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[0065] The acid labile groups represented by R$^{11 }$and R 12 in the recurring units (al) and (a2) may be selected from a variety of such groups, for example, those groups described in JP-A 2013-080033 (U.S. Pat. No. 8,574,817) and JP-A 2013-083821 (U.S. Pat. No. 8,846,303). 

[0066] Typical of the acid labile group are groups of the following formulae (AL-1) to (AL-3). 

[0067] In formulae (AL-1) and (AL-2), RL 1 and RL 2 are each independently a C$_{1 }$-C$_{40 }$ monovalent hydrocarbon group which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The monovalent hydrocarbon groups may be straight, branched or cyclic, with alkyl groups of 1 to 40 carbon atoms, especially 1 to 20 carbon atoms being preferred. In formula (AL-1), "a" is an integer of 0 to 10, especially 1 to 5. 

[0068] In formula (AL-2), RL 3 and RL 4 are each indepen› dently hydrogen or a C$_{1 }$-C$_{20 }$monovalent hydrocarbon group which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The monovalent hydrocarbon groups may be straight, branched or cyclic, with C$_{1 }$-C$_{20 }$ alkyl groups being preferred. Any two of RL2, RL 3 and RL 4 may bond together to form a ring with the carbon atom or carbon and oxygen atoms to which they are attached. The ring contains 3 to 20 carbon atoms, preferably 4 to 16 carbon atoms, and is typically alicyclic. 

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[0069] In formula (AL-3), RL 5 , RL 6 and RL $^{7 }$are each independently a C$_{1 }$-C$_{20 }$ monovalent hydrocarbon group which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The monovalent hydrocarbon groups may be straight, branched or cyclic, with C$_{1 }$-C$_{20 }$ alkyl groups being preferred. Any two of RL 5 , RL 6 and RL $^{7 }$may bond together to form a ring with the carbon atom to which they are attached. The ring contains 3 to 20 carbon atoms, preferably 4 to 16 carbon atoms and is typically alicyclic. 

[0070] The base polymer may further comprise recurring units (b) having a phenolic hydroxyl group as an adhesive group. Examples of suitable monomers from which recur› ring units (b) are derived are given below, but not limited thereto. Herein RA is as defined above. 

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