Semiconductor device with buried bit line and method for fabricating the same

1. A method of fabricating a semiconductor device, comprising:

forming a punch stop region in a substrate;

forming a plurality of pillar structures over the substrate, wherein each of the pillar structures has a stack layer of a sacrificial layer and an active layer;

removing the sacrificial layer;

forming a conductive layer between the pillar structures in the space where the sacrificial layer is removed; and

forming a plurality of buried bit lines under the pillar structures by selectively etching the conductive layer,

wherein the respective buried bit lines, the substrate, and the punch stop region are disposed in a line vertical to the substrate.

2. The method of claim 1 , wherein the punch stop region is formed by ion-implanting dopant into the substrate and formed in the substrate at some distance away from the surface of the substrate.

3. The method of claim 1 , wherein the sacrificial layer and the active layer are epitaxial layers.

4. The method of claim 3 , wherein the sacrificial layer includes an epitaxial silicon germanium layer and the active layer includes an epitaxial silicon layer.

5. The method of claim 1 , wherein the sacrificial layer is made of a substance having an etching selectivity with respect to the active layer.

6. The method of claim 1 , wherein the forming of pillar structures includes:

sequentially forming the sacrificial layer and the active layer over the substrate;

forming a hard mask pattern over the active layer; and

etching the active layer and the sacrificial layer using the hard mask pattern as an etch barrier.

7. The method of claim 6 , wherein the hard mask pattern is formed as a line pattern extending in the extension direction of the buried bit lines.

8. The method of claim 1 , wherein the forming of pillar structures includes:

forming a plurality of insulating layer patterns over the substrate;

forming portions of the pillar structures located between the insulation layer patterns and forming a stacked layer of the sacrificial layer and the active layer; and

removing the insulating layer patterns.

9. The method of claim 8 , wherein the insulation layer pattern is formed as a line pattern extending in the extension direction of the buried bit lines.

10. The method of claim 1 , wherein the removing of the sacrificial layer includes:

forming an insulation layer covering the pillar structures over the entire surface of the substrate;

forming a mask pattern covering a pair of pillar structures over the insulation layer;

exposing sides of the sacrificial layer by etching the insulating layer using the mask pattern as an etch barrier; and

removing the exposed sacrificial layer through a side wall.

11. The method of claim 1 , wherein the method further comprises:

forming an ohmic contact layer in a region where the substrate, the active layer, and the buried bit lines are in contact with each other before the forming of the conductive layer; and

forming a metal barrier layer along the surface of the pillar structure with the sacrificial layer removed before the forming of the conductive layer.

12. The method of claim 1 , wherein the conductive layer includes a metal layer.

13. The method of claim 1 , further comprising:

forming trenches by etching the substrate between the buried bit lines;

forming an isolation layer in the trenches and a portion of space between the pillar structures; and

forming a plurality of word lines over the isolation layer, wherein the word lines are in contact with the pillar structures and intersect the buried bit lines.

14. The method of claim 13 , wherein the bottoms of the trenches are formed to contact with the punch stop region.

15. The method of claim 13 , wherein the trenches are positioned to have bottoms of the trenches located inside the punch stop region or pass through the punch stop region.

16. The method of claim 13 , wherein the word lines are in contact with selected sides of the pillar structures or surround the pillar structures.