Electron Inversion Layer Mobility Enhancement by Uniaxial Stress on (001) and (110) Oriented MOSFETs

The origin of the enhancement of electron mobility in inversion layers on (001) and (110) oriented Si substrates under uniaxial stress has been investigated by solving the Boltzmann equation using the Monte Carlo method. Taking into account carrier repopulation, strain induced change of intersubband scattering and of electron effective mass, the experimentally observed mobility variation under uniaxial stress can be explained. Band structure calculations were performed to quantify the influence of stress on the effective masses. The experimentally observed pronounced anisotropy of the mobility induced by uniaxial stress for both substrate orientations is well reproduced by simulations. While on (110) substrate the anisotropy stems from the ellipsoidal shape of the lowest subband ladder, an effective mass change induced by [110] stress is responsible for the anisotropic mobility on the (001) substrate