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It is demonstrated that the gate interface breaks the equivalence between vertical and transverse direction for the mobility in 100 /(001) pMOSFETs, leading to 6 instead of 3 independent 1st order piezoconductance coefficients. This is found from Monte Carlo (MC) simulations yielding different effective mobilities for uniaxial vertical and transverse stress, which can be explained in terms of energy and parallel-momentum conservation upon specular surface scattering. A mobility model with stress-dependent 1st order piezoconductance coefficients is presented. This model is shown to reproduce well corresponding MC effective mobilities not only for low, but also for high stress.

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The on-current (Idsat) enhancement in process-simulated <110> nMOSFETs by a tensile strained cap layer is investigated by mechanical stress and Monte Carlo (MC) device simulation. Our MC model is based on an improved semi-empirical analytical two-band model for electrons. This model is found to compare favorably to pseudopotential MC results with some underestimation of the on-current improvement. The MC simulations yield Idsat gains of around 20 % and 10 % for a 60 nm thick cap layer with 2 GPa and 1 GPa intrinsic stress, respectively, with decreasing tendency upon scaling. These current gains are significantly higher than the gains predicted by drift-diffusion simulation with the linear piezoresistance model.