87  US 9,250,518 B2  88  0  R 2  )l  o- 0  ~~  0  R 2  )l  o- 0  ~~  0  ’~~)(_lij,filyo  0  ;t  I  RIO  ;t  ~’"  o~o_...,..F  (2)  Herein, R 9  and R $^{11 }$which may be the same or different is  hydrogen or methyl. Xis a single bond, a linking group of 1  to 12 carbon atoms having an ester moiety or lactone ring,  phenylene group, or naphthylene group. Y is a single bond or  ester group. R $^{10 }$and R $^{12 }$each are an acid labile group.  The recurring units (al) having an acid labile group are  preferably derived from (meth)acrylic acid, styrenecarboxy› lic acid and vinylnaphthalenecarboxylic acid by substituting  an acid labile group for the hydrogen atom of carboxyl group.  Illustrative, non-limiting, examples ofrecurring units (al) are  given below.  Herein R  2 , R $^{3 }$and mare as defined above, and Dis deuterium.  For the synthesis of the acid generator having formula (1 ),  reference may be made to JP-A 2007-145797, JP-A 2008- 106045, JP-A 2009-007327, and JP-A 2009-258695.  While the chemically amplified resist composition com› prises the basic compound of formula (1) and a base polymer  to be described below, the basic compound of formula (1) is  preferably present in the composition in an amount of0.001  to 20 parts by weight, more preferably 0.01 to 10 parts by  weight per 100 parts by weight of the base polymer.  In the embodiment wherein chemically amplified resist  compositions are positive, the base polymer comprises recur› ring units having an acid labile group. Suitable recurring units  having an acid labile group include recurring units of (meth)  acrylate, styrenecarboxylic acid and vinylnaphthalenecar› boxylic acid having an acid labile group substituted thereon,  as represented by unit (al) in the general formula (2), and  recurring units ofhydroxystyrene having an acid labile group  substituted thereon, as represented by unit (a2) in the general  formula (2).  -continued 