An onium salt monomer containing an aromatic sulfonic acid anion having a vinyl-substituted aromatic ring is provided as well as a polymer comprising repeat units derived from the monomer. A chemically amplified resist composition comprising the polymer has advantages including high sensitivity, high contrast, improved lithography properties, e.g., EL, LWR, CDU and DOF, collapse resistance during fine pattern formation, and etch resistance after development.

An onium salt monomer containing an aromatic sulfonic acid anion having a vinyl-substituted aromatic ring is provided as well as a polymer comprising repeat units derived from the monomer. A chemically amplified resist composition comprising the polymer has advantages including high sensitivity, high contrast, improved lithography properties, e.g., EL, LWR, CDU and DOF, collapse resistance during fine pattern formation, and etch resistance after development.

A radiation-sensitive composition includes: an onium salt compound represented by formula (1); a polymer including a structural unit (I) which includes an acid-dissociable group; and a solvent. W is a cyclic structure having 3 to 40 ring members formed together with the two carbon atoms; a formula between the two carbon atoms below represents a single bond or a double bond, , A is one of groups represented by formulae (A-1) to (A-7); R.sup.1 is a monovalent organic group having 1 to 20 carbon atoms, a cyano group, a nitro group, a carboxy group, a hydroxy group, an amino group, a halogen atom, or a thiol group, when there are a plurality of R.sup.1s, the plurality of R.sup.1s are same as or different from each other; m.sub.1 is an integer of 0 to 4; and Z.sup.+ is a monovalent radiation-sensitive onium cation.

##STR00001##

A radiation-sensitive composition includes: an onium salt compound represented by formula (1); a polymer including a structural unit (I) which includes an acid-dissociable group; and a solvent. W is a cyclic structure having 3 to 40 ring members formed together with the two carbon atoms; a formula between the two carbon atoms below represents a single bond or a double bond, , A is one of groups represented by formulae (A-1) to (A-7); R.sup.1 is a monovalent organic group having 1 to 20 carbon atoms, a cyano group, a nitro group, a carboxy group, a hydroxy group, an amino group, a halogen atom, or a thiol group, when there are a plurality of R.sup.1s, the plurality of R.sup.1s are same as or different from each other; m.sub.1 is an integer of 0 to 4; and Z.sup.+ is a monovalent radiation-sensitive onium cation.

##STR00001##