Method of manufacturing semiconductor device by forming first and second oxide films by use of nitridation

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

• forming an element region and an element isolation region on a semiconductor substrate of a first conductivity type;
• forming a first oxide film prospectively serving as a gate insulating film in said element region;
• performing thermal oxidation after annealing is performed in a nitrogen or ammonia atmosphere to nitrify an entire surface of said first oxide film;
• removing a portion of said nitrified first oxide film and forming a second oxide film prospectively serving as a gate insulating film in the removed portion using said nitrified first oxide film as a mask;
• forming a gate electrode constituted by a polysilicon film on each of said nitrified first oxide film and said second oxide film;
• forming diffusion layers prospectively serving as a source and a drain in areas of said semiconductor substrate lying in predetermined relation with said gate electrode;
• forming an insulating interlayer formed on said oxide film and said nitrified first oxide film including said gate electrode;
• forming contact holes in said insulting interlayer on said diffusion layers and forming wiring electrodes on said insulating interlayer;
• and
• forming a covering insulating film serving as a protection film on said insulating interlayer including said wiring electrodes.

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

• forming an element region and an element isolation region on said semiconductor substrate of the first conductivity type;
• forming a first oxide film prospectively serving as a gate insulating film in said element region;
• removing a part of said first oxide film and forming a second oxide film prospectively serving as a gate insulating film;
• performing thermal oxidation after annealing is performed in a nitrogen or ammonia atmosphere to nitrify an entire surface of the resultant structure;
• removing a portion of said nitrified first oxide film and forming a third oxide film prospectively serving as a gate insulating film using said nitrified first oxide film and a nitrified second oxide film as masks;
• and
• forming said gate electrode constituted by a polysilicon film.

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

• forming an element region and an element isolation region on a semiconductor substrate of a first conductivity type;
• forming a first oxide film prospectively serving as a gate insulating film in said element region;
• forming a first polysilicon film prospectively serving as a floating gate electrode in a predetermined region of said first oxide film;
• forming a second oxide film on said first polysilicon film and performing thermal oxidation after annealing is performed in a nitrogen or ammonia atmosphere to nitrify an entire surface of the resultant structure;
• removing a portion of the nitrified first oxide film and forming a third oxide film prospectively serving as a gate insulating film using a nitrified second oxide film as a mask;
• and
• forming a gate electrode constituted by a second silicon film on each of the nitrified second oxide film and the third oxide film.

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

• forming an element region and an element isolation region on a semiconductor substrate of a first conductivity type;
• forming a first oxide film prospectively serving as a gate insulating film in said element region;
• forming a diffusion layer having a conductivity type opposite to the first conductivity type of said semiconductor substrate in a subregion of said element region;
• removing a part of said first oxide film on said diffusion layer and forming a second oxide film;
• performing thermal oxidation after annealing is performed in a nitrogen or ammonia atmosphere to nitrify an entire surface of the resultant structure;
• forming a first polysilicon film prospectively serving as a floating gate on the nitrified first oxide film including a nitrified second oxide film;
• forming a third oxide film on said first polysilicon film and performing thermal oxidation after annealing is performed in a nitrogen or ammonia atmosphere to nitrify an entire surface of the resultant structure;
• removing a portion of the nitrified first oxide film and forming a fourth oxide film prospectively serving as a gate insulating film in the removed portion using a nitrified third oxide film as a mask;
• and
• forming a gate electrode constituted by a second silicon film on each of the nitrified third oxide film and the fourth oxide film.