Copolymer and top coating composition

Abstract

A resin composition for forming a top coat which can be formed on a photoresist film without causing intermixing with the photoresist film, can maintain a stable film coating which is not eluted into a medium during immersion lithography, does not impair pattern profiles during dry exposure (which is not immersion lithography), and can be easily dissolved in an alkaline developer. The resin is a copolymer which has a recurring unit (I) having a carboxyl group, a recurring unit (II) having a sulfo group and a recurring unit obtained by copolymerizing fluoroalkyl(meth)acrylates having 1 to 20 carbon atoms in a fluoroalkyl group thereof other than a recurring unit having a side chain that includes an alcoholic hydroxyl group having a fluoroalkyl group at least in an α-position thereof, the copolymer having a weight average molecular weight determined by gel permeation chromatography of 2,000 to 100,000.

1 . A top coating composition coated on a photoresist film for forming a pattern by applying radiation, the composition comprising at least one solvent selected from the group consisting of n-butanol and 4-methyl-2-pentanol; a non-photosensitive copolymer comprising a recurring unit (I) having a carboxyl group, a recurring unit (II) having a sulfo group and a recurring unit that can be obtained by copolymerizing fluoroalkyl(meth)acrylates having 1 to 20 carbon atoms in a fluoroalkyl group thereof other than a recurring unit having a side chain that includes an alcoholic hydroxyl group having a fluoroalkyl group at least in an α-position thereof, the copolymer having a weight average molecular weight determined by gel permeation chromatography of 2,000 to 100,000, the copolymer being scarcely dissolved in water. 
     
     
         2 . The top coating composition according to  claim 1 , wherein the recurring unit (II) having a sulfo group is produced by the radial copolymerizable monomer represented by the following formula (3), 
       
         
           
           
               
               
           
         
       
       wherein R represents a hydrogen atom, a methyl group, a hydroxymethyl group, or a trifluoromethyl group, A represents a single bond, a carbonyl group, a carbonyloxy group, an oxy carbonyl group, and B represents a single bond or a divalent organic group having 1 to 20 carbon atoms. 
     
     
         3 . The top coating composition according to  claim 2 , wherein the monomer represented by the formula (3), producing the recurring unit (II) having a sulfo group, is selected from the group consisting of vinylsulfonic acid, allylsulfonic acid, 2-(meth) acrylamide-2-methyl-1-propanesulfonic acid, and 4-vinyl-1-benzenesulfonic acid. 
     
     
         4 . The top coating composition coated on a photoresist film for forming a pattern by applying radiation according to  claim 1 , wherein the top coating composition is suitable for use in liquid immersion lithography. 
     
     
         5 . The top coating composition according to  claim 1 , wherein the copolymer is soluble in a developer for the photoresist film after exposure radiation to form a resist pattern. 
     
     
         6 . The top coating composition according to  claim 5 , wherein the developer is an alkaline developer. 
     
     
         7 . A top coating composition for a photoresist film in immersion lithography, the top coating composition containing at least one solvent selected from the group consisting of n-butanol and 4-methyl-2-pentanol; a copolymer comprising a recurring unit (I) having a carboxyl group, a recurring unit (II) having a sulfo group and a recurring unit that can be obtained by copolymerizing fluoroalkyl(meth)acrylates having 1 to 20 carbon atoms in a fluoroalkyl group thereof other than a recurring unit having a side chain that includes an alcoholic hydroxyl group having a fluoroalkyl group at least in an α-position thereof, the copolymer having a weight average molecular weight determined by gel permeation chromatography of 2,000 to 100,000, the copolymer being scarcely dissolved in water, 
       wherein the composition is soluble in a developer for the photoresist film after a pattern is formed in the photoresist film.