Process for uniformly electroplating a patterned wafer with electrically isolated devices

This article reports a technique to electroplate a patterned wafer with electrically isolated devices. A seed layer of Ti/Au was deposited on a $SiO2/InP$ substrate. After lithography, 1.2-μm-thick Au was electroplated on the patterned wafer. Then Ti (10 nm) was deposited on the wafer by vacuum evaporation. Ti on the photoresist was lifted off in PRS 2000, while Ti on the plated Au was retained and was used as an etch-protection layer. The wafer was etched in saturated KI solution to remove the unprotected Au of the seed layer. Finally, exposed Ti in the seed layer, as well as on the plated gold surface, was etched with a $HF:HNO3:H2O$ solution. Auger electron spectroscopy analysis of the wafer did not detect any residual Ti on the gold surface or on the $SiO2.$ Electrical probing between two isolated devices exhibited infinite resistance, which indicated that the unwanted seed layer was completely removed. Scanning electron microscopy confirmed that the metal (seed layer plus electroplated Au) on the devices had the desired cross section. This technique has been used to successfully fabricate T electrodes on traveling wave polarization converter devices and bond pads for p-side down bonding of uncooled directly modulated lasers.