Examination of Additive Mobility Enhancements for Uniaxial Stress Combined with Biaxially Strained Si, Biaxially Strained SiGe and Ge Channel MOSFETs

Uniaxial and biaxial strain additive mobility enhancements and their physical understandings are experimentally examined by applying mechanical stress to high mobility channel materials. As for nMOSFETs, <110> uniaxial and biaxial tensile strain are partially additive in the electron mobility enhancement due to the conduction band warping and resulting effective mass reduction under shear strain. As for pMOSFETs, it is found that an initial compressive biaxial strain is efficient to boost the impact of the shear strain component in the <110> uniaxial strain on hole mobility, demonstrating the effectiveness in combining uniaxial and biaxial stress for strained SiGe channels. The piezoresistance coefficients for (001) Germanium pMOSFETs are also experimentally evaluated for the first time.