Nonvolatile semiconductor storage device
A nonvolatile semiconductor storage device having a control gate formed on a semiconductor substrate and including a cylindrical through hole. A block insulating film, a charge storage film, a tunnel insulating film, and a semiconductor layer are formed on a side surface of the control gate inside the through hole. The tunnel insulating film includes a first insulating film having SiO 2 as a base material and containing an element that lowers a band gap of the base material by being added. A density and a density gradient of the element monotonously increase from the semiconductor layer toward the charge storage film.
1. A nonvolatile semiconductor storage device, comprising:
a substrate;
a stacked structural unit including a plurality of electrode films stacked in a first direction, the first direction crossing a surface of the substrate;
a silicon pillar extending in the first direction;
a block insulating film provided between the electrode films and the silicon pillar;
a charge storage film provided between the block insulating film and the silicon pillar; and
a tunnel insulating film provided between the charge storage film and the silicon pillar,
wherein the tunnel insulating film includes a first point, a second point, a third point, and a fourth point in this order from the silicon pillar toward the charge storage film, and
a first band gap at the first point is higher than a second band gap at the second point, a third band gap at the third point is higher than the second band gap, and the third band gap is higher than a fourth band gap at the fourth band gap.
2. The device of claim 1 , wherein the fourth band gap is higher than the second band gap.
3. The device of claim 1 , wherein the tunnel insulating film includes a fifth point between the fourth point and the charge storage film, and
the fourth band gap is higher than a fifth band gap at the fifth point.
4. The device of claim 1 , wherein the first point includes silicon oxide.
5. The device of claim 1 , wherein the third point and the fourth point includes silicon oxide and nitrogen.
6. The device of claim 5 , wherein a first density of nitrogen at the third point is lower than a second density of nitrogen at the fourth point.
7. The device of claim 1 , wherein the second point includes silicon oxide and a microcrystal.
8. The device of claim 7 , wherein the microcrystal is silicon microcrystal.