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

A sulfonium salt having the formula (1):

• wherein n1 is 0 or 1, n2 is 0, 1 or 2, n3 is 0, 1 or 2, n4 is 0, 1 or 2, meeting 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, meeting 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, meeting 0≤n10+n11+n12≤5 when n9=0, and 0≤n10+n11+n12≤7 when n9=1, 1≤n2+n6+n10≤6, and 1≤n3+n7+n11≤6,
• R1, R2 and R3 are each independently halogen, nitro, cyano, hydroxy, carboxy, a C1-C20 hydrocarbyl group which may contain a heteroatom, C1-C20 hydrocarbyloxy group which may contain a heteroatom, or C1-C20 hydrocarbylthio group which may contain a heteroatom;
• when n4=2, two R1 may be identical or different and two R1 may bond together to form a ring with the carbon atom to which they are attached;
• when n8=2, two R2 may be identical or different and two R2 may bond together to form a ring with the carbon atom to which they are attached;
• when n12=2, two R3 may be identical or different and two R3 may bond together to form a ring with the carbon atom to which they are attached;
• RAL1, RAL2 and RAL3 are each independently an acid labile group;
• when n3=2, two RAL1 may be identical or different;
• when n7=2, two RAL2 may be identical or different;
• when n11=2, two RAL3 may be identical or different;
• at least one —SF5 group is attached to a carbon atom adjoining the carbon atom to which —O—RAL1, —O—RAL2 or —O—RAL3 is 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 sulfonic acid anion having at least one cyclic structure.