The invention provides a
radiation-sensitive composition, a pattern forming method and an
onium salt which can form a
resist film or pattern with excellent sensitivity or LWR performance, DOF performance, pattern rectangularity, CDU performance, pattern roundness, EL performance and pattern collapse resistance. A
radiation-sensitive composition containing an
onium salt represented by formula (1), a
polymer containing a
structural unit (I) having an acid-dissociable group, and a
solvent (in formula (1), Q1 and Q2 are each independently a
carbon atom or a
nitrogen atom; wherein at least one of Q1 and Q2 is a
carbon atom; w represents a monocyclic or polycyclic non-aromatic ring structure having 3-40 ring members, which is configured together with Q1 and Q2 in the formula; in the formula, the following formula between Q1 and Q2 represents a
single bond or a
double bond; (AAA) R1 is a monovalent
organic group having 1-20 carbon atoms, a nitro group, a hydroxyl group, an amino group, a
thiol group, a cyano group, a carboxyl group or a
halogen atom; when a plurality of R1 are present, the plurality of R1 are the same as or different from each other; m1 is an integer of 0-4; and Z + represents a monovalent
onium cation). # imgabs0 #