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[0137] When used, the acid generator of addition type is preferably added in an amount of 0.1 to 50 parts, and more preferably 1 to 40 parts by weight per 100 parts by weight of the base polymer. When the base polymer includes recurring units (f) and/or the acid generator of addition type is added, the resist composition functions as a chemically amplified resist composition. 

[0138] Organic Solvent 

[0139] An organic solvent may be added to the resist composition. The organic solvent used herein is not particu› larly limited as long as the foregoing and other components are soluble therein. Examples of the organic solvent 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, methyl-2- n-pentyl ketone and 2-heptanone; 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 monom› ethyl ether (PGME), ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol mono› ethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; esters such as propylene glycol 

monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropi› onate, tert-butyl acetate, tert-butyl propionate, and propyl› ene glycol mono-tert-butyl ether acetate; and lactones such as y-butyrolactone, which may be used alone or in admix› ture. 

[0140] 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. 

[0141] Other Components 

[0142] With the foregoing components, other components such as a surfactant, dissolution inhibitor, and crosslinker may be blended in any desired combination to formulate a chemically amplified positive or negative resist composi› tion. 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. 

[0143] Exemplary surfactants are described in JP-A 2008- 111103, paragraphs [0165]-[0166]. Inclusion of a surfactant may improve or control the coating characteristics of the resist composition. While the surfactant may be used alone or in admixture, it is preferably added in an amount of 0.0001 to 10 parts by weight per 100 parts by weight of the base polymer. 

[0144] In the case of positive resist compositions, 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]). 

[0145] In the positive resist composition, 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 inhibitor may be used alone or in admixture. 

[0146] In the case of negative resist compositions, a nega› tive pattern may be formed by adding a crosslinker to reduce the dissolution rate of a resist film in exposed area. Suitable crosslinkers include epoxy compounds, melamine com› pounds, guanamine compounds, glycoluril compounds and urea compounds having substituted thereon at least one 

