124  US 7,851,130 B2  123  from the gradient of the straight line part of the sensitivity  curve. The greater the  y  value, the better is the dissolution  contrast.  Outgassing Performance (the Coefficient of Fluctuation in 5  the Film Thickness after Exposure):  The resist film is irradiated with 2.0 times the dose of  irradiation at the sensitivity determined by areal exposure  with EUV (mJ/cm 2 ),  and the thickness of the film after expo- sure (before post-baking) is measured, and the coefficient of  fluctuation from the film thickness at unexposed time is found  according to the following equation.  The results of evaluation are shown in Table 8 below.  From the results shown in Tables 8 and 9, it can be seen that  the resist compositions in the invention are high in both sen› sitivity and contrast and excellent in outgassing performance  in the characteristic evaluation by irradiation with EUV ray as  compared with comparative compositions.  The invention can provide a photosensitive composition  excellent in sensitivity, resolution, line edge roughness and  outgassing characteristics; a compound for use in the photo› sensitive composition; and a pattern forming method with the  photosensitive composition.  The entire disclosure of each and every foreign patent  application from which the benefit of foreign priority has  been claimed in the present application is incorporated herein  by reference, as if fully set forth.  What is claimed is:  1.  A photosensitive composition comprising:  (A) a compound represented by the following formula (I):  wherein  R$^{1 }$to R$^{13 }$each independently represents a hydrogen atom  or a substituent;  Z represents a single bond, an alkylene group, an arylene  group, an ether group or a thioether group;  x- represents an anion containing a proton acceptor func› tional group; and  the proton acceptor functional group is a functional group  having a basicity selected from the group consisting of  an amino group, an anilino group, a pyridine group, an  amidino group and a guanidino group.  Evaluation was performed in the same manner as in 65  Example 39 (EUV exposure of positive resist). The results  obtained are shown in Table 9 below.  The obtained resist film is subjected to areal exposure with  EUV ray (wavelength: 13 nm)with varying exposuredose0.5  by 0.5  ml  within the range of exposure dose of from Oto 10.0  mJ, and the resist film is further baked at 110°  C. for 90  seconds. After that, a dissolution rate of the resist film at each  exposure dose is measured with a 2.38 mass % tetramethy› lammonium hydroxide (TMAH) aqueous solution to obtain a  sensitivity curve.  The prepared negative resist solution is uniformly coated  on a silicon substrate having been subjected to hexamethyl- disilazane treatment by a spin coater, and dried by heating on  a hot plate at 120°  C. for 60 seconds to form a resist film  having a thickness of0.15  µm.  A negative resist solution having the concentration of sol- ids content of 8 mass % is prepared by dissolving the com› ponents in the solvents respectively shown in Table 5, and  filtrating the solution through a polytetrafluoroethylene filter  having a pore size of0.1 µm. Each of the prepared resists is  evaluated as follows.  Examples 45 to 50 and Comparative Example 8  Evaluation of Resist:  Sensitivity and  y  Value:  RI!  (I)  EUV Exposure of Positive Resist  Evaluation  Outgassing  Performance  (evaluation of  Sensitivity  y  film thickness)  Example No.  (mJ/cm 2 )  Value  (%)  Example 39  6.3  6.1  2.3  Example40  6.0  6.3  2.2  Example 41  5.8  6.4  2.6  Example42  5.6  6.4  2.4  Example43  5.5  6.5  2.3  Example44  5.1  6.8  2.5  Comparative  10.5  3.5  11.0  Example 7  TABLES  TABLE9  Example No.  Example45  Example46  Example47  Example48  Example49  Example 50  Comparative  Example 8  EUV Exposure of Negative Resist  Evaluation  Sensitivity  y  (mJ/cm 2 )  Value  5.6  5.4  5.3  5.6  5.4  5.4  5.5  5.9  5.1  6.1  4.9  6.2  10.3  3.2  Outgassing  Performance  (evaluation of  film thickness)  (%)  2.9  2.5  2.6  2.4  2.3  2.2  11.2  Coefficient of fluctuation in film thickness (%)~[(film  thickness at unexposed time-film thickness after  exposure )/film thickness at unexposed time ]x 100 