content_image/896736.jpg content_image/896737.jpg content_image/896738.jpg content_image/896739.jpg content_image/896740.jpg content_image/896734.jpg content_image/896735.jpg content_image/896741.jpg
wherein RA is hydrogen or methyl, R$^{21 }$is a C$_{1 }$-C$_{8 }$ straight or branched alkyl group, pis an integer of 1 to 3, and XA is an acid labile group other than the group having the formula (bl): 

<img src='content_image/896736.jpg'>

wherein R$^{21 }$and pare as defined above, and the broken line designates a valence bond. 

2. The resist composition of claim 1 wherein XA is an acid labile group having the formula (Ll), (L2) or (L3): 

<img src='content_image/896737.jpg'>

<img src='content_image/896738.jpg'>

<img src='content_image/896739.jpg'>

wherein the broken line designates a valence bond, RL 01 to RL $^{03 }$are each independently hydrogen or a C$_{1 }$ -C$_{12 }$ alkyl group, RL $^{04 }$is hydrogen or a C$_{1 }$-C$_{3 }$ straight or branched alkyl group, RLos to RL $^{15 }$are each indepen› dently hydrogen or a C$_{1 }$-C$_{6 }$ monovalent hydrocarbon group. 

3. The resist composition of claim 1 wherein the base polymer further comprises recurring units of at least one type selected from recurring units having the formulae ( c) to (e): 

<img src='content_image/896740.jpg'>

<img src='content_image/896734.jpg'>

<img src='content_image/896735.jpg'>

wherein RA is each independently hydrogen or methyl, R 23 and R 24 are each independently hydrogen or hydroxyl, R$^{25 }$is a substituent group containing a lac› tone structure, R 26 and R 27 are each independently hydrogen or C$_{1}$-C$_{15 }$ alkyl, at least one of R$^{26 }$and R 27 being C$_{1}$-C$_{15}$, alkyl, R$^{26 }$andR$^{27 }$may bond together to form a ring with the carbon atom to which they are attached, a combination ofR$^{26 }$and R$^{27 }$being a C$_{2}$ -C$_{15 }$ alkanediyl group, R$^{28 }$is a C$_{1}$-C$_{20 }$divalent hydrocarbon group in which any constituent -CH$_{2}$ - may be replaced by ---0- or -C(O)-, R 29 is -CH$_{2}$ -, ----CH$_{2}$CH$_{2}$ - or -0-, or two separate -H, and the dotted line designates a single bond or divalent organic group between the norbomane ring, bicyclo[2.2.2]oc› tane ring, 7 -oxanorbomane ring or cyclohexane ring structure and the y-butyrolactone ring structure, or a structure sharing one or two constituent carbon atoms between these ring structures. 

4. The resist composition of claim 1, further comprising 0.8 to 20.0 parts by weight of a third onium salt having the formula (3): 

<img src='content_image/896741.jpg'>

wherein A 2 and A 3 are each independently hydrogen or trifluoromethyl, q is an integer of 1 to 3, MB+ is a sulfonium, iodonium or ammonium cation, and R$^{31 }$is a C$_{1 }$-C$_{40 }$ monovalent hydrocarbon group which may contain a heteroatom. 

-continued 

