Semiconductor device with buried gates and buried bit lines and method for fabricating the same

1. A semiconductor device, comprising:

a plurality of first trenches formed inside a plurality of active regions;

a plurality of buried gates configured to partially fill insides of the plurality of the first trenches;

a plurality of second trenches formed to be extended in a direction crossing the plurality of the buried gates; and

a plurality of buried bit lines, formed at positions higher than an upper surface of each of the plurality of the buried gates, configured to fill the plurality of the second trenches.

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

a plurality of third trenches formed in a direction crossing the plurality of the second trenches between the plurality of the buried bit lines,

wherein the plurality of the buried bit lines to partially fill the plurality of the third trenches.

3. The semiconductor device of claim 2 , further comprising:

a bit line spacer layer formed on both sidewalls of each of the second trenches;

an inter-layer dielectric layer configured to gap-fill an upper portion of each buried bit line; and

a spacer layer between the plurality of the buried bit lines and the inter-layer dielectric layer.

4. The semiconductor device of claim 1 , wherein the plurality of the active regions are defined by an isolation layer over a substrate, and the plurality of the active regions are laid out to have a shape of island slanted in an oblique direction.

5. The semiconductor device of claim 4 , wherein the plurality of the buried gates and the plurality of the buried bit lines are formed crossing each other, and intersection points between the buried gates and the buried bit lines are positioned in an upper portion of the isolation layer.

6. The semiconductor device of claim 1 , wherein the plurality of the second trenches are formed at positions higher than a surface of the plurality of the buried gates.

7. A method for fabricating a semiconductor device, the method comprising:

forming a plurality of buried gates to fill insides of a plurality of active regions;

forming a plurality of trenches by etching the plurality of the active regions between the plurality of the buried gates; and

forming a plurality of buried bit lines, at positions higher than an upper surface of each of the plurality of the buried gates, to fill the plurality of the trenches.

8. The method of claim 7 , wherein the plurality of the active regions are defined by an isolation layer over a substrate, and the plurality of the active regions are laid out to have a shape of island slanted in an oblique direction.

9. The method of claim 8 , wherein the plurality of the buried gates and the plurality of the buried bit lines are formed crossing each other, and intersection points between the buried gates and the buried bit lines are positioned in an upper portion of the isolation layer.

10. The method of claim 7 , wherein the plurality of the trenches are formed at positions higher than a surface of the plurality of the buried gates.

11. A method for fabricating a semiconductor device, the method comprising:

forming a plurality of first trenches by etching a substrate;

forming a plurality of buried gates to fill the plurality of the first trenches;

forming a plurality of second trenches by etching the substrate in a direction crossing the plurality of the buried gates;

forming a plurality of third trenches by extending the plurality of the second trenches in parallel to the plurality of the buried gates; and

forming a plurality of buried bit lines to fill the plurality of the third trenches and the plurality of the second trenches.

12. The method of claim 11 , wherein the plurality of the second trenches are formed at positions higher than a surface of the plurality of the buried gates.

13. The method of claim 11 , wherein the plurality of the active regions are defined by an isolation layer over the substrate, and the plurality of the active regions are laid out to have a shape of island slanted in an oblique direction.

14. The method of claim 13 , wherein the plurality of the first trenches and the plurality of the second trenches are formed by simultaneously etching the plurality of the active regions and the isolation layer, and the plurality of the second trenches are formed shallower than the plurality of the first trenches.

15. The method of claim 11 , wherein the forming the plurality of the buried bit lines comprises:

forming a bit line spacer layer to cover a substrate including the plurality of the second trenches;

forming a sacrificial layer over the bit line spacer layer to gap-fill the plurality of the second trenches;

opening the plurality of the third trenches extending the plurality of the second trenches between the plurality of the buried gates by selectively etching the sacrificial layer and the bit line spacer layer;

removing the sacrificial layer;

forming a bit line conductive layer over the substrate to fill the plurality of the second trenches and the plurality of the third trenches; and

performing an etch-back process onto the bit line conductive layer to a depth lower than a surface of the substrate.