Strained n-Channel Transistors With Silicon Source and Drain Regions and Embedded Silicon/Germanium as Strain-Transfer Structure

摘要

We report the demonstration of 55 nm gate length $L_{G}$ strained n-channel field-effect transistors (n-FETs) having an embedded $ hbox{Si}_{1 - x}hbox{Ge}_{x}$ structure that is beneath the Si channel region and which acts as a strain-transfer structure (STS). The $hbox{Si}_{1 - x}hbox{Ge}_{x}$ STS has lattice interactions with both the silicon source and drain regions and with the overlying Si channel region. This effectively results in a transfer of lateral tensile strain to the Si channel region for electron mobility enhancement. The mechanism of strain transfer is explained. Significant drive current $I_{rm on}$ enhancement of 18% at a fixed off-state leakage $I_{rm off}$ of 100 $ hbox{nA}/muhbox{m}$ is achieved, which is attributed to the strain-induced mobility enhancement. Furthermore, continuous downsizing of transistors leads to higher $I_{rm on}$ enhancement in the strained n-FETs, which is consistent with the increasing transconductance $G_{m}$ improvement when the gate length is reduced.