Radiation-sensitive composition, method for forming pattern, and onium salt compound

A radiation-sensitive composition comprising:

• a first onium salt compound represented by formula (1);
• at least one second onium salt compound selected from the group consisting of a carboxylic acid salt compound represented by formula (2) and a carboxylic acid intramolecular salt compound represented by formula (3);
• a polymer comprising a structural unit which comprises an acid-dissociable group;
• and
• a solvent,
• wherein, in the formula (1),
• A is a (1+n)-valent organic group having 1 to 40 carbon atoms;
• Rf1 and Rf2 are each independently a hydrogen atom, a monovalent organic group, a fluorine atom, or a monovalent fluorinated hydrocarbon group;
• when there are a plurality of Rf1s and Rf2s, the plurality of Rf1s and Rf2s are the same as or different from each other;
• m1 is an integer of 1 to 8;
• n is an integer of 1 to 3;
• and
• Z1+ represents a radiation-sensitive onium cation,
• wherein, in the formula (2),
• R1 is a monovalent organic group having 2 to 40 carbon atoms;
• and
• Z2+ represents an organic cation, and
• wherein, in the formula (3),
• R2 is a single bond or a divalent organic group having 1 to 40 carbon atoms;
• and
• Z3+ is a monovalent organic onium cation.