Radiation-sensitive resin composition and method for forming pattern

A radiation-sensitive resin composition comprising:

• a solvent;
• and
• an onium salt compound represented by formula (1-1) or (1-2):
• wherein:
• Rf1 and Rf2 each independently represent a fluorine atom or a monovalent fluorinated hydrocarbon group having 1 to 20 carbon atoms;
• R1 represents a hydrogen atom, a monovalent hydrocarbon group having 1 to 20 carbon atoms, a fluorine atom, or a monovalent fluorinated hydrocarbon group having 1 to 20 carbon atoms;
• R2, R3, R4, R5, R6, and R7 each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms;
• n1 represents an integer of 0 to 4, provided that when there are a plurality of Rf1s and Rf2s, the plurality of Rf1s and Rf2s are the same or different from each other;
• n2 represents an integer of 0 to 4, provided that when there are a plurality of R1s and R2s, the plurality of R1s and R2s are the same or different from each other;
• n1+n2 is an integer of 2 to 8;
• n3 represents an integer of 0 to 5, provided that when there are a plurality of R3s and R4s, the plurality of R3s and R4s are the same as or different from each other;
• X1 and X2 each independently represent an oxygen atom or a sulfur atom;
• Z+ represents a monovalent radiation-sensitive onium cation,
• R8a and R9a each independently represents a monovalent organic group having 1 to 40 carbon atoms;
• R8b and R9b each independently represent a hydrogen atom or a monovalent organic group having 1 to 40 carbon atoms provided that at least one of R8b and R9b is a monovalent organic group having 2 to 40 carbon atoms, or R8b and R9b taken together represent a ring structure having 3 to 20 ring atoms together with the carbon atom to which R8b and R9b are bonded provided that when the ring structure represented by R8b and R9b taken together is an adamantyl or cyclohexyl, the adamantyl or cyclohexyl is substituted by an organic group;
• and
• n4 represents an integer of 1 to 4, provided that when there are a plurality of R8bs and R9bs, the plurality of R8bs and R9bs are the same or different from each other.