Onium salt, resist composition, and patterning process

An onium salt represented by the following general formula (1),

• wherein RALU represents any one of a tertiary ether, tertiary carbonate, or acetal formed together with the adjacent oxygen atom, having a cyclic structure, and optionally having a heteroatom;
• RF represents any one of a fluorine atom, a fluorine-containing alkyl group having 1 to 6 carbon atoms, and a nitro group;
• Ra represents a hydrocarbyl group having 1 to 20 carbon atoms and optionally having a heteroatom;
• n1 represents an integer of 0 or 1;
• n2 and n3 represent an integer of 1 or 2;
• when n2 and n3 represent 1, RF and —O—RALU are bonded to carbon atoms adjacent to each other, and when any one or both of n2 and n3 represent 2, one of RF and one of —O—RALU are bonded to carbon atoms adjacent to each other;
• n4 represents an integer of 0 to 3;
• when n4≥2, a plurality of Ra are optionally bonded to each other to form a cyclic structure together with the carbon atoms to which these are bonded;
• and Z+ represents an onium cation.