Device simulation for evaluating effects of mechanical stress on semiconductor devices: Impact of stress-induced variation of electron effective mass

The effects of uniaxial loading on n-type metal-oxide-semiconductor field-effect transistors (nMOSFETs) were simulated by a drift-diffusion device simulation. The device simulation includes an electron mobility model for considering the effects of mechanical stress. The variations in the relative occupancy, the intervalley scattering and the effective mass of electrons were taken into account in the electron mobility model. In this study, the effects of uniaxial stress on nMOSFETs with gate lengths of 24μm and 0.8μm were evaluated; the stress-induced variations of the drain current and transconductance were simulated. Then, the simulation results were compared with experimental results obtained by the uniaxial loading of nMOSFETs. The simulation results obtained by considering the impact of the stress-induced variation of electron effective mass were in good qualitative agreement with those obtained by the experiments; the current simulation was able to qualitatively determine the uniaxial-load-direction dependence of the stress-induced variation of the electrical characteristics of nMOSFETs.