High-temperature stable W/GaAs interface and application to metal--semiconductor field-effect transistors and digital circuits

The thermal stability of the physical, chemical, and electrical properties of W thin films sputter deposited on GaAs were investigated. A variety of characterization methods, including thin film stress analysis, Auger analysis, Rutherford backscattering spectrometry (RBS) analysis, and Schottky barrier measurements showed that the W/GaAs interface remains stable after high-temperature furnace annealing at 900 0C for 15 min or rapid-lamp annealing at 1000 0C for 11 s. Some refractory metal compounds were also investigated, including, WSi, WN/sub x/, and TaSi/sub x/. Pure W films produced the best Schottky diode characteristics. The average Schottky barrier height was 0.70 +- 0.009 V across a 2-in wafer after furnace annealing at 800 0C/15 min. Pure W self-aligned gate (SAG) metal-semiconductor field-effect transistors (MESFET) and digital circuits were also fabricated. Transconductances as high as 300 mS/mm (L/sub g/ = 1.0 μm) were measured for enhancement mode SAG MESFET's. Circuits were fabricated with SAG MESFET enhancement-resistor mode logic using pure W gates, including ring oscillators, with gate delay as low as 25 ps and divide-by-eight circuits that functioned at a frequency >1 GHz