Nonvolatile semiconductor memory device and manufacturing method of the same

A manufacturing method of a nonvolatile semiconductor memory device, comprising:

• forming a first conductive layer on a semiconductor substrate;
• forming a first mask layer on the first conductive layer;
• forming a trench by etching the first conductive layer and semiconductor substrate by using the first mask layer as a mask;
• forming a first insulating layer which completely fills the trench;
• polishing the first mask layer and first insulating layer until the upper surface of the first conductive layer is substantially leveled with the upper surface of the first insulating layer;
• forming a second insulating layer on the upper surface of the first insulating layer and the upper surface of the first conductive layer;
• and
• forming a second conductive layer on the second insulating layer.

A manufacturing method of a nonvolatile semiconductor memory device, comprising:

• forming a first conductive layer on a semiconductor substrate;
• forming a first mask layer on the first conductive layer;
• forming a trench by etching the first conductive layer and semiconductor substrate by using the first mask layer as a mask;
• forming a first insulating layer which completely fills the trench;
• polishing the first insulating layer to such an extent that at least the upper surface of the first mask layer is exposed;
• removing the first mask layer to form a recess on the first conductive layer;
• forming, in the recess, a second conductive layer having an upper surface substantially leveled with the upper surface of the first insulating layer;
• forming a second insulating layer on the upper surface of the first insulating layer and the upper surface of the second conductive layer;
• and
• forming a third conductive layer on the second insulating layer.