Overview

The scaling of silicon-based semiconductor devices continues to drive increased performance and reduced cost for many applications including wireless communications. Strained-SiGe/Si heterostructures and superlattices are essential for many advanced Si-based devices. In many ways, the ability to fabricate smaller devices controls the scaling process. While process modelling of silicon devices is well advanced, modelling of SiGe technology is still in its formative stage and many issues, specifically associated with this new material that affect passivation, oxidation, dopant diffusion and thermal stability, still need to be resolved. In particular, the ability to predict exact amounts of dopant diffusion is critical.

Diffusion of boron in SiGe is of great interest in view of obtaining boron-doped thin strained-SiGe layers resulting in a very good base layer in SiGe HBTs. One critical area is that of dopant profiles - in controlling the effect basewidth of HBTs that is, the ability to place a specific amount of impurity in one region of a device, and keep it there during the entire fabrication process.

In order to understand how to model dopant diffusion in any semiconductor, it is first important to understand the physical mechanisms governing dopant motion, which are dependent upon both the properties of the dopant and of the semiconductor. Dopants are known to diffuse through single crystal semiconductors via mediation with point defects. For a substitutional dopant to become mobile and diffuse through an undamaged silicon crystal, it must interact with a defect, where both defect and dopant may be charged. The...