Boron-doped emitters for high-performance vertical pnp transistors

The fabrication of pnp transistors is described, and their characteristics are studied as a function of the emitter process. Ideal polysilicon-emitter and LTE-emitter devices have been obtained, and the temperature dependences of the base saturation and collector saturation permit an understanding of the differences in their characteristics. For the polysilicon emitter, it appears that relatively low annealing temperatures are adequate to achieve ideal device characteristics and low emitter resistance. This will allow maximum flexibility for the integration of the vertical pnp into a complementary bipolar process and shallower emitter-base junctions (for the poly-emitter devices) than attempted here. The feasibility of the epitaxial emitter has also been demonstrated in a double-polysilicon self-aligned transistor, offering the possibility of achieving a very thin, ion-implanted base. Some performance tradeoffs may have to be made to improve the gain of the device.<
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