Examples IF to SF and Comparative Examples IF  and2F  ExampleF  These measurement results are shown in Table 8 below.  Percentage variation in film thickness (%)~[(film  thickness when not exposed-film thickness after  exposure)/film thickness when not exposed]xl00  The resist composition (resist solution) was refrigerated at  5°  C. for 2 weeks and then measured for the sensitivity in the  same manner as above to evaluate the aging stability. A  smaller variation from the sensitivity when not aged is better.  [Outgassing Performance: Percentage Variation in Film  Thickness by Exposure]  Irradiation with EUV at an exposure dose of 2.0 times the  exposure dose giving the sensitivity above was performed,  and the film thickness after exposure but before post-baking  was measured. The percentage variation from the film thick› ness when not exposed was determined by the following  formula:  The reason why in Examples IE to 9E using the compound  (Al) according to the present invention, the sensitivity and  LER were excellent, is not clearly known but is considered  that the compound (Al) represented by formula (Zl) is con› figured 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.  On the other hand, in Examples 1 E to 9E using, as the acid  generator, (Al) a compound represented by formula (Zl)  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,  revealing that the composition is suitable also as a negative  resist composition.  [Aging Stability (Variation of Sensitivity after Aging)]  A line pattern (L/S=l/1) with a line width of 50 nm was  formed at the irradiation dose giving the sensitivity above,  and the distances from the reference line where the edge  should be present was measured using a scanning electron  microscope (S-9220, manufactured by Hitachi, Ltd.) at arbi› trary 30 points included in the longitudinal range of 50  µm  of  the line pattern. The standard deviation of the distance was  determined, and  3a  was computed.  The reason why in Comparative Examples IE and 2E, the  sensitivity was poor, particularly, as to the aging stability, the  variation of sensitivity after aging was large, is considered to  be the same as the reason described above in Example A.  As apparent from the results in Table 7, with respect to  electron beam exposure (irradiation) of the negative resist  composition, in Comparative Examples IE and 2E using  Comparative Compounds 1 and 2 (both are compounds  described in Patent Document 2 (JP-A-2011-16746)) as the  acid generator, the sensitivity, resolution and LER were poor,  the variation of sensitivity after aging was large, and the  outgassing was frequently generated.  The limiting resolution for 1:1 line-and-space (the mini› mum line width below which the line and the space were not  separated and resolved) at the irradiation dose giving the  sensitivity above was taken as the resolution.  [LER (Line Edge Roughness)]  The obtained patterns was observed using a scanning elec› tron microscope (model S-9220 manufactured by Hitachi,  Ltd.). The electron beam irradiation dose when resolving a  line width of 50 nm (line: space= 1: 1) was taken as the sensi› tivity (E$_{0}$ ).  [Resolution]  This resist film was irradiated using an EUV exposure  apparatus (wavelength: 13 nm) and immediately after the  irradiation, baked on a hot plate at 110°  C. for 90 seconds.  Thereafter, the resist film was developed with an aqueous  2.38 mass % tetramethylammonium hydroxide solution at  23 °  C. for 60 seconds, rinsed with pure water for 30 seconds  and then dried to form a line-and-space pattern (line: space= 1 :  1) with a line width of 50 nm. The obtained pattern was  evaluated by the following methods.  [Sensitivity]  The positive resist solution prepared was uniformly coated  on a hexamethyldisilazane-treated silicon substrate by using  a spin coater and heated/dried on a hot plate at 120°  C. for 60  seconds to form a resist film having a thickness of0.12  µm.  The components shown in Table 8 below were dissolved in  the solvent, and the obtained solution was filtered through a  polytetrafluoroethylene filter having a pore size of0.1 µm  to  prepare a positive resist solution having a solid content con› centration of 4 mass  %.  <Evaluation of Resist>  <Preparation of Resist>  134  133  -continued  CL-2  CL-3  US 9,069,246 B2 