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Of the foregoing PAGs, those having an anion of formula (IA’) or (ID) are especially preferred because of reduced acid diffusion and high solubility in the resist solvent. Also those having an anion of formula (2’) are especially pre› ferred because of extremely reduced acid diffusion. 

The PAG 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. 

Other Components 

With the biguanide salt compound having formula (A), the base polymer, and the acid generator, all defined above, other components such as an organic solvent, surfactant, dissolution inhibitor, and crosslinker may be blended in any desired combination to formulate a chemically amplified 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 addi› tion, the resist film has a high dissolution contrast, resolu› tion, exposure latitude, and process adaptability, and pro› vides 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. Particularly 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 sen› sitivity and is further improved in the properties described above. 

In the case of positive resist compositions, inclusion of a dissolution inhibitor may lead to an increased difference in dissolution rate between exposed and unexposed regions and a further improvement in resolution. In the case of negative resist compositions, a negative pattern may be formed by adding a crosslinker to reduce the dissolution rate of the exposed region. 

Examples of the organic solvent used herein are described in JP-A 2008-111103, paragraphs t01441-[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, and l-ethoxy-2- propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propyl› ene 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-ethoxypropionate, t-butyl acetate, t-butyl propionate, and propylene glycol as mono› t-butyl ether acetate; and lactones such as y-butyrolactone, which may be used alone or in admixture. 

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. 

Exemplary surfactants are described in JP-A 2008- 111103, paragraphs [0165]-[0166]. Inclusion ofa surfactant may improve or control the coating characteristics of the resist composition. 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. 

The dissolution inhibitor which can be used herein is a compound having at least two phenolic hydroxyl groups on the molecule, in which an average of from O to 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 compounds 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]). 

In the positive resist composition, the dissolution inhibitor is preferably added in an amount of O to 50 parts, more preferably 5 to 40 parts by weight per 100 parts by weight of the base polymer. 

Suitable crosslinkers which can be used herein include epoxy compounds, melamine compounds, guanamine com› pounds, glycoluril compounds and urea compounds having substituted thereon at least one group selected from among methylol, alkoxymethyl and acyloxymethyl groups, isocya- nate compounds, azide compounds, 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 com› pounds may also be used as the crosslinker. 

Of the foregoing crosslinkers, examples of suitable epoxy compounds include tris(2,3-epoxypropyl) isocyanurate, trimethylolethane triglycidyl ether, trimethylolpropane tri› glycidyl ether, and trimethylolethane triglycidyl ether. Examples of the melamine compound include hexamethylol melamine, hexamethoxymethyl melamine, hexamethylol melamine compounds having 1 to 6 methylol groups methoxymethylated and mixtures thereof, hexamethoxy› ethyl melamine, hexaacyloxymethyl melamine, hexameth› ylol melamine compounds having 1 to 6 methylol groups acyloxymethylated and mixtures thereof. Examples of the guanamine compound include tetramethylol guanamine, tetramethoxymethyl guanamine, tetramethylol guanamine compounds having 1 to 4 methylol groups methoxymethyl› ated and mixtures thereof, tetramethoxyethyl guanamine, tetraacyloxyguanamine, tetramethylol guanamine com› pounds 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, 

