Modeling Study of the Impact of Surface Roughness on Silicon and Germanium UTB MOSFETs

We outlined a simple model to account for the surface roughness (SR)-induced enhanced threshold voltage (V/sub TH/) shifts that were recently observed in ultrathin-body MOSFETs fabricated on Si surface. The phenomena of enhanced V/sub TH/ shifts can be modeled by accounting for the fluctuation of quantization energy in the ultrathin body (UTB) MOSFETs due to SR up to a second-order approximation. Our model is then used to examine the enhanced V/sub TH/ shift phenomena in other novel surface orientations for Si and Ge and its impact on gate workfunction design. We also performed a calculation of the SR-limited hole mobility (/spl mu//sub H,SR/) of p-MOSFETs with an ultrathin Si and Ge active layer thickness, T/sub Body/ surface yields the highest /spl mu//sub H,SR/. The increasing quantization mass m/sub z/ for surface renders its /spl mu//sub H,SR/ less susceptible with the decrease of T/sub Body/. In contrast, surface exhibits smallest /spl mu//sub H,SR/ due to its smallest m/sub z/. The SR parameters, i.e. autocorrelation length (L) and root-mean-square (/spl Delta//sub rms/) used in this paper is obtained from the available experimental result of Si UTB MOSFETs, by adjusting these SR parameters to obtain a theoretical fit with experimental data on SR-limited mobility and V/sub TH/ shifts. This set of SR parameters is then employed for all orientations of both Si and Ge devices.