US 2007/0072121 Al  8  Mar. 29, 2007  [0073]  Specific examples of the repeating unit represented  by formula (A2) are set forth below, but the present inven› tion is not limited thereto.  [0074]  The resin (A) preferably further contains a repeat› ing unit represented by formula (A4).  wherein R$_{2 }$ represents a hydrogen atom, a methyl group, a  cyano group, a halogen atom or a perfluoro group having a  carbon number of 1 to 4,  [0075]  R$_{3 }$ represents a hydrogen atom, an alkyl group, a  halogen atom, an aryl group, an alkoxy group or an acyl  group, n represents an integer of O to 4, and  [0076]  W  represents a group incapable of decomposing  under the action of an acid.  [0077]  W  represents a group incapable of decomposing  under the action of an acid (sometimes referred to as an  "acid-stable group"), and specific examples thereof include  a hydrogen atom, a halogen atom, an alkyl group, a  cycloalkyl group, an alkenyl group, an aryl group, an acyl  group, an alkylamido group, an arylamidomethyl group and  an arylamido group. The acid stable group is preferably an  acyl group or an alkylamido group, more preferably an acyl  group, an alkylcarbonyloxy group, an alkyloxy group, a  cycloalkyloxy group or an aryloxy group.  (A4) 