Physical mechanisms of electron mobility enhancement in uniaxial stressed MOSFETs and impact of uniaxial stress engineering in ballistic regime

Abstract

The physical mechanisms of mu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> enhancement by uniaxial stress are investigated. From full band calculations, uniaxial-stress-induced split of conduction band edge, DeltaE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C </sub> and effective mass change, Deltam*, are quantitatively evaluated. It is experimentally and theoretically demonstrated that the energy surface of 2-fold valleys in Si (001) FETs is warped due to uniaxial lang110rang stress, resulting in lighter m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of 2-fold valleys parallel to the stress. By using calculated DeltaE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> and Deltam*, experimental (ie enhancement is accurately modeled for biaxial, uniaxial lang100rang, and uniaxial lang110rang stress. The limits of mu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> enhancement and the effectiveness of uniaxial stress engineering in enhancing nFET ballistic I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d,sat</sub> are also discussed