Gold/Niobium Thin Film Metallizations for GaAs Devices and Circuits

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Gold/Niobium Thin Film Metallizations for GaAs Devices and Circuits Robert Esser1 and Aris Christou2 1 Naval Research Lab Washington, DC 20375 2 Department of Materials Engineering University of Maryland College Park, MD 20742 ABSTRACT A refractory metallization of Au/Nb is proposed for use in first level metallization of GaAs devices. The diffusion and reaction kinetics are explored using sheet resistance measurements, along with X-ray diffraction and Auger electron spectroscopy depth profiling. The interdiffusion coefficients are reported. Diodes are fabricated using Nb/Au metallization and characterized INTRODUCTION As the information age opens, the demand for high performance electronics is increasing exponentially. High-speed communications devices and equipment are at the heart of this expansion. The building block for those devices is the gallium arsenide field effect transistor and other devices. There is a need to develop and expand the materials knowledge base in all aspects to the fabrication of III/V semiconductors. Of particular interest is developing a metallization for gallium arsenide circuits and devices that is compatible with high temperature environments as well as other semiconductor devices. Refractory metals are often used in this application. The metallization must provide adhesion to the GaAs surface, and it must be thermally and chemically stable. It must also be compatible with the other materials encountered in semiconductor processing and packaging. A niobium/gold thin film system for first level metallization on GaAs is proposed and examined. Niobium displays good adhesion to other semiconductor substrates such as Si, SiO2, and diamond. It is corrosion resistant. Niobium has the third lowest resistance of the refractory metals. Finally, the melting point of TM = 2467°C [1] suggests that niobium will have high temperature stability. KINETICS EXPERIMENTS Gold/Niobium thin film samples were prepared using electron beam evaporation deposition on thermally oxidized silicon substrates. The nominal thickness was 300nm Au and 100nm Nb. Sheet resistance measurements, XRD, and AES were used to monitor the kinetics of the films for various anneal times and temperatures. All anneals were performed in a vacuum oven. The initial anneals were isochronal and were performed for 48 hours and at temperatures from 200°C to 500°C in 25°C steps. X-Ray diffraction and sheet resistance measurements were performed on the samples to gather general information on the reaction kinetics of the system. The information acquired from the isochronal anneal experiments allowed appropriate selection of isothermal anneal conditions. Isothermal anneals were performed at 375°C for 8 to 48 hours in 8 hour increments, at 400°C for 12 to 48 hours in 12 hour increments, at 450°C for 1 to 8

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hours in one hour increments, and at 500°C for 0.25 to 1 hour in 0.25 hour increments. The presence of intermetallic formation was evident at all of the isothermal anneal temperatures. Sheet resistance A Veeco Instruments Inc. FPP