in Patent Document 2 (JP-A-2011-16746)) as the acid gen› erator, the sensitivity, resolution and LER were poor, the  variation of sensitivity after aging was large, and the outgas› sing was frequently generated.  The reason why in Comparative Examples IA and 2A, the  sensitivity was poor, particularly, as to the aging stability, the  variation of sensitivity after aging was large, is not clearly  known but is considered because the decomposition effi- ciency (acid generation efficiency) of Comparative Com› pounds 1 and 2 during exposure is low probably due to low  solubility of Comparative Compounds 1 and 2 for the solvent  in the composition.  On the other hand, in Examples IA to 19A using, as the  acid generator, (Al) a compound represented by formula (Z 1)  where when -L$_{1}$-R$_{1}$-A$_{1 }$ is substituted at the para-position  relative to  s+,  L$_{1 }$ is not an oxygen atom, the sensitivity, reso› lution and LER were excellent, the variation of sensitivity  after aging was small, and the outgassing was little generated.  The reason why in Examples IA to 19A using the com- pound (Al) according to the present invention, the sensitivity  and LER were excellent, is not clearly known but is consid› ered that the compound (Al) represented by formula (Zl) is  configured to have a specific betaine structure of not allowing  L$_{1 }$to be an oxygen atom when -L$_{1}$-R$_{1}$-A$_{1 }$is substituted at the  para-position relative to  s+,  whereby the decomposition effi› ciency (acid generation efficiency) of the compound (Al)  during exposure can be enhanced, the solubility of the com- pound (Al) for the solvent in the composition can be  increased, the compound (Al) can be prevented from precipi› tating in the resist composition during storage and exhibit  excellent aging stability (little variation of sensitivity after  aging), and because of high acid generation efficiency, a large  amount of acid can be generated, resulting in high sensitivity  andlowLER.  Furthermore, it is considered that the compound (Al)  according to the present invention has a betaine structure  having an anion moiety and a cation moiety in the same  molecule and thanks to this configuration, the cation moiety  decomposes during exposure to reduce the molecular weight,  as a result, the solubility of the exposed area for an alkali  developer is enhanced to increase the dissolution contrast,  making it possible to achieve high resolution.  Resist solutions were prepared in the same manner as in  Example IA except for adding 0.06 g of the polymer shown  below (the compositional ratio is in terms of molar ratio) to  the composition of Example IA, and the solution was coated  to obtain a resist film. The obtained resist film was pattern› wise exposed through an immersion liquid (pure water) by  using an ArF excimer laser immersion scanner (XTl 700i,  manufactured by ASML, NA: 1.2), and a pattern was formed  in the same manner as in Example Al.  The obtained pattern was evaluated for the sensitivity, reso› lution, LER, aging stability (variation of sensitivity after  aging), and outgassing performance in the same manner as in  Example A. As a result, it was confirmed that the sensitivity,  resolution and LER are excellent, the variation of sensitivity  after aging is small, and the outgassing is little generated.  The reason therefor is as described in Example A.  As apparent from the results in Table 2, with respect to ArF 65  exposure, in Comparative Examples IA and 2A using Com› parative Compounds 1 and 2 (both are compounds described  As the solvent, the following Al to A4, Bl and B2 were  used. These solvents were appropriately mixed and used.  Al: Propylene glycol monomethyl ether acetate  A2: 2-Heptanone  A3: Cyclohexanone  A4: y-Butyrolactone  Bl: Propylene glycol monomethyl ether  B2: Ethyl lactate  As the basic compound, the following Compounds C-1 to  C-3 were used.  C-1: 2,4,5-Triphenylimidazole  C-2: Tetrabutylammonium hydroxide  C-3: 1,5-Diazabicyclo[ 4.3.0]non-5-ene  <Basic Compound>  <Surfactant>  As the surfactant, the following W-1 to W-4 were used.  W-1: Megaface Fl 76 (produced by DIC Corp.; fluorine-con› taining)  W-3: Polysiloxane Polymer KP-341 (produced by Shin-Etsu  Chemical Co., Ltd.; silicon-containing)  W-4: Troysol S-366 (produced by Troy Chemical; fluorine› containing)  <Solvent>  ExampleB  Mw~ 10000  Mw/Mn~ 1.70  (RA-4)  -continued  124  US 9,069,246 B2  123 