FinFET gate structure and method for fabricating the same

1. A semiconductor device, comprising:

a semiconductor substrate;

a first semiconductor fin on the semiconductor substrate; and

a n-type gate structure over the first semiconductor fin, wherein the n-type gate structure is fluorine incorporated and comprises:

a first initial layer over the first semiconductor fin;

a first high-k dielectric layer over the first initial layer and enclosed by a first gate spacer;

a n-type work function metal layer overlying the first high-k dielectric layer, the n-type work function metal layer comprising a TiAl (titanium aluminum) alloy or TaAl (tantalum aluminum) alloy, wherein an atom ratio of Ti (titanium) to Al (aluminum) is in a range substantially from 1 to 3 when the n-type work function metal layer comprises the TiAl alloy;

a first blocking metal layer overlying the n-type work function metal layer; and

a first metal filler peripherally enclosed by the first blocking metal layer, such that the first metal filler is enclosed by a first stacked structure, wherein a side wall of the first stacked structure contains a fluorine concentration substantially from 5 atom percent (at %) to 20 at %, and a bottom of the first stacked structure contains a fluorine concentration substantially from 1 at % to 15 at %.

2. The semiconductor device of claim 1 , wherein both surfaces of the n-type work function metal layer contain an oxygen concentration substantially less than 10 atom percent (at %).

3. The semiconductor device of claim 1 , the n-type gate structure further comprising:

a capping metal layer between the first high-k dielectric layer and the n-type work function metal layer, wherein the capping metal layer comprises TiN.

4. The semiconductor device of claim 3 , the n-type gate structure further comprising:

a barrier metal layer between the capping metal layer and the n-type work function metal layer, the barrier metal layer comprising TaN (tantalum nitride); and

a TiN layer between the barrier metal layer and the n-type work function metal layer.

5. The semiconductor device of claim 1 , wherein Al atom concentrations near or at both surfaces of the n-type work function metal layer are higher than Al atom concentrations at other portions of the n-type work function metal layer.

6. The semiconductor device of claim 1 , further comprising:

a second semiconductor fin on the semiconductor substrate, wherein the first semiconductor fin and the second semiconductor fin are separated by an isolation structure;

a p-type gate structure over the second semiconductor fin, wherein the p-type gate structure is fluorine incorporated and comprises:

a second initial layer over the second semiconductor fin;

a second high-k dielectric layer over the second initial layer and enclosed by a second gate spacer;

a p-type work function metal layer overlying the second high-k dielectric layer, the p-type work function metal layer comprising titanium nitride (TiN), wherein an atom ratio of Ti to N (nitrogen) is in a range substantially from 1:0.9 to 1:1.1;

a second blocking metal layer overlying the p-type work function metal layer; and

a second metal filler peripherally enclosed by the second blocking metal layer, such that the second metal filler is enclosed by a second stacked structure, wherein a side wall of the second stacked structure contains a fluorine concentration substantially from 5 at % to 20 at %, and a bottom of the second stacked structure contains a fluorine concentration substantially from 1 at % to 15 at %.

7. The semiconductor device of claim 6 , wherein the p-type work function metal layer contains an oxygen concentration substantially less than 10 atom percent (at %).

8. The semiconductor device of claim 6 , the p-type gate structure further comprising a TiAl layer disposed between the p-type work function metal layer and the second blocking metal layer.

9. The semiconductor device of claim 6 , the p-type gate structure further comprising:

a capping metal layer between the first high-k dielectric layer and the p-type work function metal layer, wherein the capping metal layer comprises TiN.

10. The semiconductor device of claim 9 , the p-type gate structure further comprising:

a barrier metal layer between the capping metal layer and the p-type work function metal layer, wherein the barrier metal layer comprises TaN.

11. The semiconductor device of claim 6 , wherein the first metal filler or the second metal filler comprises tungsten.

12. A semiconductor device, comprising:

a semiconductor substrate;

a first semiconductor fin and a second semiconductor fin on the semiconductor substrate, wherein the first semiconductor fin and the second semiconductor fin are separated by an isolation structure;

a n-type gate structure comprising a first initial layer over the first semiconductor fin and enclosed by a first gate spacer, and a p-type gate structure comprising a second initial layer over the second semiconductor fin and enclosed by a second gate spacer, wherein each of the n-type gate structure and the p-type gate structure is fluorine incorporated and comprises:

a high-k dielectric layer over the first initial layer and the second initial layer;

a first TiN layer overlying the high-k dielectric layer;

a TaN layer overlying the first TiN layer;

a second TiN layer overlying the TaN layer;

a TiAl layer overlying the second TiN layer;

a third TiN layer overlying the TiAl layer; and

a metal filler peripherally enclosed by the third TiN layer, such that the metal filler is enclosed by a stacked structure, wherein a side wall of the stacked structure contains a fluorine concentration substantially from 5 at % to 20 at %, and a bottom of the stacked structure contains a fluorine concentration substantially from 1 at % to 15 at %;

wherein the TiAl layer enclosed by the first gate spacer is a n-type work function metal layer, wherein an atom ratio of Ti (titanium) to Al (aluminum) is in a range substantially from 1 to 3; and

the second TiN layer enclosed by the second gate spacer is a p-type work function metal layer, wherein an atom ratio of Ti to N (nitrogen) is in a range substantially from 1:0.9 to 1:1.1.

13. The semiconductor device of claim 12 , wherein both surfaces of the n-type work function metal layer contain an oxygen concentration substantially less than 10 atom percent (at %).

14. The semiconductor device of claim 12 , wherein the p-type work function metal layer contains an oxygen concentration substantially less than 10 atom percent (at %).

15. The semiconductor device of claim 12 , wherein Al atom concentrations near or at both surfaces of the n-type work function metal layer are higher than Al atom concentrations at other portions of the n-type work function metal layer.

16. A method for forming a semiconductor device, the method comprising:

forming a first semiconductor fin and a second semiconductor fin on a semiconductor substrate, wherein the first semiconductor fin and the second semiconductor fin are separated by an isolation structure;

depositing a first initial layer enclosed by a first gate spacer over the first semiconductor fin, and a second initial layer enclosed by a second gate spacer over the second semiconductor fin;

depositing a high-k dielectric layer over the first initial layer and the second initial layer;

depositing a first TiN layer over the high-k dielectric layer;

depositing a TaN layer over the first TiN layer;

depositing a second TiN layer over the TaN layer;

depositing a TiAl layer over the second TiN layer;

depositing a third TiN layer over the TiAl layer;

depositing a metal filler peripherally enclosed by the third TiN layer by using a fluorine-contained precursor; and

diffusing fluorine to a stacked structure enclosing the metal filler, such that a side wall of the stacked structure contains a fluorine concentration substantially from 5 at % to 20 at %, and a bottom of the stacked structure contains a fluorine concentration substantially from 1 at % to 15 at %.

17. The method of claim 16 , wherein operations of depositing the first TiN layer, the second TiN layer and the third TiN layer are performed by atomic layer deposition (ALD).

18. The method of claim 16 , wherein operations of depositing the TaN layer and the TiAl layer are performed by atomic layer deposition (ALD).

19. The method of claim 16 , wherein an operation of depositing the metal filler is performed by atomic layer deposition (ALD).

20. The method of claim 16 , wherein the fluorine-contained precursor is tungsten hexafluoride (WF 6 ).