Radiation-sensitive composition and pattern forming method

A radiation-sensitive composition, comprising:

• a first polymer comprising a structural unit (I) having an acid-dissociable group;
• a second polymer comprising a structural unit (i) represented by formula (f1);
• and
• a solvent,
• wherein the acid-dissociable group has an iodo group:
• wherein in the formula (f1),
• RK1 is a hydrogen atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, or a group represented by —RK2—X—RK3, in which RK2 is a single bond, an alkanediyl group having 1 to 6 carbon atoms, or a halogenated alkanediyl group having 1 to 6 carbon atoms, X is a divalent linking group having a hetero atom, and RK3 is an alkyl group having 1 to 6 carbon atoms or a halogenated alkyl group having 1 to 6 carbon atoms,
• LY1 is a divalent hydrocarbon group having 1 to 10 carbon atoms,
• LY2 is —COO—* or —OCO—*, *is a bond on an Rf1 side,
• Rf1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms or a monovalent fluorinated hydrocarbon group having 1 to 10 carbon atoms,
• Rf2 and Rf3 are each independently a fluorine atom or a monovalent fluorinated hydrocarbon group having 1 to 10 carbon atoms, when there are a plurality of Rf2 and Rf3, the plurality of Rf2 are the same as or different from each other, and the plurality of Rf3 are the same as or different from each other, and
• s is an integer of 0 to 3, and when Rf1 is the monovalent hydrocarbon group having 1 to 10 carbon atoms, s is an integer of 1 to 3.