Process of fabricating field effect transistor with ldd structure

Claim 1

A process of fabricating a field effect transistor comprising the steps of: a) preparing a semiconductor substrate of a first conductivity type having a major surface; b) forming a gate oxide film on said major surface; c) forming a gate electrode on a predetermined portion of said gate oxide film; d) carrying out a first ion-implantation through said gate oxide film for doping said semiconductor substrate with impurity atoms of a second conductivity type opposite to said first conductivity type, thereby forming lightly doped impurity regions, said gate electrode serving as a mask during said first ion-implantation; e) covering the entire surface of the structure with doped polysilicon film overlain by a protective oxide film; f) covering said protective oxide film with an intentionally undoped polysilicon film; g) anisotropically etching said intentionally undoped polysilicon film for forming a side wall on a portion of said protective oxide film covering a side surface of said gate electrode, said protective oxide film being exposed on both sides of said side wall; h) removing exposed portions of said protective oxide film substantially without etching said doped polysilicon; i) carrying out a second ion-implantation through said doped polysilicon using said gate electrode and said side wall as a mask for doping said semiconductor substrate with impurity atoms of said second conductivity type, thereby forming heavily doped impurity regions; and j) removing said side wall.