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

A radiation-sensitive resin composition comprising:

• an onium salt compound represented by formula (1),
• a resin comprising a structural unit having an acid-dissociable group, and
• a solvent:
• in the formula (1),
• R1 is a monovalent hydrocarbon group having 1 to 20 carbon atoms;
• R2 and R3 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms, or R2 and R3 taken together represent a cyclic structure having 3 to 20 ring atoms together with the carbon atom to which R2 and R3 are bonded;
• R4 is a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms and L1 is a substituted or unsubstituted divalent linking group having 1 to 40 carbon atoms, or R4 and L1 taken together represent a group comprising a heterocyclic structure having 3 to 20 ring atoms together with the nitrogen atom to which R4 and L1 are bonded;
• L2 is a single bond or a substituted or unsubstituted divalent linking group having 1 to 40 carbon atoms;
• Rf1 and Rf2 are each independently a hydrogen atom, a fluorine atom, a monovalent hydrocarbon group having 1 to 10 carbon atoms, or a monovalent fluorinated hydrocarbon group having 1 to 10 carbon atoms, when there are a plurality of Rf1s and a plurality of Rf2s, the plurality of Rf1s are the same or different from each other, and the plurality of Rf2s are the same or different from each other;
• n is an integer of 1 to 4;
• and
• Z+ is a monovalent radiation-sensitive onium cation.