Jul. 18, 2019  75  US 2019/0219920 Al  [0747]  From the results shown in Table 2, as compared to  the resist compositions of Comparative Examples 1 to 4, the  resist composition of Example 1 could improve sensitivity  and lithography properties, and a resist pattern having a  good shape could be formed.  [0748]  <Production Example of Monomer (a02)>  [0749]  Using  2,3,3-trimethyl-4-methoxy-2-butanol  obtained by reacting 3,3-dimethyl-4-methoxy-2-butanone  with methylmagnesium bromide, an objective monomer  (a02), namely, 2,3,3-trimethyl-4-methoxybutan-2-yl meth› acrylate having the following NMR properties was obtained  with reference to the synthesis example described at para› graph 0090 of WO2013/042694.  [0733]  <Formation of Resist Pattern>  [0734]  Each of the resist compositions of examples and  comparative examples was applied to an 8-inch silicon  substrate which had been treated with hexamethyldisilazane  (HMDS) using a spinner, and was then prebaked (PAB) on  a hot plate at 110°  C. for 60 seconds and dried, thereby  forming a resist film having a film thickness of 90 nm.  [0735]  Subsequently, the resist film was selectively irra› diated with an ArF excimer laser (193 nm) through a mask  pattern with a predetermined target (hole diameter: 67 nm,  pitch: 130 nm), using an ArF exposure apparatus S610C  (NA=l.20; Annular, 0.90/0.70).  [0736]  Then, a post exposure bake (PEB) treatment was  conducted at 80°  C. for 60 seconds.  [0737]  Next, a solvent development was conducted at 23°  C. for 30 seconds using butyl acetate, followed by a rinse  treatment.  [0738]  As a result, a contact hole pattern (CH) having a  hole diameter of73 nm and a pitch of 130 nm was formed.  [0739]  [Evaluation of Optimum Exposure Dose (Eop )]  [0742]  With respect to each CH pattern obtained in the  "Formation of resist pattern", 100 holes in the CH pattern  were observed from the upper side thereof using a measur› ing scanning electron microscope (SEM) (product name:  S-9380, manufactured by Hitachi High-Technologies Cor› poration; acceleration voltage: 300V), and the hole diameter  (nm) of each hole was measured. From the results, the value  of 3 times the standard deviation (  a) (3a)  was determined.  The results are indicated under "CDU (nm)" in Table 2.  [0743]  The smaller the thus determined  3a  value is, the  higher the level of the dimension uniformity (CD unifor› mity) of the holes formed in the resist film.  [0744]  [Evaluation of Circularity]  [0745]  With respect to each CH pattern obtained above  "Method of forming resist pattern", 25 holes in the CH  pattern were observed from the upper side thereof using a  length measuring scanning electron microscope (SEM)  (product name: S-9380, manufactured by Hitachi High› Technologies Corporation; acceleration voltage: 300V), and  the distance from the center of each hole to the outer  periphery of the hole was measured in 24 directions. From  the results, the value of 3 times the standard deviation  (a)  (3a)  was determined. The results are indicated under "Cir› cularity (nm)" in Table 2.  [0754]  Then, to the obtained polymer liquid was added  17.3 g of acetic acid and 246 g of methanol, followed by  conducting a deprotection reaction at 30°  C.°  C. for 8 hours.  After the reaction finished, 400 g of heptane was added to  the obtained reaction liquid and stirred, and the reaction  liquid was allowed to stand, followed by removing the upper  [0753]  To a 300 mL-flask were added 11.3 g of monomer  (a0l), 15.9 g of p-ethoxyethoxystryene (EESt), 1.1 g of  dimethyl 2,2’-azobis(isobutyrate) (V-601) as a polymeriza› tion initiator and 65 g of methyl ethyl ketone (MEK) as a  solvent, followed by conducting a polymerization reaction at  85°  C. for 5 hours.  [0752]  <Production Example of Copolymer (Al ’-1-1 )>  [0751]  $^{1}$H-NMR (CDC1$_{3}$ )  o(ppm)=6.01 (m, lH), 5.50 (m,  lH), 3.11 (s, 3H), 3.08 (s, 2H), 1.94 (t, 3H), 1.78 (s, 6H),  1.12 (s, 6H).  [0750]  The obtained monomer (a02) was analyzed by  NMR, and the structure thereof was identified by the fol› lowing results.  [Chemical Formula 73]  (a02)  (F-1)  [0746]  The smaller this  3a  value is, the higher the level of  circularity of the holes.  TABLE 2  PAB  PEB  Eop  CDU  Circularity  (" c.)  (" C.)  (mJ/cm 2 )  (nm)  (nm)  Example 1  110  80  14.4  4.4  2.7  Comparative  110  80  20.9  5.2  3.1  Example 1  Comparative  110  80  17.3  4.9  2.9  Example 2  Comparative  110  80  21.2  5.5  2.7  Example 3  Comparative  110  80  16.5  5.7  2.4  Example 4  [Chemical Formula 72]  [0740]  The optimum exposure dose Eop (mJ/cm 2 )  with  which a CH pattern having a target size was formed in the  above "Formation of resist pattern" was determined. The  results are indicated under "Eop (mJ/cm 2 )"  in Table 2.  [0741]  [Evaluation of in-Plane Uniformity (CDU) of Pat› tern Size] 