Sulfonium salt monomer, polymer, chemically amplified resist composition, and pattern forming process

A sulfonium salt monomer having the formula (A):

• wherein n1 is 0 or 1, n2 is 0, 1 or 2, n3 is 0, 1 or 2, n4 is 0, 1 or 2, n1 to n4 are in the range:
• 0≤n2+n3+n4≤5 when n1=0 and 0≤n2+n3+n4≤7 when n1=1;
• n5 is 0 or 1, n6 is 0, 1 or 2, n7 is 0, 1 or 2, n8 is 0, 1 or 2, n5 to n8 are in the range:
• 0≤n6+n7+n8≤5 when n5=0 and 0≤n6+n7+n8≤7 when n5=1;
• n9 is 0 or 1, n10 is 0, 1 or 2, n11 is 0, 1 or 2, n12 is 0, 1 or 2, n9 to n12 are in the range:
• 0≤n10+n11+n12≤5 when n9=0 and 0≤n10+n11+n12≤7 when n9=1, and 1≤n2+n6+n10≤6 and 1≤n3+n7+n11≤6,
• R1, R2 and R3 are each independently a C1-C20 hydrocarbyl group which may contain a heteroatom, two R1 may be identical or different when n3=2, two R2 may be identical or different when n7=2, two R3 may be identical or different when n11=2,
• R4, R5 and R6 are each independently halogen, nitro, hydroxy, carboxy, a C1-C20 hydrocarbyl group which may contain a heteroatom, a C1-C20 hydrocarbyloxy group which may contain a heteroatom, or a C1-C20 hydrocarbylthio group which may contain a heteroatom;
• when n4=2, two R4 may be identical or different and bond together to form a ring with the carbon atoms to which they are attached;
• when n8=2, two R5 may be identical or different and bond together to form a ring with the carbon atoms to which they are attached;
• when n12=2, two R6 may be identical or different and bond together to form a ring with the carbon atoms to which they are attached;
• two of three aromatic rings bonded to S+ may bond together to form a ring with the sulfur atom to which they are attached, and
• Z− is an aromatic sulfonate anion having a polymerizable group.