Non-volatile semiconductor storage device including a dielectric with low permittivity in memory cells arranged in a three dimensional manner
A plurality of a first conductive layers are provided at a certain interval L in a vertical direction, with a dielectric sandwiched therebetween. The certain interval L is set so that the first dielectric has an equivalent oxide thickness D EOT that satisfies the following relation (1). D sio2 <D EOT <D k (1) D sio2 denotes a thickness of the dielectric when the dielectric is composed of silicon oxide with a minimum thickness that can withstand a maximum voltage to be applied to the first conductive layers. D k denotes such an equivalent oxide thickness of a first dielectric that provides the resistance value Rsio2. The resistance value Rsio2 being defined as a resistance value of the first semiconductor layer for each of the first conductive layers when the dielectric is composed of silicon oxide and has a film thickness of D sio2 .
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 having a columnar portion extending in a vertical direction with respect to a substrate;
an electric charge accumulation layer surrounding a side surface of the first semiconductor layer; and
a plurality of first conductive layers surrounding a side surface of the electric charge accumulation layer and functioning as control electrodes of the memory cells,
the plurality of first conductive layers being provided at a certain interval L in the vertical direction, with a dielectric sandwiched therebetween,
the dielectric including a first dielectric with a lower dielectric constant than that of silicon oxide,
the certain interval L being set so that the first dielectric has an equivalent oxide thickness D EOT that satisfies the following relation (1), wherein the equivalent oxide thickness D EOT is defined as EOT=T×(∈ ox /∈ x ), in which T is a physical thickness of the first dielectric, ∈ ox is the dielectric constant of silicon oxide, and ∈ x is the dielectric constant of the first dielectric:
D sio2 <D EOT <D k (1)
in which D sio2 denotes an equivalent oxide thickness of the first dielectric with a minimum thickness that can withstand a maximum voltage to be applied to the first conductive layers, and,
R sio2 defines a resistance value of an entire part of the first semiconductor layer that is adjacent in a direction parallel to the substrate to one of the first conductive layers, and that has an extent between top and bottom surfaces of the one of the first conductive layers, if the first dielectric was composed of silicon oxide having a film thickness of D sio2 , and
D k denotes an equivalent oxide thickness of the first dielectric when the first dielectric provides the resistance value R sio2 in the part of the first semiconductor layer.
2. The non-volatile semiconductor storage device according to claim 1 , wherein
the first dielectric comprises vacuum or gas with a lower dielectric constant than that of silicon oxide.
3. The non-volatile semiconductor storage device according to claim 1 , wherein
the first dielectric comprises an interlayer insulation layer with a lower dielectric constant than that of silicon oxide.
4. The non-volatile semiconductor storage device according to claim 1 , wherein
each of the memory strings comprises:
a first insulation layer formed between the electric charge accumulation layer and the first semiconductor layer; and
a second insulation layer formed between the electric charge accumulation layer and the first conductive layers, and
the second insulation layer has a higher dielectric constant than that of silicon oxide.
5. The non-volatile semiconductor storage device according to claim 4 , wherein
the second insulation layer comprises aluminum oxide.
6. The non-volatile semiconductor storage device according to claim 1 , further comprising:
a selection transistor connected to one end of a respective one of the memory strings and controlling conduction of the memory strings,
wherein the selection transistor comprises:
a second semiconductor layer extending in the vertical direction from a top or bottom surface of the first semiconductor layer;
a third insulation layer surrounding a side surface of the second semiconductor layer; and
a second conductive layer surrounding a side surface of the third insulation layer, and
the third insulation layer has a higher dielectric constant than that of silicon oxide.
7. The non-volatile semiconductor storage device according to claim 6 , wherein
the third insulation layer comprises aluminum oxide.
8. The non-volatile semiconductor storage device according to claim 1 , wherein
the first conductive layers are formed in a stripe pattern at a certain pitch in a first direction parallel to the substrate.