Impact of Deformation Potential Increase at Si/SiO₂ Interfaces on Stress-Induced Electron Mobility Enhancement in Metal–Oxide–Semiconductor Field-Effect Transistors

Abstract

The impact of deformation potential increase at metal–oxide–semiconductor (MOS) interfaces on stress effects is thoroughly studied. In our previous study, we revealed that the deformation potential (D ac) of Si increases at MOS interfaces. The energy split between two- and four-fold valleys is proportional to D ac. Therefore, it is considered that the D ac increase at MOS interfaces has an affect on strain effects. D ac effectively changes by adjusting Si-on-insulator (SOI) thickness and carrier distribution at MOS interfaces. Therefore, the SOI thickness dependence and carrier distribution dependence of electron mobility enhancement ratio (Δµe/µe) under strain are investigated. Experimental results are explained by the model including the D ac increase at MOS interfaces. In addition, experimental data are well reproduced by calculation using the position-dependent-D ac model. By applying uniaxial strain, effective mass, subband occupation, and intervalley scattering rate are also changed. Their effects on Δµe/µe are also discussed in this paper.

Theoretical investigation of the phonon-limited carrier mobility in (001) Si films

“…To solve this issue, other authors have introduced a spatially dependent N e ac , which sharply increases close to the interfaces with the oxide. 11,25,78 The reality of this enhancement could be questioned since the mobility in bulk MOSFETs and FDSOI devices results from a complex interplay between carrier-phonon interactions, interface roughness, 17,79,80 and Coulomb scattering. 20,32,35 However, experiments show that the lowtemperature (25 K) mobility in FDSOI devices is the same for t Si ¼ 60 nm and t Si ¼ 7.2 nm, whereas at room temperature the mobility is much smaller for t Si ¼ 7.2 nm than for t Si ¼ 60 nm.…”

Analysis of the substantial reduction of strain-induced mobility enhancement in (110)-oriented ultrathin double-gate MOSFETs

“…Mobility enhancement induced by the application of uniaxial longitudinal and transverse tensile strain in (100) single-gate (SG) MOSFETs has been reported in previous studies. 5,6) However, theoretical investigations of this phenomenon have been insufficient for layers with extremely thin T Si , or of strain-induced mobility enhancement in (110) DG MOSFETs.…”

“…A position-dependent D ac has been proposed to aid the consideration of T Si -dependent D ac . 5,6,13) The D ac can increase with decreasing T Si in SG and DG MOSFETs as a result of quantum confinement.…”

“…13: 110) cases because the isotropic=anisotropic properties of the MOSFETs affect the acoustic phonon scattering differently. 5,12,16,17) The scattering rate can be assumed to be isotropic for the (100) surface and anisotropic for the (110) surface. As shown in Fig.…”

“…It is well known that the second peak appears at approximately 5 nm in the (100) orientation. 5,7) However, the origin of the monotonic decrease in mobility enhancement in (110) ultrathin layers has not been fully determined.…”