Oxidation and etching post metal gate CMP

1. A method comprising:

forming a dummy gate of a transistor at a surface of a wafer;

removing the dummy gate;

filling a metallic material into a trench left by the removed dummy gate;

performing a Chemical Mechanical Polish (CMP) on the metallic material, wherein a remaining portion of the metallic material forms a metal gate of the transistor;

after the CMP, performing a treatment on an exposed top surface of the metal gate using an oxidation-and-etching agent comprising chlorine and oxygen; and

after the treatment, forming a Contact Etch Stop Layer (CESL) over and contacting the top surface of the metal gate.

2. The method of claim 1 , wherein the oxidation-and-etching agent comprises HClO or CaClO.

3. The method of claim 1 , wherein the treatment is performed on a same polish pad used for the CMP, and wherein the treatment comprises a buffing treatment, with an oxidation-and-etching solution comprising the oxidation-and-etching agent dispensed to the wafer during the treatment.

4. The method of claim 1 , wherein the treatment comprises a megasonic treatment on the wafer, with the oxidation-and-etching agent dispensed on the wafer when an ultrasonic sound is applied on the wafer.

5. The method of claim 1 , wherein the treatment comprises a brush treatment on the wafer, with the oxidation-and-etching agent dispensed on the wafer when the wafer is brushed.

6. The method of claim 1 further comprising:

forming an opening extending into the CESL and an Inter-Layer Dielectric (ILD) underlying the CESL to expose a source/drain region of the transistor, wherein in the forming the opening in the ILD, the CESL is used as an etch stop layer.

7. The method of claim 6 further comprising:

filling a metal layer into the opening;

performing an anneal to silicide an exposed portion of the source/drain region;

removing un-reacted portions of the metal layer; and

filling a remaining portion of the opening to form a contact plug.

8. A method comprising:

forming a dummy gate of a transistor at a surface of a wafer;

removing the dummy gate;

filling a metallic material into a trench left by the removed dummy gate;

performing a Chemical Mechanical Polish (CMP) on the metallic material, wherein a remaining portion of the metallic material forms a metal gate of the transistor, and wherein during the CMP, the wafer is polished on a polish pad, with a slurry dispensed on the polish pad;

after the CMP, stopping dispensing the slurry; and

after stopping dispensing the slurry, performing a treatment on the wafer, wherein the treatment is selected from the group consisting essentially of a buffing treatment, a megasonic treatment, a brush treatment, and combinations thereof, and wherein during the treatment, an oxidation-and-etching agent comprising chlorine and oxygen is dispensed on the wafer.

9. The method of claim 8 , wherein the oxidation-and-etching agent comprises HClO.

10. The method of claim 8 , wherein the buffing treatment is performed with the wafer placed on the polish pad and rotated.

11. The method of claim 8 , wherein during the megasonic treatment, the oxidation-and-etching agent is dispensed on the wafer when an ultrasonic sound is applied on the wafer.

12. The method of claim 8 , wherein during the brush treatment, the oxidation-and-etching agent is dispensed on the wafer when the wafer is brushed.

13. The method of claim 8 further comprising:

after the treatment, forming a Contact Etch Stop Layer (CESL) over and contacting the metal gate; and

forming an opening extending into the CESL and an Inter-Layer Dielectric (ILD) underlying the CESL to expose a source/drain region of the transistor, wherein in the forming the opening in the ILD, the CESL is used as an etch stop layer.

14. The method of claim 13 further comprising:

filling a metal layer into the opening;

performing an anneal to silicide an exposed portion of the source/drain region;

removing un-reacted portions of the metal layer; and

filling an remaining portion of the opening to form a contact plug.

15. A method comprising:

forming a dummy gate of a transistor at a surface of a wafer;

removing the dummy gate;

filling a metallic material into a trench left by the removed dummy gate;

performing a Chemical Mechanical Polish (CMP) on the metallic material, wherein a remaining portion of the metallic material forms a metal gate of the transistor;

after the CMP, removing metal particles and an organic residue on an exposed top surface of the metal gate using an oxidation-and-etching solution comprising an oxidation-and-etching agent, wherein the oxidation-and-etching agent oxidizes and etches the metal particles and the organic residue simultaneously; and

after the removing the metal particles and the organic residue, forming a Contact Etch Stop Layer (CESL) on the exposed top surface of the metal gate, wherein between the CMP and the forming the CESL, no treatment using chlorine (Cl 2 ) or H 2 O 2 is performed.

16. The method of claim 15 , wherein the oxidation-and-etching agent comprises a bleach.

17. The method of claim 15 , wherein the oxidation-and-etching agent comprises HClO.

18. The method of claim 15 further comprising, after the forming the CESL:

forming an opening in the CESL and an Inter-Layer Dielectric (ILD) underlying the CESL to expose a source/drain region of the transistor;

filling a metal layer into the opening;

performing an anneal to silicide an exposed portion of the source/drain region;

removing un-reacted portions of the metal layer; and

filling an remaining portion of the opening to form a contact plug.

19. The method of claim 1 , wherein the oxidation-and-etching agent comprises CaClO.

20. The method of claim 2 , wherein the oxidation-and-etching agent comprises HClO.