Carrier Mobility in Undoped Triple-Gate FinFET Structures and Limitations of Its Description in Terms of Top and Sidewall Channel Mobilities

This paper presents an extensive experimental study of the effective mobility in the long-channel undoped triple-gate FinFETs. The mobility behavior in FinFETs is studied as compared with that in quasi-planar very wide fin FETs made on the same wafers and as a function of the fin width. Devices with two types of the gate dielectrics are investigated. New insights about the carrier transport in triple-gate FinFETs are obtained using a careful analysis of the results for various fin widths. In particular, it is shown that the model treating the triple-gate FinFET in terms of the (100) top and (110) lateral channels is not perfectly accurate for describing the transport properties in real FinFETs with relatively narrow fins; at low and moderate inversion charge densities, this is due to different inversion carrier distributions (and, thus, nonidentical scattering rates for various fin widths), and at high charge densities, it is presumably due to fin rounding which results in ambiguous crystallographic orientation, different from the postulated (100) and (110).