us 10,725,377 B2  89  90  TABLE 9-continued  Resist  Eop  Maximwn Maximum  CD  compo- (µC/ resolution resolution  change  LER  sition  cm 2 )  LIS (nm)  dot (nm)  (nm)  (mn)  Comparative  2-1  CR-1  50  65  100  1.55  6.2  Example  2-2  CR-2  49  60  95  1.57  5.9  2-3  CR-3  51  65  110  1.46  6.4  2-4  CR-4  51  60  95  1.44  6.2  Pattern  profile  undercut  footing  undercut  footing  All the inventive resist compositions (R-1 to R-48) com› prising the sulfonium compounds having formula (A) show  satisfactory results with respect to resolution, dose margin,  rectangular pattern profile, and LER. The comparative resist  compositions (CR-1 to CR-4) are inferior in resolution and  LER. This is because the acid generated upon EB writing  diffuses to the unexposed region where negative working  reaction takes place to some extent, leading to a decline of  contrast.  Since the inventive resist compositions comprising the  sulfonium compounds having formula (A) have a higher  acid-trapping ability than the resist compositions comprising  the salts of Comparative Examples 2-1 and 2-2, they are less  susceptible to the unwanted reaction than the comparative  resist compositions. After image writing, the sulfonium  compound having formula (A) converts to a phenolic com› pound, losing the acid diffusion controlling ability. As a  result, the reaction contrast between the exposed (imaged)  region and the unexposed (unimaged) region is increased.  Comparative resist compositions (CR-3 and CR-4) show a  low reaction contrast because the inhibitor Q-4 maintains its  acid diffusion controlling ability even after image writing.  Consequently, from the inventive resist compositions com› prising the sulfonium compounds, patterns with satisfactory  resolution and reduced edge roughness are formed.  and cross-sectional observation under SEM. As used herein,  the "dark pattern" refers to a layout that a resist pattern is  formed around a test pattern ( area surrounding the test  pattern is also exposed), and inversely, "bright pattern"  refers to a layout that no resist pattern is formed around a test  pattern ( only the test pattern is exposed). The results are  shown in Table 10.  TABLE 10  Resist  Eop  Size  compo- PEB  (mJ/  difference LWR  Pattern  sition  (" C.) cm 2 )  (nm)  (nm)  profile  Example  3-1 R-49  130  46  5.9  4.2  rectangular  3-2 R-50  130  55  6.0  4.0  rectangular  3-3 R-51  130  43  6.8  5.2  rectangular  3-4 R-52  120  37  3.1  3.8  rectangular  3-5 R-53  130  72  3.8  4.1  rectangular  3-6 R-54  120  49  3.3  3.7  rectangular  3-7 R-55  130  72  4.3  4.2  rectangular  3-8 R-56  130  79  3.2  4.5  rectangular  3-9 R-57  130  74  4.5  5.4  rectangular  Com- 3-1 CR-5  120  44  16.5  8.2  top reduced  parative  3-2 CR-6  120  29  22.8  7.6  footing  Example  3-3 CR-7  130  53  12.9  6.5  top reduced  3-4 CR-8  130  35  17.0  5.9  footing  5) KrF Lithography Test  Examples 3-1 to 3-9 and Comparative Examples  3-1 to 3-4  6) EUV Lithography Test  Examples 4-1 to 4-8 and Comparative Examples  4-1 to 4-8  It is evident from Table 10 that the inventive resist  composition possesses improved lithography performance  as demonstrated by little influence of chemical flare and a  good pattern profile with reduced roughness.  Each of the resist compositions (R-49 to R-57 and CR-5  to CR-8) was spin coated on a silicon wafer having an  antireflective coating (DUV42 by Nissan Chemical Indus- tries, Ltd.) of 61 nm thick, and baked on a hotplate at 100°  C. for 60 seconds to form a resist film of 240 nm thick. The  resist film was exposed to KrF laser radiation by means of  KrF excimer laser seamier NSR-S206D (Nikon Corp.,  NA=0.80), then baked (PEB) for 60 seconds, and puddle  developed in a 2.38 wt % TMAH aqueous solution for 60  seconds, thereby yielding a negative 1:1 line-and-space  pattern. In the PEB step, an optimum temperature for a  particular resist composition was employed.  The patterned wafer was observed under TD-SEM. When  a dark pattern of 150 nm line/300 nm pitch was observed  under SEM, the exposure dose (mJ/cm 2 )  which finished to  a size of 150 nm on SEM observation was defined as the  optimum dose (Eop). Also a bright pattern of 150 nm  line/150 nm pitch printed at the optimum dose was observed  under SEM. A size difference (dark pattern size-bright  pattern size, nm) was computed. A smaller difference indi› cates less chemical flare or better performance. For numeri› cally expressing the roughness of a pattern at the optimum  dose, a variation ofline width (30 points measured, 30 value  computed) was determined and reported as LWR (nm). The  pattern profile was visually judged by top-down observation  A resist composition was prepared by dissolving a poly› mer (Polymer 25 to 29), acid generator and acid diffusion  inhibitor in a solvent in accordance with the recipe shown in  Table 11, and filtering through a Teflonfi filter having a pore  size of 0.2 m. After a silicon wafer was baked at 200°  C. for  drying and vapor primed with HMDS at 100°  C. for 90  seconds, the resist composition was spin coated on the  silicon wafer and pre baked on a hotplate at 110°  C. for 60  seconds to form a resist film of30 nm thick. Using a scanner  NXE3300 (ASML, NA 0.33, dipole 90), the resist film was  exposed to EUV. The resist film was baked (PEB) at 120°  C.  for 60 seconds and puddle developed in a 2.38 wt% TMAH  aqueous solution for 60 seconds to form a negative line› and-space pattern.  The resist pattern was evaluated. The patterned wafer was  observed under TD-SEM. The exposure dose capable of  resolving a 22-nm LIS pattern at 1: 1 is reported as sensi- tivity. The minimum size at that dose is reported as resolu› tion. For numerically expressing the roughness of a 22-nm  LIS pattern at the optimum dose, a variation ofline width (30 