MOS field effect transistor with improved pocket regions for suppressing any short channel effects and method for fabricating the same

摘要

A method for ion-implantation of a first conductivity impurity into a substrate of the same conductivity type to form pocket regions at positions in the inside edge portion of source/drain regions of a second conductivity type in a MOSFET having gate electrodes with side wall silicon oxide films. Semiconductor epitaxial layers are formed on the source/drain regions of a high selectivity to the side wall oxide films so that the epitaxial layers have facets which face to the side wall oxide films and the facets are almost linearly sloped down to bottom portions of the side wall oxide films. The first conductivity type impurity is implanted into the substrate at its limited positions in the vicinity of the inside edge portion of the source/drain regions by using the epitaxial layers with the facets and the side wall oxide films as masks in an oblique direction tilted by a tilting angle &thgr; from the normal of a surface of the substrate, wherein the angle &thgr; satisfies an equation represented by &thgr;≦&thgr;.sub.1 where:&thgr;.sub. 1 is an angle by which the facets are tilted from the normal of the surface substrate, and a thickness of the silicon selective growth layers satisfies an equation Tepi (Xj'/tan &thgr;)-Xj where: Tepi is the thickness of the silicon selective growth layers except for the facet portions; Xj is a junction depth of the source/drain diffusion regions; and Xj' is a distance between a top edge portion of each of the source/drain diffusion regions and a bottom side edge of each of the side wall oxide films.