Semiconductor device having work function metal stack

1. A device, comprising:

a pair of gate spacers on a substrate; and

a gate structure on the substrate and between the pair of gate spacers, wherein the gate structure comprises:

an interfacial layer overlying the substrate;

a metal oxide layer overlying the interfacial layer;

a nitride-containing layer overlying the metal oxide layer;

a tungsten-containing layer overlying the nitride-containing layer; and

a metal compound layer overlying the tungsten-containing layer, the metal compound layer having a different material than a material of the tungsten-containing layer.

2. The device of claim 1 , wherein the device is a fin field effect transistor (FinFET).

3. The device of claim 1 , wherein the tungsten-containing layer has a thickness less than a thickness of the metal compound layer.

4. The device of claim 1 , wherein the tungsten-containing layer has a thickness less than a thickness of the nitride-containing layer.

5. The device of claim 1 , wherein the tungsten-containing layer has a thickness less than a thickness of the metal oxide layer.

6. The device of claim 1 , wherein the tungsten-containing layer has a thickness less than a thickness of the interfacial layer.

7. The device of claim 1 , wherein the metal compound layer includes a metal nitride.

8. The device of claim 7 , wherein the metal nitride of the metal compound layer is different from a material of the nitride-containing layer.

9. The device of claim 1 , wherein the tungsten-containing layer is in contact with an upper surface of the nitride-containing layer.

10. A device, comprising:

a substrate;

gate spacers over the substrate;

a gate structure disposed between the gate spacers, wherein the gate structure comprises:

an interfacial layer over the substrate;

a tungsten-containing layer over the interfacial layer, wherein from a cross-sectional view, the tungsten-containing layer has a U-shaped pattern comprising a horizontal portion and two non-horizontal portions extending upwards from opposing ends of the horizontal portion along the gate spacers; and

a metal compound layer over the tungsten-containing layer, wherein from the cross-sectional view, the metal compound layer has a U-shaped pattern comprising a horizontal portion extending along the horizontal portion of the tungsten-containing layer, and two non-horizontal portions extending along the non-horizontal portions of the tungsten-containing layer.

11. The device of claim 10 , wherein from the cross-sectional view, the interfacial layer has a shape different from the U-shaped pattern of the tungsten-containing layer.

12. The device of claim 10 , further comprising a tungsten plug cupped by the metal compound layer.

13. The device of claim 12 , wherein the tungsten plug has a bottom position higher than a bottom position of the tungsten-containing layer.

14. The device of claim 12 , wherein the tungsten-containing layer is separated from the tungsten plug at least by the metal compound layer.

15. The device of claim 10 , wherein the metal compound layer comprises titanium (Ti) or tantalum (Ta).

16. A device, comprising:

a substrate;

gate spacers over the substrate; and

a gate structure between the gate spacers, wherein the gate structure comprises:

a metal oxide layer;

a first nitride-containing layer over the metal oxide layer;

a tungsten-containing layer over the first nitride-containing layer;

a second nitride-containing layer over the tungsten-containing layer; and

a gate fill metal over the second nitride-containing layer.

17. The device of claim 16 , wherein the gate fill metal has a same metal element as the tungsten-containing layer.

18. The device of claim 16 , wherein the tungsten-containing layer has a U-shaped cross-sectional profile.

19. The device of claim 16 , wherein the gate fill metal is spaced apart from the tungsten-containing layer.

20. The device of claim 16 , wherein the tungsten-containing layer has a thickness less than a thickness of the second nitride-containing layer.