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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). 

Typical of the acid labile group are groups of the follow› ing formulae (AL-1) to (AL-3). 

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In formulae (AL-1) and (AL-2), R 15 and R 18 are each independently a monovalent hydrocarbon group of 1 to 40 carbon atoms, preferably 1 to 20 carbon atoms, typically straight, branched or cyclic alkyl, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. R 16 and R 1 7 are each independently hydrogen or a monovalent hydrocarbon group of 1 to 20 carbon atoms, typically straight, branched or cyclic alkyl, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. Al is an integer of 0 to 10, especially 1 to 5. A pair of R $^{16 }$and R 17 , R $^{16 }$and R18 , or R $^{17 }$and R$^{18 }$may bond together to form a ring, typically alicyclic, with the carbon atom or carbon and oxygen atoms to which they are attached, the ring containing 3 to 20 carbon atoms, preferably 4 to 16 carbon atoms. 19 

In formula (AL-3), R , R $^{20 }$and R21 are each indepen› dently a monovalent hydrocarbon group of 1 to 20 carbon 55 atoms, typically straight, branched or cyclic alkyl, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. A pair ofR$^{19 }$and R 20 , R $^{19 }$and R21 , or R $^{20 }$and R 21 may bond together to form a ring, typically alicyclic, with the carbon atom to which they are attached, the ring 60 containing 3 to 20 carbon atoms, preferably 4 to 16 carbon atoms. 

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

-continued 

(AL-1) 

(AL-2) 

(AL-3) 

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