Replacement metal gate transistor with controlled threshold voltage

1. A semiconductor device, comprising:

a semiconductor substrate; and

an N-channel transistor and a P-channel transistor provided on the semiconductor substrate, each of the N-channel transistor and the P-channel transistor respectively having a gate dielectric film on said semiconductor substrate, and a gate electrode respectively formed on said gate dielectric,

wherein each said gate electrode comprises a metal conductive layer,

wherein an oxygen concentration in said metal conductive layer for the N-channel transistor differs from that for the P-channel transistor,

wherein said metal conductive layer includes a component which serves to provide a work function metal having a strong bond with oxygen so as to provide a high thermal stability, and

wherein said component providing a strong bond with oxygen comprises aluminum.

2. A semiconductor device according to claim 1 , wherein the oxygen concentration in said metal conductive layer for said N-channel transistor and said P-channel transistor is 0.1 to 50 atomic %.

3. A semiconductor device according to claim 1 , wherein the metal in said metal conductive layer comprises TiA1C.

4. A semiconductor device according to claim 1 , wherein a barrier metal layer is inserted at an interface between said metal conductive layer and said gate dielectric.

5. A semiconductor device according to claim 4 , wherein said barrier metal layer comprises TiN.

6. A semiconductor device according to claim 1 , wherein said N-channel transistor and said P-channel transistor comprise a first N-channel transistor and a first P-channel transistor in a logic transistor region, said semiconductor device further comprising:

a second N-channel transistor; and

a second P-channel transistor,

wherein said second N-channel transistor and second P-channel transistor comprise transistors in a SRAM (static random access memory) region, and

wherein each of the second N-channel transistor and the second P-channel transistor respectively having a gate dielectric film on said semiconductor substrate, and a gate electrode respectively formed on said gate dielectric,

wherein each said gate electrode comprises said metal conductive layer, and

wherein an oxygen concentration in said metal conductive layer for the second N- channel transistor differs from that for the second P-channel transistor.

7. A semiconductor device according to claim 6 , wherein the oxygen concentrations in said metal conductive layer for the second N-channel transistor and second P-channel transistor differ from those for the first N-channel transistor and the first P-channel transistor.

8. A semiconductor device according to claim 7 , wherein said different oxygen concentrations provide different effective work functions (EWFs) for said first N-channel transistor, said first P-channel transistor, said second N-channel transistor, and said second P-channel transistor.

9. A method for fabricating a semiconductor device, said method comprising:

forming, on a substrate having an N-channel region and a P-channel region, a dummy gate dielectric and dummy gate electrode, respectively, for an N-channel transistor and for a P-channel transistor;

forming a pair of side wall spacers on said substrate at both sides of said dummy gate electrodes;

forming a source region and a drain region in a surface of said substrate at the both sides of said dummy gate electrode and said side wall, respectively, for said N-channel transistor and said P-channel transistor;

forming a dielectric layer over said dummy gate electrode, said side wall, said source region, and said drain region;

exposing a top surface of said dummy gate electrode;

forming a trench by removing said dummy gate electrode and said dummy gate dielectric;

forming a gate dielectric layer and a metal conductive layer comprising a gate electrode for each said N-channel transistor and P-channel transistor, using a same metal conductive layer material, said metal conductive layer including a component which serves to provide a work function metal having a strong bond with oxygen so as to provide a high thermal stability;

wherein said component providing a strong bond with oxygen comprises aluminum; selectively incorporating oxygen into said metal conductive layer on the P-channel transistor;

wherein a concentration of oxygen in said metal conductive layer for the N-channel region is different from a concentration of oxygen for the P-channel region.

10. A method for fabricating a semiconductor device according to claim 9 , wherein, in said incorporating oxygen into said metal conductive layer on the P-channel transistor selectively, the incorporating oxygen is conducted by an oxygen radical.

11. A method for fabricating a semiconductor device according to claim 9 , wherein a low energy ion implantation is used for said selectively incorporating oxygen into said metal conductive layer on the P-channel transistor.

12. A method for fabricating a semiconductor device according to claim 9 , further comprising selectively incorporating oxygen in said metal conductive layer for the N-channel transistor.

13. A method for fabricating a semiconductor device according to claim 12 , wherein said N-channel transistor and said P-channel transistor comprise a first N-channel transistor and a first P-channel transistor in a SRAM (static random access memory) transistor region, said semiconductor device further comprising:

forming a second N-channel transistor; and

forming a second P-channel transistor,

wherein said second N-channel transistor and second P-channel transistor comprise transistors in a logic transistor region, and

wherein each of the second N-channel transistor and the second P-channel transistor respectively having said gate dielectric film on said semiconductor substrate, and said gate electrode respectively formed on said gate dielectric,

wherein each said gate electrode comprises said same metal conductive layer material, and

wherein an oxygen concentration in said metal conductive layer for the second N- channel transistor differs from that for the second P-channel transistor.

14. A method for fabricating a semiconductor device according to claim 13 , wherein said different oxygen concentrations of said same metal layer causes different effective work functions (EWF) of said gate electrodes, and

wherein an order of EWF values for each of said first and second N-channel and P-channel transistors is as follows: Logic NMOS <SRAM NMOS <SRAM PMOS <Logic PMOS.

15. A method for fabricating a semiconductor device according to claim 14 , wherein said different oxygen concentrations range from 10 18 to 10 21 atoms/cm 3 .

16. A semiconductor device, comprising:

a substrate;

a first plurality of replacement metal gate (RMG) transistors in a logic region of said substrate, said first plurality of RMG transistors comprising an NMOS logic transistor and a PMOS logic transistor; and

a second plurality of RMG transistors in a SRAM (static random access memory) region of said substrate, said second plurality of RMG transistors comprising an NMOS SRAM transistor and a PMOS SRAM transistor,

wherein a same metal is used for gates in both said first plurality of RMG transistors and said second plurality of RMG transistors, and

wherein said same metal has different oxygen concentrations in each of said NMOS logic transistor, said PMOS logic transistor, said NMOS SRAM transistor, and said PMOS SRAM transistor.

17. The semiconductor device of claim 16 , wherein said metal includes a component that forms a strong bond with oxygen, thereby allowing said metal to stabilize threshold voltages in said RMG transistors.

18. The semiconductor device of claim 17 , wherein said metal comprises TiA1C.

19. A semiconductor device according to claim 17 , wherein a barrier metal layer is inserted at an interface between said metal and a gate dielectric used in said transistors.