26  US  9,104,101 B2  25  In the present invention, the cation moiety (R $^{2}$-X-S+  (R$^{3}$)(R 4 )) in formula (a0-0-1) is preferably a cation repre- sented by a general formula (I-1), (I-2), (I-3) or (I-4) shown  below.  include the same groups as those described below within the  description for the structural unit (al), and specific examples  include a tertiary alkyl ester-type acid-dissociable group and  an acetal-type acid-dissociable group.  Of these, a tertiary alkyl ester-type acid-dissociable group  is preferred, and an acid-dissociable group containing an  aliphatic cyclic group is particularly desirable.  The alkyl group which may have a non-aromatic substitu› ent for R 7 ,  and the non-aromatic substituent which this alkyl  group may have as a substituent are the same as the respective  groups mentioned within the description ofR 2 .  Examples of the alkoxy group which may have a non› aromatic substituent include groups in which -0- is  bonded to an aforementioned alkyl group which may have a  non-aromatic substituent, and examples of the non-aromatic  substituent which this alkoxy group may have as a substituent  include the same groups as those mentioned within the  description ofR 2 .  The alkyl group which may have a non-aromatic substitu› ent for R  8 ,  and the non-aromatic substituent which this alkyl  group may have as a substituent are the same as the respective  groups mentioned within the description ofR 2 .  Examples of the alkyl group for  R 9 a  to R $^{9$_{c }$}$include the same  groups as those described above for R 2 ,  and the alkyl group  preferably contains 5 to 15 carbon atoms. The alkyl group  may be linear, branched or cyclic. It is thought that a cyclic  alkyl group improves the lithography properties, and is there› fore preferred. A chain-like alkyl group, and particularly a  linear alkyl group, is preferred in terms of ease of synthesis.  Examples of the non-aromatic substituent which the alkyl  group may have as a substituent include the same groups as  those described above for the non-aromatic substituent which  the alkyl group for R $^{2 }$may have.  The structural unit (a0) of the component (Al) may be  either a single type of structural unit or a combination of two  or more types of structural units.  The amount of the structural unit ( a0) within the compo› nent (Al), based on the combined total of all the structural  units that constitute the component (Al), is preferably within  a range from 1 to 30 mo!%, and more preferably from 5 to 20  mo!%. When this amount of the structural unit (a0) is at least  5 mo! %, the sensitivity improves. Further, when the amount  is not more than 20 mo! %, satisfactory solubility within the  resist solvent (a component (S) described below) can be  ensured.  In those cases where the component (Al) is a polymeric  compound that exhibits increased polarity under the action of  acid, the component (Al) preferably contains an acid-degrad- able group that exhibits increased polarity under the action of  acid.  The "acid-degradable group" describes a group having  acid degradability which, under the action of the acid (such as  the acid generated from the structural unit ( a0) upon exposure  or the acid generated from an optional component (B)  described below), undergoes cleavage of at least some of the  bonds within the structure of the acid-degradable group. The  acid-degradable group is described in more detail below,  within the description of the structural unit (al).  In those cases where the structural unit (a0) includes an  acid-degradable group (such as the case where R 1  has an  acid-degradable region within the structure, or the case where  R  6  in the formula (I-1) is an acid-degradable group), the  component (Al) may be composed solely of the structural  unit (a0), or may also include a structural unit (al) containing  an acid-degradable group that exhibits increased polarity  under the action of acid.  The alkyl group which may have a non-aromatic substitu› ent for R  6 ,  and the non-aromatic substituent which this alkyl  group may have as a substituent are the same as the respective  groups mentioned within the description ofR 2 .  R $^{6 }$is preferably an acid-dissociable group. This improves  the resolution limit. Examples of the acid-dissociable group  Examples of the alkylene group for Rs include the same  groups as those described above for the alkylene group for  R $^{92 }$in the formula ---O----C(=O)-R92 -,  which was men› tioned in the description of A within the aforementioned  general formula -A-[C(R11-)(R12)Jm-,  and a linear or  branched alkylene group is preferred. The alkylene group  preferably contains 1 to 12 carbon atoms, more preferably 1  to 5 carbon atoms, still more preferably 1 to 3 carbon atoms,  and most preferably 1 or 2 carbon atoms. Examples of the  non-aromatic substituent which the alkylene group may have  as a substituent include the same groups as those described  above for the non-aromatic substituent which the alkyl group 60  for R $^{2 }$may have.  In formula (I-1) to (I-3), u represents an integer of 1 to 3,  and is most preferably 1 or 2.  In the formulas, u represents an integerofl to 3, Rs represents  an alkylene group which may have a non-aromatic substitu› ent, R 6  represents an alkyl group which may have a non› aromatic substituent, R $^{7 }$represents an alkyl group or alkoxy  group which may have a non-aromatic substituent, or a  hydroxy I group, R  $^{8 }$represents an alky I group which may have  a non-aromatic substituent, and each of  R 9 a  to R 9$_{c }$ indepen› dently represents an alkyl group which may have a non› aromatic substituent.  (1-4)  R9a  I  s+  R9b.,  ’-..R9c  (1-3)  Rs  10  ()H,),  (1-2)  0/  R7  I  C  0-:r  ’-Rs  10  ()H,),  (1-1)  0/  R6  I  C  0-:r  ’-Rs  10  ()H,),  [Chemical Formula 7] 