Strained-SiGe complementary MOSFETs adopting different thicknesses of silicon cap layers for low power and high performance applications

Abstract

We introduce a strained-SiGe technology adopting different thicknesses of Si cap layers towards low power and high performance CMOS applications. By simply adopting 3 and 7 nm thick Si-cap layers in n-channel and p-channel MOSFETs, respectively, the transconductances and driving currents of both devices were enhanced by 7 to 37% and 6 to 72%. These improvements seemed responsible for the formation of a lightly doped retrograde high-electron-mobility Si surface channel in nMOSFETs and a compressively strained high-hole-mobility Si0.8Ge0.2 buried channel in pMOSFETs. In addition, the nMOSFET exhibited greatly reduced subthreshold swing values (that is, reduced standby power consumption), and the pMOSFET revealed greatly suppressed IN noise and gate-leakage levels. Unlike the conventional strained-Si CMOS employing a relatively thick (typically > 2 mu m) SixGe1-x, relaxed buffer layer, the strained-SiGe CMOS with a very thin (20 nm) Si0.8Ge0.2 layer in this study showed a negligible self-heating problem. Consequently, the proposed strained-SiGe CMOS design structure should be a good candidate for low power and high performance digital/analog applications.