(Invited) Activation and Deactivation in Ultra-Highly Doped n-Type Epitaxy for nMOS Applications

Since ultra-highly doped, highly tensile strained Si:P epitaxy was reported about 10 years ago, it quickly replaced Si:CP and become key processes for advanced nodes. With greater than 3E21 doping level, these films exhibit significant tensile stress and low resistivity, both enhanced the nMOS performance. As the technology scales, contact resistance is becoming a major factor for device performance, even higher activation level is desired. In this paper, the mechanisms for high doping level and tensile strain are briefly reviewed and discussed. Despite epitaxially grown, these films showed similar thermal equilibrium behavior as implant-annealed samples and could be predicted with well established model. Diffusion and strain analysis shed some lights on the processes involved in the carrier activation and deactivation. Formation of group V - vacancy complex, V4V, or Si3P4-like, structure is key to understand the behavior, especially dopant diffusion and interaction with vacancy. Unlike Si:As, Si:P showed different behavior with different anneal and deposition approaches that might indicating a much more complicate deactivation path. And strong surface influence of P diffusion might present a challenge for contact engineering.