The drive currents improvement of FDSOI MOSFETs with undoped Si epitaxial channel and elevated source/drain structure

Fully-depleted silicon-on-insulator (FDSOI) MOSFETs are very attractive for low-voltage applications due to ideal subthreshold slope, short channel effect (SCE) immunity and reduced junction capacitance compared to bulk silicon MOSFETs. However, the channel mobility degradation due to higher channel doping for threshold voltage (V/sub th/) adjustment and higher source-drain resistance (R/sub sd/) are critical issues for FDSOI MOSFETs with top silicon thickness of less than 50 nm (Wong et al, 1998; Su et al, 1993). It has been reported that an undoped Si epitaxial channel (UEC) of the bulk MOSFETs and elevated source/drain (E-S/D) structures of the FDSOI MOSFETs are very effective for improvement of channel mobility and a low R/sub sd/, respectively (Yan et al, 1992; Kircher et al., 1992; Cao et al., 1997). In this paper, we propose the implementation of UEC for only nMOSFETs and the E-S/D structure for both n- and pMOSFETs to improve drive currents.