Phenomenological model for "stress memorization" effect from a capped-poly process

NMOSFET drive current improvement by a disposable stressor or a capped-poly process has been reported recently in the literature[1]. The retained drive current gain even after the removal of the stressor film is attributed to a stress "memorization" effect. A phenomenological model and numerical simulations showing the memorized stress are reported for the first time in this paper. An irreversible shape change of the polysilicon gate during the process is simulated by a plastic deformation model and the final resulting channel stress and associated Ids gain are analyzed.