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In a further embodiment, an acid generator (b) in the form of an onium salt having polymerizable olefin may be copo› lymerized with the foregoing monomers. JP-A 804-230645, JP-A 2005-084365, and JP-A 2006-045311 disclose sulfo› nium salts having polymerizable olefin capable of generating a specific sulfonic acid and similar iodonium salts. JP-A 2006-178317 discloses a sulfonium salt having sulfonic acid directly attached to the main chain. 

In this embodiment, the polymer may have further copo› lymerized therein recurring units (b 1) to (b3) having a sulfo› nium salt, represented by the following formula ( 4). Some› times, units (b 1) to (b3) are collectively referred to as units (b). 

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or cyclic C 1 -C 6 alkylene group, alkenylene or phenylene group, which may contain a carbonyl, ester, ether or hydroxyl moiety. M- is a non-nucleophilic counter ion. Molar fractions bl, b2 and b3 are in the range of OsblsO.3, Osb2sO.3, Osb3sO.3, and Osbl+b2+b3sO.3. 

Examples of the non-nucleophilic counter ion represented by M- include halide ions such as chloride and bromide ions; fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroet› hanesulfonate, and nonafluoro butanesulfonate; ary lsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzene› sulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; alkyl› sulfonate ions such as mesylate and butanesulfonate; imi› dates such as bis(trifluoromethylsulfonyl)imide, bis (perfluoroethylsulfonyl)imide and bis (perfluorobutylsulfonyl)imide; methidates such as tris (trifluoromethylsulfonyl)methide and tris (perfluoroethy lsulfony l)methide. 

The attachment of an acid generator to the polymer main chain is effective in restraining acid diffusion, thereby pre› venting a reduction of resolution due to blur by acid diffusion. Also edge roughness (LER or LWR) is improved since the 

acid generator is uniformly dispersed. In the polymer, recurring units (a) to (d) may be incorpo- rated in the following molar fraction: 

OsalsO.9, Osa2sO.9, O<al+a2<1.O, preferably OsalsO.8, Osa2sO.8, O.lsal+a2sO.8, and more preferably OsalsO.7, Osa2sO.7, O.2sal+a2sO.7; 

OsblsO.3, Osb2sO.3, Osb3sO.3, and Osb (=bl+b2+b3)sO.3; Osc<l .O, preferably OscsO.9, and more preferably OsCsO.8; OsdsO.5, preferably OsdsO.4, and more preferably OsdsO.3; O.5sal +a2+bl +b2+b3+csl.O, preferably O.6sal +a2+bl + b2+b3+csl.O, more preferably O.7sal+a2+bl+b2+b3+ csl.O; and al+a2+bl+b2+b3+c+d=l. 

The meaning of a+b+c= 1, for example, is that in a polymer comprising recurring units (a), (b ), and (c), the sum ofrecur› ring units (a), (b ), and ( c) is 100 mo! % based on the total amount of entire recurring units. The meaning of a+b+c<l is that the sum of recurring units (a), (b ), and (c) is less than 100 mo! % based on the total amount of entire recurring units, indicating the inclusion of other recurring units. 

There have been described a polymer of formula (1) as polymeric additive for modifying the resist film surface and an acid labile group-containing polymer of formula (2) as base resin. These polymers may be synthesized by any desired methods, for example, by dissolving one or more monomers selected from the monomers to form recurring units (p ), (q) and (r) or recurring units (a) to (d) in an organic solvent, adding a radical polymerization initiator thereto, and effecting heat polymerization. 

Examples of the organic solvent which can be used for polymerization include toluene, benzene, tetrahydrofuran, diethyl ether and dioxane. Examples of the polymerization initiator used herein include 2,2’-azobisisobutyronitrile (AIBN), 2,2’-azobis(2,4-dimethylvaleronitrile ), dimethyl 2,2-azobis(2-methylpropionate ), benzoyl peroxide, and lau› royl peroxide. Preferably the system is heated at 50 to 80° C. for polymerization to take place. The reaction time is 2 to 100 hours, preferably 5 to 20 hours. 

When hydroxyacenaphthylene is copolymerized, an alter- native method is possible. Specifically, acetoxyacenaphtha› lene is used instead of hydroxyacenaphthylene, and after polymerization, the acetoxy group is deprotected by alkaline hydrolysis as mentioned above, for thereby converting the polymer product to hydroxypolyacenaphthalene. For alkaline hydrolysis, a base such as aqueous ammonia or triethylamine may be used. The reaction temperature is -20° C. to 100° C., 

