preferable that the hetero atom is not adjacent to the atom within the base dissociable portion which has its bond cleaved by the action of a base. 

The alkylene group is the same as defined for the linear or branched alkylene group for X in the formula (I). 

The hetero atom is most preferably an oxygen atom. 

Among the above examples, R$^{53 }$is preferably a group in which a base dissociable portion is boned to a group or atom which is not base dissociable. 54 

R represents a divalent linking group, and examples thereof include the same divalent linking groups as those described above for X in the formula (I). Among these, an alkylene group or a divalent aliphatic cyclic group is prefer› able, and an alkylene group is particularly desirable. 

R$^{55 }$represents a group having an acid dissociable group. 

The acid dissociable group is an organic group which can be dissociated by the action of an acid. The acid dissociable group is not particularly limited, and any group which has been proposed as an acid dissociable, dissolution inhibiting group of a base resin for a chemically amplified resist can be used. Specific examples include the same acid dissociable, dissolution inhibiting groups as those described later for the structural unit ( a 1 ), such as a cyclic or chain-like tertiary alky 1 ester-type acid dissociable group or an acetal-type acid dis› sociable group ( e.g., an alkoxyalkyl group). Among these, a tertiary alkyl ester-type acid dissociable group is particularly desirable. 

The group having an acid dissociable group may be either the acid dissociable group itself, or a group in which an acid dissociable group is bonded to a group or atom which is not acid dissociable (a group or atom which remains bonded to the acid generator even after the dissociation of the acid dissociable group). Examples of the group or atom which is not acid dissociable include the same divalent linking groups as those described above for X in the formula (I). 

In formula (I-1-27), W $^{2 }$represents a single bond or a diva› lent linking group, t represents 0 or 1, and R$^{62 }$represents a group which is not dissociable by acid (hereafter, referred to as "acid non-dissociable group"). 

Examples of the divalent linking group for W $^{2 }$include the same divalent linking groups as those described above for X in the formula (I). Among these, as W 2 , a single bond is preferable. 

t is preferably 0. 

The acid non-dissociable group for R $^{62 }$is not particularly limited as long as it is a group which is not dissociable by acid. The acid non-dissociable group is preferably an acid non- dissociable hydrocarbon group which may have a substituent, more preferably a cyclic hydrocarbon group which may have a substituent, and still more preferably a group in which one hydrogen atom has been removed from adamantane. 9 10 

In formulae (I-1-28) and (I-1-29), each of R and R independently represents a phenyl group or naphthyl group which may have a substituent, an alkyl group of 1 to 5 carbon atoms, an alkoxy group or a hydroxy group; and u represents an integer of 1 to 3, most preferably 1 or 2. 

In formula (I-1-30), Y $^{10 }$represents a cyclic hydrocarbon group of 5 or more carbon atoms which may have a substitu› ent, and is an acid dissociable group which may be dissoci› ated by the action of an acid; each of R$^{56 }$and R$^{57 }$indepen› dently represents a hydrogen atom, an alkyl group or an aryl group, provided that R$^{56 }$and R$^{57 }$may be mutually bonded to form a ring; each ofY$^{11 }$and Y$^{12 }$independently represents an 

alkyl group or anaryl group, provided thatY$^{11 }$andY$^{12 }$maybe mutually bonded to form a ring. 

Y$^{10 }$represents a cyclic hydrocarbon group of 5 or more carbon atoms which may have a substituent, and is an acid dissociable group which may be dissociated by the action of an acid. By virtue of the Y$^{10 }$group being a cyclic hydrocarbon group of 5 or more carbon atoms which may have a substitu› ent, and is an acid dissociable group which may be dissoci- ated by the action of an acid, various lithography properties such as resolution, LWR, exposure latitude (EL margin) and resist pattern are improved. 

Examples ofY$^{10 }$include groups which form a cyclic ter› tiary alkyl ester with-C(R$^{56}$)(R$^{57}$)----C(=O)-O-. 

A "tertiary alkyl ester" refers to a structure in which a tertiary carbon atom within a cyclic hydrocarbon group of 5 or more carbon atoms is bonded to the terminal oxygen atom of-C(R$^{56}$)(R$^{57}$)----C(=O)-O-. In this tertiary alkyl ester, the action of acid causes cleavage of the bond between the oxygen atom and the tertiary carbon atom. 

The cyclic hydrocarbon group may have a substituent, and the carbon atom(s) within the substituent is not included in the number of carbon atoms of the "carbon atom of 5 or more carbon atoms". 

Examples of the "aliphatic cyclic group" include monocy› clic groups or polycyclic groups which have no aromaticity, and polycyclic groups are preferable. 

The "aliphatic cyclic group" may or may not have a sub› stituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (=0). 

As such aliphatic cyclic groups, groups in which two or more hydrogen atoms have been removed from a monocy› cloalkane or a polycycloalkane such as a bicycloalkane, tri› cycloalkane or tetracycloalkane which may or may not be substituted with an alkyl group of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group, may be used. Specific examples include groups in which two or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which two or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobor- nane, tricyclodecane or tetracyclododecane. 

Each ofR$^{56 }$and R$^{57 }$independently represents a hydrogen atom, an alkyl group or an aryl group. 

Examples of the alkyl group or aryl group for R$^{56 }$and R 57 include the same alkyl groups and aryl groups as those described above for R 1 " to R 3 ". Further, R $^{56 }$to R$^{57 }$may be mutually bonded to form a ring, like in the case of the afore- mentioned R 1 " to R 3 ". 

Among the above-mentioned examples, it is particularly desirable that both R$^{56 }$and R$^{57 }$represent a hydrogen atom. 

Each ofY 11 and Y 12 independently represents an alkyl group or an aryl group. 

Examples of the alkyl group or aryl group for Y$^{11 }$and Y 12 include the same alkyl groups and aryl groups as those described above for R 1 " to R 3 ". 

It is particularly desirable that each ofY$^{11 }$and Y$^{12 }$repre› sents a pheny 1 group or a naphthy 1 group. Further, Y $^{11 }$and Y 12 may be mutually bonded to form a ring, like in the case of the aforementioned R 1 " to R 3 ". 

