Strained n-channel transistors with silicon source and drain regions and embedded silicon/germanium as strain-transfer structure

We report the demonstration of 55 nm gate length L-G strained n-channel field-effect transistors (n-FETs) having an embedded Si1-xGex structure that is beneath the Si channel region and which acts as a strain-transfer structure (STS). The Si1-xGex 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-on enhancement of 18% at a fixed off-state leakage I-off of 100 nA/mu m is achieved, which is attributed to the strain-induced mobility enhancement. Furthermore, continuous downsizing of transistors leads to higher I-on enhancement in the strained n-FETs, which is consistent with the increasing transconductance G(m) improvement when the gate length is reduced.