Semiconductor device having fin-shaped field effect transistor and manufacturing method thereof

1. A semiconductor device comprising:

an active region defined by an element isolation region;

a gate trench crossing the active region to define source and drain regions on both sides thereof, respectively, and to define a channel region between the source and drain regions, the channel region having a first, second, and third protruding portions arranged in a gate width direction, the third protruding portion being between the first and second protruding portions to define a fin-shaped channel portion and giving the channel region a substantially W-shape; and

a gate electrode formed in the gate trench so as to cover the channel region with an intervention of a gate insulating film.

2. The semiconductor device as claimed in claim 1 , wherein

each of the first and second protruding portions of the channel region is in contact with the element isolation region.

3. The semiconductor device as claimed in claim 2 , wherein each of the first and second protruding portions of the channel region has a side wall that is inclined.

4. The semiconductor device as claimed in claim 2 , wherein a distance between an upper surface of the active region and a top portion of the third protruding portion of the channel region is greater than a distance between the upper surface of the active region and a top portion of the first protruding portion of the channel region.

5. The semiconductor device as claimed in claim 1 , wherein an upper surface of the gate electrode is disposed at a position deeper than an upper surface of the active region.

6. The semiconductor device as claimed in claim 1 , wherein the source and drain regions are impurity diffusion regions having a conductivity type different from that of the active region.

7. The semiconductor device as claimed in claim 1 further comprising a capacitive element electrically connected to one of the source and drain regions,

wherein a field-effect transistor constituted by the active region, the gate insulating film, the gate electrode, and the source and drain regions and the capacitive element constitute a memory cell.

8. The semiconductor device as claimed in claim 1 further comprising:

a plurality of field-effect transistors each of which is constituted by the active region, the gate insulating film, the gate electrode, and the source and drain regions;

a plurality of capacitive elements each of which is electrically connected to one of the source and drain regions of an associated one of the field-effect transistors; and

a conductive wire electrically connected to the other of the source and drain regions of each of the field-effect transistors so that the conductive wire is shared by the field-effect transistors.

9. A semiconductor device comprising a field-effect transistor, the field-effect transistor including:

an active region defined in a semiconductor substrate by an element isolation region;

a gate trench crossing the active region to define source and drain regions on both sides thereof, respectively, the gate trench having a bottom portion whose cross-sectional shape in an extending direction of the gate trench has a downward protruding portion and an upward protruding portion to define a fin-shaped channel portion and giving the bottom portion a substantially W-shape; and

a gate electrode buried in the gate trench included in the active region with intervention with a gate insulating film,

wherein the downward protruding portion and upward protruding portion of the gate trench share one side wall, the active region being buried between the other side wall of the downward protruding portion and the element isolation region closest to the other side wall thereof and between the one side wall of the upward protruding portion and the other side wall thereof.

10. The semiconductor device as claimed in claim 9 , wherein the gate trench has one upward protruding portion and two downward protruding portions which are arranged in the order of the downward protruding portion, the upward protruding portion, and the downward protruding portion along the extending direction of the gate trench.

11. The semiconductor device as claimed in claim 9 , wherein the other side wall of the downward protruding portion of the gate trench is in contact with the element isolation region.

12. The semiconductor device as claimed in claim 9 , wherein the other side wall of the downward protruding portion of the gate trench is inclined.

13. The semiconductor device as claimed in claim 9 , wherein the active region located below the gate insulating film covering the downward protruding portion and the upward protruding portion of the gate trench serves as a channel region of the field-effect transistor.

14. The semiconductor device as claimed in claim 9 , wherein

each of the source and drain regions includes an impurity diffusion region extending in a depth direction from an upper surface of the active region and having a conductivity type opposite to that of the active region, and

a top portion of the upward protruding portion of the gate trench that is closest to a main surface of the semiconductor substrate is disposed at a position more away from the main surface of the semiconductor substrate than lower surfaces of the impurity diffusion regions.

15. The semiconductor device as claimed in claim 9 , wherein an upper surface of the gate electrode is positioned lower than a main surface of the semiconductor substrate.

16. The semiconductor device according to claim 1 , wherein the first, second and third protruding portions allow an increase in the channel region while maintaining a channel length without reducing depths of the protruding portions from a substrate surface.

17. The semiconductor device according to claim 9 , wherein the protruding portions allow an increase in a channel region while maintaining a channel length without reducing depths of the protruding portions from a substrate surface.