The present invention provides a
radiation-sensitive composition, a pattern forming method, and an
onium salt compound which can exhibit sensitivity or CDU performance, pattern circularity, development defect suppression,
depth of focus, LWR performance, pattern rectangularity, and
exposure latitude at a sufficient level when forming a pattern. A
radiation-sensitive composition comprising: an
onium salt compound represented by formula (1); a
polymer containing a
structural unit (I) represented by formula (2); and a
solvent. (In formula (1), A represents a C3-40 (1 + n) valent
organic group containing a cyclic structure; wherein, when A contains a linear alkanediyl group, the
carbon number of the linear alkanediyl group is 1 or 2; a does not contain a cyclohexyl carbonyloxy structure; rf1 and Rf2 are each independently a
hydrogen atom, a monovalent
organic group having 1-20 carbon atoms, a
fluorine atom, or a monovalent fluorinated
hydrocarbon group; when there are a plurality of Rf1 and Rf2, the plurality of Rf1 and Rf2 are the same or different from each other. Wherein at least one of Rf1 and Rf2 is a
fluorine atom or a monovalent fluorinated
hydrocarbon group; m1 is an integer from 1 to 4; m2 is 0 or 1; n is an integer of 1-3; z + is a monovalent
radiation-sensitive
onium cation; wherein the number of
fluorine atoms in Z + is 8 or less) (In formula (2), RA is a
hydrogen atom, a fluorine atom, a
methyl group, or a
trifluoromethyl group; l is a
single bond or a
divalent linking group; w is a monocyclic
lactone structure, a monocyclic
carbonate structure, a monocyclic sultone structure, a monocyclic
sulfone structure or a monocyclic
ether structure; r11 is a monovalent
organic group with the
carbon number of 1-10, a cyano group, a nitro group, a hydroxyl group or an amino group; when a plurality of R11 exist, the plurality of R11 are the same or different; p is an integer of 0-3; q is 0 or 1.)