Patent ID: 8778803

Claim:
A polishing method for a substrate, wherein the substrate comprises: an underlay comprising concaves and convexes; and a silicon film formed on the underlay, the silicon film having a surface with a step structure, comprising the steps of: polishing the silicon film; and stopping the polishing before the underlay is made uncovered, wherein a CMP slurry for silicon film polishing is used to perform the polishing, the CMP slurry having a property of lowering a polishing rate and then automatically stopping polishing after the surface of the silicon film, with the step structure, is planarized, and before the underlay is uncovered, the CMP slurry comprising: abrasive grains, an oxidizing agent, a cationic surfactant, and water, wherein the CMP slurry has a pH within the range of 4 to 9, wherein the content of the oxidizing agent is from 0.3 to 20.0 parts by mass relative to 100 parts by mass of the CMP slurry for the silicon film polishing, and wherein the cationic surfactant is at least one selected from the group consisting of the following (A) to (E): (A) a quaternary ammonium salt cationic surfactant selected from the group consisting of monoalkyltrimethylammonium salts represented by a formula (R(CH 3 ) 3 N.X); dialkyldimethylammonium salts represented by a formula ((R) 2 N(CH 3 ) 2 N.X); alkylbenzyldimethylammonium salts represented by a formula (R(CH 2 Ph)(CH 3 ) 2 N.X); alkyl pyridinium salts represented by a formula (PyR.X); and chlorinated benzethonium salts represented by a formula (R.PhO(CH 2 ) 2 O(CH 2 )N(CH 3 ) 2 CH 2 Ph.X), wherein each R is an alkyl or alkylene group having 8 to 18 carbon atoms, Ph is a phenyl group, and Py is a pyridinium group, (B) a compound selected from the group consisting of methonium dihydroxide and a salt thereof represented by a formula (N(CH 3 ) 3 X)C n H 2n (N(CH 3 ) 3 X), wherein C n H 2n is an alkyl or alkylene group having 8 to 18 carbon atoms, (C) an alkylamideamine salt represented by a formula (R 1 CONH(CH 2 ) n N(R 2 )(R 3 ).X), wherein R 1 is an alkyl group having 8 to 18 carbon atoms, and R 2 and R 3 are each an alkyl group having 1 to 4 carbon atoms, wherein, in each of (A) to (C), X is a minus ion, (D) an aliphatic amine selected from the group consisting of octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, methyldodecylamine, and dimethyldodecylamine, and (E) an aliphatic diamine having at each terminal of its alkyl chain a cationic hydrophilic group, or a salt thereof.