Physical understanding of alloy scattering in SiGe channel for high-performance strained pFETs

Abstract

For devices beyond the 14nm node, it is important to investigate performance boosters such as high mobility channels. Although pure Ge offers a higher hole mobility than Si, conventional problems like surface passivation and its integration with Si makes SiGe alloy with low Ge mole fraction a viable option. The significance of alloy scattering, however, has been widely debated [1-3], so the accurate modeling of alloy scattering in SiGe channel has become an important issue to predict the performance of future SiGebased FETs. Usually, the calculation of alloy scattering mobility assumes an alloy scattering center in a simple analytical form with some fitting parameters, which is a good practical approach but has a limited predictability. In this paper, an atomistic tight-binding simulation is used to study alloy scattering in SiGe-based FETs, and to compare with experimental data. We conclude (i) although it is essentially impossible to avoid alloy scattering in SiGe material, (ii) high-mobility is indeed achieved in SiGe channel by combining lattice-mismatch stresses from Si virtual substrate with stresses from Source/Drain(SD) stressor.

Impact of strain on hole mobility in the inversion layer of PMOS device with SiGe alloy thin film

“…The calculation result reveals the importance of alloy scattering, which conforms to the research result of Samsung (refer to Ref. [7]). Both phonon scattering limited mobility and roughness scattering limited mobility would increase with increasing Ge concentration; however, the alloy Note that the unit of E eff is 1 MV/cm.…”

“…It is assumed that such an alloy potential value is identical to the inversion layer of PMOSFET elements. The research of Samsung, Korea [7], also proved such an argument.…”

“…Nonetheless, this study aims to stress on the strained SiGe alloy used for the hole mobility enhancement changing with Ge concentration under traditional surface channel element structure and to explore the effects of alloy scattering on the mobility degradation and the improvement of the mobility by either the strain or different wafer orientation. Experimental results from Samsung [7], Warwick University [25], and IMEC [26] are included in Fig. 4 for the comparison.…”

“…Both phonon scattering limited mobility and roughness scattering limited mobility would increase with increasing Ge concentration; however, the alloy Note that the unit of E eff is 1 MV/cm. Alloy-, phonon-, surface roughness-limited, and total hole mobility is also included for the comparison, and the simulated mobility is fixed at room temperature of 300 K. Experimental results (diamond symbols) from Samsung [7], Warwick University [25], and IMEC [26] are included for the comparison. limited mobility appears U shape-like change with Ge concentration.…”

“…Recent work on SiGe-based devices [6] suggested that a high Ge content SiGe alloy was currently investigated as a possible candidate for p-type Metal-oxide-semiconductor fieldeffect transistor (PMOSFET) applications. In 2013, Samsung research group reported the physical understanding of alloy scattering in SiGe channel PMOSFET [7]. In their paper, an atomistic sp3d5s* tightbinding simulation was used for investigating the alloy-limited mobility in SiGe devices and concluded that it was essentially impossible to avoid alloy scattering in SiGe channel materials.…”