Semiconductor device and method of manufacturing the same

1. A semiconductor device, comprising:

a pipe channel layer including a first portion and a second portion protruding upwardly from a center area of the first portion so that a center area of the pipe channel layer is thicker than both sides of the pipe channel layer;

first channel pillars protruding from the second portion of the pipe channel layer; and

second channel pillars protruding from the first portion of the pipe channel layer,

wherein a stepwise surface of the pipe channel layer is defined between an outside surface of the first portion and an outside surface of the second portion.

2. The semiconductor device of claim 1 , wherein the second channel pillars are configured to be longer than the first channel pillars.

3. The semiconductor device of claim 1 , wherein the second portion is narrower than the first portion so that both sides of the first portion protrude toward a lateral direction more than both sides of the second portion.

4. The semiconductor device of claim 1 , further comprising:

common source lines electrically coupled to the second channel pillars.

5. The semiconductor device of claim 1 , further comprising:

a bit line electrically coupled to the first channel pillars.

6. The semiconductor device of claim 1 , further comprising:

a first pipe gate surrounding a side surface and a bottom surface of the first portion.

7. The semiconductor device of claim 1 , further comprising:

a second pipe gate surrounding a side surface and a top surface of the second portion.

8. The semiconductor device of claim 1 , further comprising:

an insulating layer surrounding the side surface and the top surface of the second portion.

9. A semiconductor device, comprising:

a pipe channel layer including a first portion and a second portion protruding upwardly from a center area of the first portion so that a center area of the pipe channel layer is thicker than both sides of the pipe channel layer;

first channel pillars protruding from the second portion;

second channel pillars protruding from the first portion, with the first channel pillars therebetween;

first conductive patterns that surround the first channel pillars;

second conductive patterns that surround the second channel pillars;

a first slit disposed between the first channel pillars that separates the first conductive patterns; and

a second slit disposed between the first channel pillars and the second channel pillars that separates the first conductive patterns and the second conductive patterns,

wherein bottom portions of the second channel pillars are disposed at a lower level than a top surface of the second portion and are apart from the second portion.

10. The semiconductor device of claim 9 , wherein the first slit overlaps the second portion.

11. The semiconductor device of claim 9 , wherein the first conductive patterns comprise:

at least one layer of drain select lines; and

word lines disposed under the drain select lines.

12. The semiconductor device of claim 9 , wherein the second conductive patterns comprise:

at least one layer of source select lines; and

word lines disposed under the source select lines.

13. The semiconductor device of claim 9 , further comprising:

a first pipe gate that surrounds a side surface and a bottom surface of the first portion.

14. The semiconductor device of claim 9 , further comprising:

an insulating layer disposed between the second slit and the pipe channel layer.

15. The semiconductor device of claim 9 , further comprising:

a second pipe gate disposed between the second slit and the pipe channel layer.

16. The semiconductor device of claim 9 , wherein bottom surfaces of the first and second slits are disposed to be at a higher level than the first portion of the pipe channel layer.