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[0197] • Repeating Unit Having Structure (Acid-Decom› posable Group) in which Phenolic Hydroxyl Group is Pro› tected by Leaving Group that Leaves Through Decomposi› tion by Action of Acid 

[0198] In the present specification, the phenolic hydroxyl group is a group obtained by substituting a hydrogen atom of an aromatic hydrocarbon group with a hydroxyl group. The aromatic ring of the aromatic hydrocarbon group is a monocyclic or polycyclic aromatic ring, and examples thereof include a benzene ring and a naphthalene ring. 

[0199] Examples of the leaving group that leaves through decomposition by the action of an acid include groups represented by Formulae (Yl) to (Y4). 

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[0200] In Formulae (Yl) and (Y2), Rx$_{1 }$ to Rx$_{3 }$ each independently represent an (linear or branched) alkyl group or a (monocyclic or polycyclic) cycloalkyl group. It should be noted that in a case where all ofRx$_{1 }$ to Rx$_{3 }$ are (linear or branched) alkyl groups, it is preferable that at least two of Rxi, ... , or Rx$_{3 }$ are methyl groups. 

[0201] Among those, Rx$_{1 }$ to Rx$_{3 }$ are more preferably each independently a repeating unit which represents a linear or branched alkyl group, and Rx$_{1 }$ to Rx$_{3 }$ are still more preferably each independently a repeating unit which represents a linear alkyl group. 

[0202] Two ofRx$_{1 }$ to Rx$_{3 }$ may be bonded to each other to form a monocycle or a polycycle. 

[0203] As the alkyl group of each of Rx$_{1 }$ to Rx$_{3}$ , an alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a t-butyl group, is preferable. 

[0204] As the cycloalkyl group of each of Rx$_{1 }$ to Rx$_{3}$ , a monocyclic cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, or a polycyclic cycloal› kyl group such as a norbomyl group, a tetracyclode› canyl group, a tetracyclododecanyl group, and an ada› mantyl group is preferable. 

[0205] As the cycloalkyl group formed by the bonding of two of Rx$_{1 }$ to Rx$_{3}$ , a monocyclic cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, or a polycyclic cycloalkyl group such as a norbomyl group, a tetracyclodecanyl group, a tetracyclododeca› nyl group, and an adamantyl group is preferable. Among those, a monocyclic cycloalkyl group having 5 or 6 carbon atoms is more preferable. 

[0206] In the cycloalkyl group formed by the bonding of two ofRx$_{1 }$to Rx$_{3}$ , for example, one of the methylene groups constituting the ring may be substituted with a heteroatom such as an oxygen atom, or a group having a heteroatom, such as a carbonyl group. 

[0207] For the group represented by each of Formulae (Yl) and (Y2), for example, an aspect in which Rx$_{1 }$ is a methyl group or an ethyl group, and Rx$_{2 }$ and Rx$_{3 }$ are bonded to each other to form the above-mentioned cycloalkyl group is preferable. 

[0208] In Formula (Y3), R$_{36 }$ to R$_{38 }$ each independently represent a hydrogen atom or a monovalent organic group. 

Formula (Yl): 

Formula (Y2): 

Formula (Y3): 

Formula (Y4): 

R$_{37 }$ and R$_{38 }$ may be bonded to each other to form a ring. Examples of the monovalent organic group include an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, and an alkenyl group. R$_{36 }$ is preferably a hydrogen atom. 

[0209] In Formula (Y4), Ar represents an aromatic hydro› carbon group. Rn represents an alkyl group, a cycloalkyl group, or an aryl group. Rn and Ar may be bonded to each other to form a non-aromatic ring. Ar is more preferably an aryl group. 

[0210] The repeating unit having a structure (acid-decom› posable group) in which a phenolic hydroxyl group is protected by a leaving group that leaves through decompo› sition by the action of an acid preferably has a structure in which a hydrogen atom in the phenolic hydroxyl group is protected by a group represented by any of Formulae (Yl) to (Y4). 

[0211] As the repeating unit having a structure in which the phenolic hydroxyl group is protected by a leaving group that leaves through decomposition by the action of an acid, a repeating unit represented by General Formula (All) is preferable. 

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[0212] In General Formula (All), 

[0213] R$_{61}$, R 62 , and R $_{63 }$each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, a halogen atom, a cyano group, or an alkoxycarbonyl group. It should be noted that R$_{62 }$may be bonded to Ar$_{6 }$ to form a ring, and in this case, R$_{62 }$represents a single bond or an alkylene group. 

[0214] X$_{6 }$ represents a single bond, -COO-, or ----CONR$_{64}$-. R$_{64 }$represents a hydrogen atom or an alkyl group. 

[0215] L$_{6 }$represents a single bond or an alkylene group. 

[0216] Ar$_{6 }$ represents an (n+l)-valent aromatic hydro› carbon group, and in a case of being bonded to R $^{62 }$to form a ring, Ar represents an (n+2)-valent aromatic hydrocarbon group. 

[0217] Y/s each independently represent a hydrogen atom or a group that leaves by the action of an acid in a case of n2:2. It should be noted that at least one ofY/s represents a group that leaves by the action of an acid. The group that leaves by the action of an acid as Y2 is preferably any of Formulae (Yl) to (Y4). 

[0218] n represents an integer of 1 to 4. 

[0219] Each of the groups may have a substituent, and examples of the substituent include an alkyl group (having 1 to 4 carbon atoms), a halogen atom, a hydroxyl group, an alkoxy group (having 1 to 4 carbon atoms), a carboxyl group, and an alkoxycarbonyl group (having 2 to 6 carbon atoms), and these groups preferably have 8 or less carbon atoms. 

(All) 

