Method of selectively removing tungsten over silicon oxide

1. A method of selectively removing tungsten over silicon oxide, the method comprising:

providing a substrate having a tungsten layer directly disposed in and over a silicon oxide layer; and

selectively removing the tungsten layer over the silicon oxide layer to leave the tungsten layer in the silicon oxide layer by chemical mechanical polishing using a slurry, wherein the slurry comprises:

acidic water;

abrasive particles;

a halogen oxide, wherein the halogen oxide is a sodium salt or a potassium salt of chlorate, bromate, iodate, hypochlorite, or any combinations thereof; and

a nitroxide compound, wherein the nitroxide compound is N-methylmorpholine-N-oxide (NMO), 2-mercapto pyridine oxide, trimethyl amine oxide, or any combinations thereof, and the combination of the halogen oxide and the nitroxide compound produce a synergistic effect on the removing rate of the tungsten, compared with using the halogen oxide or the nitroxide compound alone.

2. The method of claim 1 , wherein the halogen oxide has a concentration of the halogen oxide is 100-10000 ppm.

3. The method of claim 1 , wherein the nitroxide compound has a concentration of 300-3000 ppm.

4. The method of claim 1 , wherein the abrasive particles are selected from colloidal silicon oxide, fumed silicon oxide, nano aluminum oxide, or a combination of any two or more of the above.

5. The method of claim 1 , wherein a content of the abrasive particles is 0.5-10 wt %.

6. The method of claim 1 , wherein the slurry has a pH value of 2-6.

7. The method of claim 1 , wherein the slurry further comprises a water-soluble starch having a molecular weight less than 8000.

8. The method of claim 7 , wherein a content of the water-soluble starch is 100-500 ppm.