Semiconductor device with reduced resistance of bit lines and method for manufacturing the same

1. A semiconductor device comprising:

buried bit lines formed to be brought into contact with drain areas of vertical pillar transistors, the buried bit lines being arranged along a first direction in a silicon substrate, wherein the buried bit lines are formed of epi-silicon;

a conductive pattern formed on portions of the buried bit lines between the vertical pillar transistors.

2. The semiconductor device according to claim 1 , wherein the buried bit lines formed of the epi-silicon have a thickness in the range of 100˜3,000 Å.

3. The semiconductor device according to claim 1 , wherein the conductive pattern is formed of epi-silicon.

4. The semiconductor device according to claim 3 , wherein the conductive pattern formed of the epi-silicon has a height in the range of 100˜2,000 Å and a width in the range of 100˜2,000 Å.

5. The semiconductor device according to claim 3 , wherein the conductive pattern formed of the epi-silicon is doped with impurities.

6. A semiconductor device comprising:

a silicon substrate having a plurality of silicon pillars;

gates formed to be buried in surfaces of lower portions of the silicon pillars;

source areas formed in portions of the silicon pillars over the gates;

drain areas formed in portions of the silicon substrate under the gates;

buried bit lines formed of epi-silicon in the silicon substrate such that the buried bit lines are brought into contact with the drain areas of the vertical pillar transistors, the buried bit lines being arranged along a first direction among the vertical pillar transistors including the gates, the source areas, and the drain areas;

a first insulation layer filled between the buried bit lines;

word lines formed on the first insulation layer to connect the gates of the vertical pillar transistors, the word lines being arranged along a second direction perpendicular to the first direction; and

a second insulation layer filled between the vertical pillar transistors including the word lines.

7. The semiconductor device according to claim 6 , wherein the buried bit lines formed of the epi-silicon have a thickness in the range of 100˜3,000 Å.

8. The semiconductor device according to claim 7 , further comprising:

a conductive pattern formed on portions of the buried bit lines between the vertical pillar transistors.

9. The semiconductor device according to claim 8 , wherein the conductive pattern is formed of epi-silicon.

10. The semiconductor device according to claim 9 , wherein the conductive pattern formed of the epi-silicon has a height in the range of 100˜2,000 Å and a width in the range of 100˜2,000 Å.

11. The semiconductor device according to claim 9 , wherein the conductive pattern formed of the epi-silicon is doped with impurities.

12. A method for manufacturing a semiconductor device, comprising the step of:

forming buried bit lines by growing epi-silicon in a silicon substrate to be brought into contact with drain areas of vertical pillar transistors, the buried bit lines being arranged along a first direction;

forming a conductive pattern on portions of the buried bit lines between the vertical pillar transistors.

13. The method according to claim 12 , wherein the buried bit lines formed of the epi-silicon have a thickness in the range of 100˜3,000 Å.

14. The method according to claim 12 , wherein the conductive pattern is formed of epi-silicon.

15. The method according to claim 14 , wherein the conductive pattern formed of the epi-silicon has a height in the range of 100˜2,000 Å and a width in the range of 100˜2,000 Å.

16. The method according to claim 14 , wherein the conductive pattern formed of the epi-silicon is doped with impurities.

17. A method for manufacturing a semiconductor device, comprising the steps of:

etching a silicon substrate to form a plurality of silicon pillars;

etching portions of the silicon substrate between the silicon pillars to define trenches extending along a first direction;

growing epi-silicon in the trenches to form buried bit lines;

isotropically etching surfaces of lower portions of the silicon pillars;

forming gates buried in the lower portions of the silicon pillars which are isotropically etched;

defining drain areas in portions of the silicon substrate under the gates;

etching the buried bit lines such that the buried bit lines, which adjoin each other along a second direction perpendicular to the first direction, are separated from each other;

filling a first insulation layer between and on the separated buried bit lines;

forming word lines on the first insulation layer to connect the gates, the word lines being arranged along the second direction;

filling a second insulation layer between the silicon pillars including the word lines; and

defining source areas in portions of the silicon pillars over the gates such that vertical pillar transistors are constructed.

18. The method according to claim 17 , wherein the step of forming the silicon pillars comprises the steps of:

forming a hard mask on the silicon substrate to cover silicon pillar forming areas;

etching the silicon substrate to define first grooves;

forming spacers on sidewalls of the first grooves and the hard mask; and

etching portions of the silicon substrate on bottoms of the first grooves using the hard mask and the spacers as an etch mask to define second grooves.

19. The method according to claim 17 , wherein the buried bit lines formed of the epi-silicon have a thickness in the range of 100˜3,000 Å.

20. The method according to claim 17 , further comprising the step of:

forming a conductive pattern on portions of the buried bit lines between the vertical pillar transistors.

21. The method according to claim 20 , wherein the conductive pattern is formed of epi-silicon.

22. The method according to claim 21 , wherein the conductive pattern formed of the epi-silicon has a height in the range of 100˜2,000 Å and a width in the range of 100˜2,000 Å.

23. The method according to claim 21 , wherein the conductive pattern formed of the epi-silicon is doped with impurities.