Polishing composition and polishing method using the same

1. A polishing composition for use in polishing a polishing object having a surface which is positively charged at a pH of less than 6, comprising

water,

abrasive grains, and

an anionic copolymer having a unit structure represented by the following Formula 1 or the following Formula 2, and having a pH of less than 6,

wherein the anionic copolymer has at least two acidic groups having different acidities, wherein the abrasive grains have a surface which is negatively charged at a pH of less than 6, and the abrasive grains are Al (aluminum) doped colloidal silica or colloidal silica immobilized with organic acid;

wherein the anionic copolymer has a weight average molecular weight of 5000 to 20000;

a content of the abrasive grains in the polishing composition is in a range of 2 to 10% by mass, and

a content of the anionic copolymer in the polishing composition is in a range of 50 to 500 ppm by mass,

wherein Q 1 is selected from the group consisting of hydrogen; an alkyl group with 1 to 6 carbon atoms selected from the group consisting of a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, a sec-butyl group, a tert-butyl group, a n-pentyl group, and a n-hexyl group; or an alkoxy group with 1 to 6 carbon atoms selected from the group consisting of a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, a sec-butoxy group, a tert-butoxy group, a n-pentoxy group, and a n-hexoxy group,

Q 1′ is any one of a single bond, an ether bond, an ester bond, an amide bond, and a carbonyl bond,

x is an integer of from 0 to 10,

y is an integer of from 0 to 10,

X is an acidic group selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a phosphoric acid group; an aliphatic hydrocarbon group with 1 to 10 carbon atoms having at least one acidic group selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a phosphoric acid group; or an aromatic hydrocarbon group with 6 to 12 carbon atoms having at least one acidic group selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a phosphoric acid group;

wherein Ar is a substituted or non-substituted aromatic group with 6 to 12 carbon atoms, provided that when Ar is a substituted aromatic group, a substituent includes an alkyl group with 1 to 6 carbon atoms selected from the group consisting of a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, a sec-butyl group, a tert-butyl group, a n-pentyl group, and a n-hexyl group; and an alkoxy group with 1 to 6 carbon atoms selected from the group consisting of a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, a sec-butoxy group, a tert-butoxy group, a n-pentoxy group, and a n-hexoxy group,

Q 2 is any one of a single bond, an ether bond, an ester bond, an amide bond, and a carbonyl bond,

x is an integer of from 0 to 10,

y is an integer of from 0 to 10,

Y is an acidic group selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a phosphoric acid group; an aliphatic hydrocarbon group with 1 to 10 carbon atoms having at least one acidic group selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a phosphoric acid group; or an aromatic hydrocarbon group with 6 to 12 carbon atoms having at least one acidic group selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a phosphoric acid group.

2. The polishing composition according to claim 1 , wherein the anionic copolymer is a vinyl-based copolymer which has the unit structure represented by the Formula 1.

3. The polishing composition according to claim 1 , wherein the polishing object is a substrate comprising silicon nitride.

4. The polishing composition according to claim 1 , wherein the abrasive grains are Al (aluminum) doped colloidal silica or colloidal silica immobilized with sulfonic acid.

5. The polishing composition according to claim 1 , wherein the anionic copolymer is at least one selected from the group consisting of styrene sulfonic acid-maleic acid copolymer, styrene sulfonic acid-methacrylic acid copolymer, vinyl sulfonic acid-acrylic acid copolymer, and acrylic acid-maleic acid copolymer.