been investigated to allow device processing at elevated temperatures. The incorporation of a Pt diffusion barrier into the TiAu structure gives stability of electrical characteristics up to 350°C and a Ti-W-Au contact is stable up to 400°C. To achieve higher temperature stability for use in a self aligned gate (SAG) technology, a more stable Schottky barrier material such as a TiW (30 at % Ti) alloy has been used. This has been found to be unreliable above 750°C and it has been found necessary to use a tungsten silicide contact W1.6Si (37 at % Si) to achieve reproducible Schottky contacts at the temperature used for ion implantation activation (800°C). SAGFETs have been fabricated using W1.6Si and initial results indicate good yields (91%), high gm (190 mS/mm) and good uniformity (standard deviation = 6.8% for 293 devices).