Non-volatile semiconductor memory element and method of manufacturing the same, and semiconductor integrated circuit device including the non-volatile semiconductor memory element

A non-volatile semiconductor memory element comprising:

• a semiconductor region of a first conductivity type that is formed in a plate-like form on a semiconductor substrate;
• a first insulating film that is formed on a first side face of the semiconductor region;
• a first charge accumulating layer that is formed on a face of the first insulating film opposite from the semiconductor region;
• a second insulating film that is formed on a second side face of the semiconductor region, and has a different equivalent oxide thickness from the first insulating film, the second side face being the opposite side from the first side face;
• a second charge accumulating layer that is formed on a face of the second insulating film opposite from the semiconductor region;
• a third insulating film that is provided so as to cover the first and second charge accumulating layers;
• a control gate electrode that is provided so as to cover the third insulating film;
• a channel region that is formed in a portion of the semiconductor region covered with the control gate electrode;
• and
• source/drain regions of a second conductivity type that are formed in portions of the semiconductor region on both sides of the channel region,
• the semiconductor region having a thickness smaller than twice the maximum thickness of a depletion layer determined by impurity concentration in the semiconductor region.