6  US 10,222,696 B2  5  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).  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).  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.  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.  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.  The resist composition may further comprise a surfactant.  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.  -continued  Advantageous Effects of Invention  (f2)  (fJ)  R6o  I  +s-R61  I  R62  (al)  (a2)  ~  y  OR34 