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[0022] In another aspect, the invention provides a process for forming a pattern comprising the steps of applying the resist composition defined above onto a substrate, baking to form a resist film, exposing the resist film to high-energy radiation, and developing the exposed film in a developer. 

[0023] Typically, the high-energy radiation is i-line, KrF excimer laser, ArF excimer laser, EB or EUV of wavelength 3 to 15 nm. 

[0024] The resist composition of the invention exhibits a high sensitivity, high acid diffusion-suppressing effect, and high resolution, and forms a pattern of good profile, dimen› sional uniformity, and reduced edge roughness after expo› sure. The resist composition is thus suited as fine pattern› forming material for the fabrication of VLSis and the fabrication of photomasks by EB writing, and pattern form› ing material by i-line, KrF excimer laser, ArF excimer laser, EB or EUV lithography. 

[0025] The resist composition, especially chemically amplified resist composition is used not only in the lithog› raphy for semiconductor circuit formation, but also in the formation of mask circuit patterns, micro-machines, and thin-film magnetic head circuits. 

[0026] As used herein, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. The notation (Cn-Cm) means a group containing from n to m carbon atoms per group. As used herein, the term "brominated" compound means a bromine› containing compound. In chemical formulae, Me stands for methyl, and Ac for acetyl. 

[0027] The abbreviations and acronyms have the follow› ing meaning. 

[0028] EB: electron beam 

[0029] EUV: extreme ultraviolet 

[0030] Mw: weight average molecular weight 

[0031] Mn: number average molecular weight 

[0032] sity Mw/Mn: molecular weight distribution or <lisper- 

[0033] GPC: gel permeation chromatography 

[0034] PEB: post-exposure bake 

[0035] PAG: photoacid generator 

[0036] LWR: line width roughness 

[0037] CDU: critical dimension uniformity 

## Resist Composition 

[0038] Base Resin 

[0039] The resist composition of the invention is defined as comprising a polymer comprising recurring units having the formula (a) as a base resin. For simplicity’s sake, the units are referred to as recurring units (a) and the polymer is referred to as polymer A. 

## Advantageous Effects of Invention 

## DESCRIPTION OF EMBODIMENTS 

[0040] Herein RA is hydrogen or methyl. R $^{1 }$is hydrogen or an acid labile group. R 2 is a C$_{1 }$-C$_{6 }$ straight, branched or cyclic alkyl group or a halogen atom other than bromine. X 1 is a single bond, phenylene group, or a C$_{1 }$-C$_{12 }$ straight, branched or cyclic alkylene group which may contain an ester moiety or lactone ring. X 2 is ---0-, ---O-CH$_{2}$ - or -NH-, m is an integer of 1 to 4, and n is an integer of 0 to 3. 

[0041] Suitable monomers Ma from which recurring units (a) are derived are those having the formula (Ma). 

Herein RA, R1, R 2 , X 1 , X 2 , m and n are as defined above. 

[0042] Monomer Ma may be synthesized, for example, by reacting a compound having the formula (Mal) with a compound having the formula (Ma2). 

<img src='content_image/913048.jpg'>

Herein RA, R1, R 2 , X1, X 2 , m and n are as defined above. 

[0043] Examples of the monomer Ma are shown below, but not limited thereto. RA and R 1 are as defined above. 

<img src='content_image/913046.jpg'>

<img src='content_image/913047.jpg'>

