Semiconductor device having buried gate structure and method of fabricating the same

1. A semiconductor device comprising:

a device isolation region defining an active region in a substrate;

an active gate structure in the active region; and

a field gate structure in the device isolation region, the field gate structure including a gate conductive layer,

wherein the active gate structure comprises:

an upper active gate structure including a gate conductive layer;

a lower active gate structure formed under the upper active gate structure and vertically spaced apart from the upper active gate structure, and including a gate conductive layer; and

a channel area formed between the upper active gate structure and

the lower active gate structure, and

wherein a top surface of the gate conductive layer of the field gate structure is lower than a bottom surface of the gate conductive layer of the upper active gate structure, and the top surface of the gate conductive layer of the field gate structure contacts an insulation layer.

2. The semiconductor device of claim 1 , wherein the top surface of the gate conductive layer of the field gate structure does not overlap the channel area in a horizontal direction.

3. The semiconductor device of claim 1 , wherein the upper active gate structure comprises:

an upper active gate trench formed from a surface of the substrate toward an inside of the substrate; and

an upper active gate insulating layer conformally formed on an inner wall of the upper active gate trench,

wherein the gate conductive layer of the upper active gate structure is formed on the upper active gate insulating layer of a lower portion of the upper active gate trench.

4. The semiconductor device of claim 3 , wherein the lower active gate structure comprises:

a lower active gate blocking pattern;

a lower active gate tunnel on the lower active gate blocking pattern; and

a lower active gate insulating layer conformally formed on an inner wall of the lower active gate tunnel,

wherein the gate conductive layer of the lower active gate structure is formed on the lower active gate insulating layer.

5. The semiconductor device of claim 4 , wherein a thickness of the lower active gate blocking pattern greater than a thickness of the lower active gate insulating layer and is greater than a thickness of the upper active gate insulating layer.

6. The semiconductor device of claim 4 , wherein the gate conductive layer of the upper active gate structure comprises an upper active gate barrier pattern conformally formed on the upper active gate insulating layer of the lower portion of the upper active gate trench and an upper active gate electrode pattern formed on the upper active gate barrier pattern to fill the lower portion of the upper active gate trench, and

wherein the gate conductive layer of the lower active gate structure comprises a lower active gate barrier pattern conformally formed on the lower active gate insulating layer and a lower active gate electrode pattern formed on the lower active gate barrier pattern to fill the lower active gate tunnel.

7. The semiconductor device of claim 6 , wherein a top surface of the upper active gate barrier pattern and a top surface of the upper active gate electrode pattern are coplanar.

8. The semiconductor device of claim 6 , wherein the lower active gate barrier pattern surrounds a surface of the lower active gate electrode pattern.

9. The semiconductor device of claim 1 , wherein a vertical length of the gate conductive layer of the lower active gate structure is greater than a vertical length of the gate conductive layer of the upper active gate structure.

10. The semiconductor device of claim 1 , wherein the upper active gate structure comprises:

an upper active gate trench formed from a surface of the substrate toward an inside of the substrate;

an upper active gate insulating layer conformally formed on an inner bottom surface of the upper active gate trench; and

air gaps formed on inner sidewalls of a lower portion of the upper active gate trench,

wherein the gate conductive layer of the upper active gate structure is formed on the upper active gate insulating layer and the air gaps of a lower portion of the upper active gate trench.

11. The semiconductor device of claim 1 , further comprising a plurality of intermediate active gate structures between the upper active gate structure and the lower active gate structure.

12. A semiconductor device comprising:

a device isolation region defining an active region in a substrate;

a lower active gate structure in the active region;

an upper active gate structure disposed on the lower active gate structure and vertically spaced apart from the lower active gate structure, the upper active gate structure including a gate conductive layer; and

a field gate structure in the device isolation region, the field gate structure including a gate conductive layer,

wherein a top surface of the gate conductive layer of the field gate structure is substantially coplanar with a top surface of the lower active gate structure, and the top surface of the gate conductive layer of the field gate structure contacts an insulation layer.

13. The semiconductor device of claim 12 , wherein a top surface of the gate conductive layer of the field gate structure is lower than a bottom surface of the gate conductive layer of the upper active gate structure.

14. The semiconductor device of claim 12 , wherein a channel area is formed between the upper active gate structure and the lower active gate structure, and

wherein the upper active gate structure and the lower active gate structure surround the channel area.

15. The semiconductor device of claim 12 , wherein the lower active gate structure comprises:

an active gate insulating tunnel; and

an insulating material filling the active gate insulating tunnel.

16. A semiconductor device comprising:

a device isolation region defining an active region in a substrate;

an active gate structure formed in the active region; and

a field gate structure formed in the device isolation region, the field gate structure including a field gate insulating layer and a field gate conductive layer on the field gate insulating layer,

wherein the active gate structure comprises:

a first gate structure including a blocking insulation layer, a first gate insulating layer on the blocking insulation layer, and a first gate conductive layer on the first gate insulating layer; and

a second gate structure formed on the first gate structure and vertically spaced apart from the first gate structure, and including a second gate insulating layer and a second gate conductive layer on the second gate insulating layer,

wherein a bottom surface of the blocking insulation layer of the first gate structure is lower than a bottom surface of the field gate conductive layer of the field gate structure.

17. The semiconductor device of claim 16 , wherein a thickness of the blocking insulation layer is greater than a thickness of the first gate insulating layer and is greater than a thickness of the second gate insulating layer.

18. The semiconductor device of claim 16 , wherein a top surface of the field gate conductive layer of the field gate structure is lower than a bottom surface of the second gate conductive layer of the second gate structure.

19. The semiconductor device of claim 16 , wherein a thickness of the first gate conductive layer is greater than a thickness of the second gate conductive layer.

20. The semiconductor device of claim 16 , wherein a channel area is formed between the first gate structure and the second gate structure, and

wherein the first and second gate conductive layers surround the channel area.