Semiconductor device having shallow impurity region without short-circuit between gate electrode and source and drain regions and process of fabrication thereof

Claim 1

A semiconductor device having a field effect transistor formed on a semiconductor base layer, said field effect transistor comprising: a gate insulating layer formed on a first area of said semiconductor base layer; a gate electrode formed on said gate insulating layer; side wall spacers formed on second areas of said semiconductor base layer on both sides of said first area, and held in contact with side surfaces of said gate electrode, said side wall spacers including pad layers formed of a first insulating material and respectively having first bottom surfaces respectively held in contact with said second areas, first upper surfaces and first side surfaces, and spacing layers formed of a second insulating material and respectively having second bottom surfaces respectively held in contact with said first upper surfaces of said pad layers; and source and drain regions including conductive layers formed of a semiconductor material epitaxially grown on third areas on opposite sides of said second areas to said first area and having second side surfaces respectively held in contact with said first side surfaces, said semiconductor material having a small selectivity of epitaxial growth to said first insulating material and a large selectivity of epitaxial growth to said second insulating material, and impurity portions of said semiconductor base layer respectively providing said third areas overlain by said conductive layers and opposed to each other through said first area.