Bipolar Junction Transistor Fin Structure for High Gain Miniaturization

The patent transitions from a planar BJT structure to a three-dimensional structure with fins extending vertically from the substrate. The emitter, base, and collector regions are formed as fins with varying heights, creating a vertical current path that increases the effective active area without proportionally increasing the footprint area. This dimensional change enables higher current gain while maintaining compact device area.

The BJT structure is segmented into multiple fins (emitter fins, base fins, collector fins) that are distributed across the device area. Each fin acts as an independent current path, and the collective effect of multiple fins increases the total current handling capability and gain. The segmentation also allows for optimized doping profiles and contact configurations in each region.

The patent employs a universal fin-based fabrication process that can form both FinFETs and BJTs using the same sequence of steps. The method uses selective epitaxial growth to create fins of different heights in different regions, and selective doping to create the appropriate junctions for either FinFET or BJT structures. This multi-functional approach allows concurrent formation of both device types without requiring separate process modules, thereby reducing integration complexity while achieving miniaturization.

The fabrication process applies local quality variations through selective epitaxial growth and selective doping. By controlling the growth conditions and dopant introduction at specific locations, the same process sequence can create high fins for BJTs in one region and lower fins for FinFETs in another region. This local differentiation enables both device types to be formed with optimized characteristics using a unified process flow.