AN INVESTIGATION OF NONIDEAL BASE CURRENTS IN ADVANCED SELF-ALIGNED ETCHED-POLYSILICON EMITTER BIPOLAR-TRANSISTORS

We report a physical analysis of nonideal base currents in advanced self-aligned "etched-polysilicon" emitter bipolar transistors. By studying the dependence of the leakage currents on bias voltage, temperature, device geometry, and process parameters, we have been able to identify the nature of these currents and isolate the main critical fabrication steps. The abnormal base current at forward bias is found to be a generation-recombination current involving defects along the spacer oxides. These defects also control the reverse base characteristics through a trap-assisted tunneling current mechanism. A simple modification of the spacer structure is demonstrated to result in high-performance emitter/base junction properties, showing promise for the future of this CMOS-compatible bipolar transistor structure.