US 9,152,050 B2  6  5  In a preferred embodiment, the polymer serving as a base  resin comprises recurring units having an acid labile group  and recurring units having a hydroxyl group and/or lactone  ring as an adhesive group.  In a more preferred embodiment, the polymer serving as a  base resin comprises recurring units of at least one type  selected from recurring units (al) and (a2) having a carboxyl  and/or phenolic hydroxyl group substituted with an acid  labile group, as represented by the general formula (3), and  recurring units having a phenolic hydroxyl group and/or lac› tone ring as an adhesive group and has a weight average  molecular weight of 1,000 to 500,000.  R 031  are each independently a straight, branched or cyclic  C 1  -C$_{12 }$ alkyl group which may contain a carbonyl, ester or  ether moiety, a CcC$_{12 }$aryl group, a C$_{7}$-C 20  aralkyl group, or  a thiophenyl group, Z 1  is a single bond, methylene, ethylene,  phenylene,  fluorinated  phenylene,  ---O-R 032 -, or  ----C(=O)-Z 2 -R 032 -, Z 2  is oxygen or NH, R 032  is a  straight, branched or cyclic C 1  -C 6  alkylene group, alkenylene  group or phenylene group, which may contain a carbonyl,  ester, ether or hydroxyl moiety, M- is a non-nucleophilic  counter ion, subscripts bl, b2 and b3 are numbers in the  range: Osbls0.3, Osb2s0.3, Osb3s0.3, and O<bl+b2+  b3s0.3.  In another aspect, the invention provides a pattern forming  process comprising the steps of applying the resist composi› tion defined above onto a substrate to form a coating, baking,  exposing the coating to high-energy radiation, and develop- ing the exposed coating in a developer.  The high-energy radiation is typically KrF excimer laser of  wavelength 248 nm, ArF excimer laser of wavelength 193  nm, electron beam or soft x-ray of wavelength 3 to 15 nm.  The photoresist film formed using the resist composition of  the invention is effective for minimizing the emission of  outgassing components from the resist film during the EUV  lithography, reducing edge roughness (LWR) after develop› ment, and suppressing formation of blob defects after devel› opment because of its hydrophilic surface.  In a preferred embodiment, the polymer comprising recur› ring units of at least one type selected from recurring units  (al) and (a2) having a carboxyl and/or phenolic hydroxyl  group substituted with an acid labile group, represented by  the general formula (3), has further copolymerized therein  recurring units of at least one type selected from sulfonium  salt units (bl) to (b3), as represented by the general formula  (4).  The singular forms "a," "an" and "the" include plural ref› erents unless  the context clearly  dictates  otherwise.  "Optional" or "optionally" means that the subsequently  described event or circumstances may or may not occur, and  that description includes instances where the event or circum› stance occurs and instances where it does not.  As used herein, the terminology "(meth)acrylic acid" or  "(meth)acrylate" refers collectively to acrylic and meth› acrylic acid or acrylate and methacrylate. The terminology  "Cx-Cy",  as applied to a particular unit, such as, for example,  a chemical compound or a chemical substituent group, means  having a carbon atom content of from "x" carbon atoms to "y"  carbon atoms per such unit.  The abbreviations have the following meaning.  EB: electron beam  EUV: extreme ultraviolet  PAG: photoacid generator  PEB: post-exposure bake  LER: line edge roughness  LWR: line width roughness  Mw: weight average molecular weight  Mn: number average molecular weight  Mw/Mn: dispersity or average molecular weight distribution  GPC: gel permeation chromatography  HFA: 1,1,1,3,3,3-hexafluoro-2-propanol  Making efforts to overcome the outstanding problems, the  inventors have found that a resist composition obtained by  blending an ordinary base polymer which turns alkali soluble  under the action of acid with a polymer comprising recurring  units derived from HFA styrene is effective for suppressing  the emission of outgassing components from the resist film  during exposure in vacuum by the EUV lithography. Since the  Herein R 020 , R 024 , and R 028  each are hydrogen or methyl,  R 021  is  a single bond, phenylene, ---O-R 033 -, or  -C(=O)-Y-R 033 -, Y is oxygen or NH, R 033  is a  straight, branched or cyclic C 1  -C 6 , alkylene group, alk› enylene group or phenylene group, which may contain a  carbonyl (--CO-), ester (--COO-), ether  (---0-), or  hydroxyl moiety, Ro22, Ro23, Ro2s, Ro26, Ro27, Ro29, Ro30, and  DESCRIPTION OF EMBODIMENTS  Advantageous Effects oflnvention  (4)  ~A  \  T  lb!  Ro21  I  Ro22_ 8 +_Ro23  M-