Superior <110>-Directed Mobility to <100>-Directed Mobility in Ultrathin Body (110) nMOSFETs

摘要

(110) surface orientation has attracted increasing attention because of its high hole mobility [1-7]. Even though electron mobility (μ_e) in (110) surface is inferior to that in (100), strained (110) μ_e can surpass universal mobility, namely (100) μ_e [8]. Moreover, the (110) surface can be utilized in a side surface of a FinFET structure, which will be promising for future ultra-short channel devices. Thus, it is of great importance to study μ_e behavior in (110) nFETs experimentally. However, physics behind the carrier transport in (110) surface is really complicated. The quantum confinement effects, such as surface electric field and SOI thickness, have strong effects on mobility in both pFETs [5,6] and nFETs [8]. A recent study has pointed out that μ_e anisotropy in (110) nFETs is suppressed at high inversion charge density (N_(inv)), while the anisotropy is significant at low N_(inv) [8]. In the case of strong quantum confinement, such as ultra-thin body (UTB) case, the anisotropy of μ_e has not been clarified. In this study, μ_e anisotropy in (110) UTB nFETs has been demonstrated for the first time. It is experimentally observed that <110> μ_e is higher than <100> μ_e in an ultimately thin SOI nFETs, though <110> μ_e is smaller than <100> μ_e in bulk or relatively thick SOI. The physical origin is attributed to the non-parabolicity of the 2-fold valleys in <110> direction.