Nonvolatile semiconductor memory device with twin-well
AssigneeKabushiki Kaisha Toshiba
InventorsMitsuhiro NOGUCHI, Minori Kajimoto
Life of this patent
Estimating the term…
Abstract
A nonvolatile semiconductor memory device includes a first well of a first conductivity type, which is formed in a semiconductor substrate of the first conductivity type, a plurality of memory cell transistors that are formed in the first well, a second well of a second conductivity type, which includes a first part that surrounds a side region of the first well and a second part that surrounds a lower region of the first well, and electrically isolates the first well from the semiconductor substrate, and a third well of the second conductivity type, which is formed in the semiconductor substrate. The third well has a less depth than the second part of the second well.
Claims10
1-18. (canceled)
A method for manufacturing a semiconductor memory device comprising:
- forming a first well of a second conductivity type on a semiconductor substrate of a first conductivity type;
- forming a second well of the second conductivity type and a third well of the second conductivity type simultaneously, the second well being formed to reach a top of the first well;
- forming a fourth well of the first conductivity type, the fourth well being surrounded by the first well and the second well;
- and
- forming first transistors on the fourth well and a second transistor on the third well.
Dependencies are inferred from the claim text.