Onium salt, chemically amplified positive resist composition and resist pattern forming process

Abstract

onium salt in which an aromatic ring having a sulfo group bonded thereto and another aromatic ring structure containing a bulky substituent group are linked via a sulfonamide bond generates an aromatic sulfonic acid with adequate acidity and controlled diffusion. A chemically amplified positive resist composition comprising the onium salt has a high resolution and forms a pattern of rectangular profile with reduced LER.