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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. 

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). 

<img src='content_image/887953.jpg'>

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 

<img src='content_image/887954.jpg'>

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. 

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 

## Advantageous Effects oflnvention 

## DESCRIPTION OF EMBODIMENTS 

