Non-volatile semiconductor storage device and method of manufacturing the same
A non-volatile semiconductor storage device includes a plurality of memory strings each having a plurality of electrically rewritable memory cells connected in series. Each of the memory strings comprising: a first semiconductor layer including a columnar portion extending in a vertical direction with respect to a substrate; a plurality of first conductive layers formed to surround side surfaces of the columnar portions via insulation layers, and formed at a certain pitch in the vertical direction, the first conductive layers functioning as floating gates of the memory cells; and a plurality of second conductive layers formed to surround the first conductive layers via insulation layers, and functioning as control electrodes of the memory cells. Each of the first conductive layers has a length in the vertical direction that is shorter than a length in the vertical direction of each of the second conductive layers.
1. A non-volatile semiconductor storage device comprising:
a plurality of memory strings each having a plurality of electrically rewritable memory cells connected in series,
each of the memory strings comprising:
a first semiconductor layer including a columnar portion extending in a vertical direction with respect to a substrate;
a plurality of first conductive layers formed to surround side surfaces of the columnar portions via insulation layers, and formed at a certain pitch in the vertical direction, the first conductive layers functioning as floating gates of the memory cells, and including an insulation film between the plurality of first conductive layers; and
a plurality of second conductive layers formed to surround the first conductive layers via insulation layers, and functioning as control electrodes of the memory cells,
each of the first conductive layers having a length in a longitudinal direction of the first semiconductor layer, that is shorter than a length of each of the second conductive layers in the longitudinal direction of the first semiconductor layer, and the shorter length portion of the first conductor layer being surrounded by the greater length portion of the second conductor layer.
2. The non-volatile semiconductor storage device according to claim 1 , wherein
the first conductive layers are formed of polysilicon.
3. The non-volatile semiconductor storage device according to claim 1 , wherein
the second conductive layers are formed in a stripe pattern at a certain pitch in a first direction parallel to the substrate,
each of the memory strings further comprises a first protection layer formed on a side surface of each of the second conductive layers, and
the first protection layer has a higher selection ratio associated with diluted hydrofluoric acid treatment than that of the second conductive layer.
4. The non-volatile semiconductor storage device according to claim 3 , wherein
the first protection layer is formed of silicon nitride.
5. The non-volatile semiconductor storage device according to claim 1 , further comprising a selection transistor connected to one end of each of the memory strings,
wherein the selection transistor comprises:
a second semiconductor layer extending upward from a top surface of the first semiconductor layer;
a third conductive layer formed to surround a side surface of the second semiconductor layer via an insulation layer, and formed in a stripe pattern at a certain pitch in a first direction parallel to the substrate, the third conductive layer functioning as a control electrode of the selection transistor; and
a second protection layer formed on a side surface of the third conductive layer, and
the second protection layer has a higher selection ratio associated with diluted hydrofluoric acid treatment than that of the third conductive layer.
6. The non-volatile semiconductor storage device according to claim 5 , wherein
the second protection layer is formed of silicon nitride.
7. The non-volatile semiconductor storage device according to claim 1 , wherein
the first semiconductor layer further comprises a joining portion joining lower ends of a pair of the columnar portions, and
each of the memory strings further comprises a fourth conductive layer formed to surround the joining portion via an insulation layer.
8. The non-volatile semiconductor storage device according to claim 1 , wherein
the first semiconductor layer is formed with a hollow therein.