Semiconductor devices

1. A semiconductor device, comprising:

a substrate having first, second, and third regions;

a first gate electrode layer on the first region, and including a first conductive layer;

a second gate electrode layer on the second region, the second gate electrode layer including:

the first conductive layer,

a second conductive layer on the first conductive layer, and

a barrier metal layer on the second conductive layer, uppermost surfaces of at least the second conductive layer and the barrier metal layer being level with each other; and

a third gate electrode layer on the third region and including the first conductive layer, the second conductive layer on the first conductive layer, and the barrier metal layer on the second conductive layer,

wherein an uppermost surface of the first gate electrode layer is at a lower level than an uppermost surface of the second gate electrode layer, and

wherein a thickness of the first conductive layer of the second gate electrode layer is different from a thickness of the first conductive layer of the third gate electrode layer.

2. The semiconductor device as claimed in claim 1 , wherein the first gate electrode layer has a thickness smaller than a thickness of the second gate electrode layer.

3. The semiconductor device as claimed in claim 1 , wherein a width of the second gate electrode layer is equal to or narrower than a width of the first gate electrode layer.

4. The semiconductor device as claimed in claim 1 , wherein the first conductive layer in the first gate electrode layer has a polygonal cross-section with a flat upper surface, and the first conductive layer in the second gate electrode layer has a non-polygonal cross-section with a curved surface portion.

5. The semiconductor device as claimed in claim 1 , wherein a width of an upper portion of the second conductive layer in the second gate electrode layer is wider than a width of a lower portion thereof.

6. The semiconductor device as claimed in claim 1 , wherein the first conductive layer includes a material having a work function greater than a work function of the second conductive layer.

7. The semiconductor device as claimed in claim 1 , further comprising a gate capping layer on the uppermost surfaces of the first and second gate electrode layers.

8. The semiconductor device as claimed in claim 7 , wherein a thickness of the gate capping layer is greater on the first gate electrode layer than on the second gate electrode layer.

9. The semiconductor device as claimed in claim 1 , wherein a first transistor including the first gate electrode layer and a second transistor including the second gate electrode layer are p-type MOSFETs, an operating voltage of the first transistor being lower than an operating voltage of the second transistor.

10. The semiconductor device as claimed in claim 1 , wherein:

the semiconductor device further includes first to third gate dielectric layers between each of the first to third gate electrode layers and the substrate, and

the first gate dielectric layer and the second gate dielectric layer include a same material, the third gate dielectric layer including a material different from materials of the first and second gate dielectric layers.

11. The semiconductor device as claimed in claim 10 , wherein a second transistor including the second gate electrode layer and a third transistor including the third gate electrode layer are p-type MOSFETs, an operating voltage of the second transistor being lower than an operating voltage of the third transistor.

12. A semiconductor device, comprising:

a substrate having first, second, and third regions;

a first gate electrode layer on the first region, and including a first conductive layer;

a second gate electrode layer on the second region, the second gate electrode layer including:

the first conductive layer,

a second conductive layer on the first conductive layer, and

a barrier metal layer on the second conductive layer, uppermost surfaces of at least the second conductive layer and the barrier metal layer being level with each other; and

a third gate electrode layer on the third region and including the first conductive layer, the second conductive layer on the first conductive layer, the barrier metal layer on the second conductive layer, and an upper metal layer on the barrier metal layer,

wherein an uppermost surface of the first gate electrode layer is at a lower level than an uppermost surface of the second gate electrode layer, and

wherein a width of the third gate electrode layer is wider than a width of the first gate electrode layer.

13. The semiconductor device as claimed in claim 12 , wherein first to third transistors including the first to third gate electrode layers, respectively, are p-type MOSFETs.

14. A semiconductor device, comprising:

a substrate having first, second, and third regions;

a first gate electrode layer on the first region, and including a first conductive layer;

a second gate electrode layer on the second region, the second gate electrode layer including:

the first conductive layer,

a second conductive layer on the first conductive layer, and

a barrier metal layer on the second conductive layer, uppermost surfaces of at least the second conductive layer and the barrier metal layer being level with each other; and

a third gate electrode layer on the third region and including the second conductive layer and the barrier metal layer on the second conductive layer,

wherein first and second transistors including the first and second gate electrode layers, respectively, are p-type MOSFETs, and a third transistor including the third gate electrode layer is an n-type MOSFET.

15. The semiconductor device as claimed in claim 1 , wherein the first conductive layer in the first gate electrode layer includes two layers including a same material and having different crystallinity.