Semiconductor device and method of manufacturing the same

A semiconductor device, comprising:

• a semiconductor substrate of a first conductivity type;
• a gate oxide film disposed on a surface of the semiconductor substrate and a LOCOS oxide film formed so as to be continuous with the gate oxide film;
• a gate electrode continuously disposed between a surface of the gate oxide film and a surface of the LOCOS oxide film;
• a first offset diffusion layer of a second conductivity type disposed on one end side of the gate electrode in a vicinity of the surface of the semiconductor substrate and below the LOCOS oxide film;
• a drain region disposed in a region, in which a part of the LOCOS oxide film is etched to be removed and which also corresponds to a part of the first offset diffusion, so as to be shallower than the first offset diffusion layer;
• and
• a source region of the second conductivity type disposed on another end side of the gate electrode.

A method of manufacturing a semiconductor device, comprising:

• forming a sacrificial oxide film on a semiconductor substrate of a first conductivity type;
• forming a nitride film on the sacrificial oxide film;
• etching the nitride film only in a desired region using a patterned photoresist;
• forming by ion implantation an offset diffusion layer of a second conductivity type only in a region to be a first offset diffusion layer;
• forming a LOCOS oxide film in the region in which the nitride film is etched;
• removing the nitride film and the sacrificial oxide film;
• forming a gate oxide film on a surface of the semiconductor substrate, forming a polycrystalline silicon film, and etching the polycrystalline silicon film only in a desired region using a patterned photoresist;
• etching the LOCOS oxide film in a region of the LOCOS oxide film, in which one of both of a source diffusion layer and a drain diffusion layer and only a drain diffusion layer is to be formed, using a patterned photoresist;
• and
• forming by ion implantation a source diffusion layer of the second conductivity type and a drain diffusion layer of the second conductivity type in one of only the region in which the LOCOS oxide film is removed and both the region in which the LOCOS oxide film is removed and the region in which the source diffusion layer is to be formed.

A method of manufacturing a semiconductor device, comprising:

• forming a sacrificial oxide film on a semiconductor substrate of a first conductivity type;
• forming a nitride film on the sacrificial oxide film;
• etching the nitride film only in a desired region using a patterned photoresist;
• forming by ion implantation a first offset diffusion layer of a second conductivity type only in a region to be the first offset diffusion layer;
• forming by ion implantation a second offset diffusion layer of the second conductivity type only in a region to be the second offset diffusion layer;
• forming a LOCOS oxide film in the region in which the nitride film is etched;
• removing the nitride film and the sacrificial oxide film;
• forming a gate oxide film on a surface of the semiconductor substrate, forming a polycrystalline silicon film, and etching the polycrystalline silicon film only in a desired region using a patterned photoresist;
• etching the LOCOS oxide film in a region of the LOCOS oxide film, in which one of both of a source diffusion layer and a drain diffusion layer and only a drain diffusion layer is to be formed, using a patterned photoresist;
• and
• forming by ion implantation a source diffusion layer of the second conductivity type and a drain diffusion layer of the second conductivity type in one of only the region in which the LOCOS oxide film is removed and both the region in which the LOCOS oxide film is removed and the region in which the source diffusion layer is to be formed.