SiGe HBTs in 90nm BiCMOS Technology Demonstrating fT/fMAX 285GHz/475GHz through Simultaneous Reduction of Base Resistance and Extrinsic Collector Capacitance

Development of SiGe HBTs in BiCMOS technology with both high f_T and f_MAX faces significant challenges. To increase f_T, thinning the base and collector thickness is generally the first step to reduce the carrier transit times, but increases the base resistance and the collector-base capacitance, which impacts f_MAX negatively. Increasing collector doping is also often employed to increase f_T, but again increases collector-base capacitance, which drives f_MAX down. To overcome these limits, a series of process and device structure innovations have been made in recent years. Millisecond anneal techniques, low temperature silicide and low temperature contact processes are shown to be effective in reducing the base resistance. A novel approach to reduce the extrinsic collector-base capacitance is developed, concurrent to the reduction of base resistance, without affecting the manufacturability and integration with CMOS. The simultaneous reduction of both base resistance and collector capacitance enables high performance SiGe HBT devices in 90nm BiCMOS Technology with operating frequencies of 285/475GHz f_T/f_MAX.