Method of selectively removing tungsten over silicon oxide

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.