US 2020/0192222 Al  135  Jun.  18,2020  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-