Impact of parasitic resistance and silicon layer thickness scaling for strained-silicon MOSFETs on relaxed Si1-xGex virtual substrate

This paper discusses the root causes of the fact that only slight performance improvement of MOSFET with strained-Si substrate has been achieved in short channel region (L < 100 nm). The performance improvement in short channel region is found to deteriorate mainly due to the parasitic resistance increase and tensile stress relaxation in the strained-Si layer. In regard to the parasitic resistance and the stress relaxation in small device geometry, the scaling impacts of strained-Si layer thickness (T_ss) are investigated from the viewpoint of both DC and AC characteristics. Within this work, T_ss reduction down to 5 nm improves the current drive (I_d) of nFET up to 6 % (L < 50 nm) compared with conventional bulk nFET. Propagation delay time (τ_pd) improvement in CMOS inverter is also observed to be more than 15 %. Finally, the impurity profile optimization is proposed to improve MOSFET performance toward the 45 nm node CMOS era.