The present invention provides a unique device structure and method that provides
increased transistor performance in integrated bipolar circuit devices. The preferred
embodiment of the present invention provides improved high speed performance by
providing reduced base resistence. The preferred design forms the extrinsic base
by diffusing dopants from a dopant source layer and into the extrinsic base region.
This diffusion of dopants forms at least a portion of the extrinsic base. In particular,
the portion adjacent to the intrinsic base region is formed by diffusion. This
solution avoids the problems caused by traditional solutions that implanted the
extrinsic base. Specifically, by forming at least a portion of the extrinsic base
by diffusion, the problem of damage to base region is minimized. This reduced damage
enhances dopant diffusion into the intrinsic base. Additionally, the formed extrinsic
base can have improved resistence, resulting in an improved maximum frequency for
the bipolar device. Additionally, the extrinsic base can be formed with a self-aligned
manufacturing process that reduces fabrication complexity.
