Semiconductor memory device having a stepped structure and contact wirings formed thereon

1. A semiconductor storage device comprising:

a substrate;

a stack of first insulating layers and conductive layers that are alternately formed on the substrate in a memory region and a peripheral region of the semiconductor storage device, the conductive layers being electrically insulated from each other;

a second insulating layer covering the stack of the first insulating layers and the conductive layers in the peripheral region; and

a plurality of contact wirings formed in the peripheral region, each contact wiring extending from an upper surface of the second insulating layer towards the substrate and electrically connected to a corresponding one of the conductive layers, wherein

in the peripheral region, each conductive layer has an extended portion that covers side and upper surfaces of an end portion of a first insulating layer that is formed immediately above said each conductive layer, and each contact wiring is in direct contact with the extended portion of the corresponding conductive layer.

2. The semiconductor storage device according to claim 1 , wherein

at least one of the contact wirings is in contact with the extended portion of the corresponding conductive layer and not in contact with the first insulating layer that is formed immediately above the corresponding conductive layer.

3. The semiconductor storage device according to claim 1 , wherein

at least one of the contact wirings penetrates the extended portion of the corresponding conductive layer to be in contact with the first insulating layer that is formed immediately above the corresponding conductive layer.

4. The semiconductor storage device according to claim 3 , wherein

said at least one of the contact wirings does not extend through the first insulating layer formed immediately above the corresponding conductive layer.

5. The semiconductor storage device according to claim 3 , wherein

said at least one of the contact wirings extends through the first insulating layer formed immediately above the corresponding conductive layer.

6. The semiconductor storage device according to claim 1 , wherein

a first part of the contact wirings is in contact with the extended portion of the corresponding conductive layer and not in contact with the first insulating layer that is formed immediately above the corresponding conductive layer,

a second part of the contact wirings penetrates the extended portion of the corresponding conductive layer to be in contact with the first insulating layer that is formed immediately above the corresponding conductive layer but does not extend through the first insulating layer formed immediately above the corresponding conductive layer, and

a third part of the contact wirings penetrates the extended portion of the corresponding conductive layer and the first insulating layer that is formed immediately above the corresponding conductive layer and extends through the first insulating layer formed immediately above the corresponding conductive layer.

7. The semiconductor storage device according to claim 6 , wherein

the first part of the contact wirings extends farther from the upper surface of the second insulating layer than the second part of the contact wirings, and

the second part of the contact wirings extends farther from the upper surface of the second insulating layer than the third part of the contact wiring.

8. The semiconductor storage device according to claim 1 , wherein

a thickness of an extended portion of a conductive layer is greater than a thickness of the conductive layer.