Recessed channel transistor

1. A recessed channel transistor, comprising:

a single crystalline silicon substrate having a recessed portion, a bottom surface of the recessed portion including an elevated central portion;

a doped region in the single crystalline silicon substrate below the bottom surface of the recessed portion and the elevated central portion;

a gate structure in the recessed portion; and

source/drain regions in the single crystalline silicon substrate at both sides of the recessed portion, the source/drain regions being spaced apart from the doped region and the bottom surface of the recessed portion.

2. The recessed channel transistor as claimed in claim 1 , wherein a width of the elevated central portion substantially equals a distance between the source region and the drain region, the width of the elevated central portion being measured along a direction parallel to a line connecting the source and drain regions.

3. The recessed channel transistor as claimed in claim 1 , wherein the gate structure has a non-planar bottom surface, the bottom surface of the gate structure corresponding to a surface profile of the elevated central portion.

4. The recessed channel transistor as claimed in claim 1 , wherein the elevated central portion of the bottom surface of the recessed portion includes a narrow edge protruding upward along a vertical direction, the vertical direction being perpendicular to a plane supporting the single crystalline silicon substrate, and the doped region includes impurity ions concentrated below the narrow edge.

5. The recessed channel transistor as claimed in claim 1 , wherein the source/drain regions are completely spaced apart from the bottom surface of the recessed portion along a vertical direction, the vertical direction being perpendicular to a plane supporting the single crystalline silicon substrate.

6. The recessed channel transistor as claimed in claim 1 , further comprising an isolation layer pattern in the single crystalline silicon substrate, the isolation layer pattern defining an active region.

7. The recessed channel transistor as claimed in claim 6 , wherein the recessed portion is in the active region, and the isolation layer pattern defines a sidewall of the recessed portion.

8. The recessed channel transistor as claimed in claim 6 , wherein the recessed portion is in the active region, the recessed portion having a first sidewall, a second sidewall, a third sidewall and a fourth sidewall, the single crystalline silicon substrate being exposed through the first and second sidewalls facing each other, and the isolation layer pattern being exposed through the third and fourth sidewalls facing each other.

9. The recessed channel transistor as claimed in claim 1 , wherein the doped region is doped with impurities having a conductivity different from a conductivity of impurities in the source/drain regions.

10. The recessed channel transistor as claimed in claim 1 , wherein the gate structure protrudes from the upper surface of the single crystalline silicon substrate.

11. The recessed channel transistor as claimed in claim 1 , wherein the doped region is doped with impurity ions, and the impurity ions are concentrated in the single crystalline silicon substrate under the bottom surface of the recessed portion and the elevated central portion.

12. The recessed channel transistor as claimed in claim 1 , wherein the doped region is highly doped with impurity ions under only the bottom surface of the recessed portion and the elevated central portion.

13. The recessed channel transistor as claimed in claim 1 , wherein the recessed portion includes an upper sidewall spaced apart from the bottom surface of the recessed portion and a lower sidewall adjacent to the bottom surface of the recessed portion, the upper sidewall being spaced apart from the doped region.

14. The recess channel transistor as claimed in claim 13 , wherein the upper sidewall of the recessed portion is spaced apart from impurity ions in the doped region.

15. The recessed channel transistor as claimed in claim 1 , wherein the doped region is a highly doped channel doping region, and an area in the single crystalline silicon substrate adjacent to the highly doped channel doping region is a lightly doped channel portion, the highly doped channel doping region including more ion impurities than the lightly doped channel portion.

16. The recessed channel transistor as claimed in claim 1 , wherein the bottom surface of the recessed portion and the elevated central portion include thermally treated silicon atoms of the single crystalline silicon substrate.

17. The recessed channel transistor as claimed in claim 1 , wherein the doped region includes concentrated impurity ions and thermally treated silicon atoms of the single crystalline silicon substrate.

18. The recessed channel transistor as claimed in claim 1 , wherein the elevated central portion of the single crystalline silicon substrate includes concentrated impurity ions and concentrated thermally treated silicon atoms of the single crystalline silicon substrate.

19. The recessed channel transistor as claimed in claim 18 , wherein the thermally treated silicon atoms are atoms in the single crystalline silicon substrate rapidly heated in the presence of hydrogen.

20. A semiconductor memory device, comprising:

a memory cell with at least one recessed channel transistor, the recessed channel transistor including:

a single crystalline silicon substrate having a recessed portion, a bottom surface of the recessed portion including an elevated central portion;

a doped region in the single crystalline silicon substrate below the bottom surface of the recessed portion and the elevated central portion;

a gate structure in the recessed portion, and

source/drain regions in the single crystalline silicon substrate at both sides of the recessed portion, the source/drain regions being spaced apart from the doped region and the bottom surface of the recessed portion.