115  US 10,222,696 B2  116  -continued  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  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,  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.  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. 