ELECTRICAL AND MICROSTRUCTURAL INVESTIGATION OF POLYSILICON EMITTER CONTACTS FOR HIGH-PERFORMANCE BIPOLAR VLSI

Key electrical characteristics of polysilicon emitter contacts in bipolar transistors, such as contact resistance and recombination velocity, are sensitive to the microstructure of the polysilicon/single-crystal silicon interface. We correlated the microstructural and electrical characteristics of this interface by performing cross-sectional transmission electron microscopy (XTEM) on actual transistors on the same chip where ring-oscillator speeds were measured. The base current and emitter resistance of the fastest devices approached values typical of single-crystal silicon emitters. Interpretation of these electrical data and of the SIMS impurity profile indicates that significant restructuring of the polysilicon/single-crystal interface had taken place. This conclusion was confirmed by the XTEM results.