Stress Techniques in Advanced Transistor Architectures: Bulk FinFETs and Implant-Free Quantum Well Transistors

摘要

Novel device architectures offer improved scalability but come often at the price of increased layout sensitivity and a reduced or changed effectiveness of stressors and gate-last integration schemes. This work focuses on stress effects in n-type FinFETs and p-type Si_(1-x)Ge_x-channel pFETs, and relies mainly on TCAD results. It will be shown that on n-FinFETs, tensile stressed Contact Etch-Stop Layers (t-CESL) are less effective than on planar FETs when a gate-first scheme is used. For gate-last schemes, CESL is as effective as on planar FETs, moreover a strong boost is expected when compared to gate-first schemes. Tensile stressed gates are shown to be an effective stressor on gate-first n-FinFETs, but not on gate-last: in the latter case a slight mobility degradation is predicted. For pFETs with strained Si_(1-x)Ge_x-channels like the Implant-Free Quantum Well (IFQW) FET, it will be shown that elastic relaxation during source/drain recess is an important factor that reduces the effectiveness of Si_(1-y)Ge_y source/drain stressors. For scaled technologies, omitting the source/drain recess altogether and opting for a raised source/drain scheme is preferred. In IFQW pFETs, dependence of the drive current on transistor width is an important concern. It will be shown that a Si_(1-y)Ge_y source/drain reduces the layout dependence of IFQW FETs, an effect that is enhanced further when combined with a gate-last integration scheme.