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Abstract
Amorphous Ta(,x)Cu(,1-x) alloy films are prepared by co-sputtering of pure Ta and pure Cu targets onto substrates held on a rotating sample holder table. The most thermally-stable alloy films in this alloy system are correlated with measured maximum negative temperature coefficients of resistance as a function of alloy composition.
To investigate the possible application of these materials as diffusion barriers for the Au-GaAs system, vacuum annealing and infrared rapid thermal annealing are carried out over a wide temperature range. Resistivity changes, X-ray diffraction (XRD), Auger electron spectroscopy (AES) with Ar('+) ion milling, and Rutherford backscattering spectroscopy (RBS) measurements are performed to find the chemical and metallurgical characteristics of these materials.
For high x values, the reaction temperature for Ta(,x)Cu(,1-x) with GaAs lies between 500 and 700(DEGREES)C. For Au in contact with Ta(,x)Cu(,1-x) the Ta(,x)Cu(,1-x)/Au reaction occurs at about 600(DEGREES)C. Amorphous Ta(,93)Cu(,7) exhibits different interdiffusional characteristics with surrounding elements (namely a uniform mixing) from Ta(,80)Cu(,20) which shows a phase separation. A possible mechanism for uniform mixing is discussed in terms of composition-dependent heats of formation.
Electrical characteristics of interfaces between amorphous Ta(,x)Cu(,1-x) alloy films and n-type GaAs substrates are studied using current-voltage and capacitance-voltage measurements and taking into account the effects due to series resistances and deep traps. Amorphous-Ta(,x)Cu(,1-x)/GaAs Schottky diodes are electrically stable up to annealing temperatures of 400(DEGREES)C, but are shorted after heat treatments from 500(DEGREES)C to 600(DEGREES)C.
