in the iodonium salt having formula (3-2) is as exemplified above for the cation moiety in the iodonium salt having formula (1-2). 

[0161] The acid generator of addition type may be used alone or in admixture. When used, the acid generator is preferably added in an amount of 0.1 to 200 parts, more preferably 1 to 100 parts by weight per 100 parts by weight of the base polymer. 

## Other Components 

[0162] With the foregoing components, other components such as an organic solvent, surfactant, dissolution inhibitor, and crosslinker may be blended in any desired combination to formulate a positive or negative resist composition. This positive or negative resist composition has a very high sensitivity in that the dissolution rate in developer of the base polymer in exposed areas is accelerated by catalytic reaction. In addition, the resist film has a high dissolution contrast, resolution, exposure latitude, and process adapt› ability, and provides a good pattern profile after exposure, and minimal proximity bias because of restrained acid diffusion. By virtue of these advantages, the composition is fully useful in commercial application and suited as a pattern-forming material for the fabrication of VLSis. Par› ticularly when an acid generator is incorporated to formulate a chemically amplified positive resist composition capable of utilizing acid catalyzed reaction, the composition has a higher sensitivity and is further improved in the properties described above. 

[0163] Examples of the organic solvent used herein are described in JP-A 2008-111103, paragraphs [0144]-[0145] (U.S. Pat. No. 7,537,880). Exemplary solvents include ketones such as cyclohexanone, cyclopentanone and methyl- 2-n-pentyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, l-methoxy-2-propanol, l-ethoxy-2-propanol, and diacetone alcohol (DAA); ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, eth› ylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; esters such as propylene glycol monomethyl ether acetate (PGMEA), pro› pylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, t-butyl acetate, t-butyl propionate, and propylene glycol mono-t-butyl ether acetate; and lactones such as y-butyrolactone, which may be used alone or in admixture. 

[0164] The organic solvent is preferably added in an amount of 100 to 10,000 parts, and more preferably 200 to 8,000 parts by weight per 100 parts by weight of the base polymer. 

[0165] Exemplary surfactants are described in JP-A 2008- 111103, paragraphs [0165]-[0166]. 

[0166] Inclusion of a surfactant may improve or control the coating characteristics of the resist composition. The surfactant may be used alone or in admixture. The surfactant is preferably added in an amount of 0.0001 to 10 parts by weight per 100 parts by weight of the base polymer. 

[0167] In the case of a positive resist composition, inclu› sion of a dissolution inhibitor may lead to an increased difference in dissolution rate between exposed and unex› posed areas and a further improvement in resolution. The dissolution inhibitor which can be used herein is a com› pound having at least two phenolic hydroxyl groups on the 

molecule, in which an average of from Oto 100 mo! % of all the hydrogen atoms on the phenolic hydroxyl groups are replaced by acid labile groups or a compound having at least one carboxyl group on the molecule, in which an average of 50 to 100 mo!% of all the hydrogen atoms on the carboxyl groups are replaced by acid labile groups, both the com› pounds having a molecular weight of 100 to 1,000, and preferably 150 to 800. Typical are bisphenol A, trisphenol, phenolphthalein, cresol novolac, naphthalenecarboxylic acid, adamantanecarboxylic acid, and cholic acid derivatives in which the hydrogen atom on the hydroxyl or carboxyl group is replaced by an acid labile group, as described in U.S. Pat. No. 7,771,914 (JP-A 2008-122932, paragraphs [0155]-[0178]). 

[0168] In the resist composition which is positive, the dissolution inhibitor is preferably added in an amount of 0 to 50 parts, more preferably 5 to 40 parts by weight per 100 parts by weight of the base polymer. The dissolution inhibi› tor may be used alone or in admixture. 

[0169] In the case of a negative resist composition, a crosslinker is added thereto to reduce the dissolution rate in the exposed region of a resist film, yielding a negative pattern. Suitable crosslinkers which can be used herein include epoxy compounds, melamine compounds, guan› amine compounds, glycoluril compounds and urea com› pounds having substituted thereon at least one group selected from among methylol, alkoxymethyl and acy› loxymethyl groups, isocyanate compounds, azide com› pounds, and compounds having a double bond such as an alkenyl ether group. These compounds may be used as an additive or introduced into a polymer side chain as a pendant. Hydroxy-containing compounds may also be used as the crosslinker. The crosslinker may be used alone or in admixture. 

[0170] Of the foregoing crosslinkers, suitable epoxy com› pounds include tris(2,3-epoxypropyl) isocyanurate, trimeth› ylolmethane triglycidyl ether, trimethylolpropane triglycidyl ether, and triethylolethane triglycidyl ether. Examples of the melamine compound include hexamethylol melamine, hex› amethoxymethyl melamine, hexamethylol melamine com› pounds having 1 to 6 methylol groups methoxymethylated and mixtures thereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine, hexamethylol melamine compounds having 1 to 6 methylol groups acyloxymethyl› ated and mixtures thereof. Examples of the guanamine compound include tetramethylol guanamine, tetram› ethoxymethyl guanamine, tetramethylol guanamine com› pounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, tetramethoxyethyl guanamine, tet› raacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4 methylol groups acyloxymethylated and mixtures thereof. Examples of the glycoluril compound include tetramethylol glycoluril, tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylol glycoluril compounds having 1 to 4 methylol groups methoxymethyl› ated and mixtures thereof, tetramethylol glycoluril com› pounds having 1 to 4 methylol groups acyloxymethylated and mixtures thereof. Examples of the urea compound include tetramethylol urea, tetramethoxymethyl urea, tetramethylol urea compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, and tetramethoxyethyl urea. 

[0171] Suitable isocyanate compounds include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethyl- 

