Abstract
The adhesion strength and surface morphology of commonly used n-and p-type ohmic contacts and pad metallization schemes for GaAs were investigated. GeNiAu, GePdAu, BeAu, and TiPtAu, being studied as potential ohmic contacts for internal optoelectronic device applications had quantatative measurements made using wire bond pull testing to determine adhesion. Bond pad metals deposited as evaporated TiAu, TiPtAu and 2–5 μm thick electroplated Au deposited on both semi-insulating GaAs and on Si 3N 4/GaAs were evaluated independently from the ohmic contact metals. In all the samples, we observed a strong correlation between surface treatment, surface morphology, wire bondability, and bond strength. Very high bond strenghts (pull test average values above 6.5 g force with 25 μm diameter gold wire), were obtained for n-type, p-type, and bond pad metals. Average values of 8.0 g force were achieved with a two-step GeAu/NiAu/TiPtAu metallization scheme, while the one-step deposition yielded poorer values. Adhesion was also monitored after aging at 250 °C in air for four different times up to 60 h by means of wire bond pull testing, with little degradation occurring.
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