Transistor and method for fabricating the same

In a method for fabricating a transistor wherein a semiconductor substrate is sectioned into an operational region and a device separation region by the formation of a field oxide with a bird's beak and has in said operational region a low density ion-implanted region which a high density ion-implanted region is confined within, so as not to contact said high density ion-implanted region with said semiconductor substrate when forming a source or drain region, the improvement which comprises the steps of:

• forming a gate electrode on said field oxide film said gate electrode being insulated by an insulating film formed thereon and a gate polyoxide film resulting from the oxidation of its side wall;
• forming a spacer insulating film at the side wall provided by said insulating film and said gate polyoxide film;
• depositing a pad polysilicon film entirely over the resulting structure so as to implant high density impurity ions in said pad polysilicon film;
• etching said pad polysilicon film so as to leave said pad polysilicon film atop said operational region and said spacer insulating film;
• and
• applying a thermal process to form one of said source region and said drain region within said low density ion-implanted region.