Gold-Free Fully Cu-Metallized InGaP/GaAs Heterojunction Bipolar Transistor

A gold-free, fully Cu-metallized InGaP/GaAs heterojunction bipolar transistor using platinum as the diffusion barrier has been successfully fabricated. The HBT uses Pd/Ge and Pt/Ti/Pt/Cu for n-type and p+-type ohmic contacts, respectively, and Ti/Pt/Cu for interconnect metals with platinum as the diffusion barrier. The Ti/Pt/Cu structure was stable during annealing up to 350°C judging from the X-ray diffraction (XRD) data and sheet resistance. A current-accelerated stress test was conducted on the device with a current density J C=140 kA/cm2 for 24 h, and the current gain showed no degradation. The devices were also thermally annealed at 250°C for 24 h and showed little change. We have successfully demonstrated that an Au-free, fully Cu-metallized HBT can be realized using Pt as the diffusion barrier and Pd/Ge and Pt/Ti/Pt/Cu as the ohmic contacts.