7  US 9,360,753 B2  8  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.  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).  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.  (1)  ,_Jj~  T  {;-- Rl21  I  R122_ 8 + -R123  M- ,-Ji~  T  1b-;-- Z1  oAo  I  so - Rl33~C/  3  F2  Rl29  I  +s-R130  I  Rl31  (2)  Rl25  I  +s-R126  I  Rl27 