Demonstration of the importance of the oxide breakup in polysilicon-contacted-emitter modeling

The authors demonstrate theoretically a very rapid increase in the ideal base current of poly-contacted-emitter bipolar transistors with the fraction of the interface which has realigned with the single-crystalline substrate. Polysilicon contacts have played an integral role in reducing device dimensions and increasing the gain of bipolar transistors for some time. However, the mechanism by which the gain ( beta ) enhancement occurs is still not fully understood. Simulations were performed for a device with a transparent emitter using the simulation tool DAP2D (device analysis program in two dimensions) to model the effect on the base current of the breaking up of the oxide layer between the poly contact and the emitter. The simulations show that for poly contacts typical of VLSI applications, the modeled dependence of the base current on the percentage of the oxide interface which is broken up correlates well with experimental results.>