Sulfonium salt, photoacid generator, curable composition and resist composition

A sulfonium salt represented by the following formula (1):

• wherein R1 and R2 each represent a C6-C30 aryl group, a C4-C30 heterocyclic hydrocarbon group, or a C1-C30 alkyl group, one or some of hydrogen atoms in the aryl group, the heterocyclic hydrocarbon group, or the alkyl group are optionally replaced by a substituent (t), the substituent (t) is at least one selected from the group consisting of C1-C18 alkyl groups, hydroxy groups, C1-C18 alkoxy groups, C2-C18 alkylcarbonyl groups, C7-C11 arylcarbonyl groups, C2-C19 acyloxy groups, C6-C20 arylthio groups, C1-C18 alkylthio groups, C6-C10 aryl groups, C4-C20 heterocyclic hydrocarbon groups, C6-C10 aryloxy groups, hydroxy (poly)alkyleneoxy groups represented by HO(-AO)q- (wherein AO represents at least one of an ethyleneoxy group or a propyleneoxy group, and q represents an integer of 1 to 5), and halogen atoms;
• R3 to R5 each represent an alkyl group, a hydroxy group, an alkoxy group, an alkylcarbonyl group, an arylcarbonyl group, an acyloxy group, an arylthio group, an alkylthio group, an aryl group, a heterocyclic hydrocarbon group, an aryloxy group, a hydroxy (poly)alkyleneoxy group, or a halogen atom;
• k, m, and n respectively represent the numbers of R3, R4, and R5;
• k represents an integer of 0 to 4;
• m represents an integer of 0 to 3;
• n represents an integer of 1 to 4;
• A represents a —O— group, a —S— group, a —SO— group, a —SO2— group, or a —CO— group;
• O represents an oxygen atom;
• S represents a sulfur atom;
• and X− represents a monovalent polyatomic anion.