Onium salts, photoacid generators for resist compositions, and patterning process

摘要

Onium salts of the formula (1) are novel. CHEM R1 is C1-10 alkyl or C6-14 aryl, R2 is H or C1-6 alkyl, p is an integer of 1 to 5, q is an integer of 0 to 4, p+q = 5, R3 is C1-10 alkyl or C6-14 aryl, M is a sulfur or iodine atom, and "a" is equal to 3 or 2. A chemical amplification type resist composition comprising the onium salt as a photoacid generator is suited for microfabrication, especially by deep UV lithography because of many advantages including improved resolution, minimized line width variation or shape degradation even on long-term PED, minimized defect after coating, development and stripping, and improved pattern profile after development.