Photoresist resin, method for producing photoresist resin, photoresist resin composition, and method for forming pattern

A photoresist resin comprising an acrylic resin, wherein

• when the photoresist resin is dissolved in propylene glycol monomethyl ether acetate in such a way that a resin solid content concentration is 5 wt %, a polystyrene equivalent turbidity measured using a method described in “Drinking Water Testing Methods” of Japan Water Works Association of 2003, Ministry of Health, Labor and Welfare Ordinance No. 261 of Japan is 30 or less,
• wherein the photoresist resin comprises at least one polymerization unit selected from the group consisting of polymerization units represented by Formulas (a2) to (a4) and (b1) to (b5)
• wherein R represents a hydrogen atom, a halogen atom, or an alkyl group that has from 1 to 6 carbon atoms and optionally has a halogen atom;
• A represents a single bond or a linking group;
• R4 represents a branched alkyl group that has from 1 to 6 carbon atoms;
• R5 and R6 are the same or different and represent an alkyl group that has from 1 to 6 carbon atoms and optionally has a hydrogen atom or a substituent;
• R7 represents a —COORe group, and the Rc represents a tertiary hydrocarbon group that optionally has a substituent, a tetrahydrofuranyl group, a tetrahydropyranyl group, or an oxepanyl group;
• n represents an integer from 1 to 3;
• Ra represents a substituent bonded to a ring Z1, and each Ra is the same or different and represents an oxo group, an alkyl group, a hydroxy group optionally protected with a protecting group, a hydroxyalkyl group optionally protected with a protecting group, or a carboxy group optionally protected with a protecting group;
• p of the polymerization units represented by Formulas (a2) represents an integer from 0 to 3;
• p of the polymerization units represented by Formulas (a3) represents an integer from 0 to 3;
• p of the polymerization units represented by Formulas (a4) represents an integer from 1 to 3;
• the ring Z1 of the polymerization units represented by Formulas (a2) represents a cycloalkane ring having from 3 to 20 carbon atoms;
• the ring Z1 of the polymerization units represented by Formulas (a3) represents an alicyclic hydrocarbon ring having from 3 to 20 carbon atoms;
• and the ring Z1 of the polymerization units represented by Formulas (a4) represents an alicyclic hydrocarbon ring having from 3 to 20 carbon atoms;
• X represents no bond, a methylene group, an ethylene group, an oxygen atom, or a sulfur atom;
• Y represents a methylene group or a carbonyl group;
• Z represents a divalent organic group;
• V1 to V3 are the same or different and represent —CH2—, [—C(=O)—], or [—C(=O)—O—] with the proviso that at least one of V1 to V3 is [—C(=0)—O—];
• and R9 and R11 are the same or different and represent a hydrogen atom, a fluorine atom, an alkyl group optionally having a fluorine atom, a hydroxy group optionally protected with a protecting group, a hydroxyalkyl group optionally protected with a protecting group, a carboxy group optionally protected with a protecting group, or a cyano group;
• R8 represents a cyano group;
• R9 and R12 to R14 are the same or different and represent a fluorine atom, an alkyl group optionally having a fluorine atom, or a cyano group;
• and R10 represents a fluorine atom, an alkyl group optionally having a fluorine atom, a hydroxy group optionally protected with a protecting group, a hydroxyalkyl group optionally protected with a protecting group, a carboxy group optionally protected with a protecting group, or a cyano group.