25  26  The structural unit (ZI-4) is a structural unit represented by  the following formula  (ZI-4):  In the formula, R$_{13 }$represents a hydrogen atom, a fluorine  atom, a hydroxy group, an alkyl group, a cycloalkyl group, an  alkoxy group, an alkoxycarbonyl group, or a group having a  monocyclic or polycyclic cycloalkyl skeleton. These groups  may have a substituent.  R$_{14 }$represents, when a plurality of R$_{14}$s are present, each  independently represents, an alkyl group, a cycloalkyl group,  an alkoxy group, an alkoxycarbonyl group, an alkylcarbonyl  group, an alkylsulfonyl group, a cycloalkylsulfonyl group, or  a group having a monocyclic or polycyclic cycloalkyl skel› eton. These groups may have a substituent.  Each R$_{15 }$ independently represents an alkyl group, a  cycloalkyl group or a naphthyl group. Two R$_{15}$s may combine  with each other to form a ring. These groups may have a  substituent.  1  represents an integer of  O  to 2.  r represents an integer of  O  to 8.  z- represents an acid anion that is generated by decompo- sition upon irradiation with an actinic ray or radiation and is  preferably a non-nucleophilic anion. Examples of the anion  are the same as those of  z- in formula  (ZI).  In formula  (ZI-4),  the alkyl group ofR$_{13}$, R$_{14 }$and R$_{15 }$is a  linear or branched alkyl group preferably having a carbon  number of  1  to  10,  and examples thereof include a methyl  group, an ethyl group, an n-propyl group, an i-propyl group,  ann-butyl group, a 2-methylpropyl group, a 1-methylpropyl  group, a tert-butyl group, an n-pentyl group, a neopentyl  group, ann-hexyl group, ann-heptyl group, ann-octyl group,  a 2-ethylhexyl group, an n-nonyl group and ann-decyl group.  Among these alkyl groups, a methyl group, an ethyl group, an  n-butyl group and a tert-butyl group are preferred.  (ZI-4)  0  I  /’---..s  Q~ ~I  0  0  0  ~  ~SJJ /\  ’0s  0  0  0 ~ontin"~ 