Nonuniform Mobility-Enhancement Techniques and Their Impact on Device Performance

Mobility enhancement by CESL strain in short-channel ultrathin SOI MOSFETs

“…By contrast, compressive strain degrades the electron mobility, as reported earlier [11,12], leading to a strong I on degradation in c-CESL NMOS devices (Fig. 6).…”

“…In sub-100 nm MOSFETs, the hole mobility decreases slowly recovering the long-channel value. We have noticed for N-channels that the stress is mainly localized at gate edges (stress pocket) [11,16]. Consequently, the impact of strain is not visible in long channels, but it becomes significant as the pockets get closer to each-other in shorter channels.…”

“…However a stronger mobility reduction is observed for c-CESL compared to t-CESL. This indicates that tensile CESL enhances the electron mobility in short-channels, suggesting that the strain is maximal at the channel extremities (''stress pocket" effect) [11].…”

“…In order to reach the equilibrium state, this layer should be relaxed so that the strain is transferred into the channel. Because of the layer topology, the stress induced in the channel is not uniform [11,19]. In the middle of channel, tensile stress comes from the CESL deposited on the gate top.…”

“…The finite element method has been used to model the mechanical stress propagation under the gate into the channel [3,11]. It is demonstrated that there are two components playing an important role in the mobility enhancement: the stress along the channel, r xx , and the stress perpendicular to the channel, r zz .…”