Semiconductor devices and methods of manufacturing the same

1 . A semiconductor device comprising:

a substrate including a word line trench extending in a first horizontal direction;

a gate dielectric layer in the word line trench;

a word line extending in the first horizontal direction and in a lower portion of the word line trench on the gate dielectric layer;

an insulation capping layer extending in the first horizontal direction and in an upper portion of the word line trench on the word line; and

a plurality of gate electrodes on the substrate, wherein the word line comprises:

a word line lower region extending in the first horizontal direction and including a first gate electrode of the plurality of gate electrodes on the gate dielectric layer; and

a word line upper region extending in the first horizontal direction on the word line lower region and including a plurality of second gate electrodes of the plurality of gate electrodes and the first gate electrode of the plurality of gate electrodes.

2 . The semiconductor device of claim 1 , wherein the first gate electrode has a first work function that is greater than a second work function of the plurality of second gate electrodes.

3 . The semiconductor device of claim 2 , wherein, in the word line upper region, the first gate electrode and the plurality of second gate electrodes overlap each other in the first horizontal direction.

4 . The semiconductor device of claim 2 , wherein the substrate comprises a plurality of active regions, wherein one of the plurality of active regions is adjacent to a device isolation layer, and

wherein the plurality of second gate electrodes overlaps the plurality of active regions in a vertical direction that is perpendicular to the first horizontal direction.

5 . The semiconductor device of claim 4 , wherein the first gate electrode in the word line upper region overlaps the device isolation layer in the vertical direction.

6 . The semiconductor device of claim 5 , wherein the word line trench comprises a first horizontal region and a second horizontal region that has a second width that is greater than a first width of the first horizontal region in the first horizontal direction, and wherein the first gate electrode in the word line upper region overlaps the second horizontal region in the vertical direction.

7 . The semiconductor device of claim 6 , wherein the plurality of second gate electrodes overlaps the first horizontal region in the vertical direction.

8 . The semiconductor device of claim 2 , wherein a top surface of the plurality of second gate electrodes contacts the insulation capping layer, and bottom and side surfaces of the plurality of second gate electrodes contact the first gate electrode.

9 . The semiconductor device of claim 2 , wherein the first gate electrode comprises a metal, a metal nitride, a metal carbide, and/or a combination thereof, and wherein the plurality of second gate electrodes comprises polysilicon.

10 . A semiconductor device comprising:

a substrate including a plurality of active regions;

a device isolation layer that is adjacent to one of the plurality of active regions;

a word line trench extending in a first horizontal direction across the plurality of active regions;

a gate dielectric layer that is in the word line trench and in contact with the plurality of active regions and the device isolation layer;

a word line extending in the first horizontal direction and disposed on the gate dielectric layer in a lower portion of the word line trench; and

an insulation capping layer extending in the first horizontal direction and disposed in an upper portion of the word line trench on the word line, wherein the word line comprises:

a word line lower region extending in the first horizontal direction and including a first gate electrode on the gate dielectric layer; and

a word line upper region including the first gate electrode and a second gate electrode having a second work function less than a first work function of the first gate electrode, and extending in the first horizontal direction on the word line lower region, and

wherein the second gate electrode overlaps the plurality of active regions in a vertical direction that is perpendicular to the first horizontal direction.

11 . The semiconductor device of claim 10 , wherein, in the word line upper region, the first gate electrode and the second gate electrode overlap each other in the first horizontal direction.

12 . The semiconductor device of claim 10 , wherein the first gate electrode in the word line upper region overlaps the device isolation layer in the vertical direction.

13 . The semiconductor device of claim 10 , wherein the word line trench comprises a first horizontal region and a second horizontal region that has a second width that is greater than a first width of the first horizontal region in the first horizontal direction, and wherein the first gate electrode in the word line upper region overlaps the second horizontal region in the vertical direction.

14 . The semiconductor device of claim 13 , wherein the second gate electrode overlaps the first horizontal region in the vertical direction.

15 . The semiconductor device of claim 10 , wherein a top surface of the second gate electrode contacts the insulation capping layer, and bottom and side surfaces of the second gate electrode contact the first gate electrode.

16 . The semiconductor device of claim 10 , wherein the first gate electrode comprises a metal, a metal nitride, a metal carbide, and/or a combination thereof, and

wherein the second gate electrode comprises polysilicon.

17 . A semiconductor device comprising:

a substrate including a word line trench extending in a first horizontal direction;

a gate dielectric layer in the word line trench;

a word line extending in the first horizontal direction and in a lower portion of the word line trench on the gate dielectric layer;

an insulation capping layer extending in the first horizontal direction and in an upper portion of the word line trench on the word line; and

a plurality of gate electrodes on the substrate,

wherein the word line comprises:

a word line lower region extending in the first horizontal direction and including a first gate electrode of the plurality of gate electrodes on the gate dielectric layer; and

a word line upper region extending in the first horizontal direction on the word line lower region and including a plurality of second gate electrodes of the plurality of gate electrodes and the first gate electrode of the plurality of gate electrodes, and

wherein a portion of the first gate electrode extends through the plurality of second gate electrodes in a vertical direction that is perpendicular to the first horizontal direction.

18 . The semiconductor device of claim 17 , wherein the substrate comprises a plurality of active regions, wherein one of the plurality of active regions is adjacent to a device isolation layer, and

wherein the portion of the first gate electrode overlaps the device isolation layer in the vertical direction.

19 . The semiconductor device of claim 18 , wherein the plurality of second gate electrodes overlaps the plurality of active regions in the vertical direction.

20 . The semiconductor device of claim 19 , wherein the first gate electrode comprises a metal, a metal nitride, a metal carbide, and/or a combination thereof, and

wherein the plurality of second gate electrodes comprises polysilicon.