Nonvolatile semiconductor memory device and method for operating the same

A nonvolatile semiconductor memory device comprising:

• a substrate;
• a semiconductor channel forming region in the vicinity of the surface of the substrate;
• a first and a second impurity regions formed in the vicinity of the surface of the substrate sandwiching the channel forming region between them, acting as a source and a drain in operation;
• a gate insulating film stacked on the channel forming region and comprised of a plurality of films;
• a gate electrode formed on the gate insulating film;
• and
• a charge storing means which in formed in said gate insulating film dispersed in the plane facing said channel forming region and in the direction of thickness and is primarily injected in operation with channel hot electrons, ballistic hot electrons, secondarily generated hot electrons, substrate hot electrons, and hot electrons caused by band-to-band tunneling current, and
• wherein a bottom insulating film positioned at the bottom in the gate insulating film comprises a dielectric film of a material having a dielectric constant greater than that of silicon dioxide.

A nonvolatile semiconductor memory device comprising:

• a substrate;
• a semiconductor channel forming region in the vicinity of the surface of the substrate;
• a first and a second impurity regions formed in the vicinity of the surface of the substrate sandwiching the channel forming region between them, acting an a source and a drain in operation;
• a gate insulating film stacked on the channel forming region and comprised of a plurality of films;
• a gate electrode formed on the gate insulating film;
• and
• a charge storing means which is formed in said gate insulating film dispersed in the plane facing said channel forming region and in the direction of thickness and in primarily injected in operation with channel hot electrons, ballistic hot electrons, secondarily generated hot electrons, substrate hot electrons, and hot electrons caused by band-to-band tunneling current,
• wherein the gate insulating film comprises:
• a first region at the side of the first impurity region;
• a second region at the side of the second impurity region;
• and
• a third region between the first and the second regions,
• wherein said charge storage means is formed in the first and the second regions;
• and
• wherein the distribution region of the charge storing means is spatially separated by the third region.

A method for operating a nonvolatile semiconductor memory device comprising a substrate;

• a channel forming region of a semiconductor in the vicinity of the surface of the substrate;
• a first and a second impurity regions formed in the vicinity of the surface of the substrate sandwiching the channel forming region between them and acting as a source and a drain in operation;
• a gate insulating film stacked on the channel forming region and comprised of a plurality of films;
• a gate electrode formed on the gate insulating film;
• and a charge storing means which is formed in the gate insulating film dispersed in the plane facing the channel forming region and in the direction of thickness and is primarily injected with hot electrons in operation, and a bottom insulating film positioned at the bottom in the gate insulating film comprising a dielectric film that makes the energy barrier between the bottom insulating film and the substrate lower than that between silicon dioxide and silicon,
• said method comprising, in a write operation, a step of setting the voltage applied between the first and second impurity regions lower than that when the write speed is constant and the bottom insulating film is comprised of silicon dioxide.