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and a high sensitivity and forms a pattern with a satisfactory profile and minimal LER through exposure and development. 

Seeking for a resist material having a high resolution, high sensitivity and minimal LER, the inventor has found that a resist composition, typically chemically amplified positive resist composition, comprising a polymer comprising recur› ring units having an acid labile group gives better results of lithography when a metal salt of carboxylic acid or a metal complex of ~-diketone is added thereto. 

More particularly, when a polymerobtained from polymer- ization of a monomer having an acid labile group-substituted phenolic hydroxyl group or a copolymer obtained from copo› lymerization of a monomer having an acid labile group-sub› stituted phenolic hydroxyl group with a sulfonium salt mono› mer having polymerizable olefin is used as the base resin and a salt of a mono- to tetra-functional C 1 -C$_{20 }$carboxylic acid or a complex of a ~-diketone with a metal selected from the group consisting of sodium, magnesium, chromium, manga› nese, iron, cobalt, nickel, copper, zinc, silver, cadmium, indium, tin, antimony, cesium, zirconium, and hafnium is added thereto, there is formulated a resist composition, typi› cally chemically amplified positive resist composition which has many advantages including a high sensitivity, a high resolution, controlled acid diffusion, a satisfactory pattern profile after exposure, and a minimal LER. In addition, the resist composition is effective for preventing electrostatic charges during EB image writing. The resist composition is thus suited as the micropatterning material for the fabrication ofVLSis and photomasks. 

One embodiment of the invention is a resist composition comprising a polymer comprising recurring units of acid labile group-substituted (meth)acrylic acid, styrenecarboxy- lic acid or vinylnaphthalenecarboxylic acid and/or recurring units having an acid labile group-substituted phenolic hydroxyl group, and a metal salt of a mono- to tetra-func- tional C 1 -C$_{20 }$carboxylic acid or a metal complex of a ~-dike› tone, the metal being selected from among sodium, magne› sium, chromium, manganese, iron, cobalt, nickel, copper, zinc, silver, cadmium, indium, tin, antimony, cesium, zirco- nium, and hafnium. 

Specifically, the polymer comprises recurring units (al) of acid labile group-substituted (meth)acrylic acid, styrenecar› boxylic acid or vinylnaphthalenecarboxylic acid and/or recurring units (a2) having an acid labile group-substituted phenolic hydroxyl group, which may be represented by the general formula (1). 

Herein R 1 and R 3 are each independently hydrogen or methyl, R 2 and R 4 each are an acid labile group, X 1 is a single bond, a C 1 -C$_{12 }$ linking group having at least one of ester moiety, lactone ring, phenylene moiety and naphthylene moiety, a phenylene group, or a naphthylene group, X 2 is a single bond or an ester or amide group, al and a2 are numbers in the range: Osals0.9, Osa2s0.9, and O<al+a2<1. 

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In addition to the recurring units (al) and (a2), the polymer may comprise recurring units (b 1 ), (b2) or (b3) ofa sulfonium salt having the general formula (2). 

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Herein R 120 , R 124 , and R 128 each are hydrogen or methyl. R 121 is a single bond, phenylene, ---0-R-, or----C(=O)› Y-R- wherein Y is oxygen or NH, and R is a straight, branched or cyclic C 1 -C 6 alkylene group, C 3 -C$_{10 }$alkenylene or phenylene group, which may contain a carbonyl (-CO-), ester (--COO-), ether (---0-) or hydroxyl moi› ety. R122, R123, R12s, R126, R127, R129, R130, andR131 are each independently a straight, branched or cyclic C 1 -C 2 , alkyl group which may contain a carbonyl, ester or ether moiety, or a CcC$_{12 }$aryl, C 7 -C$_{20 }$aralkyl, orthiophenyl group which may contain a straight, branched or cyclic C 1 -C$_{10 }$alkyl, halogen, trifluoromethyl, cyano, nitro, hydroxyl, alkoxy, alkoxycarbo- nyl or acyloxy radical. Z 1 is a single bond or ----C(=O)› Z3-R132-. Z$_{2 }$ is a single bond, methylene, ethylene, phe› nylene, fluorinated phenylene, -O-R 132 - or ----C( =O)› Z3-R 132 -, wherein Z 3 is oxygen or NH, and R 132 is a straight, branched or cyclic C 1 -C 6 alkylene group, alk- enylene, or phenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety. A pair ofR 122 and R 123 , R 125 and R126, R12s and R127, R126 and R127, R129 and R130, R129 and R 131 , or R 130 and R 131 may bond directly or via a meth› ylene moiety or ether bond to form a ring with the sulfur atom. R 133 is hydrogen ortrifluoromethyl. M- is a non-nucleophilic counter ion. The subscripts b 1, b2 and b3 are in the range of Osbls0.5, Osb2s0.5, Osb3s0.5, and O<bl+b2+b3s0.5. 

The binding of the acid generator with the polymer is effective for shortening the distance of acid diffusion and reducing edge roughness. 

According to the invention, a metal salt of carboxylic acid or metal complex of ~-diketone having high absorption of EUV radiation is added to the polymer comprising acid labile group-bearing recurring units (al) and/or ( a2) and optionally acid generator-bearing recurring units (b 1 ), (b2) or (b3) in the resist composition. This combination is effective for control- ling acid diffusion, improving contrast and sensitivity, improving electric conductivity, and hence, preventing elec› trostatic charging during image writing. Particularly when exposed to short-wavelength high-energy radiation and EB, the resist composition is effective for forming a fine size pattern with a high resolution, high sensitivity, minimal LER and satisfactory profile. Thus a pattern can be formed at a very high accuracy. 

