Identification of a corner tunneling current component in advanced CMOS-compatible bipolar transistors

A corner tunneling current component in the reverse-biased emitter-base junction of advanced CMOS compatible polysilicon self-aligned bipolar transistors has been identified by measuring base current as a function of temperature, bias voltage, and emitter shape. This current is found to be an excess tunneling current caused by an increase in defect density in the corners of the emitter and gives rise to three-dimensional effects in small-geometry devices. The devices used for this study were selected from batches aimed at optimizing the emitter-base system. For this reason, the starting material was n-type (~10¹⁶ cm^-3) and provided the collector regions of the transistors. The intrinsic base and lightly doped extrinsic base regions were both implanted at 30 keV to a dose of 1×10¹³ cm^-2. The activation anneal was performed at 1060°C for 20 s in a rapid thermal annealer. Under such conditions, the emitter-base junction is located about 600 Å below the polysilicon-substrate interface