Patent ID: 8017994
Filing Date: 2011-09-13
Classification: G11C,H01L

Abstract:
1. A nonvolatile semiconductor memory device comprising: a semiconductor substrate having a first conductivity type well, wherein a first area and a second area are defined in a surface of the semiconductor substrate, and the surface of the semiconductor substrate is recessed in the second area with respect to the first area thereby a step is formed at the surface of the semiconductor substrate at a boundary of the first area and a second area; a first oxide layer formed on the semiconductor substrate in the first area; a nitride layer formed over the first oxide layer, a width of the nitride layer measured along a direction parallel to the surface of the semiconductor substrate in the first area is less than 100 nm; a second oxide layer formed over the nitride layer; a polysilicon layer formed over the second oxide layer; a source region of a second conductivity type formed in the semiconductor substrate in the second area, the second conductivity type being opposite to the first conductivity type; and an insulating side wall formed on the surface of the semiconductor substrate in the second area and on a second partial area of the polysilicon layer, wherein: the insulating side wall fills in the step formed at the surface of the semiconductor substrate at the boundary of the first area and a second area; the insulating side wall is in contact to both of the first oxide layer and the second oxide layer; and one end of the nitride layer is surrounded by the first oxide layer, the insulating side wall and the second oxide layer.