Oct. 21, 2010  65  US 2010/0266955 Al  [0673]  El: Exposure dose (mJ/cm 2 )  with which a CH pat› tern having a hole diameter of 76 nm was formed  [0674]  E2: Exposure dose (mJ/cm 2 )  with which a CH pat› tern, having a hole diameter of 84 nm was formed  [0675]  The larger the value of the "EL margin", the smaller  the change in the pattern size by the variation of the exposure  dose.  [0676]  [Evaluation of Mask Error Factor (MEF)]  [0677]  The mask error factor (MEF) was evaluated with  respect to the CH pattern having a hole diameter of 80 nm  (pitch: 140 nm).  [0678]  With the above Eop, CH patterns having a pitch of  140 µm  were formed using a mask pattern targeting a hole  diameter of75 to 85 nm (11 target sizes at intervals of 1 µm).  [0679]  The value of the mask error factor was determined  as the gradient of a graph obtained by plotting the target mask  size (nm) on the horizontal axis, and the actual hole diameter  (nm) of the formed CH patterns on the vertical axis. The  results are shown in Table 4.  [0680]  [Evaluation of in-Plane Uniformity (CDU) of Pat› tern Size]  [0681]  With respect to each of the CH patterns formed with  the above Eop, the hole diameter (CD) of 25 holes were  measured. From the results, the value of3 times the standard  deviation  a  (i.e.,  3a)  was calculated as a yardstick of CD  uniformity (CDU). The results are shown in Table 4.  [0682]  The smaller this  3a  value is, the higher the level of  the in-plane uniformity (CDU) of the holes formed in the  resist film.  [0683]  [Evaluation of Circularity]  [0684]  Each of the CH patterns formed with the above Fop  was observed from the upper side thereof using a scanning  electron microscope (product name: S-9220, manufactured  by Hitachi, Ltd.), and with respect to each of 25 holes, the  distance from the center of the hole to the outer periphery  thereof was measured in 24 directions. From the results, the  value of 3 times the standard deviation  a  (i.e.,  3a)  was cal› culated as a yardstick of circularity. The results are shown in  Table 4.  [0685]  The smaller this  3a  value is, the higher the level of  circularity of the holes.  [0686]  [Evaluation of Depth of Focus (Doe)]  [0687]  The depth of focus (DOE) was evaluated with  respect to CH patterns having a hole diameter of 80 nm.  [0688]  With the above-mentioned Bop, the focus was  appropriately shifted up and down and resist patterns were  formed in the same manner as in the "formation of resist  pattern (2)", and the depth of focus (DOF; unit: µm) with  which a CH pattern was formed within the range where the  variation in the target size was –5% (i.e., 76 to 84 nm) was  determined. The results are shown in Table 4.  wherein R represents a hydrogen atom, an alkyl group of 1 to  5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon  atoms; R $^{1 }$represents an acid dissociable, dissolution inhibit› ing group; and R 2  represents a divalent hydrocarbon group  which may have a substituent; and  [Chemical Formula 2]  (I)  wherein X represents a hydrocarbon group of 3 to 30 carbon  atoms which may have a substituent; Q$^{1 }$represents a divalent  linking group containing an oxygen atom; and Y’ represents  an alkylene group of 1 to 4 carbon atoms which may have a  substituent or a fluorinated alkylene group of 1 to 4 carbon  atoms which may have a substituent.  2.  The positive resist composition according to claim  1,  wherein the structural unit (a0) is represented by general  formula (a0-1-10) shown below:  [Chemical Formula 1]  (a0-1)  What is claimed is:  1.  A positive resist composition comprising a base compo› nent (A) which exhibits increased solubility in an alkali  developing solution under action of acid and an acid-genera› tor component (B) which generates acid upon exposure,  the component (A) comprising a polymeric compound  (Al) comprised of a structural unit (a0) represented by  general formula (a0-1) shown below, and  the acid generator (B) comprising an acid generator (Bl)  having an anion moiety represented by general formula  (1) shown below:  [0689]  From the results shown in Table 4, it was confirmed  that both, of the positive resist compositions of Examples 6  and 7 according to the present invention exhibited excellent  lithography properties.  [0690]  While preferred embodiments of the invention have  been described and illustrated above, it should be understood  that these are exemplary of the invention and are not to be  considered as limiting. Additions, omissions, substitutions,  and other modifications can be made without departing from  the spirit or scope of the present invention. Accordingly, the  invention is not to be considered as being limited by the  foregoing description, and is only limited by the scope of the  appended claims.  TABLE4  Eop  EL margin  DOF  (mJ/cm 2 )  (%)  MEF CDU  Circularity (µm)  Ex. 6  24.8  8.17  6.02  7.44  3.50  0.13  Ex. 7  24.0  9.05  6.24  9.56  3.10  0.20 