Sputtered full-wafer backside metallization for n-type InP: effect of temperature annealing

A full-wafer backside n-ohmic metallization scheme for InP is reported. The contact is formed by a single-step, all-sputter process and has been used successfully in three-inch InP opto-electronic device manufacturing. The metallization is based on the combination of a nickel-germanium-gold ohmic contact followed by a titanium-titanium nitride-titanium-gold metal stack. The titanium nitride layer acts as a barrier to grain boundary diffusion of indium and other material from the substrate to the surface of the top gold layer. The top gold is required for a gold-tin solder die bond process. The sputter process provides better than 5% cross-wafer and wafer-to-wafer thickness uniformity and a contact resistance of 2.5-8.3×10−5 Ω cm2. We report the fabrication process for this metal contact and the results of a full physical characterization by transmission electron microscopy, Auger survey and depth profile analysis and X-ray analysis.