68  US 8,637,222 B2  Examples of the embodiment (2) include a combination  use of two kinds of acid generators differing in the carbon  number of the generated acid anion by 4 or more.  The content of the acid generator (in the case of using a  plurality of acid generators in combination, the total amount)  in the composition is preferably from 0.1 to 30 mass %, more  preferably from 0.5 to 20 mass%, still more preferably from  1 to 15 mass %, based on the entire solid content of the  composition.  [ 4] Basic Compound  The resist composition of the present invention preferably  contains a basic compound.  The basic compound is preferably a nitrogen-containing  organic basic compound.  Examples of the embodiment (1) include a combination  use of a sulfonic acid generator having fluorine and a tris  (fluoroalkylsulfonyl)methide acid generator, a combination  use of a sulfonic acid generator having fluorine and a sulfonic  acid generator having no fluorine, and a combination use of an  alkylsulfonic acid generator and an arylsulfonic acid genera- tor.  As for the acid generator, one kind of an acid generator may  be used alone, or two or more kinds of acid generators may be  used in combination. In the case of using two or more kinds of  acid generators in combination, for example, (1) an embodi- 55  ment where two kinds of PA Gs differing in the acid strength  are used in combination, and (2) an embodiment where two  kinds of acid generators differing in the size (molecular  weight or carbon number) of the generated acid are used in  combination, are preferred.  (zlll)  Q  F  ~  _ 0 _~  ~  ,a  I  +  11’ i  ’(  I  (’Ys~ o  o  #  ~v  (zll0)  F  ~  -o-~~ ,o~  11’ i  ’(  0  0  (zl0S)  (z109)  (z107)  Q  F  -o-~~  u"t’f  +  0  0  USD  (z105)  (z103)  (z102)  (z104)  (z106)  -continued  67 