Vertical memory devices

1. A vertical memory device, comprising:

a gate structure on a peripheral circuit region of a substrate, the substrate including a cell region and the peripheral circuit region, and the gate structure including a first gate electrode;

second, third, and fourth gate electrodes sequentially disposed at a plurality of levels, respectively, on the cell region of the substrate in a vertical direction substantially perpendicular to an upper surface of the substrate;

a first epitaxial layer extending through the second gate electrode directly on a first portion of the cell region of the substrate;

a channel extending through the third and fourth gate electrodes in the vertical direction on the first epitaxial layer; and

a second epitaxial layer directly on a second portion of the peripheral circuit region of the substrate adjacent the gate structure, the first and second portions of the cell region and the peripheral circuit region, respectively, of the substrate including undoped single crystalline semiconductor material,

wherein lower surfaces of the first and second epitaxial layers are level with each other.

2. The vertical memory device as claimed in claim 1 , wherein the first and second epitaxial layers include substantially the same material.

3. The vertical memory device as claimed in claim 2 , wherein the first and second epitaxial layers include silicon-germanium doped with p-type impurities.

4. The vertical memory device as claimed in claim 1 , wherein an upper surface of the first epitaxial layer is higher than an upper surface of the second epitaxial layer.

5. The vertical memory device as claimed in claim 1 , further comprising an etch stop pattern on a surface of the gate structure, the etch stop pattern including a nitride, and a thickness of the etch stop pattern is greater than a thickness of the second gate electrode.

6. The vertical memory device as claimed in claim 5 , further comprising a blocking pattern covering at least lower and upper surfaces of the second gate electrode,

wherein the thickness of the etch stop pattern is substantially equal to a sum of the thickness of the second gate electrode and a thickness of the blocking pattern covering the lower and upper surfaces of the second gate electrode.

7. The vertical memory device as claimed in claim 1 , wherein the gate structure includes a gate insulation pattern, the first gate electrode, and a gate mask, the first gate electrode including a first polysilicon pattern and a first metal pattern sequentially stacked.

8. The vertical memory device as claimed in claim 7 , wherein the second gate electrode includes a second polysilicon pattern and a second metal pattern sequentially stacked, the first and second metal patterns including substantially the same metal.

9. The vertical memory device as claimed in claim 8 , wherein the first and second polysilicon patterns have substantially the same thickness, and the first and second metal patterns have substantially the same thickness.

10. The vertical memory device as claimed in claim 1 , wherein the second gate electrode is at a single level, and each of the third and fourth gate electrodes is at a plurality of levels.

11. The vertical memory device as claimed in claim 1 , wherein the first epitaxial layer serves as a channel of a transistor including the second gate electrode, and the second epitaxial layer serves as a source/drain layer of a transistor including the first gate electrode.

12. A vertical memory device, comprising:

a gate structure on a peripheral circuit region of a substrate, the substrate including a cell region and the peripheral circuit region, and the gate structure including a first gate electrode;

a source/drain layer on a portion of the peripheral circuit region of the substrate adjacent the gate structure;

second, third, and fourth gate electrodes sequentially disposed at a plurality of levels, respectively, on the cell region of the substrate in a vertical direction substantially perpendicular to an upper surface of the substrate;

a lower channel extending through the second gate electrode on the cell region of the substrate;

an upper channel extending through the third and fourth gate electrodes in the vertical direction on the lower channel;

an etch stop pattern on a surface of the gate structure; and

a blocking pattern covering at least lower and upper surfaces of the second gate electrode,

wherein the lower channel and the source/drain layer include substantially a same material, and

wherein a thickness of the etch stop pattern is substantially equal to a sum of a thickness of the second gate electrode and a thickness of the blocking pattern covering the lower and upper surfaces of the second gate electrode.

13. The vertical memory device as claimed in claim 12 , wherein the etch stop pattern includes a nitride.

14. The vertical memory device as claimed in claim 12 , wherein:

the gate structure includes a gate insulation pattern, the first gate electrode, and a gate mask,

the first gate electrode includes a first polysilicon pattern and a first metal pattern sequentially stacked, and the second gate electrode includes a second polysilicon pattern and a second metal pattern sequentially stacked, and

the first and second metal patterns include substantially the same metal.

15. The vertical memory device as claimed in claim 14 , wherein the first and second polysilicon patterns have substantially the same thickness, and the first and second metal patterns have substantially the same thickness.

16. The vertical memory device as claimed in claim 12 , wherein the lower channel and the source/drain layer are epitaxial layers including a same material.

17. A vertical memory device, comprising:

a substrate including a cell region and a peripheral circuit region;

a gate structure on the peripheral circuit region of the substrate, the gate structure including a first gate electrode;

second, third, and fourth gate electrodes on the cell region of the substrate, the second through fourth gate electrodes being spaced apart from each other along a vertical direction substantially perpendicular to an upper surface of the substrate;

a first epitaxial layer extending through the second gate electrode directly on a first portion of the cell region of the substrate;

a channel on the first epitaxial layer, the channel extending through the third and fourth gate electrodes in the vertical direction; and

a second epitaxial layer directly on a second portion of the peripheral circuit region of the substrate, the second epitaxial layer being adjacent the gate structure and consisting essentially of a same material as the first epitaxial layer,

wherein the vertical memory device further comprises:

an etch stop pattern on a surface of the gate structure, and

a blocking pattern covering at least lower and upper surfaces of the second gate electrode, and

wherein a thickness of the etch stop pattern is substantially equal to a sum of a thickness of the second gate electrode and a thickness of the blocking pattern covering the lower and upper surfaces of the second gate.

18. The vertical memory device as claimed in claim 17 , wherein each of the first and second epitaxial layers is a single crystalline layer including silicon.

19. The vertical memory device as claimed in claim 17 , wherein the first epitaxial layer is a channel of a transistor including the second gate electrode, and the second epitaxial layer is a source/drain layer of a transistor including the first gate electrode.

20. The vertical memory device as claimed in claim 17 , wherein an insulating interlayer covers the gate structure, the second epitaxial layer, and the second gate electrode, the channel extending into the insulating interlayer to contact the first epitaxial layer.