Design and fabrication of high-performance indium gallium phosphide/gallium arsenide heterojunction bipolar transistors

The heterojunction bipolar transistor (HBT) is a device whose time has come. The high gains, linearity, power efficiencies, current handling capabilities, and speeds available with HBT technology make this device attractive for a wide variety of applications from wireless communications to high-speed analog-to-digital converters. Companies across the United States are investing millions of dollars in developing HBT products and manufacturing capabilities.;A manufacturable fabrication process for state-of-the-art InGaP/GaAs HBTs has been established. The process features nonalloyed emitter metal, self-aligned emitter and collector etches, self-aligned base metal, mesa isolation, polyimide planarization, and an air bridge metallization. A citric acid-based, selective GaAs etch has been developed for use in the self-aligned emitter etch/base metallization process. The etch has demonstrated excellent control and the uniformity necessary for high-yield wafer processing. The citric acid etch has also been used to implement the selective collector etch which minimizes the base-collector parasitic capacitance. An evaporated gold air bridge process has been developed and replaces a plated gold process, thereby improving yield and quality.;State-of-the-art InGaP/GaAs HBTs have been developed. A baseline device structure and the standard fabrication process have consistently produced devices with a common-emitter current gain ;Presently, the leading HBT material technology is AlGaAs/GaAs. However, the InGaP/GaAs material system offers significant advantages in device performance and manufacturability. The band alignment of InGaP/GaAs improves device performance and the absence of aluminum in the emitter improves noise characteristics and long-term reliability. In addition, the availability of highly selective etch chemistries makes it easier to manufacture InGaP/GaAs HBTs. This work demonstrates the manufacturability and performance potential of InGaP/GaAs HBTs.