Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device comprising the steps of:

• ion-implanting first impurities of an opposite conduction type in a surface layer of a semiconductor substrate of one conduction type;
• ion-implanting second impurities of the opposite conduction type in the surface layer;
• diffusing the first and the second impurities ion-implanted;
• thermally oxidizing the substrate surface using an oxidation-resistant film as a mask so that a selective oxide film is formed on the substrate;
• thermally oxidizing the substrate surface to form a gate oxide film on the other substrate regions than the selective oxide film;
• forming a a gate electrode which extends from the gate oxide film onto a part of the selective oxide film;
• ion-implanting third impurities of the opposite conduction type in the surface layer of the substrate using as a mask the selective oxide film and the gate electrode;
• annealing the substrate so that the first and third impurities ion-implanted in the surface layer of the substrate are diffused to form lightly-doped source/drain regions of the opposite conduction type on the surface layer of the substrate at the position retracted from the one end of the selective oxide film and to form highly-doped source/drain regions of the opposite conduction type on the surface layer of the substrate so as to be adjacent to the other end of the selective oxide film, and further the second impurities are diffused to form lightly-doped impurity regions of the opposite conduction type for reducing the threshold voltage so as to from the one end of the selective oxide film to the end of the lightly-doped source/drain regions.

A method of manufacturing a semiconductor device comprising the steps of:

• ion-implanting first impurities in a surface layer of a semiconductor substrate using a first resist film as a mask;
• ion-implanting second impurities in the surface layer using a second resist film as a mask;
• after having formed an oxidation-resistant film having an opening on said substrate, thermally oxidizing a substrate surface using the oxidation resistant film as a mask to form a selective oxide film on the substrate;
• thermally oxidizing the substrate surface to form a gate oxide film in a region of the substrate other than the selective oxide layer;
• after having formed a conductive film on the entire substrate surface, patterning said conductive film to form a gate electrode which extends from said gate oxide film over a part of said selective oxide film;
• implanting third impurities in the substrate surface using said selective oxide film and gate electrode;
• and
• annealing the substrate to diffuse said ion-implanted first, second and third impurities, thereby forming lightly-doped source/drain regions having a first and a second impurity density distribution and highly-doped source/drain regions having a third impurity density distribution.