Onium salts and positive resist materials using the same

Abstract

Disclosed are novel onium salts represented by general formula (R) 3 S + M, wherein three R's may be the same or different, each being an aryl group, provided that at least one of R's is a t-alkoxy substituted phenyl group, and M is an anion capable of foxing the sulfonium salts; and high energy radiation-responsive positive resist materials using said novel onium salts as acid generator.

What is claimed is:  
     
         1 . Onium salts represented by general formula (R) 3 S + M, wherein three R's may be the same or different, each being an aryl group, provided that at least one of R's is a t-alkoxy substituted phenyl group, and M is an anion capable of forming the sulfonium salts.  
     
     
         2 . The onium salts of  claim 1 , wherein the aryl group represented by R, other than the t-alkoxy substituted phenyl group, includes phenyl, 3-methylphenyl, 4-methylphenyl, 4-isopropylphenyl, 4-t-butylphenyl, 4-fluorophenyl, 3-fluorophenyl, 4-chlorophenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 4-phenoxyphenyl, 4-phenylthiophenyl, 3-trifluoromethylphenyl and 4-trifluoromethylphenyl groups.  
     
     
         3 . The onium salts of  claim 1 , wherein the anion represented by M includes hexafluorophosphate, hexafluoroantinonate, hexafluoroarsenate, trifluoromethanesulfonate, paratoluenesulfonate, tetrafluoroborate and fluorosulfonate ions.  
     
     
         4 . The onium salts of  claim 3 , wherein the anion represented by M is trifluoromethanesulfonate or paratoluenesulfonate ion.  
     
     
         5 . The onium salts of claim wherein one of three R's is a t-alkoxy substituted phenyl group, the two other R's are lower alkyl or alkoxy-substituted phenyl groups and M is trifluoromethanesulfonate ion.  
     
     
         6 . Aqueous alkali-developable high energy radiation-responsive positive resist materials comprising three components, (a) a poly(hydroxystyrene) resin in which hydrogen atoms of the hydroxy groups are partly replaced by t-butoxycarbonyl groups, (b) a dissolution inhibitor and (c) an onium salt, wherein the three components (a), (b) and (c) have the weight proportions defined by the relations: 0.55≦a, 0.07≦b≦0.40, 0.005≦c≦0.15, and a+b+c=1; said onium salt being selected from the onium salts of  claim 1 .  
     
     
         7 . The resist materials of  claim 6 , wherein from 10 to 50% of the hydrogen atoms of the hydroxy groups in the poly(hydroxystyrene) resin are replaced by t-butoxycarbonyl groups.  
     
     
         8 . The resist materials of  claim 6 , wherein the poly(hydroxystyre ne) resin as component (a) has a weight average molecular weight of at least 10,000.  
     
     
         9 . The resist materials of  claim 8 , wherein the poly(hydroxystyre ne) resin has a molecular weight distribution in the range of 1.05 to 1.50.  
     
     
         10 . The resist materials of  claim 6 , wherein the poly(hydroxystyre ne) resin is a polymer prepared by a living polymerization method.  
     
     
         11 . The resist materials of  claim 6 , wherein the dissolution inhibitor include phenols protected with a t-butoxycarbonyl group, bile acid derivatives and esters protected with a tetrahydropyranyl group, a methoxymethyl group, a t-butyl group or a t-amyl group.  
     
     
         12 . The resist materials of  claim 11 , wherein the protected phenols include d-t-butoxycarbonylhydroquinone, 4,4′-di-t-butoxycarbonyloxydiphenyl, di-t-butoxycarbonylbisphenol A and di-t-butoxycarbonylbisphenol F, the bile acid derivatives include t-butyl esters of cholic acid and deoxycholic acid, and the protected esters include 4-t-butoxycarbonylbiphenyl and di-t-butoxyacetylbisphenol A.