Experimental Investigation of Hole Transport in Strained pMOSFETs—Part I: Scattering Mechanisms in Long-Channel Devices

摘要

This paper presents a wide experimental study of hole transport in SiGe pMOSFETs. Various Ge contents, from 20% up to 60%, and growth templates [unstrained or tensely strained silicon-on-insulator (SOI)] were screened in order to study the influence of various strain levels and Ge concentrations. Electrical results have been compared with the amount of strain in the channel, characterized through dark-field electron holography and nano-beam electron diffraction. The SiGe channel/oxide interface has been investigated through spectroscopic charge pumping and low temperature measurements. We found the signature of Ge-induced defects, particularly near the valence band. The different scattering mechanisms limiting the hole mobility in long-channel transistors have been decorrelated and discussed in the light of the different experimental data provided. We have shown in particular the low contribution of alloy scattering in the SiGe devices under study, and that carrier transport is dominated by the strain effect for Ge content up to 40%. The roughness parameters of the SiGe channel/oxide interface are also modified, with a less prejudicial impact on mobility. The effect of strain and Ge content on the different scattering mechanisms has been established. The combination of all the scattering contributions leads to a maximum mobility at room temperature for a Ge content $x_{rm Ge} = hbox{0.4}$ on an SOI template, or equivalently, $x_{rm Ge} = hbox{0.6}$ on a strained SOI template.