SEMICONDUCTOR DEVICE WITH EFFECTIVE WORK FUNCTION CONTROLLED METAL GATE

1 . A gate electrode of a multi-gate metal field effect transistor, comprising:

a semiconductor substrate;

a dielectric layer over the semiconductor substrate;

a fin over the dielectric layer;

a gate insulating layer over the side surfaces of the fin, the gate electrode not comprising a gate insulating layer over the upper surface of the dielectric layer except portions of the upper surface of the dielectric layer that contact with the side surfaces of the gate insulating layer formed over the side surface of the fin;

a gate electrode layer over the fin; and

a polysilicon layer over the fin.

2 . The gate electrode of claim 1 further comprising a hard mask over the upper surface of the fin.

3 . The gate electrode of claim 1 having an effective work function smaller than about 4.6 eV.

4 . The gate electrode of claim 1 , wherein a portion of gate electrode is directly in contact with the upper surface of the dielectric layer.

5 . A gate electrode of a multi-gate metal field effect transistor, comprising:

a semiconductor substrate;

a dielectric layer over the semiconductor substrate;

a fin over the dielectric layer;

an oxygen diffusion barrier layer or a first oxygen diffusion layer over the upper surface of the dielectric layer;

a gate insulating layer over the side surfaces of the fin;

a gate electrode layer over the fin; and

a polysilicon layer over the fin.

6 . The gate electrode of claim 5 further comprising a hard mask over the upper surface of the fin.

7 . The gate electrode of claim 5 with the proviso that the gate electrode does not comprise a gate insulating layer over the upper surface of the dielectric layer except portions of the upper surface of the dielectric layer that contact with the side surfaces of the gate insulating layer formed over the side surface of the fin.

8 . The gate electrode of claim 5 further comprising a second oxygen diffusion layer over the upper surface of the fin.

9 . The gate electrode of claim 5 further comprising a second oxygen diffusion layer over the upper surface of the fin and a hard mask over the upper surface of the second oxygen diffusion layer.

10 . The gate electrode of claim 5 comprising the oxygen diffusion barrier layer over the upper surface of the dielectric layer and having an effective work function smaller than about 4.6 eV.

11 . The gate electrode of claim 5 comprising the first oxygen diffusion layer over the upper surface of the dielectric layer and having an effective work function larger than about 4.6 eV.

12 . A multi-gate metal field effect transistor comprising a first gate electrode and a second gate electrode,

the first gate electrode comprising:

a semiconductor substrate;

a dielectric layer over the semiconductor substrate;

a fin over the dielectric layer;

a gate insulating layer over the side surfaces of the fin and the upper surface of the dielectric layer;

a gate electrode layer over the fin; and

a polysilicon layer over the fin;

the second gate electrode is selected from the group consisting of the gate electrode of claim 1 and the gate electrode of claim 5 ; and

the first gate electrode having an effective work function that is smaller than an effective work function of the second gate electrode.

13 . The gate electrode of claim 12 , wherein the first gate electrode can have a smaller effective work function than the second gate electrode by about 0.2 eV or more and about 1.2 eV or less.

14 . A multi-gate metal field effect transistor comprising a first gate electrode and a second gate electrode,

the first gate electrode is selected from the group consisting of the gate electrode of claim 1 and the gate electrode of claim 5 ;

the second gate electrode is selected from the group consisting of the gate electrode of claim 1 and the gate electrode of claim 5 ; and

the first gate electrode having an effective work function smaller than about 4.6 eV and the second gate electrode having an effective work function larger than about 4.6 eV.

15 . The gate electrode of claim 14 , wherein the first gate electrode can have a smaller effective work function than the second gate electrode by about 0.2 eV or more and about 1.2 eV or less.

16 . A method of making a gate electrode of a multi-gate metal field effect transistor, comprising:

forming a fin over a dielectric layer and a semiconductor substrate;

forming a gate insulating layer over the side surfaces of the fin with the proviso that a gate insulating layer is not formed over the upper surface of the dielectric layer except portions of the upper surface of the dielectric layer that contact with the side surfaces of the gate insulating layer formed over the side surface of the fin;

forming a gate electrode layer over the fin; and

forming a polysilicon layer over the fin.

17 . The method of claim 16 further comprising forming a hard mask over the upper surface of the fin.

18 . A method of making a gate electrode of a multi-gate metal field effect transistor, comprising:

forming a fin over a dielectric layer and a semiconductor substrate;

forming an oxygen diffusion barrier layer or a first oxygen diffusion layer over the upper surface of the dielectric layer;

forming a gate insulating layer over the side surfaces of the fin;

forming a gate electrode layer over the fin; and

forming a polysilicon layer over the fin.

19 . The method of claim 18 further comprising forming a hard mask over the upper surface of the fin.

20 . The method of claim 18 further comprising forming a second oxygen diffusion layer over the upper surface of the fin and forming a hard mask layer over the second oxygen diffusion layer.