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Solid-State Electronics
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Electrical and thermal stability of AuGeNi ohmic contacts to GaAs fabricated with in situ RF sputter cleaning

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Abstract

In situ RF sputter cleaning of the GaAs surface before the AuGeNi deposition gave low contact resistance Rc {reversed tilde equals} 0.1 Ω-mm. When the contacts were annealed at 400°C for 57 hours, Rc ≤ 0.6 Ω-mm was obtained. This is still an acceptable value for 1 μm gate MESFET process. With low sputtering voltages or short sputtering times, contact resistance was large and non-uniform. Normally a short alloying time of 2 min at 440°C is used for ohmic contact formation. For the process described here, alloying times as long as 15 min at 430°C gave low contact resistance Rc {reversed tilde equals} 0.2 Ω-mm. When the AuGe films were deposited from two separate sources of Au and Ge ("layered" process) low contact resistances Rc {reversed tilde equals} 0.2 Ω-mm were obtained. However, this "layered" process did not show the same kind of uniformity and low contact resistance that was obtained when the AuGe film was deposited from a single "eutectic" source. © 1986.

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Solid-State Electronics

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