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branched or cyclic alkyl group, or CcC$_{10 }$aryl group, R$^{10 }$is fluorine, or a C$_{1 }$-C$_{10 }$straight, branched or cyclic fluoroalkyl group or fluorophenyl group, which may contain a hydroxy, ether, ester or alkoxy moiety, R$^{11 }$is hydrogen, or a C$_{1 }$-C$_{10 }$ straight, branched or cyclic alkyl group, C$_{2}$ -C$_{10 }$ straight, branched or cyclic alkenyl group, C$_{2}$ -C$_{10 }$ straight or branched alkynyl group, or CcC$_{10 }$ aryl group, which may contain a hydroxy, ether, ester or alkoxy moiety. 

In a preferred embodiment, the resist composition may further comprise an acid generator capable of generating sulfonic acid, sulfonimide or sulfonmethide, and/or an organic solvent. 

In a preferred embodiment, the base polymer comprises recurring units having the formula (al) or recurring units having the formula (a2). 

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Herein R 31 and R 33 are each independently hydrogen or methyl, R 32 and R 34 are each independently an acid labile group, X is a single bond, ester group, phenylene group, naphthylene group or a C$_{1 }$-C$_{12 }$ linking group containing lactone ring, and Y is a single bond or ester group. 

In a preferred embodiment, the resist composition may further comprise a dissolution inhibitor. Typically the resist composition is a chemically amplified positive resist com› position. 

In another preferred embodiment, the base polymer is free of an acid labile group; the resist composition may further comprise a crosslinker. Typically the resist composition is a chemically amplified negative resist composition. 

In a preferred embodiment, the base polymer further comprises recurring units of at least one type selected from the formulae (fl) to (f3). 

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Herein R 51 , R 55 and R 59 each are hydrogen or methyl; R 52 is a single bond, phenylene, -O-R 63 -, or ----C(=O)- $_{Y}$1-R 63 -, Y 1 is ---0-or-NH-, R 63 is a C 1 -C 6 straight, branched or cyclic alkylene or alkenylene group which may contain a carbonyl, ester, ether or hydroxyl moiety, or phenylene group; Rs3, Rs4, Rs6, Rs7, Rss, R6o, R61, and R62 are each independently a C$_{1 }$-C$_{12 }$straight, branched or cyclic alkyl group which may contain a carbonyl, ester or ether moiety, or a CcC$_{12 }$ aryl group, C 7 -C$_{20 }$ aralkyl group or mercaptophenyl group; A 1 is a single bond, -A $^{0}$-C(=O)› O-, -A $^{0}$-O-or -A $^{0}$-O-C(=O)-, A$^{O }$is a cl -Cl2 straight, branched or cyclic alkylene group which may contain a carbonyl, ester or ether moiety; A 2 is hydrogen or trifluo› romethyl; Z 1 is a single bond, methylene, ethylene, phe› nylene, fluorinated phenylene, ---0-R 64 -, or ----C(=O)› Z2 -R 64 -, Z$^{2 }$is ---0- or-NH-, R 64 is a cl -C6 straight, branched or cyclic alkylene or alkenylene group which may contain a carbonyl, ester, ether or hydroxyl moiety, or phenylene, fluorinated phenylene or trifluoromethyl-substi› tuted phenylene group; M- is a non-nucleophilic counter ion, and fl, f2 and f3 are numbers in the range: 0sfls0.5, 0sf2s0.5, 0sf3s0.5, and 0<fl+f2+f3s0.5. 

The resist composition may further comprise a surfactant. 

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 radia› tion, and developing the exposed film in a developer. 

In a preferred embodiment, the high-energy radiation is ArF excimer laser radiation of wavelength 193 nm, KrF excimer laser radiation of wavelength 248 nm, EB, or EUV of wavelength 3 to 15 nm. 

Since a resist film containing a specific biguanide salt compound exhibits an acid diffusion suppressing effect and a high dissolution contrast, it offers improved resolution, a wide focus margin, a reduced LWR, and no dimensional changes on PPD as a positive or negative tone resist film subject to alkaline development and as a negative tone resist film subject to organic solvent development. 

## Advantageous Effects of Invention 

-continued 

