Polymer, resist composition and patterning process

A polymer comprising recurring units of each of the following formulae (1-2) and (2-2) and having a weight average molecular weight of 1,000 to 500,000,

• wherein R1, R2, R3 and R4 each are hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, or R1 and R2, and/or R3 and R4, taken together, form a ring, in which case each combination of R1 with R2 and of R3 with R4 is a straight, branched or cyclic alkylene group of 2 to 15 carbon atoms,
• R5 and R6 each are hydrogen, a straight, branched or cyclic alkyl, acyl or alkylsulfonyl group of 1 to 15 carbon atoms or a straight, branched or cyclic alkoxycarbonyl or alkoxyalkyl group of 2 to 15 carbon atoms, in which some or all of the hydrogen atoms on constituent carbon atoms are optionally substituted with halogen atoms,
• R7 is hydrogen, methyl or CH2CO2R9,
• R8 is hydrogen, methyl or CO2R9,
• R9 is a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms,
• R10 is an acid labile group,
• R11 is selected from the class consisting of a halogen atom, a hydroxyl group, a straight, branched or cyclic alkoxy, acyloxy or alkylsulfonyloxy group of 1 to 15 carbon atoms, and a straight, branched or cyclic alkoxycarbonyloxy or alkoxyalkoxy group of 2 to 15 carbon atoms, in which some or all of the hydrogen atoms on constituent carbon atoms are optionally substituted with halogen atoms,
• Z is a single bond or a straight, branched or cyclic (p+2)-valent hydrocarbon group of 1 to 5 carbon atoms in which at least one methylene is optionally substituted with oxygen to form a chain-like or cyclic ether or two hydrogen atoms on a common carbon are optionally substituted with oxygen to form a ketone,
• k is 0 or 1, and p is 0, 1 or 2,
• said acid labile groups represented by R10 include at least one selected from the group consisting of groups of the following formulae (L1) to (L4), tertiary alkyl groups of 4 to 20 carbon atoms, trialkylsilyl groups in which each alkyl moiety has 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20 carbon atoms:
• wherein the broken line denotes the attaching bond, RL01 and RL02 are hydrogen or straight, branched or cyclic alkyl groups of 1 to 18 carbon atoms, RL03 is a monovalent hydrocarbon group of 1 to 18 carbon atoms, a pair of RL01 and RL02, RL01 and RL03, or RL02 and RL03 optionally form a ring, each of RL01, RL02 and RL03 is a straight or branched alkylene group of 1 to 18 carbon atoms when they form a ring,
• RL04 is a tertiary alkyl group of 4 to 20 carbon atoms, a trialkylsilyl group in which each alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group of formula (L1), letter y is an integer of 0 to 6,
• RL05 is a monovalent hydrocarbon group of 1 to 8 carbon atoms which may contain a hetero atom or a substituted or unsubstituted aryl group of 6 to 20 carbon atoms, letter m is equal to 0 or 1, n is equal to 0, 1, 2 or 3, and 2m+n is equal to 2 or 3,
• RL06 is a monovalent hydrocarbon group of 1 to 8 carbon atoms, which optionally contains a hetero atom, or a substituted or unsubstituted aryl group of 6 to 20 carbon atoms, and
• RL07 to RL16 independently represent hydrogen or monovalent hydrocarbon groups of 1 to 15 carbon atoms which optionally contain a hetero atom, a pair of RL07 and RL08, RL07 and RL09, RL08 and RL10, RL09 and RL10, RL11 and RL12, or RL13 and RL14, taken together, optionally form a ring, each of RL07 to RL14 represents a divalent C1-C15 hydrocarbon group which optionally contains a hetero atom when they form a ring, or a pair of RL07 and RL09, RL09 and RL15, or RL13 and RL15 optionally bond together directly to form a double bond.