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[0166] Among these, as the structural unit (a0), at least one member selected from the group consisting of structural units represented by general formulae (a0-1-1) to (a0-1-9) shown below is preferable, and at least one member selected from the group consisting of structural units represented by general formulae (a0-1-1) to (a0-1-6) shown below is more preferable. 

[0167] Among these examples, as the structural unit (a0), at least one member selected from the group consisting of structural units represented by formulae (a0-1-1) to (a0-1-3) is most preferable. 

[0168] As the structural unit (a0) contained in the com› ponent (Al), 1 kind of structural unit may be used, or 2 or more kinds of structural units may be used. 

[0169] In the component (Al), the amount of the structural unit (a0) based on the combined total (100 mo! %) of all structural units constituting the component (Al) is prefer› ably 10 to 70 mo! %, more preferably 20 to 65 mo! %, still more preferably 25 to 60 mo! %, and most preferably 30 to 50 mo!%. 

[0170] When the amount of the structural unit (a0) is at least as large as the lower limit of the above-mentioned preferable range, a resist pattern may be reliably obtained, and sensitivity and various lithography properties such as critical dimension uniformity (CDU) and circularity may be improved. On the other hand, when the amount is no more than the upper limit of the above preferable range, a good balance may be achieved with the other structural units. 

[0171] <<Other Structural Units>> 

[0172] The component (Al) may be further include a structural unit other than the structural unit (a0). 

[0173] Examples of other structural units include a struc› tural unit (al) containing an acid decomposable group that exhibits increased polarity by the action of acid, (provided that the structural unit (a0) is excluded); a structural unit (a2) containing a lactone-containing cyclic group, an -SO$_{2}$ - containing cyclic group or a carbonate-containing cyclic group; a structural unit (a3) containing a polar group› containing aliphatic hydrocarbon group (provided that the structural units (a0), (al) and (a2) are excluded); a structural unit (a4) containing an acid non-dissociable aliphatic cyclic group; and a structural unit derived from styrene or a derivative thereof. 

-continued 

[0174] Structural Unit (al): 

[0175] The component (Al) may include, in addition to the structural unit (a0), a structural unit (al) containing an acid decomposable group that exhibits increased polarity by the action of acid. 

[0176] The term "acid decomposable group" refers to a group in which at least a part of the bond within the structure thereof is cleaved by the action of an acid. 

[0177] Examples of acid decomposable groups which exhibit increased polarity by the action of an acid include groups which are decomposed by the action of an acid to form a polar group. 

[0178] Examples of the polar group include a carboxy group, a hydroxy group, an amino group and a sulfa group (-SO$_{3}$H). Among these, a polar group containing -OH in the structure thereof (hereafter, referred to as "OH-contain› ing polar group") is preferable, a carboxy group or a hydroxy group is more preferable, and a carboxy group is particularly desirable. 

[0179] More specifically, as an example of an acid decom› posable group, a group in which the aforementioned polar group has been protected with an acid dissociable group (such as a group in which the hydrogen atom of the OH-containing polar group has been protected with an acid dissociable group) can be given. 

[0180] The "acid dissociable group" refers to both (i) a group in which the bond between the acid dissociable group and the adjacent atom is cleaved by the action of acid; and (ii) a group in which one of the bonds is cleaved by the action of acid, and then a decarboxylation reaction occurs, thereby cleaving the bond between the acid dissociable group and the adjacent atom. 

[0181] It is necessary that the acid dissociable group that constitutes the acid decomposable group is a group which exhibits a lower polarity than the polar group generated by the dissociation of the acid dissociable group. Thus, when the acid dissociable group is dissociated by the action of acid, a polar group exhibiting a higher polarity than that of the acid dissociable group is generated, thereby increasing the polarity. As a result, the polarity of the entire component (Al) is increased. By the increase in the polarity, the solubility in an alkali developing solution changes, and the solubility in an alkali developing solution is relatively increased, whereas the solubility in an organic developing solution is relatively decreased. 

[0182] Examples of the acid dissociable group for the structural unit (al) include acid dissociable groups which have been proposed for a base resin of a chemically ampli› fied resist composition, provided that the acid dissociable group represented by the aforementioned general formula (a0-rl-1) is excluded. 

[0183] Specific examples of acid dissociable groups for the base resin of a conventional chemically amplified resist include "acetal-type acid dissociable group", "tertiary alkyl ester-type acid dissociable group" and "tertiary alkyloxy› carbonyl acid dissociable group" described below. 

[0184] -Acetal-Type Acid Dissociable Group 

[0185] Examples of the acid dissociable group for protect› ing the carboxy group or hydroxy group as a polar group include the acid dissociable group represented by general formula (al-r-1) shown below (hereafter, referred to as "acetal-type acid dissociable group"). 

