Sulfonium compound, chemically amplified resist composition, and patterning process

A sulfonium compound having the formula (A):

• wherein Q1 and Q2 are each independently fluorine or a C1-C6 fluoroalkyl group,
• Q3 and Q4 are each independently hydrogen, fluorine or a C1-C6 fluoroalkyl group,
• a is an integer of 1 to 4,
• b is 1 or 2,
• c is an integer of 0 to 3,
• La1 to La4 are each independently a single bond, ether bond, ester bond, sulfonic acid ester bond, carbonate bond or carbamate bond,
• XL1 and XL2 are each independently a single bond or a C2-C40 divalent hydrocarbon group which may contain a heteroatom,
• Ra is hydrogen or a C1-C20 monovalent hydrocarbon group which may contain a heteroatom,
• Rb and Rc are each independently a C2-C40 monovalent hydrocarbon group which may contain a heteroatom, Rb and Rc may bond together to form a ring with the oxygen atoms to which they are attached and the intervening carbon atom,
• R1 is a C1-C50 (a+1)-valent hydrocarbon group which may contain a heteroatom,
• R2 is a C1-C50 monovalent hydrocarbon group which may contain a heteroatom,
• R3 is a C1-C50 divalent hydrocarbon group which may contain a heteroatom,
• in the case of b=1, R1 and R2, or R2 and R3 may bond together to form a ring with the sulfur atom to which they are attached, and in the case of b=2, R1 and R3, or two R1 may bond together to form a ring with the sulfur atom to which they are attached.